THE HYDROTHERMAL FORMATION OF CALCIUM SILICATE HYDRATES.
BY
D. R. MOOREHEAD
THESIS
SUBMITTED AS REQUIRED FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF NEW SOUTH WALES.
SYDNEY, 1963. I HEREBY CERTIFY THAT THIS WORK HAS NOT BEEN SUBMITTED FOR A HIGHER DEGREE TO ANY OTHER UNIVERSITY OF INSTITUTION.
D. R. MOOREHEAD ABSTRACT
In this thesis a study is reported of the kinetics of solution of quartz and the crystallization of calcium silicate hydrates during the hydrothermal treatment of quartz in saturated lime solutions. Single crystals of quartz were used to facilitate the examination of the interaction of the lime with the quartz surface. Sectioning of the product layer and subsequent microscopic investigation showed the calcium silicate hydrate to be of fibrous crystal habit and to grow radially from nucleating centres in a general direction away from the quartz surface. X-ray analysis showed the mineral formed to be mainly xonotlite. Measurements of the weight increase of a quartz crystal were made at various times during runs at 335°C. and 235°C. Plots of the quantity of xonotlite versus square root of time gave a straight line indicating that the process was diffusion controlled. The crystallization of the mineral did not follow the receding surface of the quartz. Extension of the product layer took place only on the surface in contact with the lime solution. The silicate ions apparently diffused readily through the product layer. Measurements were made to determine the selective action of the mineral membrane towards the diffusion of calcium ions in association with chloride and hydroxyl ions and of sodium ions in association with chloride ions. These results showed the membrane had no selective action towards the diffusion of calcium ions when associated with hydroxyl ions.
The solubility data for calcium hydroxide in water was extended from 180° to 300°C. From this data, estimates -ii-
of the diffusion rates were made for the species Ca and
HoSi0,. These calculations showed the diffusion rate of the l^SiO^ species to be many orders greater than that of I | the Ca species. This information was used to account for extension of the product layer on the surface in contact with the lime solution.
Other systems including barium hydroxide-quartz and calcite-silica gel were briefly investigated. TABLE OF CONTENTS
CHAPTER (1)
1.10 Introduction 1 1.20 Literature Review 2
1.21 Structure and Morphology of Calcium Silicate-Hydrates 3 1.22 Effect of Temperature on Phases Produced 5 1.23 Some Proposed Mechanisms 9 1.24 Water of Hydration and Free Water 11
1.30 The Objective of the Work 14
CHAPTER (2)
2.00 Experimental Part 15 2.10 Reagents and Materials used 15 2.11 Preliminary Experiments 16 2.21 Physical and Chemical Examination of th^roduct Formed at 350°C 21 2.22 Microscopic Examination 23 2.23 Electronmicroscopic Study 28 2.24 Chemical Analysis 28 2.25 Thermogravimetric Study 32 2.26 Measurement of Porosity 34 2.27 Infra-Red Absorption Spectra 34 2.31 Kinetic Study of the Formation of the Product Mineral at 335° and 225°C 34 2.32 Microscopic Examination 42 2.33 X-Ray Analysis 42 2.40 Diffusion of Ions Through the Porous Product Material 44 2.50 Solubility of Calcium Hydroxide at 300°C 50 2.60 Work at Supercritical Temperatures 51 2.61 X-Ray Examination 51 2.62 Electronmicroscopic Examination 59 2.70 Experiments with Calcite Crystals 59 2.80 Barium Hydroxide-Quartz Hydrothermal Reaction 62
CHAPTER (3)
3.00 Discussion of Results 64 3.10 Preliminary Work using X-Ray Analysis 64 3.11 Products formed at 235°C 64 (a) X-Ray Analysis 66 (b) I.R. Study 67 3.12 Identification of Products formed at 335°C 69 (a) X-Ray Analysis 69 (b) I.R. Study 72 (c) Thermal Weight Loss 73 3.13 Products formed at Super Critical Temperatures 73 (a) X-Ray Analysis 3.21 Experiments with the Calcite-Silica System 74 3.22 Experiments with the Barium Hydroxide-Quartz System 75 3.30 Morphology and Macro Structure of Products 76 3.31 Microscopic Examination (a) Products formed at 235°C 76 (b) Products formed at 335°C 77 (c) Products formed at Super Critical Temperatures 77 3.32 Electronmicroscopic Study of Products 78 3.33 Macro Structure 80 (a) Pore size Distribution 80 (b) Ultrasonic Dispersion 80 3.40 Kinetics and Mechanism of Formation of Xonotlite 82 3.41 Activation Energy 82 3.42 (a) Mechanism at 335°C 82 (b) Mechanism at 500°C 83 3.43 Characteristics of the Dissolution of Quartz in Saturated Lime Solution 85 3.44 Diffusion of Ions through the Product Layer 86 3.45 Solubility of Calcium Hydroxide at 300°C 86 3.46 Diffusion Coefficients 88
CHAPTER (4)
4.00 Practical Implications 93 4.10 Further Work 94 4.20 Concluding Remarks 95 4.30 Acknowledgements 96 4.40 References 97 CHAPTER (5) 5.00 Other Publications submitted for Collateral Credit 103 5.10 Light weight Calcium Silicate Hydrate 104 5.11 Discussion of the Above Paper 111 5.12 The Sucrose Extraction Method for the Estimation of Available CaO in Hydrated Lime 112 1
1.10 INTRODUCTION:
Calcium Silicate Hydrates are of considerable importance in pure and applied chemistry and in geochemistry if for no other reason than the widespread occurrence of the materials involved in their formation. Technologically they feature as the binding or cementing minerals formed during the hydration of Portland cement and during the autoclave treatment of building units made from mixtures of lime and siliceous materials.
Previous work by Taylor^^ and the writer on some applied studies of the system CaO - SiC^ - ^0 as a cementing matrix led to this present work being under taken. These studies were concerned chiefly with the strength development of mixtures of crushed quartz and lime under a variety of hydrothermal conditions. It was found from this work that the depth of erosion on the quartz particles of these test pieces was less than one micron. The formation of a microcrystalline product surrounding the quartz particles was responsible for the development of a binding matrix. Compressive strengths in excess of 30,000 P.S.I. were achieved from some test pieces. With these facts in mind the obvious area to which to direct our efforts appeared to be towards the understanding of the mechanism of the reaction at the quartz-solution interface and the study of the thin layer of products surrounding the quartz particles. 2
1.20 LITERATURE REVIEW.
The system CaO - SiC^ - H^O has been studied extensively and there now appear in the literature some well established data of phase compositions and equilibria that exist under a variety of conditions, and using a diversity of starting materials. Most of the workers have been motivated in their investigations by the need to acquire a more complete understanding of the physical and chemical changes taking place during the hydration of Portland cement and the hardening of silica- lime mixtures during autoclave treatment. The processes of cement hydration have been studied by many workers and although the mechanisms are related to some extent, only the specific interactions of the CaO - Si02 - H^O system will be dealt with in this thesis. (2) Steinourv has made an adequate review of the literature in this field up to 1947. Until relatively recent times, the work has been hindered by lack of suitable equipment to distinguish between and make quantitative estimates of the poorly crystalline phases that are produced by the interactions mentioned above. The application of newer techniques such as X-ray diffraction, electron microscopy, differential thermal analysis, thermal balances and infra-red spectroscopy have made the contribution of workers since this time more significant. 3
1.21 Structure and Morphology of the Calcium Silicate Hydrates
These minerals have characteristic chain silicate structures which have been described by Taylor^ ' The SiO^ chains are kinked in such a way as to repeat at intervals of three tetrahedra and have therefore been called "Dreierketten". This distinguishes them from other kinked chains such as pyroxene chains or "Zweierketten". The semi-crystalline phases* C.S.H.(I) C.S.H. (II) and gels formed in the hydration of C^S and Portland cement are related structurally to tobermorite and also belong to this group. In the case of xonotlite the chains are condensed together in pairs giving an analogue of the double "Zweierketten" or amphibole chain. (Fig. 1.21 (a))
The structure of xonotlite has been determined by Mamedov^^ , and is illustrated by a photograph of the model (Fig. 1.21 (b)); it belongs to the monoclinic system with cell constants a = 16.95 b = 7.33 c = 7.03 R ft = 90°. Megaw and Kelsey^8) ^ave described the structure of tobermorite to be very nearly orthohombic with cell constants a = 11.3b = 7.33 c = 22.6 R, a layer structure with layers parallel to the (001) plane. On dehydration they noticed a shrinkage of the (002) spacing indicating
* Cement chemical nomenclature C = CaO, S = Si02, H = H20 FIG.1.21(b) ItGDBL OF XONOTLITE STRUCTURE* Cft.(white). (OH).(Blue)• (G).(clear). (si).(red). 5 that the layers were packing more closely together when the water was driven off. The suggestion is made by (18 ^ Mamedov and Belov ' that there may be a close structural resemblance between what is designated as 11.3$ tobermorite and xonotlite.
Taylor(v 9)J observed that a high degree of order is preserved in the transformation of tobermorite to xonotlite. The morphology of tobermorite apparently depends to a large extent on the conditions of formation. (19) (25) Observations by Kalousek and Prebusv ' and Grudemov indicate that with C/S ratios up to 1.4, crinkled foils were the prevalent crystal habit while, at C/S ratios higher than this or in saturated lime solutions, a fibrous habit predominates.
Brunauer and Greenber^^ have confirmed these findings and concluded that under these conditions thin platy foils or sheets roll up giving the appearance of fibres. The ability of these minerals to form fibres and their tendency to bond together in an interlocking network has been used to account for their cementing properties
1.22 Effect of Temperature on Phases Produced
Taylor^) has identified the products of the system at ordinary temperatures and established phase equilibria data for hydrous calcium silicates in contact with solution. He has also tabulated X-ray data to 6 define the two products he designates as C.S.H.(I) and C.S.H.(II), derived from the hydration of SCaO.SiC^*
It has been pointed out by many authors that metastable products occur frequently in these hetero geneous systems. Most of the reactions in slurries of lime and silica are diffusion controlled and it has been suggested by Aitken and Taylor^^ that metastable products formed in pastes may in fact differ from those formed in more dilute suspensions. The occurrence of these metastable phases has led to conflicting evidence being presented and has not helped to establish the conditions necessary to produce specific products. / c \ According to Assarsson^ ', products of the interaction of calcium hydroxide solutions with quartz and with silica gel cannot readily be compared. Reactions in calcium hydroxide - quartz pastes between. 90° - 200°C have rarely been found to go to completion.
Aitken and Taylorha\e found from their X-ray investigations that mixtures of two or more (29) hydrous calcium silicates are frequent. Assarsson shows the significance of the initial CaO/SiC^ ratio or, more accurately, the ratio of CaO/square meter of SiC^ surface available in determining the phase composition of the products.
Heller and Taylor^^ have described the transitions of hydrous calcium silicates as the 7 temperature is raised to 200°C. They found C.S.H.(I) to be the initial product below 140°C, but with more prolonged treatment at 140° - 160°C afwillite appears and on heating to 180° - 200°C, xonotlite and hillebrandite are the main products.
/ r \ Assarsson^ ' claims that, with quartz-lime systems, when the CaO/square meter of SiC^ surface in approx. 200 mg. and with temperatures of 120° - 150°C, the products first formed are gelatinous but after one month tobermorite may be detected by X-ray means. With further treatment of these preparations at 150° - 220°C, Gyrolite may become evident with the gradual disappearance of tobermorite. Preparations having CaO contents greater than 200 mg/square meter of Si02 surface results in the formation of a-dicalcium silicate hydrate within the temperature range 120° - 150°C.
At higher temperatures, 150° - 220°C,the first products formed are again amorphous, but a-dicalcium silicate hydrate was found to crystallize and further treatment leads to the formation of tobermorite and xonotlite. Assarsson found that, with even more prolonged treatment, tobermorite and xonotlite disappeared to give rise to a stable phase gyrolite. (S') In a more recent paper, Assarsson^ ' elucidates the processes by claiming that the lime-rich phases 8
described above behave as sources of calcium ions. These ions are released to form new phases poorer in lime. He postulates that the silicate ions necessary for reaction reach the reaction layer by diffusion from the underlying quartz surface. At higher temperatures the transformation of C.S.H.(I) and tobermorite to structurally related xonotlite are experienced. These transformations are described by Heller and Taylor and Taylor (9) . With treatment of preparations above 350° the main phase identified by X-ray means was xonotlite together with s ome additional lines which may have been due to a modification of xonotlite or to the presence of a yet-unidentified phase.
Other workers, Corwin^et al. describe the reaction between a silica tube and Ca(0H)2 solution at 400°C with a limited supply of Ca^H^- In these experiments at supercritical temperatures xonotlite forms first and, with more prolonged treatment, there results the modification of this phase to 0-cristobalite and finally -cristobalite as the stable phase.
Gillinghamgives an account of the transport of silica to CaO and calcite at super critical temperatures claiming Wollastonite to be formed as a product of the interaction. 9
Perhaps the phase composition data versus temperature of treatment could be summarised to the best advantage by the diagrammatic representation presented by Taylor (3) (see Fig.1.22). Although, as he emphasises, the products represented may not be truly stable ones.
1.23 Some Proposed Mechanisms
The processes involved in the interaction of lime solutions on quartz or silica particles have been (12) described by Greenberg as follows:
(i) Chemisorption of Ca(0H)2 on the surface of the silica.
(ii) Solution of the Silica —> H^SiO^-^H^SiO^ •—> H^SiO^ with increasing pH. I | (iii) Reaction of monosilic acid with Ca ions in solution.
(iv) Formation of nuclei of C.S.H.
(v) Growth of Nuclei.
(vi) Precipitation of crystals of C.S.H.
In these experiments step (ii) was found to be the rate determining step.
Logginov^"^ et a 1. have suggested a similar process in their study of the interaction of Ca(0H)2 solutions on samples of silica of various degrees of sub division. However their suggested mechanism differs in that they claim the film of product which surrounds the silica 8
'-or/?- C2S 8 Oo 9jn|DjedLuax O O CSl o o O A FIG.1 .2 2 TEMPERATURE - PHASE COMPOSITION DIAGRAM ' 11 particle reaches a maximum thickness and remains unchanged. / O £ \ Assarsson^ ' states that the formation of the tobermorite phase is based on the rate of dissolving attack on the surface of the silicate or silica as the case may be, in relation to the rate of diffusion of Ca(0H)2 through the product layer. The various chemical reaction stages have been summarised by Kalousek^^ who states that the first step in the overall reaction may be expressed as 7C + 4S + Aq -- > C7 S4 Hn. The lime rich phase then reacts in a series of steps with residual silica:- 5C-7S/Hn +8 S---- 3, 7CcS/Hn 7 4 '54 C.S/Hn + S --- > 5C .S .Hn 5 4 4CSHn + S --- > C,ScHn 4 5 He also suggests that the process is diffusion-controlled. 1.24 Water of Hydration and Free Water The nature of the bonding of water in tobermorites is still not certain. There appears to be very little distinction in binding energy between water chemically bonded and that present as "free" molecular (21) water. According to Bermal 7 tobermorite is an orthosilicate Ca^f SiO^(OH)^?2-Ca(OH)^ with two hydrogens on two of the oxygen ions in the SiO^ tetrahedra, or 12 they may be in hydroxylic form in the layers, the third being between the layer, also in hydroxylic form. (24) Brunauer and Greenberg have found the interlayer water to be molecular so that a formula of Ca£ [SiC^ (OI^)"] 2 CaO.t^O is more correct. Drying conditions of increasing severity cause the interlayer water to be lost continuously. X-ray and infra-red techniques have been useful in detecting the changes in structure at various (22) stages of dehydration of these minerals. McConnell has shown three distinct levels of hydration for C.S.H.(I) having I^O:SiC^ ratios 2.0, 1.0 and 0.5 with corresponding "d" spacings of 14.6, 11.3 and 9.6 respectively. Thermal balance curves on the dehydration of these minerals by Aitken and Taylor^^ also Butt et al. (38) indicate that even xonotlite has water associated with the structure other than that corresponding to the idealised formula Ca^Si^O-^(OH)^• They suggest some inclusion of water molecules in the centres of the rings of eight SiO^ tetrahedra. If all these holes were filled, then the formula would approximate C^S^H which agress with results found for both synthetic and natural xonotlite. Xonotlite differs markedly from tobermorite in that it has remarkable volume stability during drying and wetting. Xonotlite does not experience the "d" interlayer spacing shifts referred to above. 13 (23) Kalousek and Roy explain this as due to tobermorite losing both interlayer water and bonded (OH). 14 1.30 THE OBJECTIVE OF THIS WORK The literature review has revealed the extent of work in this field. It is clear that these minerals have captured the interest of many workers, particularly in the identification of phases formed by the hydration of Portland cement and by the interaction of lime and siliceous material under hydrothermal conditions. Much effort has also been directed toward the determination of the conditions of stability as well as the morphology of the phases formed by the reactions mentioned above. On the basis of the literature survey and the author's previous work in this field, the present investigation was directed to the elucidation of the mechanism of reaction of saturated lime solutions with single crystals of quartz and the nature of the calcium silicate hydrates formed at the quartz-solution interface. It was anticipated that further light would be thrown on the hardening process which occurs during the autoclave treatment of some commercial building units such as sand-lime bricks and other light-weight products which depend on the formation of a calcium silicate hydrate binding matrix. 15 EXPERIMENTAL PART 2.10 REAGENTS AND MATERIALS USED (a) Ca(OH)p The Ca(OH)2 used in this work was manufactured by May and Baker Ltd. and had the following limits of impurities: Chloride, not more than 0.027, as Cl. Aluminium & iron (acid insoluble), not more than 0.8%. Sulphate, not more than 0.27, SO^* Arsenic, not more than 0.00027o As. Lead, not more than 0.00017. Pb. Carbon dioxide was variable, but was estimated regularly throughout the use and found generally to be between 1 and 27. expressed as CaCO^ • SiC^ Quartz The quartz crystals used in all but the preliminary experiments were radio quality Brazilian quartz. This material gave a residue of less than 0.27, on ignition with HF. Ba(OH)2 "Analar" Ba(0H)2 8H2O was used and it contained the following limits of impurities: Acid insoluble nil Chloride Cl not more than 0.0027, Nitrate NO^ not more than 0.0027, Sulphide S not more than 0.0027, Iron Fe not more than 0.0017, Heavy metal Pb not more than 0.27, Carbonate (BaCO^) not more than 0.5% 16 Calcite. These were optical quality calcite crystals obtained from the Geology Department, University of New South Wales. Active Materials 45 Ca (0H)? Solutions were prepared from Active 45 Z Ca CO^, having a specific activity of 0.5 m.c. on September 18th, 1961, by ignition at 1000°C for several hours and subsequent solution in distilled water. The active carbonate was obtained from Australian Atomic Energy Commission. It had a half life of 106 days and an emission of 0 radiation of 0.53 MeV. 45 Ca Clp Solutions prepared by Amersham England; a 1.39 mg stock solution of 0.54 me activity on June 30th, 1961. 22 Na Cl Prepared from Amersham stock solutions of specific activity 2.1 mc/mgm Na on October 2nd 1961. 2.11 Preliminary Experiments In these experiments, single crystals of natural quartz 1.5 cm. in length were chosen and sectioned into 2 mm. plates. Some of these plates ye re weighed and then pressed into pellets with moist lime, while others were suspended in saturated lime solutions. The specimens prepared in this manner were then autoclaved for periods up to 20 hours at temperatures not exceeding 17 220°C. The autoclave used in these experiments was electrically heated, being 8 inches in internal diameter and approximately 15 inches in height. It had a maximum working temperature of 220°C in saturated water vapour. The selected maximum temperature could be preset by means of a thermostat control. After treatment, the crystals were carefully cleaned to remove adhering products and re-weighed. A weight loss of less than 1 mg. indicated clearly that the reaction under these conditions was extremely slow and limited. It was possible to mount some of these quartz crystals, which had thin films of products on their surface, in a suitable holder and to scan them with a Philips X-ray diffractometer. This instrument was used with the following settings: Target tube Cu Filter Ni High tension 40 KV Tube current 20 mA Sweep speed 2° per minute Scale settings 16 x 1 Scale range 2° to 65° Slits 1°: 0.15:1° 18 Examination of the chart (Fig. 2.11(a)) showed diffraction peaks due to Ca(OH^ together with extra lines at 20 values corresponding to 4.11 A°, 3.71 A° and 3.02 A°. It was apparent from these tests that a much greater extent of reaction was needed if a product layer of sufficient thickness for examination was to be produced. A hydrothermal bomb was then constructed which was designed to take much higher temperatures and pressures. For details of construction see Fig. 2.11(b). Examination of quartz crystals suspended in saturated lime solutions and pressed in lime pellets treated for several hours at temperatures up to 350°C showed a product layer formed of almost 1 m.m. in thickness. This made a microscopic examination of the layer possible, and a Vickers microscope was used with incident light on a section of the polished quartz product layer. This showed the material formed to be composed of fibrous micro - cry s ta3s , the largest of which could only just be resolved with xlOO miagnification. Weight loss of the quartz crystal with the product layer removed showed that 0.208 g. of SiO^ had been dissolved. Portions of the product layer that were broken away from the quartz were mounted on a glass slide for FIG .2.11(a) X-UAY DIFFRACTOMETER PATT Rli OF PRODUCT MATERIAL FORMED DURING PRELIMINARY EXPERIMENTS. FIG.2.11(e) X RAY DIFFRACTOMET R PATT' RK OF XONOTLITE FOHJH® l-J 1 J BOMB. 1 HYDROTHERMAL ( b ) 2 . 1 1 FIG. 21 X-ray diffractometer analysis. One of the charts resulting from this analysis is shown in Fig. 2.11(c). They show strong intensities of diffraction at values of 29 corresponding to the characteristic reflections of the mineral Xonotlite. Other evidence presented later confirmed this mineral as the predominant species formed at this temperature. 2.21 Physical and Chemical examination of the product material formed at 350°C. Detailed X-ray Examination of product» From the preliminary experiments it has been shown that it is possible to make an X-ray examination of the surface of the polycrystalline product formed around the quartz crystals in lime slurries. It was decided to carry this X-ray examination one stage further by sectioning the product layer parallel to the original quartz surface. A special mounting stage was constructed to enable the product layer to be sectioned in a hand-drawn microtome. This meant the product layer could be successively X-ray scanned and sectioned from one side to the other in predetermined increments. This was done, and the material cut in each sectioning was reserved for X-ray powder photography. The diffractometer charts for a typical series taken through a layer of product are shown in Fig. 2.21(a-d) C»()H)2 sid* (ft) (*) <*) (*) gUARTfc 2& sIPE rie. 2.21 X-RAY DIFFRACTOMETER PATTERNS OF SECTIONS THROUGH THE PRODUCT LATER. 23 The interpretation of these charts and the accompanying powder photographs are dealt with later under "Discussion of Results". 2.22 Microscopic Examination. (Optical). Thin sections of the product layer were prepared by saturating the porous layer with Canada balsam and lapping with fine carborundum. Typical sections of the product formed at 350°C are shown in the accompanying photo-micrographs. See Fig. 2.22 (a) (b) (c). They show the variation of crystallite size and of the number of sites of nucleation as the distance from the quartz side increases. The photomicrographs (Fig. 2.22(d,e) show some fibrous crystal formed at 235°C growing out from the face of the quartz crystal. This micrograph was taken using incident light. Some of th^naterial formed at 350°C was ground then dispersed in water and examined with a Wild M20 Microscope at high magnification. A few of the larger fibrous crystals were then examined and photomicrograph (Fig. 2.22(f)) shows two of these fibres which have been bent to a small radius by using a micro-manipulator. This illustrates their flexible nature. These fibres were also examined using phase contrast attachments and the photomicrographs (Fig. 2.22 (g)(h)) show more features of their structure. 24 yumrte bide FIG.2.22 HIOTQMICR0aSliUPBi OF Tiilfc SECTIONS TAK N HIGH FARIGU POSITIONS TffROUtiU THE PRODUCT LATER. 25 FIG. 2.22(d)(e) FIBROUS CALCIUM SILICATE BYDRATE ON TKE QUARTZ CRYSTAL. z 430 Fv’O b<3 FIG. 2.22(f). PHOTOMICROGRAPH OF XONOTLITE FIBRES BENT WITH A MICROMANIPULATOR PROBE. 27 FIG.2.22(g) (h) PHOTOfeiICROGKAPHS OF XONOTLITE FIBRES MEN USING PHASE CONTRAST TECHNIQUES. 28 2.23 Electron Microscopic Study Dispersions prepared as mentioned above were made of the product material formed at 335°C and at 500°C (supercritical temperature). These dispersions were placed on small copper grids. The grids were previously prepared with carbon stabilized collodion films, and after being dried, were introduced into a J.E.M. (6A) Electronmicroscope. Electron micrographs, Fig. 2.23 (a,b,c,d) show a variety of fields and magnifications of these crystals. They illustrate the "rolled foil" habit of Xonotlite. Some of the micrographs taken of Xonotlite fibres formed above critical temperatures show a puckering of their outermost foil. A diffraction pattern micrograph, Fig. 2.23(e), was taken of One of these fibres. It shows the layer lines normal to the fibre axis. The distance between these was accurately measured and the calculations made to determine the layer distance in A° units. (These calculations and an explanation of the broadening of the spots are dealt with in the "Discussion of Results") 2.24 Chemical Analysis of Products formed at 350°C Chemical analysis for calcium oxide, silicon dioxide and, where sample size permitted, loss on ignition were performed in conjunction with the (a) x 4000 (355°C) (b) x 13000 (c) x 6500 (€00°C) (d) x 6000 (b03°C) FIG. 2.23 ELECTRON MICROGRAPHS OF XONOTLITE FIBRES. Supplied by Metallurgy School, The University of New South Wales 30 FIG. 2.23(e) ELECTRON - DIFFRACTION PATTERN OF XONOTLITE FIBRE. Supplied by Metallurgy School, The University of New South Wales 31 sectioning mentioned earlier under "Detailed X-ray examination". Samples of approximately 100 mg. were taken of material previously dried at 100°C. for several hours. These samples were then ignited and some determinations of weight loss due to loss of 1^0 were made. These varied from 3.5 - 4.570 of the weight dry at 100°C. Digestion of this material was then carried out with fused NaOH in Ni crucibles. These melts were dissolved with distilled water and poured into standard flasks containing an excess of HC1. In this way dissolution of Si02 from the glass by the NaOH solution was avoided. Suitable aliquots of this stock solution were taken, and ammonium molybdate and tartaric acid solutions were added. A "Unispec" Spectro-Photometer was used to determine Si02 colourimetrically by comparison with Standards from pure Si02 prepared previously. Calcium oxide determinations were made from aliquots of the original stock solution. These aliquots were adjusted to pH 10.0. After addition of eriochrome indicator, the solutions were titrated against 0.01 M. E.D.T.A. solution. Results of these analyses appear in Table I, and are compared with theoretical proportions for pure Xonotlite Ca^Si^O.^(OH)^ after Mamedov. 32 TABLE (I) 1st Analysis Repeat Analysis Ca6Si6°17(OH)2 * Section Section Xonotlite 1 2 3 1 2 3 % % 7, 7> 7, 7> 7, CaO 52.1 48.4 44.0 46.5 45.7 44.3 47.1 Si02 45.8 48.6 48.8 48.5 49.6 47.8 50.4 Ignit- 3.5 4.3 -- - H20 ion loss * 2.52% Molar 1.22 1.06 0.97 1.03 0.99 0.99 1.00 CaO/SiOo 1______* Section 1. Lime solution side of product layer 2. Centre of product layer 3. Quartz crystal side of product layer. 2.25 Thermogravimetric Study A Stanton Thermo balance Model No. T.R.I. was used for this experiment, with a sample of one gram of product material. A heating rate of 5-6°C/minute was maintained. Figure 2.25 shows the loss in weight versus temperature, and an examination of this curve shows a gradual loss to 710°C of 0.67> of sample weight and then a sharp increase in the rate of weight loss of 2.37> between 710° - 800°C. An explanation of this curve is dealt with in "Discussion of results". 9 W t£ THERMOGRAM of XONOTLITE Wt. DECREASE Heating rate = 5*7DC min. 400 TEMPERATURE (°C) FIG. 2-25 34 2.26 Measurements of the porosity of the product material formed at 350°C A sample of approximately one gram of this material was supplied to the Division of Coal Research of C.S.I.R.O. where a pore size distribution analysis by mercury intrusion was carried out. Figure 2.26 shows the results of this analysis. The main pore range is seen to lie between 216,000 - 5,400 A°. A description of the apparatus used is given (37) by Ingles . This instrument is capable of measurement down to a pore diameter of 100A°. 2.27 Infra-red absorption spectra Absorption spectra were produced by the preparation of the product material in KC1 discs prepared in a manner (27) described by Hales and Kynaston. The proportion of sample to KC1 was adjusted to give a suitable absorption chart in the range used. An Infracord recording spectrophotometer was used to obtain absorption specta in the wave length range 2%-15 microns. Some of the features of these absorption curves (Figures 2.27 (a) and (b)) are discussed later, and compared with those of other workers. 2.31 Kinetics of the formation of the product mineral at 335°C and 23 5°C In these experiments, quartz cubes cut from single crystals were suspended in saturated lime 35 a LAYC PRODUCT OF o LU I— < - z tr t— d UJ CO z UJ 0- DISTRIBUTION co UJ UJ cr tr o SIZE 3 0. CO CO CL LU o or PORE CL QC UJ »— o LU d z < Q 2 .2 6 FIG. Co o) 31dWVS dO WVd9 d3d 9NllVdl3N3d Adn3d3W 30 3wmoA 36 Wavelength (MICRON. FIG.2.27(a) I.R. SPECTRA OF PRODUCT MATERIAL FORMED AT 335°C. C-D Ca(OH) vs. ABSORPTION at 3620 cm"1 2 mg Ca(OH) in 1g KCl ABSORBANCE at 3620 cm- Fig. 211 (c) 38 solutions containing a large excess of lime. These solutions were held in a silver tube within the hydrothermal bomb described earlier. The quartz cubes were suspended by means of a silver wire cage, the cube and the wire being weighed prior to the treatment at elevated temperatures. These cubes were then subjected to hydrothermal conditions for various periods and a record of the increase in weight and a photographic record of the product layer growth was made. Before weighing, the cubes surrounded by product material were rinsed with distilled water and finally with ethyl alcohol before being dried at 100°C. Plots of the weight increase are shown in Figure 2.31 (a) and (b) against time in hours and against the square root of time. The latter curve gives a straight line relationship. Photographs of some stages in the formation of the product material are shown in Figure 2.31(c). These photographs also show one face of the product material cut away after the test. From these photographs it was possible to measure the relative amounts of quartz dissolved from the basal and prism faces of the crystal. These measurements appear in Table (2) and indicate a more extensive dissolution on basal than on prism faces. PRODUCT FORMATION a t 235° C TIME (hr.) /F PRODUCT FORMATION at 335°C TIME (he) JT L r J T 41 (before reaction) (boring reaction) (SECTIONED - AFTER COMPLETION OF EXPERIMENT) FIG. 2.31(c) STAGES OF PRODUCT FORMATION 42 TABLE (2) Measurements taken from enlarged photographs of reacted quartz cubes. Before Reaction After Reaction Difference C. Axis ) Run 9 ) 1.00 0.83 0.17 cms ) ) 1.10 0.84 0.17 " Basal Face ) Run 10) 0.71 0.54 0.17 " ) ) 0.73 0.57 0.16 " A. Axis ) Run 9 ) 1.30 1.20 0.10 " ) ) 1.33 1.21 0.12 " Prism face ) ) Run 10) 1.19 1.10 0.09 " Erosion ) > 1.19 1.09 0.10 " Examination of the product material formed in the experiments 2.32 Microscopic Examination of thin sections of product material formed at 335°C show the laminations due to the interrupted period of treatment. A photomicrograph illustrating this feature is shown on Figure 2.32. 2.33 X-ray Analysis. Diffractometer scans of the product material formed at 335° were similar to that shown in Figure 2.11(c). The reflections are essentially that of pure Xonotlite, although one small peak at a 20 value of 7° could not be accounted for. Products formed at the lower temperature 235°C, consisted of only a thin film covering the quartz surface. These were X-ray scanned directly on the surface of the quartz cube. LAlTJi. 44 Figures 2.33(a)(b) and (c) show the diffraction peaks after various periods of treatment. The peaks attributed to Ca(0H)2 and quartz are labelled on the charts. There also appear other peaks; these were attributed to a product phase the identity of which is dealt with under "Discussion of Results". Table (3) shows the "d" spacings of lines other than those due to Ca(0H)2 and quartz. Results of X-ray powder photography of the product material scraped from the crystal after conclusion of these experiments appear below: TABLE (3) I "d"(X) w 3.84 vs 3.04 vw 2.92 M 2.49 s 2.286 MS 2.092 MS 2.080 VW 1.600 VW 1.524 2.40 Diffusion of Ions through the porous product Material Earlier work indicated that the product layer of Calcium silicate hydrate surrounding the quartz 45 (t) HTFJ 6>0 H 20 50° 30° 10° FIG.2*33 X ILAY PIFFRACT0MKT IR FATTFSIIS OF FHOUfJCt MAT RIAL wmm AT 235°c. scann?:p on Tnr QUARTZ CRYSTAL. 46 cubes could be less permeable to Ca ions in solution than to l^SiO^ ions. This was concluded from observations that growth of the crystalline new phase did not follow the receding surface of the quartz. The subsequent formation of this phase was invariably on the surface farthest away from the quartz. A diffusion cell was constructed to measure the rates of diffusion of various ions through a membrane « of the product. This cell consisted of two glass flasks separated by a section of about 1 square cm. area by 0.1 cm. thick of product material taken from one of the test pieces. This section was cemented with epoxy resin into one arm of the connecting tube linking the two flasks - see Figure 2.40(a). In separate experiments, solutions of 0.02 M Ca(0H)2j CaC^ and NaCl were introduced into one side of the diffusion cell, while an equal volume of distilled water was placed in the other. The cells were kept in a constant temperature bath at 30°C, ^-1°C and the solutions were continuously stirred by means of magnetic stirrers. The migration of cations was followed by using radio isotopes of Ca and Na. Detection of the movement of these isotopes through the membrane was made by taking periodic checks on the activity of the solution in the opposite cell. The activity measurements were made with a Davis cell, a photo-multiplier tube and counter * Radio active isotopes FIG. 2.40(a) DIFFU^I 4>M CELL. 48 arrangement for Ca The conditions giving optimum count to background 45 ratio for Ca source were found to be:- Gain pre.amp. 250 Discriminator 25 volts High Voltage 1,100 volts. 22 When Na activity was measured a Nal scintillation cell with photomultiplier tube counter was used. The following conditions gave optimum results: Pre.amp. 25 Discriminator 20 volts High Voltage 1,200 volts. Vc Results of concentrations versus time are shown in Figure 2.40(b). The curves show similar initial rates I | of migration but Ca ions in association with OH ions show a definitely slower ultimate rate. Further investigation by chemical analysis after the completion of the experiment with Ca(0H)2 showed that this experiment had been affected by the precipitation of the Ca as the carbonate by atmospheric carbondioxide. This had occurred despite efforts taken to prevent carbonation such as ^-sweeping of the air above the solution. The results of the chemical analysis of the calcium hydroxide diffusion experiment are shown in Table (4) * Concentrations calculated from the activities of solutions. DIFFUSION of IONS THROUGH a XONOTLITE MEMBRANE MOLAR CONCENTRATION NaCl CaCl^ Ca(OH) 50 100 log TIME (hr.) FIG, 2-40 (c) 50 TABLE (4) Weight in mg. % CaO added to cells 59.9 100.0 CaO recovered as 5.8 9.7 CaCO^ after test CaO recovered as 48.7 81.4 Ca(0H)2 after test k CaO adsorbed by 0.55 0.9 membrane “The membrane was digested after completion of the test and the activity of the solution was measured. From this measurement the quantity of active calcium adsorbed by the membrane was calculated. This was found to be between one and two percent calcium oxide based on the dry weight of the membrane. 2.50 Solubility of Ca(0H)2 at 300°C To obtain some estimates of the diffusion I | coefficients of Ca ions in solution, a measure of the solubility at 300°C was required. It was decided to measure solubility by conductivity methods and, to this end, suitable electrodes and insulated lead-throughs for 51 the hydrothermal bomb had to be designed. The materials of construction presented some difficulties as these had to be inert to water vapour at this temperature and the supports for the electrodes had to be insulating and rigid. Figure 2.50(a) shows the final design with materials used as indicated. The cell constant was determined in the manner described by Glasstone^^ using KC1 solutions. Saturated calcium hydroxide solutions were prepared by shaking an excess of this reagent with distilled water in the sij-ver reaction tube. These solutions were placed in the hydrothermal bomb and the temperature raised in a stepwise manner to a final temperature of 300°C. At each increment in temperature the conductivity was measured. The temperature was held constant until the conductivity reached a steady value. Results from the literature are available to 180°C, and these are plotted in Figure 2.50(b) with the extension to 300°C. from the calculated conductivity results obtained with the apparatus described above. 2.60 Work done at Supercritical Temperatures Some exploratory tests below the critical temperature indicated that the rate of solution of quartz in saturated lime solutions was about twice the rate of solution in the vapour phase above the solution. It was decided to explore higher temperatures and HYDROTHERMAL BOMB ELECTRODE Nimonic 80 Sealing Bolt 11*5cnr Wires in Ceramic Insulator Glass Seal’ Pyrotanax Teflon Plug Silver Rod Silver Wires Teflon Blocks 9*5cm Holes to Release Bubbles Pt with Precitated Pt Black Electrodes 0*6*cm & 0*6 cm apart FIG. 2-50 (a) 53 SOLUBILITY of Ca(OH) vs. TEMPERATURE MOLAR SOLUTION Ca(OH) ------Conductance Measurement ------Data from Lange (42) ------International Critical Tables(42) TEMPERATURES FIG, 2-50 (b) EQUIVALENT CONDUCTANCE vs. TEMPERATURE JV_ =J\- + JV_ Ca(OH) Ca+> OH 2 ^2 EQUIVALENT CONDUCTANCE _A_ OHM”'em2 Data taken from Robinson & Stokes (39) TEMPERATURE °C FIG. 2-50 (c) 55 pressures. Above critical conditions and at high degrees of fill below critical conditions, water vapour does not conform to ideal pressure-temperature relationships^611116^ . This meant that the degree of fill affected the pressure obtained to a large extent. In these tests, a 53% fill of the hydrothermal bomb was used and a temperature of 500°C. These conditions gave a pressure of 1000 atmospheres. After various periods of treatment under these conditions, the quartz cubes were withdrawn for inspection and weighing. It was found that the product material did not form a cage around the quartz as in previous experiments below critical conditions, but it appeared much more friable and was formed on the lower half only of the quartz cube - see Figure 2.60. It appeared to grow out to the sides of the tube, blocking the tube off so that lime was not available to react with the dissolved silica above this point. When a very small quartz cube was used, to avoid this effect, no product material formed around the quartz at all. A plug of product, however, was formed on top of the excess lime in the bottom of the tube. Samples of this material were rinsed with distilled water, dried and reserved for X-ray microscopic and electron microscopic inspection. FIO. 2.60 PROTHJCT FORHf.1) AT 500°C. 57 2.6)1 X-ray examination by powder photography of this material showed the main lines of Xonotlite. Table (5) compares the "d" values obtained with those of pure Xonotlite and £ - Wollastonite. Results indlicated ^-Wollastonite was not present to any extent. 58 TABLE (5) Unknown Xonotlite A.S.T.M. ft-Wollastonite A.S.T.M. I "d"C&) "d"(R) X/lo "d"C8) l/Xo vw 7.795 20 8.5 40 7.7 MS 6.945 40 7.05 10 4.05 MW 4.230 40 4.27 80 3.83 M 3.615 20 3.96 80 3.52 M 3.470 70 3.65 5 3.40 M 3.235 70 3.23 80 3.31 S 3.075 100 3.07 5 3.16 S 2.955 50 2.83 30 3.09 MS 2.821 40 2.71 100 2.97 MS 2.691 20 2.65 10 2.80 M 2.481 40 2.51 10 2.72 M 2.335 30 2.34 30 2.55 M 2.173 30 2.25 60 2.47 MS 2.028 85 2.04 40 2.33 MS 1.939 85 1.95 40 2.29 M 1.823 40 1.84 60 2.18 MW 1.753 30 1.756 5 2.08 MW 1.707 40 1.710 20 2.01 20 1.687 20 1.98 20 1.655 20 1.91 20 1.88 10 1.86 60 1.83 5 1.80 5 1.79 40 1.75 60 1.72 40 1.602 59 2.62 Electronmicroscopic examination As mentioned earlier, the crystal habit of this mineral formed above critical temperature remained essentially the same. There was however, evidence of puckering of the outermost foil on some of the specimens examined. Electronmicrographs (Figure 2.23(c) and (d)) show this characteristic. 2.70 Experiments with calcite crystals Some qualitative runs were made with calcite crystals suspended in the same manner as the quartz cubes, but in this case ground silica was placed in the bottom of the tube. This was done to determine if any interaction occurred and to identify the products if any, that were formed. The conditions of treatment were a temperature of 335°C and a period of 20 hours. The crystal was removed after this treatment and examined using incident light with a Wild M20 microscope. (Figure 2.70) shows a photograph of some of the adhering crystals. These crystals were later scraped from the surface. Table (6) shows the results of Md" values calculated from X-ray powder photographs taken of this material compared with those of ^-quartz and /3-Wollastonite 60 x 240 fig. 2.to mtoisiCRoeaAiB of frotxjct material m a gaxjcxtb oormi^ 61 TABLE (6) Unknown A Quartz AUS.T.M. A-Wollastonite A.S.T.M I "d" i/i "d"£ "d"£ R o l/To VVW 3.800 60 4.43 40 7.7 VW 3.540 10 4.05 VS 3.430 100 3.42 80 3.83 M 2.895 80 3.52 M 2.800 5 3.40 VW 2.448 60 2.55 80 3.31 W 2.298 40 2.30 5 3.16 VW 2.255 60 2.22 30 3.09 W 2.183 100 2.97 VW 2.158 10 2.80 MW 2.067 60 2.05 10 2.72 VW 1.975 30 2.55 VW 1.895 60 2.47 M 1.850 90 1.85 40 2.33 M 1.734 40 1.71 40 2.29 M 1.634 60 2.18 VW 1.590 5 2.08 VW 1.553 80 1.57 20 2.01 VW 1.513 20 1.98 VW 1.478 20 1.91 VW 1.417 80 1.421 20 1.88 VW 1.389 80 1.393 10 1.86 VW 1.312 60 1.83 VW 1.292 60 1.292 5 1.80 w 1.272 60 1.277 5 1.79 40 1.75 60 1.92 40 1.602 10 1.531 5 1.515 20 1.478 30 1.455 5 1.426 5 1.384 30 1.358 10 1.332 62 Further tests were made at 500°C and with a 257o degree of fill which gave a pressure of 500 atmospheres. This treatment gave a similar result to the previous test, and no evidence of Wollastonite was detected. 2.80 Ba(0H)2 - Quartz Hydrothermal reaction An exploratory experiment was made using a quartz cube suspended in Ba(0H)2 solution. A large excess of Ba(0H)2 was added to the tube. Similar conditions to previous tests with lime solutions were maintained during a 17 hour period at 335°C. Inspection of the resulting product showed the quartz cube had fallen from its silver wire cage to the bottom of the silver tube. It had become cemented into the polycrystalline mass. The tube had to be destroyed to recover the products. The polycrystalline material had to be chipped from the crystal. In this case a strong adhesion of the quartz to this material was noted. Powder X-ray diffraction photographs were taken, and the resulting "d" values appear in Table (7). These lines could not be assigned to any phase registered with A.S.T.M. card index. 63 TABLE (7) Unknown i "d "& M 5.695 M 4.500 M 3.650 M 2.980 M 2.890 S 2.060 M 1.461 W 1.280 64 3.0 DISCUSSION OF RESULTS 1. Identification of Products 3.10 Preliminary Work At 200°C, the diffractometer trace (Figure 2.11(a)) described earlier under "experimental work" showed that phases could be identified directly on the quartz surface. The presence of calcium hydroxide was established by reflections at 20 values of 34.3°, 18.2°, 47.3°, 51.0° and 28.6°. Reflections at 21.6°, 24.0° could be assigned to a new phase while that at a 20 value of 29.5° could be partly due to calcium hydroxide and partly to reinforcement of a new phase. These reflections correspond to "d" spacings of 4.11, 3.71, and 3.02 R. They do not fit the spacings due to oc-quartz or calcite due to the carbonation of lime. The reinforcement of the line at 3.02 R may have been due to formation of (3) C.S.H.(l) . These experiments indicated that the technique of direct x-ray diffractometer scans of the treated quartz crystals was practical. A further description of the identification of product material will be given in the next section. 3.11 X-Ray Examination X-ray examination of product material formed on quartz crystals in saturated lime solutions at 235°C. The X-ray examination was carried out in conjunction with the kinetic study. Periodic x-ray diffractometer scans were made when the quartz crystal was removed 65 for weight increase measurements. Diffractometer traces (Figure 2.33(a)(b) and (c)) show the reflections obtained after 140, 350 and 600 hours treatment respectively. The reflections due to calcium hydroxide and those corresponding to a -quartz are indicated. The growth of a new phase is indicated by the development of additional reflections particularly at 20 values of 45.5° 33° and 7.8°. The high intensity of reflections due to Ca(0H)2 is understandable since it is this surface of the product layer which is in contact with the saturated lime solution and adsorption of this phase on the surface could be expected. The presence of quartz should be indicated by a strong line at 20 value of 26.7°. A reflection of small magnitude at this value of 20 is observed in these traces together with other reflections that correspond to 20 values for a - quartz. It is concluded from this that & -quartz could be present in a small concentration in the surface layer scanned. The identification of phases other than those of calcium hydroxide and possibly a -quartz is difficult because most of the reflections are of small intensity and there is a strong possibility of preferred orientation. Preferred orientation of the product crystallites could lead to the relative intensities of reflections of any one phase being reversed or to the elimination of some reflections due to the plane of the layer of atoms being oriented 66 in the same plane as the x-rays. Diffractometer traces (Fig. 2.33 (a) (b) (c)) have been marked so that to each reflection is assigned what is possibly the phase most likely to give each reflection. Tobermorite is almost certainly present as indicated by 20 value of 7.8° which corresponds to the "d" spacing characteristic of tobermoriteButt , 11.3$ and supported by some other reflections of 20 including 16.4°, 45.5° which are equivalent to "d" spacings of 5.4^ and 1.99$ respectively. Although other reflections have been designated as due to the presence of other phases the evidence presented by these scans is not sufficient to be certain of this. X-Ray Powder Photography After completion of the run at235°C the product material was scraped from the quartz and specimens prepared for x-ray powder photography as described earlier. Measurement and subsequent calculations showed the "d" spacings in Table (3), which are the spacings other than those due to calcium hydroxide. These were assigned to some of the phases having spacings similar to those of the characteristic spacings of minerals belonging to this group, but no positive identification could be made from these results. 67 3.11(B) Infra-red Spectroscopic Examination The study of this material showed an absorption spectrum as reproduced in Figure 2.27(b). The absorption due to -OH stretching at wave number of 3620cm — 1 is most"/V probably due to ’’free" lime. . An estimate of the "free" lime was made by calibration with pure lime in various concentrations so that a curve (see Figure 2.27(C)) was established. The amount of free lime in this sample was estimated at 27%. The broader absorption peak at 3500cm ^ is due to loosely-bound water. The next major absorption centres around 1400-l600cm ^ and is due to calcium carbonate. Hunt (3D describes the carbonate ion as xy^ planar type having a doubly degenerate ^3 vibration associated with this group. He was able to establish a rough quantitative comparison of concentration to absorbance at 1460cm ^. From this work the absorption at 1460cm ^ in Figure 2.26(b) would indicate a CO2 content in the sample greater than 3%, by weight. * Xonotlite also has an -OH absorption close to this value but it would have other absorptions in this range which would be easily detected. 68 Absorption in the 1000-800cm ^ region is characterised by two absorption peaks, a rather broad peak at 945cm ^ and a well defined peak at 880cm ^. These peaks could not be associated with the absorption (31) (23) curves presented by Hunt and Kalousek and Roy of both natural and synthetic minerals belonging to the tobermorite group. The curves shown in Figure 2.27 showed a lack of spectral detail in this region which Hunt (31) attributed to the poorly crystalline nature of the material. The broad absorption in this region of the spectrum is a feature common to many silicates and represents a number of modes of vibration associated with Si-0 linkages. The region 800-650cm ^ shows two small absorptions, one rather broad at 765cm ^ and a much sharper peak at 715cm ^. This latter peak and that at 880cm ^ can be attributed to carbonated lime. It is clear that this technique offers a useful aid in the identification of minerals of this group especially with the use of an instrument having better resolution in the 2000-4000cm ^ region. In this region significant differences in the 0-H stretching frequencies have been observed which make positive identification possible. Results of the microscopic investigation will be dealt with later under "Morphology and Macro-structure". 69 3.12 Identification of Products formed at 335°C (1) The examination and identification of product material formed at 335°C presented no real difficulties. This was because the reaction had proceeded to a much greater extent than in the case of that formed at 235°C. This material consisted of a polycrystalline porous mass growing up to 5 mm in thickness; it formed a cage around the quartz cube as is illustrated by photographs (Figure 2.31(c)). One of the sides of this cage of material was cut away so that this slab of material could be mounted in the specimen frame of the x-ray diffractometer. X-ray diffractometer scans (Figure 2.21(a)(b) (c)(d)) illustrate the effects on the diffraction pattern as the product layer is progressively sectioned from the lime solution boundary to the quartz side. The pattern is that characteristic of xonotlite. The mounting of this product material and the sectioning with a microtome have been dealt with under Experimental work. A study of these traces shows that although the 29 values agree closely with those of xonotlite, the relative intensities do not correspond to those given by the A.S.T.M. card index. This observation applies particularly to the reflection at 29 value of 49.5°. It was thought that this remarkable change in relative intensity could be due to two causes 70 (a) Preferred orientation of the crystallites and (b) a non-stoichiometric concentration of highly reflective I | Ca ions through the layer. The former cause was concluded as the most probable as the chemical analysis Table (1) did not show a significant CaO concentration gradient through the layer. This conclusion was also supported by the accompanying x-ray powder photographs of the microtome shavings. The "d" spacing values from these films are shown in Table (8) and it is seen from this table that the relative intensities are similar to that presented by the A.S.T.M. Card Index. 71 TABLE (8) Lime Solution Quartz Side Centre Side I "d"£ I "d"& I "d"& M 6.97 M 6.995 M 6.685 M 4.23 M 4.23 M 4.140 VVW 3.895 M 3.590 M 3.540 MS 3.630 MS 3.195 VW 3.430 MS 3.240 MS 3.070 VW 3.305 MS 3.080 MS 2.813 MS 3.175 M 2.865 MS 2.671 M 3.030 M 2.695 M 2.514 M 2.775 MW 2.498 MW 2.321 M 2.648 W 2.338 MW 2.232 VW 2.585 W 2.247 MS 2.028 MW 2.370 MS 2.034 MW 2.298 MS 1.943 MS 1.939 MW 2.218 W 1.830 W 1.823 MS 1.928 VW 1.749 W 1.744 W 1.820 W 1.705 MS 1.702 MW 1.738 VW 1.684 VW 1.678 M 1.695 VW 1.651 VW 1.639 VW 1.669 VW 1.598 VW 1.569 VW 1.632 VW 1.563 VW 1.569 VW 1.518 W 1.511 VW 1.520 VW 1.426 W 1.422 VW 1.429 VW 1.388 W 1.382 VW 1.392 72 One further feature of the diffractometer scans is the appearance of a reflection at a 29 value of 51.3°. This is equivalent to a "d" spacing of 1.778 i?. This value of "dn was not listed in the A.S.T.M. card for xonotlite. To check whether this was a possible reflection for the xonotlite crystal the following calculations were made. Since £ 2^ 90° the cell was assumed orthorhombic( for the purposes of calculation,)and the formula ^ + was applied to d = 1.778. £ + a2 b2 The values of a, b, and c were varied systematically to obtain the values of best fit. A value of d = 1.7775 was obtained using the values corresponding to h, k, 1 indices the of (802). It was concluded from this that/reflection observed at a 20 value of 51.3° was due to plane having hkl (802) indices. (ii) The infra-red absorption spectrum of this material appears in Figure 2.27(a). The spectrum was prepared by the same pellet technique described earlier and was identical to that of xonotlite, presented by Kalousek and Ray but differed, in the 2,500-4,000 cm ^ region from the spectra presented by Hunt (31) . One feature of this curve is the characteristic of 0-H stretching absorption at 3620 cm ^ but a further absorption at 3430 cm ^ mentioned by Hunt (31) was assigned to free water. 73 3.12 THERMAL WEIGHT-LOSS. The thermal weight-loss curve for this material is shown in Figure 2.25. This curve is in a form similar to those presented by Aitken and Taylor^) but the total weight loss of 2.97> is much closer to the theoretical loss of 2.5%, than the samples used in their experiments. They obtained total weight losses of over 47, with a loss in weight in the 700-900°C range close to 3%. They claimed that pure xonotlite can incorporate water other than that allowed for in the idealised structure. It is interesting to note that, in the curve shown in Figure 2.25, a 2.37o weight loss occurs in the 700-900°C range. This is close to the theoretical loss and implies loss of structural or strongly bound water only, at this temperature. 3.13 Identification of Product Material formed at Super Critical Temperatures As mentioned earlier in the experimental part, x-ray powder photography of product material gave the characteristic "d" values of xonotlite. (see Table (5)). The strong lines of wollastonite are also presented in this table and it is seen that no evidence of wollastonite could be detected. This result is contrary to results presented by Taylor (9) who claims xonotlite to be converted to £-wollastonite above 400°C under hydro- thermal conditions, so that if /S-CaSiO^ were the stable 74 phase we should have obtained /3-wollastonite in our experiments at 500°C and 1000 ats.pressure. Periods of treatment of up to 3 hours under these conditions did not yield detectable quantities of /3-wollastonite. Electromicroscopic studies of this material dealt with later confirmed xonotlite as the predominant species. 3.20 Experiments with Calcite-Silica Gel and Barium Hydroxide-Quartz Systems The object of conducting these experiments was to obtain a cementing product layer on the calcite or on the quartz crystals which was strongly bound. Previous results had shown the calcium hydroxide-quartz system to yield a product layer which could easily be removed from the quartz. 3.21 The Calcite-Silica Gel Systan The preparation and treatment are dealt with in the experimental part. Identification was made of product material adhering to the calcite crystals as shown in photograph (Fig. 2.70). This was done by X-ray diffractometer scans of the material on the calcite crystal and also by X-ray powder photography of the product scraped from the crystal. Table (6) shows these results compared with the "d" values of /3-Quartz. There is evidence from both X-ray techniques for the presence of /3-Quartz. Most of the values not due to /3-Quartz can be assigned to calcite. The presence of Wollastonite was not detected in this 75 material. These results suggest that there is no interaction between the calcite and the silica in solution under these conditions but that /3-Quartz is precipitated from solution onto the surface of the calcite. There did not appear to be any preferential precipitation on the calcite. The walls of the silver reaction tube were also coated with the finely crystalline /3-Quartz. There was no evidence to support the results presented by Gillingham (11) that steam-borne silica is capable of converting calcite to wollastonite. 3.22 The Barium Hydroxide-Quartz System The quartz crystal, as mentioned in the experi mental part, had fallen from the silver wire during this experiment and, after removal of the silver reaction vessel, the reaction products had to be chipped away from the quartz crystal. The X-ray powder diffraction analysis gave the "d" spacings shown in table (7). The strong line at 2.06A° was matched with every other line as a possible line of second intensity in the A.ST.M. index. No match was obtained for any recorded compound. Corwin, Yalman, Edward and Owen (10) found a crystalline product formed from the interaction of solutions of Ba(0H)2 and silica glass at 400°C and 340 atmospheres 76 pressure. They were also unable to identify their product from A.S.T.M. file but claim their material to be isomorphous with Sr.SiO^* In their experiments further reaction of the silica glass was prevented by the layer of crystalline material built up on the glass. It seems reasonable to suggest that the crystalline produce formed during our experiments is a barium silicate not yet recorded with the A.S.T.M. X-ray diffraction data file. The authors (10) indicate that further work is proceeding to identify this phas e thoroughly. 3.30 Morphology and Macrostructure 3.31 (a) Microscopic Examination Products formed at 235°C Micro photographs (Fig. 2.22(d)) show crystalline phases photographed directly on the quartz crystal. These were taken using an incident light attachment with a Wild M20. microscope. The fibrous spurs of crystals are probably fibrous tobermorite or xonotlite and the hexagonal plates portlandite. It is interesting to note that a considerable surface area of the quartz is still visible even after extended periods of treatment. The predominance of the fibrous crystalline habit is consistant with the finding of Grudemo (25) in lime rich systems that have been given similar hydro-thermal treatment. 77 (b) Products formed at 335°C The phtotmicrograph 2.32 shows a thin section of the poly-crystalline product formed at this temperature. This section was taken from the product layer of the kinetic study specimen and the laminations caused by the repeated interruption of the product formation are clearly seen. This also shows that the species is easily nucleated and there is no tendency for new growth to form on existing crystallites. The fibrous crystals radiate from points of nucleation. Photomicrographs (Fig. 2.22 (a)(b)(c)) show the effect of rate of growth on crystallite size; (Fig 2.22(a) is a thin section taken near the original quartz boundary. The rate of growth of the new phase at this position was rapid and the crystallites are extremely small and close together. They formed a tightly packed polycrystalline mass as the distance is increased from the original quartz boundary. Photomicrographs (Fig. 2.22 (b)(c) illustrate the transition in crystallite size and density most probably due to slower rates of formation. (c) Products formed at 500OC supercritical temperature Material formed under these conditions was much more friable and it was not possible to obtain good thin sections for microscopic examination. Examination of dispersions of this material with transmitted light showed the crystal habit to be essentially that of the fibrous 78 xonotlite formed at 335°C but of a generally larger size. 3.32 Electronmicroscopic Study The electronmicrographs (Fig. 2.23 (c)(d) show typical fields and illustrate the fibrous habit with more definition. In some of these electronmicrographs it is possible to detect the steps due to the rolled-foil type of growth. In this way the material behaves in an analogous manner to the clay mineral halloysite. A model of the crystal structure of xonotlite was constructed (see photograph Fig. 1.21(b)) to obtain a better understanding of the three dimensional (24) characteristics of this mineral. Brunauer and Greenberg' , draw attention to the development of these laminar minerals in the a and b crystallographic directions but not in the c direction. They indicate that these extremely thin foils have a tendency to roll up to give a fibre-like crystal habit. This contrasts with the manner of fibre growth of other minerals such as chrysotile where the build up is considered to be via a screw dislocation mechanism. The puckering of the outermost foil noticed in some of the electron micrographs of Xonotlite formed under super critical conditions could be explained by several hypotheses. The material could have been quenched from 500°C too quickly causing water between the foils to burst out. Another probable cause could have been the heating of the fibres in the electron beam during examination. 79 The fine structure noticed on the fibres at high magnifications is due to defects in the structure. Diffraction pattern (Fig.2.23(e)) was taken of a selected area of one of these fibres. Some of the reflections have been indexed and the "d" spacings agree to some extent with the values taken from A.S.T.M. file. Table (9) shows a comparison of these results. TABLE 9 "D" SPACING CALCULATED FROM SELECTED AREA DIFFRACTION 5.67 3.27 3.03 2.57 PATTERN IN R FROM A.S.T.M. X-RAY FILE 3.23 3.07 2.51 PLANE INDEX (121)(202)(320) (122) Further interpretation of the pattern was not attempted as the "rolled-foil” habit of the crystal added considerably to the number of allowable reflections and the complexity of the resulting pattern. The broadening of some of the points observed in Fig. 2.23(e) may be due to strain in the crystal lattice induced also by its "rolled-foil" habit. Distortion of the diffracted beam was noticed particularly on the pattern on pure Ni metal which was used as a standard for the "d" spacing calculations. The polycrystalline Ni pattern was found to be elliptical rather than circular and a mean value 80 of "A” (the radius of the rings) was used to calculate . Note. The value "2UL." is derived from the wave length of the electron beam and the geometry of camera. The formula d =-£ was used in these calculations. The value "At" was also found to vary with increasing radius !?/i " and this also would tend to add to uncertainty of the value of "d" calculated from measurement made from the pattern. 3.33 Macro Structure of Xonotlite Formed at 335°C (a) Pore Size The thin sections of the product layer described above have given photomicrographs which show in some detail qualitatively the fibre intergrowths that occur at the quartz-lime solution interface. It was thought that the product layer formed a diffusion limiting barrier and that more quantitative data would be useful. Fig. 2.26 shows the pore size distribution of this material. The main pore range between 216,000-5,400 R in diameter shows the product membrane to be relatively open and that ion migrations through it should not be hindered to any extent by pore- wall collisions. (b) Ultrasonic agitation. Samples of product materials formed both at 335°C and above the critical temperature were subject to intense ultrasonic agitation. Brunauer and Greenberg (24) suggest 81 this method as a gauge of crystal-to-crystal bonding. They claim intergrowths of tobermorite formed by the hydration of Portland cement to be dispersed easily. In our experiments the fibrous intergrowths were not dispersed indicating a stronger fibre-to-fibre bond or more bonds per fibre in the polycrystalline mass. 82 3.40 Kinetics and Mechanism of the Formation of Xonotlite. Kinetics of the Overall Reaction at 235° and 335°C Figures 2.31 (a) (b) show the weight increase versus time and weight increase versus square root of time. The latter curves show a straight line relationship which indicates a diffusion-controlled process. From the slopes of these curves, calculations were made of the activation energy for the overall reaction and are submitted below:- 3.41 Activation Energy Slope of curve at 235°C = — M It II 500 " 335°C 8 x = wt. increase in mg. t = time in hours x 2/2 + c =kt+c x^ = 2kt + c" X = fzkt + c" = Jzk th + c" Plotting x Vs. Slope = J 2k 2 or k = (slope ) z 83 (A) From Arrhenius, A E \ _ T2T-^ The energy of activation) . R In k« (T2-T1) Where k-^ and k2 are the rate constants for the reactions at the respective temperatures the ratios 2 of the (slope) of these curves should be the same as the 2 ratios of the rate constants. Then E 608 x 508 x 1.98 x 2.303 x 2 log (500 x 32 ) 100 "IT" 28.3 608 x 508 x 1.98 x 2.303 x 2 x 1.8492 100 Activation Energy =52.1 k cals./g. mole. 3.42 (a) Mechanism of Reaction at 335°C .... ♦ From all the observations made during the experiments below critical conditions the mechanism of the formation of xonotlite from the interaction of quartz in saturated lime solutions could be postulated to follow the sequence:- (a) Dissolution of SiC^ to form a species H^SiO^ or more probably t^SiO^ (24). I | (b) The interaction of this species with Ca ions to form (Ca)^(Si^O-^y) (OH^ xonotlite phase. (c) The nucleation of this phase from solution. (d) Subsequent precipitation of this phase on the above nuclei with preferential growth on the b axis. (e) The growth becomes diffusion limited by the diffusion of l^SiO^ species through the layer. 84 It is very interesting to note that during the formation of the product layer further crystallization of xonotlite always occurred on the outer surface of the product zone. This mechanism differs from that presented by Greenbergwho claims the solution of silica as the rate determining step. It is probably true to say that this holds during the initial stages of the reaction at the interface, but as the product layer forms the rate determining step becomes the diffusion of (H9SiO,) species through the z 4 (13) product layer. The observations made by Logginov that the product film which surrounds the silica particles reaches a maximum thickness and remains unchanged can be easily accounted for from our work. We found that the product formation decreases as a logarithmic function of time, thus the formation of product would appear to terminate. (14) Assarsson also claims the formation of a tobermorite phase is limited by the rate of dissolution on the surface of the silica, but this in turn is affected to some extent by rate of diffusion of Ca(0H)2 through the layer at the phase boundary. Kalousek^^^ suggests the process is diffusion controlled but does not specify the diffusion limiting ionic species. 85 3.42 (B) Mechanism of the Reaction at 500°C and 1,000 Atmospheres Pressure In the case of the mineral formation under these conditions the mechanism is quite different. As described earlier, the product formed a plug on top of the excess lime slurry in the bottom of the reaction vessel. This plug of product material probably restricts the supply I | of Ca ions to the reaction which is in contrast to the mechanism described above. One explanation of this phenomenon is the relation of solubility of the two components i.e. Ca(0H)9 and Si09 with increasing z Z (30) temperature. The literature citedv y shows an exponential increase in the solubility of Si02 at high values of pH and with increasing temperature whereas the solubility of Ca(0H)2 decreases with increasing temperature. This probably means that under these conditions I | the concentration of the Ca ions is only sufficient to form the xonotlite phase in the vicinity of the lime slurry 86 3.43 Characteristics of the solution of quartz in saturated lime solution Measurements taken from the photographs shown in Fig. 2.3l (c) of cut-away sections of the reacted quartz cubes showed that the rate of solution of the quartz was dependent on the particular crystal face exposed to the solution. Table (2) shows the measurements taken from a quartz cube before and after 110 hours in saturated lime solution at 335°C. These results indicate the dissolution of the basal plane of quartz takes place at twice the rate of that of the prism face. It is likely that these measurements exaggerate the difference in rate of solution since the depth of the etch pits was not taken into account and these are characteristically deeper on the prism faces. Figure (3.43) shows a characteristic etch pit on a basal face of one of the quartz cubes used in the reactions. 3.44 Diffusion of ions through a section of the product layer Previous work had indicated that the fibrous poly crystalline membrane that formed around quartz in saturated lime solution may be selective towards the passage of various ions in solution. This was suspected because of the occurr ence of further crystallization only on the lime solution side of the membrane. To test this hypothesis the diffusion FIG. 3.43. PHOTOMICROGRAPH OF A*5 ETCH PIT 0# THE QUARTZ SURFACE* 88 cells described earlier were constructed. Figure 2.40 (b) shows a plot of concentration versus time for various ions, the concentrations being calculated from counts/sec. of the solution at various times compared with that of the 0.02M solutions at the start of the experiment. These curves show that the membrane had no great I | selectivity towards the migration of Ca ion in association with hydroxyl ions when compared to the rate of migration of Ca ions in association with chloride ions or Na+ ions in association with chloride ions. In the latter stages of the experiment with Ca (OH)2 the carbonation of the solution interfered with the results. This happened despite the measures taken (described earlier) to prevent it. -j-1 The absorption of Ca ions from solution by the membrane as shown by the results of the chemical analysis is characteristic of this material. See Lea (32), also Forrester and Lawrence (33). 3.45 Solubility of Ca(0H)2 at 300°C From the experiments on diffusion described above* it became apparent that it was not the selectivity of the I | membrane which did not permit the migration of Ca nor was it a factor of pore size. Another explanation could be the relative solubilities of quartz and lime under these conditions, 89 the solubilities determining the concentration gradients across the membrane of product material. In order to make some estimates of diffusion constants for the diffusing species, viz. Ca and l^SiO^ in solution at 300 C, it was necessary to know the solubilities of Ca(0H)2 and Si02 under these conditions. The solubility of quartz in ^0 could be taken from the work of Morey and Hesselgesser (34 ) and the solubility in electrolytes of increasing pH by Steinour (2) and from Greenberg and Price (35) but no solubility data for Ca(0H)2 under these conditions could be found. Figure 2.50 (b) shows an extension of existing data for the solubility of Ca(0H)2 with increasing temperature. These results were obtained using the conductivity cell described earlier. The following calculations were made:- Cell Constant K = L where L = specific conductance L and L = Measured Conductance Imole/cubic 0.1 Mole/cubic For solutions of Kcl Decimetre' Decimetre- Measured R 0.120 x 102 0.108 x 103 Specific conductance ) L from ) 0.11132 0.012856 ) ) ) Cell constant. K ) 1.33 1.38 90 RESULTS FOR SATURATED SOLUTIONS OF CALCIUM HYDROXIDE Temper Resistance Concentration ature in OHMS in gmole/litre 30°C 1.110 x 10' 0.90 x 10~2 1.23 x 10"2 0.0220 -2 -2 119 0.870 x 10' 1.15 x 10 1.56 x 10 0.0107 186 0.142 x 10' 7.06 x 10'3 9.61 x 10‘3 0.0045 250 0.380 x 10' 2.63 x 10'3 3.58 x 10*3 0.0013 -3 -3 298 0.950 x 10' 1.05 x 10 1.43 x 10 0.00044 Concentrations calculated from the expression. 1000 L C(T°C) -A(t°c) where C = concentration in gram equivalents/litre -A = equivalent conductance. Values for (-/l) at each temperature taken from Fig. 2.50(c) the curve being extrapolated from data presented by Robinson and Stokes (39). 3.46 Diffusion Constants From Fick's law • dx K A C dt dx J A A C dt K L K the diffusion coefficient x — I dt x £C where dx xonotlite/sec. dt 91 A = area of membrane square cms. L = thickness of membrane in cms. A C = concentration change In these calculations the concentration on one side of the membrane has been assumed to be zero and that on the other equal to the concentration of a saturated solution. FOR THE SPECIES (H^iO^) k1 = dx L I dt x A x AC dx _ (300 mg + 300 x 0.504) x 10 dt Molecular weight (Xonotlite) 8.78 x 10 ^ moles/sec. A = Area of membrane. 6 sides of quartz cube measured from original specimen = 5.71 sq. cm. L = Thickness of the membrane. (As this membrane was increasing in thickness while the diffusion was taking place, a mean thickness will be used for the purpose of this calculation). This was measured from photographs and found to be 0.065 cms. * 92 « -,o -,^-7 0.065 1 8.78 x 10 x x rv, 5.71 AC ./ 1.00 x 10 9 x f~77 (H2S103) 2>C NowA C concentration was taken as the solubility of Si02 under these conditions, since the concentration of Si02 will be very close to the concentration of H2Si03 = (Greenberg (24)) at high pH. Then taking a value from (Kennedy (30) we have - k.// (H9SiOo) 335^C = 1.00 x _1__ x 10“9 = 7.7 x 10 -8 J 0.013 44- Now for Ca species the same conditions should hold and the calculated value of k^, the diffusion coefficient should vary as the inverse of the solubility. Taking the solubility of Ca(0H)2 from Fig. 2.50 (b), as 0.004 g mole/litre, k^ (Ca"*""*") = 1.00 x 10 9 x 1.00 x -9 .00040 x 10 -6 2.50 x 10 These calculations indicate a large difference in the diff/usion rates under these conditions. It is probably true to say that this is the reason for the characteristic growth of the product layer on the lime solution side of the membrane. 93 4.0 Practical Implications of this work Perhaps the most significant result from the practical viewpoint is the fact that it has been shown that when calcium silicates form around quartz grains the growth always occurs on the lime solution side of the product crust. This means that if the hydrothermal treatment is too extensive the quartz grain will diminish through dissolution to such an extent that it can move freely about within the product cage. This helps to explain the decline in compressive strength with prolonged autoclave treatment of lime-silica compacts, as found by the author, Cole and Taylor (36). This work has also revealed the lack of chemical bond between the crystalline calcium silicate hydrate and the nutrient silica grain aggregates. It has shown the crystallite size of the cementing crust to be much smaller on the quartz side of the cementing crust. This implies that for maximum inter-particle friction or compressive strength of compacts the cementing crust might best be kept to a minimum. The work with ultrasonic dispersion of the poly crystalline product indicated that the xonotlite formed at temperatures above 300°C had better crystal-to-crystal bonding than the fibrous tobermorite reported by Greenberg (24). It must also be pointed cut that because xonotlite has better volume stability during wetting and drying that 94 it must make a more desirable cementing matrix than say tobermorite which experiences interlayer shifts on drying. 4.1 Further Work Furtherwork should be directed towards the study of the effect of varying the hydrothermal treatment on the species and morphology of the calcium silicate hydrates produced. The relationship between species and morphology and the rheological properties of cemented compacts could throw some light on the mechanisms involved in the cementing process. The value in the use of instruments such as the electron microscope, X-ray diffractometer and infra-red spectrometer have been made obvious during this work. It is anticipated that these instruments could be used to some advantage in the investigation of the work outlined above. The investigation of the system Ba(0H)2“ quartz could well be taken further to establish the species formed under various conditions of hydrothermal treatment and to establish the mechanism and rates of reactions. 95 4.20 Coneluding Remarks The mechanism of the interaction of saturated lime solutions on single crystals of quartz has been elucidated. The activation energy for the reaction has been estimated to be 52 K cal/g mole. The process of formation of calcium silicate hydrates was found to be diffusion controlled. The diffusion of silicate ions through the product layer appears to be the rate controlling step at temperatures up to 335°C. I | The rates of diffusion for both Ca ions and H^SiO^ have been calculated and the difference in the rates has been used to account for the preferred growth of the new product material on the surface of the product layer in contact with the lime solution. Fibrous xonotlite was found to be the stable phase formed at temperatures between 235°C and 500°C. The mechanism of xonotlite formation at 500°C follows a different process to that at 335°C. Nucleation of the calcium silicate hydrate from solution presents no difficulties and the crystallites have preferred orientation generally away from the quartz surface. The hydrothermal study of other systems including calcite-silica gel and barium hydroxide-quartz were briefly investigated. These investigations showed no detectable reaction between calcite and silica-gel under the conditions of the experi- 96 merits . The system barium hydroxide-quartz under similar conditions gave a crystalline product which could not be identified from x-ray data. The solubility data for calcium hydroxide in water o o has been extended from 180 C to 300 C. 4.30 Acknowledgements The author wishes to acknowledge the supervision, encouragement and guidance givoiby A/Professor E.R. McCartney, School of Chemical Technology University of New South Wales. Appreciation is also expressed to the Colonial Sugar Refining Company for the sponsorship of this work. Thanks are also given to Mr. A. Malin of the School of Metallurgy, University of New South Wales for electron micrographs, the C.S.I.R.O. Division of Coal Research for the pore size study, and to those officers of C.S.R. Research Department with whom useful discussions were made. REFERENCES TAYLOR W.H. and MOOREHEAD D.R. Lightweight calcium silicate hydrate. Magazine of Concrete Research Volume 8, No.24. November 1956. STEINOUR H.H. The System CaO:SiO^tH^O. Chemical Reviews 40 February-June 1947. TAYLOR H.F.W. Progress in Ceramic Science Vol.I (1961) Pergamon Press (London). TAYLOR H.F.W. Hydrated Calcium silicates Part (1) Journal of Chemical Society 1950 3683 AITKEN A. and TAYLOR H.F.W. Hydrothermal Reactions in Lime-quartz pastes. Jnl. of Applied Chemistry 10, January 1960 P.17. ASSARSSON G.0. Hydrothermal Reactions between calcium hydroxide and siliceous materials at 120' - 220’C. Zement Kalk G ips Vol. 14 No.12 1961 P.537-544. HELLER L. and TAYLOR H.F.W. Hydrated Calcium Silicates Part (II) Jnl. of Chemical Society 1951 2397. ASSARSSON G.O. Hydro Thermal Reactions of Calcium Hydroxide-Quartz at 120 - 220'C. Jnl. of Physical Chemistry 64 1960 P.328. TAYLOR H.F.W. The Transformation of Tobermorite into Xonotlite. Mineralogical Magazine 32 June 1959 P.110. 98 (10) CORWIN J.F., YALMAN R.G. , EDWARDS J.W. and SHAW E.R. Hydrothermal Reactions under supercritical conditions (II) The reaction between calcium hydroxide and silica. Jnl. of Physical Chemistry. Vol. 61 July 1957.P.941 (11) GILLINGHAM T.E. Solubility and transfer of silica in steam. Economic Geology 43, 1948 P.248. (12) GREENBERG S.A. The reaction betwen silica and Calcium Hydroxide (Kinetics in the temperature range 30 to 85 f) Jnl. of Physical Chemistry. Volume 65 Jan.26 1961 P. 12. (13) LOGGINOV G.I. REBINDER P.A. and ABROSENKOVA V.F. Interaction of Calcium Hydroxide at ordinary temperature with sand of different dispersities. Colloid Journal 21 No.4 July-August 1959 P.429. (14) ASSARSSON G.0. Hydrothermal Reactions between calcium hydroxide and Muscovite and Feldspart at 120' - 220'C. Jnl. of Physical Chemistry Vol. 64 May 18, 1960 P.621 (15) KALOUSEK G.L. Tobermorite and related phases in the system Ca0-Si02H 0. American Concrete Institute Journal 26. 1954-1955 P. 989. (16) TAYLOR H.F.W. Aspects of the Crystal structures of calcium silicates and aluminates. Jnl. of Applied Chemistry 10. August 1960. (17) MAMEDOV K.H.S. Abstract of a dissertation Institute of Crystallography. Academy of Sciences Moscow. (See Ref. (9)) 99 (18) MAMEDOV K.H.S. and BELOV H.P. The crystal structure of Tobermorites. Akad Nauk SSSR Doklady 123 Part I, 1958 P.163. (19) KALOUSEK G.L. and PREBUS A.F. Crystal chemistry of hydrous calcium silicates (III) Morphology and other properties of Tobermorite and related phases. Jnl. of the American Ceramic Society. 41 1958 P.124. (20) BRUNAUER S. and GREENBERG S.A. The hydration of Tricalcium silicate and Dicalcium silicate at room temperature. Fourth International Symposium on the chemistry of Cement. Washington D.C. 1960. (21) BERNAL J.D. The structure of cement hydration compounds. Proceedings Symposium on Chemistry of Cement. London 216-236 1952. (22) McConnell j.d.c. The hydrated calcium silicates riversideite, Tobermorite, and plombierite. The Mineralogical Magazine 30, 1953-55. P.293. (23) KALOUSEK G.L. and ROY R. Crystal Chemistry of hydrous calcium silicates (II) Jnl. of the American Ceramic Society 40, 1957 P.236. (24) BRUNAUER S. and GREENBERG S.A. The Hydration of tricalcium silicate and Dicalcium silicate at room temperature Fourth International Symposium on the Chemistry of Cement. Washington D.C. (1960). 100 (25) GRUDEMO A. An Electronographic study of the Morphology and Crystallization properties of calcium silicate hydrates. Sweden Svenska Forskningsinstit for Cement Och Betong vid. kgl. tek. hogskol. Stockholm; Handlingar No.26 103 pp. (1955). (26) ASSARSSON G. 0. Hydrothermal Reactions of Calc;um Hydroxide and Muscovite and Feldspar at 120-220°. Jnl. of Physical Chemistry, 64 (1960) p.626. (27) HALES J.L. and KYNASTON W. The Preparation of pressed discs of purified potassium chloride containing some solid samples for infra-red spectrometry. The Analyst 79, (1954) p. 702-706. (28) MEGAW H. D. and KELSEY C.H. Crystal Structure of Tobermorite. Nature. Vol.177 February 25 1956. (29) ASSARSSON G. 0. Hydrothermal reactions between calcium hydroxide and muscovite and feldspar. 120-220 C. Jl. of Physical Chemistry Vol. 64 May 18, 1960. (30) KENNEDY G.C. A portion of the system silica-H 0 Econ. Geol. Vol.45 1950 P.639. 2 (31) HUNT C.M. The infra-red spectra of some silicate and aluminates and other compounds of interest in Portland cement chemistry. Thesis University of Maryland 1959. 101 (32) LEA ,F. M. and DESH, C.H. The chemistry of cement and concrete. Edward Arnold (Publishers) Ltd., London 1956. (33; FORRESTER J. A. and LAWRENCE The self diffusion of calcium ions in the equilibrium system calcium silicate hydrate - lime solution. Jl.applied Chem. Nov. 1961 p.413. (34) MOREY and HESSELGESSER Solubility of minerals in super heated steam. Economic Geology 46 No.8 P.829. (35) GREENBERG S.A. and PRICE E. W. The solubility of silica in solutions of electrolytes. Jl. of Physical Chemistry Vol. 61. November 1957 P.1539. (36) COLE W., TAYLOR W.H. and MOOREHEAD D.R. Some unpublished work concerning the effect of varying autoclave treatments on the strength of lime-silica compacts. Division of Building Research C.S.I.R.0. Melbourne 1958. (37) INGLES 0. G. Design and operation of a high pressure mercury porosimeter. Aust. Jl. of Applied Science Vol.9. 1958. P.120. (38) BUTT J.M. , RASCHKOWITSCH L.M. , HEIKER D. M. , MAIER A.A., and GORATSCHEWA 0.I. Silikat Technik, 12 June 1961, P.281. 102 (39) ROBINSON R.A. and STOKES R.H. Electrolyte solutions Butterworths Scientific Publications 1959. London. (40) GLASSTONE S. Introduction to electro-chemistry Glass. D. Van Nostrand Company Inc. New York 1942. (41) LANGE N.A. Handbook of Chemistry 10th Edition McGraw-Hill Book Company Inc., New York. 1961. (42) INTERNATIONAL CRITICAL TABLES Compiled by West J.C. and Hull C. National Research Council McGraw-Hill Book Company Inc. New York 1933. (43) BASSETT H. Notes on the system lime-water. Jl. of the Chemical Society 1934 P.1270 (44) LEA F.M. and BESSEY G.E. The conductivity and pH values of calcium hydroxide solutions at 25 C. Jl. of the Chem. Soc. 1937. P.1612. (45) PINSKER Z.G. Electron Diffraction Butterworths Scientific Publications 1953. London 103 5.00 OTHER PUBLICATIONS SUBMITTED FOR COLLATERAL CREDIT 5.10 LIGHT-WEIGHT CALCIUM SILICATE HYDRATE 5.11 DISCUSSION OF THE ABOVE PAPER 5.12 THE SUCROSE EXTRACTION METHOD FOR THE ESTIMATION OF AVAILABLE CaO IN HYDRATED LIME 104 REPRINTED FROM MAGAZINE OF CONCRETE RESEARCH. 1956. VOL. 8, No. 24. NOVEMBER, pp. 145- 150 < f \ 8? PRIM"' Lightweight calcium silicate hydrate: some mix and strength characteristics by W. H. Taylor, m.c.e., a.m.i.c.e., a m i.E.Aust. and D. R. Moorehead, a.m.t.c BUILDING RESEARCH DIVISION COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANIZATION SUMMARY was mixed with sand, moulded under pressure and, when Developments in Europe and America suggest that hard, impregnated with calcium chloride. On washing out lightweight calcium silicate hydrate offers much promise soluble salts by slow diffusion, calcium silicate hydrate for building purposes, although the amount of published remained as a cementing matrix. Patents were taken out technical data is limited. This paper presents the results of by Van Derburgh in 1866 (British Patent 2470) and a study of some physical characteristics of autoclaved Michaelis in 1880 (German Patent 14195) for the harden products, relating to mix design and compressive strength, ing of lime-silica mixes by the action of high-pressure using five grades of silica flour that vary widely in specific steam. Modified versions of Michaelis’s method were surface area. patented and used commercially in Germany in 1898. It is shown that for each of the grades of silica flour In 1926, Smirnov12’ pointed out that the strength of lime- there is a certain value of the lime/silica ratio at which silica products was due to the formation of crystalline the ratio of the compressive strength to the unit weight calcium hydrosilicate. Axel Eriksson, a Swedish architect, reaches a maximum. A limited number of results, obtained subsequently improved aerated concrete products by under an arbitrary set of conditions without batch replica curing them with high-pressure steam. This led to the tion, show approximately linear relations between (a) the manufacture of “ Ytong ” and “ Siporex ” lightweight unit weight of dry products and the water/solids ratio of concretes in Sweden, the former starting in 1929 and the mixes, (b) the ratio of the compressive strength to the unit latter soon afterwards. In the course of two decades these weight of dry products and the water/solids ratio of mixes, materials have contributed greatly to satisfying building and (c) the lime/silica ratio (for maximum compressive requirements in certain parts of the world. strength) and the specific surface area of the silica flour Lightweight calcium silicate hydrate with an extremely used. fine pore structure was patented by Ippach and Bieligk in 1933 (French Patent 750, 117) and by Huttemann and Introduction Czernin (United States Patent 1, 932, 971). Finely ground Calcium silicate hydrate is a material of some antiquity, silica and lime were suspended in water and autoclaved, but the physico-chemical characteristics have received the unit weight of the resulting product being varied serious attention in research work and in the manufacture from 25 to 50 lb/ft3 by altering the water content of the of lightweight building products only in the last fifty mix. years. The reaction between finely ground lime and Since 1929 a number of investigators, including amorphous or semi-amorphous silica was used by the Thorvaldson and Shelton'3’, Bessey'4’, and Flint, early Romans in pozzolanic cement mixes to form McMurdie and Wells'5’, have shown that a series of calcium hydrosilicates of good strength and durability. hydrated calcium silicates can be formed by autoclaving More receht attempts to use this reaction in the manu cement mortars or lime and sand mixes at various facture of artificial stone stem from experimental work temperatures, usually below 200 C. by Ransome'1’* in 1860. In this work, sodium silicate Microsections by Bessey 16’ indicate that the structure *The index numbers refer to the items in the list of references on page 5. 1 Magazine of Concrete Research: November 1956 of these compounds may be crystalline or amorphous. ating a sample of water to dryness on a steam bath, was The degree of crystallization appears to depend upon the 30 parts per million. rate of formation of the silicate and this is controlled mainly by the fineness and surface activity of the sand EXPERIMENTAL PROCEDURE used. Taylor171 made chemical and X-ray analyses of the The investigation was divided into two parts. The first cementing constituent of a commercial lightweight lime- part (A) was carried out to ascertain if a simple mixing silica block, which had been made by foaming a mix of procedure was suitable for the programme of work on 1 part quicklime and 2 parts fine quartz aggregate (by hand. For this purpose, mixes were made with hydrated weight) and autoclaving at 183°C for four hours. The lime and silica flour (4,270 cm2/g) in constant proportion cementing material was shown to be of approximate but with varying quantities of water. The effect of the composition T28 CaO.SiO2.2 05H2O. water content on the unit weight and compressive Investigations18'91 on foamed cement-lime-sand mixes strength of autoclaved specimens was then determined. have shown that strong, dimensionally stable products The second and major part (B) was to determine the can be made by autoclaving mixes containing an ad effect of surface area of silica flour and the mix propor mixture of finely ground siliceous material. For a given tions of component materials on the compressive strength unit weight, the compressive strength of products was of autoclaved products. It was also to determine their found to be governed by the mix proportions, the degree functional relation for the manufacture of lightweight of fineness of the silica particles, and the curing cycle material with high-strength characteristics. used. As highest strengths were obtained with mixes rich in lime and silica flour, it was decided to determine TABLE 1: Details of mixes. the effect that these materials have on the compressive strength of products having unit weights varying from Specific surface Mix component ratios 45 to 85 lb/ft3. Part of area of silica investigation flour Lime/ Water/ (cm2/g) silica solids Experimental work RAW MATERIALS A 4,270 0-6 0-4 -0-7 The raw materials used were hydrated lime, silica flour B 650 01-0-5 0-35-0-45 and water. B 2,800 0-2-0-6 0-4 -0-45 The hydrated lime was prepared from Buchan (Victoria) B 4,270 0-2-10 0-4 -0-6 limestone containing 98% calcium carbonate.* The stone B 8,300 0-5-1-2 0-45-0-6 was finely crushed, calcined in a rotary kiln at a tempera B 16,800 1 0-2*5 0-7 -0-9 ture not exceeding 1,150°C and hydrated by spraying with water until the mass was reduced to a powder. The The batching procedure consisted of making a variety hydrated lime was passed through a No. 100 mesh sieve of mixes, with component ratios as indicated in Table I, and, after being dried at 110°C to minimum weight, was and curing them in saturated steam at 150 lb/in2 in a stored in airtight containers. Subsequent tests by the small autoclave. Each batch was prepared by mixing the calcium sucrate method (carried out as described in the dry constituents together, adding sufficient water to give Appendix) and the air permeability method (“ Rigden ” a consistence suitable for casting purposes and finally apparatus) showed that the product contained 92% of mixing for two minutes. In the main programme of work calcium hydroxide and had a specific surface area of the water/solids ratio of mixes was adjusted to maintain 13,500 cm2/g (average of three determinations). Steps a fairly constant consistence, as measured by a modified were taken to minimize the effects of atmospheric car- form of flow test. The procedure adopted was to give bonation during the experimental work. cylinders of paste, 1 in. diameter and 1 in. high, 10 jolts The silica flour was made by pulverizing quartz mine in six seconds on a flow table (specified in A.S.T.M. tailings from Allandale, Victoria, in a flintstone lined ball Designation C230-52T) and measure their increase in mill. Five grades of silica flour were produced with diameter. specific surface areas of 650, 2,800, 4,270, 8,300 and Stainless steel casting moulds were used, each con 16,800 cm2/g,’ determined by the air permeability method. sisting of four 1 in. cubes with tolerances of ±0 001 in. The soluble silica content of the second and third men in the sides and ± 1 minute in the angles. Each mould tioned grades of silica flour (determined in accordance was coated with mineral oil (viscosity 1,100 seconds at with S.A.A. Code for Concrete in Building, No. 100°F, Saybolt) and was then filled with paste prepared CA.2-1937) was approximately 10%. in one batch. It was then vibrated for 15 seconds at a The water used was ordinary tap water with a high frequency of 1,500 c/s and amplitude 1/32 in., lightly degree of purity. The total solids remaining, after evapor screeded off, and covered with a stainless steel plate •Calcium oxide and carbon dioxide were determined by A.S.T.M. method, Designation C25-47, and “ Scheiblier’s ” gas apparatus respectively. 2 Lightweight calcium silicate hydrate Note: specific surface area of silica flour = 4,270 cm2/g specimens I in. cubes, age I day WATER/SOLIDS RATJO (by weight) Figure 1: Relation between water/solids ratio and (a) ratio of compressive strength to unit weight, (b) unit weight. applied with a slight twisting motion to squeeze out a lb/ft3) and both the unit weight and the ratio of the small excess of moulded material. This procedure en compressive strength to the unit weight of specimens sured that the moulds were completely filled, the de- vary linearly with the water/solids ratio. moulded specimens would be dimensionally accurate, The results obtained in the second or major part of and no striations would form in them during treatment the investigation are illustrated in the family of curves in the autoclave. shown in Figure 2. It is seen that for each of the grades The moulds were bolted together in sets of four and of silica flour used there is a certain value of the autoclaved for a period of 10 hours after the steam lime/silica ratio at which the ratio of the compressive pressure had reached 150 lb/in2. This pressure was strength to the unit weight reaches a maximum. reached in 3| hours, during which time the exhaust It is evident that a deviation from the optimum valve was closed after air had been expelled from the lime/silica ratio, when medium to coarse grades of silica autoclave. These features of the steam curing cycle were flour are used, has a greater effect on the strength/weight similar to those used by manufacturers of autoclaved ratio of specimens than when very fine grades of silica foamed concrete. flour are used. Also, in the manufacture of lightweight The temperature was then reduced from approximately calcium silicate hydrate products, the higher the specific I86°C to 30°C in 6 hours, and the specimens were surface area of the silica flour used, the greater must be subsequently demoulded. (The cooling period was pro the proportion of lime to silica to obtain the best results. longed for purposes of convenience in carrying out the The optimum degree of fineness of silica flour appears experiment.) They were dried at I10°C for 3 hours, to lie between about 2,000 and 10,000 cm2/g, there being cooled in a desiccator for £ hour, weighed and tested in no advantage in using finer material. As indicated in compression at an age of one day. The rate of loading Figure 3, the optimum lime/silica ratio seems to vary was equivalent to that of a platen movement of 0 02 linearly with the fineness of the silica flour over the in/min. range of specific surface areas considered. Under the conditions prevailing in this investigation and for Results and discussion products with a maximum strength/weight ratio, the The results obtained from the first part of the investi relation between the lime/silica ratio and the specific gation are shown in Figure 1. It is seen that the unit surface area may be expressed by the following straight- weight falls below half that of ordinary concrete (145 line formula: 3 Magazine of Concrete Research: November 1956 Specific surface area Curve of silica flour in mix (cm2/g) 650 2,800 4,270 8,300 16,800 Results apply to one set of curing conditions Lime component of mixes is 92% Ca(OH)2 LIME/SILICA RATIO (by weight) Figure 2: Relation between ratio of compressive strength to unit weight and lime/silica ratio. R = 014 + 0 00009 5 TABLE 2: Relation between compressive strength and where R is the lime/silica ratio required (lime component unit weight. 100% calcium hydroxide) and S is the specific surface area of the silica flour used (cm2/g). Specific Com Unit Data relating to specimens showing maximum surface Lime/ pressive weight Strength/ strength/weight ratios are summarized in Table 2. The area of silica strength (dry) weight maximum strength and strength/weight values are silica ratio* at one day ratio governed by the particular curing cycle used and they (cm2/g) (lb/in2) (lb/ft3) may be more than doubled by an adjustment in steam 650 0-3 1,750 75 23 curing conditions. (This feature will be dealt with in a 2,800 0-4 3,950 77 51-5 subsequent publication.) 4,270 0-6 3,800 70 54 From Table 2 it is seen that as the specific surface area 8,300 0-85 3,850 64 60-5 of the silica flour increases, the lime/silica ratio of mixes 16,800 1-8 2,250 49 45-5 increases at a similar or lower rate for best results in strength/weight ratio. Variation in the specific surface * Lime is 92% calcium hydroxide. area of the silica flour between 2,800 and 8,300 crrr/g had very little effect on the compressive strength of fabricated units, provided that the lime/silica ratio of mixes was arising from the use of silica flour with a specific surface made a function of the specific surface area of silica flour area within the above-mentioned range, were due to used, as is indicated by the above straight-line formula, or changes in the unit weight of specimens. In general, the the figures in the second column of Table 2. With the higher the lime and water content of the mixes the lower latter proviso, changes in the strength/weight ratio, was the unit weight of the products. 4 Lightweight calcium silicate hydrate Lime component of mixes ii 92% Ca(OH)2 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 SPECIFIC SURFACE AREA —cmVg Figure 3: Relation between optimum lime/silica ratio and specific surface area of silica flour. Conclusions (2) smirnov, n. n. Micro-structure of silicate bricks. Calcium silicate hydrate can be readily made by auto Transactions of the State Experimental Institute on clave treatment of lime-silica mixes (within a day), with Silicates, Moscow. No. 20. 1926. pp. 5-18. a unit weight about half that of ordinary concrete and (3) thorvaldson, t. and shelton, g. r. Steam curing with a greater strength than is usually obtained with the of Portland cement mortars. A new crystalline sub latter material at an age of 28 days. stance. Canadian Journal of Research. Vol. 1, No. 2. The unit weight of the material can be reduced by in July 1929. pp. 148-154. creasing the water or the lime and water content of the (4) bessey, g. e. The calcium aluminate and silicate mixes. hydrates. Proceedings of the symposium on the The most suitable grades of silica flour to use are those chemistry of cements, Stockholm, 1938. Stockholm, which have a specific surface area in the range from about Ingeniorsvetenskapsakademien, 1939. pp. 178-213. 2,000 to 10,000 cm2/g. When mixes are designed for products with high- (5) flint, e. p., mcMurdie, h. f. and wells, l. s. Forma strength characteristics, a change in specific surface area tion of hydrated calcium silicates at elevated temper of the silica flour within the above range will produce ature and pressures. Journal of Research of the a variation in unit weight rather than in compressive National Bureau of Standards. Vol. 21. Research strength of the autoclaved product. Paper RP 1147. November 1938. pp. 617-638. For each degree of fineness of silica flour, there exists (6) bessey, G. E. Sand-lime bricks. London, H.M.S.O., a certain lime/silica ratio which will contribute to a high 1948. National Building Studies. Special Report strength/weight ratio in the finished product. The No. 3. pp. 58. relationship between these two contributory factors may (7) taylor, h. f. w. Identification of the cementing be expressed in terms of a straight-line formula. material in a lightweight sand-lime block. Journal of REFERENCES Applied Chemistry. Vol. 2, No. 1. January 1952. pp. 3-5. (1) bryson, h. c. Calcium silicate cements with special reference to sand-lime bricks. Sands, Clays and (8) taylor, w. h. Foamed concrete. Constructional Minerals. Vol. 3, No. 3. April 1938. pp. 251-257. Review. Vol. 22, No. 6. October 1949. pp. 11-18. 5 Magazine of Concrete Research: November 1956 19’ taylor, w. h. Lightweight concrete. Australia, The resulting calcium sucrate solution is filtered Commonwealth Scientific and Industrial Research through a Gooch crucible. After rejecting the first 5 ml Organization. Division of Building Research Report. collected, a 50 0 ml sample of the filtrate is titrated with 1954. pp. 37. normal hydrochloric acid, using methyl orange as indicator. The calcium hydroxide content of the lime Appendix is then calculated. Determination of calcium hydroxide content of lime by the calcium sucrate method The following materials are shaken together for 15 minutes: hydrated lime* I -60 g ethyl alcohol! 2 00 ml Contributions discussing the above paper should be in the sugar solution (10%) 100 0 ml hands of the Editor not later than 28th February, 1957. •Fully hydrated lime was used throughout the experimental programme, tAlcohol prevents the formation of lumps when sugar solution is added to lime. Printed by the Cement and Concrete Association 52 Grosvenor Gardens, London S. IV. 1 · n articles pu blisLe m the !'vl a0 azi e of Co·1crete Reseorch Vo ume 8, Num er 24 : November 1956 ,ightweight raidum siJk,ate hydrate : some mix at tl strength characteristics* y W. H. Ta l '"' r, M.C.E., A.M.I. C.E., A.MI E:..Aust. and D. R. Moorehead, A .M.T .C.. Contribution ':' . A itken a id H. F. . Taylor almost comple e reacti n has probably taken place. For ( University of Aberdeen) lo er specific surfaces so me larger and, hence, less r - a ctive particles of silica will remain unr ,acted and the Two .on mer.1 · may be made. I ) The authors show lime/silica ratio required to give maximum to bermo ri tc that very1 close co nlr I of lime/s il ica ratio and, to a les er forma tion in the period of au oclaving is correspo nd ingly extent, o f watcr/soltd ratio i. required to give m, ximum lower. strength for a given ilica Rour and a given heating cycle. The further work pr m1sed by he a uthors ho uld help It m igh t be ex.pee d that, in commercial practice where to test these hypo these and will be awaited with interest. a wider 1:ang f particle ize is no rmally employed, these rati os w·o uld be rather les critical. (2) The result would Reply by the authors have be(.':n much more valuable had the chemical nature (I) The range of particle sizes studied was confined to of the compound form d been investigated, b X -ra y or the require nen1s of lightweight calcium silicate hydrate, thermogravimctric methods. l n the a bsen e of u Jata, and no attention wa paid to the req uirements of dense o nly six,~ulation is possible as to the explanation of the autoclaved product such as sand-li111 e bricks. Within results. this range it wa found that the lime/silica ratio required At the tem pcratur o f Taylor a nd Moorehead's work, for maximum strength/weight ratio was gove rned by the four different compounds are readily formed-gyrolite, grain ize of the silica. The straight line relation between xonotlite, tobermorite and dicalcium silicate (X-hyJrate. lime/s ilica ra tio and pecific urfa e area of the silica Of the , only tobermorite is specifica lly known to be ( Figure 3 of the paper) indicates tha t the effect of varia cementit ious, while dii;;alcium sil icate '.X-hydratc is cer tions in the latter may be overco me by adjusting the ta inly n<:,n-cementit1o us. Xono tlite would be cxpe tcd to lime/silica ratio to obtain the maximum strength. have. Ct\nenting q a lities, on acco unt of it -; struct ra l (2) Since the paper wa p ublish d, Or W . F. Cole, of resemblance to tobermorite, but little 1s yd known o f the the Division of Building Research, C.S.I.R .O., has carried properties of gyrolite. out X-ray diffraction a nd differential thermal analyses o f A tentati ve expla nation can be offe,ed for the ex i. t nee some specimen. typified by curve 3, Figure 2. Results by of a n optimum lime/')ilica ratio for each grade f ·ilica both meth ds have shown that the content of tobennorite flour. The maxima in th · curves in Figure 2 of he paper was highest in specimen,; having the highest strength/ may correspond to maximum format ion of the ·trongly weight ratio, which also contain some xonotlit . These binding tobermorit . At lo-we r 111 e/ ilic ratio for a result: are in accord wit h the enta tive explanatio n particular silica specimen, less tobcrmorite is formed. o offered by Ai tken and Taylor, but it is considered that the that maximum strength is no t achieved : a t higher strength of lightweight calcium silicate hydrate is a lso lime/silica ratio, some dicak iur.1 silicate 2-hydrate may influenced by such factors as the gap-grading of pa rticles, be fonned, with a corresponding lo~s of strength. the curing cycle, and the porosity of the manufactured ln the case_ of the silica of highest specific surface, p roduct. 109 D.B.R. REPRINT NO. 124 The Sucrose Extraction Method of Determining I13- Available Calcium Oxide in Hydrated Lime By D. R. MOOREHEAD and W. H. TAYLOR COMMONWEALTH OF AUSTRALIA COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANIZATION _ __ _ Reproduced with the permission of the publishers from "ASTM Bulletin ' No.286, February 1959, pages 45-47 YY here, in the man These particulars led to some doubt platinum dishes at 950 C for 3 hr, auto ufacture of certain building materials as to the accuracy of the sucrose extrac claved in saturated steam at 200 C for such as mortars, sand-lime bricks and tion method, and it was decided to check 2 hr, and finally dried and stored in lightweight calcium silicate hydrate, the method for reliability and to modify sealed containers. the conditions of manufacture are kept it, if necessary, to obtain satisfactory The content of available calcium oxide under strict control, it is frequently results. in samples was determined in the follow necessary to determine or check the ing ways: amount of calcium oxide or calcium Experimental Details and Results (а) Total analysis by ASTM Methods hydroxide that is being incorporated in The available calcium oxide in a sam C 25,2 them. j ple of hydrated lime was determined by (б) Analysis of an aqueous extract,2 Several methods have been devised total analysis and by analysis of an (c) Sucrose extraction method (4) to measure quantitatively the propor aqueous extract of the material. Anal with modifications, and tion of “free” lime in calcareous ma yses were then made by the sucrose ex (d) Ethylenediamine tetraacetate terials, but of these only a few have come traction method, using several varia (EDTA) procedure (5) on prepared ex into general use. Bakewell and Bessey tions in procedure. These included var tracts. (l)*1 recommended the following pro iations in the period of shaking, the size (a) The analysis was made in accord cedures: (1) the glycerol extraction of sample taken, the temperature of the ance with sections 4, 7, 12, 14, 15, and method, with modifications; (2) extrac extract, and the proportion of mag 20 of ASTM Method C 25 - 47,2 tion by undersaturated lime solution; nesium oxide or hydroxide present in the and “Scheiblier’s” gas-volumetric (3) calorimetry; and (4) sucrose extrac material. The work was carried out in method for determining carbon dioxide. tion in the testing of nonhydraulic several stages, and the conclusions de The available calcium oxide was cal limes. (Note.—The term sucrose ex rived from results obtained in each step culated as a difference between the traction refers to the extraction of free were incorporated in work carried out in total amount of calcium oxide and that calcium oxide by a 10 per cent sucrose the next stage. Finally, the results ob combined with carbon dioxide and sulfur solution.) tained were compared with those deter trioxide in the sample. The results A procedure based on sucrose extrac mined in the initial analyses. from four samples are shown in tion (2) was adopted by the American Freshly prepared hydrated lime was Table I. Society for Testing Materials in 1944 obtained from Lilydale, Victoria, and TABLE I.—TOTAL ANALYSIS OF for determining “the available lime stored in sealed containers to minimize HYDRATED LIME, PER CENT. index” of high-calcium limes and hy the effect of atmospheric carbonation. Sam Sam Sam Sam Con ple ple ple ple drated limes.2 This index is defined as It was dried to constant weight at 120 stituent “those constituents which enter into C in an atmosphere free from carbon A B C D the reaction under conditions of the dioxide and passed through a 200 Si02 (in specified method.” The procedure re British Standard mesh sieve before being solubles) 3.48 3.13 3.35 3.73 R203°...... 0.76 0.91 0.84 0.63 quires a direct titration of a sucrose ex used. A hydrated lime with different Total CaO. 68.26 68.26 68.78 69.05 tract with strong acid to a phenol- content of magnesium oxide was pre MgO...... 4.05 3.93 4.12 3.93 C02...... 1.85 1.85 1.37 1.37 phthalein end point. Knibbs and Gee pared by first mixing calcite with dolo S03...... 0.28 0.28 0.28 0.28 (3) indicated that methods such as this mite (both passing a No. 100 British Loss on ig Standard mesh sieve) in a rotating nition . . . 22.07 22.00 22.35 22.40 may give results wdiich include calcium CaO, in oxide from decomposed silicates and cylinder for 30 min. The material thus CaS04... 0.20 0.20 0.20 0.20 aluminates. The apparent content of contained a predetermined amount of CaO, in CaC03. . 2.36 2.36 1.75 1.75 available lime thus obtained may include magnesium oxide in natural combination Available also a small amount of magnesium oxide with some calcium oxide and was not CaO (cal in the material. A sucrose extraction simply a mixture of these components. culated) . 65.70 66.34 66.83 67.10 method for determining calcium hydrox The mixture was then calcined on “ R2O3 includes iron and aluminum oxides. ide in limes (4) eliminates the effect of decomposition of silicates and alum inates by filtering the extract before it is titrated with acid. D. R. MOOREHEAD and W. H. NOTE—DISCUSSION OF THIS PAPER TAYLOR, of the Division of Building IS INVITED, either for publication or for Research, Commonwealth Scientific and the attention of the authors. Address all com Industrial Research Organization, Highett, munications to ASTM Headquarters, 1916 Victoria, Australia, have spent more than Race St., Philadelphia 3, Pa. five years studying the properties of 1 The boldface numbers in parentheses lightweight calcium silicate hydrate for refer to the list of references appended to this paper. building purposes. 2 Standard Methods of Chemical Analysis of Limestone, Quicklime, and Hydrated Lime (C 25-47), 1955 Book of ASTM Standards, PMF'X.' Part 3. D. R. Moorehead February 1959 ASTM BULLETIN (TP 55) 6561 Ajpnj9aJ Niianna vnisv (9S dl) 9V OS'O £8 99 ££99 .. 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JOBJJX0 0SO.I0Ilg I '86 696 ZL6 Z 66 6 86 ...... locjjxa snoonby O'OOI O'OOI 0 OOI 0 OOI 0 001 ' " (I sts.Y|iuiu iujoj. o3'Bj0Ay Q 0jdUIBg 0 3jdtu,Bg a ©iduiug y 0[dun;g tlOTJUUTUUOJOQ jo poqjoiv * (SX7 aAixYHvai\:oo) saoiaNi aaixo wnioivo aiaviivAY—*n aaavx TABLE IV.—ANALYSIS OF SUCROSE EXTRACTS. by the amount of magnesium oxide present, but it is affected by the size of Magnesium Oxide Calcium Oxide Magnesium Oxide the sample. Optimum conditions for in Raw Material, - by EDTA Per Cent by Weight Hydrochloric Acid EDTA Titration, Per Cent accurate results are a sample not ex Titration, Per Cent Titration, Per Cent ceeding 0.6 g shaken for 15 min in 4...... 67.11 67 41 0 39 100 ml of 10 per cent sucrose solu 66.83 67.18 0.66 tion titrated at 21 C and retitrated at boiling point to ensure complete hydrol Av. 66.97 Av. 67.29 Av. 0.52 ysis of the sucrate. 10...... 65.02 64 50 0 67 65.22 66.03 0.51 References Av. 65.12 Av. 65.26 Av. 0.59 (1) B. Bakewell and G. E. Bessey, “The Estimation of Free Calcium Oxide and Hydroxide,” United Kingdom, Dept, alent from the above titration for the in magnesium-containing lime when of Scientific and Industrial Research, purpose. Average results obtained are determined by the sucrose extraction Building Research Special Report No. shown in Table IV. It is apparent from method is not likely to be higher than 17 (1931). these data that magnesum oxide in (2) F. L. Brady and F. J. McConnell, the actual amount, even when mag “The Determination of Free Lime in hydrated lime is soluble to only a small nesium oxide is present to the extent of Hydraulic Cement,” United Kingdom, extent (less than 1 per cent) in sucrose 10 per cent by weight. The results for Dept, of Scientific and Industrial solution. An increase in magnesium available calcium oxide were obtained Research. Technical Paper No. 4 content from 4 to 10 per cent produces much more readily by acid titration than (1926). very little increase in the quantity ex by the EDTA procedure on the ex (3) N. V. S. Knibbs and B. J. Gee, “Lime tracted. Comparative results by the tract. and Limestone,” Part I, pp. 92-93, two methods used (titrations with H. L. Hall, Toronto (1954). EDTA and with hydrochloric acid) show Conclusions (4) A. C. Cumming and S. A. Kay, that over 99 per cent of the calcium The investigation has shown that “Quantitative Chemical Analysis,” Oliver and Boyd, Edinburgh (1954). oxide dissolved in the sucrose solution is the sucrose extraction method for deter (5) Division of Soils Report No. 9/54 available for reaction with hydrochloric mining free calcium oxide in hydrated (1954), “The Titration of Calcium and acid (Table IV), the remainder being limes gives satisfactory results in a frac Magnesium by E.D.T.A.,” Australia, possibly held as a stable complex. tion of the time taken to do a total anal Commonwealth Scientific and Indus The content of available calcium oxide ysis. Accuracy of results is not affected trial Research Organization.