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Synthesis and X-Ray Diffraction Analyses of Calcium Hydroxide Nanoparticles in Aqueous Suspension

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Synthesis and X-Ray Diffraction Analyses of Calcium Hydroxide Nanoparticles in Aqueous Suspension Advances in Materials Physics and Chemistry, 2013, 3, 108-112 http://dx.doi.org/10.4236/ampc.2013.31A013 Published Online April 2013 (http://www.scirp.org/journal/ampc) Synthesis and X-Ray Diffraction Analyses of Calcium Hydroxide Nanoparticles in Aqueous Suspension G. Taglieri1, C. Mondelli2, V. Daniele1, E. Pusceddu3, A. Trapananti4 1University of L’Aquila, Department of Industrial and Information Engineering and Economics, L’Aquila, Italy 2CNR-IOM-OGG Institut Laue Langevin, Grenoble, France 3Institut Laue Langevin, Grenoble, France 4CNR-IOM-OGG, c/o ESRF, Grenoble, France Email: [email protected], [email protected], [email protected], [email protected] Received January 24, 2013; revised March 12, 2013; accepted April 17, 2013 Copyright © 2013 G. Taglieri et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Calcium hydroxide nanoparticles in aqueous suspensions (also called nanolime) were successfully employed in Cultural Heritage conservation thanks to the ability of favoring re-adhesion of the pictorial layer on original carbonatic sub- strates or allowing to a better superficial cohesion and protection of treated stones. In this work, we have synthesized nanolime particles in aqueous suspension by two different methods. The produced particles were characterized in the laboratory, in terms of structural and morphological features, by means of X-Ray diffraction powder (XRD) and by transmission electron microscopy (TEM), respectively. Nanoparticles were crystalline, regularly shaped, hexagonally plated and with side dimensions generally ranging from 300 nm to 30 nm or less. Crystal structure of nanolime particles directly in the aqueous suspension, has been also analyzed by synchrotron diffraction from X-ray synchrotron radiation (SR-XRD); data have been analyzed by means of the Rietveld method and we have investigated the structure of Ca(OH)2 particles in suspension in terms of cell parameters, atomic coordinates, bond lengths and angles. Keywords: Nanoparticles; Calcium Hydroxide; Crystal Structure; X-Ray Diffraction; Crystal Morphology 1. Introduction directly in suspension, as they are used in the applications. It is fundamental to verify that the obtained nanoparticles, Calcium hydroxide (Ca(OH) ), has been largely employed 2 very reactive thanks to their dimensions, don’t show the thanks to the well-known carbonation reaction and to the carbonatation process inside the suspension, but only characteristics of the calcium carbonate (CaCO ) ob- 3 during the applicative use, when the solvent is com- tained. The low solubility and the compatibility between pletely evaporated. the latter compound and material substrates offer a fa- The aim of this work has been to synthesize Ca(OH) vorable use in many lime-based superficial conservative 2 treatments [1]. In all its applications, a high reactivity is nanoparticles by different methods and to compare the obtained results, in terms of structural features of the of paramount importance, so that Ca(OH)2 particles with sub micrometric dimensions (nanolime) have been re- particles both in the aqueous suspension and after the cently successfully employed on Cultural Heritage con- solvent was completely evaporated. In particular, two servation, offering the possibility to penetrate deep into nanolime synthesis methods, reported in our previous damaged zones (less limitations due to the particle size), works [2,6], have been followed. According to method high reactivity and fast reactions (such as carbonatation), (A), synthesis has been carried out by adding (drop by high purity and defined composition [2-4 and refs. there- drop) an aqueous NaOH solution into a CaCl2 one, in]. Nanolime is typically synthesized by a chemical pre- maintained at 90˚C. According to method (B), a surfac- cipitation process in supersaturated aqueous solutions of tant agent (Triton X-100) was previously added to the reactants; in particular, the method starts from aqueous two initial aqueous solutions that were later mixed si- sodium hydroxide solution (NaOH) added drop by drop multaneously, at the fixed temperature of 90˚C. The in an aqueous calcium chloride (CaCl2) solution, main- method (B) allows to obtain Ca(OH)2 nanoparticles eas- tained at high temperature [5 and refs. therein]. ily and drastically reducing the time of synthesis. In fact, The synthesis allows to obtain Ca(OH)2 nanoparticles especially if tenths of grams were prepared, we passed Copyright © 2013 SciRes. AMPC G. TAGLIERI ET AL. 109 from several hours for the drop by drop method to few and 0.6 mol/l of NaOH respectively. The NaOH alkaline minutes; this difference in time scales with the quantity solution (used as precipitator) has been added drop by of the preparation, allowing us to scale-up the nanolime drop into the CaCl2 solution (speed ≈ 4 ml/min, tem- production only when the method (B) is followed. perature of 90˚C). After about 24 hours two distinct The morphology and particles size have been investi- phases have been observed, a limpid supernatant solution gated by transmission electron microscopy (TEM). and a white precipitated phase; to remove the NaCl pro- We have investigated the phases formed after the syn- duced, several deionised water washings have been per- thesis procedure, by means of X-ray diffraction powder formed. Aqueous nanolime suspension (with a Ca(OH)2 technique (XRD). The XRD diffraction is a powerful, concentration of 10 mg/ml) has been defined as sample non-destructive and useful technique that allow to quickly A. analyze unknown materials, in terms of crystallinity and Method (B). (4.00 ± 0.02) g of Triton X-100 has been phases identification, and to perform materials charac- previously added to the initial aqueous solutions con- terization in many scientific fields such as engineering, taining 0.3 mol/l of CaCl2⋅2H2O and 0.6 mol/l of NaOH metallurgy, mineralogy, sciences, archeology, etc. The respectively (each solution was 100ml in volume). These great advantages of this technique are: the simplicity in initial solutions have been then mixed together simulta- sample preparation, the rapidity of measurement, the abil- neously, at the temperature of 90˚C. A suspension of ity to analyze mixed phases, the structure determination 200ml of final volume has been obtained, characterized directly in laboratory. In particular, XRD technique can by a Ca(OH)2 concentration of 10 mg/ml (sample B). As easily allow to investigate the reactivity, in terms of car- in method (A), we have performed several deionised wa- bonatation process efficiency, of the produced calcium ter washings to remove the NaCl produced and the sur- hydroxide nanoparticles. For this reason, we have con- factant too. sidered different agglomeration conditions of the nanopar- For both the methods, different residual water contents ticles (that could strongly influence the carbonatation pro- were considered preparing four samples, named A100, A75, cess) partially substituting water with 2-propanol, as dis- A50, A25, B100, B75, B50, B25, respectively: the subscript re- agglomerating agent [2]. In particular, for each method, presents the percentage of water content in each sample. four nanolime suspensions were prepared, characterized by different residual water contents in the precipitated 2.2. Characterization of Ca(OH)2 Nanoparticles phase. By TEM technique (Philips CM 100), the dried particles We have also investigated the Ca(OH)2 nanoparticles morphology of the samples under study have been ana- crystalline structure directly in aqueous suspension by lyzed; measurements have been performed on the sam- using synchrotron radiation at the European Synchrotron ples dried under vacuum, following the common proce- Radiation Facility (ESRF)-Grenoble, France. In fact, the dure. high energy and high flux of this source allowed diffrac- As concerns XRD measurements (Philips X’Pert PW tion measurements in transmission of the particles inside 1830), performed in our laboratory to determine the the aqueous medium. X-ray synchrotron diffraction data crystalline degree and the phases of the formed particles, have been analyzed by means of the Rietveld method and the sample was prepared maintaining each aqueous sus- we have investigated the structure of Ca(OH)2 particles pension for 20’ in ultrasonic bath (US) and then deposit- in suspension in terms of cell parameters, atomic coordi- ing 0.2 ml of the suspension itself on a silica sample nates, bond lengths and angles. holder; measures were performed on dry sample, in laboratory conditions (T = 20˚C, relative humidity RH = 2. Experimental Details 40%). Each experimental diffraction spectrum has been 2.1. Synthesis of Ca(OH) Nanoparticles elaborated by a Profile Fit Software (Philips PROFIT 2 v.1.0) and each crystalline phase has been attributed by Calcium chloride dihydrate (CaCl2·2H2O), sodium hy- JCPDS patterns; the ratio between the calcium carbonate droxide (NaOH) and 2-propanol pro analysi products, peaks area and the spectrum total area has been assumed supplied by Merck, have been used without further puri- as the carbonatation process efficiency (yield). fication. In case of method B) polyoxyethylene (10) ter- Crystal structure of the nanolime particles directly in toctylphenyl ether, Triton X-100 (C14H22O(C2H4O)10), a aqueous suspension has been investigated by SR-X ray high-purity, water-soluble, liquid, non-ionic surfactant, measurements on GILDA (BM08) beamline at ESRF; the purchased from Fluka has been used too. Water has been patterns were collected in Debye-Scherrer geometry on a purified by a Millipore Organex system (R ≥ 18 MΩ 2D image plate detector. The experiment was performed cm). at an incident beam wavelength of λ = 0.7277 Å and the Method (A). We have prepared two different aqueous sample-to-detector distance adjusted to obtain data within solutions of 100 ml, containing 0.3 mol/l of CaCl2·2H2O the 6˚ - 53˚ 2θ-angle range. Data were collected from 0.2 Copyright © 2013 SciRes. AMPC 110 G. TAGLIERI ET AL.
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