United States Patent (19) 11 Patent Number: 4,601,755 Mélard et al. 45 Date of Patent: Jul. 22, 1986

(54) CERIUM BASED GLASSPOLISHING (56) References Cited COMPOSITIONS U.S. PATENT DOCUMENTS

75 Inventors: Pierre Mélard, Lagord; Marcel 3,262,766 7/1966 Nonamaker ...... 51/309 Peltier, La Rochelle; Francis Tastu, 3,768,989 10/1973 Goetzinger et 51/309 Nieul/sur/Mer, all of France 4,161,463 7/1979 Myers et al...... SO2/263 73 Assignee: Rhone-Poulene Specialites 4,62,921 7/1979 Litvinov et al. P ... O - 0 ------A as - - 50/9 Chimiques, Courbevoie, France Primary Examiner-Amelia B. Yarbrough Attorney, Agent, or Firm-Burns, Doane, Swecker & 21 Appl. No.: 635,828 Mathis 22 Filed: Jul, 30, 1984 57 ABSTRACT (30) Foreign Application Priority Data Cerium based glass polishing compositions, well adapted for the polishing, e.g., of optical glass, are com Jul. 29, 1983 FR France ...... 83 2519 prised of (i) at least one crystalline phase of CeO2 type, 51) Int. Cl'...... C09G 1/02 and (ii) a crystalline phase which comprises a rare earth 52 U.S. C...... 106/3; 51/308; pyrosilicate having the formula Ln2-CeSi2O7, 51/309; 156/DIG. 63; 423/263 wherein Ln is at least one lanthanide or yttrium and x is 58 Field of Search ...... 106/3, 288 B, 287.34; a number ranging from zero to less than 2. 51/309, 308; 423/263; 156/DIG. 63; 502/263, 302, 304,303 59 Claims, No Drawings 4,601,755 1. 2 forming insoluble rare earth compounds, with the num CERIUM BASED GLASS POLISHING ber of equivalents of base being greater than or equal to COMPOSITIONS the number of equivalents of cerium and the pH of the reaction medium being higher than 6; BACKGROUND OF THE INVENTION 5 (b) the resultant precipitate is filtered; 1. Field of the Invention: (c) dried; and The present invention relates to novel cerium based (d) thence calcined. polishing compositions, a process for the preparation This process provides polishing compositions having thereof, and to the use of same in the polishing of glass, good homogeneity and reproducibility, good stability ceramics and other vitreous type materials. 10 upon suspension in water and good polishing efficacy. 2. Description of the Prior Art: However, the immediately aforedescribed process is Among the polishing compositions currently in use in not entirely satisfactory, since the anion typically em the glass industry, those based on the rare earths, and in ployed is fluoride which gives rise to those problems particular cerium, are generally the most effective and necessarily associated with the use of fluorides, in par efficient. Different processes too are known for the 15 production of such compositions. Thus, it has been ticular pollution which may be caused by the effluent proposed, in German Pat. No. 2,426,110, to precipitate therefrom, whether in liquid or gaseous state. an aqueous solution of a rare earth sulfate with sodium SUMMARY OF THE INVENTION hydroxide in the presence of molochite, and to then filter, wash, dry and calcine the precipitate to obtain the 20 Accordingly, a major object of the present invention desired polishing composition. Such a process does not is the provision of improved cerium based polishing permit the obtainment of polishing compositions having compositions which exhibit the following desirable completely satisfactory efficacy, particularly in view of characteristics: their heterogeneity, undefined structure and lack of (i) effectiveness, i.e., they enable the polishing of a reproducibility of the final products. These disadvan 25 generally ground glass surface as rapidly as possible; tages originate specifically from the operating condi (ii) acceptability, i.e., they will not scratch the glass tions of the process, wherein the concentration of the during the polishing operation; reagents changes over the course of the reaction and it (iii) inertness, i.e., they will not cause a detrimental is thus impossible to obtain defined products in a repro reaction on the surfare of the glass, e.g., they do not ducible fashion; they are also occasioned by the exis 30 display excessive chemical activity with respect to the tence of foreign compounds (molochite) and the pres glass, thereby avoiding the problems of burning, orange ence of sulfates, the precipitation of which by sodium peel, blisters, and the like; hydroxide yields mixtures of complex molecules, such (iv) a very long useful life or longevity, i.e., they are as double sulfates, hydroxysulfates and hydroxides, the suitable for use for the longest possible period of time amount and nature of which may vary-over the course 35 without deterioration or difficulties; of the reaction. (v) good stability in suspension, i.e., permitting a It has also been proposed, Chemical Abstracts, 80, homogeneous distribution of particulates or powder 51688 (1974), to produce cerium based polishing com thereof in appropriate bath and avoiding any deposits positions by precipitating ceric hydroxide with ammo thereof. nia from a solution of a rare earth nitrate, wherein the The dispersion, as aforesaid, is effective as soon as the cerium has been previously oxidized. Such a process composition is placed in suspension and remains so mandates a supplementary purification step by recrys during the entire operation. tallization with the ceri-ammoniacal nitrate and taking Such dispersions, moreover, do not foam; foaming up the calcined oxide in a dilute acid. The final prod causes overflowing, clogs the lines, reduces yields and ucts, moreover, do not have a satisfactory polishing 45 inconveniences the operating personnel. Furthermore, efficacy. Furthermore, such final compositions also do the subject compositions are readily re-suspended after not have satisfactory homogeneity or structural charac an extended stoppage and settling period, even if the teristics, and they are not reproducible. bath is charged with particles of polished glass (the In U.S. Pat. No. 3,768,989 a process is described for phenomenon of "caking'). the preparation of polishing compositions by the forma 50 tion of a precipitate of a rare earth carbonate-wollasto Also, the compositions of the invention are not toxic, nite, separation of the precipitate and the calcination thus preventing any problems of skin disorders or other thereof. And in U.S. Pat. No. 3,262,766 a process is diseases. They are, moreover, uniform, possess a pleas described for preparing polishing compositions by treat ing color and are easy to work with. They do not ad ing solutions of commercially available rare earth car 55 here to the glass after polishing, thereby permitting bonates with either fluosilicic or hydrofluosilicic acid. rapid cleaning, and are easy to flocculate, to eliminate Polishing compositions prepared by the processes de manufacturing rejects. scribed in either of these two U.S. patents, however, Briefly, the novel cerium based glass polishing com have disadvantages akin to those described above for positions of the present invention comprise at least one the compositions prepared according to the teachings of 60 crystallographic phase of the CeO2 type and a crystallo the 110 German patent. graphic phase comprising a rare earth pyrosilicate hav To eliminate the disadvantages of the aforementioned ing the formula Ln2-xCex.Si2O7, wherein Ln represents processes, a novel process has been proposed in French at least one element selected from among the lantha Pat. No. 2,472,601, assigned to the assignee hereof, in nides and yttrium and whereinx is greater than or equal accordance with which: 65 to 0 and less than 2. (a) a solution of a cerium salt is continuously mixed In addition to the aforesaid two essential crystallo with a basic solution and a solution of at least one acid graphic phases, the compositions of the invention may and/or salt, the anion or anions of which are capable of optionally comprise in certain cases other crystallized 4,601,755 3 4. phases of rare earth oxides or phases of silicon oxide, The normality of the basic solution used too is not a more or less crystallized. critical factor according to the invention; it also may vary over wide limits, but advantageously it ranges DETAILED DESCRIPTION OF THE from to 5N. INVENTION The proportion of the basic solution and the cerium More particularly according to the present invention, salt solution should be such that the number of equiva it has now surprisingly been found that unexpectedly lents of the basic solution introduced is greater than or desirable glass polishing properties are imparted to the equal to the number of equivalents of cerium introduced subject compositions by inclusion therein of the simultaneously. It may be advantageous to use a greater Ln2-xCex.Si2O7 phase. O than 5% excess of equivalents of base with respect to By the term "glass" as utilized herein, there are in the equivalents of cerium. The pH of the reaction me tended not only glass and ceramics, but also the other dium may range from 5 to 10. It advantageously ranges materials of vitreous type. from 7 to 9. It may be especially advantageous to con The present invention also features a novel process trol the pH at a constant value within +0.1 pH unit. for the preparation of the subject compositions, said 15 The aqueous solution of the salt of at least one triva process comprising: lent rare earth or yttrium must be soluble under the (i) simultaneously mixing a solution of a cerium salt, a operating conditions of the process of the invention. basic solution, an aqueous solution of a salt of at least Exemplary of suitable salts, representative are the chlo one trivalent rare earth or of yttrium, and a solution of rides or nitrates of lanthanum, cerium, praseodymium, at least one oxide derivative of silicon capable of form- 20 neodymium, samarium, europium, gadolinium, terbium, ing insoluble rare earth compounds; dysprosium, holmium, erbium, thulium, ytterbium, lute (ii) filtering the precipitate which results; and cium, and of yttrium. Advantageously, a solution con (iii) drying and calcining said filtered precipitate at a taining a cerium salt and salts of rare earths originating temperature higher than 850 C. directly or indirectly from the treatment of rare earth The appearance of the crystallographic phase 25 minerals is used. Preferably, salts of lanthanum or neo Ln2-CeSi2O7 has been detected under specific condi dymium are used. tions of calcination at temperatures higher than 850 C. The concentration of the solution of the salt or salts In the first stage of the process, the intimate admix of rare earths employed according to the process of the ture of the different reagents is carried out. invention is again not a critical factor and may vary The solution of the cerium salt used according to the 30 over wide limits; however, preferably it ranges from 0.2 process of the invention may comprise any aqueous to 1 mole per liter. solution of a cerium salt in the cerous and/or ceric state, The proportion of the solution of a cerium salt to the soluble under the selected operating conditions of the aqueous solution of a salt or salts of trivalent rare earths invention, and, notably, a solution of cerous chloride, or 35 is such that the ratio of the cerium dioxide to the rare cerium nitrate in the cerous or ceric state, or a mixture earth oxides (CeO2--Ln2O3) ranges from 60 to 85% by of both. weight. The cerium salt is selected such that it contains no The solution of the at least one oxide derivative of impurities which may be transferred to the final compo silicon may be any aqueous solution of an oxide deriva sition, after calcination. It may be advantageous to em 40 tive of silicon capable of forming insoluble rare earth ... ploy a cerium salt having a degree of purity in excess of compounds. The derivative or derivatives of silicon i. 99%. must be soluble in water. According to the invention, The concentration of the cerium salt solution is not a the following compounds are advantageously used: critical factor according to this invention. It may thus silicon dioxide, silicic acid and silicates of alkali metals. vary over wide limits, advantageously from 0.2 to 4 45 More precisely, amorphous silica, metasilicic acid, moles per liter; a concentration ranging from 0.5 to 2 metadisilicic acid, sodium orthosilicate, sodium silicate moles per liter is preferred. of the formula Na2O.xSio2, wherein x varies from 3 to 5, In a preferred embodiment of the process according sodium metasilicate, sodium metadisilicate, potassium to the invention, the cerium is introduced into the reac metasilicate, potassium metadisilicate, potassium tet tion medium in the cerous state and it is oxidized to the 50 rasilicate, are used. These salts may be used either in ceric state by continuously adding to the reaction mix anhydrous or hydrated form. ture an oxidizing agent compatible therewith. Exem Preferably, sodium silicate, Na2O.4SiO2, is used. plary of such oxidizing agents, the following are repre The concentration of the solution of the oxide deriva sentative: solutions of sodium, potassium or ammonium tive or derivatives of silicon too is not a critical factor perchlorate, chlorate, hypochlorite or persulfate, hy 55 according to the invention and may also vary over wide drogen peroxide, air, oxygen or ozone. The cerium may limits; when expressed in moles/liter of SiO2, it prefera also be oxidized electrochemically. bly ranges from 0.1 to 2.0. Hydrogen peroxide is preferably employed. The proportion of the solution of the oxide derivative The proportion of the oxidizing agent with respect to or derivatives of silicon and the aqueous solution of the the cerous salt to be oxidized may also vary over wide 60 salt or salts of trivalent rare earths is established such limits. It is typically higher than the stoichiometric that the ratio of equivalents of silicate (SiO3-) to the amount and preferably is from 10 to 40% in excess equivalents of trivalent rare earth ranges from 0.1 to 1, thereof. preferably from 0.2 to 0.6. The basic solution employed in the process of the In the process of the invention the number of anionic invention is advantageously an aqueous solution of am 65 equivalents is greater than or equal to the number of monia or sodium hydroxide, potassium hydroxide or cationic equivalents employed; it should not, however, sodium carbonate. give rise to the formation of adsorption compounds on The ammonia solution is preferably employed. the composition obtained by the mixture of reagents. 4,601,755 5 6 The mixture of the different solutions of the aforesaid ture is selected, a composition is obtained which does reagents may be effected by any one of numerous vari not include the crystallographic phase Ln2-Cex.Si2O7, ants. For example, admixture may be carried out under which is responsible for the desirable properties of the agitation by continuously adding, and in a separate compositions of the invention. The duration of calcina manner, the solution of the cerium salt, and then the tion ranges from 30 min to 10 hours. solution of the oxidizing agent, the solution of the salt or The calcined product is subsequently ground in a salts of the rare earth or earths, the solution of the oxide manner such that the dimensions of the aggregates derivative or derivatives of silicon, and the basic solu thereof range from 0.2 to 5.0 um. The median diameter tion. A premixture of the cerium salt solution and the is defined as a diameter such that 50% by weight of the solution of the salt or salts of the rare earth or rare 10 aggregates have a diameter larger or smaller than the earths may also be prepared and continuously added to median diameter. the reaction medium in parallel with the other two Grinding may be accompanied by any grain size se solutions. There may also be prepared a premixture of lection operation, which may be carried out simulta the solution of the oxide derivative or derivatives of neously or successively. silicon with the basic solution. In the case of use of an 15 The process of the invention may be carried out in oxidizing agent, it is possible to employ it in admixture conventional apparatus. The stage of mixing of the with a solution other than the basic solution, in particu reagents is effected in a reactor equipped with a temper lar in a mixture with the solution of the cerium salt ature controlled heating device, the usual reaction con and/or the solution of the salt or salts of the rare earths. trol means (thermometer), agitator means (anchor or Regardless of the order of the introduction of the 20 screw agitator), means to introduce the reagents and a solutions of the reagents selected, the admixture takes pH control unit placed at the outlet of the reactor. place instantaneously: a well defined concentration of The aging operation is carried out in the same type of the different species is obtained at any given instant apparatus, with the difference that it is not equipped throughout the reaction mass. This makes it possible to with means for the introduction of the reagents and the obtain homogeneous and well defined compositions, 25 pH control unit. The transfer of the reaction mass from having stable properties. one reactor to the other is by gravity. The temperature of the reaction medium should pref The suspension obtained may be subsequently filtered erably range from 10' to 95 C., more preferably from in a continuous filtering apparatus, for example, a rotat 40' to 70° C. ing Vernay type filter or a belt filter. The residence time of the mixture in the reaction 30 The filter cake is introduced by any appropriate me medium is not a critical factor according to the inven chanical means (scraper) into the drying/calcining ap tion and may also vary over wide limits; generally, paratus. residence times ranging from 30 min to 2 hours are The drying and calcining operations may be effected selected. in two different installations, or they may follow each According to another embodiment of the process 35 other in a single, rotating furnace type apparatus. Pref. according to the invention, the reaction mass may be erably, a slightly inclined rotating furance is used, per aged for a certain period of time at a temperature rang mitting the circulation of the material and carrying out, ing from 10 to 95 C., preferably from 50 to 80° C., in a first section thereof, the drying of the product and prior to filtration. In this case, the aging time is not a in a second section its calcination by means of a higher critical factor according to the invention and may vary temperature gradient due to the proximity of the flame, over wide limits; however, a period of time of from 30 preferably fuelled with natural gas. min to 2 hours is typically satisfactory. After calcination, the composition obtained may be The second stage of the process according to the subjected to a finishing operation, including grinding invention consists of filtering the reaction mass upon and grain size selection, which may be effected in the completion of the reaction; it is present in the form of a 45 same apparatus, for example, a micronizer assembly. suspension. This filtering operation is effected option According to the process of the invention, polishing ally continuously at ambient temperature, i.e., at a tem compositions are obtained having the following overall perature of from 10 to 25' C.; the reaction mass is at a chemical analysis (percentages are given by weight): temperature ranging from 10 to 90 C., preferably from (a) rare earths expressed as the oxides thereof: 75 to 35 to 45 C. 50 95% According to another embodiment of the invention, (b) silicon expressed as the dioxide thereof; 5 to 25%. the filter cake may subsequently be washed with water The percentage of cerium dioxide therein with re or a solution of an ammonium salt. After washing, the spect to the total weight of the rare earth oxides ranges water content of the filter cake ranges from 20 to 80% from 60 to 85%. by weight and generally from 30 to 50%. 55 The subject compositions have a specific surface The product obtained after filtration and optional ranging from 1 m2/g to 35 m2/g, the specific surface washing is then dried, optionally continuously. The (BET) being determined by the Brunauer/Emmett drying temperature preferably ranges from 100 to 600' /Teller method described in The Journal of the Ameri C. The drying time is also not critical and may vary can Chemical Society, 60, p. 309 (February, 1938). De under these conditions from 30 min to 24 hours. 60 pending upon its application, a composition is selected The dry product is then calcined, optionally continu preferably having a specific surface ranging from 3 to ously, at a temperature of at least 850 C., but preferably 10 m2/g. at a temperature of from 850 to 1050 C. Scanning electron microscope examination shows The upper limit of the temperature range is not criti that the calcined material comprises blocks of small cal and may attain a value as high as 1500 C. 65 dimensions, less than 100 um, which are the result of the In contrast, it has surprisingly been determined that agglomeration of grains, which themselves comprise the lower limit for the calcining temperature is critical elementary particles having particle sizes on the order and must be equal to at least 850 C. If a lower tempera of 0.2 um. 4,601,755 7 8 The three elements Si, Lin, Ce are homogeneously Furthermore, they have the added advantage in com distributed throughout the grains. parison with the compositions described in the aforesaid The compositions of the invention essentially com '601 French patent of not entailing fluoride ions in the prise two crystallographic phases: a CeO2 type phase course of their manufacture. having a cubic structure and a rare earth pyrosilicate Finally, their use is especially advantageous in that phase Ln2-CeSi2O7 having an orthorhombic struc they may be recycled into the glass after use and when ture, wherein x is greater than or equal to 0 and less than their polishing efficacy is reduced. In fact, they contain 2, and preferably x is greater than or equal to 0 and less no ions capable of interfering with the composition of than or equal to 0.2. the glass and may thus advantageously serve as a source The subject compositions further contain, in lesser O of ceric oxide. amounts, a rare earth oxide phase, generally a sesquiox In order to further illustrate the present invention and ide Ln2O3 having a cubic structure of fluorine type and the advantages thereof, the following specific examples a SiO2 silicon dioxide phase, in vitreous form, or crystal are given, it being understood that same are intended lized in the form of cristobalite when the calcining tem only as illustrative and in nowise limitative. perature is higher than 950 C. 15 In Examples 1 to 3 are exemplified compositions The proportions of the different phases vary as a wherein the ratio of cerium oxide to the oxides of the function of the raw materials used and the conditions of rare earths remained constant at 65% and the ratio of calcination. equivalents of SiO3- to equivalents of Ln3+ was 0.2, Typically, they are as follows: 0.4 and 0.6, respectively. (i) CeO2:30 to 80% 20 In Examples 4 and 5 compositions were prepared (ii) Ln2-CeSi2O7: 12 to 60% wherein the ratio of cerium dioxide to the oxides of the (iii) Ln2O3: 0 to 15% rare earths was 85% and the ratio of equivalents of (iv) SiO2; 1.5 to 8% SiO3 to equivalents of Ln3+ was 0.1 and 0.4, respec The compositions obtained according to the process tively. 25 The final products were characterized by the follow of the invention are useful in the polishing of glass and ing physical and chemical test methods: similar materials. (1) Chemical analysis: They are especially useful in the optical industry, in (i) Determination of rare earth oxides: same was con the field of production of eyeglasses, whether series or ducted following sintering of the compositions, by mass production, and also in the production of prescrip 30 calcination in the presence of sodium peroxide, and tion spectacle lenses. precipitation by means of oxalic acid after acid A particularly important field of application of said treatment, by the Kholtoff method; compositions is in the glass industry including the man (ii) Determination of SiO2: same was conducted by ufacture of crystal, mirrors, flat glass, in particular glaz X-ray fluorescence, after shaping the composition ing and double glazing, automotive rear view mirrors 35 into beads via borax treatment; and television screens. (2) Specific surface: The use of the compositions of the invention in the Same was conducted by the aforesaid Brunauer/Em polishing of glass is carried out in conventional manner. mett/Teller method; As they are typically used in a spray polishing system, (3) Apparent packed industry: they are suspended in water. Same was conducted according to the standard DIN The polishing bath is prepared simply by adding the No. 53194, powder composition to the aqueous medium, agitated The principle of this standard consists of introducing manually or by conventional agitating means (anchor or a known quantity of the product in powder form into a screw agitators, turbine agitation, etc.). graduated cylinder and to then pack it under predeter The amount of composition introduced is such that 45 mined conditions; typically the concentration of the composition ex (4) Crystalline structure: pressed in CeO2 varies from 30 to 200 g per liter of the The Debye and Scherrer transmission method: mono bath, preferably approximately 50 g/liter. chromatic molybdenum radiation. The amount of water used for the formulation of the Examples 6 to 10 are examples of use of the composi polishing bath is not critical, but it is preferable, in order SO tions prepared in Examples 1 to 5 in the polishing of to well maintain the compositions of the invention in glass, with their suitability therefor being determined in suspension, to use soft water, i.e., water having a hard a series of tests. ness of less than 30 TH. The temperature of the bath should be less than 50 EXAMPLES 1 TO 3 C. It is advantageous to operate at low temperatures on 55 Three compositions were prepared as follows: the order of 20 C., as any increase in temperature accel (i) The following solutions were respectively intro erates the settling of the suspension. duced into three different premixing vessels: The polishing compositions according to the inven (1) a 3N aqueous ammonia solution; tion have numerous advantages: (2) an aqueous solution containing cerous nitrate in a (l) they have an improved appearance: fineness, grain 60 concentration of 112 g/l, expressed as CeO2 (1.9 size, color; equivalent/liter of Ce3+) and lanthanum nitrate in (2) they possess good homogeneity and reproducibil a concentration of 60 g/l, expressed as La2O3 (1.1 ity properties; equivalent/liter of La3+), and (3) they have good density and suspension mainte 200 volumes of an aqueous solution of hydrogen per nance characteristics; 65 oxide, the proportion of hydrogen peroxide with (4) they result in an improved performance: polishing respect to the cerous salt being a 35% excess; efficacy, polishing rate, low rejection rates of polished (3) a solution of sodium silicate having the composi pieces, and the like. tion Na2O.4 SiO2, the concentration of which var 4,601,755 10 ied according to the particular example and is re ported in Table I. An amount of ammonia neces -continued sary to convert the SiO2 to SiO3 was also intro a + 0.01. A b = 0.01 A c + 0.01 A duced. Example 2 8.80 3.21 5.39 Into a temperature controlled 2-liter reactor, Example 3 8,80 3.21 5.40 equipped with an agitator system and a pH control unit placed at its outlet, the following solutions were intro The parameters of the Ln2Si2O7 phase were identical duced: within the accuracy of the measurements effected. II) the solution (2) of the rare earth nitrates at a rate of The intensity parameters of the CeO2 type structure 450 cm3/hour, 10 were as follows: II the ammonia solution (1) at a rate such that the pH of the reaction medium was controlled at pH 7.7, and a + 0.01 A Rate of crystallization" III) the sodium silicate solution (3) at a rate of 500 Example 1 5.44 cm3/hour. Example 2 5.42 e55 The reactor was operated at 45-50 C.; the residence Example 3 5.42 asS3 time of the reaction mixture therein was 1 hour. "rate calculated after correction of absorption coefficients The reaction mass was transferred by gravity into a like reactor wherein aging was carried out at a tempera The known parameters of the phases La2Si2O7 and ture of 70 C. over a residence time of 1 hour. 20 Ce2Si2O7 are reported as: (ii) The reaction mass was next filtered at ambient temperature on a Bichner filter. at 0.01 A b + 0.01 A c + 0.01 A (iii) The precipitate obtained was subsequently dried La2Si2O7 phase 8,794 13.20 5.409 in an oven at a temperature of 120° C. for 16 hours, Ce2Si2O7 phase 8.722 3.056 5.401 followed by calcination in a muffle furnace for 2 hours 25 at a temperature as also reported in Table I. (iv) A final product was obtained in a yield higher The lattice parameter for cerium dioxide alone is than 95%. Coarse particles were eliminated by passage 5.411 A (JCPDS 4.0593). of the product through an AFNOR sieve with mesh A high value of the parameter of the CeO2 type struc openings of 40 pum. 30 ture corresponds to an insertion of lanthanum in the The products thus obtained were then characterized. CeO2 structure. The results obtained are compiled in Table I. It was noted that the presence of silica facilitated the TABLE I Chemical analysis Ratio Ratio Temperature of Rare Specific Apparent -- equivalents of SiO3. calcination earth Total surface packed Example CeO2 + La2O3 equivalents of Ln3+ (°C) oxides SiO2 (m/g) density - - 65 0.2 1050 90.7 9.5 9 1.2 2 65 0.4 950 82.9 17.6 4.2 1.35 3 65 0.6 950 76.4 24.7 3.6 1.45 Scanning electron microscope examination evi migration of lanthanum from the CeO2 structure: in denced that the compositions of Examples 1 to 3 were Example 1 where there was little silica, the CeO2 pa small blocks, less than 100 um in size, resulting from the 45 rameter is raised to 5.44 A (instead of 5,411 A) in spite agglomeration of elementary particles of sizes on the of the calcination of the compound at 1050 C. order of 0.2 um, some of which began to coalesce at At the rate at which the pyrosilicate phase appeared, about 950-1000' C. the lattice parameter of the type CeO2 approached that Examination by X-ray probe evidenced that the three of cerium dioxide alone. Over the course of the calcina elements Si, La, Ce were distributed in an essentially 50 tion there was segregation on a microscopic scale (less homogeneous manner; there were no particles of silica than or equal to 1000A) between the lanthanum and the only, or particles devoid of silica. cerium. The compositions prepared according to Examples 1 In the compositions of Examples 2 and 3, cerium was to 3 were analyzed by X-ray diffraction. present essentially in a form close to La2Si2O7 and the The phases observed were the following: 55 excess silica was found in the form of cristobalite or (a) Composition of Example 1: monoclinic La208 vitreous silica. (weak)--CeO2 (strong)--Ln2Si2O7 (seak); In view of the parameters of the phases observed in (b) Composition of Example 2: the compositions of the invention and the parameters of cristobalite SiO2 (weak)--CeO2 (strong)--Ln2Si2O7 the phases La2Si2O7 and Ce2Si2O7, it was determined (medium); 60 that the pyrosilicate phase of lanthanum corresponded (c) Composition of Example 3: to the formula La2-CeSi2O7, wherein x was less than cristobalite SiO2 (medium)--CeO2 (strong)--Ln 0.2. 2Si2O7 (medium). The parameters of the Ln2Si2O7 phase were: EXAMPLES 4 AND 5 65 The procedure of Examples 1 to 3 was repeated, except that an aqueous solution was used containing a + 0.01 A b - 0.01 A c + 0.01 A cerous nitrate in a concentration of 146 g/1, expressed Example 1 8.80 3.20 S.40 as CeO2 (or 2.6 equivalents/liter of Ce3+) and lantha 4,601,755 11 12 num nitrate in a concentration of 26 g/l, expressed as representing this fraction, with respect to the amount of La2O3 (or 0.5 equivalent/liter of La3+). composition initially employed. The concentration of the sodium silicate solution was (c) Initial compaction: such that in Examples 4 and 5 a ratio of equivalents of This parameter derives chronologically from the SiO3 to equivalents of Ln3+ was established at 0.1 and 5 maintenance of the composition in suspension. In effect, 0.4, respectively. whether assisted or not, the product will always settle. The characteristics of the final products are reported Users often prepare their suspension in advance, at the in Table II. concentration desired, and store it for later use in appro TABLE II Chemical analysis Ratio Ratio Temperature of Rare Specific Apparent CeO2 equivalents of SiO3: calcination earth Total surface packed Example CeO2 + La2O3 equivalents of Lnt (C.) oxides SiO2 (m2/g) density 4 85 0.1 1050 95.2 4.8 9 1.3 5 85 0.4 980 83.4 17.6 5.3 1.4

EXAMPLES 6 TO 10 These examples illustrate the use of the compositions priate apparatus. A lapse of time, up to several days, of the invention described in Examples 1 to 5 in the 20 occurs between the preparation of the suspension and polishing of glass. its use, during which settling takes place. There are then In order to evaluate their behavior in the polishing of two possible cases: glass, the subject compositions were subjected to a (i) either the sediment forms an expanded, impalpable series of the following tests: layer; (a) Behavior in suspension: 25 (ii) or the portion resting on the bottom of the tank Into a 250 cm3 test tube, an aqueous suspension of the becomes sludge-like, adhesive, even resembles con composition to be tested was introduced in a concentra Crete. tion of 50 g/1, or 12.5g of powder in 250 cm3 of water The re-suspension of the product is instantaneous and having a hardness of 28'TH and a temperature of 20° C. complete in the first case and the original concentration After complete homogenization of the suspension, its 30 is reestablished. rate of settling was determined by means of a densitom If, however, in contrast there is compaction of the eter (graduated from 1000 to 1100) as a function of time. product as in the second case, only a part of the product A curve d=f(t) was plotted. is placed in suspension, leading to a depletion of the The TS0 is the designation for the behavior of the polishing composition in the bath. In extreme cases, product in relation to its ability to remain in suspension. 35 compaction is of a proportion such that it is impossible This is the elapsed time, expressed in decimal minutes, to detach the product from the bottom of the tank. This at the end of which the value measured is the median results in a significant loss in the new product, which between the initial density and the final density of the has become unusable. ... clear liquid. In order to appreciate the tendency of the composi (b) Caking index tion to compact, the following test was performed. It ... . Even though their effects are similar, both in relation consisted of preparing in suitable vessel 5 liters of a well to their development and the disadvantages they cause, homogenized suspension by the dispersion of 100 g of it is appropriate to dissociate compaction from caking. the composition to be tested per liter of tap water. After Compaction involves the fresh product. Caking, in con 24 hours, the condition of the settled portion was "eval trast, appears in the processing apparatus during or after 45 uated manually'. Two further determinations were the product is worked. made after 48 and 72 hours. In view of the impossibility In the case of polishing under severe conditions (high to numerically express a tactile sensation, the extent of Velocity, high pressures) the polishing composition suf compacting was evaluated according to the following fers appreciable mechanical wear: fracture of the ag scale: no compacting, light compacting, compaction. glomerates, changing of the grain size distribution in the 50 (d) Polishing efficacy: direction of fines. The suspension is on the other hand The test was conducted with different types of pol enriched in exogenic particles (silicates from the glass ishers: polyurethane foam, felt and Pellon (skin), removed). The combination of these two factors leads Efficacy on polyurethane foam: to the condition that, when at the end of the day or the An industrial CMV machine, model ICM7 was used; week the machines are stopped, as is often the case, the 55 it was equipped with two brushes and a convex polish product settles in the tanks and pipes in the form of a ing head. A pump fed the suspension of the polishing consistent and adhesive sludge. This is the phenomenon composition to be tested to the glass surface to be pol of caking. Re-suspension upon again commencing oper ished. ation is difficult and in the worst case, impossible. Operating conditions were as follows: The suspension, after having served as the polishing 60 medium (see the following test), was collected in a (i) Velocity of the head 1500 rpm stainless steel beaker to determine the caking index (ii) Velocity of the brushes 1000 rpm thereof. After being at rest for 24 hours, during which (iii) Pressure 1200 g/cm2 settling occurs, the product was re-suspended by con (iv) Concentration of suspension 50 g/l 65 (v) Hardness of water 28 TH trolled mechanical agitation (250 rpm, 5 min). The su (vi) Temperature pernatant was discarded and the beaker placed in an (vii) Polisher polyurethane foam oven to dry the fraction that had not been replaced in MPU LP 46 (1.3 mm thick) suspension. The caking index (IC) is the percentage (viii) Glass to be polished Crown white 4,601,755 13 14 -continued In order to compare the properties of the polishing diameter 55 mm. compositions and to evaluate their performance, the (ix) Pump flow rate 3.8 to 4 1/min profile of a conventional polishing composition mar (x) Experimental period 3 min keted under the trademark Cerox 1650 and having the (xi). Overall test period 60 min 5 following composition, was determined:

The concave faces of the two specimens of glass were (1) Rare earth oxides 94% worked together for 3 min, after which material re (2) Cerix oxide 66% moval was determined by weighing. The experiment (3) Lanthanum oxide 19% was repeated for one hour. O (4) Neodymium oxide 9% (5) Praseodymium less than 0.000% The weight removed is related to: (6) Fluoride expressed in F 4% (7) Phosphate expressed in P2O5 4% (1) Unit weight ng (2) Unit surface dm2 15 (i) Apparent packed density: (3) Unit time min dA = 1.6-0.2 (ii) Suspension behavior: The polishing efficacy curve is plotted as a function T50=3 min of working time. (iii) Initial compaction: From this curve, polishing efficacy is expressed as the 20 No compaction mean of the first 10 results. (iv) Caking index Efficacy on felt: IC=4.0% The experiments were conducted on a Coburn 603 (v) Polishing efficacy: machine with a single brush, the felt polishing cloth of which was sprayed uniformly with the composition to 25 Efficacy on polyurethane foam 370 mg/dm/min be tested. Efficacy on felt 38 mg/dm/min Operating conditions were as follows: Efficacy on Pelion 44 mg/dm/min

(i) Velocity of polisher 550 rpm 30 The compositions of the invention gave results as (ii) Velocity of brush identical, as the brush is borne by the polisher good or better than those of the prior art, while at the (iii) Pressure 250 g/cm2 same time providing the great advantage of being de (iv) Concentration of suspension 50 g/1 void of fluoride ions in their chemical composition, (v) Water hardness 28 TH which ions are the source of a wide variety of problems (vi) Temperature 20 C. 35 in the manufacturing sequence. (vii) Polisher felt (Blu-Streak type) (viii) Glass to be polished Crown white TABLE III (ix) Turbine flow rate 1.2 to 1.4/min (x) Duration of experiment 15 min Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 (xi). Overall test period 1 hour, 30 min Suspension behavior, T50 5 4.7 4.7 3 7.5 in min 40 Caking index, 26 9.0 3.0 2.0 1.0 3.0 The expression of polishing efficacy was completely Compaction none none none slight Oe identical to that described for the CMV machine. Polishing efficacy Polishing efficiency was determined at the efficacy (in mg/dm'/min) Polyurethane foam 260 360 350 360 370 level, i.e., the mean of 45 min to 1 hour, 30 min tests. Felt 39 40 40 47 41 Efficacy on Pellon (skin): 45 Pelion 52 53 45 56 53 The test was performed using the aforesaid Coburn machine. The polisher employed was a self-adhesive Pellon manufactured by the Hartfelt Co. and bonded to While the invention has been described in terms of a flat tool. various preferred embodiments, the skilled artisan will Operating conditions were the following: SO appreciate that various modifications, substitutions, omissions, and changes may be made without departing from the spirit thereof. Accordingly, it is intended that (i) Velocity of polisher 550 rpm the scope of the present invention be limited solely by (ii) Velocity of brush identical, as brush is borne by the polisher the scope of the following claims. (iii) Pressure 250 g/cm? 55 What is claimed is: (iv) Concentration of suspension 50 g/1 1. A polishing composition of matter comprising (i) at (v) Water hardness 28 TH least one crystalline phase of CeO2 type, and (ii) a crys (vi) Temperature 20 C. (vii) Polisher Pellon talline phase which comprises a rare earth pyrosilicate (viii) Glass to be polished Crown white having the formula Ln2-CeSi2O7, wherein Ln is at (ix) Turbine flow rate 1.2 to 1.4/min 60 least one lanthanide or yttrium and x is a number rang (x) Duration of experiment 15 min ing from zero to less than 2. (xi) Overall test period 3 hours 2. The composition of matter as defined by claim 1, wherein x is a number ranging from zero to 0.2. Polishing efficacy was determined by taking the 3. The composition of matter as defined by claim 1, mean of the efficacies obtained at 30, 45 and 60 min. 65 wherein Ln is lanthanum or neodymium. The polishing compositions of the invention sub 4. The composition of matter as defined by claim 1, jected to this test, described above, provided the results further comprising at least a second rare earth oxide reported in Table III. crystalline phase. 4,601,755 15 16 5. The composition of matter as defined by claim 4, continuously adding an oxidizing agent to the reaction further comprising a silicon dioxide phase. medium. 6. The composition of matter as defined by claim 5, 26. The process as defined by claim 25, comprising which comprises a vitreous silicon dioxide phase. adding said oxidizing agent together with a solution 7. The composition of matter as defined by claim 5, other than the solution (b). which comprises a silicon dioxide crytalline phase. 27. The process as defined by claim 25, said oxidizing 8. The composition of matter as defined by claim 3, agent comprising sodium, potassium or ammonium per comprising lanthanum, silicon and cerium homoge chlorate, chlorate, hypochlorite or persulfate; hydrogen neously distributed therethrough. peroxide; air; oxygen; ozone; or electrochemical oxida 9. The composition of matter as defined by claim 1, O tion. comprising from 75 to 95% by weight of rare earth 28. The process as defined by claim 27, comprising a oxides and from 5 to 25% by weight of silicon dioxide. 10 to 40% stoichiometric excess of said oxidizing agent 10. The composition of matter as defined by claim 9, with respect to said cerous salt. cerium dioxide comprising from 60 to 85% by weight of 29. The process as defined by claim 20, wherein said the total weight of said rare earth oxides. 15 basic solution (b) is individually added to the reaction 11. The composition of matter as defined by claim 1, medium, or is added in a mixture with said silicon oxide said phase (i) comprising a cubic crystalline phase. solution (d). 12. The composition of matter as defined by claim 11, 30. The process as defined by claim 20, said basic said phase (ii) comprising an orthorhombic crystalline solution (b) comprising an aqueous solution of ammo phase. 20 nia, sodium or potassium hydroxide, or sodium carbon 13. The composition of matter as defined by claim 4, ate. said at least second rare earth oxide crystalline phase 31. The process as defined by claim 30, the normality comprising Ln2O3. of said basic solution (b) ranging from 1 to 5N. 14. The composition of matter as defined by claim 1, 32. The process as defined by claim 30, the reaction comprising from 30 to 80% by weight of CeO2, from 12 25 medium comprising an at least about 5% excess of basic to 60% by weight of Ln2-CeSi2O7, from 0 to 15% by equivalents with respect to cerium equivalents. weight of Ln2O3 and from 1.5 to 8% by weight of SiO2. 33. The process as defined by claim 20, the pH of the 15. The composition of matter as defined by claim 1, reaction medium ranging from 5 to 10. having a BET specific surface ranging from 1 m2/g to 34. The process as defined by claim 33, the pH of the 35 m2/g. 30 reaction medium ranging from 7 to 9. 16. The composition of matter as defined by claim 15, 35. The process as defined by claim 33, the pH of the having a BET specific surface ranging from 3 m2/g to reaction medium being controlled within 0.1 of a pH 10 m2/g. unit. 17. The composition of matter as defined by claim 1, 35 36. The process as defined by claim 20, wherein an comprising particulate aggregates having a median dio aqueous solution (c) of at least one trivalent rare earth ameter ranging from 0.5 to 1.5um. or yttrium salt is individually added to the reaction 18. The composition of matter as defined by claim 1, medium, or is added in a mixture with said cerium salt comprising block particulates with dimensions of less solution (a). than 100 um. 37. The process as defined by claim 36, the aqueous 19. The composition of matter as defined by claim 7, solution (c) of at least one trivalent rare earth or yttrium comprising a cristobalite phase. salt comprising a chloride or nitrate of lanthanum, ce 20. A process for the preparation of the composition rium, praseodymium, neodymium, samarium, euro of matter as defined by claim 1, comprising (1) inti pium, gadolinium, terbium, dysprosium, holmium, er mately admixing (a) a solution of a cerium salt, (b) a 45 bium, thulium, ytterbium, lutetium or yttrium. basic solution, (c) an aqueous solution of at least one 38. The process as defined by claim 37, the aqueous trivalent rare earth or yttrium salt, and (d) a solution of solution (c) of at least one trivalent rare earth or yttrium at least one oxide of silicon adapted to form an insoluble salt comprising a salt of lanthanum or neodymium. rare earth compound; (2) separating from such reaction 39. The process as defined by claim 37, the concentra medium the precipitate which results; and thence (3) 50 tion in said aqueous solution (c) of the salt or salts of the drying and calcining said separated precipitate at a trivalent rare earths or yttrium ranging from 0.2 to 1 temperature of at least 850° C. mole per liter. 21. The process as defined by claim 20, wherein said 40. The process as defined by claim 20, the propor cerium salt solution (a) comprises an aqueous solution of tion of the solution (a) of the cerium salt to the solution cerous chloride, or cerous or ceric nitrate, or mixture 55 (c) of the salt or salts of trivalent rare earths or yttrium thereof. being such that the ratio of cerium dioxide to the oxides 22. The process as defined by claim 21, the cerium of the rare earths or yttrium ranges from 60 to 85%. salt comprising said solution (a) being more than 99% 41. The process as defined by claim 20, wherein the pure. solution (d) of at least one oxide of silicon adapted to 23. The process as defined by claim 20, the concentra 60 form an insoluble rare earth compound is individually tion of the cerium salt in said solution (a) ranging from added to the reaction medium, or is added in a mixture 0.2 to 4 moles per liter. with said basic solution (b). 24. The process as defined by claim 23, the concentra 42. The process as defined by claim 41, said solution tion of the cerium salt in said solution (a) ranging from (d) comprising an aqueous solution of silicon dioxide, 0.5 to 2 moles per liter. 65 silicic acid, or a silicate of an alkali metal. 25. The process as defined by claim 20, the solution 43. The process as defined by claim 42, said solution (a) initially comprising a cerous salt, and which further (d) comprising an aqueous solution of sodium silicate, comprises in situ oxidizing same to the ceric state by Na2O.4 SiO2. 4,601,755 17 18 44. The process as defined by claim 20, the concentra 51. The process as defined by claim 50, wherein the tion in said solution (d) of said at least one oxide of temperature of aging ranges from 50 to 80 C. silicon ranging from 0.1 to 2.0 moles/liter of SiO2. 52. The process as defined by claim 20, wherein the 45. The process as defined by claim 20, the propor separation (2) of the precipitate is by filtration. tion of the solution (d) of the at least one oxide of silicon 5 53. The process as defined by claim 52, further com to the solution (c) of the at least one trivalent rare earth prising washing the filter cake with water. or yttrium salt being such that the ratio of the equiva 54. The process as defined by claim 52, wherein the lents of silicate (SiO3) to the equivalents of the at least drying of the precipitate is carried out at a temperature one trivalent rare earth or yttrium ranges from 0.1 to 10 of from about 100 to 600° C. for a period of time of from 1.0. about 30 min to 24 hours. 46. The process as defined by claim 45, said ratio of 55. The process as defined by claim 54, wherein the the equivalents of silicate (SiO3-) to the equivalents of dried precipitate is calcined at a temperature of from 850 to about 1500 C. for a period of time of from about the at least one trivalent rare earth or yttrium ranging 30 min to 10 hours. from 0.2 to 0.6. 15 56. The process as defined by claim 55, the tempera 47. The process as defined by claim 20, wherein the ture of calcination ranging from 850 to 1050 C. temperature of the reaction medium ranges from 10 to 57. The process as defined by claim 20, further com 95° C. prising grinding and classifying the calcined precipitate. 48. The process as defined by claim 47, wherein the 58. A glass polishing bath, comprising a dispersion in temperature of the reaction medium ranges from 40 to 20 water of the composition of matter as defined by claim 70° C. 1, the concentration of CeO2 therein ranging from 30 to 49. The process as defined by claim 20, wherein the 200 g per liter. reaction time ranges from 30 min to 2 hours. 59. In a process for the polishing of a glass surface 50. The process as defined by claim 20, comprising utilizing a glass polishing bath, the improvement which aging the reaction medium prior to the separation of the 25 comprises, using as the glass polishing bath therefor, the precipitate therefrom, at a temperature of from 10 to 95 bath as defined by claim 58. C. for a period of time of from 30 minto 2 hours. sk it k sk

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