IL30525A - Synthetic wollastonite - Google Patents

Description

SYNTHETIC i State of the Prime Office Israel Ceramic and Silicate Institute Acre Ceramic Industries Israel Ceramic Works Harsa The present invention relates to an improved process for the production of a or acicular crystalline form of calcium More particularly it concerns an improved process wherein the reaction between calcium oxide or other basio calcium compounds such as calcium carbonate or hydroxide with at elevated temperature to form the form of calcium is accelerated by means of a promoter calcium or calcium chloride containing calcium chloride may serve as the sole source of calcium in the reaction with to form calcium and hydrogen chloride may be obtained as an additional useful is an acicular crystalline form of calcium metasilicate that finds many applications in the production of various ceramic for wall ceramic bonded electrical porcelains The advantages of that make it specifically suitable for use in ceramic include the improved dimensional stability in the presence of improved stability to heat reduced shrinkage during drying and and various other processing advantages it imparts to these Although some natural deposits of are the overall occurence of in nature at least to the extent that this occurence has been is rather In areas where is not naturally the cost of the material relative to the functions that it is rather prohibitive for consideration for most of its Various processes are known for the production of produots by the reaction of suitable raw materials at elevated the product usually obtained when lime or another basic oaloium compound is heated with silica although having the proper empirical formula of calcium silicate does not have the desirable physical properties that make natural so useful in its many example if lime and silica are reacted at temperatures above a calcium silicate is having the form usually referred to or This material is at best a very poor substitute in the various applications for which it is It is possible however to react lime or calcium with at temperatures below whereby a product is obtained whose properties are essentially identical to those of the naturally occurring The difficulty of producing in this manner resides the fact that the time required for the reaction to take place to an appreciable is quite being in in the vicinity of 24 This entails rather large fuel cost and for this this approach is not suitable for commercial production of It is an of this invention to provide a convenient and rapid process for the production of synthetic It is a further object of this invention to provide a process whereby can be produced from raw materials that are commonly available in most parts of the such as lime or calcium carbonate on one and such as sand and related on the other It is an additional object of this invention to provide an improved process for the reaction of lime or other calcium said reaction being accelerated with calcium chloride or calcium chloride containing that are also commonly available in most parts of the In accordance with the method of this there is provided an improved process for the production by reacting lime or an other calcium compound with at elevated said process being characterised in that the reaction is carried out in the presence of calcium chloride or calcium chloride containing the rate of the reaction being thereby The product obtained from the process is substantially identical to that of naturally occurring with respect to its oritical physical and the applications for which naturally occurring is generally The following examples are illustrations of how this invention may be EXAMPLE 1 The following materials were mixed in a ball mill for a period of 2 parts by weight of silica sand ground to 200 parts by weight of ground lime of 100 and parts by weight of calcium ground to 100 After the mixing was the reaction mixture was transferred to a o refractory vessel and baked in an oven at 1080 C for four The product obtained in this manner in addition to some calcium chloride and small of other The calcium chloride was removed in the The product was slurried with added water in a and After the filter cake containing the desired product was rinsed once more with the same amount of water that was initially used to form the reaction The rinsed product was dried at 100 to resulting in crystalline synthetic consisting mainly of the acicular crystalline that was shown by diffraction analysis to of more than of the EXAMPLE Reaotants in the same relative proportion as those utilized in example 1 were treated in essentially the same manner except that the reaction was carried out at instead of The yield of the desired product was only EXAMPLE 5 The following reaotants were mixed in a ball mill for 2 by weight of sea sand ground to 200 parts per weight of lime ground to 100 15 parts per weight of calcium chloride ground to 20 The mixture was then fired in refractory clay vessels at for four insufficientOCRQuality

Claims (9)

The reaction product was then worked up In the same manner as that described In -Example 1, In order to remove excess calcium chloride. The final product after drying at 100 to 110°C consisted df 80$ -Vollaetonite as indicated by X-ray diffraction analysis. The length of the individual crystals was on the average, 55 microns. EXAMPLE 4 The following reactants were mixed in a ball mill for 2 hours. 41.2 parts per weight of ordinary sand ground to 200 mesh, 56.8 parts of lime ground to 100 mesh A solution containing 35$ of magnesium chloride and 10 of calcium chloride was then added in an amount of 300 ml for each kilogram of lime-sand reaction mixture. After further thorough mixing, the mixture was dried at 100 to 110°C and fired at 1080°C for four hours. The product obtained in this example contained in addition toj-Wollastonite significant quantities of Akermanite (2CaO,Mg0.2Si02). The excess M Cl^ and CaClg were removed by washing the product in the same manner o described for previous examples, followed by drying at 100 to 110 C. The final product consisted of 65$ and 28$ Akermanite. It is obvious from the examples oited, that with minor modifications the production of j-Wollastonite in..accordance with the teachings of this invention can be oarried out in a continuous manner, when this is desirable. It is also obvious that many other variations in the basic teachings of this invention are possible,' e.g. where mixtures of synthetic minerals containing -Hollastonite are desired as final products, the initial charge of the reaction can be modified so as to give these products, without departing from the basio spirit of the described invention. Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, .we declare that what we claim is:

1. , An improved process for the production of p-Wollastonite by reacting a calcium compound such as lime with silica, SiO^, at temperatures between 900 and 1200°C, said improved process being characterised in that the reaction t ia carried out in the presence of calcium chloride or calcium chloride containing materials*

2. Process in accordance with C3iAim 1 wherein the calcium chloride is added to the reaction mixture as a solid.

3. The process in accordance with Claim 1 wherein the calcium chloride is added to the reaction mixture as an aqueous solution.

4. The process in accordance with any of Claims 1 - 3 where the calcium chloride content of the reaction mixture comprieea 5 to 30$ of the total reaction mixture.

5. Process in accordance with any of Claims 1 - 4 wherein the molar rationof the lime to silica is approximately 0.5 to 1.25, preferably 0.8 to 0.9·

6. The process inaaccordance with any of claims 1 - 5 wherein the reaction is carried at between about 1,000 to 1,100° C.

7. The process in accordance with any of claims 1 - 6 wherein the said calcium compound is calcium chloride.

8. Wollastonite whenever produced by a process substantially as described in any of claims 1 to 7

9. % prooess aa claimed in any one of the claims 1 to 8 subatantially as herein-before described.