CS235157B1 - Process for producing finely crystalline alpha-silicon dioxide - Google Patents

Abstract

The invention relates to a method for producing finely crystalline α-silica with crystals of 0.08 to 0.8 mm in size. The method consists in carrying out the crystallization of amorphous silica in an atmosphere of water vapor in the presence of a crystallization activator of the basic substance in an amount of from 1 . IO-3 to 1% by weight of amorphous silica at a temperature of 300 to 500 °C and a pressure of 2 to 40 MPa for a period of 5 to 100 hours. The invention can be used in the production of quartz glass and quartz ceramics

Description

The invention relates to a process for the production of finely crystalline α-silica. This product can be used for the production of quartz glass and quartz ceramics.

The expansion of the raw material base for the production of quartz glass is one of the current problems. The desired expansion of the selection of manufactured quartz products and the steady increase in demand for quartz glass products contributed to the need to search for new types of raw materials for the production of quartz ceramics. The most suitable raw material for this purpose is finely crystalline silica. Said silica is one of the crystalline modifications of silica. The silica may be present in the form of the following modifications: low temperature α-silica, high temperature β-silica, crystallite, and tridimite, which can be obtained with a considerable mineralizer content in the silica.

All crystalline modifications of silica can be used as raw material for the production of quartz glass and quartz ceramics.

At present, the most widespread raw material for the production of quartz glass and quartz ceramics is the pulp of convenient α-silica obtained by the processing of crystal or quartz. This treatment consists in crushing, sieving the natural quartz, the fraction of 0.1 to 0.5 mm is magnetically separated, floats, chemically enriched in the treatment with mineral acids, then washed and dried.

The large number of complex operations in the processing of natural quartz, the use of complex equipment in its enrichment, and the work of operators in health-damaging conditions present significant deficiencies in the use of natural silica.

High quality quartz glasses are made from crushed synthetic single crystals of silica.

There is a known method of producing single crystals of silica by the hydrothermal synthesis process (see for example VS Balickij, Ge. Je. Lisicyna "Sinteticheskii analogi i imitaci natural dragocenech komnej", Moscow, publishing house Nedra, 1981, pp. 80-81, KT Vilke "Methods vyrasčivanija kristallov , Leningrad, Nedra Publishing, 1968, p. 117). The silica monocrystals are produced by recrystallization of natural quartz in sodium or alkaline solutions at a temperature of 350 to 420 ° C and a pressure of 50 to 150 MPa. High quality single crystals weighing up to 2 kg are grown in industrial autoclaves for 3 to 12 months. Then, these crystals are crushed, enriched, dried and sieved. A 0.1 to 0.5 millimeter fraction is used to produce silica glass. Approximately% of the raw material is not used for the production of glass. This method of production is uneconomical due to high energy and raw material costs.

It is known to produce polymorphic crystalline silica by heating amorphous silica in air in the presence of alkali oxides at a temperature of 400 to 1000 ° C, see for example patents Nos. 2,743,143 and 2,751,443. Only partial crystallization of the oxide takes place of silica while producing various modifications of crystalline silica with different melting temperatures and weights as well as high water content. All this makes it difficult to manufacture the product obtained for the production of quartz glass.

A process for the production of crystallite is known which can be used as a raw material for fusing silica glass. Crystobalite can be produced by a high temperature treatment of α-silica, see, for example, US Patent No. 3,565,595 and GDR Patent No. 134,219, as well as amorphous silica in the presence of mineralizers, see, for example, USSR Authorization Nos. 600,094 and 776 994. The process is economically unsuitable and technically difficult to carry out due to the longevity of heating up to 20 hours at high temperatures, i.e. 1300 to 1700 ° C. The mineralizers used contaminate the glass made of crystallite. In addition, the method involves a large number of operations. If amorphous silica is used as a raw material, the production process is as follows: amorphous silica is soaked in a solution of mineralizers such as caustic, ammonium fluoride or soda, briquetted and heat treated at 1300 to 1700 ° C; to obtain a fraction of 0.1 to 0.5 mm. Often, prior to heat treatment, amorphous silica is formed, for example, into tubes using aqueous binder solutions: polyvinyl alcohol (Chem. Abstr. 1973, 79, 21C1, Chem. Abstr. 1976, 85, no. 14, p. 268, Report No. 98 381c, Japan Kokai 7677, 612, Class C 03B 3106 J, potassium silicate with formamide (U.S. Patent No. 4,059,658), silicon halide (British Patent No. 1168,934) etc.

For the production of quartz glass, the use of finely crystalline silica with a grain size corresponding to the requirements of current melting processes seems to be most advantageous.

A method for producing finely crystalline α-silica with crystals smaller than 0.2 mm from amorphous silica is known by hydrothermal treatment in an autoclave of solid phase mixtures of silica and ammonium fluoride in a weight ratio of 0.5: 1 to 5: 1, appropriately at a temperature of 150 to 400 ° C and a pressure of 0.5 to 1.5 MPa, see, for example, U.S. Pat. No. 489,723.

This production method is economically disadvantageous because it does not make it possible to achieve 100% crystallization of amorphous silica and, due to the aggressiveness of the environment, requires the lining of the autoclave to be platinum or of other noble metal, moreover the amount of amorphous silica charged into the autoclave is relatively small. The method is associated with the harmful working conditions of the operators. The fine-grained silicon dioxide produced contains a large number of volatile impurities (fluorine, ammonia, water, etc.), which makes it impossible to produce high-quality quartz glass.

Further, it is known to cultivate a fine-grained silica of amorphous silica dissolved in an aqueous solution of ammonium fluoride in an autoclave at a temperature of 100 to 450 ° C and a pressure of 10 to 100 MPa on seed crystals of 0.001 to 0.1 mm fine grain size. This method is characterized by the same drawbacks as the previous procedure.

It is an object of the invention to overcome these drawbacks.

SUMMARY OF THE INVENTION It is an object of the present invention to provide, for a process for producing fine-grained silica from amorphous silica, such process conditions that make it possible to produce a product suitable for producing high-quality quartz glass and quartz ceramics. and equipment.

This object is achieved by a process for the production of fine-grained α-silica with a crystal size of 0.08-0.8 mm from the amorphous silica according to the invention, characterized in that the crystallization of silica is carried out in a water vapor atmosphere in the presence substances in quantities from 1. 10 ^-3 to 1% by weight of amorphous silica at a temperature of 300 to 500 ° C and a pressure of 2 to 40 MPa for 5 to 100 hours.

The process according to the invention is simple in terms of technology and in terms of apparatus. It makes it possible to obtain the targeted product in 100% yield, while the α-silica crystals have the shape of gems with regular boundaries. The crystal size is in the range of 0.08 to 0.8 mm and the traction distribution of the crystal sizes depends on the conditions of crystallization.

The composition and amount of elemental admixtures in the produced silica determines the degree of purity of the starting amorphous silica, since crystallization occurs under the influence of water vapor and not in sodium or alkaline solutions as in the known case. The crystallization activators are added in microscopic amounts and in most cases decompose during the thermal treatment of the silica and do not destroy the crystals formed. In addition, by crystallizing amorphous silica, the content of each dopant, i.e., alkali metals and carbonaceous substances, in the finely crystalline silica produced is reduced by 1.5 to 3 times the content of the starting silica.

In addition, the water content of the product is reduced. When the amorphous silica contains 1 to 16 ^; % of water, then the finely crystalline α-silica contains from 0.03 to 0.001% by weight of water. The fine-crystalline dry silica lined out of the reactor is readily usable for the production of high-quality quartz glass and quartz ceramics without further processing such as enrichment, crushing, screening and drying.

When amorphous silica containing an alloying element is used, an alloyed quartz raw material can be obtained for the manufacture of special purpose glasses.

As the starting product for the synthesis of finely crystalline α-silica, amorphous silica which is a waste from the production of mineral fertilizers or the chemical industry can be used in the production according to the invention.

Crystallization can be carried out both in standard autoclaves used for the hydrothermal synthesis of silica monocrystals and in reactors used in the chemical industry. Reactors and autoclaves can be made of heat-stable steel, and lining is unnecessary for reactors and autoclaves because weakly alkaline or neutral environments and low water vapor pressure do not cause corrosion of reaction apparatus walls.

Crystallization is carried out at a temperature of 300-500 ° C. Higher temperatures are ineffective due to the need to use special thermally stable devices. Crystallization is incomplete at temperatures below 300 ° C.

The water vapor pressure, determined by the reactor or autoclave charge coefficient, may be 2 to 40 MPa. At a lower pressure, the crystallization process proceeds very slowly and an increase in pressure above 40 MPa has no further effect. The process time is determined by the crystallization kinetics and depends on both the crystallization activator concentration and other parameters (pressure, temperature). Optimally, crystallization can take place in 5 hours, but in some cases it is preferable to use conditions in which complete crystallization takes place in 100 hours to produce high quality crystals.

The concentration of a crystallization promoter is in the range from 1.10 ³ to 1% by weight of amorphous silica. When using a crystallization activator, in an amount of less than 1 x ^{10 3} of the weight of the starting silica, the crystallization process is incomplete. Increasing the crystallization activator concentration above 1% is not desirable because it causes contamination of the targeted product and does not result in additional process acceleration.

The type of crystallization activator and its concentration is determined by the purpose determination of the finely crystallized α-silica produced.

If it is necessary to produce cheap quartz raw material for the production of wide consumption quartz glass, then it is recommended to use alkali metal hydroxides as an activator of crystallization in an amount of from 1.10 ^-3 to 1.10 ^-1 % by weight of amorphous silica. The result is a finely crystalline silica with an alkali metal content of from 1.10 ^-3 to 1.10 ^-2 % by weight.

It is recommended to use ammonium hydroxide or ammonium tetravalent in amounts from 2 to 10% by weight for the production of high quality fine crystalline silica with low metal content (from 1. 10 ^-4 to 1.10 ^-3 % by weight). 10 ~ ² to 1% by weight of amorphous silica.

For the production of finely crystalline silica having a low alkali metal content, i.e. (1 to 5) .10 ^-4 % by weight, it is recommended to use organic polyelectrolytes - polyethyleneimines having a molecular weight of from 190 to 5000 in an amount of from 1.10 “ ³ to · 1.10 ^-1 % by weight of amorphous silica.

High molecular weight polyethyleneimine (molecular weight 10,000 to 50,000) is a widespread and inexpensive product which is used as a flocculant in water purification, as a plasticizer in paper making, etc. (see, for example, PA Gembickij, DS Zhuk, VA Kargin "Polyethyleneimine", Moscow, publishing house "Nauka", 1971, pp. 7, 8, 177).

Low molecular weight polyethyleneimine (molecular weight less than 10,000 and starting from 190) is a mixture of various polyethylene polyamines: diethylenetriamine, triethylenetetramine, tetraethylenepentamine, etc. (see, for example, PA Genbic, DS Zhuk, VA Kargin "Chimija etilenimina", Moscow, 1966 Nauka, r. 159). This product is produced on a large scale by condensation of dichloroethane with ammonia or ethylenediamine as well as the interaction of ethyleneimine with ammonia and amines in the presence of β-chloroethylamine. Low molecular weight polyethyleneimine is currently known as a hardener of epoxy resins and as an additive to rocket fuel.

For the production of finely crystalline α-silica with low content of carbonaceous substances (from 1. 10 ^-4 to 5. 10 ^-4 % by weight of carbon) and metal admixtures (from 1.10 - ⁴ to 1.10 ~ ³ % by weight) it is recommended as activator crystallization using hydrazine or its alkyl derivatives in an amount of from 2.10 ^-2 to 1% by weight of amorphous silica.

The process for producing the finely crystalline α-silica according to the invention is carried out as follows:

The amorphous silica is mixed into an aqueous solution of the crystallization activator of the desired concentration and maintained in the solution at room temperature or at 70 ° C for 0.2 to 3 days. The solution is then screened and the wet deposit is placed in an autoclave or reactor, i.e. a reaction apparatus. The total amount of residual moisture must provide the required water vapor pressure at the specified crystallization temperature.

The reaction apparatus is heated to the crystallization temperature and maintained at this temperature for 5 to 100 hours. After completion of the crystallization process, the pressure is reduced and the reaction apparatus is cooled. The finished product - finely crystalline α-silica is removed from the apparatus, packed in a polyethylene bag and sent to the consumer.

A second technological variant of the method according to the invention is also possible.

The amorphous silica is stirred into an aqueous solution of the crystallization activator of the desired concentration and maintained at room temperature or at 70 ° C for 1 to 3 days. The solution is then screened and the silica is dried at 100-300 ° C. The dry silica was charged to the reaction apparatus. Water is supplied to the apparatus to produce the desired pressure, or water is poured in an amount necessary to achieve the corresponding water vapor pressure in the apparatus at a specified crystallization temperature. Furthermore, the procedure proceeds as in the previous case.

Treatment of the amorphous silica with an aqueous solution of the crystallization activator can be carried out immediately in the reaction apparatus. At this time, the amorphous silica is charged into the apparatus, then an aqueous solution of the crystallization activator is poured, then the reaction apparatus is vented and heated to the specified temperature. Furthermore, the production process proceeds similarly as in the previous cases.

For a better understanding of the invention, the following examples of specific embodiments of the process of the invention are given.

Example 1

An aqueous NaOH solution of concentration 1 was prepared. 10 ^-3 % by weight.

100 kg of amorphous silica containing the following impurities in% by weight are placed in 100 l of the prepared solution: NéuO - 2.1.10 ^-3 , Al - 5. 10 ^-4 , Fe - 2.1.10-4, Mg - 4.10-5, t - 4. ΙΟ ^-3 , _Ca '- 4.2.10 ^-4 . The silica is kept in solution at room temperature for 5 hours. The solution is sparged and lukewarm silica is placed in an autoclave. The autoclave was aerated, heated to 500 ° C and held at this temperature for 10 hours. The water vapor pressure in the autoclave is 30 MPa. The autoclave is then cooled to 100-50 [deg.] C., opened and the product is dried in the autoclave immediately at that temperature. The product is removed and packed in polyethylene bags for delivery to the consumer. The yield of the product is 100%. The product is a finely crystalline α-silica with crystals of 0.08 to 0.3 mm and containing impurities in the following amounts (% by weight): NazO - 8. 10 ⁴ , AI-5. 10 ⁴ , Fe - 2.5. 10 ^{4 4} , Mg - 4. 10 ~ ⁵ , Ti-4.10 ^-5 , Ca-1.5.10-1

Example 2

Prepare an aqueous solution of KOH 10 first concentration ^{of 1%} by weight. Furthermore, the process proceeds as in Example 1, except that the crystallization is carried out at a temperature of 420 ° C and a water vapor pressure of 30 MPa for 5 h. The product is obtained in 100% yield. The product is finely crystalline and silica, with crystals of 0.08 to 0.15 mm in size and a K 2 O content of 5.1. O ³ o / _o weight.

Example 3

An aqueous LiOH solution of concentration 5 was prepared. O ³ o / ₀ weight. 100 kg of amorphous silica are charged into a 0.5 ml ³ autoclave and poured into 100 L of the prepared LiOH solution. The process is carried out at a temperature of 400 ° C and a water vapor pressure of 28 MPa for 10 h. In 100% yield, a finely crystalline silica is obtained, with crystals of 0.08 to 0.2 mm and containing 1.2 x ^{10 -3} %. weight of the additive LizO. Example 4

An aqueous solution of RbOH concentration 1 is prepared. 10 ^2% by weight, and the crystallization is carried out by the same procedure as in Example 1 but at 300 ° C and at a water vapor pressure of 7 MPa for 100 li. In 100% yield, finely crystalline α-silica is obtained, with crystals of 0.08-0.2 mm and containing 3.2. 10 ^3% by weight impurities RbzO.

Example 5

An aqueous solution of CsOH at a concentration of 5.10 ² % by weight is prepared. 100 kg of the amorphous silica are introduced into 100 l of the prepared solution and the silica is kept in solution at 70 ° C for 2 h. The solution is then cooled to room temperature and spun off. The silica is dried in air at 100 degrees C. The dried amorphous silica is charged into a reactor, which is supplied with steam and maintained at a temperature of 350 ° C and a water vapor pressure of 2 MPa for a period of time.

h. In 100% yield, finely crystalline α-silica is obtained, with crystals of 0.08-0.2 mm containing 3.7. . 10 ~ ³ % by weight of the additive Cs2O.

Example 6

A 1% aqueous ammonium hydroxide solution was prepared. 100 kg of the prepared solution were charged with 100 kg of amorphous silica containing the following impurities in% by weight: NacO - 4.12. 10 ² , AI - 3.2. 10 ³ . Fe - 1.3. ΙΟ ^3, Mg _ 5.7. 10 ⁴ , Ti - 7.8. ΙΟ ⁴ , Ca - 3.2. 10 ² . The silica is kept in solution at room temperature for 5 h. The solution is sparged and the residue is dried at 100 ° C. The dry silica is charged into a 0.5 m ³ reactor, where 100 l of water is also poured. Crystallization takes place at a temperature of 450 ° C and a pressure of 35.5 MPa for 36 h. Crystalline silica is obtained, consisting of 77% by weight of finely crystalline α-silica and 23% by weight of crystallobalite. The crystal size ranges from 0.08 to 0.2 mm. The product contains the following impurities in% by weight: NazO - 1.8.10 ^-3 , Al - 3.2.10-3, Fe - 1.2. ΙΟ ³ , Mg - 2.4. ΙΟ ⁴ , Ti - 7.1, ^{10 -4} , Ca - 4.2. ³ ' ³ .

Example 7

An aqueous solution of tetrabuyl ammonium hydroxide at a concentration of ⁵ % ^-1 % by weight is prepared. 100 kg of amorphous silica are added to 100 l of the prepared solution. Further, the procedure proceeds as in Example 1.

Crystallization is carried out at a temperature of 400 ° C and a water vapor pressure of 30 MPa for 72 h. A finely crystalline α-silica is obtained with 100% yield, with crystals of 0.1 to 0.5 mm in size.

Example 8

An aqueous solution of tetramethylammonium hydroxide concentration 2 is prepared. 10 ¹ % by weight. 100 kg of the prepared solution are charged with 100 kg of amorphous silica containing the following impurities in% by weight: NazO - 9.8. ΙΟ ³ , _A1 _ ₂ , 5.10Λ Fe - 2.5. 10 ³ , Mg - 1.10 “ ⁶ , Ti - 2.5. 10 ' ⁵ , Ca - 1.5.10 ⁴ , C - 2.1. ΙΟ ² . The silica is kept in the prepared solution at 50 ^° C for 5 L. Decant the solution to the bottom of an autoclave of 5.0 m ³ and place the moist silica on the plates of the autoclave equipment. Crystallization is carried out at a temperature of 380 ° C and a pressure of 24 MPa for 100 hours. A 100% yield of finely crystalline α-silica is obtained, with crystals of 0.1 to 0.5 mm in size and containing impurities in the following amounts in% by weight: NazO - 2.1. 10 ^3, Al - 2,5.10 ^-5, Fe - 4.10- ⁵ Mg - 10.1 ⁶ Ti - 2,5.10-5 Ca - 9 .ΙΟ ⁵ C - 9th ΙΟ ⁴ .

Example 9

An aqueous solution of tetraethylammonium hydroxide at a concentration of 5% by weight ² % is prepared. 100 kg of the amorphous silica are charged to 110 l of the prepared solution and kept at room temperature for 24 h. The solution is sparged, the silica is dried at 100 DEG C. and charged to a reactor in which water vapor is introduced. Crystallization is carried out at 470 ° C and a water vapor pressure of 40 MPa for 5 h. A 100% yield of finely crystalline α-silica with crystals of 0.1 to 0.5 mm is obtained.

Example 10

An aqueous sodium hydroxide concentration of 2.10 tetrapropylaimonia ^"2% by weight. Further, the process proceeds as in Example 9. A finely crystalline α-silica with crystals of 0.1 to 0.5 mm in size is obtained in 100% yield.

Example 11

An aqueous solution of high-molecular polyethyleneimine having a branched structure and a molecular weight of 30 000 to 50 000. The concentration of the solution is 1.10 ^"2% by weight. 100 kg of the prepared solution are charged with 100 kg of amorphous silica and maintained at room temperature in the solution for 72 h. The solution is sparged and the wet silica is charged to the reactor. The crystallization is carried out at a temperature of 400 ° C and a pressure of 20 MPa for 72 h. In 100% yield, finely crystalline α-silica with crystals of size 0.08-0.4 mm is obtained.

Example 12

An aqueous solution of a high molecular weight polyethyleneimine having a branched structure and a molecular weight of 30,000 to 50,000 is prepared. The concentration of the solution is 5. 10 " ³ % by weight. 100 kg of the prepared solution are charged with 100 kg of amorphous silica containing the following impurities in% by weight: NaaO - 6.4. 10 ^{4 4} , Al - 0.4. 10 ^{4 4} Fe - 2.4. 10 ^'4 Mg - 0.4. 10 “ ⁴ , Ti - 0.6. 10 ^{4 4} , Ca - 0.4. IQ ” ⁴ , Cu - 0.2 .10“ ⁴ , Mn - 0.1. . 10 ^{4 4} , C - 1,4. IO ' ² .

Further, the process proceeds as described in Example 11. Crystallization is carried out at a temperature of 400 ° C and a water vapor pressure of 30 MPa for 60 h. A 100% yield of finely crystalline α-silica with 0.08 crystals is obtained. to 0.4 mm and containing the following impurities in% by weight: NazO - 2.7.10 ⁴ , Al - 0.5. 10 ^{4 4} , Fe - 1.9. IO ⁴ , Mg - 0.5.

. 10 “ ⁴ , Ti - 0.6. 10 ^{4 4} , Ca - 0.4. IO ' ⁴ , Cu - 0.2. 10 ^"4, Mn - 0.1. 10 ^{4 4} , C - 1.8. 10 “ ³ .

Example 13

An aqueous solution of a high molecular weight polyethylenimine having a branched structure and a molecular weight of 10,000 to 20,000 is prepared. The concentration of the solution is 1.0% - ³ % by weight. 100 kg of amorphous silica are placed in 100 l of the prepared solution. The process proceeds as in Example 11. Crystallization is carried out at a temperature of 40 ° C and a water vapor pressure of 10 MPa for 48 h. Crystalline silica is obtained, consisting of 98% by weight of finely crystalline α-silica and 2% by weight of crystallinity. The crystal size ranges from 0.08 to 0.3 mm.

Example 14

An aqueous solution of low molecular weight polyethylenimine having a molecular weight of 190 to 300 is prepared. The concentration of the solution is 5. 10 ' ² % by weight. Further, the process proceeds as described in Example 11. Crystallization is carried out at a temperature of 500 ° C and a water vapor pressure of 20 MPa for 5 h. A finely crystalline α-silica with crystals of 0.08 size is obtained with 100% yield. up to 0.3 mm.

Example 15

An aqueous solution of low molecular weight polyethylenimine having a molecular weight of 300 to 450 is prepared. The concentration of the solution is 1. 10 " ⁴ % by weight. Further, the process proceeds as in Example 5. Crystallization is carried out at a temperature of 300 ° C and a water vapor pressure of 8 MPa for 100 h. A product is obtained consisting of 96% by weight of finely crystalline α-silica and 4% by weight of crystallobalite. The crystal size ranges from 0.08 to 0.3 mm.

Example 16

A 1% aqueous hydrazine solution was prepared. 100 kg of the prepared solution are charged with 100 kg of amorphous silica containing the following impurities in% by weight: Na 2 - 9. 10 ^{4 4} , Al - 0.4. 10 ^{4 4} , Fe - 0.6.

. 10 ^"4, Mn - 0.1. 10 ^{4 4} , C - 1,4. IO ' ³ . Next, the process is carried out as described in Example 8. A 100% yield of finely crystalline α-silica with crystals of 0.1 to 0.8 mm in size and containing the following impurities in% by weight is obtained: Na 2 - 6. 10 ^-4 , Al-0.4. 10 ^{4 4} , Fe - 0.6. IO ⁴ , Mg - 0.4. , 10 " ⁴ , Ti - 0.4.10" ⁴ , Ca - 0.5.10 " ⁴ , Cu - 0.1. IO ' ⁴ , Mn - 0.1. 10 “ ⁴ , C-2. IO · “ ⁴ . Example 17

Prepare an aqueous methylhydrazine solution concentration 10.5 ^"2% by weight. 100 kg of amorph235157 silica are added to 100 l of the prepared solution. The silica is kept in solution at room temperature for 24 hours. The solution is sparged to the bottom of the autoclave and the moist silica is placed on the plates of the autoclave equipment. The autoclave is heated to a temperature of 450 ° C and water vapor is supplied to a pressure of 40 MPa. Amorphous silica is crystallized at this temperature and pressure for 48 h. A finely crystalline silica with 0.1 to 0.8 mm crystals is obtained in 100% yield.

Example 18

An aqueous solution of asymmetric dimethylhydrazine 2 is prepared at a concentration of ^5.10-1 % by weight. 100 kg of amorphous silica are introduced into 100 l of the prepared solution. Further, the process proceeds as in Example 9. Crystallization is carried out at a temperature of 400 ° C and a pressure of 2 MPa for 96 h. A 100% yield of finely crystalline α-silica with crystals of 0.1 to 0.5 mm is obtained.

Example 19

An aqueous solution of symmetrical dimethylhydrazine concentration 1 is prepared. 10 " ¹ percent by weight. 100 kg of the prepared solution are charged with 100 kg of amorphous silica containing the following impurities in% by weight: Na2 [0-6.4. 10 ~ ⁴ , Al - 0.4. 10 ^-4 , Fe - 2.4. 10 ^-4 , Mg - 0.4. 10 ' ⁴ , Ti - 0.6. . ΙΟ ⁴ , Ca - 0.4. IO- ⁴ , Cu-0.2. 10 ^"4, Mn - 0.1. 10 ~ ⁴ , C = 1.4. 10 ~ ² . Further, the process proceeds as described in Example 1. The product produced in 100% yield is a finely crystalline silica with crystals of 0.1 to 0.5 mm in size and containing the following impurities in% by weight: N 0 - 5.1.10 ⁴ , Al - 0,4. ΙΟ “ ⁴ , Fe - 2.8. 10 ~ ^4, Mg - 0.4. . 10 ~ ⁴ , Ti - 0.6. ΙΟ “ ⁴ , Ca - 0.5. 10 ^{4 4} , Cu - 0.1. IO ^{1 '4} _ 0.1 Mn. ⁴ “ ⁴ , C-3. 10 “ ⁴ . Example 20

An aqueous solution of ethylhydrazine at a concentration of 2.10 ~ ² % by weight is prepared. To. 100 l of the prepared solution are charged with 100 kg of amorphous silica. Further, the process is carried out as described in Example 1. The crystallization is carried out at a temperature of 450 ° C and a water vapor pressure of 10 MPa for 72 h. A 100% yield of finely crystalline α-silica with crystals of 0.1 to 0 is obtained. , 8 millimeters.

Claims (5)

A process for the production of finely crystalline silica with a crystal size of 0.08-0.8 mm from amorphous silica, characterized in that the crystallization of amorphous silica is carried out in a water vapor atmosphere in the presence of an activator of the crystallization of the base in an amount of 1 . ^{10, and} 1% by weight of amorphous silica at a temperature of 300-500 ° C and pressure 20 to 40 MPa to 100 hours. 2. A process according to claim 1, wherein the crystallization activator is an alkali metal hydroxide in an amount of from 1.10 &^lt; ³ & gt ^; to 1. ^_1 10% by weight of amorphous silica. fYNÁLEZU 3. The process of claim 1 wherein the crystallization activator is ammonium hydroxide or ammonium hydroxide in an amount of from 2 to 2. 10 ^"2 to 1% by weight of amorphous silica. 4. Method according to claim 1, characterized in that the crystallization promoter are organic polyelectrolytes - Polyethyleneimine having a molecular weight from 190 to 50,000 in an amount of from 1 to ³ 1CF 1.10 ^_1% by weight of amorphous silica. 5. A process according to claim 1, wherein the crystallization activator is hydrazine or its alkyl derivatives in an amount of from 2.10 &^lt; ^{2 >} to 1% by weight of the amorphous silica.