JPH0118011B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method suitable for producing fibrous wollastonite crystals which can be used as reinforcing materials for Portland cement, calcium silicate, plastics and the like. US Pat. No. 3,799,836 and US Pat. No. 4,060,401 are known as patents related to the production of fibrous wollastonite (hereinafter referred to as wollastonite in the text). In these prior patents, rod-shaped mother glass was made,
The rod-shaped glass is heated to a predetermined temperature sequentially from the end with a heater to precipitate wollastonite crystals in the glass, and the heater is moved according to the precipitation to combine the bundle of wollastonite crystals and the glass matrix phase. A mixture is prepared, and the rod-shaped crystallized glass is crushed to obtain needle-shaped crystallized glass containing wollastonite. Furthermore, in Japanese Patent Publication No. 63-20780 (Japanese Patent Application No. 55-120830) by the present inventors, a glass-ceramic glass in which wollastonite crystals are precipitated by uniformly heat-treating a plate glass is disclosed. The composition is described. If crystallized glass containing wollastonite crystals produced by any of the above inventions is to be used as a reinforcing fiber material, it is necessary to loosen the wollastonite within the crystallized glass. However, in the invention, crystallized glass is crushed to extract wollastonite. However, in this method, these crystallized glasses tend to cleave along the cleavage plane of the wollastonite crystal during crushing, but they also break apart from the cleavage plane, so the aspect ratio ( The ratio of the length in the vertical direction to the length in the horizontal direction) will be small. Therefore, when such crystallized glass is used as a reinforcing material, a large reinforcing effect cannot be expected. The present invention aims to eliminate the drawbacks of the prior patents and to obtain substantially pure fibrous wollastonite crystals. That is, the present invention involves immersing crystallized glass containing oriented wollastonite crystals produced by heat-treating a glass having a composition close to that of wollastonite in an eluate, and removing the remaining glass phase as a matrix phase. It is characterized by elution and obtaining almost pure fibrous wollastonite crystals. In the method of immersion in an eluent as used in the present invention, in principle, any type of eluent may be used as long as it elutes only the glass matrix phase, but it does not react with wollastonite and elutes only the glass phase. An alkaline aqueous solution is preferable from the viewpoint of elution.As an alkaline aqueous solution, a NaOH aqueous solution or KOH
Aqueous solutions are particularly good, and their concentration is preferably 0.3N or higher. The above two types of alkaline aqueous solutions may be mixed and used, but in that case, the total alkali concentration is preferably 0.3 normal or more. The temperature of the solution to be immersed is preferably 50°C or higher because the higher the temperature, the faster the reaction. Immersion at 50° C. or lower is not preferable because the treatment time required for elution of the glass phase becomes longer. Further, an autoclave can be used for dipping at a high temperature, but in this case, the temperature is preferably 400° C. or lower in view of crystal stability. Furthermore, considering industrial production equipment, the temperature is preferably 230°C (saturated water vapor pressure about 30 kg/cm ² ) or lower. This method has the advantage that wollastonite crystals can be obtained in the same shape as they are in crystallized glass without using mechanical means such as crushing. Wollastonite consists purely of the molecular formula of CaSiO ₃ , and is a crystal containing equimolar amounts of SiO ₂ and CaO, and there are usually three types of crystal forms, among which the wollastonite crystal meant in the present invention is the low-temperature type. wollastonite, which shows fibrous growth. Therefore, this wollastonite crystal can be used as a reinforcing fiber material for various materials. Additionally, this wollastonite crystal is known to have extremely high alkali resistance, so its reinforcing effect will not deteriorate even in highly alkaline media, unlike materials such as Portland cement. . The present inventors have discovered that wollastonite crystals with a particularly large aspect ratio can be easily obtained by treating crystallized glass obtained from the glass according to claim 2 with an alkaline aqueous solution. Ta. Regarding the characteristics of the composition in this range, if SiO ₂ is less than 45%, the yield of wollastonite decreases and vitrification becomes difficult, and even if vitrified, devitrification tends to occur, and when devitrification occurs, the needle inhibits the growth of wollastonite. When SiO ₂ exceeds 55%, tridymite, cristobalite, etc. tend to precipitate together with wollastonite during the heat treatment process, inhibiting the precipitation of acicular wollastonite. When CaO is less than 35%, the yield of wollastonite decreases, and when it exceeds 45%, there is less room for SiO ₂ to enter, resulting in a decrease in the yield of wollastonite and making it difficult to vitrify. B ₂ O ₃ enters the mixture with a composition close to that of wollastonite and has the effect of assisting vitrification and lowering the melting point. It also remains as a glassy matrix at the grain boundaries of wollastonite after heat treatment, and the matrix The cleavability of acicular wollastonite is improved to increase the coefficient of thermal expansion of Tux glass. If it is less than 1%, these effects are small, and if it exceeds 6%, wollastonite is difficult to form even by heat treatment. Li ₂ O suppresses the precipitation by adding a small amount of α-type wollastonite, which does not form needle-shaped crystals that precipitate from the ternary glass of SiO ₂ −CaO−B ₂ O ₃ .
It has the effect of precipitating acicular β-type wollastonite and lowering the melting point. If Li ₂ O is less than 0.2%, the effect is small, and if it exceeds 2%, devitrification tends to occur. Al ₂ O ₃ has the effect of improving workability during glass molding, and if it is less than 1%, the effect is small, and if it exceeds 6%, devitrification tends to occur in the glass and prevents the formation of wollastonite. Alkali metal oxides Na ₂ O and K ₂ O lower the melting temperature of glass, improve workability during glass forming, and are hardly dissolved in solid solution in the wollastonite crystals precipitated by heat treatment, but remain in the glass phase. This has the effect of reducing the alkali resistance of the residual glass phase and making it more likely to be eluted with an alkaline aqueous solution. This effect occurs when Na ₂ O/(Na ₂ O + K ₂ O) starts from 0.
Significant for 0.8. In addition, since the amount of glass phase in crystallized glass is small, the amount of Na ₂ O and K ₂ O has its effect even if it is small, but if Na ₂ O + K ₂ O is less than 1%, the glass phase is easily eluted. If it exceeds 7%, wollastonite will be difficult to precipitate during heat treatment. Examples of the present invention will be described below. Example 1 A raw material mixture prepared to have the composition shown below in weight percent was placed in a platinum crucible in an electric furnace at 1450°C.
Melt for 270 minutes and pour the melt onto an iron mold with a thickness of 10 mm.
It was cast into a plate shape of mm in size and slowly cooled from 600°C to obtain a glass block. This glass block was heated from room temperature to 900°C in an electric furnace at a rate of 7.5°C/min, and kept at that temperature for 3 hours to crystallize. Glass composition SiO ₂ 49.8% by weight CaO 39.7 B ₂ O ₃ 2.0 Li ₂ O 0.5 Al ₂ O ₃ 4.0 Na ₂ O 1.0 K ₂ O 3.0 The heat-treated crystallized glass block has no crystal types other than wollastonite crystals. It wasn't recognized. Furthermore, the wollastonite crystals had excellent directionality. Grind this, take about 1 g of the material that has passed through a 14-mesh sieve, and place it in a Teflon beaker at 85°C.
It was immersed in approximately 400 ml of a specified NaOH aqueous solution for 24 hours. When the weight was measured after washing and drying, a weight loss of 15.4% was observed. In addition, the crystallized glass after this treatment can be easily made into fine fibers.
The average aspect ratio was 25.0. Chemical analysis revealed that this fibrous fine crystallized glass contained almost no glass phase and was substantially pure wollastonite crystals (see Table 1).

[Table] Example 2 A raw material mixture prepared to have the composition shown below in weight percent was made into crystallized glass in the same manner as in Example 1, and was heated in a 1N NaOH aqueous solution at 95°C for 8 hours. Alkali treatment was performed in the same manner as in 1. Glass composition SiO ₂ 49.8% by weight CaO 39.7 B ₂ O ₃ 3.0 Li ₂ O 0.5 Al ₂ O ₃ 3.0 Na ₂ O 2.0 K ₂ O 2.0 The weight loss due to alkali treatment was 14.3%, making it almost pure glass with an aspect ratio of 28.3. Last night crystals were obtained. Example 3 A raw material mixture prepared to have the composition shown below in weight% was made into crystallized glass in the same manner as in Example 1, and 24
The alkali treatment was carried out in the same manner as in Example 1. Glass composition SiO ₂ 52.5% by weight CaO 40.0 B ₂ O ₃ 1.0 Li ₂ O 0.5 Al ₂ O ₃ 3.0 Na ₂ O 2.2 K ₂ O 0.8 The weight loss due to alkali treatment was 13.3%, making it almost pure glass with an aspect ratio of 20.8. Last night crystals were obtained. Example 4 A raw material mixture prepared to have the composition shown below in weight percent was made into crystallized glass in the same manner as in Example 1, and heated in a 0.5N KOH aqueous solution at 90°C for 24 hours in the same manner as in Example 1. Alkali treatment was carried out using the method described below. Glass composition SiO ₂ 46.0% by weight CaO 42.0 B ₂ O ₃ 3.0 Li ₂ O 1.0 Al ₂ O ₃ 3.0 Na ₂ O 0 K ₂ O 5.0 Weight loss due to alkali treatment was 14.5%, almost pure glass with an aspect ratio of 15.9. Last night crystals were obtained. Example 5 About 1 g of the crystallized glass of Example 1 was immersed in about 400 ml of a 1N KOH aqueous solution at 85° C. for 24 hours. When the weight was measured after washing and drying, a weight loss of 15.8% was observed. After treatment, the crystallized glass became almost pure wollastonite crystals with an aspect ratio of 16.5. Example 6 The crystallized glass of Example 1 was heated to 1N at 45°C.
When treated with NaOH aqueous solution, it was immersed for 24 hours.
There was only a 2.0% weight reduction, and the aspect ratio was only 4.1, which was not much different from the as-pulverized state. Furthermore, when treated under these temperature conditions for 200 hours, the weight loss was 14.8% and the aspect ratio was 20.3. Example 7 A raw material mixture prepared to have the composition shown below in weight percent was made into crystallized glass in the same manner as in Example 1, and alkali treatment was performed in the same manner as in Example 1. Glass composition SiO ₂ 49.8% by weight CaO 39.7 B ₂ O ₃ 2.0 Li ₂ O 0.5 Al ₂ O ₃ 4.0 Na ₂ O 4.0 K ₂ O 0 This composition is Na ₂ O/
Na ₂ O + K ₂ O is set to 1.0. in this case,
Under the same conditions, the weight loss was 8.3%, and the aspect ratio of the fibrous crystallized glass after crushing was only 8.6.

Claims (1)

[Claims] 1. A glass body containing at least SiO ₂ and CaO as components is heat-treated to elute a crystallized glass body in which needle-shaped crystals of low-temperature calcium silicate (β-wollastonite) are produced. A method for producing fibrous wollastonite crystals, which comprises immersing the crystallized glass body in a liquid to elute the glass phase in the crystallized glass body. 2 The composition of the glass body is SiO ₂ 45 to 45% by weight.
55, CaO35~45, _{B2O3 1} ~6, _LiO2 0.2~2,
Al ₂ O ₃ 1-6, Na ₂ O 0-4, K ₂ O 1-7, Na ₂ O+
The method for producing fibrous wollastonite crystals according to claim 1, wherein K ₂ O is 1 to 7 and Na ₂ O/(Na ₂ O + K ₂ O) is in a weight ratio of 0 to 0.8.