JPS5820714A - Preparation of fibrous wollatonite crystal - Google Patents

Abstract

PURPOSE:To obtain fibrous wollastonite crystal, by immersing crystallized glass containing wollastonite crystals and obtained by the heat-treatment of glass containing SiO2 and CaO, in an etchant, thereby dissolving the glassy phase of the crystallized glass. CONSTITUTION:Crystallized glass containing acicular crystals of low calcium silicate (beta-wollastonite) is prepared by heat treating a glass containing SiO2 and CaO. The crystallized glass is immersed in an etchant, e.g. an aqueous solution of NaOH or KOH having a concentration of >=0.3 N to dissolve the glassy phase and obtain the objective fibrous wollastonite crystal. The composition of the glass used as the starting material is especially preferably SiO2, 45-55 (wt%); CaO, 35-45; B2O3, 1-6; Li2O, 0.2-2; Al2O3, 1-6; Na2O, 0-4; K2O, 1-7; Na2O+K2O, 1-7; and the ratio of Na2O (Na2O+K2O), 0-0.8.

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.

The patent related to the production of fibrous wollastonite (hereinafter referred to as wollastonite) is U.S. Patent J, 799.
, 734 and U.S. Patents 1Aoto and 1Ioi have become publicly known. In these prior patents, a rod-shaped mother glass is made, and the ends of the rod-shaped glass are sequentially heated to a predetermined temperature with a heater to inject wolast into the glass. The night crystals are precipitated, the heater is moved according to the precipitation to form a mixture of bundles of wollastonite crystals and the glass matrix phase, and the rod-shaped crystallized glass is crushed to form needle-shaped wollastonite-containing crystals. This is to obtain chemical glass.

In addition, Japanese patent application number Sho 5S-1 by the present inventors! No. 30 describes a glass composition that provides crystallized glass in which wollastonite crystals are precipitated by uniformly heat-treating a plate-shaped glass.

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, with this method, these crystallized glasses tend to form folds along the shear planes of the wollastonite crystals during crushing, but they also break at surfaces other than the interfold planes, so the aspect ratio is smaller than that existing in the crystallized glass. The ratio (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 inventor immersed a crystallized glass containing oriented wollastonite crystals produced by heat-treating a glass having a composition close to that of wollastonite in an eluate, thereby producing a glass that remains as a matrix phase. It is characterized by eluting the phase and obtaining almost pure fibrous wollastonite crystals.

In principle, the method of immersion in an eluent according to the present invention is as follows:
Any type of eluent may be used as long as it elutes only the glass matrix phase, but an alkaline aqueous solution is preferable because it does not react with bovine lastonite and elutes only the glass phase.As the alkaline aqueous solution, a BJaOH aqueous solution or a KOH aqueous solution is used. Particularly well, their concentration is 0
．． It is better to have 3 or more regulations. 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 higher the humidity of the dipping solution, the faster the reaction.5
The temperature is preferably 0°C or higher. ! ; Immersion at temperatures below 0° C. is not preferable because the treatment time required for elution of the glass phase becomes longer. Further, an autoclave can be used for immersion at high temperature, but in this case, the temperature is preferably 1looo°C or less in view of crystal stability.

Furthermore, considering industrial production equipment, the temperature is preferably 230° C. (saturated water vapor pressure about 30 Kg10W?) or less.

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 has a pure molecular formula of Qa3i03, and is a crystal containing equimolar amounts of 5i02 and CaO, and is usually 3
There are various crystal forms, and the wollastonite crystals referred to in the present invention are low-temperature wollastonite, which exhibits 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 described in claim 2 with an alkaline aqueous solution. . Regarding the characteristics of the composition in this range, when 5102 is less than IIj%, the yield of wollastonite decreases and vitrification becomes difficult, and even when vitrified, devitrification tends to occur, and when devitrification occurs, it becomes acicular. Inhibits the growth of wollastonite.

When 5i02 exceeds 8J, 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 33%, the yield of wollastonite decreases, and when it exceeds tis%, there is less room for 5 in 2 to enter, resulting in a decrease in the yield of wollastonite and making it difficult to vitrify.

B2O3 enters the mixture with a composition close to that of wollastonite and has the effect of assisting vitrification and lowering the melting point. B2O3 also remains as a glassy matrix at the grain boundaries of wollastonite after heat treatment, increasing the strength of the matrix glass. Improves the expansibility of acicular wollastonite to increase the coefficient of thermal expansion. If it is less than 1%, these effects are small, and if it exceeds 6%, it becomes difficult to generate wollastonite even by heat treatment.

Li2O suppresses the precipitation by adding a small amount of α-type wollastonite, which does not form needle-like crystals that precipitate from the Si0,2-cao-B203 ternary glass, and forms acicular β-type crystals.
It has the effect of precipitating type wollastonite and lowering the melting point. If the Li2O content is less than 2%, the effect is small, and if it exceeds 2%, devitrification tends to occur.

AA'203 has the effect of improving workability during glass molding, and if it is less than 1%, the slimming effect is small, and if it exceeds 4%, devitrification tends to occur in the glass, which prevents the formation of wollastonite.

The alkali metal oxides Na2O and Ni204 lower the melting temperature of the glass, improve workability during glass molding, and are hardly dissolved in solid solution in the wollastonite crystals precipitated by heat treatment, remaining in the glass phase. This has the effect of reducing the alkali resistance of the residual glass phase, making it more likely to be eluted with an alkaline aqueous solution.

This effect is Na 20 AHa 20 + K 20
) is significant when O to o, g (7).

In addition, since the amount of glass phase in crystallized glass is small, Na
Although the amount of 2O and 20 is small and has the effect, Nag
If O+ contains less than 1% of 20, the glass phase will not easily be eluted, and if it exceeds 7%, wollastonite will be difficult to precipitate during heat treatment.

Examples of the present invention will be described below.

[Example 1] The core was melted for 0 minutes and the melt was placed on an iron mold with a thickness of 79 m.
It was poured into a plate shape of m and then slowly cooled from too'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 7J6c/min, and maintained at that turbidity for 3 hours to crystallize.

Glass composition Sing lI9♂weight j1%QaOj9
．． 7 B203 20 Li20 θj AlzO31A (11 Na2o /, 0 K2O3,0 In the crystallized glass block after the heat treatment, no crystal types other than wollastonite crystals were observed. Also, wollastonite crystals have a very good direction had sex.

Grind this, take about 1 g of the material that has passed through an ltI mesh sieve, and place it in a Teflon beaker at 55°C under 7N.
It was immersed in an aOH aqueous solution of approximately II o mz for a period of 1 hour.

When the weight was measured after washing and drying, it was found to be 15. A reduction in the weight of Daju was observed. Further, the crystallized glass after this treatment can be easily made into fine fibers with an average aspect ratio of X&2. It was 0. Chemical analysis revealed that this fibrous fine crystallized glass contained almost no glass phase and was almost pure wollastonite crystals (see Table 1).

Table 1 Analytical results of wollastonite crystals [Example 1] A raw material mixture prepared to have the composition shown below in terms of weight was made into crystallized glass in the same manner as in Example 1, and 95°C
Glass composition 5i021 which was subjected to alkali treatment in the same manner as in Example 1 for a period of time in a specified NaOH aqueous solution.
5 wt% CaO3q, 7 B203 3.0 Li20 B3 AiI203 3.0 Na20 20 to 20x.

The weight loss due to the alkali treatment was 1 da, 3%, and almost pure wollastonite crystals with an aspect ratio of 2 g, 3 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 9j'
Glass composition 5i02 which was subjected to alkali treatment in a NaOH aqueous solution with o, s specifications for 2 hours in the same manner as in Example/! ;2.3% by weight cao
iio,.

B2O3i,.

Li2O0,'5 Al2O21O Na20 2J K2O0g The weight loss due to the alkali treatment was 13.3%, and almost pure wollastonite crystals with an aspect ratio of 20.1 were obtained.

[Example D]

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/, and a 90"
Alkali treatment was carried out in the same manner as in Example 1 for 24 hours in a KOH aqueous solution specified by O0S of C.

Glass composition 5i02 II O wt %cao l
Ix.

B2O33,0 Li20 /, 0 A1203 3.0 Na20 20 g, 0 The weight loss due to alkali treatment was 111.3%, and almost pure wollastonite crystals with aspect ratios of ts and q were obtained.

[Example S]

Example: Crystallized glass of about /g tj °C l specified KO
It was immersed for 21 hours in about 001 nl of H aqueous solution.

When the weight was measured after washing and drying, a weight loss of 1% was observed. The crystallized glass after the treatment became a substantially pure wollastonite crystal with an aspect ratio of #1.

[Friend Example 6] The crystallized glass of Example 1 was diluted with 9j'C l normal NaOH
When treated with an aqueous solution, there was only a 2.0% weight loss after immersion for 2 hours, and the aspect ratio increased, which was not much different from the as-pulverized state.

When treated under these humidity conditions for 200 hours, the weight loss was /L% and the aspect ratio was 20.3. [Example 7] 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 alkali treatment was performed in the same manner as in Example 1.

Glass composition 5i02 119J weight% Oa0 3
9.7 B203 20 bi2o o, 5 A6zO3IAO Na20 IA6 ni 20 0 This composition is NagO/NagO in the composition of Example 1.
It is calculated by dividing 20 into 10 and 0. In this case, under the same conditions, the weight loss was only 3%, and the aspect ratio of the fibrous crystallized glass after crushing was only g.

Patent applicant: Nippon Sheet Glass Co., Ltd.

Claims (2)

[Claims] (1) A glass body containing at least 5i02 and OaO as components is heat-treated to produce a low-humidity type calsila silicate,
A process for producing fibrous wollastonite crystals, characterized in that a crystallized glass body in which needle-like crystals of β-wollastonite (β-wollastonite) have been formed is immersed in an eluent to elute the glass phase in the crystallized glass body. Production method. (2) The composition of the glass body is 5i02 da j ~ j j * Cao J 3-411 t B 2 in weight%.
03/-A #L 102 (i J~2, Al
2O3/~&IN&200~lI, 20/~7 *
Na2O 120 1~7 #katsuNa204ia20+
The method for producing fibrous wollastonite crystals according to claim 1, wherein the weight ratio of KgO) is ONo.2.