JPH0676229B2 - Crystalline glass manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing crystalline glass in which needle-like crystals are deposited on soda-lime glass, that is, crystalline foam glass and dense crystalline glass.

Soda-lime glass is commonly used for buildings and other window materials, containers, etc. because it is easily vitrified and can be manufactured at low cost.

When manufacturing these materials, it is extremely important to avoid devitrification, that is, to prevent precipitation of crystals, and to maintain transparency. In that respect, the soda-lime type is the best devitrifying class among various component systems. Belongs to and has been prized since ancient times.

On the other hand, there is also an attempt to introduce a nucleating agent into the component system and forcibly crystallize it to give decorative properties or improve mechanical strength and use it in a building material or the like.

In Japanese Examined Patent Publication No. 42-2271, soda lime-based raw material contains fluorine or further titanium oxide or zirconium oxide,
JP-B-45-3554 discloses that heavy metal sulfide is added to a soda-lime-based raw material, and JP-A-49-69730 discloses that iron sulfide or manganese sulfide is added in the same manner, and molten glass is crystallized by heat treatment. Has been done.

In these methods, crystals such as cristobalite and tridymite are also precipitated in addition to needle-like crystals such as wollastonite.
However, cristobalite and the like have an abnormal volume change due to a transition in a low temperature heating region, which causes distortion or collapse of the product, which is not preferable.

Further, the uniform dispersion of the nucleating agent requires a high level of technology from the raw material preparation to the melt preparation. In general, a nucleating agent having a high specific gravity and an ultrafine powder is used, so that the segregation of the nucleating agent should be carefully performed and a corresponding technique is required.

Furthermore, the method of once forming glass and re-crystallizing by heat treatment has a bad effect such as poor production efficiency or deformation in the heat treatment process.

On the other hand, there is also a disclosed example in which crystals are deposited without a nucleating agent.

In Japanese Examined Patent Publication No. 36-16729, a soda-lime-based glass fine powder as it is, or water glass or a phosphate such as sodium, potassium, etc. integrated as a binder and integrated into a devitrified opalescent glass in the devitrification temperature range. Is disclosed.

The preceding example is characterized by being opalescent glass, which is opalified by devitrification on the surface of fine glass, but as described later, it is necessary to improve mechanical strength and thermal shock resistance. I can't reach it.

In addition to the well-known ones, a heat-resistant crystalline glass prepared by adding a lithium raw material and a nucleating agent to a silica-alumina-based raw material, heat-treating it after melting and vitrifying, and depositing eucryptite (LLAlSiO ₄ ) or spodumene (LiAlSi ₂ O ₆ ) It is used as a cooker etc., but in this case the cost of the raw material is high because a large amount of lithium raw material is introduced, and it requires a sophisticated and sophisticated technique for uniform dispersion and crystallization of the nucleating agent. It is difficult to use it as a general building material because it deteriorates the production efficiency and makes the product expensive.

The present invention solves the above problems, by precipitating acicular crystals in a soda-lime glass in a specific amount range, crystalline glass excellent in mechanical strength and thermal shock resistance, that is, dense crystalline glass or crystalline The object is to provide a suitable method for producing foam glass.

(Means for Solving Problems) The present invention is a method for producing crystalline glass containing 20 to 60% by volume of needle-shaped crystals, which is selected from carbonates or hydroxides of alkali metals with respect to soda-lime glass powder. One or more of acicular crystal precipitation accelerators, which are 1 to 1 in terms of oxide.
A mixed powder or mixed sludge added with 10 wt% was preformed, and then heated and maintained at an appropriate temperature between the softening point and the pour point of the soda-lime glass powder for 10 to 60 minutes to precipitate acicular crystals. The acicular crystals are at least one kind of wollastonite, devitrite or Na ₂ CaSi ₃ O ₈ , and are made to be densified while being heated or maintained.

In the present invention, waste of soda-lime glass (referred to as glass cullet), which is often used for plate glass, container glass, etc., is used as a starting material, and this is used as 150 mesh (100 μ
mφ) to be pulverized and prepared. In order to react favorably with the crystal precipitation accelerator described later, its specific surface area is large, and therefore it is desirable that the particles are fine particles, and it is particularly preferable that the particle size be not more than the above grain size.

As the other starting material, an acicular crystal precipitation accelerator (hereinafter simply referred to as a precipitation accelerator) is used. Needle-like crystals are crystals that develop acicularly, such as wollastonite, devitrite, and Na ₂ CaSi ₃ O ₈ .

Alkali metal salts, halides, and hydroxides, which are preferably used as components for promoting the selective precipitation of these needle-like crystals,
There are Li, Na, K carbonates, hydroxides and the like.

These are melted by heat treatment and rapidly precipitate acicular crystals by the reaction with the glass powder, and do not particularly limit the particle size, but 32 mesh (0.5 mesh as an artificial component or a naturally occurring purified product). mmφ) or less is widely marketed.

Precipitation accelerator in oxide conversion for the glass cullet powder
1 wt% to 10 wt% is added, and the mixture is wet- or dry-mixed and then press-molded into a desired shape or cast as sludge. If the addition amount is less than 1 wt%, the precipitation action of needle-like crystals is small, and if it exceeds 10 wt%, the crystal precipitation component region is changed, and especially the glass matrix is excessively alkali, which deteriorates the chemical durability and the like. More preferably 1 wt
% To 5 wt%. Preforming is necessary to maintain the shape and to bring the cullet powder into close contact with the precipitation promoter.

Then the softening point of the raw glass ( ^10.65 poise in viscosity,
720 ℃ above normal glass, pour point (also 1
The temperature is raised to an appropriate temperature within the range of 0 ⁵ poise, 900 ° C.) or less and kept for 10 to 60 minutes. If it is less than the glass softening point, the reaction with the precipitation accelerator is insufficient, and if it exceeds the pour point, the tendency of crystal precipitation is weakened by approaching the liquidus temperature, that is, the vitrification temperature. Further, if less than 10 minutes, the precipitation of needle-shaped crystals is insufficient,
If it exceeds 60 minutes, depending on the precipitation accelerator, the crystal phase and the glass phase will react again to form a new glass phase, or the needle-shaped crystal precipitation will reach the end, and crystals such as cristobalite that adversely affect the heat resistance will be formed. Easy to deposit.

In the temperature range, the softened glass reacts with the decomposed and melted precipitation accelerator, and some of the decomposed gas components are trapped in the reaction viscous liquid and become foamy glass, while on the other hand, the grain boundaries and the reaction of the glass cullet powder. Crystal precipitation begins in the glass phase.

The precipitation accelerator is a melt component suitable for the precipitation of the needle-like crystals, which imparts a viscosity, and exists as a so-called heterogeneous substance that is difficult to melt and diffuse like a so-called nucleating agent and crystallizes based on it. Is different from the type that precipitates.

Of the alkali metals, lithium has a larger effect of precipitating needle-like crystals, and sodium and potassium are slightly inferior to this. Even in the same alkali metal system, the action of carbonate is remarkable, and the hydroxide is smaller than that. However, the tendency of the needle-like crystals to precipitate is much larger than that when only glass cullet powder is used without adding them. Although the reason why the precipitation tendency differs depending on the alkali metal or the type of compound even in the same alkali metal system is not clarified,
It is presumed that the diffusion rate of the alkali metal ions, the dissociation temperature of the compound, and the like influence the cause.

In soda lime glass, wollastonite, devitrite, Na ₂ CaSi ₃ O ₈ needle crystals, cristobalite, tridymite, etc. are precipitated from the component region, and lithium silicate is added when Li ₂ CO ₃ etc. are added in large amounts. Is deposited.

In the present invention, the needle-shaped crystals in the glass 20 ~ 60vol
%, The mechanical strength and heat resistance are remarkably improved. If it is less than 20 vol%, those effects are small. 60vol
If it is attempted to cause the precipitation in excess of%, naturally, cristobalite and the like are also generated in the component region, which impairs mechanical strength and thermal shock resistance, which is not preferable.

The crystalline glass produced in this manner forms a crystalline foam glass in which numerous bubbles remain, and becomes a product in which the bubbles are made uniform by the slow cooling process.

On the other hand, during heat treatment or in a heat softened state after heat treatment, if a means for compressing, for example, a means of passing between a pair of rolls and pinching between the rolls is taken, a bubble is appropriately escaped and the crystallinity of which the specific gravity is controlled It becomes a foam glass or a dense crystalline glass with almost no bubbles. The product is obtained by further slow cooling.

(Example) As plate glass cullet powder, SiO ₂ 71% by weight%, Al ₂ O ₃ 1.6
%, CaO 11%, MgO 2.1%, Na ₂ O 13%, K ₂ O 0.8% and a particle size adjusted to 200 mesh or less were prepared. Commercially available lithium, sodium and potassium carbonates and hydroxides were prepared as precipitation accelerators.

The cullet powder and the needle-shaped crystal precipitation accelerator are dry mixed at a predetermined ratio, or 7 wt% of water is added and mixed for wet mixing, and the product obtained by dry mixing is pressed under a pressure condition of 20 kg / cm ^2. The sludge obtained by wet mixing was cast-molded and dried to obtain a preform. This was heated to a predetermined temperature in an electric furnace, held for a predetermined time, and then gradually cooled to obtain various foam samples. Further, some of the samples were taken out of the furnace after heat treatment, sandwiched between steel plates which had been preheated to the temperature in advance, and were manually rolled by a roller from above to be compressed to remove bubbles, thereby obtaining a dense sample.

The following measurements were performed on these samples.

Specific gravity measurement: By a known measuring means using a specific gravity bottle.

Crystal identification; EPMA mainly by X-ray diffraction and observation under a mirror
Combined analysis.

Measurement of the amount of crystals (volume ratio) in the solid phase: The crystal phase area ratio was measured under a mirror for a plurality of arbitrary cut surfaces of the sample and averaged to calculate the volume ratio.

Thermal shock test (quenching test); set a 50mm x 20mm thick sample in an electric furnace, hold at 500 ° C, take it out, immediately put it in water at 10 ° C, quench it, and check that there are no cracks visually. Good, those with small cracks were classified as good, and those with large cracks or collapsed were classified into three ranks.

Further, the bending strength of some of the samples was measured.

For comparison, the crystal precipitation accelerator was replaced with Japanese Patent Publication No. 36-1.
Sodium phosphate 30 wt% aqueous solution according to 6729, potassium phosphate
Measured by adding 30 wt% aqueous solution, 1.5 wt% each, 3 wt% in total (0.6 wt% in terms of oxide), press-molding, press-molding using only cullet powder, heat treating in the same manner, and measuring did.

Table 1 shows sample preparation conditions and measurement results. Example 4
In Nos. 11 to 11, strip-shaped lithium silicate is precipitated in addition to acicular wollastonite, but it itself has a low coefficient of thermal expansion and a high thermal shock resistance and does not depart from the present invention. Comparative Example 1 has an excessively small amount of precipitation accelerator, Comparative Examples 2 and 3 have a long heat treatment time, and crystals once precipitated react with the glass phase again to be melted. Comparative Example 4 has a known additive. In Comparative Example 5, the additive is not added,
In all cases, the amount of needle-shaped crystals precipitated was small, and the thermal shock resistance and bending strength were poor. In Comparative Examples 2 and 3, the thermal shock resistance is not bad, but the strength is not sufficient.

(Effects of the Invention) According to the present invention, crystalline glass including crystalline foam glass and dense crystalline glass can be very easily produced, and the obtained crystalline glass has excellent thermal shock resistance and mechanical strength, and high heat resistance. It has the effect of being useful as a strong building material.

Claims (3)

[Claims] 1. A method for producing a crystalline glass containing 20 to 60 vol% of needle-shaped crystals, which comprises at least one selected from carbonates or hydroxides of alkali metals with respect to soda-lime glass powder. Preliminary molding of a mixed powder or mixed sludge containing 1 to 10 wt% of a crystal precipitation accelerator in terms of oxide, and then heating for 10 to 60 minutes at an appropriate temperature between the softening point and pour point of the soda-lime glass powder A process for producing crystalline glass, characterized in that the glass is maintained and needle crystals are deposited. 2. The method for producing crystalline glass according to claim 1, wherein the acicular crystals are one or more of wollastonite, devitrite and Na ₂ CaSi ₃ O ₈ . 3. The method for producing crystalline glass according to claim 1 or 2, wherein the glass is made to be consolidated while being heated or after being heated.