RU2707639C1 - Method of making glass-ceramic articles of lithium aluminosilicate composition - Google Patents

Abstract

FIELD: manufacturing technology.

SUBSTANCE: invention relates to production of large-size ceramic articles for radio engineering purposes. Method of making articles from glass-ceramic lithium-aluminosilicate composition involves grinding of pre-crystallized lithium-aluminosilicate glass by wet method to obtain a slurry with given parameters, preliminary molding in gypsum molds of workpieces of arbitrary shape, their repeated processing into a slurry, molding of articles and thermal treatment. Preliminary crystallization of lithium-aluminosilicate glass is carried out in containers of glass-ceramic lithium-aluminosilicate composition at rate of temperature rise of 200–300 °C/h first at nucleation temperature of 630–670 °C, and then at crystallization temperature of 1,170–1,250 °C for 6–12 hours, wherein glass layer in vessel does not exceed 200 mm.

EFFECT: high efficiency of crystallization of the initial lithium aluminosilicate glass and high quality of the material.

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Description

The invention relates to the production of large-sized ceramic products for radio engineering purposes.

There is a method of producing glass-ceramic products, according to the classical glass technology (Macmillan P.U. leading to crystallization throughout the volume.

The disadvantages of this method include the presence of various inhomogeneities (lack of penetration, bubbles), causing heterogeneity of the material properties, which significantly complicates the use of this method for the manufacture of large-sized glass-ceramic products.

A known method of manufacturing products from glassy crystalline material of lithium aluminum-silicate composition (Suzdaltsev E.I. Synthesis of highly heat-resistant, radiolucent glass-ceramic materials and development of manufacturing technology based on them fairings of aircraft. // Thesis for the degree of Doctor of Technical Sciences M., RHTU named after DI Mendeleev, 2002, 430 pp.), Including grinding of amorphous glass by the wet method to obtain a water slurry, preliminary molding of arbitrary shapes in plaster forms, their repeated processing into a slip, molding of products and their heat treatment in two stages: first at a nucleation temperature of 630 ÷ 670 ° C, with holding for 5 hours, and then at the upper crystallization and sintering temperature of 1230 ÷ 1250 ° C, with holding for 4 +7 hours in high temperature furnaces. The temperature rise during heat treatment of the product in a high-temperature furnace is carried out at a speed of 20 ÷ 60 ° C / hour.

The disadvantages of this method include the duration of the heat treatment of workpieces obtained by ceramic technology (more than 70 hours). As a result, in the serial production of glass-ceramic products, there is a need to increase the fleet of high-temperature firing furnaces (with a working temperature within 1250 ° C).

A known method of manufacturing products from glass crystal material (RF Patent No. 2363683, 08/10/2009, bull. No. 22), including the grinding of amorphous glass by the wet method to obtain a water slurry, preliminary molding of arbitrary shapes in plaster forms, their recycling into slip, molding products and their heat treatment in two stages: first at a nucleation temperature of 630 ÷ 670 ° C, with exposure for 5 hours, and then at a lower crystallization temperature of 850 ÷ 900 ° C, with exposure for 1 ÷ 3 hours in low temperature furnace, cooling the product in the temperature range from room temperature to 250 ° C, moving the product to a high temperature furnace, final firing at the upper crystallization and sintering temperature of 1230 ÷ 1250 ° C with holding for 4 ÷ 7 hours in high temperature furnaces. The temperature rise during heat treatment of the product in a low-temperature furnace is carried out at a speed of 60 ° C / hour, and during heat treatment in a high-temperature furnace at a speed of up to 500 ° C / hour.

The disadvantages of this method include the fact that it is multi-operational and requires an additional operation of moving products from a low-temperature furnace to a high-temperature furnace, which results in a significant increase in the production cycle of the product and increases the complexity.

A known method of manufacturing products from a sintered glass crystal material of a lithium aluminum silicate composition (RF Patent No. 2222505, 01/27/2004, bull. No. 3), selected as a prototype, including grinding pre-crystallized glass by a wet method to obtain a slip with a density of 1.97 ÷ 2.05 g / cm ³ , finely ground with a sieve residue of 0.063 mm 9 ÷ 15% and pH 7.5 ÷ 9.0, pre-molding in arbitrary shapes of gypsum preforms, their recycling into slip, molding of products and heat treatment at a temperature of 1210 ÷ 1250 ° C in t chenie 1 ÷ 3 hours at a recovery rate and lowering the temperature not higher than 500 ° C per hour.

The disadvantages of this technical solution is that the crystallization of glass is carried out in chamber furnaces of periodic action, intended for firing products, while the glass is located on the bottom of the furnace. This, firstly, does not provide the maximum loading of the furnace with material, and, as a result, reduces productivity, and, secondly, there is a possibility of glass contamination during crystallization by the furnace hearth, which can adversely affect the quality of ceramic products made for radio engineering purposes.

The objective of the present invention is to increase the productivity during crystallization of the original lithium aluminum silicate glass and improve the quality of the material.

This object is achieved by the fact that a method for manufacturing glass ceramic products of a lithium aluminum silicate composition is proposed, including wet grinding of pre-crystallized lithium aluminum silicate glass to obtain a slip with predetermined parameters, preliminary molding of arbitrary shapes into plaster forms, their recycling into slip, molding of products and heat treatment, characterized in that the preliminary crystallization of lithium aluminum silicate glass is carried out in a container of st eco-ceramics of lithium aluminum silicate composition at a temperature rise rate of 200-300 ° C / hour, first at a nucleation temperature of 630-670 ° C, and then at a crystallization temperature of 1170-1250 ° C for 6-12 hours, while the glass layer in the container does not exceed 200 mm

The authors experimentally established that the use of ceramic containers to load the original glass into the kiln firing furnace allows three times to increase the productivity of furnaces. At the same time, the implementation of ceramic containers made of glass ceramics based on lithium aluminum silicate glass ensures that there is no contamination of the crystallized material with impurities.

It was found that the glass layer in the ceramic container should not exceed 200 mm, since a thicker layer does not provide complete crystallization of the material.

It was found that the duration of heat treatment at a crystallization temperature should not be less than 6 hours, since this does not ensure complete crystallization of the processed material and should not exceed 12 hours, because this leads to greater energy consumption and increases the duration of the mode, while the quality of crystallization remains unchanged.

It was also found that to ensure the completeness of the passage of the crystallization process, the rate of temperature rise should not exceed 300 ° C / hour, a decrease in speed below 200 ° C / hour leads to a significant increase in the time of the crystallization process.

The implementation of the proposed method using glass-ceramic lithium aluminum silicate composition is presented in the following examples.

Example 1

A batch of the original lithium aluminum silicate glass was loaded into ceramic containers made of glass ceramics based on lithium aluminum silicate glass and installed one on top of the other in a chamber furnace (chamber size 900 × 900 × 1,500 mm) of periodic action. The thickness of the glass layer in each tank was 100 mm. The weight of the loaded glass was 250 kg.

Glass crystallization was carried out in two stages. First, at a nucleation temperature of 650 ° C, and then at a crystallization temperature of 1185 ° C for 8 hours at a rate of temperature rise of 100 ° C / hour. The total duration of the crystallization mode (with cooling the furnace) was 53 hours. Thus, the furnace capacity was 4.7 kg / h. Checking the crystallized glass for the presence of crystalline phases, showed the full compliance of the obtained material with the requirements for it.

Example 2

Analogously to example 1. The glass was loaded into ceramic containers and crystallized. The thickness of the glass layer in ceramic containers was 200 mm. The mass of the loaded glass was 500 kg, and the rate of temperature rise was 200 ° C / hour. The duration of the crystallization mode is 10 hours at a temperature of 1200 ° C. The total duration of the crystallization mode (with furnace cooling) was 48 hours. Thus, the productivity of the furnace was 10.4 kg / h. Checking the crystallized glass for the presence of crystalline phases showed complete compliance of the obtained material with the requirements for it.

Example 3

Analogously to example 2. We carried out the loading of glass in ceramic containers in the amount of 500 kg. Conducted crystallization. The rate of temperature rise was 300 ° C / hour. The duration of the crystallization mode was 12 hours at a temperature of 1240 ° C. The total duration of the crystallization mode (with furnace cooling) was 38 hours. Thus, the productivity of the furnace was 13.2 kg / h. Checking the crystallized glass for the presence of crystalline phases showed complete compliance of the obtained material with the requirements for it.

Example 4

Analogously to example 2, the glass was loaded into ceramic containers in an amount of 500 kg and crystallized. The rate of temperature rise was 350 ° C / hour, and exposure at a crystallization temperature of 1185 ° C for 8 hours. The total duration of the crystallization mode (with furnace cooling) was 35 hours. Thus, the productivity of the furnace was 14.2 kg / h. Checking the crystallized glass for the presence of crystalline phases showed the presence of a large percentage of not crystallized glass phase, which led to the rejection of this batch of glass.

Example 5

Analogously to example 1, the glass was loaded into ceramic containers and crystallized. The rate of temperature rise was 250 ° C / hour.

In addition, the thickness of the glass layer placed in the ceramic container was increased to 250 mm. The total furnace load was 600 kg. The total duration of the crystallization mode (with cooling the furnace) was 43 hours. Thus, the productivity of the furnace was 14 kg / h. Checking the crystallized glass for the presence of crystalline phases showed the presence of a large percentage of not crystallized glass phase, which led to the rejection of this batch of glass.

A wet slurry was obtained from crystallized glass obtained according to Examples 1-4 by a wet grinding method, from which a batch of products was molded from slip slurries into porous gypsum molds by slip casting. After heat treatment, the products were checked for compliance with the requirements for material purity. No pollution contamination was found.

From the above data it follows that the application of the method according to the proposed technical solution allows to increase productivity and obtain high-quality glass ceramic products of lithium aluminum silicate composition.

Claims (1)

A method of manufacturing glass ceramic products of a lithium aluminum silicate composition, including wet grinding of pre-crystallized lithium aluminum silicate glass to obtain a slip with predetermined parameters, preforming arbitrary shapes in gypsum molds, recycling them into a slip, forming products and heat treatment, characterized in that lithium preliminarily crystallizes lithium glass is carried out in a glass-ceramic container of lithium aluminum silicate composition at grow raising the temperature 200-300 ° C / hour at a temperature of nucleation first 630-670 ° C, and then at the crystallization temperature 1170-1250 ° C for 6-12 hours, the glass layer does not exceed 200 mm in the container.