JPH042682A - Production of dense ceramics having high thermal shock resistance - Google Patents

Abstract

PURPOSE:To obtain a ceramics having dense texture and high thermal shock resistance by combining a body having a medium thermal expansion coefficient with a glazing having a restricted thermal expansion coefficient smaller than that of the body and applying the glazing to the whole surface of the fired body. CONSTITUTION:A dense ceramic material having a thermal shock resistance of >=350 deg.C can be produced by forming a body having a thermal expansion coefficient of 2.5 to 5.0X10<-6>/ deg.C, firing the formed material, coating the whole surface of the fired body with a glazing having a thermal expansion coefficient of <=3.0X10<-6>/ deg.C and smaller than that of the body by >=1.5X10<-6>/ deg.C and firing the glazed product.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention uses a so-called medium-expansion material having a thermal expansion coefficient of 2.5 to s and oxto-'/°C, and has a high heat resistance of 350°C or more. The present invention relates to a method for manufacturing dense ceramics having impact properties.

In the present invention, "dense ceramics" refers to ceramics with a water absorption rate of 0 to about 3%.

The present invention is suitable for manufacturing dense ceramic trays for ovens and microwave ovens, but it can also be used for manufacturing heat-resistant parts for various heating devices in addition to trays.

(Prior art and its problems) Glass products Traditionally, borosilicate glass and crystallized glass have been used in ceramic trays for microwave ovens, etc. However, due to manufacturing methods, these require mass production in small numbers. Therefore, it was difficult to change the shape frequently or to manufacture small lofts at a time when necessary.

Further, borosilicate glass has poor thermal shock resistance, and crystallized glass has a low coefficient of thermal expansion and excellent thermal shock resistance, but has the drawback of high cost.

Conventional thermal shock resistant porcelain Conventional thermal shock resistant porcelain is made by adding or precipitating low-expansion crystals into the matrix to lower the thermal expansion coefficient α8 of the entire matrix into the low expansion range (2.5 x 10-6/l: or less). ) to obtain thermal shock resistance (Japanese Patent Publication No. 38-4342, Japanese Patent Publication No. 44-5550). In this case, by making the thermal expansion coefficient α8 of the substrate almost zero, it is possible to create a product that has thermal shock resistance of 350°C or more, but on the other hand,
It has disadvantages such as poor moldability, high cost, narrow firing temperature range, and difficulty in adjusting the glaze which has lower thermal expansion than the base material.

When a ceramic base with a medium expansion range (αh = 2.5~B, 0x10-67℃) is used When a ceramic base with a medium expansion range is used, the strong heat generated at this time when a large thermal shock is applied The stress can destroy the glaze layer or the base itself.

In particular, the lower the water absorption rate and the more dense the structure, such as industrial solubilizable materials (water absorption rate of 3% or less), the more easily fractures due to thermal stress proceed all at once, making it difficult to achieve high thermal shock resistance. It's coming.

In this case, it has been known that thermal shock resistance can be improved by applying compressive stress to the glaze layer, such as Am, Ceram, and Soc.

Bul 1.65 [11] 1517-19 (19
86) and other examples. However, just that,
Unlike the present invention, it is not possible to obtain high thermal shock resistance of 350°C or higher, and in this example, the temperature is at most about 250°C.

On the other hand, it is possible to improve thermal shock resistance by making the substrate highly porous (water absorption rate of 10% or more).
In this case, the strength will be reduced, moisture and odors will easily be absorbed from the unglazed part (when heating food in the oven, etc.), which is unhygienic, and if the difference in thermal expansion between the base material and the glaze is too large, it will become brittle. Deterioration of product characteristics, such as easy linking, is unavoidable.

(Problem to be solved by the invention) As mentioned above, in the conventional technology, in order to obtain dense ceramics with thermal shock resistance of 350°C or higher, it was necessary to reduce the coefficient of thermal expansion of the base material to almost zero. .

However, such substrates have drawbacks such as a narrow firing temperature range and difficulty in coating with a glaze that has a lower thermal expansion than the substrate, making it relatively difficult to manufacture. As a result of intensive research, the present inventor found that the coefficient of thermal expansion is between 2.5 and 5. Ox
We found a way to solve the above-mentioned drawbacks by using a medium expansion range substrate of 10-67''C, and thus created the present invention.

(Means for Solving the Problems) The method for producing dense ceramics having thermal shock resistance of 350° C. or higher according to the present invention includes (a) a thermal expansion coefficient of 2.5 to 5.
The base material of OX 10-6/℃ is molded and baked, (b) The thermal expansion coefficient is 3.0X10-6/℃ or less, and the difference in thermal expansion coefficient with the base material is 1.5X10-67. The method is characterized in that (C) the entire fired base is glazed and then fired using a glaze adjusted to have a temperature of C or higher.

(Function) Hereinafter, the features of the present invention will be specifically explained along with its function.

In the present invention, (a) the thermal expansion coefficient of the base material is 2.5 to 5.
By setting the medium expansion range in the range of OX 10-6/℃, there is no need to introduce large amounts of low-expansion substances into the base material, so (a) the composition range in which the base material and glaze can be used is expanded. Greater freedom in billing.

(b) Manufacturing advantages such as improvements in firing temperature range, moldability, and dimensional accuracy increase.

(c) It is possible to provide functionality such as strength and reliability at the same time as high thermal shock resistance.

(d) Manufacturing costs can be reduced.

There are various advantages that conventional ceramic trays for microwave ovens and low-expansion thermal shock-resistant porcelain do not have.

(b) The coefficient of thermal expansion of the glaze is 3. OX 10-1"/℃ or less, and the difference in thermal expansion coefficient with the substrate is 1.5xlO-6/
By adjusting the temperature to be at least ℃, strong compressive stress is generated in the oil layer on the surface of the substrate, thereby improving thermal shock resistance.

(c) By covering the entire substrate, including the elevated portion, with a glaze layer, the phenomenon in which the exposed portion of the substrate is destroyed due to thermal stress is prevented.

The upper limit of the thermal expansion difference between the base material and the glaze is not particularly limited, but care must be taken to prevent shivering since the entire surface must be covered with a glaze layer. Further, the baking temperature and glaze baking temperature of the base material in the present invention are not particularly limited, and may be the baking temperature and glaze baking temperature commonly used in ceramic manufacturing methods. For example, the firing temperature is 1200-1350℃, and the glazing temperature is 1100-1100℃.
The temperature is 250°C.

In the present invention, by combining each of the requirements (a) to (C) above, a dense ceramic for microwave ovens having high thermal shock resistance of 350° C. or higher is obtained.

The reason why requirements (a) to (C) are limited to the above ranges in the present invention is as follows.

For requirement (a), the thermal expansion coefficient of the substrate is 2.5X.
Even if it is less than 10-'/l, it is possible to achieve high thermal shock resistance by, for example, reducing it to zero, but there are some manufacturing difficulties compared to the present invention. Furthermore, if the coefficient of thermal expansion increases beyond the range (a), large thermal stress will occur, making it impossible to obtain thermal shock resistance above 350°C.

Regarding the requirement (b), the purpose is to generate strong compressive stress in the glaze layer and improve the product's resistance to thermal stress. Therefore, if the difference in thermal expansion between the base material and the glaze is less than this, sufficient thermal shock resistance cannot be obtained. Also, the coefficient of thermal expansion of the glaze was set to 3. The reason for setting OX to 10-6/℃ or less is that it is necessary to generate strong compressive stress in the glaze layer of the base material, which has a large thermal expansion, but if the coefficient of thermal expansion of the shaft is increased beyond this, the difference in thermal expansion with the base material will be increased. , because it cannot be made large enough.

Regarding requirement (C), the exposed parts of the base were eliminated by applying glaze to the entire baked base, including the elevated parts. As a result, it is possible to prevent thermal stress from concentrating on the exposed portions of the base that are not glazed, resulting in destruction and a decrease in thermal shock resistance.

Next, the present invention will be specifically explained with reference to Examples.

(Example) Ceramics were manufactured using various combinations of the base materials shown in Table 1 and the glazes shown in Table 2, and their thermal shock resistance was investigated. In addition, in the example, a 10-inch size dinner plate was molded, and the size was 1200-1350.
The product was baked at 1100 to 1250°C after being glazed. Thermal shock resistance was determined by a rapid cooling test by dropping into water. The results are shown in Table 3.

As is clear from the examples, the examples according to the present invention exhibited high thermal shock resistance at temperatures of 350° C. or higher, while the other samples exhibited shivering or low thermal shock resistance.

(Effect of the invention) With the conventional technology, in order to obtain dense ceramics with thermal shock resistance of 350°C or higher, it was necessary to reduce the coefficient of thermal expansion of the base material to almost zero, which could not be said to be easy to manufacture. . According to the present invention, (a) the usable composition range of the base and glaze is expanded, and the degree of freedom in formulation is increased; (3) It is possible to provide functionality such as strength and strength at the same time as high thermal shock resistance. (2) It is possible to reduce manufacturing costs by using various types of porcelain that are not available in conventional low expansion thermal shock resistant porcelain. Benefits arise.

Claims (1)

[Claims] (a) Thermal expansion coefficient is 2.5 to 5.0 x 10^-^6/℃
(b) Next, the thermal expansion coefficient is 3.0×10^-^6/℃ or less, and the difference in thermal expansion coefficient with the base material is 1.5×10^-^ A method for producing dense ceramics having thermal shock resistance of 350° C. or higher, characterized by using a glaze adjusted to have a temperature of 6/° C. or higher, and (c) glazing the entire sintered base and then firing the glaze.