RU2405756C1 - Method of producing alumina ceramic - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of producing alumina ceramic material meant for making articles from structural ceramic with high static loads. According to the invention, alumina is mixed with a mineralising agent characterised by viscosity of 1-5 Pa·s and surface tension (50-250)·10^-3 N/m a temperature interval for burning ceramic in amount of 1-2 wt % on the cation-oxygen component. Sinter is obtained at 1300°C. The sinter is ground, pressed and burnt at 1350-1400°C. The mineralising agent used is in form of chlorides of alkali and alkali-earth metals KCl, MgCl₂, LiCl, CaCl₂, NaCl, BaCl₂.

EFFECT: high ceramic sintering temperature with increase in ultimate bending strength.

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Description

The invention relates to methods for producing corundum ceramic material intended for the manufacture of products from structural ceramics with high static loads.

A known method of producing high-quality structural corundum ceramics with glass additives - mineralizer containing oxides of silicon, calcium and boron in a mass ratio of 1: 1: 1 and sintered at 900-1000 ° C. Moreover, the charge additionally contains a fluoride-containing additive in an amount of 0.5-1 wt.%., And the firing of ceramics is carried out at a temperature of 1500-1550 ° C (US Pat. No. 2119901, IPC С04В 35/10, С04В 35/18, from 10.06. 97, published on 10/10/1998). The disadvantage of this method is the increased firing temperature of ceramics.

Closest to the claimed method is a method for producing corundum ceramic material intended for the manufacture of products from structural ceramics with a glass additive mineralizer containing oxides of magnesium, calcium, silicon and boron in a mass ratio of 0.5: 0.5: 1: 1 (US Pat. No. 2171244, IPC С04В 35/111, dated April 10, 2000, publ. July 27, 2001). Ceramics are fired at 1440-1460 ° C, and the mixture has the following ratio of components, wt.%:

Aluminum hydroxide and / or alumina in terms of alumina 88-92 Glass additive 8-12

The disadvantage of the closest to the claimed known method is the increased firing temperature of ceramics (1440-1460 ° C), as well as the need for preliminary sintering of the glass additive - mineralizer (8-12 wt.%) At sufficiently high temperatures of 900-1000 ° C. The use of a highly viscous mineralizing additive - cullet (viscosity in the temperature range of ceramic firing 10 ⁶ Pa · s) insignificantly contributes to the transfer of the sintering process to lower temperatures.

The objective of the proposed method is to obtain corundum ceramics having a lower sintering temperature with high strength characteristics.

This is a new technical result, which is in a causal relationship with the essential features of the invention.

The essential features of the invention are that alumina is mixed with a mineralizer in the form of alkali and alkaline earth metal chlorides KCl, MgCl ₂ , LiCl, CaCl ₂ , NaCl, BaCl ₂ , characterized by a viscosity of 1 to 5 Pa · s and surface tension (50-250 ) · 10 ^-3 N / m in the temperature range of firing ceramics in an amount of 1-2 wt.% By cation-oxygen component, the preparation of cake is carried out at a temperature of 1300 ° C, and firing is carried out at a temperature of 1350-1400 ° C.

Mineralizing additives were introduced into alumina taking into account the equivalent content of the mineralizing component (oxygen-cation component) in them. The actual ratio of the amount of introduced mineralizer and the amount of cation-oxygen component in it is given in table 1. Moreover, the comparison of the mineralizing effect depending on the viscosity and surface tension of the additives is carried out by the same amount of metal oxides introduced with the mineralizer.

The use of a mineralizer with a viscosity of 1 to 5 Pa · s and a surface tension of (50-250) · 10 ^-3 N / m in the temperature range of firing ceramics provides a significant reduction in the firing temperature due to the formation of the liquid phase of high reactivity with low viscosity and low surface the melt tension of the mineralizer. The content of the mineralizer in the claimed amounts (1-2 wt.% By cation-oxygen component) provides a significant increase in strength characteristics.

The method is as follows. Alumina and mineralizer with a viscosity of 1 to 5 Pa · s and a surface tension of (50-250) · 10 ^-3 N / m in the temperature range of ceramic firing in the amount of 1-2 wt.% By cation-oxygen component are carefully ground to fraction 1 -3 microns and mixed in the stated ratio. The resulting mixture is synthesized at a temperature of 1300 ° C and again crushed, mainly in a vibratory mill. Samples are molded from the resulting mixture at a molding pressure of 80-100 MPa, and then fired at a temperature of 1350-1400 ° C.

Data on the type of mineralizer, its content in the ceramic mass, sintering temperature and strength characteristics of the calcined products by the present method in comparison with the prototype are presented in table 1. The rationale for the optimal amount of mineralizer according to the claimed method is presented in table 2 and is given in relation to the most effective mineralizing additive KCl, having a minimum viscosity (viscosity 1 Pa · s in the temperature range of firing ceramics).

An analysis of the data in Table 1 indicates the promising use of mineralizing additives in the preparation of corundum ceramics, characterized by a viscosity of 1 to 5 Pa · s and a surface tension of (50-250) · 10 ^-3 N / m in the temperature range of ceramic firing. The use of high-viscosity mineralizing glass additives (viscosity in the temperature range of ceramic firing - 10 ⁶ Pa · s) does not provide advantages in sintering temperature and bending strength in comparison with the low-viscosity mineralizers claimed in the method. Low-viscosity mineralizers form a highly mobile, low-viscosity and homogeneous liquid phase, which in turn leads to earlier ripening of the material, activation of the process of formation of the main crystalline phase - corundum, and, as a result, an increase in the quality of products at lower sintering temperatures.

table 2 Type of mineralizer The content of the mineralizer Temperature Bending strength by cation oxygen firing, ° C MPa component, wt.% 1 K ₂ O 1380 430 KCl 2 K ₂ O 1350 460 3K ₂ O 1370 420

Claims (1)

A method of producing corundum ceramics, including grinding and mixing alumina with mineralizing additives, obtaining custody, grinding, pressing and firing ceramics, characterized in that the alumina is mixed with mineralizing additives in the form of alkali and alkaline earth metal chlorides KCl, MgCl ₂ , LiCl, CaCl ₂ , NaCl, BaCl ₂ with a viscosity of 1 to 5 Pa · s and surface tension (50-250) · 10 ^-3 N / m, in the temperature range of firing ceramics in the amount of 1-2 wt.% For cation-oxygen component, sintered temperature 1300 ° С, and firing of ceramics oestriasis at a temperature of 1350-1400 ° C.