RU2534864C2 - Charge based on aluminium oxide, and method for obtaining strong ceramics - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to technology for obtaining ceramic material with high strength characteristics and can be used for manufacture of wear- and chemically resistant items, as well as for manufacture of items for military equipment, namely ceramic armour elements. Charge based on aluminium oxide contains a mineralising additive. The latter consists of a eutectic additive of MgO-Al₂O₃-SiO₂ system, magnesium oxide and yttrium oxide. Charge components are contained in the following ratio, wt %: Al₂O₃ 97.50-98.70, SiO₂ 0.60-0.70, MgO 0.43-0.80, Y₂O₃ 0-0.30. In order to prepare an eutectic additive, alumina, silicone oxide and magnesium oxide are mixed; then, heat treatment is performed at the temperature of 1280±20°C (below eutectics temperature). Sinter is crushed till fine-grained powders are obtained. Alumina and mineralising additives are mixed by means of a method of wet grinding in water medium according to the proposed ratio; moulding powder is obtained by a spraying drying method, and items are pressed and baked. Ceramics baking is performed in a tunnel furnace at the temperature of 1650-1680°C and exposure of 1-2 h.

EFFECT: achieving increase of strength characteristics of the ceramic material and reducing prime cost of the ceramic material.

4 cl, 3 ex, 1 tbl, 2 dwg

Description

The invention relates to a technology for producing ceramic material with high strength characteristics and can be used for the manufacture of wear-resistant and chemically resistant products, elements of the electrical and manufacturing industries, as well as for the manufacture of military equipment, in particular for the manufacture of ceramic armored elements for ballistic protection of personnel military equipment.

A known method for producing ceramics based on alumina Al ₂ O ₃ with a eutectic additive, including SiO ₂ , CaO, MgO (ASKosmos, LIBelie, D. Social Additives in coarse grain alumina ceramics for metallization / Fizika A. - V.5, Is. 2, 1996 .-- P.85-90). An eutectic additive is prepared by dry mixing the starting components, pressing the briquettes from the obtained powder mixture and obtaining glass by melting the briquettes at 1550 ° C for 1 h, followed by quenching in water and grinding. A mixture of 2 wt.% Additives with alumina is carried out in a planetary mill for 1 hour. Products are formed from the mixture obtained by pressing, which are calcined in an electric furnace at a temperature of 1700-1750 ° C. The disadvantages of the proposed method are the high firing temperature of 1700-1750 ° C, a long exposure time of 4 hours and, as a result, a large crystalline structure (grain size of more than 15 microns), which leads to a decrease in strength characteristics.

Known technical solution according to US patent No. 6159885 (publ. 12.12.2000, C04B 35/10) "Sintered material based on aluminum oxide." A homogeneous material is made on the basis of aluminum oxide with an additive containing MgO, CaCO ₃ , SiO ₂ . All components are mixed in an aqueous medium. Sintered material is prepared on the basis of a submicron alumina powder with an average particle size of 0.68 microns. A spray powder is prepared from the resulting suspension by spray drying. Products are formed from a press powder on a hydrostatic press, which are then fired at 1650 ° C for 2 hours. The disadvantages of the material and the method of its production is the use of the original alumina with high dispersion, which increases the cost of technology, pressing products on a hydrostatic press and complicates the technology, in addition, the resulting material has a low tensile strength in bending of 320 MPa.

There is also a known method for producing ceramic material described in US Pat. No. 3,905,845 (publ. 09/16/1975, С04В 35/10) "Translucent alumina containing magnesium, yttrium and lanthanum oxides." Ceramic material contains Al ₂ O ₃ ≥99 wt.%, Y ₂ O ₃ 0.05-0.5 wt.%, La ₂ O ₃ 0.5 wt.%, MgO 0.01-0.1 wt.% . Raw samples based on a mixture prepared by thoroughly mixing these components are preliminarily fired at 1200-1450 ° C, then final firing under vacuum to 1800 ° C. The disadvantage of the proposed method is the high firing temperature, the need for firing in vacuum, preliminary heat treatment of raw samples, the high content of expensive rare earth oxides in the charge.

The closest analogue (prototype) is a ceramic material based on aluminum oxide with additives of oxides of various elements (RF patent No. 2096384, etc. from 11.20.1997, С04В 35/111, "Ceramic material"). The alumina-based ceramic material contains magnesium, silicon and titanium oxides as mineralizing additives, as well as calcium oxide, iron oxide, sodium oxide impurities in the starting components, additionally contains yttrium oxide in the following ratio of components: aluminum oxide 95.025 wt.% , silica 1.25 wt.%, calcium oxide 0.005 wt.%, iron oxide 0.04 wt.%, magnesium oxide 0.63 wt.%, titanium oxide 2.0 wt.%, yttrium oxide 1.0 wt. %, sodium oxide 0.05% by weight. The disadvantages of the material are:

- low tensile strength in bending 423 MPa;

- the presence of an additive of titanium oxide, which increases grain growth, reduces the strength characteristics and, accordingly, negatively affects the ballistic resistance of the material,

- the presence of a significant amount of impurities in talc, adversely affecting the properties of ceramics;

- instability of the composition of talc;

- high content of yttrium oxide, which is an expensive component.

Ceramic material was obtained in the following manner.

The starting materials used were GOO, GK, GN, alumina, titanium oxide, yttrium oxide, and talc of the lump of the Onotsk deposit, which includes magnesium oxide, silicon oxide, and calcium oxide, iron oxide, and sodium oxide impurities in the starting components.

Talc is pre-sorted, crushed and calcined at a temperature of 1170 ° C. All the original components of the ceramic material are dispersed separately in different mills. The components are mixed by wet grinding in a ball mill using distilled water. The prepared suspension (in the prototype slip) is dehydrated, dried, sieved, calcined at 900 ° C, again sieved, magnetized. Press powder is prepared from the resulting mixture, from which the preforms are pressed by double-pressing on hydraulic presses (Fig. 1).

The disadvantages of the method are:

- possible variability of the chemical composition of the mineralizing additive from talc in connection with its natural origin and, as a result, the unstable temperature of the formation of the melt, which can lead to variability of the properties of the ceramic material;

- the need to calcine the entire mass at 900 ° C before preparing the press powder, which complicates the technology of manufacturing ceramics;

- the need for dehydration and drying of the suspension, screening and magnetization of the mixture, which also complicates the technology of manufacturing ceramics.

The technical task of this invention is to increase the strength characteristics of the ceramic material, reducing the cost of the ceramic material by simplifying the technology and reducing the number of expensive components.

The technical result in the implementation of the invention is achieved due to the fact that the mixture is based on alumina containing a mineralizing additive, which consists of a eutectic additive system MgO-Al ₂ O ₃ -SiO2, magnesium oxide and yttrium oxide. The components of the mixture are contained in the following ratio, wt.%:

Al ₂ O ₃ 97.50-98.70 SiO ₂ 0.60-0.70 MgO 0.43-0.80 Y ₂ O ₃ 0-0.30

To implement the method of obtaining durable ceramics, the above mixture based on aluminum oxide is used. Alumina is used as alumina. The preparation of the mixture includes the preparation of a eutectic additive, mixing the components, subsequent heat treatment, grinding the cake to obtain fine powders and the introduction of yttrium oxide as an additive. Then, by wet grinding in an aqueous medium, the components are mixed and a suspension is obtained to prepare a press powder. Press powder is prepared, the products are molded by pressing and calcined. A eutectic additive is prepared by mixing alumina, silicon oxide and magnesium oxide, while heat treatment is carried out at a temperature below the eutectic temperature of 1280 ± 20 ° C, and a press powder is obtained from a suspension of alumina powders, prepared eutectic additives, yttrium oxide and magnesium oxide. The press powder from the suspension can be obtained by spray drying. Ceramics can be fired in a tunnel oven at a temperature of 1650-1680 ° C and a holding time of 1-2 hours.

Figure 1 presents a flowchart of a method for producing ceramic material of the prototype. Figure 2 presents the block diagram of the proposed method for producing durable ceramics.

The technical result of increasing the strength characteristics of the material is achieved by increasing the content of alumina in the mixture and using a mineralizing additive, which is a mixture of a pre-prepared eutectic additive of the MgO-Al ₂ O ₃ -SiO _{2 system} and Y ₂ O ₃ and MgO oxides.

The increase in the content of alumina in the mixture was achieved mainly due to the exclusion of titanium oxide from the composition of the mixture, which, by lowering the sintering temperature of ceramics, leads to a sharp increase in its grain and thereby significantly reduces the strength properties. In the prototype, to compensate for grain growth caused by the presence of titanium oxide, yttrium oxide is additionally introduced, which limits the grain growth in sintered ceramics, strengthening it. Thus, with the exclusion of titanium oxide from the composition of ceramics, the strength was increased due to an increase in the proportion of alumina and the mass fraction of the additive of yttrium oxide was reduced, thereby providing a technical result for reducing the cost of the obtained ceramics.

The technical result in the method of producing durable ceramics is achieved by preparing a eutectic additive, which is a mixture of oxides, which provides sintering of corundum to a dense state due to the formation of a liquid phase. A smaller amount of impurities in the starting components of the additive compared with the additive used in the prototype, allows to improve the properties of the material. The ability to accurately select the ratio of the components of the additives ensures the achievement of the task, in particular, in terms of ceramic strength. Yttrium oxide reduces crystal growth, allows you to maintain a fine-grained structure, reduces intracrystalline porosity and microcracks, thus increasing strength characteristics. Magnesium oxide intensively inhibits the growth of crystals, contributes to the formation of a fine-grained structure: the inhibitory growth of crystals is explained by the formation on the corundum surface of micron interlayers of magnesia spinel MgO · Al ₂ O ₃ , it also increases surface diffusion, which leads to pore mobility, reduces shrink rate and surface tension, and as a whole significantly strengthens alumina ceramics.

The need for heat treatment of the mixture of components of the eutectic additive is due to the fact that the additive is introduced in a small amount, and if it is introduced in the form of individual oxides, then these components will be dispersed throughout the alumina and will act as separate additives. Heat treatment of the mixture provides the formation of primary contacts of the components of the additive. In this case, the best results can be obtained at a heat treatment temperature below the eutectic temperature, namely at 1280 ± 20 ° C.

Ceramic material is prepared as follows. First, an eutectic supplement is prepared using alumina, silica, and magnesium salt. The mixture of components is subjected to heat treatment at 1280 ± 20 ° C. The cake is ground to a state in which the average particle size is 1-2 microns. Then, alumina, a eutectic additive of the MgO-Al ₂ O ₃ -SiO _{2 system} and Y ₂ O ₃ and MgO oxides are mixed by wet method. The resulting suspension is sprayed in a dryer to obtain a press powder, from which strong ceramic products are pressed and fired.

The costs of increasing the firing temperature of raw products are offset by the absence of a number of operations: dehydration, drying and heat treatment of the entire mass after mixing the components.

Case Studies

Example 1. A eutectic additive is prepared using 21 wt.% Alumina, 60 wt.% Silicon oxide and 19 wt.% (In terms of MgO) magnesium salt. The mixture of components is subjected to heat treatment at 1280 ° C. The cake is ground to a state in which the average particle size is 1-2 microns.

Then, wet alumina, 1 wt.% Mineralizer and modifiers are mixed: 0.23 wt.% Y ₂ O ₃ , 0.27 wt.% (In terms of MgO) magnesium salt. A ligament and a plasticizer are added to the suspension. A press powder is prepared from the resulting mass using a spray dryer, from which samples are formed by uniaxial pressing. Firing is carried out in a continuous tunnel kiln at a _firing temperature T = 1650 ° C.

Example 2. A eutectic additive is prepared using 16 wt.% Alumina, 62 wt.% Silicon oxide and 22 wt.% (In terms of MgO) magnesium salt. The mixture of components is subjected to heat treatment at 1280 ° C. The cake is ground to a state in which the average particle size is 1-2 microns.

Then, alumina, 1 wt.% Mineralizer and modifiers are mixed by wet method: 0.3 wt.% Y ₂ O ₃ , 0.5 wt.% (In terms of MgO) magnesium salt. A ligament and a plasticizer are added to the suspension. A press powder is prepared from the resulting mass using a spray dryer, from which samples are formed by uniaxial pressing. Firing is carried out in a continuous tunnel kiln at a _firing temperature T = 1650 ° C.

Example 3. A eutectic additive is prepared using 16 wt.% Alumina, 62 wt.% Silicon oxide and 22 wt.% (In terms of MgO) magnesium salt. The mixture of components is subjected to heat treatment at 1280 ° C. The cake is ground to a state in which the average particle size is 1-2 microns.

Then, alumina, 1.2 wt.% Mineralizer and modifier 0.3 wt.% (In terms of MgO) of magnesium salt are mixed wet. A ligament and a plasticizer are added to the suspension. A press powder is prepared from the resulting mass using a spray dryer, from which samples are formed by uniaxial pressing. Firing is carried out in a continuous tunnel kiln at a firing temperature of 1650 ° C.

Table 1 shows the properties of the obtained material in comparison with the prototype. The use of mineralizing additives, including eutectic additives, yttrium oxide and magnesium oxide, allows to obtain ceramics with significant strength. With the exclusion of yttrium oxide from the composition, the strength characteristics decrease. With a decrease in the amount of eutectic additives, the density and strength decrease.

Table 1 Indicators According to the proposed method According to the prototype Example 1 Example 2 Example 3 The initial particle size of alumina, microns 1-1,2 1-1,2 2.0-2.2 - Firing temperature, ° C 1650 1650 1680 1440 Exposure, h one 2 2 - The average grain size of ceramics, microns 6-8 8-9 10-12 - Density, g / cm ³ 3.84 3.82 3.79 - Strength in static bending, MPa 442 436 425 423 Microhardness, GPa 17.36 17.69 15.49 - The coefficient of crack resistance, MPa · m ^0,5 3.76 4.1 3,54 - Modulus of elasticity, GPa 421 405 380 -

Claims (4)

1. The mixture is based on alumina containing a mineralizing additive, which consists of a eutectic additive of the MgO-Al ₂ O ₃ -SiO _{2 system} , magnesium oxide and yttrium oxide, characterized in that the components included in the mixture are contained in the following ratio, wt.%:
Al ₂ O ₃ 97.50-98.70 SiO ₂ 0.60-0.70 MgO 0.43-0.80 Y ₂ O ₃ 0-0.30 2. A method of obtaining durable ceramics, consisting of preparing a mixture based on alumina, which uses alumina, which consists in preparing a eutectic additive, mixing the components, subsequent heat treatment, grinding the cake to obtain fine-grained powders and introducing yttrium oxide as an additive, then mixing by wet grinding in an aqueous medium and obtaining a suspension, preparing a press powder, molding products by pressing and subsequent firing, characterized in that ekticheskuyu additive is prepared by mixing alumina, silica and magnesium oxide, wherein the heat treatment is performed at a temperature below the eutectic temperature of 1280 ± 20 ° C, and press the powder obtained from a slurry of alumina powder prepared eutectic additive, yttrium oxide and magnesium oxide. 3. The method according to claim 2, characterized in that the press powder is obtained from a suspension of powders by spray drying. 4. The method according to claim 2, characterized in that the ceramics are fired in a tunnel furnace at a temperature of 1650-1680 ° C and a holding time of 1-2 hours

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