RU2394004C1 - Zircon based mixture for making compact refractory ceramics - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to making refractory and ceramic articles based on zircon and can be used mechanical engineering, aviation and electrical engineering industries. The mixture contains the following in wt %: 84-86 zircon concentrate with particle size of 1-2 mcm with aluminium oxide in amount of not more than 0.2% and 14-16 zirconium dioxide stabilised with 5% yttrium oxide, having particle size of 15-20 nm.

EFFECT: invention enables to obtain a dense, fine-grained zircon based ceramic which does not contain a glass phase.

1 tbl, 1 dwg

Description

The invention relates to the field of production of refractory and ceramic products based on zircon and can be used in mechanical engineering, aviation and electrical industry.

Known refractory material obtained from a mixture based on zircon and zirconium dioxide containing from 5 to 40% zircon, the following chemical composition, wt.%: ZrO ₂ + HfO ₂ 83-96; SiO ₂ 1.7-14; TiO ₂ 0.2-3; Y ₂ O ₃ 0.4-5; Al ₂ O ₃ 0.2-2.5; impurities <1 (RF Patent No. 2201906, IPC С04В 35/484, СВВ 5/43. Publ. 2003.04.10).

The disadvantage of this mixture is the use of zircon, the particles of which have an average diameter of 4.7 microns, and the average particle size of zirconium dioxide is from 3.5 to 10 microns, which does not allow to achieve a high density of the material. The introduction of additives in the mixture in the form of TiO ₂ and Al ₂ O ₃ causes the formation of a glass phase, which reduces the refractoriness of zircon ceramics.

Closest to the claimed object is the invention (US Patent No. 4888313, IPC С04В 35/48, С04В 35/66. Publ. 1989.12.19), in which refractory ceramics for working with molten metals, consisting of 80-99 wt.% Dissociated zircon and 1-20 wt.% zirconium dioxide, obtained by sintering at a temperature of 1700 ° C.

The disadvantage of this invention is the use of dissociated zircon, which is a product obtained by processing zircon sand in a plasma furnace, consisting of amorphous SiO ₂ in which crystals of ZrO _{2 are} interspersed.

The use of unstabilized zirconia promotes the formation of microcracks in ceramics, as upon cooling, polymorphic conversion of tetragonal zirconia to monoclinic occurs with an increase in volume up to 5%, and upon repeated heating, a reverse transition will occur with a decrease in volume. The particle size of the used zirconia powder is from 0.5 to 10 μm, which does not contribute to a uniform distribution of zirconia in the zircon matrix, therefore, reduces the strength of the material.

After sintering at a temperature of 1700-1710 ° C, which is higher than the dissociation temperature of zircon, the material has a phase composition, including about 7.7 wt.% Silica glass, about 69 wt.% Zircon, and about 23.1 wt.% Zirconium dioxide. Zirconia is present in the form of agglomerates with a diameter of approximately 12 microns, consisting of grains with a diameter of approximately 3 microns, as well as in the form of separate dispersed grains with an average size of approximately 3 microns, which is larger than the critical size at which the zirconia grains will undergo spontaneous polymorphic transformation from tetragonal into a monoclinic modification with an increase in volume, thereby loosening the structure of the material and reducing its strength characteristics.

The technical result of the proposed invention is to increase the density of refractory ceramics based on zircon by eliminating the glass phase.

This goal is achieved in that the mixture to obtain a dense refractory ceramic, including a zircon concentrate of a fraction of 1-2 μm with aluminum oxide in an amount of not more than 0.2 wt.%, Contains zirconia fraction of 15-20 nm, stabilized with yttrium oxide in an amount of 5 wt.%, in the following ratio of components, wt.%:

Zircon Concentrate 84-86 Zirconium dioxide 14-16

The introduction of zirconium dioxide is justified by the fact that this compound does not interact with zircon with the formation of fusible compounds and does not contribute to its decomposition at high temperatures. The introduction of zirconium dioxide in ceramic materials can increase their strength and fracture toughness. Yttrium oxide, used as a stabilizing additive to preserve zirconia in tetragonal modification, is in the form of a solid substitution solution and does not affect the formation of glass phase in contrast to magnesium and calcium oxides, which are also used to stabilize zirconia, but contribute to thermal dissociation of zircon .

The limits of the content of zirconium dioxide in the mixture are selected from the following considerations. When the content of zirconium dioxide is less than 14%, the ceramic does not have sufficient density, and the introduction of zirconium dioxide into the mixture in an amount greater than 16% leads to an increase in porosity of the ceramic. It is known that additives of nanosized powders contribute to the compaction of ceramics and lower temperatures during sintering.

The content of alumina in the zircon concentrate is not more than 0.2 wt.% Due to the fact that the presence of alumina helps to reduce the dissociation temperature of zircon.

The drawing shows a diffraction pattern of a ceramic material after sintering.

The manufacture of products from the charge is as follows.

As the starting material, zircon of the brand Zircon Standard Grade (Possen Erzconter) is used, containing impurities in an amount, wt.%: 0.18 Al ₂ O ₃ , 0.2 Fe ₂ O ₃ , 0.25 TiO ₂ , 0.1 CaO 0.03 MgO, 0.002 Cr ₂ O ₃ , 0.14 P ₂ O ₃ . The specific surface area of zircon powder determined by the BET method is 0.59 m ² / g.

The applied zirconia stabilized with 5 wt.% Yttrium oxide has a specific surface area of 47.5 m ² / g, the powder consists of almost one tetragonal phase and a small amount of monoclinic phase (traces).

Mixing the components of the charge is carried out in a SAND planetary mill in a liquid medium, the ratio of the mass of powder and grinding media is 1: 2. After drying, the powder has a specific surface area of 13.7 m ² / g. The blanks are molded by semi-dry pressing in a steel mold at a pressure of 250 MPa with the addition of 4% aqueous solution of PVA, sintering is carried out in air in an electric resistance furnace at a temperature of 1600 ° C.

The resulting ceramic material is characterized by a residual porosity of not more than 10%. The diffraction pattern of the ceramic material after sintering shows that the phase composition of the material consists of zircon and tetragonal zirconia, no traces of other compounds were found. Zircon is present in the form of grains with an average size of 1-2 microns. The average grain size of zirconium dioxide is 0.5 μm.

The table shows the composition of the charge and the properties of the products obtained by the described technology.

Charge The composition of the charge, wt.% Density, g / cm ² Zircon Concentrate Zirconium dioxide one 95 5 3.8 2 90 10 3.88 3 85 fifteen 4.05 four 80 twenty 3.89

The table shows that the highest density of the ceramic material is achieved by introducing into the mixture 15 wt.% ZrO ₂ . When the content of zirconium dioxide is less than or greater than the specified amount, the density of the material decreases.

Thus, the invention allows to obtain a dense refractory fine-grained zircon-based ceramic that does not contain glass phase.

Claims (1)

The mixture based on zircon to obtain a dense refractory ceramic containing zircon and zirconia, characterized in that it contains a zircon concentrate fraction of 1-2 microns with aluminum oxide in an amount of not more than 0.2 wt.% And zirconia fraction of 15-20 nm, stabilized with yttrium oxide in an amount of 5 wt.%, in the following ratio of components, wt.%:
Zircon Concentrate 84-86 Zirconium dioxide 14-16

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