RU2592652C2 - Method of producing ceramic gradient material - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to production of gradient ceramic materials based on powders of metal oxides. Method comprises obtaining polydispersed ceramic powder metal oxide or mixture of powders of metal oxides by spraying aqueous solutions of metal salts or mixtures of metal salts into high-frequency discharge plasma through slot nozzle of variable cross-section from 0.1 to 100 mcm, then adding organic binder to said powder, mixing moulding mixture, poured into a mould, holding moulding mixture for demixing thereof into fractions and sintering obtained workpiece with isothermal holding. Polydispersed ceramic powder may be powder of following oxides: Al₂O₃, ZrO₂, CaO, Y₂O₃, MgO. Moulding mixture can have following ratio of components: powder of metal oxide or mixture of powders of metal oxides 80-85 wt%, organic binder - balance. Organic binder used can be paraffin, or wax, or a mixture of paraffin and wax in ratio of 9:1.

EFFECT: obtaining ceramic gradient material with a structure ensuring uniform change of mechanical properties along section of article and having high resistance to thermal effects - not less than 200 cycles at temperature 1,600 °C.

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Description

The invention relates to powder metallurgy, in particular to the manufacture of gradient ceramic materials based on powders of metal oxides or their mixtures, and can be used to obtain products with variable porosity, for example, bone implants, filters, drug carriers, etc. with increased resistance to thermal effects.

Known methods for producing gradient materials, comprising:

- in the sequential deposition of layers of various powders and their selective sintering (Wang, Chunchau, Hu, Yiadong. Cu / Fe Powder Gradient Material Sintering by Laser Processing // Proceedings SPIE. Vol. 3550. Pp. 60-64. 1998) [1 ];

- in pressing and sintering a framework of titanium carbide powder followed by impregnation with titanium nickelide and alloying with iron to create a gradient structure (Sivokha V.P., Rudai V.V., Mironov Yu.P., Kulkov CH Composite materials TiC-NiTi with gradient structurally unstable matrix / Physical Mesomechanics, 2004, 7th special issue, Part 1, pp. 241-244) [2].

The disadvantages of these methods include the following.

The main disadvantage for all known is a sharp change in properties in the macro-volumes of the material.

In addition to the indicated drawback, the known method [1] does not allow to obtain sintered regions from various powders lying in the same plane, which leads to the presence of a vertical interface between the product areas, and the disadvantage of the method [2] is the multistage process of obtaining a gradient material.

A known method of producing composite materials with a gradient structure (RU 2164260, C22C 1/04, C22C 29/00, B22F 3/12, publ. 20.03.2001) [3], including the preparation of the mixture, pressing and sintering in the backfill, while the charge prepared from compounds selected from the group consisting of carbides, hydroxycarbides, carbonitrides, nitrides with the addition of steels or alloys containing elements that can evaporate during sintering, and sintering is carried out in vacuum at 1200-1500 ° C with a holding time of 10-300 min, however, one of the pressing surfaces is free from backfill.

The disadvantages of this method [3] are the multi-stage process and the limited method for using only metal impregnation materials with a melting point in the range from 1200 ° C to 1500 ° C.

The closest in technical essence is a method for producing a ceramic gradient material (RU 2454297, B22F 3/12, С04В 35/64, С22С 1/10, publ. 27.06.2012) [4] based on zirconium dioxide. Fine powder in the form of supersaturated solid solutions based on ZrO ₂ with dissolved components selected from the group of tetragonal phase stabilizing oxides is pressed at a pressure of 550-800 MPa and sintered at 1500-1700 ° C for 1-5 hours .

The disadvantage of the gradient material obtained by the known method [4] is that it has insufficiently high resistance to thermal effects during cyclic exposure and is at temperatures of 1400-1600 ° C less than 50 cycles.

SUMMARY OF THE INVENTION

An object of the invention is to develop a method for producing a ceramic gradient material, in which the structure provides a uniform change in mechanical properties over the cross section of the product and, as a result, high resistance to thermal influences.

The specified technical result is achieved by the fact that in the method of producing a ceramic gradient material, which consists in molding a preform and sintering it, a polydisperse ceramic metal oxide powder or a mixture of metal oxide powders is first obtained by the plasma-chemical method by spraying aqueous solutions of metal salts or mixtures of metal salts into a high-frequency discharge plasma through a slot nozzle of variable cross-section from 0.1 to 100 μm, then an organic binder is added to the obtained powder, mix the molding mixture, pour it into the mold, hold the molding mixture to separate it into fractions and sinter the obtained preform with isothermal exposure.

A polydisperse ceramic metal oxide powder or a mixture of metal oxide powders is obtained with a particle morphology - from individual nanocrystallites 20-50 nm in size to spherical hollow particles up to 250 microns in size.

The molding mixture has the following ratio of components, weight. %: metal oxide powder or a mixture of powders of metal oxides 80-85; organic ligament - the rest.

Polydisperse ceramic metal oxide powder or a mixture of metal oxide powders is an oxide powder: Al ₂ O ₃ , ZrO ₂ , CaO, Y ₂ O ₃ , MgO.

Paraffin, or wax, or a mixture of paraffin and wax in a ratio of 9: 1 is used as an organic ligament.

The moldable mixture is stirred at a temperature of 85-90 ° C.

The molding mixture is kept in a mold to separate it into fractions for 1-10 hours at a temperature of 75-90 ° C.

The resulting preform is sintered at a temperature of 1300-1700 ° C with an isothermal exposure of 1-5 hours.

The essence of the invention lies in the fact that a ceramic material with a gradient structure is obtained from a polydispersed ceramic metal oxide powder or a mixture of metal oxide powders obtained by the plasma-chemical method by spraying aqueous solutions of metal salts or mixtures of metal salts into a high-frequency discharge plasma through a slot nozzle of variable cross section from 0.1 up to 100 microns. As a result of the high temperature of the plasma, rapid evaporation-decomposition of the salt occurs with the formation of particles of a powder of a polydispersed metal oxide or a mixture of metal oxides. In this case, a polydisperse ceramic metal oxide powder or a mixture of metal oxide powders with particle morphology is obtained — from individual nanocrystallites 20-50 nm in size to spherical hollow particles up to 250 microns in size. The presence of polydisperse particles will provide the necessary different density of the casting when it is aged after casting.

An organic binder is added to the resulting polydisperse ceramic metal oxide powder or a mixture of metal oxide powders to obtain a molding mixture, which is: paraffin, or wax, or a mixture of paraffin and wax in a ratio of 9: 1. The ratio of the components of the molding sand is as follows, weight. %:

metal oxide powder or a mixture of metal oxide powders 80-85 organic bunch rest

At a temperature of 85-90 ° C, the molding mixture is thoroughly mixed for 25-50 hours, then it is poured into the mold and kept at the melting temperature of the organic binder 75-90 ° C for 1-10 hours. As a result, the formation mixture is stratified into fractions due to the gradient deposition of fractions of particles of the obtained powder. Varying the exposure time (1-10 hours) and the temperature at which the organic binder is located (75-90 ° C), i.e. the process of stratification of the molding mixture into fractions in the form, you can get a ceramic material with a given gradient structure and, therefore, resistance to thermal stress. After the specified time, the resulting preform is sintered at a temperature of 1300-1700 ° C with isothermal exposure for 1-5 hours.

Ceramic material obtained by the proposed method has gradually varying porosity and uniform (smooth) change in properties throughout the volume of the material obtained as it moves away from the surface into the volume. The resulting ceramic gradient material has a variable porosity structure in the volume - from 20 to 75 vol. %

The stability of the obtained ceramic gradient material during cyclic exposure at a temperature of 1600 ° C for at least 200 cycles.

EXAMPLES OF SPECIFIC IMPLEMENTATION

Example 1

To obtain a polydisperse ceramic powder of zirconium oxide, an aqueous solution of zirconium nitrate salt is taken and sprayed through a slot nozzle of variable cross section - from 0.1 to 100 μm into a high-frequency discharge plasma.

In the obtained polydisperse ceramic powder of zirconium oxide, taken in an amount of 80 weight. %, add an organic binder - a mixture of paraffin and wax (9: 1) in an amount of 20 weight. %, then stirred for 50 hours at a temperature of 85-90 ° C. The resulting moldable mixture is poured / injected into the mold and kept in this state, i.e. at a temperature of 90 ° C for 2 hours. The resulting preform is sintered at a temperature of 1550 ° C with an isothermal exposure of 1 hour.

The stability of the obtained ceramic gradient material during cyclic exposure at a temperature of 1600 ° C for 200 cycles.

Example 2

To obtain a polydisperse ceramic powder of aluminum oxide, an aqueous solution of aluminum nitrate salt is taken and sprayed through a slot nozzle of variable cross section - from 0.1 to 100 μm into a high-frequency discharge plasma.

In the obtained polydisperse ceramic powder of aluminum oxide, taken in an amount of 85 weight. %, add an organic binder - paraffin in an amount of 15 weight. %, then stirred for 35 hours at a temperature of 85-90 ° C. The resulting moldable mixture is poured / injected into the mold and kept in this state, i.e. at a temperature of 75 ° C for 10 hours. The resulting preform is sintered at a temperature of 1300 ° C with an isothermal exposure of 5 hours.

The stability of the obtained ceramic gradient material during cyclic exposure at a temperature of 1600 ° C 220 cycles.

Example 3

To obtain a polydisperse ceramic powder of zirconium, magnesium, and yttrium oxides, an aqueous solution of the nitric acid salt of zirconium, magnesium, and yttrium is taken and sprayed through a slot nozzle of variable cross section, from 0.1 to 100 μm, into a high-frequency discharge plasma.

In the obtained polydisperse ceramic powder of oxides of zirconium, magnesium and yttrium, taken in an amount of 82 weight. %, add an organic bunch - wax in the amount of 18 weight. %, then stirred for 40 hours at a temperature of 85-90 ° C. The resulting moldable mixture is poured / injected into the mold and kept in this state, i.e. at a temperature of 85 ° C for 2 hours. The resulting preform is sintered at a temperature of 1700 ° C with an isothermal exposure of 1 hour.

The stability of the obtained ceramic gradient material at cyclic exposure at a temperature of 1600 ° C 210 cycles.

Example 4

To obtain a polydisperse ceramic powder of zirconium and calcium oxides, an aqueous solution of zirconium and calcium nitrate is taken, sprayed through a slot nozzle of variable cross section - from 0.1 to 100 μm into a high-frequency discharge plasma.

In the obtained polydisperse ceramic powder of zirconium and calcium oxides, taken in an amount of 84 weight. %, add an organic binder - a mixture of paraffin and wax (9: 1) in an amount of 16 weight. %, then stirred for 25 hours at a temperature of 85-90 ° C. The resulting moldable mixture is poured / injected into the mold and kept in this state, i.e. at a melting point of organic binder 80 ° C for 6 hours. The resulting preform is sintered at a temperature of 1600 ° C with an isothermal exposure of 3 hours.

The stability of the obtained ceramic gradient material during cyclic exposure at a temperature of 1600 ° C for 200 cycles.

Claims (8)

1. A method of obtaining a ceramic gradient material, including molding a preform and sintering, characterized in that the polydisperse ceramic metal oxide powder or a mixture of metal oxide powders is first obtained by the plasma-chemical method by spraying aqueous solutions of metal salts or mixtures of metal salts into a high-frequency discharge plasma through a slot nozzle a variable cross section from 0.1 to 100 microns, then an organic binder is added to the obtained powder, the resulting molding is mixed the mixture is poured into the mold, the molding mixture is held to separate it into fractions and the resulting preform is sintered with isothermal exposure. 2. The method according to p. 1, characterized in that a polydisperse ceramic metal oxide powder or a mixture of metal oxide powders is obtained with a particle morphology - from individual nanocrystallites with a size of 20-50 nm to spherical hollow particles up to 250 microns in size. 3. The method according to p. 1, characterized in that the molding mixture has the following ratio of components, weight. %:
metal oxide powder or a mixture of metal oxide powders 80-85 organic bunch rest 4. The method according to any one of paragraphs. 1-3, characterized in that the polydisperse ceramic metal oxide powder or a mixture of metal oxide powders is an oxide powder: Al ₂ O ₃ , ZrO ₂ , CaO, Y ₂ O ₃ , MgO. 5. The method according to p. 1 or 3, characterized in that the organic binder is used paraffin, or wax, or a mixture of paraffin and wax in a ratio of 9: 1. 6. The method according to p. 1, characterized in that the molding sand is mixed at a temperature of 85-90 ° C for 25-50 hours. 7. The method according to p. 1, characterized in that they withstand the molding sand in the form for delamination into fractions for 1-10 hours at a temperature of 75-90 ° C. 8. The method according to p. 1, characterized in that the obtained preform is sintered at a temperature of 1300-1700 ° C with an isothermal exposure of 1-5 hours.