RU2760814C1 - Ceramic flame-retardant material, crucible, and method for manufacturing a crucible - Google Patents

Abstract

FIELD: ceramics.

SUBSTANCE: invention relates to the field of ceramic flame-retardant materials for manufacturing crucibles. The proposed ceramic flame-retardant material of a crucible comprises 14.8 to 45 wt.% of zirconium oxide, 6.8 to 8.54 wt.% of at least one rare earth metal oxide selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium, yttrium oxide the rest. The material comprises yttrium oxide in the form of particles of two different fractions, wherein the smaller fraction is up to 0.5 mcm and the larger is 20 to 250 mcm, oxide of at least one rare earth metal (selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium) in the form of particles of a fraction of up to 10.0 mcm, and zirconium oxide in the form of particles of two different fractions, wherein the smaller fraction is up to 10.0 mcm and the larger is 600 to 710 mcm. The components are mixed in three stages. At the first stage, a sintering additive is produced, consisting of powders of fine fractions of zirconium oxide, yttrium oxide and oxide a rare earth metal; at the second stage, said additive is mixed dry with granular powders of zirconium oxide and yttrium oxide, resulting in a dry ceramic charge; at the third stage, said charge is mixed with a suspension containing yttrium oxide particles. The resulting plastic mass is moulded and dried for 12 to 25 hours producing a crucible preform further subjected to high temperature sintering at a temperature from 1,650 to 1,750°C for 3 to 5 hours.

EFFECT: ensured resistance of the material of the crucible to the influence of melts of high temperature reactive zirconium-containing alloys and alloys of the chromium-molybdenum-iron system at temperatures up to 1,820 and 2,050°C, respectively, increased heat resistance of the crucible, and increased accuracy of moulding the crucible.

4 cl, 6 tbl, 7 ex

Description

The invention relates to the field of ceramic refractory materials for the manufacture of crucibles used for induction smelting of high-temperature reactive alloys containing zirconium, used as targets for applying heat-shielding coatings of rotor blades of gas turbine engines and installations by magnetron sputtering of targets in an oxidizing environment, and alloys of the chromium system -molybdenum-iron, used for the manufacture of high-resource die tooling with a working temperature of 1250 ° C.

From the prior art, a crucible material is known for melting alloys with a high chromium content (up to 97 wt.%), Alloyed with boron, manganese or vanadium. The material contains 89-93 mass. % zirconium oxide, 7-11 wt. % yttrium oxide and up to 0.6 wt. % silicon oxide. A crucible from this material is made by molding and further sintering or firing the workpiece. The crucible is designed for melting alloys intended for the manufacture of sputtered targets with a high chromium content, and provides a low oxygen content in the alloy at a level of 300 ppm or less (US 2008269041 A1, 30.10.2008).

The known material has low resistance to high-temperature melts with a high content of refractory metals, such as molybdenum, as the main alloying elements.

Known composite oxide refractory material containing from 20 to 50 mass. % calcium oxide, from 45 to 75 wt. % zirconium oxide and auxiliary material, which is used as a flux. A method for making a crucible from this material includes pre-processing, shaping, pre-sintering and sintering. The crucible is designed for smelting titanium and its alloys (CN 101456749 A, 17.06.2009).

The disadvantages of this crucible include its low resistance to the action of molten chromium and rare earth metals (REM), as well as a low operating temperature in the range from 1500 to 1800 ° C.

Known ceramic material crucible for smelting titanium and its alloys, containing barium oxide in an amount of 45 to 70 mass. %, zirconium oxide in an amount from 30 to 50 wt. % and flux in the form of titanium oxide, aluminum oxide or boron oxide in an amount of up to 0.5 wt. %. The crucible manufacturing method includes preliminary sintering of a crucible blank at a temperature of 800 to 1200 ° C for 4 to 10 h, sintering at a temperature of 900 to 1300 ° C for 8 to 15 h, and subsequent high-temperature sintering at a temperature of up to 1800 ° C with the formation of barium zirconate by the solid-phase transformation mechanism (CN 103922769 A, July 16, 2014).

The disadvantages of the known ceramic material include the low resistance of a crucible made of it to the action of high-temperature reactive alloys based on chromium and rare-earth metals, as well as a low operating temperature at a level not higher than 1800 ° C. The crucible manufacturing method is a long-term multistage process that includes several annealing stages.

The closest analogue of the proposed material is a refractory ceramic crucible material, consisting of zirconium oxide doped with lanthanum oxide, and 10 g of zirconium oxide accounts for 0.2-1.2 g of lanthanum oxide, and the particles of these oxides have different fractions ranging from 0, 01 to 20 microns.

The crucible manufacturing method includes the following stages. First, a suspension is prepared by uniformly mixing zirconium oxide with a particle size of 0.01-20 microns, lanthanum oxide with a particle size of 0.01-20 microns and anhydrous ethanol. The components are taken in the following proportion: 0.2-1.2 g of lanthanum oxide per 10 g of zirconium dioxide, 0.05-0.2 l of anhydrous ethanol per 100 g of zirconium dioxide. Then the suspension is dried in an oven at a temperature of 60-100 ° C for 8-15 hours, the resulting workpiece is sintered by hot pressing at a pressure of 10-20 MPa, a heating rate of 5-10 ° C / min, a temperature of 1400-1650 ° C within 5-10 hours. To prepare a mixture of powders of oxide ceramics, several fractions of zirconium oxide powder are used: from 0.01 to 0.5 μm, from 0.5 to 2 μm, from 2 to 6 μm and from 6 to 20 μm.

The crucible can be used for vacuum induction smelting of reactive metals such as titanium, niobium, hafnium, at a temperature of 1800 ° C, with a controlled content of gas impurities (oxygen, nitrogen, hydrogen in an amount not exceeding 5 ppm, 5 ppm and 1 ppm, respectively) in the alloy (CN 105819853 A, abstract, page 4 of the description, lines 0016-0017, 0019, 03.11.2016).

The disadvantages of the prototype method include the high density of the obtained ceramic material due to the use of fine fractions (up to 20 microns) of particles of zirconium oxide and lanthanum oxide, which in the process of hot pressing reaches 99% of the theoretical density, in connection with which a high-strength material is formed with a fine-grained structure. The absence of open and closed porosity worsens the resistance of the material to thermal changes (heating-cooling cycles) when heated to temperatures of the order of 2000 ° C, since a high-density material is less resistant to stresses arising from thermal expansion. In addition, the material of the crucible based on zirconium oxide, due to the insufficient chemical inertness of the latter, is not resistant to the physicochemical effects of high-temperature reactive alloys of the chromium-molybdenum-iron system, and alloys containing zirconium.

The technical objective of the present invention is the development of a ceramic refractory material based on REM and zirconium oxides and a method for manufacturing a crucible from it, suitable for smelting high-temperature reactive alloys containing zirconium and alloys of the chromium-molybdenum-iron system.

The technical result is to ensure the physicochemical resistance of the crucible material to the effects of melts of high-temperature reactive alloys containing zirconium and alloys of the chromium-molybdenum-iron system at temperatures up to 1820 and 2050 ° C, respectively, ensuring a high resource of the crucible due to the resistance of its material to 15-20 thermal shifts (heating cycles to the melting temperature and subsequent cooling to room temperature), as well as increasing the accuracy of crucible molding and, as a consequence, increasing the utilization rate of the crucible material.

The technical result is achieved due to the fact that the proposed ceramic refractory material of the crucible containing rare earth metal oxide and zirconium oxide, while it contains oxides of at least two rare earth metals, one of which is yttrium, and at least one other is selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium, with the following ratio of components, wt. %:

zirconium oxide 14.8-45

at least one oxide of a rare earth metal selected from the group:

gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium 6.8-8.54 yttrium oxide rest,

at the same time, it contains yttrium oxide in the form of particles of different fractions, the smaller of which is up to 0.5 microns, and the larger one is at least 20 microns, an oxide of at least one rare earth metal selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium - in the form of particles of fraction up to 10.0 microns and zirconium oxide - in the form of particles of different fractions, the smaller of which is up to 10.0 microns, and the larger one is at least 600 microns.

To achieve the technical result, a method for manufacturing a crucible from the specified ceramic refractory material is also proposed, including mixing components, including particles of oxides of different fractions, drying the resulting mixture with the formation of a crucible blank and high-temperature sintering of the blank, while mixing the components is carried out in three stages, at the first of which a sintering additive is obtained by dry mixing 5-20 mass. % of zirconium oxide particles with a fraction of up to 10 microns, 35-55 wt. % of yttrium oxide particles with a fraction of up to 0.5 microns and 40-45 wt. % of rare earth metal oxide particles selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium, fraction up to 10 microns, at the second stage 17-20.5 wt. % of the sintering additive is dry mixed with 11-44 mass. %) of zirconium oxide powder with a fraction of at least 600 microns and 36-70 wt. % yttrium oxide fraction of at least 20 microns, obtaining a dry ceramic mixture, at the third stage, the specified mixture is mixed with a suspension containing particles of yttrium oxide in an amount from 8.5 to 14 wt. %, in a ratio of 0.01-0.05 liters of suspension per 0.1-0.32 kg of ceramic mixture, obtaining a plastic mass, then the specified mass is molded and dried for 12-25 hours, obtaining a crucible blank, which is subsequently subjected to high-temperature sintering at a temperature from 1650 to 1750 ° C for 3-5 hours.

Also proposed is a crucible made by the described method.

In contrast to the prototype crucible material, which is based on zirconium oxide, in the proposed material, the basis is yttrium oxide, which is more resistant to the physicochemical effects of high-temperature reactive melts containing zirconium and melts of the Cr-Mo-Fe system.

In the proposed invention, the mixing of the components for the manufacture of the crucible is carried out in three stages. In the first two stages, the oxide powders are dry mixed using alundum balls, taken in a ratio of 0.5 to 1.0 part of the oxide mixture to 1.5 to 2 parts of the balls for 1 to 3 hours. At the third stage, a suspension of yttrium oxide is added to the resulting mixture.

At the first stage, by mixing the components dry, a sintering additive is prepared, which consists of a mixture of powders of zirconium oxide fractions up to 10 microns, yttrium oxide fractions up to 0.5 microns and an oxide of at least one more rare earth material selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium, fractions up to 10 microns.

The presence of yttrium oxide particles of the specified fraction in the sintering additive helps to stabilize the crystal lattice of zirconium oxide particles of the fraction up to 10 μm, excluding the occurrence of polymorphic transformations in the temperature range above 1000 ° C. In turn, polymorphic transformations of material particles can cause its destruction.

The presence in the composition of the sintering additive of a fine powder of at least one REM oxide selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium, leads in the process of further high-temperature sintering to the formation of thermo- and chemically resistant zirconates of the formula P3M ₂ Zr ₂ O ₇ , where REM is gadolinium, neodymium, samarium, lanthanum, praseodymium or dysprosium.

REM zirconate is a refractory material with micropores, which increases the resistance of the crucible to thermal changes. The presence of rare-earth zirconate formed in the pores between the coarse fractions of zirconium oxide and yttrium oxide particles due to the reaction of solid-phase formation increases the adhesion of these particles.

The stated ranges of concentrations of zirconium oxide and additional oxide (s) of rare-earth metals contribute to the formation of a sufficient amount of zirconate to ensure the best resistance of the material to thermal changes and its strength. At the same time, an excess of the amount of zirconium oxide leads to a significant decrease in the material's resistance to reactive alloys.

By mixing the components of the sintering additives dry using alundum balls, additional grinding of particles of oxide ceramics is achieved, which increases the efficiency of further molding and sintering of the ceramic material.

At the second stage, dry mixing of the sintering additive with zirconium oxide powder of a fraction of at least 600 μm and yttrium oxide of a fraction of at least 20 μm is carried out, obtaining a ceramic mixture of oxide ceramics. Mixing of the components of the oxide ceramic charge is also carried out dry using alundum balls, taken in a ratio of 1: 1, for 1 to 1.5 hours, achieving a uniform distribution of the components of the charge.

The use of large fractions of particles of zirconium oxide and yttrium oxide of the specified size in the process of molding and sintering provides a porous material, which increases its resistance to thermal changes.

At the third stage, a suspension containing 8.5-14.0 wt. % of yttrium oxide, in a ratio of 0.01-0.05 liters of suspension per 0.1-0.32 kg of dry ceramic mixture, until a plastic mass is formed, from which a workpiece of the required configuration and shape is formed using a shaping tooling.

The presence of finely dispersed yttrium oxide in the dry charge (due to the use of a sintering additive) and also in the suspension mixed with it contributes to the formation of a homogeneous bulk-hardening dispersion system, which ensures the best plastic properties of the crucible blank, allows the blank to be given the required configuration and shape and, accordingly, to increase the material utilization rate crucible.

The use of a suspension of yttrium oxide is due to the fact that yttrium oxide is the main component of the manufactured material.

The presence of zirconium oxide in the suspension can lead to an excessive content of the latter in the composition of the final material and thus reduce its resistance to reactive alloys.

A suspension with a content of yttrium oxide particles exceeding 14 wt. % is not stable, and with a content less than 8.5 wt. %, the homogeneity of the plastic mass formed from a mixture of dry charge and suspension decreases.

The suspension may contain various surfactants and stabilizers. Suspensions such as Nyacol (USA), a suspension from ShenZhen Cerametek Materials Co., Ltd. can be used as a suspension. (PRC) and others.

The resulting workpiece is recommended to be kept in the shaping tooling for 0.25-0.5 hours at room temperature - for the most accurate shaping, after which the internal elements are removed, for example, shaping rods that can interfere with shrinkage processes, and natural drying is carried out for 12 -25 hours.

Then the workpiece is removed from the forming tooling and sintered at a temperature of 1650-1750 ° C for 3-5 hours - depending on the composition of the material and the massiveness of the workpiece. The indicated time interval is necessary for the most complete solid-phase physicochemical interaction of the components of the ceramic material with the formation of REM zirconates.

Examples of implementation.

For the manufacture of a refractory ceramic crucible based on yttrium oxide, a sintering additive was first prepared. To do this, dry mixing of zirconium oxide and REM oxides with alundum balls in a ratio of 0.5 to 1.0 parts of a mixture of oxides to 1.5 to 2.0 parts of balls for 1 to 3 hours was performed on a roller mill. The composition of the sintering additive and the size of the used oxide particles are shown in Table 1.

Next, the resulting sintering additive was mixed with powders of yttrium oxide and coarse zirconium oxide to obtain a mixture of oxide ceramics. The ratio of the components of the mixture of oxide ceramics and sintering additives, as well as the size of the used oxide particles are shown in Table 2.

At the third stage of mixing, a suspension based on yttrium oxide was introduced into a dry mixture of zirconium oxides and rare-earth metals. The content of yttrium oxide in the suspension and the ratio of the components of the resulting plastic mass are shown in Table 3.

The final composition of the ceramic material is shown in Table 4.

The resulting plastic mass was molded to give the workpiece the required crucible shape using a shaping tooling (mold), dried and sintered. Forming, drying and sintering modes are shown in Table 5.

The high homogeneity and plasticity of the ceramic mass made it possible to form a crucible blank with high geometry accuracy and, accordingly, with minimal production waste, which significantly increases the utilization rate of the crucible material and provides a high yield.

Then, the obtained crucibles were tested for resistance to the action of melts of high-temperature reactive alloys containing zirconium and alloys of the chromium-molybdenum-iron system at temperatures up to 1820 and 2050 ° C, respectively, and for resistance to thermal changes. After each melting, the crucibles were naturally cooled to room temperature, after which a new melting was carried out in them.

The modes of melting and the values of resistance of crucibles to thermal changes are given in Table 6.

As can be seen from the data obtained, the proposed crucibles withstand 15-20 melting cycles of these reactive alloys with cooling to room temperature after each melting. After the specified number of cycles, traces of erosion with a depth of 4-5 mm were observed on the working surface of the crucibles.

Claims (8)

1. Ceramic crucible refractory material containing rare earth metal oxide and zirconium oxide, characterized in that it contains oxides of at least two rare earth metals, one of which is yttrium, and at least one other is selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium, with the following ratio of components, wt. %: zirconium oxide 14.8-45 at least one oxide of a rare earth metal selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium 6.8-8.54 yttrium oxide rest, while it contains yttrium oxide in the form of particles of two different fractions, the smaller of which is up to 0.5 microns, and the larger one is from 20 to 250 microns, an oxide of at least one rare earth metal selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium - in the form of particles of fraction up to 10.0 microns and zirconium oxide - in the form of particles of two different fractions, the smaller of which is up to 10.0 microns, and the larger - from 600 to 710 microns. 2. A method for manufacturing a crucible from a ceramic refractory material according to claim 1, including mixing components, including particles of oxides of different fractions, drying the resulting mixture to form a crucible blank and high-temperature sintering of the blank, characterized in that the components are mixed in three stages, on the first of which a sintering additive is obtained by dry mixing of 5-20 mass. % of zirconium oxide particles with a fraction of up to 10 microns, 35-55 wt. % of yttrium oxide particles with a fraction of up to 0.5 microns and 40-45 wt. % of rare earth metal oxide particles selected from the group: gadolinium, neodymium, samarium, lanthanum, praseodymium and dysprosium, fraction up to 10 microns, at the second stage 17-20.5 wt. % of the sintering additive is dry mixed with 11-44 mass. % of zirconium oxide powder with a fraction of at least 600 microns and 36-70 wt. % yttrium oxide fraction of at least 20 microns, obtaining a dry ceramic mixture, at the third stage, the specified mixture is mixed with a suspension of the Nyacol brand or with a suspension of the ShenZhen Cerametek Materials Co Ltd., containing particles of yttrium oxide in an amount of 8.5 to 14 wt. %, in a ratio of 0.01-0.05 liters of suspension per 0.1-0.32 kg of ceramic mixture, obtaining a plastic mass, then the specified mass is molded and dried for 12-25 hours, obtaining a crucible blank, which is subsequently subjected to high-temperature sintering at a temperature from 1650 to 1750 ° C for 3-5 hours. 3. A method according to claim 2, characterized in that the plastic mass is formed within 0.25-0.5 hours. 4. Crucible, characterized in that it is a sintered ceramic refractory product made by the method of claim 2.