RU2713541C1 - Method of hardening workpieces from corundum-quartz ceramics - Google Patents

Abstract

FIELD: ceramics.

SUBSTANCE: invention relates to industrial production of corundum ceramics, modified with inorganic binding agents, and can be used, mainly, for production of large-size ceramic articles operating under high temperatures. Method of hardening articles from corundum-quartz ceramics involves preparing an aqueous corundum-quartz suspension, where the amount of quartz glass is 0.1–0.3 wt % to total weight of system "electrocorundum-quartz glass", and suspension stabilization. Hardening of the workpieces is carried out using an aluminum-chromium-phosphate binder having the following composition, wt %: 9–13 Al₂O₃; 31–38 P₂O₅; 4–7 Cr₂O₃; up to 1.5 CrO₃; 40.5–56 H₂O in amount of 2–7 % of the weight of the initial suspension, which is added to the suspension at the end of the stabilization step. Then, ceramic blanks are formed by a method of slip casting in gypsum molds with further thermal treatment. Heat treatment is carried out according to a mode which includes heating in range of 20–200 °C at a rate of not more than 1.5 °C/min; in range of 200–300 °C – not more than 2 °C/min; in range of 300–700 °C – not more than 3 °C/min. Finally, workpieces are held at 700 °C for 1 hour.

EFFECT: technical result consists in ensuring bending strength of articles at least 300 MPa without using high temperature roasting while maintaining fire resistance, strength and heat resistance of material.

1 cl, 3 ex, 1 tbl

Description

The invention relates to the industrial production of technical ceramics, namely, the technology of corundum ceramics obtained by slip casting, modified with inorganic binders, which increase the strength of the workpieces. The invention can be used for the manufacture of ceramic products that operate at high temperatures when in contact with metal, salt, silicate, glass melts, a gas medium, in particular, in the manufacture of refractories for the glass industry and metallurgy: crucibles, ladles, mixers, nozzles, dispensers, steel-pouring glasses, funnels for casting metals and alloys, plungers, shafts, heat-protective products of various installations, furnaces, etc.

The relevance of the invention is most manifested in the formation of large-sized ceramic products, since the energy-intensive technological stage of their high-temperature processing is excluded in the proposed corundum ceramic technology.

A known method for producing products from quartz ceramics for various purposes, including the preparation of an aqueous suspension of quartz glass, slip casting ceramic billets of the desired configuration and size in plaster molds, drying and firing. Moreover, an increase in compressive strength of up to 200 MPa for products made of quartz ceramics is achieved by sintering castings at temperatures of 1200–1300 ° C (Walton JD, Poulos NE Slip-cast fused silica. Technical documentary report No. ML-TDR-64-195 - Atlanta, 1964. - 131 p. Harris JN, Welsh EA Fused silica design manual. Volume 1. Technical report A-1403. - Atlanta, 1973. - 140 p.). The disadvantages of the method are the increased energy consumption for high-temperature firing and cristobalitization of quartz glass particles, which dramatically impairs the strength, heat resistance, long-term high temperature strength (service life) and other properties of the material.

There is also known a method of manufacturing quartz ceramics according to a. from. USSR No. 804607, IPC С04В35 / 14, publ. 02/15/1979, and close to it by a. from. USSR No. 771052, IPC С04В 15/06, publ. 10/15/1978, including wet grinding of quartz glass to obtain an aqueous slurry, stabilization of the suspension, molding of products by slip casting, drying and curing of castings in aqueous solutions of liquid glass or soda with a density of 1.002-1.07 g / cm ³ for 24 hours In order to harden the product is subjected to autoclaving at a temperature of 110-220 ° C for 1-10 hours. Bending strength of products reaches 55-72 MPa. The disadvantage of this method is a significant deterioration in heat resistance and heat resistance due to the presence in the structure of the material of silicates of alkaline elements (in particular, Na), as well as low resistance to certain metal melts. In addition, undesirable crystallization processes are amplified, which reduces the operating temperature of such products. Another disadvantage is the use of the apparatus operating under high pressure, and the duration of the autoclave treatment. All this narrows the scope of the material.

In the invention according to the patent of the Russian Federation No. 2525892, IPC С04В35 / 14 publ. 08/20/2014, the method for producing quartz ceramics relates to the technology for producing modified ceramic materials based on quartz glass. The method includes the production of a slip from a quartz glass battle, the formation of a crude billet by casting in plaster molds, the impregnation of a raw billet with a liquid impregnating solution, drying of the impregnated billet of quartz ceramic and subsequent heat treatment. The disadvantages of the method are the use of an organo-organic substance and an organic solvent, which increases the cost of the product and requires organization special conditions for safe production, and low involvement in the formation of bonds between particles dehydrated sections of quartz glass grains, in comparison with the methods described above, causes a relatively low bending strength even after firing (not more than 32 MPa).

It is also known that to increase refractoriness and high-temperature strength, ceramic materials based on quartz glass with Al ₂ O ₃ additives have been developed (Pivinsky Yu.E., Timoshenko K.V. Rheotechnological properties of mixed suspensions in the SiO ₂ -Al ₂ O _{3 system} and some properties of materials based on them // Refractories and technical ceramics. - 2000. - No. 7 - P. 18-23; 2001. - No. 9 - P. 42-46). Tangible results were obtained only with the introduction of more than 20% Al ₂ O ₃ . However, such materials have high porosity, low heat resistance, and poor dielectric characteristics. The deterioration of the physical and technical properties of the materials is associated with unsatisfactory rheological parameters of the combined slips and increased crystallization during firing.

The hardening technology of quartz ceramics described in the patent of the Russian Federation 2458022, IPC S 04B 35/14, publ. 08/10/2012, includes the manufacture of a semi-finished product and its impregnation with an aqueous solution of aluminum salt of Al (NO ₃ ) ₃ · 9H ₂ O, drying and pyrolysis at a temperature of 400-600 ° C. The declared maximum strength of the products in bending to firing 65 MPa, after medium temperature firing 110 MPa. The disadvantage of this method is that the Al ₂ O ₃ nanoparticles introduced into the joint zones of the ceramic only fill part of the voids of the material and slightly increase its density, while at the same time practically not contributing to the additional binding of siliceous particles into a single framework.

Closest to the mechanism of action to the proposed is the method described in the patent of the Russian Federation No. 2667969, IPC С04В35 / 14, publ. 09/25/2018, which is adopted as a prototype. In the prototype, the method for producing hardened quartz ceramics consists in the method comprising preparing an aqueous suspension of quartz glass, stabilizing the suspension, molding ceramic preforms by slip casting in gypsum molds, and hardening the preforms of products in which hardening is carried out using aluminoborphosphate binder having a composition, wt. . %: 7.5-11 - Al ₂ O ₃ ; 33-36 - P ₂ O ₅ ; 0-5 - B ₂ O ₃ ; 53-59.5 - H ₂ O, in which the product blanks are impregnated for 1 h at a temperature of 50 ° C, or which is added to the quartz glass suspension at the end of the stabilization stage in an amount of 1-5% by weight of the initial suspension, followed by heat treatment product blanks according to a regime that includes heating in the range of 20-100 ° C with a heating rate of not more than 2 ° C / min, then heating in the range of 100-200 ° C - not more than 1.5 ° C / min, and heating in the range of 200 -3 50 ° С - not more than 2 ° С / min, and at the end - holding at 350 ° С for 1 h. The disadvantages of the method are relatively low so far STUDIO strength of finished products, as well as low operating temperature refractories.

The objective of the invention is to increase the high temperature strength of corundum-quartz ceramics without deterioration in a wide temperature range of the remaining properties: low coefficient of thermal expansion and refractoriness without using the stage of high-temperature firing.

The problem is solved by obtaining corundum-quartz water slurry, where the quartz glass is mass, hours: 0.1-0.3 to the total mass of the corundum-quartz glass system and due to the introduction of a binder solution in the amount of 2-7 wt. . % having a composition, wt. %: 9-13 - Al ₂ O ₃ ; 31-38 - P ₂ O ₅ ; 4-7 - Cr ₂ O ₃ ; up to 1.5 - CrO ₃ ; 40.5-56 - H ₂ O; with subsequent heat treatment according to the regime: heating in the range of 20-200 ° C with a heating rate of not more than 1.5 ° C / min, in the range of 200-300 ° C - not more than 2 ° C / min, 300-700 ° C - not more than 3 ° C / min, holding at 700 ° C for 1 hour.

The technical result of the invention is to ensure the strength of the billets of products at a bend of at least 300 MPa without the use of high-temperature firing while maintaining fire resistance, and the strength of the material in operating conditions at high temperatures. These effects are caused by the similarity of aluminum phosphate with alumina in structure and properties, mutual inhibitory effect on crystallization processes, activation of sintering and hardening due to the presence of phosphorus and chromium in the composition, and more complete involvement of the grain surface in the formation of bonds.

The essence of the proposed method of hardening products from corundum-quartz ceramics is that the method includes the preparation of corundum-quartz water suspension, where the ratio of quartz glass is mass, h .: 0.1-0.3 with respect to the corundum-quartz glass system, stabilization of the suspension, the molding of ceramic billets by slip casting in gypsum molds and hardening of the product blanks, in which hardening is carried out using an aluminochromophosphate binder having a composition, wt. %: 9-13 - Al ₂ O ₃ ; 31-38 - P ₂ O ₅ ; 4-7 - Cr2O3; up to 1.5 - CrO3 40.5-56 - H ₂ O, which is added to the corundum-quartz suspension at the end of the stabilization stage in an amount of 2-7% by weight of the initial suspension, followed by heat treatment of the product blanks according to a regime that includes heating in the range 20-200 ° C with a heating rate of not more than 1.5 ° C / min, in the range 200-300 ° C - not more than 2 ° C / min, 300-700 ° C - not more than 3 ° C / min, at the end the process is holding the workpieces at 700 ° C for 1 hour.

The method of hardening products from corundum-quartz ceramics in the corundum-quartz glass system is as follows.

In a ball mill with a capacity of 200 l load electrocorundum fractions of 0-1.0 mm, quartz glass of a fraction of 0.1-0.5 mm, uralitic grinding media and distilled water in a mass ratio of 5.1-6.9: 0.8-2 2: 14.4-15.4: 1.3-1.4. The grinding is carried out for 10-18 hours. In this case, the suspension at the end of the grinding should have a moisture content of 12-15 wt. %, density 2590-2920 kg / m ³ and fractional composition, vol. %: 7-12 for particles with diameters in the range of 63-120 microns; 40-60 for particles with diameters in the range of 5-63 microns; 35-50 for particles with diameters less than 5 microns. After removing the suspension from the mill, it is stabilized by stirring for 20-30 hours. Then the binder is added to the suspension and used for molding products by casting into plaster molds. The density of the raw workpiece is in the range of 2720-3240 kg / m ³ . Then carry out the drying of the product blanks at room conditions for 24-48 hours, depending on the size or drying of the products.

Hardening using a solution of aluminochromophosphate binder having a composition, wt. %: 9-13 - Al ₂ O ₃ ; 31-38 - P ₂ O ₅ ; 4-7 - Cr2O3; up to 1.5 - CrO3 40.5-56 - H ₂ O, can be carried out in two ways.

1) By adding to the suspension at the end of the stabilization step a solution of alumino-chromophosphate binder in an amount of 2-7 wt. % by weight of the suspension with stirring for 1 h

2) Exposure for 1 h of pre-dried workpieces of products in a solution of aluminum-chromophosphate binder heated to 50 ° C.

In all cases of hardening the workpiece blank, the last technological stage is heat treatment in electric furnaces according to the regime: heating in the range of 20-200 ° C with a heating rate of not more than 1.5 ° C / min, in the range of 200-300 ° C - not more than 2 ° C / min, 300-700 ° C - not more than 3 ° C / min, holding at 700 ° C for 1 hour.

The specific method and technological parameters of hardening using aluminochromophosphate binder are selected depending on the size and complexity of the shape of the product. However, the optimal technological parameters are within the limits indicated above.

Examples of the method.

Example 1

In a ball mill with a capacity of 200 l load electrocorundum fractions of 0-1.0 mm, silica glass of a fraction of 0.1-0.5 mm, uralitic grinding media and distilled water in a mass ratio of 6.9: 0.8: 15: 1.4 . The grinding is carried out for 15 hours. The suspension at the end of the grinding had a moisture content of 14.5 wt. %, density 2890 kg / m ³ and fractional composition, vol. %: 7.1 for particles with diameters in the range of 63-120 microns; 52.9 for particles with diameters in the range of 5-63 microns; 40.0 for particles with diameters less than 5 microns. After removing the suspension from the mill, stabilization was carried out by stirring for 20 hours in a mill without grinding media. Then, an aluminochromophosphate binder solution having the composition, wt. %: 12 - Al ₂ O ₃ ; 33 - P ₂ O ₅ ; 6.5 - Cr2O3; 1.2 - CrO3; 47.3 - H ₂ O, in an amount of 5% by weight of the suspension. Next, mixing was carried out for 1 h, followed by molding of the products (test plates with dimensions, mm: 200 × 100 × 20) by casting into plaster molds. The density of the crude billet was 3170 kg / m ³ . Then, the blanks of the products were dried up at room temperature for 48 hours and the heat treatment was carried out according to the regime: heating in the range of 20-200 ° C with a heating rate of not more than 1.5 ° C / min, in the range of 200-300 ° C - not more than 2 ° C / min, 300-700 ° C - not more than 3 ° C / min, holding at 700 ° C for 1 hour.

Shrinkage after heat treatment was 0.6-0.8%, porosity 5.0-7.4%. The bending strength was 327 MPa. Refractoriness after firing products amounted to 1720 ° C.

Example 2

In a ball mill with a capacity of 200 l load electrocorundum fractions of 0-1.0 mm, quartz glass fractions of 0.1-0.5 mm, uralitic grinding media and distilled water in a mass ratio of 5.1: 1.7: 15: 1.4 . The grinding is carried out for 17 hours. The suspension at the end of the grinding had a moisture content of 13.7 wt. %, density 2780 kg / m ³ and fractional composition, vol. %: 7.8 for particles with diameters in the range of 63-120 microns; 47.2 for particles with diameters in the range of 5-63 microns; 45 for particles with diameters less than 5 microns. After removing the suspension from the mill, stabilization was carried out by stirring for 20 hours in a mill without grinding media. Then, an aluminochromophosphate binder solution having the composition, wt. %: 10 - Al ₂ O ₃ ; 35 - P ₂ O ₅ ; 5.5 - Cr2O3; 0.9 - CrO3; 48.6 - H ₂ O, in an amount of 6.0% by weight of the suspension. Next, stirring was carried out for 1 h, followed by molding of the products (test plates with dimensions, mm: 200 × 100 × 20) by casting in plaster molds. The density of the raw billet was 2927 kg / m ³ . Then, the blanks of the products were dried up at room temperature for 48 hours and the heat treatment was carried out according to the regime: heating in the range of 20-200 ° C with a heating rate of not more than 1.5 ° C / min, in the range of 200-300 ° C - not more than 2 ° C / min, 300-700 ° C - not more than 3 ° C / min, holding at 700 ° C for 1 hour.

Shrinkage after heat treatment was 0.7-0.9%, porosity 6.2-8.3%. The bending strength was 319 MPa. Refractoriness after firing products amounted to 1690 ° C.

Example 3

In a ball mill with a capacity of 200 l load electrocorundum fractions of 0-1.0 mm, quartz glass fractions of 0.1-0.5 mm, uralite grinding media and distilled water in a mass ratio of 5.1: 2.2: 14.5: 1 , 3. The grinding is carried out for 14 hours. The suspension at the end of the grinding had a moisture content of 13.2 wt. %, density 2685 kg / m ³ and fractional composition, vol. %: 10.4 for particles with diameters in the range of 63-120 microns; 53.9 for particles with diameters in the range of 5-63 microns; 35.7 for particles with diameters less than 5 microns. After removing the suspension from the mill, stabilization was carried out by stirring for 20 hours in a mill without grinding media. Then, an aluminochromophosphate binder solution having the composition, wt. %: 9 - Al ₂ O ₃ ; 38 - P ₂ O ₅ ; 6.5 - Cr2O3; 0.5 - CrO3; 46 - H ₂ O, in an amount of 3.0% by weight of the suspension. Next, mixing was carried out for 1 h, followed by molding of the products (test plates with dimensions, mm: 200 × 100 × 20) by casting into plaster molds. The density of the crude billet was 2883 kg / m ³ . Then, the blanks of the products were dried up at room temperature for 48 hours and the heat treatment was carried out according to the regime: heating in the range of 20-200 ° C with a heating rate of not more than 1.5 ° C / min, in the range of 200-300 ° C - not more than 2 ° C / min, 300-700 ° C - not more than 3 ° C / min, holding at 700 ° C for 1 hour.

Shrinkage after heat treatment was 0.8-0.9%, porosity 6.5-8.7%. The bending strength was 312 MPa. Refractoriness after firing products was 1685 ° C.

The properties of corundum-quartz ceramics, and the distinctive technological parameters of its production, according to the proposed method, in comparison with the prototype, are shown in the table.

Using the proposed method of hardening provides the opportunity to obtain corundum-quartz ceramics and products from it with a bending strength of at least 300 MPa without using the stage of high-temperature firing. Moreover, the properties of corundum-quartz ceramics according to the proposed method are not inferior to other methods of hardening. In addition, the use of aluminochromophosphate binder allows to inhibit the crystallization of quartz glass during the operation of ceramic products at high temperatures. These effects are caused by the similarity of aluminum phosphate with alumina in structure and properties, mutual inhibitory effect on crystallization processes, activation of sintering and hardening due to the presence of phosphorus and chromium in the composition, more complete involvement of the grain surface in the formation of bonds, and thereby increase their refractoriness, and the exclusion of high-temperature firing makes it possible to simplify the manufacture of large-sized products.

Thus, the task of the invention is solved.

Claims (1)

The method of hardening products from corundum-quartz ceramics, including the preparation of an aqueous suspension, stabilization of the suspension, molding of ceramic billets by slip casting in gypsum molds and hardening of the product blanks using a binder, which is added to the suspension at the end of the stabilization stage, followed by heat treatment of the product blanks the fact that in the corundum-quartz aqueous suspension, the mass fraction of quartz glass is 0.1-0.3 with respect to the electrocorundum-quartz glass system, hardening the blanks are produced using aluminochromophosphate binder having the composition, wt. %: 9-13 Al ₂ O ₃ ; 31-38 P ₂ O ₅ ; 4-7 Cr ₂ O ₃ ; up to 1.5 CrO ₃ ; 40.5-56 H ₂ O, and the additive at the end of the stabilization stage is carried out in an amount of 2-7% by weight of the initial suspension, while the subsequent heat treatment is carried out according to a regime that includes heating in the range of 20-200 ° C with a heating rate of not more than 1 , 5 ° C / min, in the range of 200-300 ° C - not more than 2 ° C / min, 300-700 ° C - not more than 3 ° C / min and, at the end, the workpieces are aged at 700 ° C for 1 hour .

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