RU2791757C1 - Method for producing self-shaped high-temperature fiber heat-shielding material and products from it - Google Patents

Abstract

FIELD: high-temperature ceramic materials.

SUBSTANCE: technology for producing high-temperature ceramic materials for heat-shielding and heat-insulating purposes. Method for obtaining a fibrous high-temperature heat-shielding material includes dispersing a refractory fibre in two stages to obtain a homogeneous aqueous semi-finished paste, obtaining a raw workpiece by filling a mould, drying and baking the resulting workpiece. At the second stage of dispersion with a binder, a heat-releasing component is simultaneously introduced. At the same time, the billet baking is carried out using out-of-furnace self-heating of a dry primary billet by thermal initiation of the exothermic reaction of the fuel component in any part of the billet volume due to its local heating to a temperature of 450-650°C with subsequent sintering of the fibres with a binder component and formation of a fibrous high-temperature heat-shielding material in form of a final product.

EFFECT: invention makes it possible to reduce manufacturing costs, improve the manufacturability of the formation and increase the thermal energy efficiency of the final product.

5 cl, 1 tbl, 4 ex

Description

The invention relates to a technology for producing fibrous ceramic materials for heat-shielding and heat-insulating purposes, in particular for the manufacture of products in the form of a single monolithic protective coating, an intermediate layer or a shaped heat-shielding structural element at a separate production plant or "at the place of use" in hot metallurgical shops of non-ferrous and ferrous metallurgy , products and structures of the aerospace, defense and jewelry industries, energy, biotechnology, construction, in the production of composite materials, etc.

Ceramic fibrous materials formed by oxide, quartz or glass-ceramic fibers are good inexpensive thermal insulation for hot parts of various types of industrial installations with operating temperatures up to 1600°C due to low specific gravity, low thermal conductivity, high resistance to thermal shock and high chemical resistance to oxidation. One of the main requirements for products of this class is the uniformity of their thermal properties, which is ensured by the uniform distribution of the fiber in the ceramic matrix and the uniform distribution of the introduced binder. The main way to obtain them is to obtain a suspension of fibers and a binder, molding the original workpiece, drying and firing.

Known (RU 2213074 C1, publ. 27.09.2003) is a method for producing a fibrous material based on quartz fiber, according to which, to obtain a product, the fiber is crushed in the preparation of a water-fiber molding mass by wet grinding in a ball mill to obtain fiber particles with a size of 0.1-500 microns at a fiber concentration of 20-60 wt. %, blank molding followed by drying and firing. The method is applicable to the manufacture of high-density compressive-resistant articles that are not required to provide high thermal insulation properties in combination with low weight and high resistance to vibration loads.

Known (RU 2127712 C1, publ. 20.03.1999) method for producing heat-insulating material by casting and dehydration of a suspension of mullite-silica fiber, 5-25% silicic acid sol with a particle size of 2-8 microns. Two-stage molding of a heat-insulating refractory product is carried out by casting a suspension based on mineral fiber in a mesh form, the inner side and bottom surfaces of which have a profile of the outer surfaces of the product, dehydration, evacuation and subsequent mechanical and heat treatment. At the first stage, the shell of the product is formed, and at the second stage, a less dense inner bulk part of the product.

Known (US 3952083 A, publ. 20.04.1976) a method of obtaining a fibrous heat-insulating material based on silicon oxide fibers, including obtaining a slurry from silicon oxide fibers and a binder containing colloidal silicon oxide, starch and ammonia water, mixing the slurry for 30 minutes in U-shaped blender, molding tiles from slip under pressure of 0.7-1.4 atm, drying the resulting tiles for 18 hours at 150°C and firing at temperatures up to 1315°C. Shrinkage during firing was 25–45 vol. %.

Known (US 4828774 A, publ. 09.05.1989) a method of obtaining a fibrous ceramic material, including the preparation of a ceramic polymer solution containing an alcohol solution of glass-forming oxides (oxides of Si, Al, Ti or Zr) with the addition of Mg or B, mixing high-strength fibers (carbon , silicon oxide, silicon carbide, boron aluminosilicate, etc.) with an alcohol solution in the amount of 0.25-2.5 g per 100 g of alcohol solution, felting the mixture by vacuum filtration, drying and firing the resulting workpiece.

Known (RU 2726800 C1, publ. 15.07.2020) is a method for obtaining a heat-shielding and heat-insulating fibrous ceramic material, including the preparation of a refractory nanofiber gel when it is dispersed in a liquid medium with a binder at a nanofiber concentration of 1-8 wt. %, subsequent preparation of the workpiece by dehydration of the obtained gel of refractory nanofibers to its residual concentration in the gel of 10-20 wt. %, drying and firing the resulting workpiece. As a refractory fiber, mullite-silica or aluminum oxide nanofibers are used, and boric acid or clay is used as a binder in an amount of 3-30 wt. % by weight of dry refractory fiber.

The method disclosed in RU 2358954 C1 (publ. 20.06.2009) for producing fibrous ceramic material was adopted as a prototype. The method includes dispersing a refractory fiber with a binder, obtaining a raw billet by vacuum filtration, drying and firing the resulting billet. The dispersion of the refractory fiber is carried out in two stages: at the first stage, the refractory fiber is dispersed in water at a fiber concentration of 0.5-1.0 wt. % to obtain an aspect ratio of fiber length to diameter l/d=50-130, then part of the water is removed to obtain a suspension concentration of 4-8 wt. % and carry out the second stage of dispersion without changing the aspect ratio of fiber length to diameter with the simultaneous introduction of a binder. The resulting suspension is placed evenly by volume in a mold with vacuum suction, where it is thoroughly mixed and water is removed. Uniform stacking of the fibrous mass with its simultaneous mixing before vacuum suction contributes to obtaining an evenly dense isotropic material structure in which the fibers are not arranged in layers parallel to the filter plane, but are mixed in all planes. The uniform isotropic structure of the resulting material provides the necessary strength properties and helps reduce thermal conductivity, while maintaining a low specific gravity of the material. Basalt, quartz, silica, mullite-silica, aluminosilicate, alumina and other oxide-based fibers are used as refractory fibers. As a binder, boron, silica sol, salt solutions are used, which form refractory oxides during decomposition, introduced in the form of alcohol or water emulsions or in the form of a powder.

The disadvantage of all the methods presented above is the fundamental need to carry out the molding of the product, its drying and firing on specialized equipment that is not associated with a specific place of end use. At the same time, in the manufacture of the final heat-insulating heat-shielding structure, there is a fundamental need for additional work on the machining of each individual element, as well as on articulating and fastening them together to achieve tightness and the required geometry of the final product “at the place of use”, which leads to the formation joints and local inhomogeneities of the material, reduces its integral thermal characteristics and overall energy efficiency during operation.

DISCLOSURE OF THE INVENTION

The objective of the claimed invention is to develop a simple and inexpensive method for obtaining a fibrous ceramic material with the required geometric characteristics, low thermal conductivity, low specific gravity, a high degree of uniformity, providing isotropic thermal and mechanical properties of the fibrous ceramic material directly "at the place of use".

The technical result of the invention is to increase the thermal and physical-mechanical characteristics of the fibrous ceramic material for the set of forming a single heat-shielding heat-insulating layer in accordance with the design geometric requirements of the final product without joints and joints.

The specified technical result is achieved due to the fact that the method of obtaining a heat-shielding and heat-insulating fibrous ceramic material includes the manufacture of a semi-finished paste from a refractory fiber (nanofiber) by dispersing the fiber in water at a fiber concentration of 1-15 wt. % on a high-speed mixer to reduce the fiber elongation index and obtain a homogeneous primary pulp, dehydration of the primary fiber pulp to increase the fiber concentration to a level of 15-22 wt. %, adding a binder and a fuel component to the secondary pulp and mixing the secondary pulp with additives on a low-speed mixer without changing the fiber elongation index to obtain a uniform distribution of fibers, a binder and a fuel component. From the obtained paste-semi-finished product, a raw primary billet is formed by filling a mold, filtering on a suction filter, or applying to protected surfaces by plastering. Next, the raw primary workpiece is dried to obtain a dry primary workpiece. On a dry primary billet, a local thermal initiation of the exothermic reaction of the fuel component is performed. The exothermic reaction of the heat-releasing component leads to self-heating of the dry primary billet in a volume limited by the region of local thermal initiation and provides in this volume the initial sintering of the fibers by the binder component with the formation of a heat-shielding material with a primary complex of thermophysical characteristics at the level of 95-100%, and mechanical - at the level 50 - 90% of the final. The energy effect of self-heating of a dry primary workpiece is sufficient to carry out spontaneous thermal initiation of an exothermic reaction in the adjacent volumes of the workpiece and the formation of an undamped exothermic reaction front propagating outward from the area of local thermal initiation in a chain reaction mode. The undamped front of the exothermic reaction over time bypasses the entire volume of the dry primary billet, forming in it the primary heat-shielding material. Further, during the use of the material for its intended purpose, in the process of high-temperature heating, the material reaches its maximum characteristics. When using the material as a lining for heating equipment, if necessary, regular heating and operation of equipment with a newly formed primary heat-shielding layer in thermal modes with heating up to 900°C are carried out. After a certain operating time, depending on the volume and mass of the primary heat-shielding material, the characteristics of the latter reach their final values, and the equipment from that moment can operate in all planned modes with high energy efficiency. The basis of the material is ceramic refractory fibers, whiskers or nanofibers, such as boron, carbon, silicon carbide, basalt, quartz, silica, mullite-silica, aluminosilicate, alumina, based on hafnium and zirconium oxides. As a binder, boron, boron-containing materials or clay are used in the amount of 3-30 wt. % by weight of dry refractory fiber, and materials such as titanium, magnesium, zirconium, carbon, boron are used as a heat-releasing component, in an amount of 3-30 wt. % by weight of dry refractory fiber.

Example 1

For the manufacture of a rectangular slab of high-temperature heat-shielding material with a size of 30×30×4 cm, take 1500 g of mullite-silica fiber, disperse it in water at a concentration of 9 wt. % for 30 min using a paddle mixer at a speed of 600 rpm, then filter the water on a sieve to achieve a fiber concentration in the pulp of 17 wt. %, 60 g of amorphous boron powder (binder component) and 150 g of magnesium powder (heat-releasing component) are added to the pulp and mixed at a speed of 100 rpm for 5 minutes. The resulting homogeneous mass is formed by vacuum filtration on a laboratory suction filter with a filter element of square section 30×30 cm to obtain a wet rectangular billet. The resulting workpiece is dried at a temperature of 200°C until the weight loss stops. The dry billet is locally heated by a gas burner to a temperature of 450-650°C to initiate the oxidation of the fuel component, after which the front of the exothermic reaction diverges from the area of local thermal initiation in all directions over the volume of the dry billet, causing its self-heating, firing and the formation of a ceramic bond from the binder element . After cooling down, the plate made of heat-shielding material is ready for use.

Example 2

For the manufacture of a round plate of high-temperature heat-shielding material with a diameter of 22 cm and a thickness of 2 cm, take 450 g of alumina fiber, disperse it in water at a concentration of 12 wt. % for 20 min using a paddle mixer at a speed of 600 rpm, then the water is filtered on a sieve until the fiber concentration in the pulp is 21 wt. %, 90 g of clay powder (binding component) and 60 g of titanium powder (heat-releasing component) are added to the pulp and mixed at a speed of 100 rpm for 5 minutes. The resulting homogeneous mass is poured into a mold with a diameter of 22 cm and dried at a temperature of 200°C until the weight loss stops. The dry billet is removed from the mold and locally heated by a gas burner to a temperature of 450-650°C to initiate an exothermic oxidation reaction of the fuel component. The front of the exothermic reaction diverges over the volume of the dry workpiece from the area of local thermal initiation in all directions, causing its self-heating, firing and the formation of a ceramic bond from the binder. After cooling, the cylindrical plate of heat-shielding material is ready for use.

Example 3

For the manufacture of a heat-shielding coating directly "at the place of application" on the concrete bed of the trough for the flow of aluminum melt (coating thickness 3 cm, area - 2 m ² ), 24000 g of mullite-silica fiber is taken, it is dispersed in water at a concentration of 9 wt. % for 60 min using a paddle mixer at a speed of 600 rpm, then filter the water on a sieve to achieve a fiber concentration in the pulp of 17 wt. %, 2400 g of amorphous boron powder (a binder and heat-releasing component) is added to the pulp and mixed at a speed of 100 rpm for 10, applied with a spatula on the concrete bed of the gutter. The resulting workpiece is dried in natural conditions for two days. The dry billet is locally heated by a gas burner to a temperature of 450-650°C to initiate an exothermic oxidation reaction of the fuel component, after which the front of the exothermic oxidation reaction of the fuel component diverges from the region of local thermal initiation over the volume of the dry billet, causing its self-heating, firing and formation of a ceramic bond from connecting element. After cooling, the coating of heat-shielding material in the form of a trough for the flow of aluminum melt is ready for use.

Example 4 (prototype).

According to the prototype, it is impossible to carry out the process of self-formation of high-temperature heat-shielding material.

Samples for tensile testing were cut from the obtained products from self-forming high-temperature heat-shielding material both in the state after self-heating and after additional annealing. Mechanical properties are given in the table.

Table Mechanical properties of samples of heat-shielding material Example Density, g / cm ³ Strength, kgf / cm ² After self-heating After additional annealing 1 0.41 2.1 2.6 2 0.55 1.4 1.5 3 0.42 3.8 4.1 4 - -

The table shows that the materials obtained by the proposed method have sufficient technological strength to be used as a heat-shielding material. With additional heating, the strength increases.

Thus, the fibrous ceramic material made according to the proposed method has a low specific gravity, low thermal conductivity and high mechanical strength. The method, being out-of-furnace, does not require complex equipment and a long technological cycle. The material is inexpensive, meeting the requirements for its use as a reusable heat-shielding and heat-insulating material with a working temperature of up to 1300 ° C, in particular for the manufacture of facing tiles for furnaces, mold glasses and chutes in hot aluminum casting shops.

The invention has been described above with reference to a specific embodiment. For specialists, other embodiments of the invention may be obvious, without changing its essence, as it is disclosed in the present description.

Accordingly, the invention is to be considered limited in scope by the following claims only.

Claims (5)

1. A method for obtaining a fibrous high-temperature heat-shielding material, including dispersion of a refractory fiber in two stages: at the first stage, the refractory fiber is dispersed in water on a high-speed mixer to reduce the elongation index of the fibers and obtain a homogeneous primary pulp, then part of the water is removed and the second stage of dispersion is carried out without change elongation index of the fibers with the introduction of a binder to obtain a homogeneous aqueous semi-finished paste, obtaining a raw workpiece by filling the mold, drying and firing the resulting workpiece, characterized in that the concentration of the fiber in the first stage of dispersion is 1-9 wt. %, after removing water, the fiber concentration is increased to the level of 15-18 wt. %, at the second stage of dispersion with a binder, a heat-releasing component is simultaneously introduced, the resulting homogeneous semi-finished paste is formed by filtration on a suction filter or applied to the protected surfaces, while the workpiece is fired by out-of-furnace self-heating of a dry primary workpiece by thermal initiation of the exothermic reaction of the heat-releasing component in any part workpiece volume due to its local heating to a temperature of 450-650°C, followed by sintering of the fibers with a binder component and the formation of a fibrous high-temperature heat-shielding material in the form of a final product. 2. The method according to claim 1, characterized in that at least one of the following types of ceramic refractory fibers, whiskers or nanofibers is used as the basis of a fibrous high-temperature heat-shielding material: boron, carbon, silicon carbide, basalt, quartz, silica, mullite-silica, aluminosilicate, alumina, based on hafnium and zirconium oxides. 3. The method according to p. 1, characterized in that at least one of the following materials is used as a binder: boron, boron-containing materials, clay in an amount of 3-30 wt. % by weight of dry refractory fiber. 4. The method according to p. 1, characterized in that at least one of the following materials is used as a fuel component: titanium, magnesium, zirconium, carbon, boron in an amount of 3-30 wt. % by weight of dry refractory fiber. 5. The method according to claim 1, characterized in that the final product is formed at a separate manufacturing plant or at the place of use in the form of a single monolithic coating, intermediate layer or shaped product from a semi-finished paste by direct application to a substrate, filtration on a suction filter or filling out the appropriate form.