RU2726800C1 - Nanoxylene heat-protective and heat insulating fibrous ceramic material and method of production thereof - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to production of fibrous ceramic materials of heat-shielding and heat-insulating purpose, in particular, for production of flat and shaped articles for hot metallurgical shops, aircrafts, power plants, and so forth. Method of producing heat-shielding and heat insulating fibrous ceramic material comprises obtaining gel of refractory nanofibre when dispersed in a liquid medium with binder at concentration of nanofibres of 1–8 wt. %, further preparation of the workpiece by dehydration of the obtained gel of refractory nanofibres to its residual concentration in gel of 10–20 wt. %, drying and annealing of the obtained workpiece. Refractory fibres are represented by nanofibers of mullite-silica or aluminium oxide, and the binder is represented by boric acid or clay in amount of 3–30 wt. % of dry refractory fibre weight.EFFECT: technical result is improved thermal and physical-mechanical characteristics of fibrous ceramic material due to high degree of uniform density.4 cl, 5 ex, 1 tbl, 2 dwg

Description

AREA OF TECHNOLOGY

The invention relates to a technology for producing fibrous ceramic materials for heat-shielding and heat-insulating purposes, in particular for the manufacture of flat and shaped products for hot metallurgical workshops, aircraft, power plants, etc.

LEVEL OF TECHNOLOGY

Ceramic fibrous materials, formed by oxide, quartz or glass-ceramic fibers, are a good inexpensive thermal insulation for hot parts of various types of industrial installations with operating temperatures up to 1100 ° C due to their low specific gravity, low thermal conductivity 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 binder introduced during impregnation. The main way to obtain them is to obtain a suspension of fibers, to form the initial blank, impregnate it with a binder, followed by drying and firing.

There is a known method of producing a fibrous material based on quartz fiber, according to which, to obtain a product, the fibers are pulverized during 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%, forming a blank with subsequent drying and firing (RU 2213074 C1, publ. 27.09.2003).

The disadvantage of the above method is a high degree of fiber damage during grinding, which reduces the specific strength of the resulting material. This method is applicable to the manufacture of high-density compression-resistant products, which do not require high thermal insulation properties combined with low weight and high resistance to vibration loads.

From RU 2127712 C1, publ. 03/20/1999 known method for producing heat-insulating material by ebb and dehydration of a suspension of mullite-silica fiber, 5-25% silica sol with a particle size of 2-8 microns. A two-stage molding of a heat-insulating refractory product is carried out by casting a suspension based on a mineral fiber in a mesh form, the inner side and bottom surfaces of which have a profile of the outer surfaces of the product, by dehydration, evacuation and subsequent mechanical and heat treatment. At the first stage, the shell of the product is formed, and at the second, the less dense inner volumetric part of the product.

The disadvantage of the above-disclosed method is the fundamental production of material that is non-uniform in volume and differs in all mechanical and thermophysical characteristics.

A known method of producing a fibrous heat-insulating material based on silicon oxide fibers, including obtaining a slip from silicon oxide fibers and a binder containing colloidal silicon oxide, starch and ammonia water, stirring the slip for 30 minutes in a U-shaped blender, molding a tile from a slip under pressure 0.7-1.4 atm, drying the resulting tile for 18 hours at 150 ° C and firing it at temperatures up to 1315 ° C. The shrinkage during firing was 25-45 vol.% (US 3952083 A, publ. 04/20/1976).

The disadvantage of the above method is the layered structure of the resulting material, arising from the use of dilute suspensions in the formation of tiles. In addition, high shrinkage combined with an anisotropic structure leads to warping and lenticular delamination in the thickness of the tile, which increases the volume of waste during machining and reduces the thermal insulation properties of the material and its resistance to delamination.

A known method of producing 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, boroaluminosilicate, 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 (US 4828774 A, publ. 09.05.1989).

The disadvantage of the above method is the need to work with a large volume of ceramic polymer solution with limited pot life. In addition, obtaining a green preform by vacuum filtration from a solution with a low concentration promotes the laying of fibers parallel to the plane of the filter, which leads to the formation of a layered structure of the resulting material, causes warping of the preform during firing, increased anisotropy of mechanical properties, which increases the likelihood of delamination of the formed material in the vertical direction.

In addition, the prior art knows a method for producing a fibrous ceramic material disclosed in RU 2358954 C1, publ. 06/20/2009, prototype. The method includes dispersing a refractory fiber with a binder, obtaining a crude preform by vacuum filtration, drying and firing the resulting preform. The refractory fiber is dispersed in two stages: at the first stage, the refractory fiber is dispersed in water at a fiber concentration of 0.5-1.0 wt% until the aspect ratio of the fiber length to the diameter is l / d = 50-130, then part of the water is removed to obtaining a suspension concentration of 4-8 wt.% and carrying out the second stage of dispersion without changing the aspect ratio of the length of the fiber to the diameter with the simultaneous introduction of a binder. The resulting suspension is uniformly placed in volume in a mold with vacuum suction, where it is thoroughly mixed and water is removed. Uniform laying of the pulp with its simultaneous mixing before vacuum suction contributes to obtaining an equally dense isotropic structure of the material, in which the fibers are arranged not in layers parallel to the filter plane, but are mixed in all planes. The uniform isotropic structure of the obtained material provides the required strength properties and contributes to a decrease in thermal conductivity, while maintaining a low specific gravity of the material.

The disadvantage of the above method is the use of micron-diameter fibers, which limits the achievement of low thermal conductivity, as well as the relatively low operating temperature of the resulting heat-shielding material, limited to 1000 ° C.

DISCLOSURE OF THE INVENTION

The object of the claimed invention is to develop a simple and inexpensive method for producing a fibrous ceramic material with low thermal conductivity, low specific gravity, with a high degree of uniformity, providing isotropic thermal and mechanical properties of the fibrous ceramic material.

The technical result of the invention is to improve the thermal and physical and mechanical characteristics of the fibrous ceramic material.

The specified technical result is achieved due to the fact that the method for producing a heat-shielding and heat-insulating fibrous ceramic material includes obtaining a refractory nanofiber gel when it is dispersed in a liquid medium with a binder at a nanofiber concentration of 1-8 wt.%, The subsequent preparation of a workpiece by dehydrating the obtained refractory nanofiber gel to its residual concentration in the gel is 10-20 wt%, drying and firing of the resulting workpiece, while nanofibers of mullite silica or aluminum oxide are used as a refractory fiber, and boric acid or clay as a binder.

Water and lower alcohols (ethyl or isopropyl alcohols) are used as a liquid medium for dispersing nanofibers.

Dispersion is carried out with a quantitative binder content of 3-30 wt% based on the weight of dry refractory fiber.

The specified technical result is also achieved due to the fact that the heat-shielding and heat-insulating fibrous ceramic material obtained by the above disclosed method in the form of ceramic tiles made of refractory nanofiber with a diameter of 5-10 nm has the following characteristics: specific gravity - 0.5-1.0 g / cm ³ , density difference - 1.0-2.0%; thermal conductivity at 900 ° C - 0.1-0.14 W / m ∙ K; operating temperature - 1400 ° C, while nanofibers made of mullite silica or aluminum oxide are used as a refractory fiber.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be better understood from the description, which is not restrictive and given with reference to the accompanying drawings, which depict:

FIG. 1 - Unidirectional distribution of nanofibers at the initial stage of the method.

FIG. 2 - Isotropic distribution of fibers in the final material.

CARRYING OUT THE INVENTION

To obtain the claimed heat-shielding and heat-insulating fibrous ceramic material in the form of ceramic tiles made of refractory nanofiber with a diameter of 5-10 nm, having the following characteristics: specific gravity - 0.5-1.0 g / cm ³ , density - 1.0-2.0 %; thermal conductivity at 900 ° C - 0.1-0.14 W / m ∙ K; working temperature - 1400 ° C is carried out as follows.

First, a refractory nanofiber gel is obtained when it is dispersed in a liquid medium (water, ethyl or isopropyl alcohol) with a binder (boric acid or clay) at a nanofiber concentration of 1-8 wt%. Then, the workpiece is obtained by dehydrating the previously obtained refractory nanofiber gel to its residual concentration in the gel of 10-20 wt%, followed by drying and firing of the obtained workpiece. Nanofibers made of mullite-silica or aluminum oxide are used as a refractory fiber, and boric acid or clay as a binder. Dispersion is carried out with a quantitative binder content of 3-30 wt% based on the weight of dry refractory fiber.

Example 1

For the manufacture of a workpiece with a size of 50 × 50 × 50 mm, a sample of a nanofiber from mullite silica weighing 200 g was taken, 20 g of boric acid was added and dispersed in water at a concentration of 7 wt. % for 10 minutes using a paddle mixer at a speed of 500 rpm. The resulting homogeneous gel was dehydrated by natural filtration in the form of a polymeric filter cloth to a residual content of nanofibers in the preform of 10 wt. %. The resulting workpiece was dried for 1 hour at a temperature of 120 ° C. Firing was carried out for 1 hour at a temperature of 800 ° C. The resulting sintered semi-finished product was mechanically processed to obtain the required dimensions and geometry.

Example 2

To make a workpiece with a size of 20 × 50 × 50 mm, we took a sample of a nanofiber from mullite silica weighing 100 g, added 10 g of clay and dispersed it in water at a concentration of 2 wt% for 25 min using a paddle mixer at a speed of 500 rpm. The resulting homogeneous gel was dehydrated by natural filtration in the form of a polymer filter cloth to a residual nanofiber content in the preform of 20 wt%. The resulting workpiece was dried for 0.5 hour at a temperature of 150 ° C. Firing was carried out for 0.5 hour at a temperature of 800 ° C. The resulting sintered semi-finished product was mechanically processed to obtain the required dimensions and geometry.

Example 3

For the manufacture of a workpiece with a size of 50 × 50 × 50 mm, a sample of nanofiber made of aluminum oxide weighing 200 g was taken, 20 g of boric acid was added and dispersed in water at a concentration of 7 wt. % for 10 minutes using a paddle mixer at a speed of 500 rpm. The resulting homogeneous gel was dehydrated by natural filtration in the form of a polymeric filter cloth to a residual nanofiber content in the preform of 10 wt%. The resulting workpiece was dried for 1 hour at a temperature of 120 ° C. Firing was carried out for 1 hour at a temperature of 800 ° C. The resulting sintered semi-finished product was mechanically processed to obtain the required dimensions and geometry.

Example 4

To make a workpiece with a size of 50 × 50 × 50 mm, a sample of a nanofiber made of mullite silica weighing 200 g was added 20 g of boric acid and dispersed in isopropyl alcohol at a concentration of 7 wt% for 10 min using a paddle mixer at a speed of 500 rpm. The resulting homogeneous gel was dehydrated by natural filtration in the form of a polymeric filter cloth to a residual nanofiber content in the preform of 10 wt%. The resulting workpiece was dried for 0.5 hour at a temperature of 80 ° C. Firing was carried out for 1 hour at a temperature of 800 ° C. The resulting sintered semi-finished product was mechanically processed to obtain the required dimensions and geometry.

Example 5 (prototype)

For the manufacture of a billet with a size of 200 × 200 × 60 mm, a sample of quartz fiber of 300 g was taken, dispersed in water at a concentration of 0.7 wt% for 40 min using a paddle stirrer at a speed of 3500 rpm to obtain a l / d fiber of about 80 , then the water was filtered using vacuum suction until its content in the semi-finished product is 500 wt%. From the obtained semi-finished product, an aqueous fibrous suspension with a concentration of 4.0 wt% was prepared, a binder was introduced into it in the form of an aqueous emulsion of boron powder and stirred at a speed of 1000 rpm for 5 minutes. The resulting homogeneous mass was molded by vacuum filtration in a laboratory setup with vacuum suction to a residual water content in the workpiece of 150 wt%. The resulting workpiece was dried for 3 hours at a temperature of 200 ° C. Firing was carried out for 2 hours at a temperature of 1200 ° C.

The obtained samples were tested, their properties are shown in the table. The table shows that the materials obtained by the proposed method have lower values of density difference, have a higher operating temperature and lower thermal conductivity compared to the material obtained by the prototype method.

Thus, the fibrous ceramic material produced according to the proposed method has an equal density isotropic structure, low specific gravity, and low thermal conductivity. The method does not require complex equipment and a long technological cycle. The material is inexpensive, satisfying the requirements for its use as a reusable heat-shielding and heat-insulating material with an operating temperature of up to 1400 ° C, in particular for the manufacture of facing tiles of furnaces, nozzles-crystallizers and lining of thermostatic ladles for liquid metal. In addition, one of the advantages of this material is the almost complete adhesion of molten metal residues.

Table

Example No. Specific gravity, g / cm ³ Density,% Thermal conductivity at 900 ° C, W / m K Working temperature, ° С Example 1 0.5 2.0 0.12 1400 Example 2 0.6 1.5 0.14 1400 Example 3 0.5 1.7 0.12 1100 Example 4 0,4 1,6 0.10 1400 Prototype example 5 0.15 five 0.2 1000

The invention has been disclosed above with reference to a specific embodiment. Other embodiments of the invention may be obvious to specialists without changing its essence, as it is disclosed in the present description. Accordingly, the invention should be considered limited in scope only by the following claims.

Claims (4)

1. A method of obtaining a heat-shielding and heat-insulating fibrous ceramic material, including obtaining a gel of a refractory nanofiber when it is dispersed in a liquid medium with a binder at a nanofiber concentration of 1-8 wt.%, Then obtaining a blank by dehydrating the resulting gel of a refractory nanofiber to its residual concentration in the gel 10 -20 wt.%, Drying and roasting of the obtained workpiece, while as a refractory fiber nanofibers of mullite silica or aluminum oxide are used, and as a binder boric acid or clay. 2. The method according to claim 1, characterized in that water and lower alcohols are used as a liquid medium for dispersing nanofibers. 3. The method according to claim. 1, characterized in that the dispersion is carried out with a quantitative content of the binder 3-30 wt.% By weight of dry refractory fiber. 4. Heat-shielding and heat-insulating fibrous ceramic material obtained by the method according to any one of paragraphs. 1-3, in the form of ceramic tiles made of refractory nanofiber with a diameter of 5-10 nm, having the following characteristics: specific gravity - 0.5-1.0 g / cm ³ , density difference - 1.0-2.0%; thermal conductivity at 900 ° C - 0.1-0.14 W / m ∙ K; operating temperature - 1400 ° C, while nanofibers made of mullite silica or aluminum oxide are used as a refractory fiber.

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