RU2030369C1 - Charge for preparing of porous refractory material - Google Patents

Abstract

FIELD: heat insulating porous materials. SUBSTANCE: charge has, wt.-%: hollow corundum microspheres 20-30; niobium oxide (particle size is below 0.1 mcm) 20-30, and aluminium oxide (particle size is below 0.1 mcm) - the rest. Material properties: material shows close-grained structure of high mechanical strength (compression limit strength is 460-550 MPa). EFFECT: enhanced quality of charge. 2 dwg, 1 tbl

Description

 The invention relates to the production of porous ceramic materials, in particular based on alumina, which can be used as structural heat-insulating materials operating at high temperatures and significant mechanical stresses.

 The aim of the invention is to increase the mechanical strength of the porous material and lower sintering temperature.

This is achieved by the fact that the mixture to obtain a porous refractory material, including hollow corundum microspheres, aluminum oxide, contains aluminum oxide with a particle size of up to 0.1 μm and additionally niobium oxide (Nb ₂ O ₅ ) with a particle size of up to 0.1 μm in the following ratio of components, wt.%:
Hollow corundum
microspheres 20-30
Niobium oxide 2-3
Alumina Else
Powders of aluminum oxide and niobium oxide, respectively, used as a binder and a filler having a particle size of 0.1 microns, can reduce the sintering temperature of the porous material to 1600 ^{° C,} which contributes to the inhibition of recrystallization process and ultimately results in a more fine-grained structure by compared with the prototype and improve the mechanical properties of the porous material.

 An increase in the particle size of alumina and niobium oxide over 0.1 μm leads to the need to increase the sintering temperature, which in turn negatively affects the grain size of sintered materials, which increases with increasing temperature. Products from such masses have a coarse-grained structure and are characterized by low strength.

 The decrease in the content of corundum microspheres in the composition of the mixture below 20 wt. % limits the use of these materials as high-temperature thermal insulation due to their destruction from thermal stresses. The increase in the content of corundum microspheres in the charge above 30 wt.% Contributes to the formation of a discontinuous skeleton with open porosity, formed due to the partial destruction of the microspheres, which reduces the mechanical strength of the refractory material. The decrease in the content of niobium oxide in the mixture below 2 wt. % leads to the formation of a coarse-grained heterogeneous structure with intergrowths of crystallites. There are practically no grains of pseudospheroidal shape. With an increase in the content of niobium oxide above 3 wt.%, The grain size of sintered materials increases by an order of magnitude, which leads to a decrease in mechanical strength.

 In FIG. 1 shows the structure of a porous material obtained from the proposed mixture (as filler - magnesium oxide); figure 2 - the same as a filler - niobium oxide.

 The introduction of niobium oxide provides the formation of a crystalline structure having a pseudospheroidal grain shape with clearly defined boundaries. The density of the matrix structure of such a material is high, as evidenced by the practical absence of pores and the presence of contact points (cleavages) of grains formed due to strong intergranular adhesion. The presence of niobium oxide has a positive effect on the mechanical strength of the material.

 The mixture is prepared as follows.

Alumina is pre-mixed thoroughly with niobium oxide. In order to more evenly distribute them over the volume of the material, the microspheres are pre-moistened with a 7% aqueous solution of polyvinyl alcohol, the mass fraction of which is 10% by dry weight of the initial mixtures of components. To a suspension of microspheres and polyvinyl alcohol, a mixture of aluminum oxide and niobium oxide is gradually added with constant stirring. The resulting mass is formed by double-sided single pressing in a metal mold at a pressure of 60 MPa, the excess of which is impractical due to the destruction of the microspheres. Molded samples were sintered in air at 1600 ^{° C} with a four-hour isothermal exposure. The compositions of the prepared blends and the properties of the refractory porous materials obtained from them are shown in the table (examples 1-3 - according to the invention).

 From the data of the table it follows that when at least one of the components of the proposed composition exceeds the declared limits (examples 4, 5), it is not possible to achieve the goal: the strength of the material decreases. The strength of the material obtained by the prototype, 230 MPa.

Thus, based on highly dispersed aluminum oxide with particle size of 0.1 microns with the introduction of niobium oxide with a particle size of 0.1 microns at 1600 ^{° C} can be obtained by heat-insulating material having, compared with the prior art higher strength (in 2- 2.5 times) with a total porosity of 27-42%.

 The mixture to obtain a porous material based on aluminum oxide reduces the need for scarce materials and alloys and increases the service life of heat-insulating units of high-temperature plants.

Claims (1)

MIXTURE FOR PRODUCING POROUS REFRACTORY MATERIAL, including hollow corundum microspheres and alumina, characterized in that, in order to increase mechanical strength and reduce sintering temperature, it contains alumina with a particle size of up to 0.1 μm and additionally niobium oxide with a particle size of up to 0.1 μm in the following ratio of components, wt.%:
Hollow corundum microspheres - 20 - 30
Niobium oxide - 2 - 3
Alumina - Else

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