JPS5988360A - Porous high alumina cast refractories - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to porous high-density alumina cast refractories.

Conventionally, CA alumina internal refractories have been mainly used as large-sized materials for glass melting tanks, and the aim has been to reduce the porosity as much as possible in order to provide physical and chemical corrosion resistance to glass. In order to reduce the porosity in this way, a method has been adopted in which an appropriate amount of alkali metal oxide is added to the alumina raw material and then cast, thereby crystallizing β-At203'e in an appropriate ratio depending on the application. There is. If you keep it, MONOFRAX-M
(trade name manufactured by Carborundum) contains about 3% Na by weight.
20, containing 45% α-At203 and 55% β-
It has a structure in which At203 is crystallized and these two phases intersect. Similarly, MONOFRAX-H (trade name, manufactured by Kerr Random Co., Ltd.) contains about 5% Na20 and has a structure consisting of about 100 β-At203.

In general, if an alumina molten cast body is not added with an alkali metal oxide, only α-At203 (corundum) will crystallize (it is said that some δ-At203 is also present, but due to heat treatment in the atmosphere) υα-At205), but the porosity, pore diameter and pore distribution cannot be controlled at all.

Therefore, the dense α-At205 electrocast refractory disclosed in Japanese Patent Publication No. 49-17845 contains 1.50% by weight or less of alkali metal oxide and 1.0% in addition.
The following S i O2 is added. In addition, the special public
3-14247 discloses a method for obtaining dense alumina castings without adding additives, but since it is melted in a closed bed atmosphere, special equipment such as a closed melting furnace is required, making it economical. If you look at it, it can only be applied to very specific purposes.

The present invention has been made in view of the above circumstances.The present invention has been made by increasing the porosity of a high-alumina hook-made large-sized material with good heat resistance. The aim is to provide high quality alumina cast refractories.

We have found that containing a small amount of alkali metal oxides, -
It was discovered that high-alumina cast refractories cast without the addition of any intentional additives have high porosity, an extremely uniformly controlled pore distribution, and excellent spalling resistance. .

That is, the porous high alumina cast refractory of the present invention contains 0.25% or less of alkali metal oxide and has a porosity of 20.
% or more of uniformly distributed pores.

In the present invention, the content of alkali metal oxide is Q, 2
The reason why the alkali metal oxide is 0.25% is 5% or less.
This is because if it exceeds 20%, the porosity decreases to less than 20, pores become unevenly distributed, the pore diameter becomes irregular, and the spalling resistance becomes poor. Further, the lower limit of the alkali metal oxide content is preferably about 0.03% for normal industrial use, considering the economic efficiency of low-alkali alumina, but is not particularly limited.

The present invention will be explained in detail below.

Examples 1 to 3 and Comparative Examples 1 to 4 Raw material alumina powder having the composition shown in the table below was melted in an open arc furnace according to a conventional method and cast in a graphite mold. In addition, no intentional additives were added to Examples 1 to 3 and Comparative Examples 1 and 4.

Regarding the obtained casting, the porosity was measured, the pore distribution was observed, and the crystal phase and spalling resistance were examined. The results are also listed in the table below.

As is clear from the table above, all of the castings of Comparative Examples 1 to 4 either have alkali metal oxide content outside the range of the present invention, or have a porosity of 20% due to the addition of 8*02. If it is less than that, the pore distribution will not be uniform and the spalling resistance will be poor.

On the other hand, in all of the castings of Examples 1 to 3, the content of alkali metal oxides is within the range of the present invention, and no intentional additives such as red or black are included, so the porosity is 20. % or more, and showed a uniform pore distribution, and the spalling resistance was significantly improved.

Although the castings of Examples 1 to 3 are porous, the part that contacts the graphite mold during casting has a thickness of 1 to 2 m++.
Since it becomes dense over the course of the process, the presence of pores will not be recognized in appearance unless the surface is ground, and internal pores will not be a problem at all in simple heat-resistant applications without surface erosion. On the other hand, the porosity of the internal pores is as high as 20% or more, and the pore distribution is uniform, indicating excellent spalling resistance. It was possible to easily manufacture a sagger or a cylinder with a wall thickness of 5+a+x, an outer diameter of 300 gourd, and a growth of about 50 otm without any cracks. This was unexpected since the general evaluation of conventional large rot-resistant materials was low spalling resistance, and it has become possible to apply it to fields that could not be applied in the past. IFIJ uses various heating f+7) burner tiles and frame bricks.

Hydrogen furnace lining and hanging bricks for firing objects.

It was tested as a requipelator cheap, and it was confirmed that there were no problems with spalling resistance.

Additionally, due to its low alkaline content, it can be used as kiln linings, saggers, and post base plates for firing electronic components.

Even when used for shelf boards, etc., it not only reduces the effects of alkali metal oxides, but also makes it possible to form extremely thin jigs.
It has a small heat capacity and has a large energy saving effect.

As detailed above, the present invention has heat resistance.

It is possible to provide a porous high alumina cast refractory that has excellent spalling resistance and can reduce the influence of impurities.

Claims (1)

[Claims] Contains 0.25% or less of alkali metal oxide and has a porosity of 2
A porous high alumina cast refractory characterized by having 0% or more uniformly distributed pores.