JPH0725604B2 - Ceramic porous molding - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ceramic porous molded body, and particularly to an impurity removal filter in a molten metal that does not react or melt even in an alkaline atmosphere, or seawater as cooling water. The present invention relates to those used as a breathable solid used in continuous casting in the steel industry used.

[Prior Art] A ceramic porous molded body that has been conventionally used as a filter for removing impurities in a molten metal and as an air-permeable solid used in continuous casting in the steel industry is made of cordierite, alumina, mullite, SiO ₂ or the like. It was based on acidic and amphoteric oxides, or based on complex oxides thereof.

This is to reduce the coefficient of thermal expansion and keep good thermal shock resistance.

[Problems to be Solved by the Invention] By the way, it has been pointed out that a porous molded article using a substrate as described above reacts in an alkaline atmosphere and cannot withstand long-term use.

For example, when casting an aluminum alloy, the alkali content of sodium or strontium is adjusted to 50% to control its structure.
Approximately 200 ppm is added to refine the crystal grains.
When the above-described porous molded body is used as an impurity filter in the molten aluminum alloy, the porous molded body itself reacts with the alkali component in the molten metal, and the grain boundary phase changes to a glass composition having a low melting point, and countless cracks are generated. As a result, the composition of the porous molded article changes during use and becomes brittle.

This phenomenon can be explained by the following phenomenon.

Alkali-free aluminum melt should not be melted even by cordierite filter.

It is not considered that the conventional filter melts because the temperature of the molten alkali alloy is about 700 to 800 ° C at most, so that it does not melt above the melting point.

In a molded body mainly composed of an acidic oxide or an amphoteric oxide, to which an alkali component such as sodium or strontium is added, the melting point is rapidly lowered by the addition of the alkali component, and a glass phase is formed especially in the grain boundary phase in the structure. To deposit a large amount.

Therefore, the acidic oxide or the amphoteric oxide precipitates a low-melting glass phase in the composite oxide or the grain boundary with the alkali due to the alkali content in the molten metal, and further the alkali content is added to the composite oxide or the grain boundary glass phase. Will react,
As a result, the oxide is changed to a glass phase having a higher alkalinity or a grain boundary glass phase, and the melting point and the strength are lowered, so that the glass becomes weak.

In addition, this is not only the case of casting aluminum alloy,
The same can be said when the above-mentioned porous molded body is used as the air-permeable solid in continuous casting in the steel industry using seawater as cooling water.

Therefore, the present invention was created for the purpose of providing a ceramic porous molded body that does not become brittle even in an alkaline atmosphere as described above and is optimal for use as an impurity removal filter or a breathable solid in an alkaline atmosphere. It was

[Means for Solving Problems] The present invention is one in which raw materials are mixed, extruded into a linear rolling laminate, and then dried and baked, and magnesium oxide is 20 to 95 wt% in terms of MgO. , And zirconium oxide in an amount of 5 to 80 wt% in terms of ZrO ₂ .

[Operation] The present invention is that the composite oxide of magnesium oxide and zirconium oxide has a large corrosion resistance even in an alkaline atmosphere, and the grain boundary composition is a composition that is unlikely to vitrify to an alkali. It was realized on the basis of the finding that the molding can eliminate the drawbacks of the prior art and can sufficiently withstand a long-term use as an impurity removal filter or an air permeable solid under an alkaline atmosphere.

Hereinafter, the reasons for limiting the components in the present invention will be described.

If the magnesium oxide content is more than 95 wt% in terms of MgO, the coefficient of thermal expansion becomes too large and becomes weak against thermal shock. On the other hand, if it is less than 20 wt% in terms of MgO, it is resistant to alkali. This is because the corrosiveness will deteriorate.

When the zirconium oxide content is more than 80 wt% in terms of ZrO ₂ , corrosion resistance to alkali deteriorates.
This is because if it is less than 5 wt% in terms of O ₂ , the strength as a molded body cannot be obtained and a porous molded body cannot be formed.

A small amount of a basic oxide such as CaO or SrO can be added to improve the strength of the molded body. However, it should be noted that if the amount of addition is excessively increased, abnormal grain growth may occur in the crystal and conversely the strength may decrease.

[Examples] Example 1 Commercially available magnesia and zirconia were mixed and mixed in appropriate amounts, and then an organic additive such as a binder and a solvent were added thereto, and the mixture was kneaded uniformly, and was extruded by an extruder as shown in FIG. Thread diameter 1.5mm
It was molded into a φ linear laminate 1 (φ100 mm × t30 mm). After this was dried and fired, its characteristics were tested by the following methods.

The porous molded body 1 is held in a Stokes tube 2 as shown in FIG. 2, and an aluminum alloy melt containing 200 ppm of alkali in a soda content is flowed in the direction of 3 at a flow rate of 50 kg / min for one week, and every day. The shape change of the porous compact and the impurities in the alloy after filtration were investigated.

The results are shown in Table 1. With respect to the samples included in the scope of the present invention, very good results were obtained with respect to <change in shape> and <impurities in alloy after filtration>.

Example 2 Seawater may be used to cool the steel ingot in the steelmaking-related fields,
A gas containing a large amount of sodium was brought into the heating furnace as an atmosphere at that time, and there was a defect that the materials used so far could not withstand long-term use as a radiator by reacting with the alkali.

Therefore, in this example, it was decided to test how much effect is exhibited by using the ceramic porous molded body of the present invention as the radiator.

In the test, by using a small test furnace 4 as shown in Fig. 3, the combustion conditions were adjusted so that the temperature of the heating part was 1200 ° C, and the temperature was increased by arranging NaCl5 under the burner side furnace body 4a. At temperatures above 800 ° C, NaCl5 decomposes and volatilizes, and is mixed in the atmosphere gas. Also, the following two types (a)
Create a radiator 6 consisting of the material and shape of (b), and
The radiator was heated under the condition of ℃ × 5hr, and the appearance was checked each time.

As for this result, for (b), the 5th day (5hr / day x 5 =
The linear aggregate composed of 25 hr) began to vitrify and partially started to crack after the 6th day, whereas in (a), no deterioration was observed in 10 days (50 hr). There wasn't.

That is, both the radiant emitters (a) and (b) were satisfied with respect to the radiation effect, but the conventional cordierite material was expected to break from cracks within a few months, so that the actual operation furnace The use of is unrealistic.

[Effects of the Invention] As described above, when the ceramic porous molded body of the present invention is used as an impurity filter in a molten aluminum alloy, it is possible to improve the efficiency of removing impurities and improve the quality of products. In addition, it can be used for a long period of time in an alkaline atmosphere, greatly improving the yield in alloy production.

In addition, when used as a breathable solid in continuous casting in the steel industry that uses seawater as cooling water, heat dissipation of the furnace such as continuous casting is extremely reduced, which contributes to energy saving and long-term use under alkaline atmosphere. Since it withstands use in, it provides the optimum constituent material.

[Brief description of drawings]

FIG. 1 is a perspective view of a filamentous laminate according to an embodiment, FIG. 2 is a perspective view in which the filamentous laminate is held by a Stokes tube (partially broken), and FIG. 3 is a sectional view of a small test furnace. is there. 1 ... Filament laminate, 2 ... Stokes tube 3 ... Direction of molten alloy, 4 ... Small test furnace 4a ... Burner side furnace, 5 ... NaCl6 ... Radiator

Claims (1)

[Claims] 1. A raw material were mixed, the mixture was extruded into a linear施回laminates, be one obtained by drying and firing, 20～95Wt% magnesium oxide in terms of MgO, and zirconium oxide in terms of ZrO ₂ The ceramic porous molded article is characterized by containing 5 to 80 wt%.