JPS62138327A - Direct production of electromelting stabilized zirconia - Google Patents

Abstract

PURPOSE:To efficiently obtain electromelting stabilized ZrO2 without providing a new oxidation treatment process by blowing O2 into an electric oven in case of melting a raw material in the electric oven to perform oxidation and calcination treatment and controlling the cooling of a melt after tapping the melt and performing regulation of degree of stabilization. CONSTITUTION:A raw material such as vaterite powder and calcined lime is introduced into an electric oven 1 and melted as shown in a figure A. At this time, pure O2 is blown into a melt through an O2 lance 2 to perform oxidation, calcination and decarburization. Then after tapping the obtained melt on a casting bed 3 as shown in a figure B, it is cooled in 80-300 deg.C/hr cooling velocity within the range of 1,500-1,000 deg.C. In the control of this cooling velocity, the following apparatus is used which is constituted so that heating and cooling are properly performed by providing the gas burners 30 and the axial-flow fans 31 as shown in a figure C. After cooling, it is made to a required grain size by crushing without performing newly calcination treatment and the aimed electromelting stabilized ZrO2 is obtained by removing iron grain in a magnetic separation process. Still further a thermocouple fitted to the castting bed 3 is shown by 32 in the figure.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for directly producing electrofused stabilized zirconia.

<Prior art> Zirconia (Zr0z) has a high melting point (approximately 2700°C
), it has the characteristics of high penetration resistance and extremely low heat conduction, and is used as a refractory material.

However, %ZrO2 is a polymorphic material having monoclinic, tetragonal, and cubic crystals, and undergoes a phase transformation from monoclinic to tetragonal at around 1100°C, and at this time it exhibits abnormal contraction and expansion of about 3.5%. The problem is that it repeatedly contracts and expands due to the thermal cycle of heating and cooling, eventually leading to destruction.

Therefore, when using ZrO2 as a refractory material,
By adding CaO, MgO, Y2O3, etc. and treating it at high temperature, the above-mentioned abnormal expansion and contraction are suppressed as a tetragonal or cubic solid solution, resulting in stable zirconia.Electrically melted and solidified by adding CaO, etc. Cracking occurs because the product still contains carbides and suboxides during the melting process and distortion within the crystal due to overcooling during the cooling process. After the magnetic separation process, an oxidation firing treatment is usually performed to adjust the oxidation, decarburization, and stabilization rate. If this treatment is not carried out, the thermal cycle of increasing and decreasing around 1100° C. will cause a desensitization phenomenon and the stability rate will decrease.

However, this oxidation firing process involves reheating and raising the temperature of the molten material once it has been cooled, resulting in a large loss of thermal energy, which is undesirable from an energy saving perspective, and improvements have long been desired. .

<Summary of the Invention> The present invention was made to improve the above-mentioned drawbacks of the prior art, and involves blowing oxygen into the raw material when melting it in an electric furnace to perform an oxidation firing process, and reducing the cooling rate after tapping. The basic feature is that the stabilization rate can be adjusted through control.

With this configuration, a new oxidation firing process after tapping can be omitted, and the effects of improving the efficiency of the manufacturing process and energy saving can be obtained.

Hereinafter, one method of the present invention will be sequentially explained with reference to the drawings.

As shown in FIG. 1(A), raw materials such as baddellite powder and burnt lime are charged into a 1ML air furnace (1) and melted. At this time, pure oxygen is blown into the molten metal using an oxygen lance (2) or the like to perform oxidation firing and decarburization.

Figure 2 shows the relationship between the 02 injection amount and 0% in the molten metal. This graph shows 6 tons of baddellite powder.

This figure shows the change in 0% when 02 was injected into a set of melted calcined limestone grains (CaO: 4.2%) at 46Kf. When o2 is injected at 50 t/min.

It takes about 50 minutes to reach C=0.01%, making it difficult to tap the hot water. When 02 is injected at 100 t/min, the decarburization rate naturally increases, but the molten metal scatters violently, resulting in a one-year yield drop. Furthermore, the lance (2) is also subject to considerable wear and tear.

With 02 blowing at 80 t/min, it takes about 30 minutes to reach C: 0.01%, and there is no drop in molten metal temperature and there is no problem in tapping. There is also less molten metal splash, 70~8
Injection of about 0.017 m1n is suitable.

Although various materials can be used for the oxygen lance (2), it is preferable to use zirconium so as not to affect product quality.

The molten metal produced as described above is tapped from the cast bed as shown in Figure (B) and cooled.The cooling rate after tapping is controlled.

This is the most distinctive feature of the method of the present invention, and is the finding that there is a strong correlation between the cooling rate and the stabilization rate. Third
The figure shows the relationship between cooling rate and stabilization rate. It can be seen that the stabilization rate increases almost linearly as the cooling rate increases.

In the method of the present invention, the stabilization rate is controlled to be 80% to well over 86, and any desired stabilization rate is obtained by adjusting it to 80 to b, which can be obtained with relatively simple equipment.

In addition, the stabilization rate is most affected by the cooling rate between 1500 and 1000°C, so the above cooling rate is between 1500 and 1000°C.
The cooling rate is in the range of 100°C.

Figure 1 (C) shows a concrete example of equipment for controlling the cooling rate, including a gas burner flash and an axial fan (
31) is installed and configured to control heating and cooling as appropriate. (32) is a thermocouple attached to the cast bed (3).

After cooling, the product is made into a product by crushing it to the desired particle size and removing iron grains in a magnetic separation process without performing a new firing process.

<Example> 6 tons of baddeleyite powder and calcinedite grains (product CaO:
4.2%) Contains 46suke, secondary voltage 170-210
The mixture was dissolved for 4 hours at

Zr02 when the molten metal temperature reaches 2400-2500℃
Pure oxygen was blown into the furnace at a rate of 70 to 80 t/min using a lance made by the company, and the blowing was stopped after 30 minutes. And 1m1 figure (C
) The melt was poured into a variable cooling rate casting bed and cooled. As shown in Fig. 4, the molten metal was cooled by forced air cooling for 2 hours from 2500 to 1500°C.

Between 1500 and 1000℃, 80℃/hr, 130℃
/hr, at a cooling rate of 300°C/hr. After cooling, it was crushed and subjected to magnetic separation to obtain a product.

The ingredients and stabilization rate of each product are shown in the table below. Also, as a comparative example, the ingredients of a product processed by conventional oxidation firing treatment without cooling control are shown.

According to the method of the present invention, a sufficient stabilization rate can be obtained without performing oxidation firing treatment, and the stabilization rate can also be adjusted as desired.

Also, decarburization has been sufficiently carried out.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the method of the present invention, and FIG. 2 is a graph showing the relationship between 0° injection amount and C% in molten metal. Figure 3 is a graph showing the relationship between cooling rate and stabilization rate.
The figure is an explanatory diagram of the cooling rate of the example. (1)...Electric furnace, (2)...Oxygen lance, (3)
...Casthouse. Patent applicant Nippon Kokan Co., Ltd. Inventor Masa Kitahara Human
Mitsuaki Shimomura Patent Attorney Sho Yoshihara Sando
Attorney Takahashi
Hiroko Yoshihara Figure 2 Figure 3 Cold ridge speed ('C/Hr) (A) (B) (C)

Claims (1)

[Claims] Raw materials are melted in an electric furnace, oxygen is blown into the molten material to perform oxidation treatment, and then the melt is tapped.
A method for directly producing electrofused stabilized zirconia, characterized by cooling between 1000°C at a cooling rate of 80 to 300°C/hour.