JPS6272526A - Production of fine particles of zirconia - Google Patents

Abstract

PURPOSE:To obtain the titled fine particles having a high purity by effecting thermal treatment of a mixture of zircon powders and a carbonaceous material under a prescribed condition to desiliconize. CONSTITUTION:The zircon powders (A) and the carbonaceous material (B) (for example, a petroleum coke) are mixed in such an amount that a molar ratio (C/SiO2) of a silica contd. in the component (A) and a carbon obtd. in the component (B) is 0.6-1.7. And then, the obtd. mixture is effected the thermal treatment in a nonoxidative atmosphere under a pressure of <=0.1atom at a temp. of 1,100-1,400 deg.C to desiliconize and, if necessary, is oxidized it at a temp. of 600-900 deg.C. Thus, the unstabilized fine zirconia powders having a high purity and <=5mum a mean particle size may be produced cheaply and with high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing highly pure zirconia (zirconium oxide: Zr0t) powder, particularly fine zirconia powder, from zircon powder.

The zirconia powder obtained by the method of the present invention has a high melting point (
2700℃ or higher), and is used as a variety of fire-resistant materials, and has recently been used as a solid electrolyte in oxygen sensors,
It is used as an abrasive, a raw material for ceramics for electronic parts, glass, etc.

(Prior technology) The main technologies currently known as general zirconia powder manufacturing technologies are: ■Carbon desiliconization arc furnace melting method, ■Alkaline powder melting method,
There are various methods such as melting method, etc.

First of all, the manufacturing method mentioned above is by adding coke to zircon sand,
Furthermore, iron scraps are added and heated in an arc furnace.
In this method, 1 minute of 5iO is volatilized into the gas phase or reacted with iron to be removed as ferrosilicon, thereby separating it from the so-called Zr0t component and obtaining zirconia powder. Although this method is suitable for producing large amounts of inexpensive zirconia powder, it has the problem that high purity powder cannot be obtained. Furthermore, melting in an arc furnace requires a considerable high temperature, which takes time, and energy is also required to crush the obtained zirconia block, which remains a problem from an energy saving perspective.

In the production method (■) above, zircon sand and an alkali are melted and reacted to remove SiO2 in the zircon as an alkali silicate, while the ZrO□ component is converted into sodium zirconate and then subjected to processes such as acid treatment. Then, it is converted into zirconium oxychloride (ZrOClz).

Then, this zirconium oxychloride (soluble in water) was adjusted to pH
This is a method of preparing zirconium hydroxide and heat-treating it to obtain zirconia. This method yields highly purified zirconia with a purity of 99% or more compared to the production method (①) above, but
The disadvantage is that the manufacturing process is complicated, resulting in poor productivity.
The cost is extremely high.

Other manufacturing technologies for zirconia powder include JP-A No. 5
There are those disclosed in No. 8-9808 and Japanese Unexamined Patent Publication No. 15021/1983. These technologies mix and granulate zircon sand and carbon powder, and then attach carbon granules around the granules and heat them in a non-oxidizing atmosphere to release SiO2 into the gas phase. This relates to a technology that simultaneously produces zirconia and SiC by expelling it and simultaneously reacting it with carbon particles. However, the known technology for producing this zirconia powder also uses SiO in ZrOt.
There is a risk that a considerable amount of the □ component may remain or SiC may be mixed into the ZrO□, and the reaction requires high temperature and a long time, resulting in problems in terms of purity and productivity.

(Problems to be Solved by the Invention) As a result of further research into the conventional carbon desiliconization method for producing zirconia powder from zircon powder, the present inventors discovered how efficient it is in desiliconizing zircon powder. It has been found that removing SiO vapor is very important in manufacturing. For this purpose, the present inventors have previously published Japanese Patent Application No. 59-65130 or Japanese Patent Application No. 59-9575.
As No. 6, we proposed a new technology of carbon desiliconization under reduced pressure.

However, the problem with this prior proposed technology is that from zircon powder to micron-order zirconia fine powder (≦5 μl).
11), and the present invention solves the problem that such prior art has, namely, that high-purity, fine, unstabilized zirconia fine powder cannot be manufactured inexpensively and efficiently. It's about solving.

(Means for Solving the Problems) Therefore, the present inventors reexamined the vacuum carbonization conditions for zircon powder, which is the above-mentioned zirconia powder production technology proposed earlier, and determined that the optimal vacuum desiliconization conditions could be selected. , average particle size: δμ
We have discovered that it is possible to produce fine zirconia on the upper and lower sides of steel.

In general, when producing zirconia by heat-treating a mixture of zircon powder and carbon-containing material under reduced pressure to desiliconize it, the main manufacturing factors that affect the particle size of the obtained zirconia are: The mixing ratio of materials, pressure, heat treatment temperature, or heat treatment time may be considered. As a result of studying these various manufacturing conditions, it was found that in order to obtain fine zirconia powder, it was necessary to lower the heat treatment temperature and pressure.

That is, the first feature of the present invention is that the zircon powder and the carbon-containing material are mixed in such a way that the molar ratio (C/SiO2) of silica in the zircon powder to carbon in the carbon-containing material is 0.6 to 1. ．．
7, and this mixture is subjected to desiliconization heat treatment at a temperature of 1100 to 1400°C under 0.1 atm, and secondly, following the above-described reduced pressure desiliconization heat treatment, oxidation treatment is performed. The goal is to do the following.

(Function) Since the zircon powder used in the method of the present invention is produced as a highly pure zirconia fine powder, it is naturally essential to use high-purity raw materials, and impurity components other than ZrO and SiO□ are as much as possible. Less is better; for example, pulverized zircon sand can be used. However, it is preferable to use finer particles to speed up the reaction with carbon.

Next, regarding the amount of carbon to be mixed with the zircon powder in the present invention, in order to maintain high purity of the obtained zirconia powder, it is desirable that the amount of ash remaining in the vacuum desiliconized zirconia is as small as possible. For example, carbon-containing substances suitably used in the present invention include petroleum coke, petroleum pitch, coal pitch, carbon blank, etc., which have little natural properties, but also phenolic resins, polyethylene, etc., which produce carbon when heated. Organic resins can also be used.

The carbon-containing material is used as a mixed powder with zircon powder, or as a molded body of the mixed powder, but it is necessary to thoroughly mix the material in order to allow the desiliconization reaction to proceed completely.

Next, in the present invention, the molar ratio of silica in the zircon powder to carbon in the carbon-containing material (C/SiO2) is 0.6 to
The zircon powder and the carbon-containing material are blended at a ratio of 1.7, but the reason for limiting the ratio to this range is as follows. In other words, if the molar ratio of zircon and carbon-containing material (molar ratio C/5t(h)) is smaller than 0.6, there will be insufficient carbon to completely remove zircon (volatize Sing as SiO vapor). Zircon remains even after silica treatment.

Conversely, if C/5iOz (molar ratio) is greater than 1.7,
Although the amount of carbon is sufficient to reduce 5ift in zircon and remove it as SiO vapor, the large amount of carbon makes it too reducing, and in addition to Sing, ZrC'PZrSi,
This is not good because Zr5Sis remains and the amount of SiO□ in the ZrO finally obtained (after oxidation treatment) increases and the purity deteriorates. Therefore, in order to maintain good purity of zirconia, the amount of carbon in the silica and carbon-containing substances in the zircon powder should be 0.6 to 1 expressed as C/5iOz (molar ratio).
．． It is necessary to limit it within the range of 7. Note that the carbon in the carbon-containing material used in the present invention refers to fixed carbon that participates in the desiliconization reaction at high temperatures after removing components that volatilize at temperatures below 1000°C.

Next, in the present invention, the mixture of zircon powder and carbon-containing material, or the compact thereof, is subjected to desiliconization heat treatment at a pressure of 0.1 atm or less, but the reason for limiting the temperature to 0.1 atm or less is that This is because if the pressure is high, the SiO vapor cannot be effectively volatilized and removed, resulting in poor efficiency and difficulty in obtaining fine, high-purity zirconia powder.

In addition, the reduced pressure atmosphere used in carrying out the present invention is NZ
+ A non-oxidizing gas atmosphere such as Ar or co is suitable.

Next, in the present invention, the desiliconization heat treatment temperature is set at 1100 to
The temperature was limited to 1400°C, but the reason is 1100°C.
If it is lower than 1400°C, a long heat treatment is required to desilicate, which is economically disadvantageous, and if it is higher than 1400°C, the average particle size of the obtained zirconia will exceed 5 μm. , Fine powder (≦5μm) that the present invention aims at
It will no longer be suitable as

Now, in the present invention, most of the crystals produced by the reduced pressure heat treatment are ZrO□, but depending on the mixing ratio of zircon and carbon, some ZrO, ZrC, etc. are produced. In such a case, after the heat treatment for desiliconization, further oxidation treatment is performed to convert ZrO, ZrC, etc. to ZrO, thereby achieving even higher purity.

That is, in the present invention, in order to completely desiliconize the silica powder in zircon, the carbon-containing material is blended so that the amount of carbon is slightly in excess of the molar ratio corresponding to silica in zircon. When heated in this way, depending on the desiliconization heat treatment conditions, ZrO and ZrC may be oxidized and ZrO□
It can be done.

Furthermore, carbon remaining after heat treatment can also be oxidized and removed by volatilization into the gas phase. The temperature during oxidation treatment is 600~
A range of 900°C is suitable.

(Example) Zircon powder with an average particle size of 0.97 μm and a total content of ZrO□ and 5i02 of 99.5% and quartz pitch (66% fixed carbon, 0.3% ash) with a particle size of 100 μm or less were used. , mixed at various C/5iOz molar ratios as shown in Table 1, thoroughly mixed using a ball mill, and then molded into 10 mmφ x 29 mm using a mold forming machine.
A large number of molded bodies of Dragon II were molded. These molded bodies were subjected to vacuum desiliconization treatment under the heat treatment conditions shown in Table 1.

After heat treatment, the existing crystal phase was identified by powder X-ray diffraction. Further, the powder was oxidized in the atmosphere at 800° C., and the presence of crystals was similarly identified, the ZrO□ purity was analyzed, and the average particle size of the Zr0z powder after crushing was examined using a scanning electron microscope. The results are also shown in Table 1.

As is clear from Table 1, fine unstabilized zirconia powder was obtained according to the present invention.

(Effects of the Invention) As described above, according to the present invention, highly pure, fine, unstabilized zirconia finely divided powder can be efficiently produced on a mass production scale.

Claims (1)

[Claims] 1. When producing zirconia powder by desiliconizing a mixture of zircon powder and a carbon-containing material by heat treatment, and the carbon in the carbon-containing material (
C/SiO_2) is mixed so that the ratio is within the range of 0.6 to 1.7, and this mixture is heated to 1100
A method for producing fine zirconia powder, characterized by carrying out a desiliconization heat treatment at a temperature of ~1400°C. 2. When producing zirconia powder by desiliconizing a mixture of zircon powder and a carbon-containing material by heat-treating the mixture, the zircon powder and the carbon-containing material are combined with the silica in the zircon powder and the carbon-containing material. molar ratio of carbon to carbon (
C/SiO_2) is mixed so that the ratio is within the range of 0.6 to 1.7, and this mixture is heated to 1100
A method for producing fine zirconia powder, which comprises performing a desiliconization heat treatment at a temperature of ~1400°C, followed by an oxidation treatment.