JPS6278114A - Production of zirconia powder - Google Patents

Abstract

PURPOSE:To produce zirconia powder having high purity in high efficiency at a low cost, by desiliconizing a mixture of zircon powder, a carbon-containing material and/or metallic silicon powder under reduced pressure at a temperature suitable for the target particle diameter. CONSTITUTION:(A) zircon powder having a purity of >=99.0% and particle diameter of <=1.0mum is mixed with (B) a carbon-containing material (e.g. carbon black) and/or metallic silicon powder at a molar ratio (Si+C)/SiO2 of 0.4-1.5. The mixture is dsiliconized by heatingn under reduced pressure at a temperature suitable for the target size of the particle to be recovered and, if necessary, the desiliconized product is oxidized. Unstabilized zirconia powder having prescribed particle diameter can be surely produced in high efficiency by this process.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing high-purity zirconia (zirconium oxide: Zr 02 ) powder from zircon powder. By mixing zircon powder with a carbon-containing material and/or metal silicon powder, and performing a vacuum desiliconization heat treatment with temperature control, the silica component in the zircon powder is removed by volatilization into the gas phase, and various desired particle sizes can be obtained. An advantageous method for producing high purity unstabilized zirconia powder is proposed.

(Prior Art) The main techniques currently known as general zirconia powder manufacturing techniques include (1) carbon-removal arc furnace melting method, (2) alkaline melting method, and the like.

First of all, the manufacturing method described in (■) above uses zircon sand,
Furthermore, iron scraps are added and heated in an arc furnace.
This is a method of separating Si02 from the so-called Zr02 component and obtaining zirconia powder by volatilizing Si02 into the gas phase or reacting with iron to remove it as ferrosilicon. Although this method is suitable for producing large quantities of inexpensive zirconia powder, it has a problem in that highly pure zirconia 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 (2) above, zircon sand and an alkali are melted and reacted, and the St 02 component in the zircon is washed and removed as an alkali silicate, while the Zr 02 component is converted into sodium zirconate and then subjected to processes such as acid treatment. Then, it is converted into zirconium oxychloride (Zr OCI 2 ). This zirconium oxychloride (soluble in water) is then pH-adjusted to form zirconium hydroxide, which is then heat-treated to obtain zirconia. This method yields highly purified zirconia with a purity of 99% or more compared to the production method (2) above, but the disadvantage is that the production process is complicated, resulting in poor productivity and very high costs.

Other manufacturing technologies for zirconia powder include JP-A No. 5
There are those disclosed in No. 19808 and Japanese Patent Application Laid-open No. 15021/1983. These techniques involve mixing zircon sand and carbon powder, granulating the mixture, attaching carbon granules around the granules, and heating them in a non-oxidizing atmosphere. This technology involves producing zirconia and SiC at the same time by reacting them with carbon particles. However, the known technology to produce this zirconia powder also consists of 3i 0 in Zr 02
There is a risk that a considerable amount of the two components may remain or SiC may be mixed into Zr 02, and the reaction requires high temperature and a long time, which poses problems in terms of purity and productivity.

(Problems to be Solved by the Invention) The general purpose of the present invention is to solve the above-mentioned problems of the prior art regarding the method of producing zirconia powder from zircon powder, namely, high purity unstabilized zirconia powder. The objective is to solve the problem that it cannot be manufactured cheaply and efficiently.

According to the research conducted by the present inventors, as a result of intensive studies on the conventional carbon desiliconization method for producing zirconia powder from zircon powder, it has been found that it is difficult to efficiently remove S10 vapor during desiliconization of zircon powder. The inventors of the present invention first filed a patent application filed in 1983 for this purpose.
As proposed in No. 65130 or Japanese Patent Application No. 59-95756, we came up with a new technique of carbon desiliconization under reduced pressure.

In short, if carbon desiliconization is performed under reduced pressure, high-purity zirconia powder can be produced more efficiently with heat treatment at a lower temperature and in a shorter time than with conventional carbon desiliconization methods.

It has also been found that silicon metal powder can be used in place of the carbon-containing material to efficiently remove silicon.

However, even though we say zirconia powder, industrially it ranges from relatively coarse refractory grade and thermal spray material grade to fine ceramic grade, which uses so-called submicron ultrafine powder. There are zirconia powders with various particle sizes. Among the conventional zirconia powder manufacturing techniques described above, the carbon-desiliconization arc furnace melting method is primarily a technique for manufacturing coarse-grained refractory grade products. On the other hand, the alkaline fusion method is a technology that takes advantage of the characteristics of high purity and ultra-fine powder to produce products for fine ceramics and electroceramics. In short, the reality is that there has never been an example in which zirconia powder ranging from coarse particles to ultra-fine powder can be freely produced using conventional methods.

Therefore, a specific object of the present invention is to propose an advantageous technique that allows zirconia powder of various particle sizes to be taken out as needed in the same manufacturing process.

<Means for Solving the Problems> Therefore, in the vacuum desiliconization method of zircon sand, which is the zirconia powder production technology proposed earlier, the present inventors
As a result of a detailed study on the relationship between the vacuum desiliconization temperature and the particle size of the obtained zirconia powder, we found that by controlling the vacuum desiliconization temperature, it is possible to create any particle size from coarse zirconia powder to ultra-fine zirconia powder. The present invention was completed by discovering that a zirconia powder of 100% can be obtained.

That is, the present invention, as a means to solve the above-mentioned problem, is based on the target particle size to be recovered when producing zirconia powder by heat-treating a mixture of zircon powder, carbon-containing material, and/or metal silicon powder. A method of producing zirconia powder is employed in which the heating temperature during the heat treatment is selected and the desiliconization is performed under reduced pressure.

(effect) Next, the specific contents of the present invention will be explained according to experimental examples.

First, the raw materials were adjusted as follows.

Zr○2+3iQ2 is 99.0wt%, average particle size 1.0
Carbon black is blended into μm zircon powder so that the molar ratio (C/5iO2) to 3i02 in the zircon powder is within the range of 0.4 to 2.5, and after thorough mixing, A molded body of 10Ill11φX 20mmH was prepared from the mixture using a mold forming machine.

The above molded body raw material) was placed in a reduced pressure atmosphere at 1300°C for 50 minutes.
A desiliconization heat treatment was performed by holding the sample for a certain period of time. The pressure is 0.2. 0
．． 1. The pressure was 0.05 atm. In addition, desiliconization heat treatment,
Oxidation treatment was performed in the air at 800° C. for 2 hours, and 5i02Ji in the obtained zirconia powder was analyzed. 3 in Figure 1
Effect of Si in zircon powder on i02 residual amount analysis value
02 and carbon black (C/SiO2 molar ratio) and the influence of pressure.

As is clear from FIG. 1, in order to obtain zirconia powder with a small residual amount of Si 02 (<1.0 wt%), the pressure is preferably 0.1 atmosphere or less. Also C/5i02
(Molar ratio) is more preferably within the range of 0.6 to 1.7.

Next, using a mixture of zircon powder and carbon black blended in the same proportions as above, the influence of desiliconization heat treatment temperature was investigated. That is, the blending ratio of zircon powder and carbon black (C/5i02 molar ratio) was 1.2, and the pressure was 0.01 atm. Desiliconization heat treatment temperature is 1050~18
The temperature was within the range of 00°C, and the heat treatment time was longer for lower temperature heat treatment conditions. FIG. 2 shows the effect of heat treatment temperature on the amount of $102 remaining in the zirconia powder.

Furthermore, the oxidized zirconia powder was lightly ground using a mortar and examined using a scanning electron microscope. Similarly, FIG. 2 shows the influence of heat treatment temperature on the average particle size of zirconia powder.

As is clear from FIG. 2, in the case of the present invention, 3i
In order to obtain a high-purity zirconia powder containing as little as 1.0 wt% or less, a heat treatment temperature of 1100° C. or higher is required. If the temperature is lower than 1100° C., desiliconization takes a long time, which is economically disadvantageous.

On the other hand, in order to obtain fine zirconia with an average particle size of 1 μm or less, a processing temperature of 1350°C or less is required.
In the case of coarse zirconia powder with an average particle size of 10 μm or more, a temperature of 1700° C. or higher is required.

From the above, the mixing ratio of the zircon powder and the carbon-containing material is set such that the molar ratio of Si 02 in the zircon powder to carbon in the carbon-containing material (C/Si 02 ) is 0.6 to 1.7, and the pressure is reduced. It has been found that by performing the desiliconization heat treatment at a temperature of 0.1 atm or lower and 1100° C. or higher, a highly pure zirconia powder having an arbitrary particle size can be obtained.

The above results show similar results even when metallic silicon powder is used instead of the carbon-containing material, and the mixing ratio Si/Si 02
) Aruiha (C+Si /Si 02) ff10
．． It was found that 4 to 1.5 is preferable.

The zircon powder used in the present invention is preferably one that is as fine as possible and has a high purity with few components other than ZrO2 and Si02. Further, as for the carbon-containing material, it is preferable that the ash content remaining in the zirconia powder after vacuum desiliconization is as low as possible.

Carbon-containing substances suitably used in carrying out the present invention are not particularly limited, but coal coke with a low ash content, coal coke with a low ash content,
Examples include petroleum coke, coal-based or petroleum-based pitch, pitch coke, carbon black, and organic resins. Such carbon-containing substances are produced by heat-treating zircon powder and mixed powder, or compacts made from the mixed powder, for desiliconization under reduced pressure. In particular, when mixing zircon powder and carbon-containing substances, the desiliconization reaction must proceed completely. It is necessary to do enough for this purpose.

Figures 3 and 4 are temperature 1300℃ x 50)-
1r, 1600°C x 2) - 1r is a scanning electron micrograph showing the particle structure of the obtained zirconia powder after the desiliconization heat treatment. In the case of FIG. 3, the zirconia powder is fine, whereas in the case of the one shown in FIG. 4, it is clear that the zirconia powder is sintered with each other and becomes coarse.

In addition, when producing zirconia powder according to the method of the present invention,
When using a continuous vacuum heating furnace, the particle size of the generated zirconia powder can be analyzed online and the results can be fed back to control the heating conditions to achieve a more desirable particle size. It becomes possible.

In addition, the zirconia powder produced by the method of the present invention is mostly z'02, but depending on the mixing ratio of zircon and carbon, some zr o, zr c, etc. may also be produced. After the heat treatment, oxidation treatment is performed to convert Zr o, Zr c, etc. to Zr 02,
Furthermore, high purity is achieved.

(Example) Zr 02 Si 02 (7) Total content 1 99
．． 5% (7) Zircon powder with an average particle size of 0.97 μ■ and carbon black with an average particle size of 210 people (fixed carbon 99
%, distribution 0.1%) and C/5 as shown in Table 581.
Mix and adjust to iOz (molar ratio), and add 1
A molded body of 011φX 201111H was obtained. This was subjected to vacuum desiliconization treatment under the heat treatment conditions shown in Table 1, and after the heat treatment, the existing crystal phase was identified by powder X-ray analysis and the Zr 02 purity was analyzed. Further, the powder was oxidized in the atmosphere at 800° C., and 3iQ2ffi remaining in the zirconia powder was also analyzed along with the same <ZrO2 purity analysis. Furthermore, the average particle size of the Zr 02 powder was examined using a scanning electron microscope during crushing and erosion.

The results of these analyzes are shown in Table 1.

Furthermore, Table 2 shows the results of similar treatment of a mixture of zircon powder, metal silicon powder, and carbon black.

As is clear from Tables 1 and 2, unstabilized zirconia powder having an arbitrary particle size as shown in FIG. 2 can be obtained by desiliconization treatment, particularly by changing the temperature.

(Effects of the Invention) As described above, according to the present invention, unstabilized zirconia powder having a desired particle size can be reliably and efficiently produced simply by controlling the heat treatment temperature.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between C/Si 02 <molar ratio) and the residual amount of 5io2. Figure 2 is the average of heat treatment conditions (temperature, time), residual M of Si 02, and desiliconization/disintegration erosion. A graph showing the relationship with particle size; Figure 3 is an electron micrograph showing the particle structure of zirconia powder when treated at 1300°C (low temperature); Figure 4 is an electron micrograph showing the relationship between zirconia powder
It is an electron micrograph showing the particle structure of zirconia powder during treatment at a high temperature (°C).

Claims (1)

[Claims] 1. When producing zirconia powder by heat-treating a mixture consisting of zircon powder, carbon-containing material and/or metal silicon powder, depending on the target particle size to be recovered. A method for producing zirconia powder, characterized in that the heating temperature during the heat treatment is selected and the desiliconization treatment is performed in a reduced pressure atmosphere.