JPH0623041B2 - Method for producing high-purity stabilized zirconia powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a highly purified stabilized zirconia (zirconium oxide: ZrO ₂ ) powder from zircon powder, and the technical contents described in this specification are as follows. By mixing the zircon powder, the carbon-containing material, and the stabilizer, and subjecting them to vacuum desiliconization heat treatment, the silica component in the zircon powder is volatilized and removed into the gas phase, and a large amount of high-purity stabilized zirconia powder is obtained. It proposes an advantageous method of manufacturing.

Such zirconia (ZrO ₂ ) is an oxide having a high melting point (2700 ° C. or higher) and is widely used as various refractory materials. Furthermore, in recent years, oxygen sensors and abrasives as solid electrolytes,
It is used as a raw material in fields such as electronic ceramics. Furthermore, recently, partially stabilized zirconia has a high strength and a high toughness function, and therefore, its use as an engineering ceramics has been attracting attention.

(Prior Art) The main techniques currently known as general zirconia powder production technology are the carbon desiliconization arc furnace melting method and the alkali melting method.

The above manufacturing method is based on zircon sand with coke and CaO.
By adding a stabilizer such as iron scrap and heating and reducing and melting in an arc furnace, SiO _{2 in} zircon
It is separated from the ZrO ₂ component by volatilizing it into the gas phase or reacting with iron to form ferrosilicon, and at the same time Ca
In this method, a stabilizing agent such as O is dissolved in ZrO ₂ to obtain a stabilized zirconia. Although this method can obtain inexpensive zirconia and is suitable for large-scale production, it has a problem that high-purity zirconia powder cannot be obtained.
Further, melting in an arc furnace requires a considerably high temperature and it takes time, and energy is required for crushing the obtained zirconia block, and there remains a problem from the viewpoint of energy saving.

The above-mentioned manufacturing method involves melting and reacting zircon sand with an alkali to wash and remove SiO ₂ content in zircon as an alkali silicate, while ZrO ₂ component is sodium zirconate, and then undergoes a process such as acid treatment. , Zirconium oxychloride (ZrOCl ₂ ). Since this zirconium oxychloride is soluble in water, the pH is adjusted to obtain zirconium hydroxide, which is then heat treated to obtain zirconia.
This method can obtain high-purity zirconia having a purity of 99% or more as compared with the above-mentioned manufacturing method, but its disadvantages are that the manufacturing process is complicated and thus the productivity is poor and the cost is very high.

Other techniques for producing zirconia powder are disclosed in Japanese Patent Laid-Open No. 58-58
-15021 has been disclosed. In this technique, a mixture of zircon sand and carbon powder is further mixed with stabilizers such as CaO, MgO and Y ₂ O _{3 for} granulation, and carbon particles are attached to the periphery of the particles. The present invention relates to a technique of simultaneously producing zirconia and SiC by heating SiO _{2 in} a non-oxidizing atmosphere to bring out SiO ₂ in the gas phase and reacting with carbon particulates. However, known techniques for producing the zirconia powder is also or residual SiO ₂ component is considerably during ZrO _2, there is a risk that SiC is or mixed in the ZrO _2, also high temperature to react,
It took a long time, and there were problems in terms of purity and productivity.

(Problems to be Solved by the Invention) An object of the present invention is to solve the above-mentioned problems of the prior art regarding a method for producing a stabilized zirconia powder from zircon powder, that is, to provide a highly purified stabilized zirconia at low cost. And it is to solve the problem that it cannot be manufactured efficiently.

According to the research conducted by the present inventors, as a result of earnestly studying a conventional carbon desiliconizing method for producing zirconia powder from zircon powder, it was found that SiO vapor from a silica component is efficiently removed during desiliconizing of zircon powder. Has been found to be very important in manufacturing, and for this reason, the inventors of the present invention have previously disclosed Japanese Patent Application Laid-Open No. 60-210530 or Japanese Patent Application Laid-Open No. 60-239325.
As proposed in Japanese Patent Application Laid-Open No. 60-239326, a new technique of desiliconizing carbon under reduced pressure was conceived.
In short, if carbon desiliconization is performed under reduced pressure, zirconia powder can be efficiently produced by heat treatment at low temperature for a short time even by the conventional carbon desiliconization method, but depending on the production conditions (mass production scale)
In some cases, SiO ₂ remained and high-purity zirconia powder could not be obtained.

(Means for Solving Problems) Therefore, the present inventors have studied a method for stably producing a highly pure stabilized zirconia powder even in the case of large-scale treatment.

In the case of producing zirconia by heat treating a mixture of zircon powder and carbon-containing material under reduced pressure, in the case of producing zirconia, as a main factor affecting the purity of the obtained zirconia, the combination of zircon powder and carbon-containing material The ratio, pressure, heat treatment temperature, heat treatment time and the like can be mentioned. The present inventors have made various investigations regarding these factors, and in order to stably produce a large amount of stabilized zirconia powder with high purity, in order to stably produce high-purity stabilized zirconia powder, the zircon powder, the carbon-containing material, and various stabilizers have been blended. We have reached the fact that it is effective not only to adjust the blending ratio, but also to select an appropriate temperature condition and perform heat treatment.

Therefore, in order to solve the above problems, the present invention, when producing a zirconia by desiliconizing by heating a mixture of zircon powder and a carbon-containing material, SiO ₂ in the zircon powder and C in the carbon-containing material With respect to the zircon powder and the carbon-containing material adjusted to have a mixing ratio such that the molar ratio (C / SiO ₂ ) of the zircon powder is within the range of 0.4 to 2.0, 0.5 to 20 mol of the ZrO ₂ component in the zircon powder. % Of each of MgO, CaO, Y ₂ O ₃ and CeO ₂ oxide or one or more stabilizers selected from compounds that become such oxides by heating, and zircon powder, carbon-containing material, A mixture of stabilizers or a molded product of the mixture is obtained, and the mixture or the molded product is first heated and maintained at a temperature of 1200 to 1550 ° C under a reduced pressure of 0.6 atm or less, and then a temperature of more than 1550 to 2000 ° C. Keep it heated to By adopting a method of firing in stages, it was made possible to stably produce a large amount of highly pure zirconia powder, and if necessary, further oxidize to obtain a higher purity product. .

(Operation) Zircon powder used in the method of the present invention, of course, the use of high-purity raw material is indispensable for producing high-purity zirconia powder, and it is better that the impurity components other than ZrO ₂ and SiO ₂ are as small as possible, For example, crushed zircon sand may be used. However, the finer one is desirable in order to promptly proceed the reaction with carbon. In concrete terms, ZrO ₂ + SiO ₂
Zircon powder with a particle size of 98.5% or more and a particle size of 44 μm or less is suitable.

Next, regarding the carbon-containing material mixed with the zircon powder in the present invention, it is desirable that the ash content is as small as possible in order to keep the purity of the obtained zirconia powder high. For example, as the carbon-containing material preferably used in the present invention,
Examples include petroleum coke and petroleum having a low ash content, coal pitch, carbon black, and the like. Further, organic resins such as phenol resin and polyethylene that generate carbon by heating can also be used.

Next, in the present invention, the zircon powder and the carbon-containing material are blended so that the molar ratio (C / SiO ₂ ) of silica in the zircon powder and carbon of the carbon-containing material is 0.4 to 2.0. The reason for being limited within this range is as follows. That is, the ratio of zircon to carbon-containing material (molar ratio C / SiO ₂ ).
Is less than 0.4, the zircon is completely desiliconized (SiO ₂
Although it is vaporized as steam, carbon is insufficient, and zircon remains after desiliconization. On the other hand, if C / SiO ₂ (molar ratio) is larger than ₂ , the amount of carbon is sufficient to reduce SiO ₂ in zircon to remove it as SiO vapor, but it is too reductive because of the large amount of carbon. Zirconium silicides such as ZrSi and Zr ₅ Si ₃ are generated, the amount of residual Si increases, and the amount of SiO ₂ in ZrO ₂ finally obtained (after oxidation treatment) increases, which deteriorates the purity. . Therefore, in order to keep the purity of zirconia in good condition, it is necessary to limit the amount of silica in the zircon powder and the amount of carbon in the carbon-containing material within the range of 0.4 to 2.0 in terms of C / SiO ₂ (molar ratio). . The carbon in the carbon-containing material used in the present invention is fixed carbon that participates in the desiliconization reaction at high temperature from which components that volatilize at 1000 ° C. or less are removed.

Next, in the present invention, the mixture of zircon powder and carbon-containing material, or a compact thereof, is subjected to desiliconization heat treatment at a pressure of 0.6 atm or less. This is because the zirconia cannot be effectively volatilized and removed, and SiO ₂ remains in the obtained zirconia so that a high-purity zirconia powder cannot be obtained.

The reduced pressure atmosphere used in the practice of the present invention is N ₂ , N ₂
A non-oxidizing gas atmosphere such as Ar or CO is suitable.

In the above description, the method of the present invention in which a mixture of zircon sand and carbon is simply desiliconized under reduced pressure has been described, but this desiliconization treatment produces high-purity zirconia powder. However, the zirconia powder obtained in this way is also called unstabilized zirconia, and the main uses of this powder are electronic materials such as piezoelectric elements and ceramic contents, raw material powders for producing optical glass and the like.

Such unstable zirconia belongs to the monoclinic type crystal, 11
It transforms to a tetragonal crystal at around 00 ° C, and a large volume change occurs at this time. Due to this volume change, even if the unstabilized zirconia powder alone is compacted and sintered as it is to obtain a sintered body, it is not possible to obtain one having the required strength at room temperature. Therefore, in the present invention, in order to eliminate the volume change due to the monoclinic type ← → tetragonal type transition of the unstabilized zirconia, in addition to the zircon powder and the carbon-containing material, the unstabilized zirconia further forms a solid solution in the structure of zirconia. The mixture to which the stabilizing oxide component was also added was subjected to heat treatment under reduced pressure to promote desiliconization by carbon reduction, and at the same time to produce stabilized zirconia.

As described above, the present invention as a stabilizing component includes MgO, CaO, Y ₂ O ₃ and
CeO ₂ or _{MgCO 3, Ca (OH) 2} , CaCO 3, YCl 3 · 6H 2 O, Ce (NO 3) 3
0.5 to 20 mol% in terms of oxide, based on the ZrO ₂ component in the zircon powder, of one or two or more selected from compounds such as 6H ₂ O that become oxides when heated.
In addition to the zircon powder and the carbon-containing material, the mixed powder or a molded body thereof is subjected to the above-mentioned desiliconization treatment by carbon reduction under reduced pressure to stabilize zirconia.

Zr in zirconia powder with the amount of stabilizer added as oxide
The reason for limiting the range of 0.5 to 20 mol% relative to the O component is that the amount is insufficient to stabilize ZrO ₂ if the amount is less than 0.5 mol%, and conversely if the amount is more than 20 mol%, the zirconia is single. This is because not only the phase but also the second phase, for example, a crystal phase such as CaZr ₄ O ₉ or Zr ₃ Y ₄ O ₁₂ is precipitated, and the strength of the crystal body is reduced.

The high-purity zirconia powder can also be produced by appropriately subjecting a mixture obtained by selecting the above-mentioned raw materials and appropriately blending them or a molded body thereof to heat treatment for desiliconization. However, it is limited to the case of a small amount production of 100 g or less as in the conventional case, and the situation is different when the mass production is performed as in the present invention. That is, when the amount becomes large, depending on the location of the mixture of the zircon powder and the carbon-containing material, zircon may remain and a high-purity (> 98%) zirconia powder cannot be stably obtained. In order to solve these problems, the present inventors further studied the reduced pressure heat treatment conditions, and by performing two-stage firing of a temperature range of 1200 to 1550 ° C. and a temperature range of over 1550 to 2000 ° C., They have found that a high-purity zirconia powder of 99% or more can be obtained even in a large amount of 1 kg or more.

The findings of the present inventors regarding the above-mentioned two-step firing peculiar to the vacuum desiliconization heat treatment of the present invention are as follows. That is, when a high temperature of more than 1550 ° C is applied from the beginning, a rapid dissociation of zircon into ZrO ₂ and SiO ₂ occurs and MgO, CaO, Y ₂
Stabilizers such as O ₃ and CeO ₂ react with SiO ₂ and the reaction products prevent the evolution of SiO 2 vapor. Therefore, in order to achieve high purity, it is first necessary to gradually remove silicon at a temperature of 1200 to 1550 ° C. as the first stage firing. After desiliconization is almost completed in this temperature range, the second stage of firing is 15
When the temperature is raised from more than 50 to 2000 ° C, the remaining SiO ₂ component is completely volatilized as SiO vapor, and the stabilizer Zr
The increase in the diffusion rate of O ₂ promotes solid solution.

The upper and lower limits of steam heat treatment temperature are 1200 ° C.
If it is lower than 2000 ° C., it takes a long time to desiliconize and the productivity is deteriorated. If it is higher than 2000 ° C., the energy cost is increased due to the heat treatment.

In the present invention, most of the crystals produced by the reduced pressure heat treatment are ZrO ₂ , and depending on the mixing ratio of zircon and carbon the second
As shown in the table, some ZrO and ZrC are generated. In such a case, after the heat treatment for desiliconization, oxidation treatment is performed and Zr
O, ZrC, etc. are changed to ZrO ₂ , and further high purification is achieved.

In the present invention, in order to completely desiliconize the silica powder in the zircon, the carbon-containing material may be blended so that the carbon content may be slightly in excess of the molar ratio corresponding to the silica in the zircon. In such a case, ZrO, ZrC, and further a solid solution of these may be formed depending on the heat treatment conditions for desiliconization.
In short, the oxidation treatment in the present invention is a treatment performed to oxidize ZrO or ZrC to ZrO ₂ . At the same time, if any carbon remains after the heat treatment, it is also oxidized and volatilized in the gas phase to be removed. The temperature during the oxidation treatment is 600-900
A range of ° C is suitable.

(Example) Average particle size of 1.5 μ at which the total content of ZrO ₂ and SiO ₂ becomes 99.0%
m zircon powder and carbon black with an average particle size of 560Å (fixed carbon 99%, ash content 0.1%)
The molar ratio of SiO ₂ and fixed carbon in carbon black (C / SiO
₂ ) was mixed in a large amount so as to be 1.2, and then a stabilizer as shown in Table 1 was mixed and mixed well, and then a 10 mmφ × 20 mm H cylindrical tube was prepared using a mold molding machine. Many samples were molded. Using these compacts, vacuum desiliconization treatment was performed under the heat treatment conditions shown in Table 1. The amount of treatment per treatment was 5 kg in terms of the mixture amount of zircon powder and carbon black.

After the heat treatment, powder X-ray diffraction was used to identify the existing crystal phases, and after the oxidation treatment at 800 ° C, the residual amount of SiO ₂ and Zr
O ₂ purity analysis was performed. The results are also shown in Table 1.

As is clear from Table 1, by employing the vacuum degassing珪熱process over two stages of calcination at higher temperatures than 1550 ° C. or lower temperature firing and 1550 ° C., the high-purity low SiO ₂ remaining amount Stabilized zirconia powder can now be manufactured on a mass production scale. Moreover, with the oxidation treatment, a high purity of 99% or more was obtained.

(Effects of the Invention) As described above, according to the present invention, it is possible to accurately and efficiently manufacture inexpensive, highly pure, stabilized zirconia powder in a mass production scale.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masao Oguchi 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Division

Claims (2)

[Claims] 1. When producing a zirconia powder by desiliconizing a mixture of zircon powder and carbon-containing material by heat treatment for a predetermined time, the molar ratio of SiO ₂ in the zircon powder and C in the carbon-containing material. (C
/ SiO ₂ ), with respect to the zircon powder and the carbon-containing material having a compounding ratio of 0.4 to 2.0, the amount of MgO corresponding to 0.5 to 20 mol% with respect to the ZrO ₂ component in the zircon powder, A mixture prepared by adding one or more stabilizers selected from the oxides of CaO, Y ₂ O ₃ and CeO ₂ or compounds that become such oxides by heating, or a molded product of the mixture, 0.
A method for producing a high-purity stabilized zirconia powder, which comprises performing a heat treatment in which the temperature is maintained at 1200 to 1550 ° C under a reduced pressure of 6 atm or less, and then the temperature is maintained above 1550 to 2000 ° C. 2. When producing a zirconia powder by desiliconizing a mixture of zircon powder and carbon-containing material for a predetermined time, the molar ratio of SiO ₂ in the zircon powder and C in the carbon-containing material. (C
/ SiO ₂ ), with respect to the zircon powder and the carbon-containing material having a compounding ratio of 0.4 to 2.0, the amount of MgO corresponding to 0.5 to 20 mol% with respect to the ZrO ₂ component in the zircon powder, A mixture prepared by adding one or more stabilizers selected from the oxides of CaO, Y ₂ O ₃ and CeO ₂ or compounds that become such oxides by heating, or a molded product of the mixture, 0.
High-purity stability characterized by performing heat treatment by first heating and holding at a temperature of 1200 to 1550 ° C and then holding at a temperature of more than 1550 to 2000 ° C under a reduced pressure of 6 atm or less, and subsequently performing an oxidation treatment. Method for producing powdered zirconia powder.