JPH0256288B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing zirconia, and in particular,
The present invention relates to a manufacturing method for obtaining highly pure and ultrafine zirconia required as a material for new ceramics. Zirconia has been used as a pigment and a heat-resistant material for a long time, and is industrially manufactured by various methods. Among these, the dry method and wet method described below have been widely used as manufacturing methods using zircon as a starting material. Dry method This is a method of manufacturing zirconia by blending carbon powder with zircon and reducing and melting this mixture in an arc furnace. It is difficult to remove silica using this dry method. Note that since the reduction to completely remove silica progresses excessively and zirconium carbide is produced, it must be returned to zirconia by heating and oxidation later. Furthermore, since the product is in the form of lumps, a mechanical pulverization process is required to obtain powdered zirconia, and impurities are mixed in during this process, which inevitably lowers the purity. Wet method By melting zircon with an alkali, silica is removed as water glass and zirconium is recovered as sodium zirconate. continue,
A mineral acid is added to the recovered sodium zirconate to form a zirconyl salt, which is then converted to zirconia via a hydroxide. Although silica can be removed by this wet method, the yield is low due to poor reactivity between zircon and alkali, and moreover, a large amount of water glass is generated. Moreover, the Na ⁺ of the recovered zirconyl salt
Since the degree of removal is incomplete, the purity of the obtained zirconia decreases and it tends to aggregate more easily. By the way, when zirconia is to be used for new ceramic applications that have been in the spotlight in recent years, such as engine piston heads and cylinder inner cylinders, zirconia is required to have high purity and ultrafine particles. In particular, it is known that the particle size greatly affects the physical properties of zirconia sintered bodies, such as toughness, and it has been reported that when the particle size exceeds 0.5 μm, rapid changes in the physical properties of the sintered body occur over time. (FCREPORT Vol. 1, No. 6, pp. 8-14, published by Fine Ceramics Association, June 25, 1981).
With the conventional manufacturing method described above, it has been extremely difficult to obtain zirconia that satisfies these requirements. Therefore, various new production methods have been proposed in order to produce highly pure and ultrafine zirconia. The following two manufacturing methods are representative among them. In the first method, zircon sand is thermally dissociated into zirconia and silica in a plasma furnace, and then treated with sodium hydroxide to recover zirconia and remove silica as water glass. Hereinafter, this first method will be referred to as the improved dry method. The second method involves blending carbon powder with zircon sand, directly chlorinating this mixture at a high temperature of 1000°C or higher, converting components such as Zr contained in zircon into chlorides, and gasifying them. Zirconium tetrachloride contained in the gas is isolated from other components as basic zirconium hydrochloride (ZrOCl ₂ (OH) ₂ ), and this is converted into zirconia by firing. Hereinafter, this second method will be referred to as the direct chlorination method. These new methods have made it possible to obtain zirconia of considerably higher purity and finer particles than in the case of conventional dry or wet methods. However, even with these new production methods, high purity and ultrafine particle size that are fully satisfactory as a new ceramic material have not been achieved, and the above-mentioned direct chlorination method has the problem of low yield. . In view of the above circumstances, the present invention was made with the object of obtaining zirconia that satisfies the requirements of high purity and ultrafine grains required for use as a new ceramic material. As a result of intensive research to achieve the above object, the inventor combined the above-mentioned improved dry method and direct chlorination method to thermally dissociate zircon into zirconia and silica, and then applied the chlorination method to this. The inventors have discovered that by applying this method, it is possible to obtain ultrafine zirconia of high purity and ultrafine particles in a high yield, which has not been achieved in the past, leading to the present invention. That is, the present invention comprises a step of thermally dissociating zircon, a step of reacting a mixture of the thermally dissociated zircon and carbon powder with chlorine at 400 to 600°C, and a gas containing zirconium tetrachloride from the reaction step. converting the zirconium tetrachloride to zirconyl chloride (ZrOCl ₂ ) by extracting the product and introducing it into water; isolating basic zirconium hydrochloride from the aqueous solution containing the zirconyl chloride; This method of producing zirconia is characterized by comprising a step of firing zirconium to obtain zirconia. The details of the present invention will be explained below. In the present invention, first, zircon sand used as a raw material is thermally dissociated into zirconia and silica at a high temperature. The dissociation temperature at that time varies depending on researchers' reports, but it is said that dissociation is almost complete at 1760°C. This thermal dissociation can be performed in an electric furnace or the like, but if it is performed in a plasma furnace, the thermal dissociation occurs in a short time, resulting in less heat consumption, and the process can be transferred to the next step continuously. Excellent. Next, carbon powder is added to the thermally dissociated zircon to form a mixture, which is heated to 400 to 600℃.
to react with chlorine. As a result, zirconia and silica contained in the mixture become tetrachloride through the following reaction. ZrO ₂ +C+2Cl ₂ →ZrCl ₄ +CO ₂ SiO ₂ +C+2Cl ₂ →SiCl ₄ +CO ₂ ZrCl ₄ (sub.p. 300°C) and SiCl ₄ (bp 57°C) become gaseous products under the above reaction conditions. In addition, Ti, Al, which were contained as impurities in the raw materials,
Fe also reacts in the same way as above, producing gaseous products.
They become TiCl ₄ , AlCl ₃ , FeCl ₂ , and FeCl ₃ . Note that the trace impurities Mg and Ca also become chlorides through the same reaction, but their bp is 1412℃ and 1412℃, respectively.
Because it is as high as 1600°C, it does not enter the gaseous product system at the above reaction temperature. The most important feature of the present invention is to perform chlorination after thermally dissociating zircon as described above, and its action is as follows. That is, zirconia produced by thermal dissociation and silica have significantly different coefficients of thermal expansion. Therefore, due to the dissociation, the zircon is violently disintegrated and pulverized by the increased strain stress. This is considered to be the biggest reason why ultrafine zircon particles can be obtained in the present invention. Moreover, since the raw material zircon is pulverized in this way, the reactivity in the subsequent chlorination step becomes extremely good. In other words, in the conventional direct chlorination method that does not perform thermal dissociation in advance, in order to perform chlorination at a sufficient reaction rate,
Whereas chlorination requires a high temperature of 1000°C or higher and has a low reaction rate, in the case of the present invention, chlorination can be carried out at a low temperature of 400 to 600°C with a high reaction rate. As a result, as mentioned above, trace impurities such as Mg and Ca are eliminated at this stage. Next, a process for obtaining zirconia from the gaseous product obtained in the above chlorination process will be explained.
This process is almost the same as in conventional direct chlorination methods. First, the gaseous mixed product described above is introduced into water. As a result, zirconium tetrachloride and silicon tetrachloride are immediately hydrolyzed according to the following formula, zirconium tetrachloride is converted to zirconyl chloride, and silicon tetrachloride is precipitated as silica. ZrCl ₄ +H ₂ O→ZrOCl ₂ +2HCl SiCl ₄ +H ₂ O→SiO ₂ ↓+4HCl At the same time, titanium tetrachloride contained as an impurity is also hydrolyzed and precipitated as titanic acid. Subsequently, after removing the above precipitate by filtration, the filtrate is acidified with hydrochloric acid. As a result, zirconyl chloride in the filtrate precipitates as basic zirconium hydrochloride, while aluminum and iron chlorides remain in the filtrate. Therefore, basic zirconium hydrochloride is isolated by filtering this. Zirconia can be obtained by firing the basic zirconium hydrochloride thus obtained. In this case, it is difficult to completely remove chlorine, so the purity must be slightly lowered. Therefore, as described below, basic zirconium hydrochloride is reacted with an aqueous alkali carbonate solution to form basic zirconium carbonate (ZrCO ₃ (OH) ₂ ), which is then fired at a temperature of 1000°C or higher to form zirconia. It is desirable to do so. More preferably, a mineral acid such as hydrochloric acid or sulfuric acid is added to the basic zirconium hydrochloride to produce zirconyl chloride or zirconyl sulfate (ZrOSO ₄ ), and then aqueous ammonia is added to precipitate zirconium hydroxide. After drying the precipitate after filtration, it is possible to obtain the most excellent result, that is, ultrafine zirconia particles with a purity of 99.9% and a maximum particle size of 0.08 μm, by calcining at 1000° C. or higher. Examples of the present invention will be described below. Example 1 Zircon sand having the composition shown in Table 1 below,
Thermal dissociation was completed by contacting it with a flame in an arc plasma furnace (35kW, 11000℃) for about 0.2 seconds.
For each 100 parts by weight of zircon powder with a particle size of 100 mesh or less that has been thermally dissociated, 25 parts of carbon powder is added.
Parts by weight were blended. Subsequently, the obtained mixture was placed in a quartz boat and placed in a 30 mmφ quartz reaction tube. Next, 200 ml/min of chlorine was passed through the reaction tube placed in a tubular electric furnace, and annealing was performed at 500° C. for 1 hour. The gaseous product resulting from this reaction was introduced into water, and the precipitated silica and titanic acid were filtered off. 1N hydrochloric acid was added to the filtrate to obtain a precipitate of basic zirconium hydrochloride. After filtration, the basic zirconium hydrochloride precipitate was dried at 110°C and fired in an electric furnace at 1000°C for 1 hour to obtain zirconia powder. The yield, purity and maximum particle size at this time are shown in Table 2 below. Example 2 A basic zirconium hydrochloride precipitate obtained in the same manner as in Example 1 was poured into a 50% aqueous sodium carbonate solution,
By stirring, basic zirconium hydrochloride was precipitated and separated by filtration. Then, the basic zirconium hydrochloride precipitate
Zirconia powder was obtained by drying at 110°C and firing at 1000°C for 1 hour. The yield, purity and maximum particle size at this time are shown in Table 2 below. Example 3 Basic zirconium carbonate obtained in the same manner as in Example 2 was dissolved in a 30% hydrochloric acid solution to obtain a zirconyl chloride solution. Add 20% alkaline water to this,
When the pH was adjusted to 8, a precipitate of zirconium hydroxide was formed. This precipitate was filtered, dried at 110°C, and then calcined at 1000°C in an electric furnace to obtain zirconia powder. The yield, purity and maximum particle size at this time are shown in Table 2 below. Comparative Example Zirconia powder was produced from zircon sand having the composition shown in Table 1 by a direct chlorination method. The yield, purity and maximum particle size at this time are shown in Table 2 below.

【table】

[Table] As is clear from the results in Table 2, according to the production method of the present invention, ultrafine, highly pure zirconia, which could not be obtained conventionally, can be obtained at a high yield.
In particular, the fact that the particle size of the obtained zirconia is smaller than 0.5 μm is extremely important in expanding the use of zirconia to the field of new ceramic materials, such as engine piston heads and cylinder inner cylinders. be.

Claims (1)

[Claims] 1. A step of thermally dissociating zircon, and adding a mixture of the thermally dissociated zircon and carbon powder.
reacting with chlorine at 400 to 600° C.; converting the zirconium tetrachloride to zirconyl chloride by extracting a gaseous product containing zirconium tetrachloride from the reaction step and introducing it into water;
A method for producing zirconia, comprising the steps of isolating basic zirconium hydrochloride from an aqueous solution containing the zirconyl chloride, and firing the basic zirconium hydrochloride to obtain zirconia. 2. The method for producing zirconia according to claim 1, characterized in that the isolated basic zirconium hydrochloride is converted into basic zirconium carbonate and then calcined. 3. The method for producing zirconia according to claim 1, characterized in that the isolated basic zirconium hydrochloride is converted into basic zirconium carbonate, further converted into zirconium hydroxide, and then fired. .