JPH0212884B2 - - Google Patents

Description

Detailed Description of the Invention The present invention reliably produces ultrafine powder of hafnium oxide (HfO ₂ ) (hereinafter referred to as hafnia), which could hardly be obtained by conventional methods, and also improves the fineness and its range. The present invention relates to a method that can obtain highly pure products by controlling substantially as intended. Conventionally, fine powder of hafnium oxide has generally been obtained by a method for producing fine powder particles of metal oxide. In other words, these conventional methods can be roughly divided into mechanical,
It can be classified into chemical, physical, etc. methods, but on the other hand, due to the recent advances in technology, it is necessary for materials to satisfy not only ultrafine powder but also high purity and homogeneity. However, when using mechanical methods such as pulverization or grinding, if the particle diameter is below a certain level, for example, 10 μm (100,000 Å) or less, agglomeration of the particles occurs, so it is almost impossible to obtain fine powder smaller than that. The high purity cannot be maintained by mixing fine particles of the upper grinding media or the material of the attritor. Next, as a chemical method, there is a method of thermally decomposing a hafnium salt directly or a hydroxide precipitated from a solution thereof to form an oxide. The fine particles produced by this method have the disadvantage that they contain impurities such as salts of the starting materials and components contained in the precipitant. In particular, if the thermal decomposition temperature is set to a low temperature for the purpose of obtaining fine particles, there will be a large amount of residual impurities, and if heated to a high temperature to remove these impurities, grain growth will occur and become large particles. Therefore, it is almost impossible to obtain highly pure ultrafine powder by such a thermal decomposition method. Next, there is a physical method of volatilizing the metal itself, oxidizing it, and then condensing it, but in the case of Hf, it is extremely difficult because the boiling point is as high as 3200℃, and many particles aggregate when cooled, so it is difficult to cannot be manufactured. In the end, the size of the high-purity hafnia oxide fine particles obtained by the conventional technique outlined above is only 500 Å at the minimum.
Moreover, the range of variation was extremely wide, ranging from 50,000 to 500 Å, and it was completely impossible for the operator to freely adjust the range at will. Furthermore, the finer the particles, the more likely they are to contain impurities. However, in general, fine particles or ultrafine particles are better for obtaining dense ceramics, and sensors, other electronic materials, precision mechanical tools, etc. cannot be made with high performance unless materials with finer particles are used. On the other hand, if coarse particles are mixed in or the particle size distribution is uneven, the resulting ceramic product will have poor mechanical strength and poor light-transmitting and insulating properties, making it impossible to obtain a product of good quality. The same applies to ceramics made from hafnia, and the conventional level of fineness is still insufficient. The present invention compensates for the deficiencies of the prior art, and involves processing hafnium in the presence of water under a specific range of high temperature and pressure as detailed below to produce ultra-high purity hafnia that has never been obtained before. We have developed a method that can obtain fine powder, and we have also developed an interim method that allows us to control the degree of ultra-fine powder, the degree of fine powder, and its range as much as possible. As well as announcing this, further disclosure and provision is hereby made. From the results of many basic experiments, the present inventors were able to infer that hafnium turns into hafnia through the following three-step reaction under high-temperature, high-pressure water. That is, the first stage reaction Hf+2H ₂ O→HfO ₂ +2H ₂ [Formation of HFO ₂ film on the HF surface] Second stage reaction Hf+x/2H ₂ →HfHx Third stage reaction HfHx+O ₂ →HfO ₂ +x/2H ₂ be. In this reaction process, the generated _H2
It was thought that the second stage of reaction with Hf metal promoted pulverization. As a result of repeated experiments, they were able to create a method to obtain highly pure hafnia (HfO ₂ ) as an ultrafine powder. The conditions for this are as follows: First, from the three-step reaction mentioned above, it is necessary to have at least 2 moles of water (H ₂ O) per mole of hafnium (Hf) in a weight ratio, and based on many experiments, the temperature conditions are as follows. It was found that the reaction did not occur at all below 300°C, so the temperature had to be above 300°C, and it was found that if the temperature exceeded 1300°C, it would be difficult to carry out and the particles would become large. Must be below ℃. Next, as for pressure conditions, there is almost no reaction under 0.1 MPa (about 1 atm), and 1000 MPa (about 10,000 atm).
If it exceeds 0.1 MPa or more, it becomes almost impossible to carry out the reaction, so the range in which the reaction is possible is 0.1 MPa or more and 1000 MPa.
It is necessary that the following is true. Furthermore, as for the time factor, the reaction is completed immediately if the temperature and pressure are high to a certain extent, so the time requirement is not particularly necessary. These conditions described above will be described in detail later in the Examples and further explained in detail with reference to the drawings. The specific means for producing ultrafine hafnia powder under these conditions is as follows, although it is on a trial scale. The means for producing ultrafine powder hafnia under these conditions is to heat metal hafnium (Hf) together with high-purity water in the proportions described above in a heat-resistant and pressure-resistant container. In this case, the container may be made of a material and in any shape (for example, a test tube type high-temperature, high-pressure container) that does not react with the high-temperature, high-pressure water or hafnium under the above conditions, but a large autoclave or the like may also be used. If contamination of the product is a problem due to erosion of the high-temperature, high-pressure container by water, it is possible to isolate the product from the container by using a capsule made of platinum or the like, and the capsule can be sealed by welding or other means. Then, the interior will only contain high-purity water and Hf metal, and there will be no room for any impurities to enter. Another feature of the present invention is that metal hafnium is chemically refined by reaction with water or hydrogen, so the hafnium used as a starting material is not subject to any restrictions on shape, size, particle size, etc. It is. When Hf strips and high-purity water (bi-distilled water) are sealed in a platinum capsule and reacted in a test tube type container, the reaction temperature and pressure are as described above, 300-300℃.
1300℃There are many combination methods in the range of pressure 0.1MPa to 1000MPa, but for example, if the pressure is
If it is 100MPa (approximately 1000Kg/cm ² ), the temperature is 300℃
From the time the reaction starts, some unreacted substances exist until about 600℃, and when the temperature exceeds 600℃, most of it changes to HfO ₂ and 700℃.
If the temperature exceeds ℃, everything becomes HfO ₂ . Also increase the temperature to approx.
If the temperature is kept at around 500℃, the reaction will start if the pressure is 0.1MPa or higher, and at around 150MPa it will mostly change to HfO ₂ , and if it exceeds 170MPa, it will all be HfO _2.As for the time, if the pressure and temperature are high, the reaction will start. It reacts almost immediately, but for example at a temperature of 500℃ and a pressure of 100MPa.
By the way, most of it becomes HfO 2 in 30 hours, and all of it becomes HfO ₂ in 120 hours. When the reaction was complete, the temperature and pressure were gradually lowered, and HfO ₂ was taken out and heated to 100°C.
Dry at around temperature. The product may appear to be agglomerated at first glance, but if you move it gently, you will get a smooth, ultra-fine powder as a whole. When observed under a microscope, the fineness of the powder obtained by the method of the present invention is far below the minimum particle size of 500 Å according to the prior art, and the minimum particle size is about 100 Å.
It ranges from an average of 200 Å to a maximum of 400 Å depending on temperature conditions. Furthermore, by selecting the temperature, pressure and time of the reaction, the average particle size and range of the product can be controlled with considerable freedom. For example, if the reaction temperature is lowered and the reaction pressure is increased, the average particle size of the HfO ₂ produced will decrease, that is, the fineness will increase; Fineness can be reduced. As described above, according to the method of the present invention, ultrafine powder of high-purity hafnia (HfO ₂ ) of 500 Å or less, which could not be obtained at all using conventional techniques, can be obtained in the range of up to 100 Å, and the average It can be said that we were also able to provide an epoch-making new method in which the particle size can be freely controlled by the producer. This has also made it possible to provide more advanced materials for use in electronic industry materials, precision processing, and machine tools. Example 1 In a reaction experiment between Hf and high-temperature, high-pressure water, Hf metal pieces with an average size of 1 x 0.2 x 0.02 mm and redistilled water were sealed in a platinum capsule at a molar ratio of H ₂ O / Hf = 2:1. death,
Put it in a test tube type pressure vessel and check the temperature
This was done by heating in the range of 300 to 700°C. The pressure and time at that time are 25MPa to 150MPa and
It ranges from 3h to 120h. We also conducted an open system experiment under similar experimental conditions. The products were examined using a scanning electron microscope (SEM) and an X-ray powder diffractometer. In addition, the product was partially quantified using the X-ray powder pattern matching method. The products are unreacted Hf metal, Hf hydride and _HfO2
Consists of. Changes in the quantity ratio of products obtained in closed system experiments with respect to temperature, pressure, and time are first
This is shown in FIGS. These results show that the HfO ₂ generation reaction becomes active at temperatures above 600℃ and at a pressure of 75MPa.
The reaction rate decreases rapidly below 500
It has become clear that the reaction can proceed completely even at ℃ by long-term heating. Furthermore, experiments in an open system revealed that the reaction proceeded more slowly at 500°C and faster at 600°C than in a closed system. Figure 1 is an example of the range of conditions that can produce intermediate products HfHx and HfO 2 when the pressure is 100 MPa and the reaction temperature is varied, and Figure 2 is an example of the range of conditions that can produce the intermediate products HfHx and HfO ₂ when the reaction temperature is 500°C and the reaction pressure is varied. Figure 3 is a diagram of the range of conditions under which a similar product can be produced when
FIG. 2 is a diagram showing the range of conditions for producing similar target products and intermediate products with respect to reaction time when the pressure is 100 MPa and the temperature is 500°C. Example 2 Using the same high-temperature and high-pressure container as in Example 1, and using the same materials, the target material was made finer by lowering the processing temperature and increasing the processing pressure, and vice versa. By this method, it is possible to obtain the target hafnia with reduced fineness. Examples are shown in Table 1. 【table】

[Brief explanation of drawings]

Figure 1 shows the intermediate products and target product (HfO ₂ ) when the processing pressure is 100 MPa and the processing temperature is changed.
Generation condition range diagram. Figure 2 is a diagram showing the range of production conditions for intermediate products and the target product (HfO ₂ ) when the processing temperature is 500°C and the processing pressure is varied. FIG. 3 is a diagram showing the range of production conditions for intermediate products and the target product (HfO ₂ ) with respect to reaction time when the processing pressure is 100 MPa and the processing temperature is 500°C.

Claims (1)

[Claims] 1 2 to 1 mole of hafnium (Hf) by weight
0.1 MPa (megapascal) or more in a temperature range of 300°C to 1300°C by adding more than mol of water (H ₂ O)
A method for producing ultrafine powder of hafnium oxide, characterized by carrying out hydrothermal synthesis at a pressure in the range of 1000 MPa or less. 2. The method of hydrothermal synthesis is defined in claim 1.
A patent claim that is a method of increasing the fineness by lowering the reaction temperature and/or increasing the reaction pressure, or decreasing the fineness by increasing the reaction temperature and/or lowering the reaction pressure, within the range specified in paragraph 1. A method for producing ultrafine hafnium oxide powder according to item 1.