JPS62256703A - Production of aluminum nitride powder - Google Patents

Abstract

PURPOSE:To obtain the title high-purity powder with high production efficiency and at a low cost by controlling the partial pressure and temp. of a nitriding gas to heat specified aluminum powder or fiber, and allowing the aluminum material to react with the gas in two steps. CONSTITUTION:The atomized aluminum powder having <=200mu particle diameter or the aluminum fiber having <=100mu diameter is used as the raw material, and 1-3wt% catalyst such as NaF and CaF2 is added, as required. The material is kept at 600-800 deg.C for >=3hr in the nitriding gas atmosphere contg. <=0.5atm partial pressure N2 or NH3, and the material is allowed to react with the gas to convert only the surface of the material into AlN. The partial pressure of the nitriding gas is then increased to >0.5atm, the temp. is increased to >800 deg.C, hence the material is allowed to react with the gas, and the whole material is nitrided. In this case, the content of the mixed impurities is adjusted to <=0.1%, and the title powder is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing high-purity aluminum nitride powder with a low content of oxygen as an impurity.

<Prior art and its problems> Aluminum nitride has high thermal conductivity, electrical insulation, and corrosion resistance, and its sintered body has high mechanical strength, so it is used as a high-temperature heat-resistant material and an electronic device material. It is used in many fields such as By the way, as methods for producing aluminum nitride powder, the direct nitriding method of metallic aluminum powder and the reductive nitriding method of alumina powder are well known. Among these methods, the direct nitriding method of metal aluminum powder is used because if the aluminum powder as a raw material is not fine, the heat generated by the nitriding reaction will cause the aluminum powder to become molten and agglomerate, making complete nitriding impossible. aluminum powder is used, and atomized aluminum powder and aluminum fiber, which have larger particles, are rarely used. Flake-like aluminum powder is excellent in that it is fine and easy to carry out the nitriding reaction, but because of its large specific surface area, it contains a large amount of surface oxide, and this surface oxide is thermochemically stable and nitriding reaction takes place easily. The oxygen content of aluminum nitride, which remains as it is after the process, increases, and impurities are unavoidable from the grinding process to make it into flakes, so high-purity aluminum nitride powder is There was a problem. Another typical method, the reduction nitriding method of alumina powder, requires a temperature of 1700°C in order to obtain a good nitriding rate.
It is expensive in terms of equipment and energy because it requires a high temperature of about 1000 yen, and a combustion process is also required to remove excess carbon, resulting in the aluminum nitride powder being expensive. There is a problem.

<Means for solving the problems> The present invention aims to solve the above-mentioned problems and provide a method for manufacturing high-purity aluminum nitride powder at low cost. Using aluminum powder or aluminum fibers with a diameter of 100 μm or less as a starting material, holding the starting material at a temperature range of 600 to 800 ° C. with a gas partial pressure of nitriding gas containing nitrogen gas or ammonia gas at 0.5 atmospheres or less for 3 hours or more, This is a method for producing aluminum nitride powder, which is characterized in that the partial pressure of the nitriding gas is then set to 0.5 atm or higher and heated and maintained at 800° C. or higher.

In the method of the present invention, conventionally known catalysts that are used when directly nitriding aluminum in a nitrogen gas atmosphere may also be used, such as alkali metal fluorides such as NaF and LiF, and catalysts such as CaF2. In some cases, alkaline earth metal fluorides such as fluorides, and further oxides and fluorides of rare earth elements are added to the above starting materials in an amount of 1 to 3% by weight.

<Function> In the present invention, the above-mentioned starting material is first maintained at a temperature range of 600 to 800°C with a partial pressure of nitriding gas of 0.5 atm or less, but in this temperature range an oxide film is formed on the surface of the starting material. As a result, it has not yet turned into a molten metal, but retains its solid form, and gradually begins to be nitrided from its surface. Experiments have shown that almost no nitriding occurs when this temperature is below 600°C, and at 800°C.
It was confirmed that when the temperature was exceeded, some molten metal appeared and the starting materials began to coagulate together. The partial pressure of the nitriding gas during this period is also closely related to the temperature, and if the partial pressure of the nitriding gas is made higher than 0.5 atm, the nitriding reaction will proceed rapidly and the temperature of the reaction system will become too high due to the heat generated. As the starting material begins to melt, an aluminum nitride layer of a certain thickness is formed on the surface, and the partial pressure of the nitriding gas is kept at 0.5 atm or less until the aluminum nitride layer becomes a protective layer for the inner metal aluminum layer. As the nitriding gas of the present invention, nitrogen gas is used in a predetermined reduced pressure state, mixed with argon gas or hydrogen gas and used in a predetermined partial pressure state, and ammonia gas is used alone or as a mixed gas with argon gas. There are various methods to use. Next, this 6
Regarding the holding time in the temperature range of 00 to 800℃, when no catalyst is used, the nitriding gas pressure is 0.2℃.
Preferably, the holding time is 5 hours or more under the atmospheric pressure condition, and 3 hours or more under the same 0.5 atmosphere condition. Although this holding time can be somewhat shortened by using the various catalysts mentioned above, the retention time is due to the promotion of the nitriding reaction. Sufficient attention must be paid to temperature rise. This 600~800℃
Temperature control may be carried out by holding the temperature at an intermediate temperature for a predetermined period of time, but in actual operation, a method is adopted in which the reactor is maintained at 600°C and is raised at a rate of, for example, 05°C/min. do.

In this way, after first forming an aluminum nitride layer of the required thickness on the surface layer of the starting material, the nitriding gas partial pressure is subsequently increased to 0.5 atm or more and 800°C or more, preferably 12
The entire raw material is nitrided by raising the temperature to around 00°C. In other words, the nitriding reaction is further promoted by increasing the nitriding gas partial pressure and temperature, and the reaction is further accelerated by the reaction heat generated by the reaction, and the raw material is heated to its core. Everything down to the top is nitrided.

Here, the atomized aluminum powder or aluminum fiber used as the starting material of the present invention is preferably coarse to some extent in order to avoid contamination with surface oxides, but conversely, if it is too coarse, the nitriding reaction will not take place sufficiently. So 200
It is preferable that the thickness be less than μm, preferably up to about 10 μm. The filling thickness of these starting materials into the reaction vessel is also important; if the filling thickness exceeds 5 cm, the oxide film or nitride film on the surface of the starting materials will be destroyed due to their own weight, leading to agglomeration of metal aluminum. occurs and the nitriding reaction does not proceed sufficiently, so it is desirable that the thickness of the filling in the reaction vessel be 5 cm or less.

<Example> Examples and comparative examples of the present invention will be shown below.

Zuko 1 Do LL 300 g of atomized aluminum powder with a particle size of 100 μm or less and a purity of 9999% was filled into a graphite crucible with a diameter of 10 cm to a filling thickness of 3 cm, and this was charged into a closed container and heated to 0.2 atm. After 3 hours at 650°C in a nitrogen atmosphere,
The temperature was maintained at 750° C. for 2 hours, and then the pressure of nitrogen gas was increased to 1 atm and the temperature was continued to rise. When the temperature reached about 850° C., a rapid reaction occurred and the nitrogen gas pressure in the closed container suddenly decreased. At this point, nitrogen gas was replenished into the sealed container to maintain the pressure at 1 atm, while the temperature was further raised to 1000° C. and held for 3 hours. When the sample was taken out after cooling, it turned out to be a grayish white mass, and when this sample was subjected to chemical analysis of crushed wheat, it was found that
It was aluminum nitride with a purity of 986%, metal aluminum was less than 0.1%, and oxygen content was 0.7%.

Fill a graphite crucible with a diameter of 10 cm with 300 g of atomized aluminum powder with a particle size of 100 μm or less and a purity of 9999% to a thickness of 3 cm.The crucible was charged into a sealed container and placed in a nitrogen atmosphere of 1 atm. The temperature was raised to 1000°C at a heating rate of 5°C/min in the chamber, and the temperature was maintained at 1000°C for 3 hours. When the sample was taken out after cooling, the surface was grayish-white aluminum nitride, but the inside was metal aluminum.

1 example: Aluminum short fiber with a diameter of 100 μm or less and a purity of 9999% (
(Length 10 m or less) 400 g was filled into a graphite crucible with a diameter of 10 cm so that the filling thickness was 5 cm, and this was placed in a sealed container, and the temperature was rapidly raised to 600 ° C in a nitrogen atmosphere of 0.5 atm. Thereafter, the temperature was raised to 800°C at a rate of 05°C/min. After that, when the nitrogen gas pressure was set to 1 atm and the temperature was further raised, a rapid reaction occurred at around 850℃, and the nitrogen gas pressure inside the sealed container suddenly decreased, so nitrogen gas was replenished from the outside and the nitrogen gas inside the sealed container was While maintaining the pressure at 1 atm, the temperature was raised to 1200°C and held at that temperature for 3 hours. When the sample was taken out after cooling, it turned out to be a grayish-white mass. After the sample was stopped, chemical analysis was performed, and it was found that the purity was 990% aluminum nitride, with less than 0.1% metallic aluminum.
The oxygen content was 0.5%.

10 Kado 1i A mixed powder obtained by dry mixing 300 g of atomized aluminum powder with a particle size of 200 μm or less and a purity of 9999% and 3 g of NaF powder as a catalyst is packed into a graphite crucible with a diameter of 10 cm so that the filling thickness is 3 cm, This was charged into a closed container and heated at 600°C for 1 hour in a nitrogen atmosphere of 0.2 atm.
After holding each temperature at 0°C, 700°C, 750°C, and 800°C for 30 minutes, the nitrogen gas pressure was set to 1 atm and the temperature continued to rise.A rapid reaction occurred around 850°C, causing the nitrogen gas pressure inside the sealed container to drop. As the pressure suddenly decreased, nitrogen gas was replenished from the outside and the nitrogen gas pressure inside the sealed container was maintained at 1 atm.
The temperature was raised to 0°C and maintained at this temperature for 3 hours. When the sample was taken out after cooling, it turned out to be a soft mass with beige surroundings and white inside. Chemical analysis of this sample revealed that it was aluminum nitride with a purity of 992%, and that the NaF added as a catalyst was It was less than 100 p, p, rm. This is thought to be because NaF was evaporated due to heat generated during the nitriding reaction. Further, the oxygen content in the obtained aluminum nitride was 0.4%.

Aluminum nitride was analyzed using an alkaline aqueous solution dissolution nitrogen distillation method, and aluminum not bonded to nitrogen is considered an impurity.

Further, the oxygen content was measured using an oxygen nitrogen analyzer manufactured by LECO.

<Effects of the Invention> As described above, according to the method of the present invention, the degree of reaction in the initial stage of the nitriding reaction is suppressed, that is, the temperature and partial pressure of the nitriding gas are kept below a certain limit, and only the surface of the raw material is first treated. Because this is a two-step reaction in which aluminum nitride is formed, and then the entire product is nitrided, atomized aluminum powder and Al-Em fibers, which are somewhat coarse particles or large-diameter fibers, can be used as raw materials. It is possible to suppress the intrusion of impurities such as oxygen into the aluminum nitride product to 1% or less.

Furthermore, the starting material used in the method of the present invention has the economic advantage of being cheaper than conventional flaky aluminum powder.
When filled into a reaction vessel during production, the packing density can be greater than that of flake aluminum powder even if the filling thickness is the same, so production efficiency can be improved, and from this point of view, the product is also cheaper. Therefore, its real social value is great.

Patent applicant: Mitsui Aluminum Industries Co., Ltd. Agent: Noriharu Haruki

Claims (1)

[Claims] 1. Atomized aluminum powder with a particle size of 200 μm or less or aluminum fiber with a diameter of 100 μm or less is used as a starting material, and the starting material is heated in a temperature range of 600 to 800°C with a nitriding gas containing nitrogen gas or ammonia gas. A method for producing aluminum nitride powder, which comprises keeping the gas partial pressure at 0.5 atm or less for 3 hours or more, then increasing the nitriding gas partial pressure to 0.5 atm or more and heating and holding at 800° C. or higher. 2. The method for producing aluminum nitride powder according to claim 1, characterized in that the thickness of filling the starting material into the reaction vessel is 5 cm or less.