JPS58181708A - Method for purifying boron nitride - Google Patents

Abstract

PURPOSE:To obtain superhigh purity BN without damaging heating furnaces by heating BN powder to a specified temp. in a heating furnace using a graphite furnace material and further heating it in a heating furnace using a furnace material generating no gas contg. carbon under specified conditions. CONSTITUTION:BN powder or a sintered BN body is heat treated at 2,000- 2,200 deg.C, preferably 2,050-2,150 deg.C in a heating furnace using a graphite furnace material such as a graphite heater to remove most of hydrogen, carbon impurities and oxygen. It is further heated to 2,000-2,200 deg.C, preferably 2,050-2,150 deg.C in an atmosphere having a higher partial pressure of nitrogen than the decomposition pressure of BN in a heating furnace using a furnace material generating no gas contg. carbon such as an Mo heater. Thus, superhigh purity BN can be manufactured over a long term without damaging the Mo heater, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying boron nitride, particularly a method for purifying boron nitride that does not contain impurities of oxygen and carbon. In addition, the sintered body also contains oxygen with a strength of 7 to 1, and a small amount of carbon. In addition, commercially available hBN (
Hexagonal II BN (hereinafter referred to as hBN) high purity II
! Even BN contains oxygen at about O and S%.

,C:・When OBN (cubic crystal type BN, hereinafter referred to as OBN) is produced by high-pressure wood transfer using these oxygen-containing BN as raw materials, the yield of OBN is very poor. The strength and optical clarity of the product will also be poor. Furthermore, when this oxygen is contained, the BM material reacts with the metal material at high temperatures. For example, BN containing oxygen reacts with molybdenum at temperatures below 1100°C. Furthermore, the electrical insulation properties at high temperatures, for example, zoooo°C, are also poor. Although BN is heat resistant, the -stunability is not proportionally high because it contains impurities such as oxygen and carbon. According to the Super High Single Point Material Handbook (published by Nisso Tsushinsha in 1939), as shown in Figure 1, the conventional B N Fi3
At a temperature of 00℃, the electrical resistivity value is high, but 1200℃
℃, and is below 10Ωα at 2000℃.

In order to prevent these drawbacks, it is necessary to remove oxygen, carbon, etc. contained in BN as much as possible.

Conventionally, as a method for purifying boron nitride, there is a known method in which boron nitride powder is heated in a nitrogen atmosphere using a 90°C heating furnace using molybdenum as the furnace material. There is.

The reason why molybdenum is used as a furnace material and a nine-heating furnace is because molybdenum has a high melting point that does not generate carbon or oxygen up to a high temperature of about 2≦OO°C, and has good workability. However, if the raw material BN contains oxygen, it reacts with molybdenum and has a major disadvantage of causing the heating furnace to deteriorate in a short period of time.

4. An object of the present invention is to provide a purification method capable of obtaining ultra-high purity BN and BN sintered bodies in which oxygen and carbonaceous impurities are below the detection limit.

The present inventor discovered that when BN powder is heated, impurities such as C, 111°0, etc. are n2. B20, Co, co2.
(32N, .

We studied the situation in which B20゜l escapes as a vaporized substance such as B2O5, and clarified the following.9. Hydrogen begins to escape when heated to 100°C, and can be reduced to below the detection limit in about 7 hours when heated to 7200°C. Carbon is treated at 1900°C for 1 hour to reduce the initial carbon concentration to l.
When the detection limit of 0.2% by weight falls below Δ0 in 2 hours, the rate of decrease suddenly decreases, and in order to remove this trace amount of oxygen, the temperature needs to be 2000°C or higher, and B2
0. The vaporization of boron oxide rapidly progresses around the boiling point (20 degrees Celsius) (3 degrees Celsius). Make it clear.

However, when the temperature exceeds 2200°C, decomposition of BN occurs.

There are two types of high-temperature heating furnaces: those that use graphite as the furnace material, and those that use shell or livedenum as the furnace material.At high temperatures of around 200°C, graphite remains as a volatile substance containing carbon, so
It was thought that a furnace material made of molybdenum, which does not generate this, would be better.

However, when BN powder or a sintered body containing oxygen as an impurity is heated with a molybdenum heater, the cracked gas and molybdenum react and the heater is damaged in a short period of time.

The present invention improves this drawback by preparing the BN powder in advance by heating the sintered body in a heating furnace using a graphite furnace material such as a graphite heater to
After heat treatment at 10℃ to remove most of hydrogen and carbon impurities, it was further heated for 20 minutes in a heating furnace using a furnace material that does not generate gases containing carbon, such as 1 molybdenum hysterer.
It has been found that when heated to 00 to 2400°C, preferably λosoNalso°C, an ultra-high purity product can be obtained and can be manufactured over a long period of time without damaging molybdenum heaters and the like.

In addition to molybdenum, tungsten, stabilized steel, etc. can also be used as a furnace material that does not generate carbon-containing gas, but molybdenum is preferable because it is easy to process, uses open water, and is relatively inexpensive.

- The actual and embodiment of the heating furnace using molybdenum as the furnace material used in the method of the invention is shown in FIG. 2.

2 shows a longitudinal sectional view of the heating furnace. In the figure, /F
iBN sintered body crucible, C is a molybdenum heat shield, 3 is a molybdenum heating element, 3 is a raw material BH powder or sintered body,
j is a high frequency heating coil which heats the molybdenum heating element 3; B is a quartz tube, 7 is a nitrogen gas inlet, l is a glass window for temperature measurement, li is a vacuum exhaust port, and 10 is a gas outlet.

The heating furnace using graphite as the furnace material is shown in Figure 2 above! Graphite is used instead of molybdenum.

According to the method of the present invention, the obtained BN or its sintered body can be of ultra-high purity, containing almost no oxygen as well as impurities such as hydrogen and carbon. The furnace can also be used for a long time without being damaged. Moreover, the obtained insulation specific resistance cannot be obtained by using both heating furnaces or by using a single furnace. As shown in FIG. 1, at 1too°C, the resistance is 1. It exhibits a high value of 0×lθ4Ω at 00°C, and there has never been a disclosure of such a high specific resistance value, which confirms that it is a highly pure product. .

Due to this high purity, OBN
When used as a raw material for manufacturing OBM, OBM can be obtained with extremely good yield, and has a high insulation resistivity.
Insulation for thermocouples used at high temperatures around 000℃; can be used even if it is a material, and is also non-reactive, so it can be used as a nozzle material for injection molding of molten metal, and is widely used in high-temperature industrial fields. There are excellent effects that can be achieved.

In Fig. 2 of the embodiment, in the furnace material made of graphite, BN
Put the sintered body into the BN sintered body melter ff/, and heat the inside of the heating furnace.
Graphite was heated with a high-frequency heating filter under reduced pressure below torr to bring the temperature of the sintered body to 1700°C, and held for 2 hours to remove most of the nona-oxide, which was added as an unreacted B1 synthesis raw material and sintering aid. It was removed. In the heating furnace described next, the atmosphere was made into a nitrogen gas atmosphere and heated at λ/jO°C for 2 hours, and after cooling, the sintered body was taken out.

The obtained sintered body contained impurities below the detection limit, and its insulation specific resistance was 2x/θ4Ω1 at 2000°C.

[Brief explanation of the drawing]

FIG. 1 shows electrical resistivity and temperature diagrams of various high melting point materials. / : BN sintered body melt, Konimolybdenum heat shielding plate,
J: Molybdenum heating element, Reference: Raw material BM powder and #'! Sintered body, j: high frequency heating coil, 6: quartz tube, 7: nitrogen gas inlet, l: glass window for fIA heating, ri: vacuum exhaust port, /θ: gas output 0° Patent applicant Science and Technology Agency Inorganic material Shinkyusho No. 1) Hiroyoshi Nakahiro Diagram 2

Claims (1)

[Claims] Boron nitride powder or sintered body is heated at 0°C using a heating furnace using graphite as a heating element.
．． . After removing impurities, the nitriding is heated to 00°C in an atmosphere with a nitrogen partial pressure higher than the decomposition pressure of boron in a heating furnace that does not generate carbon-containing gas. A method for purifying boron nitride, which is characterized by the following steps: