A kind of high-strength boron nitride ceramic and its preparation method

Abstract

The invention relates to a high-strength boron nitride ceramic and a preparation method thereof. The preparation method comprises the following steps: a) material charging: a certain mass of single-particle-size nano cubic boron nitride powder is weighed, pre-pressing forming is conducted, and a pre-pressed blank obtained after pre-pressing forming is placed into a sintering mold; B) sintering: the pre-pressed blank in the step A) and a sintering mold are placed into spark plasma sintering equipment or hot-pressing sintering equipment for sintering; and C) discharging: after the temperature inthe equipment is cooled to room temperature, the mold is moved out and the sintered product is demolded to obtain the high-strength boron nitride ceramic block. In the method, the high-strength boronnitride ceramic can be obtained by sintering the nano cubic boron nitride powder with the single particle size.

Description

technical field [0001] The invention relates to the technical field of preparation of structural ceramics, in particular to a high-strength boron nitride ceramic and a preparation method thereof. Background technique [0002] Hexagonal boron nitride (hBN) ceramics are generally blocks formed by sintering hexagonal boron nitride powder, which is an advanced structural ceramic. It has excellent physical properties, including high insulation, low dielectric constant, high thermal conductivity, and excellent thermal shock resistance, so it has been widely used. However, due to the special layered structure of hexagonal boron nitride ceramics, the bonding force in the direction of the C-axis is much smaller than that perpendicular to the direction of the C-axis. The crystals mainly grow along the direction of the plate surface, and the growth along the thickness direction is relatively slow. Form a flaky crystal structure, which forms a card bridging structure when sintered, whi...

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Problems solved by technology

However, due to the special layered structure of hexagonal boron nitride ceramics, the bonding force in the direction of the C-axis is much smaller than that perpendicular to the direction of the C-axis. The crystals mainly grow along the direction of the plate surface, and the growth along the thickness direction is relatively slow. Form a flaky crystal structure, which forms a card bridging structure when sintered, which supports each other and hinders the shrinkage of the material, so that the obtained hBN ceramics have a low density, and the van der Waals between layers Due to the weak influence of the force, the prepared hexagonal boron nitride ceramics have poor mechanical properties and low strength, which greatly limits its further development and application.

[0003] Because hexagonal boron nitride ceramics are difficult to sinter, the relative density of pure hexagonal boron nitride can only reach about 70% after sintering, such as a method for preparing high-purity hexagonal boron nitride ceramics by pressureless sintering with application number 201410422994.6. The density of hexagonal boron nitride ceramics prepared from pure hexagonal boron nitride powder is only about 56%, and in order to improve the density of hexagonal boron nitride ceramics, most methods are to add sintering aids during the sintering process, such as B 2 o 3 , Y 2 o 3 、Al 2 o 3 , SiO 2 , AlN, etc. Although the density of hexagonal boron nitride obtained by adding sintering aids is improved to a certain extent, it will reduce its high-temperature performance

For example, the application number is 201410393724.7, a preparation method of a high-density hexagonal boron nitride ceramic material, which discloses coating SiO on the surface of hBN powder 2 Realize SiO 2 Uniform distribution of sintering aids, through spark plasma sintering or hot isostatic pressing sintering, to obtain high-density hBN blocks, but it is coated with SiO on the surface of hBN powder 2 The process is complex and the high-density h-BN block prepared by it has a density of only 86.4% and a compressive strength of 79MPa.

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