GRAPHITE BEHAVIOR DURING A GAS PHASE METHOD
FOR ALUMINUM NITRIDE PREPARATION
R. A. Shishkin,
A. A. Elagin,
A. R. Beketov,
and M. V. Baranov
Translated from Novye Ogneupory, No. 3, pp. 113 – 118, March 2015.
Original article submitted December 2, 2014.
Purity of AlN, synthesized by means of gas-phase technology, depends to a considerable extent on charge
component and intermediate compound reactions with structural materials. Chemical aspects are considered
for transformations and the nature of reaction of aluminium fluoride and nitride with different types of graph
ite, the effect of fluorides on final synthesis product is revealed, and chemical aspects of their reaction with
graphite during AlN synthesis are explained. The possibility is established of creating a protective coating on
graphite made of chemically deposited AlN. Calculated and experimental data are obtained for developing a
modernized industrial test unit for preparing high purity fine AlN.
Keywords: aluminium nitride, gas-phase synthesis, graphite, aluminium fluoride.
Aluminium nitride is a promising material exhibiting
good thermal conductivity, hardness, large width of the for-
bidden gap, and low LTEC and density [1 – 3]. However no
method exists providing industrial preparation of high-purity
aluminium nitride [4, 5]. A number of works [4 – 7] consider
new promising gas-phase synthesis of aluminium nitride.
This technology according the author makes it possible pre
pare high-purity aluminium nitride on an industrial scale.
Nonetheless, there is almost no mention of the reaction of
structural materials with charge components and the behav
ior of impurities during synthesis, which considerably affect
final product purity. It should be noted that lining material of
the reaction zone is subject to action of aluminum metal (va
por) and also aluminum trifluoride and monofluoride. In this
connection it is necessary to select structural materials care
fully. The graphite proposed exhibits a number features in re
lation grade and density; chemical aspects of surface reaction
may vary over considerable ranges.
Creation of a nitride protective layer on graphite may
significantly change the nature of charge material and graph
ite reaction [8 – 10]. As a result of a complex
multicomponent mixture, the varying composition of the gas
phase, and the effect of impurities on the mechanism of
nitride coating formation, through nitriding of fluoride has
not been studied completely.
THEORY AND CALCULATIONS
In analyzing the gas-phase method for AlN preparation
the question of the effect of functional and structural materi
als in the reaction zone on final product properties, i.e., alu
minium nitride, is open. The most well-known and widely
applied lining material during operation with fluorides at
above 1000°C is graphite. Many scientists have studied reac
tion of metal fluorides and graphite [11 – 16]. These studies
included the following: metal fluoride powder has been
heated in a fluorine atmosphere (1 – 3 bar) to a temperature
of the order of 550°C in a graphite tube or a mixture of metal
fluoride and carbon powders has been studied under these
(gas) + 2C = C
(gas) + 3C = Al
(gas) + 4C = 2YC
4AlF (gas) + 3C = Al
Data confirmed by thermodynamic calculations and ex
periments show; reactions (1) – (4) do not proceed during
Refractories and Industrial Ceramics Vol. 56, No. 2, July, 2015
1083-4877/15/05602-0155 © 2015 Springer Science+Business Media New York
FGAOU VPO Ural Federal University, Ekaterinburg, Russia.