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Properties of TiN and TiN Deposited by CVD on Graphite for Pyrochemical Applications

Published online by Cambridge University Press:  10 February 2011

P. S. Maiya  and
B. M. Moon
P. S. Maiya
Affiliation:
Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439, subraya_maiya@qmgate.anl.gov
B. M. Moon
Affiliation:
SGL Carbon Corporation, Dallas, 75247
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Abstract

High-density TiN (>098% of theoretical) has been prepared by hot pressing TiN powder with 2–4 wt.% Li2CO3 at temperatures between 1150–1550°C and pressures of ≈40–50 MPa. The Li2CO3 served as a fugitive sintering aid, enabling attainment of high density at low temperatures without adversely affecting the inherently good properties. Variation in processing variables and TiN powder characteristics resulted in material with various porosities. Measurement of mechanical properties such as flexural strength and fracture toughness showed that the high-density material has mechanical properties that are superior to those of several oxide ceramics. We have also quantified the effects of porosity on mechanical properties. In addition, adhesion and chemical stability tests were used to investigate graphite coated with TiN by chemical vapor deposition (CVD). Pin-pull tests were used to determine coating adhesion and failure stresses were analyzed by Weibull statistics. All pin-pull tests resulted in fracture of the graphite substrate, rather than separation at the TiN/graphite interface. The data showed a good fit to the two-parameter Weibull expression, with a failure strength of 16.4 MPa and Weibull modulus of 9.3. Both the high-density TiN and the TiN coating on the graphite were exposed to a corrosive molten salt CaCl2-7 wt.% CaO and a liquid metal alloy (Zn-10 wt.% Mg) at 800°C for 168 h to determine chemical interactions. No reaction was detected by scanning electron microscopy (SEM) or energy-dispersive X-ray (EDX) analysis. Thus, graphite coated with TiN by CVD combines the thermodynamic stability of TiN when exposed to reactive molten metals and salts, with the excellent machinability of graphite, and hence is promising for use in container vessels for pyrochemical processing of certain rare-earth and nuclear metals, where chemical inertness and good matching of thermal expansion coefficients are required.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 495: Symposium W – Chemical Aspects of Electronic Ceramics Processing , 1997 , 317
Copyright
Copyright © Materials Research Society 1998

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