Hydrogen Interaction with CVD Titanium Carbide Coatings on Metals: A Study by a Volume Modulation Technique*

Pressure-Composition Isotherms of TiC<SUB>1&minus;<I>x</I></SUB>&ndash;H System at Elevated Temperatures

“…According to their work, dissolution of hydrogen in TiC is endothermic process and ÁH ¼ 21:53 kJ mol À1 . 14) One of the possible explanations for this clear discrepancy is the unique pressure dependence of C H in TiC observed in the present study. Caorlin et al 14) analyzed their data under the assumption that Sieverts' law held under their experimental conditions.…”

“…14) One of the possible explanations for this clear discrepancy is the unique pressure dependence of C H in TiC observed in the present study. Caorlin et al 14) analyzed their data under the assumption that Sieverts' law held under their experimental conditions. As discussed above, this assumption could be wrong if the C H in TiC is close to the concentration of carbon vacancies.…”

“…The very small jÁHj could be one of the reasons that hydrogen absorption up to overstoichiometric composition [Ti(C,H) 1þx ] was not obvious in the previous studies. 4,5,7,13) Caorlin et al 14) examined the interaction between H 2 gas and TiC coating prepared on molybdenum alloy by a volume modulation technique at temperatures from 883 to 1083 K and equilibrium pressures from 4 to 74 Pa. According to their work, dissolution of hydrogen in TiC is endothermic process and ÁH ¼ 21:53 kJ mol À1 .…”

“…Caorlin et al 14) have examined the dissolution of hydrogen in TiC coating prepared by chemical vapor deposition technique on molybdenum alloy by a volume modulation technique and reported that hydrogen dissolution in TiC is endothermic process (the enthalpy of solution is positive). Renaudin et al, 11) however, examined desorption of deuterium from superstoichiometric carbodeuteride by thermogravimetry (TG) and differential thermal analysis (DTA) and reported that deuterium desorption was endothermic process.…”

“…In other words, hydrogen dissolution in TiC is exothermic process (the enthalpy of solution is negative) according to Renaudin et al 11) Hydrogen absorption by carbides on cooling was also reported, 5,6) and these observations indicate exothermic dissolution of hydrogen in the carbides. Thermodynamic parameters such as entropy and enthalpy of hydrogen solution have not been evaluated in these studies except the investigation of Caorlin et al 14) that shows opposite tendency. In the case of metal-hydrogen systems, it is common to measure pressure-composition (PC) isotherms to determine thermodynamic parameters.…”