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Vaporization Thermodynamics and Enthalpy of Formation of Aluminum Silicon Carbide
Author(s) -
BEHRENS ROBERT G.,
RINEHART GARY H.
Publication year - 1984
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1984.tb19175.x
Subject(s) - vaporization , enthalpy , standard enthalpy of formation , vapor pressure , thermodynamics , silicon carbide , carbide , graphite , enthalpy of vaporization , chemistry , aluminium , materials science , analytical chemistry (journal) , metallurgy , organic chemistry , physics
The vaporization thermodynamics of aluminum silicon carbide was investigated using Knudsen effusion mass spectrometry. Vaporization occurred incongruently to give Al( g ), SiC( s ), and graphite as reaction products. The vapor pressure of aluminum above (Al 4 SiC 4 + SiC + C) was measured using graphite effusion cells with orifice areas between 1.1 × 10 −2 and 3.9X10 −4 cm 2 . The vapor pressure of aluminum obtained between 1427 and 1784 K using an effusion cell with the smallest orifice area, 3.9X10 −4 cm 2 , is expressed as log p (Pa) =−(18567 ± 86) ( K/T ) + (12.143 ± 0.054) The third‐law calculation of the enthalpy change for the reaction Al 4 SiC 4 ( s ) = 4Al( g ) + SiC( hex ) + 3C( s ) using the present aluminum pressures gives Δ H °(298.15 K) = (1455 ± 79) kJ·mol −1 . The corresponding second‐law result is Δ H °(298.15 K) = (1456 ± 47) kJ·mol −1 . The standard enthalpy of formation of Al 4 SiC 4 ( s ) from the elements calculated from the present vaporization enthalpy (third‐law calculation) and the enthalpies of formation of Al( g ) and hexagonal SiC is Δ H ° f = ‐(221 ± 85) kJ·mol −1 . The standard enthalpy of formation of Al 4 SiC 4 ( s ) from its constituent carbides Al 4 C 3 ( s ) and SiC( c, hex ) is calculated to be Δ H °(298.15 K) = (38 ± 92) KJ·mol −1 .