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Thermodynamic Analysis of Urea Physical Vapour Transport
Author(s) -
Paorici C.,
Zha M.,
Zanotti L.,
Attolini G.,
Traldi P.,
Catinella S.
Publication year - 1995
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.2170300513
Subject(s) - sublimation (psychology) , biuret test , chemistry , decomposition , urea , melting point , thermodynamics , ammonia , condensation , vapor pressure , torr , thermal decomposition , nitrogen , analytical chemistry (journal) , organic chemistry , psychology , physics , psychotherapist
The vaporisation‐condensation scheme of urea has been investigated in the temperature region below the melting point, in order to establish the thermodynamic reactions on which the physical vapour transport (PVT) of urea is based. By making use of both reported data and experimental results of MS, DTA, DTG, and HPLC analysis, it was shown that PVT relevant reactions are basically molecular sublimation and partial decomposition in solid biuret and ammonia. MS analysis of urea crystals and source residues have also shown that no decomposition can be observed in the growing crystals, unless reheated during growth. The temperature dependence of the decomposition pressure has been found to be: log 10 P NH3 [torr] = 38 – 13840/ T [K]. The use of this relation in diffusive mass transport calculations brought to linear growth rate values not in disagreement with the experimental values found in closed tube PVT grown crystals.