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Mechanism and Parameters Controlling the Decomposition Kinetics of Na 2 SiF 6 Powder to SiF 4
Author(s) -
Soltani N.,
PechCanul M. I.,
González L. A.,
Bahrami A.
Publication year - 2016
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20999
Subject(s) - chemistry , analytical chemistry (journal) , decomposition , activation energy , chemical decomposition , dissociation (chemistry) , nitrogen , volumetric flow rate , chemical vapor deposition , kinetics , thermodynamics , organic chemistry , physics , quantum mechanics
Sodium hexafluorosilicate (Na 2 SiF 6 ) powder has been used as a silicon source for formation of Si 3 N 4 coatings by the hybrid precursor system‐chemical vapor deposition (HYSY‐CVD) route. The quantitative effect of processing time, temperature, gas flow rate, and process atmosphere (N 2 and N 2 :5% NH 3 ) upon the fractional weight loss during the decomposition of Na 2 SiF 6 was studied using a standard L 9 Taguchi experimental design and analysis of variance. The decomposition kinetics of Na 2 SiF 6 (s) was studied theoretically and experimentally in the temperature range of 550–650ºC by applying the shrinking core model. It was found that regardless of atmosphere type, the reaction order is n ≈ 0.12 and that a two‐stage mixed mechanism consisting of chemical reaction and boundary layer gas transfer controls the decomposition rate. The determined fractional weight loss during Na 2 SiF 6 decomposition in nitrogen atmosphere is about 1.05–1.5 orders of magnitude greater than that in N 2 :NH 3 . The gas flow rate affects the dissociation activation energy, being of 121, 109, and 94 kJ/mol in N 2 and of 140, 120, and 115 kJ/mol in N 2 :NH 3 , for the flow rates of 20, 60, and 100 cm 3 /min, respectively, in both atmosphere types. A good agreement is observed by comparing experimental weight loss data with model predictions.