In situ synthesis of Si3N4 in the Na2SiF6-N2 system via CVD: Kinetics and mechanism of solid-precursor decomposition: Kinetics and mechanism of solid-precursor decomposition

A.L. Leal-Cruz, M.I. Pech-Canul

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Abstract

The kinetics of decomposition of Na2SiF6 in nitrogen to in situ synthesize Si3N4 was investigated. First, an optimization of the following parameters for the thermal decomposition was performed: nitrogen precursor (N2 or N2:NH3), processing time and temperature range. According to the analysis of variance (ANOVA), the optimum conditions to maximize the decomposition of Na2SiF6 are: N2, 120 min, and 465-873 K. Based on thermodynamic predictions and evidence on the synthesis of Si3N4 during the thermal decomposition, it is proposed that in nitrogen Na2SiF6 decomposes endothermically into various gaseous species (SiF4, SiF3, SiF2, SiF and Si) denoted as SiFx, through a series of complex reactions of zero-order with respect to the gaseous products, with activation energy of 156 kJ mol- 1 and a rate-determining-step given by the chemical reaction itself. The gaseous species are formed through a set of simultaneous reactions represented by the next general equation:Na2SiF6 → 2 NaF + SiFx(g) + n F2(g)Where x varies from 0 to 4 and n given by (2-0.5x) takes the values 0, 1/2, 1, 3/2 and 2. Silicon nitride is formed according to:3 SiFx(g) + 2 N2 → Si3N4 + m F2m = 1.5x and takes the values 6, 9/2, 3, 3/2 and 0.

Original languageUndefined/Unknown
Pages (from-to)3529-3536
Number of pages8
JournalSolid State Ionics
Volume177
Issue number39-40
DOIs
StatePublished - 2007

Bibliographical note

Funding Information:
Authors gratefully acknowledge Conacyt for financial support under project contract 34826-U. Thanks also to Mr. Francisco Botello Rionda and Mr. Felipe Marquez Torres for technical assistance during the thermogravimetric and microscopic analyses, respectively. Authors are also indebted to Dr. J. Escobedo-Bocardo, Dr. A. Flores-Valdés and Dr. M. Almanza-Robles for providing the software for thermodynamic calculations.

Keywords

  • CVD-SiN
  • Kinetics
  • Reaction mechanisms
  • Silicon precursor
  • Sodium silicofluoride

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