Effect of the Deposition Time and Heating Temperature on the Structure of Chromium Silicides Synthesized by Pack Cementation Process

Evangelia Tarani,Sofia A Tsipas,Konstantinos Chrissafis,Dimitrios Stathokostopoulos,George Vourlias

doi:10.3390/cmd2020012

Abstract

Transition metal silicides have attracted great interest for their potential use in optoelectronic devices, photovoltaic cells, and thermoelectric conversion elements because of their high melting point, high oxidation resistance, and satisfactory thermoelectric properties. This study focuses on the effect of the deposition time and the heating temperature on the morphology and structure of the chromium silicides synthesized by the pack cementation method. A series of experiments were carried out at various temperatures (1000–1150 °C) with different deposition times (15–120 min). The morphology and the chemical composition of the samples were determined using SEM with an EDS analyzer. The structure determination and phase identification were performed by XRD analysis. The examination of the as-formed materials was completed by performing thermal stability tests. The most suitable conditions for producing CrSi2 sample with satisfactory properties and simultaneously minimizing the cost and production time are listed. It was found that the sample synthesized at 1000 °C for 15 min during the chromizing step, in combination with the siliconizing step at 1000 °C for 60 min, presents the best thermal stability and these selected temperatures offer appropriate, economical, and repeatable results.

Highlights

Transition metal silicides have long been promising materials in microelectronic devices, photovoltaic cells, and thermoelectric conversion elements operating at high temperature under ambient atmosphere because of their low electrical resistivity, excellent chemical stability, high melting point, and satisfactory thermoelectric properties [1]
This study focuses on the effect of the deposition time and the heating temperature on the morphology and structure of the chromium silicides synthesized by the pack cementation method
The chromium–silicon (Cr–Si) system is technologically interesting, as several chromium silicides phases exist in the binary phase diagram, such as the cubic intermediate phase Cr3Si, the tetragonal intermediate phase Cr5Si3 (W5Si3 type-tetragonal I4/mcm), the cubic intermediate phase CrSi and the hexagonal phase CrSi2 [5]

Summary

Introduction

Transition metal silicides have long been promising materials in microelectronic devices, photovoltaic cells, and thermoelectric conversion elements operating at high temperature under ambient atmosphere because of their low electrical resistivity, excellent chemical stability, high melting point, and satisfactory thermoelectric properties [1]. Theoretical thermodynamic calculations were performed to predict the equilibrium Cr–Si phases which can be formed during the pack cementation process. The higher chromium silicide was the subject of numerous investigations, mainly because of its good oxidation resistance, semiconducting properties at elevated temperatures, and thermoelectric properties For this reason, a second step of the pack cementation process (siliconizing step) was performed for selective samples synthesized under various heating temperatures and deposition times in the chromizing step. A second step of the pack cementation process (siliconizing step) was performed for selective samples synthesized under various heating temperatures and deposition times in the chromizing step In this case, the pack mixture includes 15 wt.% Si (donor material), 3 wt.% NH4Cl (activator) and 82 wt. The samples in bulk form (expressed in mg/mm2) were put in alumina crucibles, with an empty alumina crucible used as a reference; sample temperature and weight were continuously recorded to obtain in situ quantitative data relating to the rate of oxidation of the samples

Thermodynamic Prediction of Pack Compounds Formed

Effect of Deposition Temperature

Conclusions