Surface and grain boundary energies of tin dioxide at low and high temperatures and effects on densification behavior
- PDF / 513,339 Bytes
- 13 Pages / 584.957 x 782.986 pts Page_size
- 82 Downloads / 158 Views
Ricardo H.R. Castroa) Peter A. Rock Thermochemistry Laboratory at NEAT ORU, University of California, Davis, California; and Department of Chemical Engineering and Materials Science, University of California, Davis, California 95616 (Received 18 January 2014; accepted 31 March 2014)
This work presents experimental data on the surface and grain boundary energies of tin dioxide nanoparticles at room temperature and high temperature conditions (quenched from 1300 °C), and a discussion of impacts on the fundamental understanding of the nondensification mechanism of SnO2 during sintering. The results were obtained using a combination of water adsorption microcalorimetry, high-temperature oxide melt drop solution calorimetry, and scanning electron transmission microscopy. At room temperature, the average surface and grain boundary energies of anhydrous SnO2 were 1.20 6 0.02 and 0.71 6 0.08 J m2, respectively. At high temperature, SnO2 showed a surface energy of 0.94 6 0.03 J m2. This remarkable decrease was attributed to the lower oxygen pressure and was associated with a decrease in contact angle during sintering. This observation indicates a moderate but significant thermodynamic reason behind nondensification behavior of SnO2 in addition to common kinetic descriptions: high sintering temperatures and atmospheres cause smaller dihedral angles that decrease sintering stresses. I. INTRODUCTION
SnO2 is a semiconductor oxide widely used as transparent conductive layers, oxidation catalysts, gas sensors, and other technologies.1–3 The control of its microstructure upon synthesis and processing is therefore of key importance for the optimization of those devices. While processing conditions can be optimized by trial and error, a fundamental knowledge on the mechanisms and driving forces for mass transports can enable a more refined control of the microstructure and the development of new processing strategies. For SnO2, enabling high densification is particularly important for the fabrication of sputter targets. However, many reports have proposed that upon processing at high temperatures (sintering), SnO2 shows predominantly nondensification mechanisms, such as surface diffusion and evaporation–condensation mechanism. These mechanisms result in limited pore elimination and leading to difficulties in achieving high densities using conventional sintering on this material.4–7 Leite et al. have shown that the oxygen atoms can desorb and rebond at the SnO2 surfaces at temperature above 600 °C, suggesting an active surface diffusion process, whereas the decomposition of SnO2 at temperatures around 1300 °C suggested that SnO2 was dynamically releasing a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.88 1034
J. Mater. Res., Vol. 29, No. 9, May 14, 2014
http://journals.cambridge.org
Downloaded: 05 Apr 2015
oxygen atoms, suffering partial reduction to SnO and supporting the argument for an evaporation–condensation mechanism under that condition.6 In a recent review by Batzill et al., i
Data Loading...
