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Bonding and structures
Published in Ash Ahmed, John Sturges, Materials Science in Construction: An Introduction, 2014
Bonding is the name given to the mechanism by which two (or more) atoms join together to form compounds. There are several types of primary bond that can be formed, and these are all determined by the extra-nuclear or electronic make-up of the elements. It is the electrons, and not the nuclei, that form the various types of bond. Furthermore, these bond types can vary widely in their strengths; the energy required to separate two bonded atoms is the bond energy, and this governs not only mechanical strength but also other properties such as melting temperature. An element or compound with a high bond strength will be more difficult to melt, i.e. it will tend to have a higher melting temperature. It will also have a higher value of stiffness (Young’s modulus of elasticity, E).
Investigation of thermophysical properties of ZrO2-Sm3TaO7 ceramics
Published in Journal of Asian Ceramic Societies, 2021
Ying Zhou, Guoyou Gan, Zhenhua Ge, Jing Feng, Song Peng
Figure 8(a) shows the thermal expansion of ZrO2-Sm3TaO7. All the ceramic data showed good linearity, except for those for 2 mol% ZrO2 doping, caused by a phase transition. According to previous research on TiO2-Sm3TaO7 ceramics [22], the phase transition of Sm3TaO7 ceramics is eliminated via the TiO2 alloying effect. The TEC of the samples increased with increasing temperature and ZrO2 content, as shown in Figure 8(b). The 8 mol% ZrO2-Sm3TaO7 sample has a high TEC of 10.9 × 10−6 K−1, which is close to that of 7–8 wt.% YSZ (10 ~ 11 × 10−6 K−1) and higher than that of Sm3TaO7 (9.8 × 10−6 K−1, 1200°C). As discussed in previous studies [30,31], the thermal expansion of the samples can be explained by the asymmetric anharmonic vibrations of chemical bonds. Generally, the macrothermal expansion of bulk ceramics originates from the crystal binding energy. The longer the bond, the lower the bond energy. The bond lengths of ZrO2-Sm3TaO7 decrease with increasing ZrO2 content, and the thermal expansion is mainly affected by the Sm–O bond. The measurement of the Young’s modulus shows that the value decreases with increasing ZrO2 content.