Effect of the sintering method on microstructure and thermal and mechanical properties of zirconium oxophosphate ceramics Zr2O(PO4)2

Abstract

Due to an ultra-low thermal expansion, Zr 2 O(PO 4) 2 could find many applications as a thermal shock resistant material. To this end, ceramic processing is a key step in order to reach best properties. In this work, Zr 2 O(PO 4) 2 was sintered by conventional sintering and by the spark plasma sintering technique (SPS) with and without additive. Samples made by conventional sintering with ZnO as sintering aid have a maximum relative density of around 92 %. Microstructure is composed of large grains and microcracks can be observed. When doped with 5 wt. % of MgO, samples can be densified by SPS up to 99.6 % of the relative density and the grain size maintained between 0.5 and 1.5 m. Thermal conductivity and Vickers microhardness were investigated as a function of the microstructure. Best values were obtained for the ceramic doped with 5 wt.% MgO and sintered by SPS, thanks to a fine microstructure and a small amount of residual microcracks.

Dysprosium doping of Ca2MnO4: Effect on crystal structure at room temperature and thermal behavior

“…On heating however, O4 shifts progressively towards the ideal position, resulting in a homogenization of the Ca-O4 distances, hence the contraction of the The resulting linear thermal expansion αl of the studied compound Ca1.8Dy0.2MnO4 is 13.7 ×10 -6 K -1 , which is a little bit less than that observed for CaMnO3 calcium manganate (15.6 ×10 -6 K -1 [32]) and Sr2TiO4 Ruddlesden Popper (19.5 ×10 -6 K -1 at 327 °C [33]). At the microstructure scale, the strong anisotropy in the thermal expansion coefficient of the Ca2-xDyxMnO4 structure must be considered with a great care since in these conditions, microcracking can occur when grain size exceeds a value called transition (or critical) grain size [34,35]. For example, the critical grain size for microcracking of Li1.3Al0.3Ti1.7(PO4)3 is estimated to be less than or equal to 1.6 µm (∆αa-c = 12 ×10 -6 K -1 ) and to 1.1 µm for hydroxyapatite (∆αa-c = 8 ×10 -6 K -1 ) [36,37].…”

Evaluation of mechanical properties of Ni/BaTiO3 functionally graded material

“…For instance, BaTiO 3 is sintered in the range 1200 -1300 °C for several hours [22]. Innovative processing methods, including SPS [23], allow to decrease the sintering temperature up to approximately 900 °C and to achieve a full densification in only few minutes [24][25][26]. Metal with a melting point higher than the ceramic sintering temperature, i.e., 900 °C, is required.…”