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Crucible Materials
Published in Nagaiyar Krishnamurthy, Metal–Crucible Interactions, 2023
For the use of a ceramic as a crucible material, it is essential that the compound shows no crystallographic phase transitions in the temperature region of interest. This is, in fact, the case for BaZrO3. Apart from a a melting point of about 2600°C, BaZrO3 has a smaller thermal expansion coefficient than ZrO2 and therefore, better thermal shock resistance. In a binary ceramic, any deviation from the stoichiometric composition will lead to precipitation of the off-stoichiometric surplus at the grain boundaries of the ceramic. This region will be prone to corrosion. This is remedied by additives such as calcia and yttria, resulting in CaO-doped BaZrO3 and yttria-doped BaZrO3. Calcium zirconate (CaZrO3) has a high melting point of 2368°C and chemical stability as good as that of CaO. The zirconate, unlike CaO, is inert to hydration. As in barium zirconate, the formation of off-stoichiometric compounds was restored by incorporating CaO as additive. The crucible was used to melt NiTi and Ti6Al4V alloys at 1500 and 1750°C, respectively, without contamination.
Structural Materials
Published in C. K. Gupta, Materials in Nuclear Energy Applications, 1989
To the list of the two solvent extraction processes, one must now add a new one developed recently.15 In the new process, zircon is similarly fused with a caustic to convert it to sodium zirconate, which is digested into zirconium oxysulfate, H2ZrO(SO4)2, by sulfuric acid. The feed thus prepared contains zirconium plus hafnium oxysulfate, free sulfuric acid, and some sodium sulfate. Separation of zirconium and hafnium is carried out by solvent extraction with tri-n-octyl amine (TNOA). A flowchart of the process is shown in Figure 8. At first, all zirconium and a part of the accompanying hafnium are extracted into the organic solvent consisting of amine, tridecyl alcohol, and diluent (extraction process). The organic phase loaded with zirconium, (R3NH)2Zr0(SO4)2, is then scrubbed with an aqueous solution containing hafnium-free zirconium oxysulfate (scrubbing process). Finally, zirconium in the organic solvent is stripped with a solution of alkali chloride and concentrated in liquid phase as hafnium-free zirconium oxysulfate (stripping process). Stripped organic is regenerated by contacting with sodium carbonate; the regenerated organic goes to the extraction circuit, and the sodium chloride goes to the stripping circuit (regeneration process). The zirconium solution recovered in the stripping process is neutralized directly with alkali, precipitated, filtrated, and calcined by conventional methods to reactor-grade zirconium oxide, with a hafnium content of less than 50 ppm. The hafnium obtained from the raffinate in the extraction process can be fed to various applications, as hafnium oxide and hafnium metal, by removing contained impurities such as iron and titanium. This flowchart using the new extractant ha been developed by the Nippon Mining Company Ltd. (NMC), and a plant based on the flowchart for zirconium production is currently in operation in Japan.
Ultrasound
Published in John G Webster, Minimally Invasive Medical Technology, 2016
The piezoelectric crystal is central to the ultrasound system. Some of the materials used to create the crystal are different types of zirconate titanate, which is a ceramic. This crystal has inherent impedance that is by no means optimal for power transmission. To overcome this transfer problem a matching layer is needed.
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
As a thermal barrier coating (TBC) material, yttria-stabilized zirconia (YSZ) is the most extensively used material for high-temperature applications. In addition to YSZ, the most studied TBCs are RE2Zr2O7 (rare earth (RE)) ceramics. RE2Zr2O7 ceramics have low thermal conductivity, demonstrating their potential as effective TBC materials [1,2]. Several potential zirconate ceramics, such as Sm2Zr2O7, La2Zr2O7, Gd2Zr2O7, and Nd2Zr2O7 have been studied for this purpose [3–5]. For example, the thermal diffusivity and thermal conductivity of 4 mol% ZrO2-Y2O3 decreased with increasing Gd2O3 content. The fluorite-type Gd2Zr2O7 phase was formed as the second phase in the tetragonal ZrO2 matrix [6]. However, compared to YSZ, the thermal expansion coefficients of these zirconate ceramics are considerably low. As reported in [7], RE2Sn2O7 is also a type of pyrochlore oxide ceramic; however, its high thermal conductivity is not suitable for TBCs. RE3MO7 [8–11] (M5+ = Mo5+, Sb5+, Nb5+, Ta5+, etc.) ceramics have excellent magnetic and dielectric properties. Based on previous investigations [12–15], RE3MO7 ceramics have low thermal conductivity because of lattice defects in their crystal structure that can enhance phonon scattering. In previous studies, ordered orthorhombic phases were observed in RE3TaO7 ceramics (RE = Y–Dy), whereas the rest of the ceramics exhibited disordered cubic phases [16,17]. Because of their fluorite-type crystal structure, RE tantalate RE3TaO7 ceramics may be promising candidates for TBCs.