Zirconium carbide and oxycarbide bulks were produced via Reactive Spark Plasma Sintering (RSPS) using zirconia and carbon powders. The effects of dwell temperature, uniaxial pressure and heating rate on final chemical composition/stoichiometry were investigated. Heating rates (20-200°C min-1) had no significant effect on RSPS. The carbothermal reduction was hindered by increasing the sintering pressure. This was because of gases entrapped within the closed porosity. Under pressure-less conditions, the reaction onset started at ∼1300°C and the reduction was completed within 10 min resulting in an oxygen content as low as 1.47 at.-%. Under 16 MPa applied pressure, the reaction onset was shifted to 1830°C. Sub-micrometric zirconia powder (<0.1 µm) impacted negatively on the carbothermal reaction because of enhanced ZrO 2 sintering preceding the carbothermic reaction. The RSPS reaction mechanism began with zirconia particle densifications between 900 and 1400°C followed by nucleation and growth of an intermediate O-rich ZrOC phase, between 1800 and 2100°C almost all zirconia was consumed. The ZrOC phase then reacted out its oxygen while simultaneously sintering. The results suggest that an optimised RSPS involve a two-step process employing a pressure-less SPS synthesis followed by a pressure-assisted sintering.
The difficulties in finding a suitable unoccupied volume to accommodate a nonevaporable getter (NEG) in the restricted spaces of certain devices may sometimes limit their use. Moreover, the getter porosity often has to be maximized to provide the best gas sorption performance. A new getter family is presented based on highly porous getter coatings having a thickness range of 50-150 pm. They are obtainable on almost any metallic surface (even device parts) and are suitable as a solution to fit special geometry and high sorption speed requirements. As is known, to become active, getters need to be heated in vacuum for times and temperatures that are to be specifically selected to be compatible with the various application constraints. The materials of this getter family can be of different natures to cope with this need. Practical use considerations are given. The sorption performance of this new getter family, for various gases (CO, H1, CH4), are reported and discussed together with other characteristics such as porosity and mechanical stability.
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