Study On The Effect Of Phase Transition Properties On The Thermal Shock Resistance Of MgO-PSZ Tube For Monitoring Oxygen Dissolved In Molten Steels

The probe for monitoring oxygen dissolved in molten steels should meet the need of thermal shock resistance as well as the need of good electrical conductivity. The most important part is the thermal shock resistance of MgO-PSZ tube which directly affects the success of monitoring oxygen. Firstly, this paper explored different preparation processes of power to co-dope other oxides into 8 mol% Magnesia partially-stabilized zirconia (MgO-PSZ) based on coprecipitation method. The effects of pH value of precipitant and washing mediums on the MgO content in powder have also been analyzed.Then,φ10 mm column specimens and rod samples with a length of about 40 mm have been respectively produced by dry-press and extrusion moulding. And the optimum preparation process, the sinter process and heat-treatment process of the specimen were explored. X-ray diffraction analyses have been carried out to study the phases qualitatively and quantitively. Dilatometry and scanning electron microscopy observations have also been performed. At last, the MgO-PSZ powder was shaped into tubes by injection machine. Then the tubes treated with technics that had been explored were assembled into probes and were tested in the simulation test of thermal shock resistance.Experiments suggest that the MgO-PSZ samples directly co-droped with CeO2, Y2O3 and CaO by the coprecipitation method could get enough density and suitable phases after sintered at 1 700℃for half an hour. In the samples holded at 1 420℃for 2 hours and then at 1 100℃for 6 hours, the fine m-phases precipitating from the grain inner and boundary of c-phases obtained by sintering, which makes the samples offer good thermal expansion behavior. Two-step heat treatment, at high temperature section, fine t-phases precipitate from the c-phases substrate and the grain boundary; at low temperature section, bigger t-phases will change to m-phases with the fine ones preserving. It could control the phase proportions and phase structures of MgO-PSZ well, and to some extent is superior to the heat treatment by one step. The simulation test of thermal shock resistance also confirmed this result.