SINTERING AND CHARACTERIZATION STUDIES OF NiO

Abstract

High purity NiO polycrystals have been prepared by hotpressing and by sintering. They were characterized by optical and electron microscopy. Their creep behaviour was studied above 1200°C. I INTRODUCTION Nickel oxide polycrystals have been prepared with the aim of studying their plastic deformation. For mechanical testing, materials with stabilized microstructure (grain size, porosity, ...) are needed. We have prepared NiO polycrystals two ways similar to those previously used for NiO/l/ or Co0/2,3,4/ and characterized the resulting specimens by microstructural observations and creep testing. I1 PREPARATION OF POLYCRYSTALS 11-1 Initial sintering The starting powder was high purity NiO provided by Johnson-Matthey (total impurity content below 15 ppm) with an average particle size of 0.1 Qm. The powder was first cold-pressed in a die under 400 MPa. It was then annealed 3 days in air at 1200°C on a boat made of NiO to avoid contamination. The density of the sintered body was 65 % of the theoretical density taken as 6.8 g/cm3 and the grain size of the order of 1 vm. Such a material is not appropriate for high temperature mechanical testing and two types of additional treatment were required. 11-2 Ultra-high temperature sintering Since most of the creep tests were to be performed below 1400°C, sintering treatments between 1500°C and 1700°C (0.80 TM and 0.88 TM ; TM = 2230 K, melting temperature) were performed in air during 3 days. To avoid contamination, the specimens were separated from the alumina crucible by a bed of NiO. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986157