An investigation on sinterability and static grain growth behaviour of various amount of SiO2 doped cubic zirconia (8YSCZ)

AN INVESTIGATION ON SINTERABILITY AND STATIC GRAINGROWTH BEHAVIOUR OF VARIOUS AMOUNT OF SiO2 DOPEDCUBIC ZIRCONIA (8YSCZ)(M. Sc. Thesis)Onur Emre SAĞLAMGAZI UNIVERSITYINSTUTE OF SCINCE AND TECHNOLOGYDecember 2005ABSTRACTEffect of SiO2 addition on densification and grain growth behaviour of8YSCZ was investigated using high purity 8 mol% yttria-stabilized cubiczirconia powder (8YSCZ) doped with 0, 1, 5 and 10 wt% SiO2 . the solidsolubility of SiO2 in 8 mol% yttria-stabilized cubic zirconia (8YSCZ)specimes as sintered at 1400 0C was determined by XRD as a functionof composition based on the lattice parameter change. It was seen thatthe average lattice parameter of 8YSCZ linearly decreased from 5,139Ao to 5.143 Ao, as the SiO2 content increased up to 0,3 wt% and theparameter did not vary with further increase in the SiO2 content. Thislinearity shows that solid solubility limit of SiO2 in 8YSCZ is about 0,3wt%. The lower values of the lattice parameter found for the SiO2 doped8YSCZ could be due to the dissolution in the cubic lattice of some SiO2which has a smallr ionic radius than Zr+4 and Y+3 and thus replacing thesmaller Si+4 ions with Zr+4 and Y+3 in the cubic lattice. For thedetermination of densification in the SiO2 doped 8YSCZ, the specimenswere sintered at a temparature 1400 oC for 1 h. It was seen that thesintered density increased with SiO2 content up to 1 wt% and furtherincrease in the SiO2 content led to a decrease in density. The enhanceddensity with increasing SiO2 content up to 1 wt% could be attributableto liquid phase sintering and rearrangement of grains at the early stageof sintering. The decreased density in higher amount of SiO2 dopedspecimens was due to the lower grain boundary diffusivity. For graingrowth measurements, the specimens sintered at 1400oC wereannealed at 1400, 1500 and 1600 oC for 10, 50 and 100 hours. Theexperimental results showed that the grain growth in the SiO2 doped8YSCZs occurred slowly and more sluggish than that in undoped8YSCZ. Also, the grain growth rate decreased with increasing SiO2content. The grain growth exponent value and the activation energy forundoped 8YSCZ were found to be 2 and 289 kJ/mol, respectively. Theaddition of SiO2 raised the grain growth exponent value to 3 andactivation energy for the grain growth process was increased from 289to 420 kJ/mol for the addition of SiO2 from 0 to 10 wt%. The slow graingrowth in the SiO2 doped 8YSCZs is due to the lower grain boundarymobility and energy which result from the solute segregation in thegrain boundary and its drag in the SiO2 doped 8YSCZ but not in theundoped 8YSCZ. The drag effect arises from any preferred segregationof impurities either to or from grain boundary area because of size andcharge differences. The SiO2 is expected to segregate to grainboundaries. This segregation layer is believed to hinder grain growthby resulting in limiting matter transfer along the grain boundary.Science code : 948. 1.122Key words : Cubic Zirconia, Sinterebility, Grain GrowthPage Number : 87Adviser : Assoc. Prof. Dr. Süleyman TEKELIAssoc. Prof. Dr. Metin GÜRÜ