Slip casting of partially stabilized zirconia

Casting behaviour and rheological properties are studied in order to define the appropriate conditions under which to prepare slips for the production of high-temperature ceramics. Various commercial powders have been used, which were characterized with respect to morphology, particle size distribution and specific surface area. Zirconia slips with 75 wt% solid content were prepared with distilled water and ethanol as dispersing agent, with and without deflocculant. Hydrochloric acid and tetramethylammonium hydroxide were used to control the pH. Investigations into rheology, i.e. the dependence of viscosity and shear stress on shear rate, were performed. The slip, green and sedimentation bulk densities were measured.     

Features of a technique for investigation of partially stabilized zirconia crystals

The structure of partially stabilized zirconia crystals is investigated by X-ray diffractometry and transmission electron microscopy. It is shown that the combination of structural methods allowed one to reveal features of the structure and phase composition of these materials. Partially stabilized zirconia has a complex twin-domain structure. X-ray diffractometry with the use of K _β radiation shows the presence of two phases of the tetragonal modification of zirconia with different tetragonality in all investigated samples independently of the content of the stabilizing impurity. The combination of the locality of transmission microscopy with the integral nature of X-ray diffractometry allowed one to reveal the dependence of the dispersion of twin domains on the concentration of the stabilizing impurity. The use of transmission microscopy with high resolution demonstrates the hierarchy of twinning and the presence of twin domains ～10 nm in width.     

The effect of electric field intensity on the microwave sintering of zirconia

One variable in the conventional sintering of a dielectric material such as zirconia is the thermal intensity of phonons incident on the zirconia particles. When sintering is accomplished through the impression of a microwave field on zirconia particles, the rate that sintering occurs is a partial function of the electric field intensity. How the electric field intensity “E” varies over the surface of the zirconia particles will be discussed in this communication.     

Growth morphology of the tetragonal phase in partially stabilized zirconia

The zirconia-rich, metastable tetragonal phase in partially stabilized zirconia—magnesia, zirconia—calcia and zirconia—yttria is examined using electron microscopy and electron and X-ray diffraction. The tetragonal phase precipitate distribution is that normally associated with homogeneously nucleated coherent precipitation. An attempt is made to explain the growth morphology of the tetragonal phase in terms of the cubic—tetragonal lattice parameter mismatch. It is found that the tetragonal phase is retained at room temperature provided coherency with the cubic matrix is retained. Once coherency is lost, due to growth strains or mechanical influences, the precipitate reverts to the room temperature stable monoclinic form.     

Plasma spraying of nanostructured partially yttria stabilized zirconia powders

Nanosized partially yttria stabilized zirconia particles, prepared using a co-precipitation method, were reprocessed into agglomerate powders using two methods for plasma spraying. The first method was to make micrometer-sized agglomerates directly following the grinding of the calcined yttria–zirconia agglomerates. The second method was to reconstitute the nanosized particles into micrometer agglomerates using spray drying. The deposition efficiency, porosity, microhardness and average grain size of the deposits made from these two reprocessed powders were studied. Distinct results related to the process parameters were obtained for the two types of powders. The second type of powder was more suitable for plasma spraying than the first one. Using the second type of powder, some unique results distinguished from those of the conventional partially yttria stabilized zirconia powders were observed and an optimized coating with a porosity of 3.8%, Hv_0.3 of 953 and mainly consisting of 1–3 μm columnar grains in the columnar direction and smaller than 100 nm in their cross-sections was achieved.     

Subcritical crack growth in partially stabilized zirconia(PSZ)

Studies on the subcritical crack growth behaviour of partially stabilized zirconia (ZrO₂-I, 5 to 10 vol% tetragonal phase; ZrO₂-II, 35%) were carried out using the double-torsion technique and data from the dynamic fatigue of unnotched bend specimens. The results of subcritical crack growth support the model of stress induced transformation from the tetragonal to monoclinic modification. Differences in the crack growth parameter n (as-received condition) using the double-torsion technique or bend specimens may be explained by the special nature of subcritical crack extension at stressed surfaces for these different specimen types. The log v-log K _i plot of ZrO₂-I using the double torsion technique shows a plateau of constant velocity, which has to be attributed to a tetragonal-monoclinic transformation. After annealing (1500° C, 5 h) the plateau has vanished and the n value is comparable to bend test in an as-received condition.     

A Raman microprobe study of a magnesia partially stabilized zirconia fracture surface

Raman microprobe analysis has been used to determine the extent of phase transformation on the fracture surface of a magnesia partially stabilized zirconia test bar. This has been found to vary across the fracture face and is considered to be related to the amount of microcracking which occurs in the sample during fracture.     

The effect of partially stabilized zirconia on the biological properties of HA/HDPE composites in vitro

The effect of partially stabilized zirconia (PSZ) on the biological properties of the hyroxyapatite - high density polyethylene (HA/HDPE) composites was studied by investigating the simultaneous effect of hydroxyapatite and PSZ volume fractions on the in vitro response of human osteoblast cells. The biocompatibility of composite samples with different volume fraction of HA and PSZ powders was assessed by proliferation, alkaline phosphatase (ALP) and cell attachment assays on the osteoblast cell line (G-292) in different time periods. The effect of composites on the behavior of G-292 cells was compared with those of HDPE and TPS (Tissue Culture Poly Styrene as negative control) samples. Results showed a higher proliferation rate of G-292 cells in the presence of composite samples as compared to the HDPE sample after 7 and 14 days of incubation period. ALP production rate in all composite samples was higher than HDPE and TPS samples. The number of adhered cells on the composite samples was higher than the number adhered on the HDPE and TPS samples after the above mentioned incubation periods. These findings indicates that the addition of PSZ does not have any adverse affect on the biocompatibility of HA/HDPE composites. In fact in some experiments PSZ added HA/HDPE composites performed better in proliferation, differentiation and attachment of osteoblastic cells.     

Phase transitions of partially stabilized zirconia under stepwise shock-wave loading

High-density partially yttria-stabilized zirconia ceramics were manufactured. The primary properties of the manufactured ceramics, such as crack resistance, ultimate bending strength, hardness, elastic moduli, etc., were characterized. The microstructure of the ceramics and the phase transitions under mechanical (including shock-wave) and thermal actions were studied.