Amount Of ZrO2 Research Articles

Factors Influencing Residual Surface Stresses due to a Stress‐Induced Phase Bansformation

An X‐ray diffraction technique was used to measure the residual surface stresses on ground surfaces of Al2O3/ZrO2 (tetragonal) composites. To accomplish this, it was necessary to use a radiation for which the penetration depth was small (large wavelength), e.g. CrKα radiation. It was found that these materials could have compressive stresses as high as 1 GPa on their surface, which is a result of the molar volume associated with the tetragonal‐to‐monoclinic ZrO2 phase transformation. This transformation was induced by the grinding stresses and a reasonable correlation between the amount of ZrO2 transformed and the magnitude of the residual stresses was established. Evidence was found that the transformation depth is controlled by the amount of stabilizing oxide added to the ZrO2 and by the ZrO2 grain size. In the materials studied, transformation depths were found to be typically <20 μm.

Critical Microstructures for Microcracking in Al2O3-ZrO2 Composites

The internal strains asSociated with the martensitic phase transformation of zirconia were used to introduce microcracks into Al2O3/ZrO2 composites. The degree of transformation was found to be dependent on the volume fraction of ZrO2 and its size, the latter of which could be controlled by suitable heat treatments. The microstructural changes that occurred during the heat treatments were studied using quantitative microscopy and X-ray diffraction. For materials containing more than 7.5 vol% Zr02, the ZrO2 particles were found to pin the Al2O3 grain boundaries, thus limiting the Al2O3 grain growth. The limiting grain size was found to be dependent on size and volume fraction of ZrO2. Heat treatments for the higher volume fraction materials (>7.5 vol% ZrO2) caused micro-structural changes which resulted in increased amounts of monoclinic ZrO2 at room temperature; elastic modulus measurements indicated that this was occurring concurrently with microcracking. By combining the ZrO2 grain-size distributions with the X-ray analysis it was possible to calculate the critical ZrO2 size required for the transformation. The critical size was found to decrease with increasing amounts of ZrO2. Hardness and indentation fracture toughness were measured on the composites. Grain fragmentation was observed at the edge of the indentations and microcracks were observed directly, using an AgNO3 decoration technique, near the indentations.

Cordierite glass-ceramics-effect of TiO2 and ZrO2 content on phase sequence during heat treatment

A series of glasses of stoichiometric composition with varying proportions of TiO2 and/or ZrO2 as nucleating agent have been studied to examine the effect of nucleation addition on the sequence of crystallization and transformation to the stable phase, cordierite. It is shown that TiO2 is the most effective nucleating agent and that if large amounts of ZrO2 are substituted for TiO2 cristobalite forms as an intermediate phase and is associated with rapid volume changes and consequently with weak porous products. Substitution of ZrO2 for TiO2 also causes other changes in phase development, especially in the relative proportions of β-quartz solid solution and magnesian petalite produced during the early stages of crystallization. The use of a combination of experimental techniques (dilatometry, DTA, X-ray diffraction and electron microscopy) has proved most effective in studying phase development and the relationship between processing characteristics and composition.

Determination of SiO2 in silicate materials containing large amounts of ZrO2 and TiO2

Determination of SiO2 in silicate materials containing large amounts of ZrO2 and TiO2

Sintering in the Binary System MoSi<sub>2</sub>-WSi<sub>2</sub>

Molybdenum disilicide has recently been developed as an excellent heating element of high refractoriness and of high oxidation resistivity. The binary system of MoSi2-ZrO2 was studied for the purpose of improving the too low electrical resistivity of MoSi2 without changing the other favorable characteristics.ZrO2 used was previously stabilized by dissolving 10 mol % of Y2O3 at 1600°C. Samples of six different chemical compositions differing from each other by 20% in ZrO2 content, were formed under the pressure of 6ton/cm2 and sintered at five different temperatures between 1300° and 1650°C in H2 gas.The electrical resistivity, density and modulus of rupture were measured on sintered specimens and expressed as functions of sintering temperature, chemical composition and sintering time.The density becomes minimum at about 60% of ZrO2 content and the modulus of rupture varies approximately with the density.The electrical resistivity at a room temperature increases rapidly with the amount of ZrO2 above 60%. The change of the electrical resistivity was also investigated up to the surface temperature of 1700°C. The resistivity increases with temperature on the MoSi2 side, while decreases on the ZrO2 side.The thermal shock test by repeated rapid heating and cooling between a room temperature and 1400°C, showed that the samples of the medium composition had the least thermal shock resistance.

Immiscibility Area in the System TiO2–ZrO2–SiO2

A furnace for use in conjunction with the X‐ray spectrometer was developed which was capable of heating small powdered specimens in air to temperatures as high as 1850°C. This furnace was also used for the heating and quenching of specimens in air from temperatures as high as 1850°C. An area of two liquids coexisting between 20 and 93 weight % TiO2 above 1765°± 10°C. was found to exist in the system TiO2–SiO2, which is in substantial agreement with the previous work of other investigators. The area of immiscibility in the system TiO2–SiO2 was found to extend well into the system TiO2–ZrO2–SiO2. The two liquids were found to coexist over a major portion of the TiO2 (rutile) primary‐phase area with TiO2 (rutile) being the primary crystal beneath both liquids. The temperature of two‐liquid formation in the ternary was found to fall about 80°C. with the first additions of ZrO2 up to 3%. With larger amounts of ZrO2 the change in the temperature of the boundary of the two‐liquid area was so slight as to be within the limits of error of the temperature measurement. Primary‐phase fields for TiO2 (rutile), tetragonal ZrO2, and ZrTiO4 were found to exist in the system TiO2–ZrO2–SiO2. SiO2 as high cristobalite is known to exist in the system TiO2–ZrO2–SiO2.

System zirconium-oxygen

Iodide zirconium was combined with calculated amounts of ZrO2 or master alloys and arc-melted. Annealing treatments were carried out at 21 temperature levels. Metallographic examination of the heat treated specimens permitted construction of the binary phase diagram from zirconium to ZrO2. Oxygen additions to zirconium raise the transformation temperature as well as the melting point. Features of the diagram include the peritectic formation of beta, the formation of alpha directly from the melt, an intermediate phase ZrO2 with a range of homogeneity, and a eutectic between alpha and ZrO2.