Phase Equilibrium Studies in the System Iron Oxide-Al2O3-Cr2O3

Subsolidus phase relations in the system iron oride-Al₂O₂-Cr₂O₃ in air and at 1 atm. O₂ pressure have been studied in the. temperature interval 1250° to 1500°C. At temperatures below 1318° C. only sesquioxides with hexagonal corundum structure are present as equilibrium phases. In the temperature interval 1318° to 1410°C. in air and 1318° to 1495° C. at 1 atm. O₂, pressure the monoclinic phase Fe₂O₃. Al₂O₃ with some Cr₂O₃ in solid solution is present in the phase assemblage of certain mixtures. At temperatures above 1380°C. in air and above 1445°C. at 1 atm. O₂ pressure a complex spinel solid solution is one of the phases present in appropriate composition areas of the system. X-ray data relating d- spacing to composition of solid solution phases are given.     

Quantitative Analysis of Monoclinic-Stabilized Cubic ZrO2 Systems by X-Ray Diffraction

An equation for a nonlinear calibration curve of volume fraction vs integrated intensity ratio is presented for monoclinic-stabilized cubic ZrO₂ systems containing YO_1.5, CaO, and MgO. A parameter in the equation was evaluated theoretically and is given for a range of cubic solid solution compositions.     

Reaction Kinetics in the Hydrothermal Oxidation of Hf

The hydrothermal oxidation of Hf was studied using metal powders and chips to change the surface-area effect. Fine monoclinic HfO₂ powders (32 to 34 nm) were formed through two parallel reaction paths, one the oxidation of Hf with H₂O and the other the consecutive reaction via formation of Hf hydride. Based on the experimental results at 500°C under 100 MPa, three reaction rate constants were determined for two kinds of starting materials. The relative widths of two paths were proved to be independent of the size of starting materials, and the pulverization and oxidation of both metal powders and chips could be explained by the same mechanism, where the formation of hydride was a driving force in pulverization.     

Phase Relations in the System FeO-Fe2O3-ZrO2-SiO2

Phase equilibrium relations in the liquidus-temperature region of the system iron oxide-ZrO₂-SiO₂ in air were delineated by the quenching technique. Additional equilibration runs were made at other controlled oxygen pressures as well as in sealed containers. The results of all runs have been combined with literature data for the system in contact with metallic iron to locate approximately the quaternary liquidus invariant points within the system FeO-Fe₂O₃-ZrO₂-SiO₂.     

Strength-Toughness Relations in Sintered and Isostatically Hot-Pressed ZrO2-Toughened Al2O3

The fracture toughness of fine-grained undoped ZrO₂-toughened Al₂O₃ (ZTA) was essentially unchanged by postsintering hot isostatic pressing and increased monotonically with ZrO₂ additions up to 25 wt%. The strength of ZTA with 5 to 15 wt% tetragonal ZrO₂, which depended monotonically on the amount of ZrO₂ present before hot isostatic pressing, was increased by pressing but became almost constant between 5 and 15 wt% ZrO₂ addition. The strength appeared to be controlled by pores before pressing and by surface flaws after pressing; the size of flaws after pressing increased with ZrO₂ content. The strength of ZTA containing mostly monoclinic ZrO₂ (20 to 25 wt%) remained almost constant despite the noticeable density increase upon hot isostatic pressing because the strength was controlled by preexisting microcracks whose extent did not change on postsintering pressing. These strength-toughness relations in sintered and isostatically hot-pressed ZTA are explained on the basis of R -curve behavior. The importance of the contribution of microcracks to the toughness of ZTA is emphasized.     

Revised Phase Diagram of the System ZrO2-CeO2 Below 1400°C

The phase diagram of the system ZrO₂-CeO₂ was rein-vestigated using hydrothermal techniques. Cubic, tetragonal, and monoclinic solid solutions are present in this system. The tetragonal solid solution decomposes to monoclinic and cubic solid solutions by a eutectoid reaction at 1050°50°C. The solubility limits of the tetragonal and cubic solid solutions are about 18 and 70 mol% CeO₂, respectively, at 1400°C, and about 16 and 80 mol% CeO₂, respectively, at 1200°C. Solubility limits of the monoclinic and cubic solid solutions are about 1.5 and 88 mol% CeO₂ at 1000°C, and 1.5 and 98 mol% CeO₂ at 800°C, respectively. The compound Ce₂Zr₃O₁₀ is not found in this system.     

Formation of Ultrafine Tetragonal ZrO2 Powder Under Hydrothermal Conditions

Ultrafine tetragonal ZrO₂ powder was prepared by hydrothermal treatment at 100 MPa of amorphous hydrous zirconia with distilled water and LiCl and KBr solutions. The resulting powder consisted of well-crystallized particles; at 200°C, the particle size was 16 nm and at 500°C, 30 nm. Under hydrothermal conditions tetragonal ZrO₂ appears to crystallize topotactically on nuclei in the amorphous hydrous zirconia.     

IgG Antibody from Hen Egg Yolks: Purification by Ethanol Fractionation

A procedure was developed for large-scale preparation of IgG antibodies from egg yolks. The supernatant from egg yolks was obtained after an initial 9–fold dilution with water. The lipids in the supernatant were then almost completely eliminated from the water-soluble protein fraction containing the antibody, by precipitation with 60% ethanol and filtration. Yolk antibody was purified from the lipid-free water-soluble protein fraction by ethanol fractionation at final concentration 30% (pH unadjusted), and again at 25% (pH 7.4). The purified fraction was composed of >99% pure IgG. Recovery of antibody was calculated as 40%.     

Hydrothermal Oxidation of Hf Metal Chips in the Preparation of Monoclinic HfO2 Powders

Fine monoclinic HfO₂ powders were prepared from Hf metal chips by reaction with high-temperature high-pressure water. Dependence of the reaction on temperature-pressure-time was examined in both closed and open systems. Hydrothermal oxidation of Hf proceeded through three stages: the surface oxidation of Hf metal chips with H₂O, the reaction of the Hf with released H₂ to form hydrides, and the succeeding oxidation of the hydrides with H₂O to form HfO₂. Most of the fine HfO₂ powders were, however, considered to be formed by the latter two reactions after the cracking and pulverizing of metal chips associated with hydriding. The difference in the reaction rates between the closed and open systems was explained by taking into account the fugacity relations of H₂ and H₂O in the respective systems.     

Phase Relations in the System Iron Oxide—Cr2O3 in Air

The quenching method has been used to determine approximate phase relations in the system iron oxide-Cr₂O₃ in air. Only two crystalline phases, a sesquioxide solid solution (Fe₂O₃–Cr₂O₃) with corundum structure and a spinel solid solution (approximately FeO ·Fe₂O₃–FeO – Cr₂O₃), occur in this system at conditions of temperature and O₂ partial pressure (0.21 atm.) used in this investigation. Liquidus temperatures increase rapidly as Cr₂O₃ is added to iron oxide, from 1591°C. for the pure iron oxide end member to a maximum of approximately 2265°C. for Cr₂O₃. Spinel(ss) is the primary crystalline phase in iron oxide-rich mixtures and sesquioxide (ss) in Cr₂O₃–rich mixtures. These two crystalline phases are present together in equilibrium with a liquid and gas (po₂= 0.21 atm.) at approximately 2075°C.