Recovery of Crack-Tip Transformation Zones in Zirconia After High-Temperature Annealing

Annealing at temperatures between 500° and 1000°C reverses the stress-induced tetragonal-to-monoclinic phase transformation in precipitates within crack-tip zones in MgO-partially-stabilized ZrO₂ (Mg-PSZ). The stability of such reverse-transformed tetragonal precipitates during subsequent room-temperature aging has been examined using Raman spectroscopy, surface displacement measurements, and crack-opening measurements. Partial spontaneous retransformation of material within the original zone from tetragonal-to-monoclinic symmetry occurred over periods of several months.     

Novel Two-Step Sintering Process to Obtain a Bimodal Microstructure in Silicon Nitride

A two-step sintering process is described in which the first step suppresses densification while allowing the α-to-β phase transformation to proceed, and the second step, at higher temperatures, promotes densification and grain growth. This process allows one to obtain a bimodal microstructure in Si₃N₄ without using β-Si₃N₄ seed crystals. A carbothermal reduction process was used in the first step to modify the densification and transformation rates of the compacts consisting of Si₃N₄, Y₂O₃, Al₂O₃, and a carbon mixture. The carbothermal reduction process reduces the oxygen:nitrogen ratio of the Y-Si-Al-O-N glass that forms, which leads to the precipitation of crystalline oxynitride phases, in particular, the apatite phase. Precipitation of the apatite phase reduces the amount of liquid phase and retards the densification process up to 1750°C; however, the α-to-β phase transformation is not hindered. This results in the distribution of large β-nuclei in a porous fine-grained β-Si₃N₄ matrix. Above 1750°C, liquid formed by the melting of apatite resulted in a rapid increase in densification rates, and the larger β-nuclei also grew rapidly, which promoted the development of a bimodal microstructure.     

Recent Advances on TiO2‐ZrO2 Mixed Oxides as Catalysts and Catalyst Supports

This is the first review of titanium dioxide‐zirconium dioxide (TiO₂‐ZrO₂) mixed oxides, which are frequently employed as catalysts and catalyst supports. In this review many details pertaining to the synthesis of these mixed oxides by various conventional and nonconventional methods and their characterization by several techniques, as reported in the literature, are assessed. These mixed oxides have been synthesized by different preparative analogies and were extensively characterized by employing various spectroscopic and nonspectroscopic techniques. The TiO₂‐ZrO₂ mixed oxides are also extensively used as supports with metals, nonmetals, and metal oxides for various catalytic applications. These supported catalysts have also been thoroughly investigated by different techniques. The influence of TiO₂‐ZrO₂ on the dispersion and surface structure of the supported active components as examined by various techniques in the literature has been contemplated. A variety of reactions catalyzed by TiO₂‐ZrO₂ and supported titania‐zirconia mixed oxides, namely; dehydrogenation, decomposition of chlorofluoro carbons (CFCs), alcohols from epoxides, synthesis of ?‐caprolactam, partial oxidation, deep oxidation, hydrogenation, hydroprocessing, organic transformations, NO_x abatement, and photo catalytic VOC oxidations that have been pursued in the literature are presented with relevant references.     

Macroscopic and structural effects of hydrogen-bond transformations: some recent directions

The main directions and achievements in the research on transformations of hydrogen-bonds during the last decade have been briefly outlined.     

Competing chemical transformations in the combustion wave in the Fe2O3-Cr2O3-Al mixture

Laws of combustion of a thermit-type mixture Fe₂O₃-2Al-γCr₂O₃ are considered. The limits of liquid-phase combustion and separation of the oxide and metal phases in the final products are determined. Chromium oxide is demonstrated to weakly compete with iron oxide in the oxidation-reduction reaction with aluminum and to participate mainly in oxide-phase formation. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 89–91, May–June, 2006.     

Boundary Layer Flow of Rotating Two Phase Nanofluid Over a Stretching Surface

An analysis is carried out to discover the influence of a rotating nanofluid over a stretching surface. The two phase nanofluid model is used for this study. Two types of nanoparticles, namely copper and titanium oxide are used in our analysis with water as the base fluid. The governing system of partial differential equations along with the corresponding boundary conditions are presented and then transformed into a set of nonlinear ordinary differential equations using suitable similarity transformations. These equations are solved numerically by means of an iterative procedure called the midpoint integration scheme along with Richardson extrapolation. The results for flow and heat transfer characteristics are presented through graphs against nanoparticle volume fraction and rotation parameter for both types of nanoparticles. Quantities of physical interest such as local skin friction coefficients and local heat flux rate at the stretching surface are computed and analyzed. Numerical values for skin frictions and local heat flux rate are computed in the absence of nanoparticle volume fraction and rotation and they are found to be in very good agreement with the existing published literature.     

Phase transformation studies on pure and doped strontium carbonate

The orthorhombic-hexagonal transformation of strontium carbonate is a reversible reconstructive transformation. Cationic impurities like K⁺, Ca²⁺, Ba²⁺, Cd²⁺, Y³⁺, La³⁺, Nd³⁺, Sm³⁺, Gd³⁺, Dy³⁺, Ho³⁺, Bi³⁺, Zr⁴⁺ doped in pure strontium carbonate affect the kinetics and energetics of the transformation. Paper presented at the Annual Convention of Chemists held at Andhra University, Waltair, December 1978.     

GF（q）^n上具有线性结构的函数的谱特征

本文在ＧＦ（ｑ）＾ｎ上讨论了密码上的一类弱函数－具有线性结构的函数，证明了其谱特性及有关性质。