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Rate-controlling Mechanism (rate-controlling + mechanism)
Selected AbstractsHot Workability, Microstructural Control and Rate-Controlling Mechanisms in Cast-Homogenized AZ31 Magnesium Alloy,ADVANCED ENGINEERING MATERIALS, Issue 3 2009Yellapregada Venkata Rama Krishna Prasad Optimum conditions for microstructural control in industrial hot working of cast and homogenized AZ31 magnesium alloys are evaluated by using a processing map. The recommended window for bulk metal working of this alloy is the domain in the temperature range 300,450,°C and strain rate range 1,10,s,1, and the optimum processing parameters are 400,°C and 10,s,1, where grain-boundary self diffusion is the rate-controlling mechanism. [source] The Reaction-Bonded Aluminum Oxide (RBAO) Process: II, The Solid-State Oxidation of RBAO CompactsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Ender Suvaci The oxidation kinetics and the fraction of aluminum that is oxidized via solid,gas reaction in reaction-bonded aluminum oxide (RBAO) compacts are shown to be strongly dependent on the oxidation temperature and the characteristics (size and green density) of the RBAO compact. Based on the Biot number, the oxidation process of RBAO compacts is controlled by convective heat transfer. Low heat transfer from the surface of the compact results in too-rapid oxidation, thermal gradients, and core,shell oxidation of the compacts. Uniform oxidation of RBAO compacts is possible by oxidizing at low temperatures (400°,470°C), where slow surface reaction of the aluminum particles controls the oxidation of the compact. A grain model is presented to cover both linear and nonlinear oxidation regimes during the oxidation of a RBAO compact, and this model predicts the experimental results when surface reaction of the aluminum particles is the rate-controlling mechanism and oxidation of the compact occurs uniformly. [source] Mullitization from a Multicomponent Oxide System in the Temperature Range 1200°,1500°CJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2000Hyunho Shin Mullitization from a multicomponent oxide system (alumina,kaolin,quartz,feldspar,talc) was analyzed as a function of firing temperature from 1200° to 1500°C based on quantitative XRD and SEM. In the present study, whisker forms of mullite grew in three characteristic stages. In the first stage (1255°,1295°C), mullitization (nucleation) took place from glass via alumina dissolution into glass under the condition of no apparent change in glass content. The reaction in this stage was rate-limited by alumina dissolution into glass. Extensive mullitization occurred in the 1295°,1335°C range (second stage) directly from glass. Unlike in the sol,gel-based binary system, alumina dissolution into glass was not shown to be the rate-controlling mechanism during this extensive mullitization stage. Finally (>1335°C, third stage), the reaction was saturated, accompanied by an apparent decrease in glass consumption rate. The impingement of mullite whiskers by other whiskers and crystals was speculated to cause mullite to grow in the transverse direction, yielding a diminished reaction rate in the final stage. Mullitization stages in this work were compared with those of the alumina,silica binary system shown in the literature. [source] Coarsening of Lamellar Microstructures in Directionally Solidified Yttrium Aluminate/Alumina Eutectic FiberJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2001Deok-Yong Park Coarsening of the fine lamellar structure of a directionally solidified Y3Al5O12 (yttrium aluminum garnet, YAG)/Al2O3 eutectic fiber at elevated temperatures was investigated. The fibers were grown continuously by an edge-defined film-fed growth (EFG) technique. To study the thermal stability of the lamellar structure, the fibers were heat-treated in air at 1360°,1460°C for up to 200 h. X-ray diffractometry and scanning electron microscopy were used to characterize the microstructures of the fibers. Image analysis was used to measure the length of the interface line between Y3Al5O12 and Al2O3 phases. The kinetics of coarsening and the rate-controlling mechanisms were investigated. Also, the Graham and Kraft model for describing the coarsening behavior of the lamellar Al-CuAl2 eutectic alloy was used to explain the coarsening behavior of Y3Al5O12/Al2O3 eutectic fiber. [source] | ||||||||||