Peritectoid reaction

The foregoing classification is not without ambiguity. For example, it is common practice to call the reaction A - B +C° (see Fig. 6-1) induced by decreasing the temperature a phase transformation. The similar (peritectoid) reaction C = a+fi (Fig. 12-2) induced by a temperature increase, however, is named a decomposition reaction. In addition, the isothermal reaction AO = A+j02, which occurs if the intensive variable fio2 is decreased so that AO decomposes, is called a metal oxide reduction. It is thus categorized as a genuine heterogeneous solid state reaction (the... 

This low misfit accompanied with very low solid solubility of Zr in A1 favors the stability of the precipitates. The reason of stability was showed by the study of peritectoid reaction (998+12 °C) ((3Zr)+Zr2Al <- Zr3Al [1], These small precipitates act to inhibit recrystallization and pin grain boundaries through a Zener drag process. 

Phase diagrams are the roadmaps from which the number of phases, their compositions, and their fractions can determined as a function of temperature. In general, binary-phase diagrams can be characterized as exhibiting complete or partial solid solubility between the end members. In case of the latter, they will contain one or both of the following reactions depending on the species present. The first is the eutectic reaction is which a liquid becomes saturated with respect to the end members such that at the eutectic temperature two solids precipitate out of the liquid simultaneously. The second reaction is known as the peritectic reaction in which a solid dissociates into a liquid and a second solid of a different composition at the peritectic temperature. The eutectic and peritectic transformations also have their solid state analogues, which are called eutectoid and peritectoid reactions, respectively. 

The investigation on the phase transition in U-Zr alloy has been conducted. According to the characteristics of the transformation in the U-Zr alloy, the transition temperature were determined by the Differential Scanning Calorimeter method (DSC) analysis as following the peritectoid reaction UZra- — -aU+ya, the eutectoid reaction / U- — aU+yz and... 

It is accompanied by a peritectoid reaction as a-Pd+Ll2-type PdsR iPdyR ... 

The transition temperature (order-disorder transition) decreases with decreasing R content, it corresponds to the solid solubility limit of R in the a-Pd solid solution below the peritectoid reaction temperature ... 

The cerium-yttrium system as reported by Lundin and Klodt (1958) showed the intermediate Sm-type phase to be formed by a peritectoid reaction. Later, a systematic study of the formation of the Sm-type structure by Lundin (1966) and by Nachman et al. (1963), using metallographic. X-ray diffraction, thermal, dilatomet-... 

The equilibrium phase diagram for the cerium-yttrium system is presented in fig. 40. This diagram does not show a peritectoid reaction to form the Sm phase as did that of Lundin and Klodt. Instead, a congruent transformation is presented, based on the results of the investigations into the nature of the formation of the 5 phase. The melting points and transformation temperatures of the pure metals have been adjusted to conform with the accepted data listed in table 1. 

Systems in which the components have different valences produce complex phase diagrams with a number of different solid phases and peritectic reactions as well as eutectoid and peritectoid reactions. These transitions can be explained in terms of interactions between the Fermi sphere and the Brillouin zones. 

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