Part I. Kinetics of coarsening of the gamma-prime precipitate in nickel-silicon alloys. Part II. Rate of crystallization of an amorphous Fe-P-C alloy

The coarsening kinetics of Ni₃ Si(γ') precipitate in a binary Ni-Si alloy containing 6.5 wt. % silicon was studied by magnetic techniques and transmission electronmicroscopy. A calibration curve was established to determine the concentration of silicon in the matrix. The variation of the Si content of the Ni-rich matrix as a function of time follows Lifshitz and Wagner theory for diffusion controlled coarsening phenomena. The estimated values of equilibrium solubility of silicon in the matrix represent the true coherent equilibrium solubilities.

The experimental particle-size distributions and average particle size were determined from dark field electron micrographs. The average particle size varies linearly with t^-1/3 as suggested by Lifshitz and Wagner. The experimental distributions of particle sizes differ slightly from the theoretical curve at the early stages of aging, but the agreement is satisfactory at the later stages. The values of diffusion coefficient of silicon, interfacial free energy and activation energy were calculated from the results of coarsening kinetics. The experimental value of effective diffusion coefficient is in satisfactory agreement with the value predicted by the application of irreversible the rmodynamics to the process of volume constrained growth of coherent precipitate during coarsening. The coherent γ' particles in Ni-Sialloy unlike those in Ni-Al and Ni-Ti seem to lose coherency at high temperature. A mechanism for the formation of semi-coherent precipitate is suggested.

Conduction-electron localized-moment interaction in palladium-silicon base amorphous alloys containing transition metals

The electrical and magnetic properties of amorphous alloys obtained by rapid quenching from the liquid state have been studied. The composition of these alloys corresponds to the general formula M_xPd_80-xSi₂₀, in which M stands for a metal of the first transition series between chromium and nickel and x is its atomic concentration. The concentration ranges within which an amorphous structure could be obtained were: from 0 to 7 for Cr, Mn and Fe, from 0 to 11 for Co and from 0 to 15 for Ni. A well-defined minimum in the resistivity vs temperature curve was observed for all alloys except those containing nickel. The alloys for which a resistivity minimum was observed had a negative magnetoresistivity approximately proportional to the square of the magnetization and their susceptibility obeyed the Curie-Weiss law in a wide temperature range. For concentrated Fe and Co alloys the resistivity minimum was found to coexist with ferromagnetism. These observations lead to the conclusion that the present results are due to a s-d exchange interaction. The unusually high resistivity minimum temperature observed in the Cr alloys is interpreted as a result of a high Kondo temperature and a large s-d exchange integral. A low Fermi energy of the amorphous alloys (3.5 eV) is also responsible for the anomalies due to the s-d exchange interaction.

Synthesis and characterization of room-temperature ferromagnetism in Fe- and Ni-co-doped In2O3

Observation of room-temperature ferromagnetisin in Fe- and Ni-co-doped In2O3 samples (In0.9Fe0.1-xNix)(2)O-3 (0 <= x <= 0.1) prepared by citric acid sol-gel auto-igniting method is reported. All of the samples with intermediate x values are ferromagnetic at roomtemperature. The highest saturation magnetization (0.453 mu B/Fe + Ni ions) moment is reached in the sample with x = 0.04. The highest solubility of Fe and Ni ions in the In2O3 lattice is around 10 and 4 at%, respectively. The 10 at% Fe-doped sample is found to be weakly ferromagnetic, while the 10at% Ni-doped sample is paramagnetic. Extensive structure including Extended X-ray absorption fine structure (EXAFS), magnetic and magneto-transport including Hall effects studies on the samples indicate the observed ferromagnetism is intrinsic rather than from the secondary impurity phases. (c) 2007 Elsevier Ltd. All rights reserved.

Heterogeneous catalytic activity on Mn, Fe and Co-based metalloporphyrinic Solid Coordination Frameworks (SCFs)

Comunicación al congreso 1st European Conference on Metal Organic Frameworks and Porous Polymers, celebrado en Postdam del 11 al 14 de octubre de 2015

Mechanical alloying of Fe-Mn and Fe-Mn-Si

The ball milling of Fe-24Mn and Fe-24Mn-6Si mixed powders has been performed by the high energy ball milling technique. By employing X-ray diffraction and Mossbauer measurements, the composition evolution during the milling process has been investigated. The results indicate the formation of paramagnetic Fe-Mn or Fe-Mn-Si alloys with a metastable fee phase as final products, which imply that the Fe and Mn proceed a co-diffusion mechanism through the surface of fragmented powders. The thermal stability and composition evolution of the as-milled alloys were discussed comparing with the bulk alloy. (C) 1999 Published by Elsevier Science S.A. All rights reserved.

钙钛石型复合氧化物La_xSr_(1-x)M_yM'_(1-y)O_3(M, M' = Mn, Fe, Co)的固体物理化学性质和催化性能的研究

钙钛石型复合氧化物由于具有许多独特的物理化学性质，如多种类型的磁性和导电性、对多种物理和化学因素的敏感性、高温下的稳定性和结构的明确易调性等长期以来一直受到固体物理、固体化学和催化科技工作者重视，本文第一部分详细总结了文献中有关这类氧化物的结构、电子状态、电磁性质、表面吸附性能、稳定性以及反应机理和催化性能等方面的重要结果。第二部分为催化剂的制备和表征方法。第三部分针对文献中研究较少的B位取代钙钛石型氧化物，系统研究了系列化合物LaM_yM'_(1-y)O_a (M, M' = Mn, Fe, Co)的固体物理化学性质和对NH3和CO氧化反应的催化性能，讨论了它们之间的关系。1. 催化剂的制备、晶体结构与光谱性质。2. LaM_yM'_(1-y)O_3(M、M' = Mn、Fe、Co)r的氧化还原性质和稳定性。3. 过渡金属离子的状态及其之间的相互作用。4. 催化剂中氧的形态。5. 氨氧化性能与固体物化性质之间的关系。6. 一氧化碳氧化与固体物化性质之间的关系。