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Kinetics of homogeneous reactions in solids
dbslracts
low temperature, to yield a~ atomically mixed high surface area reactive intermediate; followed by controlled conversion of the intermediate in a thermodynamically well defined environment to the desired product phases. The approach will be illustrated for the synthesis of pure component phases and binary composites in the ternary system Co-W-C. ,l~e Reduction Process of Copper-Zinc Oxide(Alumina) Methanol Catalysts Piero Porta. Roberto Dragox-Je, Guiseppe Fierro, Mariano I,o lacano and Giuliano Moretti, Roma University, Italy. The reduction process of the copper oxide component in w_-,ll defined copper oxide-zinc oxide (alumina) specimens at different C u / Z n contents and obtained by thermal decomposition at 623 K in air of initial hydroxycarbonate precursors has been studied by in situ XRD, XPS, magnetic susceptibility m e a s u r e m e n t s , and oxidation and reduction cycling. Reductions were carried out in 2% H2/N2, or in pure hydrogen gas, at different temperatures and at several intervals of time. The results have shown that in pure CuO and in the two component CuO-ZnO catalysts the reduction proceeds from cupric oxide *.o metallic copper through the formation of inte:n~diate cuprous oxide, which is in any case present, together with metallic copper, even at higher reduction extent. In the three comp o n e n t CuO-ZnO-AI203 catalysts the reduction process is much slower than in CuO-ZnO samples; the presence of alumina in intimate contact with copper and zinc oxides thus hinders the reduction of CuO and prevents the nucleation of both Cu20 and Cu.
,,
which subsequently affect the deprotonation rate of the excited molecule. By comparing the fluorescence of some rhodamines and coumarins embedded in different oxide gels, we analyze the parameters that control the optical activity. We discuss the conditions that the matrix imposes on the organic dopant as a function of the gel structure (polarity, chemical factors) and the nature of the dyes (mobility of the chromophore, aggregation ability, hydrogen bonding). Kinetics of Homogeneous Reactions in Solids W. Primal<, Wolfe Loeb & Co., USA Such reac.*ons are the transformations in disordered sohds. They are studied, e.g., by differential or other thermal analysis by thermoluminescence, by thermal annealing. In isothermal studies, the changes characteristically are nearly linear in log t over several decades of time: and, in differential thermal analysis, peaks shift when the heating rate is changed. The kinetic description is an equation that gives the behavior as a function of temperature and time. Thus, there are two parameters: a thermal parameter and a temporal one, usually termed the activation energy and the frequency factor. The behavior of these systems can be described by first order kinetic processes distributed in activation energy. It was generally assumed that the frequency factor was of the order of magnitude of the vibration frequency in solids, ,q014/sec. This investigator showed how to determine the frequency factors and found that they varied by many orders of magnitude. Only several examples have been explored in such detail, and each shows a different behavior for the two parameters.
Interaction between Organic Dyes and Sol Gel Matrices lean-Claude Pouxviel, Edward Knobbe and Bruce Duma, Univ. of California at Los Angeles, USA.
Ultrafine Mn-Zn Fen'ites: Preparation Properties P. Ravindranathan, T. T. Sriniva~n, Newnham, P e n n 3tate Univ., S. Carnegie Mellon Univ., USA and Indian Inst of Sciences, india.
and
Sol-gel matrices in the SIO2-A1203 system have been p-epared by the ">olymerization of alkoxides. Organic dyes are incorporated during the process to obtain materials with optical activity. The fluorescence properties can be used to probe the different stages of the process and the structure of the gels. ~:er i.nstance, the changes of the ?yranine emission during the gelation, aging and drying of an aluminosilicate composition reflect the formation of the polymeric network and the decrease of free water
High density Mn-Zr ferrites have been extensively used in recording head applications. The properties like permeability, los~, etc., depend on the preparation method. The :roperfies play major role in selecting these materials for various applications. In this present work., we have prepared Mn-Zn ferrites using metal hydrazine carboxylate precursors (N2Hs)3Mn0.sZn0.sFe2(N2H3COO)3"3H20. The precursor decomposes at very low temperature
R. Roy, R. E. G. Sankar, K. C. Patti,
low temperature, to yield a~ atomically mixed high surface area reactive intermediate; followed by controlled conversion of the intermediate in a thermodynamically well defined environment to the desired product phases. The approach will be illustrated for the synthesis of pure component phases and binary composites in the ternary system Co-W-C. ,l~e Reduction Process of Copper-Zinc Oxide(Alumina) Methanol Catalysts Piero Porta. Roberto Dragox-Je, Guiseppe Fierro, Mariano I,o lacano and Giuliano Moretti, Roma University, Italy. The reduction process of the copper oxide component in w_-,ll defined copper oxide-zinc oxide (alumina) specimens at different C u / Z n contents and obtained by thermal decomposition at 623 K in air of initial hydroxycarbonate precursors has been studied by in situ XRD, XPS, magnetic susceptibility m e a s u r e m e n t s , and oxidation and reduction cycling. Reductions were carried out in 2% H2/N2, or in pure hydrogen gas, at different temperatures and at several intervals of time. The results have shown that in pure CuO and in the two component CuO-ZnO catalysts the reduction proceeds from cupric oxide *.o metallic copper through the formation of inte:n~diate cuprous oxide, which is in any case present, together with metallic copper, even at higher reduction extent. In the three comp o n e n t CuO-ZnO-AI203 catalysts the reduction process is much slower than in CuO-ZnO samples; the presence of alumina in intimate contact with copper and zinc oxides thus hinders the reduction of CuO and prevents the nucleation of both Cu20 and Cu.
,,
which subsequently affect the deprotonation rate of the excited molecule. By comparing the fluorescence of some rhodamines and coumarins embedded in different oxide gels, we analyze the parameters that control the optical activity. We discuss the conditions that the matrix imposes on the organic dopant as a function of the gel structure (polarity, chemical factors) and the nature of the dyes (mobility of the chromophore, aggregation ability, hydrogen bonding). Kinetics of Homogeneous Reactions in Solids W. Primal<, Wolfe Loeb & Co., USA Such reac.*ons are the transformations in disordered sohds. They are studied, e.g., by differential or other thermal analysis by thermoluminescence, by thermal annealing. In isothermal studies, the changes characteristically are nearly linear in log t over several decades of time: and, in differential thermal analysis, peaks shift when the heating rate is changed. The kinetic description is an equation that gives the behavior as a function of temperature and time. Thus, there are two parameters: a thermal parameter and a temporal one, usually termed the activation energy and the frequency factor. The behavior of these systems can be described by first order kinetic processes distributed in activation energy. It was generally assumed that the frequency factor was of the order of magnitude of the vibration frequency in solids, ,q014/sec. This investigator showed how to determine the frequency factors and found that they varied by many orders of magnitude. Only several examples have been explored in such detail, and each shows a different behavior for the two parameters.
Interaction between Organic Dyes and Sol Gel Matrices lean-Claude Pouxviel, Edward Knobbe and Bruce Duma, Univ. of California at Los Angeles, USA.
Ultrafine Mn-Zn Fen'ites: Preparation Properties P. Ravindranathan, T. T. Sriniva~n, Newnham, P e n n 3tate Univ., S. Carnegie Mellon Univ., USA and Indian Inst of Sciences, india.
and
Sol-gel matrices in the SIO2-A1203 system have been p-epared by the ">olymerization of alkoxides. Organic dyes are incorporated during the process to obtain materials with optical activity. The fluorescence properties can be used to probe the different stages of the process and the structure of the gels. ~:er i.nstance, the changes of the ?yranine emission during the gelation, aging and drying of an aluminosilicate composition reflect the formation of the polymeric network and the decrease of free water
High density Mn-Zr ferrites have been extensively used in recording head applications. The properties like permeability, los~, etc., depend on the preparation method. The :roperfies play major role in selecting these materials for various applications. In this present work., we have prepared Mn-Zn ferrites using metal hydrazine carboxylate precursors (N2Hs)3Mn0.sZn0.sFe2(N2H3COO)3"3H20. The precursor decomposes at very low temperature
R. Roy, R. E. G. Sankar, K. C. Patti,