In this paper we present sol-gel synthesis and thermal and structural characterization of some lithium borophosphates. The as-prepared samples are mostly partially crystalline, and densification heat treatments at 500 °C cause samples to crystallize. In the phosphorus-rich part of the composition triangle we have lithium excess with respect to the nominal composition, which is likely due to the low reactivity of the phosphorus precursor. On the boron-rich side, in contrast, lithium losses are found which probably occur during syneresis.
The current usa of non-isothermal DTA or DSC for the investigation of polymers is based upon assumptions which allow a number of conclusions supported only by data drawn from the DTA or DSC traces of prepolymer samples.A more adequate procedure involving the analysis of the DTA or DSC traces of several samples previously cured to different polymerization degrees under isothermal conditions is proposed.A comparison of the results obtained with the two procedures is reported for two composite materials.Calorimetric investigations on polymers are currently carried out under non-isothermal conditions, viz. through DTA or DSC at a given heating rate.This kind of approach, although experimentally simple and rapid, must be considered with some caution, as it can result in misleading conclusions when the chemical process investigated occurs with a complex mechanism, as in the polymerization and reticulation of resins.The present work reports some typical examples of the misuse of non-isothermal DTA and DSC data and suggests how this kind of investigation should be employed to characterize the kinetics of a polymerization process.A direct comparison of the results obtained with the misleading and the correct approaches is also reported. General considerations Typical misuseMany authors and qualified firms report the kinetic parameters of curing processes, drawn from the evaluation of point derivatives, dQ/dT, along the profile of the exothermic peak recorded in the DTA or DSC scan for the so called prepolymer.This procedure is based on the following assumptions [1 ]:the heat Q delivered at a given time in the DSC scan is proportional to the curing degree (~ reached at that time;
This volume reviews the metal and ammonium formate solubility data published up to 1995. So far as the editors are aware, all the solubility data published during this period have been reviewed. Preference has been given to data published in numerical form. Data that appeared only in graphical form may not appear in this volume. In each section the metal atoms are arranged in the order (group) in which they appear in the Periodic Table. Metal formates are crystalline solids having some interesting chemical and physical properties. Several of these salts are important because they have nonlinear optical properties. Specific examples are: LiCHO2⋅H2O (3), NaCHO2 (4), Sr(CHO2)2, and Sr(CHO2)2⋅2H2O, Ba(CHO2)2, formates of Sc, Y and the rare earth elements having the general formula Me(CHO2)3⋅nH2O (where Me=Sc, Y, La, Ce, Pr, Nd, Sm…Lu) and some double salts and mixed salts such as NaCd(CHO2)3, BaCd(CHO2)4⋅2H2O and Li0.9Na0.1CHO2. Some metal formates have useful electric or magnetic characteristics. Thus, Cu(CHO2)2⋅4H2O has ferroelectric properties, Cu(CHO2)2 is ferromagnetic, Mn(CHO2)2⋅2H2O is antiferromagnetic, CuBa2(CHO2)6⋅4H2O is paramagnetic, and the formates of Ca, Cd, and Sr have elastic and thermoplastic properties. Bivalent metal formates could be used as precursors for the production of catalysts because they show excellent miscibility in the solid state, i.e., they form mixed crystals that dissociate at relatively low temperatures (about 300 °C) to form the respective oxides and mixed oxides. There are also additional smaller-scale uses of metal formates. The wide interest in the applications and uses of metal formates will lead to an interest in seeking methods for the preparation of these materials. Solubility data for the metal formates will be helpful in devising the methods of preparation. Therefore, this volume has been prepared to present and evaluate solubility data for the binary, ternary and multicomponent systems containing metal formates in aqueous and in nonaqueous solutions.
We have shown that H02 forms transient complexes with the peroxovanadium(V) species but not with V02+. This is in agreement with the results of Samuni5 who detected ESR-active transients only in V(V) solutions containing peroxide. The presence of a faster decaying complex, which we have designated V05"O2H, was not detected by Samuni and Czapski6 in a perchloric acid medium. The faster rate of decomposition of V-05"•02 relative to V03+-02H reflects the respective oxidizing strengths of V05~a nd V03+. Also, high proton concentration increases the rate of peroxide decomposition by V(V) complexes. This may explain the [H+] dependence of kH (Figure 3), if, at pH < 1, protonation of a water molecule in the solvation sphere of V03+.02H occurs, thus decreasing the stability of the complex.
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