Kinetics and mechanism of thermal decomposition of copper hypophosphite

Synthesis, characterization and non-isothermal decomposition kinetics of manganese hypophosphite monohydrate

Abstract: The manganese hypophosphite monohydrate (α-Mn(H2PO2)2·H2O) was synthesized and characterized by differential thermal analysis–thermogravimetry (TG/DTG/DTA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The thermal transformation products form the synthesized Mn(H2PO2)2·H2O according to the thermal treatment at 160 and 450 °C were found to be α-Mn(H2PO2)2·xH2O and Mn2P2O7, respectively. The activation energies of two decomposition reaction steps of Mn(H2PO2)2·H2O were calculated through the isoconversional methods of Ozawa and KAS. The obtained activation energies can be concluded that the reactions of the dehydration and the decomposition steps for Mn(H2PO2)2·H2O were the single and multi-step mechanisms, respectively.

Topochemistry of thermal decompositions of solids

Abstract: This survey systematically considers the factors responsible for localization and autolocalization of thermal decomposition processes of solids. The specificity and complexity of nucleation and nuclei growth in topochemical processes are shown.

Synthesis of copper hydride (CuH) from CuCO3·Cu(OH)2 – a path to electrically conductive thin films of Cu

Abstract: The most common synthesis methods for copper hydride (CuH) employ hard ligands that lead to the formation of considerable amounts of metallic Cu as side-product. Here we explore a synthesis method for CuH(s) through the reaction of CuCO3·Cu(OH)2(s) with hypophosphorous acid (H3PO2) in solution, via the formation of the intermediate Cu(H2PO2)2(aq) complex. The reaction products were characterized with XRD, FTIR and SEM at different reaction times, and the kinetics of the transformation of Cu(H2PO2)2(aq) to CuH(s) were followed with NMR and are discussed. We show that our synthesis method provides a simple way for obtaining large amounts of CuH(s) even when the synthesis is performed in air. Compared to the classic Wurtz method, where CuSO4 is used as an initial source of Cu2+, our synthesis produces CuH particles with less metallic Cu side-product. We attribute this to the fact that our reaction medium is free from the hard SO42− ligand that can disproportionate Cu(I). We discuss a mechanism for the reaction based on the known reactivity of the reagents and intermediates involved. We explored the possibility of using CuH(s) for making electrically conductive films. Tests that employed water-dispersed CuH particles show that this compound can be reduced with H3PO2 leading to electrically conductive thin films of Cu. These films were made on regular office paper and were found to be Ohmic conductors even after several weeks of exposure to ambient conditions. The fact that the synthesis reported here produces large amounts of CuH particles in aqueous media, with very little impurities, and the fact that these can then be converted to a stable electrically conductive film can open up new applications for CuH such as for printing electrically conductive films or manufacturing surface coatings.

Spectroscopic probing of site symmetry in solids

Abstract: Infrared (IR), electronic absorption and Raman spectroscopy are employed to probe the site symmetry, coordination geometry and structural changes in rare-earth complexes of high and low symmetry. The results of these studies are compared with X-ray data. Although unpolarized IR spectra do not enable, a priori, determination of the site symmetry of an ion in a crystal, the spectra can be shown to be consistent with crystallographic data. In addition, IR spectra can be employed to indicate subtle changes in the distances of nuclei bonded to hydrogen, which are not available from X-ray data, as exemplified herein for PH bonds in hypophosphite complexes. The use of electronic absorption spectra to explore the coordination geometry (rather than the site symmetry) of a complexed rare-earth ion is considered. Both the IR and electronic absorption techniques are found to be useful in fingerprinting given structural types. Small perturbations on distant neighbours of a chromophore may be silent in IR and Raman spectra, but significant in electronic absorption spectra.

Variation of the reactivity of solids near the interface reagent-product of the topochemical reaction

Abstract: During the topochemical decomposition of ammonium perchlorate and copper hypophosphite an enhanced acid concentration occurs near the reagent-product interface. Concentration profiles of the acid were observed after the treatment of the partially decomposed crystals by indicator solution and by microphotometry. Profiles exhibit the diffusive characteristics. The diffusion coefficient is 10−10 cm2/sec for ammonium perchlorate and 10−9 cm2/sec for copper hypophosphite at 20°C. It is concluded that the variation of the reactivity near the interface is due to the enhanced acid concentration.