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Papers by Chris Capobianco
American Mineralogist, 1998
Solid binary oxides of the platinum-group elements (PGE) decompose on heating in air to metal, ox... more Solid binary oxides of the platinum-group elements (PGE) decompose on heating in air to metal, oxygen, and often, a mixture of volatile PGE oxides. Compared to most other transition metal oxides, these decomposition temperatures are low, generally below 1100 ЊC. The modest exception is RuO 2 , which remains stable in air until 1400 ЊC. Because of its comparatively high oxide stability, Ru, among all the PGE, is the one with the greatest potential for a significant oxidic, i.e., lithophile, geochemistry. A series of 1 atm phase equilibrium experiments were made to establish the limits of solid solution of Ru in hematite (Fe 2 O 3 ) and help evaluate the significance of the oxidic geochemistry of Ru.
Journal of Solid State Chemistry, 1987
The disordering of CdMg(CO& was studied near room temperature by powder X-ray diffraction and sol... more The disordering of CdMg(CO& was studied near room temperature by powder X-ray diffraction and solution calorimetry using samples quenched from 600 to 850°C. The long-range order parameter changes from unity to zero in this range and the enthalpy of disordering is 13.7 * 0.8 k.I/mole. The enthalpy of formation of ordered CdMg(CO& from CdCOs and MgC09 is -5.6 + 0.8 k.I/mole; that of the disordered phase is +8.1 + 0.8 Id/mole. These data support energetic models which assume positive interactions of Cd and Mg within cation layers and negative interactions (leading to ordering) between layers. A reasonable fit to the observed phase relations is achieved using either the point approximation (PA) of the generalized Bragg-Williams model or the tetrahedron approximation (TA) of the cluster variation method (CVM). These models however, do not give a quantitative fit to the variation of enthalpy and long-range order parameter with temperature. In particular, the observed order-disorder transition occurs more sharply over a smaller temperature range than predicted, perhaps because of more strongly cooperative behavior in which the carbonate groups as well as the divalent cations play a role.
Meteoritics, Nov 29, 1990
The American Mineralogist, 1989
Lunar and Planetary Science Conference, 1991
Lunar and Planetary Science Conference, Mar 1, 1996
American Mineralogist, Aug 1, 1982
Lunar and Planetary Science Conference, Feb 28, 1992
Core formation in terrestrial planets was concomitant with accretion. Siderophile and chalcophile... more Core formation in terrestrial planets was concomitant with accretion. Siderophile and chalcophile element signatures in the mantles of planets are the result of these processes. For Earth, abundances of most siderophile and chalcophile elements are elevated relative to predictions from simple metal/silicate equilibria at low pressures [1]. This observation has led to three hypotheses for how these abundances were established:
American Mineralogist, 1998
Solid binary oxides of the platinum-group elements (PGE) decompose on heating in air to metal, ox... more Solid binary oxides of the platinum-group elements (PGE) decompose on heating in air to metal, oxygen, and often, a mixture of volatile PGE oxides. Compared to most other transition metal oxides, these decomposition temperatures are low, generally below 1100 ЊC. The modest exception is RuO 2 , which remains stable in air until 1400 ЊC. Because of its comparatively high oxide stability, Ru, among all the PGE, is the one with the greatest potential for a significant oxidic, i.e., lithophile, geochemistry. A series of 1 atm phase equilibrium experiments were made to establish the limits of solid solution of Ru in hematite (Fe 2 O 3 ) and help evaluate the significance of the oxidic geochemistry of Ru.
Journal of Solid State Chemistry, 1987
The disordering of CdMg(CO& was studied near room temperature by powder X-ray diffraction and sol... more The disordering of CdMg(CO& was studied near room temperature by powder X-ray diffraction and solution calorimetry using samples quenched from 600 to 850°C. The long-range order parameter changes from unity to zero in this range and the enthalpy of disordering is 13.7 * 0.8 k.I/mole. The enthalpy of formation of ordered CdMg(CO& from CdCOs and MgC09 is -5.6 + 0.8 k.I/mole; that of the disordered phase is +8.1 + 0.8 Id/mole. These data support energetic models which assume positive interactions of Cd and Mg within cation layers and negative interactions (leading to ordering) between layers. A reasonable fit to the observed phase relations is achieved using either the point approximation (PA) of the generalized Bragg-Williams model or the tetrahedron approximation (TA) of the cluster variation method (CVM). These models however, do not give a quantitative fit to the variation of enthalpy and long-range order parameter with temperature. In particular, the observed order-disorder transition occurs more sharply over a smaller temperature range than predicted, perhaps because of more strongly cooperative behavior in which the carbonate groups as well as the divalent cations play a role.
Meteoritics, Nov 29, 1990
The American Mineralogist, 1989
Lunar and Planetary Science Conference, 1991
Lunar and Planetary Science Conference, Mar 1, 1996
American Mineralogist, Aug 1, 1982
Lunar and Planetary Science Conference, Feb 28, 1992
Core formation in terrestrial planets was concomitant with accretion. Siderophile and chalcophile... more Core formation in terrestrial planets was concomitant with accretion. Siderophile and chalcophile element signatures in the mantles of planets are the result of these processes. For Earth, abundances of most siderophile and chalcophile elements are elevated relative to predictions from simple metal/silicate equilibria at low pressures [1]. This observation has led to three hypotheses for how these abundances were established: