The bulk density of graphitized ultradisperse diamond (UDD) was measured by a gamma-ray attenuation method at 1370–1870 K. These data combined with small angle x-ray scattering and true density measurements of the samples heated at various fixed temperatures were used to study the graphitization kinetics of the UDD. The reaction rate was modeled as a migration rate of the interface between the developing graphite-like carbon and the remaining diamond phase. A “reducing sphere” model was used to obtain the rates from the changes in densities. The estimated kinetic parameters in an Arrhenius expression, namely the activation energy, E=45±4 kcal/mol, and the pre-exponential factor, A=74±5 nm/s, allow quantitative calculations of the diamond graphitization rates in and around the indicated temperature range. The calculated graphitization rates agree well with the graphitization rates of diamonds with different dispersity estimated from high-resolution transmission electron microscopy data. The large difference between the rates and the kinetic parameters obtained in this study and those estimated by G. Davies and T. Evans [Proc. R. Soc. London 328, 413 (1972)] for the temperature range 2150–2300 K indicates that there are different graphitization mechanisms operating in the “low” and “high” temperatures regions.

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The paper presents the results of an investigation of the nickel density and thermal expansion over the temperature range from 145 K to 2030 K. The measurements have been carried out by using the dilatometer method and the γ -ray attenuation technique (gamma method). The errors of the density and coefficients of thermal expansion measurements are estimated to be within 0.05 % to 0.25 % and 1 % to 2.5 %, respectively. The accuracy of determination of the volumetric thermal expansion coefficient of the melt by the γ -ray attenuation technique is substantiated. The density change on melting (4.70 ± 0.15) % has been directly measured. The temperature dependences and reference tables of the volumetric properties of solid and liquid nickel have been developed. A comparison of the obtained results with literature data has been made.