The NiSi melting curve to 70 GPa

• Published in: Physics of the earth and planetary interiors Vol. 233; pp. 13 - 23
• Main Authors: Lord, Oliver T, Wann, Elizabeth TH, Hunt, Simon A, Walker, Andrew M, Santangeli, James, Walter, Michael J, Dobson, David P, Wood, Ian G, Vocadlo, Lidunka, Morard, Guillaume, Mezouar, Mohamed
• Format: Journal Article
• Language: English
• Published: United States Elsevier 01.08.2014
• Subjects: Core-mantle boundary; Criteria; Diffraction patterns; Earth Sciences; Liquids; Liquidus; Melting; Nickel silicide; Sciences of the Universe; Slopes; LH-DAC; Melting; NiSi; High-pressure; In situ
• ISSN: 0031-9201; 0031-9201; 1872-7395
• DOI: 10.1016/j.pepi.2014.05.005

The melting curve of NiSi has been determined to 70 GPa on the basis of laser-heated diamond anvil cell (LH-DAC) experiments in which changes in the gradient of temperature vs. laser power functions were used as the melting criterion. The melting curve was corroborated with in situ X-ray diffraction experiments in both the LH-DAC and multi-anvil press in which the appearance of liquid diffuse scattering in the diffraction patterns was used as the melting criterion. At all pressures, the NiSi melting curve is lower than that of FeSi, with the difference in melting temperature reaching a maximum of 900 K at 14 GPa. The location of the B31 + B20 + L triple point has been constrained to 12 plus or minus 2 GPa and 1550 plus or minus 100 K and the B20 + B2 + L triple point to 28.5 plus or minus 1.5 GPa and 2165 plus or minus 60 K. On the basis of the in situ LH-DAC experiments the Clapeyron slope of the B20 arrow right B2 transition is estimated at -67 MPa K super(-1). Extrapolation of the B2-NiSi liquidus to core-mantle boundary (CMB) conditions (135 GPa) suggests the melting point of NiSi (3700 plus or minus 400 K) will be only marginally lower than that of isostructural FeSi (4000 plus or minus 200 K). Thus any (Fe,Ni)Si solid solution present within the D double prime layer is expected to remain solid, with the possible exception of the very hottest region adjacent to the CMB.