High pressure (P)–temperature (T) experiments
This protocol is extracted from research article:
Delivery of carbon, nitrogen, and sulfur to the silicate Earth by a giant impact
Sci Adv, Jan 23, 2019; DOI: 10.1126/sciadv.aau3669

The experiments at 1 to 3 GPa and 1600° to 1800°C were performed using an end-loaded PC device, and experiments at >3 GPa were performed using a 1100–metric ton Walker-style MA device at Rice University. The PC experiments used a 12.7 mm BaCO3/MgO assembly, following the P-T calibrations and procedural details similar to several previous studies (24, 25, 43). MA experiments were performed using WC anvils with 8-mm truncations and an octahedral assembly with a 14-mm edge length following calibrations detailed in a previous study (14). Both PC and MA experiments used type C thermocouples placed within 1 mm of the capsule to control and monitor the experimental temperature set using Eurotherm controllers.

Three sets of experiments with different alloy mixes (S-free, intermediate S-bearing, and high S-bearing) were repeated at a given pressure (1 to 7 GPa) and in a narrow temperature interval (1600° to 1800°C) to study the effect of S content in the alloy on Embedded Image and Embedded Image. Graphite capsules were used to hold the alloy-silicate mixes to study C solubility in the alloy and the silicate melt, as well as to achieve a T approaching planetary MO conditions. MA experiments were conducted using three-chambered graphite capsules with starting compositions loaded in separate sample chambers, while PC experiments were conducted by loading a single composition into graphite capsules. All the experiments were pressurized to the target pressure at room temperature, followed by heating at a rate of 100°C/min. To reduce the porosity in the graphite capsules and prevent leakage of the alloy melt, the experiments were held at 850° to 900°C overnight and then raised to the target temperature. The experiments were quenched by cutting off power to the heater, and after depressurization, the recovered samples were cut into half using a tungsten-wire saw. Three-chambered capsules were cut transversely into two halves using a tungsten-wire saw to observe all three sample chambers simultaneously, while single-chambered capsules were cut longitudinally. Both halves were mounted in Crystalbond, ground using 1200-grit sandpaper, and polished using a 0.3-μm alumina slurry on a velvet cloth. Polished samples were soaked in acetone overnight to remove the Crystalbond. The polished surfaces were analyzed using an electron microprobe, an ion microprobe [secondary ion mass spectrometry (SIMS)], and Raman spectroscopy.

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