Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions

The overall goal of this procedure is to determine the partitioning of highly cphi elements between metal and silicone melts. This is accomplished by first preparing a synthetic silicone melt and metal starting material. Highly acidophile elements are introduced as gold coated beads or centered mixtures of platinum, iridium, and iron by either physically separating HSCs from the silicone melts or introducing a strong reducing agent.

The formation of metal iuss that complicate chemical analysis can be avoided. The second step is to load a graphite sample capsule first with the metal and then the silicate starting materials, so they are in a gravitationally stable arrangement. Next, complete assembly of the sample components and load into either a piston cylinder or multi anvil apparatus as appropriate.

The final step is to pressure the sample and then heat to the desired temperature after enough time has passed to achieve equilibrium, the sample is quenched by cutting power to the resistance heater. Ultimately laser ablation inductively coupled plasma mass spectrometry is used to measure the trace element concentrations in the silicone melt. The main advantage of this technique over high pressure methods that do not suppress metal inclusions is that it avoids ambiguity and analysis of certain cphi elements.

In the silicon melt, A Baltic composition is used as a silicone starting material. Since more depolymerizing compositions are difficult to quench to a glass, weigh the desired amounts of component oxide or carbonate powders and add to an agate mortar and iron free mixture. Weighing approximately four grams should provide sufficient starting material for an extensive suite of experiments.

Add ethanol to the agate mortar until the powders are submerged. Then grind for at least two hours using an agate pestle to homogenize both the composition and grain size of the mixture. Once thoroughly homogenized, place the mortar under a 250 watt heat lamp at a distance of approximately 20 centimeters.

After the powdered mixture is dry, which may take 20 to 60 minutes, transfer it to either an Illumina or Maite crucible to decarbonation the mixture. Placed a crucible with a powdered mixture into a box furnace at room temperature, and ramp to 1, 273 Kelvin over the course of three to five hours. Leave the mixture in the furnace at 1, 273 Kelvin overnight.

Store the resulting basalt powder in a desiccate until ready to load the sample capsule. See the text protocol for preparation of the highly acidophile element source material in the form of gold coated beads or centered mixtures of platinum iridium and iron. Load the graphite sample capsule by first inserting the highly oph element source material and then adding synthetic masal powder until the capsule is filled.

Use of a gravitationally stable arrangement minimizes the chance for overturn during the experiment and is intended to prevent dispersion of the metallic phase through mechanical action. Place a small amount of dry magnesium oxide powder at the base of the cavity designed to hold the sample capsule. This flattens the tapered surface created when drilling the hole and in turn reduces sheer forces during sample compression that may crack the capsule after assembling all the previously made components as shown in the text protocol wrap a piece of 30 micron thick lead foil around the assembly, folding a small portion of foil over the exposed end of the lower barium carbonate sleeve.

Insert the assembly into a 12.7 millimeter bore tungsten carbide pressure vessel along with a base plug position the bridge pressure vessel and base plate between the hydraulic rams. Next, make a C type thermocouple using a four hold hard fired Illumina tube with an outer diameter of 1.6 millimeters. The Illumina tube should be sufficiently long to allow approximately one to two millimeters of the tube to protrude from the upper surface of the top plate.

Feed both wire compositions through adjacent holes in the tube. Turn the ends through 180 degrees and secure them in the opposing holes so that the wires cross. Insert the thermocouple through the top plate and into the assembly so that the junction is directly above the sample.

Insulate the remainder of the thermocouple wires using flexible Teflon tubes, leaving a 10 to 20 millimeter portion exposed at the end. Put in place any metal spacers that are required between the top plate and the upper ram During assembly position. Mylar sheets directly above the pressure vessel and between the top of the assembly and the upper ram.

These sheets electrically isolate the sample heating circuit from the rest of the apparatus. Make a C type thermocouple using a four hole hard fired Illumina tube by feeding both wires through adjacent holes in the tube, turning the ends through 180 degrees and securing them in the opposing holes. Insulate the remainder of the wires with a short length of Illumina tube and then Teflon insulating material leaving a 10 to 20 millimeter portion of exposed wire at the end.

Insert the zirconia sleeve and graphite heater into the octahedron before cutting grooves as indicated in the text protocol. Then insert the thermocouple into the top of the octahedron and position the Illumina covered arms into the grooves. Use zirconia cement to fill the void space surrounding the thermocouple and allow to dry.

In order to isolate the thermocouple junction from the graphite capsule. Add magnesium oxide powder from the base of the octahedron until the exposed wires are covered. Less than 50 milligrams of powder are usually sufficient to surround the exposed wire.

To ensure tight packing of the powder, use a drill blank to tamp down the loose powder. Load a graphite capsule with the previously prepared sample material and place it into the octahedron from the open side. Insert the Illumina plug to complete assembly of the octahedron on four of the tungsten carbide cubes.

Use polyvinyl acetate to glue short lengths of balsa wood on each of the three faces adjacent to the truncated corner of the cube. On each face, position the balsa wood pieces in the quadrant opposite the truncated edge. Each balsa wood piece would measure approximately 4.4 millimeters in height and width by nine millimeters in length.

For the octahedron size shown here, assemble four of the cubes to form a square. In plan, view two width and two without wooden pieces attached. Orient the truncated edges to face the center of the square.

Position the octahedron in the center of the cubes so that it is supported by the truncated edges. Then angle the thermocouple arms so that they emerge from opposite corners of the square. Place the remaining tungsten carbide cubes into position to form a cube with the Okta heater at its center, ensuring that the cubes with wooden pieces attached rest the top cubes that have no wooden spacers.

Next glue square pieces of about 0.5 millimeter thick G 10 sheet to each face of the assembled cube using a Sano ACRL type adhesive for 30 millimeter tungsten carbide cubes, use G 10 sheets measuring 55 millimeters by 55 millimeters. Two of the tungsten carbide cubes have truncation that contact the resistance heater and thus form part of the electrical heating circuit for sheets which contact these cubes. Cut two narrow slits and place a piece of copper foils so that it provides a point of contact between the first and second stage.

Anvils then cut two sheets of 0.0 76 millimeter thick mylar to the dimensions shown in the text protocol and coat them using a dry PTFE lubricant. Position one of the precut sheets into the ring and insert the lower set of first stage anvils, which themselves are backed with 0.076 millimeter thick mylar and coated with PTFE lubricant. The lower set of anvils may be left in place between runs.

Place the assembled cube into the lower set of first stage anvils and connect the thermocouple arms to the balanced thermocouple wires that exit the pressure module. Position the second precut Mylar sheet into the retaining ring and insert the upper set of first stage anvils, which should be Mylar backed and lubricated in the same manner as the lower set. This arrangement yields a lubricated Mylar to Mylar contact between the first stage anvils and the retaining ring.

That reduces the loss of ram thrust friction by approximately 30%compared to a single Mylar sheet arrangement. Once the sample is brought to the required pressure heat at a rate of 100 kelvin per minute until the desired dwell temperature is reached during the heating step, oil in the sample RAM may need to be adjusted in order to maintain a constant oil pressure contamination of the silicate glass and low oxygen fity. Highly cphi elements solubility experiments are most readily identified by the presence of heterogeneity in time.

Resolved LA I-C-P-M-S spectra. This heterogeneity manifests as peaks and troughs in the spectra that result from the ablation of varying proportions of inclusion bearing versus inclusion. Free glass displayed.

Here is the time resolved spectrum for a platinum solubility experiment that did not employ methods to prevent the formation of metal inclusions for comparison. Also displayed are time resolved spectra typical for ate run products synthesized using the techniques outlined in this video. The imaginality of these spectra indicates the absence of dispersed HSE inclusions in the ATE portion of experimental run products.

The imaginality of the Ruthenium spectrum suggests that this approach is also successful in avoiding the formation of metal inclusions found in previous ruthenium solubility experiments performed at similar reducing conditions. After watching this video, you should be able to prepare metal sate partitioning experiments for the PIs and cylinder and multi amble apparatus. By preparing the starting materials as described, dispersed metal inclusions can be avoided in experiments for the highly cphi elements.