Cold-seal pressure vessels

Hydrothermal- and carbonate-exchange techniques. The majority of available experimental fractionation data are for oxygen isotope fractionations involving minerals. Much of the data, particularly the early data, were obtained using water as the isotopic exchange medium. These experiments were either done at ambient pressure (typically synthesis experiments), or in cold-seal pressure vessels at pressures of 1 to 3 kbar (e.g. O Neil and Taylor 1967 O Neil et al. 1969 Clayton et al. 1972). Later experiments were done in a piston cylinder apparatus (at 15 kbar) to exploit the pressure enhancement of exchange rates (Clayton et al. 1975 Matsuhisa et al. 1979 Matthews et al. 1983a,b). 

The 0 diffusion in naturai and synthetic single-crystal titanite was characterized under both dry and water-present conditions. Hydrothermal experiments were performed by encapsulating polished titanite crystals with l 0-enriched water and holding at 700 to 900C and 10 to 160MPa in cold-sealed pressure vessels for between 24h and several weeks. The diffusion profiles exhibited 2 segments. 

Figure 1.8 Schematic diagram of cold-seal pressure vessel for high temperamre/high pressure phase equilibria smdies with quenching method (The Ejqterimental Determination of Solubilities, Vol 6, Better Tomkins).

Xhe experimental procedure to produce synthetic fluid inclusions uses quartz cores approximately 4 mm in diameter and 1-2 cm in length, which are fractured by thermal-shock technique at 350°C. Xhe cleaned and dried cores are placed into platinum capsules along with the fluid sample, sealed with and arc-welder and placed into cold-sealed pressure vessels and taken rapidly to the desired temperature. After quenching the quartz cores were cut into 1 mm thick disks, polished, and homogenization temperatures of the inclusions were determined ( 2 ""C) on a microscope heating stage. 

Because chloroprene is a flammable, polymerisable Hquid with significant toxicity, it must be handled with care even in the laboratory. In commercial quantities, precaution must be taken against temperature rise from dimerisation and polymerisation and possible accumulation of explosive vapor concentrations. Storage vessels for inhibited monomer require adequate cooling capacity and vessel pressure rehef faciUties, with care that the latter are free of polymer deposits. When transportation of monomer is required, it is loaded cold (< — 10° C) into sealed, insulated vessels with careful monitoring of loading and arrival temperature and duration of transit. 

Figure 1.8 shows the construction of a cold-seal vessel originally developed by Tuttle (1949). Most hydrothermal research in experimental petrology at pressures up to 300 MPa and at temperatures below 900 °C has been conducted in such relatively simple autoclaves where the sealed capsules with charges are placed. Specially modified equipment of this type permits the attainment of pressures up to 1000 MPa at temperatures below 750 °C. 

The recrystallized a-oxoamide 1 (100-300 mg) was sandwiched between a pair of Pyrex plates (diickness 2 mm) and put into a polyethylene envelope. The envelope was sealed and placed in a cold medium (water, ice-water, or dry ice-methanol) and irradiated with a high-pressure mercury lamp (100 W) for 1-10 h. The lamp was used with a vessel for immersion type irradiation which contained dry air. The products were isolated by column chromatography on silica gel. 

The prewetted samples were placed in the AFEX unit, and the vessel was sealed and warmed to the desired temperature as described in the previous section. To avoid overheating, the reactor was taken out of the heater at approx 10°C less than the target temperature, and if needed the unit was placed in a bath of cold water to maintain the system at the set temperature. The system was kept at the target temperature for 5 min. Since there was no ammonia in this system, no increase in pressure was observed during the experiment. At the end of 5 min, the heat-treated samples were removed from the vessel and kept in plastic bags at 4°C until further analysis. 

The reaction vessel is a 550-ml. Pyrex cylindrical flask with a Hanovia internally sealed cold-cathode low-pressure mercury resonance coil lamp (2537 A.). The lamp is fitted to the reactor... 

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