Application of a Differential Method for Determining the Quasi-Hydrostatic Pressures in the Cells of Six-Punch Presses

Abstract Some methodical approaches to the measurement of high quasi-hydrostatic pressures in the cells of six-punch presses with consideration for the effect of high temperatures up to 1400°C were described, and the combined load characteristic p = f(Q), where p is the pressure in a quasi-hydrostatic cell, and Q is the plunger system force, was constructed. The compression zone pressure is measured by determining the difference between the temperatures of polymorphic Fe(α→γ) and Co(α→β) transitions and the Cu and Ag melting temperatures and melting temperature by means of resistometry at a pressure of 4–7 GPa and a temperature of 500–700°С for Fe–Co sensors and 1150–1400°C for Cu–Ag sensors. To determine the high temperatures at the characteristic points of growth cells in six-punch presses, a method of manufacturing their thermocouple modules with the use of cesium chloride as an electroinsulating medium and Pt/PtRh10 and PtRh6/PtRh30 thermocouples was developed alongside with some basic requirements to their manufacturing to provide reliable electroinsulation for their thermocouple wires with continuous temperature control for growth cycles lasting for 200 h and longer. The effect produced by parasitic thermal electromotive forces (TEMFs) appearing due to the use of high pressures and additional contact through hard-alloy punches on thermocouple readings was estimated, and calibrating curves improving the measurement precision were plotted. The proposed approaches to estimating the pressures and temperatures in the growth cells of six-punch cubic high-pressure apparatuses can be especially useful when growing coarse diamond single crystals of more than 10 carats in weight.