Determining High Quasi­hydrostatic Pressure Up to 7 GPa at a Temperature to 1,400 °С Using Resistive Sensors

A differential method for measuring high quasi‒hydrostatic pressures for six‒punch pressing installations has been constructed by building a load‒carrying characteristic р=f(Q), where p is the value for pressure in a quasi‒hydrostatic cell of high‒pressure, Q is the force of the press. Pressure in the cell is measured by using the measurement of a temperature difference between the polymorphic transformations into Co(α→β) and Fe(α→γ), melting of Cu and Ag; the measurements are performed by resistometry. The initial data used were the lines of polymorphic transitions in iron (BCC‒FCC) and cobalt (FCC‒HCP) within the ranges p=4‒7 GPa and T=500‒700 °C, examined in detail earlier in the p, T‒diagrams, as well as copper and silver melting curves at p=4‒7 and T=1,150‒1,400 °C.The database of initial data is represented in the analytical form, which has made it possible to use them to determine pressure in the cell at high temperatures based on the values for magnitudes of the differential temperature difference ΔTd, which was measured experimentally for the Coα‒β–Feα‒γ and AgL.–CuL. sensors, designed in the current paper; we have described the features in assembling differential sensors and their electrical connections in order to perform the process of measuring the magnitudes for ΔTd. We have designed structures for the high-pressure cells to conduct experiments on measuring ΔTd using thermocouples and a circuit that registers a change in the resistance of sensors at phase transformations.The procedure applied has made it possible to determine pressure in the quasi-hydrostatic cells of six-punch setups by building load characteristics. The main benefits of the devised method for measuring quasi‒hydrostatic pressures by resistometry are its relative simplicity and a significant increase in the accuracy of pressure determination. The latter is achieved through the mutual elimination of corrections of pressure impact and parasitic components for the magnitude of thermo‒EMF of thermocouples in determining the values for a temperature of phase transformations in the resistive sensors Co‒Fe and Ag‒Cu.The data obtained could be used for monitoring and measuring pressures in the cells of six-punch pressing installations with a plunger diameter of 560‒950 mm