NEW HIGH-TEMPERATURE ROTATIONAL RHEOMETER FOR SILICATE MELTS, MAGMATIC SUSPENSIONS, AND EMULSIONS

A new wide-annulus Couette-type viscometer/rheometer has been designed , fabricated, and tested with the objective of measuring the shear flo w properties of silicate melts and magmatic suspensions containing vap or bubbles and/or solid particles at 10(-4) GPa and temperatures from 600 to 1500 degrees C. The goal of this development has been to advanc e the precision of high-temperature multiphase silicate rheometry in t he viscosity regime of 10(4)-10(10) Pa s, and to attempt experiments o n multiphase magmatic mixtures that have heretofore been difficult to perform in the concentric cylinder geometry. With this instrument, flu ids with viscosities in the design viscosity range may be tested at sh ear rates From 10(-5) to 1 s(-1), employing a series of interchangeabl e torque transducers capable of measurements from 0.003 to 3 Nm, prese rving precision of the stress measurement across the entire dynamic sp an. A microprocessor-controlled motor drive enables precisely specifie d rotational motions (position and/or speed of the sample container) f or accurate constant-shear-rate or finite-strain experiments. Use of h igh-purity cast ceramic components rather than platinum alloy for the rotating sample container (cup) and fixed cylindrical bob permit secti oning of the sample following an experiment to inspect and analyze tex tural characteristics of the magmatic suspensions. Computerized data a cquisition is accomplished via a standard microcomputer interface and commercially available software system that allows data to be recorded , visualized, and statistically modeled as an experiment progresses. T he instrument has been tested using NIST (NBS) reference material 717 (a borosilicate glass) at viscosities rum 10(4) to 10(9) Pa s. Value o f the standard viscosity has been recovered within the published preci sion (0.03 log units) at temperatures between 650 and 850 degrees C. ( C) 1998 American Institute of Physics. [S0034-6748(98)02309-0]