A moissanite cell apparatus for optical in situ observation of crystallizing melts at high temperature

Abstract

An experimental apparatus is described that allows for optical in situ observation of samples at 1 bar and temperatures up to 1250 °C for durations up to several days. The apparatus resembles a Bassett-type externally heated diamond cell, where the diamond anvils are replaced by cylinders of synthetic moissanite (SiC). The sample is placed inside a gasket of glassy carbon between the two moissanite windows. The moissanite cell allows for the direct and continuous observation of the sample with an optical resolution in the range of a few micrometers. Partially molten systems can be investigated during cooling-heating cycles within a single experimental run. Texture evolution can be observed continuously through time. The technique also allows for direct measurements of crystal growth and dissolution rates at defined cooling and heating rates. The method was tested by observing the crystallization of KNO3-LiNO3 and NaCl-KCl salt melts as well as of a basaltic-trachyandesi tic melt. Dendrite formation, static grain growth, and dissolution were observed in the salt melts. During textural coarsening (static grain growth) of rock salt in the presence of melt, grain coalescence was observed. Both nitrate and rock salt grains growing in contact with melt generally showed curved boundaries and roundish shapes, rather than facets. In one experiment, the final texture did not contain any traces of the previous textural evolution anymore. In a basaltic trachyandesite at temperatures near the liquidus several phenomena, in particular the interactions between crystals, magmatic flow and bubbles during nucleation, growth and dissolution of crystals, and crystal-clusters were observed simultaneously. Crystal growth rates and dissolution rates were also measured

How deceptive are microstructures in granitic rocks? Answers from integrated physical theory, phase equilibrium, and direct observations

“…For a system in which crystals are in mutual contact, a loss of small grains can also occur by coalescence if the grain boundaries can sweep through the smaller grains (e.g., Schiavi et al 2009 , 2010 ), a process known as grain-boundary migration recrystallisation or ‘fast’ grain-boundary migration in deformed rocks metamorphosed at high temperatures and/or high H 2 O contents; see Vernon ( 2004 ) for a review. Fast grain-boundary migration has been suggested as an important syn-magmatic process in plagioclase-rich rocks undergoing mild deformation, since it requires only very small gradients in plastic strain energy (LaFrance et al 1996 ).…”

A new hydrothermal moissanite cell apparatus for optical in-situ observations at high pressure and high temperature, with applications to bubble nucleation in silicate melts

“…Nevertheless, it precludes the evaluation of the early stage of vesiculation or possible effects due to the interaction between the sample and the capsule (e.g., Mangan and Sisson, 2000). The recent development of in-situ experimental techniques (Gondé et al 2006;Schiavi et al, 2010) improved the understanding of bubble nucleation and growth in silicate melts (Martel and Bureau, 2001;Gondé et al 2011;Masotta et al, 2014), and helped to validate theoretical models (Fiege and Cichy, 2015;Ryan et al, 2015). The moissanite cell is a recently developed tool that allows in situ experiments at temperature up to 1250 °C (Schiavi et al, 2010).…”

“…The recent development of in-situ experimental techniques (Gondé et al 2006;Schiavi et al, 2010) improved the understanding of bubble nucleation and growth in silicate melts (Martel and Bureau, 2001;Gondé et al 2011;Masotta et al, 2014), and helped to validate theoretical models (Fiege and Cichy, 2015;Ryan et al, 2015). The moissanite cell is a recently developed tool that allows in situ experiments at temperature up to 1250 °C (Schiavi et al, 2010). Compared to other in-situ techniques, such as the hydrothermal diamond anvil cell and modified internally heated autoclaves (e.g., Bureau, 2001, Gondé et al 2006;Gondé et al 2011), the moissanite cell allows high-resolution observations of relatively large samples (several mm in size), with a simple device fitting onto a microscope stage.…”

“…The major limitation of this technique is given by the fact that experiments are performed at 1 bar, which prevents the investigation bubble nucleation and growth at realistic T-P conditions. In order to overcome this major limitation, we have modified the setup of the original moissanite cell presented in Schiavi et al (2010) and designed new components that allow using the cell for experiments at precisely controlled hydrostatic pressures up to at least 1000 bar and at temperatures up to 850 °C. In this paper, we describe the new hydrothermal moissanite cell and illustrate its applications to the in-situ study of bubble growth in a haplogranitic melt.…”

“…The new hydrothermal moissanite cell The new hydrothermal moissanite cell resembles the Bassett-type externally heated diamond anvil cell and represents an evolution and re-design of the original moissanite cell presented by Schiavi et al (2010). Construction diagrams and pictures of the hydrothermal cell are shown in Figure 1; more details are given in the supplementary material.…”