Forsterite Formation Research Articles

The effect of initial components on the synthesis of forsterite produced by the sol-gel method

The effect of the type of magnesium salts and the silicon-containing component on the synthesis and properties of forsterite powder synthesized by the sol-gel method are considered. It is established that the use of magnesium acetate significantly decreases the starting temperature of forsterite formation, and the amorphous type of silica is preferable as a silicon-containing component.

Influence of mechanical activation and fluorine ion on forsterite formation

The influence of mechanical activation of the mixture basic MgCO 3–amorphous SiO 2 on reaction of forsterite formation was studied with and without the presence of fluorine ion. Beneficial influence of mechanical activation on the reaction in the mixture without fluorine ion is a consequence of the change of the granulometry during the intense milling. Mechanical activation in the presence of fluorine ion affects the mechanism of forsterite formation via different compounds from the humite group. With non-activated mixture dominant transition phase is hondrodite, while with activated mixture, clinohumite is the transition compound in the process of formation of end reaction products. Fluorine ion is released from the system by hydrolysis.

フォルステライトの生成に及ぼす粉砕雰囲気の影響

Grinding a powder mixture of talc and MgCO3 was conducted under dry (in air) and wet (with water) conditions to investigate the effects of these conditions on the formation of forsterite in sintered bodies from the ground products.Dry grinding caused size reduction in the initial stage, followed by the aggregation of fine particles due to mechanical activation. This operation produced homogeneous mixture with structural change into amorphous state. The homogeneous mixture leads to acceleration of solid state reaction on its firing. On the contrary, wet grinding reduced the particle size in the mixture, but the crystal structure was maintained even in a prolonged grinding period. This is the main reason that different phases of forsterite are formed in the sintered bodies. Consequently, dry grinding is more advantageous than wet grinding in terms of forsterite formation in a body sintered at relative low temperatures.

Cathodoluminescence of meteoritic and synthetic forsterite at 296 and 77 K using TEM

Cathodoluminescence (CL) emission spectra of forsterite from the Allende (CV3) and Murchison (C2) meteorites and from Cr-doped and pure synthetic forsterite samples have been obtained at room (296 K) and liquid nitrogen (77 K) temperatures using a transmission electron microscope. At room temperature, three broad CL emissions centered near 420, 640, and 800 nm occur in the meteoritic forsterite, and one peak at 800 nm occurs in one Cr (super 3+) -doped forsterite sample. Only the 420 nm peak is present in pure synthetic forsterite. Relative to room temperature, at liquid-nitrogen temperature there is a general increase in overall CL intensity, whereas a broad peak located between 700 and 800 nm changes to a series of sharp emissions centered near 700 nm and a narrower but still broad peak centered near 800 nm. The portion of the broad peak near 700 nm at room temperature and equivalent sharp peaks at low temperature are assigned to Cr (super 3+) in octahedral coordination, whereas the broad peak near 800 nm is attributed to Cr associated with structural defects. The peak at 640 nm is consistent with a similar peak in Mn (super 2+) -doped forsterite. The peak at 420 nm results from an unknown structural effect that can be eliminated in synthetic forsterite by mechanical deformation. The variation of relative intensities at room temperature for the two broad peaks at 700 and 800 nm in meteoritic forsterite can be correlated with meteorite type and may reflect different processes in forsterite formation or subsequent processing.

Thermal Transformation of Antigorite as Studied by Electron-Optical Methods

AbstractThe thermal transformation of a Brazilian antigorite heated dry from 600° to 1300°C, was studied by high resolution electron microscopy and selected area electron diffraction (SAD). Below 600°C, the antigorite particles did not change morphologically or crystallographically, as evidence by the presence of the superlattice in the SAD patterns and lattice images. At 650°C, traces of antigorite remained, although the superlattice structure had disappeared and the first indications of forsterite formation were observed in the same SAD. Diffraction patterns of the transition phases showed various topotactical relationships between antigorite and forsterite. At 800°C, the crystallization to forsterite was much more pronounced. At 900°C, the individual particles retained their original shapes, but they were actually pseudomorphs, for their SAD patterns showed only forsterite. Between 1000° and 1300°C various topotactical relationships were observed. Although the overall transformation to forsterite appears to be similar for both chrysotile and antigorite, the transformation of antigorite took place at a slightly higher temperature (~50°C) with a larger number of topotactical relationships than for chrysotile. Enstatite was formed at 1300°C, but it was impossible to determine the topotactic relations between enstatite and forsterite, which was possible with chrysotile.