Pyrophyllite gaskets

Fig. 7.17 The structure of the reaction ceii used with a belt equipment (A) a cylindrical body made of pyrophyllite, (B) a pyrophyllite gasket, (C) PTFE seals, (D) a capsule containing the reactants, (E) a microfurnace, and (F) a La203 layer.

In the Bridgman anvil device the sample is compressed between supported anvils of tungsten carbide, and lateral containment is ensured by a gasket that can be made of pyrophyllite or metallic material. A variety of cells based on the Bridgman opposed anvils has been developed [38 0]. Pressures up to 20GPa... 

Gasket materials are chosen primarily on the basis of their internal friction or extrusion resistance under pressure, compressibilities, thermal stabilities, chemical inertness, and ease of fabrication. Often several materials comprise the gaskets of a particular apparatus. Suitable materials include certain kinds of slightly porous natural stone (e.g., pyrophyllite, or various ceramic materials, and some metals such as copper and steel). Usually slippery or organic materials are unsatisfactory because they tend to fail catastrophically in shear and thereby allow violent extrusion of the gasket and part of the chamber contents. 

The principle of a Bridgman opposed-anvil apparatus is shown in Fig. 1.13. The sample is compressed between supported tungsten carbide (WC) anvils. It is contained by gaskets which may be pyrophyllite or metallic materials, depending on the measurement to be performed. This design makes use of the massive-support mechanism, in that the maximum pressure which may be... 

Place the sample and its protective capsule in a porous ceramic tube, which is itself introduced in a microfurnace (platinum or graphite see Fig. 7.17). This microfurnace is later inserted in the pyrophyllite body, which is itself placed inside the die of the belt see A in Fig. 7.16(b). The gaskets (B in Fig. 7.17) and the pyrophyllite body of the reaction cell are machined in advance from blocks of the raw pyrophyllite material, according to the shape of the anvils and the die. 

If the die is reinforced by prestressing with concentric rings with interference fits, the device can sustain a pressure of about 6 GPa through use of an appropriate gasket (talc, pyrophyllite, and mixtures thereof) at the die/anvil interface. 

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