What are the types of impermeable graphite and how are they prepared?
According to different production processes, impermeable graphite can be divided into the following 4 categories:
(1) Impregnated impermeable graphite. The substrate preparation process is the same as the graphite electrode production process. Generally, fine particle formulations are used. Graphite electrode blanks or graphite blocks can also be used as substrates. A vacuum-pressure impregnation method is used to make the impregnant penetrate into the pores of the graphite substrate. After heating and curing, impermeable (or micro-permeable) impregnated impermeable graphite can be obtained. The most commonly used impregnants are synthetic resins such as thermosetting phenolic resins and furan series resins, as well as water glass and modified coal pitch. Typical products are various graphite heat exchangers impregnated with phenolic resin.
(2) Pressed type impermeable graphite. Graphite powder is used as an aggregate and a binder is mixed and kneaded into a paste, then extruded or molded in a mold, and heated and solidified to obtain a pressed type impermeable graphite. Extrusion molding is mainly used to produce phenolic resin graphite tubes. These pressure-type impermeable graphite tubes can be used to assemble tubular graphite heat exchangers or used as material transportation pipelines in chemical production. Compression molding is mainly used to produce impermeable graphite plates or blocks for assembling graphite chemical equipment or for independent use.
(3) Pouring impermeable graphite. The paste obtained by mixing graphite powder, thermosetting resin, curing agent, etc., is poured into a mold, and then solidified to form a cast impermeable graphite. Pouring impermeable graphite is mainly used to make impermeable graphite parts.
(4) Composite impermeable graphite. The composite impermeable graphite can be obtained by compounding the reinforcing material and the graphite substrate. The reinforced graphite substrate can be a block, a plate or a pipe. Carbon fiber and its fabric are often selected as reinforcement materials.
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