Steel replacement with polymers

Bipolar plates are currently made from milled graphite or gold-coated stainless steel. Ongoing research is aiming to replace these materials with polymers or low-cost steel alloys, which will allow the use of low-cost production techniques. Even today, bipolar plates can be produced at 200 /kW, if the production volume... 

In the short term, replacing heavy steel components with materials such as high-strength steel, aluminium or glass fibre-reinforced polymer composites can decrease component weight by 10-60%. 

Many polymers have a coefficient of linear thermal expansion in the range of 2-20 X 10" K", compared to that for steel which is about 1 x 10". This complicates the design of molds for precision parts and the design of metal inserts in polymer parts. Of course, varies with the state of the polymer, as indicated earlier in comments on the variations of specific volume at 7 and T (Section 3.4). Replacement of polymer by less expansile fillers lowers the overall expansion. 

In order to be successful as part of a medical device a polymer has to resist both biological rejection by the patient s body and degradation. The human body is an enviromnent which is simultaneously hostile and sensitive, so that materials for application in medicine must be carefully selected. The essential requirement is that these materials are biocompafible with the particular part of the body in which they are placed. The extent to which polymers fulfil this requirement of biocompafibility depends partly on the properties of the polymer and partly on the location in which they are expected to perform. For example the requirements for blood biocompafibility are stringent since blood coagulation may be triggered by a variety of materials. By contrast, the requirements for materials to be used in replacement joints in orthopaedic surgery are less severe and materials as diverse as poly (methyl methacrylate) and stainless steel can be used with minimal adverse reaction from the body. 

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