Graphite alternative materials

Many alternative materials have been investigated to replace graphite in the fabrication of bipolar plates. The major candidate materials with potential to overcome the technical barriers and reach the targets mentioned in... 

Bipolar plates in PEMFCs were conventionally made of graphite with excellent corrosion resistance, chemical stability, and high thermal conductivity. However, graphite has a high cost, poor mechanical properties, and very little formability due to its microstructural nature. This limits its further applications as plate material and forces a search for alternative solutions. Nevertheless, the performance, durabilify, and cosf of fhe graphite plate (e.g., POCO graphite and graphite plates) have been taken as benchmark references to compare with those of alternative materials. 

The slider boat is usually constructed of graphite, although alternative materials such as boron nitride and silica (14) have been used. Graphite is readily obtained in high purity, easily machined, relatively inert with respect to the solution, and nearly frictionless in operation. Graphite boats do have a limited lifetime, and care must be exercised in desorbing gases contained in this relatively porous material. 

Alternative materials for bipolar plates include graphite, stainless steels, titanium and aluminium, all with a developed fabrication technique, and coating technique if needed. Major competitors UTC Fuel Cells has an active fuel cell bus programme, but give sparse details of its flow plate and other technology. (See UTC web site.)... 

Although graphite furnaces are the most widely used in atomizers, alternative materials have also been employed for this purpose. 

Carbon composites have been developed as alternative materials for carbon paste electrodes because of the limited utility of the latter in most organic solvents. These composites include polyethylene/carbon black [49], Kel-F/graphite [50], carbon black immobilized in cross-hnked polyethylene [51], and epoxy/graphite [52]. A collection of for these materials is available [20]. Thus, for platinum = 0.24 cm/s, for pyrolytic graphites 0.002 <... 

Glassware is such a universal material used for sample preparation that it is very difficult to completely avoid it. However, serious consideration should be given to looking for alternative materials in as many of the ICP-MS sample preparation steps as possible. Today, the most common materials used to manufacture beakers, volumetric containers, and autosampler tubes for ultratrace elanent techniques such as graphite furnace atomic absorption (GFAA) and ICP-MS are mainly plastic based. Over the past 10-15 years, the demand for these kinds of materials has increased significantly becanse of the contamination issues associated with glassware. 

Alternate materials as the basic core element structural material are under investigation as a backup to the graphite development. These include KT silicon carbide, molybdenum, molybdenum carbide, niobium, niobium carbide, zirconium carbide, tantalum, and tantalum carbide, all of which have properties indicating promi.se for LMF-GCR application. 

The gravimetric capacity (b) and volume (a) for some alternative materials. The capacity of graphite is given as references. 

Fused Salt Electrolysis. Only light RE metals (La to Nd) can be produced by molten salt electrolysis because these have a relatively low melting point compared to those of medium and heavy RE metals. Deposition of an alloy with another metal, Zn for example, is an alternative. The feed is a mixture of anhydrous RE chlorides and fluorides. The materials from which the electrolysis cell is constmcted are of great importance because of the high reactivity of the rare-earth metals. Molybdenum, tungsten, tantalum, or alternatively iron with ceramic or graphite linings are used as cmcible materials. Carbon is frequently used as an anode material. 

Carbon Composites. In this class of materials, carbon or graphite fibers are embedded in a carbon or graphite matrix. The matrix can be formed by two methods chemical vapor deposition (CVD) and coking. In the case of chemical vapor deposition (see Film deposition techniques) a hydrocarbon gas is introduced into a reaction chamber in which carbon formed from the decomposition of the gas condenses on the surface of carbon fibers. An alternative method is to mold a carbon fiber—resin mixture into shape and coke the resin precursor at high temperatures and then foUow with CVD. In both methods the process has to be repeated until a desired density is obtained. 

For chemical service, some lubrication qualities may be sacrificed in order to obtain a fluid compatible with the process gas. In these applications, alternate bearing materials such as graphite or silver have been required. While the requirements may make the operation somewhat special and require considerable care, the life of the compressor and service can be greatly improved. 

Lower cost alternatives to PTFE-modified polymers have also been introduced for low-friction applications. These materials use graphite and chemical lubricants of undisclosed composition. 

Alternative explanations of the high conductivity of composite materials obtained by polymerization filling are given in works [62, 63] where conductivity higher than that of the graphite proper is attributed to a polymer interlayer between graphite particles, are, in our opinion, insufficiently convincing and cannot explain the whole of the experimental data. 

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