in corrosive liquid-metal vapors. Bioceramics Bioceramics play an extensive role in biomedical materials. The development of these materials and diversity of manufacturing techniques has broadened the applications that can be used in the human body. They can be in the form of thin layers on metallic implants, composites with a polymer component, or even just porous networks. These materials work well within the human body for several reasons. They are inert, and because they are resorbable and active, the materials can remain in the body unchanged. They can also dissolve and actively take part in physiological processes, for example, when hydroxylapatite, a material chemically similar to bone structure, can integrate and help bone grow into it. Common materials used for bioceramics include alumina, zirconia, calcium phosphate, glass ceramics, and pyrolytic carbons. One important use of bioceramics is in hip replacement surgery. The materials used for the replacement hip joints were usually metals such as titanium, with the hip socket usually lined with plastic. The multiaxial ball was tough metal ball but was eventually replaced with a longer-lasting ceramic ball. This reduced the roughening associated with the metal wall against the plastic lining of the artificial hip socket. The use of ceramic implants extended the life of the hip replacement parts. Dental cermets are also used in dentistry as a material for fillings and prostheses. Transportation Ceramic parts have been used in conjunction with metal parts as friction materials for brakes and clutches. Electrical heaters Cermets are used as heating elements in electric resistance heaters. One construction technique starts with the cermet material formulated as an ink, then prints it on a substrate and cures it with heat. This technique allows manufacture of complex shapes of heating elements. Examples of applications for cermet heating elements include thermostat heaters, heat sources for bottle sterilization, coffee carafe warmers, heaters for oven control, and laser printer fuser heaters. Other applications The United States Army and British Army have had extensive research in the development of cermets. These include the development of lightweight ceramic projectile-proof armor for soldiers and also Chobham armor. Cermets are also used in machining on cutting tools. Cermets are also used as the ring material in high-quality line guides for fishing rods. A cermet of depleted fissiable material (e.g. uranium, plutonium) and sodalite has been researched for its benefits in the storage of nuclear waste. Similar composites have also been researched