Silicon carbide is also used in a sintered form for diesel particulate filters. This method is only applicable to sintered alumina core porcelain. Sintered beryllium oxide is a very stable ceramic. These first sintered tantalum capacitors used a liquid electrolyte. It was made not from glass but from sintered silicon carbide. Sintered alnico magnets are formed using powdered metal manufacturing methods. The strip is then sintered and subjected to another rolling and further sintering. The resulting metal is sintered until sufficiently ductile for metalworking. Porous pumping is created by the use of sintered glass. The green pellet can then be sintered into mixed uranium and plutonium oxide pellet. From these powder mixtures, the ceramic is sintered at high temperatures. It is also prepared as sheets and sintered powder for coating metals. The cylinder head has sintered iron valve seats and cast iron valve seats. The foam must then be sintered for final densification. The initial development of cemented and sintered carbides occurred in Germany in the 1920s.