Ceramic powder processing finishing

Ceramics. The properties of ferroelectrics, basically deterrnined by composition, are also affected by the microstmcture of the densifted body which depends on the fabrication method and condition. The ferroelectric ceramic process is comprised of the following steps (10,24,25) (/) selection of raw oxide materials, (2) preparation of a powder composition, (J) shaping, (4) densification, and (5) finishing. 

Ceramic raw materials are powders. Together with a mixture of additives these powders are moulded into a particular shape and subsequently dried and baked. After the baking or sintering process it is possible to apply a finishing coat if necessary and then the ceramic object is ready. The entire route from raw material to finished product was elaborately discussed in chapter 9. 

Germanium powder is mixed with an equimolar quantity of CaHg, previously pulverized under Ng blanket. The hydride is taken in slight excess. The mixture is placed in an iron boat and the latter inserted into an electrically heated ceramic tube. The atmosphere within the tube is inert at that point. The tube is then connected to a high-vacuum system. The reaction b ins at about 450°C and is finished at about 950°C, provided the Bg formed in the process is removed at regular Intervals. The temperature Is then raised to 1000°C and gas removal continued for another half hour to achieve complete removal of the last traces of Bg. After cooling under vacuum, the tube is opened and the product Is pulverized as rapidly as possible and placed in sealed ampoules. It still contains traces of Ca. 

Sample preparation for purposes of examination in the SEM is very simple. In order to avoid disruptive charges, electrically nonconductive ceramic materials must be coated with a film of gold, carbon, or platinum about 20 nm thick by a sputtering process. Etched and unetched sections, fracture surfaces, glazes, firing skins, powder compacts, and prefired and finished sintered products can then be examined directly in the scanning electron microscope. 

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