Beryllia,

Alumina ceramics are widely used for thick-film circuit substrates and for integrated circuit packaging. This aspect is discussed in Section 5.5.5. 

Beryllia has broadly similar properties to alumina (Table 5.3) but its thermal conductivity is 5-10 times greater. It is therefore used when thermal dissipation combined with electrical isolation is of major importance, e.g. in high-power 

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Beryllia and Thoria. These are specialty oxides for highly specialized appHcations that require electrical resistance and high thermal conductivity. BeryUia is highly toxic and must be used with care. Both are very expensive and are used only in small quantities. 

Chemical Designations - Synonyms Beryllia Bromellite Chemical Formula BeO. 

Glover-saure, /. Glover acid (acid from the Glover tower), -tunn, m. Glover tower. Glucinerde,/. glucina (beryllia). 

Furthermore, even though a consistent quality of beryllium is now produced, the chemical composition falls far short of the standards found for instance in aluminium generally, the main impurities consist of about 1% of beryllia at grain boundaries, about 0-15% of iron and 0-05-01% of other elements such as silicon, aluminium and carbon. 

Beryllium is readily attacked by most acids and, being amphoteric, is slowly attacked by caustic alkalis with the evolution of hydrogen. As might be anticipated, in view of the controlling influence of the surface film of beryllia on corrosion behaviour, concentrated nitric acid has little effect on beryllium , while the dilute acid results in slow attack. Hot acid is much more reactive. Nitric acid is in fact often used to pickle-off residual mild steel from hot-extruded clad beryllium. 

Conversely to the above, any factor which tends to maintain the protective character of the beryllia film will obviously increase corrosion resistance, and, in this respect, the presence of anodic inhibitors such as sodium dichromate, up to about 40 p.p.m., will effectively suppress pitting of beryllium in water. 

Heat dissipation can be effectively dealt with by using substrate materials such as aluminum nitride, beryllia and, more recently, diamond which combine electrical insulation with high thermal conductivity. The relevant properties of these three materials are shown in Table 14.1. 

Beryllia (BeO) is an excellent heat-sink material which is presently widely used but is being phased out because it presents acute safety problems.It is being replaced by aluminum nitride which extensively produced by CVD, mostly in Japan (see Ch. 10, Sec. 2).P2]... 

Diamond is an electrical insulator with the highest thermal conductivity at room temperature of any material and compares favorably with beryllia and aluminum nitride. P3]-P5] jg undoubtedly the optimum heat-sink material and should allow clock speeds greater than 100 GHz compared to the current speed of less than 40 GHz. 

The function of the carbon coating is to contain the byproducts of the fission reaction, thereby reducing the shielding requirements. It also protects the nuclear fuel from embrittlement and corrosive attack and from hydrolysis during subsequent processing steps. CVD coatings of alumina deposited at 1000°C and beryllia deposited at 1400°C have also been studied for that purpose.P l... 

Typically, Be-containing alloys and intermetallic phases have been prepared in beryllia or alumina crucibles Mg-containing products have been synthesized in graphite, magnesia or alumina crucibles. Alloys and compounds containing Ca, Sr and Ba have been synthesized in alumina , boron nitride, zircon, molybdenum, iron , or steel crucibles. Both zircon and molybdenum are satisfactory only for alloys with low group-IIA metal content and are replaced by boron nitride and iron, respectively, for group-IIA metal-rich systems . Crucibles are sealed in silica, quartz, iron or steel vessels, usually under either vacuum or purified inert cover gas in a few cases, the samples were melted under a halide flux . 

Beryllia can be chlorinated using chlorine in the presence of carbon at 700 to 800 °C as... 

The magnesium-reduced beryllium pebbles generally assay 96% beryllium and are always associated with residual magnesium and slag. These pebbles are purified to about 99.5% by vacuum induction melting in beryllia crucibles at temperatures of about 1400 °C. The ingots are machined and machined scarf is milled to produce beryllium powder. The ground metal powder is pressed and sintered under vacuum. The product is called vacuum hot-pressed beryllium, and this is machined for component manufacture. 

Espig A process for making synthetic emeralds by the flux reaction technique. Beryllia and alumina are dissolved in molten lithium molybdate, and silica is floated on the melt. The emerald crystals form at the base of the melt, but because they tend to float and mix with the silica, a platinum screen is suspended in the middle of the melt. Invented by H. Espig. 

Fuse-quench Also called the Kjellgren-Sawyer process. A process for extracting beryllium from beryl. The beryl is fused at 1,600°C and then rapidly quenched by pouring through a water jet of high velocity. The glassy product is heated to 900°C to precipitate beryllia from its solid solution in silica, and then extracted with sulfuric acid. Operated by the Brush Beryllium Company, Cleveland, OH. 

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