Particular beryllium oxide

The possible employment of beryllium in nuclear engineering and in the aircraft industry has encouraged considerable investigation into its oxidation characteristics. In particular, behaviour in carbon dioxide up to temperatures of 1 000°C has been extensively studied and it has been shown that up to a temperature of 600°C the formation of beryllium oxide follows a parabolic law but with continued exposure break-away oxidation occurs in a similar fashion to that described for zirconium. The presence of moisture in the carbon dioxide enhances the break-away reaction . It has been suggested that film growth proceeds by cation diffusion and that oxidation takes place at the oxide/air interface. ... 

Chronic exposure to insoluble beryllium compounds, particularly the oxide, leads to berylliosis (a chronic granulomatous disease), which begins with a cough and chest pains. In most cases, these symptoms soon lead to pulmonary dysfunction. The latency period ranges from months to 25 years. Diagnosis based on clinical, radiographic, and lung function evidence has been found to be difficult. 

On the whole, pure metals are the most resistant of all materials to radiation damage and recover most easily, presumably because the atoms in metals are most mobile. But reactions like those in metals have been found in valence compounds such as diamond, silicon and germanium, and in simple salts and oxides such as sodium chloride and beryllium oxide. On the other hand, organic materials, particularly polymers such as plastics, are exceedingly sensitive to radiation and suffer permanent and irreparable changes. In these cases the damage is associated with the breaking of chemical bonds which are diffi-... 

Beryllium oxide materials are particularly attractive for use in power vacuum tubes because of their electrical, physical, and chemical properties. The thermal conductivity of BeO is approximately 10 times higher than that of alumina-based materials. Figure 5.35 compares the thermal conductivity of BeO to that of alumina and some alternative materials. As the chart iUustrates, BeO has a lower dielectric constant and coefficient of thermal expansion than alumina, ft is, however, also sHghtly lower in strength. 

It is also shown that theoretically a binary compound should have the sphalerite or wurzite structure instead of the sodium chloride structure if the radius ratio is less than 0.33. The oxide, sulfide, selenide and telluride of beryllium conform to this requirement, and are to be considered as ionic crystals. It is found, however, that such tetrahedral crystals are particularly apt to show deformation, and it is suggested that this is a tendency of the anion to share an electron pair with each cation. 

A different situation obtains in compounds such as the basic beryllium monocarboxylates (140-142). In particular the acetate derivative, Be40(02CCH3)6, has been known in the solid state for nearly 100 years (143). A partial structure of this compound is in Fig. 13 (144). The central oxide ion is surrounded by a tetrahedron of beryllium atoms. The acetate ions form bridges across the six edges of the Be4 tetrahedron, with each acetate bonding with two Be atoms. Each berylium atom in surrounded by an approximate tetrahedron of... 

The vacuum microbalance can be applied to the study of vapor pressures of metals and in particular to the effect on the vapor pressure of films of oxide, nitride, and other protective layers on the metal surfaces. We studied the vapor pressure of several metals including beryllium and chromium and in this section will discuss the work on beryllium (43). 

Two studies on the vapor pressure of beryllium have been published. The earlier work was by Schuman and Garrett (44) in 1944, and the more recent was reported by Holden, Speiser, and Johnston (45) in 1948. The values given for the vapor pressure P in the two publications differ by about 300%. We were particularly interested in studying the effect of oxide and nitride films on the vapor pressure and the relation of this effect to the rate of oxidation. 

The extraction of Be from its ore is attended by exposure to acid salts of the metal, particularly the fluoride (Bep2), the ammonium fluoride and sulfate (BeS04), and also to ber rllium oxide (BeO), and hydroxide [Be(OH)2], Exposure to the oxide also occurs in the casting of beryllium alloys and in operations with beryUia ceramics. In the manufacture of fluorescent powders, lamps, and sign tubes, there may be exposure to beryllium carbonate and to more complex salts, such as ZnMnBe silicate. Exposure to beryllium compounds encountered in the extraction of the metal... 

Fuels usually consist of hydrocarbons, except in particularly exotic applications such as rocketry, where nitrogen, aluminium (Al) and even beryllium (Be) are sometimes used. Normal fuel combustion is an oxidation reaction (see Box 4.3) and can be described ... 

The octet rule is remarkable in its ability to realistically model bonding and structure in covalent compounds. But, like any model, it does not adequately describe all systems. Beryllium, boron, and aluminum, in particular, tend to form compounds in which they are surrounded by fewer than eight electrons. This situation is termed an incomplete octet. Other molecules, such as nitric oxide ... 

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