Melting beryllium compounds

The USA consumption of beryllium was ca. 300 t/a Be in 1986. Of the beryllium compounds beryllium oxide is, as a result of its high melting point and its high chemical resistance, utilized for oxide-ceramic materials. 

Beryllium oxide is a high melting compound with an exceptionally high thermal conductivity, very low electrical conductivity, and a remarkable chemical stability. The breaking strength of BeO is comparable to that of a-Al203, however, the industrial production of BeO is more expensive. The high toxicity of beryllium compounds, for example abrasive dust of BeO, prevents a broad use of this material. 

Two other factors are noteworthy the deleterious effects on chemical and mechanical properties of small amounts of impurities residual from extraction of the metal, and its toxicity. The first of these factors is obviated by vacuum melting the raw metal (for purification) as an essential prerequisite to further processing. The toxicity of beryllium is essentially a pulmonary problem and great care must be taken in handling the finely divided metal or its compounds. In practice, this type of activity is usually carried out under well-ventilated conditions. Certain tolerance levels for atmospheric beryllium are now internationally accepted and merit careful study before work on beryllium is embarked upon. 

To investigate complexes of the Lewis acid BeO may seem strange from the experimental point of view. BeO is a polymeric solid with a high melting point and it is very difficult to obtain monomeric BeO. Moreover, beryllium is very poisonous and its compounds are difficult... 

The crystal structure of beryllium carbide is cubic, density = 2.44 g/mL. The melting point is 2250—2400°C and the compound dissociates under vacuum at 2100°C (1). This compound is not used industrially, but Be2C is a potential first-wall material for fusion reactors, one on the very limited list of possible candidates (see Fusion energy). 

Beryllium chloride, [CAS 7787-47-5], BeCF, with a melting point of 440 C, is used as a component of molten salt baths for electrowinning or electrorefining of the metal. The compound hydrolyzes readily with atmospheric moisture, evolving HO, so protective atmospheres are required during processing. 

Some of the halides of the alkaline earth metals have a similar identity problem. Calcium chloride and magnesium chloride have melting points almost as high as that of sodium chloride. Those compounds are clearly held together by ionic bonds. Beryllium chloride, on the other hand, melts at about half the temperature of table salt. And it boils at 520°C compared to salt s 1,465°C. The differences in properties are due to the partially covalent bond formed between beryllium and chlorine. 

Beryllium diethyl, Be(CgH5)2, prepared in a similar manner to the preceding compound, is a colourless liquid, B.pt. 93° to 95° C. at 4 mm. or 110° C. at 15 mm. It distils at 180° to 240° C. at ordinary pressure, with considerable decomposition, and when solidified in carbon dioxide-ether freezing mixture white crystals are formed, which melt on warming to — 13° to —11° C. It resembles the corresponding dimethyl derivative in oxidisability and inflammability. With water it yields... 

I herc is also an interesting series of basic beryllium complexes with the carboxylic acids which are covalent compounds of remarkable stability. Basic beryllium acetate, Be40(00C.CH3)g melts at 283°, boils at 330° without decomposition and dissolves in CHCI3 as the monomer it lacks ionic properties. Its structure has a central O atom surrounded tetrahedrally by tour... 

Medieval alchemists classified solids that did not melt in their fires as earths. Group 2A elements form compounds with oxygen, called oxides, that qualify as earths by this definition. Except for beryllium oxide, these oxides produce alkaline solutions when they react with water. The label alkaline earth reflects these two properties. 

Beryllium chloride is a substance of low melting point, is non-conducting when in the molten state, and is soluble in many organic solvents. All these characteristics point to a covalent compound, but it is difficult to see how this is to result from a beryllium atom with a fully filled outer s orbital. X-ray studies have established that the molecule contains two linear Be—Cl bonds, of equal strength. The problem is solved with the introduction of a concept of hybrid orbitals. 

Beryllium is used in nuclear reactors as a reflector or moderator for it has a low thermal neutron absorption cross section. It is used in gyroscopes, computer parts, and instruments where lightness, stiffness, and dimensional stability are required. The oxide has a very high melting point and is also used in nuclear work and ceramic applications. Beryllium and its salts are toxic and should be handled with the greatest of care. Beryllium and its compounds should not be tasted to verify the sweetish nature of beryllium (as did early experimenters). The metal, its alloys, and its salts can be handled safely if certain work codes are observed, but no attempt should be made to work with beryllium before becoming familiar with proper safeguards. Beryllium metal is available at a cost of about 5/g (99.5% pure). 

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