Beryllium oxide thermal properties

Beryllium oxide shows excellent thermal conductivity, resistance to thermal shock, and high electrical resistance. Also, it is unreactive to most chemicals. Because of these properties the compound has several applications. It is used to make refractory crucible materials and precision resistor cores as a reflector in nuclear power reactors in microwave energy windows and as an additive to glass, ceramics and plastics. 

Beryllium oxide ceramics exhibit the highest thermal conductivity of all the ceramic products and are the best electrical insulators at high temperatures. Despite these exceptional properties, beryllium oxide ceramics have only found limited application due to their high cost and poisonousness. They are manufactured by sintering dry or plastically pressed fine particulate beryllium oxide at 1400 to 1450°C in a hydrogen atmosphere. 

Figure 3-7 HastelloyX Thermal Properties 3.5 Beryllium Oxide...

Beryllium is used commercially in three major forms as a pure metal, as an alloy with other metals, and as a ceramic. The favorable mechanical properties of beryllium, e.g., its specific stiffness, have made it a major component for certain aerospace applications in satellites and spacecraft. As a modulator and reflector of neutrons, beryllium is of interest in fusion reactions and for nuclear devices that have defense applications. When a small amount of beryllium is added to copper, the desirable properties of copper (i.e., thermal and electrical conductivity) are kept but the material is considerably stronger. The superior thermal conductivity of beryllium oxide ceramics has made the product useful for circuit boards and laser tubes. A more complete discussion of the applications of beryllium was recently reviewed [2]. 

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. 

Beryllium oxide, BeO, (Beryllia). Beryllia has excellent thermal properties (almost 10 times better than alumina at 250°C), and also has a lower dielectric constant (6.5). 

Sources From Krum, A. and Sergent, J.E., Thermal Management Handbook for Electronic Assemblies, McGraw-Hill, New York, 1998 MatWeb The Online Materials Information Resource, www.matweb.com, accessed September 26, 2003 TechnicalCeramics.net, Material Properties, http / /www.mcelwee.net/html/material properties.html, M.M.C., accessed September 26, 2003 Brush Wellman Inc., Internal data on beryllium oxide toughness. 

Beryllium oxide-filled resins gain high conductivity without loss of electrical properties. Metal particles have heen used as fillers for plastics to improve or impart certain properties. Thus, aluminum has heen used for applications ranging from making a decorative finish to improving thermal conductivity. Copper particles are used in plastics to provide electrical conductivity. Lead is used because it dampens vibrations, acts as barrier to gamma-radiation, and has high density. 

Functional Fillers. A variety of fillers can be used to add specific properties. Metals, and beryllium and aluminum oxides, can be added to increase thermal conductivity (Table 3.33). Metals can be added to increase electrical conductivity (Table 3.34). Graphite increases lubricity and electrical conductivity. Mica increases elec-... 

Beryllium is also used as a missile part and in other weapons. Owing to both its high thermal conductivity and high electrical resistivity, it is also used as a heat-sink material in electronic devices requiring good electrical insulation properties. In conclusion, some 60% of beryllium consumption is as a constituent of alloys and oxides in electronic parts and some 20% in the same form for electrical components. Approximately 13% is consumed as an alloy, oxide, or metal in aerospace and defense applications, while the balance is used as an alloy, metal, or oxide for other purposes. 

BeO is a metallic oxide with a very high thermal conductivity. BeO is chemically compatible with UO2, most sheath materials including zirconium alloys, and water. In addition to its chemical compatibility, BeO is insoluble with UO2 at temperatures up to 2160°C. As a result, BeO remains as a continuous second solid phase in the UO2 fuel matrix while being in good contact with UO2 molecules at the grain boundaries. BeO has desirable thermochemical and neutronic properties, which have resulted in the use of BeO in aerospace, electrical, and nuclear applications. For example, BeO has been used as the moderator and the reflector in some nuclear reactors. However, the major concern with beryllium is its toxicity. But the requirements for safe handling of BeO are similar to those of UO2. Therefore, the toxicity of BeO is not a limiting factor in the use of this material with UO2 (Solomon et al., 2005). 

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