Impurity Phases in Beryllium Oxide Ceramic

Abstract

An x-ray spectrographic method with an electron probe and a scanning electron microscope are used to study industrial ceramic specimen surface composition, distinguished by presence of a different color for both the main part, and impurity phases. BeO-ceramic specimens, having a visually differing color, are conditionally separated into three types. In reflected electron microphotographs impurities are distinguished qualitatively with respect to electrical conductivity. Iron impurity is invariably present within the composition of electrically conducting phases and inclusions. Apart from iron, all impurity phases contain carbon, aluminum, silicon, and calcium, and within individual phases there are admixtures of manganese, magnesium, chromium, potassium, sodium, zinc, phosphorus, and chlorine, which may be introduced into BeO-ceramic during production and sintering in repeatedly used industrial furnaces from linings and residual atmosphere.Keywords: BeO-ceramic, impurity phases, inclusions, microstructure, color of impurity phases in reflected electrons, specimens, electrically conducting phases, phase composition.Ceramics based on beryllium oxide due to its high thermal conductivity (reaching 330 W/(m·K)), thermal, chemical, and radiation resistance, high dielectric and strength properties, are used extensively in special metallurgy, nuclear, space, electron, and laser technology [1 -6]. It is a transparent material for vacuum ultraviolet, x-ray, and UHF radiation. Beryllium ceramic is a most promising material for quantum electronics, where it is used in powerful ion and molecular gas optical quantum generators as dielectric tubes of optical resonators and hollow dielectric waveguides in waveguide gas discharge lasers of the central IR-range (1,3,5]. Light-transmitting BeO-ceramic is considered as a new material for creating solid-state lasers in the ultraviolet region of the spectrum [7]. Recently BeO-ceramic has been used as a material for high-voltage insulators in chambers with magnetic compression in order to obtain high-temperature magnetized hydrogen plasma, within which there is thermonuclear reaction [1]. It is well known that impurity atoms have a considerable effect on electrical and physicochemical properties of beryllium oxide [8]. Impurities may change thermal conductivity, dielectric permittivity, and optical properties, and affect microstructure morphology, rate of BeO crystal growth, and ceramic operating properties. After modification with certain impurities BeO-ceramic may be used as effective scintillators, working bodies in thermoluminescent, exoemission, and electron paramagnetic resonance dosimeters of ionizing radiation [1].Impurities connected with beryllium oxide may be separated into several groups [1, 2]: -anionic, affecting object density during sintering (fluorides, sulphates, and phosphates); isomorphic substituting beryllium ions in a cation sub-lattice (Li + , B 3+ , Zn 2+ , Al 3+ ) or arranged predominantly in octahedral internodes of BeO (Na + ); -covering ceramic objects and...