No abstract

No abstract

Engineering ceramics such as alumina, zirconia, silicon nitride and silicon carbide can now be manufactured reliably with reproducible properties. As such, they are of increasing interest to industry, particularly for use in demanding environments, where their thermomechanical performance is of critical importance, with applications ranging from fuel cells to cutting tools. One aspect common to virtually all applications of engineering ceramics is that eventually they must be joined with another material, most usually a metal. The joining of engineering ceramics to metals is not always easy. There are two main considerations. The first consideration is the basic difference in atomic bonding: the ionic or covalent bonding of the ceramic, compared to the metallic bond. The second consideration is the mismatch in the coefficient of thermal expansion. In general, ceramics have a lower coefficient of thermal expansion than metals and, if high tensile forces are produced in the ceramic, either as a consequence of operating conditions or from the joining procedure itself, failure can occur. The plethora of joining processes available will be reviewed in this article, placing them in context from both an academic and commercial perspective. Comment will be made on research reporting advances on known technology, as well as introducing 'newer' technologies developed over the last 10 years. Finally, reviews and commentary will be made on the potential applications of the various joining processes in the commercial environment.

Spatially resolved electron energy loss spectroscopy is used to characterize the cross-sectional structure of highly tetrahedral amorphous carbon films, particularly concentrating on the sp 2 bonded surface layer. The surface layer is shown to be due to subsurface conversion from sp 2 to sp 3 bonding at the depth of carbon ion implantation during film growth. The thickness of the surface layer is used as a measure of the ion penetration depth, varying from 0.4 6 0.2 nm for 35 eV ions to 1.3 6 0.3 nm for 320 eV ions. The influence of growth temperature is investigated, and it is found that the temperature above which sp 3 bonding is not stable is greatly reduced in the region affected by ion bombardment.[S0031-9007(98)05863-3]

Originally developed in the late 1960s, anodic bonding, also known as electrostatic bonding, field-assisted bonding or Mallory bonding, has become one of the most important silicon packaging techniques. Despite its industrial relevance the bonding mechanism is mainly only qualitatively understood and is almost solely applied to the bonding of silicon to Pyrex glass. The objective of the present paper is to review the current state of knowledge of the anodic bonding process. Possible material combinations and current scientific and industrial applications of this bonding technique are reviewed. The various aspects of the bonding process, such as the creation of intimate contact, the cation movement in the glass and the interfacial chemical reactions, are discussed in detail and related to the external current measured during bonding to describe the bonding process quantitatively. A better understanding of the process itself should help not only to improve the process control and the quality of devices, but also to broaden the application of this successful bonding technique to more challenging designs, to smaller device sizes and to systems other than silicon-Pyrex glass.

No abstract

No abstract

The effects of the oxide additives MnO 2 , Co 3 O 4 , and Sb 2 O 3, commonly incorporated in commercial Bi 2 O 3 -doped ZnO varistors, on the current-voltage characteristics and microstructure of 0.25 mol% V 2 O 5 -doped ZnO varistors have been studied. MnO 2 is the most significant additive in terms of its effects on varistor performance. Varistor performance can also be improved by increasing the V 2 O 5 content to 0.5 mol% in a ZnO ceramic containing 1 mol% MnO 2 . Further increases in the V 2 O 5 content of 1 mol% MnO 2 -doped material cause a deterioration in varistor behavior. The microstructure of the samples consists mainly of ZnO grains with zinc vanadates as the minority secondary phases. Additional spinel phase is formed when Sb 2 O 3 is incorporated.