PREPARED BY:
R.G. Munro
National Institute of Standards and Technology
Gaithersburg, MD 20899
DISTRIBUTED BY:
Standard Reference Data Program
National Institute of Standards and Technology
Gaithersburg, MD 20899
Copyright 1998 by the U. S. Department of Commerce
on behalf of the United States.
All rights reserved.
DISCLAIMERS:
A substantial effort has been made to select data for this database on the basis of sound scientific judgment. However, the National Institute of Standards and Technology (NIST) makes no warranties regarding its use, and NIST shall not be liable for any damage that may result from errors or omissions in the database.
Certain trade names and other commercial designations are used in this work for the purpose of clarity. In no case does such identification imply endorsement by the National Institute of Standards and Technology, nor does it imply that products or services so identified are necessarily the best available for the purpose.
The NIST WWW Structural Ceramics Database (WebSCD) provides evaluated materials property data for a wide range of advanced ceramics known variously as structural ceramics, engineering ceramics, and fine ceramics. These materials tend to have low mass densities and high strengths and tend to be resistant to corrosion. These characteristics form the basis for applications of these materials in high-temperature, energy-efficient heat exchangers, advanced engine designs, bearings, wear resistant parts, and stable electronic substrates and electronic packaging.
The range of materials covers the major series of compounds derived from the ceramic oxide, carbide, nitride, boride, and oxynitride chemical families. The materials are described by specification and characterization information that includes processing details and chemical compositions. Physical characteristics such as density and crystal structure are given in numeric tables. All measured values are evaluated and supported by descriptions of the measurement methods, procedures, and conditions. In all cases, the sources of the data are fully documented in a detailed bibliography.
At the outset of this project, it was recognized that sources of comprehensive data for advanced ceramic materials were difficult to find [1]. Several barriers to the development of advanced applications of these materials could be attributed to the limited availability of data, including delays due to uncertainties in design properties, costly trial-and-error efforts, and a reluctance to commit the needed resources to assess the data. The NIST WWW Structural Ceramics Database was established to reduce these barriers and to provide industry with the reliable data most critically needed.
The initial interest in the Structural Ceramics Database originated in the demanding requirements for strength, thermal and mechanical stability, and corrosion resistance that are needed for high efficiency, high temperature heat exchangers, turbines, and combustion engine components [2-4]. For those applications, the primary interest was focused on the properties of silicon carbide and silicon nitride materials. Subsequently, the range of materials was expanded in response to the strong interests in using ceramics for other applications [5-6]. High-alumina ceramics are used for electronic substrates, seals, liners, nozzles, spacers, and thermal and electrical insulators. Zirconia, in various partially stabilized or toughened forms, is being considered for hot extrusion dies, fuel cells, oxygen sensors, and for cylinder liners, piston caps, and other components in low-heat-rejection engines. Beryllia has a relatively high thermal conductivity and excellent dielectric properties making it very useful for heat sinks, spacers, or supports in electronic devices. Mullite is often used as a structural refractory and is gaining use in infrared-transmitting windows, electronic substrates, and as a matrix material for ceramic composites. Nitrides and carbides other than silicon nitride and silicon carbide also have numerous applications in electronic substrates, electronic packaging materials, and high-hardness abrasives and cutting tools. In the latter cases, the principal materials are aluminum nitride, cubic boron nitride, sialons, and boron carbide. High melting-point borides, including TiB2, TaB2, HfB2, and ZrB2, generally have high hardness, high thermal conductivity, and relatively high electrical conductivity, as well as a melting point in excess of 3000 C. These borides are used as cathode materials and for crucibles for molten metals, and other applications exploiting their oxidation resistance and thermal shock resistance are evolving.
In all of these applications, the thermal and mechanical properties of the materials play critical roles. The maintenance of dimensional tolerances and the retention of strength at extreme temperatures are essential for robust designs. Low failure rates and long material lifetimes are fundamental to economic feasibility and are essential for minimized disruptions of production schedules. All of these essential measures of strength and stability, along with their dependencies on environmental factors and important details regarding the fabrication of the material and the measurement methodologies used in determining the material properties, are provided in the NIST Structural Ceramics Database.
Certain conventions regarding materials specification warrant special discussion.
Several progressively more restrictive descriptors are used for the classification of a material: material class, chemical class, chemical family, informal name, chemical formula, and commercial name. In the Structural Ceramics Database, only one material class is considered, viz. structural ceramics, and the chemical classes that are considered are: boride, carbide, nitride, oxide, and oxynitride.
The term "chemical family" has been adapted from the NIST database on high temperature ceramic superconductors. The chemical family is a specification derived from the principal elements in the chemical composition; for example, Al2O3 belongs to the Al-O family. This specification is particularly useful as a collective designation of a series of related, possibly nonstoichiometric, compositions such as Al-Si-O for mullite (Al4+2xSi2-2xO10-x). A modified specification is used for composite materials; for example, an alumina matrix material with silicon carbide whisker inclusions belongs to the Al-O:SiC family.
The Structural Ceramics Database also uses another popular but imprecisely defined term, structure type, for a special purpose. In this database, the structure type specification is used to describe the bulk material as being a single crystal, a polycrystalline material, a noncrystalline (glassy) material, or a mixed material consisting of substantial crystalline and noncrystalline regions. This specification is important, for example, for understanding the anisotropy of certain material properties.