Crystal structures types, ceramics

Here again certain trends were observed, and the most influential factor was the crystal structure which the superconducting material adopted. The most fruitful system was the NaCl-type structure (also referred to as the B1 structure by metallurgists). Many of the important superconductors in this ceramic class are based on this common structure, or one derived from it. Other crystal structures of importance for these ceramic materials include the Pu2C3 and MoB2 (or ThSi2) prototypes. A plot of transition temperature versus the number of valence electrons for binary and ternary carbides shows a broad maximum at 5 electrons per atom, with a Tc maximum at 13 K. 

As with metals, ceramic crystals are not perfect. They can contain all of the same types of defects previously described in Sections 1.1.3-1.1.5. What is unique about ceramic crystals, particularly oxide ceramics, is that the concentration of point defects, such as vacancies and interstitials, is not only determined not only by temperature, pressure, and composition, but can be influenced greatly by the concentration of gaseous species in which they come in contact (e.g., gaseous oxygen). The concentration of gaseous species affects the crystal structure, which in turn can affect physical properties such... 

Rutile Ceramic Pigments. Structurally, all rutile pigments are derived from the most stable titanium dioxide structure, ie, rutile. The crystal structure of rutile is very common for AX2-type compounds such as the oxides of four valent metals, eg, Ti, V, Nb, Mo, W, Mn, Ru, Ge, Sn, Pb, and Te as well as halides of divalent elements, eg, fluorides of Mg, Mn, Fe, Co, Ni, and Zn. 

The hardness of a material is determined by its structure. For ceramic materials, this means that among other things the type of crystal structure and the firmness of the bonds can be of influence. 

Microabrasion using compressed air is a modification based on sandblasting, the micropowder blasting. This process enables all types of glass, ceramics and semiconductor materials, irrespective of their chemical composition and crystal structure, to be inexpensively processed down to the micrometer scale. The micropowder blasting is a masked procedure and works quasi-parallel on the whole substrate. A powder jet drives systematically over the substrate. Material is removed at the mask openings (see Figure 2.17). 

A majority of the important oxide ceramics fall into a few particular structure types. One omission from this review is the structure of silicates, which can be found in many ceramics [1, 26] or mineralogy [19, 20] texts. Silicate structures are composed of silicon-oxygen tetrahedral that form a variety of chain and network type structures depending on whether the tetrahedra share comers, edges, or faces. For most nonsilicate ceramics, the crystal structures are variations of either the face-centered cubic (FCC) lattice or a hexagonal close-packed (HCP) lattice with different cation and anion occupancies of the available sites [25]. Common structure names, examples of compounds with those structures, site occupancies, and coordination numbers are summarized in Tables 9 and 10 for FCC and HCP-based structures [13,25], The FCC-based structures are rock salt, fluorite, anti-fluorite, perovskite, and spinel. The HCP-based structures are wurtzite, rutile, and corundum. 

Uranium dioxide has a number of properties that make it suitable for a fuel. The crystal structure is the fluorite (CaF2) type, similar to that of calcia-stabilised zirconia, and is stable to temperatures in excess of 2000 °C. Because it is a ceramic oxide, the material is refractory, chemically inert and resistant to corrosion Enrichment does not change these features. The oxide powder is pressed into pellets and sintered to a density of about 95 % maximum by traditional ceramic processing technology but is carried out in conditions that minimise risks from radiation effects. The pellets are contained in zirconium alloy (zircaloy) containers, which are then introduced into the reactor. The moderator, which... 

This chapter was a review of things that you already knew. There are three types of primary bonds that are used to hold atoms together. In introductory materials science classes we tend to think of each type of bond as being a distinct form, with materials adopting one type or another. At a qualitative level this approach might work, and in the cases of many metals, semiconductors, and polymers it is usually quite close to the actual situation we encounter. However, in ceramics almost every bond has a mixture of covalent, ionic, and, in some cases, metallic character. The type of interatomic bond affects the crystal structure that a material adopts. The influence of mixed bonding can mean that the type of structure predicted, based... 

Most ceramics are crystalline. The exception is glass, which we usually discuss separately. Not only do the properties of ceramic crystals depend on how the atoms or ions are arranged, but the type and nature of defects also depend on crystal structure. You probably first encountered crystallography when discussing metals. Sixty-five (almost 90%) of the metallic elements are either cubic or hexagonal. In ceramics, many of the most important materials are neither cubic nor hexagonal, so we need to be more familiar with the rest of the subject. It is recommended that you memorize the main structures described in Chapters 6 and 7. In this chapter we provide the means to make this study more systematic. 

Thus, this contribution is aimed at the state of the art in boride ceramics with their problems in densification, microstructural peculiarities and exceptional mechanical properties. Starting with the unique interaction of metallic, covalent and ionic types of bonding and the crystal structures of technically important compounds, phase diagrams will be presented as far as they are of technical interest. The major part consists of the description of the synthesis and properties of ceramics and cermets, reflecting the development of suitable sintering procedures and the consequent improvement of the thermal and mechanical properties. 

The thermal expansion coefficients are related to the crystal structure and to the type and strength of the bond. Many ceramics have low to medium expansion coefficients, as can be seen in Table 4.10. The coefficients may or may not depend strongly on temperature. In many cases the thermal expansion is anisotropic and can have negative values in certain temperature regions. 

The LIB cathode materials are transition metal oxides containing lithium, and they are a type of functional ceramics. For such a material to be used as LIB cathode, the Li ions must be able to diffuse freely through the crystal stmcture. The morphology of the crystal structure, being one-, two-, or three-dimensional, determines the number of dimensions in which Li ions are able to move. Cathode materials currently in use or under development are described below in accordance with the following three morphologies. 

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