Crystallographic Systems

The translational direction of the lattice (c), which is the direction that the crystallite axis is not, because of the triclinic crystallographic system, is perpendicular to the plane of the unit cell base (ab). 

Alloys with ruthenium Additions of ruthenium have a most marked effect upon the hardness of platinum, but the limit of workability is reached at about 15% ruthenium, owing to the fact that ruthenium belongs to a crystallographic system different from that of platinum. Apart from a somewhat greater tendency to oxide formation at temperatures above 800°C, the resistance to corrosion of ruthenium-platinum alloys is comparable to that of iridium-platinum alloys of similar composition. 

Structure type" Compound Ref. a (A) b (A) c (A) Degrees Crystallographic system... 

The combination of the point lattices constructed on the basis of the crystallographic systems with the possible centring translation results in the 14 so-called Bravais lattice type, illustrated in Fig. 3.4. Substituting (decorating) each lattice... 

Brunzelle, J. S., Shafaee, P, Yang, X., Weigand, S., Ren, Z. and Anderson, W. F. (2003). Automated crystallographic system for high-throughput protein structure determination. Acta Crystallogr. D 59,1138-1144. 

Compound Crystallographic system Space group Stacking of close packed anions Unit cell dimensions nm a b c Z... 

Nevertheless, fluoride does lead to a reduction in the solubility of hydroxyapatite in aqueous solution, even in the absence of trace levels of fluoride in solution, and hence can be seen to have an effect in the solid state as well [57], Apatites are complex and diverse materials which have the general formula Caio(P04)eX2 (X = F, Cl, OH) and they represent a crystallographic system, in which there can be considerable replacement of species. Thus, with little or no change in the dimensions of the crystal lattice, there can be exchanges of OH for F, Ca + for Sr +, and PO4 for CO and all of these are known to occur in biological systems. Natural hydroxyapatite, for example, is often partially carbonate substituted [58]. 

These seven crystallographic systems are illustrated in Fig. 1 and may be described as follows ... 

There are five main types of crystals, and these types have been arranged into seven crystallographic systems based on the crystal interfacial angles and the relative length of its axes. The treatment of the description and arrangement of the atomic structure of crystals is the science of crystallography. The material in this discussion will be limited to a treatment of the growth and production of crystals as a unit operation. 

Despite the fact that the triclinic system is the only crystallographic system that unequivocally allows singlecrystal orientations to provide both enhanced in-plane and out-of-plane NRVS spectra, many other crystalline heme derivatives fortunately have all porphyrin planes close to being parallel to a common crystallographic plane. For example, [Fe(TPP)(l-MeIm)(NO)] has four independent porphyrin plane orientations, but all planes are within 13.8° of a common plane in the crystal. Data were collected using this common plane as the crystal-orienting plane to obtain an in-plane and an out-of-plane spectrum. As shown in Figure 10, a comparison of the in-plane , out-of-plane , and powder spectra show that useful intensity enhancements are still evident. Moreover, and fortunately, this situation of nearly coincident planes appears to be moderately frequently observed. 

As regards to crystal shape and more information on crystallographic systems - see 5]. 

---