Melt crystallization structure

The melting and boiling points of the aluminium halides, in contrast to the boron compounds, are irregular. It might reasonably be expected that aluminium, being a more metallic element than boron, would form an ionic fluoride and indeed the fact that it remains solid until 1564 K. when it sublimes, would tend to confirm this, although it should not be concluded that the fluoride is, therefore, wholly ionic. The crystal structure is such that each aluminium has a coordination number of six, being surrounded by six fluoride ions. 

It is stable up to 2000 K and melts under pressure at 2500 K. The crystal structure of aluminium nitride resembles that of boron nitride and diamond, but unlike both of these it is rapidly and exothermically hydrolysed by cold water ... 

In addition to the nucleating agents discussed in Section 18.4, many other materials have been found to be effective. Whilst the nylons may be self-nucleating, partieularly if there is some unmelted crystal structure, seeding with higher melting point polymers can be effective. Thus nylon 66 and poly(ethylene terephthalate) are reported to be especially attractive for nylon 6. 

Another recent database, still in evolution, is the Linus Pauling File (covering both metals and other inorganics) and, like the Cambridge Crystallographic Database, it has a "smart software part which allows derivative information, such as the statistical distribution of structures between symmetry types, to be obtained. Such uses are described in an article about the file (Villars et al. 1998). The Linus Pauling File incorporates other data besides crystal structures, such as melting temperature, and this feature allows numerous correlations to be displayed. 

When inserted into an oil bath at 200°, the compound undergoes an immediate change in crystal structure and melts at 232-234°. The mother liquor affords two further crops, mp 228-230° and 227-228.5°, amounting to 3.5 and 10.6 g, respectively. Further recrystallization of the first crop from the same solvent pair raises the mp to 244-245° (70% recovery). 

Addition of the appropriate amount of water to anhydrous H3PO4, or crystallization from a concentrated aqueous solution of syrupy phosphoric acid, yields the hemihydrale 2H3PO4.H2O as a congruently melting compound (mp 29.3 "). The crystal structure shows the presence of 2 similar H3P()4 molecules which, together with the H2O molecule, are linked into... 

A lomic Atomic Crystal structure Melting point (°C) Density Thermal conduc- tivity (W/m K- ) at 20 C Electrical resistivity Specific heat Thermal expansion Magnetic susceptibility Electrode potential w.r.i. sal calomel (V) z c 2... 

Atomic number Atomic weight Crystal structure Melting Density Thermal Electrical resistivity (at 20°C) Temperature coefficient of resistivity Specific Thermal Standard electrode potential Thermal neutron absorption cross-section. 

The pretreated metalwork to be coated is heated in an oven to a temperature of between 260 and 360°C, depending on the metal thicknesses and the coating to be applied. It is then withdrawn from the oven and dipped into the fluidised powder. Here the fine powder particles are blown onto the hot metal where they melt. After a few seconds (5-lOs is normal), the item is removed from the powder and the unfused outer particles are allowed to fuse. Then either the item is allowed to air cool or it is water quenched. The cooling method can affect crystal structure and hence surface finish and... 

This monograph compiles the latest research on the chemistry of complex fluorides and oxyfluorides of tantalum and niobium, and covers synthesis and fluorination processes, crystal structure peculiarities and crystal chemical classification, as well as the behavior of complex ions in fluorine solutions and melts. 

Hydrogen bonds play an important part in determining such properties as solubility, melting points, and boiling points, and in affecting the form and stability of crystal structures. They play a crucial role in biological systems. For ex-... 

ELEMENT CRYSTAL STRUCTURE DENSITY (g/ml) MELTING POINT (°Q HEAT OF vaporization (kcal/mole) ELECTRICAL CONDUCTIVITY (ohm-cm)r ... 

At high pressures, solid II can be converted (slowly) to solid III. Solid III has a body-centered cubic crystal structure. Line bd is the equilibrium line between solid II and solid III, while line be is the melting line for solid III.P A triple point is present between solid II, solid III, and liquid at point b. Two other triple points are present in this system, but they are at too low a pressure to show on the phase diagram. One involves solid II, liquid, and vapor while the other has solid I, solid II, and vapor in equilibrium. 

Determination of the influence of crystal structure and reactant environment on deammination and dehydration processes is complicated by the several solid phase transformations that are a characteristic feature of many ammonium salts. Sublimation and/or melting may also occur. Deammination and dehydration steps are generally reversible. At high temperatures, however, particularly in the presence of a residual oxide... 

A.R. Ubbelohde, Melting and Crystal Structure, Clarendon Press, Oxford, 1965. 

---