Crystallites small

It was assumed that the nickel crystallites are rapidly enveloped in a skin of a copper-rich alloy, from which diffusion towards the center of each crystallite then takes place. If xx and x2 are the atomic fractions of copper in the two equilibrium phases and x is the atomic fraction of copper in the alloy film under consideration, then the crystallites in the annealed film may have a variety of forms. Solid solutions occur at either end of the composition range but the values of Xi and x2 at 200°C are <0.1 and 0.8. Hence, over much of the composition range (i.e., where x lies between X and xi), the Cu-Ni films should consist of crystallites with a kernel which is almost pure nickel (composition xi) enveloped in a skin of a copper-rich alloy (composition x2). Eventually, when x is only slightly larger than Xi, the alloy skin does not completely surround the nickel crystallites small patches of alloy (x2) and almost pure nickel ( ci) are both exposed. 

Courdinaiion chemists have prepared a variety of clusteis containing CO as a ligand. The withdrawal of electrons by CO seems to stabilize low-valence states. Complexes with up to 38 metal atoms (Pt j(C0)44 units) have been prepared. This number of atoms corresponds to that present in surface crystallites. Small crystallites have stronger surface atom interactions, which could mean that CO adsorption miglit change with crystallite size. 

Small crystallites large crystallites Small amorphous particles -> large amorphous particles Amorphous solid —> crystalline solids Crystallites ( )-> crystallites (2)... 

High-purity alumina contains at least 99.99 wt.% Al Oj, with crystallites small in size and morphology. Nearly half the hig i-purity alumina produced annually is used to manufacture sapphires and, to a lesser extent, as polishing medium for metallographical and optical processes. Four manufacturing processes of ultrapure aluminas are used, using either Bayer gibbsite or aluminum metal. 

Rossetti R ef al 1984 Size effects In the excited electronic states of small colloidal CdS crystallites J. Chem. Phys. 80 4464... 

Brus L E 1984 Electron-electron and electron-hole Interactions In small semiconductor crystallites the size dependence of the lowest excited electronic state J. Chem. Phys. 80 4403-9... 

Stretching a polymer sample tends to orient chain segments and thereby facilitate crystallization. The incorporation of different polymer chains into small patches of crystallinity is equivalent to additional crosslinking and changes the modulus accordingly. Likewise, the presence of finely subdivided solid particles, such as carbon black in rubber, reinforces the polymer in a way that imitates the effect of crystallites. Spontaneous crystal formation and reinforcement... 

Detector elements are prepared either by sublimation in the presence of a small partial pressure of O2 or by chemical deposition from alkaline solution containing a lead salt and thiourea or selenourea (63). Lead sulfide and lead selenide deposit from solutions as mirror-like coatings made up of cubic crystallites 0.2—1 p.m on a side. The reaction may nominally be represented by the following ... 

The small precious metal crystals can exist as metal crystallites or as metal oxides, both of which are catalytic (31). Rodium oxide has a tendency to react with alumina to form a soHd solution (35). To minimize this reaction, zirconia is used with the alumina (36). PubHcations regarding the TWC function of precious metals abound (37—42). 

The mode of action of plasticizers can be explained using the Gel theory [35 ]. According to this theory, the deformation resistance of amorphous polymers can be ascribed to the cross-links between active centres which are continuously formed and destroyed. The cross-links are constituted by micro-aggregates or crystallites of small size. When a plasticizer is added, its molecules also participate in the breaking down and re-forming of these cross-links. As a consequence, a proportion of the active centres of the polymer are solvated and do not become available for polymer-to-polymer links, the polymer structure being correspondingly loosened. 

Fig. 6. PCNTs with partially deposited carbon layers (arrow indicates the bare PCNT), (a) as-grown, (b) partially exposed nanolube and (c) 002 dark-field image showing small crystallites on the tube and wall of the tube heat treated at 2500 C.

In addition to purely energetical heterogeneity one should also take into account some basic aspects of possible heterogeneities resulting from geometrical effects. The simplest and yet experimentally quite important geometric effects are due to the finite size of crystallites. Experimental measurements ave clearly demonstrated that the size of typical crystallites may be quite small (of the order of 50-100 A [116,132] and quite large (of the order of 10 A [61]. 

An intimate mixture of betaine hydrate (67.5 g) and chloral hydrate (100 g) was warmed to ca. 60°C when an exothermic reaction occurred and the mixture became pasty. It was then stirred at 60°C for 30 minutes. The residue solidified on cooling and was crystallited from a small amount of water. The product separated in hard, colorless prisms of MP 122.5° to 124.5°C (corr). 

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