Amorphous solids ambient temperatures

Therefore, the ideal solution in this field would he the use of solid plasticisers , namely of solid additives which would promote amorphicity at ambient temperature without affecting the mechanical and the interfacial properties of the electrolyte. A result that approaches this ideal condition has been obtained by dispersing selected ceramic powders, such as Ti02, AI2O3 and Si02, at the nanoscale particle size, in the PEO-LiX matrix [35-41]. The conductivity behaviour of a selected example of these nanocomposite polymer electrolytes is shown in Figure 7.5. 

Three different forms of beryllium hydroxide in the solid state have been described (10, 52, 53, 100). The amorphous form of Be(OH)2 is obtained as a gelatinous precipitate when alkali is added to a beryllium-containing solution at ambient temperatures. The gelatinous precipitate is slowly transformed into the metastable a form when the mixture is allowed to stand. The stable fi form is obtained after the mixture has aged for some months or by precipitation at 70°C. The value of log K for the equilibrium between a and (3 forms,... 

The Step 4 product (14.4 mmol) was dissolved in 160 ml THF and treated with 5 A molecular sieves (16 g) and L-valine methyl ester hydrochloride (28.8 mmol), then stirred 30 minutes at ambient temperature. The solution was further treated with the dropwise addition of sodium cyanoborohydride (14.4 mmol) in 18 ml methyl alcohol at 0—5°C and the mixture stirred overnight at ambient temperature. The solution was concentrated, the residue purified by chromatography using EtOAc/n-heptane, 1 2, and 4.41 g of product isolated as an amorphous solid... 

The chemistry of a finely divided solid with high surface area is at the borderline between molecular chemistry and physics of solid surfaces. The surface of a finely divided amorphous silica may be understood as a two-dimensional projection of the three-dimensionally linked silicon dioxide tetrahedra. By this the chemistry of the fumed silica surface is dominated by Si-O-Si units and, in particular, dangling surface Si-0 bonds, which will create silanol groups under the influence of humidity at ambient temperature. 

Instability attributable to excipient-mediated water distribution in solids and powders has been explained by excipient physical properties. " Crystalline materials will not uptake moisture until the deliquescent point is reached. In contrast, amorphous excipients will absorb water until their glass transition temperatures fall below the ambient temperature when the mobility of the molecules has increased so much that excipient crystallization will occur to expel the absorbed water from the crystal lattice. Before crystal-... 

As isolated from toluene solution, neat MAO is an amorphous, friable white solid containing 43-44% Al (theory 46.5%). Like most commercially available aluminum alkyls, it is pyrophoric and explosively reactive with water. Freshly prepared MAO solutions form gels within a few days when stored at ambient temperatures (>20 °C). However, lower storage temperatures (0-5 °C) delay gel formation. Consequently, manufacturers store and transport MAO solutions in refrigerated containers. Commercially available MAO contains residual TMAL (15-30%), called "free TMAL" or "active aluminum." The literature is contradictory on the influence of free TMAL on activity of single site catalysts both reductions and increases have been reported (18-20). Perhaps the most important drawback of methylaluminoxane is its cost, which is substantially higher than conventional aluminum alkyls. Despite these untoward aspects, methylaluminoxane remains the most widely used cocatalyst for industrial single site catalysts. 

In the late 1970s, Flanigen found that zeolite X could directly crystallize from pure solid phase. In this study, the synthetic system that had passed the induction period was filtered and the hydrogel was dried at an appropriate temperature. The dried gel was amorphous at this stage and had a molar composition of 1.1 Na20 A1203 2.7 Si02 4.6 H20. After 10 days of treatment of this dry amorphous gel at ambient temperature in air, 2% zeolite X formed, and this amount increased to 20% after 47 days. 

Among the polymers which contain clear crystalline phases are poly(ethylene) and PTFE. Their properties, however, are very different from those usually associated with crystalline solids in particular, they tend to exhibit low rigidity and at ambient temperatures are soft and deformable rather than brittle. This is because, unlike say sodium chloride or copper sulphate, crystalline polymers include both amorphous and crystalline regions. 

Thermodynamically more stable crystalline phases will be favoured as the nuclei grow in size since the bulk lattice energy terms, rather than the surface energy terms, become more important in stabilising the solid phase, particularly (as in the case of amorphous CaCOs) when the amorphous phase is relatively soluble. In cases where the amorphous phase is relatively insoluble, for example, amorphous calcium phosphate, the transformation to crystalline states may be slow at ambient temperature and pressure. In other cases, for example, biogenic silica, the amorphous phase is metastable and not transformed into a crystalline phase under normal conditions due to the high activation energies required to be overcome for this transformation. ... 

A comparison has been made of the radial atomic distribution functions of three forms of selenium the liquid at 250 and 350 °C, the amorphous solid (quenched from 550 to 0 °C) at 20 °C, and as hexagonal crystals at ambient temperature. In the liquid, the number of parallel atomic chain... 

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