Amorphous glass

The writing process, that is, the transition crystalline — amorphous, is caused by briefly (<50 100 ns) heating up the selected storage area (diameter (( )) ca 0.5—1 Hm) by a laser pulse to a temperature above the melting point of the memory layer (Eig. 15, Record), such that the film locally melts. When cooled faster than a critical quench rate (10 -10 ° K/s), the formation of crystalline nuclei is suppressed and the melted area sohdifies into the amorphous (glass-like) state. 

Total sugar products are also produced by dehydrating hydroly2ate to a mixture of crystals and amorphous glass. This product is not produced in significant quantities in the United States or Europe but is popular in Japan and Korea where it represents 40—50% of total crystalline dextrose sold (14). 

Arsenic III oxide (arsenic trioxide, arsenious oxide) [1327-53-3] M 197.8, three forms m 200°(amorphous glass), m 275°(sealed tube, octahedral, common form, sublimes > 125° without fusion but melts under pressure), m 312°, pKj 9.27, pK 13.54, pK 13.99 (for H3ASO3). Crystd in octahedral form from H2O or from dil HCl (1 2), washed, dried and sublimed (193°/760mm). Analytical reagent grade material is suitable for use as an analytical standard after it has been dried by heating at 105° for l-2h or has been left in a desiccator for several hours over cone H2SO4. POISONOUS (particulary the vapour, handle in a ventilated fume cupboard). 

Relation of Structure to Thermal and Mechanical Properties AMORPHOUS,GLASS-LIKE CRYSTALLINE, FIBRE-FORMING... 

When the temperamre is lowered, rubbers become stiff and brittle. All rubbers eventually stiffen to a rigid, amorphous glass at the glass transition temperature (Tg). This temperature also indicates the low-temperature service limit of the rubber. Tg values are dependent on the structure, degree of cross-linking (vulcanization) and isomeric composition of the rubber. 

The compound is lachrymatory it quickly polymerizes to an amorphous glass at 20 X. 

Inside ABCD, the crystalline solid is stable, above ABC the liquid, whilst to the right of CD the stable form is the amorphous glass. Roozeboom, however, holds a different opinion as to the latter part of the curve Heterogene Gleichge-u ichte, vol. I.). 

Continuous transition of state is possible only between isotropic states it may thus occur between amorphous glass (i.e., supercooled liquid of great viscosity) and liquid ( sealing-wax type of fusion ), or between liquid and vapour, but probably never between anisotropic forms, or between these and isotropic states. This conclusion, derived from purely thermodynamic considerations, is also supported by molecular theory. 

A solid that has no translational symmetry at all is said to be amorphous. Glasses are amorphous solids that behave like liquids with very high viscosity. The viscosity decreases with increasing temperature, i.e. the material softens, but it has no melting point. 

With respect to point 1, it has appeared that in oxidative detection, carbon is the best choice in nearly all cases. Therefore glassy carbon (an amorphous glass-like carbon) is the standard working electrode material in most cells for HPLC-EC. 

An interesting series of high Ts HTMs based on novel indolo[3,2-b]carbazoles has been discovered by the Xerox group [85]. These compounds not only showed the desired hole transport properties and high Ts of 164°C but also display an unusual atropisomerism with two discrete trans- and U.v-rotational isomers (Scheme 3.14), which greatly improves their tendency to form stable amorphous glasses. 

Bis(dimesitylboryl)-2,2 -bithiophene (BMB-2T, 242) forms a stable amorphous glass and emits pure blue color with a high fluorescence QE of 86% in THF solution [270]. However, an OLED with ITO/m-MTDATA/TPD/BMB-2T/Mg Ag emits with a broad emission due to an exciplex with TPD. The exciplex can be prevented by insertion of a thin layer of 1,3,5-tris(biphenyl-4-yl)benzene (TBB) between TPD and BMB-2T, leading to a pure blue emission. It seems that the boron complex or boron-containing compounds easily form an exciplex with common HTMs. Other similar blue emitter materials also demonstrate such behavior. 

Figure 3.2. Differential calorimetric curves for the molecular glasses (a) Spiro-sexiphenyl (second heating curve) and (b) Spiro-PBD (first and second heating curve). The glass transition is indicated by a characteristic step, the melting point by an endothermic peak. In (a) recrystallization occurs above Tg, which can be seen by an exothermic peak. The material in (b) forms a stable amorphous glass without recrystallization. The melting point from the first heating curve of a crystalline sample (dotted line) disappears in the second heating cycle (solid line). Only the glass transition is visible.

Most of the devices described up to now are based on materials that tend to crystallize [phthalocyanines, porphyrins and perylenetetracarboxydiimids, (59)] [276, 277], or form liquid crystalline phases [278, 279]. With respect to amorphous glasses, light sensitive donor-acceptor type molecules, for example, the p-type triarylamines tris [4-methylphenyl(4-nitrophenyl)ammo]triphenylamine and tris[5-(dimesitylboryl)thiophen-2-yl]triphenylamine have been combined with an n-type material in a double-layer heterostructure [280]. The cells respond to visible light from 400 to 800 nm with overall efficiencies of 0.1%. 

A method of characterising transport mechanisms in solid ionic conductors has been proposed which involves a comparison of a structural relaxation time, t, and a conductivity relaxation time, t . This differentiates between the amorphous glass electrolyte and the amorphous polymer electrolyte, the latter being a very poor conductor below the 7. A decoupling index has been defined where... 

Amorphous. Strictly speaking, characterized by noncrystalline structure, i.e., having no. lattice structure that most solids have. Liquids are amorphous. Glass is a solid but is amorphous because it is considered a high viscosity liquid.. 

With semi-crystalline polymers we should always carefully distinguish between the behaviour below Tg and above Tg. Below Tg (such as with PEEK) the crystalline fraction, which is somewhat stiffer than the amorphous glass, dominates, so that E is somewhat higher. Above Tg, such as with PE and PP, the amorphous fraction, which is in the rubbery condition, is responsible for a significantly lower E. 

Much of the quartz in the fly ash originates from the coal as silt- and sand-sized particles, and it remains in the ash because it survives thermal transformation during the combustion process (Helmuth 1987). Small amounts of volatilized Si may also oxidize to form very fine crystals of quartz within the fly ash glass (Diamond 1984 Hubbard et al. 1984). Although bituminous coal ash may contain more than 50 wt% analytical Si02, only 5-10 wt% of it is present in the form of quartz (McCarthy et al. 1990). Some Si is present in the mineral mullite, but the majority of it is in the amorphous glass phase. 

Applying the phase rule, it is found that, in the two component system NaP03 + H20, a maximum of four phases is possible at the quadruple points 199,302). In addition to, at the most, two crystalline substances and water vapor, an amorphous glass-like phase is always present. This phase consists of mixtures of polyphosphates, the chain length of which rises with increasing temperature. Only Na2H2P207, Maddrell s salt (h) and trimetaphosphate occur as stable solid phases in addition to NaH2P04. 

---