Quenched glass

The precursor glass powders may be produced by various methods, the simplest being the milling of quenched glass to an average particle size of 3—15 p.m. Sol gel processes, in which highly uniform, ultrafine amorphous particles are grown in a chemical solution, may be preferable for certain apphcations. 

After the molten glass has become a homogeneous Hquid, it is poured in a thin stream into water or between closely spaced, water-cooled rotating metal rollers. This quenched glass, termed frit, is a friable material easily reduced to small-sized particles by a ball-milling operation. Ball-milling the glass frit into small-sized particles can be carried out whether the frit is to be used wet or dry (see Size reduction). 

Direct evidence of nucleation during the induction period will also solve a recent argument within the field of polymer science as to whether the mechanism of the induction of polymers is related to the nucleation process or to the phase separation process (including spinodal decomposition). The latter was proposed by Imai et al. based on SAXS observation of so-called cold crystallization from the quenched glass (amorphous state) of polyethylene terephthalate) (PET) [19]. They supposed that the latter mechanism could be expanded to the usual melt crystallization, but there is no experimental support for the supposition. Our results will confirm that the nucleation mechanism is correct, in the case of melt crystallization. 

In the case of the higher temperature crystallization, as will be shown in Sect. 4, the theory of Doi et al. is applicable without doubt since the primary phase separation involves the transition from the isotropic to nematic phase, but in the case of the glass crystallization near Tg described above its applicability is unclear since the observed data may correspond to the secondary phase separation. However, if the secondary phase separation occurs, the primary phase separation must have proceeded prior to that. In a rapidly quenched glass even if the primary phase separation had already taken place, it would be still incomplete, so that it will re-start by heating. 

When mixtures of NaH2P04 and NaH2As04 are melted, and the melts are quenched, glasses are formed consisting of polyarsenatophosphates with anions of the type,... 

Fig. 1. Schematic of continuous smelter for porcelain enamel glass production where A is a raw batch hopper B, batch hopper mixer C, screw feeder D, refractory furnace E, burner for gas and air (oxygen) F, spout G, water-cooled rollers for quenching glass H, finger breakers to break glass ribbon I, horizontal vibratory conveyer J, hammer mill K, vertical vibratory conveyer L, surge bin M, rotary magnetic separator N, product container O, exhaust...

The second aspect of lava flows that must be determined is flow emplacement history. Because the calculation of ambient pressure and thus paleoelevation is based on flow thickness at the time the bubbles at the top and base of the flow were trapped in quenched glass, it is critical to be sure that flow thickness did not vary before the entire flow solidified. Inflation and deflation of lava flows is a common process during emplacement, so it is critical in the field to examine the criteria for the identification of inflated, deflated, and simply emplaced flows. Only flows with simple emplacement can be used in paleoelevation analysis. 

Figure 7.9 Thermal expansion behavior of reheated soda-lime-silica glass. The decrease in slope just before Tg implies the thermally induced relaxation of a rapidly quenched glass.

We propose to rationalize the observation by a phenomenon known as residual thermal stresses. Residual thermal stresses arise from the fact that carbon-fiber and epoxy have different thermal expansion coefficients and a quenching of the composite would conceivably produce residual stresses. Apparently, the quenching process may produce enough residual stresses to lower the toughness of the composite. In the absence of such residual stresses the free volume concept alone would predict a quenched glass to have larger amount of free volume and hence constitute a less brittle substance. 

Consider a polymer is quenched from liquid to glass where the sample is annealed. During isothermal annealing, the number of holes is close to a conserved quantity. The local excess of number density of the quenched glass relaxes by spreading slowly over the entire region, and is governed by... 

During isothermal annealing, the frozen-in structure of quenched glass relaxes, and F(r) can be interpreted as the probability that holes have not reached their equilibrium states. The probability of a hole in the ith wave number state having reached equilibrium in a time interval t is (nt/n) (R/l) R/Ll. Thus, we write [12]... 

K2FeSi308 (Waychunas et al., 1988). The EXAFS spectra of the melts along with certain model compounds and a quenched glass are shown in Fig. 8.11. There is no doubt that such direct studies of melts by x-ray absorption and related spectroscopic methods are the techniques of the future. 

Dobson et al. (1995) measured water contents in melt inclusions in pyroxenes in boninites from the Bonin Islands. These melt inclusions contained 2.8-3.2 wt.% H2O, whereas quenched glass from pillow lava rims had 2.2-2.4wt.% H2O, which Dobson et al. interpreted as a result of degassing between the time of entrapment of the melt inclusions and the eruption on the seafloor. They also measured the water content of the orthopyroxene, which contained 80-120 ppm H2O. 

At equilibrium. Tf = T, and the equilibrium version of the Adam-Gibbs theory, discussed earlier, is recovered. For a glass that is not able to relax, T/ is constant, and then follows an Arrhenius temperature-dependence, which accords well with experimental measurements on deeply quenched glasses. 

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