Glassy structure

Glasses are oxides which have hardened and become rigid without crystallizing. The glassy structure consists of silica tetra-hedra or other ionic groups that provide a solid, non-crystalline structure. 

The Fourier transforms for both films are again quite similar, but as for the ex situ measurements, the chromate-passivated films appear to have a more glassy structure. It should be mentioned that these studies employed a rather limited data range which makes spectral differentiation difficult. 

Figure 14.1 Schematic comparison of dislocation lines in a crystalline and a glassy structure. Dashed line indicates the center of a dislocation line. The vectors indicate the displacement of the atoms in the next level above the plane of the figure. At (a) the displacement (Burgers) vectors In the periodic crystal have a constant value. At (b) the displacements in the glass fluctuate in both magnitude and direction.

The stress needed to move a dislocation line in a glassy medium is expected to be the amount needed to overcome the maximum barrier to the motion less a stress concentration factor that depends on the shape of the line. The macro-scopic behavior suggests that this factor is not large, so it will be assumed to be unity. The barrier is quasi-periodic where the quasi-period is the average mesh size, A of the glassy structure. The resistive stress, initially zero, rises with displacement to a maximum and then declines to zero. Since this happens at a dislocation line, the maximum lies at about A/4. The initial rise can be described by means of a shear modulus, G, which starts at its maximum value, G0, and then declines to zero at A/4. A simple function that describes this is, G = G0 cos (4jix/A) where x is the displacement of the dislocation line. The resistive force is then approximately G(x) A2, and the resistive energy, U, is ... 

The visual observation of the condenser coils shows, in the visible zone, a compact solid, glassy structure. Inclusions of permanent gasses resulting in snow like surfaces were not seen. 

When a silicate solution such as sodium silicate is acidified, a gel of polymeric colloidal silicilic acid is formed as an agglomerate of micro-particles. When the gel is heated, water is expelled leaving a hard, glassy structure with voids between the micro-particles equivalent to a mean pore diameter of about 3 nm and an internal surface of about 500,000 m2/kg. As discussed by Everett and Stone(8) these properties may be varied by controlling the pH of the solution from which the gel is precipitated. 

Metastable amorphous materials can be produced by the rapid quenching of melts in the form of metallic alloys with glassy structures [149]. These materials have attracted the attention of metallurgists, physicists, and, recently, chemists because of their exceptional properties (easy magnetisation, superior corrosion resistance, high mechanical toughness, interesting electronic properties) [150]. The use of these materials in catalysis was reported some years ago [151]. 

Recent systematic studies on the relation between network structure and substituents in kraft lignin, steam exploded, have shown that the lignin containing networks can be modified in new ways, cf. e.g. (80). Also the toughening of glassy, structural thermosets can be achieved by incorporating a variety of polyether and rubber-type soft segment components in the polymer network structure. 

The observation that the self-diffusion exhibits Arrhenius behavior is consistent with a direct collective mechanism because the thermally activated displacement chains are spread over a considerable number of atomic distances. Irregularities in the disordered glassy structure are therefore averaged in the activated state, and all activation energies for displacements are then closely... 

In the case of 3,5 substitution, the excluded volume from the rotation of the disubstituted phenyl is large leading to an increased free volume. The local motions thus becomes easier in the glassy state. On the contrary, the 2,5 substitution, for which the net effect of the steric hindrance, the overall bulkiness of the substituents and absence of dipole-dipole interaction result in a higher segmental mobility, has not an important available free volume in the glassy structure. The... 

Part of the volcanism in the deep sea produces volcanic ash — small glassy splinters of basaltic matter, which widely occur in deep- sediments. This material (called pyroclastica) weathers relatively quickly because of its instable glassy structure and large surface. How far it contributes to the manganese supply of the deep sea, we cannot say yet, but Beiersdorf considers that it plays a dominant role in the creation of manganese nodule fields. 

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