Phase composition glasses

AH commercial as well as most experimental glass-ceramics are based on siUcate bulk glass compositions. Glass-ceramics can be further classified by the composition of thek primary crystalline phases, which may consist of siUcates, oxides, phosphates, or borates. 

Engineering thermoplastics have also been used ia preimpregaated coastmctioas. The thermoplastic is thoroughly dispersed as a coatiauous phase ia glass, other resias, carboa fibers (qv), or other reinforcement. Articles can be produced from these constmctions usiag thermoforming techaiques. For example, the aerospace iadustry uses polyetheretherketoae (PEEK) ia wovea carboa-fiber tapes (26). Experimental uses of other composite coastmctioas have beea reported (27) (see also Composite materials, polymer-matrix). 

Ellison Warrens (1987) have reported NMR results on an atypical phase-separated glass of extreme composition G-309 (Table 5.8) finding... 

A visible sign for the phase separation is that glass exhibits increasing opalescence with increasing temperature. Because the pore sizes are regulated with the annealing temperature (at a constant time and composition) glass becomes completely opaque near the temperature limit of the miscibility gap (800 C). 

For blends consisting of components with sufficiently different glass transition temperatures, like PS/PPE (Tg(PS) = 105 °C, Tg(PPE) = 220 °C),two phases (two glass transition temperatures) can still be detected for the blended powder. However, the melt and the solid obtained from the melt are only composed of a single phase (with only one glass transition temperature, depending on the composition of the blend). 

Glass-ceramics Na20 K2O MgO CaO AI2O3 Si02 P2O5 CaF 2 Phase Composition Bending strength (MPa)... 

The ultimate analysis of a mixture of organic compounds, however important it may be, is not decisive for its structural identification likewise, knowledge of the elementary composition of an alloy is not sufficient to describe its physical and mechanical behaviour, because the nature and phase composition of the alloy are left undetermined. The properties of silicates, e.g. glass, may be greatly influenced by thermal treatment while the chemical composition of the products remains unaltered. 

Oxynitride glasses may be heat treated to form glass-ceramics, effectively multi-phase composites. The process involves heat treatment at two different temperatures, firstly to induce nucleation, then to allow crystal growth of the nuclei. The crystalline phases formed depend on both the composition of the parent glass and the temperatures used for heat treatment. The extent of their formation and growth, the relative amounts and distributions of different phases (including residual glass) and their characteristics will determine the overall properties of the particular composite. The formation of these types of materials and their properties is outlined below. 

Further studies on the crystallisation of B and Iw phase composites from Y-Si-Al-O-N (and Er-Si-Al-O-N) glasses with similar compositions to those... 

As a demonstration of the use of DSC in the characterization of zeolites and related materials, Figure 4.37 illustrates the DSC profile of the LECA zeolite [53], The LECA zeolite has a phase composition of 13 4 [%], in wt %, of gismondine and 87 4 [%] of quartz, anorthite, and glass. The DSC profile presented two endothermic peaks at 112°C and 195°C, and an exothermic peak at 312°C. As is very well known, zeolites evolve adsorbed water in the course of heating [97]. Consequently, the endothermic peaks in the DSC profile of LECA zeolite sample were clearly related to adsorbed water located in different sites of the LECA zeolite surface and the framework of the gismondine contained in the LECA zeolite [53],... 

The mineralogical phase composition of the sample SW [86] (in wt %) is 90% 5% clinoptilolite and 10% 5% others, which include montmorillonite (2-10 wt %), quartz (1-5 wt %), calcite (1-6 wt %), feldspars (0-1 wt %), magnetite (0-1 wt %), and volcanic glass (3-6 wt %). Employing this sample and a pure clinoptilolite, whose TCEC fluctuates between 2.0-2.2 mequiv/g depending on the Si/Al relation of the clinoptilolite monocrystal, it is possible to indirectly evaluate the total cation-exchange capacity of the sample SW as follows ... 

Phase Composition and Simultaneous Polymerization. Theoretically the phase composition of the SIN s should not be determined by the true solubility of one polymer in the other. Even though the true solubility of one polymer in the other is low because the components of the SIN s are incompatible, simultaneous polymerization and gelation are expected to cause entrapment of one component in the other. The degree of entrapment presumably will be controlled by the relative rates of the two reactions and their degree of simultaneity. The phase composition is reflected in the glass transition behavior of the material. Thus a close look at the dynamic mechanical spectra of the SIN s is necessary to determine the effect of simultaneous polymerization on phase composition. 

There are two main sources of drift, both due to non equilibrium conditions in the column and the detector. If the detector, column and mobile phase are not in thermal equilibrium, then serious drift will occur. This can be eliminated by careful temperature control of column and detector. Another and more common source of drift arises when the stationary phase and mobile phase have not been given sufficient time to come into equilibrium. This type of drift often occurs when changing the mobile phase composition and mobile phase should be pumped through the chromatographic system until a stable baseline is achieved. Trace impurities in the mobile phase can cause prolonged drift and longterm noise and so very pure solvents must be used for the mobile phase. Distilled in glass solvents may not necessarily be sufficiently pure to ensure drift-free detector operation. 

In principle, some types of materials of similar phase compositions can be made by sintering powdered mixtures, i.e. by ceramic manufacturing techniques. However, it is impossible to achieve the fine-grained and uniform structures which are the main feature and advantage of glass-ceramics. 

The results of practical tests with glasses and slags indicate that with porous refractories melt infiltration takes place which may change the mineralogical (phase) composition in zones even quite distant from the interface. If the melt penetrates to points of lower temperature, reactions with the melt may create new minerals, in the form of quite distinct zones parallel to the surface. The infiltration can be effected not only through pores but also by faster dissolution of the finer bond between the Coarser grog grains. Such a transformed surface layer may cause faster destruction. 

Chemical reactions between the individual mix components can take place simultaneously with sintering. The initial phase composition is thus changed and new crystalline phases are formed, possibly together with a liquid phase solidifying into a glass, or into a mixture of fine crystals. 

---