Quartz deformation

The following subsections are concerned with the grown-in defects in synthetic quartz and the dislocation microstructures associated with the various stages of the creep and stress-strain curves. The microstructural evolution in natural quartz deformed under various conditions of water fugacity, and other experimental variables, will be considered in Section 9.5. 

Figure 9.10. BF image (g = lOTl) of the dislocation microstructure in a specimen of wet synthetic quartz deformed about 0.3 percent in creep with an axial stress of 100 MPa normal to (lOTl) at 550°C for 30 minutes, after a preheat of 2 hours without a load. (From McLaren et al. 1989.)...

Figure 9.16. BF images (g = lOU) showing the dislocation microstructure in wet synthetic quartz deformed at 475°C and subsequently annealed at atmospheric pressure at 600°C for 2 hours. Note the bubbles in (a) and the dislocation networks in (b). This microstructure should be compared with that shown in Figure 9.IS.

Figure 9.19. Stress-strain curves for single crystals of natural quartz deformed in buffered assemblies at 1.64 GPa confining pressure, 800°C, and strain-rate of 10 s after 20 hours preconditioning. (From Ord and Hobbs 1986.)...

Kekulawala, K. R. S. S., Paterson, M. S., Boland, J. N. (1981). An experimental study of the role of water in quartz deformation. In Mechanical Behaviour of Crustal Rocks, The Handin Volume, Geophysical Monograph 24, edited by N. L. Carter, M. Friedman, J. M. Logan, D. W. Stearns, pp. 49-60. Washington, DC American Geophysical Union. 

Cements cc, calcite qz, quartz. Deformation characteristics IFF, interparticulate flow Ph, enrichment of phyllosilicates CS, clay smear ShS, shale smear BR, brecciation CC, cataclasis. 

Figure 9.14 Stress-strain curves of quartz deformed in compression under a confining pressure of 1.6 C Pa in various buffered assemblies at 800°C and a strain rate of 10 s The effective water content increases from the top to the bottom curve. Data from Ref. [87].

Dislocation-dissociation in quartz was first observed by McLaren ef al. [32] in a natural dry quartz deformed at 500 °C, and has been studied most recently by Cordier and Doukhan [33] in a synthetic crystal containing 100 at. ppm [H]/[Si]. By using a crystal oriented to have high Schmid factors for (0001)1/3 (1120)basal slip, 1120 [0001] prismplaneslip, and 1010 1/3 (1213) pyramidal slip, and deformed under a hydrostatic pressure of 1.0-1.1 GPa, Cordier and Doukhan found a flow stress at 500 °C of almost 3 GPa, which decreased to 2 GPa at 900 °C. These high flow stresses correspond to a significant fraction of the shear modulus and reflect the fact that the quartz is relatively dry. Slip at 500 °C was heterogeneous (in slip bands). 

Hardness. The Knoop indentation hardness of vitreous sihca is in the range of 473—593 kg/mm and the diamond pyramidal (Vickers) hardness is in the range of 600—750 kg/mm (1 4). The Vickers hardness for fused quartz decreases with increasing temperature but suddenly decreases at approximately 70°C. In addition, a small positive discontinuity occurs at 570°C, which may result from a memory of quartz stmcture (165). A maximum at 570°C is attributed to the presence of small amounts of quartz microcrystals (166). Scanning electron microscopic (sem) examination of the indentation area indicates that deformation is mainly from material compaction. There is htfle evidence of shear flow (167). 

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

Resins are also used for permanent tooth-colored veneers on fixed prostheses, ie, crown and bridges. Compositions for this application include acryflcs, vinyl—acryflcs, and dimethacrylates, as well as silica- or quartz-microfilled composites. The resins are placed on the metallic substrates of the prostheses and cured by heat or light. These resins are inexpensive, easy to fabricate, and can be matched to the color of tooth stmcture. Acrylic facings do not chemically adhere to the metals and are retained only by curing the resin into mechanical undercuts designed into the metal substrate. They have relatively low mechanical strength and color stability, and poor abrasion and strain resistance they also deform more under the stress of mastication than porcelain veneers or facings. 

Thin sheets of mica or polymer films, which are coated with silver on the back side, are adhered to two cylindrical quartz lenses using an adhesive. It may be noted that it is necessary to use an adhesive that deforms elastically. One of the lenses, with a polymer film adhered on it, is mounted on a weak cantilever spring, and the other is mounted on a rigid support. The axes of these lenses are aligned perpendicular to each other, and the geometry of two orthogonally crossed cylinders corresponds to a sphere on a flat surface. The back-silvered tbin films form an optical interferometer which makes it possible... 

The piezoelectric response investigation also provides direct evidence that significant inelastic deformation and defect generation can occur well within the elastic range as determined by the Hugoniot elastic limit. In quartz, the Hugoniot elastic limit is 6 GPa, but there is clear evidence for strong nonideal mechanical and electrical effects between 2.5 and 6 GPa. The unusual dielectric breakdown phenomenon that occurs at 800 MPa under certain... 

In this chapter studies of physical effects within the elastic deformation range were extended into stress regions where there are substantial contributions to physical processes from both elastic and inelastic deformation. Those studies include the piezoelectric responses of the piezoelectric crystals, quartz and lithium niobate, similar work on the piezoelectric polymer PVDF, ferroelectric solids, and ferromagnetic alloys which exhibit second- and first-order phase transformations. The resistance of metals has been investigated along with the distinctive shock phenomenon, shock-induced polarization. 

Piezoelectric energy is a form of electric energy produced by certain solid materials when they are deformed. (The word piezo has its roots in the Greek word piezein meaning to press. ) Discovery of the piezoelectric effect is credited to Pierre and Jacques Curie who observed in 1880 that certain quartz crystals produced electricity when put under pressure. 

Ceramic materials are typically noncrystalline inorganic oxides prepared by heat-treatment of a powder and have a network structure. They include many silicate minerals, such as quartz (silicon dioxide, which has the empirical formula SiO,), and high-temperature superconductors (Box 5.2). Ceramic materials have great strength and stability, because covalent bonds must be broken to cause any deformation in the crystal. As a result, ceramic materials under physical stress tend to shatter rather than bend. Section 14.22 contains further information on the properties of ceramic materials. 

The susceptibility of hardness measurements of silica and silicate glasses to environmental factors is consistent with the effects of water on the deformation of quartz. The load effect and indentation size effect appear to be a result of the frictional forces at the indenter-specimen interfaces. 

Wintsch ana Dunning (8) calculated that the solubility of plasticly deformed quartz in water should not be significantly higher than the ideal equilibrium value. However, enhanced dissolution at dislocations could significantly increase the dissolution... 

In order to determine the efficiency of the surface production process, tests were carried out with sodium chloride and it was found that 90 J was required to produce 1 m2 of new surface. As the theoretical value of the surface energy of sodium chloride is only 0.08 J/m2, the efficiency of the process is about 0.1 per cent. Zeleny and Piret(18) have reported calorimetric studies on the crushing of glass and quartz. It was found that a fairly constant energy was required of 77 J/m2 of new surface created, compared with a surface-energy value of less than 5 J/m2. In some cases over 50 per cent of the energy supplied was used to produce plastic deformation of the steel crusher surfaces. 

To model this, Duncan-Hewitt and Thompson [50] developed a four-layer model for a transverse-shear mode acoustic wave sensor with one face immersed in a liquid, comprised of a solid substrate (quartz/electrode) layer, an ordered surface-adjacent layer, a thin transition layer, and the bulk liquid layer. The ordered surface-adjacent layer was assumed to be more structured than the bulk, with a greater density and viscosity. For the transition layer, based on an expansion of the analysis of Tolstoi [3] and then Blake [12], the authors developed a model based on the nucleation of vacancies in the layer caused by shear stress in the liquid. The aim of this work was to explore the concept of graded surface and liquid properties, as well as their effect on observable boundary conditions. They calculated the hrst-order rate of deformation, as the product of the rate constant of densities and the concentration of vacancies in the liquid. 

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