Brittle materials recovery

Metallic Versus Ceramic/Brittle Materials Recovery... 

While the structure/property behavior of numerous shock-recovered metals and alloys has received considerable attention in the literature to date, the response of ceramics, cermets, and other brittle solids (including geological materials) to shock loading remains poorly understood [9], The majority of shock-recovery studies on brittle materials have concentrated on examining... 

Figure 6.11. Schematic drawing of a shock-recovery assembly for brittle materials.

Plastics generally have intermediate tensile moduli, usually 0.5 x 1O to 4 x 1O psi (3.5 X 10 to 3 X 10 MN/m ), and Iheir breaking strain varies from a few percent for brittle materials like polystyrene to about 400% for tough, semicrystalline polyethylene. Their strain recovery behavior is variable, but the elastic component is generally much less significant than in the case of fibers (Fig. I-3c). Increased temperatures result in lower stiffness and greater elongation at break. 

The Tg of PAA has been variously reported as 75,106, and 126°C, depending on the mode of measurement. However, the highest value is probably the most accurate. Solid polymers are hard, clear, brittle materials. In aqueous solutions, viscosity increases with increasing molecular weight. PAA imdergoes a munber of reactions in solution, ie, hydrolysis, esterification, dehydration, and complex formation with polyethers. PAA is an excellent thickener for lattices. PAA has been used in oil recovery, as a dispersant for inorganic pigments, as a flocculant, and as an adhesive. 

In this chapter, we will review the effects of shock-wave deform.ation on material response after the completion of the shock cycle. The techniques and design parameters necessary to implement successful shock-recovery experiments in metallic and brittle solids will be discussed. The influence of shock parameters, including peak pressure and pulse duration, loading-rate effects, and the Bauschinger effect (in some shock-loaded materials) on postshock structure/property material behavior will be detailed. 

Observations of the specificity of indentations, excluding measurement of the magnitude of Vickers pyramid penetration, enable a description of the properties of minerals, ceramic materials, or other brittle bodies (Vigdo-rovich and Yelenskaya, 1967 A. Szymanski et al., 1969). The action of elastic-recovery forces after removal of the pressure often causes perturbation in the structure of the test surface, around the site subjected to loading (Fig. 6.3.1). This is described in Section 6.2. 

If desired, the methylmagnesium carbonate can be recovered as a white, brittle solid by evaporation of the solution under vacuum at temperatures up to 100°C. Unlike magnesium methoxide, which becomes almost completely insoluble on recovery as a solid, methylmagnesium carbonate solid is very soluble in methanol but tends to dissolve faster if the methanol is presaturated with carbon dioxide. The solid form provides a convenient method of storage or shipment of the material, much like instant coffee. 

Recovery of properties already lost through aging would require efforts to modify molecular order along two lines. The first would involve a decrystallizing treatment that can reduce the dimensions of the brittle domains and increase the capacity of fibers to respond to deformation in an elastic mode. Although a number of approaches to decrystallization of cellulosic materials are available, most are unsuited for conservation applications. This approach might be pursued in search of suitable methods. 

As mentioned previously, for certain types of products, precompression at a force level higher than that of main compression may increase tablet hardness. The author has found that for materials that primarily undergo brittle fracture, application of a precompression force higher than the main compression force can result in a higher tablet hardness. However, this is typically not the case for materials with elastic properties (e.g., products prone to capping and lamination) because these products require gradual application of force to minimize elastic recovery and allow stress relaxation. 

Hiestand Tableting Indices Likelihood of failure during decompression depends on the ability of the material to relieve elastic stress by plastic deformation without undergoing brittle fracture, and this is time-dependent. Those which relieve stress rapidly are less likely to cap or delaminate. Hiestand and Smith [Powder Technol., 38, 145 (1984)] developed three pharmaceutical tableting indices, which are applicable for gener characterization of powder com-pactiability. The strain index (SI) is a measure of the elastic recovery following plastic deformation, the bonding index (BI) is a measure of plastic deFormation at contacts and bond survival, and the brittle fracture index (BFI) is a measure of compact brittleness. 

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