Elastic powder

Tamarind kernel powder is insoluble in cold water, but upon heating forms thick viscous coUoidal dispersions at relatively low concentrations (2—3%). Upon drying, elastic films are formed. Tamarind seed polysaccharide is used as a low cost textile sizing agent in India. 

Beryllium and aluminum are virtually insoluble in one another in the soHd state. The potential therefore exists for an aluminum—beryllium metal matrix composite with lower density and higher elastic modulus, ie, improved specific modulus, than conventional aluminum alloys produced by ingot or powder metal processing. At least one wrought composite system with nominally 62 wt % Be and 38 wt % A1 has seen limited use in aerospace appheations (see Composites). 

The high elastic modulus, compressive strength, and wear resistance of cemented carbides make them ideal candidates for use in boring bars, long shafts, and plungers, where reduction in deflection, chatter, and vibration are concerns. Metal, ceramic, and carbide powder-compacting dies and punches are generahy made of 6 wt % and 11 wt % Co ahoys, respectively. Another apphcation area for carbides is the synthetic diamond industry where carbides are used for dies and pistons (see Carbon). 

Most ceramics (as we have seen) contain flaws holes and cracks left by processing, cracks caused by thermal stress, corrosion or abrasion. Even if there are no cracks to start with, differences in elastic moduli between phases will nucleate cracks on loading. And most of these flaws have a size which is roughly that of the powder particles from which the ceramic was made. If the flaw size can be reduced, or if samples containing abnormally large flaws can be detected and rejected, the mean strength of the ceramic component is increased. 

Tensile Strength of Cast Double-Base Powder as a Function of Nitrocellulose Content P 423 Elongation of Cast Double-Base Powder as a Function of Nitrocellulose. Content. .. P 423 Modulus of Elasticity of Cast Double-Base Powder as a Function of 1 1 ... 

Fig 4 Modulus of elasticity of cast double-base powder as a function of nitrocellulose content... 

Higuchi et al. [98] postulated that an additional increase in surface area occurs after this point and that this effect may cause lamination of the tablet due to extensive rebound at decompression. In other words, at the tablet punch powder interface, there may be zones of high density during compression, but upon decompression these zones have elastic rebound and are pulled apart from the rest of the tablet that did not contain this high density. 

Another approach to determining the contribution being made by each of the possible com-pression/decompression mechanisms involves monitoring the degree and rate of relaxation in tablets immediately after the point of maximum applied force has been reached. Once a powder bed exceeds a certain yield stress, it behaves as a fluid and exhibits plastic flow [121,122], Certain investigators [122] have studied plastic flow in terms of viscous and elastic elements and have derived the following equation ... 

There are now many synthetic polymeric materials available for film coating, many of which meet all the requirements of a good film former. These include lack of toxicity and a suitable solubility profile for film application and upon ingestion, together with the ability to produce a tough, yet elastic film even in the presence of powdered additives such as pigments. The film must, of course, be stable to heat, light, and moisture and be free from undesirable taste or odor. 

Rietma, K., Cottaar, E. J. A., and Piepers, H. W., The Effect of Interparticle Forces on the Stability of Gas-fluidized Beds — II. Theoretical Derivation of Bed Elasticity on the Basis of Van der Waals Forces between powder Particles, Chem. Eng. Sci., 48 1687 (1993)... 

The mechanical properties of a material play an important role in powder flow and compaction by influencing particle-particle interaction and cohesion, that is to say, by influencing the true area of contact between particles. For example, Hertz [26] demonstrated that both the size and shape of the zone of contact followed simply from the elastic properties of a material. Clearly then, the true area of contact is affected by elastic properties. From the laws of elasticity, one can predict the area of contact between two elastic bodies. More recent work has demonstrated, however, that additional factors must be taken... 

The mechanical properties of materials, though not often studied in detail, can have a profound effect on solids processing. Clearly, tableting properties are influenced by the elastic and plastic deformation properties as well as the viscoelastic properties of a material. As we have pointed out, the powder flow properties are also affected, as well as the tendency of materials to set up on storage. Because of the importance of mechanical properties, it is important to be able to... 

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