Spongy material

The stationary phase matrices used in classic column chromatography are spongy materials whose compress-ibihty hmits flow of the mobile phase. High-pressure liquid chromatography (HPLC) employs incompressible silica or alumina microbeads as the stationary phase and pressures of up to a few thousand psi. Incompressible matrices permit both high flow rates and enhanced resolution. HPLC can resolve complex mixtures of Upids or peptides whose properties differ only slightly. Reversed-phase HPLC exploits a hydrophobic stationary phase of... 

The iron thus produced does not appear to he a useful material, however, since it occurs as spongy material mixed with slag and ash. It is only after these impurities have been removed and the iron has been hammered into a solid mass that it becomes useful for the manufacture of weapons, tools, and other implements. This technology apparently first appeared among the Hittites in about 1500 b.c.e., after which it diffused throughout Anatolia and, eventually, other parts of the world. 

Pith balls Pith is the spongy material found in the center of the stem of most plants. Pith balls are bits of pith attached to a string for use in scientific demonstrations to show how like electrical charges can attract and repel the balls. These days, pith is usually replaced by lightweight plastics in these demonstrations. 

Due to the presence of hollow spheres and spongy material, the density of pfa is difficult to define. The smaller spheres are not readily broken by grinding, and values of 2100-2400 kg m", increasing with iron oxide content, are typical (K44), but these must be influenced by the presence of... 

Bone is the hard material that forms the skeleton of most vertebrate animals. It consists of a network of collagen fibres impregnated with mineral salts, mostly calcium phosphate. Bone varies in strength and can be as tough as reinforced concrete. Most bones are hollow, the cavity being filled with soft, spongy material. The solid part is interspersed by Haversian canals, which are tiny canals carrying blood, nerves and lymphatics. 

The measurement of surface areas and Af/j has increased our knowledge of surface structure enormously and is particularly valuable in the study of catalysts. One important point to note is that the actual area of any solid surface is substantially greater than its apparent geometric area. Even a mirror-smooth surface has hills and valleys on the atomic scale the actual area is perhaps 2 to 3 times the apparent area. For finely divided powders or porous spongy material the ratio is often much higher 10 to 1000 times in some instances. 

After the reaction has been completed, decant the liquid (Laboratory Methods H), and wash the lump of spongy material several times with cold water. Carefully examine the product for stretch and bounce. Describe what you observe in TABLE 32.1B4. 

Nickel is an important catalyst, e.g. for the hydrogenation of unsaturated organic compounds and in the water-gas shift reaction (see Section 10.4). Raney nickel is prepared by treating a NiAl alloy with NaOH and is a spongy material (pyrophoric when dry) which is a highly active catalyst. 

The shape, roughness, and size of the particles determine their contact area and hence affect the packing density and autohe-sive interaction. The greatest autohesion occurs for powder prepared from spongy material, for example metallic sponge, and the least for powders consisting of spherical particles. The shape of the majority of metallic powders differs appreciably from spherical. 

Soft white spongy material found in the center of certain plant stems. It is not usually consumed as a food. 

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