Kaolin structured

The 1 1 kaolin structures are chemically simpler the tetrahedral sites are occupied by silicon and the octahedral sites by aluminum. There is a minor amount of substitution, largely of ferric iron for aluminum, but the amounts are generally only a few tenths of a percent by weight of oxide. The kaolin minerals do not expand in the presence of water and their surface area, approximately 10 to 15 m2/g, represents the external area of the crystals. 

Figure 3.7. Schematic of the kaolin structure showing one silicate and one gibbsite sheet in each layer, which has been expanded along the c-axis to show bonding. The basic unit is repeated along the two horizontal axes to form layers. Adjacent layers are held together by hydrogen bonding (from Taylor and Ashcroft, 1972, with permission).

Figure 3.11 Stmcture of one layer of the ideal kaolin structure, (Al(OH)2)2. 0.(8102)2- [Reproduced with permission from R. J. Hunter, Foundations of Colloid Science, Vol. I, Oxford University Press, Oxford (1989)]...

Pyrophyllite - If the kaolin structure is boimd through shared oxygens to a layer of silica rings on its alumina side, the pyrophyllite structure of Figure 9 results. Because both faces of a pyrophylHte platelet are composed of silica oxygens, interlaminar bonding is by relatively weak van der Waals forces. Pure pyrophylhte is therefore soft with talc-like slipperiness, because its laminae will slide past each other or separate fairly easily. 

Radoslovich [1963] and Bailey [1966], making use of earlier studies and of many studies on related minerals, have made painstaking analyses of the nature and causes of the distortions in the kaolin structures. Much still remains to be proved, however, and there is no doubt that further advances will soon be made. 

Figure 11. The ideal trioctahedral kaolin structure projected on the Oyz plane.

It is likely that the amount of tetrahedral rotation is governed primarily by the misfit within the 2 1 layer, but that the interlayer sheet has a secondary and modifying influence on a and on b (obs.). This influence can be seen especially well in the dioctahedral chlorites. Chlorites with two dioctahedral sheets have b (obs.) values near 8.94 A, similar to b (obs.) for the dioctahedral kaolin minerals. Most chlorites, believed to have a dioctahedral 2 1 layer, but a larger and trioctahedral interlayer sheet, have b (obs.) near 9.05 A so that the interlayer sheet is probably stretching the 2 1 octahedral sheet and reducing the amount of tetrahedral rotation required. The interlayer sheet itself must be compressed within the (001) plane and thickened. This misfit of 2 1 layer and interlayer sheets would be minimized by restricting the amount of tetrahedral substitution, as is often observed. Cookeite also has di,trioctahedral sheets, but b (obs.) is smaller and quite similar to b (obs.) for the kaolin minerals. The reason for this similarity is that the composition of the interlayer sheet in cookeite is 2A1 -1- ILi. The Li is just about the right size to fit in the octahedral site that is normally vacant in a kaolin structure. 

In the pulp and paper industry, anionic and cationic acrylamide polymers are used as chemical additives or processing aids. The positive effect is achieved due to a fuller retention of the filler (basically kaoline) in the paper pulp, so that the structure of the paper sheet surface layer improves. Copolymers of acrylamide with vi-nylamine not only attach better qualities to the surface layer of.paper, they also add to the tensile properties of paper in the wet state. Paper reinforcement with anionic polymers is due to the formation of complexes between the polymer additive and ions of Cr and Cu incorporated in the paper pulp. The direct effect of acrylamide polymers on strength increases and improved surface properties of paper sheets is accompanied by a fuller extraction of metallic ions (iron and cobalt, in addition to those mentioned above), which improves effluent water quality. 

Kaolin, China clay, terra alba, argille, porcelain clay, and white bole are the generic names used to refer to primary clays that include three distinct white minerals - kaolinite, nacrite, and dickite - all of which share a very similar composition but differ slightly in their structure. Kaolin is rarely found pure, but as a natural mixture with other varieties of clay together, the various clays make up over 95% of the total weight of the mixture, other earthy... 

Halloysite Similar in composition to kaolin but of different structure... 

In addition to the ICDD, publications dealing solely with the powder patterns of drugs appear occasionally [12-15], In 1971, Sadik et al. pointed out that the identification test for kaolin (in NF XIII) was a test for the presence of aluminum, and therefore both kaolin and bentonite gave positive results [16]. Since the two compounds have different crystal structures, their x-ray diffraction patterns are different, and therefore XPD was recommended for identification of these compounds. In the current edition of USP, the identification of bentonite is based on its powder x-ray pattern [3]. 

Kaolinite, 2 345t 6 659-664, 686-687, 718 composition in bauxite used for alumina production, 2 346t structure and composition, 6 668 in unit layer mixtures, 6 671 Kaolins, 6 686. See also Kaolin dry process, 6 673-675 estimated total production, 6 683 grades for polymer applications, 6 694t properties relating to applictions, 6 686t uses, 6 686-696 wet process, 6 675-679 Kapok, 11 297... 

The two types of clay mineral structures which are of interest in the present discussion are the expanding 2 1 structures (the smectites and vermiculites) and the 1 1 structures (the kaolins). 

Kaolin Minerals. The 1 1 structures include a group of aluminosilicate minerals which are termed collectively the kaolin minerals specifically these are kaolinite, dickite, nacrite, and halloysite. The basic 1 1 layer for all of these minerals has the composition AlgSigOj-fOHJj, there is a small amount of substitution of iron for aluminum, ana fluoride for hydroxyl ion. All, except halloysite, are normally anhydrous and do not expand (as do the smectites) upon exposure to water and most organic molecules. As a result, they generally have a rather small surface area, on the order of 10 nr... 

Phyllosilicates are clay-related compounds with a sheet structure such as talc, mica, kaolin, etc. for which the nucleation mechanism of PET is known to be heterogeneous, although still uncertain. 

Tubular fibrous morphology has also been described for a hydrated kaolin (Honjo et al., 1954), a mineral known to have a structure different from that of kaolinite or halloysite. 

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