Excess hydroxyl

Synthetic Ge-muscovite crystals exhibit a Ge deficiency and an excess of A1 and display additional OH vibrations at 3480 and 1165 cm compared to ideal Ge-muscovite (Ackermann et al. 1993). The substitution mechanism Ge + O = Al + OH leads to Ge-muscovites with the general formula KAl2(Ge3-xAli+x Oio-x(OH)x)(OH)2 (x = 0.15). The additional OH groups presumably replace some of the apical oxygen atoms of the tetrahedral sheet. This substitution is likely to occur in tetrahedra occupied by Al. The normal OH stretching vibration of muscovite at 3629 cm is found at 3640 cm in single-crystal spectra of Ge-muscovite. The bands at 3640, 3480, and 1165 cm show a similar pleochroic behaviour within the ac plane. 

Excess OH in partially dioctahedral micas of the K20-Mg0-Be0-Si02-H20 system, described as a TMM-KMg3(Si3.5M o.5)Oio(OH)2 solid solution series with tetrahedrally coordinated cations, were reported by Robert et al. (1995). This is demonstrated by the increase of a broad band at 3700 cm The most likely hydrogen acceptors are the strongly underbonded apical oxygens of (Be or Mg) tetrahedra adjacent to two octahedrally coordinated Mg and an octahedral vacancy. 

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Table 7. Excess Hydroxyl Content Required in Alkyd Formulations...

Noncarbonate or permanent calcium hardness, if present, is not affected by treatment with lime alone. If noncarbonate magnesium hardness is present in an amount greater than 70 ppm and an excess hydroxyl alkalinity of about 5 ppm is maintained, the magnesium will be reduced to about 70 ppm, but the calcium will increase in proportion to the magnesium reduction. 

Paints used for protecting the bottoms of ships encounter conditions not met by structural steelwork. The corrosion of steel immersed in sea-water with an ample supply of dissolved oxygen proceeds by an electrochemical mechanism whereby excess hydroxyl ions are formed at the cathodic areas. Consequently, paints for use on steel immersed in sea-water (pH 8-0-8-2) must resist alkaline conditions, i.e. media such as linseed oil which are readily saponified must not be used. In addition, the paint films should have a high electrical resistance to impede the flow of corrosion currents between the metal and the water. Paints used on structural steelwork ashore do not meet these requirements. It should be particularly noted that the well-known structural steel priming paint, i.e. red lead in linseed oil, is not suitable for use on ships bottoms. Conventional protective paints are based on phenolic media, pitches and bitumens, but in recent years high performance paints based on the newer types of non-saponifiable resins such as epoxies. 

Because of the definition of acidity and pH, we can conclude that liquids with a pH of less than 7 are acidic, and have excess hydrogen ions, and that pHs greater than 7 are basic, with excess hydroxyl ions. Because of the autodissociation of water, however, the concentrations of hydrogen ions and hydroxyl ions (i.e., pH and pOH) are inextricably linked, but calculable through the above simple formula. 

TABLE 3. EXCESS HYDROXYL CONTENT REQUIRED IN ALKYD... 

Fig. 1. Steps in the formation of an olefin polymerization catalyst. Chromium is thought to bind the high-surface-area carrier by reaction with hydroxyl groups. Activation is accomplished by calcining the support at a temperature of 600° C or higher, which removes much of the excess hydroxyl group population.

This equation sets the pH scale to 0-14, which gives a convenient way to express 14 orders of magnitude of [H ]. Any solution with pH > 7 contains excessive hydroxyl ions, and is alkaline those with pH < 7 are acidic, containing excess hydrogen ions. Figure 2 shows pH values of common fluids. 

In fact, these cyclic trimers may be incorporated into silicone resins of the type employed in surface coatings. In such products, a silanetriol is incorporated to cross-link the resin (this cross-linking reaction has been previously described) and to allow the presence of excess hydroxyl groups after resin preparation. These materials containing excess hydroxyl groups are then applied to a substrate as a surface coating and subsequently cured via a thermal cycle of up to 60 min at 500 °F. When catalyzed, their cure cycle may be reduced to 30-60 min at 400 °F. Some typical catalysts and the levels at which they are usually employed are listed in Table II. 

Ackermann L, Langer K, Rieder M (1993) Germanium muscovites with excess hydroxyl water, KAl2lGe3. xA1i+xOio-x(OH)x(OH)2] and the question of excess OH in natural muscovites. Eur J Mineral 5 19-29... 

This reaction is associated with the formation of new isocyanate groups, which immediately add to excess hydroxyl groups to form more urethane species. The emergence of carbodiimide is still incomplete after 4 h of post-curing in films on Au and A1 and in the bulk. Only on copper are no carbodiimide bands observed after post-curing, even in thick films (e.g., dpu = 2pm in Fig. 6.7). Instead, a new chemical species develops with an IR band at 1660 cm , which is probably a reaction product of the carbodiimide consumption. 

In reaction (1), the metal tungsten is oxidized to tungstate (WO3). In reaction (2), the tungstate becomes ion (WO ") by reacting with excess hydroxyl ions and remains dissolved in the electrolyte. In reaction (3), water is converted to hydroxyl ions and hydrogen evolves speedily at the cathode. 

Poly(vinyl alcohol) (PVA) is one of the hydrogels most often used in biomaterial applications. Because of the presence of excessive hydroxyl groups, PVA contained a significant amount of water. PVA was also claimed to have good mechanical strength. Another hydrogel, poly(2-hydroxyethyl methacrylate) (poly-HEMA), is well known for its excellent biocompatibility. xhe versatile biomedical applications of poly-HEMA are demonstrated by its uses in contact lenses, vitreous humor replacements and suture materials. To explore a new formulation and other usages of these two pol ers, we have copolymerized HEMA with PVA-MA (PVA esterified with maleic anhydride), the preparation and properties of this copolymer are discussed in this article. 

Medium oil length mahua oil-based pentalkyds (polyesters) were prepared with varying degrees of excess hydroxyl, which was converted into liquid crystalhne form by copolymerising with p-hydroxybenzoic acid in the presence of dicyclohexyl carbodiimide (DCC) (Fig. 4.3). An improvement was observed in the resistance to scratching and the drying time of the hquid crystalhne resins. These have low viscosity and good film properties. 

Earlier work recommends a molecular excess of the hydroxyl compound to favor the formation of the monomers. However, the excess hydroxyl compounds can be a negative during the final sulfonation and would require removal by distillation or other separation means. It has been discovered that small amounts of higher oligomers actually have some benefits in the sulfonated product and is discussed in more detail in Section 8.5. An excess of 5 molar percent of the epichlorohydrin is recommended to maximize the amount of monomer as seen in Figure 8.2. If a purified monomer is desired, the oligomers can be separated through distillation but with increased production costs. 

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