Alkaline attack

The accelerating effect of turbulence in alkaline attack on aluminum alloys is well illustrated in this case history. 

Conventional mineral dressing yields concentrates of the minerals of better than 90% purity. These can then be broken down ( opened ) by either acidic or alkaline attack, the latter being more usual nowadays. Details vary considerably since they depend on the ore being used and on the extent to which the metals are to be separated from each other, but the schemes... 

An aluminium ladder was used (instead of the usual wooden one) to gain access to a tank containing the alkaline arsenical mixture. Hydrogen produced by alkaline attack on the ladder generated arsine, which poisoned the three workers involved. 

During the distillation of hexane from potassium hydroxide pellets, it was found that the 2 1 flask had become perforated by alkaline attack, and that hexane was leaking through two pinholes, generating much flammable vapour. The high rate... 

For most pH values and at most potentials, titanium is passive and no corrosion takes place. This is revealed by the white areas of Fig. 23.2. However, there are some exceptions. Consider alkaline attack (Fig. 23.3). It is occasionally assumed that titanium cannot be used in the alkaline conditions of hypochlorite and excess alkalinity, etc. Corrosion data do not sustain this assumption. It is only at high temperatures and high concentrations that corrosion becomes a factor of concern, as does the increase in erosion under such conditions. 

The major unknown in the cathodic delamination process is the mechanism by which the interfacial bond is broken. Alkaline attack of the polymer, surface energy considerations, and attack of the oxide at the interface have all been proposed, but none of the available evidence allows an unequivocal answer. 

Because of its high chemical inertia, the chemical modification of PTFE may appear as a challenge. However, although this polymer resists to acidic or alkaline attacks. 

A large number of archaeological artifacts are found in burial conditions. Water acting as a solvent, as well as a carrier of ionic species coming from the soil, is responsible for the migration of the latter—the acid/alkaline attack on the object material and further lixiviation of materials and ionic species from the object. Thus, determination of physical and chemical properties of the soil (pH, conductivity, chemical composition, etc.) is of great importance. 

Nickel confers excellent resistance to alkaline attack and to stress-cracking corrosion and is also quite resistant to nonoxidizing acids. It is widely used to the extent of a few percent in stainless steels (300 series, see Section 16.8), and in several high nickel alloys, including the following proprietary metals ... 

The cellulose polymer exhibits a greater resistance to alkaline attack, which, unlike the random progress of acid hydrolysis, occurs only at the ends of... 

Fibre-included weighting agents can promote hydrolysis of the fibroin -e.g. over time tin salts are themselves hydrolysed to amphoteric species that can affect both acid and alkaline attack. 

Alumino-silicates are known to be less soluble in alkaU than pure silica and Sears [9] used this fact to produce and patent a product having a high degree of alumina surface modification which resisted alkaline attack and therefore would retain a high pH for a longer period. This allowed it to be a more effective polishing agent. 

Long-chain silanes are stable against alkaline attack. 

Long-chain siloxanes are stable to alkaline attack. Rapid reaction to form silicone resin network. 

Acid-catalysed hydrolysis of PET is facilitated by carboxyl end groups in the polymer, but this is not the case with alkaline-catalysed hydrolysis. The reaction is therefore largely confined to the outer layers of a substrate under alkaline attack, although the irreversibility of the reaction and likely removal of products from the reaction site means that prolonged exposure can result in the gradual eating away of the polymer. This phenomenon has been used to good effect by the fibre industry, where alkaline treatments have been used to produce aesthetically useful effects on fabric surfaces [22, 23]. 

Even without added stabilizer, however, part of the poly(oxymethylene) molecules are stable toward alkaline attack. The reason for this is not quite clear. Three transfer reactions are conceivable ... 

The improved thermal and chemical stability of the copolymer vs. the homopolymer is a result of randomly distributed oxyethylene groups, which is circled in Figure 3.26. All poly acetals are subject to oxidative and acidic degradation, which leads to molecular weight decline. Deterioration in the copolymer ceases, however, when one of the randomly distributed oxyethylene linkages is reached. These groups offer stability to oxidative, thermal, acidic, and alkaline attack. The raw copolymer is hydrolyzed to an oxyethylene end cap to provide thermally stable polyacetal copolymer. 

On the other hand, when binary zirconia-silica aerogel is considered, the resulting materials exhibit superior chemical resistance to alkaline attack [54], fracture toughness [55], and optical properties. 

The principle of the chemical analysis of nitrogen is based on the reaction of the nitride ions N - with a strong base and the formation of anunonia which is then titrated, hi the case of refractmy oxynitrides, the difficulties of the alkaline attack in solution has been solved by using another procedure (30). The oxynitrides are reacted at 400 with melted potassium hydroxide under inert atmosphere. 

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