Acidic smuts

Acidic smuts Solid and liquid conglomerates formed by the condensation of water vapor and sulfur trioxide on a cold surface. A typical case is combustion products in a flue, which come into contact with surfaces at temperatures below the flue gas dew point temperature. These products contain metallic sulfate and carbon aqueous particles approximately 1-3 mm in size. 

Where stack temperatures are low and sulfur gases are present, problems of dry soot emissions give way to wet acid smutting. 

NOTE Acid smuts can cause severe damage because the pH level is often below 2.0 Where, for example, acid smuts fall on a vehicle, the body paint is likely to be discolored or spotty and may be eaten away. The effect on the environment is even greater. 

Where the fuel contains sulfur compounds, sulfuric acid is ultimately formed, causing acid smutting and both hot-end (high temperature zone) and cold-end (low temperature zone) acid corrosion and fouling, and adds to the total volume of unwanted furnace area deposits. 

Alkaline permanganate pretreatment of steel for the removal of heat scale and smut prior to acid pickling results in faster descaling and reduced metal attack (see Metal surface treatments Metal treatments). Stainless steel alloys can also be cleaned by alkaline permanganate followed by pickling in nonoxidi2ing acids (260). 

Fig. 28. Pho.sphoric acid etched A606 steel surfaces showing normal heavy smut formation [54].

Fig. 29. Phosphoric acid etched A606. steel surface showing smut-free, smooth-walled crevice morphology [54].

Smuts Unburned carbon emitted from chimneys. If sulfur is present in the fuel these smuts will be acidic. 

Smuts, C. M., H. Y. Tichelaar, M. A. Dhansay, M. Faber, J. Smith, and G. F. Kirsten. Smoking and alcohol use during pregnancy affects preterm infants docosahexaenoic acid (DHA) status. Acta Paediatr 1999 88(7) 757—762. Filippini, G., M. Farinotti, G. Lovicu, P. Maisonneuve, and P. Boyle. Mothers active and passive smoking during pregnancy and risk of brain tumours in children. Int J Cancer 1994 57(6) 769-774. 

This contamination, as in aluminum, is called smut. The usual method for desmutting is to wipe the work piece after rinsing, while it is still wet or to brush mechanically with a stiff wire bristle brush. However, it has been found that only a portion of the smut is removed by these methods and chemical etches are required to remove all of the material. An example of smut on stainless steel is shown in Figure 5 (12), where a surface which had been treated in hot sulfuric acid is shown. 

The elements which are observed are silicon and oxygen with some carbon present on the surface and only a slight amount of the matrix stainless steel. The SIMS spectra were taken simultaneously with the ISS data and show primarily silicon and cluster peaks of silicon and oxygen together with a small amount of the matrix material. Even when the surface of the 304 stainless steel was wiped after rinsing the appeared visably clean some smut remained behind as detected by both positive SIMS and ISS. The smut was completely removed by dipping the work in hot caustic soda solution or in chromic acid solution conventionally used in the industry. The analysis of the smutted surface and the desmutted surface by a variety of techniques is shown in Table V. Each of the techniques has its strong points. In AES, for instance, both sulfur and chlorine are readily detected in... 

Acid etching can be used to treat types 301 and 302 of stainless. These processes result in a heavy black smut formation on the surface. This material must be removed if maximum adhesion is to be obtained. The acid etch process produces bonds with high peel and shear strengths. The 400 series of straight chromium stainless steels should be handled in the same manner as the plain carbon steels. The various types of precipitation hardening (PH) stainless steels each present an individual problem. Processes must be adopted or developed for each type. 

Workers in Japan have shown that ultrasound can be used in electrochemical pickling and etching and smut removal in plating a beryllium-copper alloy [98]. The plating surface of Be-Cu alloys which are used commercially as electrical connectors, need to be pretreated by anodic treatment in an acid aqueous solution. These workers have shown that the smut may be effectively removed by application of ultrasound. This leads to a more resilient finish and a thickness of 0.2—3 p coating being achieved more rapidly. 

It is used mainly for seed treatment against smut and diseases of vegetable seeds (Schoene et al., 1949). Its use as a foliage fungicide is limited because it decomposes partly by hydrolysis and partly photochemically (Burchfield and McNew, 1950), and sublimates in hot weather. Neither can it be used efficiently as a soil fungicide, because it also rapidly decomposes in the soil (Domsch, 1958). One of its degradation products is chloroanilic acid (21), 2,5-dichloro-3,6-dihydroxy-l,4-benzoquinone, which is also biologically inactive. The acute oral lDj chloranil for rats is 4000 mg/kg. 

MAJOR USES Used in the production of antifreeze, acids, vitamins, hormones, plastics, pharmaceuticals and gas treatment against onion smut and Dutch elm disease. 

Kruger, M., Claassen, N., Smuts, C., and Potgeiter, H. (1997) Correlation Between Essential Fatty Acids and Parameters of Bone Farmation and Degradation, Asia Pac. J. Clin. Nutr. 6,235-238. 

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