Grain corrosion

Bupuytren s Pills. Take 120 grains powdered guaiacum, 4 grains corrosive chlorido of mercury (coiTosivo sublimate), and 5 grains powdered opium mako into 40 pills. 

Hunter s Bed Drop, Triturate in a glass mortar, 10 grains corrosive sublim-ato in 12 dropa muriatic acid, uud add grivdu-... 

Bellas Gargle for Syphilitic Sore Throat. Mix together 2 grains corrosive sublimate 1 ounce rectided spirits of wine 3 ounces tincture of Peravion bark, and 1 ounce each honey of roses and tincture of myrrh. 

The Oxide as a Physical Barrier. The oxide surface layer can be interpreted as a physical barrier to mass transport (similar to the role of an oxide film on a passivated electrode) that inhibits ET from the iron metal to RX (4). If the oxide layer is a non-conductive physical barrier, then ET may occur from the metal to the dissolved substrate through defects such as pits or grain boundaries. Pitting and crevice (grain) corrosion are localized forms of corrosion, where rupture of the oxide layer introduces new paths for diffusion (i.e., pore diffusion) and new catalytic dissolution pathways (34, 35). 

Remove the Nitric Acid Test from ASTM A 262 and establish it as a separate ASTM Test At present, the boiling 65 % nitric acid test (Practice C) is specified for materials to be used in nitric acid service. Only this test is sensitive to sigma-phase in molybdenum-bearing austenitic stainless steels. Also, problems such as end-grain corrosion associated with hexavalent chromium derived from corrosion products are unique to this solution. While this test also detects susceptibility to intergranular attack associated with chromium carbide precipitates, there are other tests that perform this function in less time and with greater simplicity. 

The etching process is similar to a corrosion process. Therefore, special acids and etching techniques are required for graining corrosion resistant steels. The steel should be selected together with the steel manufacturer and the graining experts. 

Within the metal, at the level of the grain, corrosion may propagate in two different ways ... 

The Fe, Co, and Ni deposits are extremely fine grained at high current density and pH. Electroless nickel, cobalt, and nickel—cobalt alloy plating from fluoroborate-containing baths yields a deposit of superior corrosion resistance, low stress, and excellent hardenabiUty (114). Lead is plated alone or ia combination with tin, iadium, and antimony (115). Sound iasulators are made as lead—plastic laminates by electrolyticaHy coating Pb from a fluoroborate bath to 0.5 mm on a copper-coated nylon or polypropylene film (116) (see Insulation, acoustic). Steel plates can be simultaneously electrocoated with lead and poly(tetrafluoroethylene) (117). Solder is plated ia solutioas containing Pb(Bp4)2 and Sn(Bp4)2 thus the lustrous solder-plated object is coated with a Pb—Sn alloy (118). 

The following mechanisms in corrosion behavior have been affected by implantation and have been reviewed (119) (/) expansion of the passive range of potential, (2) enhancement of resistance to localized breakdown of passive film, (J) formation of amorphous surface alloy to eliminate grain boundaries and stabilize an amorphous passive film, (4) shift open circuit (corrosion) potential into passive range of potential, (5) reduce/eliminate attack at second-phase particles, and (6) inhibit cathodic kinetics. 

Rea.ctivity ofLea.d—Ca.lcium Alloys. Precise control of the calcium content is required to control the grain stmcture, corrosion resistance, and mechanical properties of lead—calcium alloys. Calcium reacts readily with air and other elements such as antimony, arsenic, and sulfur to produce oxides or intermetaUic compounds (see Calciumand calciumalloys). In these reactions, calcium is lost and suspended soHds reduce fluidity and castibiUty. The very thin grids that are required for automotive batteries are difficult to cast from lead—calcium alloys. 

Cast lead—calcium—tin alloys usually contain 0.06—0.11 wt % calcium and 0.3 wt % tin. These have excellent fluidity, harden rapidly, have a fine grain stmcture, and are resistant to corrosion. Table 4 Hsts the mechanical properties of cast lead—calcium—tin alloys and other alloys. 

Wrought lead—calcium—tin anodes have replaced many cast lead—calcium anodes (14). Superior mechanical properties, uniform grain stmcture, low corrosion rates, and lack of casting defects result in increased life for wrought lead—calcium—tin anodes compared to other lead alloy anodes. 

Other methods of metal powder manufacture are also employed for specific metals. Selective corrosion of carbide-rich grain boundaries in stainless steel, a process called intergranular corrosion, also yields a powder. 

Addition of niobium to austenitic stainless steels inhibits intergranular corrosion by forming niobium carbide with the carbon that is present in the steel. Without the niobium addition, chromium precipitates as a chromium carbide film at the grain boundaries and thus depletes the adjacent areas of chromium and reduces the corrosion resistance. An amount of niobium equal to 10 times the carbon content is necessary to prevent precipitation of the chromium carbide. 

X-Ray Emission and Fluorescence. X-ray analysis by direct emission foUowing electron excitation is of Hmited usefulness because of inconveniences in making the sample the anode of an x-ray tube. An important exception is the x-ray microphobe (275), in which an electron beam focused to - 1 fim diameter excites characteristic x-rays from a small sample area. Surface corrosion, grain boundaries, and inclusions in alloys can be studied with detectabiHty Hmits of -- 10 g (see Surface and interface analysis). 

The formation of anodic and cathodic sites, necessary to produce corrosion, can occur for any of a number of reasons impurities in the metal, localized stresses, metal grain size or composition differences, discontinuities on the surface, and differences in the local environment (eg, temperature, oxygen, or salt concentration). When these local differences are not large and the anodic and cathodic sites can shift from place to place on the metal surface, corrosion is uniform. With uniform corrosion, fouling is usually a more serious problem than equipment failure. 

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