Mill-scale

In atomization, a stream of molten metal is stmck with air or water jets. The particles formed are collected, sieved, and aimealed. This is the most common commercial method in use for all powders. Reduction of iron oxides or other compounds in soHd or gaseous media gives sponge iron or hydrogen-reduced mill scale. Decomposition of Hquid or gaseous metal carbonyls (qv) (iron or nickel) yields a fine powder (see Nickel and nickel alloys). Electrolytic deposition from molten salts or solutions either gives powder direcdy, or an adherent mass that has to be mechanically comminuted. 

The choice of selected raw materials is very wide, but they must provide calcium oxide (lime), iron oxide [1309-37-1/, siHca, and aluminum oxide (alumina). Examples of the calcereous (calcium oxide) sources are calcium carbonate minerals (aragonite [14791-73-2] calcite [13397-26-7] limestone [1317-65-3] or mad), seasheUs, or shale. Examples of argillaceous (siHca and alumina) sources are clays, fly ash, mad, shale, and sand. The iron oxide commonly comes from iron ore, clays, or mill scale. Some raw matedals supply more than one ingredient, and the mixture of raw matedals is a function of their chemical composition, as deterrnined by cost and availabiHty. 

Because calcium oxide comprises about 65% of Pordand cement, these plants are frequendy situated near the source of their calcareous material. The requisite silica and alumina may be derived from a clay, shale, or overburden from a limestone quarry. Such materials usually contain some of the required iron oxide, but many plants need to supplement the iron with mill scale, pyrite cinders, or iron ore. Silica may be supplemented by adding sand to the raw mix, whereas alumina can be furnished by bauxites and Al202-rich flint clays. 

Metal Cleaning. Citric acid, partially neutralized to - pH 3.5 with ammonia or triethanolamine, is used to clean metal oxides from the water side of steam boilers and nuclear reactors with a two-step single fill operation (104—122). The resulting surface is clean and passivated. This process has a low corrosion rate and is used for both pre-operational mill scale removal and operational cleaning to restore heat-transfer efficiency. 

Homogeneous galvanic corrosion may also occur on the surface of steel components that are covered or partially covered with mill scale (magnetite, Fe304) or iron sulfide corrosion products. Both mill scale and iron sulfide are noble with respect to steel. Significant galvanic corrosion can occur where breaks or holidays in these corrosion products expose unprotected metal. 

Note that nonmetallic substances such as mill scale (Fe304) and iron sulfide (FeaS) are not listed. Nevertheless, on the surface of steel these substances can produce galvanic corrosion of the steel due to their relatively noble character. 

The surface formed by the treatment must be reproducible. Reproducibility requires that the prepared surface be independent of surface contamination, mill-scale, and other variations of nominally identical alloy surfaces. Reproducibility is facilitated if the treatment has wide processing windows so that... 

Mill Scale—an oxide layer on metals produced by metal rolling, hot forming, welding or heat treatment. 

Pickling—a form of chemical and electrolytic removal of mill scale and corrosion products from the surfaces of metals in an acidic solution. Electrolytic pickling may be anodic or cathodic, depending on the polarization of the metal in the solution. 

Walz-kupfer, m. sheet copper, -messing, n. sheet brass, rolled brass, -normale,/. normal to the plane of rolling, -produkt, n. rolled product, sheet, plate, -reibung, /. rolling friction, -schlacke, /. mill scale, mill cinder, -sinter, m. mill scale, mill cinder, -stahl, m. rolled steel, -strasse, -strecke, /. roll train. 

Walz-werk, n. rolls, roll train, rolling mill, blooming mill, crushing mill, etc. -zink, n. rolled zinc, sheet zinc, -zizm, n. rolled tin, sheet tin. -zunder, m. mill scale, mill cinder, -zustand, m. rolled state. 

Conductive films such as magnetite (Fe,0 ) or mill scale on steel, and conductive nonmetals such as carbon can function as cathodes when in contact with anodes... 

Dry abrasive blast cleaning should be used on new steelwork where the main contaminant is mill scale. For heavily rusted and pitted steelwork, increased durability can be obtained by the use of wet abrasive blasting where this is practicable. The water will be more effective in removing the potentially destructive and corrosive soluble iron-corrosion products that form at the bottom of corrosion pits. 

This method is generally not capable of achieving a uniform standard of cleanliness on structural steel. It is not effective in removing intact mill scale or corrosion products from pitted surfaces. The durability of subsequent coats is therefore variable and unpredictable, and depends on the thoroughness of the operation and the exact nature of the contaminants left on the surface. The method should be confined to non-aggressive environments or where short-term durability is economically acceptable. 

Rusty pipe should not be used. The rust and loosened mill scale will travel around the circuit to block the suction strainer and the drier. Other avoidable debris are loose pieces of weld, flux, and the short stubs of welding rod often used as temporary spacers for butt welds. Pipe should only be cut with a gas torch if all the oxidized metal can be cleaned out again before closing the pipe. 

Control of foulants and corrosion debris Because of the very large volume in these HW systems, there is an obvious reluctance to unnecessarily drain them down because of the development of waterside problems. Therefore, it is important to ensure that before regular operation they are provided with a proper precommission cleaning procedure. This process removes silt, mill-scale, grease, and other foulants, thus enabling passivation and subsequent maintenance inhibition to take place. 

For the most part, iron, copper, nickel, and zinc deposits found in the boiler section are the result of corrosion processes taking place somewhere else within the overall system. Similarly, mill scale from new boilers may be released and redeposited elsewhere, plugging BD lines and boiler tubes. 

Mill scale is a three-layer structure, typically with Fe203 (1-5%) at the atmospheric surface, Fe304 (10-15%) in the middle, and FeO (80-85%) at the metal surface. 

New boilers, heat exchangers, and other equipment must be provided with a PCC program to remove oil, grease, mill scale, pipe-threading compounds, drawing compounds, and other detritus that otherwise prevent the formation of clean, passivated metal surfaces and encourage... 

Cleaning solutions also vary in complexity, depending on the ratios of oil/grease to rust/mill scale and other factors. The most common components include ... 

Herbert T. Pratt. Textile Mill Scale-Up of Nylon Hosiery, 1937-1938. In Manmade Fibers Their Origin and Development. Raymond B. Seymour and Roger S. Porter, eds. London Elsevier Applied Science, 1993. Source for marketing nylon and 80 percent of silk for hosiery in United States. 

Energy use per ton of Largest source teeming Sources vacuum degassing, Mill scale, sludge... 

Cleaned steel products (e.g., sheets, plates, bars, pipe) Process wastewater containing mill scale, oils, other pollutants, and low levels of metals Wastewater sludge Air pollution control (APC) dust Spent pickle liquor (K062)... 

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