Steels chemical cleaning

When freshly mixed, the carboxyHc acid groups convert to carboxjiates, which seems to signify chemical adhesion mainly via the calcium of the hydroxyapatite phase of tooth stmcture (32,34—39). The adhesion to dentin is reduced because there is less mineral available in this substrate, but bonding can be enhanced by the use of minerali2ing solutions (35—38). Polycarboxylate cement also adheres to stainless steel and clean alloys based on multivalent metals, but not to dental porcelain, resin-based materials, or gold alloys (28,40). It has been shown that basic calcium phosphate powders, eg, tetracalcium phosphate [1306-01-0], Ca4(P0 20, can be substituted for 2inc oxide to form strong, hydrolytically stable cements from aqueous solution of polyacids (41,42). 

Stainless steels Clean stainless steels in 20% nitric acid at 60°C for 20 min. In place of chemical cleaning, use a brass scraper or brass bristle brush or both, followed by scrubbing with a wet bristle brush and fine scouring powder. 

Mechanical cleaning of a multitubular stainless steel condenser (blocked by a rigid polyurethane foam) by rodding the tubes was laborious, so chemical cleaning with cone, nitric acid was attempted. When the initial vigorous reaction ( fireworks ) subsided, owing to crust formation, the rod was again inserted, but a sudden explosion occurred which ruptured the condenser. 

Chemical reactions that remove gases from the head space. The corrosion of the interior of a steel vessel, especially if the vessel is newly fabricated or has been chemically cleaned, can consume and... 

The use of hydroxyacetic/formic acid in the chemical cleaning of utility boilers is common. It is used in boilers containing austenitic steels because its low chloride content prevents possible chloride stress corrosion cracking of the austenitic-type alloys. It has also found extensive use in the cleaning operations for once-through supercritical boilers. Hydroxyacetic/formic acid has chelation properties and a high iron pick-up capability thus it is used on high iron content systems. It is not effective on hardness scales. 

Shortening units are constructed of carbon steel. The water phase in margarine is corrosive, and sanitation procedures require that all of the equipment used to manufacture it must be chemically cleaned. Margarine processing units contain chromium-plated commercially pure nickel heat transfer tubes and stainless steel for all product-contacted metal surfaces. 

Because shortening is a 100% oil product, expensive stainless steel equipment for a shortening is not required, and the Votator model LSI82 shortening system is constructed entirely of mild steel. AU of the equipment is cleaned simply by circulating oil until all of the fat has been melted and then purging with air or inert gas. No chemical cleaning is necessary. 

Using light microscopy, Bird and Bartlett [170] observed that the deposit on sintered stainless steel MF membrane (2.0 pim) fouled with whey consists of a loose sheet-like protein-rich stmcmre which is removed during the first few minutes of chemical cleaning (Figure 22.11). Cleaning with sodium hydroxide removes the loose top proteinaceous layer, which results to the sharp... 

Polyamide membranes are also not resistant to the strong oxidizing actions of disinfectants such as hydrogen peroxide and hypochlorite. Acids used to the clean membrane system must be rinsed out thoroughly before application of hypochlorite for disinfection as hypochlorite at low pH can cause corrosion in stainless steel. The pH of the chemical cleaning solution must fall within the tolerable range of pH 1-13 for polysulfone membranes and pH 3-8 for CA membranes (87). 

Passivation is usually part of a chemical cleaning process using a sodium nitrite solution. (Chromates, once used extensively, are now considered to be too toxic.) Austenitic stainless steels are usually passivated in air after pickling and neutrahzation. Pickling is a chemical process to descale or clean new stainless steel. (See ASTM A380 for recommended procedures.) For heavily oxidized materials, the pickling process removes the chromium-depleted surface beneath the layer of scale. The acid solutions used contain sufficient nitric acid (a good oxidizer) so that a subsequent passivation step is unnecessary. 

Plate-fin Aluminium, stainless steel, titanium Only chemical cleaning possible Highly compact... 

The relatively complex procedure that may be required and the associated safety considerations for chemical cleaning of heat exchangers is illustrated by a case study published by French [1981]. The deposit on the surfaces of a stainless steel heat exchanger had the aproximate composition given in Table 15.12. 

Descaling of hot worked stainless steels can be accomplished by mechanical or by chemical cleaning, or by a combination of both methods. The surface can be cleaned by sand blasting, but unless it is machined after blasting, only nonmetallic blast material should be used in order to avoid contamination and a reduction of the corrosion resistance. Following blast cleaning stainless steels are usually acid pickled and washed with water. Common etching acids are ... 

Clean zinc-coated steel is a suitable base for paint or adhesive systems, but the first treatment may be different from those used on uncoated steel. Chemical conversion coatings (chromate, phosphate, or oxide types) and primers have been specially formulated for first treatment of zinc-coated steel. Some passivated surfaces (e.g., chromated) are not suitable for phosphating... 

Steel cord for the Selby belt is purchased from Bekaert (Belgium). As already described, the steel cord used in conveyor belting is derived from that used in tyres. It is purchased from specialist suppliers, such as Bekaert and Steel Cords Ltd. Ordinary suppliers of steel cable for other purposes do not usually supply the rubber industry. There are two reasons for this one is the fluctuation and lack of standardization of demand, and the other is the chemically clean, zinc-coated finish required. 

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