Enamel preparation

Fig. 2. Process flow diagram for sheet-steel enameling where COM iadicates clean-only metal and PM, pickled metal, for (a) enamel preparation and...

Fig. 4. Process flow diagram for aluminum enameling showing (a) enamel preparation and application, and (b) metal preparation, where the cleaning processes A, B, and C represent primarily sheet D, primarily castings and E, aluminized steel (11).

Pretreatment ofFUlojs for Pone lain Enameling A.luminum, PEI Bulletin P-403 (70) and Enamel Preparation, Application, and Firingfor Porcelain Enameling Aluminum, PEI Bulletin P-404(70), Porcelain Enamel Institute, Washington, D.C., 1970. 

The introduction of enamel into the wastestream results in an increase in the concentration of metals, but these metals (antimony, titanium, zirconium, tin, cobalt, and manganese) are in solid form whereas the metals generated by surface preparation are normally in dissolved form. These solid metals increase the suspended solids concentration of the stream. Other metals that may be found in the enamel preparation and application wastestream in significant amounts include aluminum, copper, iron, lead, nickel, and zinc. Table 8.2 presents pollutant sampling data for the processes used in the porcelain enameling on steel industry. 

Enamel Preparation. Soluble oligoester diols (Ib-ld, 2a-2g, and 3a-3g), HMMM, methyl isobutyl ketone (MIBK) and -toluenesulfonic acid ( -TSA) were thoroughly mixed in a 70/30/30/0.3 wt. ratio. The solution was cast on panels and baked at 150" for 30 min. Less soluble LC diols le-lg were melted, dispersed in MIBK, mixed with HMMM and -TSA in the above proportions and immediately cast as films. Oligoester diol la was too insoluble for enamel formation. 

Properties of Enamels Prepared from Ib-lg and 2a-2g. Diol HMMM -TSA 70 30 0.3 by wt., cure cycle 150°/30 nrin... 

Enamel preparation. Solutions or mixtures of polyol, HMMM and p-TSA in a 75/25/0.25 wt. ratio were cast on steel panels and were baked at 175° for the specified time. Dry film thicknesses were 20 to 25 ym. 

Fig. 9.12. Acoustic images and V(z) curves for a specimen of human tooth enamel prepared with the left half slightly demineralized and the right half sound. V(z) curves ---- sound enamel - - - - slightly demineralized. Micrographs (a) z = 0 ...

Pigmented industrial enamels prepared from the castor oil alkyds were different, particularly for gloss and humidity resistance. The alkyds prepared directly from oil had better properties. 

Lithium Borates. Lithium metaborate [13453-69-5], LLBO2 2H20, is prepared from reaction of lithium hydroxide and boric acid. It is used as the fluxing agent for the matrix for x-ray fluorescence analytical techniques and in specialty glasses and enamels. The anhydrous salt melts at 847°C. 

Lithium carbonate is used to prepare Hthium aluminosiHcate glass ceramics which have low thermal coefficients of expansion, allowing use over a wide temperature range. It also finds uses in specialty glasses and enamels. 

Barium nitrate is prepared by reaction of BaCO and nitric acid, filtration and evaporative crystallization, or by dissolving sodium nitrate in a saturated solution of barium chloride, with subsequent precipitation of barium nitrate. The precipitate is centrifuged, washed, and dried. Barium nitrate is used in pyrotechnic green flares, tracer buUets, primers, and in detonators. These make use of its property of easy decomposition as well as its characteristic green flame. A small amount is used as a source of barium oxide in enamels. 

The uses of boric oxide relate to its behavior as a flux, an acid catalyst, or a chemical iatermediate. The fluxing action of B2O2 is important ia preparing many types of glass, gla2es, frits, ceramic coatings, and porcelain enamels (qv). 

Cobalt(Il) dicobalt(Ill) tetroxide [1308-06-17, Co O, is a black cubic crystalline material containing about 72% cobalt. It is prepared by oxidation of cobalt metal at temperatures below 900°C or by pyrolysis in air of cobalt salts, usually the nitrate or chloride. The mixed valence oxide is insoluble in water and organic solvents and only partially soluble in mineral acids. Complete solubiUty can be effected by dissolution in acids under reducing conditions. It is used in enamels, semiconductors, and grinding wheels. Both oxides adsorb molecular oxygen at room temperatures. 

Gold purple, often caHed Purple of Cassius, is a tin oxide gel colored by finely divided gold (7). It has good coverage and brilliance in low temperature coatings such as porcelain enamels. It is a very expensive pigment, because of its difficult preparation as well as the price of gold. 

Only synthetically prepared Ti02 can be used as a color additive. It is permitted ia foods to 1% and is used to color such products as confectionary paimed goods, cheeses, and icings. It is also widely used ia tableted dmg products and ia numerous cosmetics such as Upsticks, nail enamels, face powder, eye makeup, and rouges, ia amounts consistent with good manufactuting practice (42). 

Other Metals. Metals such as the austenitic series. Types 301—347, and the ferritic series. Types 409—446, of stainless steels may be enameled, as well as a number of other alloys (17). The metal preparation usually consists of degreasiag and grit blasting. Copper, gold, and silver are also enameled. These metals are usually prepared for appHcation by degreasiag. Copper is pickled usiag either a nitric acid [7697-37-2] or a sulfuric acid [7664-93-9] solution, followed by a dilute nitric acid dip. Silver may be pickled in hot dilute sulfuric acid followed by a dip in a nitric acid solution (18). 

Metal Preparation. Sheet-steel parts are formed by stamping, bending, and shearing. Many parts require welding (qv), which needs to be carried out in a uniform, smooth manner so that the welded joint can be enameled without defects. Cast-iron parts are formed by the usual cast-iron foundry methods however, additional care is given to prevent contamination of the surface. Surface contamination causes defects in the enamel, particularly bUsters and bubbles. Aluminum metal can be formed in sheets, extmsions, and as castings. 

Perfumes, cosmetics, and othertoilet preparations 2851 Paints, varnishes, lacquers, enamels, and allied... 

Recent trends in protective coatings used on buried pipelines have been away from reinforced hot applied coal tar and asphalt enamels and butyl rubber laminate tapes, particularly where applied over-the-ditch . The more recently developed coatings based on fusion bonded epoxies, extruded poly-ethylenes, liquid-applied epoxies and polyurethanes, require factory application where superior levels of pipe preparation and quality control of the application process can be achieved. 

---