Spray conversion

M.Y. Song, S.N. Kwon, S.H. Hong, D.R. Mumm, l.S. Bae, Improvement of hydrogen-sorption characteristics of Mg by reactive mechanical grinding with Cr Oj prepared by spray conversion, Int. J. Hydrogen Ener. 31 (2006) 2284-2291. 

The Spray Conversion Process (Nanodyne Inc.) [9.22, 9.23]. In comparison to all the above-described methods, the process outlined here yields a final product which is already an intimate mixture of WC and Co. The process is composed of three major stages ... 

Powders made by spray conversion are further processed similar to conventional powders. Prior to compaction, the agglomerates are milled down in ball mills or attritors to fragments of about 0.5 pm. 

Spray Conversion and Aerosol Routes for Powder Manufacturing... 

Figure 20.4. Scauniag electron micrographs of a) aggregates obtained in a conventional electrocatalyst synthesis and b) aggregate size distribution of the electrocatalyst powders obtamed by spray conversion. (Images courtesy of NRC-IFCI.)...

Residual monomers in the latex are avoided either by effectively reacting the monomers to polymer or by physical or chemical removal. The use of tert-huty peroxypivalate as a second initiator toward the end of the polymeri2ation or the use of mixed initiator systems of K2S20g and tert-huty peroxyben2oate (56) effectively increases final conversion and decreases residual monomer levels. Spray devolatili2ation of hot latex under reduced pressure has been claimed to be effective (56). Residual acrylonitrile also can be reduced by postreaction with a number of agents such as monoamines (57) and dialkylamines (58), ammonium—alkali metal sulfites (59), unsaturated fatty acids or their glycerides (60,61), their aldehydes, esters of olefinic alcohols, cyanuric acid (62,63), andmyrcene (64). 

The appHcation of this type of conversion coating can be by spray or immersion and is easily tailored to the needs of the user (see Coating processes). The number of stages may vary from two, ie, clean and phosphate then rinse, to as many as five, ie, clean, rinse, phosphate, rinse, and post-treat. The performance requirements dictate the number of operation stages as well as the need for a post-treatment. 

Product Utilization. The principal appHcation for chromium phosphate coatings is as a paint base for painted aluminum extmsions and aluminum beverage can stock. In these appHcations, extremely demanding performance criteria are met by the chromium phosphate conversion coatings. As an example, the Architectural Aluminum Manufacturer s Association Voluntary Specification 605.2-92 requires humidity and salt spray testing for 3000 hours and allows only minimal incidence of paint failure after testing (26). 

Naphthalenesulfonic Acid. The sulfonation of naphthalene with excess 96 wt % sulfuric acid at < 80°C gives > 85 wt % 1-naphthalenesulfonic acid (a-acid) the balance is mainly the 2-isomer (P-acid). An older German commercial process is based on the reaction of naphthalene with 96 wt % sulfuric acid at 20—50°C (13). The product can be used unpurifted to make dyestuff intermediates by nitration or can be sulfonated further. The sodium salt of 1-naphthalenesulfonic acid is required, for example, for the conversion of 1-naphthalenol (1-naphthol) by caustic fusion. In this case, the excess sulfuric acid first is separated by the addition of lime and is filtered to remove the insoluble calcium sulfate the filtrate is treated with sodium carbonate to precipitate calcium carbonate and leave the sodium l-naphthalenesulfonate/7J(9-/4-J7 in solution. The dry salt then is recovered, typically, by spray-drying the solution. 

Flow Regimes in Multiphase Reactors. Reactant contacting, product separations, rates of mass and heat transport, and ultimately reaction conversion and product yields are strong functions of the gas and Hquid flow patterns within the reactors. The nomenclature of commonly observed flow patterns or flow regimes reflects observed flow characteristics, ie, armular, bubbly, plug, slug, spray, stratified, and wavy. 

Fig. 24. Effect of residence time and outiet temperature on the chemical and biochemical conversions of skim milk in a spray column, where (—)...

Symps of 25—30 DE are used as spray-drying aids in products such as coffee. High conversion symp, maltose symp, and 42-DE symp are used in jams and jeUies. Com symp is also used in table symps, baby food, meat packing, breakfast foods, salad dressing, pickles, dehydrated powdered foods, medicinal symps, textile flirnishings, adhesives, and numerous other products and processes. 

This conversion is normally accompHshed by immersion, but spraying, swabbing, bmshing, and electrolytic methods are also employed (178) (see Metal SURFACE treatments). The metals that benefit from chromium surface conversion are aluminum, cadmium, copper, magnesium, silver, and 2inc. Zinc is the largest consumer of chromium conversion baths, and more formulations are developed for 2inc than for any other metal. 

In Section 4.3 several recently developed and experimental surface preparation methods for steel such as conversion coatings, plasma spray and sol-gel that attempt to simultaneously improve durability and bond strength over grit blasting will be discussed. 

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