Emulsions, deposition

The H1680 emulsion deposit shows no irisation, so the layer thickness is greater than the visible light wavelengths, in contrast to the market reference. 

The slurry is pumped iato another stock chest, where wax ia emulsion form, usually about 0.5—1.0% wax-to-fiber weight, and 1—3% PF resia are added. PF resia is also added on the basis of resia soHds-to-dry fiber. Thea a small amouat of alum is added, which changes the pH (acidity) of the slurry, causiag the resia to precipitate from solutioa and deposit on the fibers. Resia is required ia greater quantity than ia the Masonite process because only light bonding occurs between fibers prepared ia a refiner. The fiber slurry is thea pumped to the headbox of a Fourdrioier mat former, and from this poiat the process is similar to the Masonite process. 

Classification of the many different encapsulation processes is usehil. Previous schemes employing the categories chemical or physical are unsatisfactory because many so-called chemical processes involve exclusively physical phenomena, whereas so-called physical processes can utilize chemical phenomena. An alternative approach is to classify all encapsulation processes as either Type A or Type B processes. Type A processes are defined as those in which capsule formation occurs entirely in a Hquid-filled stirred tank or tubular reactor. Emulsion and dispersion stabiUty play a key role in determining the success of such processes. Type B processes are processes in which capsule formation occurs because a coating is sprayed or deposited in some manner onto the surface of a Hquid or soHd core material dispersed in a gas phase or vacuum. This category also includes processes in which Hquid droplets containing core material are sprayed into a gas phase and subsequentiy solidified to produce microcapsules. Emulsion and dispersion stabilization can play a key role in the success of Type B processes also. 

These rosin-based sizes, whether paste, Hquid, or emulsions, can be used to size all grades of paper that are produced at acid pH. The latter include bleached or unbleached kraft Hnerboard and bag paper, bleached printing and writing grades, and cylinder board. In addition, polyaluminum compounds have been used in place of alum, most notably, polyaluminum chloride (48), which can reduce barium deposits where these have been a problem. The barium chloride by-product is more water-soluble than barium sulfate. Other polyaluminum compounds such as polyhydroxylated forms of alum and polyaluminum siHcosulfate have been evaluated as alum replacements. 

Hydroxyhydroquinone and pyrogaHol can be used for lining reactors for vinyl chloride suspension polymerization to prevent formation of polymer deposits on the reactor walls (98). Hydroxyhydroquinone and certain of its derivatives are useful as auxiUary developers for silver haUde emulsions in photographic material their action is based on the dye diffusion-transfer process. The transferred picture has good contrast and stain-free highlights (99). 5-Acylhydroxyhydroquinones are useful as stabilizer components for poly(alkylene oxide)s (100). 

Most tanks store Hquid rather than gases or soHds. Characteristics and properties such as corrosiveness, internal pressures of multicomponent solutions, tendency to scale or sublime, and formation of deposits and sludges are vital for the tank designer and the operator of the tank and are discussed herein. Excluded from the discussion are the unique properties and hazards of aerosols (qv), unstable Hquids, and emulsions (qv). A good source of information for Hquid properties for a wide range of compounds is available (2). 

Waterborne Costing s. These coatings utilize either Hquid or soHd epoxy resins that have been modified to allow their use with water. They are usually in the form of emulsions, suspensions, dispersions, or water-dilutable resins that can be heat- or RT-cured. They are appHed by convenient methods such as roUer-coating, dipping, spray, or electro deposition. 

Rolling oil tanks were corroded on surfaces contacting the emulsion. Small pitlike depressions were present beneath aluminum soap deposits. Each pit was surrounded by a lightly etched region exactly mirroring deposit patterns (Fig. 6.26). 

To accelerate the polymerization process, some water-soluble salts of heavy metals (Fe, Co, Ni, Pb) are added to the reaction system (0.01-1% with respect to the monomer mass). These additions facilitate the reaction heat removal and allow the reaction to be carried out at lower temperatures. To reduce the coagulate formation and deposits of polymers on the reactor walls, the additions of water-soluble salts (borates, phosphates, and silicates of alkali metals) are introduced into the reaction mixture. The residual monomer content in the emulsion can be decreased by hydrogenizing the double bond in the presence of catalysts (Raney Ni, and salts of Ru, Co, Fe, Pd, Pt, Ir, Ro, and Co on alumina). The same purpose can be achieved by adding amidase to the emulsion. 

Cresylic acid is mainly used as degreasing agent and as a disinfectant of a stabilized emulsion in a soap solution. Cresols are used as flotation agents and as wire enamel solvents. Tricresyl phosphates are produced from a mixture of cresols and phosphorous oxychloride. The esters are plasticizers for vinyl chloride polymers. They are also gasoline additives for reducing carbon deposits in the combustion chamber. 

Electrodeposition This method of paint application is basically a dipping process. The paint is water-based and is either an emulsion or a stabilised dispersion. The solids of the paint are usually very low and the viscosity lower than that used in conventional dipping. The workpiece is made one electrode, usually the cathode, in a d.c. circuit and the anode can be either the tank itself or suitably sized electrodes sited to give optimum coating conditions. The current is applied for a few minutes and after withdrawal and draining the article is rinsed with de-ionised water to remove the thin layer of dipped paint. The deposited film is firmly adherent and contains a minimum of water and can be stoved without any flash-off period. This process is used for metal fabrications, notably car bodies. Complete coverage of inaccessible areas can be achieved and the corrosion resistance of the coating is excellent (Fig. 14.1). 

There are many temporary protectives on the market and it would be impracticable to describe them individually. However, they may be classified according to the type of film formed, i.e. soft film, hard film and oil film the soft film may be further sub-divided into solvent-deposited thin film, hot-dip thick film, smearing and slushing types. All these types are removable with common petroleum solvents. There are also strippable types based on plastics (deposited by hot dipping or from solvents) or rubber latex (deposited from emulsions) these do not adhere to the metal surfaces and are removed by peeling. In addition there are volatile corrosion inhibitors (V.C.I.) consisting of substances, the vapour from which inhibits corrosion of ferrous metals. 

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