Deposits tacky

In classifying deposits by structure, the adherent layer can be characterized as loose (ash and soot deposits), tacky, dense (sintered and cemented), or liquid. The properties of the adherent layer are determined by the particular stage at which the deposit formation process ends, this process consisting of the deposition of fly ash, adhesion of ash particles to the heating surface, sintering of the ash particles, and melting of the outer layer of deposits. We will be considering three types of deposits loose, tacky, and dense. 

High Water Velocities. The abiUty of high water velocities to minimize fouling depends on the nature of the foulant. Clay and silt deposits are more effectively removed by high water velocities than aluminum and iron deposits, which are more tacky and form interlocking networks with other precipitates. Operation at high water velocities is not always a viable solution to clay and silt deposition because of design limitations, economic considerations, and the potential for erosion corrosion. 

The inherent tackiness of the coating, especially during the critical time immediately after deposition onto the surface of the substrate. 

Automatic and quantitative microscopes tend to give erroneous results for transparent particles. To overcome this problem Amor and Block [49] a silver staining technique to make the particles opaque. The particles are dry-mounted on to a thin film of tacky colloidon on a microscope slide. Silver is then deposited from solution using the silver mirror reaction. Preliminary sensitizing the crystalline surface ensures that much more silver is deposited on the particles than on the colloidon. A method of staining particles in aqueous solution prior to deposition on a membrane filter for analysis is also given. 

Depositability of the organic material is obviously required for a deposit to be formed. It is also easy to conceptually understand the relevance of this parameter. Depositability can be seen as the tackiness of the material. Consider a sitnation where the colloidal organic material is present in a certain content in the system. With a low viscosity this material has a low viscosity, and is not really tacky, so deposition of this material is not going to be extensive. At high viscosity, on the other hand, a material is brittle in nature so this material will not readily form deposits either. However, if the viscosity is in between these two extremes, and of a tacky nature, deposition can be expected to be extensive. 

A deposit may also be formed when two components, each of them not forming a deposit, are combined within the papermaking system. The combined material can then obtain the tackiness required for deposition a tackiness none of the components alone have. 

The term "pressure-sensitive adhesive" (PSA) refers to a permanently tacky composition which will adhere to a variety of surfaces merely by application of light hand pressure. Such materials find widespread application in tapes labels, wall coverings, floor tiles, and protective maskings (1). Typical property requirements for various pressure-sensitive products are shown in Table 1. For decades, such products have been manufactured by the deposition of preformed polymers from solution. However, as concern over energy and environmental problems began to surface, the pressure to find alternate methods of manufacture intensified and the use of solvents declined. The use of radiation to cure such materials in place is but one alternate to the conventional solvent-based approach. 

Loose deposits consist of an adherent layer of solid particles. Tacky deposits are caused by the presence of tacky (liquid or oily) components. Dense deposits consist of a single dense mass for which the autohesive interaction between particles is much greater than the adhesive force. Dense deposits are formed, for example, in the combustion of Estonian shales at temperatures of 500-1000°C and also in the combustion of lean coal from the Moscow area. Also, dense deposits are formed by the combustion of certain residual fuel oils. Under the operating conditions encountered in practice, all types of deposits may be present at the same time, and it is sometimes difficult to observe the distinctions between these types. 

Tacky Deposits. If the deposit includes particles with a tacky surface, the adhesion of such deposits increases sharply, and the deposits themselves change over from loose to tacky type. Tacky deposits can be distinguished from loose deposits by visual examination. 

We have examined examples in which the formation of a dense deposit is accompanied by the formation of a loose deposit. Also possible are cases in which tacky and dense deposits are formed together, for example, in the combustion of residual fuel oil. The ash from residual fuel oil consists of metal corrosion products (iron salts and oxides), residues from substances used in the caustic and acid treatment of petroleum, salts from drilling water, contaminant particles, and particles of unburned carbon (soot and carboids). When the individual components of the ash interact with each other and with the gas medium, dense and tacky deposits are formed. Even though residual fuel oil combustion gives much less ash than is obtained in anthracite combustion, by a factor of 50 less than in peat combustion, by a factor of 100 and less than in shale combustion, by a factor of 200, the deposits formed by the fuel oil com-... 

Simple addition of silanes to a rubbery polymer latex cannot impart water-resistant bonds to a mineral unless the silane deposits a resinous or tacky layer at the interface. A silane-modified resin or plasticizer will be effective if it can be retained as a separate phase in the emulsion and deposited as a primer layer on the mineral. 

Hubbe MA, Rojas O, Venditti RA (2006) Control of tacky deposits on paper machines - a review. Nordic Pulp Paper Res J 21 154... 

A thin, pure resin and sometimes pigmented finish, applied as a final operation to the reverse face only of a hand-laminated or spray-deposited thermoset composites moulding. The purpose is to seal, or offer further moisture and other protection to that irregular, fibre-textured surface, it prevents the reinforcement at the surface layer from becoming exposed during the components in-service life. To ensure that there is no residual surface tackiness, flowcoats often contain a small percentage of paraffin wax. 

For a flow velocity exceeding a certain value (first critical velocity) the particles will rebound. The value of the first critical velocity depends on the elastic properties of the particle and obstacle surfaces and is inversely proportional to the particle size [see formula (V.ll)l. The coefficient of deposition increases when the possibility of particle rebound is eliminated. This may be achieved by making the surface tacky or increasing the adhesive force, particularly by virtue of the triboeffect and the cooling of the molten zone of contact. 

The symbol a denotes only the proportion of dense deposits formed as a result of the reactivity of the particles the influence of tackiness on adhesion is not taken into account. 

On pipes subjected to a flow in the longitudinal direction, dense deposits 2-4 mm high and 10-20 mm long developed in the form of islands. The rupture strength of the deposits not removed by blowing in shale furnaces was 100-1000 kg/ cm. However, in view of the tackiness of the ash, it was difficult to remove deposits formed in the combustion of fuel oil. 

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