Consolidated layer thickness

This equation identical to equation 13.12 for slip casting, where a is now the resistance of the frit. Using this equation, a plot of the consolidated layer thickness, L, versus gives a straight line where F is the slope, from which the permeability of the cake of consolidated ceramic powder, o, and frit, a , can be determined. 

One form of film break-up has been mentioned previously, in which the surface of a relatively thick film becomes consolidated over a soft unconsolidated layer. This can lead to shear in the soft layer, especially with high non-conformal loading, and the consolidated layer will break away. Loss of adhesion and film break-up can also occur, especially with a bonded film, if the surface pre-treatment has been badly performed, so that the coating simply fails to adhere and breaks away. These cases may be considered as premature failures caused by poor film preparation. 

Dip coating is analogous to a slip casting process for making ceramic parts. The membrane deposition behavior by slip casting can be described by a theory of colloidal filtration for incompressible cakes [Aksay and Schilling, 1984] and compressible cakes [Tiller and Tsai, 1986). The theory predicts that the thickness of the consolidated layer, L, is given by... 

Other important factors include cation type (K, Na, Ca. ..), clay specie charge deficiency, temperature, and so on. For example, increased kinetic energy at high temperatures overcomes bonding forces and reduces adsorbed layer thickness, leading to additional shale compaction under high T (thermal consolidation). 

The MCVD modified chemical vapor deposition) method also relies on the production of glass from halide vapors. The deposition process occurs inside a vitreous silica tube, which is heated from the outside and which serves as the cladding for the fiber. The reaction of the vapors now occurs without contamination by gases from the flames, which never contact the deposited material. Consolidation of the soot occurs simultaneously with deposition. The process continues until the desired layer thickness is reached, after which the entire tube is collapsed by increasing the external temperature to complete the preform. 

If the resistance of the mold to liquid flow is neglected and the hquid flow is considered to flow through the porous consolidated layer, the model of Adcock and McDowall can be used [117], In this case, the thickness of the cast increases with time t, following a parabolic relation, given by ... 

It adopted the method of layered filling for making slope. Every layer thickness was 5 cm. It made each layered soil heavy bag according to the first control needed for the soil density. We scattered the soil in uniform and consolidate step by step in the model box. We firstly made the soil level before compacting the soil. We tamped the soil in a certain direction with a half tamping pressure. 

A recent review of slip casting is given by Fries and Rand (35) and much practical details of the process can be found in a set of earlier articles (36). In the process, a slurry is poured into a microporous plasto- of Paris mold. The porous nature of the mold provides a capillary suction pressure, estimated to be of the ordo- of —0.1-0.2 MPa, which draws the liquid from the slurry into the mold. A consolidated layer of solids, referred to as a cast (or cake), forms on the walls of the mold (Fig. 6.33). After a sufficient thickness of the cast is formed, the surplus slip is poured out and the mold and cast are allowed to dry. Normally, the cast shrinks away from the mold during drying and can be easily removed. Once fully dried, the cast is heated to burn out the binder and sintered to produce the final article. Examples of slip casting compositions are given in Table 6.9. 

The uniformity of film thickness is dependent upon temperature and pressure. The nucleation rate rises with pressure, such that at pressures above atmospheric the high rate of nucleation can lead to comparatively uniform oxide films, while increase in temperature reduces the density of oxide nuclei, and results in non-uniformity. Subsequently, lateral growth of nuclei over the surface is faster than the rate of thickening until uniform coverage is attained, when the consolidated film grows as a continuous layer ... 

The attack of most glasses in water and acid is diffusion controlled and the thickness of the porous layer formed on the glass surface consequently depends on the square root of the time. There is ample evidence that the diffusion of alkali ions and basic oxides is thermally activated, suggesting that diffusion occurs either through small pores or through a compact body. The reacted zone is porous and can be further modified by attack and dissolution, if alkali is still present, or by further polymerisation. Consolidation of the structure generally requires thermal treatment. 

Above the water table, groundwater can also occur in perched aquifer conditions. In these instances, groundwater occurs in relatively permeable soil that is suspended over a relatively low permeability layer of limited lateral extent and thickness at some elevation above the water table. Perched groundwater occurrences are common within the vadose zone high-permeability zones overlie low-permeability zones of limited lateral extent in unconsolidated deposits. However, perched conditions can also occur within low-permeability units overlying zones of higher permeability in both unconsolidated and consolidated deposits. In the latter case, for example, a siltstone or clay stone overlies jointed and fractured bedrock such that groundwater presence reflects the inability of the water to drain at a rate that exceeds replenishment from above. 

In another set of studies, it has been reported that the in vitro digestibility of lipid droplets by pancreatic lipase is significantly affected by emulsifier type (Mun et al, 2006, 2007 Park et al., 2007). Intuitively, one might expect that a thick dense layer of strongly bound protein-polysaccharide complex at the oil-water interface would reduce considerably the in vivo accessibility of lipases, and hence would reduce the rate of human metabolism of fats. Establishment of the validity of this hypothesis must still await consolidation of a substantial body of detailed results from independent systematic studies on a broad range of mixed biopolymer systems. 

Figure 6.7 The effect of pressure on ultrafiltration membrane flux and the formation of a secondary gel layer. Ultrafiltration membranes are best operated at pressures between p2 and p3 at which the gel layer is thin. Operation at high pressures such as p4 leads to formation of thick gel layers, which can consolidate over time, resulting in permanent fouling of the membrane...

Gibson, R. 1958. The progress of consolidation in a clay layer increasing in thickness with time. Geotechnique, 8 171-182. 

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