Pores closure

Trapped gas in closed pores often limits densification when sintering witlr a liquid or viscous (glass) phase because rapid material transport tlirough tlie liquid often results in pore closure early in tlie sintering process. 

CaMKI and CaMKII) Dynamin-1 GTPase required for endocytosis that is phosphorylated by protein kinase C and dephosphorylated by calcineurin upon membrane depolarization and binds to AP2. Important for budding and fusion pore closure. 

Figure 9.2 shows that, during recycling of chemically delignified (Kraft) pulp fibres, irreversible pore closure within the cell wall takes place which leads to a reduction in their cell wall water content as measured by the fibre saturation point (see Chapter 5). The net effect of this is a loss in fibre flexibility which, in turn, leads to less effective inter-fibre bonding. 

In lithium ion rechargeable batteries, shutdown separators are used as part of the overall battery safety system. These devices prevent, or substantially reduce the likelihood of thermal runaway, which may arise from short circuiting caused by physical damage, internal defect, or overcharging. The shutdown separators, will shutdown by a sufficient pore closure to substantially stop ion or current flow within the cell (37). 

Yttria stabilized zirconia formed by this reaction fills the air electrode pores. The dynamics of this CVD stage has been modeled by Carolan and Michaels [120], who observed that films produced in this manner penetrate the substrate no more than 2-3 pore diameters from the chloride face of the substrate. It has also been shown that the penetration depth is independent of water concentration. The second step of this method is the EVD step. Once pore closure is achieved, the reactants are not longer in contact. Electrochemical semipermeability related to the existence of small electronic conductivity and large gradient of oxygen partial pressure leads to oxygen transport from the steam side to the chloride side through the deposited electrolyte. The electrochemical reactions involved are ... 

In air, the mechanical properties are influenced by the oxidation processes [543], In materials with a fine overall porosity the oxidation at > 1100 °C closes the pores with the help of an Si02 surface layer. This layer protects the material from further oxidation and heals surface defects. This and the formation of compressive stresses due to the different thermal expansion coefficients between Si02 and RBSN are the reasons for strength increase after oxidation. Materials with a high amount of macropores (>1 pm) oxidise not only at the surface but also inside the volume due to longer closing times of the surface pores. In consequence these oxidation mechanisms result in more intensive oxidation at low temperatures < 1100 °C, due to the slow rate of pore closure and higher internal oxidation. 

The other detrimental effect of fouling is that it changes the separation properties of the membrane. For microporous membranes that transmit some species and retain others the effect of fouling is usually to increase retention of partially transmitted species. This is because fouling leads to pore closure or blockage (see Section 6.1.3), making the membrane tighter. In some cases, such as water... 

Yu, H. C, and Sotirchos, S. A generalized pore model of noncatalystic gas-solid reaction exhibiting pore closure, AIChE J., 33, 782 (1987). 

At lower temperatures hydrated lime, Ca(OH)2, can be injected into the flue gas stream near the economiser zone (300-650 C). In this temperature range, CaCOj can be formed, which is undesirable because it not only consumes sorbent but pore closure also blocks the access of SO2 to the active sorbent surface. Carbonation significantly increases with reaction temperature, and therefore, the flue gas duct process where the temperature is about 150 C, may be more effective. This process yields S02-removal efficiencies of approx, 80% in actual commercial installations if small particles with an open pore structure are applied. 

In EVD, a modified form of chemical vapor deposition (CVD), an electrochemical potential gradient is used to grow a thin, dense layer of the ionic conducting oxide (e.g., yttria-stabilized zirconia) on a porous substrate. EVD is either a single-step or a two-step process depending on the nature of the substrate. For a porous substrate, the first step involves pore closure by CVD (i.e., deposition from the vapor of an oxide layer by reaction of a chloride gas precursor compound with water vapor or oxygen) ... 

Assuming that the vanadium deposits consist mainly of vanadium sulphides, it is then possible to extend the arguments of Tamm et al [20] to calculate possible effects of deposition of coke and metals on pore closure. Accepting that 200 mV is a typical surface area for hydrotreating catalysts, it is known that ca 50% of the surface area is lost during the initial deactivation [19-21], It is also known that V deposition occurs in the outermost part of the pellet [20,31,37,38]. As a result, the amount of V needed to provide a monolayer over the surface area available can be calculated to be between 0.034 and 0.079g cm ... 

Compaction conditions affect the total pore volume and shape of pores for some materials. In general, pore volume is smaller for a catalyst granulated by a tabletting machine than that by a pellet press. Partial pore closure is possible for tablets having a very high crush strength. 

Ramachandran and Smith obtained satisfactory agreement with experimental results on the reduction of nickel oxide with carbon monoxide (pore opening case) by considering the product layer diffusion coefficient as an adjustable parameter. Similarly, the model predicted pore closure and reaction die-off for the reaction of calcium oxide with sulfur dioxide, where the molar volume of calcium sulfate product is about three times that of the calcium oxide reactant. 

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