Patterned porosity

Close examination of these areas under a low-power microscope revealed smoothly rippled, spherical surfaces in the weld region and a chevron pattern that pointed back to the weld in the plate. Cross sections cut through the weld revealed substantial subsurface porosity and regions where oxidized surfaces prevented metallurgical bonding of the weld (Fig. 

Because the porous growth patterns of wood vary, the densities of various dry woods also vary (200-1200 kg/m- ). The porosity of wood, of course, greatly influences the wood s utility as a substrate. The wood porosity affects also the type and form of the adhesive as it affects the ability of the substrate to absorb water and other solvents from the adhesive, as well as allowing some of the adhesive to be absorbed over larger surface areas. 

The use of a chromium deposit with a fine porosity pattern of 15 000 to 45 000 pores per square centimetre in the usual thickness results in a sharp... 

Zeolites. In heterogeneous catalysis porosity is nearly always of essential importance. In most cases porous materials are synthesized using the above de.scribed sol-gel techniques resulting in so-called amorphous catalysts. Porosity is introduced in the agglomeration process in which the sol is transformed into a gel. From X-ray Diffraction patterns it is clear that the material shows only weak broad lines, characteristic of non-crystalline materials. Silica and alumina are typical examples. Zeolites are an exception they are crystalline materials but nevertheless exhibit high (micro) porosity. Zeolites belong to the class of molecular sieves, which are porous solids with pores of molecular dimensions, i.e., typically the pore diameter ranges from 0.3 to 10 nm. Examples of molecular sieves are carbons, oxides and zeolites. 

The washing of filter cake is carried out to remove liquid impurities from valuable solid product or to increase recovery of valuable filtrates from the cake. Wakeman (1990) has shown that the axial dispersion flow model, as developed in Sec. 4.3.6, provides a fundamental description of cake washing. It takes into account such situations as non-uniformities in the liquid flow pattern, non-uniform porosity distributions, the initial spread of washing liquid onto the topmost surface of the filter cake and the desorption of solute from the solid surfaces. 

A term applied to a moulded product which has failed to fill out the pattern details, showing rounded edges and porosity, either surface and/or internal. It does not necessarily mean that insufficient weight of compound has been used. Light Ageing... 

As a result of the crystal growth process Si wafers usually show striations, a variation in the bulk Si resistivity in a concentric ring pattern with a spacing in the order of millimeters. This variation of the bulk Si resistivity modulates the current density and thereby the porosity, which results in an interface roughness [Lel6]. Mesopore formation due to breakdown at the pore tips is very sensitive to striations and can be used for their delineation. 

Fig. 6.7 Calculated values of porosity as a function of the pore diameter to pore pitch ratio for pore arrays of different pore shapes and pore patterns.

Note that Eq. (9.1) applies to pore arrays as well as to randomly distributed pores. For simple orthogonal or hexagonal arrays of macropores with one pore per unit cell of the pattern, the porosity can be defined locally as the ratio between the cross-sectional area of the pore AP and the area of the unit cell AU as shown in Fig. 9.15 a ... 

Arrays with pore diameters d as small as about 0.3 pm have been achieved [Lel7]. The lower limit for the pore diameter is established by breakdown, according to Fig. 8.1b, which leads to light-independent pore growth and spiking. There seems to be no upper limit for the pore diameter, because the formation of 100 pm wide pores has been shown to be feasible [Kl3]. Array porosities may range from 0.01 to close to 1. The porosity, which is controlled by the etching current, determines the ratio between pore diameter and pitch of the pore pattern. 

Contaminants may reach the subsurface in a gaseous phase, dissolved in water, as an immiscible hquid, or as suspended particles. Contaminant partitioning in the subsurface is controlled by the physicochemical properties and the porosity of the earth materials, the composition of the subsurface water, as well as the properties of the contaminants themselves. While the physicochemical and mineralogical characteristics of the subsurface sohd phase define the retention capacity of contaminants, the porosity and aggregation stams determine the potential volume of liquid and air that are accessible for contaminant redistribution among the subsurface phases. Enviromnental factors, such as temperature and water content in the subsurface prior to contamination, also affect the pollution pattern. 

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