Entrance diameter

Hopper entrance diameter Angie of cone Desired catalyst density Catalyst velocity... 

The most successful example is the control of window size of caged mesoporous silica materials synthesized with block copolymer as templates. The pore-entrance diameter of SBA-16 increases as a function of synthesis or hydrothermal-treatment temperature. This is likely to be related to the known phenomenon of the decrease in hydrophilicity of PEO blocks as the temperature increases. In the mesostructure of the F127-silica composite, the cores of the (spherical) micelles are constituted by PPO blocks, whereas the micelle corona, which consists of PEO blocks, interacts with the silica framework. At lower temperature, PEO blocks are expected to favorably interact with hydrophilic silica species and thus to have a tendency to be intimately mixed with the silica framework. When the F127-silica composite is subjected to the treatment at higher temperatures,... 

Figure 6.6 Mean entrance diameter of microholes obtained by SACE glass gravity-feed drilling as a function of the machining voltage and the drilling depth for a 0.4 mm stainless steel tool-cathode. Reprinted from [84] with the permission of the Journal of Micromechanics and Microengineering.

As in the case of tool-electrode vibration, the electrolyte flow can be promoted by tool-electrode rotation. An example combining gravity-feed drilling with tool-electrode rotation is shown in Fig. 7.6. A tungsten carbide flat sidewall tool-electrode (Fig. 7.3b) with pulsed voltage supply was used [136]. The drilling time for the fixed depth of 450 p,m increases with the tool-electrode rotation rate due to the reduced heat power. The entrance diameter shows an inverse volcano dependence on the tool-electrode rotation rate. This effect was attributed by the authors to the competition between the promotion of the electrolyte flow and the increased drilling time [136]. 

The promotion of the electrolyte flow results not only in reduced entrance diameters, but also in sharper microhole sidewalls and reduced roundness errors [136]. 

The entrance diameter decreases with T due to the reduced mean heat power supplied to the workpiece. Another reason for this behaviour is the periodic destruction of the gas film. This allows the electrolyte to flow inside the microhole and therefore results in a more homogenous chemical etching of the hole compared with DC voltage machining where the spark activity progressively moves to the top of the tool-electrode as the drilling goes deeper. 

Melt fracture for highly filled composite materials has a more complex character compared to that of neat plastics. And this is, of course, due to the effect of the filler. For example, using a cone die (the entrance diameter 2.5 in., the exit diameter 0.300 in., the length of the die 12 in.) it was shown for the neat HDPE that there was no visual signs of extrudate distortion for any of the flow rate tested (5.5-177 g/min), unlike that for filled plastics. Similarly, the 10%-filled (ground rice hulls) HDPE did not exhibit any observable extrudate distortion. However, the 60% -filled composite... 

Fig. la,b demonstrates the top view of the as-anodized porous alumina and the LC alignment on this surface. The LC alignment on the porous alumina film was the same as on the planar non anodized area of the aluminum film (the top left part in Fig. lb). It means that the LC could not penetrate in the pore space through the narrow pore entrance. The porosity of as-anodized films was about 15 %, and pore had the bottleneck form with the entrance diameter of about 5-10nm[6]. Such narrow pore entrance was not enough for the LC penetration into the closed porous space resulting in its horizontal alignment on the porous surface as on the planar non anodized aluminum surface. 

The entrance diameter (in the narrowest point) for one of the LP-FDU-12 samples calcined at 450°C was estimated to be 2 nm on the basis of the pore accessibility after the surface modification with triorganomonochlorosilanes of gradually increasing size. As can be seen in Figure 11.5, the introduction of trimethylsilyl (TMS) groups on the surface of LP-FDU-12 resulted in a slight decrease in uptake of... 

On the basis of the unit-cell size and pore diameter, one can estimate that the distance between adjacent spherical mesopores of the LP-FDU-12 sample calcined at 450°C was 6 nm. This distance is likely to correspond to the pore entrance length. Given that the pore entrance diameter (in the narrowest point) was 2 nm, the pore entrance length-to-diameter ratio was 3 1, and thus one can readily envision that the reduction of the pore entrance diameter through the thermal treatment would eventually lead to the closure of the entrance. The obtained ordered closed-pore silicas were white powders. It is clear that the block copolymer template was removed without the formation of the carbon residue, which was observed in an ordered closed-pore silica templated by PEO-PS copolymer. Pluronic (PEO-PPO-PEO) copolymers usually decompose at relatively low temperatures, so they may be inherently more convenient than PEO-PS copolymers, whose PS block has an appreciable tendency to carbonize. 

Pore entrance diameter much smaller than the pore cage diameter... 

The pyrolysis of benzene over the active carbon surface results in the deposition of the carbon on the surface of the substrate carbon as weU as in the microporous system and at some preferred sites. The adsorption isotherms of organic molecules of varying sizes and shapes indicated that the carbon gets deposited preferentially in the pore entrances reducing entrance diameter resulting in the formation of carbon molecular sieves. Pore-size distribution curves indicated that the treatment with benzene between 3 and 6 hrs reduces the mean pore dimensions to 0.6 nm, and a larger time of treatment reduces pore entrances to less than 0.6 nm. 

It appears that the adsorption of sulfur takes place in the narrow necks of the pores and reduces dimensions of the entrances to the pore cavity. An adsorption up to 1.6% of sulfur does not sufficiently reduce the pore entrance diameter to make it inaccessible to benzene molecule. However, when larger amounts of sulfur are retained, a fraction of the pores becomes inaccessible to even benzene molecules (molecular diam. 0.37 nm). This was further supported by the adsorption isotherms of organic molecules with larger molecular dimensions such as cyclohexane (mol. diam. 0.48 nm), n.heptane (mol. diam. 0.675 nm), isooctane (mol. diam. 0.68 nm), and a-pinene (mol. diam 0.80 nm). The adsorption of these molecules was found to decrease considerably... 

Spme and runners should be as small as possible to avoid rework of the polymeric material. The entrance diameter of the sprue should be larger in diameter than the nozzle diameter. Full round and trapezoidal runners have been used successfully to mold polymeric materials. Runner layout should be balanced and generously radius for smooth and uniform melt flow. Holdup spots can cause resin degradation, color changes, and property loss, especially in the flame-retardant and toughened grades. 

A second approach to control the entrance diameters to microporosities is to co-carbonize a parent material with a binder, as reported by Bello et al. (2002) using Eucalyptus globulus... 

Most MCP detectors employ two plates in series to achieve a high gain. A typical configuration is shown in Figure 3.25. Each individual channel has an entrance diameter in the region of 10 pm and the channel walls are oriented at an angle to the surface of... 

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