Powdered performance

Ofher fypes of carbon blacks, such as Kefjenblack EC-600JD and Denka, have also been used in MPLs for carbon fiber paper DLs [139,162]. Compared to Vulcan XC-72R, bofh carbon black powders performed better due to their lower resistance and their excellent water transport capabilities, which limit water flooding af higher currenf densifies [162]. 

Because particle size is so intimately intertwined with powder performance, it is one of the prime considerations in selecting excipients to develop or improve a formulation. This is particularly important with direct compression formulations where excipient flowability and compaction performance are critical. Typically, excipients for these applications exhibit narrow size distributions with moderate-to-coarse particle size, having a mean size from 100 to 200 pm. 

Subsequently, 3 grams (at least 60 pellets) of the pellets were homogenized by dissolution and precipitation as suggested by H. L. Wagner of NBS. Table II shows the results of 13 analyses on the homogenized fine powder performed over a period of about 10 days. 

The carrier properties have been studied in numerous in vitro studies to understand the influence on powder performance, especially drug detachment. The particle size distribution of the carrier is of paramount importance for the delivery and dispersion of drug particles by a device at given flow-rate conditions (Steckel and Mueller 1997 French et al. 1996 Kassem et al. 1989). An increased proportion of fine particles results in more efficient dispersion (Podczeck 1999), which has led to the proposal to deliberately add microfine lactose as a ternary agent (Lukas et al. 1998). 

Group A represents the best powders. They are fine and aeratable, such as cracking catalyst. They fluidize nicely, and expand particulately after reaching the point of incipient fluidization mf, until the first bubbles appear at a higher velocity, the minimum bubbling velocity umb. It is thus evident that the ratio of umJum is always greater than unity, and the greater is this value, the better the powder performs in fluidization. 

Chemical Vapor Deposition (CVD) has been defined as a materials synthesis process whereby constituents of the vapor phase react chemically near or on a substrate surface to form a solid product. With these traditional processes a reaction chamber and secondary energy (heat) source are mandatory making them different from the Combustion CVD process. Numerous flame-based variations of CVD have been used to generate powders, perform spray pyrolysis, create glass forms, and form carbon films including diamond films. 

Jokanovic, V., Janackovic, Dj., Curcic, R., Zivanovic, P., and Uskokovic, D., Synthesis of cordierite powder performed under the conditions of periodical ultrasonic fields activity. Mat. Set Forum, 282-283, 65-70, 1998. 

A similar effect of anions on the adsorption behavior of inhibitors is also observed on oxides [24], Figure 12.35 shows adsorption measurements on iron oxide powder performed with a inhibitor molecule similar as used for the experiments of Fig. 12.34. The behaviour in different neutral electrolyte solutions and in water is compared. It follows from these data that the inhibitor adsorbs less readily from the sodium sulfate solution than from distilled water or from perchlorate solution, the reason being that sulfate ions adsorb more strongly than perchlorate ions. The examples illustrate the importance of competitive adsorption for corrosion inhibition and they point out the complexity of the phenomena involved. While the presence of adsorbing anions affects the inhibition efficiency of adsorption type inhibitors, the presence of certain cations, for example Ca, can have a profound effect on the formation of three-dimensional surface films and thus on the efficiency of film forming inhibitors [26]. 

The calcination is necessaiy for two advantages firstly, the precalcined powder performed... 

Figure 4.7. Stokes diameter distribution data obtained for line start sedimentation of a glass powder performed at various concentrations, a) Data for a water suspension floated onto a water column, b) Data for a water suspension placed on a brine column.

The Direct Current Potential Drop method (DCPD) has been evaluated for non destructive testing of uniaxially produced Powder Metallurgical (P/M) parts. The aim is to adapt DCPD to be functional as an ndt tool during production of parts. Defects can occur at different stages in the production cycle which means that DCPD has to be performed on components in different states and searching for different defects. 

Decolorisation by Animal Charcoal. It sometimes hap pens (particularly with aromatic and heterocyclic compounds) that a crude product may contain a coloured impurity, which on recrystallisation dissolves in the boiling solvent, but is then partly occluded by crystals as they form and grow in the cooling solution. Sometimes a very tenacious occlusion may thus occur, and repeated and very wasteful recrystallisation may be necessary to eliminate the impurity. Moreover, the amount of the impurity present may be so small that the melting-point and analytical values of the compound are not sensibly affected, yet the appearance of the sample is ruined. Such impurities can usually be readily removed by boiling the substance in solution with a small quantity of finely powdered animal charcoal for a short time, and then filtering the solution while hot. The animal charcoal adsorbs the coloured impurity, and the filtrate is usually almost free from extraneous colour and deposits therefore pure crystals. This decolorisation by animal charcoal occurs most readily in aqueous solution, but can be performed in almost any organic solvent. Care should be taken not to use an excessive quantity... 

CAUTION. The vapour of selenium dioxide is poisonous, and all operations involving the hot material, alone or in solution, should be performed in a fume-cupboard. If lumps of selenium dioxide have to be powdered in a mortar, the latter should also be in a fume-cupboard, with the window lowered as far as possible, to avoid inhaling the fine dust. (cf. p. 191)... 

Reduction of a nitro compound to a hydroxylamine. Dissolve 0-5 g. of the compound in 10 ml. of 50 per cent, alcohol, add 0-5 g. of solid ammonium chloride and about 0 5 g. of zinc powder. Heat to boiling and allow the ensuing chemical reaction to proceed for 5 minutes. Filter from the excess of zinc powder and test the filtrate with ToUen s reagent see Section III,70,(i). An immediate black or grey precipitate or a silver mirror indicates the presence of a hydroxylamine formed by the reduction of the nitro compound. Alternatively, warm the filtrate with Fehling s solution a hydroxylamine will precipitate red cuprous oxide. (A blank test should be performed with the original compound.)... 

Powder Preparation. The goal in powder preparation is to achieve a ceramic powder which yields a product satisfying specified performance standards. Examples of the most important powder preparation methods for electronic ceramics include mixing/calcination, coprecipitation from solvents, hydrothermal processing, and metal organic decomposition. The trend in powder synthesis is toward powders having particle sizes less than 1 p.m and Httie or no hard agglomerates for enhanced reactivity and uniformity. Examples of the four basic methods are presented in Table 2 for the preparation of BaTiO powder. Reviews of these synthesis techniques can be found in the Hterature (2,5). 

Black Powder. Black powder is mainly used as an igniter for nitrocellulose gun propellant, and to some extent in safety blasting fuse, delay fuses, and in firecrackers. Potassium nitrate black powder (74 wt %, 15.6 wt % carbon, 10.4 wt % sulfur) is used for military appHcations. The slower-burning, less cosdy, and more hygroscopic sodium nitrate black powder (71.0 wt %, 16.5 wt % carbon, 12.5 wt % sulfur) is used industrially. The reaction products of black powder are complex (Table 12) and change with the conditions of initia tion, confinement, and density. The reported thermochemical and performance characteristics vary greatly and depend on the source of material, its physical form, and the method of determination. Typical values are Hsted in Table 13. 

The performance of black powder is critically dependent on the degree of intimacy of the components in the product. The manufacture of black powder is essentially a procedure for bringing the ingredients into maximum mutual contact. A detailed flow chart for the conventional process is presented in Figure 10. 

Prices for the different material groups (F —F ) are largely influenced by product size and shape and the quantity of production. Apart from product shape, the main price-determining factor is the performance factor K Prices for the powder, a sintered anisotropic ring, and a sintered anisotropic segment are roughly on the order of 1, 2, and 5, respectively. 

In 1954 the surface fluorination of polyethylene sheets by using a soHd CO2 cooled heat sink was patented (44). Later patents covered the fluorination of PVC (45) and polyethylene bottles (46). Studies of surface fluorination of polymer films have been reported (47). The fluorination of polyethylene powder was described (48) as a fiery intense reaction, which was finally controlled by dilution with an inert gas at reduced pressures. Direct fluorination of polymers was achieved in 1970 (8,49). More recently, surface fluorinations of poly(vinyl fluoride), polycarbonates, polystyrene, and poly(methyl methacrylate), and the surface fluorination of containers have been described (50,51). Partially fluorinated poly(ethylene terephthalate) and polyamides such as nylon have excellent soil release properties as well as high wettabiUty (52,53). The most advanced direct fluorination technology in the area of single-compound synthesis and synthesis of high performance fluids is currently practiced by 3M Co. of St. Paul, Minnesota, and by Exfluor Research Corp. of Austin, Texas. 

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