Powder-modified

M.B. Powder (Modified Black Powder). Consisted of BkPdr in which part of the K nitrate was replaced by K perchlorate. The finely pulverized ingredients were preliminarily mixed, as in the prepn of BkPdr, and then incorporated together in a steam jacketed pan. The last operation was dangerous and some fires occurred, which were ascribed to friction in the hot, dry caked material. A similar expl was called Roslin Giant Powder Ref Marshall 1,385 (1917)... 

A batch of black powder, modified by addition of potassium chlorate, was being mixed mechanically with added water. A friction-sensitive crust appears to have formed, leading to initiation of the explosion which followed. 

The anodic polarization curves of a Pt powder modified by adsorbed Bi are shown in Figure 1. The ionization of adsorbed hydrogen on unmodified Pt (curve a) ranges between -0.8 and -0.4 V ... 

Most modern materials are formed empirically by solid-state methods. These methods generally involve more processing activity than chemical synthesis (for example, sintering of ceramic powders, modifying concrete by polymers, thermomechanical processing of alloys, layering polymeric membranes for... 

To construct and apply a biosensor based on Nujol/graphite powder modified with zucchini tissue (Cucurbita pepo) as the source of peroxidase to determine paracetamol in pharmaceutical formulations by linear sweep voltammetry (LSV). 

Figure 27.Cyclic voltammograms of Ni-powder modified CCE in 0.1 M NaOH Solution at scan rate lOOmVs 1. The cycle numbers are written on the voltammograms. Reprinted from Electrochimica Acta, 51 A. Salimi, M. Roushani, R. Hallaj, Micromolar determination of sulfur oxoanions and sulfide ata renewable sol-gel carbon ceramic electrode modified with nickel powder, 1954, Copyrights(2006) with permission from Elsevier.

Alumina Silica gel Modified silica gel Kieselguhr Cellulose powder Modified cellulose, e.g. D E A E and C M Sephadex gels Adsorption or partition Adsorption or partition Adsorption, partition Partition Partition Ion-exchange Exclusion... 

The stability improvement of Ti02 suspensions is important not only for water-based paints, but also for paints based on non-polar or low-polar solvents. It is shown in [208] that Ti02 powders modified with an anionic surfactant, e.g. sodium dodecyl sulphate, are dispersed to smaller sizes, and their sedimentation stability increases. The production of water-alkyd emulsions is inhibited due to low mechanical stability. These emulsions can easily break when exposed to shear forces such as those produced by pumps, and when intensively agitated during dispersion. [209] demonstrates that most stable emulsions can be obtained with alkyds showing high acid numbers, as well as with highly polymerised alkyds of low viscosities. 

Instead of the conventionally used modification by pre-immersion of the catalyst in a solution of modifier, Osawa et al. used an in situ modification during the enantioselective hydrogenation of MAA. Fine nickel powder modified with (2R,3R)-tartaric acid was used and sodium salt was added to the reaction media. By this method the optical yield was increased up to an ee of 79%. Improvement of this method consists in modification in situ of finely reduced Ni-powder by addition of (2R,3R)-tartaric acid and NaBr to the reaction media. In this case, an ee of 89% was obtained in the hydrogenation of MAA. The addition of small amounts of NaBr to the reaction media increased both the ee and the reaction rate, while, in contrast, the rate decreased with the addition of NaBr to the modification solution in... 

This invention relates to catalysts. More particularly it is directed to amorphous silica powders modified with a metal-containing constituent, to processes for making such powders by drying silica sols containing said modifiers, to a process for making metal-modified amorphous silica catalysts by molding the metal-modified amorphous silica powders, and to the uniformly porous and uniformly metal-modified catalysts so produced. 

Fabrication and Properties of Redispersible Polymer Powder-Modified Systems... 

Redi ersiNe Pofymer Powder-Modified System 159... 

The fabrication technique of redispersible polymer powder-modified mortar and concrete is about the same as that for latex-modified mortar and concrete. The materials and mix prc rtions used in this nnodified mortar and concrete are the same as those used in the latex-modified systems except that the addition of the redispersible polymer powders is involved. At present, commercially available redispersible polymer powders as cement modifiers are classified in Fig. 5.2. Table 5.2 gives the properties of typical redispersible polymer powders. The rediqretsible polymer powders are usually free-flowing powders, and have ash contents of 5 to 15%, whidi primarily come from the anti-blockirig aids. When the polymer powders are placed in water under agitation, they redtsperse or re-emulsify easily, and provide the polymer latexes with polymer particle sizes of 1 to 10 pm. 

Similar to latex-modified systems, the properties of redispersible polymer powder-modified systems are improved in comparison with ordinary cement mortar and concrete, and these depend on the nature of polymer and polymer-cement ratio. Figs. 5.3 to 5.5i l represent the strengths, adhesion to cement mortar, water resistance, and water absorption of the redispersible polymer powder-modified mortars. The properties are improved with an increase in the polymer-cement ratio. This tendency is very similar to that of the latex-modified systems. In general, the redispersible polymer powder-modified mortars are inferior to SBR-modified mortar (control) in certain properties. VAA eoVa powder-modified mortars show tetter properties than EVA powder-modified mortars as seen in Fig. 5.5. The film formation characteristics of recent redispersible polymer powders for cement modifiers are improved, and continuous polymer films can be found in the redispersible polymer powder-modified systems as seen in Fig. 5.6. This contributes greatly to improvements in their properties. 

Figure 5.3 Polymer-cement ratio vs. flexural and compressive strengths of redispersible polymer powder-modified mortars.

Figure 5 Electron micrograpb of polymer films formed in redispersible EVA powder-modified mortar.

According to a recent study, Bright, et al.1 1 compared the physical properties of various latex-modified mortars and redispersible EVA powder-modified mortars, and showed that the properti of EVA powder-modified mortars are at least equal to those of the latex-modified mortars as seen in Fi. 5.7 to 5.9i i Figure 5.10 exhibits the strength properties of patching mortars using redispersible polymer powders.i l... 

Afridi, et al.l found that redispersible polymer powder-modified mortars provide a freeze-thaw durability similar to that of latex-modified mortars. Fig. 5,11 shows the polymer-cement ratio vs. freeze-thaw durability of redispersible polymer powder- and latex-modified mortars.I 1 Figure 5.12 sho % the weatherability of patching mortars using redispersible polymer powders. " ... 

Figure 5.7 Comparison of tensile strength of latex- and redispersible EVA powder-modified mortars. ( 1993, ASTM, reprinted with permission.)...

Schneider, et examined the effect of glass transition temperature (Tg) on the adhesion (to plywood) and flexibility of redispersible EVA powder-modified mortars for plywood substrates, and found that EVA powder with a glass transition temperature of -10°C is more effective than one with a glass transition temperature of 10°C. 

Recently, redispersible polymer powder-modified mortar has been increasingly used in much the same applications as ordinary mortar and concrete. 

Abstract. Hydration of cement in the presence of SBR dispersion and powder respectively was investigated using the methods of ITC, XRD and ESEM. The results show that both the dispersion and powder of SBR facilitate the formation, enhance the stability of AFt and inhibit the formation of C4AH13 in cement paste the effect of the powder is more evident than the dispersion. Both the dispersion and powder of SBR delay the formation of C-S-H and Ca(OH)2 in cement paste, and the effect of the dispersion is more evident. Up to 3 days, the structure of the SBR dispersion - or powder - modified cement pastes has no significant difference with that of control paste except due to a thin polymer film on the surface. The two polymers delay the early cement hydration, but have no significant effect after 3 days. 

The cluster C-S-H gel becomes prominent after 12 hours but not the same as that after 6 hours in the control paste (Fig. 4 (g)) while fiber C-S-H gel appears in the SBR dispersion - or powder -modified pastes with few polymer particles among the cement hydrates (Fig. 4 (h) (i)), indicating most polymer particles coagulate together forming film structure. 

After 3 days, no outstanding difference exists between the SBR dispersion - or powder -modified pastes and the control paste except due to a thin polymer film on the surface [6]. The structure of both the modified and control pastes develops stably and becomes more and more compact with time. 

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