Wet techniques

Harrison s reagent (a mixture of non-aqueous solutions of 4-(lV,iV-dimethylamino)-benzaldehyde and diphenylamine) yields a yellow, orange, or brown colour on contact with phosgene, according to concentration [165,1742]. A more marked colour change (yellow to blue) is observed when N,yV-dialkylanilines are coupled to the above aldehyde, and exposed to phosgene [1255]  

Similarly, an intense blue-violet colour is generated when phosgene is exposed to 4- N,N-dimethylamino)benzaldehyde and the resulting aryldichloromethane is reacted with 3- N,N-dimethylamino)phenol [1928], 

Mixing of ethereal solutions of phosgene and 4-(4 -nitrobenzyl)pyridine results in the formation of a precipitate (3.1), which gives a violet product (3.2) on addition of an alkali [1202]  

Colorimetric methods have been developed for the detection of phosgene in trichloromethane or tetrachloromethane [33,52,425,1360b,1504,1815]. A sensitive visual test involves the addition of an excess of phenylhydrazine (usually as its tra/w-3-phenylpropenoate salt), which reacts with phosgene according to equation (3.4) [52,425]. The diphenylcarbazide 

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Chemical Analysis. Chemical analysis is deterrnined with conventional atomic absorption methods. Rehable wet techniques are sometimes employed (see Table 5). 

Vitreous enamel is normally applied to the prepared metal or over a ground-coat by spraying or dipping. Alternative wet techniques are used, of which the most common has been electrostatic wet spraying. Electrophoretic deposition from the slurry has been found to be highly suitable for some components. 

A 5 wt.% CoOx/Ti02 catalyst was prepared via an incipient wetness technique in which an aqueous solution of Co(N03)2 6H20 (Aldrich, 99.999%) was impregnated onto a shaped Ti02 (Milleimium Chemicals, commercially designated as DT51D, 30/40 mesh), as described in detail elsewhere [6]. Other supported metal oxide catalysts, such as FeOx, CuO, and NiOx, were obtained in a fashion similar to that used for preparing the CoO, catalyst. 

A Pt catalyst was applied by dry and wet techniques. By means of sputtering using a mask process protecting parts of the microstructure, the micro channel bottom was coated selectively. In addition, an y-alumina layer was applied by the sol-gel technique. Initially, the whole micro structure was covered by such a layer. Then, photoresist was applied and patterned so that only the channel part remained covered. After removal of the exposed photoresist and unprotected y-alumina, only the channel bottom was coated with y-alumina. 

The catalysts were prepared by impregnation of Si02 with an aqueous solution of H2PtCI6 and the appropriate promoting metal salts, using the incipient wetness technique. Si02, type M from Chemische Werke Uetikon, Switzerland, was used (20-35 mesh (ASTM), BET surface area 470 m2/g, pore volume 0,38 ml/g, composition 41,9% Si, 860 ppm Ca, 150 ppm Mg, <200 ppm Na, <200 ppm Al, <200 ppm Ti, <150 ppm Fe, 50 ppm S, 50 ppm Cl). The presence of Ca and... 

Instrumental Methods. Engineers in the IC industry prefer to use X-ray or FTIR spectroscopy to determine the quantities of phosphorus in thin films because of the speed of these methods. These spectroscopic methods are satisfactory for a relative indication of the dopant level in thin films or additives to metallization layers, but they do have serious drawbacks. X-ray spectroscopy is seriously affected by matrix effects and can easily be off by 15-20% of the actual concentration of dopant in thin films if the equipment is not properly calibrated against a material that has been analyzed by wet techniques. X-ray spectroscopy is further affected by the film thickness and the dopant profile throughout the film. 

Preparation of Pt-TiOx/Pd membranes. It was also desirable to prepare metalloceramic membranes in which the catalytic activity of the ceramic phase was enhanced through the addition of a noble metal. The very low surface area of the titania films prepared as described above made them difficult to impregnate with adequate dispersion by traditional incipient wetness techniques. Instead, finely ground titania (>200 mesh) was impregnated with platinum via the incipient wetness method with a chloroplatinic acid solution. This powder was then sprinkled onto the surface of a freshly dipped membrane, which was dried and heat treated as described. These materials were activated before use at 350°C in hydrogen for three hours. 

Most of the published methods for preparing gold catalysts in small research quantities are unlikely to prove suitable for commercial applications.1 Complete removal of precious metal from the liquid phase is desirable when using solution methods deposition-precipitation (DP) techniques, whilst producing highly active catalysts, also consume large quantities of water and the cost of treatment of wastewater is an expensive additional process. Other preparation methods such as appropriate modifications of impregnation via incipient wetness techniques are more likely to be suitable for commercial production if they lead to reproducible, stable... 

The usual preparation of supported micrycrystalline samples by the incipient wetness technique involves the impregnation of a support, e.g., silica gel or alumina, with a solution of a metal salt to form a thick slurry that is subsequently dried and sometimes heat-treated. 

The most direct evidence for the development of metallic platinum and PtSn alloy, by reduction of a catalyst prepared by the incipient wetness technique on low area Degussa alumina (110 irf/g) / was presented by Davis, et al. (11). Their conclusions were based on detailed XRD patterns, recorded in situ at elevated temperatures under flowing hydrogen. With 0.68% platinum samples containing tin, only Pt/Sn alloy diffraction lines were observed. 

This phenomenon has also been observed for catalysts prepared using an aqueous route (182). Both the iron and cobalt promoters led to an increase in selectivity. The iron-promoted catalyst was characterized by an increase in activity, but the cobalt-promoted catalyst was characterized by a decrease in activity. The decrease in activity of the cobalt-doped catalyst was attributed to the formation of VOPO4 in the final catalyst. The VOPO4 is formed by the oxidation of V0HP04 1 H20 during the introduction of the promoters in the incipient wetness technique. A similar effect was reported for catalysts doped with indium and tetraethy-lorthosilicate (TEOS) (181). The improved performance was observed only with both promoters in the catalyst. It was proposed that the... 

Pelletized granular resins can be obtained by agglomeration of fine-cut resins. The agglomeration process increases the powder flow and apparent density. The goal of this process is to make the small PTFE particles adhere together. Essentially, there are two processes of agglomeration namely, dry and wet techniques [24]. 

Experimental Procedure. FCC catalysts employing the submicron zeolite structure were used in this study. These catalysts were synthesized, spray-dried into 60 /tm pellets and impregnated with the metals by the incipient wetness technique at CREC-UWO. 

In a much earlier patent, the removal of organics from exhaust gases by oxidation over a supported uranium oxide catalyst was reported by Hofer and Anderson [39]. The catalyst was 4% U3O8 supported on alumina spheres. The authors used the incipient wetness technique to impregnate alumina with uranyl nitrate solution. In this case the catalyst precursors were calcined at 700°C for 3 h to decompose the uranium salt. The use of other uranium compounds as starting materials was mentioned and these included uranyl acetate, uranium ammonium carbonate and uranyl chloride. The alumina-supported catalyst had a surface area of ca 400m g and further added components, such as copper, chromium and iron, were highlighted as efficient additives to increase activity. 

A full-scale pyrolysis-catalytic process in which the catalytic cracking zone is directly connected to the pyrolysis zone was developed in Japan (Fuji Process) [19]. In this process, after separation of PVC and impurities by wet techniques, waste plastics are thermally pretreated at 300°C for dechlorination and then introduced into the pyrolysis reactor and thermally cracked at 400°C. Subsequently, degradation products are fed directly to the fixed-bed reactor using a ZSM-5 catalyst. 

Supported metal catalyst were prepared by the incipient wetness techniques. SiOn. supported Ni and other metal catalysts (10wt%) were used for both CO, methanation and CH4 decomposition. Catalytic activity to COj methanation and the decomposition of methane were performed with a pair of conventional fixed bed micro flow reactors at an atmospheric pressure connected in series, of which temperature controlled separately. 

Figure 5 Determination of 7 and 7 of the coated fibre 3 by the wetting technique.

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