Active coatings

Fig. 8. Anode for monopolar diaphragm cells a, activated (coated) expanded metal b, expanding spring c, titanium-clad copper bar d, copper thread to fix...

Catalytic Unit. The catalytic unit consists of an activated coating layer spread uniformly on a monolithic substrate. The catalyst predominantly used in the United States and Canada is known as the three-way conversion (TWC) catalyst, because it destroys aU three types of regulated poUutants HC, CO, and NO. Between 1975 and the early 1980s, an oxidation catalyst was used. Its use declined with the development of the TWC catalyst. The TWC catalytic efficiency is shown in Figure 5. At temperatures of >300° C a TWC destroys HC, CO, and NO effectively when the air/fuel mixture is close to... 

Alumina is used because it is relatively inert and provides the high surface area needed to efftciendy disperse the expensive active catalytic components. However, no one alumina phase possesses the thermal, physical, and chemical properties ideal for the perfect activated coating layer. A great deal of research has been carried out in search of modifications that can make one or more of the alumina crystalline phases more suitable. Eor instance, components such as ceria, baria, lanthana, or 2irconia are added to enhance the thermal characteristics of the alumina. Eigure 6 shows the thermal performance of an alumina-activated coating material. 

The activated coating layer must possess two additional properties. It must adhere tenaciously to the monolithic honeycomb surface under conditions of rapid thermal changes, high flow, and moisture condensation, evaporation, or freezing. It must have an open porous stmcture to permit easy gas passage iato the coating layer and back iato the main exhaust stream. It must maintain this porous stmcture even after exposure to temperatures exceeding 900°C. 

Precious Meta.1 Ca.ta.lysts, Precious metals are deposited throughout the TWC-activated coating layer. Rhodium plays an important role ia the reduction of NO, and is combiaed with platinum and/or palladium for the oxidation of HC and CO. Only a small amount of these expensive materials is used (31) (see Platinum-GROUP metals). The metals are dispersed on the high surface area particles as precious metal solutions, and then reduced to small metal crystals by various techniques. Catalytic reactions occur on the precious metal surfaces. Whereas metal within the crystal caimot directly participate ia the catalytic process, it can play a role when surface metal oxides are influenced through strong metal to support reactions (SMSI) (32,33). Some exhaust gas reactions, for instance the oxidation of alkanes, require larger Pt crystals than other reactions, such as the oxidation of CO (34). 

Catalytic Support Body Monolithic Honeycomb Unit. The terms substrate and brick are also used to describe the high geometric surface area material upon which the active coating material is placed. Monolithic honeycomb catalytic support material comes in both ceramic and metallic form. Both are used in automobile catalysts and each possesses unique properties. A common property is a high geometric surface area which is inert and does not react with the catalytic layer. 

Lead compounds were not found on the surrounding activated coating layer, rather only associated with the precious metal. The Pt sites are less poisoned by lead than are Pd or Rh sites because the Pt sites are protected by the sulfur in the fuel. Fuel sulfur is converted to SO2 in the combustion process, and Pt easily oxidizes SO2 to SO on the catalyst site. The SO reacts with the lead compounds to form PbSO, which then moves off the catalyst site so that lead sulfate is not a severe catalyst poison. Neither Pd nor Rh is as active for the SO2 to SO reaction, and therefore do not enjoy the same protection as Pt. 

The active coating consists of a thermally deposited mixed metal oxide coating, the composition of which is considered proprietary information, although it is known that certain filler materials, e.g. Ta, may be added to the mixed metal oxide to reduce the precious metal content of the coating, and hence the cost of the anode. 

There are preprepared plates having an active coating on a thin plastic sheet, also with or without the fluorescent indicator. You can cut these to any size (they are about 8 in. by 8 in.) with a pair of scissors. Don t touch the active surface with your fingers — handle them only by the edge. The layers on the plate are much thinner than those you would make by spreading adsorbent on a microscope slide, so you have to use smaller amounts of your compounds so you don t overload the adsorbent. 

Electrodes may consist of a homogeneous material - frequently, with an in situ formed active layer on the surface - or of a carrier material with an active coating. A proper connection to the current feeder and a suitable assembling of the cell must be enabled often, a leakproof installation of electrodes in the cell body is required. Therefore, the mechanical properties of the electrode material have to pass practical selection criteria ... 

A chitosan oligomer film was used as an active coating for the immobihza-tion of ssDNA at a GC electrode. Chitosan oligomer is a kind of /1-1,4-linked... 

Active Coatings of Flame-Sprayed, Doped Nickel Oxide... 

In The Netherlands the firm Cam Implants in Leiden manufactures a series of implants on the basis of HA, among which bio-active coatings on orthopaedic and dental implants, implants for the small bones of the middle ear, which are made of dense ceramics, porous ceramics for the middle ear and jaw and facial implants. The latter are e.g. small blocks to fill holes resulting from the removal of cysts and tumours. 

Three different pharmacodynamic principles of action can be distinguished for mAbs, comprising lysis or apoptotic activity, coating activity, and inactivating activity (see Section 3.5.2), depending on the type of antigen and the antigen-antibody interaction. 

Many working groups have modeled the performance of diesel particulate traps during the past few decades. Concentrated parameter models (CSTR assumption) have been applied for the evaluation of formal kinetic models and model parameters. The formal kinetic parameters lump the heat and mass transfer effects with the reaction kinetics of the complicated reaction network of diesel soot combustion. Those models and model parameters were used for the characterization of the performance of different filter geometries and filter materials, as well as of the performance of a variety of catalytically active coatings and fuel additives [58],... 

Most of the existing processes for nitrogen oxide removal are chemically based requiring high temperature or expensive catalysts. The main techniques involve either selective noncatalytic reduction (SNCR) or selective catalytic reduction (SCR). SNCR uses ammonia for conversion of NO to N2 and H20 at elevated temperatures (550-850 K). SCR can use catalysts such as Ti02 with active coatings of V2Os and WO, . 

Certain reactants, carrier solvents, catalysts and chemically active coatings applied to inert substrates directly absorb microwave energy. 

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