Reducing gas

A dichromate or chromate solution is reduced under pressure to produce a hydrous oxide, which is filtered, washed, and calcined at 1000°C. The calcined oxide is washed to remove sodium chromate, dried, and ground. Sulfur, glucose, sulfite, and reducing gases may be used as reducing agent, and temperatures may reach 210°C and pressures 4—5 MPa (600—700 psi). 

Table 7.29 Service experience with thermocouple protection tubes in reducing gases and other...

Gas-phase deposition In this process, a halide of the solute metal is passed in vapour form over the surface of the metal to be coated, which is heated to a temperature at which diffusion can take place. Temperatures of 500-1 300°C or more can be used, depending on the particular system considered. Generally, filler atmospheres are provided to carry the halide vapour these atmospheres are usually reducing gases such as hydrogen, cracked ammonia, etc. or inert gases (helium, argon). 

For certain applications it is important that the glass-ceramic should be unaffected by contact with reducing gases at high temperatures. In such... 

When reducing gases interact with the oxygen adsorbed in a charged form there is a product created that easily delivers electron into the conductivity zone with fast desorption [85-88] ... 

Storage-reduction experiments were also performed with synthetic exhaust and by reducing gases containing 3% C02 at 300°C, as well as at 350°C, and the same effects described above were observed. 

Critics of such experiments may And the concentration of reducing gases too high. It is, however, possible that there were localized areas on Earth where conditions were more strongly reducing for short periods (e.g., after volcanic eruptions). In the search for potential prebiotic syntheses of condensed phosphates, Keefe and Miller (1996) allowed a series of condensation agents to act on o-phosphate or tripolyphosphate, and determined the yields of diphosphate and trimetaphosphate obtained. 

The reaction mechanism for the solid state reduction is the same as that described above for the hydrogen reduction of haematite, namely the formation of a porous iron product which results from the penetration of pores in the reacting pellets by reducing gases, and the migration of the reaction products, C02 and H20 through these pores back into the gaseous phase. 

Circofer A DR process for finely divided ores using reducing gases made from coal in a circulating fluidized bed. Under development by Lurgi in 1995. 

COREX A two-stage ironmaking process. Iron ore is reduced in a vertical shaft furnace and then melted in a melter gasifier, which also generates reducing gases for the shaft furnace. Developed by DVAI, Dtisseldorf, and first used in 1989 at the Pretoria works of Iscor, South Africa. Ten plants were being planned in 1997. 

SPIREX A DR process for making iron powder or hot briquetted iron from iron ore fines. Three stages are used. The first is a circulating fluidized bed preheater whose turbulent conditions reduce the particle size of the ore. The second and third stages achieve the reduction in fluidized beds, fed by reducing gases from a MIDREX reformer. Developed by Midrex Direct Reduction Corporation and Kobe Steel. A demonstration plant was scheduled to be built at the Kobe Steel plant in Venezuela in 1997. 

---