Iron oxide, precipitation technique

Although iron oxides precipitate out of water readily, it is difficult to control the precipitation process to form uniform particles of the desired size. The variability in the local environment results in variability in the product. Coprecipitation techniques require strict control of many variables (pH, temperature, mixing times, etc.) and provide no guarantees that a uniform solution environment will be obtained in the precipitation reaction. In addition, a period of... 

Nanocrystalline gamma iron oxide (y-Fe203) recently been studied as a gas sensing material, has been synthesised at 70°C using sonication-assisted precipitation technique [21]. The synthesised material was then used for fabricating the... 

For a precipitated iron catalyst, several authors propose that the WGS reaction occurs on an iron oxide (magnetite) surface,1213 and there are also some reports that the FT reaction occurs on a carbide surface.14 There seems to be a general consensus that the FT and WGS reactions occur on different active sites,13 and some strong evidence indicates that iron carbide is active for the FT reaction and that an iron oxide is active for the WGS reaction,15 and this is the process we propose in this report. The most widely accepted mechanism for the FT reaction is surface polymerization on a carbide surface by CH2 insertion.16 The most widely accepted mechanism for the WGS reaction is the direct oxidation of CO with surface 0 (from water dissociation).17 Analysis done on a precipitated iron catalyst using bulk characterization techniques always shows iron oxides and iron carbides, and the question of whether there can be a sensible correlation made between the bulk composition and activity or selectivity is still a contentious issue.18... 

Table III suggests some of the proton transfer kinetic studies one is likely to hear most about in the near future. The very first entry, colloidal suspensions, is one that Professor Langford mentioned earlier in these proceedings. In the relaxation field, one of the comparatively new developments has been the measurement of kinetics of ion transfer to and from colloidal suspensions. Yasunaga at Hiroshima University is a pioneer in this type of study (20, 21, 22). His students take materials such as iron oxides that form colloidal suspensions that do not precipitate rapidly and measure the kinetics of proton transfer to the colloidal particles using relaxation techniques such as the pressure-jump method.

Synthetic Iron Oxides. Advantages of synthetic iron oxides over their natural counterparts include chemical purity, more uniform particle size and size distribution, and in the case of precipitated oxides the ability to prepare the pigment in predispersed vehicle systems by flushing techniques. 

To date Sasol has used only iron-based catalysts. Not only is iron much cheaper than the alternative metals, but it also produces more olefins. For the fixed-bed reactors the silica-supported and alkali-promoted catalyst is prepared by precipitation techniques (ref. 2). A recent improvement in catalyst formulation has resulted in a more reactive catalyst as well as a lower cost per reactor charge. The catalyst used in the fluidized-bed reactors is prepared by fusing suitable iron oxides together with the... 

We have completed experiments label the ionic domains. We have found evidence of a precipitation phenomenon of particles of iron oxide or hydroxide when an iron form of membrane was exchanged by different other ions like K+, Na+, etc. We therefore have analyzed these particles by different techniques -like X rays, Mossbauer spectroscopy, magnetic measurements and electron microscopy- with two goals in mind. First of all the formation of ultra thin particles is very important in different domains and especially in catalysis when these membranes are used in the solid polymer electrolyte process. Second, we expect some correlation between the sizes and distribution of precipitates with the starting ionic domains. 

LTFT iron catalysts are commonly prepared by precipitation techniques, with a typical composition of potassium oxide, copper, silica and iron (1 1 5 20 by mass). Before use in the LTFT process, the catalysts are prereduced with either hydrogen or a syngas mixture.HTFT catalysts can be formed from the fusion of magnetite with various promoters, typically potassium oxide and aluminium oxide or magnesium oxide. Similarly, HTFT catalysts require a pre-reduction with hydrogen at ca. 400 °C. 

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