Iron-aluminium-chromium

Determination of titanium with tannic acid and phenazone Discussion. This method affords a separation from iron, aluminium, chromium, manganese, nickel, cobalt, and zinc, and is applicable in the presence of phosphates and silicates. Small quantities of titanium (2-50 mg) may be readily determined. 

Other methods reported for the determination of beryllium include UV-visible spectrophotometry [80,81,83], gas chromatography (GC) [82], flame atomic absorption spectrometry (AAS) [84-88] and graphite furnace (GF) AAS [89-96]. The ligand acetylacetone (acac) reacts with beryllium to form a beryllium-acac complex, and has been extensively used as an extracting reagent of beryllium. Indeed, the solvent extraction of beryllium as the acety-lacetonate complex in the presence of EDTA has been used as a pretreatment method prior to atomic absorption spectrometry [85-87]. Less than 1 p,g of beryllium can be separated from milligram levels of iron, aluminium, chromium, zinc, copper, manganese, silver, selenium, and uranium by this method. See also Sect. 5.74.9. 

The preparation of lyophilic sols is easy and most of the time a mixture of the dispersion medium and the substance to be dispersed need only be stirred. Gelatine, for example, disperses almost spontaneously in water. The hydroxides of iron, aluminium, chromium and zirconium as well as vanadium pentoxide and silicic acids all belong to the group of hydrophilic colloids. 

High Temperature Corrosion Behaviour of Iron Aluminides and Iron-Aluminium Chromium Alloys... 

Table 3. Composition of iron-aluminium-chromium alloys investigated MM mischmetal, a mixture of reactive elements (mainly cerium and lanthanum) composition of alloy 800H nominal composition...

Table 5. Mass change, maximum depth of internal oxidation and maximum scale thickness "S" of iron-aluminium-chromium alloys after 1008 hours of cyclic exposure in air at 1100 C These alloys contain 0.15- 0.18 wt% mischmetal...

Fig. 3. Mass change versus time plots of different iron-aluminium-chromium alloys after cyclic exposure in air at 1100°C.

Fig. 6. Topical corrosion attack of an iron-aluminium-chromium alloy and 800H after 1008 hours of cyclic exposure in carburising CH4/II2 gas atmosphere at 1000°C a) Fe-A110-Cr2, b) Alloy 800H...

Fig. 11. Typical corrosion attack of iron-aluminium-chromium alloys after 2016 hours of cyclic exposure in sulphidising 1 %H2S/10 %C02/H2 gas atmosphere at 550°C a) Fe-A16-Cr2, b) Fe-A110-Cr2, c) Fe-A115-Cr2, d) Fe-A16-Crl0...

While additions of mischmetal have a huge impact on the oxidation behaviour of iron-aluminium-chromium alloys, changes in the concentration of aluminium or chromium do not effect the corrosion behaviour significantly. The differences between the... 

As expected, no carburisation attack at all was detected on iron-aluminium-chromium alloys after 1000 hours exposure in CH4/H2 environments at 850°C, 1000°C and 1100°C. Since the formation of chromia and iron requires relatively high oxygen partial pressures, alumina is the only stable phase at the low partial pressure of the used gas. If once formed, alumina is impervious to carbon, provided the scale remains intact [20], Excellent resistance to carburisation was also found for other alumina forming alloys like nickel aluminides [21] and Ni-Al-Cr alloys [22], The results of the present work show that 10 wt% aluminium are sufficient to prevent carburisation. It is expected, that the minimum aluminium concentration is even lower than 10 wt%. 

Iron-aluminium-chromium alloys should, however, not be applied in conditions where carbon activities above 1 are encountered. In C0-C02-H2 gas atmospheres, which were oversaturated with carbon (ac 1), rapid material wastage by so-called metal dusting was observed [23,24], As long as the carbon activity is below 1, however, excellent resistance of iron-aluminium-chromium alloys to carburisation can be expected even in oxygen deficient atmospheres. 

In sulphidising SOz/air environments between 650°C and 850°C the iron-aluminium-chromium alloys did not suffer any significant sulphidation attack. Although formation of a-Al203 cannot be expected at temperatures as low as 650 to 850°C, the scales formed were protective enough to prevent internal and external sulphidation. 

The high temperature corrosion behaviour of different iron aluminides and iron-aluminium-chromium alloys containing 6-17 wt% aluminium, 2-10 wt% chromium and additions of mischmetal has been investigated in both air and hot process gases. 

The degree to which soils in the urban and industrial environment have already been contaminated with the elements, boron, cobalt, copper, cadmium, lead, mercury, nickel and zinc, is already so high that we can only speculate about some of the possible long-term consequences of this kind of environmental pollution. There is also widespread dispersion, on a large scale, of other elements, such as iron, aluminium, chromium, silver and tin in the environment, but since iron and aluminium are already major components of the-earth s crust, and since chromium, silver and tin are not often involved in toxicity problems, we are mainly concerned with the eight elements in the former group. 

Klower J. High Temperature Corrosion Behaviourof Iron Aluminides and Iron- Aluminium-Chromium Alloys In Grabke HJ, Schiitze M, editors. Oxidation of intermetaUics. Weinheim - Germany Wiley-VCH Verlag GmbH 1997. p. 203-20. 

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