Alloy oxidation/sulfidation

The use of EM (except in the special case of SEM) demands that the catalyst, whether mono-or multi-phasic, be thin enough to be electron transparent. But, as we show below, this seemingly severe condition by no means restricts its applicability to the study of metals, alloys, oxides, sulfides, halides, carbons, and a wide variety of other materials. Most catalyst powder preparations and supported metallic catalysts, provided that representative thin regions are selected for characterization, are found to be electron transparent and thus amenable to study by EM without the need for further sample preparation. 

Almost all new metallic surfaces exposed to the environment are sooner or later coated with a layer of corrosion products metal oxides, sulfides, and carbonates, for example, are common corrosion products formed when a metal or alloy interacts with contaminants in the environment. If the layer is continuous and stable, as in uniform corrosion, it may conceal the underlying metal from further exposure and protect it from additional corrosion if it is discontinuous, or chemically unstable, however, the metal surface below the initial layer of corrosion products remains in contact with the environment. Exposed to humidity and pollutants, the corrosion process continues, penetrating deeper into the metallic bulk and eventually resulting in its total destruction. 

Mixtures of inorganic oxygenated compounds (halide oxides or oxide sulfides) or oxygen-rich organic compounds (alkyl oxalates) with sodium (or its alloy with potassium) are shock-sensitive explosives. 

Apart from inorganic ionic oxides, sulfides, alloys, many minerals, porous solids, and the like also show composition variation. These materials raise a problem How does the structure accommodate the alteration in composition A vast number of different structural ways to account for composition variation are now known. 

This chapter has been devoted to the coordination chemistry of titanium and has made no attempt to describe the more basic chemistry of this element. References to alloys, to the simple halides and oxyhalides, the oxides, sulfides, selenides, tellurides, nitrides, azides, phosphides, arsenides and antimonides are well reviewed by Clark,14 and the recent text by Greenwood and Earnshaw180 contains a good section on titanium. 

The structure of clean surfaces of polyatomic solids (alloys, halides, oxides, sulfides, etc.) should be explored along with molecular solid surfaces (organic systems). More open, rough surfaces with high Miller indices should be investigated, including the structure of atoms and molecules bonded to steps and kinks on surfaces. Such sites are known to be key for some important surface chemical processes, but little is known of their structure. 

Fig. 1. The decreasing element concentration ratio of CM- over Cl chondrites indicates volatility related fractionations in CM meteorites and makes them of limited use as an abundance standard. The different symbol shapes indicate the principal mineral host phase for the elements (circle lithophile elements in silicate and oxides box siderophile elements in metal alloy chalcophile sulfides triangle halogen). Data sources for CM chondrites [21] plus updates Cl chondrites [17]...

Wells, A. F., Structural Inorganic Chemistry, 3rd ed., Clarendon Press, Oxford, 1962. The third edition of this well-known book is an exceedingly comprehensive source book for experimental methods of structural chemistry and detailed solid-state structures of oxides, sulfides, silicates, metals and alloys, etc., as well as of compounds of a number of the elements. It can be strongly recommended as general reading for the student. 

HNO3 Strong acid, strong oxidizing agent Metals, nonferrous alloys Metal sulfides Most organics... 

Composites containing different types of guests (metal or alloy particles, oxides, sulfides, complexes, polymers) in the cavities of zeolite hosts are prepared for various appHcations in materials research and catalysis. Except for quality assessment by detection of extra-zeolite material after synthesis or thermal treatments, photoemission plays a largely auxiliary role in this area, cooperating with bulk techniques such as X-ray absorption, UV-Vis, IR of probe molecules, and temperature-programmed reduction. The attention drawn to the significance of intra-zeolite potentials by XPS studies [12] has, however, contributed to the elaboration of a new theory of metal-support interactions [18,19]. 

In the oxidation, sulfidation, and so on of metals and alloys, solid reaction products are growing as film, scale, crystals, or in other morphologies, on the metal phase. A frequent case is the formation of a dense scale, separating the metal and gas phase. In this case, generally, a parabolic rate law is observed for the increase of film thickness x ... 

Chlorination technique has been developed to make the precious metals water soluble that is, effective for a low concentration sample, alloy, or sulfide mineral. Chlorination consists of both dry and wet methods. Chlorination gives a low reagent blank, and is used in combination with high-sensitivity detection. In the wet chlorination method, the samples are pressurized in a closed vessel with an oxidizing agent and hydrochloric acid, and dissolved... 

Ammonia and sulfides can also be produced from the decay of organic matter within the slime film, resulting in increased corrosion of some alloys [28], Sulfur-oxidizing organisms produce sulfuric acid from sulfur or other reduced sulfur species [2S]. The presence of anunonia is known to cause stress corrosion cracking of copper alloys, while sulfides may lead to accelerated attack on copper alloys and steel. The presence of the slime film on the metal surface can locally change the local environment at the liquid/metal interface such that the corrosion behavior of a metal can be considerably altered from one that nonnally displays low corrosion rates in seawater to conditions where corrosion is accelerated [6]. 

Another laboratory test that has been successfully used in screening candidate gas turbine alloys uses a mixture of 96 % O2 and 4 % SO2 [35]. When using O2-SO2 gas mixtures a platinum catalyst should be used to aid establishment of equilibrium. In this oxidation/sulfidation environment, subsurface sulfides normally get oxidized, releasing sulfur for further ingress into the metal. The extent of corrosion in this case should be assessed by cross section metallographic examination of the test specimens at the conclusion of the test, in addition to the measurement of mass change. 

Another oxidation/sulfidation test to assess the performance of gas turbine alloys is the burner rig test A schematic of the burner rig is shown in Fig. 6. Here a jet fuel is burned in a combustion chamber with an air-fuel ratio of 30 1. The flame jrasses down a tube at the end of which are the samples to be evaluated, mounted in a rotating platen. The samples are in the form of pins. The jet fuel normally contains a certain amount of sulfur. There are provisions to add additional sulfur in the form of volatile sulfur compounds. In addition, seawater can be added into the gas stream to simulate a marine environment. The setmples are typicaDy exposed to the flame temperature for 58 min and cooling air for 2 min in a 1-h cycle. The test is typiccJly conducted for about 500 h. 

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