Removal of Surface Oxides

Sulfuric acid is number one in synthetic chemical production. It is used to produce phosphate fertilizer, high octane gasoline, and a wide variety of inorganic and organic chemicals. Large quantities are consumed to pickle steel (cleaning and removal of surface oxides) disposal of spent pickling liquor can be a problem. 

From the above discussion it becomes apparent that some conflicting experimental evidence exists on hydrocarbon adsorption and on surface intermediates. This arises primarily from the use of electrocatalysts of varying histories and pretreatments. It should be stressed that many adsorption studies were performed on anodically pretreated platinum. The removal of surfaces oxides from such electrodes may have not been always accomplished when the surface was cathodically reduced in some experiments, as outlined in Section IV,D. Obviously, different surface species could exist on bare or on oxygen-covered electrocatalysts. Characterization of surface structure and activity and of adsorbed species using modern spectroscopic techniques would provide useful information for fuel cell and selective electrocatalytic oxidations and reductions. 

The depth of the layer exponentially depends on the potential barrier E, which determines the stability of AHi in the matrix 5i 00 in the extreme case if E 00. We should mention that atomic hydrogen also provides effective removal of surface oxides before hydrogenation. 

The heats of immersion in both water and methanoP decreased continuously on evacuation of the carbon samples at temperatures above 300°C. The continuous decrease in the case of water resulted from the removal of surface oxides that provide hydrophilic centers for hydrogen bonding. The final heat of immersion value, when all the surface oxygen has been removed, agreed fairly well with the value obtained by Wade on graphon, which was completely free of any combined oxygen and... 

In mechanical brushing and machining normal metal finishing processes are used, which are applied e. g. for removal of surface oxides or rust. These processes normally generate aerosols and associated radioactive contamination, a problem which has to be met by the use of appropriate installations (e. g. glove boxes). 

Figure 2). The removal of surface oxides was accomplished by polishing the electroactive surface in a reduced oxygen environment (degassed cyclohexane). The simultaneous detection of multiple analytes is possible providing that both molecules react electrochemically at sufficiently separated potentials. This... 

Etch removal of the loose surface, gasification, and removal of surface oxidation products in the liquid-phase volume. 

Vacuuming and blowing remove the contaminant from the component by negative or positive air currents. These methods may be used to remove loose dirt, slag, scale, and various particles, but are not suited for the removal of surface oxides, greases, and oils. 

It is worthnoting that the inhibition of sintering in non-oxide ceramics is generally attributed to the presence of oxide impurities on the powder particle surface (Zou, 2011). In this respect, the above mentioned reactions help the removal of surface oxides, like B2O3, from the borides particle surfaces. 

Fretting Corrosion This attack occurs when metals shde over each other and cause mechanical damage to one or both. In such a case, frictional heat oxidizes the metal and this oxide then wears away or the mechanical removal of protective oxides results in exposure of fresh surface for corrosive attack. Fretting corrosion is minimized by using harder materials, minimiziug friction (via lubrication), or designing equipment so that no relative movement of parts takes place. 

Metal Oxide - Since metals are less electrophilic than silicon, metal oxide adsorbents show even stronger selectivity for polar molecules than do siliceous materials. The most commonly used metal oxide adsorbent is activated alumina, used primarily for gas drying. Occasionally, metal oxides find applications in specific chemisorption systems. For example, several processes are under development utilizing lime or limestone for removal of sulfur oxides from flue gases. Activated aluminas have surface areas in the range of 200 to 1,000 ftVft Average pore diameters range from about 30 to 80 A. 

Mercury. Double distilled mercury is usually recommended for polarographic work. The re-distilled mercury of commerce is generally satisfactory for most determinations it should be filtered through a filter-paper cone with a small pin-hole in the tip (or through a sintered-glass funnel) before use in order to remove any surface oxides or dust. 

The presence of PSCs also leads to the removal of nitrogen oxides (NO and NO2) from the gas phase. As long as there are significant amounts of NO2 it will react with chlorine monoxide (CIO) to produce chlorine nitrate (reaction 11). This species subsequently reacts with HQ on PSC surfaces to produce nitric acid (reaction 13), which remains in the condensed phase. Also, nitric acid directly condenses with water to form nitric acid trihydrate particles, hence it is not available to regenerate NO2 by photochemical processes, as it does when it is in the gas phase. 

Fig. 59. Molecular modification of semiconductor silicon surfaces. Removal of the oxide generates a hydrogen-terminated layer that reacts with a range of molecular functional groups including alkenes. 

After degreasing, metals have to be blasted with a sufficiently abrasive material to remove the surface oxidation layer. Application of the abrasive to the metal surface to be cleaned depends very much on the dimensions and type of metal. Large dimensioned metals and interiors of such articles as tanks, will require application of the abrasive by means of air blasting techniques. Smaller metals of suitable strength can be treated in rumbler machines where the metals are tumbled whilst being blasted by the abrasive carried in an airstream. 

V to +0.7 V vs. RHE for a Pd surface. Normally, this is anodic, or positive, with respect to the Em value of the electroless reaction (Fig. 1). Following removal of the oxide species from the catalyst surface, whether deposition subsequently initiates or not depends on the interplay between the kinetics of the parallel metal ion and O2 reduction reactions, and oxidation of the reducing agent. Once an appropriate Em value is reached, metal deposition will occur. 

An increased selectivity for phenol in the oxidation of benzene by H202 with TS-1 catalyst in sulfolane solvent was attributed to the formation of a bulky sulfolane-phenol adduct which cannot enter the pores of TS-1. Further oxidation of phenol to give quinones, tar, etc. is thus avoided. Removal of Ti ions from the surface regions of TS-1 crystals by treatment with NH4HF2 and H202 was also found to improve the activity and selectivity (227). The beneficial effects of removal of surface Al ions on the catalytic performance of zeolite catalysts for acid-catalyzed reactions have been known for a long time. 

The electron-rich oxygen anions exhibit basic electron donor capacity. Basic metal oxides are commonly used for neutralizing or scrubbing acidic gases. Alkaline earth metal oxides have been used for the removal of NOx. The surfaces of cubic alkaline metal oxide such as MgO, CaO, and BaO are dominated by the Lewis basicity of surface oxide anions. The basicity increases down the alkaline earth family as the metal ion radii become larger and the chaige on the metal ion becomes more positive. 

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