Preoxidized material

Amorphous films were prepared by thermal evaporation of the Sb Sei-, source material from an open stainless steel boat onto preoxidized A1 substrates in a vacuum of approximately 10 Torr. The substrate was cleaned in neutral detergent, deionized water, ethyl alcohol, and acetone and then oxidized in air at 1800°C before deposition. Deposition of the Sb Sei-, alloys was performed at a substrate temperature of 300K. It should be noted that while the substrate is aluminum, the layer directly under the film is aluminum oxide. Care was taken to avoid Sb fractionation. It should also be noted that... 

Results—High Temperature Oxidation. Two studies have shown that oxidation of annealed wrought 40 pm grain sized 304 stainless steel in air at 800°C produced a rapidly growing iron-rich oxide (47, 48). Oxidation of the same material in 10 Pa oxygen allowed the equilibrium Cr-rich oxide to form as shown in Fig. 10a. Additional oxidation in air at 800°C caused very little change in this protective layer (Fig. 10b), while other parts of the sample without the preoxidation treatment grew a thick Fe-rich oxide layer. 

Reduction of 02 by Atom Transfer. In contrast to the preceding electron-transfer mechanism with inert electrodes, the reduction of dioxygen at freshly preoxidized metal electrodes is pH-dependent, yields negligible amounts of hydrogen peroxide, and occurs at the same potential as that for the metal oxide of the electrode material. A plausible explanation for these observations is represented by the reaction sequence... 

A process involving preoxidation of lignocellulosic materials in particle form with HNO3, oxygen, or nitrous gases, and molding them into various shapes has been patented (SJ). The covalent bonding arises by formation of ester links between carboxyls and hydroxyls on the surface. 

At catalytic active electrodes, such as Devarda copper, Raney nickel or copper preoxidized to Cu(OH)2, nitrobenzene can be reduced to aniline in good material and current yield [104]. 

Experiments were carried out (a) in which the material of the reactor tube remained constant and the formation of coke was measured on foils of different materials and (b) in which the material of the reactor tube was varied and coke formation was measured on a foil of the same material. Both prereduction and preoxidation of the reactor system have been used as standard pretreatment in different cases. 

It is seen that coke formation on the sample of foil is dependent on the material of the tubular reactor as is the product gas composition. With the steel reactor, preoxidation leads to a substantial increase in the coke formation on the steel foil (Figures 6 and 7). The effect of preoxidation is even more pronounced with Ni as the foil material (Figure 8). On the other hand, preoxidation does not lead to a high rate of coke formation on the steel foil if a quartz liner is used in the tubular reactor (Figure 9). 

Using the quartz liner, coke formation on the foils was substantially less and so were the difference between the coke formation of preoxidized and prereduced foils. Quartz has been found to be catalytically inert and any effect on steam-cracking of propane should not and does not reflect the chemical nature of the surface. Gaseous and solid products obtained in the quartz reactor are shown in Figures 2, 3 and 9. The gas phase product spectrum is typical of a quartz reactor (Figure 2) and is unaffected by the foil material. The initial rate of coke formation on the foil depends on the foil material, but the rate of coke formation on all foils appears to approach a value similar to that for coke formation on coke. 

Preoxidation of the material at high temperatures (>1000°C) and high oxygen partial pressures. 

One example is the hot corrosion of a preoxidized nickel specimen by a thin Na2S04 melt film in a 0.1 wt. % SO2-O2 gas mixture at 1200 K [29]. By variation of the oxide scale thickness and the purity of the material, different regimes of corrosion were investigated passive state, pseudopassive state, and active state. The passive state of 99.9975% of pure nickel, preoxidized in pure O2 for 2 h at 1200 K is controlled by diffusion of 8207 in the salt melt. The corresponding Nyquist plot of impedance data shows linear behavior in the low-frequency range withaslope of45° (Fig. 16).The semicircle at higher frequencies was attributed to the resistance of the NiO layer itself The active state was established on less pure nickel... 

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