Surface preparation stainless steel alloys

Table IV shows X-ray data (55) on the homogeneity of Pd-Ag films prepared by simultaneous evaporation from separate sources, either in conventional vacuum or in UHV, with the substrate maintained at 0°C. The second group of films was prepared using a stainless steel system incorporating a large (100 1/sec) getter-ion pump, sorption trap, etc., but deposited inside a glass vessel. By the tests of homogeneity adopted, alloy films evaporated in conventional vacuum were not satisfactory, i.e., the lattice constants were generally outside the limits of the experimental error, 0.004 A, and the X-ray line profiles were not always symmetrical. In contrast, alloy films evaporated in UHV were satisfactorily homogeneous. Further, electron micrographs showed that these latter films were reasonably unsintered and thus, this method provides clean Pd-Ag alloy films with the required characteristics for surface studies.

Coupons of Type 304 stainless steel were prepared by mechanical abrasion and rinsed with methanol. Each sample was analyzed by XPS prior to treatment to ensure that no detectable casually-introduced chlorine was present. Two separate series of laboratory experiments were done one series (a) followed the effects of short-term contact between chlorocarbon and the alloy surface, a second series (b) investigated the effects of prolonged vapor and liquid contact with the alloy in a glass refluxer. In series (a) the clean alloy surface was swabbed using trichloroethane-soaked tissue and immediately inserted into the vacuum chamber of an XPS spectrometer for analysis. After analysis, the same coupon was exposed to the atmosphere for periods of 72 and 336 hours... 

Experimental Apparatus and Procedures. The amorphous alloys of about 15 microns thick and 3 mm wide ribbons were prepared by the disk method (8), the details of which have been described elsewhere (5). The important step of the method is the impinging of the molten mother alloy, held in a quartz tube with a small nozzle, onto the surface of a rotating disk of stainless steel. A flow type of a reactor apparatus, previously described (5), was used for the catalytic reaction. The reaction was carried out under atmospheric pressure and at temperatures from 220 to 370°C. The catalysts were pretreated with a stream of hydrogen in advance of a run. A gas chromatography was used for analyzing the hydrocarbons methane, ethylene, ethane, propylene, propane, butenes, butanes, total C5 hydrocarbons, and higher hydrocarbons (C6 to Cj0, not separated), as well as carbon monoxide, carbon dioxide and water. Alcohols and aldehydes could be detected by the gas chro-motography but were not found to be produced in sizable amounts. 

A two-step membrane manufacturing process has been reported where a defect free Pd-alloy membrane is first prepared by sputtering deposition onto the perfect surface of a silicon wafer, for example. In a second step the membrane is removed from the wafer and transferred to a porous stainless steel support (see Figure 11.1). This allows the preparation of very thin ( 1-2 pm) defect-free membranes supported on macroporous substrates (pore size equals 2 pm). By this technique, the ratio of the membrane thickness over the pore size of the support may become less than 1, which is two orders of magnitude smaller than obtained by more conventional membrane preparation techniques. Tubular-supported palladium membranes prepared by the two-step method show a H2/N2 permselectivity equal to 2600 at 26 bars and hydrogen flux of 2477 mL(STP) min cm . Since the method enables the combination of macro-porous stainless steel supports and thin membrane layers, the support resistance is negligible. ... 

The surface preparation procedures described in ASTM F 86 passivate stainless steels and cobalt alloys. Titanium materials do not require this passivation. It is not clear what the ideal surface for the metal implants should be, and this will continue to be an aspect of studies relating to interfaces of these materials with the body. The condition of the surface may influence ion release. 

To avoid classical corrosion mechanisms, ceramics and composite materials have also been tested (some of these materials are also common components in heterogeneous catalysts). An alumina reactor for SCWO was proposed among ceramic materials only a few aluminas and zirconias did not corrode severely, whereas SiC or BN lost up to 90% by weight under SCWO conditions in the presence of HCl. The combination of steel and ceramic coatings should theoretically provide high-pressure stability and improved corrosion resistance, but only slight improvements were reported for stainless steel SS316 coated with sol-gel-prepared Ti, Zr or Hf oxides, stainless steel SUS-304 with TiN or Ni alloys and ceramics. Often the adhesion of the ceramic layer on the steel surface is not sufficient. 

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