PtFe alloys

Fig. 10. STM images of fcc(l 11) alloy surfaces. The bright atoms are Pt in PtCo and PtCu, but Fe in PtFe and Ni in PtNi. Compositions given are bulk compositions, except for PtFe, which is a surface alloy with =8 PtFe layers obtained by annealing a4 ML Fe film on Pt(111). The ordering of the PtFe alloy depends on the preparation frame (a) corresponds to an annealing tem-peramre of 470 °C, frame (b) to 530 C.

As can be known, the second additive can change the electric performance of a noble metal, so that the catalytic ability of the alloy catalyst will be improved a lot. In this section, we investigate the relation between the structural properties and the PROX catalytic performance of PtFe alloy nanoparticles catalysts supported with alumina. Table 29.1 shows the compositions of the samples used in this study. The weight percent of Pt was fixed as 3 wt% in the samples three Fe/Pt atomic ratios (I/I, 2/1, and 3/1) of PtFe alloy nanoparticle catalysts were prepared. 

Fe Mossbauer spectra of the as-prepared alumina-supported PtFe f alloy nanoparticles at room temperature, also including that of the as-prepared fee disordered PtFe alloy nanoparticles and Fe/AbOs. 

Taking into consideration on a very recent report that small monodispersed FeO nanoparticles were synthesized through reductive decomposition of Fe(acac)3 with oleic acid and oleylamine both as surfoctants and solvents at 220-300 °C [24], we can speculate that partial ferric irons were only reduced and stabilized in ferrous state due to the addition of-y-Al203 even in the existence of a noble metal promoter such as Pt in the chemical process used in the present study. This is reasonable since the ethylene glycol and oleic acid or oleylamine are relatively soft reducers. The results also implied that a strong chemical interaction existed between the support of Y-AI2O3 and the PtFe alloy nanoparticles. 

TABLE 29.2 Fe Mossbauer Parameters of PtFe Alloy Nanoparticles and Novel Alumina-Supported PtFe Alloy Nanoparticles at Room Temperature ... 

Figure 16.6 shows examples of saturated CO coverage on Pt and flie alloys after H2 oxidation for a prolonged period in the presence of 100 ppm CO. The CO coverage (6bo) on all of the CO-tolerant alloys is suppressed to values less than 0.6, while the other groups of alloys and pure Pt are almost completely covered with CO [228]. In the ease of PtFe alloys, for example, the addition of only 5% Fe to Pt reduees the saturated Oco to less than 0.3, resulting in the same activity level as those of other eompositions or combinations. 

Composites. Another type of electro deposit in commercial use is the composite form, in which insoluble materials are codeposited along with the electro-deposited metal or alloy to produce particular desirable properties. Polytetrafluoroethylene (PTFE) particles are codeposited with nickel to improve lubricity (see Lubrication and lubricants). SiHcon carbide and other hard particles including diamond are co-deposited with nickel to improve wear properties or to make cutting and grinding tools (see Carbides Tool materials). 

Carbon steel Sch. 40 Fiberglass reinforced polyester Fiberglass reinforced vinylester Glass pipe Aluminum Sch. 40 304 stainless steel Sch. 5 Saran-lined steel Polypropylene- lined steel Rubber-linedsteel Sch. 40 316 stainless steel Sch. 5 304 stainless steel Sch. 40 Kynar-Ifned steel 316 stainless steel Sch. 40 Alloy 20 Sch. 5 FEP Teflon-lined steel PFA Teflon-lined steel Armored-glass pipe PTFE Teflon-lined steel Monel 400 Sch. 5 Nickel 200 Sch. 5 Alloy 20 Sch. 40 Monel 400 Sch. 40 Inconel 600 Sch. 5 Titanium Sch. 5 Nickel 200 Sch. 40 Titanium Sch. 40 Inconel 600 Sch. 40 Glass-lined steel Sch. 40 Hastelloy C-276 Sch. 5 Zirconium Sch. 5 Hastelloy B Sch. 5 Zirconium Sch. 40 Hastelloy C-276 Sch. 40 Hastelloy B Sch. 40 Tantalum-lined steel Sch. 5 Tantalum-lined steel Sch. 40... 

Phosphoric Acid Fuel Cell This type of fuel cell was developed in response to the industiy s desire to expand the natural-gas market. The electrolyte is 93 to 98 percent phosphoric acid contained in a matrix of silicon carbide. The electrodes consist of finely divided platinum or platinum alloys supported on carbon black and bonded with PTFE latex. The latter provides enough hydrophobicity to the electrodes to prevent flooding of the structure by the electrolyte. The carbon support of the air elec trode is specially formulated for oxidation resistance at 473 K (392°F) in air and positive potentials. 

Fluorinated polymers stand out sharply against other construction materials for their excellent corrosion resistance and high-temperature stability. In this respect they are not only superior to other plastics but also to platinum, gold, glass, enamel and special alloys. The fluorinated plastics used in process plants are polytetrafluorethylene (PTFE), fluorinated ethylene/ propylene (FEP), polytrifiuoromonochlorethylene (PTFCE) and polyvinyl fluoride (PVF). They are much more expensive than other polymers and so are only economical in special situations [59]. 

Flange face areas experience stagnant conditions. Additionally, some gasket materials, such as asbestos fiber, contain leachable chloride ions. This creates crevice and stress corrosion cracking problems on sealing surfaces. Where necessary, flange faces that are at risk can be overlaid with nickel-based alloys. Alternatively, compressed asbestos fiber gaskets shrouded in PTFE may be used. 

Fluoropolymers utilizing high molecular weights and copolymerized and alloyed with polyethylene, should be used in most radiation applications. High-dose-rate E-beam processing may reduce oxidative degradation. When irradiated, PTFE and PFA are... 

Selection of Corrosion-Resistant Materials The concentrated sofutions of acids, alkalies, or salts, salt melts, and the like used as electrolytes in reactors as a rule are highly corrosive, particularly so at elevated temperatures. Hence, the design materials, both metallic and nonmetallic, should have a sufficiently high corrosion and chemical resistance. Low-alloy steels are a universal structural material for reactors with alkaline solutions, whereas for reactors with acidic solutions, high-alloy steels and other expensive materials must be used. Polymers, including highly stable fluoropolymers such as PTFE, become more and more common as structural materials for reactors. Corrosion problems are of particular importance, of course, when materials for nonconsumable electrodes (and especially anodes) are selected, which must be sufficiently stable and at the same time catalytically active. 

In applications where Nafion is not suitable, at temperatures above 200 °C with feed gas heavily contaminated with CO and sulfur species, a phosphoric acid fuel cell (PAFC)-based concentrator has been effective [15]. Treating the gas shown in Table 1, a H2 product containing 0.2% CO, 0.5%CO2 and only 6 ppm H2S was produced. The anode electrode was formed from a catalyst consisting basically of Pt-alloy mixed with 50% PTFE on a support of Vulcan XC-72 carbon. The cathode was... 

In a study of thermal stability and hydrogen sorption characteristics of a series of sorbent tablets composed of hydride-forming metals dispersed in polymers under a 50% hydrogen in argon atmosphere, it was found that tablets of 80% palladium in PTFE, and 80% of 1 5 atom lanthanum-nickel alloy in PTFE could not be used above 247° C because of explosive decomposition of the PTFE. 

Pt-alloy catalysts, 40 132-133 PTFE-bonded carbon electrodes, 40 133-134 Pt microcrystal particle size on soot, 40 131-132... 

Mkaline Fuel Cell The electrolyte for NASA s space shnttle orbiter fuel cell is 35 percent potassinm hydroxide. The cell operates between 353 and 363 K (176 and I94°F) at 0.4 MPa (59 psia) on hydrogen and oxygen. The electrodes contain platinnm-palladinm and platinum-gold alloy powder catalysts bonded with polytetraflnoro-ethylene (PTFE) latex and snpported on gold-plated nickel screens for cnrrent collection and gas distribution. A variety of materials, inclnding asbestos and potassinm titanate, are used to form a micro-porous separator that retains the electrolyte between the electrodes. The cell structural materials, bipolar plates, and external housing are nsnally nickel-plated to resist corrosion. The complete orbiter fuel cell power plant is shown in Fig. 24-48. 

The sample introduction unit was constructed from inert materials, which minimizes the introduction of metal contamination into the system. The samples or digestion acids make contact only with PTFE, Kel-F, glass, acid-resistant rubber and platinum-iridium (9 + 1) alloy. In addition, the construction materials were Hmited to acid-grade Arborite (ureaformaldehyde laminate). Perspex and stainless-steel. The unit was constructed in three continuous sections a heated sample compartment, a turntable mechanism and heat-exchanger compartment, and a pump compartment. 

Low-temperature p-hydrogen requires the use of materials that retain good ductility at low temperatures. Austenitic stainless steel (e.g. AISI 316L and 304L) or aluminum and aluminum alloys (Series 5000) are recommended. Polytetrafluor-oethylene (PTFE, Teflon) and 2-chloro-l,l,2-trifluoroethylene (Kel-F) can also be used. 

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