Platinum sample preparation

Platinum surfaces Mith (111) and (100) orientations treated in this May have been checked by using LEED characterization on as received" samples, both shoued the characteristic LEED pattern Hith their respective (lxl) surface symmetry. The non observation of the (5x20) symmetry for the (100) orientation Mas due to the presence of residual adsorbed impurities at the surface of as received samples. Simply this confirms the crystalline surface quality of the platinum samples prepared according to this technique (10). 

As shown in Fig. 1.28, a reaction vessel (cylinder) was made of 18-8 Cr stainless steel. The inner room for sample preparation, into which a platinum crucible was fitted, was sealed by screwing up a stainless steel disc wrapped in aluminium foil. This vessel can be used under the conditions that the reaction temperature is below 600 °C and the oxygen pressure is lower than 1000 atm. The experimental procedure is as follows place the weighed CrOj into the crucible, seal quickly, heat the vessel using an outer heater, and then keep it at a set temperature. 

The details of the sample preparation and studies of the nature of the supported-metal samples have been described in a paper dealing with the effect of surface coverage on the spectra of carbon monoxide chemisorbed on platinum, nickel, and palladium (1). The samples consist of small particles of metal dispersed on a nonporous silica which is produced commercially under the names Cabosil or Aerosil.f This type of silica is suitable as a support because it is relatively inert and has a small particle size (150-200 A.). The small particle size is important because it reduces the amount of radiation which is lost by scattering. A nonporous small particle form of gamma-alumina, known as Alon-C, is also available. This material is not so inert as the silica and will react with gases such as CO and CO2 at elevated temperatures. 

Turning to assays using sensors that require more than a simple cut in the sample, Bergann et al. [37] paid considerable attention to sample preparation in attempts to measure lactate in meat with a sensor (not thick film) based on reaction of hydrogen peroxide with a platinum electrode or on the reaction of ferrocene carboxylate with the active site of lactate oxidase. Sample preparation entailed extraction into buffer following grinding. In some cases, ground samples were left to allow the lactate to diffuse into the buffer solution. This was quite effective but slow (up to 90 min). Ultimately, the quality of the assay was dependent on the method of sample preparation. 

Kappes et al. evaluated the potentiometric detection of acetylcholine and other neurotransmitters through capillary electrophoresis [209]. Experiments were performed on an in-house capillary electrophoresis instrument that made use of detection at a platinum wire, dip-coated in 3.4% potassium tetrakis (4-chlorophenyl) borate/64.4% o-nitrohenyl octyl ether/32.2% PVC in THF. The results were compared to those obtained using capillary electrophoresis with amperometric detection at a graphite electrode. Samples prepared in the capillary electrophoresis buffer were electrokinetically injected (7 s at 5 kV) into an untreated fused silica capillary (88 cm x 25 pm i.d.) and separated with 20mM tartaric acid adjusted to pH 3 with MgO as the running buffer. The system used an applied potential of 30 kV, and detection versus the capillary electrophoresis ground electrode. 

The most direct evidence for the development of metallic platinum and PtSn alloy, by reduction of a catalyst prepared by the incipient wetness technique on low area Degussa alumina (110 irf/g) / was presented by Davis, et al. (11). Their conclusions were based on detailed XRD patterns, recorded in situ at elevated temperatures under flowing hydrogen. With 0.68% platinum samples containing tin, only Pt/Sn alloy diffraction lines were observed. 

Ultrasonic nebulizers have also been employed in continuous flow systems as interfaces between sample preparation steps in the analytical process and detection by virtue of their suitability for operating in a continuous mode. Thus, preconcentration devices have commonly been coupled to atomic spectrometers in order to increase the sensitivity of some analytical methods. An enhancement factor of 100 (10 due to USNn and 10 due to preconcentration) was obtained in the determination of platinum in water using a column packed with polyurethane foam loaded with thiocyanate to form a platinum-thiocyanate complex [51]. An enhancement factor of 216 (12 with USNn and 18 with preconcentration) was obtained in the determination of low cadmium concentrations in wine by sorption of metallic complexes with pyridylazo reagents on the inner walls of a PTFE knotted reactor [52]. One special example is the sequential determination of As(lll) and As(V) in water by coupling a preconcentration system to an ICP-AES instrument equipped with a USN. For this purpose, two columns packed with two different resins selective for each arsenic species were connected via a 16-port valve in order to concentrate them for their subsequent sequential elution to the spectrometer [53]. 

The Pt NMR of small platinum particles on classic oxide supports show s that the clean-surface LDOS is largely independent of the support (sihca, alumina, and titania) and of the method of preparation (impregnation, ion exchange, and deposition of colloids). At a given resonance position, one always finds the same relaxation rate, independent of particle size or support. The shape of the spectrum is related to the sample dispersion. The same is true lor particles protected in fihiis of PVP. [However, samples prepared under conditions giving strong SMSIs behave differently 171)]... 

Properties of the adduct Samples prepared in silica and of uncertain composition were deep red. X-ray powder photographs of this material showed only a faint, sharp pattern, perhaps belonging to a minor phase. A similar faint pattern appeared on photographs of some xenon-platinum hexafluoride specimens. 

Wollaston s Second Process. A solution of 0.73 mL nitric acid (35%), water (6 mL), sodium chloride (1.32 g) and 0.51 mL sulfuric acid (96%) was added to 1.00 g crude platinum in a 10-mL round-bottomed flask and heated at 55 °C in a sand bath for 6 days. Further treatment and sample preparation were similar to the procedures described above for Wollaston s first process. 

The ZrF sample employed by McDonald et al. ( ) for enthalpy measurement was prepared by dissolving hafnium-free zirconium metal in 48% aqueous HF, and the resulting solution was evaporated to dryness. The crystalline product was heated slowly to 773 K in a platinum boat in a slow current of anhydrous HF. X-ray diffraction showed only crysalline ZrF. Wet analysis indicated 54.6% Zr (theory 54.55) and 44.9% F (theory 45.45). Due to the above facts we are uncertain whether the sample prepared is a mixture of a and B forms of a pure ZrF (B). Smith et al. (4) obtained their ZrF sample from the Oak Ridge National Laboratories, Oak Ridge, Tenn. Since the method of preparation of the compound is unavailable from the report, we do not know what kind of sample they used for measurement. 

In the present work, porous boron nitride samples have been prepared from different molecular precursors. The nature and the pretreatment of the precursors have been investigated in order to determine accurately the optimal conditions leading to high surface area porous boron nitride materials suitable to be used as catalysts supports. The best results led to BN powders presenting surface areas of about 250 to 300 m. g. The porosity resulted from the presence of two kind of pores mesopores down to 2 nm, and a microporosity corresponding to pores from 0.5 to 1 nm. Attempts were made to incorporate directly a noble metal precursor into the BN precursor. Up to 1100°C, Pd or Pt were kept in the porous structure, but the very high temperature required to stabilise BN powders lowered drastically the metal concentration on the catalyst As a consequence, only the platinum sample could be obtained and characterized this catalyst is currently being tested. 

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