Nickel sample preparations

Ammonium pyrrolidine dithiocarbamate (APDC) chelate coprecipitation coupled with flameless atomic absorption provides a simple and precise method for the determination of nanomol kg 1 levels of copper, nickel, and cadmium in seawater. With practice, the method is not overly time-consuming. It is reasonable to expect to complete sample concentration in less than 20 min, digestion in about 4 h, and sample preparation in another hour. Atomic absorption time should average about 5 min per element. Excellent results have been obtained on the distribution of nickel and cadmium in the ocean by this technique. 

LDHs with Ni/Al molar ratio of 2.5 have been synthesized by a sol-gel method using nickel acetylacetonate and aluminium isopropylate as precursors. The sol-gel synthesized samples exhibited lower crystalhte dimensions and greater BET surface areas compared with coprecipitated samples prepared from an aqueous solution of nickel and aluminium nitrates [19,172]. 

Measurement of trace metals, including nickel in seawater can be completed using an in-line system with stripping voltammetry or chronopotentiometry (van den Berg and Achterberg 1994). These methods provide rapid analysis (1-15 minutes) with little sample preparation. The detection limit of these methods for nickel was not stated. Recommended EPA methods for soil sediment, sludge, and solid waste are Methods 7520 (AAS) and 6010 (ICP-AES). Before the widespread use of AAS, colorimetric methods were employed, and a mrmber of colorimetric reagents have been used (Stoeppler 1980). 

The unsymmetrical nature of / -mercaptoethylamine should lead to geometric isomerism among its metal complexes, cis and trans isomers might be expected with the square planar nickel (II) and palladium (II) derivatives and facial and peripheral isomers with cobalt (III). However, during the course of the preparation of various samples in which the procedure and experimental conditions were varied, no evidence of such isomerism was apparent (6, 15). This is particularly evident in the case of the cobalt (III) complex, CoL3. Samples prepared by the addition of cobalt (II) chloride 6-hydrate to strongly basic aqueous solution of the ligand and by displacement of ammonia and (ethylenedinitrilo)-... 

With the exception of the high initial heat of adsorption of CO on NiO(200), the differential heats of adsorption as a function of the amount of CO adsorbed are similar for both catalysts. Metallic nickel which exists in the sample prepared at 250°C. may chemisorb carbon monoxide (15). However, the metal content is small and cannot account for the heat released in these experiments on NiO(250), since the heat of chemisorption of CO on metallic nickel is still higher (42 kcal. per mole) than the heat registered during adsorption of the first dose (29 kcal. per mole). 

All samples prepared in this study showed XRD patterns atca. 20= 8°, 20°, 35°, 53° and 61° that are assigned to (001), (020, 110), (130, 200), (240, 310, 150) and (060, 330) diffraction peaks of smectite structure [6], The diffraction patterns derived from metal oxides (nickel, cobalt and zinc oxides) did not appear in XRD patterns of all samples after calcination at 873 K. 

Figure 1 shows Fourier transforms of EXAFS spectra of a few samples prepared. The radial distribution functions of these samples are different from that of nickel oxide or cobalt oxide [7]. All the Fourier transforms showed two peaks at similar distances (phase uncorrected) the peak between 1 and 2 A is ascribed to the M-0 bond (M divalent cation) and the peak between 2 and 3 A is ascribed to the M-O-M and M-O-Si bonds. The similar radial distribution functions in Figure 1 indicate that the local structures of X-ray absorbing atoms (Ni, Co, and Zn) are similar. No other bonds derived from metal oxides (nickel, cobalt and zinc oxides) were observed in the EXAFS Fourier transforms of the samples calcined at 873 K, which suggests that the divalent cations are incorporated in the octahedral lattice. 

Modular construction of the ternary complex begins with the epitope tag immobilization of Gfly subunits on beads. Scheme A represents the display of > d 1, 4) subunits tethered to the bead, by an epitope tag (hexahistidine or FLAG), with soluble oq subunit completing the hetero-trimer assembly (G-beads). The typical G-bead sample preparation involves the initial capture and immobilization of the fly subunits, on beads bearing chelated nickel or biotinylated M2 anti-FLAG antibodies. The bead samples are then washed and resuspended in buffer. For the anti-FLAG... 

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. 

Howlett and Taylor (1978) used an atomic absorption spectroscopy fitted with a micro-cup assembly (MCAAS) for determining silver levels in human whole blood. The MCAAS technique affords a rapid, precise, and relatively simple method for the measurement of silver in blood. Furthermore, this technique requires no sample preparation prior to analysis except pipetting and drying. A detection limit level of 0.27 pg/100 ml of blood sample was measured. Flowlett and Taylor (1978) noted that repeated measurement of silver in blood using a single nickel cup showed a gradual decrease in sensitivity. 

The samples prepared have a good surface area after calcination at 500°C, as can be seen in table 1. Alumina-titania mixed oxide supported samples have surface areas larger than those of the alumina and titania single oxides. As expected x-ray diffraction results show that the mixed oxide catalysts are amorphous, but alumina shows a y phase structure, and Ti02 is a well crystallized anatase phase. No nickel metal or nickel oxide was detected in any of the samples, including Ti02 sample, suggesting the metal was well dispersed, and present as small crystallites (< 50A). 

Kooli, F., Rives, V. and Ulibarri, M. A. (1995). Preparation and study of decavanadate-pillared hydrotalcite-like anionic clays containing transition metal cations in the layers. 1. Samples containing nickel-aluminium prepared by anionic exchange and reconstruction. Inorg. Chem. 34, 5114. 

Even in relatively large programs, few laboratories will justify the initial expense and calibration effort required for development of the emission spectrographic method. As reported by Scott etal. [3], sample preparation will generally not differ significantly from that required for AAS. Instrumental neutron activation analysis (INAA) is only attractive where a reactor is already available, and multielement analysis by this technique requires the use of high resolution Ge(Li) crystals and multiple irradiations for elements with differing activation product half-lives. The key elements, cadmium, nickel and lead still require analysis by AAS because of limitations of the INAA method [4]. 

We observed some differences in morphology between the samples prepared by these two ways. For the systems obtained in situ the formation of NiO phase proceeded both on the surface of the spheres of the silicate and inside its pores. The composite material obtained by the second (two-step) way differed from the in situ obtained material by preferable incorporation of the NiO inside mesoporous and nanotubes of the Ti-silicate (Fig. la). It is likely that microemulsion provides a uniform distribution of the chelated nickel ions Inside the micelles over the total surface of the silicate, whereas suspension guarantees higher completeness of a transfer and concentration of the NiO crystallites inside the pores of the silicate. 

Fig. 7. Thermograms of nickel silicate xerogels. Rate of raising temperature 10°/ minute a and b, for the samples prepared by the SHOP method at final pH s of 6.6 and 8.4, respectively c, for the sample prepared by mixing of individual precipitates.

NiO(250°) contains more metallic nickel than NiO(200°). Magnetic susceptibility measurements have shown that carbon monoxide is adsorbed in part on the metal (33) and infrared absorption spectra have confirmed this result since the intensity of the bands at 2060 cm-i and 1960-1970 cm-1 is greater when carbon monoxide is adsorbed at room temperature on samples of nickel oxide prepared at temperatures higher than 200° and containing therefore more metallic nickel (60). Differences in the adsorption of carbon monoxide on both oxides are not explained entirely, however, by a different metal content in NiO(200°) and NiO(250°). Differences in the surface structures of the oxides are most probably responsible also for the modification of their reactivity toward carbon monoxide. In the surface of NiO(250°), anionic vacancies are formed by the removal of oxygen at 250° and cationic vacancies are created by the migration of nickel atoms to form metal crystallites. Carbon monoxide may be adsorbed in principle on both types of surface vacancies. Adsorption experiments on doped nickel oxides, which are reported in Section VI, B, have shown, however, that anionic vacancies present a very small affinity for carbon monoxide whereas cationic vacancies are very active sites. It appears, therefore, that a modification of the surface defect structure of nickel oxide influences the affinity of the surface for the adsorption of carbon monoxide. The same conclusion has already been proposed in the case of the adsorption of oxygen. 

When pure and doped nickel oxides, prepared in vacuo, are heated in oxygen at 250°, their electrical conductivity increases and their color changes from yellowish green or green to black (77). Increase of electrical conductivity is associated with the increase of the number of Ni + ions resulting from the oxygen sorption. The electrical conductivity of the lithium-doped sample [NiO(10 Li)(250°)] is larger (0250° = 1-86 x IO-2... 

Removal of lattice oxygen from the surface of nickel oxide in vcumo at 250° or incorporation of gallium ions at the same temperature [Eq. (14)] causes the reduction of surface nickel ions into metal atoms. Nucleation of nickel crystallites leaves cationic vacancies in the surface layer of the oxide lattice. The existence of these metal crystallites was demonstrated by magnetic susceptibility measurements (33). Cationic vacancies should thus exist on the surface of all samples prepared in vacuo at 250°. However, since incorporation of lithium ions at 250° creates anionic vacancies, the probability of formation of vacancy pairs (anion and cation) increases and consequently, the number of free cationic vacancies should be low on the surface of lithiated nickel oxides. Carbon monoxide is liable to be adsorbed at room temperature on cationic vacancies and the differences in the chemisorption of this gas are related to the different number of isolated cationic vacancies on the surface of the different samples. 

Atomic absorption spectroscopy has been used to determine the amount of impurities in talc samples based on the chemical composition [35]. The detection of calcium, iron, and aluminum gave an indication of the mineral and chemical purity of the talc, whereas, analyses for chromium, manganese, nickel, and copper were of toxicological interest. The sample preparation involved an acid extraction with dilute hydrochloric acid to remove magnesium and calcium carbonates. Total dissolution of the sample was achieved with nitric/hydrofluoric acid mixture, followed by nitric/perchloric acid mixtures. Calcium was determined in the nitrous oxide/acetyiene flame and the other elements were detected in the air/acetylene flame. 

Table I summarizes the characteristics of nickel catalysts prepared onto these supports. For brevity these catalysts will be referred to by a notation in the form aA-fi. For example, 7AAP-573 represents a 7 wt % Ni catalyst supported on A O 2A1P0 reduced at 573 K for 1 h. Incidentally, this sample did not reduce under these conditions and was excluded from further kinetic studies. Notations for the other catalysts are shown in the first column of Table I. All samples were reduced at the specified temperature for 1 h unless noted otherwise. The percent reduction was determined by measuring oxygen uptake at 673 K in a commercial thermogravimetric system (Cahn 113). The average particle size was determined by either X-ray diffraction line broadening or magnetic measurements (see below).

The nitrogen adsorption isotherms of the H(3 zeolite and the Ni/H(3-CE samples (Fig. 2) are, as expected, very similar. In the sample prepared by DP, the presence of a hysteresis caused by the formation of a secondary porous system is evidenced in the Ni/H 32 and Ni/Hp4. The shape of the newly formed hysteresis suggests the formation of a laminar type porous structure [21, 22], possibly nickel phyllosilicates. 

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