Spontaneous deposition

Figure 12.17 Representation of a scanning tunneling microscope image of Ru spontaneously deposited on aPt(lll) surface [Crown et al., 2002], The Ru coverage was about 0.2 ML. (Ru is in white on the figure and inset.) The inset indicates that monoatomic Ru deposition predominates diatomic deposition is found only with 10% of the Ru deposit.

Crown A, Johnston C, Wieckowski A. 2002. Growth of ruthenium islands on Pt(M/) electrodes obtained via repetitive spontaneous deposition. Surf Sci 506 L268-L274. 

Brankovic SR, McBreen J, Adzic RR. 2001a. Spontaneous deposition of Pt on the Ru(OOOl) surface. J Electroanal Chem 503 99. 

Herrero E, Leliu JM, Wieckowski A. 1999. Scanning tunneling microscopy images of ruthenium submonolayers spontaneously deposited on a Pt(lll) electrodes. Langmuir 15 4944. 

Human body fluid and SBF contain calcium and phosphate ions that are already supersaturated with respect to hydroxyapatite [20]. However, these fluids do not spontaneously deposit hydroxyapatite under normal conditions. This is because the activation energy barrier for hydroxyapatite nudeation is very high. Therefore, the ability of substrates to induce heterogeneous nudeation of hydroxyapatite and the degree of supersaturation of SBF with respect to hydroxyapatite are important factors for hydroxyapatite formation on materials in the body fluid and SBF. 

Tsunogai and Nozaki [6] analysed Pacific Oceans surface water by consecutive coprecipitations of polonium with calcium carbonate and bismuth oxychloride after addition of lead and bismuth carriers to acidified seawater samples. After concentration, polonium was spontaneously deposited onto silver planchets. Quantitative recoveries of polonium were assumed at the extraction steps and plating step. Shannon et al. [7], who analysed surface water from the Atlantic Ocean near the tip of South Africa, extracted polonium from acidified samples as the ammonium pyrrolidine dithiocarbamate complex into methyl isobutyl ketone. They also autoplated polonium onto silver counting disks. An average efficiency of 92% was assigned to their procedure after calibration with 210Po-210Pb tracer experiments. 

Ft partial and full monolayers have been deposited onto alternative metal particle cores. Brankovic, Wang, and Adzic found Ft spontaneously deposited onto hydrogen-reduced Ru particles at a surface coverage of 0.11 and 0.50. An alternative method of depositing Ft onto Fd, Fd alloy, and Au particles has been developed by Sasaki et al. and Zhang et al. This involves the deposition of a Cu overlayer by underpotential deposition followed by galvanic displacement by Ft. Complete monolayers of Ft have been claimed and the technique has been extended to preparation of mixed monolayers of Ft and other precious metals. ... 

Bert, P., Bianchini, C., Emiliani, C., Giambastiani, G., Santiccioli, S., Tampucci, A. and Vizza, E. (2006) Anode catalysts made of noble metal spontaneously deposited onto nanostructured catalysts based on transition metals, their preparation and use and fuel cells containing them, Republica Italiana Dom. It. FI2006A000180. 

Plates containing varying numbers of silver atoms per unit area were immersed for 5 minutes in a hydroquinone-silver nitrate physical developer which gave no spontaneous deposition of silver within 30 minutes. The number of developed centers per unit area wras counted under dark field illumination at a magnification of 500 X. 

After neutron irradiation bismuth (canned in aluminum jackets) is dissolved in a mixture of hydrochloric and nitric acids and excess NO3 is removed by adding a reducing agent, such as, urea or formic acid. If bismuth is used as an anode, the reducing agent is dissolved in HCl. Various methods are applied for concentration of polonium in the acid mixture and its subsequent separation from bismuth. Such processes include spontaneous deposition of polonium over a less electropositive metal and coprecipitation with tellurium. In the latter method, a Te + or Te + salt is added to the extract, followed by addition of stannous chloride, which reduces both the tellurium and polonium to their metallic state, coprecipitating them from bismuth in the extract mixture. 

Gao CY, Donath E, Mohwald H, Shen JC. Spontaneous deposition of water-soluble substances into microcapsules phenomenon, mechanism, and application. Angew Chem Int Ed 2002 41 3789-3793. 

Gao CY, Liu XY, Shen JC, Mohwald H. Spontaneous deposition of horseradish peroxidase into polyelectrolyte multilayer capsules to improve its activity and stability. Chem Commun 2002 1928-1929. 

Step 21. Suspend a clean nickel metal strip into the solution and stir for two hours to collect polonium by spontaneous deposition. 

Tin, in contrast to the other metals, deposited spontaneously onto Pt (that is, at open circuit, without the need for current flow in an external circuit) [51]. Auger spectra following spontaneous deposition showed a strong oxygen signal. Anodic electrolysis (oxidation) increased the oxidation state of the surface layer somewhat and rendered the surface passive except for evolution of H2 at very negative potentials and 02 at very positive potentials. Once immersion of Pt(lll) in Sn2+ (C1 or Br ) solution had taken place, the Sn deposit could not be removed from the surface by electrolysis in the same electrolyte. LEED patterns of the Sn layer were diffuse, indicating that the tin oxide layer was disordered. The pathway of spontaneous Sn deposition probably involves disproportionation, followed by oxidation of the metallic tin. 

The Irradiated Nl foils are dissolved in HHOg end the Cu activity is separated by spontaneous deposition on Zb dust In weakly acidic medium or by pptn. of Cu(I) thiocyanate after reduction with sulfurous acid. Then the filtrate Is counted for the zinc. 

Our experiments, begun in 1968, have demonstrated the reality of such adsorption on the surfaces of intrauterine contraceptives qualitative analyses were made of the spontaneously deposited material. Although evidence for protein denaturation and antibody response was not sought in this study, we do speculate on the importance of such a mechanism in fertility regulation. 

The determination of Po is relatively straightforward, due to the ease of source preparation by spontaneous deposition onto metal surfaces and the uncomplicated alpha spectrum. Although several optimisation studies have been carried out, published source preparation methods remain remarkably diverse. For this review about 130 papers mainly focussed on analytical methodology of Po were collected and critically examined. The literature surveyed included analysis of air, fresh water, rainwater, seawater, soil, sediment, coal, tobacco, phosphogypsum, foodstuffs, marine organisms, vegetation, human bone, and biota (Table 3). 

A number of electro-oxidation studies on ruthenium-modified, platinum singlecrystal surfaces have recently appeared. Ruthenium has most commonly been deposited from solution on single-crystal platinum surfaces through spontaneous deposition or under electrochemical control [80-82,88-93]. In some cases MVD... 

In order to demonstrate the importance of a local ensemble in the promotion by ruthenium of the L-H oxidation of CO, a number of experiments were carried out on stepped platinum surfaces [98]. The results of these experiments also provide an interesting comparison between surfaces modified by MVD ruthenium and through deposition from solution. Experiments were carried out [98] on Pt(lll), Pt(533), and Pt(311) single-crystal surfaces. Ruthenium was dosed from an aged solution of 5 X 10 RuCls in 0.5 M H2SO4 (believed to contain the complex Ru0(H20)] by spontaneous deposition at open-circuit potential) [80]. Experiments were carried out on the clean surfaces, following the spontaneously deposition of ruthenium, and on surfaces where the deposited ruthenium was reduced in a 10% H2 in Ar gas mixture. CO was adsorbed on the variously prepared surfaces from solution and stripped in CO-free H2SO4 electrolyte. 

Eigure 16a shows CO stripping on Pt(lll), Pt(lll)-Ru (following spontaneous deposition), and Pt(lll)-Ru (where the spontaneously deposited ruthenium has been reduced in hydrogen). Only a very small reduction in overpotential for CO electro-oxidation is observed for Pt(lll)-Ru . The overpotential for CO electro-oxidation on the Pt(l 11) surface has been reduced, however, on the Pt(lll)-Ru surface, and the latter exhibits a doublet structure. This CO stripping result on Pt(l 11)-Ru is nearly identical to that found on the Pt(l 11)-Ru surface where the ruthenium was MVD deposited (Eigure 15) It was concluded that Pt(lll)-Ru ° was decorated islands of Ru . 

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