Nickel colloidal

The UV-visible spectra of Ni and Nia have also been identified in argon matrices (93) Ni absorbed at 377, 529, and 4l0 nm, with vi-bronic structure on the first two bands, and with spacing of—330 cm , and Nis absorbed at 420 and 480 nm, the latter band showing vibrational spacing of -200 cm" . Higher-nuclearity clusters were observed, but not characterized. After prolonged warm-up of these matrices, nickel colloid was formed (93). 

Greater durability of the colloidal Pd/C catalysts was also observed in this case. The catalytic activity was found to have declined much less than a conventionally manufactured Pd/C catalyst after recycling both catalysts 25 times under similar conditions. Obviously, the lipophilic (Oct)4NCl surfactant layer prevents the colloid particles from coagulating and being poisoned in the alkaline aqueous reaction medium. Shape-selective hydrocarbon oxidation catalysts have been described, where active Pt colloid particles are present exclusively in the pores of ultramicroscopic tungsten heteropoly compounds [162], Phosphine-free Suzuki and Heck reactions involving iodo-, bromo-or activated chloroatoms were performed catalytically with ammonium salt- or poly(vinylpyrroli-done)-stabilized palladium or palladium nickel colloids (Equation 3.9) [162, 163],... 

Figure 15 TEM image of nickel colloid. Some of the spherical particles show 19, 20 or 21 (111) layers, corresponding to 3.9, 4.1, or 4.3 nm diameter. Most of the particles have diameters in between the size range 3.9-4.3 nm. The insert shows a magnified image of a single colloidal particle consisting of 21 atomic layers. (From Ref. 129.)...

G Platz, C Thunig, J Policke, W Kirchhoff, D Nickel. Colloids Surf A 88 113, 1994. 

Chemical reduction is used extensively nowadays for the deposition of nickel or copper as the first stage in the electroplating of plastics. The most widely used plastic as a basis for electroplating is acrylonitrile-butadiene-styrene co-polymer (ABS). Immersion of the plastic in a chromic acid-sulphuric acid mixture causes the butadiene particles to be attacked and oxidised, whilst making the material hydrophilic at the same time. The activation process which follows is necessary to enable the subsequent electroless nickel or copper to be deposited, since this will only take place in the presence of certain catalytic metals (especially silver and palladium), which are adsorbed on to the surface of the plastic. The adsorbed metallic film is produced by a prior immersion in a stannous chloride solution, which reduces the palladium or silver ions to the metallic state. The solutions mostly employed are acid palladium chloride or ammoniacal silver nitrate. The etched plastic can also be immersed first in acidified palladium chloride and then in an alkylamine borane, which likewise form metallic palladium catalytic nuclei. Colloidal copper catalysts are of some interest, as they are cheaper and are also claimed to promote better coverage of electroless copper. 

Cobalt, sepn. of from nickel, (cm) 532 Codeine and morphine, D. of 740 Coefficient of variation 135 Colloidal state 418 See also Lyophilic, Lyophobic Colorimeters light filters for, 661 photoelectric, 645, 666 Colorimetric analysis 645 criteria for, 672 general remarks on, 645, 672 procedure, 675 solvent selection, 674 titration, 652... 

Sintered metal fibers with filaments of uniform size (2-40 (tm), made of SS, Inconel, or Fecralloy , are fabricated in the form of panels. Gauzes based on thicker wires (100-250 tm) are made from SS, nickel, or copper. They have a low surface area of about 10 m g. Several procedures are used to increase the surface area, for example, leaching procedures, analogous to the production of Ra-Nickel, and electrophoretic deposition of particles or colloid suspensions. The porosity of structures formed from metal fibers range from 70 to 90%. The heat transfer coefficients are high, up to 2 times larger than for random packed beds [67]. 

As early as 1954, Karl Ziegler [301,302] has assumed that colloidal nickel in triethylaluminium is the crucial co-catalyst which effects the controlled polymerization... 

Late transition metal or 3d-transition metal irons, such as cobalt, nickel, and copper, are important for catalysis, magnetism, and optics. Reduction of 3d-transition metal ions to zero-valent metals is quite difficult because of their lower redox potentials than those of noble metal ions. A production of bimetallic nanoparticles between 3d-transi-tion metal and noble metal, however, is not so difficult. In 1993, we successfully established a new preparation method of PVP-protected CuPd bimetallic nanoparticles [71-73]. In this method, bimetallic hydroxide colloid forms in the first step by adjusting the pH value with a sodium hydroxide solution before the reduction process, which is designed to overcome the problems caused by the difference in redox potentials. Then, the bimetallic species... 

In the study of effects of ultrasound on the aqueous reactions of nickel, we found some interesting results, for example, the colloidal formation of Ni-DMG complex and degassing of NH3 during different experiments. When 25 ml of 0.001 M NiSC>4 solution was complexed with 5 ml of 1% dimethyl glyoxime (DMG) in faintly alkaline ammonia medium and sonicated for 30 minutes and compared with another set of 25 ml of complexed solution which was stirred mechanically, a colloidal solution of Ni-DMG complex was formed in sonicated condition. Particles of Ni-DMG complex did not settle even after keeping 3 1 h because of their smaller size, in sonicated solution, whereas in the unsonicated condition large particles of Ni-DMG complex settled down immediately. 

From the above, it could be observed that ultrasound broke down the agglomerated precipitate of Ni-DMG complex to very fine particles, resulting in the formation of colloidal solution of Ni-DMG complex in the presence of an ultrasonic held. The settlement of particles was slow in the sonicated sample than in control sample. However, in the normal reaction, green precipitate of nickel (II) hydroxide dissolved in the excess NH3 solution and formed deep blue solution of hexammi-nenickel(II) ions, as under ... 

Violence of reaction depends on concentration of acid and scale and proportion of reactants. The following observations were made with additions to 2-3 drops of ca. 90% acid. Nickel powder, becomes violent mercury, colloidal silver and thallium powder readily cause explosions zinc powder causes a violent explosion immediately. Iron powder is ineffective alone, but a trace of manganese dioxide promotes deflagration. Barium peroxide, copper(I) oxide, impure chromium trioxide, iridium dioxide, lead dioxide, manganese dioxide and vanadium pentoxide all cause violent decomposition, sometimes accelerating to explosion. Lead(II) oxide, lead(II),(IV) oxide and sodium peroxide all cause an immediate violent explosion. 

For comparison, less superior test results of ECs with conductive additives of colloidal graphite and powdered nickel are shown in Figure 4. ESR of EC with refined graphite has increased by 56% after 36,000 cycles, and with nickel powder by 81% already after 1,400 cycles. Resistance of EC colloidal graphite increased by as high as 4,5 times compared to initial values already by the 500th cycle. 

Carried out testing confirmed the supposition about the degradation mechanism of electrode in NiOx-carbon ultra capacitors (Figure 1). Obviously, the smaller are the dimensions of particles of conductive additive (colloidal graphite) and the more active its surface is (nickel powder), the faster oxidation processes are taking place on the surface of these particles. 

Semibatch operation safety, 21 843 Semibatch polymer colloid process, 20 376 Semibatch polymerization of vinyl acetate, 25 608 Semibatch reactors, 21 332 Semibright nickel, 9 820 Semibulk containers, 18 5-6 Semibullvalene... 

In the industrial scale of hydrogenation of fats and oils, the most frequently used catalysts are Ni based. The 20-30% Ni is supported on silica. When partial hydrogenation is needed, the temperature applied is between 140 and 200 °C and the pressure between 4 and 10 bar. The total hydrogenation requires higher temperature and pressure (200 °C, 20 bar). Nickel is not a perfect catalyst due to its relative low activity and also due to the formation of Ni-soaps. Recently, a colloidal Pd catalyst was applied successfully in a two-phase system for this type of hydrogenation, at room temperature and atmospheric pressure. The complete conversion of multiunsaturated compounds could be achieved during 15-45 minutes. In dimethylformamide as the second phase solvent, 92% monoene yield with a 70/30 cis/trans ratio could be produced48. 

In ethanol nickel(II) acetate treated with NaBFLt produces a nearly colloidal black suspension63. Variation of the solvent in the preparation of the nickel catalyst results in an amorphous nickel boride catalyst67,68. This P-2 nickel catalyst is much more sensitive to the double-bond structure69,70. In the hydrogenation of the strained double bonds of nor-bomadienes, P-2 nickel shows high selectivity (95%) and low isomerization characteristics (equations 20 and 21). 

Isolation of the products is usually carried out by filtration. Suction filtration is faster and preferable to gravity filtration. When pyrophoric noble metal catalysts and Raney nickel are filtered with suction the suction must be stopped before the catalyst on the filter paper becomes dry. Otherwise it can ignite and cause fire. Where feasible centrifugation and decantation should be used for the separation of the catalyst. Sometimes the filtrate contains colloidal catalyst which has passed through the filter paper. Stirring of such filtrate with activated charcoal followed by another filtration usually solves this problem. Evaporation of the filtrate and crystallization or distillation of the residue completes the isolation. 

To a stirred suspension of 1.24 g (5 mmol) of powdered nickel acetate in 50 ml of 95% ethanol in a 250 ml flask is added 5 ml of 1 m solution of sodium borohydride in 95% ethanol at room temperature. Stirring is continued until the evolution of gas has ceased, usually within 30 minutes. The flask with the colloidal material is used directly in the hydrogenation. 

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