Effect of pressure on the ignition temperature of compact samples of nickel alloys in oxygen

It is found that compact samples of nickel and its alloys heated in “cold” (323 K) and “hot” (≤1573 K) oxygen ignite at temperatures exceeding the melting point of the materials. The ignition temperature is independent of the oxygen pressure up to 70 MPa. It is suggested that the drop in the ignition temperature of alloys with rising oxygen pressure reported in several papers is related to systematic errors in measuring the surface temperature of the samples. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 2, pp. 54–58, March–April 1999.     

Effect of an inert filler on the ignition conditions of a powder mixture of nickel and aluminum

The effect of an inert filler on the time-temperature characteristics of ignition of a nickel-aluminum powder mixture including intermetallide nucleation is examined to determine the possibilities of high-temperature synthesis of composites based on nickel aluminide. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 31–33, January–February, 1998.     

Mechanism of metal ignition due to fracture

A mechanism of ignition of compact metal samples during their fracture in oxygen is proposed. Ignition is assumed to be initiated by microfragments of the fractured sample at the moment when a crack passes through the volume of the metal, and the limiting stage of interaction is dissociative chemical adsorption of oxygen molecules on the surface of microfragments, which defines the dependence between the capability of materials to ignite during fracture and the pressure of the oxygen-containing medium. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 39–48, July–August, 2007.     

Burning through steel tubes by gas-dispersed products of thermite combustion

Numerical results of an experimental study of burning through steel tubes in a water medium by thermite-combustion products are presented. Based on the analysis of experimental data, recommendations on the optimal organization of the process are given, and an empirical formula for calculating the thermite mass necessary for burning through a steel wall is derived. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 79–82, July–August, 2000.     

Explosive-hazard estimates for several fluorine-containing monomers and their mixtures, based on the minimum ignition pressure with a fixed igniter energy

The minimum pressures necessary to ignite vapors of several fluorine-containing monomers and their mixtures were determined in experiments with one type of the igniter, a spiral made of molybdenum—rhenium wire. The energy supplied to the igniter is adjusted to be sufficient for pure tetrafluoroethylene ignition at pressures over 0.6 MPa. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 19–22, March–April, 2006.     

Effect of aluminum content on thermograms of synthesis of intermetallide Ni3Al by thermal shock

Thermograms of high-temperature synthesis of nickel aluminide Ni₃Al by thermal shock of powder mixtures of pure elements were studied experimentally by varying the proportion of mixture components within the single-phase composition of the intermetallic compound. A qualitative analysis of the main thermokinetic parameters of the thermal shock versus the aluminum content of the starting powder mixture was made. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 6, pp. 39–42, November–December 1998.     

Optimization of process variables for a biosorption of nickel(II) using response surface method

The biosorption of nickel(II) was studied by using crab shell particles of diameter (d _p =0.012 mm) under different initial concentrations of nickel(II) in solution (0.01–5.0 g/l), temperature (20–40 °C), pH (2–6.5), and biosorbent dosages (0.5–10 g/l). The maximum removal of nickel(II) occurred at pH 6.5 and temperature 40 °C for a biosorbent dosage of 6 g/l. The results were modeled by response surface methodology (RSM), which determines the maximum biosorption of nickel(II) as a function of the above four independent variables, and the optimum values for the efficient biosorption of nickel(II) were obtained. The RSM studies were carried out using Box-Behnken design and the analysis of variance confirms the adequacy of the quadratic model with coefficient of correlation R² to be 0.9999. The quadratic model fitted the data well with Prob>F to be <0.0001, indicating the applicability of the present proposed model.     

Black nickel electrodeposition from a modified Watts bath

Black nickel coatings were electrodeposited on to steel substrates from a Watts bath containing potassium nitrate. The best operating conditions necessary to produce smooth and highly adherent black nickel were found to be NiSO₄ · 6H₂O 0.63 M, NiCl₂ · 6H₂O 0.09 M, H₃BO₃ 0.3 M and KNO₃ 0.2 M at pH of 4.6, i=0.5 A dm⁻², T=25 °C and t=10 min. The modified Watts bath has a throwing power (TP) of 61%, which is higher than that reported, not only for nickel, but also for many other metals electrodeposited from different baths. The potentiostatic current–time transients indicate instantaneous nucleation. X-ray diffraction (XRD) analysis shows that the black nickel deposit is pure metallic nickel with Ni(111) preferred orientation.     

On the ignition of a layer of combustible forest materials by light radiation

The ignition of a layer of combustible forest materials by luminous radiation was studied experimentally. The minimum radiant heat flux densities required to ignite combustible forest materials are determined for a neodymium-doped glass laser and a tungsten lamp. It is established that the heat flux, density increases with increase in the moisture content and density of the layer of combustible forest materials and decreases with increase in the diameter of the light spot, and the critical flux density is higher for the laser radiation than for the incandescent lamp. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 22–25, November–December 1999.     

Damage of a steel plate from hypervelocity impact

We presents the results of damage of a carbon steel plate30 mm thick upon its loading by the impact of a steel ball5.55 mm in diameter at a velocity of up to7.4 km/sec. The dimensions of the crater formed and the bending flexure of the spalling layer are in good agreement with the results obtained upon a less intense loading of the target. One more feature of damage, namely, a crack passing through the target at the level of the crater bottom, has been revealed for the first time. Institute of Experimental Physics, Sarov 607200. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 119–121, January–February, 1997.     

Hydrogenation of alkali-conjugated linoleate: Isomeric monoene profiles obtained with nickel,palladium and platinum catalysts

Alkali-conjugated linoleate (cis-9,trans-11- andtrans-10,cis-12-octadecadienoate) was hydrogenated with nickel, palladium and platinum catalysts. Thetrans andcis monoenes formed during reduction were isolated, and their double bond distribution was determined by reductive ozonolysis and gas liquid chromatography. About 44–69% of the monoenes were composed of δ¹⁰ and δ¹¹ trans monoene isomers, whereas the δ⁹ and δ¹² cis monoenes amounted to 20–26%. With nickel catalyst, composition of monoene isomers remained the same, even when the hydrogenation temperature was increased. The monoene isomer profiles between nickel and palladium catalysts were indistinguishable. Isomerization of monoenes with platinum catalyst was suppressed at 80 psi. The position of the double bonds in unreacted conjugated diene was always retained, except with nickel at both temperatures and with platinum at 150 C when a slight migration occurred. Geometrical isomerization totrans,trans-conjugated diene was observed in the unreacted diene with nickel (ca. 15% of diene) at both 100 C and 195 C, and with platinum (ca. 7% of diene) at 150 C. ARS, USDA.     

Hydrogenation of linolenate. VIII. Effects of catalyst concentration and of temperature on rate,selectivity, andtrans formation

The effects of catalyst concentration and of temperature on linolenate selectivity,trans formation, and rate of hydrogenation have been studied for a commercial electrolytic nickel catalyst. Results obtained with an equimixture of linoleate and linolenate, following the procedure previously described, are presented as isometric drawings, which cover the experimentally practicable temperature ranges from 70–230C and nickel concentration from 0.05–10%. Whereas the rate of hydrogenation depends upon both temperature and catalyst concentration,trans formation is essentially a function of temperature while selectivity is little influenced by either parameter. Presented at the AOCS meeting in New Orleans, La., 1962. A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, U. S. D. A.     

Influence of surface support properties on the liquid-phase selective hydrogenation of phenylacetylene on supported nickel catalysts

The role of textural and acid–base properties of supports on metal–support interaction effects has been evaluated through the results obtained in the liquid-phase selective hydrogenation of phenylacetylene carried out on 20 wt% supported nickel catalysts. SiO₂, Al₂O₃, AlPO₄, active carbon and a natural sepiolite were used as supports. The effects of Ni–Cu alloying were also studied. The relative adsorption constants, K__T,D, and the relative reactivities, R_T,D, obtained in the consecutive hydrogenation process, were used to follow the effects of any electron transfer between the nickel atoms and acid–basic sites on the support surface. Structural defects of supported nickel crystallites were determined by X-ray diffraction line broadening analysis and used for measuring the participation of geometric effects of supported nickel crystallites in the catalytic activity. Results obtained may be better explained within a framework of simultaneous electronic and structural metal–support interaction effects. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation of Mesoporous Ni–alumina Catalyst by One-step Sol–gel Method: Control of Textural Properties and Catalytic Application to the Hydrodechlorination of o-dichlorobenzene

Mesoporous Ni–alumina catalysts (Ni–alumina-pre and Ni–alumina-post) were synthesized by one-step sol–gel method using micelle complex comprising lauric acid and nickel ion as a template with metal source and using aluminum sec-butoxide as an aluminum source. The Ni–alumina catalysts showed relatively high surface areas (303 m²/g for Ni–alumina-pre and 331 m²/g for Ni–alumina-post) and narrow pore size distributions centered at ca. 4 nm. Highly dispersed Ni particles were observed in the Ni–alumina catalysts (ca. 5.2 nm for Ni–alumina-pre and ca. 6.8 nm for Ni–alumina-post) after reduction at 550 °C, while a catalyst prepared without a template (NiAl-comp) exhibited inferior porosity with large metal particles (ca. 12.3 nm). Mesoporous Ni–alumina catalysts with different porosity were obtained by employing different hydrolysis step of aluminum source. When aluminum source was hydrolyzed under the presence of micelle complex, a supported Ni catalyst with highly developed framework mesoporosity was obtained (Ni–alumina-post). On the other hand, when aluminum source was pre-hydrolyzed followed by mixing with micelle solution, the resulting catalyst (Ni–alumina-pre) retained high portion of textural porosity. It was revealed that the hydrolysis method employed in this research affected not only textural properties but also metal-support interaction in the Ni–alumina catalysts. It was also found that the Ni–alumina-pre catalyst exhibited weaker interaction between nickel and alumina than the Ni–alumina-post, leading to higher degree of reduction in the Ni–alumina-pre catalyst. In the hydrodechlorination of o-dichlorobenzene, the Ni–alumina catalysts exhibited better catalytic performance than the NiAl-comp catalyst, which was attributed to higher metal dispersion in the Ni–alumina catalysts. In particular, the Ni–alumina-pre catalyst showing 1.5 times higher degree of reduction and larger amounts of o-dichlorobenzene adsorption exhibited better catalytic performance than the Ni–alumina-post catalyst.     

Effects of MgO promoter on properties of Ni/Al2O3 catalysts for partial oxidation of methane to syngas

The effects of MgO promoter on the physicochemical properties and catalytic performance of Ni/Al₂O₃ catalysts for the partial oxidation of methane to syngas were studied by means of BET, XRD, H₂-TPR, TEM and performance evaluation. It was found that the MgO promoter benefited from the uniformity of nickel species in the catalysts, inhibited the formation of NiAl₂O₄ spinel and improved the interaction between nickel species and support. These results were related to the formation of NiO-MgO solid solution and MgAl₂O₄ spinel. Moreover, for the catalysts with a proper amount of MgO promoter, the nickel dispersiveness was enhanced, therefore making their catalytic performance in methane partial oxidation improved. However, the excessive MgO promoter exerted a negative effect on the catalytic performance. Meanwhile, the basicity of MgO promoted the reversed water-gas shift reaction, which led to an increase in CO selectivity and a decrease in H₂ selectivity. The suitable content of MgO promoter in Ni/Al₂O₃ catalyst was ∼7 wt-%. Translated from Journal of Fuel Chemistry and Technology, 2006, 34(4): 450–455 [译自: 燃料化学学报]     

High P–T Nano-Mechanics of Polycrystalline Nickel

We have conducted high P–T synchrotron X-ray and time-of-flight neutron diffraction experiments as well as indentation measurements to study equation of state, constitutive properties, and hardness of nanocrystalline and bulk nickel. Our lattice volume–pressure data present a clear evidence of elastic softening in nanocrystalline Ni as compared with the bulk nickel. We show that the enhanced overall compressibility of nanocrystalline Ni is a consequence of the higher compressibility of the surface shell of Ni nanocrystals, which supports the results of molecular dynamics simulation and a generalized model of a nanocrystal with expanded surface layer. The analytical methods we developed based on the peak-profile of diffraction data allow us to identify “micro/local” yield due to high stress concentration at the grain-to-grain contacts and “macro/bulk” yield due to deviatoric stress over the entire sample. The graphic approach of our strain/stress analyses can also reveal the corresponding yield strength, grain crushing/growth, work hardening/softening, and thermal relaxation under high P–T conditions, as well as the intrinsic residual/surface strains in the polycrystalline bulks. From micro-indentation measurements, we found that a low-temperature annealing (T < 0.4 T_m) hardens nanocrystalline Ni, leading to an inverse Hall–Petch relationship. We explain this abnormal Hall–Petch effect in terms of impurity segregation to the grain boundaries of the nanocrystalline Ni.     

The transition state for metal-catalyzed dehalogenation

Substituent effects have been used to probe the nature of the transition state to catalytic carbon–halogen bond breaking. Kinetics measurements have determined the activation energies (E _act to C–Cl bond breaking on the Pd(111) surface and C–I bond breaking on the Pd(111) and Ag(111) surfaces. These barriers have been measured using alkyl halides with varying degrees of fluorine substitution. The activation energies have been correlated with the inductive or field substituent constants (σ_F) of the fluorinated alkyl groups in order to determine reaction constants (E _act=E₀+ρσ_F) for the dehalogenation reactions. In all three cases it has been found that the barriers are insensitive to inductive substituent effects and the reaction constants are all relatively small: ρ= −0.5± 1.0 kcal/mol for C–Cl cleavage on Pd(111), ρ= −0.3±0.8 kcal/mol for C–I cleavage on Pd(111), and ρ= −2.9±0.4 kcal/mol for C–I cleavage on Ag(111). This implies that the transition state for dehalogenation is homolytic and occurs early in the reaction coordinate. The implications of this result are discussed for catalytic dehalogenation processes such as hydrodechlorination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of a mass force on the combustion of the Ni−Al system

The effect ofg-load (in the range of 1 to 1000g) on the combustion of the Ni−Al system was studied experimentally. It is shown that a mass force has a significant effect on the burning rate of the mixture, compaction, and the chemical and phase compositions of the combustion products. A mechanism for the effect ofg-load on the burning rate and compaction of the system is proposed. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 34–38, January–February, 1998.     

Synthesis and Structural Characterizations of “Core–Shell”-Type Nickel-Coated Polymeric Particles

A polystyrene seed with a narrow size distribution was synthesized by the dispersion polymerization method first, then uniformly “swollen up” and cross-linked with divinylbenzene (DVB) utilizing the dynamic swelling polymerization technique. The surface of hollow poly(styrene-co-DVB) particles was coated with nickel by the electroless plating method. The density of the synthesized “core–shell”-type conductive particle was 3.06 g/cm³, significantly lower than the density of pure metallurgical nickel of 8.91 g/cm³. Hence, the sedimentation problem, which often occurs in the blend of high-density metal fillers with a relatively low density polymer matrix, could be overcome as the metal fillers were replaced by the synthesized core–shell-type conductive particles.     

Synthesis of borosilicalite-1 with more than four boron per unit cell from fluoride containing media

More than four boron per unit cell has been introduced into the framework of silicalite-1, using fluorine containing media. The initial gels were of composition 9MF–xH₃BO₃–10SiO₂–1.25TPABr–330 H₂O with M = NH₄, Na, K and Cs and x = 0.1–10. The syntheses were carried out in hydrothermal conditions at 170°C. The amount of incorporated TPA⁺ ions remains quasi constant (3.5–3.8/u.c.) up to 4 B/u.c., while it decreases with increasing boron content. The amount of tetrahedral B/u.c. can be as high as 8 in presence of K⁺ or Cs⁺ ions in the as-synthesized samples. It is observed that the preferential countercations to framework negative charges related to the presence of tetrahedral boron, [SiOB]⁻, are TPA⁺, K⁺ and Cs⁺ ions. It is interpreted, that the −4.0 ppm versus BF₃.OEt₂ NMR line stems from tetrahedral framework boron, while the −2.9 ppm NMR line represents both extraframework and/or tetracoordinated deformed framework boron in the structure.