Influence of composition on the thermal behaviour of chemically deposited nickel-phosphorus alloys

The thermal behaviour of a series of Ni-P alloys obtained by electroless plating from chloride-glycollate solutions at different pH values was studied by means of DSC analysis and X-ray diffraction.Alloys of composition up to Ni₇₈P₂₂ are microcrystalline or partially amorphous, depending on the P content; on heating up to 773 K, the amorphous phase is transformed into an equilibrium mixture of Ni and Ni₃P crystals.Most of the alloys crystallize in two exothermic stages, these occurring ever closer to each other as the P concentration approaches the eutectic value; the alloys with near-eutectic compositions are the only ones crystallizing in one stage.The first thermal effect in hypo-eutectic alloys is due to the separation of Ni crystallites from the primary amorphous phase and/or to the growth of pre-existing solid-solution crystals; the second one is due to the crystallization of intermediate amorphous phase into Ni₃P plus Ni. The first stage of crystallization in hyper-eutectic alloys corresponds to the formation of randomly-oriented Ni₃P crystals, while in the second one the residual amorphous phase yields the eutectic mixture.

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Zusammenfassung Das thermische Verhalten einer Reihe von durch stromlose Platierung mit Chlorid-Clykollat-Lösungen bei verschiedenen pH-Werten erhaltenen Ni-P-Legierungen wurde mittels DSC und Röntgendiffraktion untersucht. Legierungen mit einer Zusammensetzung bis Ni₇₈P₂₂ sind abhängig vom P-Gehalt, kristallin oder teilweise amorph. Beim Erhitzen auf 773 K wird die amorphe Phase in ein Gleichgewichtsgemisch von Ni- und Ni₃P-Kristallen überführt. Die meisten Legierungen kristallisieren in zwei exothermen Schritten, die sich einander umso mehr nähern, je mehr sich die P-Konzentration dem eutektischen Wert nähert. Als einzige kristallisieren die in der Zusammensetzung dem Eutektikum nahekommenden Legierungen in einem Schritt. Bei hypoeutektischen Legierungen ist der erste thermische Effekt der Ausscheidung von Ni-Kristallen aus der primären amorphen Phase und/oder dem Wachstum von bereits in der festen Lösung vorliegenden Kristallen, der zweite der Kristallization von Ni₃P und Ni aus der intermediären amorphen Phase zuzuschreiben. Bei hypereutektischen Legierungen entspricht der erste Schritt der Kristallisation der Bildung von random-orientierten Ni₃P-Kristallen, während des zweiten wird dagegen die verbleibende amorphe Phase in das eutektische Gemisch überführt.

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Ni-P , - pH. Ni₇₈P₂₂ , , . 773 Ni Ni₃P . , . . - . Ni₃P . - Ni₃P, .

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The authors wish to thank Professor P. Lanza and Mr. A. Garulli for their valuable assistance in the analytical studies.     

Role of the nature of copper sites in the activity of copper-based catalysts for no conversion

The activities of the copper-based catalysts, Cu²⁺ /SiO²,Cu²⁺ /Vycor and Cu²⁺/ZSM-5, and V²O⁵/TiO² for NO conversion to N² in the presence or absence of NH³ and/or O² have been investigated. The Cu²⁺ /ZSM-5 catalyst exhibited the highest activity, even higher than that of V²O⁵/TiO². Photoluminescence studies of the dehydrated copper-based catalysts have suggested that the copper ions anchored onto ZSM-5 locate as isolated copper species near Brönsted sites in the zeolite channels while the copper ions anchored onto Vycor and SiO² locate mainly as copper dimer forms. These results suggest the role of copper ions which are stabilized with near-lying oxygen vacancies created by dehydroxylation of the zeolite, in NO conversion. As a result, it may be concluded that the isolated copper ions near Brönsted sites play a significant role in NO conversion but dimeric or polynuclear copper species are less effective for the reaction.     

CW laser-induced photothermal conversion and shape transformation of gold nanodogbones in hydrated chitosan films

We investigate the photothermal conversion and transformation of gold nanoparticles with an initial dogbone shape after dispersion in hydrated chitosan films, which is a representative model of biological tissue, and excitation by a CW diode laser for 1 min. Gold nanodogbones are observed to undergo a distinct modification above a sharp threshold of ~11 W cm⁻² and 110 °C. Surprisingly, the very same modification is achieved up to at least 36 W cm⁻² and 250 °C. We use an analytical model derived from Gans theory to associate the change in color of the films with the change in shape statistics of these gold nanoparticles. This model proves both convenient and dependable. We interpret the photothermal transformation as a rearrangement of particles with a dogbone shape and an aspect ratio of 4.1 into rods with an aspect ratio of 2.5, where material from the end lobes of the dogbones may relocate to the waists of the rods. In turn, additional transitions to stable gold nanospheres may exhibit fairly slower kinetics.     

Synthesis,Characterization, and Magnetic Behavior of Cobalt-Ferrite Nanoparticles under Variant Temperature Conditions

Physics of the Solid State - Wet chemical method was applied for the synthesis of cobalt-ferrite nanoparticles. The physicochemical properties were investigated by number of analytical techniques....     

Structure and reactivity of vanadium-phosphorus oxides

The contribution of thermal methods of analysis to the study of the structure and reactivity of vanadium-phosphorus oxides is examined. In particular, data are reported on the solid-state reaction VOHPO₄·1/2H₂O(VO)₂P₂O₇+2 H₂O for VOHPO₄·1/2H₂O prepared in different ways, on the redox properties of oxidation and reduction of vanadium for catalysts prepared with different PV atomic ratios in the range 0.9–1.3, and on the surface properties determined by TPD of catalysts with different PV ratios. The relationship between these properties and the catalytic properties in the selective oxidation ofn-butane and but-1-ene is discussed.

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Zusammenfassung Der Beitrag thermischer Analysenmethoden zur Untersuchung der Struktur und Reaktivität von Vanadin-Phosphor-Oxiden wird erörtert. Insbesondere werden sich auf die Festkörperreaktion 2VOHPO₄.1/2H₂O(VO)₂P₂O₇+2H₂O für auf verschiedene Weise dargestelltes VOHPO₄.1/2H₂O, auf die Redox-Eigenschaften von Vanadin in Katalysatoren mit P/V-Atomverhältnissen im Bereich 0.9–1.3 und auf durch TPD bestimmte Oberflächeneigenschaften von Katalysatoren mit unterschiedlichen P/V-Verhältnissen beziehende Angaben gemacht. Zusammenhänge zwischen diesen Eigenschaften und den katalytischen Eigenschaften bei der selektiven Oxydation von n-Butan und N-Buten werden diskutiert.

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- . , VOHPO₄ · 1/2H₂O, VOHPO₄ · 1/2H₂O(VO)₂P₂O₇ + 2H₂O, - PV 0,91,3. - 1-.

     

Creating and mastering nano-objects to design advanced catalytic materials

New developments in the synthesis of nano-materials have opened new possibilities for creating and mastering nano-objects in order to design novel advanced catalytic materials. This concise conceptual review will give a glimpse into this fast growing research area discussing some of the possibilities in this direction, the perspectives and the gap to reduce to develop selective catalysts for complex multistep reactions. Emphasis is given to the opportunities offered by a tailored nano-design of the catalysts, from exploiting nano-confinement effects and supramolecular active sites synergies in nano-reactors to the new possibilities offered by new concepts such as the reduction of the relaxation time between two consecutive turnover cycles on a single active site and forcing a vectorial active site sequence in complex, multistep reactions. Other aspects discussed include the development of hierarchic pore structure to maximize catalyst effectiveness, metal complexes confined with solid cavities and the concept of nano-reactors, nanostructured composites and ordered 1D-type metal oxides. It is shown how significant progress in nano-materials has still not corresponded with progress in understanding the relationship between nanostructure and catalytic performance and the development of a more general strategy on the design of next-generation nano-catalysts.     

Development of an Electrochemical Immunoassay Based on the Use of an Eight‐Electrodes Screen‐Printed Array Coupled with Magnetic Beads for the Detection of Antimicrobial Sulfonamides in Honey

In this work an electrochemical immunoassay, based on a direct competitive assay, was developed using magnetic beads as solid phase and carbon screen‐printed arrays as transducers for the detection of sulfonamides in food matrices such as honey. Magnetic beads coated with protein A were modified by immobilisation of specific antibodies and then the competition between the target analyte and the corresponding analyte‐labelled with an enzyme was carried out; after the immunosensing step, beads were captured by a magnet onto the working surfaces of a screen‐printed eight‐electrodes array for a multiple electrochemical detection. Screen‐printed eight‐electrodes arrays were chosen as transducers due to the possibility to repeat multiple analysis and to test different samples simultaneously. Alkaline Phosphatase (AP) was used as enzyme label and Differential Pulse Voltammetry (DPV) as fast electrochemical technique. Calibration curves demonstrate that the developed electrochemical immunoassay was able to detect this class of drugs in standard solutions at low concentrations (ng/mL levels). The short incubation times (25 min) and the fast electrochemical measurement (10 sec) make of these systems a possible alternative to classic ELISA tests.     

Electrocatalytic conversion of CO2 to liquid fuels using nanocarbon-based electrodes

Recent advances on the use of nanocarbon-based electrodes for the electrocatalytic conversion of gaseous streams of CO₂ to liquid fuels are discussed in this perspective paper. A novel gas-phase electrocatalytic cell, different from the typical electrochemical systems working in liquid phase, was developed. There are several advantages to work in gas phase, e.g. no need to recover the products from a liquid phase and no problems of CO₂ solubility, etc. Operating under these conditions and using electrodes based on metal nanoparticles supported over carbon nanotube (CNT) type materials, long C-chain products (in particular isopropanol under optimized conditions, but also hydrocarbons up to C8–C9) were obtained from the reduction of CO₂. Pt-CNT are more stable and give in some cases a higher productivity, but Fe-CNT, particular using N-doped carbon nanotubes, give excellent properties and are preferable to noble-metal-based electrocatalysts for the lower cost. The control of the localization of metal particles at the inner or outer surface of CNT is an importact factor for the product distribution. The nature of the nanocarbon substrate also plays a relevant role in enhancing the productivity and tuning the selectivity towards long C-chain products. The electrodes for the electrocatalytic conversion of CO₂ are part of a photoelectrocatalytic (PEC) solar cell concept, aimed to develop knowledge for the new generation artificial leaf-type solar cells which can use sunlight and water to convert CO₂ to fuels and chemicals. The CO₂ reduction to liquid fuels by solar energy is a good attempt to introduce renewables into the existing energy and chemical infrastructures, having a higher energy density and easier transport/storage than other competing solutions (i.e. H₂).     

非晶碳纳米球的低温石墨化(英文)

The investigation by SEM/TEM, porosity, and X-ray diffraction measurements of the graphitization process starting from amorphous carbon nanospheres, prepared by glucose carbonization, is reported. Aspects studied are the annealing temperature in the 750–1000 °C range, the type of inert carrier gas, and time of treatment in the 2–6 h range. It is investigated how these parameters influence the structural and morphological characteristics of the carbon materials obtained as well as their nanostructure. It is shown that it is possible to maintain after graphitization the round-shaped macro morphology, a high surface area and porosity, and especially a large structural disorder in the graphitic layers stacking, with the presence of rather small ordered domains. These are characteristics interesting for various catalytic applications. The key in obtaining these characteristics is the thermal treatment in a flow of N2. It was demonstrated that the use of He rather than N2 does not allow obtaining the same results. The effect is attributed to the presence of traces of oxygen, enough to create the presence of oxygen functional groups on the surface temperatures higher than 750 °C, when graphitization occurs. These oxygen functional groups favor the graphitization process.