18,584 research outputs found
Comparative Study Of The Influence Of Natural Convection On Directional Solidification Of Al-3.5 Wt% Ni And Al-7 Wt% Si Alloys
No full textWe present numerical simulations of thermosolutal convection for directional solidification of Al-3.5 wt% Ni and Al-7 wt% Si. Numerical results predict that fragmentation of dendrite arms resulting from dissolution could be favored in Al-7 wt% Si, but not in Al-3.5 wt% Ni. Corresponding experiments are in qualitative agreement with the numerical predictions. Distinguishing the two fragmentation mechanisms, namely dissolution and remelting, is critical during experiments on earth, when fluid flow is dominant. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved
Hydriding/dehydriding properties of MgH2/5 wt.% Ni coated CNFs composite
No full textIn this paper, we reported that the prepared nickel coated carbon nanofibers (NiCNFs) by electroless plating method exhibited superior catalytic effect on hydrogen absorption/desorption of magnesium (Mg). It is demonstrated that the nanocomposites of MgH/5 wt.% NiCNFs prepared by ball milling could absorb hydrogen very fast at low temperatures, e.g. absorb ∼6.0 wt.% hydrogen in 5 min at 473 K and ∼5.0 wt.% hydrogen in 10 min even at a temperature as low as 423 K. More importantly, the desorption of hydrogen was also significantly improved with additives of NiCNFs. Diffraction scanning calorimetry (DSC) measurement indicated that the peak desorption temperature decreased 50 K and the on-set temperature for desorption decreased 123 K. The composites also desorbed hydrogen fast, e.g. desorb 5.5 wt.% hydrogen within 20 min at 573 K. It is suggested that the new phase of MgNi, and the nano-sized dispersed distribution of Ni and carbon contributed to this significant improvement. Johnson-Mehl-Avrami (JMA) analysis illustrated that hydrogen diffusion is the rate-limiting step for hydrogen absorption/desorption
Improved CO2 Hydrogenation on Ni–ZnO/MCM-41 Catalysts with Cooperative Ni and ZnO Sites
No full textA set of Ni–ZnO/MCM-41 catalysts with different proportional Ni and ZnO loadings (up to 10 wt % in total) were synthesized for the carbon dioxide (CO2) hydrogenation reaction. Ni nanoparticles and ZnO promoter were both loaded onto a MCM-41 support via the impregnation method. The catalysts were comprehensively characterized by Brunauer–Emmett–Teller, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and hydrogen temperature-programmed reduction measurements. Catalyst properties, including the porosity, Ni metal particle size, and Ni particle location, were all found to be influenced by the presence of the ZnO promoter. ZnO was suspected to improve Ni nanoparticle insertion into the MCM-41 mesoporous channels to form Ni–ZnO interfaces. Both CO and CH4 were produced during the CO2 hydrogenation reaction under the molar ratio of CO2/H2 at 1:3 at 350 °C. The CO2 conversion rate and CO selectivity were found to increase as the reaction temperature increased from 350 to 700 °C. Among all studied materials, the catalyst containing 9 wt % Ni and 1 wt % Zn (denoted as sample E throughout the report) revealed the highest CO2 conversion and selectivity toward CO (∼60% CO2 conversion and 98.5% CO selectivity at 600 °C), while the catalyst containing 1 wt % Ni and 9 wt % Zn (denoted as sample A throughout the report) revealed the lowest activity (∼2.5% CO2 conversion and 95% CO selectivity at 600 °C). This study illustrated that cooperative catalysis can be applied to tune the CO2 hydrogenation reaction toward the reverse water–gas shift reaction for value-added CO production. When both Ni and ZnO are coupled in MCM-41, a hybrid system was designed and synthesized, in which Ni functions for H2 dissociation and ZnO functions for CO2 adsorption and accumulation.Full Tex
Effects of Ni Content and Heat Treatment on the Properties, Microstructures, and Precipitates of Cu-0.2 wt% Be-x wt% Ni Alloys
No full textCu-Be alloys exhibit excellent comprehensive performance in electrics, thermotics, and mechanics, and hence, they attract much attention. Among them, low-Be copper alloys are more environmentally friendly and promising. This study explores the effects of different Ni contents and heat treatment parameters on the properties, microstructures, and precipitates of Cu-0.2 wt% Be-x wt% Ni (0 < x < 2.0) alloys. The experimental results demonstrate that the fast cooling rate of cast alloys during solidification contributes to retention of the solute atoms in the copper matrix, which is beneficial for subsequent solid solution treatment. Furthermore, solid solution treatment slightly reduces the electrical conductivities, microhardness values, and compressive yield strengths of Cu-0.2 wt% Be-1.0/1.6 wt% Ni alloys. The optimal solution temperature and time are about 925 ℃ and 60 min, respectively. Aging treatment significantly increases the electrical conductivities, microhardness values, and compressive yield strengths of Cu-0.2 wt% Be-1.0/1.6 wt% Ni alloys. The best aging temperature is around 450 ℃. However, the properties of Cu-0.2 wt%Be-0.4 wt%Ni alloys remain unaffected by solution and aging treatments. Around x = 1.0, Cu-0.2 wt% Be-x wt% Ni alloys possess the best comprehensive properties, which are about 72%IACS of electrical conductivity, 241 HV of microhardness, and 281MPa of compressive yield strength, respectively. TEM and EDS analyses reveal that the precipitate evolution of Cu-0.2 wt% Be-1.0 wt% Ni alloys with aging time is GP zones → γ″ → γ′. Notably, a distinct double-peak age strengthening phenomenon emerges with Cu-0.2 wt% Be-1.0/1.6 wt% Ni alloys. The precipitation of plenty of GP zones at the early stage of aging should account for the first strengthening peak, and the strengthening mechanism transformation of the γ″ or γ′ phase from shear to Orowan should induce the second strengthening peak. This work may help to design new low-Be copper alloys and their preparation processes
Comparative study of the dry reforming of methane on fluidised aerogel and xerogel Ni/Al2O3 catalysts
No full textThe xerogel and aerogel Ni(20 wt %)/Al2O3 catalysts were prepared through incipient-wetness-impregnation and co-precipitation-supercritical drying (CP-SCD), respectively. All the fresh and used catalysts were well characterised using FESEM, BET, XRD, H2-TPR and H2-TPD techniques. Their properties and catalytic performance in dry reforming of CH4 in a fluidised bed reactor were comparatively investigated. In comparison with the xerogel catalyst, the aerogel catalyst possessed smaller crystallite size of nickel, larger specific surface area, higher nickel dispersion, lower bulky density and better fluidization quality. More importantly, the aerosol catalyst showed higher catalytic activity, stability and less carbon deposition in dry reforming, due to the excellent physicochemical properties of the aerogel catalyst and its enhanced fluidization quality
The application of trace element and isotopic analyses to the study of Celtic gold coins and their metal sources
No full textThe focus of this study were Celtic gold coins excavated from the Martberg, a Celtic oppidium and sanctuary, occupied in the first century B.C. by a Celtic tribe known as the Treveri. These coins and a number of associated coinages, were characterised in terms of their alloy compositions and their geochemical and isotopic signatures so as to answer archaeological and numismatic questions of coinage development and metal sources. This required the development of analytical methods involving; Electron Microprobe (EPMA), Laser Ablation-ICP-MS, solution Multicollector-ICPMS and LA-MC-ICP-MS. The alloy compositions (Au-Ag-Cu-Sn) were determined by EPMA on a small polished area on the edge of the coins. A large beam size, 50µm (diameter), was used to overcome the extreme heterogeneity of these alloys. These analyses were shown to be representative of the bulk composition of the coins. The metallurgical development of the coinages was defined and showed that the earlier coinages followed a debasement trend, which was superceded by a trend of increasing copper at the expense of sliver while gold compositions remained stable. This change occurred with the appearance of the inscribed "POTTINA" coinage, Scheers 30/V. Two typologically different coinages, Scheers 16 and 18 ("Armorican Types") were found to have markedly different compositions which do not fit into the trends described above. A Flan for a gold coin, which may indicate the presence of a mint at the Martberg, was found to have an identicle weight and composition as the Scheers 30/I coins, which preceeded the majority of the coins found at the Martberg in the coin development chronology. The trace element anaylses were made by Laser Ablation-ICPMS using an AridusTM desolvating nebuliser to introduce matrix matched solution standards to calibrate the measurements, which were then normalised to 100%. Quantitative results were obtained for the following elements: Sc, Ti, Cr, Mn, Co, Ni, Cu, Zn, Se, Ru, Rh, Pd, Ag, Sb, Te, W, Ir, Pt, Pb, Bi. The remaining elements remain problematic as they produced incorrect standardisations mainly due to chemical effects in solution such as adsorption onto the beaker walls or oxidation : V, Fe, Ga, Ge, As, Mo, Sn, Re, Os, Hg. Changes in the sources of Au, Ag and Cu were observed during the development of the coinages through the variation of trace elements, which correlate positively with the major components of the coin alloys. Changes in the Pt/Au ratios show that the Scheers 23 coins contain distinctly different gold from the later coinages and that the Scheers 18 gold source was also different. Te/Ag was used to show that the Sch.23 coins also contained different silver and some subgroups were observed in the Sch. 30/V coins. A major change in copper source is indicated by the sudden increase of Sb and Ni with the introduction of the Sch. 30/V coins (POTTINA), which can be linked to a similar change in copper observed in the contemporary silver coinage, Sch. 55 (with a ring). Lead isotopic analyses were made by solution- and Laser Ablation - MC-ICP-MS, The laser technique proved to be in good agreement with the solution analyses with precisions between 1 and 0.1%o (per mil). The development of the laser method opens the way for easy and virtually non-destructive Pb isotopic determinations of ancient gold coins. The results showed that Sch. 23 is very different from the following coinages, Sch. 16 and 18 are also different, forming their own group, and all the later "Eye" staters (Sch. 30/I-VI) lie on a mixing line controlled by the addition of copper from a Mediterranean source, probably Sardinia or Spain. An indication of gold and silver sources should be possible with further analyses of the Sch. 23 and Rainbow Cup gold coins and the Sch. 54 and 55 silver coinages. Copper Isotopic analyses were made by solution- and Laser Ablation - MC-ICP-MS. Both techniques require further development to produce more reproducible results. The results show that there appears to be a trend to more positive d Cu65 values for the later coinages and that the link between the copper used in the Sch. 30/V (POTTINA) coins and the silver Sch. 55 (with a ring) coins is also shown by similarly postive d Cu65 values. The full suite of analyses were also made on samples of gold from the region. They were mostly composed of "placer gold", alluvial gold found in rivers. It was found that when a study is restricted to a limited number of deposits or areas then it is possible to distinguish between deposits based on the concentration of those elements which are least affected by transport related alteration processes. These elements include; the PGE's, due to their refractory nature, and those elements which are usually present in high enough concentrations to remain relatively unaffected, eg: Cu, Pb and Sb. Due to the nature of the coin alloy it is not possible to link the gold used in the coins studied here with gold deposits, as the large amounts of Ag and Cu, added to the coin alloys, have masked the Au signature. However, further Pb isotopic analyses of gold deposits should prove useful in determining from which regions Celtic gold was derived.Ziel dieser Arbeit war die Charakterisierung keltischer Goldmünzen, die am Martberg, einem keltischen oppidum und Kultstätte, ausgegraben wurden; diese Fundstelle wurde im ersten Jahrhundert vor Christus vom keltischem Stamm der Treveri bewohnt. Die Münzen und mit ihnen assoziierte Münzfunde wurden im Hinblick auf ihre Legierungszusammensetzung, ihre geochemischen und ihre Isotopen-Signaturen untersucht, um archäologische und numismatische Fragen der Münzentwicklung und der Rohstoffquellen zu klären. Dies geschah unter Zuhilfenahme analytischer Methoden; im Genaueren sind die Elektronenstrahlmikrosonde (EPMA), Laser-Ablation (LA-) Inductively Coupled (IC)- Mass Spectrometry (MS), Lösungs-Multicollector (MC)-ICP-MS und LA-MC-ICPMS. Die Zusammensetzungen der Legierungen im System Gold-Silber-Kupfer-Zinn wurden durch EPMA an einer kleinen, planpolierten Stelle an den Rändern der Münzen durchgeführt. Durch Verwendung eines auf 50 µm aufgeweiteten Strahldurchmessers konnten räumlich gemittelte Analysen erstellt werden, die große Heterogenitäten der Proben kompensieren, und mit Bulk-Analysen der Münzen übereinstimmen. Die metallurgische Entwicklung der Münzen konnte so erkannt werden; bei späteren Prägungen wurde zunächst der Goldanteil zugunsten eines erhöhten, festen Silber/Kupferanteils abgesenkt. Im Anschluss hieran gefertigte Prägungen zeigen erhöhte Kupfer/Silber-Verhältnisse bei konstantem Goldanteil. Dieser Wechsel ereignete sich mit dem Aufkommen der beschrifteten "Pottina"-Münzen, Scheers 30/V. Zwei typologisch unterschiedliche Münzgruppen, Scheers 16 und 18 ("Armorica"-Typ) fallen aus dem beschriebenen Trend heraus. Auch ein Rohling einer Goldmünze wurde am Martberg entdeckt und deutet so auf eine mögliche Prägestätte an diesem Ort hin, zudem dieser das gleiche Gewicht und die gleiche chemische Zusammensetzung wie die Scheers 30/I-Münzen aufweist. Diese stellen in einer zeitlichen Abfolge die Vorläufer der Hauptfunde am Martberg dar. Die Spurenelemente wurden durch LA-ICP-MS mit einem Aridus (TM) Zerstäuber analysiert, der Matrix-angepasste Standardlösungen zur Kalibrierung der Messungen einbrachte. Im Anschluss wurden die Ergebnisse durch die EPMA-Analytik auf 100% normalisiert. Quantitativ wurden folgende Elemente bestimmt: Sc, Ti, Cr, Mn, Co, Ni, Cu, Zn, Se, Ru, Rh, Pd, Ag, Sb, Te, W, It, Pt, Pb, Bi Die weiterer analysierten Elemente waren aufgrund falscher Standardisierungen problematisch; was vor allem auf physikalisch-chemische Lösungseffekte wie Adsorption an Gefäßwänden und Oxidation multivalenter Kationen zurückzuführen ist. Ihre Liste umfaßt: V, Fe, Ga, Ge, As, Mo, Sn, Re, Os, Hg. Veränderungen der Gold-, Silber- und Kupferquellen im Laufe der Münzentwicklung wurden durch die Variation der Spurenelemente belegt, die mit den Hauptelementen der Münzlegierungen positiv korreliert sind. Ein Wandel des Platin/Gold-Verhältnisses zeigt, dass die Scheers 23 Münzen eine deutlich von späteren Prägungen verschiedene Goldquelle beinhalten, ebenso ist die Herkunft der Scheers 18 Münzen eine andere. Das Tellur/Silber-Verhältnis kann aufzeigen, dass bei den Scheers 23 Proben auch eine andere Silberquelle benutzt wurde; ähnliche Schlüsse können aus der graphischen Auswertung bei einigen Untergruppen der Scheers 30/V Münzen gefunden werden. Ein deutlicher Wechsel der Kupferlagerstätte ist durch den signifikanten Anstieg der Antimon- und Nickelgehalte bei den Scheers 30/V Münzen ("Pottina") aufgezeichnet; dieser stimmt mit ähnlichen Veränderungen der Kupferkomponente bei zeitgleichen Silbermünzen überein (Probe Scheers 44 (mit Ring)). Die Blei-Isotopie wurde durch Lösungs- und LA-MC-ICP-MS analysiert. Laser- und Lösungstechniken zeigen gute Übereinstimmung mit einer Präzision zwischen 0,1 und 10/00. Die erstmalige Entwicklung adäquater Protokolle zur Bestimmung der Blei-Isotopie mittels Laser-Ablation eröffnet einen einfachen und quasi zerstörungsfreien Weg zur Charakterisierung antiker Goldmünzen. Die Ergebnisse zeigen einen deutliche Unterschied zwischen Scheers 23 und späteren Münzprägungen. Ähnlich hierzu Scheers 16 und 18, die eine eigene Gruppe bilden, und alle "Eye-staters"-Münzen (Scheers 30/I-VI), die auf einem Mischbereich aufspannen, der durch die Zugabe von Kupfer aus einer mediterranen Quelle - Sardinien oder Spanien - erzeugt wird. Hinweise auf die Gold- und Silberlagerstätten sollten in Zukunft möglich sein, wenn die Scheers 23 und "Rainbow cup"-Münzen wie auch die Scheers 54 und 55 Silbermünzen genauer untersucht werden. Kupferisotopische Analysen wurden durch Lösungs- und LA- MC-ICP-MS durchgeführt. Beide Techniken verlangen der Weiterentwicklung, um reproduzierbarere Ergebnisse zu erhalten. Die bisherigen Resultate zeigen einen Trend der späteren Prägungen zu erhöhten d 65Cu-Werten. Die bereits erwähnte Verbindung zwischen Scheers 55 (mit Ring) und den Scheers 30/V (Pottina)- Prägungen wird durch ähnliche d 65Cu-Werte bestätigt. Alle erwähnten analytischen Techniken wurden auch verwandt, um Goldproben aus der Region zu untersuchen. Meist handelt es sich hierbei um Goldseifen, alluviale Vorkommen in Flüssen. Es konnte gezeigt werden, dass eine Studie einer limitierten Anzahl von Lagerstätten oder Gebieten eine Unterscheidung zulässt, wenn man die Elemente betrachtet, die bei transportbedingten Alterierungsprozessen am wenigsten verändert werden. Diese umfassen neben den refraktären und inerten Platingruppenelementen die Elemente, die in solch hoher Konzentration auftreten, dass Alterierung sie nur unwesentlich beeinflusst, d.h. Kupfer, Blei und Antimon. Aufgrund der genutzten Legierungen ist es jedoch nicht möglich, das Gold der Münzen mit dem der Lagerstätte zu korrelieren, da die großen Beimengungen von Silber und Kupfer die Goldsignatur überlagern. Mit weiteren blei-isotopischen Analysen der Goldlagerstätten könnten jedoch weitere Rückschlüsse auf die Herkunft des keltischen Goldes gezogen werden
Laser powder bed fusion of a Cu-Ni-Al alloy using the compositional grading approach
No full textUsing a modified laser powder bed fusion (LPBF) technique, a compositionally graded Cu-Ni alloy was fabricated. Through microstructural and mechanical characterization on the samples extracted from it, the addition of 7.6 wt.% Ni to Cu is identified as the minimum required for obtaining a crack-free and nearly-fully-dense coupons using LPBF. Subsequently, 3 wt.% Al was added to the Cu-7.6 wt.% alloy to deplete the solute Ni atoms from the matrix through the precipitation of Ni3Al upon aging of the LPBF Cu-Ni-Al alloy, which simultaneously enhances the strength and electrical conductance of the alloy. Through this example, we demonstrate the potential of high?throughput screening of alloys suitable for LPBF through the fabrication of the compositionally graded alloys and subsequent alloy design for optimum property combinations.</p
Room Temperature Mechanical Properties of A356 Alloy with Ni Additions from 0.5 Wt to 2 Wt %
No full textIn recent years, the influence of Ni on high-temperature mechanical properties of casting Al alloys has been extensively examined in the literature. In the present study, room temperature mechanical properties of an A356 alloy with Ni additions from 0.5 to 2 wt % were investigated. The role of Ni-based compounds and eutectic Si particles in reinforcing the Al matrix was studied with image analysis and was then related to tensile properties and microhardness. In the as-cast condition, the formation of the 3D network is not sufficient to determine an increase of mechanical properties of the alloys since fracture propagates by cleavage through eutectic Si particles and Ni aluminides or by the debonding of brittle phases from the aluminum matrix. After T6 heat treatment the increasing amount of Ni aluminides, due to further addition of Ni to the alloy, together with their brittle behavior, leads to a decrease of yield strength, ultimate tensile strength, and Vickers microhardness. Despite the fact that Ni addition up to 2 wt % hinders spheroidization of eutectic Si particles during T6 heat treatment, it also promotes the formation of a higher number of brittle Ni-based compounds that easily promote fracture propagation
Microstructure and physical properties of melt spun Al-17 wt.% Ni-10 wt.% Cu alloy
No full textAl-17 wt.% Ni-10 wt.% Cu alloy was prepared by melt spinning
technique and characterized by X-ray diffraction, energy dispersive X-ray
spectroscopy, and scanning electron microscopy. The resulting ribbon
microstructure consists of intermetallic Al7Cu4Ni globular-like
structure embedded within an aluminum matrix. The resulting effect of rapid
solidification on mechanical properties is the enhancement of the alloy
hardness up to 700 HV. The ternary phase Al7Cu4Ni exhibits
hardness as high as 1300 HV
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