Large Metal Particles Research Articles

Comparison of Direct Ink Writing and Binder Jetting for additive manufacturing of Pt/Al2O3 catalysts for the dehydrogenation of perhydro-dibenzyltoluene

Two additive manufacturing (AM) techniques, namely extrusion-based Direct Ink Writing (DIW) and powder-based Binder Jetting (BJ), were thoroughly compared to assess their respective advantages and drawbacks for catalyst shaping. The 3D printed monolithic Al2O3 supports were wet impregnated with H3Pt(SO3)2(OH) and tested for the dehydrogenation of perhydro-dibenzyltoluene (18H-DBT), a liquid organic hydrogen carrier (LOHC). The supports were analyzed regarding their specific surface area, compression strength, shrinkage behavior and pore size distribution with calcination temperatures ranging from 600 - 1200°C as well as 3D print specific characteristics. Benefiting the liquid phase reaction, pore diameters below 26nm were diminished above Tcalc = 1050°C, revealing a BET surface area of 26m2/g for BJ and 11m2/g for DIW printed supports. Furthermore, increasing the impregnation duration from 0.5h to 12h showed increased Pt loading, larger metal particles, and a deeper penetration into the support. Most notably, for BJ the Pt loading is generally higher due to higher meso- and macroporosity of the support. Catalytic 18H-DBT dehydrogenation with powder and monolithic catalysts showed equal dehydrogenation rates with both 3D printing methods, respectively. The achieved Pt productivity was about 4.3gH2gPt−1min−1 for powder tests and 2.7gH2gPt−1min−1 for monolithic pellets.

Effect of the support material of IrRu catalysts on CO-assisted NOx reduction

Aluminum oxide (Al2O3)- and titanium dioxide (TiO2)-supported iridium–ruthenium (IrRu) catalysts were synthesized and the effect that their metal particle size and metal–support interactions have on their catalytic performance toward carbon monoxide (CO)-assisted nitric oxide (NO) reduction was investigated. A series of spectroscopic analyses revealed that IrRu bimetallic particles were well-alloyed on both the Al2O3 and TiO2 supports, but that the latter exhibited a smaller size due to the strong interactions between the metal and support. Despite the large metal particle size of IrRu/Al2O3, the selective conversion of NOx to N2 assisted by of CO oxidation was more efficient than that of IrRu/TiO2. Mechanistic and microkinetics analyses suggested that the defect-free flat surface structure of the IrRu alloy was beneficial for selective NOx reduction and CO oxidation due to the moderate binding strength of the intermediates of desired reactions. The metal–support interfaces were found to be inactive regardless of their interaction strength. This analysis provides an explanation for the superior performance of IrRu/Al2O3 compared to its TiO2-supported counterpart due to its few defects, large metal size, and small proportion of metal–support interfaces.

Estimates of noble metal particle growth in a molten salt reactor

Within the H2020-Euratom project SAMOSAFER, research is currently ongoing into the Molten Salt Fast Reactor (MSFR) concept in which nuclear fuel is dissolved in a liquid salt. A major challenge in the MSFR is the online and offline treatment of salt in order to remove a plethora of fission products. Noble metals are a type of such fission products, the atoms of which are thought to coagulate into particles as a result of diffusion. Due to their low solubility, noble metal particles will deposit onto interfaces such as solid walls but also on bubbles, as was observed in the Molten Salt Reactor Experiment (MSRE) at Oak Ridge national laboratory. The relatively large interfacial area generated by bubbles makes online or offline bubbling, therefore, an interesting option to extract noble metals from the MSFR and to limit wall deposition. However, to understand the performance of the bubbling process, particle sizes must be known. Particle size distributions arise from a complex interplay of atomic formation by fission and decay, growth by coagulation and removal by interfacial deposition. In this paper, theory is developed to understand these mechanisms on a semi-analytical level, in order to provide estimates of noble metal particle growth in the MSFR. The governing partial differential equation is reduced to a set of ordinary differential equations using the method of moments, revealing the dynamics of the underlying physics. We show that large noble metal particles, up to the micrometer scale, can arise in the reactor, but only at very long operational times. Moreover, we show that the previously assumed ‘cycle time’ of noble metal particle removal of 30 s is only feasible at very high bubbling void fractions. The theory developed in this work contributes significantly to a qualitative understanding of the behavior of noble metals in an MSR. The theory can potentially help to explain certain phenomena observed in the MSRE and can assist in the future design of safe and reliable MSRs.

Computational Prediction of Graphdiyne-Supported Three-Atom Single-Cluster Catalysts

Computational Prediction of Graphdiyne-Supported Three-Atom Single-Cluster Catalysts

Properties of Al2O3/Ti/Ni composites fabricated via centrifugal slip casting under environmentally assessed conditions as a step toward climate-neutral society

The paper concerns functionally graded composites obtained by centrifugal slip casting method. Al2O3, Ni, Ti, differed is size and morphology, were used as starting powders. The influence of metallic phase content (2 vol% and 20 vol%) and homogenisation process (planetary-ball milling) on suspension viscosity as well as density, phase composition, microstructure and mechanical properties of sintered bodies was investigated. Planetary-ball milling decrease the viscosity of suspensions of lower metallic content due to increase of their homogeneity. Slurries of higher metallic content, after homogenisation process, exhibit higher viscosity due to refinement of large metallic particles which leads to more intense surface interactions. CSC was applied to shape samples in form of thick-wall tubes with gradient microstructure across the wall thickness. Relative densities, after sintering, were about 10% higher for the samples containing 2 vol% of metallic phase (99.40% and 98.42%) compared to specimens of higher metallic content (90.57% and 86.86%), regardless of homogenisation process. Planetary ball milling had a positive effect on microstructure of obtained graded composites, leading to more homogeneous microstructure with well defined zones and lower number of defects, in both types of sample (2 vol% and 20 vol% of metallic content). Higher content of Ti and Ni caused that metal-rich zone was thicker, but microstructure was more defected. Hardness was higher for samples of more homogeneous microstructure. XRD confirmed the presence of Al2O3 and Ni, Ti phases but also evinced occurrence additional intermetallic phases form Ni–Ti system. The environmental impact accompanying fabrication of composites was evaluated using the LCA method. It was done in order to determine burdens caused at the early beginning of the research and development stage, creating a reliable basis for further development of an environmentally friendly industrial process, simultaneously being a step toward transition to a climate-neutral society which is one of the main objectives of European Green Deal.

Synthesis of Secondary Monoalcohols from Terminal Vicinal Alcohols over Silica-Supported Rhenium-Modified Ruthenium Catalyst

The selective synthesis of secondary alcohols from 1,2-alkanediol by C–O hydrogenolysis, which has been less investigated than the synthesis of primary alcohols, was investigated with Ru-based catalysts and 1,2-propanediol (1,2-PrD) as a model substrate. The modification of Ru/SiO2 with ReOx achieved significant improvement of activity. The hydrogenolysis of 1,2-PrD over Ru–ReOx/SiO2 (Re/Ru = 0.5) initially formed both 2-propanol (2-PrOH) and 1-propanol (1-PrOH) with similar selectivity along with the formation of ≤ C2 compounds, and then 1-PrOH was preferably converted to propane; as a result, only 2-PrOH remained in the liquid phase with 23% yield at longer reaction time. This catalyst was reusable at least twice. The characterization with H2-TPR, XRD, TEM-EDX, XANES, and EXAFS showed that the Ru species in the Ru–ReOx/SiO2 catalysts were completely reduced in the reaction conditions, while a part of Re species were also reduced to partially reduced monomeric species (Reδ+Ox) without Re–Re direct bond located on the surface of Ru metal particles. This ReOx-modified Ru metal surface probably works as the active sites. The excess Re species was reduced to large Re metal particles; however, these Re metal particles are not involved in the catalysis.

Facile synthesis of carbon quantum dot ‑carbon nanotube composites on an eggshell-derived catalyst by one-step chemical vapor deposition

Carbon nanotubes (CNTs) based composites such as carbon quantum dot-CNT (CQD-CNT) demonstrate excellent performance in the fields of bioimaging and biomedicine. Nevertheless, CQD-CNT composites were mostly prepared by multiple and cumbersome steps, including the synthesis of CQDs, functionalization of CNTs and subsequent assembly of CQDs on CNTs. Here, a facile one-step synthesis of CQD-CNT was successfully conducted on an active CaO supported FeCo (Fe-Co/CaO) catalyst derived from waste eggshells via chemical vapor deposition, and other CNT-based composites such as carbon fiber-graphene sheet-CNT (CNF-GNS-CNT) and CNF-CNT as well as CNTs were also synthesized by modulating the catalyst support, growth temperature and growth time. The catalysts and produced CNTs and CNT-based composites were analyzed by multiple characterization tools. The results showed that nano CaO supported FeCo catalyst only synthesized MWCNTs, whereas Fe-Co/CaO was favorable for the synthesis of CNT-based composites. Cobalt oxides and iron oxides were well dispersed in the fresh Fe-Co/CaO catalyst, and FeCo alloy particles of different sizes were formed after catalyst reduction and heating to different growth temperatures. At a low growth temperature of 750 °C, CNF-GNS-CNT was synthesized on Fe-Co/CaO, in which CNTs and CNFs were grown on small (~10 nm) and larger (~30 nm) metal particles, respectively, whereas GNSs were mainly produced on CaO. At a high growth temperature of 850 °C, surface area and pore volume of catalysts decreased greatly, and higher solubility of carbon atoms in metal particles resulted in less desorbed CHx, which is not favorable for the growth of GNSs. Instead, CQD-CNT composites were selectively synthesized at 850 °C, which was ascribed to the oxidation corrosion of CNFs by OH radicals, but with the extension of growth time, only CNTs were produced due to the complete oxidation of CQDs. Further, larger metal particles were produced at a higher temperature of 950 °C, which were wrapped by graphite, and the partial deactivation of metal particles led to a few small particles remained active for CNT growth with a low carbon yield.

Enhancing the CO2 methanation activity of γ-Al2O3 supported mono- and bi-metallic catalysts prepared by glycerol assisted impregnation

Conventional Ni/Al2O3 catalyst, currently used for COx removal in ammonia production, admits room for improvement as catalysts for application in low temperature CO2 methanation, which is the aim of this work. The Incipient Wetness Impregnation (IWI) has been replaced by Glycerol Assisted Impregnation (GAI) method and, afterwards, a secondary metal (Ru) has been co-impregnated forming a bimetallic system. The monometallic as well as bimetallic systems have been characterized by several techniques (TGA, XRD, N2-physisorption, TEM, H2-TPR, H2-TPD, STEM-EDX and operando FTIR) and tested for CO2 methanation reaction in a downflow fixed bed reactor (conditions: P =1 bar, H2: CO2 ratio = 4 and WHSV = 30,000 mL h−1 g−1). GAI method together with a reducing calcination atmosphere (20 %H2/N2) results effective to avoid the formation of large metal particles during the synthesis, especially for Ru/Al2O3 formulation. In fact, the Ru dispersion of the catalyst prepared by GAI (RuAlGAI) is around 5 times higher than that of RuAlIWI catalyst. On the other hand, NiAlGAI presents larger population of reduced particles but bigger in size than NiAlIWI catalyst, which finally provides the former with slightly higher metal surface and superior catalytic performance. By co-impregnating small amounts of Ru (0.5, 1.0 or 1.5 wt%) the Ni surface is considerably increased which, together with Ru synergistic collaboration, results in a methane yield rise from 20 to 44 % at 300 °C. The operando FTIR results show no differences in the reaction pathway with GAI preparation method and incorporation of Ru, but different evolution of reaction intermediates concentration with temperature. The bimetallic Ni-RuAl system presents much higher capacity to adsorb CO and hydrogenate the reaction intermediates (adsorbed formates and carbonyls) by dissociated H2 than its monometallic counterparts.

Impregnating Subnanometer Metallic Nanocatalysts into Self-Pillared Zeolite Nanosheets

Impregnation is the most commonly used approach to prepare supported metal catalysts in industry. However, this method suffers from the formation of large metal particles with uneven dispersion, poor thermal stability, and thus unsatisfied catalytic performance. Here, we demonstrate that the self-pillared MFI zeolite (silicalite-1 and ZSM-5) nanosheets with larger surface area and abundant Si-OH groups are ideal supports to immobilize ultrasmall monometallic (e.g., Rh and Ru) and various bimetallic clusters via simple incipient wetness impregnation method. The loaded subnanometric metal clusters are uniformly dispersed within sinusoidal five-membered rings of MFI and remain stable at high temperatures. The Rh/SP-S-1 is highly efficient in ammonia borane (AB) hydrolysis, showing a TOF value of 430 molH2 molRh-1 min-1 at 298 K, which is more than 6-fold improvement over that of nanosized zeolite-supported Rh catalyst and even comparable with that of zeolite-supported Rh single-atom catalyst. Because of the synergistic effect between bimetallic Rh-Ru clusters and zeolite acidity, the H2 generation rate from AB hydrolysis over Rh0.8Ru0.2/SP-ZSM-5-100 reaches up to 1006 molH2 molmetal-1 min-1 at 298 K, and also shows record activities in cascade hydrogenation of various nitroarenes by coupling with the hydrolysis of AB. This work demonstrates that zeolite nanosheets are excellent supports to anchor diverse ultrasmall metallic species via the simple impregnation method, and the obtained nanocatalysts can be applied in various industrially important catalytic reactions.

Cobalt sulfide catalysts for single-walled carbon nanotube synthesis

Catalysts play a critical role in carbon nanotube (CNT) synthesis. The challenge in precisely controlling CNT structures for various applications creates a long-standing goal to develop new and efficient CNT synthesis catalysts. Although sulfur-containing compounds are often used as promoters in CNT synthesis, metal sulfides have not been directly used as catalysts in CNT synthesis. Here, we study a series of cobalt sulfide catalysts supported on porous silica (CoS/SiO2) for CNT synthesis. Catalysts were first reduced in H2 at different temperatures and then exposed to ethanol at 900 °C to grow CNTs. We found the reduction temperature in H2 and the Co mass loading can strongly influence their catalytic performance. After the CoS/SiO2 catalyst with 1 wt% Co was reduced in H2 at 700 °C, it yields single-walled CNTs (SWCNTs) with a relatively narrow diameter distribution from 0.8 to 1.1 nm. We found that Co9S8 in the catalyst was partially reduced to metallic Co. The coexistence of Co9S8 and metallic Co nanoparticles can stabilize metallic Co nanoparticles and limit their fast aggregation. The Co mass loading in CoS/SiO2 catalysts can be further increased to 5 wt% while retaining catalysts' selectivity towards SWCNTs. When the Co mass loading increases to 7 or 10 wt%, aggregated large Co metal particles result in mainly multi-walled CNTs and graphite. Overall, our results show that CoS/SiO2 catalysts are a potential catalyst candidate for CNT synthesis.

Pengaruh Doping Cu terhadap Karakteristik Material dan Ketahanan Karbon pada Anoda Ni1-X-CuX-BCZY untuk PSOFC

The purpose of this study is to investigate the microstructure characteristics of the Ni1-xCux-BCZY anode and to analyze the carbon resistance by doping Cu into the Ni-BCZY anode. Ni1-xCux and BaCe0.7Zr0.1Y0.2O3-𝛿 (BCZY) powder were prepared by solid-state reaction with Ni1-xCux /BCZY = 60:40 wt%. The powder is calcined at a temperature of 700 °C, sintered at 1450 °C, and reduced by pure H2. The results of the Ni1-xCux-BCZY microstructure show an increase in the average particle size from 2.71 to 2.88 µm with increasing calcination time from 0.5 to 1.5 hours. Furthermore, the conductivity of Ni1-xCux-BCZY (x = 0.1) is lower than Ni1-xCux-BCZY (x = 0), this is associated with enhancement electron scattering, which correlatives with large metal particle obtained. The optimum conductivity of Ni1-xCux-BCZY(x=0.1) is obtained at a calcination time of 0.5 hours. Furthermore, NiCu anode can effectively increase the carbon resistance while using methane as a fuel.

Facile Top-Down Strategy for Direct Metal Atomization and Coordination Achieving a High Turnover Number in CO2 Photoreduction.

Developing unique single atoms as active sites is vitally important to boosting the efficiency of photocatalytic CO2 reduction, but directly atomizing metal particles and simultaneously adjusting the configuration of individual atoms remain challenging. Herein, we demonstrate a facile strategy at a relatively low temperature (500 °C) to access the in situ metal atomization and coordination adjustment via the thermo-driven gaseous acid. Using this strategy, the pyrolytic gaseous acid (HCl) from NH4Cl could downsize the large metal particles into corresponding ions, which subsequently anchored onto the surface defects of a nitrogen-rich carbon (NC) matrix. Additionally, the low-temperature treatment-induced C═O motifs within the interlayer of NC could bond with the discrete Fe sites in a perpendicular direction and finally create stabilized Fe-N4O species with high valence status (Fe3+) on the shallow surface of the NC matrix. It was found that the Fe-N4O species can achieve a highly efficient CO2 conversion when accepting energetic electrons from both homogeneous and heterogeneous photocatalysts. The optimized sample achieves a maximum turnover number (TON) of 1494 within 1 h in CO generation with a high selectivity of 86.7% as well as excellent stability. Experimental and theoretical results unravel that high valence Fe sites in Fe-N4O species can promote the adsorption of CO2 and lower the formation barrier of key intermediate COOH* compared with the traditional Fe-N4 moiety with lower chemical valence. Our discovery provides new points of view in the construction of more efficient single-atom cocatalysts by considering the optimization of the atomic configuration for high-performance CO2 photoreduction.

Heavy metal pollution by road-deposited sediments and its contribution to total suspended solids in rainfall runoff from intensive industrial areas

Understanding the relationship between road-deposited sediments (RDS) and total suspended solids (TSS) is essential for managing non-point pollution. Studying the heavy metal concentrations of RDS and TSS in rainfall is important to the development of RDS management strategies and to the design of effective stormwater management practices. We investigated the heavy metal (V, Cr, Mn, Co, Ni, Cu, Zn, As, Mo, Cd, Sn, Pb) in RDS and TSS in rainfall runoff to assess the metal pollution level and to evaluate the contribution of RDS heavy metal pollution in the TSS. The heavy metal pollution in RDS and TSS in industrial areas was relatively higher in small particles (<125 μm), while TSS had a higher heavy metal concentration than RDS. In addition, the concentration of heavy metals in TSS increased rapidly during the initial rainfall. The amount of particles larger than 125 μm also increased, suggesting that large metal particles accumulated in industrial areas were also discharged in the form of non-point pollution. The amount of RDS per unit of industrial area (g/m2) and the accumulation of heavy metals (Pb, Cu, and Zn) (mg/m2) were 15- and 8–54-fold higher than those of urban areas, respectively. Considering particles <125 μm, which can be easily transported or discharged during rainfall, the contribution rate of RDS to TSS was 41.3%, but the average contribution rate to heavy metals in TSS was 22.1%. The average load of heavy metals from industrial areas in TSS was 77.9%. The load of Cu, Ni, As, Cd, and Sn exceeded 90%, indicating that most of these metals were attributed to industrial activities related to metal processing. Our results suggest the importance of efficient road cleaning and rainfall runoff management strategies to solve the heavy metal pollution problem caused by non-point sources in industrial areas.

Panoramic view of particle morphology for growth mechanism exploration: A case study of micron-sized five-fold twinned Ag particles from vapor condensation

Abstract Nobel metal particles of designed morphology have found many ingenious applications in fields such as catalysis, plasmonics, metamaterials, etc. A thorough investigation of influential factors that determine the particle morphology is desirable. Micron-sized Ag particles prepared by physical vapor deposition usually result from two-step growth: condensation from dense vapor followed by continual growth of the sessile particles landing on substrate. The primary particle-substrate contact may be the decisive factor in determining the particle morphology which in turn needs be precisely characterized. Here we report investigation on the growth process of five-fold twinned Ag particles towards targeted morphology by using scanning electron microscopic imaging at variable incidence angles, in conjunction with 3D modelling, so as to reveal the particle–substrate contact profile and to infer the growth mechanism. Five-fold twinned Ag particles were obtained at large yield on SiO2/Si(1 0 0), MgO(1 0 0) and LaAlO3(1 0 0) substrates. Results show that fivefold twinned Ag particles on SiO2/Si(1 0 0) substrate are usually fully developed, demonstrating higher symmetries ( I h or D 5 h ) and acute contact angles, while on MgO(1 0 0) and LaAlO3(1 0 0) substrates the particles are usually heavily truncated with a contact characterized by also some obtuse angles. Difference in morphology occurs in the secondary growth stage where Ag atom migration along the particle-substrate interface may or may not be allowed. A set of parameters including contacting facet/contact angles and the height-edge length ratio are proposed for the morphology description of the five-fold twinned particles on support. Our work has resolved the influential factors in determining the morphology of large metal particles from physical vapor deposition where continual growth of sessile particles landing on substrate plays a pivotal role. By manipulating the particle-substrate contact and the secondary growth stage, five-fold twinned metal particles with designed morphology can be prepared for specific applications.

Simultaneous Selective Chlorination and Carbothermic Reduction of High-Iron Manganese Ore for the Recovery of Manganese Chloride and Metallic Iron

Metallurgical processing of low-grade manganese ore with high iron content is gaining increasing attention due to the gradual depletion of high-grade Mn ores, amid the difficulties in its efficient extraction for both Mn and Fe values in an environmentally-friendly manner. Attempting to tackle the difficulties, this paper describes an innovative process for selectively chlorinating and reducing the high-Fe manganese ore in a simultaneous manner, aiming to produce water-soluble MnCl2 and metallic Fe. After pre-mixing with carbonaceous reductant, CaCl2 and MgCl2 as the chlorinating agent, the Mn ore was heated at 1000 °C. As much as 89.4% Mn can be chlorinated in its water-soluble form, with dissolution of only 3.0% Fe. The presence of CaCl2 during carbothermic reduction resulted in significant promotion in both the Fe reduction rate and formation of large metallic Fe particles due to the segregation effect, facilitating subsequent separation. Selective Mn chlorination by MgCl2 took place with or without the involvement of SiO2, forming MgSiO4 or MgO, respectively.

Oxygen Reduction Reaction Activity of Cobalt Platinum Bronze Nano-Particles Prepared By a Silica Template Method

Platinum metal-based materials have been mostly used as the catalysts for polymer electrolyte fuel cells and extensively studied to improve their performance by alloying and shape-controlling. Although these advanced technologies are pursued mainly for enhancing the catalytic activities and showed significant improvement in deed, their durabilities under realistic conditions do not often accompany. For wider distribution of fuel cell vehicles, however, both high activity and high durability should be compatibly achieved. Recently we have focused on metal-platinum oxide bronzes as a durable cathode catalyst and reported a study on their fundamental properties [1,2], in which a platinum bronze containing cobalt (Co-Pt bronze) was synthesized by solid state reaction using platinum dioxide and cobalt nitrate hexahydrates as the raw materials. Its oxygen reduction reaction (ORR) was enhanced after potential cycles down to the hydrogen region, which formed a thin Pt metallic layer over the oxide. While its specific activity was as high as that of pure platinum nanoparticles, its durability against the potential cycles was much higher. However, its mass-specific electrochemical surface area (ECSA) and mass activity were much lower than those of pure platinum nanoparticles because of its large particle size (20-50 nm). In the present study, a novel preparation process was applied to obtain smaller Co-Pt bronze nanoparticles and their characteristics and electrochemical performances for PEFC application were examined. Co-Pt bronze nano powder was prepared by a template method using a mesoporous silica, TMPS-4R (pore diameter: 3.8 nm, Taiyo Kagaku Co., Ltd.). Hexachloroplatinate hexahydrates and cobalt nitrate hexahydrates were dissolved in ultrapure water and then mixed with the silica template powder. The mixed powder was heat-treated under O2 flow (200 mL min-1) at 650 ºC for 1 hour. The obtained powder was dispersed in NaOH to dissolve the silica template and subsequently washed with ultrapure water. Co-Pt bronze nano power was collected from the supernatant of the washed suspension after centrifuged at 5,000 g (large Co-Pt bronze and metallic platinum particles were precipitated.). The obtained powder was characterized by XRD, SEM, TEM and the nitrogen sorption method. The electrochemical behaviors including ORR activity of the obtained Co-Pt bronze nano particles were evaluated by the thin-film RDE method in 0.1 M HClO4 at 30 ºC. XRD measurement confirmed that the heat-treated powder is comprised of platinum bronze and platinum metal phases and that the latter was removed by the centrifuge process. The nanoparticles collected from the supernatant was comprised of the platinum bronze only and showed a much larger N2-sorption surface area than the precipitate (58 and 7.3 m2 g-1 for the supernatant and precipitation, respectively). The SEM observation revealed that the platinum bronze particles collected from supernatant are cylindrically shaped with ca. 4 nm in diameter (Fig. 1A). This shape reflects the mesopores of the templated silica. Electrochemical measurement showed that the surface of the prepared nanoparticles was gradually metallized over potential cycling. The ECSA and ORR mass activity after potential cycling were respectively larger than those of large particles made by the solid state reaction. This work was financially supported by NEDO, Japan.

Kinetics and mechanism of mechanochemical synthesis of hafnium nitride ceramics in a planetary ball mill

Mechanochemical synthesis of hafnium nitride ceramic powder was accomplished through direct nitridation of hafnium particles in nitrogen atmosphere during high-energy milling in a planetary ball mill. The nitrogen content was measured and evaluated to determine the reaction kinetics for hafnium – nitrogen across a range of treatment durations. The observed reaction rates are notably faster than for conventional thermal treatment, and, for hafnium treated for 5 min in the ball mill, the onset of nitridation begins at a temperature 200 °C lower than for the initial hafnium metal. The crystal structure and microstructure transformations were also investigated. A mechanism for the rapid hafnium nitridation occurring under high-energy ball milling conditions is proposed and discussed. Based on this proposed mechanism of metal nitridation via ball mill treatment in nitrogen atmosphere, we may suggest this process as an effective method for fabrication of fine (sub-micron) hafnium nitride powder from relatively large (10–100 μm) initial metal particles.

Effect of Carbon Support on the Electrocatalytic Properties of Pt−Ru Catalysts

AbstractIn this study, we explore the effect of carbon support on the performance of anodic electrodes for polymer electrolyte membrane fuel cells (PEMFCs). Pt−Ru catalysts supported on different carbon materials were synthesized by wet impregnation method and characterized by means of Raman, XRD, TEM, and N2 adsorption analysis. The electrocatalytic activity of the prepared catalysts was studied during hydrogen oxidation reaction experiments (HOR) as well as during the operation of a fuel cell using pure H2, and H2‐carbon monoxide anode feeding. The results show that the crystalline phase and the point of zero charge (pzc) of the carbon supports play an important role in the metal particle size and consequently in the catalyst electrocatalytic activity. Carbon supports with amorphous phase and high values of pzc, result in catalysts with large metal particle size leading to low electrocatalytic activity. On the other hand, using graphene derivative or carbon nanotubes (CNT) in different catalysts generates smaller metal particle size which results in higher electrocatalytic activity.

Modeling of Structure Formation in Mixtures Using the Method of Self-Propagating High-Temperature Synthesis

An investigation is made of the specific features of compaction of thin layers consisting of monodisperse calibrated solid balls that model a bidisperse powder mixture of large metallic and fine nonmetallic particles used for fabricating layer-by-layer compressed long-measuring blanks intended for the production of high-melting materials by the method of self-propagating high-temperature synthesis. Consideration is given to the case of one-sided axial compression of thin layers of balls in a matrix of hexagonal cross section at the ratio of the cross-sectional dimension of the matrix to the ball diameter equal to L/d ≈ 15.

Copper Behavior and Fayalite Microstructure Changes Influenced by Cu2O Dissolution

The dissolution of Cu2O in fayalite is one of the chief processes that cause copper loss in metallurgical processes. In this paper, the interaction between fayalite and Cu2O is systematically studied to verify the main mechanism of copper loss as well as the variation in the fayalite microstructure. The results indicate the simultaneous occurrence of melting and dissolution of copper in fayalite. The redox reaction of \( {\text{Cu}}^{ + } + {\text{Fe}}^{2 + } = {\text{Cu}} + {\text{Fe}}^{3 + } \) occurs in the melt phase, resulting in the generation of metallic copper and amorphous iron. The copper dissolution impacts the fayalite microscopically. With the increase of Cu2O, the obvious phase separation is seen in the fayalite melt, and large metal particles are dispersed in the melt. In addition, the dissolution mechanism of copper and the change in the fayalite microstructure are analyzed by x-ray photoelectron spectroscopy and Raman spectroscopy. The results show that amorphous iron trapping Cu(I) and the formation of fayalite-combined copper are the most probable mechanisms for copper dissolution and the fayalite microstructure changes. These findings provide theoretical support for the secondary extraction of copper resources from copper slag.