Special Issue "Advances in Synthesis of Metallic, Oxidic and Composite Powders"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (30 June 2020).

Special Issue Editors

Dr. Srecko Stopic
Website
Guest Editor
IME Process Metallurgy and Metal Recycling Department, RWTH Aachen University, Germany
Interests: hydrometallurgy; recycling; nanotechnology; waste water treatment; recycling; materials engineering; environmental protection
Special Issues and Collections in MDPI journals
Prof. Dr. Bernd Friedrich
Website SciProfiles
Guest Editor
IME Process Metallurgy and Metal Recycling Department, RWTH Aachen University, Germany
Interests: pyrometallurgy, process technology; metals; recycling; purification; alloying; WEEE; spent batteries; critical materials; circular economy, electrometallurgy
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

The high demand for new materials, such as metals, oxides, and composites, raises the need for an advanced synthesis of different materials, which are crucial for technological applications. Different process synthesis routes, such as atomization, reduction in aqueous phase, crystallization, chemical precipitation, high pressure reaction in autoclave, and electrolysis, can be used to create controlled powder characteristics with specific properties for a particular application or industry. Advances in synthesis explores a range of materials and techniques used for powder metallurgy and the use of this technology across a variety of application areas such as medicine, catalysis and automotive industry. This Special Issue, "Advances in the Synthesis of Metallic, Oxidic and Composite Powders", is dedicated to the latest scientific achievements in an efficient preparation of metals, oxides and composite materials. In this issue, we will be focus on description of the synthesis of metal, oxide and composite particles from the water, metalorganic and colloid solution using different synthesis methods. The main challenge of this issue is the controlled synthesis via process parameters (conditions and modes atomization, the concentration of solution, residence time of aerosol in a reactor, presence of additives, flow rate, decomposition and reduction temperature, different precursors with reducing agents, and surrounding atmosphere) in order to guide the process to obtain powders with such a morphology that satisfies more and more complex requirements for the properties of advanced engineering materials.

The synthesis of powders has two different strategies: “Top-Down” and “Bottom-Up”. The meaning of “Top-Down” is based on mechanical grinding of initial materials to small dimensions. It is necessary to decrease the powder size in order to perform Hall-Petch strengthening and apply a severe plastic deformation to powder particles to perform work hardening. High energy milling has a potential for realizing the new ideas of materials designers. The meaning of “Bottom-Up“ is related to the physico-chemical preparation methods in gas phase (ultrasonic spray pyrolysis, flame pyrolysis and chemical vapor deposition) and in liquid phase (sol gel, hydrothermal processes, precipitation, electrolytic synthesis, high pressure reactions in an autoclave and crystallization). The precipitation methods are usually used for the purification of spent solution.

In this regard, new approaches in material and synthesis design, structural engineering and morphological characteristics are provided. Preparation of metal particles by spray pyrolysis of metal salts is especially challenging. Using aerosol synthesis, a single-step and multistep preparation process of different core-shall particles is possible, thus avoiding several steps like drying, shrinkage, solute precipitation, thermolysis, and sintering to form uniform spherical particles in nanosized and submicron range. Technical limitations of this technique, as well as a comparison with other synthesis methods (difficulty in controlling morphology-porous or hollow particles, relatively low production rate and process of large volume of gas), will be partly considered in order to prevent or solve these problems.

Especially, the newest results in the synthesis of nanosized particles by ultrasonic spray pyrolysis method and other methods will be published. By addressing the complex problems faced in the synthesis procedures, the scaling–up of the aerosol droplet production and other methods shall be considered.

Dr. Srecko Stopic
Prof. Dr. Bernd Friedrich
Guest Editors

Manuscript Submission Information

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Keywords

  • Powder metallurgy
  • Hydrometallurgy
  • Atomization
  • Spray pyrolysis
  • Electrochemistry
  • Sol-gel
  • Metal
  • Oxide
  • Composite
  • Reduction
  • Grinding
  • Crystallization

Published Papers (17 papers)

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Research

Open AccessArticle
Recovery of Diamond and Cobalt Powders from Polycrystalline Drawing Die Blanks via Ultrasound Assisted Leaching Process—Part 2: Kinetics and Mechanisms
Metals 2020, 10(6), 741; https://doi.org/10.3390/met10060741 - 03 Jun 2020
Abstract
The leaching of industrial polycrystalline diamond (PCD) blanks in aqua regia at atmospheric pressure between 60 °C and 80 °C was performed using an ultrasound to improve the rate of cobalt removal in order to be able to reuse very expensive polycrystalline diamond. [...] Read more.
The leaching of industrial polycrystalline diamond (PCD) blanks in aqua regia at atmospheric pressure between 60 °C and 80 °C was performed using an ultrasound to improve the rate of cobalt removal in order to be able to reuse very expensive polycrystalline diamond. Because cobalt (20 wt.%) is used as a solvent catalyst in the production of PCD, its recovery is very important. The cleaned PCD are returned to the production process. Kinetic models were used in the study of cobalt dissolution from polycrystalline diamond blanks by measuring the declining ferromagnetic properties over time. For a better understanding of this leaching process, thermochemical aspects are included in this work. The lowest free Gibbs energy value was obtained with a low solid/liquid ratio and the full use of an ultrasound. A transition from a reaction-controlled to a diffusion-controlled shrinking core model was observed for PCD with a thickness greater than 2.8–3.4 mm. Intermittent ultrasound doubles the reaction rate constant, and the full use of ultrasound provides a 1.5-fold further increase. The obtained maximum activation energy between 60 °C and 80 °C is 20 kJ/mol, for a leaching of diamond blank with grain size of 5 µm. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Recovery of Diamond and Cobalt Powder from Polycrystalline Drawing Die Blanks via Ultrasound-Assisted Leaching Process—Part 1: Process Design and Efficiencies
Metals 2020, 10(6), 731; https://doi.org/10.3390/met10060731 - 01 Jun 2020
Abstract
The treatment of industrial polycrystalline diamond (PCD) blanks in aqua regia at atmospheric pressure between 333 K and 353 K was performed via the ultrasound-assisted leaching process to investigate whether the influence of ultrasound is beneficial. Cobalt content in the solution and in [...] Read more.
The treatment of industrial polycrystalline diamond (PCD) blanks in aqua regia at atmospheric pressure between 333 K and 353 K was performed via the ultrasound-assisted leaching process to investigate whether the influence of ultrasound is beneficial. Cobalt content in the solution and in the blanks was monitored as well as the effects of leaching temperature, solid-to-liquid ratio, and PCD blank size. The use of intermittent and permanent ultrasound helped reduce the leaching time and thus energy consumption by up to 50%. In all trials with ultrasound, higher temperature only has a slight effect. Solid-to-liquid ratio does not have a positive or negative impact. A new process design was tested using an innovative experimental setup for ultrasound-assisted leaching aiming at maximum cobalt and diamond recovery from PCD and final reuse of fine PCD for cutting and polishing other hard materials in different important industrial applications. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Advances in Thermochemical Synthesis and Characterization of the Prepared Copper/Alumina Nanocomposites
Metals 2020, 10(6), 719; https://doi.org/10.3390/met10060719 - 28 May 2020
Abstract
This paper presents thermochemical synthesis of copper/alumina nanocomposites in a Cu-Al2O3 system with 1–2.5 wt.% of alumina and their characterization, which included: transmission electron microscopy: focused ion beam (FIB), analytical electron microscopy (AEM) and high resolution transmission electron microscopy (HRTEM). [...] Read more.
This paper presents thermochemical synthesis of copper/alumina nanocomposites in a Cu-Al2O3 system with 1–2.5 wt.% of alumina and their characterization, which included: transmission electron microscopy: focused ion beam (FIB), analytical electron microscopy (AEM) and high resolution transmission electron microscopy (HRTEM). Thermodynamic analysis was used to study the formation mechanism of desirable products during drying, thermal decomposition and reduction processes. Upon synthesis of powders, samples were cold pressed (2 GPa) in tools dimension 8 × 32 × 2 mm and sintered at temperatures within the range 800–1000 °C for 15 to 120 min in a hydrogen atmosphere. Results of characterization showed that dispersion-strengthened compacts could be produced by sintering of thermo-chemically prepared Cu-Al2O3 powders with properties suitable for material application, such as a contact material exhibiting high strength and high electrical conductivity at the same time. Additional research was carried out in order to analyze the application of the obtained nanocomposite powders for the synthesis of copper/alumina nanocomposites by a new method, which is a combination of a thermochemical procedure and mechanical alloying. The measured values of an electric conductivity and hardness were compared with ones in literature, confirming an advantage of the proposed combined strategy. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Reaction Mechanism and Process Control of Hydrogen Reduction of Ammonium Perrhenate
Metals 2020, 10(5), 640; https://doi.org/10.3390/met10050640 - 15 May 2020
Abstract
The preparation of rhenium powder by a hydrogen reduction of ammonium perrhenate is the only industrial production method. However, due to the uneven particle size distribution and large particle size of rhenium powder, it is difficult to prepare high-density rhenium ingot. Moreover, the [...] Read more.
The preparation of rhenium powder by a hydrogen reduction of ammonium perrhenate is the only industrial production method. However, due to the uneven particle size distribution and large particle size of rhenium powder, it is difficult to prepare high-density rhenium ingot. Moreover, the existing process requires a secondary high-temperature reduction and the deoxidization process is complex and requires a high-temperature resistance of the equipment. Attempting to tackle the difficulties, this paper described a novel process to improve the particle size distribution uniformity and reduce the particle size of rhenium powder, aiming to produce a high-density rhenium ingot, and ammonium perrhenate is completely reduced by hydrogen at a low temperature. When the particle size of the rhenium powder was 19.74 µm, the density of the pressed rhenium ingot was 20.106 g/cm3, which was close to the theoretical density of rhenium. In addition, the hydrogen reduction mechanism of ammonium perrhenate was investigated in this paper. The results showed that the disproportionation of ReO3 decreased the rate of the reduction reaction, and the XRD and XPS patterns showed that the increase in the reduction temperature was conducive to increasing the reduction reaction rate and reducing the influence of disproportionation on the reduction process. At the same reduction temperature, reducing the particle sizes of ammonium perrhenate was conducive to increasing the hydrogen reduction rate and reducing the influence of the disproportionation. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Electrochemical Deposition of Al-Ti Alloys from Equimolar AlCl3 + NaCl Containing Electrochemically Dissolved Titanium
Metals 2020, 10(1), 88; https://doi.org/10.3390/met10010088 - 04 Jan 2020
Abstract
Al-Ti alloys were electrodeposited from equimolar chloroaluminate molten salts containing up to 0.1 M of titanium ions, which were added to the electrolyte by potentiostatic dissolution of metallic Ti. Titanium dissolution and titanium and aluminium deposition were investigated by linear sweep voltammetry and [...] Read more.
Al-Ti alloys were electrodeposited from equimolar chloroaluminate molten salts containing up to 0.1 M of titanium ions, which were added to the electrolyte by potentiostatic dissolution of metallic Ti. Titanium dissolution and titanium and aluminium deposition were investigated by linear sweep voltammetry and chronoamperometry at 200 and 300 °C. Working electrodes used were titanium and glassy carbon. The voltammograms on Ti obtained in the electrolyte without added Ti ions indicated titanium deposition and dissolution proceeding in three reversible steps: Ti4+ ⇄ Ti3+, Ti3+ ⇄ Ti2+ and Ti2+ ⇄ Ti. The voltammograms recorded with glassy carbon in the electrolyte containing added titanium ions did not always clearly register all of the three processes. However, peak currents, which were characteristics of Al, Ti and Al-Ti alloy deposition and dissolution, were evident in voltammograms on both working electrodes used. A constant potential electrodeposition regime was used to obtain deposits on the glassy carbon working electrode. The obtained deposits were characterized by SEM, energy-dispersive spectrometry and XRD. In the deposits on the glassy carbon electrode, the analysis identified an Al and AlTi3 alloy formed at 200 °C and an Al2Ti and Al3Ti alloy obtained at 300 °C. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Application of the Flotation Tailings as an Alternative Material for an Acid Mine Drainage Remediation: A Case Study of the Extremely Acidic Lake Robule (Serbia)
Metals 2020, 10(1), 16; https://doi.org/10.3390/met10010016 - 20 Dec 2019
Abstract
Flotation tailings rich in carbonate minerals from the tailings deposit of the copper mine Majdanpek (Serbia) were applied for neutralization of the water taken from the extremely acidic Lake Robule (Bor, Serbia). Tests conducted in Erlenmeyer flasks showed that after neutralization of the [...] Read more.
Flotation tailings rich in carbonate minerals from the tailings deposit of the copper mine Majdanpek (Serbia) were applied for neutralization of the water taken from the extremely acidic Lake Robule (Bor, Serbia). Tests conducted in Erlenmeyer flasks showed that after neutralization of the lake water to pH 7, over 99% of aluminum (Al), iron (Fe), and copper (Cu) precipitated, as well as 92% of Zn and 98% of Pb. In order to remove residual Mn and Ag, the water was further treated with NaOH. After treatment with NaOH, all concentrations of the metals in the lake water samples were below discharge limits for municipal wastewater according to the national legislation of the Republic of Serbia. The results of this work suggest that mining waste could be used for active neutralization of the acid mine drainage. The use of the mining waste instead of lime could reduce the costs of the active treatment of the acid mine drainage. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Structural and Electrochemical Properties of Nesting and Core/Shell Pt/TiO2 Spherical Particles Synthesized by Ultrasonic Spray Pyrolysis
Metals 2020, 10(1), 11; https://doi.org/10.3390/met10010011 - 20 Dec 2019
Abstract
Pt/TiO2 composites were synthesized by single-step ultrasonic spray pyrolysis (USP) at different temperatures. In an in-situ method, Pt and TiO2 particles were generated from tetra-n-butyl orthotitanate and chloroplatinic acid, and hydrothermally-prepared TiO2 colloidal dispersion served as Pt support [...] Read more.
Pt/TiO2 composites were synthesized by single-step ultrasonic spray pyrolysis (USP) at different temperatures. In an in-situ method, Pt and TiO2 particles were generated from tetra-n-butyl orthotitanate and chloroplatinic acid, and hydrothermally-prepared TiO2 colloidal dispersion served as Pt support in an ex-situ USP approach. USP-synthesized Pt/TiO2 composites were generated in the form of a solid mixture, morphologically organized in nesting huge hollow and small solid spheres, or TiO2 core/Pt shell regular spheroids by in-situ or ex-situ method, respectively. This paper exclusively reports on characteristic mechanisms of the formation of novel two-component solid composites, which are intrinsic from the USP approach and controlled precursor composition. The generation of the two morphological components within the in-situ approach, the hollow spheres and all-solid spheres, was indicated to be caused by characteristic sol-gel/solid phase transition of TiO2. Both the walls of the hollow spheres and the cores of all-solid ones consist of TiO2 matrix populated by 10 nm-sized Pt. On the other hand, spherical, uniformly-sized, Pt particles of a few nanometers in size created a shell uniformly deposited onto TiO2 spheres of ca. 150 nm size. Activities of the prepared samples in an oxygen reduction reaction and combined oxygen reduction and hydrogen evolution reactions were electrochemically tested. The ex-situ synthesized Pt/TiO2 was more active for oxygen reduction and combined oxygen reduction and hydrogen reactions in comparison to the in-situ Pt/TiO2 samples, due to better availability of Pt within a core/shell structure for the reactions. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Synthesis of Poly-Alumino-Ferric Sulphate Coagulant from Acid Mine Drainage by Precipitation
Metals 2019, 9(11), 1166; https://doi.org/10.3390/met9111166 - 29 Oct 2019
Cited by 1
Abstract
The wastes generated from both operational and abandoned coal and metal mining are an environmental concern. These wastes, including acid mine drainage (AMD), are treated to abate the devastating effects they have on the environment before disposal. However, AMD contains valuable resources that [...] Read more.
The wastes generated from both operational and abandoned coal and metal mining are an environmental concern. These wastes, including acid mine drainage (AMD), are treated to abate the devastating effects they have on the environment before disposal. However, AMD contains valuable resources that can be recovered to subsidize treatment costs. Two of the major constituents of coal AMD are iron and aluminium, which can be recovered and engineered to function as coagulants. This work examines the potential of producing a poly-alumino-ferric sulphate (AMD-PAFS) coagulant from coal acidic drainage solutions. The co-precipitation of iron and aluminium is conducted at pH values of 5.0, 6.0 and 7.0 using sodium hydroxide in order to evaluate the recovery of iron and aluminium as hydroxide precipitates while minimizing the co-precipitation of the other heavy metals. The precipitation at pH 5.0 yields iron and aluminium recovery of 99.9 and 94.7%, respectively. An increase in the pH from 5.0 to 7.0 increases the recovery of aluminium to 99.1%, while the recovery of iron remains the same. The precipitate formed at pH 5.0 is used to produce a coagulant consisting of 89.5% and 10.0% iron and aluminium, respectively. The production of the coagulant is carried out by dissolving the precipitate in 5.0% (w/w) sulphuric acid. Subsequently, the treatment of the brewery wastewater shows that the AMD-PAFS coagulant is as efficient as the conventional poly ferric sulphate (PFS) coagulant. The turbidity removal is 91.9 and 87.8%, while the chemical oxygen demand (COD) removal is 56.0 and 64.0% for AMD-PAFS and PFS coagulants, respectively. The developed process, which can easily be incorporated into existing AMD treatment plants, not only reduces the sludge disposal problems but also creates revenue from waste. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Chemical Stability of Zirconolite for Proliferation Resistance under Conditions Typically Required for the Leaching of Highly Refractory Uranium Minerals
Metals 2019, 9(10), 1070; https://doi.org/10.3390/met9101070 - 01 Oct 2019
Abstract
In this study, synthetic zirconolite samples with a target composition Ca0.75Ce0.25ZrTi2O7, prepared using two different methods, were used to study the stability of zirconolite for nuclear waste immobilisation. Particular focus was on plutonium, with cerium [...] Read more.
In this study, synthetic zirconolite samples with a target composition Ca0.75Ce0.25ZrTi2O7, prepared using two different methods, were used to study the stability of zirconolite for nuclear waste immobilisation. Particular focus was on plutonium, with cerium used as a substitute. The testing of destabilisation was conducted under conditions previously applied to other highly refractory uranium minerals that have been considered for safe storage of nuclear waste, brannerite and betafite. Acid (HCl, H2SO4) leaching for up to 5 h and alkaline (NaHCO₃, Na2CO3) leaching for up to 24 h was done to enable comparison with brannerite leached under the same conditions. Ferric ion was added as an oxidant. Under these conditions, the synthetic zirconolite dissolved much slower than brannerite and betafite. While the most intense conditions were observed previously to result in near complete dissolution of brannerite in under 5 h, zirconolite was not observed to undergo significant attack over this timescale. Fine zirconolite dissolved faster than the coarse material, indicating that dissolution rate is related to surface area. This data and the long term stability of zirconolite indicate that it is a good material for long-term sequestration of radioisotopes. Besides its long term durability in the disposal environment, a wasteform for fissile material immobilisation must demonstrate proliferation resistance such that the fissile elements cannot be retrieved by leaching of the wasteform. This study, in conjunction with the previous studies on brannerite and betafite leaching, strongly indicates that the addition of depleted uranium to the wasteform, to avert long term criticality events, is detrimental to proliferation resistance. Given the demonstrated durability of zirconolite, long term criticality risks in the disposal environment seem a remote possibility, which supports its selection, above brannerite or betafite, as the optimal wasteform for the disposition of nuclear waste, including of surplus plutonium. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Synthesis of Nanosilica via Olivine Mineral Carbonation under High Pressure in an Autoclave
Metals 2019, 9(6), 708; https://doi.org/10.3390/met9060708 - 24 Jun 2019
Cited by 4
Abstract
Silicon dioxide nanoparticles, also known as silica nanoparticles or nanosilica, are the basis for a great deal of biomedical and catalytic research due to their stability, low toxicity and ability to be functionalized with a range of molecules and polymers. A novel synthesis [...] Read more.
Silicon dioxide nanoparticles, also known as silica nanoparticles or nanosilica, are the basis for a great deal of biomedical and catalytic research due to their stability, low toxicity and ability to be functionalized with a range of molecules and polymers. A novel synthesis route is based on CO2 absorption/sequestration in an autoclave by forsterite (Mg2SiO4), which is part of the mineral group of olivines. Therefore, it is a feasible and safe method to bind carbon dioxide in carbonate compounds such as magnesite forming at the same time as the spherical particles of silica. Indifference to traditional methods of synthesis of nanosilica such as sol gel, ultrasonic spray pyrolysis method and hydrothermal synthesis using some acids and alkaline solutions, this synthesis method takes place in water solution at 175 °C and above 100 bar. Our first experiments have studied the influence of some additives such as sodium bicarbonate, oxalic acid and ascorbic acid, solid/liquid ratio and particle size on the carbonation efficiency, without any consideration of formed silica. This paper focuses on a carbonation mechanism for synthesis of nanosilica under high pressure and high temperature in an autoclave, its morphological characteristics and important parameters for silica precipitation such as pH-value and rotating speed. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessFeature PaperArticle
Synthesis of Tribological WS2 Powder from WO3 Prepared by Ultrasonic Spray Pyrolysis (USP)
Metals 2019, 9(3), 277; https://doi.org/10.3390/met9030277 - 28 Feb 2019
Cited by 2
Abstract
This paper describes the synthesis of tungsten disulfide (WS2) powder by the sulfurization of tungsten trioxide (WO3) particles in the presence of additive potassium carbonate (K2CO3) in nitrogen (N2) atmosphere, first at lower [...] Read more.
This paper describes the synthesis of tungsten disulfide (WS2) powder by the sulfurization of tungsten trioxide (WO3) particles in the presence of additive potassium carbonate (K2CO3) in nitrogen (N2) atmosphere, first at lower temperature (200 °C) and followed by reduction at higher temperature (900 °C). In addition, the ultrasonic spray pyrolysis of ammonium meta-tungstate hydrate (AMT) was used for the production of WO3 particles at 650 °C in air. The HSC Chemistry® software package 9.0 was used for the analysis of chemistry and thermodynamic parameters of the processes for WS2 powder synthesis. The crystalline structure and phase composition of all synthesized powders were analyzed by X-ray diffraction (XRD) measurements. The morphology and chemical composition of these samples were examined by scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX). Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Influence of the Shape of Copper Powder Particles on the Crystal Structure and Some Decisive Characteristics of the Metal Powders
Metals 2019, 9(1), 56; https://doi.org/10.3390/met9010056 - 09 Jan 2019
Cited by 6
Abstract
Three different forms of Cu powder particles obtained by either galvanostatic electrolysis or a non-electrolytic method were analyzed by a scanning electron microscope (SEM), X-ray diffraction (XRD) and particle size distribution (PSD). Electrolytic procedures were performed under different hydrogen evolution conditions, leading to [...] Read more.
Three different forms of Cu powder particles obtained by either galvanostatic electrolysis or a non-electrolytic method were analyzed by a scanning electron microscope (SEM), X-ray diffraction (XRD) and particle size distribution (PSD). Electrolytic procedures were performed under different hydrogen evolution conditions, leading to the formation of either 3D branched dendrites or disperse cauliflower-like particles. The third type of particles were compact agglomerates of the Cu grains, whose structural characteristics indicated that they were formed by a non-electrolytic method. Unlike the sharp tips that characterize the usual form of Cu dendrites, the ends of both the trunk and branches were globules in the formed dendrites, indicating that a novel type of Cu dendrites was formed in this investigation. Although the macro structures of the particles were extremely varied, they had very similar micro structures because they were constructed by spherical grains. The Cu crystallites were randomly oriented in the dendrites and compact agglomerates of the Cu grains, while the disperse cauliflower-like particles showed (220) and (311) preferred orientation. This indicates that the applied current density affects not only the morphology of the particles, but also their crystal structure. The best performance, defined by the largest specific surface area and the smallest particle size, was by the galvanostatically produced powder consisting of disperse cauliflower-like particles. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Preparation of Vanadium Oxides from a Vanadium (IV) Strip Liquor Extracted from Vanadium-Bearing Shale Using an Eco-Friendly Method
Metals 2018, 8(12), 994; https://doi.org/10.3390/met8120994 - 27 Nov 2018
Cited by 2
Abstract
In the traditional vanadium precipitation process, the use of ammonium salts can produce serious pollution problems from the ammonia waste-water and the ammonia gas generated during the processing. In this reported study, an eco-friendly technology was investigated to prepare vanadium oxides from a [...] Read more.
In the traditional vanadium precipitation process, the use of ammonium salts can produce serious pollution problems from the ammonia waste-water and the ammonia gas generated during the processing. In this reported study, an eco-friendly technology was investigated to prepare vanadium oxides from a typical vanadium (IV) strip liquor, obtained after the hydrometallurgical treatment of a vanadium-bearing shale. Thermodynamic analysis demonstrated that VO(OH)2 could be prepared as a precursor over a suitable solution pH range. Experimental results showed that by adjusting the pH to around 5.6, at room temperature, 98.6% of the vanadium in the strip liquor was formed into hydroxide, in 5 min. After obtaining the VO(OH)2, it was washed with dilute acid to minimize the level of impurities. VO2 and V2O5 were then produced by reacting the VO(OH)2 with air or argon, in a tube furnace. The XRD analyses of the products showed that VO2 had been produced in air and V2O5 had been produced in argon. The purity of the VO2 was 98.82% after calcining for 2 h at 550 °C, in argon flow, at a rate of 50 mL/min. It was found that the purity of the V2O5 was 98.70%, using the same reaction conditions in air. Compared to the traditional precipitation method that uses ammonium salt, followed by calcination, this proposed method is eco-friendly and employs less quantities of reagents and energy, and two types of products can be produced. Consequently, this process could promote the sustainable development of the vanadium chemical industry. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Synthesis of Magnesium Carbonate via Carbonation under High Pressure in an Autoclave
Metals 2018, 8(12), 993; https://doi.org/10.3390/met8120993 - 27 Nov 2018
Cited by 7
Abstract
Magnesium carbonate powders are essential in the manufacture of basic refractories capable of withstanding extremely high temperatures and for special types of cement and powders used in the paper, rubber, and pharmaceutical industries. A novel synthesis route is based on CO2 absorption/sequestration [...] Read more.
Magnesium carbonate powders are essential in the manufacture of basic refractories capable of withstanding extremely high temperatures and for special types of cement and powders used in the paper, rubber, and pharmaceutical industries. A novel synthesis route is based on CO2 absorption/sequestration by minerals. This combines the global challenge of climate change with materials development. Carbon dioxide has the fourth highest composition in earth’s atmosphere next to nitrogen, oxygen and argon and plays a big role in global warming due to the greenhouse effect. Because of the significant increase of CO2 emissions, mineral carbonation is a promising process in which carbon oxide reacts with materials with high metal oxide composition to form chemically stable and insoluble metal carbonate. The formed carbonate has long-term stability and does not influence the earth’s atmosphere. Therefore, it is a feasible and safe method to bind carbon dioxide in carbonate compounds such as magnesite. The subject of this work is the carbonation of an olivine (Mg2SiO4) and synthetic magnesia sample (>97 wt% MgO) under high pressure and temperature in an autoclave. Early experiments have studied the influence of some additives such as sodium bicarbonate, oxalic acid and ascorbic acid, solid/liquid ratio, and particle size on the carbonation efficiency. The obtained results for carbonation of olivine have confirmed the formation of magnesium carbonate in the presence of additives and complete carbonation of the MgO sample in the absence of additives. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Preparation of Spherical Mo5Si3 Powder by Inductively Coupled Thermal Plasma Treatment
Metals 2018, 8(8), 604; https://doi.org/10.3390/met8080604 - 03 Aug 2018
Cited by 1
Abstract
A method was developed to fabricate spherical Mo5Si3 powder by milling and spheroidizing using inductively coupled thermal plasma. A Mo5Si3 alloy ingot was fabricated by vacuum arc melting, after which it was easily pulverized into powder by [...] Read more.
A method was developed to fabricate spherical Mo5Si3 powder by milling and spheroidizing using inductively coupled thermal plasma. A Mo5Si3 alloy ingot was fabricated by vacuum arc melting, after which it was easily pulverized into powder by milling due to its brittle nature. The milled powders had an irregular shape, but after being spheroidized by the thermal plasma treatment, they had a spherical shape. Sphericity was increased with increasing plasma power. After plasma treatment, the percentage of the Mo3Si phase had increased due to Si evaporation. The possibility of Si evaporation was thermodynamically analyzed based on the vapor pressure of Mo and Si in the Mo5Si3 liquid mixture. By this process, spherical Mo silicide powders with high purity could be fabricated successfully. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Tuning the Morphology of ZnO Nanostructures with the Ultrasonic Spray Pyrolysis Process
Metals 2018, 8(8), 569; https://doi.org/10.3390/met8080569 - 24 Jul 2018
Cited by 8
Abstract
Nanostructured zinc oxide (ZnO) particles were synthesized by the one step Ultrasonic Spray Pyrolysis (USP) process from nitrate salt solution (Zn(NO3)2·6H2O). Various influential parameters, from Zn(NO3)2·6H2O concentrations (0.01875–0.0375 M) in the [...] Read more.
Nanostructured zinc oxide (ZnO) particles were synthesized by the one step Ultrasonic Spray Pyrolysis (USP) process from nitrate salt solution (Zn(NO3)2·6H2O). Various influential parameters, from Zn(NO3)2·6H2O concentrations (0.01875–0.0375 M) in the initial solution, carrier gas (N2) flow rates (0.5–0.75 L/min) to reaction temperature (400–800 °C), were tested to investigate their role on the final ZnO particles’ morphology. For this purpose, Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM) and (Selected Area Electron Diffraction) SAED techniques were used to gain insight into how the ZnO morphology is dependent on the USP process. It was revealed that, by certain parameter selection, different ZnO morphology could be achieved, from spherical to sphere-like structures assembled by interwoven nanoplate and nanoplate ZnO particles. Further, a more detailed crystallographic investigation was performed by XRD and Williamson-Hall (W-H) analysis on the ZnO with unique and non-typical planar morphology that was not reported before by USP synthesis. Moreover, for the first time, a flexible USP formation model was proposed, ending up in various ZnO morphologies rather than only ideal spheres, which is highly promising to target a wide application area. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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Open AccessArticle
Characteristics of Ti6Al4V Powders Recycled from Turnings via the HDH Technique
Metals 2018, 8(5), 336; https://doi.org/10.3390/met8050336 - 09 May 2018
Cited by 4
Abstract
The objective of this research is for Ti6Al4V alloy turnings, generated during the machining of implants, to produce powders for the fabrication of Ti base coating via the cold spray method. In order to decrease the cost of powder production and increase the [...] Read more.
The objective of this research is for Ti6Al4V alloy turnings, generated during the machining of implants, to produce powders for the fabrication of Ti base coating via the cold spray method. In order to decrease the cost of powder production and increase the recycling rate of the turnings, the hydrogenation-dehydrogenation (HDH) process has been utilised. The HDH process consists of the following sequence: surface conditioning of the turnings, hydrogenation, ball milling (for powder production), and dehydrogenation. Afterwards, the properties of the recycled powder were analysed via phase, chemical, and morphological examinations, and size and flowability measurements. Usability of the powder in additive manufacturing applications has been evaluated via examining the characteristics of the deposit produced from this powder by the cold spray method. In short, promising results were obtained regarding the potential of the recycled powders in additive manufacturing after making minor adjustments in the HDH process. Full article
(This article belongs to the Special Issue Advances in Synthesis of Metallic, Oxidic and Composite Powders)
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