Nanoscale Powders Research Articles

Synthesis of La2Ti2O7 nanoscale powder and ceramics based on it by sol-gel and spark plasma sintering

The application of ceramics as matrices for the immobilization of radionuclides for the purpose of their safe long-term disposal or beneficial use is being studied with an emphasis on phase stability, structural integrity, hydrolytic stability, etc. In this work, a combined approach was investigated, based on the sol-gel citrate synthesis of nanosized La2Ti2O7 powder and its subsequent spark plasma sintering to produce dense ceramics. The phase composition and structure of the nanosized La2Ti2O7 powder and ceramic samples based on it, obtained in the temperature range of 900–1300 °C, were studied by XRD and SEM. It has been shown that the powder synthesis conditions ensure the formation of nanosized crystalline La2Ti2O7 grains, whose consolidation under spark plasma heating conditions proceeds with a change in the phase composition from single-phase La2Ti2O7 of monoclinic structure to orthorhombic with an admixture of LaTiO3 at temperatures above 1200 °C. It was revealed that the change in the ceramic structure is accompanied by the formation of non-porous and defect-free monolithic samples. It was determined that such a change leads to an increase in relative density (81.3–95.7%) and compressive strength (78–566 MPa) of the ceramic samples. However, the hydrolytic stability of the ceramics decreases, as indicated by an increase in the leaching rate of La3+ from 10–7 to 10–5 g/cm2·day. The obtained results are useful for the systematic study of materials suitable for immobilization technologies of radioactive waste in ceramics.

Ultrasonic-assisted electrochemical strategy for ITO scraps recovery through anodic dissolution

The conversion of ITO scraps into oxide powders that can be employed to prepare targets is integral to the closed-loop utilization of scare metal indium. Herein, we present a novel route for electrochemical coupled ultrasonic recovery of ITO scraps, which averts the consumption of strong acids, alkalis and carbon containing reducing agents in traditional hydrometallurgical or pyrometallurgical recovery processes. In an ammonium salt solution, the ITO anode dissolves under the action of electrons: oxygen ions are oxidized, while metal ions are leached out, and then combines with hydroxide ions in the solution to form flocculent precipitates, which is attributed to the extremely low solubility product of indium hydroxide and tin hydroxide. The ultrasonic field can promote the mass transfer between the electrode and electrolyte interface, thereby accelerating the reaction process regulating the morphology and size of the product. After calcination, the precipitates become uniformly mixed nano-scale oxide powders with dimensions that meet the requirements for target preparation. The recycling strategy, with its green, straightforward operation, and feasible for scale-up, suggests potential industrial uses for recovering ITO scraps.

Synthesis of La2Ti2O7 Nanoscale Powder and Ceramics Based on It by Sol–Gel Synthesis and Spark Plasma Sintering

Synthesis of La2Ti2O7 Nanoscale Powder and Ceramics Based on It by Sol–Gel Synthesis and Spark Plasma Sintering

Anticorrosion Performance of Waterborne Coatings with Modified Nanoscale Titania under Subtropical Maritime Climate.

Steel structures located in subtropical marine climates face harsh conditions such as strong sunlight and heavy rain, and they are extremely corroded. In this study, a waterborne coating with excellent corrosion resistance, hydrophobic ability, high-temperature resistance and high density was successfully prepared by using modified nanoscale titania powders and grafted polymers. The effects of three modifiers on titania nanoparticles and waterborne coatings' properties were studied independently. The experimental results showed that the activation index of the modification employing methacryloxy silane reached 97.5%, which achieved the best modification effect at 64.4 °C for 43.3 min. The waterborne coating with nanoscale titania modified by methacryloxy silane exhibited the best hydrophobic effect, with a drop contact angle of 115.4° and excellent heat resistance of up to 317.2 °C. The application of the waterborne modified coating in steel structures under subtropical maritime climates showed that the waterborne titania coatings demonstrated excellent resistance to corrosion, high temperatures and harsh sunlight, with a maximum service life of up to five years. Economic analysis indicated that, considering a conservative three-year effective lifespan, this coating could save more than 50% in cost compared with conventional industrial coatings. Finally, the strengthening mechanism of the polymer coatings with modified nanoscale titania was analyzed.

Synthesis of NiCrAlY nano-scale powder by high-energy ball milling process for thermal spray coating application

These days, during the issues of climate change, there has been a shift in the energy industry from using fossil fuels to more environmentally friendly fuels such as biomass fuels. Biomass fuel is considered CO2 neutral because the carbon produced during combustion in the form of CO2 emissions can be used for new plant growth. However, besides the advantages of using biomass fuel, a problem arises when biomass fuel contains a high concentration of corrosive agents, which can be released along with hot fuel gas. These corrosive agents can damage the boiler components. Coating technology is one of the solutions to protect components that work at high temperatures against the corrosion threat. One type of coating that can be used in high-temperature applications is NiCrAlY coating by the high-velocity oxide (HVOF) process. One interesting topic that people are developing is using nano-scale coating to increase the coating’s resistance against hot corrosion and cracking. Nano-scale powder feedstock is needed to produce nano-scale coating material. In this research, top-down method is used to synthesis nano-scale powder. One of top down method, the high-energy ball milling processs, is a promising method to synthesize nano-scale powder material. Therefore, in this research, the ball milling process is used to prepare nano-scale product. The results showed that this method was successful to make the nano-scale powder. The nano-scale powder was characterized by several methods to investigate the morphology and properties of the powders. However, there are still many challenges in producing nano-scale powder that meets HVOF feedstock powder requirements. In the long run, it is expected that this research can answer those challenges so that at the end, the good quality of nano-scale powder can be achieved

Quantification of Airborne Concentrations of Nanoscale Dusts by Particle Gravimetry Using Ionic‐Liquid Modified Polymeric Electrospun Fibers

AbstractIn this work, functional polymeric filters are prepared by electrospinning using four different non‐ionic polymers or their blends together with deliberately selected additives, and then tested for quantification of the nano‐sized powders. Particle gravimetry is used for the quantitative determination of the dusts. Validation studies are carried out using the ICP‐OES technique. The polymeric fibers prepared with different contents consist of PS/PMMA, PVDF/EC/PMMA, chitosan, chitosan/PMMA and PMMA/PVDF, respectively. The ionic liquids of tetra‐n‐butylammonium tetrafluoroborate, 1‐ethyl‐3‐methylimidazolium hexafluorophosphate and hexadecyltrimethylammonium bromide are used as additives for the preparation of the functional polymeric fibers. The prepared nanoscale dusts and electrospun fibers are characterized by SEM, XRD, XPS, and size distribution analysis techniques, respectively. Among them, the CTAB‐modified chitosan fibers exhibit the highest dust retention efficiency. This study introduces a new approach to the quantification of nano‐sized powders. In addition, it is concluded that the proposed method can be used in pre‐concentration before testing, cleaning powders from the working environment and quantitative analysis of nanoscale powders. The presented materials can also be used to improve indoor air quality and potential worker exposure in workplaces.

Influence of powder feedstock characteristics on extrusion-based 3D printing of magnetocaloric structures

A significant barrier to the commercialization of magnetic heat pumping is the lack of scalable, low-cost manufacturing techniques that enable shaping brittle magnetocaloric materials into heat exchange structures with porous geometries, controlled chemical gradients, and advantageous anisotropic microstructures. Though direct ink writing additive manufacturing has the potential to expand into a viable net-shaping technology for functional magnetic alloys, it is typically challenging to fabricate dense parts—an observation ascribed to the constraint on powder particle size that inevitably impacts both green density of 3D printed parts and shrinkage during sintering. To this end, we report a comprehensive study on the influence of precursor powder characteristics on the magnetic and structural properties of 3D printed test coupons produced using La0.67Ca0.33MnO3 magnetocaloric particles. Ink formulations comprising powders with nano-scaled, micron-scaled, and bimodal size distributions were printed and sintered. The impact of particle size on part quality and magnetofunctional response was examined, and it was found that test coupon fabricated using nano-scaled powders (∼100–200 nm) demonstrated the lowest part porosity (∼17%) and the highest magnetocaloric response (8 J kg−1·K−1 at μ 0H = 5T). The results presented in this work address critical technical questions about the process feasibility of making magnetic heat pumps with additive manufacturing schemes.

Embedding and cross-sectioning as a sample preparation procedure for accurate and representative size and shape measurement of nanopowders

Reliable measurement of the size of polydisperse, complex-shaped commercial nanopowders is a difficult but necessary task, e.g., for regulatory requirements and toxicity risk assessment. Suitable methods exist for the accurate characterization of the size of non-aggregated, stabilized, spherical and monodisperse nanoparticles. In contrast, industrial nanoscale powders usually require dedicated sample preparation procedures developed for the analysis method of choice. These nano-powders tend to agglomerate and/or aggregate, a behavior which in combination with an innate broad particle size distribution and irregular shape often significantly alters the achievable accuracy of the measured size parameters. The present study systematically tests two commercially available nanoscale powders using different sample preparation methods for correlative analysis by scanning electron microscopy, dynamic light scattering, Brunauer–Emmet–Teller method and differential mobility analysis. One focus was set on the sample preparation by embedding nanoparticles in carbon-based hot-mounting resin. Literature on this topic is scarce and the accuracy of the data extracted from cross sections of these particles is unclearly stated. In this paper systematic simulations on the deviation of the size parameters of well-defined series of nanoparticles with different shapes from the nominal value were carried out and the contributing factors are discussed.

Carbothermal reduction assisted by hydrogenation treatment for preparing single-phase CeC2 nanoscale powders

Single-phase CeC2 powders can be successfully prepared through the carbothermal reduction assisted by hydrogenation treatment (CRHT) using 20–50 nm CeO2 as cerium source and 100–200 nm carbon black as carbon source. During the hydrogenation process, the interaction of CeO2 with H2 leads to a partial valence reduction of Ce ions, yielding a partially anoxic phase (CeO1.675) and a hydrogenated phase (CeH2). CeO1.675 can increase the oxygen vacancies required in the reaction process, while CeH2 can produce gas-phase reductant H2 at the reaction temperature, which together promotes the reduction reaction. The results show that the CRHT can obtain single-phase CeC2 powders at a temperature of 1550 °C, which is 100 °C lower than its theoretical temperature. For the preparation of CeC2 powders, the CRHT is a low-temperature and efficient method.

Experimental research on the compression behavior of ultrafine alumina powders under gas pressurization

The compression behavior of powder bed under gas pressurization plays a crucial role in the performance of pressurized powder pneumatic conveying systems. The compression behavior of ultrafine powder, especially nanoscale powder, is more complicated. In this study, a visualization method was employed to compare the compression behaviors of alumina powders with different particle sizes ranging from the microscale to the nanoscale. The experimental results revealed that the strong agglomeration led to a higher compressibility percentage of about 58% for the nanoscale powders compared to the microscale powders with the percentage of about 44% under gas pressurization. However, the compression degree of powders shows a non-monotonic relationship with particle size. In particular, the most compressible nanoscale powder exhibited the ability to significantly reduce the compressibility at a lower gas pressurization rate. This finding provides a new optimization method for the pressurized pneumatic conveying and feeding systems of ultrafine powder.

Water Purification Using Active Charcoal with Microbes and Chelated Iron Soaked into Its Micropores

Urbanization in China has led to a significant increase in surface water pollution, posing a threat to the health and safety of residents and hindering sustainable economic development. Individual traditional methods have been used to purify polluted water, including the use of bamboo-derived activated charcoal, microbial material, and zero-valent iron. However, these methods have been found to have certain limitations. This study investigates the effects of an activated charcoal material combined with beneficial microbes and chelated nano-iron in removing nitrates. The experiments were conducted at various scales, including a bench-scale study, and studies of a small river, sewage plant tailwater, and artificially constructed wetlands. The microbes used included Bacillus spp., Lactobacillus spp., and yeasts. During the fermentation process, nano-scale iron powder was added, resulting in the formation of bivalent iron ions under anaerobic conditions. These ions were subsequently chelated by organic acids. Bamboo-derived activated charcoal was then soaked in the fermented liquid, allowing the microbes, chelated iron ions, and organic acids to infiltrate the pores of the activated charcoal. This activated charcoal material, containing microbes and chelated iron ions, demonstrated effective nitrate removal in laboratory experiments and sewage plant tailwater treatment, and water purification in wetlands and rivers. It is important to note that this research solely focused on the removal of nitrates, and further studies are required to confirm its effectiveness in other aspects of water purification.

Optimization of In Situ Formation of a Titanium Carbide Nanohybrid via Mechanical Alloying Using Stearic Acid and Carbon Nanotubes as Carbon Sources

The current work shows the optimization of the preparation of nanosized titanium carbide in situ through mechanical alloying. Metallic titanium powders, along with two carbon sources, carbon nanotubes, and stearic acid, were used to reduce the particle size (around 11 nm) using an SPEX 800 high-energy mill. The combined use of 2 wt % of these carbon sources and n-heptane as a liquid process control agent proved crucial in generating nanoscale powder composites through a simple and scalable synthesis process within a 4 h timeframe. The uses of 20 wt % of both carbon sources were compared to determine the ability of carbon nanotubes to form carbides and the decomposition of process control agent during mechanical milling. The structure of the composites and starting materials were evaluated through X-ray diffraction and Raman spectroscopy, while the morphology features (average particle size and shape) were monitored via scanning electron microscopy and transmission electron microscopy.

Preparation and Characterization of Nano-waste glass powder

This experimental study investigates top-down grinding to turn used waste glass into nano-glass powder. The study explores a new instrument locally manufactured to synthesize nano-glass powder. The high-energy ball mill was manufactured based on design, material, assembly, testing, optimization, and quality control. Two milling environments were examined: wet with water as a surfactant liquid and dry with varying grinding times. In addition, this study compared the output of nano glass created from mechanical and chemical grinding processes. Blaine's method for surface area measurement results of nanoscale powder samples produced by the wet grinding method showed a steady increase commensurate with the grinding duration, as the 12-h grinding specimen was the highest in surface area. In contrast, dry grinding samples showed anomalies in some instances due to the agglomerate phenomenon, such as 8- and 10-h grinding samples. Moreover, FE-SEM showed that the 12-h grinding specimen has the smallest particle size. But the AFM illustrated accurately with the 2D measurement that these particles have cortical shapes, which may describe the secret beyond the high surface area. X-ray diffraction (XRD) and AFM tests showed that in the case of nanoscale glass particles, regardless of their morphology status, the shape of the particle itself is the deciding factor in giving the Nano powder the highest particle surface area. The specimen milled with 4 h of dry grinding is best suited for civil engineering research applications, while other applications that need a small amount of nano glass are recommended to use chemical methods despite their dangerous processes.

Synergistic effects of multi-strengthening mechanisms in exceptionally high-strength W-Ni-Fe composites

Tungsten heavy alloys (WHAs) are typical tungsten-based composites and are considered as important materials in kinetic energy penetrators that currently use depleted uranium munitions. However, the incongruity between strength and plasticity is the “Achilles’ heel”, which restricts further application in national defense and military industries. Herein, a novel fine-grained La2O3 strengthened W-Mo-Ni-Fe composites were fabricated successfully via using nanoscale solid-solution composite powder and the optimized two-stage sintering as well as vacuum heat-treatment techniques. In the model W-xMo-4.9Ni-2.1Fe-1La2O3 composites (x = 2.5, 5, 10 and 20 wt%), the heat-treated alloys had a highly homogeneous microstructure, consisting of equiaxed W grains, matrix phase and dispersed La2O3 reinforced particles. Increasing Mo content promoted microstructure refinement and caused the formation of MoNi3 intermetallic compound (IMC). As a result, benefiting from the multiple strengthening mechanisms containing fine-grained, solid-solution and oxide dispersion strengthening effects, the 88 W-5Mo-4.9Ni-2.1Fe-1La2O3 composite exhibited a superb synergy of tensile strength and ductility (1116 MPa and ∼ 15%). Moreover, the analysis of the lattice strain fluctuations and dislocation behaviors of WHAs were conducted by means of the geometric phase analysis (GPA) approach for the first time. The plastic deformation mechanism was studied to elucidate the fracture characteristics and slip systems with Schmid factor (SF) and Kernel Average Misorientation (KAM) analysis. Our findings not only shed light on the understanding of the deformation mechanisms of WHAs, but also provide a new avenue for the design of WHAs with outstanding mechanical properties.

Investigations of microstructures and thermoelectric properties of TiNiSn half-Heusler compounds with micro- and nano-scale copper additions

The TiNiSn-based half-Heusler compounds have been considered as a promising thermoelectric material system for waste heat recovery applications. There have been numerous studies dedicated to improving its intrinsic low thermoelectric performance, and one strategy is to incorporate certain types of metal dopants into the host materials. Only a few research works have been focused on the effects of the dimensions of metal particles on the thermoelectric properties of materials. In this study, we investigate the roles of micro- (M) and nano-scale (N) Cu powders in affecting the microstructures and thermoelectric properties of TiNiCuxSn (x = 0−0.1) compounds. Owing to the ease of oxidation of Cu nanoparticles and the tedious preparation procedure, TiNiCux, NSn shows lower carrier concentration and electrical conductivity compared to the TiNiCux, MSn with the same nominal Cu content. The high-temperature Seebeck coefficient of TiNiCux, NSn gradually deteriorates as the temperature rises, partly due to the impurities-induced bandgap narrowing effect. The maximum power factor achieved for TiNiCux, NSn is about 20.2% lower than that for TiNiCux, MSn. Even though the reduced contribution of electronic component leads to a lower total thermal conductivity at low temperatures, the highest zT obtained in TiNiCux, NSn is markedly lower than that in the corresponding TiNiCux, MSn. These findings highlight the importance of investigating the dimensions of metal dopants in studies of the thermoelectric properties of materials.

Preparation and properties of porous mullite-based ceramics fabricated by solid state reaction

In this study, the effect of the alumina particle size on the formation of mullite using a silica gel powder and micro- and nano-scale Al2O3 powders as raw materials was investigated. The optimized Al2O3 source was then reacted with the silica gel to prepare porous mullite-based ceramics. The results revealed that the highly reactive nano-Al2O3 powder could form mullite at a relatively low firing temperature. Therefore, the nano-Al2O3 powder was used to prepare porous mullite-based ceramics by firing at 1600 °C, 1650 °C and 1700 °C. The pore size of the prepared porous mullite-based ceramics ranges from tens to hundreds of micrometres, with the apparent porosity being 42.8–58.0%. Further, the mullite content in the samples increased with increasing firing temperature, and a higher firing temperature promoted sintering, resulting in improved strength of the sample. After calcination at 1700 °C, the mullite content in the sample reached 81.8%, and the sample showed excellent thermal shock resistance. The strengths of the samples before and after thermal shock were found to be 23.6 and 15.58 MPa, with the residual strength ratio being 66%.

Production of nano-scale cellulose nanocrystal powder via electrospray drying (ESD) for sustainable composites

This research introduces the use of electrospray drying (ESD) using the electro-hydro dynamic atomization (EHDA) mechanism to produce dry nano-scale cellulose nanocrystal (CNC) powder from a 3 wt% aqueous suspension. The nano-scale CNC suspensions being mostly water are energy intensive to dry. Gas atomization in convection spray drying (SD) produces micron-scale CNC powder during dehydration. The ESD mechanism utilizes coulomb repulsion to overcome the suspension’s liquid surface tension and produces ultra-fine droplets. The droplets dehydrate after falling a fixed distance at atmospheric temperature and pressure, leaving nano-scale powder CNCs. Drying CNCs in suspension occurred after reducing the liquid’s surface tension by mixing 40% (wt) ethanol and 60 (wt) de-ionized (DI) water. The suspension feed rate was optimized at 6 µL min−1 and four syringes were employed to increase CNC powder production rates. Particle dimensions, observed by scanning electron microscopy (SEM) and measured by image analysis software, ranged from 40 to 1200 nm in length and 10–500 nm in width. Up to 80% of the sprayed CNCs in suspension were recovered from a parallel plate collector and contained ~ 5 wt% water content. Adding 0.5 wt% nano-scale powder CNCs in the poly-lactic acid (PLA) tensile strength by 10.3% and elastic modulus by 9.9%. The tensile yield strength and elastic modulus of nano-scale CNC/PLA composite specimens were 62.5 MPa and 3.66 GPa, respectively. For comparison, 0.5 wt% SD micron scale CNC/PLA composite only increased strength 5.1 and stiffness 1.3% at the same processing conditions.Graphical abstract

Facile Production Method of PbS Nanoparticles via Mechanical Milling of Galena Ore

In this research, some physical properties such as the density, specific heat capacity, and micro-hardness of galena ore lumps purchased from the public market were determined. The microscopic study, using the scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), confirmed that the as-received galena ore was mostly lead sulfide (PbS). The XRD pattern of the galena powder also elucidated that all the peaks were assigned to PbS. In addition, the as-received galena was roughly crushed, and fine-milled using a high-vibration milling machine with tungsten carbide rings. Nanoscale particles of about 90 nm were produced in a very short milling time of around 15 min. The obtained nanoscale powder was well investigated in the SEM at low and high magnifications to assess the exact range of particle size. Meanwhile, the SEM was employed to investigate the microstructure of sintered samples, where a part of the milled galena powder was compacted and sintered at 700 °C for 2 h. Again, the result of this investigation proved the formation of PbS with even smaller grain size compared with the grain size of the starting galena ore. A high relative sinter density of approximately 97% for galena powder was achieved by sintering under vacuum.

Nanoscale reinforcement efficiency analysis in Al2O3–MgO–C refractory composites

This work proposes a materials design parameter, known as the reinforcement index (Ri) to classify the reinforcements in Al2O3–MgO–C refractory system, based on their performance. They are tensile reinforcements (Ri>+1, e.g., YAG, EG\\YAG) that favour the refractory load-bearing capacity enhancement while compared with compressive and neutral reinforcements. Two kinds of tensile reinforcements, namely, pure YAG (yttrium aluminium garnet; Y3Al5O12) and EG\\YAG (expandable graphite (EG) hybridized YAG) nanoscale powders were prepared in-house and evaluated their performance in a high-temperature treated Al2O3–MgO–C refractory system at 1600 °C. For a given reinforcement concentration (Xf = 0.003–0.02), the experimental findings based on structural properties, mechanical reliability, and microstructure stability corroborated that EG\\YAG as an efficient reinforcement than pure YAG. These reinforcement benefits were attributed to the core-sheath microstructure formed with EG dispersed YAG framework. Implication of these results to design and development of thermal shock resistant refractory compositions with end-use in steel making products are discussed.

Supercritical Hydrothermal Synthesis of Nano-Zirconia: Reaction Path and Crystallization Mechanisms of Different Precursors

Nano-zirconia exhibits excellent mechanical properties (fracture toughness, hardness and flexural strength), thermal performance (thermal conductivity), optical properties and biological properties for various ceramic-based applications. Supercritical hydrothermal synthesis technology is an advanced and environmental-friendly method for preparing nanoscale powders. In this paper, the formation and crystallization of nano-zirconia during supercritical hydrothermal synthesis were systematically investigated. Different precursors (zirconium nitrate, zirconium oxychloride, zirconium acetate) reacted in supercritical water and the quality of nano-zirconia in different systems were comprehensively evaluated using XRD, TEM, IR, BET analysis. Finally, the most suitable precursor type was identified and the reaction path as well as crystallization mechanisms of different precursors were revealed.