Oxide Nanopowders Research Articles

Experimental Study of Thermal Contacts for the Enhancement of Interfacial Heat Transfer

Abstract The thermal management in high-performance electronic devices demands the enhanced rate of heat dissipation for controlling operational temperatures and achieving optimal functioning. There are many interfaces in the heat dissipation circuit where thermal interface materials are applied to enhance heat transfer rate. An experimental investigation is presented on metallic contacts to study the interfacial heat transfer with and without a thermal interface material. Thermal contact conductance is known to be an important parameter estimated for the analysis of interfacial heat transfer across the thermal contacts. Therefore, the thermal contact conductance has been evaluated to identify an effective thermal interface material suitable for the present range of contact pressure and heat flux conditions. Silicone grease is a widely used thermal interface material in electronic industry. Thus, commercially available Silicone grease is evaluated in different boundary line thicknesses for a range of contact pressure and mean interface temperatures. Further, a novel composite thermal paste has been prepared by mixing cupric oxide nanopowder and Silicone grease in three different mass concentrations. Eventually, the results for the new thermal paste showed improved thermal contact conductance and lower interfacial temperature drops as compared to Silicone grease for similar test conditions with few limitations.

Impact of pH on structural, morphological, optical, and magnetic properties of zinc oxide nanopowders synthesized by co-precipitation method

Impact of pH on structural, morphological, optical, and magnetic properties of zinc oxide nanopowders synthesized by co-precipitation method

Synthesis, characterization, DFT calculations, and anticancer properties of VI-period and f-block elements-substituted zinc oxide nanopowders

Nanotechnology provides promising ways in which a wide range of new materials can be manufactured which appear to have enormous potential in the field of biomedicine and life sciences. ZnO can be applied in many physical and optical processes and used as a good anti-cancer agent. ZnO NPs are recognized as SAFE or GRAS, non-toxic and biocompatible particles. In this study, wurtzite ZnO samples co-doped by rare earth elements (Tb, Er) were prepared via sol-gel auto-combustion route and their crystallographic structure as well as their morphologies were examined using XRD and TEM techniques. The analysis disclosed that all synthesized products crystallized in a hexagonal structure and the crystallites/particles size diminished with the increase of co-doping content. The electronic structure and optical properties of the different products were assessed using DFT calculations. Doping Tb and Er rare earth elements into ZnO has a significant effect on its optoelectronic properties. The computational study showed that the co-doping of Tb and Er on pure ZnO decreased the band gap and increased the refractive index. The extinction spectrum of pristine ZnO showed a peak in the ultraviolet region at 5 eV, while those of the co-doped ZnO samples displayed stronger peaks in the infrared region (near 0.4 eV). The anticancer properties of Tb/Er co-doped ZnO nanoparticles were examined on cervical cancer (HeLa cells) and colon cancer (HCT-116) by using an in vitro MTT assay. The cell viability assay findings indicated a reduction in HeLa and HCT-116 cells after 48 h of treatment of the synthesized samples. The treatment with co-doped ZnO nanoparticles produced chromatin condensation and formation of apoptotic bodies in HCT-166 cells, which indicates that the prepared co-doped ZnO nanoparticles induced programmed cell death in HCT-116 cells. According to these results, it can be concluded that the prepared Tb/Er co-doped ZnO nanoparticles have promising applications in developing new optoelectronic devices and also in treating cervical and colon cancers.

Environmental-related applications of ZnO nanopowders: Photocatalytic activity and photoluminescence response to ethanol

Zinc oxide (ZnO) and copper-doped zinc oxide (ZnO:Cu) nanopowders were synthesized via solvothermal methods using methanol and hexamethylenetetramine (HMTA). Undoped ZnO nanopowders underwent calcination in O2-rich and H2-rich atmospheres at 600 °C. Samples were studied by scanning electron microscopy, Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), and Raman, photoluminescence (PL) and UV–vis absorbance spectroscopies. The doping and calcinations led to a reduction of the optical bandgap of the nanopowders, while their structure remained hexagonal wurtzite with some changes in lattice parameters and average nanoparticle sizes. The Cu2+ doping led to a BET surface area and violet PL component increase. Samples were also examined for environmental related applications, namely as photocatalyzers for dye degradation and as ethanol optical sensors. For photocatalytic activity in methylene blue degradation under UV, H2-rich calcined powders excelled, with a rate constant of −0.076 min−1, surpassing −0.057 min−1 (ZnO:Cu), −0.056 min−1 (O2-rich calcination), and −0.041 min−1 (as-grown ZnO). We propose that this improvement can be attributed to the formation of ZnO/Zn interfaces stemming from the reduction of surface interstitial zinc by H2 during calcination, in addition to the observed reduction of the ZnO bandgap. The doped nanopowders PL also showed excellent response when exposed to ethanol vapor.

One step synthesis of FeOx magnetic nanoparticles in the microreactor with intensively swirling flows

One step method of iron oxides nanoparticles synthesis using novel type of microreactors was reported. All the data received from analysis of physical and chemical properties demonstrated that the nanoparticles obtained by means of the new method are similar to the nanopowders synthesized by wet precipitation. They are magnetite-maghemite solid solutions with unit cell parameter between 8.362 and 8.374 Å, with coherent scattering range values about 9 nm. In comparison with precipitated nanopowders they have lesser degree of agglomeration. Samples obtained in microreactor have smaller value and smaller spread in regard of the specific surface (76–86 m2/g) in comparison with precipitated ones (75–125 m2/g). All the samples from microreactor consist of spherical inhomogeneities with a diffuse surface, while sample of iron oxide nanopowder synthesized by the co-precipitation method consists of scattering cylindrical inhomogeneities with nearly smooth phase boundary. It was shown that microreactor with intensively swirling flows has demonstrated several advantages: (i) possibility to control the degree of oxidation of the product which depends on the flow rates of reagents solutions to the reactor; (ii) high productivity (up to 7 L/min for the suspension with particles, approx. 200 kg/day for the dried particles) that eases the scaling-up of the proposed synthesis method.

Antifungal and Coagulation Properties of a Copper (I) Oxide Nanopowder Produced by Out-of-Phase Pulsed Sonoelectrochemistry.

Copper (I) oxide (cuprite) is a material widely used nowadays, and its versatility is further amplified when it is brought to the nanometric size. Among the possible applications of this nanomaterial, one of the most interesting is that in the medical field. This paper presents a cuprite nanopowder study with the aim of employing it in medical applications. With regards to the environmental context, the synthesis used is related to green chemistry since the technique (out-of-phase pulsed electrochemistry) uses few chemical products via electricity consumption and soft conditions of temperature and pressure. After different physico-chemical characterizations, the nanopowder was tested on the Candida albicans to determine its fungicide activity and on human blood to estimate its hemocompatibility. The results show that 2 mg of this nanopowder diluted in 30 µL Sabouraud broth was able to react with Candida albicans. The hemocompatibility tests indicate that for 25 to 100 µg/mL of nanopowder in an aqueous medium, the powder was not toxic for human blood (no hemolysis nor platelet aggregation) but promoted blood coagulation. It appears, therefore, as a potential candidate for the functionalization of matrices for medical applications (wound dressing or operating field, for example).

Synthesis of ZnO nanopowder using zinc Zamak dross and adsorption of Pb

In this study, zinc oxide nanopowder (ZnONPDs) was successfully recovered from zinc die casting alloys’ (ZAMAK) dross using a facile dissolution and pH-controlled precipitation approach for removal of lead (II) ions from aqueous solutions. XRD patterns showed that ZnONPDs, calcined at 240°C, exhibited a hexagonal unit cell structure with an average crystallite size of 36.46 nm. FE-SEM micrographs revealed that the ZnONPDs are spherical and hexagonal in shape. TEM images showed the morphology and particle size of synthesized ZnONPDs with an average size of 23.81 nm. XRF and EDS analyses confirmed the high purity of the prepared ZnONPDs. The BET surface area of ZnONPDs was 33.85 m²/g. Adsorption experiments exhibited the maximum removal of Pb2+ ions 100% at the optimal conditions (25 ppm Pb2+ ions, 20 min contact time, 30 mg adsorbent per 100 ml of solution). The pH and zeta potential confirmed that a pH range from 5 to 9 was optimal for the adsorption study. The zeta potential within this range indicated a high level of stability for the particles in the suspensions, effectively preventing flocculation and agglomeration. XPS results conclusively demonstrated the successful adsorption of Pb onto the surface of ZnONPDs. The ZnONPDs synthesized in this study were shown to be promising candidates for use in adsorption processes, indicating that they could be highly useful in wastewater treatments removing toxic metal ions.

High performance fluoroelastomer composites filled with graphite and/or bismuth oxide for applications in gamma‐ray shielding

AbstractFluoroelastomer‐based composites with nano‐sized bismuth oxide (B) and/or graphite (G) as fillers were prepared and characterized using FKM type 1 fluoroelastomer as a matrix. The effects of these fillers used singly or in combination on the crosslinking process, mechanical, thermal, dynamic mechanical, electrical, optical, and high‐energy radiation attenuation properties of FKM were investigated. The results showed that graphite significantly increased the moduli E50 (MPa) of FKM/G and FKM/GB composites by 1026% and 1459%, respectively, compared to FKM. On the other hand, bismuth(III) oxide did not affect the stiffness or elongation at break of FKM significantly. Graphite also imparted electrical conductivity to FKM (10−6 Scm−1), which was reduced by bismuth oxide to 10−12 Scm−1. Furthermore, the linear attenuation coefficients (μ), half‐value layer (HVL), and tenth‐value layer (THV) of pure FKM and FKM composites were evaluated using a 137Cs (662 keV) source, revealing that FKM/B and FKM/GB composites show 47.4% and 35.8% higher μ values, respectively, than FKM. Taking into consideration that the attenuation coefficient of FKM is 10 times higher than conventional elastomers such as natural rubber, these results indicate that thin flexible shielding against high electromagnetic radiation can be achieved to protect different sensitive equipment such as electronic devices used in nuclear power plants, gamma radiation facilities, telescopes, and artificial satellites.Highlights A fluoroelastomer‐based composite containing 40 phr of bismuth(III) oxide nanopowder presents a gamma attenuation coefficient 47.4% higher than that of the polymer matrix. A fluoroelastomer‐based composite containing bismuth(III) presents a band gap of 2.40 eV. Bismuth(III) oxide nanopowder hinders the electrical conductivity imparted by a conducting filler contained in the fluoroelastomer‐based composite. Fluoroelastomer‐based composites containing graphite or bismuth(III) oxide present enhanced mechanical and thermal properties.

Study on sintering properties of aluminum oxide nano-powder for electronics packaging

The microstructures of two kinds of nano powders (ɑ-Al2O3, γ-Al2O3) are studied using a scanning electron microscope (SEM), X-ray diffraction (XRD) under the customized low-temperature sintering process (under the maximum sintering temperature 1600 °C) for the frame material of the customized ceramic for high power electronics packaging application. The experimental results show that the structure of ɑ-Al2O3 is stable while the structure of γ-Al2O3 is unstable. The crystalline form of γ-Al2O3 is changed to ɑ-Al2O3 under the sintering process. The two kinds of powders are all bonded together with a laminate structure. The sintered samples of the γ-Al2O3 are the most compacted.

Enhancing Mechanical Properties and Antimicrobial Activity of Portland Cement through Titanium Oxide Incorporation

The impact of various factors such as microbes, allergens, inadequate environmental conditions, pollutants, and suboptimal building materials on human health within indoor environments is of utmost importance due to the significant amount of time people spend inside buildings. The objective of this study was to assess the combination of Portland cement (PC) with Titanium Oxide (TiO2) nano powder for antimicrobial properties with good physical and mechanical strength. TiO2 was added to PC at various percentages (0.5%, 1.0% and 1.5% by the weight of cement) and analysis of slump flow, compressive strength and flexural strength were determined. The antimicrobial activity was evaluated by agar diffusion test, utilizing 4 bacteria strains: Escherichia coli, Staphylococcus aureus, Enterococcus faecalis and Pseudomonas aeruginosa. Results showed that the addition of TiO2 increased the mechanical strength of the specimen with 1.0% TiO2 displaying the optimum result. For the antimicrobial activity, samples with 1.05% TiO2 had the highest efficiency in inhibiting bacteria growth. The findings showed that a lower percentage of TiO2 added to the PC mortar significantly enhances its mechanical properties and is efficient in inhibiting the growth of bacteria. Such mortar mixture with antibacterial properties should be utilized to enhance hygiene conditions in diverse environments, including hospitals, institutional kitchens, etc., where such properties are necessary.

Mild oxidizing synthesis of non-agglomerated Fe2O3 nanoparticles for H2S gas sensing

Agglomeration is the most common phenomenon in synthesizing nanopowders, which strictly reduces the quality of the products. In the present study, a non-agglomerated iron oxide nanopowder was synthesized via direct oxidation method from metallic iron by hydrogen peroxide. The H2S gas sensing of the nanoparticles was also investigated. The products were evaluated via XRD, TEM, XPS and BET techniques. The results showed that a precisely size-controlled iron oxide with an average particle size of 12 nm was obtained. XRD results confirmed the amorphous nature of the particles. The produced nanoparticles had a high surface area of about 92 m2/g. The powders were dispersed in water for more than three months without sedimentation. XPS results showed the existence of Fe3+ in the samples which confirms the formation of the Fe2O3 phase. The finding showed that the produced samples exhibited a high H2S detection ability. The detection limit was about 100 ppb, and the greatest sensitivity was attained at 100 ppm concentration of H2S. Additionally, the sensor's behavior in the presence of other gases shows that it has high H2S selectivity. This synthesis method introduces a new approach for producing non-agglomerated oxide ceramics with nanoscale via a mild oxidizing media from metal powders.

Electrochemical investigations and antimicrobial activity of Au nanoparticles photodeposited on titania nanoparticles

Titanium oxide nanopowder (TiO2 NPs) was synthesized via anodization in 0.7 M perchloric acid then annealed in nitrogen at 450 °C for 3 h to prepared the Titanium Oxide Nitrogen annealed nanoparticles (TiO2 NPs-N2) powder as catalytic support. Using a photodeposition process, gold was added with isopropanol as a sacrificial donor and H[AuCl4] acid, producing gold nanoparticles on nitrogen-annealed titanium oxide nanoparticles (Au-NPs on TiO2-NPs-N2). The mass loading of Au NPs was 2.86 × 10−4 (g/cm2). TEM images of Au NPs on TiO2-NPs-N2 suggest circular particles with a tendency to agglomerate. Cyclic voltammetry (CV) was used to investigate the electrocatalytic performance of the Au NPs/TiO2-NPs-N2 catalysts in ferrocyanide, KOH, and H2SO4, and the results were compared to those of a polycrystalline Au electrode that is readily accessible in the market. In KOH, H2SO4, and (2 M KOH + 0.1 M glycerol) solutions, the Au NPs/TiO2-NPs-N2 electrode displayed a startlingly high electrocatalytic performance. Using CV, the electrocatalytic oxygen reduction reaction (ORR) of Au NPs/TiO2-NPs-N2 and Au-NPs against glycerol oxidation in basic media was studied. The results indicated that Au NPs/TiO2-NPs-N2 is a promising support material for improving the electrocatalytic activity for acidic and basic oxidation. The electrode made of Au NPs/TiO2-NTs-N2 has steady electrocatalytic activity and may be reused repeatedly. TiO2 NPs and Au NPs/TiO2NPs-N2 showed satisfactory antibacterial activity against some human pathogenic bacteria using the disc diffusion method.

Flexible Ultraviolet Sensor Based on Zinc Oxide Nanoparticle Powder

Zinc oxide nanopowder was synthesized by the coprecipitation method. FT-IR and EDS analyses were performed to qualitatively determine the composition of the nanopowder. FE-SEM images revealed the morphology of the nanopowder formed by clusters of nanoparticles. An XRD analysis confirmed the wurtzite structure with a crystallite size of ~21.2 nm. UV–Vis measurements were performed to determine the ZnO bandgap (~3.05 eV) using the Tauc plot method in the absorbance spectra. The ZnO nanopowder and two comb-like metal contacts were confined and compacted between two polymeric layers by a low-temperature thermal lamination method, resulting in a flexible Polymer/ZnO/Metal/ZnO/Polymer structure. Part of each comb-like metal was kept uncovered by a polymeric layer in order to be used for electrical characterization. I-V measurements of the flexible structure were performed in the dark and under UV illumination, showing the capacity to detect UV radiation and its potential application as a visible-blind UV sensor. A facile and low-cost flexible optoelectronic device is presented, avoiding using high-vacuum or high-temperature technology. This new and novel approach to developing optoelectronic devices proposes using powder materials as semiconducting active regions instead of thin films; this could eliminate the cracking and delamination problems of flexible devices based on thin film technology.

Foamy ceramic filters and new possibilities of their applications

Peculiarities of sintering of foamy ceramic filters based on submicron aluminum oxide powders with additions of titanium oxide and manganese dioxide nanopowders are considered. The processes of removal of polymeric and binder paraffin material during sintering have been studied. The physical and mechanical properties of the obtained porous permeable filters with a foamy structure were analyzed in details. At a sintering temperature in an air atmosphere of 1350 °C, sufficiently high physical and mechanical properties were obtained, which made it possible to use the developed filters as catalyst carriers for vehicle exhaust gases. Bench comparative tests have shown that ceramic filters with a foamed structure are promising catalysts for afterburning car exhaust gases instead of ceramic honeycomb blocks of catalyst carriers. The developed technology allows reducing the sintering temperature of porous foam ceramic filters to 1350 °C and replacing expensive high-temperature ceramic heaters with cheaper nickel-chromium ones.

A New Method for Tungsten Oxide Nanopowder Deposition on Carbon-Fiber-Reinforced Polymer Composites for X-ray Attenuation

A new method for the synthesis and deposition of tungsten oxide nanopowders directly on the surface of a carbon-fiber-reinforced polymer composite (CFRP) is presented. The CFRP was chosen because this material has very good thermal and mechanical properties and chemical resistance. Also, CFRPs have low melting points and are transparent under ionized radiation. The synthesis is based on the direct interaction between high-power-density microwaves and metallic wires to generate a high-temperature plasma in an oxygen-containing atmosphere, which afterward condenses as metallic oxide nanoparticles on the CFRP. During microwave discharge, the value of the electronic temperature of the plasma, estimated from Boltzmann plots, reached up to 4 eV, and tungsten oxide crystals with a size between 5 nm and 100 nm were obtained. Transmission electron microscopy (TEM) analysis of the tungsten oxide nanoparticles showed they were single crystals without any extended defects. Scanning electron microscopy (SEM) analysis showed that the surface of the CFRP sample does not degrade during microwave plasma deposition. The X-ray attenuation of CFRP samples covered with tungsten oxide nanopowder layers of 2 µm and 21 µm thickness was measured. The X-ray attenuation analysis indicated that the thin film with 2 µm thickness attenuated 10% of the photon flux with 20 to 29 KeV of energy, while the sample with 21 µm thickness attenuated 60% of the photon flux.

Effect of conductive particles embedded phase change material on the productivity of a solar still in a controlled environment

A solar still’s performance using 3 different conductive particles embedded in the phase change material (PCM) has been studied. The conductive particles involved are aluminium scrap (Al), aluminium oxide (Al2O3) nano powder and copper (Cu) nano powder, whereas the PCM is paraffin wax. Four similar solar still models were built with different PCMs, differentiated as Model A, B, C, and D, filled with Al scrap-PCM, Al2O3 nano-PCM, Cu nano-PCM, and Al2O3 + Cu-nano PCM combinations, respectively. The productivity of the solar stills for Models A, B, C, and D are 1.93, 2.15, 1.93, and 2.20 kg/kJ.m2 respectively. It was concluded that Al2O3 + Cu-nano PCM is the most efficient PCM-conductive particle combination and Cu nano powder can be replaced by aluminium scrap as an economical alternative.

Dielectric Properties of Aluminium and Silver Doped Zinc Oxide Nano Powder Prepared by Solution Combustion Synthesis

Aluminium and Silver doped Zinc Oxide nano powder were synthesized by Solution Combustion method using Sucrose (C12H22O11) as fuel at 600o C. X-Ray diffraction pattern analysis confirms synthesized nano powders crystalized in single phase wurtzite structure matched with JCPDS-36-1451. Addition of dopant controls the crystallite size of the synthesized nano powder. The study of dielectric permittivity, dielectric loss, AC conductivity and impedance were investigated in the frequency range of 100Hz to 5MHz at room temperature. It is evident from the analysis that dielectric properties of the samples depends on the nature of the dopant.

Acoustic Emission and K-S Metric Entropy as Methods to Analyze the Influence of Gamma-Aluminum Oxide Nanopowder on the Destruction Process of GFRP Composite Materials

Composites are materials that are widely used in industry, including yachting, railway and aviation. The properties of these materials can be modified by changing the type of reinforcement, the type of matrix, as well as the use of additives in the form of fillers and nanofillers that improve their mechanical or specific parameters. Due to the fact that these materials are often used for important structures, computational models using FEM tools may not be sufficient to determine the actual strength parameters, and what is more, to check them during operation. When designing structures made of composite materials, it is necessary to use high safety factors due to their behavior under several different types of loads, which is still difficult to determine precisely. This situation makes these structures much heavier and characterized by much higher strength properties than those that would actually be needed. In this article, the Kolmogorov-Sinai (K-S) metric entropy was used to determine the transition from the elastic to the viscoelastic state in GFRP (glass fiber reinforced polymer) composite materials without and with the addition of nanoaluminum, during a static tensile test. Additionally, the acoustic emission method was used during the research. This signal was further processed, and graphs were made of the number of events and the amplitude as a function of time. The obtained values were plotted on tensile graphs. The influence of the nano-filler on these parameters was also analyzed. The presented results show that it is possible to determine additional parameters affecting the strength of the structure for any composite materials.

Synthesis of nano Fe2O3 cement compositions for concrete shielding

The world's most popular building material, concrete, is in constant demand. Because concrete is so widely used, the research trend to improve its sustainability and reduce its adverse effects during its production has gradually expanded. The future of contemporary concrete technology will be the addition of nanoparticles to concrete. Nanomaterials are now used to create inventive, resilient, and cutting-edge concrete constructions since they require less cement to be poured, have reduced overall project costs, and are environmentally conscious. Due to their distinctive features, titanium dioxide and nanocrystalline silica are among the best prospective nanomaterials for a variety of applications. Over the past ten years, there has been a significant rise in interest in nanotechnology as it relates to building materials. The workability of specimens containing 3% nano ferric oxide improves by up to 13.25% compared to control concrete. For concrete elements made with nano-Fe2O3, the values for flexural, split tensile, and compressive strength are respectively 7.90%, 7.4%, and 6.07% higher than for conventional concrete. Hydrophobic properties are produced when nano ferric oxide is used to substitute cement in concrete mixtures up to a particular amount. They aid in improving the self-sensing properties of concrete. Anti-iron oxide nanopowder has been employed in many products, such as corrosion coatings, plastics, silicones, rubber, alloys, lithium batteries, magnetic seals and certain drug delivery. Temperatures of around 450 degrees Celsius can be withstood by Fe2O3. Once they reach this temperature, the particles lose their magnetic characteristics. Because of their high aspect ratio, those particles cannot exist in nanoform without surface treatment.

Coprecipitation synthesis of transition metal (Al, Mn, Cu, Ag) doped zinc oxide nanopowders: characterization, photocatalytic test, and comparison study

Coprecipitation synthesis of transition metal (Al, Mn, Cu, Ag) doped zinc oxide nanopowders: characterization, photocatalytic test, and comparison study