Types Of Nanopowders Research Articles

Enhancing Transparency in Non-Cubic Calcium Phosphate Ceramics: Effect of Starting Powder, LiF Doping, and Spark Plasma Sintering Parameters

Our objective is to achieve a new good-quality and mechanically durable high-transparency material that, when activated by rare earth ions, can be used as laser sources, scintillators, or phosphors. The best functional transparent ceramics are formed from high-symmetry systems, mainly cubic. Considering hexagonal hydroxyapatite, which shows anisotropy, the particle size of the initial powder is extremely important and should be of the order of several tens of nanometers. In this work, transparent micro-crystalline ceramics of non-cubic Ca10(PO4)6(OH)2 calcium phosphate were fabricated via Spark Plasma Sintering (SPS) from two types of nanopowders i.e., commercially available (COM. HA) and laboratory-made (LAB. HA) via the hydrothermal (HT) protocol. Our study centered on examining how the quality of sintered bodies is affected by the following parameters: the addition of LiF sintering agent, the temperature during the SPS process, and the quality of the starting nanopowders. The phase purity, microstructure, and optical transmittance of the ceramics were investigated to determine suitable sintering conditions. The best optical ceramics were obtained from LAB. HA nanopowder with the addition of 0.25 wt.% of LiF sintered at 1000 °C and 1050 °C.

Enhancing physico-mechanical properties and thermal stability of geopolymer composites through nano-material incorporation

Influence of various types of nano powder on the physico-mechanical properties of geopolymer materials has been studied, in addition to studying their firing stability up to 1000 °C. Alumino–silicate materials used are kaolin, fired kaolin and lime stone. Materials prepared at water/binder ratios of 0.40; whereas the used equal volume of activator 5 M sodium hydroxide with liquid sodium silicate. Nano-kaolin admixed with Nano-powder as a partial replacement from metakaolin material. The control mixes incorporating either 7% Nano-glass or 5% Nano-silica fume. Nano-kaolin was partially replaced Nano-glass powder and Nano-silica fume. It is possible to use the mixes containing limestone and nano materials to solve the problem of using heat curing, thermal energy consumption and pollution by reducing the MK used for MK-geopolymer cement. Results indicated an enhancement in the physico-mechanical properties of mix incorporating 1: 6% and 2:3% of NK:N-glass and NK:N-silica fume, respectively. Firing of hardened geopolymer resulted in high thermal resistance up to 700 °C then exposed to decrease up to 1000 °C. However, no micro-cracks were noticed up to 800 °C for all samples as recorded by visual examination of the fired samples, while micro-cracks were recorded for hardened composites at 1000 °C.Graphical

Nanopowder derived Al/h-BN composites with high strength and ductility

Al/h-BN composites with high tensile and compressive strength at room and elevated temperatures, as well as enhanced ductility, were obtained by a combination of ball milling (BM) and spark plasma sintering (SPS) using Al and hexagonal BN nanopowders (0, 1, 2, 3, 4, 5, and 10 wt% of h-BN). The use of two types of nanopowders is intended to ensure uniform distribution of the reinforcing phase and improve Al-BN chemical interaction at the manufacturing stages by increasing the surface-to-volume ratio. Due to Al with h-BN interaction, the Al/h-BN composites were simultaneously strengthened by three types of nanoparticles: Al2O3, AlN(O) and h-BN, predominantly located along the Al grain boundaries. Compared to BM+SPS aluminum, the tensile strength of Al-2 wt%BN composite increased by 82% (25 °C), 64% (300 °C), and 65% (500 °C), and the compressive strength by 107–119% (25–500 °C) while maintaining high elongation to failure in tension (13.6%, 11.6% and 10.8%) and compression (12.6%, 13.1% and 8.1%) at 25 °C, 300 °C, and 500 °C, respectively. In terms of combination of tensile and compressive strength at room and elevated temperatures, the Al/h-BN materials are superior to many other Al-based composites. The high strength and relative elongation to fracture of the Al/h-BN composites can be explained by the formation of a heterogeneous microstructure consisting of pure Al grains surrounded by a metal-matrix composite material with fine metal grains and reinforcing ceramic nanoinclusions. The obtained results significantly expand the scope of Al/h-BN materials, since their strength at 500 °C is higher than that of pure Al at room temperature.

Composition and electronic structure of porous silicon nanoparticles after oxidation under air- or freeze-drying conditions

A controlled change in the composition and electronic structure of porous silicon nanoparticles by variation the drying conditions is proposed. Two types of nanopowders were obtained from mechanically milled porous silicon films with subsequent air- or freeze-drying processing. Obtained nanoparticles surface morphology and structure were investigated. Silicon atoms local surrounding specificity and electronic structure probing of studied powders were performed with the use of synchrotron ultrasoft X-ray absorption near edge structure spectroscopy technique. Noticeable changes in surface composition and structure are observed. The air-dried porous silicon nanoparticles were characterized by the presence of a thick surface oxide layer, while the presence of unoxidized silicon atoms at a depth of less than 3 nm was demonstrated for the lyophilized ones.

Sintering Kinetics of Austenitic Stainless Steel AISI 316L Modified with Nanographite Particles with Highly Developed BET Specific Surface Area.

The subject of this work was the study of processes occurring during sintering of water atomized AISI 316L austenitic stainless steel powder modified by the addition of graphite nanoparticles. The main purpose of the work was to determine the effect of modification of the AISI 316L stainless steel austenitic powder by the addition of graphite nanopowder on the sintering kinetics and oxide reduction mechanism. The phenomena occurring during the sintering process and oxide reduction mechanisms were subjected to detailed characterizations. Mixtures with two types of nanopowder with a high BET (measurement technique of the specific surface area of materials based on Brunauer–Emmett–Teller theory) specific surface area of 350 and 400 m2/g and for comparison with graphite micropowder with a poorly developed BET specific surface area of 15 m2/g were tested. The conducted thermal analysis showed that the samples made of austenitic stainless steel doped with 0.2% and 0.3% by weight graphite nanopowder with a BET specific surface area of 400 m2/g, sintered best the oxide reduction reactions, with a more intensive participation of carbon, for these samples.

Investigation of state, trends and structure of the world market of nanopowders

The object of research is the state, trends and structure of the global market of nanopowders. One of the most problematic places is the ambiguity of literary data on this subject. The systematization of available literary data will solve this problem. For the marketing analysis, method of searching for literature data concerning the research subject and method of analysis were used. The analysis of literary sources made it possible to identify nanomaterials as the most commercial sector of the modern nanotechnology market. Information is provided about the most common throughout the world nanopowders of metals and oxides, as well as about their application fields. It is shown that complex nanopowders consisting of mixtures of oxides have a limited usage scope. The composition, size, and shape of the nanopowders particles depend on the obtaining method and the process conditions. The forecast of the share of different countries in the market of nanopowders and of the potential demand for nanoproducts in the future is carried out. The structure of investments by industries and predicted volume of nanotechnology market were shown. The structure of the nanopowders market according to the directions of use and types of nanopowders is given. In the course of the research the method of systematization and classification were used. The data on the world-wide volume of nanopowders production by the nature of metals and the structure of their production by particle size are systematized. A common problem in the nanotechnology market is the high cost of production and low volume of production. The high cost of nanoparticles is determined by the high cost of raw materials and by a small volume of production. The nanopowders consumption volume is influenced by the nature of their industrial use. The structure of consumption of nanopowders by industries at the world level is shown, about 70 % of consumption is accounted for electronics, optics and defense industry. The systematization of literature data allowed to present the problems of nanopowders in the form of tables and diagrams giving certain advantage to the comprehension and use of the material.

Synthesis of ceramic active Nd:YAG laser medium

The research results on the synthesis of highly transparent YAG ceramics and the generation of radiation in samples are reported. The possibilities of the synthesis of highly transparent ceramics from nanopowders in the garnet stoichiometry (Nd3+:Y3Al5O12) and a mixture of nanopowders (Nd3+:Y2O3, Al2O3) are studied. Data on phase transformations in compacts fabricated from both types of nanopowder obtained from results of calorimetric and X-ray analyses are presented. It is shown that a higher transparency (∼83%) is achieved in samples synthesized from a mixture of powders. According to the optical microscopy of the extinction centers in ceramics, it is established that a lower transparency compared to the theoretical one (83.8%) is caused by the dispersion by pores that appears near large agglomerates of particles. Experimental results on continuous lasing at the 1.064-μm wavelength with a power of 3.8 W and a slope efficiency of 19.1% in the ceramic sample with the best transparency are reported.

A comparative study on the magnetic properties of Fe-doped CuO nanopowders prepared by sol–gel and co-precipitation method

The Fe-doped CuO nanopowders (Cu 0.95Fe 0.05O) were prepared by the sol–gel and the co-precipitation methods. The effects of synthesis methods on the structure, magnetic property and exchange bias effect of Cu 0.95Fe 0.05O nanopowders were investigated. The microstructure and magnetic properties of the two types of nanopowders were characterized by X-ray diffraction and physics property measuring systems, respectively. It was found that the sol–gel method tended to lead the formation of CuFe 2O 4 phase, which dominated the magnetic behaviors of the sample; the co-precipitation tended to lead larger exchange bias field at low temperature in samples, comparing with sol–gel method.

Resistance of nanostructured titanium dioxide coatings to erosion corrosion

Investigations were undertaken to determine the erosion corrosion resistance of nanostructured titanium dioxide coatings in 5 vol.-%–3·5 wt-% NaCl slurry at velocities ranging from 1 to 4 m s–1 in a recirculating loop. Two types of nanopowders, spray dried and densified (AE 9342) and chemically precipitated and spray dried (AE 9303) were used. The results were compared with a conventional TiO2 coated samples (SM 102). Specimen AE 9342 showed a higher resistance compared to AE 9303. No localised corrosion on the above specimen was observed. The erosion corrosion was caused by etching of intersplat boundaries. The erosion corrosion is dependent on surface topography. A homogeneous distribution of nanoagglomerates of unmelted, partially melted nanoparticles embedded in coatings, a large area of melted zone and porosity less than 1% enhances the erosion corrosion resistance of nanostructured titanium dioxide coatings.

Composite alkaline polymer electrolytes and its application to nickel–metal hydride batteries

In order to enhance the ionic conductivity of polyethylene oxide (PEO)-KOH based alkaline polymer electrolytes, three types of nano-powders, i.e., TiO 2, β-Al 2O 3 and SiO 2 were added to PEO-KOH complex, respectively, and the corresponding composite alkaline polymer electrolytes were prepared. The experimental results showed that the prepared polymer electrolytes exhibited higher ionic conductivities at room temperature, typically 10 −3 S cm −1 as measured by ac impedance method, and good electrochemical stability. The electrochemical stability window of ca. 1.6 V was determined by cyclic voltammetry with stainless steel blocking electrodes. The influence of the film composition such as KOH, H 2O and nano-additives on ion conductivity was investigated and explained. The temperature dependence of conductivity was also determined. In addition, polyvinyl alcohol (PVA)-sodium carboxymethyl cellulose (CMC)-KOH alkaline polymer electrolytes were obtained using solvent casting method. The properties of the polymer electrolytes were characterized by ac impedance, cyclic voltammetry and differential thermal analysis methods. The ionic conductivity of the prepared PVA-CMC-KOH-H 2O electrolytes can reach the order of 10 −2 S cm −1. The effect of CMC addition on the alkaline polymer electrolytes was also explained. The experimental results demonstrated that the PVA-CMC-KOH-H 2O polymer electrolyte could be used in Ni/MH battery.

Structure of Nanocrystalline Titania Ceramics Studied by X-ray Diffraction, Atomic Force Microscopy, and Thermal Phonon Kinetics

The structure of TiO2 nanocrystalline ceramics prepared from two types of nanopowders by shock compression followed by sintering in a conventional resistance furnace or via microwave heating is investigated by x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and thermal phonon kinetics. The results demonstrate that microwave sintering ensures a denser ceramic microstructure as compared to conventional sintering. Data are presented on the structure and thickness of intergranular films in the titania ceramics prepared by the two sintering processes.