Synthesis of nanocrystalline LaF3 doped silica glasses by hydrofluoric acid catalyzed sol–gel process

Silica glasses doped with LaF₃ nanocrystals were prepared by HF-catalyzed sol–gel method. HF was used both as fluorine source and as catalyst of the sol–gel reaction, making it possible to shorten the processing time with reducing the concentration of SiOH groups to ～10¹⁸ cm^?3. The resultant glasses are transparent at visible spectral range, and the optical loss at the ultraviolet absorption edge is dominated by the Rayleigh scattering from LaF₃ crystallites. The size of LaF₃ crystallites increases with an increase in the sintering temperature and time, and is smaller than ～40 nm in samples showing good visible transparency. Green upconversion photoluminescence is observed in an Er³⁺-doped sample under excitation at 980 nm.     

Synthesis of nanocrystalline carbonated hydroxyapatite powder via nonalkoxide sol–gel method

Nanocrystalline hydroxyapatite powder was synthesized via nonalkoxide sol–gel method. Ca(NO₃)₂·4H₂O and P₂O₅ were mixed in ethanol, which led to a stable sol. STA, XRD and FTIR were used to characterize the calcined powders. The degrees of crystallinity and crystallite sizes were thereafter calculated from XRD patterns. The microscopic observations of the powder were performed using SEM and TEM. Results showed that a nanocrystalline hydroxyapatite powder was obtained after being heated at 450 °C for 6 h. Furthermore, increasing the calcining temperature caused both the formation of carbonate bonds and the increase in the crystallite sizes, and the degree of crystallinity.     

Synthesis of nanocrystalline LaFeO3 powders via glucose sol–gel route

LaFeO₃ were prepared by sol–gel process using glucose as a complexing agent. Thermogravimetric (TG), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Field emission scanning electron microscope (FSEM) and Transmission electron microscope (TEM) techniques were used to characterize precursor and derived oxide powders. The effect of the mol ratios of glucose to metal ions (glucose/M) on the formation of LaFeO₃ was investigated. XRD analysis showed that single-phase and well-crystallized LaFeO₃ was obtained from precursor with glucose/M = 3:5 and 3:10 at 500 °C. LaFeO₃ nanoparticles with a diameter of about 30 nm were obtained. However, for precursor with glucose/M = 3:20, pure LaFeO₃ was not obtained at temperature below 600 °C.     

Life cycle assessment on boron production: is boric acid extraction from salt-lake brine environmentally friendly?

Clean Technologies and Environmental Policy - No information is currently available on potential environmental impact of boric acid solvent extraction from salt-lake brine although boron production...     

Synthesis of boron nitride from ferroboron Part 1 – Nitriding

Abstract

Thermodynamic calculations and nitriding experiments have been carried out to convert ferroboron precursor to boron nitride in a mixture of NH₃ with N₂ gases under ambient pressure. The results show that complete nitridation can be achieved at 673 K with 20 vol.-%NH₃ in the gas mixture. The nitrided product consists of amorphous boron nitride, iron, and metastable iron nitrides. The measured weight gain follows a two stage, near parabolic kinetics accompanied by volume expansion, which causes spalling of the outer nitrided layer and facilitates further nitriding. An alternative reaction route using 100 vol.-%N₂ is also possible, but a higher reaction temperature (≥～1700 K) is needed. The product from the high temperature route contains partially crystallised (hexagonal) boron nitride, iron, and virtually no metastable iron nitride.     

Synthesis of boron nitride from ferroboron Part 2 – Leaching

Abstract

Fully nitrided ferroboron powder is leached in simple mineral acids (including hydrochloric acid and sulphuric acid) in order to separate iron/iron nitrides from boron nitride. Weight loss is used to indicate the extent of leaching. Leaching begins with violent chemical reaction and this is followed by a slower, parabolic-like kinetics lasting from 24 to 48 h. In 1 M to 5 M hydrochloric acid leaching can be effectively carried out within 24 h. Amorphous boron nitride produced in mixed NH₃–N₂ at low temperature (400°C) leaches more readily than partially hexagonal boron nitride produced at higher temperatures in pure N₂. The possibility of recycling the leaching acid is also demonstrated using an electrochemical cell.     

Carbonization behavior of oxidized viscose rayon fibers in the presence of boric acid–phosphoric acid impregnation

The oxidation and carbonization stages of viscose rayon fibers were performed in the presence of 3 % phosphoric acid and 4 % boric acid (PA–BA) impregnation. The results showed that PA–BA impregnation enhanced thermal stability and prevented the evolution of volatile by-products. During the oxidation stage carried out at 250 °C, the cellulose II crystalline structure was totally lost due to the decrystallization process. Carbonization was carried out in a pure nitrogen atmosphere at temperatures ranging from 600 to 1000 °C. The results obtained from the fiber thickness, linear density, carbon fiber yield, elemental analysis, volume density, X-ray diffraction, infrared (IR) and Raman spectroscopy, tensile testing, and electrical conductivity measurements showed that the carbonization temperature had a significant effect on the structure and properties of the resulting carbon fibers. Carbon fibers obtained from the oxidized viscose rayon fibers showed physical and chemical transformations with increasing carbonization temperature and were characterized by a reduction in fiber thickness and linear density values due to the removal of non-carbon elements together with increases in the carbon content, carbon to hydrogen ratio (C/H), volume density, tensile strength, tensile modulus, and electrical conductivity values. X-ray diffraction analysis showed that the interplanar d-spacing (d ₀₀₂) decreased, and that the apparent crystallite thickness (L _c) and the apparent crystallite width (L _a) increased with increasing temperature. IR spectroscopy in agreement with the elemental analysis showed the total loss of OH, CH, C=O, CH₂, C–O, and C–O–C groups arising from the completion of dehydration and dehydrogenation reactions indicating total elimination of the cellulose structure and the formation of amorphous carbon during high temperature treatment.     

Synthesis of α-alumina fibre from modified aluminium alkoxide precursor

Polycrystalline alumina fibre was successfully synthesized by pyrolysis of a preceramic fibre formed from aluminium compounds with alkoxy and chelate ligands. A mixture of ethyl 3-oxobutanoatodiisopropoxyaluminium (EOPA) and tri-sec-butoxyaluminium (SBA) was reacted with glacial acetic acid yielding a polymeric product. The IR absorptions at 630 and 700 cm^–1 due to the Al-O bond changed from sharp to broad bands by treatment with acetic acid. The ²⁷Al resonance at 35 p.p.m. increased in intensity when EOPA-SBA (7/3) was treated with 30 mol% acetic acid. An increase in the EOPA to SBA ratio 5/5 to 9/1 also raised the intensity of the signal at 35 p.p.m. The viscosity of the polymeric product increased in intensity as the amount of acetic acid increased. The viscosity of precursor increased with increasing the ratio of EOPA to SBA, and decreased with increasing measurement temperature from 45 to 75°C. The precursor polymer pyrolysed at 500°C in air was amorphous to X-rays, and crystallized in -alumina at 840°C. The precursor fibres were pyrolysed to yield finegrained fibres of -alumina at 1200°C for 1 h.     

Synthesis and characterization of superfine pure tetragonal nanocrystalline sulfated zirconia powder by a non-alkoxide sol–gel route

Nanocrystalline sulfated zirconia powder was prepared by a non-alkoxide sol–gel route using acidic condition (pH 1–2). The samples had superfine crystallites and pure tetragonal phase at 700 °C. Zr(acac)₄ was used as zirconium precursor due to a better retention of sulfate species and H₂SO₄ 0.5 M was used as sulfating agent. Fourier transform infrared (FT-IR) spectra have shown Zr–O–Zr and sulfate bonds. Crystal phase and crystallite size have been determined by X-ray Diffraction (XRD) analysis. Besides, the morphology of the samples has been investigated by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The optical properties of the samples have been analyzed using photoluminescence (PL) spectroscopy, too. All the analyses consistently have shown fairly uniform nanoparticles (calcined at 600 and 700 °C) with very small size and pure tetragonal phase with crystallite size between 5 and 10 nm.     

Development of injectable biocomposites from hyaluronic acid and bioactive glass nano-particles obtained from different sol–gel routes

Bioactive glass nano-powders with the same chemical composition and different particle characteristics were synthesized by acid-catalyzed (the glass is called BG1) and acid–base catalyzed (BG2) sol–gel processes. Morphological characteristics of powders were determined by TEM and BET methods. The powders were separately mixed with 3% hyaluronic acid solution to form a paste. In vitro reactivity of pastes was determined by soaking them in simulated body fluid. Rheological behaviors of paste in both rotation and oscillation modes were also measured. The results showed that BG1 particles was microporous with mean pore diameter of 1.6 nm and particle size of ~ 300 nm while BG2 was mesoporous with average pore diameter of 8 and 17 nm and particle size of 20–30 nm. The paste made of BG2 revealed better washout resistance and in vitro apatite formation ability than BG1. According to the rheological evaluations, both pastes exhibited shear thinning but non-thixotropic behavior, meanwhile paste of BG2 had higher viscosity than BG1. The oscillatory tests revealed that the pastes were viscoelastic materials with more viscous nature. Both pastes could be completely injected through standard syringe using low compressive load of 5–50 N. Overall, The biocomposites can potentially be used as bioactive paste for the treatment of hard and even soft tissues.     

Synthesis of doubly functional nanowhiskers from a colloid solution including a V–Ti complex precursor

In this study, we synthesized vanadium (V) nanoparticles precursor (NH₄)₅[(VO)₆(CO₃)₄(OH)₉]·10H₂O a two-phase system of toluene and water. Colloid solution including titanium(IV) isopropoxide and polyvinylpyrrolidone (PVP) was subsequently deposited onto the nanoparticles to form urchin-like structures in a toluene solution as the vanadium–titanium (V–Ti) complex precursor. Calcining the urchin-like precursor at 700 °C generated nanowhiskers of the Ti/V oxide complex after annealing process. These nanowhiskers were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron microscopy (XPS). Films of the Ti/V oxide nanowhisker structure exhibited good visible transparency and a large change in transmittance at near-infrared (NIR) wavelengths before and after the metal–insulator phase transition. For a 44-nm-thick single-layer nanowhisker thin film, the transmittances at 700 nm in the metallic (M) and semiconductive (S) states were 75 and 72.2 %, respectively; the NIR switching efficiency (ΔT ₂₀₀₀) increased from 17 to 21.3 % at 2000 nm under UV light irradiation. In addition, the nanowhisker thin film of the Ti/V oxide complex significantly enhanced the photodecomposition of methylene blue under UV irradiation, relative to that of the unmodified TiO₂. The dual functions of this material—thermochromicity and photocatalytic behavior—suggest that it might have interesting applications in energy-saving smart windows.     

Electrolytic concentration effect on the abrasive assisted-electrochemical machining of an aluminum–boron carbide composite

All engineering materials can be machined by one or combination of processes in such a way that the material’s potential is fully exploited. Electrochemical machining is found to be a most promising process that produces various components from the hard-to-machine materials for the various applications. Electrolyte concentration is playing a positive role by improving the electrolyte conductivity, but negatively forming the passivation layer on the cut surfaces. In order to improve the surface finish and removal of generated residual materials from the cut surfaces, abrasive particles were fed along with electrolyte into the machining zone. This present paper investigates the sodium chloride (NaCl) electrolyte with varied concentration (10–30%) in association with SiC abrasive particles on the material removal rate, surface roughness, and radial overcut while machining of aluminum 6061–boron carbide (5–15?wt%) composites. This study conclusively derived that electrolyte concentration up to 20% exhibited a positive role in the material removal rate for the machining of composites because the rate of dissolution was of higher magnitude. Externally supplied abrasive particles along with electrolyte reduced the surface roughness and radial over cut to an extent. Conversely, at higher electrolyte concentration, the externally supplied abrasive particles have a little effect on the removal of the formed passivation layer as confirmed by SEM analysis.     

Effects of Mg doping on sol–gel derived nanocrystalline hydroxyapatite thin films

Abstract

Both pure and Mg doped thin films were fabricated by sol–gel dip coating. The films were sintered either at 800 or 1000°C. The average grain size of the films was significantly affected by Mg substitution in the hydroxyapatite (HA) structure and change in the sintering temperature. The grains were considerably larger in the films sintered at higher temperatures. In addition, Mg doped films contained significantly larger grains compared to undoped HA films. Mg doping also caused rodlike grains at 800°C, and led to whitlockite (β-TCP) formation at 1000°C. The ratio of the existing phases was estimated as β-TCP/HA=27 : 73. All the films had rough surfaces with high porosity. It was also observed that undoped films had higher surface roughness than Mg doped ones.     

Influence of precursor source on sol–gel deposited ZnO thin films properties

Zinc oxide thin films were deposited by sol gel technique on glass substrates using different precursors (zinc acetate, zinc nitrate and zinc chloride). In the present work we investigate the precursor nature influence on structural, morphological, optical, electrical properties and photocatalytic activity of ZnO thin films. For this purpose we have used X-rays diffraction (XRD), atomic force microscopy (AFM), UV–visible spectroscopy and Hall effect measurements for films characterization. The obtained results indicated that ZnO films properties are strongly influenced by the nature of the used precursor as reactant. Films photocatalytic activity was evaluated by the photo-degradation of methylene blue (MB) dissolved in aqueous solution under UV-A light. The obtained results indicated that ZnO thin films prepared from zinc acetate are more efficient than those prepared from zinc nitrate and zinc chloride.     

Synthesis and characterization of nanocrystalline Ni–YSZ cermet anode for SOFC

Ni–YSZ cermet anode has been synthesized in one step using a simple and cost effective combustion synthesis process. The processed powder of NiO–YSZ is found to be nanocrystalline with crystallite sizes of 29 and 22 nm for NiO and YSZ respectively by X-ray diffraction and transmission electron microscopy analysis. X-ray diffraction analysis also shows that the precursor salts are converted to highly crystalline phases of NiO and YSZ (8 mol% Y₂O₃) without any intermediate calcination step and no undesirable phases are present. Comparison with the X-ray diffraction pattern of a commercial YSZ sample shows that the process is also effective in maintaining a close compositional control. The microstructure of the sintered and reduced sample shows a well defined network of pores which is necessary for the effective functioning of the anode. The electrical conductivity as a function of temperature shows metallic behavior.     

Synthesis of β-silicon carbide nanofiber from an exfoliated graphite and amorphous silica

Silicon carbide (SiC) nanofibers were synthesized from exfoliated graphite containing silica particles at 1425 °C in a 25% H₂/Ar atmosphere. Two types of SiC nanofibers with different morphologies were formed depending on the silica content. A higher silica content led to straight nanofibers with a regular diameter size. The SiC nanofibers derived from the exfoliated graphite/40 wt% SiO₂ powder mixture contained a large number of stacking faults and grew along the [1 1 1] direction. A gas–gas reaction mechanism was proposed to explain the formation of SiC nanofibers.     

Synthesis and characterization of NiO nanoparticles by sol–gel method

Nickel oxide nanoparticles have been synthesized in the presence of agarose polysaccharide by sol–gel method. The structure, morphology, optical and magnetic properties of the product was examined by X-ray diffraction, transmission electron microscopy, UV–visible spectrophotometer and superconducting quantum interference device magnetometer. The result of thermogravimetric analysis of the precursor product showed that the proper calcination temperature was 400 °C. X-ray diffraction result revealed that the obtained product was nickel oxide with face-centered cubic structure. TEM image demonstrated that the nickel oxide nanoparticles have spherical shape with size around 3 nm. Analysis of FTIR spectra confirmed the composition of product. The optical absorption band gap of the NiO nanoparticles was estimated to be 3.51 eV. Magnetic measurement showed that the nickel oxide nanoparticles exhibit superparamagnetic behavior at 300 K. Moreover, the nanoparticles show ferromagnetic interactions at 4.2 K owing to the existence of uncompensated moments on the surface of the nanoparticles.     

Phase transformation kinetics of precursor gel to α-alumina

The kinetic analysis of the transformation of gels to -alumina in the Al (OPr ⁱ )₃-Al(N0₃)₃-(citric acid) system, was studied; the relationship between -alumina and the gel structure, presumed from the solution structure and the transformation to -alumina by calcination, was also investigated. It was shown that the gel structure effects the formation of -alumina nuclei and their growth. The former was confirmed by the apparent activation energy obtained from incubation time, namely the gel obtained from the spinnable solution showed a smaller apparent activation energy than that from the unspinnable solution. Evidence for the latter was derived from the apparent activation energy, obtained from annealing time. That is, contrary to above, the gel obtained from the spinnable solution showed a larger apparent activation energy. However, the gel structure did not affect the manner of crystal growth. These phenomena can be explained by the difference in gel structure, i.e. by the kind of Al-O structure it is composed of, and by the conditions of formation of the -alumina grains in the first place.     

Synthesis of nanocomposite powders of γ-alumina-carbon nanotube by sol–gel method

The nanocomposite powders of γ-alumina-carbon nanotube were successfully synthesized by a sol–gel process. The homogeneous mixture of carbon nanotubes and alumina particles was obtained by mixing the carbon nanotubes within alumina solution and followed by heating into gel. The resultant gel was dried and calcined at 200 °C into boehmite-carbon nanotubes composite powders. The mean particle size of synthesized boehmite was of the order of 4 nm. The boehmite-carbon nanotubes composite powders were calcined at different temperatures and XRD investigations revealed that as the amount of carbon nanotube increases, γ- to α-alumina phase transformation is completed at higher temperatures. The specific surface area and mean particle size of resultant nanocomposite powders increased and decreased, respectively by increasing the content of carbon nanotubes.