Preparation of amorphous carbon nanotubes using attapulgite as template and furfuryl alcohol as carbon source

Amorphous carbon nanotubes were synthesized by vapor deposition polymerization (VDP) method using attapulgite as template and furfuryl alcohol as carbon source. The morphology and microstructure analysis of the as-prepared samples showed that highly pure amorphous carbon nanotubes were obtained, and determined by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SEAD) and energy dispersive X-ray (EDX) spectrum. The Brunauer–Emmett–Teller (BET) surface area analysis indicated that the specific surface area of the as-prepared amorphous carbon nanotubes reaches up to 503.1 m²/g. A hypothesis about the formation mechanism of the amorphous carbon nanotubes was also proposed accordingly.     

Electrical conductivity improvement of aeronautical carbon fiber reinforced polyepoxy composites by insertion of carbon nanotubes

An increase and homogenization of electrical conductivity is essential in epoxy carbon fiber laminar aeronautical composites. Dynamic conductivity measurements have shown a very poor transversal conductivity. Double wall carbon nanotubes have been introduced into the epoxy matrix to increase the electrical conductivity. The conductivity and the degree of dispersion of carbon nanotubes in epoxy matrix were evaluated. The epoxy matrix was filled with 0.4 wt.% of CNTs to establish the percolation threshold. A very low value of carbon nanotubes is crucial to maintain the mechanical properties and avoid an overload of the composite weight. The final carbon fiber aeronautical composite realized with the carbon nanotubes epoxy filled was studied. The conductivity measurements have shown a large increase of the transversal electrical conductivity. The percolative network has been established and scanning electron microscopy images confirm the presence of the carbon nanotube conductive pathway in the carbon fiber ply. The transversal bulk conductivity has been homogenized and improved to 10^? 1 S·m^? 1 for a carbon nanotubes loading near 0.12 wt.%.     

Study of mechanical properties of concrete with low concentration of magnetic nanoparticles

Concrete samples containing small amounts (0.6 wt%) of agglomerated magnetic nanoparticles of cobalt (Co/C) or iron carbide (Fe₃C/C) coated with carbon have been synthesized. The time dependence of the compression, bending and contraction strength of samples with and without magnetic nanoparticles have been investigated. Twelve different samples have been prepared and tested during 28 days to detect variation in compression, bending and contraction properties. The temporal change of the bending strength for concrete with and without nanoparticles has showed measurable differences. During the initial stage (first 3 days) of hardening all samples with nanoparticles were less resistant to bending than samples without nanoparticles. After 1 week samples with iron carbide agglomerates and cobalt nanoparticles showed an increase in resistance to bending in comparison with undoped concrete, 3% and 6%, respectively. After 28 days in both cases the bending strength slowly decreased for samples containing magnetic nanoparticles. The compression strength after 28 days decreased by about 9% for samples containing cobalt and 12% with iron carbide. The contraction increased by about 38% for sample with cobalt ions, however no change was observed for samples containing iron carbide. The FMR investigation has shown that the resonance line has shifted more for samples with cobalt and it has been suggested that this process could be connected with contraction caused by decreasing temperature after freezing [P.C. Aitcin, Cement Concrete Res. 30 (2000) 1349]. This study can be very important for magnetic shielding effects and the selection of optimal conditions for building materials with magnetic nanoparticles. It can also be useful for new technological solutions aimed at increasing the functionality of these materials.     

Diffusion barrier properties of amorphous ZrCN films for copper metallization

A novel amorphous zirconium carbon nitrides (ZrCN) material was deposited by reactive sputtering using a ZrC target (99.5% in purity) in a mixture of Ar and N₂ ambient. The microstructure and mechanical properties of the ZrCN films were examined with respect to N₂ pressure. For thermal stability characterization, the stacked structure of Cu/ZrCN/Si was subsequently subject to thermal treatments at temperatures from 300 °C to 900 °C for 30 min in a vacuum tube with the base pressure of 3 × 10⁻⁵ torr. The results show that the amorphous ZrCN films exhibit superior mechanical properties to either ZrN or ZrC including hardness and elastic modulus. The stacked samples were shown to be thermally stable up to about 800 °C from Auger electron spectroscopy and X-ray diffraction, where the ZrCN still remains its amorphous phase. The device completely fails at 900 °C and the mechanism is discussed in the paper.     

Formation and structure of Na2S + P2S5 amorphous materials prepared by melt-quenching and mechanical milling

xNa₂S + (1 ? x)P₂S₅ amorphous and partially crystalline materials were prepared by melt-quenching and mechanical milling. These products were characterized using x-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and Raman spectroscopy. Compared to the narrower x-ray amorphous range for this system obtained through melt-quenching as found in this study, 0.50 ≤ x ≤ 0.67, the x-ray amorphous range for this system could be extended from the low-alkali ultra-thiophosphate composition of x ~ 0.25 to slightly above the high-alkali pyro-thiophosphate composition of x ~ 0.70 using mechanical milling. Mechanically milled samples with Na₂S of composition x = 0.75 yielded a partially crystalline material that had diffuse XRD peaks associated to the α-Na₃PS₄ phase. A similar result was obtained for the x = 0.80 composition except that, as expected, it also showed peaks for unreacted (over stoichiometric) Na₂S. The melt-quenched and mechanically milled samples with the same compositions 0.50 ≤ x ≤ 0.67 showed similar FT-IR and Raman spectra, indicating very similar chemical short-range structures are present in both of these amorphous materials. It was found that the Na₂S + P₂S₅ system exhibited similar behavior to that of the Li₂S + P₂S₅ in that chemical reaction between Na₂S and P₂S₅ could be induced by mechanical milling near room temperature to produce both amorphous and polycrystalline materials.     

Polyaniline nanofiber–silica composite aerogels

Strong, electrically conducting aerogels were prepared by introducing polyaniline nanofibers to a silica sol just prior to gelation and drying through supercritical carbon dioxide processing. The addition of a few milligrams of polyaniline per cm³ increased the flexural strength of the cylindrical monoliths by 200%. Using preformed polymeric nanofibers avoided filling of microporosity often observed with polymer reinforcement of aerogels and allowed preparation of polyaniline–silica composite aerogels with surface areas over 900 m²/g. Despite the small amount of polyaniline nanofibers (1.3–16.5 wt.%), the composite aerogels were electrically conducting (8.0 × 10^? 8–1.83 × 10^? 5 S/cm) and it was possible to prepare chemiresistor sensors for detection of acidic (HCl) and basic (ammonia) gaseous molecules with response times similar to thin film sensors containing orders of magnitude more polyaniline.     

Study of magnetoimpedance effect of Co-based amorphous ribbons after current annealing at various kinds of ambient pressure

The physical properties of magnetic amorphous alloys can be improved by using different annealing processes. In this paper, for annealing purposes, different driving currents were flowed through Co-based magnetic amorphous ribbons at different ambient air pressures between 5 × 10^?5 mbar and 10³ mbar. The magnetoimpedance effect in the annealed samples was studied at a frequency interval between 250 kHz and 10 MHz. Magnetic properties and microstructures of samples were investigated by means of alternative gradient force magnetometers and X-ray diffraction. Regarding the giant magnetoimpedance (GMI) effect, annealing at different ambient pressures with the same current can lead to various responses. For annealing at higher pressures such as in air, higher current is necessary for crystallization of samples which results in the development of greater transverse magnetic anisotropy.     

Anatase phase formation kinetics in Ti and TiOx nanoparticles produced by gas-phase condensation

Anatase TiO₂ nanoparticles were successfully synthesized by post-heat treatments of partially crystalline Ti and amorphous TiO_x nanoparticles, respectively produced by inert gas condensation and subsequent oxidation. The nanoparticles condensed on a liquid-nitrogen containing cooling finger (sample LN) were identified to be partially crystalline Ti phase with ~ 10–20 vol.% amorphous TiO_x. On the other hand, those condensed on a room-temperature cooling finger (sample RT) were almost completely amorphous TiO_x phase. Differential scanning calorimetry scan curves of as-oxidized samples were interpreted using Kissinger analysis, the non-isothermal kinetics, and activation energy for the anatase formation was determined as ~ 455 and 865 kJ/mol for samples LN and RT, respectively. As-oxidized samples LN and RT were heat treated at 400 °C for 2 h, respectively (samples LN-H and RT-H). Samples LN-H and RT-H showed the onset of UV–visible light absorption near 400 nm and the optical band gap of 3.12 and 3.21 eV, respectively, corresponding to anatase. The sample LN-H showed faster photocatalytic decomposition of methylene blue and rhodamine B dyes compared to the sample RT-H due to high crystallinity of anatase and rutile phases.     

Conductivity,thermal and infrared studies on plasticized polymer electrolytes with carbon nanotubes as filler

New composite polymer electrolytes (CPE) are prepared using solution-casting technique. The CPE are based on polyethylene oxide (PEO) and employ lithium hexafluorate (LiPF₆) as the doping salt, ethylene carbonate (EC) as the plasticizer and amorphous carbon nanotubes (αCNTs) as the filler. The crystallinity and ionic conductivity of the CPE are examined in this work. The conductivity increases from 10^?10 to 10^?5 S cm^?1 upon the addition of salt. The incorporation of EC and αCNTs into the salted polymer enhances the conductivity significantly to 10^?4 and 10^?3 S cm^?1. The Vogel–Tamman–Fulcher (VTF) plots suggest that the temperature dependence of conductivity is a thermally activated process. Differential Scanning Calorimetry (DSC) studies show that the melting transition temperature and crystallinity decrease upon the addition of salt, EC and αCNTs into the polymer electrolyte system. The complexation, nature and concentration of the various ionic species are examined using Fourier Transform Infrared Spectroscopy (FTIR). Scanning electron microscopy (SEM) images show the changes in morphologies of the composite polymer electrolytes. The application of CPE especially in batteries and the advantages of this composite are highly conductive and stable at elevated temperature.     

Structural and magnetic properties of nanocrystalline particles in an amorphous Fe73.5Nb3CuSi13.5B9 matrix

We report structural and magnetic properties of fine particles embedded in an amorphous magnetic matrix. As-quenched amorphous Fe_73.5Nb₃CuSi_13.5B₉ ribbons (FINEMET) were submitted to the thermal treatments of several times (1 ? t ? 240 min) at 570 °C using a conventional furnace. The analyses of the X-ray diffraction patterns at room temperature reveal that our samples consist of single phase Fe₃Si nanocrystals embedded in a residual amorphous phase. Magnetic measurements show that the saturation moment at T = 450 °C increases as a function of annealing time. This behavior is attributed to an increase of the fraction of nanocrystallites in the residual amorphous phase.     

Textural and adsorption characteristics of carbon xerogel adsorbents for removal of Cu (II) ions from aqueous solution

Resorcinol–formaldehyde (RF) carbon xerogels were synthesized using different resorcinol/sodium carbonate catalyst molar ratios (R/C = 50, 200, 500 and 1000) and heat treatment temperatures (HTT = 500, 600 and 700) under no external gas flow. The carbon adsorbents were extensively characterized by CHO content, FTIR, TEM and nitrogen adsorption isotherm at 77 K. The effect of R/C, HTT and oxygen content on the development of porosity within carbons was studied. Also, the adsorption capacity of these adsorbents was investigated by the removal of copper (II) ions from aqueous solution using single bottle test. The produced carbon xerogels exhibit a micro-mesopore character, but with different extents depending on the mechanism of porosity generation in relation to R/C, HTT and oxygen functional groups. Results show that the optimum conditions to obtain porous carbon xerogels were the highest R/C = 500–1000 in combination with carbonization preferably at 600 or 700 °C. Single bottle removal of Cu (II) ions indicated the developed carbons with appreciable capacity (q_u = 32–130 mg/g) which are controlled by the surface area and surface chemical nature (acidic O-functional groups). Finally, the present investigation provides a new, nanoporous type of porous carbon adsorbents with high adsorption capacity for removal of heavy metals from wastewater media.     

Comparative study on photoluminescence of amorphous and nano-crystalline YAG:Tb phosphors prepared by a combustion method

Amorphous and nano-crystalline Y₃Al₅O₁₂:Tb phosphor samples were obtained via a facile combustion method by calcination at various temperatures, using yttrium oxide and aluminum nitrite as starting materials and citric acid as fuel. XRD, FT-IR and TEM results showed that the products were amorphous if prepared at 750 °C, well-crystalline when treated above 850 °C. In addition, partially crystalline YAG phase was observed at 800 °C (in air). The excitation spectra of the samples calcined at 750 °C and 800 °C exhibited some difference in the 230–255 nm range in comparison to those of nano-crystalline YAG:Tb, i.e. an extra band centered at 250 nm was detected via Gaussian curve-fitting. Furthermore, the photoluminescence intensity of as-synthesized samples decreased obviously with increasing the crystallinity under 250 nm excitation. Contrary, it increased monotonously when altering the excitation wavelength to 323 nm. The concentration-dependent emission spectra of samples calcined at 800 °C revealed that the strongest intensity could be obtained with 10% Tb doping. Red-shifts indicated changes of the inter-atomic distances within the Tb³⁺ coordination polyhedron with increasing Tb concentration. The low temperature photoluminescence of partially crystalline YAG:10% Tb was also investigated, displaying good-resolution but reduced intensity compared to the room-temperature photoluminescence.     

Electrochemical properties of conductive filler/carbon aerogel composites as electrodes of supercapacitors

Carbon black, multi-walls carbon nanotube (CNT) and vapor grown carbon nano-fiber with different contents were added to the carbon aerogels (CAs) electrodes as conductive fillers to improve their capacitive properties. The results show that maximum capacitance exists when the content of the conductive filler gets to its percolation threshold. CNT is the most ideal conductive filler. The CA with 1 wt% content of CNT has the best electrochemical performance; its specific capacitances are 141.3 F g^?1 at 5 mV s^?1 and 127.1 F g^?1 at 100 mV s^?1, 1.4 times and 2.2 times as high as that of CA electrode, respectively.     

Effects on the structural and magnetic properties of amorphous ribbons of (Co0.94Fe0.06)72.5Si12.5B15 caused by 4 MeV Cl2+ ion irradiation

The use of energetic ion irradiation to modify magnetic materials has attracted increasing interest in recent years. The possibility of patterning surfaces on these materials offers a wide range of potential applications particularly in technologies related to magnetic storage media, sensing devices and electromagnetic shielding materials. In this work, ultrasoft non-magnetostrictive (Co_0.94Fe_0.06)72.5Si_12.5B₁₅ amorphous ribbons, 50 μm thick and 0.85 mm wide, fabricated by the chilly block melt spinning technique are irradiated, in their amorphous state, by 4 MeV Cl²⁺ ions with a fluence of 5 × 10¹³ cm⁻². The hysteresis properties of both irradiated and non-irradiated samples are characterized by means of a vibrating sample magnetometer while surface magnetic domain structure is observed by Bitter technique. The presence of an induced magnetic anisotropy in irradiated samples is ascribed to the local damage, caused by ion irradiation treatment, which results in modified coercive field and permeability of the samples. X-ray diffraction results are presented to confirm the amorphicity of the structure even after irradiation with ions.     

Electrical conductivity studies on carbon black loaded ethylene butylacrylate polymer composites

In this work we studied the electrical properties of carbon black mixed into ethylene butylacrylate copolymer, using impedance spectroscopy, in the frequency range from 100 Hz to 100 kHz and over the temperature range from 150 to 360 K. A series of samples was prepared with several filler contents, below and above the percolation threshold, which was calculated using direct current conductivity measurements. For concentrations below the critical concentration the negative temperature coefficient in resistivity effect is observed, and for concentrations above that threshold the positive temperature coefficient in resistivity effect is present. The dielectric response was analyzed using complex permittivity or modulus formalisms, depending on the concentration of filler in the polymer matrix. Havriliak–Negami model was used to fit the experimental results.     

Influence of Ar/C2H2 ratio on the structure of hydrogenated carbon films

The amorphous hydrogenated carbon films (a-C:H) were obtained on Si (1 1 1) wafers by plasma jet chemical vapor deposition (PJCVD). a-C:H coatings have been prepared at 1000 Pa in argon/acetylene mixture. The Ar/C₂H₂ gas volume ratio varied from 1:1 to 8:1. It was demonstrated that by varying the Ar/C₂H₂ ratio the composition, growth rate of the coatings, and consequently the structure of the film, can be controlled. The growth rate and surface porosity of coatings deposited at Ar/C₂H₂ = 8:1 ratio decrease slightly with an increase in the distance between the plasma torch nozzle and substrate from 0.04 to 0.095 m. The transmittance of the coatings in the IR region of 2.5–25 μm slightly increases, while the absorption peaks at 2850–2960 cm^?1 related with sp³ CH_2–3 modes remain unchanged with an increase in the distance. The Raman spectroscopy indicated that the a-C:H coating formed at the Ar/C₂H₂ = 8:1 and 0.06 m has the highest sp³ C–C fraction. The proposed PJCVD technique allows to achieve the growth rates up to 300 nm/s.     

Preparation and electrochemical characterizations of MnO2-dispersed carbon aerogel as supercapacitor electrode material

The nano-sized amorphous α-MnO₂-dispersed carbon aerogels (CAs) were prepared by liquid phase co-precipitation technique. Different MnO₂ contents and heating temperatures were taken to prepare the composites. The composites prepared were used to make electrodes of electrochemical supercapacitors. Electrochemical properties of the electrodes were studied by cyclic voltammetry and galvanostatic charge–discharge. The specific capacitances of the MnO₂-dispersed CAs and the nano-MnO₂ ingredient in the composite are up to 219 F g^?1 and 401 F g^?1 at 5 mA.cm^?2, 1.6 times and 5.0 times greater than that of neat CA and MnO₂, respectively.     

Conductivity and dielectric properties of polyvinyl alcohol–polyvinylpyrrolidone poly blend film using non-aqueous medium

Several methods such as copolymerization, plasticization and blending etc., have been used to modulate the conductivity of polymer electrolytes. Polymer blending is one of the most important contemporary ways for the development of new polymeric materials and it is a useful technique for designing materials with a wide variety of properties. Polymer blend electrolyte has been prepared with different concentrations of PVA and PVP by solution casting technique using DMSO as solvent. The prepared films have been investigated by different techniques. The increase in amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. The FTIR analysis reveals that the interchain hydrogen bonding within a PVA–PVP blends. The dielectric permittivity (ε*) and modulus (M*) have been calculated from the ac impedance spectroscopy in the frequency range 42 Hz– 1 MHz and the temperature range 308–373 K. The maximum conductivity has been found to be 1.58 × 10^? 6 S cm^? 1 at room temperature for 70PVA:30PVP concentration. The conductivity has been increased to 5.49 × 10^? 5 S cm^? 1 when the temperature is increased to 373 K. The activation energy of all samples was calculated using the Arrhenius plot and it has been found to be 0.53 eV to 0.78 eV.     

Crystallization of amorphous silicates far from equilibrium part I: A versatile nitrate-based sol–gel synthesis of amorphous porous Ca,Mg-rich silicates

An easy-to-use, comprehensive sol–gel method is developed to produce amorphous calcium and magnesium silicates from nitrate precursors and TetraEthOxySilane (TEOS). Final products were designed to suit basic prerequisites of starting materials for experimental investigation of crystallization around the glass transition temperature range. After gelification, thermo-gravimetric methods and infrared-spectroscopy were used to follow dehydration, decarbonation and denitrification of the xerogel. A temperature of 500 °C is found to successfully remove volatiles without causing crystallization. The microstructure revealed by transmission electron microscopy (TEM) consists of 10–20 nm individual mesoparticles of 10–20 nm. Samples annealed at 500 °C were found entirely amorphous at the TEM scale. The porosity observed by TEM and characterized by nitrogen adsorption–desorption is homogeneous and varies from 4.6 to 8.5 nm as a function of the composition. Bulk analyses by ICPMS and local analyses by EDS-TEM demonstrate that the stoichiometry can be achieved and the homogeneity is confirmed at least down to 100 × 100 nm. At lower scale, irradiation by the electron beam produces a significant volatilization of Ca and Mg, which makes chemical analyses unreliable. Pros and cons of the method and special cares for specific applications are discussed. The method was also successfully used to produce a wider range of amorphous analogs having complex compositions or containing trace elements for applications in the field of mineral physics and chemistry.