The use of calcination in exposing the entrapped Fe particles from multi-walled carbon nanotubes grown by chemical vapour deposition

Multi-walled carbon nanotubes (MWCNTs) were synthesized a by chemical vapour deposition method. The effect of calcination at temperatures ranging from 300 to 550°C in exposing the metal nanoparticles within the nanotube bundles was studied. The degree of degradation of the structural integrity of the MWCNTs during the thermal process was studied by Raman spectroscopy, X-ray diffraction analysis, field-emission scanning electron microscopy, and transmission electron microscopy. The thermal behaviour of the as-prepared and calcined samples was investigated by thermogravimetric analysis. Calcination in air, at 400°C for 1 h, was found to be an efficient and simple method to extract metallic impurities from the amorphous carbon shells with minimal damage to the tube walls and lengths. The nanotubes were observed to be damaged at temperatures higher than 450°C.     

Microstructural Evolution and Its Effect on Mechanical Properties of Isotactic Polypropylene by Shear Plastic Deformation at Elevated Temperatures

Isotactic polypropylene (iPP) was plastically shear deformed by equal channel angular extrusion (ECAE) at extrusion temperatures varied from 45 to 125°C (25 mm/min). The evolutions of morphology and crystal orientation were studied by reflected optical microscopy (ROM), scanning electron microscopy (SEM), and X-ray diffraction. It was found that the original spherulites were deformed into nearly ellipsoids with their long axis tilted at an angle away from the flow direction. Azimuthal scanning results revealed that two preferred crystal orientations were formed after ECAE. The crystal plasticity was activated by increasing the extrusion temperature, followed by fast rotation of crystallites toward the shear direction. The thermal mechanical analysis (TMA) indicated that low extrusion temperature was favorable to fix the molecular orientation. The iPP samples processed at the investigated temperatures displayed a significant increase in the impact strength, especially for those extruded at 45°C and 65°C. The tensile results revealed a greater elongation at break in the samples deformed at low temperatures (45°C and 65°C) but not in those deformed at high temperatures (85°C or above).     

X-ray study of structural phase transitions in nanocrystalline LaMnO3+δ perovskite

The nanocrystalline LaMnO_3+δ perovskite was synthesized by the microwave-assisted glycothermal method and calcined at several temperatures up to 1500°C. The prepared samples were examined by the X-ray powder diffraction with the aim to show that LaMnO_3+δ exhibits the size-induced structural phase transitions. The as-received nanocrystals of LaMnO_3+δ are of tetragonal, pseudo-cubic symmetry not known for bulk material. The samples calcined at temperatures 750–1100°C have trigonal symmetry known from the high-temperature phase of LaMnO₃ single crystal. The samples calcined from 1200°C to 1500°C have two phases: trigonal and orthorhombic. Thus, the observed phase sequence is inverted with respect to that of the bulk material, which is the characteristic of the size-induced mechanism of phase transitions in the nanocrystals. The critical crystallite sizes for both structural transitions were evaluated as 20 and 100?nm.     

Polyhedral carbon nanoparticles at high pressures

The solid-phase transformations of polyhedral nanoparticles at a pressure of 8.0 GPa and various temperatures have been investigated by X-ray diffraction, small-angle X-ray scattering, and transmission electron microscopy. It has been found that the graphene layers of the inner cavities of polyhedral particles are transformed into onion-like structures at temperatures above ～1000°C. This transformation gives rise to the formation of hybrid-type sp2 carbon nanoparticles, which combine the outer polyhedral shape with the quasispherical onion-like core. Polyhedral nanoparticles smaller than ～40 nm are completely transformed into onion-like particles at 1600°C.     

Structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering

286 , 176 (1996)]. (1) The interdiffusion critical wavelengths were calculated as 2.00–2.04 nm at temperatures ranging from 473 to 523 K, which is equal to those of Co/C multilayers within the experimental error, indicating that the interdiffusion behaviours in the CoN/CN multilayers are still decided by the thermodynamic properties of the Co-C system. (2) The effective interdiffusivities and macroscopic diffusion coefficients are smaller. (3) The activation energy for diffusion is larger. The features imply that it is possible to improve the thermal stability of Co/C multilayers by doping with N atoms. The high-temperature annealing results imply that the destructive threshold of the CoN/CN multilayers is 100–200 °C higher than that of Co/C multilayers. The small-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4% at 400 °C, and the interface pattern still exists even if they were annealed at 700 °C. The large-angle X-ray diffraction and transmission electron microscopy analysis reveal that the crystalline process is significantly retarded if doped with N atoms, leading to a smaller grain size at higher annealing temperatures. The significant improvement of the thermal stability can be interpreted with Raman spectroscopy and X-ray photoelectron spectroscopy analysis. The Raman spectra give the evidence that the formation of the sp³ bonding in the CN sublayers can be suppressed effectively by doping with N atoms, and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra give information about existence of the strong covalent bonding between N atoms and the ionic bonding between Co and N atoms, which can slow down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc Co and hcp Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420 °C, leading to the suppression of the grain growth. Received: 29 May 1997/Accepted: 8 September 1997     

Effect of annealing temperature on the structure of pyrolysates of diphthalocyanines of rare-earth elements: Neutron research

Small-angle neutron scattering is used to study the structure of carbon matrices—the pyrolysis products of diphthalocyanines with embedded metal atoms (Y, La, and Ce), synthesized at annealing temperatures of 800–1700°C. It is shown that the structure of the porous matrix on the scale of ～10⁰–10² nm is characterized by a level of small pores (3–10 nm in radius) and the next level of the structure is associated with the formation of their aggregates (above 100 nm in size). The quantity and size of the scattering objects increases sharply at annealing temperatures above 1000°C. The results are consistent with X-ray diffraction data.     

Effect of annealing temperature on optical and magnetic properties of Cr doped ZnS nanoparticles

ZnS:Cr (3 at.%) nanoparticles were synthesized by chemical co-precipitation method using EDTA as capping agent. The samples were annealed in air for 3 h in steps of 100 °C in the temperature range of 200–700 °C. The effect of annealing temperatures on the structural and photoluminescence properties of Cr doped ZnS nanoparticles was investigated using X-ray Diffraction (XRD), a Scanning Electron Microscope (SEM), Energy Dispersive X-ray spectroscopy (EDS), Diffuse Reflectance Spectra (DRS), Vibrating Sample Magnetometer (VSM) and Photoluminescence (PL) techniques. EDS spectra confirmed the presence of Cr in the samples with expected stoichiometry. XRD studies confirmed the formation of ZnO above 500 °C. Photoluminescence studies on ZnS:Cr nanoparticles indicated that the emission wavelength is tunable in the range of 440–675 nm as a function of annealing temperature. VSM results indicated a decrease in ferromagnetism with increase in annealing temperature, perhaps due to appreciable variation in structural defects that are sensitive to annealing temperature.     

Relaxation phenomena of poly-γ-benzyl-L-glutamate,poly-γ-methyl-L-glutamate,and copoly(γ-methyl-L-glutamate, γ-benzyl-L-glutamate)

Relaxation phenomena of poly-α-amino acids in the solid state have been investigated using poly-γ-benzyl-L-glutamate (PBLG), poly-γ-methyl-L-glutamate (PMLG), and copoly (γ-methyl-L-glutamate, γ-benzyl-L-glutamate) (PMBG) by means of dielectric, dynamic mechanical, NMR, dilatometric, and X-ray diffraction measurements at temperatures between ?196 and 180°C.

Each of the samples exhibits two relaxation regions, one at room temperature (β-relaxation) and the other in the range from ?150 to ?100°C (γ-relaxation). The γ-relaxation is attributed to motion of the side chains with small amplitude. The β-relaxation is due to large-scale motion of the side chain. It has been found that the β-relaxation is well described by the WLF-equation.

The intensity of the X-ray diffraction peak at 2θ = 7° for PBLG increases with increasing temperature, which is similar to results obtained in small-angle X-ray scattering for polymer crystals consisting of two phases, amorphous and crystalline. A break point is observed at 18°C where the specific volumetemperature curve also shows a break point.

It is concluded that the side chains of these polymers are almost amorphous, and that they undergo a glass-like transition while the backbones keep an α-helical conformation.     

In-situ and ex-situ study of crystallization behaviour of magnetron sputtered Ni63Zr37 amorphous thin film

ABSTRACT

The stages of crystallization of magnetron sputter-deposited Ni₆₃Zr₃₇ film with mostly amorphous structure have been investigated by differential scanning calorimetry (DSC) and in-situ annealing at 300°C by use of heating stage on a high-resolution transmission electron microscope (HRTEM). These results have been further confirmed by grazing incidence X-ray diffraction analyses of thin film specimens annealed ex-situ at 300°C for various durations. The temperature for crystallization found by DSC has been found to increase from 371°C to 434°C with an increase in heating rate from 3°C/min to 10°C/min, and the apparent activation energy for amorphous to crystalline transformation has been found as ～260.2?kJ/mol from the Kissinger plot. Studies on HRTEM using in-situ heating stage have shown the crystallization to occur on annealing at 300°C for ～10?min. Crystallization at a temperature lower than that found by DSC is attributed to structural relaxation with reduction of free volume due to thermal activation. It has been observed that Ni₃Zr forms first due to its large negative enthalpy of formation, and is followed by the formation of Ni-rich solid solution (Ni_ss) grains. HRTEM studies have shown grain rotation with the formation of partial dislocations at Ni₃Zr-Ni_ss interfaces as well as twinning followed by detwinning with dislocation formation in the Ni_ss matrix possibly to reduce the interfacial energy.     

Thermal neutron equivalent dose measurements with nanostructured zirconia

This paper reports the experimental results concerning the thermoluminescent measurements of thermal neutron using nanostructured zirconium oxide (ZrO₂) powder prepared by the sol–gel method. Transmission electron microscopy and X-ray diffraction techniques were used for morphological and structural characterization of the compound. Thermal annealing processes for the precipitates were studied. It was observed that the crystalline structure and the crystallinity of the powders depend on the annealing temperature. For temperatures higher than 1100 °C, the material presents the monoclinic phase with average nanocrystallite sizes ranging from 8–10 nm up to ～40 nm. These zirconium oxide materials developed in our laboratory were used in this investigation. Within the experimental uncertainties, these measurements were compared with those obtained using the well-known gamma rays sensitive lithium fluoride (LiF:Mg,Cu,P), also developed in our laboratory.     

First-principles study of ground- and metastable-state properties of XO (X = Be,Mg, Ca,Sr, Ba,Zn and Cd)

The evolution of the local atomic order of an amorphous Ni₄₆Ti₅₄ alloy produced by mechanical alloying as a function of temperature was studied by synchrotron X-ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. XRD measurements at several temperatures (25 °C, 350 °C, 412 °C, 430 °C, 450 °C and 515 °C) were performed and analyzed using the reverse Monte Carlo (RMC) simulations method or the Rietveld refinement procedure. The experimental total structure factor for samples at 25 °C and 350 °C, which are amorphous in nature, were simulated by using the RMC method, and the local structures of the alloy at both temperatures were determined, indicating a decrease in its density as the temperature increases. At 412 °C, the XRD pattern shows a partially crystalline sample, indicating that the crystallization process is in progress. At 430 °C, 450 °C and 515 °C, the XRD measurements indicate the presence of two crystalline phases, NiTi and NiTi₂, whose structural parameters (lattice parameters, coherently diffracting domains (CDD) sizes, microstrains and relative amount of phases) were determined using the Rietveld refinement procedure. DSC measurements at different heating rates furnished the crystallization temperature, enthalpy and activation energy of the crystallization process, and these values are similar to those found in other amorphous alloys of the Ni-Ti system. They also showed the existence of a second exothermic process, which was related to diffusive processes in the crystalline phases, which could be associated with the changes in the CDD sizes happening from 450 °C to 515 °C.     

Characterization and organic electric-double-layer-capacitor application of KOH activated coal-tar-pitch-based carbons: Effect of carbonization temperature

The present study reports the influence of pre-carbonization on the properties of KOH-activated coal tar pitch (CTP). The change of crystallinity and pore structure of pre-carbonized CTPs as well as their activated carbons (ACs) as function of pre-carbonization temperature are investigated. The crystallinity of pre-carbonized CTPs increases with increasing the carbonization temperature up to 600 °C, but a disorder occurs during the carbonization around 700 °C and an order happens gradually with increasing the carbonization temperatures in range of 800–1000 °C. The CTPs pre-carbonized at high temperatures are more difficult to be activated with KOH than those pre-carbonized at low temperatures due to the increase of micro-crystalline size and the decrease of surface functional groups. The micro-pores and meso-pores are well developed at around 1.0 nm and 2.4 nm, respectively, as the ACs are pre-carbonized at temperatures of 500–600 °C, exhibiting high specific capacitances as electrode materials for electric double layer capacitor (EDLC). Although the specific surface area (SSA) and pore volume of ACs pre-carbonized at temperatures of 900–1000 °C are extraordinary low (non-porous) as compared to those of AC pre-carbonized at 600 °C, their specific capacitances are comparable to each other. The large specific capacitances with low SSA ACs can be attributed to the structural change resulting from the electrochemical activation during the 1st charge above 2.0 V.     

Formation of Local Defects and Mesopores in a Structure of UiO-66-NDC Metal-Organic Framework

A UiO-66 metal-organic framework is synthesized using the solvothermal method. The framework of the obtained compound consists of Zr6O4(OH)4 clusters connected by 1,4-naphthalenedicarboxylate linkers. During synthesis two organic acids are introduced to control alterations in the properties of the material. It is shown that adding acetic acid results in a material with local defects, whereas benzoic acid in the compound structure leads to the creation of mesopores. The samples are comprehensively characterized via various experimental techniques. According to X-ray powder diffraction data, all of the samples possess a single-phase UiO-66 cubic structure. The thermal stability of the samples is studied via thermogravimetry and in-situ X-ray diffraction upon heating. Local defects are found to exert no significant influence on the thermal stability; furthermore, the samples retain their structure unchanged at temperatures of up to 500°C. The presence of mesopores lead to framework failure already at 300°C. The use of thermogravimetric analysis (TGA) and X-ray absorption spectroscopy along with evaluation of the degree of porosity makes it possible to monitor the formation of defects at both local and large scales.     

Thermal stability of organic layered systems based on lead stearate

The structural variation in multilayer Langmuir-Blodgett films of lead stearate caused by heat treatment under different conditions in the temperature range 20–100°C is investigated by X-ray reflectometry and high-resolution electron diffraction. Successive annealing of the samples is shown to not alter the initial layered structure at temperatures of 60, 80, and 100°C; partial disturbance of the layered structure occurs upon successive annealing at 80°C and 100°C. Significant disturbance of the structure is observed when the films are heated immediately to 100°C. In all these cases, the orthorhombic (pseudomonoclinic) lattice, with the lattice constants: a = 0.496, b = 0.738, c = 9.60 nm, α = β = γ = 90°, space group P2/1b, formed by transferring monolayers onto the substrate is retained in the crystalline domains of the film.     

Optimization of cuprous oxide nanocrystals deposition on multiwalled carbon nanotubes

Cu (I) phenyl acetylide was used as a source of copper to achieve a homogeneous distribution of Cu₂O nanocrystals (10–80 nm) decorated on multiwalled carbon nanotubes (MWCNTs) having an average diameter of 10 nm. Pristine MWCNTs were first oxygen-functionalized by treating them with a mixture of concentrated (H₂SO₄/HNO₃ : 3/1) acids and the products were characterized by X-ray powder diffraction, transmission and scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and thermogravimetric analysis. An easy, efficient and one-step impregnation method was followed to produce copper-containing nanoparticles on the MWCNTs. The copper-treated MWCNTs dried at room temperature were seen to be well decorated by copper-containing nanoparticles on their outer surface. The MWCNTs were then heat-treated at 400 °C in a nitrogen atmosphere to produce a homogeneous distribution of cuprous oxide nanocrystals on their surface. By varying the ratio of copper to oxygen-functionalized MWCNTs, Cu₂O nanocrystals decorated on MWCNTs with different copper content can be obtained.     

Effect of phase transformation on optical and dielectric properties of zirconium oxide nanoparticles

Zirconium oxide nanoparticle (ZrO₂) is synthesized by the hydrothermal method at different calcination temperatures. The structural analysis is carried out by X-ray diffraction and Raman spectra. The sample prepared at 400 °C and 1100 °C showed the cubic and monoclinic phase, respectively, and the sample calcined at 600 °C and 800 °C showed the mixed phase with co-existence of cubic and monoclinic phases. Furthermore, the morphology and particle size of these samples were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. The band gap estimated from UV–Vis spectra of ZrO₂ (zirconia) nanocrystalline materials calcined at different temperatures from 400 °C to 1100 °C was in the range of 2.6–4.2 eV. The frequency dependence of dielectric constant and dielectric loss was investigated at room temperature. The low frequency region of dielectric constant is attributed to space charge effects.     

Ammonia gas sensor based on SnO2 nanostructure with the enhanced sensing capability at low temperatures

ABSTRACT

We investigated the gas-sensing performance of tin oxide nanowires for ammonia gas at low temperature (～ 50°C). Tin oxide nanostructures were deposited at 1000°C and 1100°C on gold-coated silicon substrates using the physical vapor deposition method. Gas-sensing measurements were made for ammonia gas at various strengths (i.e. 50, 100 and 200?ppm) and the sensing performance was compared at low temperature for both the samples e.g. nanostructures deposited at 1000°C and 1100°C. Due to the highly oriented structure, the sample deposited at 1000°C shows high sensing capability at low temperature as compared to the regular tetragonal phase observed at 1100°C. The morphological and structural properties of nanowires were systematically examined using the scanning electron microscopy and X-ray diffraction.     

Relaxation of the state with induced transverse magnetic anisotropy in the soft magnetic nanocrystalline alloy Fe73.5Si13.5Nb3B9Cu1

The residual lattice strains of nanocrystals, which are responsible for the formation of states with transverse magnetic anisotropy in samples of the Fe-Si-Nb-B-Cu alloys (Finemets) subjected to annealing under tensile loading with the subsequent relaxation annealing at temperatures in the range from 500 to 600°C, have been measured using X-ray diffraction. The relative extension and compression of interplanar spacings have been compared with the induced magnetic anisotropy constants determined from the magnetic hysteresis loops. It has been shown that, during the relaxation annealing at the nanocrystallization temperature (500?C540°C), the observed decrease in the residual strains is accompanied by a decrease in the transverse magnetic anisotropy constant. A linear correlation between the relative extension and compression of the interplanar spacings for different crystallographic planes and magnetic anisotropy constant has been revealed. The deviation from linearity is observed after annealing at a temperature of 600°C, which is explained by a possible increase in sizes of nanocrystals, changes in their structure, and partial crystallization of the amorphous matrix.     

Magnetic properties of the nanocrystalline DyMnO3

We report on the X-ray and neutron diffraction and magnetic measurements of the nanosamples of DyMnO₃ annealed at temperatures of 800 °C, 850 °C and 900 °C. The diffraction data indicate that all the samples crystallize in an orthorhombic crystal structure (space group Pnma). The crystal structure parameters change slightly with preparation. All the samples are antiferromagnets at low temperatures. The Mn magnetic moments order near 40 K, while those of Dy below 8.4 K. The macroscopic magnetic and neutron diffraction data indicate a small difference of properties between the DyMnO₃ samples synthesized at different temperatures. The observed broadening of magnetic peaks connected with the Dy sublattice suggests a cluster-like character of magnetic ordering.     

Electron microscopy studies of void swelling and annealing of voids in aluminium irradiated with aluminium ions

Abstract

MgO single crystals implanted with Au⁺ ions (180 keV, 6 10¹⁶-10¹⁷ ions cm^?2) and annealed at temperatures between 25°C and 1100°C, have been analysed—by optical spectrophotometry—by Rutherford back-scattering (to confirm the effective presence and to study the distribution profile of Au atoms), and by TEM and X-ray diffraction (to identify the phases precipitated by thermal treatment).

Thermal annealing between 550°C and 1100°C produced an optical absorption band located between 565 nm and 600 nm. This band can be attributed to a fee Au precipitate with diameter varying from 50 to 200 Å. Larger metallic colloids 1000 Å are in simple orientation with the matrix.

Annealing at temperatures higher than 500°C produces a supplementary optical absorption located at 425 nm. This band can be attributed to Au plasma resonance.

After annealing for 15 min at 1100°C, a new phase is detected by X-ray diffraction and TEM and identified as Au₃Mg alloy with hexagonal structure.