Structure Changes and Thermal Behaviors of Polymer in PP/BaTiO3 Nanocomposites during Solid State Shear Milling

Polypropylene/barium titanate (PP/BaTiO₃) nanocomposites were prepared by a novel method—solid state shear milling (S³M). The effects of S³M on the structure changes and thermal behaviors of PP were investigated by X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC) study. The results showed that PP underwent significant amorphization. The crystallinity of PP decreased from 50.29% to 35.65% after 20 cycles of milling. During the subsequent heating process, the destroyed crystalline structure of PP can readily be recovered, though incompletely. Double melting characteristics were detected by DSC in the milled samples. It was inferred that the milling process resulted in enhanced intimacy between PP and BaTiO₃, which would significantly influence the melting behavior of the polymer phase. The abnormal thermal behaviors can be interpreted using an inferred nanocrystalline morphology, during which residual lamellae fragments randomly distribute in the amorphous bulk PP. The conclusions were also strongly supported by quantitative analysis of the XRD.     

A co-precipitation method for preparation of Bi3TiNbO9 powders

A simple co-precipitation technique has been successfully used for the preparation of pure, ultrafine, single phase Bi₃TiNbO₉ (BTN). An aqueous ammonium hydroxide solution was used to simultaneously precipitate Bi³⁺, Ti⁴⁺ and Nb⁵⁺ cations as hydroxides under basic conditions (pH ∼9). No pyrochlore phase was found while heating powder at 500 °C and pure BTN phase was found to be formed by X-ray diffraction (XRD). For comparison, BTN samples were also synthesized by the traditional solid state method. The sequence of phase formation in both cases were investigated by XRD studies.     

Effect of heating rate on dielectric and pyroelectric properties of double doped PZT

Abstract

Double doped lead zirconium titanate (PZT) was synthesised by solid state reaction method. Calcination and sintering was carried out at various heating rates in order to study the effect of heating rate on the extent of phase formation of double doped PZT. Furthermore, the effect of heating rate on dielectric and pyroelectric properties was also investigated. Rhombohedral perovskite phase was confirmed in the double doped PZT samples. Quantitative X-ray diffraction (XRD) analysis suggests that the extent of PZT formation decreases beyond 8°C min^?1 heating rate. The crystallite and grain sizes calculated from Scherrer's equation and field emission scanning electron microscope (FE-SEM) photographs respectively show the decreasing behaviour with increasing heating rate. Dielectric and pyroelectric properties show the increasing behaviour up to 8°C min^?1 and decreasing behaviour beyond this heating rate.     

Effects of microwave heating on dielectric and piezoelectric properties of PZT ceramic tapes

Commercial lead zirconate titanate (PZT) perovskite powders were used to fabricate ceramic tape and then sintered by microwave and conventional methods. Both dielectric and piezoelectric properties of PZT ceramic tapes were studied in terms of sintering process. X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) show the PZT perovskite phase with smaller grain size and dense microstructure can be obtained at a lower sintering temperature by microwave process. It was also observed that shrinkage ratio and bulk density of the tapes sintered at 800 °C were obtained about 19% and 7.46 g/cm³ by the microwave heating method, respectively, that is corresponding to those values of sintered PZT tapes at 950 °C by conventional process. Moreover, the dielectric constant and maximum permittivity are increased about 30% as compared with conventional processing method. The experimental results demonstrated that the characteristics of the PZT tapes could be significantly improved by microwave heating method. These results demonstrate that such a simple approach can upswing the piezoelectric and dielectric properties of these tapes by using microwave process with a short heating time.     

The production of a carbon-coated alumina foam

A method for producing ultra light carbon-coated alumina foam with a density of 0.04 g cm⁻³ and 99% porosity has been developed. It was synthesised from an aqueous aluminum nitrate–sucrose solution. The resin formed by heating this solution underwent foaming and set into solid green foam, which was sintered in the temperature range 1073–1873 K. The thermogram obtained by heating the green foam in argon showed 62 wt% mass loss occurring in three stages. The sintered foam constituted 81 wt% of γ-alumina in three-dimensional network and 19 wt% of carbon present as coating over the alumina framework. Phase analysis by X-ray diffraction revealed that carbon is in outer phase and γ-alumina is in the inner phase. Surface morphology of this foam, examined by scanning electron microscope showed open, fully interconnected and near spherical pores held together by hexagonal edges with a 300 μm average pore size. Energy dispersive X-ray spectroscopy revealed peaks corresponding to carbon, oxygen and aluminum indicating that the foam is free from nitrogen impurity. The surface concentration of carbon is nearly 85 wt% while it coating thickness is about 10 μm.     

Microwave-assisted synthesis of nanosized α-Al2O3

Nanosized alumina powder was prepared from a mixture of aluminium nitrate and carbon black through microwave heating (2.45 GHz and 900 W) for different times. The products were characterized by powder X-ray diffraction. The results showed that γ-Al₂O₃ was the main phase for powder samples heated for 4 and 6 min. When heating was extended to 8 min, weak peaks of α-Al₂O₃ also appeared. For heating times longer than 10 min, α-Al₂O₃ was the only crystalline phase present. The resultant particles were observed by SEM and TEM methods. The average particle size was found to be 96 nm. The surface area of powder was 48 m²/g after 15 min heating.     

Facile preparation of Bi nanoparticles by novel cathodic dispersion of bulk bismuth electrodes

A novel electrochemical approach has been developed to prepare clean bismuth nanoparticles (NPs) with a bulk Bi electrode in a 0.5 mol dm⁻³ NaOH solution under highly cathodic polarization of −8 V versus a saturated mercurous sulfate electrode, requiring no any precursor ions and organic protective agents. The bulk Bi electrode can be facilely dispersed into Bi NPs at the condition of intensive hydrogen evolution. This cathodic dispersion of the bulk Bi electrode involves the formation and decomposition of unstable bismuth hydrides and the aggregation of atomic bismuth from the decomposition. Moreover, Bi₂O₃ NPs have also been achieved by heating the precursor Bi NPs. Field-emission scanning electron microscopy, transmission electron microscope and X-ray diffraction were used to characterize these NPs. The as-prepared Bi NPs mainly existed in rhombohedral phase.     

Interactions of Carbaryl with homoionic montmorillonite

Adsorption and catalytic degradation of the insecticide Carbaryl on montmorillonite self-supporting films (Upton, Wyoming) saturated with different cations (Al³⁺, Ca²⁺, Cu²⁺, Na⁺) was studied using thin-layer chromatography, X-ray diffraction, infrared and mass spectroscopy techniques. Carbaryl is adsorbed at room temperature by a coordination bond, through a water bridge, between the C=O group and the exchangeable cation. X-ray diffraction patterns showed that the molecule is always intercalated in the smectite layers except for Na-montmorillonite. On moderate heating (90°C for 30 h) the Carbaryl adsorbed on Cu- and Al-montmorillonite decomposes to CO₂, N-methylammonium cation, and 1-naphthol and polymerization products, di- and tri-condensate of 1-naphthol, are formed. By contrast for Ca- and Na-montmorillonite systems no degradation of Carbaryl was observed on heating at 90°C for 30 h. The Carbaryl decomposition can be ascribed to the concurrent effect, enhanced by dehydration, of the stronger polarizing power of Cu²⁺ and Al³⁺ ions and the acidity of the residual solvation water.     

The System UO2-ZrO2

A phase diagram is proposed for the system UO₂-ZrO₂ on the basis of earlier work and the results of new studies in which the mixed oxides were melted in a solar furnace to avoid contamination. X-ray diffraction measurements were made on specimens melted in helium and on the same specimens after heating to 1350°C. in helium. The system shows a narrow two-phase region about the eutectic at high temperatures which increases in extent at lower temperatures. The high-temperature form of zirconia cannot be stabilized by the addition of UO₂.     

A co-precipitation technique to prepare BiNbO4 powders

A simple co-precipitation technique was successfully used for the preparation of pure ultrafine single phase BiNbO₄. A standard ammonium hydroxide solution was used to precipitate Bi³⁺ and Ta⁵⁺ cations as hydroxides simultaneously under basic conditions. For comparison, BN powders were also prepared by the traditional solid-state method. It is observed that the co-precipitation technique produces BiNbO₄ on heating at 600 °C, whereas complete phase formation occurs only at 800 °C in the solid-state method. The phase contents and lattice parameters were studied by powder X-ray diffraction (XRD).     

Structural investigation of nanocrystalline diamond/amorphous carbon composite films

Nanocrystalline diamond/amorphous carbon (NCD/a-C) composite films have been prepared by microwave plasma chemical vapor deposition (MWCVD) from methane/nitrogen mixtures. The complex nature of the coatings required the application of a variety of complementary analytical techniques in order to elucidate their structure. The crystallinity of the samples was studied by selected-area electron diffraction (SAED). The diffraction patterns revealed the presence of diamond crystallites within the films. From the images taken by transmission electron microscopy (TEM) the crystallite size was determined to be on the order of 3–5 nm. The results were confirmed by X-ray diffraction (XRD) measurements exhibiting broad (111) and (220) peaks of diamond from which the average size of the crystallites was calculated. The grain boundary width is 1–1.5 nm as observed by TEM images which corresponds to a matrix volume fraction of about 40–50%. This correlates very well with the crystalline phase content of about 50% in the films estimated from their density (2.75 g/cm³ as determined by X-ray reflectivity). The bonding structure of the composite films was studied by electron energy loss spectroscopy (EELS) in the region of carbon core level. The spectra were dominated by a peak at 292 eV indicating the diamond nature of the investigated films. In addition, the spectra of NCD/a-C films possessed a shoulder at 284 eV due to the presence of a small sp² bonded fraction. This phase was identified also by X-ray photoelectron spectroscopy (XPS). The sp²/sp³ ratio was on the order of 10% as determined by deconvolution of the C1s XPS peak.     

Electric field-assisted solid-state reaction of BaCO3-TiO2 system

We report phase transition process during the solid-state reaction of BaCO₃-TiO₂ system under the assistance of electric field. Experiments were conducted at a constant heating rate with preset field strength and current limit. Solid-state reaction was completed upon reactive flash sintering taking place at ~1002℃ under 200 V/cm. Hexagonal BaTiO₃ phase, which rarely occurs at such temperatures, was obtained after flash sintering at a current density of 23.5 mA/mm². It is speculated that oxygen deficiency during flash sintering triggered cubic-to-hexagonal transition of BaTiO₃. Furthermore, X-ray diffraction results show that solid-state reaction takes place prior to flash sintering. Electric field could accelerate the reaction but did not alter the sequence of phase evolution.     

Assessment of crystallographic and electronic phase stability of shock wave loaded cubic cerium oxide nanoparticles

Rapid progress has been documented during the last couple of years in understanding the crystallographic structural features of a few functional materials that have been achieved under dynamic shock wave loaded conditions. In this context, we report the crystallographic and electronic phase stability of shock wave loaded Cerium oxide nano-crystalline (CeO₂ NPs) material and the results have been evaluated by X-ray diffraction (XRD), Raman spectroscopy and ultra-violet diffuse reflectance spectroscopy (UV-DRS). XRD and Raman spectroscopic results show that the title material doesn't undergo any crystallographic phase transitions. UV-DRS spectral results demonstrate that the Ce⁴⁺ ionic state is not affected by the impact of shock waves. The obtained FE-SEM micrographs provide the substantiation for the stability of the sample. Based on the observed results, the title material can be suggested for the making of medical glassware, spaceship windows and technological applications of coating.     

Mechanochemical activation of mixtures of wolframite (FeWO4) with carbon,studied by 57Fe Mössbauer spectroscopy

The effect of mechanochemical activation (high-energy grinding) on mixtures of natural FeWO₄ with two forms of carbon has been investigated by X-ray powder diffraction and Mössbauer spectroscopy. The crystallinity of the mechanically activated mixtures, which have previously been found to exhibit enhanced reactivity as precursors for carbothermal production of tungsten carbide, is shown by X-ray powder diffraction to decrease on grinding, but without detectable formation of new crystalline phases. Mössbauer spectroscopy shows that the grinding process is accompanied by the appearance of an unexpected new singlet resonance, attributed to the formation of dilute FeC regions. The Mössbauer spectra also show that mechanochemical activation under the present conditions results in progressive oxidation of the Fe²⁺ in the wolframite to Fe³⁺; this oxidation is more marked in wolframite ground in the absence of carbon, suggesting that the latter exerts an oxygen-scavenging effect on the system. Similar results are obtained irrespective of whether the carbon source is activated carbon or graphite. The crystallization of iron tungsten carbides on subsequent heating of the ground mixtures in argon suggests that the regions identified by Mössbauer spectroscopy as containing iron–carbon interactions may also be associated with tungsten.     

27Al and 29Si MAS–NMR studies of structural changes in hybrid aluminosilicate gels

Aluminosilicate gels with stoichiometric and nonstoichiometric compositions were synthesized by means of colloidal sol-gel method and their mullitization behavior was studied by X-ray diffraction (XRD), ²⁷Al and ²⁹Si magic angle spinning nuclear magnetic resonance (MAS–NMR) experiments. Particular attention was given to the structural changes of matrix accompanying the formation of mullite. The various coordinated Al occupancies were clarified by simulating the ²⁷Al MAS–NMR spectra with Gaussian lines. The results demonstrate that the so-synthesized aluminosilicate gel is a hybrid gel containing a mixture of a single-phase gel and a diphasic gel. The mullitization of so-formed hybrid gel exhibits a consecutive one-step conversion process, but not a two-step process, much similar to that of a true diphasic mullite gel. The mullite formation from hybrid aluminosilicate gel mainly depends on the nature of dominant matrix part, but not on the nature of minor matrix part in gel. During the formation process of mullite, amorphous Si-rich phase appears as a transitional phase. The effects of gel composition and heating rate on the phase transformation behavior of hybrid aluminosilicate gel were also discussed here.     

Spark plasma sintering of titanium nitride in nitrogen: Does it affect the sinterability and the mechanical properties?

Titanium nitride ceramics have an intrinsic interest due to its optical and structural applications. However, the conditions for sintering of dense pieces are not still clarified. This research work is focused on the spark plasma sintering (SPS) of near-fully dense fine-grained TiN. The main goal is giving a response to a longstanding debate: can the external atmosphere favor sintering? Different sintering atmospheres, either vacuum or a nitrogen flow, have been used during SPS heating to this purpose. X ray diffraction analysis has showed the presence of TiN as the main phase with traces of Ti₄O₇ in optimal SPS conditions (1600?°C, one minute dwell time). Our results show that the use of a nitrogen flow while heating can improve sinterability very slightly, but mechanical properties are essentially unaltered within the experimental uncertainty. The hardness reaches values as high as 20GPa whereas fracture toughness can be evaluated around 4?MPam^1/2.     

Preparation and characterization of nano-sized LiFePO4 by low heating solid-state coordination method and microwave heating

The precursors of LiFePO₄ were prepared by low heating solid-state coordination method using lithium acetate, ammonium dihydric phosphate, ferrous oxalate and citric acid as raw materials. Olivine phase LiFePO₄ as a cathode material for lithium-ion batteries was successfully synthesized by microwave heating in a few minutes. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to characterize its structure and morphology. Cyclic voltammetry (CV) and charge-discharge cycling performance were used to characterize its electrochemical properties. The results showed that the grain size of the optimal sample was about 40-50 nm, and the as-prepared particles were homogeneous. The nano-sized LiFePO₄ obtained has a high electrochemical capacity (125 mAh g⁻¹) and stable cycle ability.     

Synthesis and characterization of nanoflaky maghemite (γ-Fe2O3) as a versatile anode for Li-ion batteries

In this study, nanoflaky maghemite (γ-Fe₂O₃) was successfully prepared by heating of synthesized lepidocrocite (γ-FeO(OH)). Once maghemite obtained, the electrochemical performance of nanoflaky maghemite, as an anode for Li-ion batteries, was investigated. Synthesis of lepidocrocite was optimized by adjusting the heating time and ratio of ethylene glycol (EG) to water in solution. The results revealed that with equal ratio of EG to water, the obtained phase was crystalline lepidocrocite whereas in other ratios lepidocrocite was not the only emerged phase. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) results revealed that increasing heating time has no effect on morphology. This increment only led to the slight crystallite growth and agglomeration of precipitation. The optimized lepidocrocite were heated at 230?°C for 2?h to form maghemite, which was confirmed by using XRD. FESEM, high-resolution transmission electron microscopy, and nitrogen adsorption-desorption results disclosed that the particles have flaky morphology with thickness of less than 10?nm and surface area of 105?m² g^?1. Cyclic voltammetry results of anode body (prepared using nanoflaky maghemite) demonstrated reversible formation pathway of iron and lithium oxide through discharging and charging. Moreover, galvanostatic charge–discharge cycling showed a reversible capacity of about 480?mAh?g^?1 after 50 cycles at current density of 500?mA?g^?1. Good cyclability, and capacity retention of the anode is due to the nananometric size and flaky shape of the maghemite particles. These particles’ shape made it easier for them to expand and contract in thickness direction with minimized destructions imposed.     

X-ray studies of multiple melting behavior of poly(butylene-2,6-naphthalate)

Multiple melting behavior of poly(butylene-2,6-naphthalate) (PBN) was studied with X-ray analysis and differential scanning calorimetry (DSC). Double endothermic peaks L and H attributed to the α-form crystal modification, a small peak attributed to the β-form crystal modification, and a new shoulder peak S at a lower temperature of peak H appeared in the DSC melting curves. Wide-angle X-ray diffraction patterns of the samples isothermally crystallized at 200 and 220 °C were obtained at a heating rate of 1 K min⁻¹, successively. In this heating process, change of crystal structure and increase of quantity of the β-form crystallites could not be observed up to the final melting. With increasing temperature, the diffraction intensity decreased gradually and then increased distinctly before a steep decrease due to the final melting. The X-ray analysis clearly proved the melt-recrystallization during heating. The β-form crystal modification was formed during slow heating process in the high temperature region.     

Thermal stability of lead sulfide nanocrystalline films

Thermally stable nanocrystalline films of lead sulfide PbS were prepared using the chemical deposition method. The thickness of the films measured by interferometry was approximately equal to 100 nm, and the average particle size determined from the broadening of the X-ray diffraction reflections was approximately 80 nm. X-ray diffraction analysis revealed that annealing of the film at a temperature of 350°C in air results in the formation of a protective oxide sulfate phase of the composition PbO · PbSO₄ on the surface of the film. It was established that the oxide sulfate phase prevents a further oxidation of the film and serves as an inhibitor of the growth of PbS nanoparticles upon heating up to a temperature of 500°C. The factors responsible for the high thermal stability of the sizes of nanoparticles and the optical properties of the PbS nanocrystalline film were discussed.