Comparative study of conventional and microwave sintered mullite fibres: structural study

Mullite fibres were synthesised from a mixture of aluminium, aluminium chloride and acidic silica solutions as monophasic salts using a sol–gel technique. The viscosity and rheological behaviour of the mullite precursor sol were examined. Mullite fibres were synthesised using both conventional and microwave sintering techniques. The samples were characterised by X-ray diffraction and scanning electron microscopy. Pure mullite fibres were synthesised by microwave sintering at a relatively low temperature of 1200°C. The grain size of the fibre samples sintered using the microwave technique was finer than that produced by conventional sintering. These results show that microwave sintering is a promising technique for processing mullite fibres.     

Adsorption of aluminium from wastewater by chitin and chitosan produced from silkworm chrysalides

Chitin, extracted from silkworm chrysalides, was employed for the production of a high‐purity and porous chitosan, as observed by scanning electron microscopy. Chitin and the chitosan produced from it were also analysed using ¹³C NMR spectroscopy to show the efficiency of deacetylation. The extracted chitin was investigated as an adsorbent material for aluminium removal from textile wastewater, by the column chromatographic method. After the treatment, the residual aluminium was lower than the limitation criterion of 0.2 mg L^?1. The isotherms of adsorption on chitin and chitosan surfaces were investigated and the best fits were observed using the Freundlich isotherm. At pH 5.0, the maximum adsorption capacity was 21.3 mg of aluminium per gram of chitosan over 70 h of experiments. Copyright © 2006 Society of Chemical Industry     

X-ray photoelectron spectroscopy of aluminium-substituted tobermorite

We have synthesised 11-Å tobermorite hydrothermally, both pure and with increasing isomorphic substitution of aluminium for silicon. The samples were analysed by X-ray photoelectron spectroscopy (XPS). Aluminium was found, on the basis of its Al 2p binding energies, to be tetrahedrally coordinated. We observed no changes in Ca/(Si+Al) ratio upon aluminium substitution, implying that charge balancing does not occur via the incorporation of additional calcium into the tobermorite structure. Aluminium substitution into the silicate structure led to a decrease in Si 2p binding energies. This implies one of two alternatives. Firstly, that charge balancing occurs via substitution of OH⁻ for O²⁻ in the tobermorite structure. Secondly, the presence of aluminium in the tobermorite structure may negatively influence the degree of silicate polymerisation. Further work is required to determine which of these possibilities is the case.     

Influence of Particle Size and Mixing Technology on Combustion of HMX/Al Compositions

In this work, two widely used components of high‐energy condensed systems – HMX and aluminium – were studied. Morphology, thermal behaviour, chemical purity and combustion parameters of HMX as a monopropellant and Al/HMX as a binary system were investigated using particles of different sizes. It was shown that in spite of the differences in composition and particle size, combustion velocities are almost identical for micrometer‐sized HMX (m‐HMX) and ultrafine HMX (u‐HMX) monopropellants under pressure from 2 to 10 MPa. Replacement of the micrometer‐sized aluminium with ultrafine one in the system with m‐HMX leads to a burning rate increase by a factor of 2.5 and the combustion completeness raise by a factor of 4. Two mixing techniques to prepare binary Al/HMX compositions were applied: conventional and ‘wet’ technique with ultrasonic processing in liquid. Applying wet mixing results in a burning rate increase of 18% compared to the conventional mixing for systems with ultrafine metal. The influence of the component's particle size and the composition microstructure on the burning rate of energetic systems is discussed and analysed.     

铝粉对刚玉-氮化硅复合材料微观结构和性能的影响

借鉴"过渡塑性相工艺"思想,在刚玉-氮化砖复合材料中引入12.5%(质量分数)的铝粉,研究了铝粉对刚玉-氮化硅复合材料成型性能以及1 600℃空气中烧成后样品的体积密度、显气孔率和耐压强度的影响:利用X射线衍射仪和扫描电镜对材料的物相和微观结构进行了分析.结果表明:在刚玉-氮化硅复合材料中引入铝粉,有利于成型过程中孔隙...     

Structural and ion transport properties of sodium ion conducting Na2MTeO6 (M= MgNi and MgZn) solid electrolytes

Solid-state electrolytes Na₂MTeO₆ (M = MgNi and MgZn) were prepared via a conventional solid-state reaction method. Structural properties of the samples were investigated by using powder X-ray diffraction (XRD), Raman, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS) techniques. XPS and XRD studies indicate the phase pure hexagonal layered P2-type structure of samples. Raman and FTIR spectroscopy reveal the possible bending and stretching vibration modes for Te–O and other metal oxides. The ion transport properties of the solid electrolytes were investigated by using AC impedance spectroscopy. The electrical properties were examined by means of classical brick layer model. The specific grain conductivity (σ_g) is found to be 2.13 × 10⁻⁵ S cm⁻¹ and 0.90 × 10⁻⁵ S cm⁻¹ at 20 °C for Na₂MgNiTeO₆ and Na₂MgZnTeO₆ electrolytes, respectively. The activation energy of σ_g for Na₂MgNiTeO₆ and Na₂MgZnTeO₆ is found to be 0.59 eV and 0.36 eV respectively for the temperature below 30 °C. Summerfield AC conductivity scaling analysis of samples is performed. These electrolytes could be potential candidates in solid-state Na⁺ battery applications.     

Sol-gel preparation and thermo-mechanical properties of porous xAl2O3–ySiO2 coatings on SiC Hi-Nicalon fibres

Porous thin films of mixed aluminium silica oxides were elaborated by the sol-gel process from aluminium tri-sec-butoxide and tetraethylorthosilicate on Hi-Nicalon fibres. The porosity was generated by addition of a surfactant, namely cetyltrimethylammonium bromide (CTAB). SiC Hi-Nicalon fibres were coated by the dip-coating technique. After annealing in air (500–1200 °C) crack-free coatings were observed, with a thickness in the range 100–1000 nm. The fibres were tensile tested and results were analysed by the Weibull statistic. They showed good mechanical properties compared to the commercial fibres. The systems were characterized by thermal gravimetry, differential scanning calorimetry, X-ray diffraction, BET and scanning electron microscopy. The powders obtained in the same conditions as the coatings were highly porous with surface areas in the range 540–150 m²/g depending on the annealing temperature (400–1000 °C).     

Structure and catalytic activity of Al-MCM-48 materials synthesised at room temperature: Influence of the aluminium source and calcination conditions

MCM-48 aluminosilicates with different aluminium contents were synthesised by a room temperature procedure using tetraethoxysilane and aluminium sulfate, isopropoxide or tert-butoxide as metal sources. The samples were characterised by X-ray diffraction, nitrogen adsorption at 77 K, and ²⁷Al MAS NMR and the catalytic activity tested in the reaction of 1-butene double bond position isomerisation. The influence of the synthesis time and calcination conditions, such as heating rate and time at final temperature, on the structural and catalytic properties of the materials was also evaluated. Aluminium isopropoxide and sulfate allowed the preparation of well structured Al-MCM-48 materials, with high specific pore volume and uniform pore size, and with the majority of the aluminium incorporated in tetracoordinated environment after calcination, at least down to Si/Al of 15. The highest initial conversions were found for samples with Si/Al = 20 and 30 prepared with aluminium isopropoxide and calcined using a heating rate of 3 K min⁻¹, with those of samples prepared with aluminium sulfate being slightly lower. Al-MCM-48 materials with high specific pore volume and uniform size were also synthesised using aluminium tert-butoxide, but the materials were less well ordered, presented a higher proportion of hexa- and pentacoordinated Al species and exhibited lower initial conversions, independently of the synthesis time or calcination conditions tested. It is concluded that aluminium isopropoxide and sulfate are more adequate metal sources than aluminium tert-butoxide to prepare Al-MCM-48 catalysts by this room temperature method and a calcination heating rate of 3 K min⁻¹ instead of 1 K min⁻¹ produces more effectively active catalysts.     

Technical and economic comparison of conventional and electrochemical coagulation processes

BACKGROUND: Electrocoagulation is an alternative to the conventional coagulation method, to treat different types of waters and wastewaters. Although there have been many reports on the technical suitability of electrocoagulation, no study has made a direct comparison of the economics of the two processes. RESULTS: Concerning the technical feasibility, no significant differences were found in the results achieved by the two technologies in the treatment of synthetic suspensions, emulsions and solutions of dyes, when the same values of pH and aluminium concentration were adopted in the reaction systems. Regarding the economic comparison, the electrocoagulation process presents lower operating costs for low and intermediate aluminium doses, but results depend on the particular coagulant reagent selected at high doses. The highest operational costs were obtained with conventional coagulation with aluminium sulphate (in the range 3–60 mg dm^?3 aluminium). Comparing electrocoagulation and conventional coagulation with aluminium polychloride, the electrocoagulation process presents lower operational costs for low and intermediate doses. However, this situation changes for high aluminium doses. CONCLUSION: Coagulation and electrocoagulation techniques give very similar yields in the removal of different types of pollutants; therefore an economic comparison is of major importance in order to recommend the use of one of the technologies. Nevertheless, it has to be noted that operational costs are of the same order of magnitude for the two processes. Thus, the cost of the electrocoagulation process compares favourably with that of conventional coagulation for small coagulant demands, but the results at high doses depend on the particular coagulant reagent selected. Copyright © 2008 Society of Chemical Industry     

Quantitative description and modification of cocarbonization compatibility of pitch fractions

The cocarbonization properties of the benzene-soluble fractions (BS) of several pitches with benzene-insoluble fractions (BI) of SRC pitches were studied, changing their mixing ratio in order to evaluate their compatibility for needle-coke formation; the smallest BS content required may reflect its cocarbonization ability to provide the carbonizing mixture with fusibility or suitable reactivity for this purpose. More than 90% of BS content was required for the BS—BI mixture of smallest compatibility, whereas only 10% was enough for the mixture of best compatibility. Ethylene tar BS of poor compatibility with solvent-refined-coal BI could be modified and improved for this purpose by catalytic reaction with aluminium chloride at 260 ° C, whereas ferric or cupric chloride failed. Based on the analytical study of BS and these results, the compatibility of pitch fractions is discussed from the viewpoint of pitch structure.     

Pillaring of smectites using an aluminium oligomer: A study of pillar density and thermal stability

Two smectite samples having different layer charges were pillared using hydroxy aluminium oligomers at a OH/Al ratio of 2.5 and at pH 4.3 to 4.6. Pillaring was carried out at different conditions such as ageing, temperature and base addition time of the pillaring solution, and also in the presence of nonionic surfactant polyoxyethylene sorbitanmonooleate (Tween-80). The primary objective of preparing at different conditions was to introduce varied quantities of aluminium oligomer between the layers and to study its effect on the properties of the pillared products. A simple method has been followed to estimate the amount of interlayer aluminium. A quantity called pillar density number (PDN) based on the ratio of interlayer Al adsorbed to CEC of the parent clay has been effectively used to evaluate the nature of the resulting pillared product. PDN, for a given clay, was found to correlate well with the sharpness of the d(0001) peaks for the air dried samples. The calculated number of pillars, varied from 3.00 × 10¹⁸ to 5.32 × 10¹⁸ per meq charge. The present study shows that a higher value of PDN is indicative of better thermal stability. Pillar density number may be conveniently used as a measure of the thermal stability of pillared samples.     

Structural,thermal and thermoluminescence response of transition and alkaline earth metals activated on aluminium borate [Al2(B4O7)3:Mn,Mg]

Aluminium borate doped with manganese (Mn) and magnesium (Mg) at different concentrations are studied. The samples were synthesized by solid state sintering. The structure, morphology and crystallite size of the aluminium borate are affected by the dopants used. The crystallite size values calculated for different concentrations of manganese and magnesium used in doping of aluminium borate are within a range of 32.5–35.1 nm and 21.3–28.7 nm respectively. The particle size obtained using a scanning electron spectroscopy for Mn and Mg-doped aluminium borate are in the range of 30–40 nm and 20–30 nm respectively. A loss in weight from the thermal analysis performed for Mn and Mg-doped aluminium borate are observed to be 10.43% and 20.06%. The thermoluminescence glow peaks from all the samples measured at 1 °C.s^?1 following irradiation to 50 Gy showed a prominent glow peak at 96 °C with minor peak observed at higher temperature (178 °C) region of the glow curve. The activation energy for Mn and Mg-doped aluminium borate were determined to be approximately 0.78 ± 0.30 eV and 0.76 ± 0.25 eV by using the initial rise, glow curve deconvolution and variable heating rate method. The dose responses were considered from 1 to 300 Gy for Mn (0.4%) and Mg (0.3%) doped aluminium borate and were further studied by using the g(D) and f(D) functions.     

Integrated instrumental analysis of soft brown coals

A method for the simultaneous determination of calorific value Q^r, ash yieldA^r and total water content W^r_t of soft brown coals is described. The method involves instrumental analysis of brown coal samples using neutron thermalization and gamma back-scattering techniques. Over 80 coal samples (1.1 kg) were analysed, having Q^rvalues up to 15.5 MJ kg^?1,A^r ranging from 3.6 to 76.1 wt% and W^r_t ranging from 11.4 to 61.7 wt%. A comparison of the results from the instrumental method with those of standard laboratory analyses is given, followed by a discussion of the accuracy of the method and of possible ways for improving it.     

Evidence for non-site-isolation in ZSM-5 from ion-exchange and catalytic studies

Ion exchange of HZSM-5 samples with alkali metal cations, using metal chloride solutions, results in partially exchanged zeolites, MHZSM-5, M = Li, Na, K or Cs. The degree of exchange is found to increase with increasing ionic radius of the cations. The catalytic properties of the alkalized zeolites were evaluated using the reaction conditions under which the catalytic activity of the HZSM-5 samples in terms of n-hexane cracking is proportional to the aluminium content. From the residual catalytic activity exhibited by the Na-, K- and CsHZSM-5 samples it is concluded that each of the larger Na⁺, K⁺ and Cs⁺ ions is influencing more than one AlO ₄ ^– tetrahedron, implying that the aluminium sites in ZSM-5 are not isolated. The ion-exchange results are then interpreted in terms of non-isolated aluminium sites. The ion-exchange and catalytic properties of the zeolites as a function of aluminium content are also discussed.     

Study of arsenic in Famille rose porcelain from the Imperial Palace of Qing Dynasty,Beijing, China

Famille rose porcelain from the imperial workshop was one of the symbols of the highest level of manufacturing techniques in ancient China. It was very precious and only owned by the royals at the early stage. The major feature of famille rose is the use of opaque white pigment. Considered to originate in Europe, this technique was a witness of technological exchanges between China and European countries in the 17th–18th centuries. However, limited by its preciousness, most of the previous studies focused on the chemical composition of famille rose relics via nondestructive analysis methods. In this work, selected samples excavated at the Forbidden City of China were analysed by microscopy observation, Laser Ablation Inductive Coupled Plasma-Atomic Emission Spectrometry (LA-ICP-AES), synchrotron radiation X-ray Absorption Near-Edge Spectroscopy (XANES) and micro X-ray Diffraction (μXRD). The results revealed that two painting methods which related to Chinese and European techniques were applied. Chemical composition indicate that opaque white is a kind of arsenic-lead white. Moreover, the synchrotron radiation results show that As⁵⁺ is the major state in opaque white and exists mostly probably as AsO₄^3- -ion.     

Microstructural evaluation and thermal oxidation behaviors of YSZ/NiCoCrAlYTa coatings deposited by different thermal techniques

In this paper, two coating techniques, the high velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques, were used to deposit a bond coat of NiCoCrAlYTa on the Inconel 625 substrate, followed by applying a topcoat of yttria-stabilized zirconia (YSZ). The samples were preoxidized in an argon-controlled furnace at a temperature of 1000 °C for 12 and 24 h to characterize the microstructure of a thermally grown oxide (TGO) using the two coating techniques. The most suitable preoxidized samples were further tested for isothermal oxidation at 1000 °C for up to 120 h, and a hot corrosion test was performed at 1000 °C for up to 52 h or until spalling occurred. As-sprayed and oxidized samples prepared with different coating techniques were evaluated in terms of their microstructure using different characterization methods, such as field emission scanning electron microscopy (FESEM), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) equipped with energy dispersive X-ray and X-ray diffraction (XRD) analyses. In addition, the mechanical properties of these samples were evaluated using adhesion tests. The results show that the YSZ/NiCoCrAlYTa coating applied with the HVOF technique forms a more thin and continuous layer of TGO than that obtained when applying a YSZ/NiCoCrAlYTa coating using the APS technique, indicating that a severe brittle oxidation interface exists between the two layers. The results also indicate that the mechanical strength obtained from the adhesion test of the coated samples is observably affected by the oxidation behaviors obtained with the different deposition techniques chosen.     

Effect of salting techniques on salt uptake and drying kinetics of African catfish (Clarias gariepinus)

Effect of dry salting (DS) and brine salting (BS) techniques on salt uptake and drying kinetics of African catfish (ACF) was investigated. Salt uptake kinetics during BS using the Peleg model at different salt concentrations (0.15–0.27 gNaCl/g) and salting temperatures (30–38 °C) was studied while the drying experiments took place at 60 °C and 1.5 m/s under forced convection. Salt uptake was affected by brine concentration, salting time and temperature during the BS technique but its diffusion among the treated samples was similar. Salt uptake was rapid at the initial salting time but decreases as the process progresses. The Peleg model predicted the salt uptake of ACF better than Zugarramurdi and Lupin model during BS based on high values of coefficient of determination (R²) of 0.930–0.999, very low Chi square (χ²) of 0.16–8.0 × 10⁻¹² and low root mean square error (RMSE) of 0.97–13.93 × 10⁻². The effective salt diffusivity was observed to vary between 1.1 and 9.72 × 10⁻⁷ m²/s. Significant differences in the drying pattern was not observed for both techniques but took place in the falling rate period, although drying rate was faster in DS samples. The Page and modified Page models based on high R² (0.999), low χ² (2 × 10⁻²) and low root mean square error of 1.05 × 10⁻⁴ predicted appropriately the drying kinetics of ACF irrespective of the technique used.     

Galvanostatic electrodeposition of aluminium nano-rods for Li-ion three-dimensional micro-battery current collectors

Constant current and pulsed current electrodeposition of aluminium nano-rods, for use as three-dimensional (3D) Li-ion micro-battery current collectors, have been studied using an ionic liquid electrolyte (1-ethyl-3-methylimidazolium chloride/aluminium chloride) and a template consisting of a commercial alumina membrane. It is shown that the homogeneity of the height of the rods can be improved significantly by inclusion of a short (i.e. 50 ms) potential pulse prior to the controlled current deposition step. The latter potential step increased the number of aluminium nuclei on the aluminium substrate and the best results were obtained for a potential of −0.9 V vs. Al/Al³⁺. The obtained nanostructured surfaces, which were characterized using electron microscopy and X-ray diffraction, consisted of parallel aligned aluminium nano-rods homogeneously distributed over the entire surface of the substrate. A narrower height distribution for the rods was obtained using a pulsed galvanostatic approach then when using a constant current, most likely due to the less favourable diffusion conditions in the latter case. The results also indicate that depletion and iR drop effects within the nano-pores result in a more homogeneous height distribution. It is concluded that the height distribution of the nano-rods is controlled by a combination of the nucleation probability in each pore at the start of the experiment, and the homogeneity of the diameters of the pores within the commercial alumina membranes employed as the electrodeposition template.     

Chemical structure of bitumen-derived asphaltenes by nuclear magnetic resonance spectroscopy and X-ray diffractometry

Asphaltene samples obtained from bitumen processed at three Indian refineries were characterized for chemical composition and structure by nuclear magnetic resonance (n.m.r.) spectroscopy and X-ray diffractometry (XRD). The average structural parameters were obtained by combined ¹H, ¹³C and DEPT spectral editing techniques. New equations were used for the estimation of n.m.r. average structure parameters. The macrostructure and crystalline parameters of these samples were obtained by XRD. A combined n.m.r. and XRD procedure was used to estimate the size of the average aromatic structural unit. Asphaltenes from one of the bitumens (ASP-D) was found to have different structural parameters from those of the asphaltenes from the other two bitumens. The number of aromatic rings per unit sheet in ASP-D was eight, compared with 13 for both ASP-M and ASP-H. XRD data indicated that the aromatic sheets are randomly oriented in ASP-D. The structural parameters allowed a model structure of the asphaltenes to be constructed.     

Low-energy He-ion beam modifications the surface properties of biomaterial

In the present work, ultra-high-molecular-weight polyethylene (UHMWPE) films were irradiated with 130 keV He ions. The fluence of the ion beam was ranged from 1 × 10¹² to 1 × 10¹⁶ cm^?2. The chemical, morphological, and crystallite structure changes resulted from the ion bombardment were obtained using different spectroscopic techniques. These techniques were Fourier transform infrared spectrometer, scanning electron microscope, X-ray diffraction, and UV–vis spectrophotometry. The surface free energy for untreated and ion-beam-treated samples was determined by means of contact angle measurements of three different liquids. Our results showed a decrease in the crystallinity of UHMWPE and formation of C=O groups on the polymer surface for modified samples as well. A remarkable shifting in the UV–vis spectra toward lower energy and increase in the optical absorption were observed as the ion fluence increases. Measurements of the contact angle indicate remarkable increase in the surface free energy as a function of ion fluence.