In situ wetting of aluminium during the growth of porous alumina by anodic oxidation

The growth of nanoporous alumina at an aluminium surface which is not completely covered by an electrolyte has been investigated. At one point the electrolyte forms three interfaces: oxide/electrolyte, metal/electrolyte, electrolyte/air. At this three-interfaces-point a self-wetting induced oxide growth occurs. The wetting increases up to 7 mm from the electrolyte contact edge. At this final stage of wetting an equilibrium between the wetting induced flow (bottom-up) and the gravity-driven flow (top-down) is reached. The thickness of the nonporous layer decreases with the distance from the starting point.     

Anodic formation of low-aspect-ratio porous alumina films for metal-oxide sensor application

Thin nanoporous anodic alumina films, of low aspect ratio (1:1), with two distinctive pore sizes and morphologies were prepared by two-step constant-current anodising of aluminium layers on SiO₂/Si substrates in 0.4 mol dm⁻³ tartaric (TA) and malonic acid (MA) electrolytes and then modified by open-circuit dissolution. The anodic films were employed as a support material for sputtering-deposition of thin WO₃ layers in view of exploiting their gas sensing properties. The films and deposits were characterized by scanning electron microscopy, X-ray diffraction and electric resistance measurements at fixed temperatures in the range of 100-300 °C upon NH₃ and CO gas exposures. Test sensors prepared from the annealed and stabilized alumina-supported WO₃ active layers were insensitive to CO but showed considerably enhanced responses to NH₃ at 300 °C, the sensitivity depending upon the anodic film nature, the pore size and the surface morphology. The increased sensor sensitivity is due to the substantially enlarged film surface area of the TA-supported WO₃ films and the nanostructured, camomile-like morphology of the MA-supported WO₃ films. Sensing mechanisms in the alumina-supported WO₃ active layers are discussed.     

A study on the formation of titania nanopillars during porous anodic alumina through-mask anodization of Ti substrates

The formation of anodic titania during porous anodic alumina (PAA) through-mask anodization has been analysed for varying anodization conditions on mechanically polished bulk Ti surfaces. Titania nanopillars were formed through the porous masks in both oxalic and phosphoric acid electrolytes. For applied potentials above 40 V the titania formed along narrow channels through the alumina pore bottoms resulting in root-like attachments of the titania pillars to the Ti substrate. We further demonstrated that high-field anodization can be used for PAA through-mask anodization. The formation of titania changed with increased current density which resulted in more efficient oxide growth through the alumina pores. When the Al/Ti samples were immersed in the electrolyte without exclusively exposing the Al surface to the electrolyte the titania formed solely on top of the alumina pore bottoms which resulted in that the titania structures were detached from the Ti substrates during selective removal of the PAA templates.     

Stress-affected and stress-affecting instabilities during the growth of anodic oxide films

The objective of the current paper is to (re-)address the question whether internal stress is a fundamental parameter driving some generic cases of growth instabilities commonly encountered during the growth of anodic oxide films, namely breakdown and pore initiation. This has been done by unraveling possible correlations between a key electrochemical characteristic of the instability event and the internal stress evolution, the latter being measured in situ during the very same anodising experiment. As such, we have been able to make more conclusive statements as compared to the merely speculative arguments in the literature whether these instabilities have a mechanical origin or not. In the case of breakdown, the two well-documented types of breakdown events encountered during galvanostatic Zr anodising were both found to be stress-affected: instantaneous compressive internal stresses were identified as the driving force for both the densifying phase transformation responsible for type-I breakdown, as well as for the buckling-induced delamination events observed during type-II breakdown. Pore initiation in anodic Al₂O₃ on the other hand was found not be stress-affected. Instead, pore formation is rather believed to induce itself a modification in the mechanical behaviour, and was therefore classified as stress-affecting.     

Effects of a magnetic field on growth of porous alumina films on aluminum

The effects induced by a magnetic field on the oxide film growth on aluminum in sulfuric, oxalic, phosphoric and sulfamic acid, and on current transients during re-anodizing of porous alumina films in the barrier-type electrolyte, were studied. Aluminum films of 100 nm thickness were prepared by thermal evaporation on Si wafer substrates. We could show that the duration of the anodizing process increased by 33% during anodizing in sulfuric acid when a magnetic field was applied (0.7 T), compared to the process without a magnetic field. Interestingly, such a magnetic field effect was not found during anodizing in oxalic and sulfamic acid. The pore intervals were decreased by ca. 17% in oxalic acid. These findings were attributed to variations in electronic properties of the anodic oxide films formed in various electrolytes and interpreted on the basis of the influence of trapped electrons on the mobility of ions migrating during the film growth. The spin dependent tunneling of electrons into the surface layer of the oxide under the magnetic field could be responsible for the shifts of the current transients to lower potentials during re-anodizing of heat-treated oxalic and phosphoric acid alumina films.     

阳极氧化法制备大面积双面多孔氧化铝膜及其应用

室温下,以纯铝箔为基材,采用二步阳极氧化法,在0.3 mol/L草酸溶液中制备了大面积的双面氧化铝膜.在氧化过程中,电流呈现降低、升高、平稳、再降低的变化,最后接近于零.X射线衍射结果显示,双面氧化铝膜为无定型结构.扫描电镜结果显示:每面氧化铝膜的总厚度约为50 μm,孔径分布为50～100 nm.利用制得的双面氧化铝...     

Fabrication and structural control of anodic alumina films with inverted cone porous structure using multi-step anodizing

Porous anodic alumina (PAA) film has recently attracted much attention as a key material for the fabrication of various nanostructures. In this study, a multi-step anodization and leaching process was employed to produce three-dimensional nanometer scale structured film. During the leaching process, the porous alumina film was dipped in phosphoric acid solution for pore widening. Each anodization process was followed by this leaching process. This method produced alumina film with multi-step structure. Meanwhile, with five-step film production, the structure showed inverted cone structure. We produced the low aspect ratio pores of this structure, which would be applicable for fabrications of nanomaterials. In addition, the aspect ratio was controlled by changing the anodization duration.     

Control of the spatial distribution of porous alumina micro-domes formed during anodic oxidation

We found that micro-domes of porous alumina are self-assembled during anodic oxidation of an aluminum plate. We investigated the effects of the morphology of the initial aluminum surfaces on the formation of these micro-domes and found that the formation of micro-domes depends on the initial surface roughness of the substrate. We have also achieved spatial control over the distribution of these micro-domes through the use of artificial scratches on the initial surface. The origin of this control is the fact that micro-domes are preferentially formed inside hollow areas formed by the scratch. We investigated the inner structure of the micro-dome by separating it from the substrate. Inside the micro-domes, we observed nano-pore arrays similar to a porous alumina membrane, though the regularity of these pores is slightly worse than for the nano-pores around the micro-dome. These results indicate that the porous alumina micro-domes can be used as microscale nanoporous components.     

Preparation of ultra-active alumina of designed porous structure by successive hydrothermal and thermal treatments of porous anodic Al2O3 films

A porous anodic alumina film was prepared by the anodic oxidation of Al metal sheet in a thermostated and vigorously stirred bath of H₂SO₄ 15% (w/v) at a temperature of 25°C and a current density of 15 mA cm⁻². It had a geometric surface area of 33 cm², a surface density of pores 1.269×10¹¹ cm⁻² and the maximum limiting thickness and porosity achieved at these conditions which are 50.3 μm and 0.42, respectively. This oxide was tried in the catalytic test reaction of the decomposition of HCOOH at temperatures 270–390°C. Then, the oxide was treated hydrothermally in H₂O at 100°C for 5 h and tried in the same test reaction. The procedure of hydrothermal treatment and catalysis experiment was repeated 40 times. In all cases the oxide showed an almost exclusively dehydrative catalytic effect, 98–100%. Both the total activity of the alumina film with the aforementioned constant geometric surface area and its specific activity referred to the unit of oxide mass gave a maximum in the first and a minimum about the fourth hydrothermal treatment; then, they increased strongly with the order of hydrothermal treatment. Despite the decrease of the oxide mass during hydrothermal treatment, the final promotion of the total catalytic activity of oxide was 13.7–10.6 times that of non-treated oxide for temperatures 330–390°C. The corresponding promotion of specific activity was 31.5–24.5 times that of the non-treated oxide. The results of the present study showed that the successive hydrothermal and thermal treatments of porous anodic Al₂O₃ films produce more and more active alumina catalysts. In this way ultra-active alumina catalysts or supports can be prepared.     

Fabrication of cobalt nanowires from mixture of 1-ethyl-3-methylimidazolium chloride ionic liquid and ethylene glycol using porous anodic alumina template

Porous anodic alumina template is synthesized by electrochemical anodization of aluminum and used to grow cobalt nanowires. The cobalt nanowires produced by direct current electrodeposition are characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and physical property measurement system. Test results indicate that the average diameter of cobalt nanowires is about 45 nm, which is generally the same as the pore diameter of porous anodic alumina template, and the cobalt nanowires electrodeposited from mixture of 1-ethyl-3-methylimidazolium chloride ionic liquid and ethylene glycol have a smoother surface and better magnetic properties than cobalt nanowires electrodeposited from aqueous solution, and they show a better squareness. Therefore it can be concluded that the cobalt nanowires electrodeposited from mixture of 1-ethyl-3-methylimidazolium chloride ionic liquid and ethylene glycol using porous anodic alumina template can be used as a perpendicular magnetic recording film.     

An adaptable steady state Aspen Hysys model for the methane fuelled solid oxide fuel cell

An adaptable model for the methane fed internal reforming SOFC using the in built features of Aspen Hysys is presented in this paper. The model includes the electrochemistry, the diffusion phenomena and the reforming kinetics in detail. Three potential methods for representing the SOFC are investigated out of which the recycled reforming model is found to be capable of providing reasonable results over a wide range of operating conditions. The electrochemical model that gives good agreement with experimental data is also identified. From the simulations, it is concluded that the developed model is reasonably accurate over a wide operating range and can be used for steady state analysis. The computational challenges in the modelling are discussed. The model will be used for system level optimisation studies of the SOFC system especially in conjuncture with gas turbines and steam turbines.     

Development of a mathematical model for Bacillus circulans growth and alkaline protease production kinetics

BACKGROUND: An unstructured mathematical model was developed to understand information on the relationship between Bacillus circulans growth and metabolism‐related protease production (using logistic and Luedeking–Piret equations respectively) in a batch reactor with respect to glucose consumption and fermentation time. The objective was to develop an indispensable tool for the optimisation, control, design and analysis of alkaline protease production. RESULTS: Biomass growth and enzyme production titres changed with a change in substrate concentration. Modelling analysis of biomass and enzyme production titres at different substrate concentrations revealed significant accuracy in terms of statistical consistency and robustness with respect to fermentation kinetic profiles. CONCLUSION: With the B. circulans strain used, an economic protease yield (2837 × 10³ U g^?1) with respect to biomass and glucose ratio was achieved at low substrate concentration (10 g L^?1). The developed model could be effectively utilised for designing, controlling and up‐scaling the protease production process in high‐density fermentation in selected bioreactors with statistical consistency. Copyright © 2008 Society of Chemical Industry     

Analysis of stability of the interphase front with evaporation and exothermic reaction in the porous catalyst slab

Using a two-dimensional mathematical model and a number of simplifying assumptions, the analytical (linear) analysis of stability of the reaction-evaporation front inside the half-wetted porous catalyst slab was made. Based on the obtained spectral equation, the effect of different parameters on possible types of instability was studied.     

燃料乙醇系统模拟平台开发及应用

对典型燃料乙醇系统进行了分析,阐述了目前该系统相关全流程模拟模型的不足以及由非线性和复杂性等特征导致的系统建模难点。在此基础上,运用VC#编程工具和SQLSERVE开发了全新的燃料乙醇系统模拟平台,该平台可模拟燃料乙醇实际生产过程,能够从物质流、能量流、水流、价值流等方面对系统开展工业生态学分析。最后利用实际生产过程中出现的两个问题案例对平台进行了检验。     

Development and application starch films: PBAT with additives for evaluating the shelf life of Tommy Atkins mango in the fresh-cut state

In this study, formulations of cassava starch and poly(butylene adipate-co-terephthalate) flexible films were developed, with glycerol, coconut nanocellulose, annatto, and citric acid in different concentrations, as well as the effectiveness of the selected materials in fresh-cut mangoes storage was evaluated. The tensile strength of the different formulations varied from 1.90 (E4) to 6.65 MPa (E3c), and the strain varied from 206.31 (E1c) to 278.41% (E8); this variation was dependent on the percentage of the polymer matrix incorporated. The a_w values of the formulations ranged from 0.396 (E2) to 0.569 (E3c). The Formulations E4 and E7 (with additives) presented good properties and were selected to condition mangoes. The micrographs of these films showed regions of micropores that can facilitate the diffusion of water from the packaged product to the surface, allowing decreases in moisture and a_w, which is associated with higher color maintenance during fruit storage. E7 presented better barrier properties than E4 (lower values of WVP and water solubility) which may have influenced in a positive way to maintain the stability of the package in the studied period. E7 can be considered as a viable alternative for minimally processed mango storage. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48150.     

分段进水生物脱氮工艺稳态模型的开发与试验评价

In this article,a steady-state mathematical model was developed and experimentally evaluated to inves- tigate the effect of influent flow distribution and volume ratios of anoxic and aerobic zones in each stage on the to- tal nitrogen concentration of the effluent in the step-feed biological nitrogen removal process.Unlike the previous modeling methods,this model can be used to calculate the removal rates of ammonia and nitrate in each stage and thereby predict the concentrations of ammonia,nitrate,and total nitrogen in the effluent.To verify the simulation results,pilot-scale experimental studies were carried out in a four-stage step feed process.Good correlations were achieved between the measured data and the simulation results,which proved the validity of the developed model. The sensitivity of the model predictions was analyzed.After verification of the validity,the step feed process was optimally operated for five months using the model and the criteria developed for the design and operation.During the pilot-scale experimental period,the effluent total nitrogen concentrations were all below 5mg·L ^-1 ,with more than 90%removal efficiency.     

Development of a kinetic model for the moderate temperature chemical vapor deposition of SiO2 films from tetraethyl orthosilicate and oxygen

An apparent kinetic model for the chemical vapor deposition of SiO₂ from tetraethyl orthosilicate (TEOS) and O₂ was developed in a poorly investigated range of operating conditions, that is, at atmospheric pressure and between 350 and 500°C, based on literature survey and experimental results obtained in a hot wall tubular reactor. The kinetic model was implemented into the computational fluid dynamics code FLUENT and validated both in shape and value by comparison with experimental deposition rate profiles. It reveals that for the conditions tested, a possible mechanism of SiO ₂ deposition involves two intermediate species formed from TEOS homogeneous decomposition, the first one being active from 300°C and the second one contributing to deposition for temperatures higher than 370°C. The calculated local profiles of gas flow, gas temperature, species mass fraction, and silica deposition rate indicate that the first intermediate species leads to marked film thickness gradients, the second one being more stable as producing uniform thicknesses. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3958–3966, 2018     

Development of highly sensitive non-enzymatic sensor for the selective determination of glucose and fabrication of a working model

Copper oxide (CuO)/copper oxalate (CuOx) modified non-enzymatic electrochemical sensor for the detection of glucose in alkaline medium was fabricated by electrochemical anodisation of copper electrodes in potassium oxalate solution. Morphology of the modified copper electrode was studied by Scanning Electron Microscopy (SEM) and its electrochemical behaviour by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The formation of CuOx on the copper electrode was confirmed by the Infra-red Reflection Absorption Spectrum (IRRAS). The modified electrodes were found to be microporous and rough. Linear Sweep Voltammetry (LSV) and amperometry were adopted to investigate the direct electrocatalytic oxidation of glucose on CuO/CuOx modified electrode in alkaline medium which showed excellent catalytic activity. The best performance of the sensor was obtained at 0.7 V and in 0.1 M sodium hydroxide (NaOH). At this optimum potential, the sensor was highly selective to glucose in the presence of ascorbic acid (AA) and uric acid (UA) which are common interfering species in biological fluids. The sensitivity was found to be very high (1890 μA mM⁻¹ cm⁻²) with excellent linearity (R = 0.9999) up to 15 mM having a low detection limit of 0.05 μM (S/N = 3). The modified electrode was tested for glucose level in blood serum. Based on the optimised conditions, a working model of the sensor was made and successfully tested for glucose.     

A practical equation of state for non‐spherical and asymmetric systems for application at high pressures. Part 1: Development of the pure component model

A practical, mathematically and computationally simple, equation of state (EOS) has been developed to accurately describe pure component phase behaviour of spherical and chain‐like molecules. The EOS consists of a newly developed hard sphere model and a perturbation term based on the Barker and Henderson approach using the Chen and Kreglewski intermolecular potential model and a double constrained summation as a mathematical expression thereof. The perturbed hard chain theory (PHCT) approach is used to extend the EOS to non‐spherical molecules. The EOS compares well with other more complex models such as the simplified perturbed hard chain theory (SPHCT) and statistically associating fluid theory (SAFT) models and will be extended to describe mixtures in Part 2 of this series. © 2011 Canadian Society for Chemical Engineering