DSC of etched aluminum foils for use in electrolytic capacitors

A DSC method for evaluating the surface area of etched Al foils for use in high performance electrolytic capacitors is presented. A linear relationship between the etching degree (effective surface area) and the thermal resistance of the sample is obtained by means of DSC, based on the transient phenomenon. This method using the transient state in DSC measurement is not only novel, but also rapid and simple in evaluating the surface area of an etched aluminum foil. The method is effective even when the Al foil has a naturally oxidized surface.The authors wish to thank to Mr. Adachi and Mr. Koike of ELNA Co., Ltd. for supplying us with etched aluminum foils. This work is partially supported by the Research Fund of North Shore College of SONY Institute. R. O. whishes to express her gratitude to the support.     

Analysis of electrochemical impedance spectra of anodised pure aluminium foil with various etch tunnel length distributions used for electrolytic capacitors

The present work analyses the electrochemical impedance spectra of anodized pure Al foil with various etch tunnel length distributions, used for electrolytic capacitors. The lengths of the etch tunnels formed on the Al foil specimen were more widely distributed with increasing etching time. The etch tunnel length distributions were quantitatively measured by scanning electron microscopy. All the measured impedance spectra hardly exhibited the ideal capacitive behaviour in the high-frequency region and they deviated more significantly from the ideal capacitive behaviour with increasing etching time. For the numerical calculation of the total impedance of the electrode, the transmission line model was modified to reflect the etch tunnel length distribution, which represents the respective contributions of etch tunnels with different lengths to the total impedance. The total impedance was calculated by the integration of the impedance of one etch tunnel with respect to the etch tunnel length by taking the value of the etch tunnel length distribution determined experimentally. From the coincidence of the impedance spectra calculated numerically with those spectra measured experimentally, it is concluded that the deviation of the impedance spectra from the ideal capacitive behaviour in the high-frequency region originates from the characteristic frequency dispersion that depends upon the etch tunnel length distribution.     

Thermogravimetric studies on some Iraqi crude oils

A rapid method for the characterization of some Iraqi crude oils is described, based on thermogravimetric data obtained using a selected heating program. The data relating to light, middle and heavy cuts of the crudes, together with their residues estimated from the thermal curves, correlated well with the API gravity as well as with the sulphur and metal contents. With the above technique, these parameters were also shown to change with depth in a given well.     

Threshold Al KLL Auger spectra of oxidized aluminium foils

Threshold Al KLL Auger electron spectroscopy and K‐edge x‐ray absorption fine structure spectroscopy have been used to examine technical purity (99.5%) aluminium foil before and after chemical treatment that altered the thickness and degree of hydroxylation of the oxidized layer. Comprehensive surface chemical characterization was effected by means of monochromatized Al Kα‐excited photoelectron spectroscopy. Threshold Al KL_{2, 3}L_{2, 3} spectra were obtained for three of the foils investigated and these spectra were in broad agreement with those observed previously for pure Al foil. The relative intensities of the spectral components for two of the foils were clearly consistent with the previously proposed assignment of the resonantly enhanced Auger component, situated between those arising from the metal and Al(III) oxide, to a thin interfacial layer. The threshold Auger spectra from the aluminium foil bearing the thickest and most hydroxylated oxidized layer were not obviously consistent with the interfacial layer model but O K‐edge spectra revealed that this surface layer was fundamentally different from the others and could have had a greater interfacial surface area. Copyright © 2003 John Wiley & Sons, Ltd.     

Optimisation of the plasma electrolytic oxidation process efficiency on aluminium

Plasma electrolytic oxidation (PEO) is a surface treatment technology enabling fabrication of adherent thick (50–150 µm) coatings on light metal alloys with significantly enhanced hardness, wear and corrosion resistance compared with other conventional treatments. The technology has the potential to play a significant role in the transport sector for replacement of steel with light‐weight materials of improved durability. A main limitation of PEO lies in its relatively high cost, associated with high energy consumption and low coating efficiency. The present work explores possible routes to improve the process efficiency. It is shown that a combination of conventional pre‐anodising with sequential PEO treatment reduces specific energy consumption up to five times because of an increase of the coating growth rate, up to 10 µm/min, compared with existing PEO processes. A further approach to improved coating efficiency involves PEO in electrolytes with suspended fine or nanoparticles, which results in the formation of thicker coatings in reduced time as a result of the incorporation of the particles from the electrolyte into the coating. Additionally, melting of the coating material during the micro‐arc discharge process leads to formation of stabilised high‐temperature phases, such as tetragonal and cubic zirconia, which provide significantly improved microhardness of the coating material and give a potential for thermal barrier applications. Copyright © 2009 John Wiley & Sons, Ltd.     

火焰原子吸收光谱法测定电解铝用冰晶石中锂

含锂冰晶石取代锂盐添加到电解质中被广泛应用于电解铝工业,其质量直接影响到电解铝工业的电解效率、吨铝能耗高低和电解铝产品质量优劣。控制冰晶石中锂含量是保证产品质量和应对废旧电解质再生对氟化盐市场冲击的一个重要举措。通过在铂坩埚中加入一定量高氯酸在高温条件下加热冒烟赶氟后再加入盐酸酸化至盐类完全溶解,建立了波长670.80 nm处采用火焰原子吸收光谱法测定铝用冰晶石中锂含量的方法,避免了大量氟基体的干扰,选择一定量的铝钠基体匹配来保证测试灵敏度和准确性;通过加标回收实验得知锂的回收率为102%;锂元素校准曲线线性相关系数≥0.9994;锂的检出限为0.0065μg/mL;不同含量含锂冰晶石的锂标准偏差均小于0.01%,与电感耦合等离子体原子发射光谱(ICP-AES)法测定结果相一致。方法准确可靠、简单易操作,满足铝电解工业生产分析的需要。     

Thermogravimetric and FTIR studies of chitosan blends

Results of spectrophotometric and thermogravimetric studies of chitosan (CH) blends with polyvinyl alcohol (PVAL), starch (S) and hydroxypropylcellulose (HPC) obtained by casting from solutions in the form of transparent films containing 0–1.0 weight fraction of CH were discussed. Blends containing S are homogeneous only in the case of low-weight fraction of S (to 0.3).On the basis of results of thermodegradation in dynamic and isothermal conditions, thermal stability of the tested systems was estimated. Thermogravimetric measurements in dynamic conditions were carried out in the temperature range of 100–450 °C at constant heating rate 15 °C/min. From thermogravimetry (TG) and DTG curves the activation energy and characteristic parameters of degradation of the tested blends were determined. The observed growth of activation energy and T_p—temperature of initial weight loss, T_max—temperature of maximal rate and C_e—degree of conversion at the end of the measurement (at temperature 450 °C) along with the increase of polymer fraction (HPC and S) in the CH blend provides an evidence of improved thermal stability of the systems tested.Investigations in isothermal conditions in air at temperature from 100 to 200 °C confirmed appreciable improvement of CH thermal stability in the blends being tested.Infrared spectroscopic analysis of the blends showed a distinct stabilization of the process of chain scission. In the band at 1080 cm⁻¹ associated with absorption in –C–O–C– group during degradation of the blends at temperature 200 °C much smaller decrease due to molecular scission were observed than in the case of pure CH.     

A new approach to nickel electrolytic colouring of anodised aluminium

Energy dispersive X-ray spectroscopy and scanning electron microscopy were used to analyse nickel on anodic aluminium surfaces after stripping the anodic aluminium oxide. The metal was electroplated at the bottom of the pores of anodised aluminium during electrolytic colouring in solutions without (Watts) and with (citrate) complexing agents, respectively. A relation between the anodic-cathodic processes, changes of the structure and composition of the coating in dependence on the used solution were studied. A morphology study performed after stripping the anodic aluminium oxide revealed the crucial influence of the anodic process/cycle and the complexing agent on the nickel structure on the aluminium surface. Off-time of half-way rectified current influenced the nickel deposition in the pores of anodic alumina negatively.     

Thermogravimetric studies on some Cu(II) amine complexes

Thermogravimetric analysis of solid state bis-Cu(II) amine complexes CuL₂X₂, whereX=Cl^– or NO ₃ ^– andL=ethylenediamine (en), tetramethylethylenediamine (tmn),o-phenylenediamine (opd) and 2,2 bipyridyl (bpy), has been carried out and the kinetic parameters have been determined by fitting the observed mass losses corresponding to various steps using the Coats and Redfern equation. These studies show that the activation energies of these complexes decrease on changing the ligand in the order: bpy > opd > en > tmn. This trend can be attributed to the rigidity of the N-C-C-N skeleton in the bpy and opd ligands and steric crowding at the nitrogens in the tmn ligand. The majority of the decomposition steps were found to be composite in nature and frequently involved fractional groups expelled from the complexes. From the observation ofE _a> H, the thermal decomposition process of these complexes appears to be governed by the nucleation and growth mechanism.

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Zusammenfassung Kupfer(II)-bisaminkomplexe der Formel CuL₂X₂ mitX=Cl^– oder NO ₃ ^– undL=Äthylendiamin (en), Tetramethyläthylendiamin (tmn),o-Phenylendiamin (opd) und 2,2-Bipyridyl (bpy) wurden thermogravimetrisch untersucht und die kinetischen Parameter aus den gemessenen, zu den entsprechenden Schritten gehörenden Masseverlustwerten unter Anwendung der Gleichung von Coats und Redfern bestimmt. Es ergab sich, daß die Aktivierungsenergie dieser Komplexe entsprechend folgender Ligandenreihe abnimmt: bpy > opd > en > tmn. Dies kann bei den bpy und opd Liganden auf die Starrheit des N-C-C-N Fragmentes und im Falle der tmn Liganden auf eine räumliche Überfülltheit am Stickstoffatom zurückgeführt werden. Die Mehrzahl der Zersetzungsschritte sind komplexer Natur und haben häufig aus den Komplexen stammende Teilgruppen zum Ergebnis. Aufgrund der BeobachtungE _a>H scheint der thermische Zersetzungsvorgang dieser Komplexe durch einen Keimbildungs und -Wachstums mechanismus bestimmt zu werden.

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-() (II) CuL₂X₂, X = , aL= (en), (tmn),o- (opd) 2,2- (bpy). C - . , bpy\s>opd\s>en\s>tmn. N-C-C-N o- . , , . E _a H, , « ».

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A research grant from the University Grants Commission (India) to LSP and a JRF to JKK are thankfully acknowledged.     

Real-time NMR studies of electrochemical double-layer capacitors

(11)B NMR spectroscopy has been used to investigate the sorption of BF(4)(-) anions on a highly porous, high surface area carbon, and different binding sites have been identified. By implementing in situ NMR approaches, the migration of ions between the electrodes of the supercapacitors and changes in the nature of ion binding to the surface have been observed in real time.     

Selenium in electrolytic manganese as a reference material for the quality control of aluminium melts

Electrolytic manganese is an important alloying element for aluminium and steel melts. It is mainly added to melts of aluminium in the holding furnace as tablets or minitablets (compressed compacts of manganese and aluminium powders). Selenium derivates are usually added during the production of electrolytic manganese, so some selenium is present in the alloys produced when electrolytic manganese is added to the aluminium furnace. Since the selenium contents of many alloys are of concern from health and environmental perspectives, their values should be provided. In this work, a laboratory reference material (LRM) based on electrolytic manganese was produced to assure our routine quality control method, where selenium is analysed by hydride generation followed by optical emission spectrometry with inductively coupled plasma (HG–ICP–OES). Therefore, the present paper describes in detail the preparation procedure for and the results from homogeneity and stability studies performed on electrolytic manganese LRM. For this purpose, a commercial electrolytic manganese lot was selected and the main factors involved in the preparation of the material (pretreatment step, homogenization, bottling and storage) were carefully studied and established in order to guarantee the long-term stability of the LRM. The results obtained showed that the LRM developed was a fit-for-purpose material for the quality control of the routine analysis of selenium.     

Thermogravimetric studies of the hydrogen reduction of nickel tungstate

Thermogravimetry, using a C.I. Electronics thermobalance, has been incorporated with X-ray diffraction analysis to study the mechanism of the hydrogen reduction of nickel tungstate, over the temperature range 200–900°C. Nickel tungstate was prepared in a hydrated form by precipitation from aqueous solution. Both the hydrated precipitate and the anhydrous salt were reduced so that results could be compared. The reduction behaviour of the nickel tungstate was shown to be similar to that of cobalt tungstate as predicted from the relative thermochemical stabilities.     

UV-spectroscopic studies on the interaction of triethyl aluminium with cobalt and aluminium acetylacetonates

The Al(acac)₃/Et₂Al(acac) ratio depends on the Al/Co and the solvent. The solvent contains Et₂Al(acac) as a dimer, which is stabilized in the presence of Co(O) and arenes. The role of Et₂Al(acac) dimer in the formation of active Co(O) complexes is discussed.

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, Al(acac)₃/Et₂ Al(acac) Al/Co . (Et₂Al(acac) Co(O) . Et₂Al(acac) Co(O).

     

Thermogravimetric studies of the reaction of CaO with SO2

The high temperature sulfation of CaO with SO₂ was investigated under vacuum by TG. Experimental data indicated that the sulfation process was a two-stage reaction, a very fast surface reaction in the beginning, and followed by a product-layer diffusion-controlled reaction. The initial period was about 7 s. This process of sulfation was affected by type of limestone, micro structure, particle size and temperature, but hardly affected by SO₂ concentration. A 59% CaO conversion can be achieved in 30 s at 1000°C and 1 mbar.     

Thermogravimetric studies in prediction of coal behaviour during coal liquefaction

Different chemical and petrographical methods were earlier proposed for the prediction of coal liquefaction. Thermogravimetric studies (DTG, TG) of coals were now performed and the same coals were liquefied. A good correlation was found between ΔA _max (the main decomposition area during the maximum rate of decomposition in DTG) andSk (the degree of conversion of organic substances during coal liquefaction). ΔA _max measurement may be a good, quick and quite reliable method for the prediction of coal liquefaction, which needs to be standardized.     

Thermogravimetric studies on Polyamide-6,6 modified by electron beam irradiation and by nanofillers

This paper reports the results of thermogravimetric studies on: (a) Polyamide-6,6 (abbreviated henceforth as PA66) specimens which were modified by electron beam radiation in air, (b) organic-inorganic hybrid nanocomposite films of PA66/silica prepared by the sol-gel technique and (c) unmodified multi-walled carbon nanotube (abbreviated henceforth as MWCNT) reinforced PA66 films. The activation energies were determined using the Kissinger and the Flynn-Wall-Ozawa methods, which do not require knowledge of the reaction mechanism. The results showed that PA66 specimens which received an irradiation dose of 200 kGy in air had a higher thermal stability than both the neat PA66 and PA66 specimens which received a radiation dose of 500 kGy in air. The PA66/silica hybrid nanocomposites up to a silica loading of 1.5 wt% also showed higher thermal stability over neat PA66 films. At MWCNT loadings of 0.5-1.0 wt% the composite films exhibited higher activation energies than the neat PA66 film but at higher MWCNT loading the activation energy was lower than that obtained for the neat PA66 film.     

Thermogravimetric studies of polymeric reagents: a polymeric o-benzyne precursor

Thermogravimetry for the study of polymeric reagents is described and used to demonstrate the thermic behavior of a polymeric o-benzyne precursor