Electrochemical instabilities due to pitting corrosion of iron

Electrochemical instabilities induced by chlorides and bromides due to pitting corrosion of iron in sulfuric acid solutions are investigated. Analysis of the electrochemical instabilities as a function of the applied potential and the nature and concentration of the aggressive chemical species shows that the system exhibits a transition from aperiodic bursting of large-amplitude to small-amplitude chaotic oscillations at a critical potential (bifurcation potential, E _bif). The E _bif is determined by the halide concentration inside the pits and coincides with the repassivation potential defined in corrosion studies to explain pit repassivation due to changes in pit chemistry. Surface observations show that, at E < E _bif, an active-passive state dissolution (etching) occurs, while at E > E _bif, a polishing state dissolution is reached. Spatial interactions between early initiated pits and the adjacent electrode surface, oxide film alteration, aggressive species accumulation around active pits, and formation of ferrous salt layers in front of the Fe electrode are all considered to be associated with electrochemical instabilities emerging during pitting corrosion of iron under different dissolution states. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 535–550. The text was submitted by the authors in English.     

Preparation of sulfur‐quinone polyurethanes and their use to inhibit the corrosion of iron particles

A sulfur‐quinone diol monomer, 2,5‐bis‐(2‐hydroxyethylthio)‐1,4‐benzoquinone (SQM‐2), was prepared by the reaction of 2‐mercaptoethanol with benzoquinone. SQM‐2 and polycaprolactone diol (number‐average molecular weight = 1250) were condensed with toluene diisocyanate to give sulfur‐quinone polyurethanes. Two compositions were prepared, SQPU‐1 containing 7 mol % SQM‐2 and SQPU‐2 containing 35 mol % SQM‐2. These thermoplastic polyurethanes were soluble in solvents used in magnetic tape coating processes. The polymers were used to prepare magnetic coatings containing state‐of‐the‐art commercial iron particles. The sulfur‐quinone polyurethanes protected the iron particles against corrosion from a pH 2.0 aqueous buffer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3278–3283, 2000     

热分析技术在药物研究中的应用

本文简要介绍了热分析技术在药学领域中的重要性及其应用。由于热分析技术具有试样微量化、快速简便、不用分离试样、不用溶剂、适用范围广、曲线易于解析等优点,在药学研究和药品质量检验等方面,热分析技术将发挥更重要的作用。     

Hydration studies of modified OPC pastes by differential scanning calorimetry and thermogravimetry

Thermal methods are used extensively in investigating cements and effects of additives on their hydration behaviour. Calcium chloride is the most effective and widely used accelerator for cement hydration, but the result is largely dependent on the rate at which it is added. In this study the influence of calcium chloride dosage on the hydration behaviour of OPC pastes aged for different periods has been investigated by means of differential scanning calorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD) methods. The results are discussed in relation to the relative amounts of calcium hydroxide and total reaction product formed. Chloroaluminate was a product of hydration in the samples dosed with greater than 1% calcium chloride. XRD was unable of itself to differentiate between monochloroaluminate and the calcium aluminate hydrate C₄AH₁₃ when present in small amounts. Thermal methods proved effective in characterising the products of hydration in the presence of chloride.

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Zusammenfassung Bei der Untersuchung von Zement und des Einflusses von Additiven auf das Hydratationsverhalten von Zement finden thermoanalytische Methoden eine breite Anwendung. Der effektivste und meistbenutzte Beschleuniger für die Hydratation von Zement ist Calciumchlorid, aber die Ergebnisse hängen stark von der Dosiergeschwindigkeit ab. In vorliegender Studie wird mittels DSC-, TG- und Röntgendiffraktionsmethoden der Einflu\ der Dosierung von Calciumchlorid auf das Hydratationsverhalten von verschieden alten OPC-Zementbreiproben untersucht. Die Ergebnisse wurden in Bezug auf die relativen Mengen Calciumhydroxid und das gebildete Gesamtreaktionsprodukt gewertet.Bei Dosen von mehr als 1% Calciumchlorid konnte als Hydratationsprodukt Chloraluminat festgestellt werden. Sind Monochloraluminat und das Calciumaluminathydrat C₄AH₁₃ in geringen Mengen vorhanden, kann man zwischen den beiden mittels Röntgendiffraktion nicht unterscheiden. Thermoanalytische Methoden erwiesen sich als effektives Hilfsmittel bei der Charakterisierung der Produkte der Hydratation in Gegenwart von Chlorid.

     

Use of thermomagnetometry in the study of iron-containing pyrotechnic systems

Thermal analysis is routinely used to characterize pyrotechnic fuels, oxidants and fuel/oxidant mixtures [1]. Thermomagnetometry (TM) can provide additional information if the magnetic properties of the materials change during reaction. TG, TM and DTA results for the iron/potassium permanganate, iron/barium peroxide, and iron/strontium peroxide systems as loose powders or pressed pellets indicate predominantly solid-gas mechanisms for reactions in these systems.     

TG and DSC studies on plaster residues as recycled material

The aim of the present work is to study plaster residues produced in industries in Goiás State (Brazil). The study analyzes the trituration and dehydrating processes of the plaster and compares its chemical, mechanical and physical characteristics to the natural plaster samples aiming its possible recycling. Plaster samples were submitted to X-ray diffraction, infrared spectroscopy, thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses. By the comparison of the results obtained for both samples it was observed that they have similar chemical characteristics. No reason was found against the use of recycled plaster.     

Co-curing studies of ethynyl terminated oligoimide and (methyl) nadicimide resins

The paper describes the co-curing studies of ethynyl and ethenyl end-capped imide resins. The effect of composition and chemical structure of ethenyl end-capped resins (nadicimides) on thermal behavior of ethynyl end-capped resins was evaluated using DSC and thermogravimetric analysis. An increase in char yield was observed on co-curing of few resin formulations. A mechanism has been proposed to account for this observation.Paper presented at Intern. Symposium on Macromolecules at Trivandrum, Jan. 11–13, 1995.     

Amine–quinone polyimide: A new high‐temperature polymer and its use to protect iron against corrosion

A new diamine monomer was synthesized by the Michael addition of 4,4′‐methylene dianiline with 1,4‐benzoquinone. The monomer was condensed with 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride to give a polyamic acid that was soluble in NMP. The polyamic acid was cast onto iron and thermally imidized to yield the amine–quinone polyimide (AQPI‐2). AQPI‐2 had a thermal decomposition temperature of 540 °C (10% TGA weight loss in N₂) and a glass transition at 292 °C, values typical of polyimides. The degradation of the coating on iron after exposure to 0.1 M NaCl electrolyte was followed by electrochemical impedance spectroscopy. Under these conditions a conventional polyimide failed after 3 days exposure, while AQPI‐2 survived more than 24 days exposure. The adhesive bond between the amine–quinone polyimide and the iron surface was so strong that it could not be broken by the electrolyte. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2893–2899, 2000     

正二十二烷醇的热力学性质

用精密自动绝热量热仪测定了广谱抗病毒药物正二十二烷醇在78-400 K温区的热容. 根据实验测定的热容数据, 用最小二乘法拟合计算出热容对温度的多项式方程, 得到其相变温度、相变焓、相变熵分别为340.844 K、85.07 kJ·mol-1、249.6 J·K-1·mol-1. 根据热力学函数关系式计算了其在80-400 K温区每隔5 K的热力学函数[HT-H298.15]和[ST-298.15]. 用DSC、TG热分析技术进一步考查了该物质在400-900 K的热稳定性.     

Application of Thermogravimetry in the Quality Control of Chloramphenicol Tablets

The stability and thermal behaviour of chloramphenicol and various of its mixtures were investigated. The thermogravimetric and stability constant results showed that the chloramphenicol base is thermally more stable than the tablet in the studied formulation. The reduction in stability was attributed to the presence of starch in the formulation. The thermal decompositions of the chloramphenicol base and the tablet obey first-order kinetics. This revised version was published online in August 2006 with corrections to the Cover Date.     

生物降解材料胆酸-乳酸共聚物的热性能研究

通过直接熔融共聚法合成了系列的不同乳酸／胆酸组成比（LA／CA）的胆酸．乳酸共聚物,用DSC、TG等手段研究生物降解材料胆酸-乳酸共聚物的热性能。结果表明,共聚物的热性能与其组成、结构有关。LA／CA小的多核共聚物无明显熔融峰,热失重分两步进行;LA／CA大的单核共聚物出现明显双头熔融峰,其热失重一步进行,其Tg随着LA／CA增加而升高。     

Thermal analysis applied in the osmotic tablets pre-formulation studies

Osmotically controlled and oral drug delivery systems utilize osmotic pressure for controlled delivery of active agent(s). Drug delivery from these systems, to a large extent, is independent of the physiological factors of the gastrointestinal tract and these systems can be utilized for systemic as well as targeted delivery of drugs. We apply the thermal methods and IR spectroscopy to study compatibility between atenolol and several excipients usually found in the osmotic systems formulations (Polyethylene oxide, MW 3350, 100000, 200000 and 5000000; HPMC K4000, magnesium stearate and cellulose acetate. Cellulose acetate, HPMC K4000 and magnesium stearate have essentially no interaction with atenolol otherwise all Polyethylene oxide excipients modifies significantly the drug melting point indicating some extend of interaction.     

Thermal studies on mixtures of aminosalicylic acids with cyclodextrins

The thermal behaviour of the aminosalicylic acids is compared with the behaviour of their 1:1 molar ratio physical and kneaded mixtures with each of three different cyclodextrins (b-, hydroxypropyl-b-, and g-cyclodextrin), using differential scanning calorimetry and thermogravimetry coupled with evolved gas analysis by Fourier transform infrared spectroscopy. X-ray powder diffraction and infrared spectroscopy provided complementary information. Comparison of the effects of the different cyclodextrins on the behaviour of the individual aminosalicylic acid isomers shows that hydroxypropyl-b-cyclodextrin has the greatest interaction with 3-aminosalicylic acid and 5-aminosalicylic acid, followed by g-cyclodextrin, while b-cyclodextrin generally shows the least interaction. For 4-aminosalicylic acid, the effect of g-cyclodextrin seems to be more marked than for 3-aminosalicylic acid and 5-aminosalicylic acid. This revised version was published online in July 2006 with corrections to the Cover Date.     

H~2S对硫酸溶液中铁腐蚀作用的CNDO/2研究

动电位扫描得出工业纯铁在含H~2S的H~2SO~4溶液中腐蚀的电化学行为。应用CNDO/2法确定了阴、阳极电位下H~2S,HS^-在金属Fe晶面上的稳定吸附取向与最佳吸附间距,通过对吸附物总能量、结合能、净电荷分布的计算,得出H~2S体系阴、阳极反应被加速的微观机制。阳极电位下,大量HS^-为S原子的平行吸附方式,HS^-负电荷大部分向Fe转移,促进铁的溶解。阴极电位下,少量H~2S则为H原子的平行吸附方式,Fe表面负电荷向H~2S分子中与Fe作用的H转移,促进析氢。在CNDO/2法计算的基础上,圆满地解释了实验结果。     

Thermal studies of solvent exchange in isostructural solvates of a tetroxoprim-sulfametrole complex

Isostructural solvates of the 1:1 molecular complex between the antibacterial drugs tetroxoprim (TXP) and sulfametrole (SMTR) with formulae TXP·SMTR·CH₃OH (I), TXP·SMTR·C₂H₅OH (II) and TXP·SMTR·H₂O (III), were investigated to establish their propensity for guest exchange. Separate exposure of powdered (I), (II) and (III) to a saturated atmosphere of each solvent of the complementary solvate pair at ambient temperature resulted in reversible solvent exchange in all cases. DSC and TG were the methods of choice for monitoring the exchange processes since (I)-(III) have distinct onset temperatures of desolvation and characteristic mass losses. Interpretation of the results in terms of the known locations of the solvent molecules in crystals of (I)-(III) led to the conclusion that solvent exchange probably proceeds by a co-operative mechanism involving material transport through channels while the common host framework is maintained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal studies on nickel(II) 4-iodopyrazole complexes

This work describes the synthesis, IR and UV-Vis spectroscopic characterization as well the thermal behavior of the [NiCl₂(HIPz)₄]⋅C₃H₆O (1), [Ni(H₂O)₂(HIPz)₄](NO₃)₂ (2), [Ni(NCS)₂(HIPz)₄] (3) and [Ni(N₃)₂(HIPz)₄] (4) (HIPz=4-iodopyrazole) pyrazolyl complexes. TG experiments reveal that the compounds 1–4 undergo thermal decomposition in three or four mass loss steps yielding NiO as final residue, which was identified by X-ray powder diffraction.     

Isothermal and rising temperature kinetic studies of doped nonstoichiometric basic nickel carbonate

The techniques of thermal analysis are used to determine the mode of decomposition of nickel carbonates doped by the method of coprecipitation. Nickel carbonate prepared by this method is basic in nature with the stoichiometryxNiCO₃·yNi(OH)₂·zH₂O. Isothermal Thermogravimetry was applied to determine the mechanism of decomposition. Rising temperature Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) were used to study the effects of doping on the kinetics of the decomposition. Doping was found to strongly influence the kinetics of the decomposition. The kinetics of thermal decomposition of the doped carbonates were compared with conductivity studies. A compensation effect has been observed and is discussed, in the thermal decomposition of the doped nickel carbonates. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Thermal analysis of the rice and by-products

The thermogravimetry (TG) is a technique used in the quality control of foods. In this work the moisture and ash contents in the rice and by-products (bran and husk), the thermal stability and the gelatinization process by conventional, thermogravimetric and calorimetric methods were studied. The moisture and ash contents obtained by TG and conventional methods did not present significant differences. The rice presented higher starch content, while the bran presented higher protein content. The thermogravimetric data presented the following thermal stability order: rice>bran>husk. The calorimetric curves indicated the gelatinization of the starch. The kinetic parameters were compatible. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dehydration studies of Co(II), Cu(II) and Zn(II) methanesulfonates

The dehydration process of Co(II), Cu(II) and Zn(II) methanesulfonates was studied by thermogravimetry/derivative thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC) techniques in dynamic N₂ atmosphere. The TG/DTG curves show that all of them contain four crystallization water molecules, which are lost in two steps. The peak temperature and dehydration enthalpies ΔH were measured from DSC curves for each compound. The effect of procedural variables on the TG and DSC curves was investigated. In this work, the procedural variables included heating rate, Al pan state (unsealed and sealed) and sample mass.     

聚缩水甘油硝酸酯的热安定性和相容性研究

采用DSC、TG热分析方法研究了聚缩水甘油硝酸酯(PolyGLYN)的热安定性和与1,3,5-三硝基-1,3,5-三氮杂环己烷(RDX)间的相容性.结果表明,PolyGLYN在100℃以前较为稳定.当加热速率趋于零时PolyGLYN的热分解峰温为196.4℃,由Ozawa法计算的热分解表观活化能为182.0 kJ·mol-1,分别比RDX的低15.1℃和高22.2 kJ·mol-1.PolyGLYN热稳定性与RDX接近,两者之间的相容性较好.