A new reaction calorimeter and calorimetric tools for safety testing at laboratory scale

Calorimetry combined with thermal analysis is an essential tool for the evaluation of thermal risks linked with chemical reactions at industrial scale. The energies of synthesis reactions or decomposition reactions as well as the heat capacities of reaction masses can be measured using such techniques. The capacity of the SETARAM differential reaction calorimeter (DRC) to determine essential safety data has been demonstrated with the measurement of heat capacities of cyclohexane and propanoic acid. Results of an industrial reaction are also presented.     

A new relaxation process in the high-elastic state at low temperatures

A new relaxation process, explaining the change of elasticity in rubberlike polymers at critical stress (0.1?0.5 kgf/cm²) has been discovered. This process is characterized by the low value of activation energy (weak temperature dependence of relaxation times) and large sizes of kinetic units (strong dependence of relaxation time on stress). Critical stress depend on temperature and for rubberlike polymers turns to zero at 40°?60°C. Mechanism of the phenomena can be explained by the existence of the ordered molecular microregions, creating additional crosslinking points of nonchemical nature with free chains of the network, breaking up at critical stress. Observed phenomena is analogous to the process of forced rubber elasticity of those polymers in glassy state. Critical stress is analogous to the limit of forced rubber elasticity below glass transition temperature.     

A thermogravimetric technique for continuous quantitative sulphur analysis at elevated temperatures

The problems of conventional methods for determining sulphur content at elevated temperatures are discussed and a thermogravimetric technique for a direct continuous analysis is described. The technique is illustrated by employing the Cu-S system at 1200 and with a discussion of the necessary correction factors for buoyancy and volatilization being included.

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Zusammenfassung Es werden die Probleme der üblichen Methoden der Schwefelbestimmung bei hohen Temperaturen erörtert und eine thermogravimetrische Methode zur direkten kontinuierlichen Analyse vorgeschlagen. Das Verfahren wird an dem Beispiel des Systems Cu-S bei 1200 gezeigt mit Hinweis auf die infolge Auftrieb und Verflüchtigung nötige Korrektur.

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Résumé On discute les problèmes posés par les méthodes conventionnelles pour doser le soufre aux températures élevées et l'on décrit une méthode thermogravimétrique pour l'analyse directe en continu. La technique est illustrée sur l'exemple du système Cu-S à 1200; on discute les facteurs correctifs que l'on doit appliquer pour tenir compte de la poussée et de la volatilisation.

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. Cu-S 1200 .

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One of the authors, C. W. B., is grateful to the Noranda Research Centre for a graduate fellowship. We are also grateful to the Canadian National Research Council for financial assistance.     

Reactions at very low temperatures: gas kinetics at a new frontier

Advances in experimental techniques, especially the development of the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) method, allow many gas-phase molecular processes to be studied at very low temperatures. This Review focuses on the reactions of molecular and atomic radicals with neutral molecules. Rate constants for almost 50 such reactions have been measured at temperatures as low as 13 K by using the CRESU method. The surprising demonstration that so many reactions between electrically neutral species can be extremely rapid at these very low temperatures has excited interest both from theoreticians and from those seeking to understand the chemistry that gives rise to the 135 or so molecules that are present in low-temperature molecular clouds in the interstellar medium. Theoretical treatments of these reactions are based on the idea that a reaction occurs when the long-range potential between the reagent species brings them into close contact. The astrochemical context, theoretical studies, and the determination of the rate constants of these low-temperature reactions are critically discussed.     

Preparation and properties of new oxygen ion conductors for use at low temperatures

Two new systems, Bi₂O₃Er₂O₃ and ZrO₂Y₂O₃(CaO)Bi₂O₃ were investigated. The first system has a homogeneous cubic, fluorite phase between 17.5 and 45.5 mol % Er₂O₃ and can be sintered to densities near 95% at 1200 K. At temperatures between 700 K and 1000 K the highest value of the a.c. oxygen ion conduction in this system is twice as much as the highest value found in the literature. In the second system concentrations of 1–3 mol % Bi₂O₃ act as an excellent sintering aid for ZrO₂Y₂O₃ and ZrO₂CaO samples which can be sintered to densities higher than 95% at temperatures of 1350 K. During this procedure a liquid ZrO₂Bi₂O₃ phase exists from which Bi₂O₃ partly evaporates with increasing sintering time. The oxygen ion conduction is little affected by the Bi₂O₃-rich second phase. The influence of annealing procedures up to 1570 K on the conduction in the ZrO₂Y₂O₃Bi₂O₃ system is small despite weight losses up to 4%.     

A theory for environmental craze yielding of polymers at low temperatures

It has been recently discovered that polymers craze at low temperatures in the presence of nitrogen or argon. A quantitative theory has been developed which explains (1) the critical temperature above which the phenomenon disappears, (2) the critical stress for nucleating a craze, (3) the effect of strain rate on the yield point and size of crazes, (4) the drop in the load during craze yielding, and (5) the increase in strength of the polymer in N₂ or Ar at high strain rates so that the ultimate strength may exceed that in He or vacuum. The crazing action of the gases is described qualitatively at the molecular level.     

The use of electroosmotic flow as a pumping mechanism for semi-preparative scale continuous flow synthesis

By employing a series of reactions we demonstrate the use of electroosmotic flow as a continuous pumping mechanism suitable for semi-preparative scale synthesis, affording an array of small organic compounds, of analytical purity, with yields ranging from 0.57-1.71 g h(-1).     

Discrete breathers for understanding reconstructive mineral processes at low temperatures

Reconstructive transformations in layered silicates need a high temperature in order to be observed. However, very recently, some systems have been found where transformation can be studied at temperatures 600 degrees C below the lowest experimental results previously reported, including sol-gel methods. We explore the possible relation with the existence of intrinsic localized modes, known as discrete breathers. We construct a model for nonlinear vibrations within the cation layer, obtain their parameters, and calculate them numerically, obtaining their energies. Their statistics show that, although there are far less breathers than phonons, there are much more above the activation energy, making them good candidates to explain the reconstructive transformations at low temperatures.     

A new convenient method for the synthesis of cardiolipin

A novel dichlorophosphate coupling method is developed for the synthesis of the title compound. O-Chlorophenyl dichlorophosphate can be used as a mild phosphorylating reagent to effectively couple with optically active 1,2-O-diacyl-sn-glycerol and 2-O-protected glycerol to assemble cardiolipin bearing different fatty acid chains.     

Magnetic behavior of copper diethyldithiocarbamate at low temperatures: A reinvestigation

The title compound, Cu(S₂CNEt₂)₂, behaves at low temperatures (1–20 K) as a normal spin-1/2 molecule, with 〈g〉 =2.06 and the Curie-Weiss θ = +0.25 K. This result contradicts an earlier investigation that led to the suggestion that the crystallographically-occurring dimers are coupled ferromagnetically.     

Water-protein dynamic coupling and new opportunities for probing it at low to physiological temperatures in aqueous solutions

Both the structure and dynamics of biomolecules are known to be essential for their biological function. In the dehydrated state, the function of biomolecules, such as proteins, is severely impeded, so hydration is required for bioactivity. The dynamics of the hydrated biomolecules and their hydration water are related - but how closely? The problem involves several layers of complexity. Even for water in the bulk state, the contribution from various dynamic components to the overall dynamics is not fully understood. In biological systems, the effects of confinement on the hydration water further complicate the picture. Even if the various components of the hydration water dynamics are properly understood, which of them are coupled to the protein dynamics, and how? The studies of protein dynamics over the wide temperature range, from physiological to low temperatures, provide some answers to these question. At low temperatures, both the protein and its hydration water behave as solids, with only vibrational degrees of freedom. As the temperature is increased, non-vibrational dynamic components start contributing to the measurable dynamics and eventually become dominant at physiological temperatures. Thus, the temperature dependence of the dynamics of protein and its hydration water may allow probing various dynamic components separately. In order to suppress the water freezing, the low-temperature studies of protein rely on either low-hydrated samples (essentially, hydrated protein powders), or cryo-protective solutions. Both approaches introduce the hydration environments not characteristic of the protein environments in living systems, which are typically aqueous protein solutions of various concentrations. In this paper, we discuss the coupling between the dynamic components of the protein and its hydration water by critical examining of the existing literature, and then propose that proteins can be studied in an aqueous solution that is remarkably similar in its dynamic properties to pure water, yet does not freeze down to about 200 K, even in the bulk form. The first experiment of this kind using quasielastic neutron scattering is discussed, and more experiments are proposed.     

A temperature independent pH (TIP) buffer for biomedical biophysical applications at low temperatures

A temperature independent pH buffer has been developed from a combination of buffers of opposite-sign temperature coefficients, and utility in low temperature spectroscopy and storage of pH sensitive compounds is demonstrated.     

A convenient new procedure for converting primary amides into nitriles

An operationally simple and high-yielding procedure has been developed for the conversion of primary amides to the corresponding nitriles, using ethyl dichlorophosphate/DBU as the mild dehydrating agent.     

A new convenient synthetic method for 3,4-diaryl-2,6-piperidinediones

A one-pot reaction for the preparation of 3,4-diaryl-2,6-piperidinediones through acid hydrolysis of the corresponding ethyl 3,4-diaryl-4-cyanobutyrates is described.

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Ein neuer einfacher Syntheseweg für 3,4-Diaryl-2,6-piperidindione

Zusammenfassung Durch saure Hydrolyse der entsprechenden Ethyl-3,4-diaryl-4-cyanobutyrate wurden in einem Schritt (Eintopfreaktion) die 3,4-Diaryl-2,6-piperidindione dargestellt.

     

A new pulsed electric field microreactor: comparison between the laboratory and microtechnology scale

This paper presents a new microreactor dedicated for pulsed electric field treatment (PEF), which is a pasteurization method that inactivates microorganisms with short electric pulses. The PEF microreactor consists of a flow-through channel with a constriction where the electric field is focussed. Compared to a laboratory-scale setup 25 times lower voltages were needed to obtain the same electric field strength due to the close electrode spacing. A finite element model showed that the electric field intensity is very homogeneous throughout the channel, which is crucial for the pasteurization processes. Experiments where artificial vesicles, loaded with carboxyfluorescein, were electroporated showed that the maximum transmembrane potential adequately described the processes both in the microreactor and the laboratory-scale setup, although the length scales are different. Electroporation started at a transmembrane potential of 0.5 V, reaching a maximum fraction of electroporated vesicles of 51% at a transmembrane potential of 1.5 V. The partial electroporation is not a result of the heterogenity of the vesicles or the electric field. With this new PEF microreactor it is possible to study the PEF process in more detail.     

MoO_x促进的Pt基催化剂用于低温水汽变换反应(英文)

通过浸渍还原法制备了不同比例的Pt-Mo/SiO_2催化剂,采用X射线衍射、透射电镜、X射线近边吸收谱和X射线光电子能谱表征了Pt-Mo/SiO_2催化剂的组成、结构及价态.研究结果表明,少量MoO_x修饰Pt-Mo/SiO_2催化剂在低温水汽变换反应中表现出比Pt/SiO_2催化剂更高的催化活性,过量MoO_x包覆的Pt-Mo/SiO_2催化剂活性较低.低温水汽变换反应活性来自于Pt与表面MoO_x的界面协同作用,限域在Pt纳米颗粒表面的MoO_x表现出较低价态,高分散MoO_x纳米岛修饰的Pt纳米颗粒是低温水汽变换反应的活性结构.     

A diffusive anomaly of water in aqueous sodium chloride solutions at low temperatures

Molecular dynamics simulations are presented for the self-diffusion coefficient of water in aqueous sodium chloride solutions. At temperatures above the freezing point of pure water, the self-diffusion coefficient is a monotonically decreasing function of salt concentration. Below the freezing point of pure water, however, the self-diffusion coefficient is a non-monotonic function of salt concentration, showing a maximum at approximately one molal salt. This suggests that sodium chloride, which is considered a structure-making salt at room temperature, becomes a structure-breaking salt at low temperatures. A qualitative understanding of this effect can be obtained by considering the effect of ions on the residence time of water molecules near other water molecules. A consideration of the freezing point depression of aqueous sodium chloride solutions suggests that the self-diffusion coefficient of water in supercooled sodium chloride solutions is always higher than that in pure (supercooled) water at the same temperature.