热动力学对比进度法IV. 热导式热量计的单参数理论模型与热谱重建

本文建立了热导式热量计的单参数理论模型, 在此基础上系统地提出了热谱重建法, 并结合热动力学对比进度法, 对几个化学反应体系进行了热动力学研究。实验结果验证了本文方法及其理论基础的正确性。     

Thermodynamic study of the liquid Fe-S system by use of a drop calorimeter

Heat contents of the Fe-S system were measured with a drop calorimeter in the sulfur composition range X_s = 0.380–0.500 (FeS) and in the temperature range 942–1506 K to construct an (H_T - H_298.15)-temperature-composition ternary diagram. By use of a thermodynamic analysis method, the mixing free energy, enthalpy and entropy of the liquid Fe-S mixtures were determined at 1473 and 1523 K, based on the measured heat contents. The partial molar free energies (activity of iron and partial pressure of diatomic sulfur) agreed well with the literature values, suggesting the applicability of the thermodynamic analysis method for liquid mixtures with semi-metals or chalcogen.     

On the construction and use of cheap digitalized calorimeter

Summary The physical properties of electrical calorimeter constructed at Mendel University and the corresponding data processing are presented. The calorimeter is used for measurement of the specific heats, namely foods. It is built from widely used equipment, the main parts are frequent digital multimeters and an older computer. Its main advantage is low costs, simplicity, rate of the measurement and digital data output and storage. Lower accuracy of the measurement, ~5%, is its partial disadvantage.     

Unusual use of the term “differential scanning calorimeter”

Derivatograph was used to investigate pseudohomogeneous ion-exchange membranes. Two membrane types were examined: a) a membrane obtained from polyethylene film modified with the copolymer of styrene and DVB; and b) membrane AMF C-311 obtained on a film of fluorinated polymeric material.Although differential thermal analysis (DTA) has been used in the investigation of polymers only recently, a large number of papers concerning different problems in this field have already appeared. Only a few of these papers, however, have been devoted to cross-linked polyelectrolytes and more exclusively to ion-exchange resins [1–5], i.e. homogeneous polyelectrolytes. Up to date no publication dealing with pseudohomogeneous ion-exchange membranes has appeared. The pseudohomogeneous membrane is a system of two phases: a polymer film (polyethylene is most often used as matrix), with a cross-linked acid (e.g.polystyrenesulphonic acid) dispersed in the polymer film. The present investigation was undertaken to find the correlation between the thermal curves of a pseudohomogeneous cation-exchange membrane and the thermal properties of both phases of the membrane.The authors wish to thank T. Grodzicka, Institute of Chemistry, N. Copernicus University, Toru>n for determinations carried out with the MOM Derivatograph.     

Fully automated measurement of the modulation transfer function of charge-coupled devices above the Nyquist frequency

The charge-coupled devices used in electron microscopy are coated with a scintillating crystal that gives rise to a severe modulation transfer function (MTF). Exact knowledge of the MTF is imperative for a good correspondence between image simulation and experiment. We present a practical method to measure the MTF above the Nyquist frequency from the beam blocker's shadow image. The image processing has been fully automated and the program is made public. The method is successfully tested on three cameras with various beam blocker shapes.     

Thermal curve interpretation by spectral resolution into a basic set of rectangular pulse curves

A generalized spectral resolution method for thermokinetic determination is presented and tested. Any kind and number of identification thermal curves can be used in a single calculation.     

Thermal curve interpretation by spectral resolution into a basic set of rectangular pulse curves

An improvement of the algorithm of the spectral resolution method for the determination of thermokinetics is presented. With the aid of the modified computer program and an experimental thermal curve, an analysis of the method has been performed.     

塔板理论色谱流出曲线性质的研究

塔板理论是色谱动力学理论的重要部分。本文采用数学方法把塔板理论色谱流出曲线从离散函数形式变换为连续函数形式。在此基础上运用计算机进一步研究了塔板理论色谱流出曲线的性质。     

Metal-ion-dependent folding of a uranyl-specific DNAzyme: insight into function from fluorescence resonance energy transfer studies

Fluorescence resonance energy transfer (FRET) has been used to study the global folding of an uranyl (UO₂²⁺)‐specific 39E DNAzyme in the presence of Mg²⁺, Zn²⁺, Pb²⁺, or UO₂²⁺. At pH 5.5 and physiological ionic strength (100 mM Na⁺), two of the three stems in this DNAzyme folded into a compact structure in the presence of Mg²⁺ or Zn²⁺. However, no folding occurred in the presence of Pb²⁺ or UO₂²⁺; this is analogous to the “lock‐and‐key” catalysis mode first observed in the Pb²⁺‐specific 8–17 DNAzyme. However, Mg²⁺ and Zn²⁺ exert different effects on the 8–17 and 39E DNAzymes. Whereas Mg²⁺ or Zn²⁺‐dependent folding promoted 8–17 DNAzyme activity, the 39E DNAzyme folding induced by Mg²⁺ or Zn²⁺ inhibited UO₂²⁺‐specific activity. Group IIA series of metal ions (Mg²⁺, Ca²⁺, Sr²⁺) also caused global folding of the 39E DNAzyme, for which the apparent binding affinity between these metal ions and the DNAzyme decreases as the ionic radius of the metal ions increases. Because the ionic radius of Sr²⁺ (1.12 Å) is comparable to that of Pb²⁺ (1.20 Å), but contrary to Pb²⁺, Sr²⁺ induces the DNAzyme to fold under identical conditions, ionic size alone cannot account for the unique folding behaviors induced by Pb²⁺ and UO₂²⁺. Under low ionic strength (30 mM Na⁺), all four metal ions (Mg²⁺, Zn²⁺, Pb²⁺, and UO₂²⁺), caused 39E DNAzyme folding, suggesting that metal ions can neutralize the negative charge of DNA‐backbone phosphates in addition to playing specific catalytic roles. Mg²⁺ at low (<2 mM ) concentration promoted UO₂²⁺‐specific activity, whereas Mg²⁺ at high (>2 mM ) concentration inhibited the UO₂²⁺‐specific activity. Therefore, the lock‐and‐key mode of DNAzymes depends on ionic strength, and the 39E DNAzyme is in the lock‐and‐key mode only at ionic strengths of 100 mM or greater.     

Thermodynamic investigation of the liquid PbS system by using a drop calorimeter

Heat contents of the PbS system were measured by a drop calorimeter in the composition range of sulfur X_s = 0 to 0.5 (PbS) and in the temperature range of 560 to 1500 K, and a heat content-temperature-composition ternary diagram was constructed. By using a quantitative thermodynamic analysis method, free energy, heat and entropy of mixing in the liquid PbS binary and PbPbS pseudo-binary systems were derived from the measured heat contents. The obtained partial molar free energies of mixing (activities) are considerably different from those estimated by the use of a regular solution model.     

Thermal curve interpretation by spectral resolution into the basic set of rectangular pulse curves

A new numerical method for the determination of thermokinetics is proposed. This is based on the spectral resolution of a thermal curve into the basic set of unit rectangular pulse curves orthogonalized by Löwdin's transformation. A numerical example shows that the present method can be successfully applied to experimental curves.

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Zusammenfassung Eine neue numerische Methode zur Bestimmung von Thermokinetika wird vorgeschlagen. Sie beruht auf der spektralen Auflösung einer thermischen Kurve in die Grundfolge von Einheiten rechteckiger Pulskurven, welche durch eine Löwdins Transformation orthogonalisiert worden sind. Ein numerisches Beispiel zeigt, dass diese Methode bei experimentellen Kurven mit Erfolg eingesetzt werden kann.

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Introduction of clutch function into a molecular gear system by silane-silicate interconversion

Introduction of the clutch-declutch mechanism into a new gear system, bis(4-methyl-9-triptycyl)difluorosilane 1, is achieved by the reversible attachment of fluoride ion giving the corresponding fluorosilicate 2. Although the phase isomers of 1 (1(dl) and 1(meso)) cannot be separated because of the equilibrium via a slow gear slippage process (DeltaH(double dagger) = 17.2 +/- 0.2 kcal x mol(-1) and DeltaS(double dagger) = 0.9 +/- 0.9 cal x mol(-1) x K(-1)), 1 works as meshed molecular gears in solution at room temperature. On the other hand, silicate 2 in the solid state has quite an unusual TBP structure having two organic triptycyl groups at the apical positions and three electronegative fluorine atoms at the equatorial positions against the Muetterties rule. Rotation of the two triptycyl groups around Si-C bonds in 2 is facile and independent to each other in solution. Silicate 2 is reverted to the corresponding silane mixture by treating with excess water.     

Mathematical analysis of the heat measured by a power-compensated differential scanning calorimeter during the solidification of a multiphase alloy

The determination of the solidification characteristics of alloys using differential scanning calorimetry (DSC) is difficult because of the unknowns associated with the kinetic of phase transformations and the thermal resistance between the sample and the temperature measuring device. This paper shows how appropriate assumptions coupled with a thermodynamic software package and an accurate mathematical analysis of a power-compensated DSC, can enable a direct comparison between the experimental and the theoretical heat evolutions obtained during the solidification of a multiphase alloy. This comparison is helpful in order to assess the thermodynamic database and to validate the different assumptions made in the solidification model.

     

Details of the emulsion polymerization of styrene using a reaction calorimeter

An automated reaction calorimeter was used to directly monitor the rate of emulsion polymerization of styrene using different emulsifier (sodium lauryl sulfate) and initiator (potassium persulfate) concentrations. By using this technique in conjunction with off-line measurements of the evolution of the particle size distributions, important details of the process were observed. The classical constant rate period (Interval II) often reported for the batch emulsion polymerization of styrene was not seen in this work. Instead, the experimental results suggest that the end of nucleation and the disappearance of monomer droplets take place at approximately the same conversion (36–40%). From the polymerization rate data, important parameters such as the monomer concentration in the polymer particles and the average number of radicals per particle were calculated. © 1996 John Wiley & Sons, Inc.     

Phase-response characteristics of the transfer function of a spatially limited electrochemical cell

Investigation of the dynamic characteristics of diffusion transducers is of great practical importance because of the wide utility of these devices in instruments for measuring the movement parameters and wave fields. Previously, cathode currents were the object of investigation because their difference was used as an output signal in several useful devices. In this work we investigated the amplitude and phase relationships between currents measured on both cathodes and anodes over a wide range of frequencies in a four-electrode electrochemical cell. It was shown in experiment that the sum of the currents recorded on the four electrodes of a molecular electronic cell (MEC) is zero, as follows from the condition of conservation of an electric charge. At frequencies as low as ～0.1 Hz the frequencies of the signal currents of the anode and the nearest cathode coincided. As the frequency grew to f ～80 Hz, the phase difference monotonously increased to values close to π. Previous theoretical models suggested, explicitly or implicitly, that the phases of the signal currents coincided over the whole range of frequencies in each anode-cathode pair. The results of the experiment were explained within the framework of the theoretical model of a four-electrode electrochemical cell, which is based on the one-dimensional equation of convective diffusion and takes into account the limited space of the cell.     

Interpolation and extrapolation of gamma detection efficiency curve as a function of distance

Summary The paper deals with the common mistake of interpolating calculation of the efficiency of gamma-detectors by the inverse square law of the distance of the source from the detector cap and suggests the use of the distance from the virtual point detector instead.     

Assessing the fire risk of electrical cables using a cone calorimeter

Journal of Thermal Analysis and Calorimetry - The presented study deals with the fire risk of electrical cables. Samples of three-core electrical power cables and two-core electrical control cables...     

Estimating the fire behavior of wood flooring using a cone calorimeter

This article analyzes the flammability characteristics in order to investigate the adequacy of a newly proposed sampling method for wood and PVC materials that are commonly used for residential flooring. Experiments on commercial products were performed using a cone calorimeter according to ISO 5660-1 specifications. Samples for the test procedure were prepared in two methods: either using a cone calorimeter sample preparation method (case 1), or the proposed sample preparation method, which a simplified form for the actual constructed shape (case 2). The thermal characteristics of the common wood products differed depending on the sampling method, where the peak heat release rate (PHRR) had either two peaks for case 1 or a single peak for case 2, and the total heat rate (THR) and smoke production rate (SPR) also differed according to the case. Especially, the wood flooring differed significantly between the two cases in terms of the number of PHRR peaks and the trend of the SPR curves. Due to these differences, we presented another HRR evaluation method depending on the raw material and the size of HRR to reduce the fire hazards in flooring.     

过氧化苯甲酰的热分解研究

The thermal decomposition process of benzoyl peroxide was investigated by Accelerating Rate Calorimeter. The curves of thermal decomposition temperature and pressure versus time for the systems were obtained. The curves of temperature rising-rate versus thermal decomposition temperature were also obtained. After the data revision disposal and analysis processing, thermal decomposition parameters and kinetic data of benzoyl peroxide were calculated, respectively.