Determination of adhesion in bitumen-mineral systems by heat-of-immersion calorimetry

Chemical factors influencing bitumen-mineral adhesion have been examined by heat-of-immersion calorimetry. Two chosen minerals (quartz and calcite) and bitumen derived from Venezuelan and Middle East crude oils were characterised and the energy released by the bitumen-mineral interaction measured. Heat-of-immersion data are correlated with the concentration of heteroatomic species present in the bitumen and the structure of the mineral surfaces. Bitumen-quartz bonding is promoted by the presence of basic species in the bitumen and bitumen-calcite adhesion is favoured by the presence of acidic groups. A mechanism is proposed to account for the observed bond energies.     

差示扫描量热法测定对乙酰氨基酚原料药纯度

建立差示扫描量热(DSC)法测定对乙酰氨基酚原料药纯度的方法。考察升温速率、称样量、坩埚类型对测定结果的影响,确定最佳测定条件:升温速率为1.0℃/min,称样量为2.0~2.2 mg,选用Tzero密封铝坩埚作为样品盘。DSC法测定对乙酰氨基酚原料药纯度为99.91%,测定结果的相对标准偏差为0.03%(n=6),DSC法测定结果与紫外可见分光光度法测定结果(99.85%)基本一致,且DSC法测定结果的相对标准偏差较小。该方法简便、快速、准确,无需标准品,可用于对乙酰氨基酚原料药纯度的测定。     

Determination of the stability of omeprazole by means of differential scanning calorimetry

Differential scanning calorimetry was used to study the stability of omeprazole in two forms: granules and powder. The drug was subjected to light, elevated temperature (40 and 60°C) and different pH values. The greatest alterations in stability were caused by pH, followed by light.     

Construction of solid-liquid phase diagrams in ternary systems by titration calorimetry

Titration calorimetry was used to construct the solid-liquid equilibrium line in ternary systems containing the solute and an aqueous mixed solvent by measuring the heat of dissolution of the solid solute during successive additions of the liquid solvent. The plot of cumulated heats versus the mole ratio, n_solvent/n_solute, yields two (almost) linear increases of different slopes. These two lines represent successively the enthalpy of dissolution then the enthalpy of dilution of the medium; their intersection gives the solubility and the enthalpy of dissolution of the solute. Phase diagrams have been established over the whole concentration range for o-anisaldehyde, 1,3,5-trimethoxybenzene and vanillin, in water + methanol, +ethanol, or +n-propanol at 303, 313 and 318 K.     

Isothermal crystallization of concentrated amorphous starch systems measured by modulated differential scanning calorimetry

The slow isothermal crystallization of concentrated amorphous starch systems is measured by Modulated Differential Scanning Calorimetry (MDSC). It can be followed continuously by the evolution (stepwise decrease) of the MDSC heat capacity signal (Cp), as confirmed with data from X-ray diffractometry, Dynamic Mechanical Analysis, Raman spectroscopy, and conventional Differential Scanning Calorimetry. Isothermal MDSC measurements enable a systematic study of the slow crystallization process of a concentrated starch system, such as a pregelatinized waxy corn starch with 24 wt % water and 76 wt % starch. After isothermal crystallization, a broad melting endotherm with a bimodal distribution is observed, starting about 10°C beyond the crystallization temperature. The bulk glass transition temperature (T_g) decreases about 15°C during crystallization. The isothermal crystallization rate goes through a maximum as a function of crystallization time. The maximum rate is characterized by the time at the local extreme in the derivative of Cp (t_max), or by the time to reach half the decrease in Cp (t_1/2). Both t_max and t_1/2 show a bell-shaped curve as a function of crystallization temperature. The temperature of maximum crystallization rate, for the system studied, lies as high as 75°C. This is approximately 65°C above the initial value of T_g. Normalized Cp curves indicate the temperature dependence of the starch crystallization mechanism. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2881–2892, 1999     

Cone calorimetry studies of benzoxazine-epoxy systems flame retarded by chemically bonded phosphorus or silicon

The combustion behaviour of phosphorus- and silicon-containing benzoxazine-epoxy systems has been studied by LOI and cone calorimetry giving clear evidence that incorporation of 3.5% P into the benzoxazine-epoxy systems resulted in flame retardation while the silicon-containing copolymer was found to have no improvement in the LOI and cone calorimeter data, with values similar to the polymers without heteroatom, thus indicating that the 3.9% silicon content has no flame retarding effect. The peak heat release rate is reduced significantly for the phosphorus-containing benzoxazine as a result of a combination of condensed-phase and gas-phase mechanisms. The incorporation of phosphorus or silicon into the modified benzoxazine-epoxy system increases the smoke hazard and the CO emissions compared to the heteroatom-free system.     

Combined use of adiabatic calorimetry and heat conduction calorimetry for quantifying propellant cook-off hazards

Recent work performed at DERA (now QinetiQ) has shown how accelerating rate calorimetry (ARC) can be used to obtain time to maximum rate curves using larger samples of energetic materials. The use of larger samples reduces the influence of thermal inertia, permitting experimental data to be gathered at temperatures closer to those likely to be encountered during manufacture, transportation or storage of an explosive device. However, in many cases, extrapolation of the time to maximum rate curve will still be necessary. Because of its low detection limit compared to the ARC, heat conduction calorimetry can be used to obtain data points at, or below, the region where an explosive system might exceed its temperature of no return and undergo a thermal explosion.Paired ARC and heat conduction calorimetry experiments have been conducted on some energetic material samples to explore this possibility further. Examples of where both agreement and disagreement are found between the two techniques are reported and the significance of these discussed. Ways in which combining ARC and heat conduction calorimetry experiments can enhance, complement and validate the results obtained from each technique are examined.     

Electrolysis in calorimetry

The procedure used by many electrochemists in calculating enthalpy in calorimetric measurements of electrolysis reactions is compared to a purely thermodynamic approach, using the data published by Fleischmannet al. [J. Electroanal. Chem., 287 (1990) 293.] as a case study.The set of excess values dH _ex/dt=dH _obs/dt -dH_calo/dt obtained with the former procedure was neither correlated to any of the experimental parameters nor to the set of values found using thermodynamics. The latter, smaller by factors of up to two orders of magnitude, are shown to follow an expression of the form dH _ex/dt=–kI exp (–E _a/RT) with an activation enthalpy of about 85 kJ·mol^–1. It is suggested that recombination of electrolysis gases may account for this.

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Zusammenfassung Das von vielen Elektrochemikern verwendete Verfahren zur Berechnung der Enthalpie in kalorimetrischen Messungen an Elektrolysereaktionen wurde unter Anwendung der von Fleischmann et.al. in einer Fallstudie [J. Electroanal. Chem., 287 (1990) 293.] veröffentlichten Angaben mit einer rein thermodynamischen Näherung verglichen.Eine Reihe von mit der ersten Methode erhaltenen überschu\werten dH _ex/dt=dH _obs/dt-dH _calc/dt korrelierte weder mit den experimentellen Parametern noch mit den entsprechenden, thermodynamisch gefundenen Werten. Letztere, um etwa zwei Grö\enordnungen kleinere Werte konnten durch die Gleichung dH _ex/dt= -kI exp (-E _a/RT) mit einer Aktivierungsenthalpie von etwa 85 kJ·mol^–1 beschrieben werden. Es wird deshalb nahegelegt, da\ dies einer Rekombinierung der Elektrolysegase zugeschrieben werden kann.

     

Reaction-induced phase separation in polyethersulfone-modified epoxy-amine systems studied by temperature modulated differential scanning calorimetry

In epoxy-amine systems with a thermoplastic additive, the initially homogeneous reaction mixture can change into a multi-phase morphology as a result of the increase in molecular weight or network formation of the curing matrix. Temperature modulated DSC (TMDSC) allows the real-time monitoring of this reaction-induced phase separation. A linear polymerizing epoxy-amine (DGEBA–aniline) and a network-forming epoxy-amine (DGEBA–methylene dianiline), both with an amorphous engineering thermoplastic additive (polyethersulfone, PES), are used to illustrate the effects of phase separation on the signals of the TMDSC experiment. The non-reversing heat flow gives information about the reaction kinetics. The heat capacity signal also contains information about the reaction mechanism in combination with effects induced by the changing morphology and rheology such as phase separation and vitrification. In quasi-isothermal (partial cure) TMDSC experiments, the compositional changes resulting from the proceeding phase separation are shown by distinct stepwise heat capacity decreases. The heat flow phase signal is a sensitive indication of relaxation phenomena accompanying the effects of phase separation and vitrification. Non-isothermal (post-cure) TMDSC experiments provide additional real-time information on further reaction and phase separation, and on the effect of temperature on phase separation, giving support to an LCST phase diagram. They also allow measurement of the thermal properties of the in situ formed multi-phase materials.     

Equilibrium and non-equilibrium phase transitions studied by adiabatic calorimetry

An adiabatic calorimetry was used for some investigations of equilibrium and non-equilibrium phase transitions. For one of the substances studied (4,4′-di-n-heptyloxyazoxybenzene) it was possible to determine temperature dependence of an order parameter and number of clusters of high temperature phase in a region of a phase transition. For another substance (liquid 3,4 dimethylpiridine) an anomaly on the specific heat curves was interpreted as being responsible for a decay of molecules’ clusters. Non-equilibrium phase transitions were investigated for some liquid crystal substances. The process of transformation between metastable and stable phases was described quantitatively. The conclusions obtained concern the stability of metastable phases.     

Pseudo-adiabatic calorimetry

A procedure is described for dealing with the error sources inherently present in any real calorimeter: work of powerP _s input from stirrer and possibly temperature sensor, and heat exchange at a rate ?G(T?T _e ) whereT andT _c are the temperatures of calorimeter and surroundings respectively. The constantsP _s andG are calculated from a period of thermal decay, and afterwards are used to correct the entire run. A calorimeter was designed with high thermal homogeneity and used in a test. The curve of calculated temperature exactly traces the heater energy, even after 5 h, with a standard deviation of about 1 mK. The relative error inC _p is less than 1/1000.     

The advantages and disadvantages of direct and indirect calorimetry

Kleiber's definitions of what constitutes direct and indirect calorimetry are accepted as the beginning of a commentary on the advantages and disadvantages of direct and indirect calorimetry in which calorimetry is divided into a number of categories based on the kind of calorimetric measurement. For non-reaction calorimetry such as entropy determinations and differential scanning calorimetry, the only means of measurement is by direct calorimetry. For reaction calorimetry, a preference of direct over indirect calorimetry depends on the accuracy needed and the ability of the experimenter to define the system. The data necessary to correct the observed heat loss in direct calorimetry are often all that are needed to make an indirect calculation of the true heat loss. In general, because they are convenient and inexpensive to use, indirect calorimetric methods are preferable to direct methods. However, when possible, one method can be used to verify the results of the other.     

Water transfer in mixed water-in-oil emulsions studied by differential scanning calorimetry

Water transfers are observed within complex systems containing aqueous phases separated by a membrane or an oil phase, such as biological cells or multiple emulsions. In order to better understand water transfer mechanism, a system made of a mixed water-in-oil (W/O) emulsion containing two kinds of aqueous droplets — pure water and a 30 % urea solution — was developed. Water transfer from pure water droplets to urea solution droplets was evidenced by Differential Scanning Calorimetry (DSC). Finally the mixed emulsion contains one kind of droplets made of a diluted urea solution which composition is in agreement with formulation and data obtained from experiments performed on single W/O emusions which dispersed phase is a diluted urea solution of the same composition. These mixed emulsions have been pictured as a three-fluid phases system containing two aqueous phases separated by a plane oil membrane. From a homogeneous solubility-diffusion model applied to a quasi-stationnary regime, the water intra-diffusion coefficient has been obtained and compared to the value calculated from the Stokes-Einstein equation. A factor ten makes the discrepancy between the two values, the value deduced from the model being the highest. A possible influence of the emulsifier molecules has been evoked.     

Deformation calorimetry of polyurethane block-copolymers

A thermodynamic analysis of the uniaxial stretching of polyurethanes of various compositions and mechanical histories was carried out by using deformation calorimetry. The initial small strain deformations were found to result from the volume elasticity of the hard phase. The intramolecular energy contributions of the soft blocks were estimated. The hard block contributions were shown to depend on their content and on the degree of sample stretching. The predominant role of the soft component is proved to be manifested only in softened samples with a hard block content not exceeding 30%. The thermodynamics of the softening and hysteresis phenomena were studied. The dependence of the deformation mechanism on the hard block content and mechanical history is discussed.The authors express their thanks to Dr. A. R. Korigodsky and Dr. M. P. Letunovsky for the PU samples.     

Binding isotherm determination by isothermal titration calorimetry

Journal of Thermal Analysis and Calorimetry - A simple method for determination of binding isotherm in the protein-ligand interaction was introduced using isothermal titration calorimetric data....     

Some remarks on heat capacity measurements by temperature-modulated calorimetry

In temperature-modulated calorimetry, the condition in sample amount, especially thickness, required for high-accuracy heat capacity measurement should be made clear. We propose the condition of maximum thickness of a sample for measuring heat capacity within an accuracy of 1%. The other important factor for high-accuracy heat capacity measurement is thermal contact conductance between a sample and a sample pan and also that between a pan and a base plate of an apparatus. The conditions in these thermal contact conductances required for high-accuracy heat capacity measurement are discussed. Among them, if only thermal contact conductance between a pan and a base plate is significant, there is an ingenious method to measure heat capacity with high accuracy. Furthermore, if the thermal contact conductance between a pan and a base plate is infinite, we offer a simple method to obtain complex heat capacity.     

Crystallinity of poly(3‐hexylthiophene) in thin films determined by fast scanning calorimetry

Using fast scanning calorimetry, we determined the crystallinity of thin films of poly(3‐hexylthiophene) crystallized from the melt from measurements of the specific melting enthalpy. A broad range of film thicknesses from 10 µm down to 26 nm was covered. The sample mass was determined from measurements of the specific heat capacity in the molten state allowing a quantitative analysis of the heat flow data. Films with a thickness 400 nm slowly cooled from the melt showed the same crystallinity as bulk samples measured with conventional DSC. Below 350 nm the melting enthalpy decreased strongly. We assign this strongly reduced crystallinity to the restricted crystallization kinetics originating from hindered spherulitic growth under thin film confinement. A higher crystallinity could be partially regained by extended isothermal crystallization at elevated temperatures. Much faster cooling, with rates above about 100 Ks^?1 led to a partial suppression of crystallization even for thick films. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1791–1801     

Pulsed bed calorimetry

Conventional calorimetry has always the difficulty of choosing between near to equilibrium working conditions and high thermal ramp rates. Thus, either the transport phenomena and sample homogeneities are good but the signals become weak due to thermal losses, or the signals are sharp, but strong gradients across the sample lead to chemical and thermal heterogeneities. The described pulsed fluidized bed technique, by strongly stirring the sample, allows good sample homogeneities even at high ramp rates. Moreover, the permanently regenerated cover gas allows as well a good heat transfer towards the thermocouples as a constant atmosphere composition leading to very precise onset temperatures.     

Kinetic method by using calorimetry to mechanism of epoxy-amine cure reaction

In this paper, it is clearly demonstrated that the dependence of the rate of evolving heat on time is completely described by using Mangelsdorf's method in terms of three processes with excellent precision. The first two exothermic processes take into account the fact, that the reaction occurs by two competitive mechanisms: one is a non-catalytic mechanism and the other is catalyzed by OH-groups formed during the reaction. The third one refers to the endothermic process where the reaction is accompanied by diffusion of the reaction products. The distinctive feature of this diffusion process is that it is the coupling of the reaction kinetics and rearrangement of the chains built to the rigid supramolecular structure. This simple model allows accurate simulation of kinetic behaviour. This revised version was published online in July 2006 with corrections to the Cover Date.