Rate Of Heat Evolution Research Articles

The Microstructure of Anhydrous Cement and its Effect on Hydration

ABSTRACTThe hydration and microstructural development of cement are affected by the arrangement of anhydrous phases within the cement grains. Backscattered electron images and X-ray microanalysis can be used to characterize the microstructure of anhydrous cement. An image analyzer has been used to measure the overall proportions of silicate and interstitial phases in several cements and to measure the proportions of these phases that are exposed on the surface. These results are compared with the rates of heat evolution during the hydration of the cements.

Kinetics of the epoxide binder curing process under conditions of mutual diffusion of the components

The kinetics of the curing process in curing epoxide compositions under conditions of mutual diffusion of the reagents is studied on model systems. A relation is obtained for the initial rate of heat evolution as a function of the thickness of the layer of binder components, which is used as the basis for determining the coefficient of mutual diffusion as a function of the degree of conversion. A mathematical model of the process is derived, numerical calculations are made, and the conversion profile for the course of the reaction is obtained.

Computer analysis of kinetic data for microbial growth thermograms observed with a batch calorimeter.

Methods are investigated for evaluating the kinetic parameters in a modified Monod’s equation which give the best fit to the growth thermograms for bacterial cultures observed in batch calorimeters. Four mathematical methods were employed as parameter fitting techniques. The growth thermograms observed for soil microbes cultured with glucose as a limiting substrate were used as the objects of the analysis. For the calculation of the heat evolution rate, the Runge-Kutta method, which is commonly used for the numerical analysis, was employed. A comparison of the results obtained by the four methods in terms of closeness of fit to the actual thermograms showed that optimization by direct searching with the Simplex method is the most effective procedure for obtaining the best values of the parameters to reproduce the observed thermograms.

Heat exchange calorimetry for the estimation of instantaneous caloric effect

Abstract In the heat exchange calorimetry, heat evolved in a vessel placed in a water bath is exchanged freely with the ambient water. The thermal phenomena are expressed by a simple differential equation. An instantaneous calorie effect or rate of heat evolution q, as well as total heat Q, is estimated on line from the temperature θ observed via each thermistor in sample and reference vessels. After the estimation of Q from θ by using an analog computation technique, the values of Q corresponding to several successive points were used to calculate a point of q by the on-line numerical differentiation carried out with a microcomputer. The q thus obtained was by far better than that obtained by solely analog or numerical differentiation.

A simple principle of reaction calorimetry

Abstract A new measuring principle for following a rate of heat evolution in exothermic reactions under isothermal conditions has been proposed and experimentally tested. The reaction is carried but in an insulated vessel equipped with a cooling coil. The reaction heat is removed by stepwise addition of a coolant into the cooling coil. Using the oxidation of ethenol by hydrogen peroxide catalyzed by ferric ions as a model reaction, practically the same precision in estimation of rate data has been achieved with this thermokinetic method as with the chemical analysis of reaction mixture.

The application of heat flow sensor to study the hydration of inorganic binders

Abstract In studying the rate of heat evolution during the hydration of binder samples a sheet differential multlcouple was used. Its application can be exemplified by hydration of aluminous and Portland white cement mixtures.

Use of a novel heat-flux calorimeter for the measurement of heat generated during growth of [formula omitted] on lactose

A novel bench-scale calorimeter, which is based on a heat-flux principle and has been modified to accommodate biological reactions, has been used to investigate the heat evolution rate of an aerobic culture of the yeast K. fragilis grown on lactose. The instantaneous heat evolution rate was an accurate indicator for the instantaneous overall metabolic activity. On the other hand, the integrated heat production increased in parallel to the accumulated cell dry weight. The ratios of heat generated per gram biomass produced and of heat generated per mole of consumed oxygen were found to be constant throughout the experiment despite changing growth rates and metabolism.

Effect of mixing time on heat evolution pattern of cement pastes

This study reports the effect of mixing time on the heat evolution pattern of Portland cement/silica fume/superplasticizer (Aalborg cement). An isothermal conduction calorimeter was used to evaluate the rate of heat evolution and total heat hydration for a period of 72 hours at 20.0°C with a water/solid ratio of 0.25. The mixing period varied from 2 minutes to 30 minutes. The results are compared with Portland cement (PC) and Portland cement/ superplasticizer (PCS)

Calorimetric studies of crystallization and relaxation of amorphous Si and Ge prepared by ion implantation

Amorphous Si and Ge layers, produced by noble gas (Ar or Xe) implantation of single crystal substrates, have been crystallized in a differential scanning calorimeter (DSC). The MeV implantation energies resulted in amorphous layers of micron thickness whose areal densities were determined using the Rutherford backscattering and channeling of 1-MeV protons. These techniques allow determination of the amorphous-crystal interface velocity (which is proportional to the rate of heat evolution ΔḢac) and the total enthalpy of crystallization ΔHac. Amorphous Ge was found to relax continuously to an amorphous state of lower free energy, with a total enthalpy of relaxation of 6.0 kJ/mol before the onset of rapid crystallization. The interface velocity for crystallization on (100) substrates, was found to have an Arrhenius form with an activation energy of 2.17 eV. The value of ΔHac was found to be 11.6±0.7 kJ/mol, the same as for samples prepared by deposition. For Si, ΔHac was determined to be 11.9±0.7 kJ/mol without any evidence of heat release due to relaxation. The (100) interface velocity was found to have an activation energy of 2.24 eV. The effects of the implant depth profile on the regrowth velocity could also be observed directly in the DSC signal. From the value of ΔHac and Gibbs free-energy calculations, the melting temperature of amorphous Si has been determined to be Taℓ =1420 K.

Evolución del color en la fermentation de orujos de manzana

The heat evolution in the solid state fermentation of apple pomace to produce ethanol was measured by means of an adiabatic system. The average rate of heat evolution in the fermentation system was 669 cal (2.8 kJ)/kg/h. The total amount of heat generated was 12.4 kcal (52.1 kJ)/kg of apple pomace fermented.

Calorimetry of Nitrogenase-Mediated Reductions in Detached Soybean Nodules

Heat evolved by isolated soybean (Glycine max cv Clark) nodules was measured to estimate more directly the metabolic cost associated with the symbiotic N(2) fixation system. A calorimeter constructed by modifying standard laboratory equipment allowed measurement on 1 gram of detached nodules under a controlled gas stream. Simultaneous gas balance and heat output determinations were made.There was major heat output by nodules for all of the nitrogenase substrates tested (H(+), N(2), N(2)O, and C(2)H(2)) further establishing the in vivo energy inefficiency of biological N(2) fixation. Exposure to a short burst of 100% O(2) partially inactivated nitrogenase to permit calculations of heat evolved per mole of substrate reduced. The specific rate of heat evolution for H(+) reductions was 171 +/- 6 kilocalories per mole H(2) evolved in an Ar-O(2) atmosphere, that for N(2) fixation was 784 +/- 26 kilocalories per mole H(2) evolved and N(2) fixed, and that for C(2)H(2) reduction was 250 +/- 12 kilocalories/mole C(2)H(4) formed. When the appropriate thermodynamic parameters are taken into account for the different substrates and products, a DeltaH' of -200 kilocalories per mole 2e(-) is shown to be associated with active transfer of electrons by the nitrogenase system. These values lead to a calculated N(2) fixation cost of 9.5 grams glucose per gram N(2) fixed or 3.8 grams C per gram N(2), which is in close agreement with earlier calculations based on nodular CO(2) production.

A classification of inorganic and organic admixtures by conduction calorimetry

A wide range of inorganic and organic admixtures have been investigated using isothermal conduction calorimetry. The results are presented as a series of maximum rate of heat evolution (Q̇ max) versus reciprocal to peak height (1/t max) plots. Using equivalent molar concentrations of admixture under controlled conditions a comparative ranking system of inorganic and organic admixtures has been devised. Some general conclusions are drawn about the mechanism of action of accelerating and retarding admixtures.

Dilatometric and thermographic investigation of the reactive sintering of titanium nickelide. I. Production of porous titanium nickelide by reactive sintering

The results of simultaneous differential thermographic and dilatometric analyses have shown that the diffusional reaction accompanying the sintering of an equiatomic mixture of titanium and nickel powders takes place in several distinct stages: solid-phase reactive diffusion; diffusion in the presence of a liquid phase forming as a result of contact melting; and solid-phase reaction. Data yielded by dilatometric and differential thermographic analyses match. The following phenomena are observed: shrinkage in the range of the ascending branch of the first heat evolution peak; shrinkage or growth, depending on the porosity in the range of the descending branch; stepwise growth in the range of the second peak; and shrinkage in the third stage. Growth is apparently due to the difference in the partial diffusion coefficients of s titanium and nickel. The phase composition of the sintering products depends on the specimen porosity. With increasing porosity the material becomes more homogeneous, which is apparently due to a rise in the true temperature attained in the specimen during sintering as a result of a change in the relative rates of heat evolution and removal.

Monitoring and Thermochemical Analysis of Fermentation Process with a Calorimeter

The pattern of heat evolution rate was obtained in situ for aerobic growth of bacteria (E.coli) in both batch and continuous cultivation, using a microcalorimetric system. The thermograms of batch culture revealed the difference of nutritional condition with high sinsitivity. The specific heat production rate in continuous culture showed a linear relationship against dilution rate. Efficiency of catabolic energy utilization for anabolism calculated reflected the degree of coupling between catabolism and anabolism. Heat balance in continuous culture showed the metabolic characteristics in each dilution rate. Thermograms of yeasts were also obtained.

Calorimetric analysis of Escherichia coli in continuous culture

The heat evolution rate was measured in continuous culture of Escherichia coli k-12 on glucose-limiting medium. The specific heat production rate based on the dry cell mass increased in proportion to increase of dilution rate. The specific heat production rate based on a viable cell increased nonlinearly because the cell size varied in each dilution rate. Several thermochemical data were calculated for each dilution rate from the stoichiometric equation which was derived from elementary analysis of the cells. Growth yields based on energy measured directly was found to be less influenced by dilution rate than the growth yield based on consumed glucose. This suggested that the energy efficiency of utilization of catabolic energy for anabolism was almost constant.

The thermokinetic reactor TKR and its possible applications in chemical research and engineering

A reactor-calorimeter is described which makes it possible to perform accurate measurements of the thermal power (rate of heat evolution) of chemical and physicochemical processes in essentially fluid reaction systems to be carried out a) continuously under isothermal conditions, b) without interfering with the course of the reaction, c) using large quantities of reaction mix, d) allowing for considerable variations in the consistency and/or the volume of the mix during reaction, e) providing for conditions which are very close to those of industrial practice. In addition, the equipment provides information on the heat transmittance of the reactor and the stirring power.

Surface temperature gradients and rates of internal heat evolution at criticality for generalized heat transfer (arbitrary Biot number)

The dependence on the heat-transfer conditions (Biot number, Bi) of the temperature gradient at the surface, Γ, of an exothermic reactant mass at criticality is presented. Bodies of slab, cylindrical and spherical geometry have the same values of Γcr at the Frank-Kameneskii extreme (Bi→∞, Γcr= 2) and also at the Semenov extreme (Bi= 0, Γcr= 0). For general boundary conditions the critical surface temperature gradient depends on the Biot number and shape.

Exothermic systems with diminishing reaction rates: Mathematical analysis

There are many practical instances of materials in which the rate of an exothermic reaction decays with time t like ( t + t pr) − α, t pr ≥ 0, 0 ≤ α < 1. The origin of such systems is described in Boddington et al. in Proc. Royal. Soc. (1980). For such systems critical behavior is characterized easily by the conditions separating the two types of behavior: supercritical ones which reach infinite temperatures in a finite time and subcritical ones which pass through a maximum and then (asymptotically with time) fall to zero. The problem of determining the critical conditions does not, for all values of the exponent α, admit to analytical solution even for the uniform temperature case (Semenov model). The results of this paper give an asymptotic estimate for the critical values of a dimensionless parameter δ 1 in the expression for the rate of heat evolution δ 1 cr ∼ δ 0 cr (1 − 1 2 αln α) for small α, where δ 0 cr is the critical value of the usual Frank-Kamenetskii parameter (for α = 0) for the same geometry and Biot number and includes the uniform temperature case. Here τ pr will be the dimensionless parameter corresponding to the time τ pr in the rate equation. Although the true form of δ 1 cr versus α cannot be determined analytically, it can be shown that for τ pr = 0, δ 1 cr = 0 at α = 1; and for 0 < τ pr, δ 1 cr as a function of α has only one maximum and δ 1 cr → 0 + as α → ∞. Further, for the uniform temperature case it is shown that when τ pr = 0, δ 1 cr ∼ 1 − α near α = 1. The analytical results are supported by the computed results reported for the sphere with infinite Biot number for the case τ pr = 0. This shows that the maximum of δ 1 cr occurs for α ⋍ 0.04 and is close to the classical value for α = 0.

瞬間気流焼成によって得られたＩＩ型無水石こうの性質

This paper is concerned with a process of manufacturing II-CaSO4 from powdered gypsum (CaSO4·2H2O) and the properties of the products obtained from the process.Apart from fluorogypsum (II-CaSO4) formed as by-product in the industrial manufacture of hydrofluoric acid, II-CaSO4 is usually produced by calcining (at 600-800°C) in a rotary kiln or shaft kiln, which consumes a larger amount of heat energy.In order to manufacture II-CaSO4 at lower cost, the authors have developed a new technique of manufacturing II-CaSO4 which calcines powdered gypsum (CaSO4·2H2O) instantly by dispersing it into an atmosphere of high temperature gas including flames.The main characteristics of this technique are as follows:(1) Time for calcining is a few seconds.(2) Heat for calcining is below half of those of the old techniques.(3) II-CaSO4 can be produced even at 250°C which is below the conversion temperature, from III-β-CaSO4 to II-CaSO4, obtained by DTA.The properties of the products calcined at 250, 600 and 800°C, such as pore size distribution, heat of hydration and micro-structures of hydrated bodies were investigated.On the basis of these results, it has been proven that the hydration reaction of each product proceeds under the same mechanism. The rate of heat evolution depends upon their micropore distribution and size of crystallite which are characterized by the calcining temperatures.Using this new calcining technique, consequently, various types of II-CaSO4 can be obtained only by changing the calcining temperature.

Thermodynamics and Kinetics of Crystallization of Amorphous Si and Ge Produced by Ion Implantation

ABSTRACTAmorphous Si and Ge layers, produced by noble gas (Ar or Xe) implantation of single crystal substrates, have been crystallized in a differential scanning calorimeter (DSC). This technique allows determination of the growth velocity (which is proportional to the rate of heat evolution, ΔHac), and the total enthalpy of crystallization ΔHacAmorphous Ge was found to relax continuously to an amorphous state of lower free energy, with a total enthalpy of relaxation of 6.0 kJ.mole−1 before crystallization started. The regrowth velocity on (100) substrates,measured to be 4.2×1017 exp (−2.17eV/kT)Å/sec, is compared to other determinations. The value of ΔHac was found to be 11.66± 0.7 kJ.mole, in good agreement with ΔHac for amorphous Ge produced by other methods. For Si, ΔHac was determined to be 11.95± 0.7 kJ.mole without any evidence of heat release due to relaxation. The kinetics of crystallization measured by DSC are compared with those determined by other techniques. The effects of the implant profile on the regrowth velocity could also be observed directly in the DSC signal. The more accurate value of ΔHac allowed a more precise determination of the melting temperature of amorphous Si: Taℓ= 1420K.