Isothermal Heat Conduction Calorimetry Research Articles

How Do Isothermal Calorimeters Age? Repeatability and Reproducibility Across Calorimeter Generations

AbstractReliable experimental data is essential for reproducible science. As our lab has access to five instruments of the isothermal (heat conduction) type of different age and product generations, we became interested in the quality of experimental data obtained from the different instruments. Each instrument consists of 8 individual calorimeters. An intralaboratory study of the first 72 hours of cement hydration was conducted with all five instruments. The objective was to determine the differences between the available instruments with respect to repeatability (precision of the 8 calorimeters within one instrument) and reproducibility (precision between the different instruments). The experimental program comprises 120 calorimetry runs in total (5 instruments each with 8 calorimeters, triple measurement performed). Results show that the oldest instrument version with its 8 calorimeters has a stronger higher standard deviation of the heat released after 72 hours compared to the latest state‐of‐the‐art instrument model (246.7 ± 2.7 vs. 232.3 ± 0.5 Jg–1). This is attributed to the technical design differences of the instruments and continuous use over time. In terms of reproducibility, an increasing standard deviation for the heat released from 1 day to 3 days (136.2 ± 2.6 and 236.4 ± 5.9 J g–1) is observed. From our point of view, this test study indicates that isothermal heat conduction calorimetry is a robust and precise measurement method to determine the heat of cement hydration for 72 hours.

Effects of Calcination Conditions on the Formation and Hydration Performance of High-Alite White Portland Cement Clinker

The purpose of this study was to evaluate the effects of sintering temperature and sintering time on mineral composition of high-alite white Portland cement clinker and hydration activity of the clinker. Effects of sintering temperature and sintering time on clinker mineral composition, C3S polymorph and size and hydration heat release rate were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry&Thermogravimetric Analysis (DSC-TG) and isothermal heat-conduction calorimetry. Results shown that, with the increase of sintering temperature (1450–1525 °C) and sintering time (60–240 min), free lime (f-CaO) in clinker decreased, C3S grain size increased, and C3S crystal type changed from T3 to M type and R type, which exhibits higher symmetry. The hydration activity of different C3S crystals ranged from high to low as follows: T3→M1→M3→R@.

Coal fly ash activation—Comparison of isothermal calorimetric data and mortar strength

The aim of this study was to determine the effect of mechano-chemical activation of fly ash on the early strength of Portland cement fly ash blends. Triethanolamine (TEA) and alkalis (NaOH or Na2SO4) were used as chemical activators. The mechanical treatment was carried out with a vibratory disc mill. The effect of activation was determined by the combination of isothermal heat conduction calorimetry over 48h in combination with measurements of compressive strength between 1 and 28 d. Direct comparison of the features of the heat flow curves with compressive strength evolution was enabled by applying a numerical quantification method to the calorimetric results. This procedure revealed a systematic increase in early strength produced by the combination of the fly ash activation methods (grinding, TEA, alkalis). In addition, the acceleration of the pozzolanic reaction by fly ash activation was verified by replacing the cement in a cement fly ash blend by the equivalent amount of portlandite.

Analysis of aluminum concentrations in the pore solution during hydration of tricalcium silicate

The hydration of two batches of tricalcium silicate was followed by isothermal heat conduction calorimetry and analysis of pore solution composition. These two samples were different in Al2O3-content and free lime concentration. It was observed that the material containing aluminum reacts slower than the pure one. The reactivity was also analyzed in the presence of ettringite, gypsum and tricalcium aluminate, respectively.The aluminum concentration in the pore solution was always below the limit of detection during hydration of the samples independent of the presence of aluminum in tricalcium silicate or the addition of most supplementary phases. Elevated aluminum concentrations were only observed in the presence of tricalcium aluminate.The experimental investigations confirm earlier results that aluminum can reduce the reactivity of tricalcium silicate. It is shown in this study that this mechanism is not based on elevated aluminum concentrations in the pore solution.

The potential role of isothermal calorimetry in studies of the stability of fresh-cut fruits

Attention is drawn to the feasibility of using high sensitivity isothermal heat conduction calorimetry to study metabolic responses of differently processed and stored fresh-cut fruit. The heat production of endogenous (tissue metabolism during 12 h of analysis at 10 °C for kiwifruit and strawberry) and exogenous (microbial growth during 18 d of analysis at 10 °C for cantaloupe) biological processes was investigated.Osmotic dehydration of fresh kiwifruit in sucrose solution (61.5 g/L) at different treatment times (30, 60 and 180 min), resulted in metabolic heat production decrease, confirming the progressive cell death induced by osmotic dehydration.Analysis on strawberry slices under two atmospheric conditions (air and innovative modified atmosphere) seemed to confirm the inhibitory effect of N2O on metabolic activity.Cantaloupe samples immersed in three different syrups (SS: sucrose syrup (20 °Brix); SS1: SS + 0.5 g/L ascorbic acid + 0.5 g/L citric acid; SS2: SS1 + 0.1 g/L potassium sorbate) showed a stability increase when additives with antimicrobial properties were included.Our findings confirm that isothermal calorimetry provides a versatile and high sensitive tool for conducting fundamental metabolic studies on the effect of different processing operations on the quality and shelf life of fresh-cut fruit and vegetables.

Effect of CuO on the formation of clinker minerals and the hydration properties

The purposes of this study are to explore the mechanisms of Cu element in clinker burning and hydration processes and to make effective use of waste containing copper in cement production. The effect of CuO on clinker mineral composition, C 3S polymorph and size, Cu element distribution and state, compressive strengths, hydration products, non-evaporable water quantity and hydration heat release rate was analyzed by XRD, SEM, DTA, isothermal heat-conduction calorimetry, etc. Results show that as the amount of CuO increases the formation and growth of C 3S grain are accelerated, R C 3S is gradually transformed into M 3 and the content of C 4AF increases; a small quantity of CuO increases the 3-day and 28-day strengths and the hydration degree of clinker, but excessive CuO has adverse effects. Those effects of CuO on clinker burning process are attributed to the formation of low-melting Cu 2O and the dissolution of CuO in C 4AF which decrease the formation temperature of liquid phase and increase its quantity. The effects on hydration process result from the combined action of the following factors: the induction period is prolonged; the hydration reactions in the initial and acceleration periods are accelerated.

Hydration characteristics and hydration products of tricalcium silicate doped with a combination of MgO, Al 2O 3 and Fe 2O 3

Tricalcium silicate is the major component of ordinary Portland cement and the hydration products are responsible for the high strength of cementitious products. It is known that the crystal structure of tricalcium silicate depends on the kind and amount of foreign oxides incorporated into the lattice. In this study the influence of multiple doping with MgO, Al 2O 3 and Fe 2O 3 on the hydration characteristics was analysed by isothermal heat-conduction calorimetry. The hydration products were characterised by differential scanning calorimetry, X-ray diffraction, 29Si solid-state nuclear magnetic resonance spectroscopy and scanning electron microscopy. The hydration is dominated by the kind and concentration of foreign oxides, independent of the influence of the doped oxide on the crystal structure of C 3S. Combined doping with MgO + Al 2O 3 or MgO + Fe 2O 3 shows no interactions between the foreign oxides on their influence on hydration. In the case of combined doping with Al 2O 3 + Fe 2O 3, the retarding effect of Fe 2O 3 on the main reaction is much stronger in the presence of Al 2O 3.

Kinetics of interaction of hardened oil-well cement slurries with acidic solutions from isothermal heat-conduction calorimetry

The kinetics of interaction of hydrochloric acid with oil-well cement slurries treated with the silane coupling agents, tetraethyl orthosilicate, 3-(trimethoxysilyl)-1-propanethiol and 3-(chloropropyl)-trimethoxysilane have been investigated isothermal heat-conduction calorimetry at 298.15 K. The Avrami kinetic model gives a better fit to the experimental data than the traditional Lagergren kinetics models. A pore diffusion model suggests acid diffusion only for the standard slurry. The results indicate that isothermal heat-conduction calorimetry is suitable to evaluate the protective role of silane coupling agents on hardened oil-well cement slurries.

The Isothermal Heat Conduction Calorimeter: A Versatile Instrument for Studying Processes in Physics, Chemistry, and Biology

An approach to teaching calorimetry is offered through practical, versatile undergraduate experiments using an isothermal heat conduction calorimeter, which measures a variety of heat changes--enthalpies of phase changes, hydration, dissolution, adsorption and desorption, and reaction--as well as the metabolic rate of living organisms. Isothermal heat-conduction calorimetry is contrasted with adiabatic calorimetry. The general design and calibration of an instrument is discussed and five student experiments are described: heat capacity of solids, enthalpy of acid-base reaction, enthalpy of vaporization, hydration of cement, and metabolic rates of insects.

The Use of Isothermal Heat-Conduction Calorimetry in Direct Measurements of Solvent Vapor Pressure+

Principles for applying isothermal heat-conduction calorimetry for direct studies of vapor/liquid equilibria are presented. The ideas have been tested by measurements of the vapor pressure of water over aqueous NaCl(aq) solutions at 25°C. Seven different stock solutions were used with a composition ranging from 0.0879 mol-kg−1 to saturated solution. The imprecision and inaccuracy were not dependent on the composition and were found to be about ±2 Pa over the entire composition range. The sample solution was placed in a container separated from the pure solvent which was kept in the calorimetric cell. Solvent vapor was transported isothermally between the container and the cell by means of an inert carrier gas. The vapor pressure was evaluated by measuring the heat-flow rate associated with the process where the vapor equilibrated with a NaCl(aq) solution is fully saturated by passing through pure solvent. Corrections for treating vapor phase imperfections are presented. The method was found to be fast, accurate, and easy to use. The concept developed here can easily be applied in any commercial heat-conduction calorimeter of modular design.

Stability testing of pharmaceuticals by isothermal heat conduction calorimetry: Ampicillin in aqueous solution

The utility of isothermal heat conduction calorimetry for the study of stability of pharmaceuticals in solution is demonstrated in this study. The rate of heat evolution is measured as a function of the concentration of ampicillin, pH and the temperature. The pseudo first-order reaction rate constants, k, for the hydrolysis reaction are calculated from the variation of the heat evolution with time. The pH-rate profile for this reaction, as determined from the calorimetric data, is shown to correlate well with the literature data determined by other standard analytical methodology. The molal enthalpy of reaction was also calculated as function of pH and temperature.