Isothermal conduction calorimetry

The isothermal conduction calorimetry offers a method to follow the rate of hydration of cement at different temperatures of curing. Calorimetric curves of cement hydrated at 25,30,40, 50,60, and 80°C have been analyzed.It was found that as the temperature increased the C3S hydration peak appeared at earlier times. The shape of the curves also underwent changes. The apparent activation energy of hydration could be calculated. 

ASTM C1702 (2014). Standard test method for measurement of heat of hydration of hydraulic cementitious materials using isothermal conduction calorimetry. 

Lipus, K., and S. Baetzner (2008). Determination of the heat of hydration of cement by isothermal conduction calorimetry . Cement International 6(4) ... 

Instrumentation. H and NMR spectra were recorded on a Bruker AV 400 spectrometer (400.2 MHz for proton and 100.6 MHz for carbon) at 310 K. Chemical shifts (< are expressed in ppm coupling constants (J) in Hz. Deuterated DMSO and/or water were used as solvent chemical shift values are reported relative to residual signals (DMSO 5 = 2.50 for H and 5 = 39.5 for C). ESl-MS data were obtained on a VG Trio-2000 Fisons Instruments Mass Spectrometer with VG MassLynx software. Vers. 2.00 in CH3CN/H2O at 60°C. Isothermal titration calorimetry (ITC) experiments were conducted on a VP isothermal titration calorimeter from Microcal at 30°C. 

Oliyai R, Lindenbaum S. Stability testing of pharmaceuticals by isothermal heat conduction calorimetry ampicillin in aqueous solution. Int J Pharm 1991 73(1) 33—36. 

Solution calorimetry involves the measurement of heat flow when a compotmd dissolves into a solvent. There are two types of solution calorimeters, that is, isoperibol and isothermal. In the isoperibol technique, the heat change caused by the dissolution of the solute gives rise to a change in the temperature of the solution. This results in a temperature-time plot from which the heat of the solution is calculated. In contrast, in isothermal solution calorimetry (where, by definition, the temperature is maintained constant), any heat change is compensated by an equal, but opposite, energy change, which is then the heat of solution. The latest microsolution calorimeter can be used with 3-5 mg of compound. Experimentally, the sample is introduced into the equilibrated solvent system, and the heat flow is measured using a heat conduction calorimeter. 

R. Oliyai and S. Lindenbaum, Stability testing ofpharmaceuticals by isothermal heat conduction calorimetry Ampicillin in aqueous solution, Int. J. Pharm. 73, 33-36(1991). 

Activity of the purified en2ymes was assessed on methyl ferulate (methyl 4-hydroxy 3-methoxy cinnamate, MF). Assays were run for 30 min at 50 °C in 50 mM eitrate buffer at pH 4.8 with initial MF concentrations of 50 to 750 pM and an enzyme concentration of 50 nM. The reactions were terminated after 30 min by boiling for 10 min and analyzed for MF and ferulic acid content via C18 high performance liquid chromatography (HPLC) over a 0 to 100% acetonitrile gradient with 0.1% formic acid in all solutions. Preliminary isothermal titration calorimetry (ITC) on both ferulic acid esterase proteins was conducted in SEC buffer on a Microcal VP-ITC system. All reactions were carried out at 37 °C using MF as a substrate. 

H.M. Shirazi, (Quartz Crystal Microbalance/Heat Conduction Calorimetry (QCM/HCC), a new technology capable of isothermal, high sensitivity, mass and heat flow measurements at a solid/gas interface., PhD Thesis, Drexel University, Philadelphia, PA, 2000. 

Calorimetry is the measurement of the heat changes which occur during a process. The calorimetric experiment is conducted under particular, controlled conditions, for example, either at constant volume in a bomb calorimeter or at constant temperature in an isothermal calorimeter. Calorimetry encompasses a very large variety of techniques, including titration, flow, reaction and sorption, and is used to study reactions of all sorts of materials from pyrotechnics to pharmaceuticals. 

Conduction calorimetry is another technique that is extensively used for following the hydration reactions of cement and cement compounds. In this method, heat evolved during the hydration reactions is followed as a function of time from the moment water comes into contact with the cement. The curves are obtained under isothermal conditions. This technique can also be used to study the rate of hydration at different temperatures. Conduction calorimetry has been used to determine kinetics of hydration and for studying the role of admixtures, relative setting times of cement, and for identification purposes. 

A Tian-Calvet heat flux calorimeter was used in the measurements described in ref. [2]. This type of calorimeter is also called isothermal [4, 5], in contrast to other kinds of calorimeter. A tutorial [6] on heat-conduction calorimetry gives a good account of the technique. Peak integration of the heat flux against time may be performed by a numerical integration method, such as Simpson s method, on a personal computer interfaced to the calorimeter [7]. 

There are many different types of calorimeters that can be used in the cement field, and some of them have many uses. The most common technique is isothermal (heat conduction) calorimetry in which the heat production rate (thermal power) from small samples of paste or mortar is directly measured. This technique is the focus of this chapter as it is the most versatile calorimetric technique in the cement field. Typical commercial instruments of this type used in the cement field are TAM Air (TA Instruments, U.S.), TCal (Calmetrix, U.S.), MC CAL (C3 Prozess- und Analysentechnik, Germany), ToniCAL III and ToniCAL TRIO (Toni Technik, Germany) and C80 (Setaram, France). 

Isothermal and semiadiabatic calorimeters both quantify cement hydration kinetics, but they do so in different ways. This is illustrated in Figure 2.1. In isothermal (heat conduction) calorimetry the heat production rate ( ) in a small sample (S) is measured by a heat flow sensor as heat is conducted to a heat sink that is placed in a thermostated environment. It is also necessary to have a reference sample (R) with the same properties (especially the same heat capacity) as the sample but without any heat production. This arrangement significantly reduces the noise in the measurements. The output from the calorimeter is the difference between the sample signal and the reference signal. 

Figure 2.1 Schematic illustrations of (a) isothermal (heat conduction) calorimetry and (b) semiadiabatic calorimetry. P thermal power R reference S sample T temperature t time.

Ozone can be analyzed by titrimetry, direct and colorimetric spectrometry, amperometry, oxidation—reduction potential (ORP), chemiluminescence, calorimetry, thermal conductivity, and isothermal pressure change on decomposition. The last three methods ate not frequently employed. Proper measurement of ozone in water requites an awareness of its reactivity, instabiUty, volatility, and the potential effect of interfering substances. To eliminate interferences, ozone sometimes is sparged out of solution by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution. Historically, the most common analytical procedure has been the iodometric method in which gaseous ozone is absorbed by aqueous KI. 

The various terms appearing in these equations are self-evident. The differential heat release, dkidt, data are computed from differential scanning calorimetry (DSC). A typical DSC isotherm for a polyurethane reactive system appears in Fig. 11. Energetic composite processing is normally conducted under isothermal conditions so that Eq. (15) is more applicable. 

In order to get a quantitative idea of the magnitude of the effects of these temperature variations on molecular structure and morphology an experimental study was undertaken. Two types of polymerizations were conducted. One type was isothermal polymerization at fixed reaction time at a series of temperatures. The other type was a nonisothermal polymerization in the geometry of a RIM mold. Intrinsic viscosities, size exclusion chromotograms (gpc) and differential scanning calorimetry traces (dsc) were obtained for the various isothermal products and from spatially different sections of the nonisothermal products. Complete experimental details are given below. 

The kinetics were studied by adiabatic calorimetry [18] and high vacuum isothermal dilatometry [21, 22]. The calorimeter and the dilatometers were fitted with electrodes [21] for measuring the conductivity of the reaction mixtures. 

The problems associated with direct reaction calorimetry are mainly associated with (1) the temperature at which reaction can occur (2) reaction of the sample with its surroundings and (3) the rate of reaction which usually takes place in an uncontrolled matmer. For low melting elements such as Zn, Pb, etc., reaction may take place quite readily below S00°C. Therefore, the materials used to construct the calorimeter are not subjected to particularly high temperatures and it is easy to select a suitably non-reactive metal to encase the sample. However, for materials such as carbides, borides and many intermetallic compounds these temperatures are insufficient to instigate reaction between the components of the compound and the materials of construction must be able to withstand high temperatures. It seems simple to construct the calorimeter from some refractory material. However, problems may arise if its thermal conductivity is very low. It is then difficult to control the heat flow within the calorimeter if some form of adiabatic or isothermal condition needs to be maintained, which is further exacerbated if the reaction rates are fast. 

The kinetics of degradation can be studied using isothermal calorimetry, that is, calorimetry performed at constant temperature. Recently, sensitive thermal conductivity microcalorimeters useful for detecting even small amounts of degradation at room temperature have become available. For example, the slow solid-state degradation of cephalosporins at a rate of approximately 1% per year was successfully measured by microcalorimetry.624... 

Alkene hydrogenation is significantly exothermic, and it is not always easy to keep the catalyst isothermal except at low rates. Heats of hydrogenation for a number of alkenes were measured many years ago (Table 7.1), the use of a catalyst ensuring that calorimetry could be conducted at ambient temperature. The values are similar to but perhaps more accurate than those derived from heats of combustion, where subtraction of two large numbers is involved they reflect the extents to which the jt electrons interact with the electrons in the C—H bonds by hyperconjugation. This electron delocalisation is also reflected in the relative stabilities of alkene complexes with Ag+ cations. ... 

Instrumental. All Differential Scanning Calorimetry (DSC) runs were conducted on a Perkin-Elmer DSC-7 attached through a TAC-7 Thermal Analysis Controller to a DEC computer station 325c. All runs were conducted at 10°C/min. in N2 unless otherwise stated. Thermogravimetry was run on a Perkin Elmer TGA-7 attached through the same system as the DSC. Isothermal aging of samples in sealed capillaries were conducted in the DSC cell of a DuPont 9(X) Thermal Analyzer after temperature calibration. 

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