Conduction calorimetry

Hansen LD, Lewis EA, Eatough DJ, Bergstrom RG, DeGraft-Johnson D. Kinetics of drag decomposition by heat conduction calorimetry. Pharm Res 1989 6 20-27. 

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. 

Hansen, L.D., Lewis, E.A., Eastough, D.J., Bergstrom, R.G., DeGraft-Johnson, D. (1989). Kinetics of drug decomposition by heat conduction calorimetry. Pharm. Res. 6,20-27. 

Phase-change adsorption calorimetry. This was the earliest type of diathermal-conduction calorimetry and was originally developed in the form of ice calorimetry by Lavoisier and Laplace (1783), who weighed the liquid water, and by Bunsen (1870), who measured the change of volume. Dewar (1904) devised an elegant adsorption calorimeter at liquid air temperature the heat was evaluated from the volume of air vaporized. Of course, the temperature of the calorimeter is imposed by the temperature of the phase change. Because these calorimeters lack adaptability and cannot be readily automated, they are mainly of historical interest. 

Fig. 5.13 shows the general form of the curve relating the fraction of C3S consumed (a) to time in a paste of w/s 0.5 at about 25°C and with moist curing. Such curves have been determined using QXDA for unreacted C3S (e.g. Refs K20,OI0), though the precision is low for values of a below about 0.1. At low values of a, other methods are available, such as conduction calorimetry (e.g. Ref. P22), aqueous phase analyses (e.g. Ref. B63) or determinations of CH content or of non-evaporable water. At very early ages, it may be necessary to allow for the fact that the property determined depends on the nature of the hydration products e.g. precipitation of C-S-H begins before that of CH. 

Copeland et al. (C38) reviewed the energetics of cement hydration. After the first few days, the rate of heat liberation is too low for conduction calorimetry to be a practicable means of investigation, but the total amount of heat liberated after any desired time can be determined from the heat of solution in acid, which is compared with that of the unhydrated cement. Fig. 7.9 gives average results thus obtained for different US types of Portland cements. 

Fig. 11.5 shows heat evolution curves, obtained by conduction calorimetry, for a CjS paste with and without addition of CaCU. When the latter is present, the main heat evolution peak begins earlier and rises and falls more steeply its maximum is reached earlier. The rate of heat evolution at the maximum is positively correlated with the reciprocal of the time at which the maximum occurs (D18). The linear relation extends to organic retarders. As these probably act by hindering the growth of C-S H (Section 11.2.2), this evidence suggests that the accelerators act by promoting it. 

Strong WH, Yu DH-S, Zhu C. Determination of solution aggregation using solubility, conductivity, calorimetry, and pH measurements. Int J Pharm 1996 135 43-52. 

Chandra, D., et al.. Vanadium Hydrides at Low and High Pressure, Final Report to Tritium Science and Engineering Group, 2006, Los Alamos National Laboratory. Luo, W.R, Clewley, J.D. and Flanagan, T.B., Thermodynamics and isotope effects of the vanadium-hydrogen system using differential heat conduction calorimetry. Journal of Chemical Physics, 1990, 93(9) p. 6710-6722. 

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

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. 

Other gases Single gas Thermal conductivity calorimetry... 

The reactions of various types of cements and their components with water is an exothermic process. The intensity of heat liberated with time depends on the type of chemical, surface area, reactivity, etc. Measurement of the total heat and rate of heat development provides information on the kinetics of hydration, degree of hydration, mechanism of hydration, the effect of additives, setting phenomenon, etc. Conduction calorimetry finds extensive applications in concrete technology. 

Applications. Conduction calorimetry has been widely used for a study ofthe hydration reactions ofvarious cementitious systems. Tricalcium silicate, being the dominant compound in portland cement, determines to a large extent the strength and other properties of concrete. Conduction calorimetric curves of tricalcium silicate and portland cement show five steps during the hydration process (Fig. In the first stage, as soon as... 

Figure 10. Conduction calorimetry curves of hydrating tricaleium silicate and cement.

Chemical admixtures in small amounts are added to concrete to enhance the physical, mechanical, chemical, and durability characteristics of concrete. Superplasticizers are admixtures that have the ability to increase the workability of concrete (for easy placement), but also produce high strength concretes. The relative rates of hydration of cement containing superplasticizers at different temperatures are conveniently followed by conduction calorimetry. In Fig. 11 both the rates of hydration and the cumulative amounts of heat developed in cement pastes hydrated at temperatures of20,40, and 55" C are plotted as a function of time. In the figure, SMF refers to the superplasticizer based on sulfonated melamine formaldehyde. The addition of the superplasticizer retards the hydration of cement. The retardation increases with the dosage of the superplasticizer. Also, the retardation effect becomes less significant as the temperature of hydration is increased. 

Bensted, J., and Aukett, P. N., Applications of Higher Temperature Conduction Calorimetry of Oil Cements, World Ceffrent, 21 308-320 (1990)... 

At the time of the initial set of cement paste, the hydration of C3S will have just started. According to some investigators, the crystallization of ettringite is the major contributing factor to the initial set. The final set generally occurs before the paste shows the maximum rate of heat development, i.e., before the end ofthe third stage in conduction calorimetry. 

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. 

Conduction Calorimetry may also be used to follow the hydration of C3S at different temperatures. In Fig. 14, the calorimetric curves for C3S hydrated at 30 and 80°C are given. The intense peak for the aceelerated hydration of C3S occurs with apeak at about 2 hrs at 80°C, but the hydration proceeds at a slower rate at 3 0°C as evident from a hump that oeeurs at about 7 hrs.t ]... 

The alkali in clinker is combined as a solid solution with the C3A phase. The crystalline stmcture changes from cubic to orthorhombic or monoclininc structure, depending on the content of Na in the C3A phase. Shin and Han studied the effect of different forms of tricalcium aluminate on the hydration of tricalcium silicate by applying DTA, TG, and conduction calorimetry. It was concluded that the hydration of tricalcium silicate is accelerated when orthorhombic, monoclinic, or melt C3A was present in the mixture. The cubic form of tricalcium aluminate was least effective for accelerating the hydration of the silicate phase. 

---