Authors:S. M. A. El-Gamal, F. S. Hashem, and M. S. Amin
as in control specimens. Such results lead to an important conclusion that, the thermalresistance found in specimens containing V was due to its insulation character rather than its pozzolanic reactivity. However, at 600 and 800 °C, in XRD of A2, new
Results of theoretical and experimental investigations of the thermal behaviour of InGa-AsP/InP laser diodes with a ridge-waveguide structure are presented. It is shown that, in contrast to GaAlAs/GaAs laser diodes, most of the heat flux is carried through the InP-substrate, less than 1/4 through the ridge. The temperature rise in the active region was determined and the thermal resistance calculated for various structure and bond parameters. The theoretical and experimental results fit very well. The change of the thermal resistance compared to a norm value of 67 K/W with variation of structure parameters is discussed. It is strongly affected by the device length, the ridge width and the bonding parameters.
Authors:R. Puchert, U. Menzel, A. Bärwolff, M. Voβ, and Ch. Lier
The thermal behaviour of high-power GaAlAs/GaAs laser arrays is described by a comprehensive thermal two-dimensional finite-element model which takes several heat sources into account. The influence of these different heat sources on the two-dimensional temperature distribution in the laser array has been investigated. The power densities of the heat sources related to the active region were calculated by an analytic description of the temperature dependent processes as spontaneous emission, Auger recombination and interface recombination. The results of our numerical calculation show, that the local distribution of the heat sources has a strong influence on the lateral temperature profile and on the maximum temperature in the active region of the array, i.e. on the thermal resistance. The calculated temperature profiles are in a good agreement with the measured lateral temperatures at different injection currents and heat sink temperatures. The difference between calculated and measured maximum temperature is lower than 0.75°C.
With the aims of accounting for the effects of the internal thermal resistance of the sample holder on the parameters of recorded DTA curves, and of estimating the difference between the instrument with a thermally insulated sample holder and the gradientless model, a novel two-point method of differential thermal analysis has been developed. Its essence is that two thermoanalytical curves are recorded simultaneously, with the differential thermocouple at central and side positions relative to the sample. The theory of the method has been elaborated, and formulae are derived which allow quantitative estimation of the thermal resistance of the sample holder, depending on the manner of packing and on the state of the sample in the holder, and which also indicate the optimum manner of packing. If the packing is not dense and not uniform, the thermal resistance of the holder increases and the accuracy of instrument calibration at the tail-end of the differential curve decreases by 10–20%. Through introduction of a correction term into the formula, this effect can be eliminated. A basic formula is given for DTA calculation in the general case of a sample holder with non-zero internal thermal résistance.
Authors:R. Ozao, H. Ogura, M. Ochiai, and S. Tsutsumi
A DSC method for evaluating the surface area of etched Al foils for use in high performance electrolytic capacitors is presented. A linear relationship between the etching degree (effective surface area) and the thermal resistance of the sample is obtained by means of DSC, based on the transient phenomenon. This method using the transient state in DSC measurement is not only novel, but also rapid and simple in evaluating the surface area of an etched aluminum foil. The method is effective even when the Al foil has a naturally oxidized surface.
Authors:J. Pak, W. Qiu, M. Pyda, E. Nowak-Pyda, and B. Wunderlich
During a prior study of gel-spun fibers of ultrahigh-molar-mass polyethylene, a substantial error was observed on calculating
the heat capacity with a deformed pan, caused by the lateral expansion of the fibers on shrinking during fusion. In this paper,
the causes of this and other effects that limit the precision of heat capacity measurements by DSC and TMDSC are explored.
It is shown that the major cause of error in the DSC is not a change in thermal resistance due to the limited contact of the
fibers with the pan or the deformed pan with the platform, but a change in the baseline. In TMDSC, the frequency-dependence
is changed. Since irreversible changes in the baseline can occur also for other reasons, inspections of the pan after the
measurement are necessary for precision measurements.
Authors:Riko Ozao, Hiroshi Ogura, Moyuru Ochiai, and Sadao Tsutsumi
How a DSC result is influenced by the particle size distribution of a powder sample is shown, and a simple and optimal method
to be included in a routine DSC analysis (e.g., purity determination) to improve the reliability of the analysis is proposed.
In case ofα-Al2O3 powder, most reliable heat capacity data can be obtained by preparing a powder with a self-similar particle size distribution
with a distribution constant of 0.7, and by compressing it under a pressure of 1.5 MPa for a duration of 5 min or longer.