Wrocław University of Technology

About: Wrocław University of Technology is a education organization based out in Wrocław, Poland. It is known for research contribution in the topics: Laser & Computer science. The organization has 13115 authors who have published 31279 publications receiving 338694 citations.

Practical remarks concerning phase diagrams determination on the basis of differential scanning calorimetry measurements

Abstract: Phase diagrams of binary systems at constant pressure are representations of oneand two-phase regions with their boundaries being functions of temperature and concentration. The most popular techniques used in determination of phase diagrams are thermal analysis (TA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The first of them, based on recording of cooling curves, has no significant meaning nowadays; however, it is still used, especially in didactics. Actually DTA and DSC are widely used in phase diagrams determination. DSC has an advantage over DTA, because in addition to temperature it gives precise value of enthalpy of thermal effect. Two types of DSCs must be distinguished: the heat flux DSC and the power compensation DSC. The characteristic feature of all DSC measuring systems is the twin-type design and the direct in-difference connection of the two measuring systems which are of the same kind. It is the decisive advantage of the differential principle that, in first approximation, disturbances such as temperature variations in the environment of the measuring system and the like, affect the two measuring systems in the same way and are compensated when the difference between the individual signals is formed [1]. The differential signal is the essential characteristic of each DSC. Another characteristic—which distinguishes it from most classic calorimeters—is the dynamic mode of operation. The DSC can be heated or cooled at a preset heating or cooling rate. A characteristic common to both types of DSC is that the measured signal is proportional to a heat flow rate (in opposition to classical calorimeters where heat flow is measured). This fact—directly measured heat flow rates—enables the DSC to solve problems arising in many fields of application [1]. In the heat flux DSC a defined exchange of the heat to be measured takes place via a thermal resistance. The measurement signal is the temperature difference; it describes the intensity of the exchange and is proportional to the heat flow rate. There are two main types of the heat flux DSC: the disc-type measuring system with solid sample support (disc) and the cylinder-type measuring system with integrated sample cavities. Heat flux DSCs with a disctype measuring system are available for temperatures between -190 and 1,500 C [1]. In the heat flux DSC with a cylindertype measuring system, the outer surfaces of each sample container are in contact with a great number of thermocouples connected in a series between the container and furnace cavity. The thermocouples bands or wires are the dominating heat conduction path from the furnace to samples. Both sample containers are thermally decoupled; heat exchange takes place only with parts of the massive furnace. These apparatuses are available for temperature range between -190 and 1,500 C [1]. The power compensation DSC belongs to the class of heat-compensating calorimeters. The heat to be measured is compensated with electric energy, by increasing or decreasing an adjustable Joule’s effect. The measuring temperature range extends from -175 to 725 C [1]. Differential scanning calorimetry is a relative technique. Because of its dynamic temperature characteristics, the measurements are not made in thermal equilibrium. The relative data must be converted to absolute values by a calibration procedure requiring the employment of standards whose property values and their associated uncertainties are known and established following a metrological procedure [2]. Practical remarks concerning phase diagrams determination on the basis of DSC measurements are illustrated by numerous examples of binary lanthanide halide–alkali halide systems.

Silicon anisotropic etching in alkaline solutions I. The geometric description of figures developed under etching Si(100) in various solutions

Abstract: The influence of alkaline solution concentration, type of cation (K+ or Na+) and IPA additive on etching rate of various crystallographic planes and shape of etched figures were examined. The simulation of the etching course for concave and convex figures was proposed. The results of the simulation were compared with SEM images.