Band 49, Heft 2

In order to understand the relationships which exist between the microstructures and mechanical properties of ceramic materials and to clarify their respective mechanisms of corrosion, a detailed picture of their microstructures is of particular importance. The examination of such structures using field emission scanning electron microscopy in combination with EDX analysis as well as the FIB technique are demonstrated on polished and electrochemically corroded LPS (liquid phase sintered SiC) and SSiC materials. The possibilities for revealing the diffusion zones in semi-conducting SiC grains are presented. These methods also help to explain the core-shell structures caused by electrochemical corrosion.

Lithium ion accumulators are widely used already in numerous electronic devices. However, a great deal of research will still be required as to their use as a reliable and efficient energy storage unit in the automotive industry. Their characterization using physical and electrochemical methods has made great progress and was published already. In contrast, the classical materialographic characterization of their microstructure by means of microscopy is applied only to a small extent nowadays. Access by the public to relevant results is scarcely possible. Properties like capacity and power as well as safety und stability also depend very much on the cell design (e. g. geometry, layer thicknesses) and microstructure (e. g. volume fraction, grain size) of the materials employed. A microstructure analysis by microscopy is intended to provide for a more profound comprehension of the connection between the basic parameters and function here. A challenge is posed by the preparation of a microsection to reveal a representative image of the microstructure without artefacts. The process of materialographic preparation and the potential of various microscopy techniques for visualizing and quantifying the cell components and ageing effects are presented here. The opportunities of characterizing the basic parameters specific to the cells furnishes new knowledge on the properties of battery materials and, hence, will be of great utility for future examinations and further developments of the lithium ion technology.

The dendrite coherency point (DCP) temperature refers to the state of a solidifying alloy at which a coherent dendrite network is established during the formation of grains. There are three main approaches for detection of DCP: (i) the thermal analysis method, (ii) mechanical (or rheological) technique and (iii) physical method based on the thermal diffusivity measurement technique. There are two basic variants of the thermal analysis method. In the late 1980's Bäckerud developed a method that utilizes two thermocouples. The DCP is determined by identifying the point of minimum temperature difference at the δT curve (TW–TC). Recently, has been revealed that utilization of the first derivative curve (dT/dt) plotted versus temperature also allows for analysis of the α-Al dendrite nucleation and growth characteristics and consequently determination of the DCT. This paper will illustrate that the dendrite coherency temperature could be identified by the 1 st derivative curve (the one-thermocouple method) with the same accuracy as well as by using two thermocouples technique.