Using the latest electrophysical methods for nondestructive property monitoring on graphitized carbon materials and components

Abstract

It is possible to monitor the quality of graphitized carbon components by measuring the electrophysical properties, which is demonstrated from experimental studies on the relation between the thermo-EMFs of carbon fibers in relation to the normal elasticity modulus for a particular type of high-modulus carbon fiber. It is shown that current devices can be used to measure the properties in making carbon items with continuous recording of the monitoring results.Graphitized carbon materials are used in heating and other forms of equipment, and their quality is subject to fairly stringent requirements. Nondestructive test methods can be employed in their production to provide prompt monitoring not only during production but also during use.A basic quality criterion for a graphitized material is provided by the physicomechanical properties. To evaluate those, standard methods based on manufacture and subsequent testing of special specimens may also be accompanied by nondestructive methods such as ultrasonic ones (instruments of the type of Pulsar and UK-10PM), as well as methods based on natural frequencies of the items (instruments of Zvuk, IChSK, and other types) [1]. When one determines those properties of high-modulus carbon fibers, one can also use an ultrasonic method (instruments of UIMU type).The properties of graphitized materials can also be judged from the electrophysical parameters, since those properties are substantially influenced by the structural characteristics. Tests have been done on the correlations between structure, physicomechanical properties and electrophysical properties, which show that it is possible to evaluate the physicomechanical properties and the quality not only by direct measurement of those properties but also by measuring the electrophysical ones. These data are based on researches by S. V. Shulepov, A. I. Lutkov, R. M. Levit, A. A. Konkin, V. Ya. Varshavskii, and various other researchers [2 -13].A carbon-base material may have conductivity of metal type or semiconductor type. Also, the anisotropy in the properties of graphite substantially influences the electrical conductivity. The electrical conductivity varies very widely in solids. The bulk specific resistivity is 10 5 -10 6 W × m for insulators, while for full conductors it is less than 10 -6 W × m. This means that electrophysical methods can be applied to researching and monitoring graphitized carbon materials.We consider that the most promising methods for monitoring graphitized materials are the electromagnetic one (eddy currents), and the thermoelectric and electrical-capacity ones. In the mid-1960s, the Soviet Union had developed and routinely produced several types of electrical conductivity meter, including the IE-20 for measuring the electrical conductivity of graphite components by means of eddy currents [2]. Similar instruments were produced and are being produced by foreign firms, but there has been no general use of such instruments in Russian industry up to the present. Most often, Russian industry employs ins...

The possibility of using a thermoelectric instrument PT-102 for evaluating the stability of technological production of heat-resistant carbon fiber materials

“…Within these conditions a particular role is played both by methods for monitoring the finished product, and also non-destructive monitoring methods for the stability of production parameters for producing CFM in its various versions. Previous studies [3] have shown the possibility of using for these purposes such informative CFM characteristics as thermo-emf. An example is shown in Fig.…”