H." Tawara

O. Motojima

Y. "Nakayama

National Institute for Fusion Science (NIFS-Repository)

§21 . Resistivities of Metal-Powder-Loaded Graphites for Oxidation in Air at High Temperatures -III Nakayama, Y. (Pac. Eng., Ehime Univ.) Motojima, 0., Tawara, H. In order to investigate the resistivities of graphite for oxidation, we measured the weight loss of 6 different types of graphite (isotropic graphite: IG-l T, isotropic graphite: IG-2R, highly graphitized isotropic graphite: IG-3Q, electri-cal high resistivity isotropic graphite: IG-4U, high density graphite: IG-5S, and ultra high density isotropic graphite: IG-6P) exposed in air at 650 °e for 3 hours. Also we studied chemical resistivities for 7 chemical reagent grade alloy-powders of Koval (CoNiFe), Cupro-nickel (CuNi), Nickel silver (CuNiZn), Brass (CuZn), Lead brass (CuZnPb), Bronze (CuSn), and Lead bronze (CuSnPb). The symbol in the parenthesis represents the main elements in each alloy and is also used as code in the following. The test pieces, cut from a single lot block having the size of 20mm X 10mm X 60 mm with a hole of 15 mm in diameter X 5 mm in depth for mounting metal powder, were checked for appearance, weight change, size, density, and SEM picture before and after being heated. The measured weight losses of pure graphite are found to be 2.7% for IG-IT, 6.0% for IG-2R, and 7.2% for IG-3Q and the others show 10% or more at 650 °e. Fig. 1 shows three types of weight losses. In type 1 (IG-IT), the weight loss at 650 °e is 1% or less with the alloy powders, except for CuZnPb and CuSnPb. Pb-containing alloys show the largest weight losses of a graph-ite sample. The small weight loss of IG-l T for all alloy powders suggests that alloys do not play any role for oxida-tion. In type 2 (IG-2R, IG-3Q, and IG-4U), the weight loss decreases when the alloy-powder is loaded, except for CuZnPb and CuSnPb. These results suggest that, at 650 °e, some alloy powder may block air diffusion into graphite pieces which in tum decreases apparent weight loss. Type 3 (IG-5S and IG-6P), show the largest weight losses with CuZnPb and CuSnPb, but the other alloys show complex results. These results are similar to the results reported!) on metal powders. The hole volume changes between samples with and without alloy powder were estimated by size mea-surements and the results are summarized in Fig. 2. Gener-ally, the Pb-containing alloys greatly oxidize graphite: CuSnPb is the most, CuZnPb next and the others only small changes. These results suggest that lead would carry oxygen from the air to graphite, and the volume of oxygen is almost constant in al-loys. The pres-ent results of the weight loss measurements of various graphites can be summarized as follows: 1) Apparent weight clwrgc raIio % w~--~----~--~----~--~ 15 +---___+----_+__----+-----+----T\ 10 +----+-----+------+--------'=-t-~---I -10 +----+-----+-----+-----1------1 IG1T IG2R IG3Q IG4U IG5S IG6P Fig. 1. Weight change ratio(%) of weight loss does graphite materials with and without alloy not show a clear heated at 650 °e in air for 3 hrs. relationship be-tween alloy Abscissa:code of alloy. _ DOD-alloy powders and graphite materials. 2) Pb- containing alloys greatly oxidize graphite materials at their contact surface. _ I CoNiP'e I I I I CuNi _ I I CuNlZn _ CuZn _ I II CuZoPb 3) Volume changes of alloy-loaded holes represent the direct interac-tion strength of alloys and graphite. These results _ CuSn _ I CuSoPb ratio of hole volume Y. 80,---------,-----,---------,-----,-------, --40-+-----+-----+-----+-----+----~1 ,.- .. -............... J 20~--·-·--'-'-_+__·--"---"_+__--___+---··-....... ~·-~,,-~'·l i ."",j o~~~ __ ~ __ ~~~~~ i -20 _+__--___+----_+__--___+----_+__----11 IGlT IG2R lG3Q IG4U IG5S lG6P Fig. 2. Hole volume changes (%) of were presented graphite materials with alloys heated at at symposium in Toky0 2) and at conference in Strasbourg3) . 650 °e in air for 3 hrs. Abscissa:code of alloy. References 1) NIFS annual report (1998) p.80. 2)Nakayama, Y., Veda, S., and Hirano, H., Internationl Symposium on Carbon, Tokyo, Japan, 1111998, pp.443-444 3)Nakayama, Y., Kitamura, T, Hirano. H.,and Hosokawa, K., Carbon '98, Strasbourg, France, 7/1998, pp.638-639. 89 

Resistivities of Metal-Powder-Loaded Graphites for Oxidation in Air at High Temperatures -III

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)