Specimen Geometry Effects on Oxidation Behavior of Nuclear Graphite

Carbon Science Vol. 7, No. 3 September 2006 pp. 196-200 Specimen Geometry Effects on Oxidation Behavior of Nuclear Graphite Kwang-Youn Cho, Kyung-Ja Kim, Yun-Soo Lim 1, Yun-Joong Chung 1 and Se-Hwan Chi 2 Division of Nano Materials Application, KICET, Seoul 153-801, Korea 1 Department of Ceramic Engineering, Myongji University, Yongin 449-728, Korea 2 Department of Nuclear Hydrogen Project, KAERI, Daejeon 305-353, Korea Ì e-mail: kycho@kicet.re.kr (Received July 3, 2006; Accepted September 18, 2006) Abstract Graphite has hexagonal closed packing structure with two bonding characteristics of van der Waals bonding between the carbon layers at c axis, and covalent bonding in the carbon layer at a and b axis. Graphite has high tolerant to the extreme conditions of high temperature and neutron irradiations rather than any other materials of metals and ceramics. However, carbon elements easily react with oxygen at as low as 400C. Considering the increasing production of today of hydrogen and electricity with a nuclear reactor, study of oxidation characteristics of graphite is very important, and essential for the life evaluation and design of the nuclear reactor. Since the oxidation behaviors of graphite are dependent on the shapes of testing specimen, critical care is required for evaluation of nuclear reactor graphite materials. In this work, oxidation rate and amounts of the isotropic graphite (IG-110, Toyo Carbon), currently being used for the Koran nuclear reactor, are investigated at various temperature. Oxidation process or principle of graphite was figured out by measuring the oxidation rate, and relation between oxidation rate and sample shape are understood. In the oxidation process, shape effect of volume, surface area, and surface to volume ratio are investigated at 600 C, based on the sample of ASTM C 1179-91. Keywords : Oxidation, Nuclear, Geometry, Thermal Gravimetry, Chemical Reaction 1. lp c p van der Waals, a b p o p p s p ~v s p p sp. p k c p d r q o p, p a b p r r m lr. lp l p p p s v p. lp o ˆ po l pp r p n kr l pl e p n. lp p p r rq,, q ll n p. lp p t q s l p lˆ p l o rp. q oq o p l p l o p q ~, vv~ l lp n p. o q lp 800 o C p ml t q s pl n p. t q vl s rp p p oq vr l r ql pˆ p o r qp oq l r rp rp p p oq p v. t q s l k v p e rp dp v rp v lp t q s l p rp r e q }k r ql o p ˆo. t q s l l r v p rl p pl. l lp t q s v p Ž}p eq lp Ž}p oq l p p e oq krl rp p p l lp Ž}p eq e v lp ~ p r p. oq l n lp ~ rp t q s pnl m p p. l p o ˆ (C) p vp ll rp p l p. p oq ml nm p p, q vtp n oq nms p 1000 o C p p l o m kr o p n tn. v lp l l v k. lp 450 o Cl 1000 o C p v m ml o ˆ p [1] p oq l n ll pp oq p er nms l l r. ll 600 o C p rml r l e p p ASTM C 1179-91[2]l re l p. v ASTM C 1179-91l p p r p m p p

Specimen Geometry Effects on Oxidation Behavior of Nuclear Graphite 197 ˆ oq e, l l m v. l oq l n nˆ p l IG-110p m l m m. m, e l v r l o p p l m p m. e p l o e p ASTM C 1179-91l p l 600 o C l qe ov l, r, r/ l m p m. 2. p l l n e p oq l t n lq p nˆ p IG-110p. l(ig- 110)p CIP p ~ rs l p p 1p ˆ p. oq p q, ~, vv~ l n l ~ p < 20 ppmp. 1.77 g/cm 3 p ˆ p 8.93 GPa, 37.4 MPa, k 51p. oq l IG-110p p p 10 μm n p p v p. y m l e p Mettler toledo p SDTA 851e n l l p p l (%) (wt%/min) r m. 600, 700, 800, 900, 1000, 1100, 1200 o Cl 12 e ov l lp e. (dry air) 40 ml/min tp m. le p l q, ASTM C 1179-91p e r l Muffle Funace n l lp l 600 o Cl t 12 e ov l m [2]. p e p o p v p p m. e p v 1 mm, 4 mm, 6 mm, 10 mm 60 mm 5sp e p 5 j e e p, r, r/ Table 1. Properties of nuclear graphite (IG-110) Properties IG-110 Bulk Density (g/cm 3 ) 1.76 Young's Modulus (GPa) 8.93 Flexural Strength (MPa) 37.4 Shore Hardness 51 Impurity (ppm) < 20 Ave. Grain Size (μm) 10 p l m p m. 3. y yp Fig. 1, 2 l(ig-110) 600, 700, 800, 900, 1000, 1100 1200 o Cl 12 e ov l l ˆ p. m v l l p pl. 600 o Cl 1000 o C v m v l r 1000 o C p l d r. m l ove p v l p v e m. p Fuller Okoh 750 o C l e l m p p [3]. eq l l p p p p n r v. s v l p p ƒv m r rp eq l r l 0p p. p p l 40~50 wt% v v kk p f l p p p ƒv p p p. v ove v l v l p l p l v r l t pp p mlp 1000 o C p l v p v. 1000 o C p l pp l vt l l p p v kpl v e p. lp o p v lp r ˆl p l k p. o p rt o, Fig. 1. TG Curves of nuclear graphite in terms of temperatures.

198 K.-Y. Cho et al. / Carbon Science Vol. 7, No. 3 (2006) 196-200 l p pl 1000 o C p l pp l vt l pl o l p p [3, 6]. x w *( yp Fig. 2. Oxidation rate of nuclear graphite in terms of temperatures. p rp l eq [4]. rl (O 2 )m ˆ (C) CO 2 po oq kr p l rp. p rp v 3n j v. v, e p v 3n v. l l p CO 2 p v eq l l l p r p eˆ eq. rp 3n v l v v CO 2 p p dm }pl v pr rrp rp. p rp 600~1200 o C r m mll p rn 1000 o C p l l vt pp l v k v p p p. Fig. 3p l p p ˆ p. 1000 o C p l 5 wt% l ˆ l 700 o Cl 33 wt% l ˆ p. p 500~600 o Cp rm mll pl p pl lp Fig. 4p e p l ˆ l. qp e p v p l. 600 o Cl 1000 o Cl l p v p lp qp e p v p l. p rp lp eq 500 o C p l 1000 o C p v lp m ml o. 500 o C l pp l p p, l v k e p m l el pl p v l p l. 800 o C l pp l v kr v rp l t l v Fig. 3. Oxidation weight of nuclear graphite at the maximum oxidation rate as a function of oxidation temperature. Fig. 4. TG of nuclear graphite as a function of diameter.

Specimen Geometry Effects on Oxidation Behavior of Nuclear Graphite 199 Fig. 5. TG curves of nuclear graphite in terms of diameter at 800 o C. pl. 1000 o Cl pp l v n k p l. l v p m e r~p r r v k. 600 o C p pp e p l el l e p p m p lp qp v, qp e p v p l. 1000 o Cl p pp l vt l pl l e p rp e p p m p lp qk rp qp e l v p l. Fig. 5, 6p 800 o Cl e p r v ˆ p. qp e p ˆ. l e p qp e p q ˆ Fig. 7. Oxidation rate of nuclear graphite in terms of surface area. 600 o Cm 1000 o C m p ˆ p. p p o l p m qp e p ˆ o m l vm e e p pl l p m p p p Ž [7]. v, l v r l m p p Ž, e p l p ˆ p Ž. Fig. 6p l e p ˆ p pre ov p p p. p p e p p CO 2 p r o kk p re ov p Ž. Fig. 7, 8, 9p ASTM C 1179-91l p l Muffle Furnacel e p l pp r,, r/ ˆ l. r l. Fig. 6. Oxidation rate of nuclear graphite in terms of diameter at 800 o C. Fig. 8. Oxidation rate of nuclear graphite in terms of volume.

200 K.-Y. Cho et al. / Carbon Science Vol. 7, No. 3 (2006) 196-200 Fig. 9. Oxidation rate of nuclear graphite in terms of S/V ratio. 600 o C pl p v l r~l v p l m v p m p lp [5] r m. p v p r/ ˆ e (1)l p d m. r/ =6/D (1) *l D e p Fig. 9p r/ l ˆ l. r/ l r v p. p Fig. 6 l p e p pl vp CO 2 r m p p p qp e p r/ ƒ CO 2 r o l p Ž r/ qp e p pl vp CO 2 r o kk qk v p Ž. l r/ l p n lq p l p ˆ l op p p p. v, ls l osv o l v m o p p. 4. 600 o Cl 1000 o C v m v l r 1000 o C p l m v l v ll. m l ove p v l p v e m. 1000 o C p l 5 wt% l ˆ l 700 o Cl 33 wt%l ˆ p. p 500~600 o Cp rmmll p l p pl lp l p pl 1000 o C p l pp l vt l pl o l p p. qp e p v p l. 600 o Cl 1000 o Cl l p v p lp qp e p v p l. p o l p m qp e p ˆ o m l vm e e p pl l p m p p p Ž. e p ˆ p pre ov l. p p e p p CO 2 p r o kk pre ov p Ž. r/ l r v p. y [1] Xiaowei, L.; Charles, R. J.; Suyuan, Y. Nuclear Engineering and Design 2004, 227, 273. [2] ASTM C 1179-91 [3] Fuller, E. L.; Okoh, J. M. Journal of Nuclear Materials 1997, 240, 241. [4] Chunhe, T.; Jie, G. Journal of Nuclear Materials 1995, 224, 103 [5] Neighbour, G. B.; Hacker, P. J. Materials Letters 2001, 51, 307 [6] Kurumada, A.; Oku, T.; Harada, K.; Kawamata, K.; Sato, S.; Hiraoka, T. Carbon 1997, 35, 1157. [7] Moormann, R.; Hinssen, H. K.; Kuhn, K. Nuclear Engineering and Design 2004, 227, 281. [8] Mitchell, B. C.; Smart, J.; Fok, S. L.; Marsden, B. J. Journal of Nuclear Materials 2003, 322, 126. m v l l p pl.