handbook of carbon, graphite, diamond and fullerenes

More documents

Recommendations

Info

5.0 ELECTRICAL PROPERTIES OF GRAPHITE 5.1 Electrical Resistivity Graphite Structure and Properties 61 In electrical conductors such as metals, the attraction between the outer electrons and the nucleus of the atom is weak; the outer electrons can move readily and, since an electric current is essentially a flow of electrons, metals are good conductors of electricity. In electrical insulators (or dielectrics), electrons are strongly bonded to the nucleus and are not free to move.I 18 K 19 l Electrically, graphite can be considered as a semi-metal, that is a conductor in the basal plane and an insulator normal to the basal plane. Its atomic structure is such that the highest-filled valence band overlaps the lowest-empty conduction band by approximately 36 meV and the delocalized fourth-valence electrons form a partially-filled conduction band between the basal planes where they can moved readily in a wave pattern as they respond to electric fields. [2 °) Consequently, the electrical resistivity of graphite parallel to the basal planes (ab directions) is low and the material is a relatively good conductor of electricity. In the c direction, the spacing between planes is comparatively large, and there is no comparable mechanism for the electrons to move from one plane to another, in other words, normal to the basal plane. As a result the electrical resistivity in that direction is high and the material is considered an electrical insulator. In some cases, it may be 10,000 times higher than in the ab directions.^ 20 ' Often quoted resistivity values are 3000 x 10" 6 ohm.m in the c direction and 2.5 - 5.0 x 10" 8 ohm.m in the ab directions. 5.2 Resistivity and Temperature The electrical resistivity of the graphite crystal in the ab directions increases with temperature, as does that of metals. This increase is the result of the decrease in the electron mean free path, in a mechanism similar to the increase in thermal conductivity reviewed above in Sec. 4.3. The electrical resistivity in the c direction, however, decreases slightly with increasing temperature, possibly because electrons can jump ortunnel from one plane to another due to increased thermal activation J 14 1
62 Carbon, Graphite, Diamond, and Fullerenes 6.0 MECHANICAL PROPERTIES OF GRAPHITE As mentioned in Sec. 1.2, the bond between atoms within the basal plane of a graphite crystal is considerably stronger than the bond between the planes with an anisotropy ratio of approximately 75. This means that, while the strength in the ab directions is considerable, that in the c direction (interlaminar strength) is low and graphite shears easily between basal planes. The elastic constants are;! 17 ! C^ = 1060 GPa (a direction) C33 = 36.5 GPa (c direction) C44 = 4.5 GPa (parallel to the planes) The Young's modulus of elasticity of the crystal varies up to two orders of magnitude with the direction. It is plotted in Fig. 3.13 as a function of the angle between the c direction and the direction of measurement.! 2 ' 900 800 SM °. 600 (0 1 500 w 400 I 300 > 20 40 60 80 90 , Degrees Figure 3.13. Young's modulus of graphite crystal as a function of angle (0) with c axis.' 2 '
Page 1 and 2:
HANDBOOK OF CARBON, GRAPHITE, DIAMO
Page 3 and 4:
Contents 1 Introduction and General
Page 5 and 6:
xii Contents 5.0 ELECTRICAL PROPERT
Page 7 and 8:
xiv Contents 2.0 THE CVD OF PYROLYT
Page 9 and 10:
xvi Contents 6.0 CERAMIC-MATRIX, CA
Page 11 and 12:
xviii Contents 4.0 NATURAL AND HIGH
Page 13 and 14:
xx Contents 2.0 STRUCTURE OF THE FU
Page 15 and 16:
Preface ix technology, processes, e
Page 17 and 18:
2 Carbon, Graphite, Diamond, and Fu
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26: 10 Carbon, Graphite, Diamond, and F
Page 75: 60 Carbon, Graphite, Diamond, and F
Page 85 and 86: Synthetic Carbon and Graphite: Carb
Page 115 and 116: 100 Carbon, Graphite, Diamond, and
Page 127 and 128:
112 Carbon, Graphite, Diamond, and
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Vitreous Carbon 1.0 GENERAL CONSIDE
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
8 Carbon Fibers 1.0 GENERAL CONSIDE
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 213 and 214:
Applications of Carbon Fibers 1.0 C
Page 215 and 216:
Page 217 and 218:
Page 219 and 220:
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
Page 235 and 236:
Page 237 and 238:
Page 239 and 240:
Page 241 and 242:
10 Natural Graphite, Graphite Powde
Page 243 and 244:
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
Page 251 and 252:
Page 253 and 254:
Page 255 and 256:
Page 257 and 258:
Page 259 and 260:
11 Structure and Properties of Diam
Page 261 and 262:
Page 263 and 264:
Page 265 and 266:
Page 267 and 268:
Page 269 and 270:
Page 271 and 272:
Page 273 and 274:
Page 275 and 276:
Page 277 and 278:
Page 279 and 280:
Page 281 and 282:
Page 283 and 284:
Page 285 and 286:
Page 287 and 288:
Page 289 and 290:
Page 291 and 292:
Page 293 and 294:
12 Natural and High-Pressure Synthe
Page 295 and 296:
Page 297 and 298:
Page 299 and 300:
Page 301 and 302:
Page 303 and 304:
Page 305 and 306:
Page 307 and 308:
Page 309 and 310:
Page 311 and 312:
Page 313 and 314:
Page 315 and 316:
Page 317 and 318:
13 CVD Diamond 1.0 INTRODUCTION The
Page 319 and 320:
Page 321 and 322:
Page 323 and 324:
Page 325 and 326:
Page 327 and 328:
Page 329 and 330:
Page 331 and 332:
Page 333 and 334:
Page 335 and 336:
Page 337 and 338:
Page 339 and 340:
Page 341 and 342:
Page 343 and 344:
Page 345 and 346:
Page 347 and 348:
Page 349 and 350:
Page 351 and 352:
Page 353 and 354:
Page 355 and 356:
Page 357 and 358:
Page 359 and 360:
Page 361 and 362:
Page 363 and 364:
Page 365 and 366:
Page 367 and 368:
Page 369 and 370:
Page 371 and 372:
15 The Fullerene Molecules 1.0 GENE
Page 373 and 374:
Page 375 and 376:
Page 377 and 378:
Page 379 and 380:
Page 381 and 382:
Page 383 and 384:
Page 385 and 386:
Page 387 and 388:
Page 389 and 390:
Glossary Ablation: The removal of m
Page 391 and 392:
Page 393 and 394:
Page 395 and 396:
Page 397 and 398:
Page 399 and 400:
Index Ablation 38 Absorption bands
Page 401 and 402:
Page 403 and 404:
Page 405 and 406:
Page 407 and 408:
Page 409 and 410:
Page 411 and 412:
Page 413 and 414:
Page 415 and 416:
Copyright © 1993 by Noyes Publicat
Page 417:
vi Series HANDBOOK OF CHEMICAL VAPO
show all

handbook of carbon, graphite, diamond and fullerenes

Create successful ePaper yourself

Delete template?

Save as template?