Amorphization Of Graphite Research Articles

Nanostructured Al/Al4C3 composites reinforced with graphite or fullerene and manufactured by mechanical milling and spark plasma sintering

Nanostructured Al matrix composites with reinforcements of graphite or fullerene (C60+C70+soot) have been produced by mechanical milling and spark plasma sintering (SPS). X-ray diffraction and transmission electron microscopy show that C60+C70 withstand longer mechanical milling/alloying times than graphite. Fullerene is a good control agent during mechanical alloying resulting in a denser Al/fullerene composite when compared to the Al/graphite one. A refinement mechanism that takes place during mechanical alloying of fullerene and graphite is experimentally found and correspondingly discussed. Such a mechanism plays a major role in the amorphization of graphite. The larger surface area of the fullerene mix after milling promotes a better interaction with Al and hence allows its complete transformation into Al4C3 during the SPS process. The sintered products show an increase in hardness for the Al/fullerene composite of 6 times and only 4 times for the Al/graphite composite. The SPS technique shows to be an excellent method to transform the fullerene into Al4C3 while preserving its nanostructured nature.

Induced Amorphization in Pyrographite by Radiation Using High Voltage Transmission Electron Microscope

A high dose of electron irradiation generates amorphous zones with critical vacancy concentrations in the pyrographite. The degree of disorder “” of amorphization of Graphite, natural graphite, pyrographite and polycrystal pyrographite are analyzed as a function of time “t”, and the amorphization kinetics under different voltages inside the HVTEM.

Effect of mechanical grinding in argon and hydrogen atmosphere on microstructure of graphite

Structural transformations and amorphization of graphite upon high-energy ball-milling under argon and hydrogen atmosphere are studied. Nano-scale carbon particles were characterized by nitrogen adsorption measurements (BET surface area) and high-resolution transmission electron microscopy (HRTEM). The pore size distribution (PSD) was determined by the Dollimore-Heal analysis. Maxima on PSD curves can be attributed to nanoscale structures formed by exfoliated graphite sheets or stacks of graphite sheets. The pore volume for each kind of pores strongly depends on the milling atmosphere. In contrast to that the maximal contribution of ultra micropores to the total porosity reaches about 40 vol.% independently of the milling atmosphere.

Effect of mechanical grinding in argon and hydrogen atmosphere on microstructure of graphite

Structural transformations and amorphization of graphite upon high-energy ball-milling under argon and hydrogen atmosphere are studied. Nano-scale carbon particles were characterized by nitrogen adsorption measurements (BET surface area) and high-resolution transmission electron microscopy (HRTEM). The pore size distribution (PSD) was determined by the Dollimore–Heal analysis. Maxima on PSD curves can be attributed to nanoscale structures formed by exfoliated graphite sheets or stacks of graphite sheets. The pore volume for each kind of pores strongly depends on the milling atmosphere. In contrast to that the maximal contribution of ultra micropores to the total porosity reaches about 40 vol.% independently of the milling atmosphere.

HRTEM and EELS studies of defects structure and amorphous-like graphite induced by ball-milling

Deformation structures and amorphization kinetics of graphite with high crystallinity upon ball-milling (BM) are studied by high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). Basal plane stacking disorder, cleavage, delamination cracks, misorientation bands and low-angle (0002) twist boundaries are observed. The basal plane stacking disorder is probably produced by simultaneous shearing of all the lattice planes involved. Other defects such as half Frank loops or interstitial loops and significant bending and buckling of the basal planes are also frequently observed. Sustained shearing of (0002) planes acting in parallel with the increase of the Frank loops finally leads to the breakage of the hexagonal network in a very fine scale until an amorphous-like structure results. Although the amorphous-like phase exhibits amorphous halo diffraction patterns, HRTEM investigations indicate that it consists of highly curled small flakes with average basal plane diameter less than 5 nm and thickness (normal to the basal planes) less than 2 nm. EELS investigations demonstrate that its bonding is essentially sp 2. The present study clarifies the defect configuration appearing in heavily deformed graphite and also shows evidence that the amorphization of graphite is a defect-controlled process.

Raman Spectra of Graphite and Diamond Mechanically Milled with Agate or Stainless Steel Ball-Mill

The reduction of crystalline size and amorphization of graphite and diamond during agate and stainless ball-milling are investigated by Raman spectroscopy. The ultimate crystalline size of graphite, estimated by the Raman intensity ratio, of 2.5 nm for the agate ball-mill is smaller than that of 3.5 nm for the stainless ball-mill, while the milling time to reach the ultimate size for the former is about 10 times larger than for the latter, indicating more stability of the nanocrystalline graphite. After reaching the ultimate crystalline size, a significant broadening of the Raman spectra, which indicates the completion of amorphization, is detected only for the stainless ball-milled graphite at ∼ 500 h of milling. Also the increase rate of the Raman peakwidth for the stainless ball-milled graphite before amorphization is higher than that for the agate ball-milled graphite, indicating a larger introduction of disorder from the start of milling. Amorphization of diamond is also observed for the stainless ball-mill. The difference in the results between the agate and the stainless ball-mill is discussed in terms of the effect of impurity mixed from the milling apparatus on the stability of nanocrystalline carbon materials.

Electron microscope study of radiation damage in graphite produced by D + and He + bombardment

Cleaved highly oriented pyrolytic graphite was irradiated at temperatures between 100 and 700°C, with D + and He + ions with the acceleration voltage of 25 keV and the doses up to 3.0 × 10 18 ions/cm 2 , and examined by transmission electron microscopy. The graphite irradiated by either D + or He + ions is amorphized at a critical dose, which is monitored by the structureless electron image and the appearance of a halo in the diffraction pattern. The critical dose increases with the irradiation temperature and even the irradiation at high temperature as 500°C gives the amorphization. Though the critical dose for D + irradiation is higher than for He + irradiation, the critical dpa calculated from the energy deposition agrees well between the two cases. Therefore it seems that the amorphization of graphite by energetic ion bombardment is mainly controlled by the energy deposition and the difference in chemical nature of the incident particles plays a minor role. The macroscopic defect structures which appeared after the amorphization are, however, somewhat different between the two cases.