Microstructure, elastic and inelastic properties of partially graphitized biomorphic carbons

Abstract

Abstract-The microstructural characteristics and amplitude dependences of the Young's modulus E and internal friction (logarithmic decrement δ) of biocarbon matrices prepared by beech wood carbonization at temperatures T carb = 850-1600°C in the presence of a nickel containing catalyst have been studied. Using X ray diffraction and electron microscopy, it has been shown that the use of a nickel catalyst during carbon ization results in a partial graphitization of biocarbons at T carb ≥ 1000°C: the graphite phase is formed as 50 to 100 nm globules at T carb = 1000°C and as 0.5 to 3.0 μm globules at T carb = 1600°C. It has been found that the measured dependences E(T carb ) and δ(T carb ) contain three characteristic ranges of variations in the Young's modulus and logarithmic decrement with a change in the carbonization temperature: E increases and δ decreases in the ranges T carb < 1000°C and T carb > 1300°C; in the range 1000 < T carb < 1300°C, E sharply decreases and δ increases. The observed behavior of E(T carb ) and δ(T carb ) for biocarbons carbonized in the presence of nickel correlates with the evolution of their microstructure. The largest values of E are obtained for samples with T carb = 1000 and 1600°C. However, the samples with T carb = 1600°C exhibit a higher suscep tibility to microplasticity due to the presence of a globular graphite phase that is significantly larger in size and total volume.

Thermal conductivity of Fe graphitized wood derived carbon

“…For the calculation of crystallite size, measured solid densities and a value of ℎ = 725 / [53] were used; results are detailed in Table 1, along with the rest of relevant results from this paper. Consistent with previous observations [37,53,58,63,64], increasing pyrolysis temperature results in an increase in crystallite size to which we attribute the enhancement of transport properties, either thermal or electrical.…”

“…As the pyrolysis temperature is increased, both thermal and electrical conductivity increase, suggesting a higher degree of crystalline ordering in materials pyrolyzed at higher temperatures. It has been shown in wood-derived porous carbons that increasing pyrolysis temperature increases the degree of crystalline long-range ordering, both when catalysts are used to promote graphitization [24,30,[36][37][38][55][56][57][58] but also when they are not [29,53,[59][60][61], by increasing the size of the graphitic regions in the turbostratic carbon layers (increasing crystallite size). In the case of Ni-catalyzed samples, the precipitation of large, micron sized graphite crystals has been observed [24,37] by transmission electron diffraction, even if they are absent in Fe-catalyzed samples.…”

Thermal conductivity of partially graphitized biocarbon obtained by carbonization of medium-density fiberboard in the presence of a Ni-based catalyst

“…The dependence of k ~ T 1.3 for MDF-C-1500(Ni) is closer to the dependence of k ~ T, characteristic of an amorphous phase, than the dependence of k ~ T n (n = 1.6 ± 0.1), characteristic of MDF-C-1500, BE- [15], and PI-C-2400 [13]. The resulting dependence of k ~ T 1.3 supports our assumption made in the study of elastic [23] and strength properties [24] of partially graphitized beech wood carbon that the emerging phase of bulk graphite inhibits to some extent the formation of the nanocrystalline phase, causing the formed graphite globules "float" in an amorphous medium.…”

“…Recent studies have shown that the bulk graphite phase can be introduced into biocarbon materials carbonized from natural wood, if a catalyst based on transition metals (Ni or Fe) is used in the carbonization process [19][20][21][22]. The elastic, microplastic, strength [23,24], and electrotransport properties [25] of the partially graphitized carbon obtained by carbonizing beech wood in the presence of a Ni-based catalyst have been studied previously.…”