(Coal, tar, bitumen) New Opportunities \”dirty\” materials – Laser Engineering heavier hydrocarbons

Comparative graphene and carbon nanotubes and other synthetic materials, based on heavy hydrocarbons (HH) of the material (coal, tar, and pitch) is rarely used as a material of electronic and optoelectronic applications. However, in HH extensive chemical and structural heterogeneity provides a complex network of carbon nanostructures, these networks have built-in chemical and functional diversity but not yet utilized. Thus, a better understanding of the relationship between the HH alone or in mixtures the chemical nature and functions of materials, and their adjustability of the processed material, can better utilize HHs potential as an additive raw material, the physical custom synthesis materials and chemical properties. In fact, raw HHs mainly polycyclic aromatic hydrocarbons (PAHs), alkanes. Although HHs poor conductivity, but it can be compensated by the overall annealing, the conductivity of the graphitized by several orders of magnitude. Compared to traditional furnace annealing (mass loss> 80%), laser ablation, rapid heating to a graphitization temperature the rate of incorporation of the material almost immediately, to reduce loss of material (about 50%). Therefore, laser ablation allowed to explore fast pyrolysis, and loss of control material. In addition, the annealing method is not suitable for bulk spatially control the heating process, and they require the support substrate and the thin film can be maintained the same annealing temperature.

[introduction] achievement

Based on this, Massachusetts Institute of Technology (MIT) in the JC Grossman and [ . 123] N Ferralis (co-author) coverage of initial carbon source – structure heterogeneous mixture HHs (especially aromatic, aliphatic and heteroatoms concentration) and a feature greatly affects the chemical structure and properties of the resulting carbon thin film, for example, porosity and conductivity. binding material Chemistry (H: C and an aromatic content) is selected, the control of the laser process parameters (laser power, speed, focal length) changes in , can fully control the product H: C ratio, SP2 concentration and graphitized stacking sequence. To achieve a large range of crystallinity carbon material from amorphous to highly graphitized regulation, and conductivity 10 3 S / m or more regulation range. The research results, entitled \”Laser-engineered heavy hydrocarbons: Old materials with new opportunities \”published in internationally renowned journals Sci Adv on “脏”材料(煤、焦油、沥青)新机遇——激光工程重碳氢化合物

[graphic interpretation] [123… ] first, using a CO2 laser chemical researchers adjusted HHs, shape and electrical conductivity, including tar the steam cracking of oil

, low-volatile bituminous (LvB) coal , intermediate phase (the MP) asphalt , and mixtures thereof due to the tar (the tar) , and coal pitch H:. wide range of initial structure consistent C ratio, and a high aromatic content, they therefore chosen as a representative material of the intermediate contrast HHs mesophase pitch and coal tar having the highest H:. C and higher paraffin content is processed by a low pitch .MP formed thermotropic crystalline, isotropic pitch wherein is polymerized to a higher molecular weight having a higher ordinal number of aromatic structures with the lowest component .MP H: C and maximum aromatic content, and with a sheet neatly arranged aromatics, and aromatics LvB initial nucleus is the largest, intermediate H:. C and an aromatic content of more than

FIG. 1, a laser natural HH (coal, MO tar and bitumen) is a schematic view of the ablation “脏”材料(煤、焦油、沥青)新机遇——激光工程重碳氢化合物
Further, in an oxygen-rich environment by oxygen-induced crosslinking of aromatic clusters low temperature annealing can be obtained. unoxidized tar with broadband fluorescent in contrast, the tar oxidized film (300 deg.] C, in air 4 h) display having a plurality of fingerprint Raman aromatic character. laser Raman spectra of all HHs ablation summarized in Figure 2A, taking into account the peak position G, G peak full width at half maximum (FWHM), the presence of ID / IG peak ratio and 2D laser ablation fall HH microcrystalline / nanocrystalline (mc / nc) graphite carbon and amorphous states, and may be found in Raman label transition between the different crystal structures. amorphous carbon region, laser ablation, and coal, and other additives belong MP mc / nc graphite category. Meanwhile, researchers also estimated laser ablation of the graphite crystallite size La HHS in amorphous carbon states, ID / IG proportional to the square of the La. in nc- graphite states, ID / IG and La.Proportional to the reciprocal. It must be noted that, although the peak positions by G asphaltenes ablated MP G shows the lowest peak position (~1581cm
-1

) and the highest peak 2D, but the ID / IG ratio with FWHM the increases.

FIG 2, HHs, laser ablation and oxidation HHS HHS Raman analysis “脏”材料(煤、焦油、沥青)新机遇——激光工程重碳氢化合物
The research shows that after laser ablation, ablation of tar after oxidation to provide electrical conduction rate 36 times higher than the non-oxidized tar ablated. Laser ablation of graphite oxide tar having a larger size having higher conductivity (~2990 S / m) ratio of laser ablation oxide MP (~1133 S / cm). Comparative ablation tar (~80 S / m), ablated LvB higher graphitized coal results in higher conductivity (~800 S / m), whereas a poor degree of graphitization than the ablation still showed MP a large electrical conductivity (~500 S / m). The presence of molecular bridges can greatly increase the charge-transfer and electronic coupling and the electrical conductivity can be similar in size graphite-like network. The results showed that the use of laser ablation as a chemical HHs kit may produce carbon black, amorphous carbon and graphite carbon equivalent more carbon materials. Furthermore, adjustability and MP coal is poor, the structure more robust, lower fat content, but results in the formation and accumulation amount larger new location more conjugated bonds, resulting in higher conductivity. CO2 laser can produce a higher local temperature at a relatively low incident power (1.6-4.8 W), so that the carbonized film tar surroundings. FIG 4 illustrates a detailed optimization parameters include power, speed and laser focusing rasterization including. Light absorption spectrum by a laser ablation process variations and the tar content of aromatic dehydrogenation indicate aromatic / aliphatic ratio increased from ~0.35 to ~0.55, H: C ratio from ~1.20 ~0.95 reduced. The increase in power will increase the 2D peak, indicating a higher annealing temperature can cause the accumulation of graphite. Below the power / defocus optimized ratio, the power increase will lead to increased electrical conductivity dehydrogenation.
FIG. 3, HH conductivity and electrical transmission “脏”材料(煤、焦油、沥青)新机遇——激光工程重碳氢化合物
FIG 4, laser ablation tar (the Tar) conductivity Optimization [123 ] “脏”材料(煤、焦油、沥青)新机遇——激光工程重碳氢化合物
[Summary]

In summary, researchers processing and controlling environmental parameters selected HH material in the laser annealing process, is widely demonstrated adjustable ablative performance, covering a range of crystal structure, conductivity and electron transport mechanism. Best conductivity and engineering structure by the molecular arrangement of the obtained stability permit manufacture of these devices. In essence, by different chemical and structural customized HH, the use of a simple material processing, carried out on the carbon engineering to achieve the desired level of device performance levels. In short, the development of treatment methods used in this work as a low-cost raw material directly HH provides scalable and inexpensive way of manufacturing a device as an active device layer or the additive has many potential applications. Document Link: Laser-engineered heavy hydrocarbons: Old materials with new opportunities (Sci Adv, 2020, DOI:.. 10.1126 / sciadv.aaz5231)

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