Carbonaceous Network Research Articles

The Synergistic Effect of Flame Retardants on Flammability, Thermal and Mechanical Properties of Natural Fiber Reinforced Epoxy Composite

Epoxy was effectively resin infused with 15 %wt intumescing Alumina Trihydrate (ATH) flame retardant (FR) formulations into a 10 %wt palm EFB natural fiber (NF) mat. The effects of ATH and its intumescing blend with Zinc Borate (ZB) and Ammonium Polyphosphate (APP) on flammability, thermal and mechanical properties of the composites were investigated. Compared to neat NF filled epoxy composites, specimens loaded with intumescing blend of FR formulations demonstrated an improved thermal properties, showing greater mass residual which can be attributed to the formation of cross-linked network amongst the NF, FRs and epoxy matrix upon combustion at elevated temperature tested within a TGA instrument. Incorporation of fibers drastically enhanced the mass residue and lowered the heat release compare to the pure epoxy. Addition of the intumescing blend of FR formulations also drastically reduces the combustion heat release, total mass loss and zero drip flame in the NF composites. The optimum FRs formulation with 5 %wt ATH and 10 %wt APP exhibited self-extinguishing property, achieved lowest mass loss and no drip flame under Bunsen burner tests, signifying the synergistic effects between ATH and APP within the NF epoxy composites. APP reacts with the carbonaceous network of NF throughout the ignition period, such interaction formed a thick char layer acting as gas and thermal barrier against the fire mechanism. This reaction does not take place in NF composite specimens without APP. In terms of mechanical properties, NF composites loaded with FRs broadly showed poorer tensile strength, mainly due to the existence of FRs, which acted as a nucleating agent affected the physico-mechanical characteristics of the composites. Amongst the FR rich formulations, specimens with APP or ZB blends seem to possess a more superior tensile strength compared with the neat ATH filled formulation. In addition, composites loaded with FRs showed enhanced Young’s modulus relative to those without addition of FRs.

Hierarchically structured carbon-coated SnO2-Fe3O4 microparticles with enhanced lithium storage performance

A facile and scalable strategy was developed to fabricate SnO2-Fe3O4@C micrometer-sized particles as a good lithium-ion battery anode. The obtained materials were constructed by aggregated nanoclusters (100–200nm) consisting of SnO2-Fe3O4@C nanospheres (20∼30nm), in which SnO2 and Fe3O4 nanoparticles (5∼8nm) were homogeneously embedded in a percolating carbonaceous network with an average thickness of about 3nm. SnO2-Fe3O4@C microparticles were synthesized by a one-pot hydrothermal process followed by annealing under Ar and subsequent chemical vapor transformation (CVT) under vacuum. The peculiar strategy allows to obtain hierarchical structure of micrometer-sized particles including nanospheres, nanoclusters and micro-scale particles, and the combination of SnO2 and Fe3O4 could promote the synergistic effects to enhance the reversible capacity as well as the structural stability. Meanwhile, the carbon layer, homogeneously covering the nanoparticles does not only accommodate the volume change of active materials to maintain the structural integrity but also forms a conductive network throughout the whole micro-sized structure during charge/discharge processes. As a result, the electrode of SnO2-Fe3O4@C microparticles exhibits good rate performance (1056mAhg−1 at 0.1C, 734mAhg−1 at 0.2C, 449mAhg−1 at 0.5C, 212mAhg−1 at 1C and 133mAhg−1 at 2C, 1C=1Ag−1), high reversible capacity and good cycling stability (a high initial charge capacity of 1131.8mAhg−1 was achieved and the capacity maintained 853.3mAhg−1 after 50 cycles at 0.1Ag−1).

Vacuum ultraviolet photolysis of hydrogenated amorphous carbons

Context. The interstellar hydrogenated amorphous carbons (HAC or a-C:H) observed in the diffuse medium are expected to disappear in a few million years, according to the destruction time scale from laboratory measurements. The existence of a-C:H results from the equilibrium between photodesorption, radiolysis, hydrogenation and resilience of the carbonaceous network. During this processing, many species are therefore injected into the gas phase, in particular H2, but also small organic molecules, radicals or fragments.

Fabrication of novel polymeric and carbonaceous nanoscale networks by the union of self-assembly and hypercrosslinking

Download options Please wait... Supplementary files Supplementary information PDF (4552K) Article information DOI https://doi.org/10.1039/C4EE00941J Article type Paper Submitted 24 Mar 2014 Accepted 12 Jun 2014 First published 12 Jun 2014 Download Citation Energy Environ. Sci., 2014,7, 3006-3012 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Fabrication of novel polymeric and carbonaceous nanoscale networks by the union of self-assembly and hypercrosslinking Z. Li, D. Wu, X. Huang, J. Ma, H. Liu, Y. Liang, R. Fu and K. Matyjaszewski, Energy Environ. Sci., 2014, 7, 3006 DOI: 10.1039/C4EE00941J To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Zhenghui Li Dingcai Wu Xin Huang Junhao Ma Hao Liu Yeru Liang Ruowen Fu Krzysztof Matyjaszewski

High Capacity Li/S Battery for Advancing Commercialization

Rechargeable Li/S batteries are promising candidates for portable electronics, electric vehicles and energy storage system due to their high specific energy and low cost. Many researchers have reported remarkable results in this area, but there are still huge obstacles for commercialization in terms of sulfur loading level for higher specific energy and higher stabilization for lithium metal anode. To solve these problems, we have researched with two aspects. One is attempting to realize highly loaded sulfur cathode with large utilization by impregnating carbonaceous conductive network with nano-sized sulfur. The other is preventing sulfide-shuttle by separator coated with negatively charged material. Using nano-sized sulfur has advantages not only for increasing networks for sulfur-carbon, but also for obtaining enough space against expansion during lithiation. Furthermore, the conductive network of sulfur-carbon can be more stably maintained with cycling which gives long life span as compared to micro-sized sulfur cathode. Nano-sulfur was fabricated using the conventional milling process in water added with glycerol. Ketjen Black with high surface area and aqueous PVP-PEO mixture were used as a conductive material and binder respectively. Finally, cathode electrodes were prepared with high sulfur contents of 70 wt% and elevated sulfur loading of 3.0 mg/cm2. Electrochemical measurements were carried out using CR2032 coin-type cell system. Initial specific capacity and capacity retention were more than 1,000mAh/g(sulfur) and 80% after 100 cycle respectively. Adapting separator coated with negatively charged moiety significantly decreased the over-charging. This phenomenon can be interpreted as an effect of the negative moiety on separator to repulse the soluble polysulfides which move toward the surface of anode. Detailed properties up to 300 cycles for pouch cell will be discussed. We believe that the nano-sized sulfur and separator coated with negative moiety can be helpful to advance the commercialization of lithium sulfur battery with high specific energy density more than 300Wh/kg.

Synthesis of high-performance LiFePO4/C composite with a grape bunch structure through the hydrothermal method

The LiFePO4/C composite with a grape bunch structure was synthesized through the hydrothermal method at 170 °C for 7 h and followed by being fired at 750 °C for 4 h. Commercial Li2CO3, (NH4)2Fe(SO4)2 · 6H2O, and (NH4)2HPO4 were used as raw materials. Glucose was used as in situ coating carbon source, and the hydroxylated MWCNTs were used as connecting carbon wires which could be embedded into the carbon coating to form a uniform grape bunch structure. The resultant samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), elementary analysis (EA), Raman spectroscopy, and electrochemical tests. The results show that the grape bunch structure with a low disordered/graphene (D/G) ratio was found to be well dispersed in the LiFePO4/C composite, and a three-dimensional carbonaceous network was formed which could enhance the electronic conductivity of the LiFePO4/C composite remarkably. The resultant LiFePO4/C composite shows a high discharge capacity of 160.3 mAh g−1 at 0.1 C and 110.9 mAh g−1 even at 10 C, and the cycling capacity retention rate reaches 99.6 % over 60 cycles. Besides, it also exhibits high conductivity, good reversibility, and excellent stability in EIS and CV tests.

Influence of the carbonaceous conductive network on the electrochemical performance of ZnFe2O4 nanoparticles

Herein, the influence of the carbon precursor used for the realization of carbonaceous percolating network incorporating ZnFe2O4 is investigated. Three different precursors, namely sucrose (Suc), citric acid (CA), and oleic acid (OLEA) were used for the realization of such carbonaceous matrix. The composite materials were characterized by means of thermogravimetric analysis (TGA), gas adsorption using the BET isotherm, Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Electrodes based on the resulting composite materials were investigated, performing electrochemical impedance spectroscopy and galvanostatic cycling. The results showed that the homogeneity of the carbon coating rather than the absolute amount of carbon enhanced the electrochemical performance of ZnFe2O4 nanoparticles. The most advantageous coating properties were obtained with sucrose as carbon precursor, obtaining a highly stable specific capacity higher than 1000 mAh g−1 for more than 60 cycles.

Kr++ Ion Implantation-Induced Changes in Optical Properties of Polycarbonate

Transparent polycarbonate samples were implanted with 200 keV Kr++ ions to various doses ranging from 1 × 1015 to 8.4 × 1016 ions cm−2 with a beam current density of 1 µA cm−2. Modification in the optical and chemical properties of polycarbonate as a function of the implantation fluence was investigated for UV-visible spectroscopy. UV-visible absorption analysis suggests the formation of a carbonaceous layer and a drastic decrease in optical band gap from 4.12 eV for unimplanted polycarbonate to 0.71 eV at an implanted dose of 8.4 × 1016 ions cm−2 has been observed. The width of the tail of localized states in the band gap was evaluated using the Urbach edge method and it increased from 0.10 eV for unimplanted polycarbonate to 2.46 eV for Kr++ implanted polycarbonate at the highest dose of 8.4 × 1016 ions cm−2, indicating an increase in disorder. The decrease in optical band gap points towards the formation of carbonaceous clusters and/or networks of conjugated unsaturated bonds. The number of carbon atoms, N, in a cluster can be calculated from absorption spectra and it increases from a value of 83 at a dose of 1 × 1015 ions cm−2 to 2333 at a dose of 8.4 × 1016 ions cm−2. The correlation between the decline in band gap and change in structure has been discussed.

An advanced carbonaceous porous network for high-performance organic electrolyte supercapacitors

A new class of advanced porous network structured carbon materials exhibits very attractive capacitive properties when utilized as electrodes for organic electrolyte supercapacitors, including large capacitances up to 210 F g−1, unusually high energy densities of 21.4–41.8 W h kg−1 at power densities of 67.5–10 800 W kg−1, and excellent cycling stability.

Percolating networks of TiO2 nanorods and carbon for high power lithium insertion electrodes

Anatase TiO2 nanorods (NRs), with an average diameter of 3–4nm and an average length of 25–30nm were investigated as Li-insertion material. The NRs, capped with oleic acid, were synthesized by a low temperature colloidal route based on thermal decomposition of the precursors in presence of coordinating agents. A highly porous and connective network of NRs and carbon was prepared by taking advantage of this organic capping to inhibit the nanoparticle agglomeration and to act as a precursor for the formation of a carbonaceous percolating network. Composite electrodes, made of such material, were able to deliver reversible capacities of about 250mAhg−1 (corresponding to 0.75equiv. of Li per TiO2 unit). Reversible capacities of 210mAhg−1 (0.63 Li per TiO2), 194mAhg−1 (0.58 Li per TiO2), 165mAhg−1 (0.49 Li per TiO2), and 130mAhg−1 (0.39 Li per TiO2) were observed during cycle tests at 1C, 2C, 5C, and 10C, respectively, confirming the excellent high rate performance of the well-dispersed NRs. Finally, the electrodes showed excellent cycle life performance.

Soil organic matter in nano-scale structures of a cultivated Black Chernozem

We report on the spatial arrangement, chemical composition and stabilization of soil organic matter (SOM) in nano-size structures isolated from a clay fraction of a cultivated Black Chernozem of Canada. Both soil fractions were characterized by Transmission Electron Microscopy (TEM), Pyrolysis Field Ionization Mass Spectrometry (Py-FIMS) and radiocarbon dating, which assisted to better understand the role of SOM and inorganic colloids in the stabilization of carbon and nitrogen at the nm scale. Observations made by TEM indicated that SOM in nano-size fractions occurred mainly in organo-mineral complexes but also in solitary structures of humic substances that formed a carbonaceous network of single strands linking clusters of humic materials and minerals, ranging from a few nm to μm in size. Observations by TEM indicate that humic substances facilitated the spatial arrangement of minerals, thus contributing to physical and physico-chemical stabilization of SOM in nano-size structures. The thermal products evolved during Py-FIMS analyses showed that SOM had greater thermal stability in nano-size structures than in the clay fraction, indicating differences in physical adsorption, cross-linking, polymerization, and/or polycondensation reactions. The SOM in nano-size structures accumulated carbohydrates, N-heterocyclics, peptides, alkylaromatics but was depleted in fatty acids, whereas SOM in the clay fraction was enriched in phenols, lignin monomers, lipids and fatty acids.

“Everything is surface”: tunable polymer organic frameworks with ultrahigh dye sorption capacity

Carbonaceous polymer networks with tunable porosity were found to behave as exceptional adsorbents toward large organic molecules such as organic dyes.

Structural characterization of kerogen in 3.4 Ga Archaean cherts from the Pilbara Craton, Western Australia

Hydrogen-lean kerogen (atomic H/C < 0.46) isolated from the 3.4 Ga Strelley Pool Chert in the North Pole area, Pilbara Craton, Western Australia, were studied by vibrational spectroscopy (Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy), nuclear magnetic resonance spectroscopy (solid state 13C NMR spectroscopy), catalytic hydropyrolysis followed by gas chromatography mass spectrometry (HyPy–GC–MS), and isotope ratio mass spectrometry (IRMS). The kerogen occurs in sedimentary rocks as clasts and clots deposited together with other detrital materials that are finely disseminated throughout a chert matrix. The bulk kerogen δ 13C values range from −28.3 to −35.8‰. Solid-state 13C NMR spectroscopy and FTIR spectroscopy reveals that the kerogen is highly aromatic ( f a varying from 0.90 to 0.92) and contains only minor aliphatic carbon or carbon-oxygenated (C–O) functionalities. The Raman carbon first-order spectra for the isolated kerogens are typical of spectra obtained from disordered sp 2 carbons with low 2-D ordering (biperiodic structure). The implications of the Raman results show low 2-D ordering throughout the carbonaceous network indicate the incorrect usage of the term graphite in the literature to describe the kerogen or carbonaceous material in the Warrawoona cherts. Hydropyrolysates contain aromatic compounds consisting of 1-ring to 7-ring polycyclic aromatic hydrocarbons which were covalently bound into the kerogen as well as alkanes (linear, branched and cyclic) which were most probably trapped in the microporous network of the kerogen. These PAHs have mainly C1- and C2-alkylation while C 3+-substitued aromatics are low in abundance and do not show a high degree of branched alkylation. For the first time we have shown a correlation between elemental analysis (H/C atomic ratios), Raman spectroscopic parameters ( I D1/ I G, I D1/( I D1 + I G), and L a), and the degree of alkylation of bound polyaromatic molecular constituents generated from HyPy for Archaean kerogens. Similarities in molecular profiles exist between HyPy products of Strelley Pool Chert kerogens and an oil-window-mature Mesoproterozoic kerogen from Roper Group (ca. 1.45 Ga), which is biogenic in origin, suggesting that the Strelley Pool Chert kerogens may also be derived from diagenesis and thermal processing of biogenic organic matter. A combination of Raman spectroscopy, for identifying the least metamorphosed kerogens, used together with HyPy for liberating trapped and bound molecular components of these kerogens, offers a powerful strategy for assessing the origins of Earth's oldest preserved organic matter.

Low erosion behavior of polystyrene films under erbium ion implantation

Erbium ion implantation in polystyrene (PS) thin films has been performed with 40 and 60 keV ions to a dose range between 1×1014 and 1×1016ions∕cm2. The x-ray reflectivity technique was applied to determine the ion-induced eroded layer thickness and interestingly, the erosion rate is found to decrease with increasing ion doses exhibiting simple power law behavior of the form ∼(dose)−b. We propose the formation of a carbonaceous network at the top surface, which seems to prevent further erosion of the polymer with increasing the duration of implantation time. These findings may open up a possibility of loading a large amount of erbium in a polymer matrix by the implantation technique to make it suitable for various optoelectronic applications.

Nanostructured coatings of metal containing diamond-like carbon films deposited by femtosecond pulsed laser ablation

Nanocrystallized metal (Me)/carbon-based films (a-C:Me) have been deposited by femtosecond pulsed laser ablation (PLD). The films have been obtained by ablating alternatively and sequentially graphite and metallic targets in vacuum conditions, with an amplified femtosecond Ti:sapphire laser (wavelength 800 nm, pulsed duration of 150 fs). The metals selected, regarding of their opposite chemical affinity with carbon, are nickel and tantalum. The deposition procedure allowed to control accurately the metal concentration introduced in the carbonaceous matrix, in the 15 at.% range. The composition and nanostructure of the films have been characterized by X-ray photoelectron spectroscopy, grazing incident angle X-ray diffraction and energy filtered transmission electron microscopy. The nanocomposite coatings contain metallic clusters in the 10–250 nm size range, embedded in the carbonaceous network. The interface between the metallic clusters and the carbon matrix depends on the chemical affinity of the metal in respect to carbon.

Tribochemistry between hydrogen and diamond-like carbon films

The objective of the present work is to propose a model related to the role of hydrogen on the friction mechanism of DLC films. An up-to-date review of the effect of hydrogen on the tribology of DLC films is presented first. Selected experiments performed on two model hydrogenated DLC films are then presented to demonstrate how hydrogen, both as a constituent of the carbonaceous film or as a gaseous species introduced in the surrounding environment during the friction process can influence the intermediate and steady-state friction regimes, in the absence of any oxidating species. For the film with the highest hydrogen content, superlow friction (10 −3 range) is reached rapidly in an ultrahigh vacuum. For the film containing the lowest hydrogen content, the combination of a controlled temperature during friction (150°C) with hydrogen diffusion from the bulk of the film towards the sliding activated surfaces of the hydrogen carbon-to-carbon is responsible for an intermediate period with friction in the 10 −3 to 10 −2 range. Then the steady-state friction coefficient rises up to 0.6, typical for low hydrogenated a-C:H films in vacuum or inert atmospheres. A superlow friction steady-state regime may be controlled over longer periods by introducing a significant pressure of pure hydrogen surrounding the contact during the friction process. Argon at the same pressure does not have any similar lubricating effects. Tribochemistry between hydrogen and the carbonaceous network is thus responsible for the control of the superlow friction regime observed with a-C:H coatings in selected conditions of film composition and atmosphere.

A Carbon Macro-network From the Controlled Pyrolysis of Saccharose

Well de®ned, molecular networks such as fullerenes and nanotubes have been some of the most remarkable discoveries in the area of carbon research in recent years. Another non-well de®ned carbon network, such as that represented by the microporous structure of activated carbons, a material with many applications [1], is assumed to be constituted by polyhexagon sheets of carbon forming micropores and mesopores of widths around 2 nm [2, 3]. In addition, other networks have been observed by microscopy in activated carbons [4]. In this case, the macropore (. 50 nm width) structure observed is originated from the preservation after carbonization of the biological tissue skeleton of the raw material (wood, coconut shell, etc.). Accordingly, three carbonaceous network structures can be considered according to the scale: the molecular (fullerenes, nanotubes), and micro (microporous carbon), and the macro (macroporous carbon). Although in the case of carbon materials, synthetic routes for both molecular-networks and micro-networks have been extensively investigated, few studies exist regarding the synthesis and characterization of macronetworks. This communication presents the synthesis and de®nition of the topological organization of a carbonaceous macronetwork obtained from a step-wise heat treatment of saccharose. A solution composed of 1 ml of water plus 2 g of D(‡)-saccharose (Merck, bacteriology grade) was placed inside a common pyrex 100 ml beaker. This was submitted to two consecutive heat treatments: First, a low temperature stabilization inside an oven at the following temperatures: 60, 90, 110, and 130 8C, for 10 min at each temperature, using heating rates of about 3 8C miny1. Secondly a heat treatment consisting of a carbonization under an inert (nitrogen) ow using the following step temperatures: 50, 100, 150, 200, 250, 350 8C, leaving 30 min at each temperature, and ®nally 1 h at 450 8C, using heating rates of about 5 8C miny1. This ®nal temperature was chosen as this had been found to be the optimun for the preparation of lowtemperature (L-type) activated carbon from lignocellulosic raw materials [5, 6]. A statistical analysis of the macronetwork obtained was carried out as described in previous studies for other cell structural systems [7]. The macronetwork material was submitted to other measurements: N2 adsorption at 77 K to obtain the BET surface area, employing a Micromeritics ASAP-2000 apparatus; temperature-programmed reduction (TPR) with H2 employing a Micromeritics TPR=TPD 29000 apparatus; and elemental analysis with an Eager 200 apparatus. After carbonization, a macronetwork ®lm was obtained that adhered both to the bottom of the beaker and around the cylindrical beaker wall, covering approximately one ®fth of the beaker height. This network was constituted by a net of cells in the form of polygonal rings (Fig. 1), each ring formed by grains of carbonaceous material. Polygons from three up to eight sides were identi®ed. In addition, an irregular sponge ball featuring a similar structure to that seen in the ®lm was also obtained in the bottom of the beaker. This was apparently loosely connected to the ®lm network, i.e. it changed position when the beaker was shaken. Therefore, both twoand three-dimensional networks were obtained simultaneously. Also, the noticeable separation of the grains constituting the polygons (Fig. 1) suggest weak linking, which most probably caused the easy disconnection of the sponge ball from the ®lm adhered to the wall. During carbonization, there was a remarkable

Properties of carbonaceous nanoparticles in flat premixed C 2H 4/air flames with C/O ranging from 0.4 to soot appearance limit

The presence of very fine carbonaceous particles in the ambient causes concern either for their toxic properties or for their influence on atmospheric chemistry and physics. Previous work has shown that carbonaceous nanoparticles with a typical size of about 2–3 nm are formed in the reaction zone of rich premixed sooting flames and may act as soot precursors. This paper ascertains the presence of nanoparticles in rich laminar C 2 H 4 /air premixed flames with C/O ratio ranging over a wide interval below the soot limit. Ultraviolet (UV)-visible absorption starting from 200-nm, laser-induced fluorescence (LIF), and laser light scattering (LLS) methods were used for the in situ measurements and for the characterization of the material collected from the flames as hydrosol in water traps. It was found that the absorption spectra from 200 to 300 nm were due both to hot CO 2 , whose absorption cross sections are orders of magnitude higher than those found at room temperature, and to carbonaceous high molecular mass structures. The absorption spectra of those structures, obtained by subtracting the CO 2 contribution, and the fluorescence spectra show the same behavior as those measured on the hydrosol suspension. The monochromatic absorption coefficient in the UV due to high molecular mass structures have their onset at C/O=0.4, whereas the fluorescence excited at λ 0 =266 nm appears around C/O=0.5, where also light scattering coefficients, in the UV and visible, in excess with respect to those due to burned gases, start to be measurable. These results are interpreted in terms of a carbonaceous network of one-and two-ring aromatic functionalities, connected by aliphatic bonds, with typical size around 2 nm. The high-temperature formation of these carbonaceous nanoparticles below soot formation limit is considered an important route for explaining the presence of organic carbon aerosols in the atmosphere.

Physical and chemical characteristics of densified low-rank coals

The conversion of Victorian brown coal into a hard densified product is described. Densified brown coal (DBC) is readily moulded or extruded into a convenient form and is characterized by reduced moisture content, greater bulk density and increased strength. Removal of water is initiated by a kneading process and continues during drying under ambient conditions. The loss of water is also accompanied by pellet shrinkage and an increase in crush strength. The development of crush strength is attributed to an increase in pellet density arising from greater coal compaction through the formation of a particulate gel network. The extent of compaction and the strength of the carbonaceous gel network depends on the pH and the nature of the acidic oxygenated functional groups in the coal. Derivatization of acidic functionalities, by O-methylation, results in a collapse of the coal network structure to give a product with inferior physical properties owing to the blockage of potential bonding sites. Acidic coals produce DBC of moderate density and strength, whereas base-treated coals produce very dense and stronger products. The improved physical properties of the base-treated DBCs is attributed in part to the presence of ionic associations between the coal particles to give a stronger three-dimensional network.

An ESCA investigation of low energy electron beam interactions with polymers: II. PVDF and a mechanistic comparison between PTFE and PVDF

Poly(vinylidene fluoride) (PVDF) has been irradiated by low energy (< 2 keV) electrons and the changes in structure and bonding monitored by ESCA. Defluorination is found to occur, ultimately leading to an unsaturated crosslinked, partially fluorinated carbonaceous network. For 2 keV electron bombardment the changes are found to be vertically homogeneous when studied using Mg Kα 1,2 ESCA analysis but a comparison with Ti Kα 1,2 excited spectra reveals a depth heterogeneity. The effect of electron energy is also only revealed by the use of Ti Kα 1,2 X-ray excited ESCA analysis. The results obtained are compared with a previous study on electron beam effects on PTFE. The differences between the two systems are seen to be explained by the ability of PVDF to form HF as a route to defluorination.