Raman study of the microstructure changes of phenolic resin during pyrolysis

After curing, phenol‐formaldehyde resins were post‐cured at 160°C, and then carbonized and graphitized from 300°C to 2400°C. The structure of the resulting carbonized and graphitized resins were studied using X‐ray diffraction and Raman spectroscopy. Thermal fragmentation and condensation of the polymer structure occurred above 300°C. The crystal size of the cured phenolic resins increased with an increase in temperature. The crystal size increased from 0.997 nm to 1.085 nm when the heat‐treatment temperature rose from 160°C to 500°C. Above 600°C, the original resin structures disappeared completely. Below 1000°C, the stack size (L_c) increased very slowly. The values increased from 0.992 to 1.192 nm when the heattreatment temperature rose from 600°C to 1000°C. Above 1000°C, the stack size showed an increase with the increase in heat‐treatment temperature. The values increased from 1.192 to 2.366 nm when the temperature rose from 1000°C to 2400°C. The carbonized and graphitized resins were characterized using Raman spectroscopy. The Raman spectrra were recorded between 700 and 2000 cm⁻¹. Below 400°C, there were no carbon structures in the Raman spectra analysis. Above 500°C, G and D bands appeared. Raman spectra confirmed progressive structure ordering as heat‐treatment temperature increased. The frequency of the G band of all carbonized and graphitized samples shifted to 1600 cm⁻¹ from the 1582 cm⁻¹ of graphite. At the same temperature, the D band shifted to 1330 cm⁻¹ from the 1357 cm⁻¹ of the imperfect carbon. In the curve fitting analysis of the Raman spectra, a Gaussian shaped band centered at 1165 cm⁻¹ was included. This band has not been described before in the literature and is attributed to disordered structures, which are formed from the original polymeric structures. These polymeric structures formed unknown disordered structures and remained in the carbonized phenolic resins. Above 1800°C, this band disappeared completely. But, a weak peak is present near 1620 cm⁻¹. This indicated that those disoriented molecules and some disordered carbons were removed as volatiles or repacked into the glassy carbon structures during graphitization. The carbonized and graphitized phenolic resins were found to correspond to low order sp² bonded carbon, but cannot be considered as truly glassy or amorphous carbon materials since they have some degree of order in the basal plane.     

Raman spectroscopic study of the microstructure of carbon films developed from cobalt chloride‐modified polyacrylonitrile

Polyacrylonitrile (PAN) was modified with cobalt chloride at 90°C for 5 min. The carbon films prepared from original and modified PAN films were carbonized up to 1300°C. The structure of the resulting carbon film was studied using X‐ray diffraction and Raman spectroscopy. The stacking size obtained from X‐ray diffraction approaches the L_c value of the resulting carbon films as the heat treatment temperature increased. The mean average carbon basal planes in crystalline (Lc/d) also increased with increasing pyrolysis temperature. Raman spectra confirmed the progressive structural ordering as treatment temperature increased. During pyrolysis, a substantial decrease in the intensity of the band near the 1350 cm⁻¹ region was observed, indicating a decrease in the disordered structure. The crystal size (L_a) of the resulting carbon films also showed a remarkable increase with increased heat treatment temperature. The resulting carbon films developed from the modified PAN films had higher L_c and L_a than those developed from the original PAN film. It was established that cobalt catalyzes graphitization of amorphous carbon during pyrolysis. This modification not only promoted the growth of crystal size but also increased the close packing of the carbon basal planes. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2219–2225, 1999     

Processes in sulfur dioxide treatment of PAN fibers

When PAN fibers containing 4% methyl acrylate, 3.2 denier, react with SO₂ at increasing temperature up to 290°C, the reaction is slow below 230°C and rapidly increases thereafter. The effects of up to 20 w/o S have been studied. The incorporation of S leads to an increase in fiber diameter. Reduction of DTA exotherm with increasing S content suggests that the fibers become more oxidation resistant, which is confirmed experimentally. Increase of secondary modulus and decrease of extension to failure values suggest the presence of cross-links; this is also indicated by IR absorption at 1690 cm^?1 which may be ascribed to

groups, with S atoms forming intermolecular bridges. Elemental analysis shows that per each incorporated S atom 2.7 to 3.8 H atoms are removed; the O/S ratio approaches 2 or is closer to 1 for the reaction taking place up to 230 or at 290°C, respectively. Above 230°C there is a certain degradation of the fibers, but this is diminished by pre-treatment at 230°C. The IR evidence (behavior of the 2240 and 2190 cm^?1 peaks, presence of the 810 and 1590cm^?1 absorption, behavior of the 2870 and 2940 cm^?1 peaks) indicates that CN groups react slowly at 230°C but rapidly at 290°C, giving rise to a cyclized and aromatized product. Combining low-temperature (230°C) and high-temperature (290°C) SO₂ treatment coupled with higher stretching force, fibers that retain the maximum of their initial carbon content and possess maximum amount of cross-linking, giving rise to highest mechanical properties of carbonized fibers, can be produced.     

Oxidation of carbon derived from phenolic resin

The oxidation of carbon derived from phenolic resin and heat-treated at temperatures ranging from 1000 to 2400°C for 1 hr was studied in a flowing oxygen atmosphere at temperatures between 424 and 692°C. The heat-treatment alters the crystallite size, L_c, from 10.7 to 21.4 Å; the interlayer spacing, d₀₀₂, from 3.74 to 3.52 Å and the surface area from 0.22 to 1.34 m²/g. $\text{L}{}_{\mathrm{a}}\text{L}{}_{\mathrm{c}}$ ratio ranges from 1.62 to 2.22 and appears to be independent of heat treatment temperature and oxidation level. The surface area of the carbon and its change with oxidation were found to be sensitive to the heat treatment process. Heat treatments at 1000 and 1400°C produce carbon with surface area which increases by nearly two orders of magnitude after 10% oxidation. The oxidation rate decreases with increasing heat treatment temperature with the largest change between 1000 and 1400°C. Samples heat-treated at different temperatures give slightly different activation energies with an average value of 41.5 kcal/mole.     

Variations in the microstructure of carbon fibers prepared from liquefied wood during carbonization

After spinning by adding hexamethylenetetramine and the curing treatment, carbon fibers from liquefied wood (LWCFs) were prepared by direct carbonization. Microstructure change of LWCFs during carbonization is studied by X‐ray, Raman spectroscopy, and FTIR. Raman spectroscopy shows both the D peak at 1360 cm^?1 and the G peak at 1595 cm^?1 exist after 600°C, and a significant decrease is found in I_D/I_G during carbonization. X‐ray diffraction shows the crystallite size (L_c(002) and L_a(100)) of LWCFs firstly decreases before 800°C and then increases with heat treatment temperature (HTT) increasing, whereas the interlayer spacing (d₀₀₂) gradually decreases during carbonization. It is also found that the crystallite shape (L_a/L_c) and the degree of graphitization (G) all increase with increasing HTT. It is also found that structure of the precursor fibers from liquefied wood has been completely changed after carbonization. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Straining phenomena of POY revealed by thermal retraction and other techniques

Partially oriented polyesters yarns (POY) were strained at different strain rates (0.03–12.00 min^?1) and temperatures above and below T_g (3–92°C). Thermal retraction, density, DSC, and WAXS techniques show that strain-induced crystallization takes place by straining at temperatures above as well as below T_g. Above T_g, depending upon the strain rate, two regimes are observed: Below the strain rate of 1.5 min^?1, the flow regime; the degree of crystallinity is reduced as the strain rate increases. Above the strain rate of 1.5 min^?1, the strain-induced crystallization regime; the degree of crystallinity increases as the strain rate increases. Thermal retraction, stress–relaxation, and sonic modulus techniques indicate that, upon cold straining, instead of the original T_g at 65–69°C, two glass transitions occur: an upper T_g (u) and a lower T_g (l). For POY strained at 3°C and at a strain rate of 10 min^?1, the values are 78°C and 37°C, respectively. The higher the strain rate and the lower the straining temperature, the large the difference between T_g (u) and T_g (l).     

Catalytic graphitization of carbons by borons

Boron is known as a unique graphitization catalyst, because it accelerates the homogeneous continuous graphitization process of the entire carbon without any formation of specific carbon components such as graphitic carbon. This study uses various amounts of boron and several kinds of carbon in an attempt to reveal whether the boron exhibits other kinds of catalytic effect. For the non-graphitizing phenol-formaldehyde resin carbon, a boron addition of 1 wt % accelerates the homogeneous continuous graphitization process of the entire carbon at heat-treatment temperatures from 1800 to 2600 °C. As the amount was increased to 5 and 10 wt %, the boron catalysed the formation of specific turbostratic carbon (no three-dimensional ordered structure, d₀₀₂ 3.38 Å, L_c 200 Ź) at 2200 °C, and graphitic carbon (three-dimensional ordered structure, $\text{d}{}_{002}\text{3.36}\text{A}\text{?}\text{, L}{}_{\mathrm{c}}\text{1000}\text{A}\text{?}$) above 2400 °C, besides the homogeneous effect, which was enhanced by increased heat-treatment temperature and an increase in the amount of boron. For the graphitizing 3,5-dimethylphenol-formaldehyde resin carbon, only the homogeneous acceleration was catalysed by 1 wt % boron. Additions of 5 and 10 wt % boron resulted in the formation of graphitic carbon above 2400 °C in addition to the homogeneous effect observed above 1800 °C. Turbostratic carbon was never found. The catalytic mechanisms for these effects are discussed.     

Kinetics of leaching of tunisian phosphate ore particles in dilute phosphoric acid solutions

Van der Sluis et al.'s model was used to determine the rate of the partial dissolution of a Tunisian phosphate rock with dilute phosphoric acid (1.5 mass% P₂O₅). When the temperature rises from 25 to 90°C, for a given particle size, the mass-transfer coefficients, k_L°, vary from 3 × 10^?3 to 8 × 10^?3 m ·s^?1. The corresponding diffusion coefficients, D, lies between 6 × 10^?7 and 27 × 10^?7 m²·s^?1. Activation energy is equal to 14 kJ·mol^?1 and values of k_L°, at 25°C, are in the range of 0.28 × 10^?3 and 4 × 10^?3 m·s^?1 when the agitation speed goes from 220 to 1030 rpm, showing that the leaching process is controlled by diffusion rather than by chemical reaction.     

The carbonization of colloidal polyaniline nanoparticles to nitrogen‐containing carbon analogues

The carbonization of nanostructures afforded by conducting polymers represents a new route to the preparation of functional nanostructured carbons. The exposure of colloidal polyaniline particles stabilized with poly(N‐vinylpyrrolidone) or silica nanoparticles at 650 °C in inert atmosphere led, in both cases, to nitrogen‐containing carbonaceous materials with specific surface areas of 200 and 205 m² g^?1, respectively, and conductivities of 8.3 × 10^?7 and 1.9 × 10^?10 S cm^?1, respectively. The latter material contained 77 wt% of silica. The original particulate nanostructure of the samples was preserved after carbonization. The carbon‐to‐nitrogen atomic ratio was 7.2 and 7.9; the nitrogen content in the carbonized polyaniline–poly(N‐vinylpyrrolidone) particles was 10.8 wt%. Thermogravimetric analysis in air revealed their stability to be up to 500 °C. This is comparable with commercial multi‐wall carbon nanotubes, which have similar areas of application. The nitrogen‐containing carbons are potentially useful as supports for catalysts and in applications where carbon of higher hydrophilicity would be of benefit. Copyright © 2010 Society of Chemical Industry     

Raman spectroscopic study of effect of steam and carbon dioxide activation on microstructure of polyacrylonitrile‐based activated carbon fabrics

This work presents the different effects of steam and carbon dioxide activation on the microstructure of an oxidized polyacrylonitrile (PAN) fabric. An investigation was conducted on a series of carbonized fabrics and two series of activated carbon fabrics. The fabrics were activated by steam and carbon dioxide using heat‐treatment temperatures of 900–1100°C. Steam and carbon dioxide developed the microstructure initially present in the PAN‐based activated carbon fabrics, but with different effects. These fabrics in the form of fabric and powder were examined by X‐ray diffraction and Raman spectrometry. This study indicated that carbon dioxide only reacted with the crystalline edges or the irregular carbon on the fiber surface and that the inside structure of the fibers was not greatly affected. When the fabrics were activated using steam, water molecules reacted not only on the fiber surface but also with the carbon at the crystal edge and/or the nonregular carbon in the fibers, which led to communicating pore structures on the surface and in the inner portions of the fiber. This activation also promoted the denitrogenation reactions. Because of these structures and reactions, the activated carbon fabrics, which were activated by steam, had the highest stacking height for carbon layer planes (L_c), the highest number of layer planes (L_c/d₀₀₂), the highest oxygen content, the largest crystal size (L_a), and the highest density over the other samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1090–1099, 2001     

Modulated gluconic acid production from immobilized cells of Aspergillus niger ORS‐4.410 utilizing grape must

BACKGROUND: Gluconic acid (GA) production by immobilized cells of mutant Aspergillus niger ORS‐4.410 on polyurethane sponge (PUS) and calcium‐alginate (Ca‐alginate) was evaluated in repeated batches of solid state surface fermentation (SSF) and submerged fermentation (SmF) conditions, respectively, utilizing rectified grape must as carbon source. RESULTS: The passive immobilization of cells in fermentation medium solid support of having 0.4 cm³ cube size, 4% spore suspension, 0.6 g inoculum of PUS immobilized cells at 32 °C and 2.0 L min^?1 resulted in the maximum GA production (88.16 g L^?1) with a 92.8% yield, while the Ca‐alginate matrix with a 0.5 cm diameter bead size, 2–3% spore suspension, 15 g inoculum at 34 °C and 150 rpm agitation speed revealed 67.19 g L^?1 GA with a 85.2% yield. Repeated use of PUS showed higher levels of GA (110.94 g L^?1) in the third–fourth fermentation cycles with 95–98% yield and 22.50 g L^?1 d^?1 productivity under SSF that was 2.5‐fold higher than the productivity obtained from a typical fermentation cycle, and 54% greater than the productivity obtained with repetitive use of Ca‐alginate immobilized cells of A. niger under SmF. CONCLUSION: Using immobilized cells of A. niger in PUS, the rectified form of grape must can be utilized for GA production as an alternative source of carbohydrate by replacing the conventional fermentation conditions. Copyright © 2008 Society of Chemical Industry     

Effect of post-curing on the mechanical properties of carbonized phenolic resins

After curing, phenol-formaldehyde resins were post-cured at 160°C, 230°C, and 300°C in air for several hours, and then those post-cured samples were carbonized at 1000°C. The effect of post-curing on the physical properties and microstructure of the carbonized phenolic resin is reported in this article. The purpose of post-curing was to improve the mechanical properties of the carbonized resins. The post-curing process promoted the crosslinking reaction and the evolution of gases. The cured resin post-cured at a higher post-curing temperature (300°C) had a significantly higher weight loss, greater linear shrinkage and lower density than others samples. During carbonization the post-curing process not only decreased the weight loss but also limited the shrinkage. Post-curing also promoted the formation of carbon basal planes and the chemical densification in structures of the final carbonized resins. The increase in post-curing temperature and time had the effect of reducing the linear shrinkage of the resin during carbonization. The TGA thermal analysis showed that the post-cured resins improved the total weight loss more than 15 wt% over the unpost-cured resin. The carbonized resins developed from the post-cured resins had a greater flexural modulus by about 10–50% and improved the linear shrinkage by about 10% over that developed from unpost-cured resin.     

Detection of polymer transition temperatures by infrared absorption spectrometry

Infrared bands in the 900–1100 cm^?1 region are sensitive to thermal energy. These bands can result from intermolecular coupling, producing the crystal lattice, or from intramolecular coupling of the various atomic groups in a regular helix or coiled chain. In either case an increase in temperature will disrupt the coupling mode, resulting in a form of structural relaxation and a reduction in the integrated absorbance. It is proposed that the temperature at which the peak areas begin to decrease be assigned as the T_g. This is measured by continuously scanning a selected peak in the infrared spectrum of a polymer film while it is heated at a rate of about 1°C/min. Using this technique polyamides (nos. 6,66, and 610) exhibited transitions in the 30–50°C range, and by studying the increase in the free NH region (3440 cm^?1) of nylon 66 two other transitions were detected at 80 and 137°C; the latter represents a change in the nylon 66 crystal state. An amorphous film of poly(ethylene terephthalate) displayed a transition at 58–68°C (T_g) and at 85°C, which is the crystallization temperature. Films of poly(vinyl acetate) and polystyrene exhibited transitions at 25–37°C and at 70°C, respectively.     

Preparation of carbon fibers from syndiotactic 1,2-polybutadiene

Carbon fibers having good mechanical properties were produced from syndiotactic 1,2-polybutadiene (s-PB). Melt-spun s-PB fibers were made infusible by oxidation, irradiation, or treatments with Lewis acids, protonic acids, or peroxides. The infusibilized fibers were dehydrogenated with oxygen, chloranil, or sulfur and then carbonized. The preparative method by the AlBr₃–sulfur–heat treatment process gave carbon fibers with good mechanical strength in a high yield. A filaments bundle was immersed in a benzene solution of AlBr₃ (2g/100mL) at 42°C for 78 min under tension, washed with methanol, and then immersed in molten sulfur at 275°C for 14 min. After the adhering sulfur was purged with nitrogen at 290°C for 7 min, the bundle was heated up to a temperature of 700–3000°C under tension in a flow of nitrogen or argon for a few minutes. Carbon fibers heated to 1400°C were obtained with the tensile strength of 16.6 t/cm² and the modulus of 1420 t/cm² in a carbon yield of 82% and strain-graphitized fibers at 3000°C with 20 t/cm² and 4010 t/cm² in 70%.     

Effect of pitch powder addition on the microstructure and properties of carbon blocks for blast furnace

The phase composition and microstructural evolution of pitch-containing matrix sample with additive of silicon had been compared with pitch-free or resin-containing matrix sample to illustrate the strengthening effect of pitch. Two different pitch powders (CARBORES^@P and High temperature pitch) were then incorporated into carbon blocks, respectively and the effect of pitch powder addition on microstructure and properties of carbon blocks fired at 1000?°C and 1400?°C in a coke bed was evaluated systematically. The results showed that compared with amorphous carbonized resin, carbonized pitch was a kind of highly graphitized carbon and could react with silicon and form SiC whiskers at 1400?°C. In carbon blocks, pitch powder accelerated the formation of AlN at 1000?°C and growth of β-SiC whiskers at 1400?°C, respectively, which enhanced the cold compressive strength, thermal conductivity and hot metal erosion resistance of carbon blocks. Moreover, carbon blocks containing CARBORES^@P pitch with higher carbon yield exhibited better properties because of formation of more ceramic whiskers. The strengthening mechanism of pitch powder for carbon blocks was attributed to the pore-blocking effect of pitch carbonization and more in-situ formed whiskers derived from the reaction between carbonized pitch with silicon at 1400?°C.     

Worm-hole structured mesoporous carbon monoliths synthesized with amphiphilic triblock copolymer

In the present work, mesoporous carbon monoliths with worm-hole structure had been synthesized through hydrothermal reaction by using amphiphilic triblock copolymer F127 and P123 as templates and resole as carbon precursor. Synthesis conditions, carbonization temperature and pore structure were studied by Fourier transform infrared, thermogravimetric analysis, transmission electron microscopy and N₂ adsorption–desorption. The results indicated that the ideal pyrolysis temperature of the template is 450 °C. The organic ingredients were almost removed after further carbonized at 600 °C and the mesoporous carbon monoliths with worm-hole structure were obtained. The mesoporous carbon synthesized with P123 as single template exhibited larger pore size (6.6 nm), higher specific surface area (747 m² g^?1), lower pore ratio (45.9 %) in comparison with the mesoporous carbon synthesized with F127 as single template (with the corresponding value of 4.9 nm, 681 m² g^?1, 49.6 %, respectively), and also exhibited wider pore size distribution and lower structure regularity. Moreover, the higher mass ratio of template P123/resole induced similar pore size, larger specific surface area and lower pore ratio at the same synthesizing condition. It was also found that the textural structure of mesoporous carbon was affect by calcination atmosphere.     

Studies on polycrystalline layered ceramic oxide: LiFeVO4

Abstract

A new polycrystalline layered ceramic oxide, LiFeVO₄, has been prepared by a standard solid state reaction technique. The preparation conditions were optimised using thermogravimmetric analysis (TGA) technique. Material formation under the reported conditions was confirmed by X-ray diffraction studies. A preliminary structural analysis indicated that the crystal structure was orthorhombic with lattice parameters: a=4·3368 Å, b=13·1119 Å and c=16·3426 Å. The phase morphology and surface property were studied by scanning electron microscopy. Complex impedance analysis of the sample indicated bulk contribution to electrical properties at T≤125°C, grain boundary effects at the temperatures ≥125°C, negative temperature coefficient of resistance (NTCR) effect and evidence of temperature dependent electrical relaxation phenomena in the sample. The dc conductivity σ_dc shows typical Arrhenius behaviour when observed as a function of temperature. The activation energy value was estimated to be 0·24 eV. The value of σ_dc, evaluated from complex impedance spectrum, shows a jump of nearly two orders of magnitude at higher temperature (～1·24 × 10^?5 S cm^?1 at 350°C) when compared with that of σ_dc (1·14 × 10^?6 S cm^?1 at 50°C). Alternating current conductivity spectrum obeys Jonscher's universal power law. The results of σ_ac v. temperature are also discussed.     

Structural changes and crystallization kinetics of polylactide under CO2 investigated using high‐pressure Fourier transform infrared spectroscopy

The structural changes and crystallization kinetics of polylactide (PLA) during cold crystallization under CO₂ at 80 °C were studied using in situ high‐pressure Fourier transform infrared (FTIR) spectroscopy. The FTIR spectra show that PLA can crystallize under air and CO₂, and some differences are observed. In the second‐derivative spectra, the 1220 cm^?1 band is only found for PLA crystallized under CO₂, and the tt conformer of PLA crystallized under CO₂ is located at 1749 cm^?1, while that of PLA crystallized under air is located at 1751 cm^?1. From wide‐angle X‐ray diffraction, only the α′‐crystal is observed when PLA is crystallized under air, whereas the α‐crystal appears when crystallized under CO₂. The crystalline‐sensitive bands at 921 and 1458 cm^?1 were used to analyze the crystallization kinetics of PLA. When PLA crystallizes under air, the 1458 cm^?1 band changes faster than the 921 cm^?1 one; when it crystallizes under CO₂, the result reverses. This suggests that CO₂ hinders interchain interactions while promoting the helix conformation. © 2015 Society of Chemical Industry     

Study of the oligoester maleinates containing an isocyanuric ring by infrared spectroscopy

Processes taking place in crosslinked oligoester maleinates containing an isocyanuric ring were studied by means of infrared and ESR spectroscopy and heating from 110° to 600°C. By determining the optical density of the carbonyl groups at 1690 cm^?1, of the CH₂? groups at 1460 cm^?1, ether and ester groups at 1120 and 1260 cm^?1, and vinyl groups at 935 and 990 cm^?1, their mutation by hardening and tempering of the polymers was followed. The investigation shows that the carbonyl absorption of the oligoester maleinates containing an isocyanuric ring is double and that of the oligoester propylene-glycol maleinate phthalate is single. By modification of the isocyanuric oligoester maleinates with phthalic, adipic, sebacic, and other acids, and increase of the speed of isomerization of maleric groupings to fumaric is observed. By building of isocyanuric links in oligoester maleinates, a more stable structure is obtained. Above 330°C, isocyanuric links probably regroup into polycyanic links. The typical carbonyl absorption precipitously decreases at 400°C and disappears altogether at 600°C. On the basis of the investigations carried out, it is assumed that, in the process of hardening and thermodestruction of the polymers investigated, and radical processes obviously play an essential part     

Adsorption/Desorption of Hg(II) on FDU-1 Silica and FDU-1 Silica Modified with Humic Acid

Incorporation of humic acid in the FDU-1 mesoporous silica improved Hg(II) adsorption and did not destroy the ordered network, providing surface area of 500 m² g^?1, pore volume of 0.9 cm³ g^?1, and mean pore diameter of 10 nm. Carboxylic and phenolic groups increased the affinity by forming surface complexes with Hg(II). Isotherms (25.0 ± 0.1°C) were fitted to the Freundlich equation, exhibiting K_f values that increased with pH and 1/n that decreased to values < 1 with the heterogeneity of sites. Hg(II) desorption in 0.10 mol L^?1 acetic acid was lower than 10%, suggesting that chemisorption processes govern the Hg(II) removal.