Anodic oxidation effects on pyrolytic graphite surfaces in acid

Anodic oxidation effects on the basal and edge surfaces of pyrolytic graphite in acid were studied by laser Raman spectroscopy, and by a gas-phase chemical modification method coupled with X-ray photoelectron spectroscopy. Surface covering fractions were also studied by -epichlorohydrin monolayer formation. It was found that the species of surface chemical groups added by anodic oxidation was closely related to the structure of the oxidized surface. In the case of the basal surface, carboxyl groups were added by anodic oxidation, being always accompanied by the destruction of its surface structure. On the other hand, in the case of the edge surface, hydroxyl groups were added without the destruction of its structure with a mild treatment. With more severe treatment, carboxyl groups were added and this addition was also accompanied by destruction of the surface structure. There was a range of treatment in which hydroxyl groups could be added without destroying the structure. Finally it was confirmed that both carboxyl and hydroxyl groups could make covalent bonds with epoxy groups of -epichlorohydrin.     

Interfacial debonding strength between the edge surfaces of pyrolytic graphite and epoxy resins

The edge surfaces of pyrolytic graphite have been treated by anodic oxidation and the interfacial debonding strength (IFDS) between the oxidized edge surfaces and epoxy resin measured. The unoxidized and oxidized edge surfaces were examined by X-ray photoelectron spectroscopy. The edge and epoxy resin surfaces after debonding test were examined by a field-emission scanning electron microscope. Carboxyl groups were expected to be added in great quantities by breaking the carbon-carbon bonds at the edge surface. On the other hand, hydroxyl groups could be added to edge carbon atoms at the edge surface without breaking the carbon-carbon bonds. The rise in IFDS with anodic oxidation does not correspond directly to the O/C ratios or the amount of carboxyl groups present on the edge surface. Hydroxyl groups added to the edge surface are considered to play an important role in improving the adhesion between the edge surface and epoxy resin through covalent bonds between hydroxyl and epoxy groups. In the case of epoxy resin used in this study, IFDS initially increased to 9 MPa with increasing -OH/C ratio up to about 0.02; thereafter it remains constant at this value. This strength is lower than those of PG and epoxy resin.     

FT-IR ATR spectroscopy of the edge surface of pyrolytic graphite and its surface/PVC interface

The edge surface of pyrolytic graphite (PG) has been oxidized by electrochemical and oxygen plasma treatments. The structure of the oxidized edge surfaces of PG and the interaction between the oxidized surface and poly(vinyl chloride) (PVC) have been studied by means of Fourier transform — infrared attenuated total reflection (FT-IR ATR) spectroscopy. Phenolic hydroxyl groups and functional groups with a carbonyl group are present on the untreated and all oxidized edge surfaces. For all the surfaces, some of the phenolic hydroxyl groups are linked by hydrogen bonds to each other or functional groups with a carbonyl group, part of the carboxyl groups also being linked by hydrogen bonds to each other. Lactone, carboxyl, and quinone structure moieties are formed on the edge surface by the electrochemical treatment. Among the moieties, quinones are mainly introduced to the edge surface by the severe electrochemical treatment. Quinones are not present on the untreated and the plasma-treated edge surfaces. FT-IR ATR spectra provide evidence for the existence of hydrogen bonds between the > C = O groups present on the edge surface and PVC.     

Modification of pyrolytic graphite surface with plasma irradiation

The effects of oxygen plasma treatment on the basal and edge surfaces of pyrolytic graphite have been investigated and compared with those of electrochemical treatment on their surfaces. The structural changes caused by the plasma and electrochemical treatments have been characterized by laser Raman and X-ray photoelectron spectroscopies. For the basal surface the plasma treatment causes the slight destruction of the graphitic structure, whereas for the edge surface it causes no marked destruction of the graphitic structure unlike the electrochemical treatment. The amount of surface oxygen both on the basal and edge surfaces increases after the plasma treatment. In particular, for the edge surface, a high surface oxygen concentration can be attained in a short treatment time. In addition, carbonyl-type groups appear to dominate in the plasma-treated basal and edge surfaces over -O- type groups. It can be concluded that oxidation by the plasma treatment is restricted to the vicinities of the surfaces and does not proceed to the internal structure of graphite, unlike the electrochemical treatment.     

Modification of oxidized graphite edge surface with poly(vinyl chloride)

An oxidized edge surface of pyrolytic graphite (PG) has been prepared by electrochemical treatment. A thin layer of poly(vinyl chloride) (PVC) was coated on the oxidized edge surface, and the PVC-coated sample heat treated at 300, 400, and 500 °C, respectively. The influence of the PVC coating on the structural change of the oxidized edge surface of PG caused by the heat treatment was studied by laser Raman and Fourier transform-infrared attenuated total reflection spectroscopies. For the electrochemical treatment, the formation of oxygen-containing functional groups proceeds over the edge surface of PG. With increasing degree of oxidation, the functional groups are formed in the following order; hydroxyl groups, carboxyl groups, lactone groups, quinones, and acid anhydrides. Acid anhydrides are formed on the outermost surface and completely eliminated by heat treatment up to 300 °C. The other functional groups remain even after heat treatment up to 500 °C. However, the functional groups are eliminated by the PVC coating, the elimination temperature depending on the type of functional groups: quinones, lactone groups, and carboxyl groups are eliminated at 300, 400, and 500 °C, respectively. PVC coated on the edge surface is found to play an important role in the complete elimination of oxygen-containing functional groups with >C=O through heat treatment at 500 °C.     

Effect of anodic oxidation of coal tar pitch-based carbon fibre on adhesion in epoxy matrix: Part 1. Comparison between H2SO4 and NaOH solutions

Anodic oxidation of high modulus coal tar pitch-based carbon fibre in alkaline and sulfuric solutions was investigated. X-ray photoelectron spectroscopy (XPS) analysis was used to evaluate the oxygen concentration (O_1S/C_1S) and surface functional groups (---OH, C=O and COOH). The interfacial shear strength between the epoxy matrix and carbon fibre was measured by a fragmentation test. The results showed that the oxygen concentration on fibre surfaces increased rapidly as electrical charge increased, in both alkaline and acidic solution. The best bonding between epoxy matrix and carbon fibre was achieved in alkaline solution. The Raman spectra of carbon fibre oxidized in alkaline and sulfuric solutions suggested that the weak adhesive strength between the epoxy resin and oxidized carbon fibre in sulfuric solution was due to the existence of an oxidized graphite layer, which might easily come off the surface.     

Structural changes of a pyrolytic graphite surface oxidized by electrochemical and plasma treatment

Pyrolytic graphite (PG) surfaces have been oxidized by electrochemical and oxygen plasma treatment. The oxidized PG surfaces have been studied by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared attenuated total reflection spectroscopy (FT-IR-ATR). Oxidation caused by the plasma treatment results in a small increment of the oxygen: carbon (O/C) ratio, compared to electrochemical treatment. Moreover, the increment of the O/C ratio for the plasma treated edge surface is smaller than that for the plasma treated basal surface. A steep gradient in oxygen concentration exists within the edge subsurface of PG for samples subjected to severe electrochemical treatment, as compared to those samples subjected to plasma treatment. For the electrochemical treatment, carbonyl, carboxyl, ester and lactone groups are introduced to the edge surface following relatively severe treatment. The ratio of ester and lactone groups to carboxyl groups increases with the extent of electrochemical treatment. For plasma treated samples, other types of oxygen-containing groups, which are probably keto-enol groups, are added to the edge surface, unlike during electrochemical treatment.     

Modification of carbon surfaces in cold plasmas

Various forms of carbon, including carbon black, carbon fibre and pyrolytic graphite, have been surface-modified in a cold-plasma reactor. Plasma fluorination of the carbon surfaces was performed using variable flow rates, treatment times, and types of gas. The plasma-modified carbon surfaces were characterized using electron spectroscopy (ESCA), contact angle measurements, and scanning electron microscopy (SEM). The surface chemical structure of the plasma-fluorinated carbon blacks appeared to be similar to that of commercial Fluorographite. Nitrogen-containing groups were introduced into the surfaces of carbon blacks and carbon fibres by exposure to glow discharges in mixtures of ammonia and N₂-H₂. The surface concentration of functional groups containing nitrogen decreased with time. Several mechanisms for this degradation have been proposed. Plasma-modified carbon blacks and carbon fibres have potential for improving the properties of composites by achieving appropriate levels of adhesion between filler and matrix through physical compatibility and/or chemical bonding.     

Effect of anodic oxidation of coal tar pitch-based carbon fibre on adhesion in epoxy matrix: Part 2. Comparative study of three alkaline solutions

Anodic oxidation of coal tar pitch-based carbon fibre was performed in various alkaline solutions, such as NaOH, NaHCO₃ and Na₂CO₃, to examine the effect of various kinds of electrolytes on the surface chemical nature of treated fibres and the adhesive strength between treated fibres and epoxy resin. Evaluation of the oxygen concentration and surface functional groups of the carbon fibre surface was conducted by X-ray photoelectron spectroscopy (XPS). A fragmentation test was adopted for evaluation of the adhesive strength between the carbon fibre and epoxy matrix. As a result, it was shown that the highest O_1S/C_1S value was obtained in NaOH aqueous solution, and the highest interfacial shear strength (IFSS) was also obtained from the carbon fibre oxidized in NaOH solution. It was recognized that the IFSS values increase with increasing of O_1S/C_1S in every solution at the initial stage of oxidation below 1.0 × 10⁻³ C mm⁻². However, above this level of electrical charge in NaOH solution, decreasing IFSS values may occur, regardless of an increasing O_1S/C_1S value. SEM analysis inferred that in the case of the fibre treated in NaOH solution, grooves on the carbon fibre surfaces had become deeper over 1.0 × 10⁻³ C mm⁻². Presumably, the amorphous part of the carbon fibres could be oxidized intensively, and the remaining graphite layer become very thin and easy to break when a shear stress is loaded on its interface.     

Characterization of surface oxide films on titanium and bioactivity

Biological properties of titanium implant depend on its surface oxide film. In the present study, the surface oxide films on titanium were characterized and the relationship between the characterization and bioactivity of titanium was studied. The surface oxide films on titanium were obtained by heat-treatment in different oxidation atmospheres, such as air, oxygen and water vapor. The bioactivity of heat-treated titanium plates was investigated by immersion test in a supersaturated calcium phosphate solution. The surface roughness, energy morphology, chemical composition and crystal structure were used to characterize the titanium surfaces. The characterization was performed using profilometer, scanning electronic microscopy, ssesile drop method, X-ray photoelectron spectroscopy, common Bragg X-ray diffraction and sample tilting X-ray diffraction. Percentage of surface hydroxyl groups was determined by X-ray photoelectron spectroscopy analysis for titanium plates and density of surface hydroxyl groups was measured by chemical method for titanium powders. The results indicated that heat-treatment uniformly roughened the titanium surface and increased surface energy. After heat-treatment the surface titanium oxide was predominantly rutile TiO₂, and crystal planes in the rutile films preferentially orientated in (1 1 0) plane with the highest density of titanium ions. Heat-treatment increased the amount of surface hydroxyl groups on titanium. The different oxidation atmospheres resulted in different percentages of oxygen species in TiO₂, in physisorbed water and acidic hydroxyl groups, and in basic hydroxyl groups on the titanium surfaces. The immersion test in the supersaturated calcium phosphate solution showed that apatite spontaneously formed on to the rutile films. This revealed that rutile could be bioactivated. The analyses for the apatite coatings confirmed that the surface characterization of titanium has strong effect on bioactivity of titanium. The bioactivity of the rutile films on titanium was related not only to their surface basic hydroxyl groups, but also to acidic hydroxyl groups, and surface energy. Heat-treatment endowed titanium with bioactivity by increasing the amount of surface hydroxyl groups on titanium and its surface energy.     

羰基化石墨片催化丙烷氧化脱氢制丙烯

以资源丰富的石墨片为原材料, 通过简单的气相氧化处理制得羰基化石墨片, 并发现羰基化石墨片可以高选择性催化丙烷氧化脱氢制丙烯: 当丙烷转化率为12.4%时, 丙烯的选择性高达73.9%, 且副产物乙烯的选择性为13%。羰基化石墨片优良的烯烃选择性远超利用相同气相氧化处理的碳管, 并且可以媲美目前催化性能最优的六方氮化硼材料。催化剂具有良好的稳定性, 在505 ℃的反应温度下, 经过48 h的氧化脱氢反应测试后, 催化剂性能无明显的衰减。多种表征技术表明: 气相氧化处理不会破坏石墨片的结构, 且保留了石墨自身的高温抗氧化性, 而经过气相氧化处理羰基官能团的比例大幅度提高, 羰基作为活性位与丙烷中的氢原子发生反应, 自身形成羟基而丙烷则转换为丙烯, 羟基在高温下与氧原子反应生成为羰基, 从而完成催化剂的重生, 继续下一个循环。这种发生在催化剂表面的可控催化方式, 保证了丙烷氧化脱氢过程中选择性生成丙烯, 避免了深度氧化。另外, 石墨材料的来源广泛, 成本低, 作为催化剂可以极大地推动丙烷氧化脱氢的工业化。     

Pyrolytic surface treatment of graphite fibres

Thornel 50 was continuously coated with pyrolytic carbon from an atmosphere of acetylene. Using resistance heating to raise the temperature of the graphite fibre yarn to 1100 to 1200° C, as much as 60% increase in weight of pyrolytic carbon could be uniformly applied to the surfaces of the individual filaments. The treated fibres gave improved interlaminar shear strengths up to 60 MN m^?2 and improved flexural strengths up to 900 MN m^?2 in epoxy resin composites. Visual examination of the fractured surfaces indicated that while the adhesion of the resin to the pyrolytic carbon was satisfactory, the adhesion of the pyrolytic carbon to the Thornel 50 fibre surface may have been less satisfactory and led to premature failure. Such continuous one stage treatments of graphite fibres offer advantages in terms of improved handling characteristics, greater oxidation and corrosion resistance, improved wettability, and slightly better impact toughness than other commercially available treated fibres. The resultant increase in the weight of the treated yarn may improve the economic aspects for applications which do not require highly flexible yarns.     

钒液流电池用石墨毡电极的电化学修饰

研究了钒液流电池用石墨毡电极的电化学处理,结果发现,电化学处理能提高电极活性,30mA·cm-2电流密度下,电压效率可达90．96％,电流效率达92％．XPS分析表明,电化学处理后,石墨毡表面的O／C比例由0．085增加至0．15,且主要增加的是COOH官能团,与FT-IR分析结果一致．SEM表明碳纤维表面被刻蚀,BET测试结果表明比表面积有所增加．电极活性的提高归因于碳纤维表面COOH官能团数目的增加及比表面积的增大．     

碳纤维-氧化石墨烯/环氧树脂复合材料的制备及表征

采用改进的Hummers法制备了五种具有不同氧化程度的氧化石墨烯（GO）。借助元素分析、X射线光电子能谱及FTIR红外光谱测试对所制备GO的组成及结构衍变进行了表征。利用光学显微镜对不同GO在固化剂异佛尔酮二胺（IPDA）中的分散状态进行观察,并将分散效果最佳的GO试样用于改性碳纤维/环氧树脂（CF/EP）复合材料。结果表明,随着氧化剂用量及反应时间的增加,GO的氧化程度也随之增加。在氧化程度较低时,GO表面官能团主要以羰基、羧基和酚羟基为主。随着氧化程度的不断提高,GO表面官能团主要为醚、环氧和醇羟基结构。GO在IPDA中的分散状态与其氧化程度密切相关,氧化程度最低和最高的GO均出现明显的聚集现象。另外,GO表面在分散过程中可被IPDA化学改性。在EP基体中加入分散效果最佳的GO（0.2wt%）后,与CF/EP复合材料相比,CF-GO/EP复合材料的弯曲强度、层间剪切强度和Ⅱ型层间断裂韧性分别提高了14%、17%和14%。     

氧化镍掺杂酚醛树脂热解炭的结构及抗氧化性

在普通酚醛树脂中直接掺杂氧化镍粉末,研究氧化镍掺量和炭化处理温度对树脂热解炭的结构与氧化过程的影响,用X射线衍射仪、拉曼光谱分析仪、扫描电镜和综合差热分析仪等对掺杂改性树脂热解炭的石墨化度、显微结构及氧化过程分析表征,结果表明,在埋炭条件下掺杂改性树脂在450-750℃的炭化处理中三氧化二镍被逐级还原为一氧化镍和单质镍后,碳原子在镍颗粒上沉积生长,形成晶须、片状或块状结构的热解炭,热解炭石墨化程度取决于炭化温度和氧化镍掺杂量,在高于1050℃炭化处理的热解炭中出现明显的石墨化炭峰,随着掺杂量增加,热解炭石墨化程度大大增加,氧化温度比普通树脂明显提高,且以3~5%的掺杂量为佳。     

碳纤维阳极氧化法处理对复合材料界面性能的影响

利用阳极氧化法对碳纤维进行表面改性处理,研究了碳纤维处理前后表面化学组成,纤维复丝拉伸强度和复合材料的层间剪切强度（ＩＬＳＳ）。结果表明,经阳极氧化处理碳纤维表面的含氧、含氮极性官能团数目增加,纤维复丝拉伸强度有所下降,复合材料的ＩＬＳＳ值提高。同时通过实验结果分析,阐明阳极氧化处理使复合材料界面性能改善的机理。     

电化学氧化对高强高模碳纤维表面结构及力学性能的影响

利用循环伏安多重扫描法分析了不同电解质的氧化能力及其氧化特点,讨论了在表面氧化处理中不同电解液体系对高模高强碳纤维力学性能的影响,提出了适合高强高模碳纤维表面处理的工艺条件,并通过Raman光谱、XPS与SEM的表征,研究了电化学氧化对高强高模碳纤维表面结构及力学性能的影响。研究结果表明,与NH₄H₂PO₄溶液相比,用NH₄H₂PO₄与CH₃COONH₄复合的电解质溶液对碳纤维进行表面处理,能大幅度提高纤维表面含氧官能团,而且纤维表面sp²杂化碳原子相对含量也较多,在提高了碳纤维/环氧树脂复合材料层间剪切强度(ILSS)的同时,还较好地保持了高强高模碳纤维本体力学性能。当CH₃COONH₄与NH₄H₂PO₄的物质的量之比为2:1时,碳纤维/环氧树脂复合材料的ILSS与未处理纤维相比提高了168%,而碳纤维拉伸强度却下降很小,此复合电解质溶液是一种较为理想的对高强高模碳纤维进行表面改性的电解质体系。     

Preparation and properties of exfoliated graphite modified with iron compounds

Using the anodic oxidation of graphite in Fe(NO₃)3-HNO₃ mixed electrolytes, followed by heat treatment, we obtained exfoliated graphite modified with iron oxides. All of the samples obtained were characterized by X-ray diffraction, M?ssbauer spectroscopy, and scanning electron microscopy. The results demonstrate that the proposed approach allows one to produce exfoliated graphite containing up to 14% Fe in the form of oxides and hydroxides, whose composition depends on the exfoliation temperature.     

Detailed analysis of the electron-transfer properties of azurin adsorbed on graphite electrodes using DC and large-amplitude Fourier transformed AC voltammetry

The analysis of dc cyclic voltammograms of surface-confined metalloproteins is complicated by large background currents, significant ohmic iRu drop, and frequency dispersion related to protein and electrode surface inhomogeneity. The use of large-amplitude Fourier transform ac voltammetry for the quantification of the electron-transfer properties of a thin film of redox-active protein azurin adsorbed onto edge-plane, basal-plane, and highly oriented pyrolytic graphite electrode surfaces has been evaluated and compared to results obtained by dc cyclic voltammetry. In principle, it has been established that fourth and higher harmonic sine-wave data are ideally suited for analysis of electron-transfer processes as they are almost completely devoid of background capacitance current contributions. However, uncompensated resistance has a higher impact on these components, as is the case with fast scan rate dc techniques, so strategies to include this term in the simulations have been investigated. Application of recommended strategies for the evaluation of the electron-transfer properties of azurin adsorbed onto three forms of graphite, each having different background or uncompensated resistance values, is described and compared to results obtained by traditionally used forms of cyclic voltammetry. The electron-transfer rate constant, k0', of azurin at a highly oriented pyrolytic graphite electrode surface was approximately 250 s(-1), compared with > or =1000 s(-1) at edge-plane and basal-plane graphite electrodes. The significantly lower k0' value found at the highly oriented pyrolytic graphite electrode was related to the relatively low level of edge-plane defect sites present at the surface of this electrode. However, analysis of high ac harmonics suggests that frequency dispersion is substantial at all electrode surfaces. Such effects in these diffusionless situations are significantly enhanced relative to solution-phase voltammetry, where overlay of diffusion layers minimizes the impact of heterogeneity.     

Implementation of atomically defined field ion microscopy tips in scanning probe microscopy

The field ion microscope (FIM) can be used to characterize the atomic configuration of the apices of sharp tips. These tips are well suited for scanning probe microscope (SPM) use since they predetermine the SPM resolution and the electronic structure for spectroscopy. A protocol is proposed for preserving the atomic structure of the tip apex from etching due to gas impurities during the period of transfer from the FIM to the SPM, and estimations are made regarding the time limitations of such an experiment due to contamination with ultra-high vacuum rest gases. While avoiding any current setpoint overshoot to preserve the tip integrity, we present results from approaches of atomically defined tungsten tips to the tunneling regime with Au(111), HOPG (highly oriented pyrolytic graphite) and Si(111) surfaces at room temperature. We conclude from these experiments that adatom mobility and physisorbed gas on the sample surface limit the choice of surfaces for which the tip integrity is preserved in tunneling experiments at room temperature. The atomic structure of FIM tip apices is unchanged only after tunneling to the highly reactive Si(111) surface.