Factors affecting the adsorption of stabilisers on to carbon black (flow micro-calorimetry and FTIR studies) Part I Primary phenolic antioxidants

The surface activity of different types of carbon black with phenolic antioxidants is examined using flow micro-calorimetry (FMC), X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared spectroscopy (FTIR). Significant differences in both the overall adsorption activity and the levels of probe adsorption are observed. Differences in behaviour between types of carbon black are evident and show that the specific surface area is not the most important factor affecting the adsorption activity, but also the chemical nature of its surface. Essentially, two factors were found to affect the behaviour of phenolic stabilisers: Phenolic hydroxyl and ester groups were found to form the strongest interactions with carbon black. Furthermore, steric hinderance of phenolic hydroxyls by alkyl groups is the main factor which influences adsorption activity. In order to characterise different carbon blacks, FTIR and XPS analysis have been used in an attempt to determine the nature of functional groups present on the surface of the carbon blacks. FTIR analysis also shows that some adsorbed antioxidants on the surface of the carbon black could be successfully detected. This provides valuable information regarding the adsorption mechanisms on to carbon black surfaces. Other techniques included thermogravimetric analysis (TGA), N₂ BET adsorption studies and Karl Fisher analysis. The latter were performed in order to determine differences in the volatile and water contents, respectively, of the carbon black samples.     

硅烷偶联剂对电子束固化碳纤维复合材料的增效研究

根据碳纤维表面的特点及其复合材料中树脂基体进行电子束固化的机理,对碳纤维表面进行预氧化以提高碳纤维表面含氧官能团的含量,利用偶联剂的化学架桥作用对电子束固化复合材料界面进行了增效研究。采用X射线光电子能谱（XPS）对处理后碳纤维表面化学成分进行了分析,并采用层间剪切强度对电子束固化复合材料界面粘合性能进行了评价。结果表明,碳纤维表面的含氮官能团使电子束固化复合材料中碳纤维与环氧树脂基体之间的粘合强度减弱,偶联剂与预氧化碳纤维表面进行了强相互作用,使电子束固化复合材料层间剪切强度得到提高。     

ESCA studies of carbon fibres: Part II—Surface reactions of carbon fibres with epoxides

The reactions between epoxides and Courtaulds AS carbon fibre surfaces have been studied by the ESCA technique. The carbon fibres were oxidized in a mixture of H₂SO₄ and HNO₃, and then refluxed in epoxide. The formation of epoxide overlayers on the carbon fibres is confirmed. The average epoxide depths (in Å) have been calculated from the ESCA data. The fractions of the carbon fibre surfaces covered by epoxide monolayers are also estimated. The epoxides are assumed to be covalently bonded to the fibre surfaces by ether and ester links.     

Thermal stability of interfaces in Ti-6Al-4V reinforced by SiC Sigma fibres

Interfacial reactions in Ti-6Al-4V/SiC Sigma fibres (coated with carbon and TiB₂) were studied at different temperatures (600, 700 and 1000 °C). Interface microstructure was investigated by scanning electron microscopy and Auger electron spectroscopy. A simulation of the chemical phenomena occurring at the interfaces was carried out using powders of pure titanium, carbon and TiB₂; the reaction products were identified by X-ray diffraction. The double coating of Sigma fibres is effective in delaying detrimental reactions with the matrix. At the interfaces matrix/TiB₂ and TiB₂/C, the TiB and TiC_x phases form, respectively. The protective coating of fibres shows a lifetime greater than 1000 and 750 h at 600 and 700 °C, respectively.     

Morphology,structure, and mechanical properties of the surface of PbTe crystals after etching with H<Subscript>2</Subscript>O<Subscript>2</Subscript>–HBr–ethylene glycol solutions

The morphology and microstructure of PbTe surfaces polished with H₂O₂–HBr–ethylene glycol solutions have been studied by atomic force and electron microscopy techniques. The surface of PbTe single crystals after chemical–mechanical and dynamic chemical polishing with bromine-releasing etchants has been examined by optical microscopy and profilometry. The structural perfection and composition of the PbTe surface after chemical treatment have been determined by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. The mechanical properties of the crystals have been studied using microindentation. Using X-ray microanalysis, we have monitored the concentrations of the host elements (Pb and Te) and possible contamination with chemical compounds present in the etchants and the solutions used to rinse the samples.     

Mechanical properties of T300/Al composites. Embrittlement effects due to a B4C coating

During the preheating treatment preceding the processing of C/Al composites, a decrease in the mechanical properties of the carbon fibres is generally observed, owing to the oxidation of the fibres. Thus, it implies the use of a surface coating likely to resist the oxidation of the fibres. In this work, we chose to protect the carbon fibres by a B₄C coating, using a RCVD process. This coating leads to an effective protection against oxidation, as was shown by the mechanical properties obtained by single fibre tests on the coated fibres before and after preheating. However, although this coating also protects the fibres against the reaction with liquid aluminium during processing, the tensile properties of the composite were very weak. An analysis of these results based both on the use of loose bundle tests and on a microstructural characterization of the reinforcement and of the composite by transmission electron microscopy (TEM) observations and by electron spectroscopy for chemical analysis (ESCA) led us to the conclusion that the local overthicknesses of the B₄C coating have an embrittling effect, leading to a premature failure of the composite.     

Abrasive erosion of polyurethane

The surface physical and chemical effects of abrasive erosion of polyurethane in three different fluids (H₂O, polyacrylamide and NaOH) containing quartz particles have been investigated respectively. The surface profiles, elements constitutions, binding energies and functional groups of polyurethane surfaces before and after abrasive eroding have been analyzed with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectrometer (FT-IR). The surface physical effects of the abrasive erosion process were found to be microcutting, high-cycle fatigue and plastic fracture. The surface chemical effects turned out to be mechanical rupture of macromolecular chains, thermal decomposition of the allophanate groups and the biuret groups, hydrolysis of carbamate groups, and surface oxidative degradation.     

Interface characterization by TEM,AES and SIMS in tough SiC (ex-PCS) fibre-SiC (CVI) matrix composites with a BN interphase

The fibre-matrix interfacial zone formed during the isothermal/isobaric chemical vapour infiltration processing of SiC fibres (ex-polycarbosilane)/boron nitride/SiC matrix composites has been analysed by TEM/electron energy loss spectroscopy, Auger electron spectroscopy, and secondary ion mass spectroscopy. In the composites, the boron nitride interphase (deposited from BF₃-NH₃) is made of turbostratic boron nitride, almost stoichiometric but containing some oxygen (less than 5 at %). The boron nitride layer stacks are randomly orientated except in the very vicinity of the fibre surface where they lie almost parallel to the substrate. The long chemical vapour infiltration treatment at 1000 °C used to infiltrate the SiC matrix acts as an annealing treatment for the metastable ex-polycarbosilane fibres which gives rise to the growth of an SiO₂/carbon amorphous double layer at the boron nitride/fibre interface. Deflection of microcracks arising from the failure of the brittle SiC-matrix occurs at the boron nitride/SiO₂ interface considered to be the weaker link in the matrix/boron nitride interphase/SiO₂/carbon/fibre sequence. It is suggested that the combination of the boron nitride layered interphase and SiO₂/carbon fibre decomposition products might play an important role in determining the propagation path of microcracks in the fibre/matrix interfacial zones and could be responsible, at least to some extent, for the non-brittle behaviour of such composites.     

Effect of oxygen plasma treatment on bonding states for columnar structured a-CNx thin films prepared by reactive sputtering

Amorphous carbon nitride (a-CN) thin films were deposited on silicon single crystal substrates by rf-reactive sputtering method using a graphite target and nitrogen gas. The substrate temperature was varied from room temperature (RT) to 853 K. After deposition, the effect of oxygen plasma treatment on bonding structures of the film surface has been studied by using an oxygen discharge at 16 Pa and rf power of 85 W. The chemical bonding states and film composition were analyzed by X-ray photoelectron spectroscopy (XPS), while film thickness was obtained from scanning electron microscopy (SEM) and ellipsometer. XPS study revealed that the films have NO₂ and NO₃ bonding structures when the films are deposited at temperatures higher than 673 K. After exposure to oxygen plasma, carbon in the film surface was etched selectively and this phenomenon was observed in all films. In contrast, the surface concentration of nitrogen was ket at constant values before and after oxygen plasma treatment. The NO₃ bonding state had dramatically increased after oxygen plasma treatment for films deposited at higher deposition temperatures. The film surfaces have been observed to change the function from hydrophobic to hydrophilic after oxygen plasma treatment.     

TEM study of the surface morphology of extracted ZrO2-Al2O3 fibres

The surface morphology and microstructure of a series of melt extracted ZrO₂-Al₂O₃ based fibres (ZA, ZAT and ZAS) have been imaged at the nanometre scale by transmission electron microscopy (TEM) using an advanced Pt/C replica technique. Growth characteristics of ZrO₂, Al₂O₃ and other crystalline phases formed upon heating up to 1550 °C are illustrated and described. Several grain morphologies including spherical and polygonal grains, as well as grains with rounded plate-like growth were observed indicating different active growth mechanisms. ZrO₂ particles on the surface of the fibres were almost spherical with some facetting and rounding of corners. These grains were very fine (< 50 nm) in the ZA and ZAS fibres while they were several microns in size in the ZAT fibres. Al₂O₃ grains were generally much larger (up to several microns) and exhibited two distinct growth morphologies of layered and rhombohedral type. Different grain morphologies of the ZA and ZAS fibres have been correlated to the phases identified by X-ray diffraction.     

Proliferation of osteoblasts and fibroblasts on model surfaces of varying roughness and surface chemistry

Physical and chemical properties of the surfaces of implants are of considerable interest for dental and orthopedic applications. We used self-assembled monolayers (SAMs) terminated by various functional chemical groups to study the effect of surface chemistry on cell behavior. Cell morphology and proliferation on silicon wafers of various roughnesses and topographies created by chemical etching in caustic solution and by corundum sandblasting were analyzed as well. Water contact angle data indicated that oxidized wafer surfaces displayed high hydrophilicity, modification with poly(ethylene glycol) (PEG) created a hydrophilic surface, and an amino group (NH₂) led to a moderately wettable surface. A hydrophobic surface was formed by hydrocarbon chains terminated by CH₃, but this hydrophobicity was even further increased by a fluorocarbon (CF₃) group. Cell proliferation on these surfaces was different depending primarily on the chemistry of the terminating groups rather than on wettability. Cell proliferation on CH₃ was as high as on NH₂ and hydrophilic oxidized surfaces, but significantly lower on CF₃. Precoating of silicon wafers with cell culture serum had no significant influence on cell proliferation. Scanning electron microscopy indicated a very weak initial cell-surface contact on CF₃. The cell number of osteoblasts was significantly lower on sandblasted surfaces compared with other rough surfaces but no differences were detected with 3T3 mouse fibroblasts. The different surface roughnesses and topographies were recognized by MG-63 osteoblasts. The cells spread well on smooth surfaces but appeared smaller on a rough and unique pyramid-shaped surface and on a rough sandblasted surface.     

Preparation of cellulose fibres with antibacterial Ag-loading nano-SiO<Subscript>2</Subscript>

The antibacterial cellulose fibres with acrylamide polymerization and Ag-loading SiO₂ nanoantibacterial materials were successfully prepared. The chemical structures and morphologies of antibacterial cellulose fibres were characterized by Fourier transformation infrared spectrum (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that acrylamide was adsorbed on the surface of the cellulose fibres and formed a layer with thickness of 50–100 nm. The nano-SiO₂ composite antibacterial materials were combined with cellulose fibres firmly by infiltrating into polyacrylamide layer about 100 nm. The antibacterial cellulose fibres with antibacterial layer owned excellent antibacterial effect.     

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.     

Synthesis of TiC from porous carbon coating on Si–C–O (Nicalon) fibres by reactive chemical vapour deposition in pressure-pulsed mode or at atmospheric pressure

TiC coatings were synthesised on NL202 Nicalon fibres through the treatment of a porous carbon coating at the surface of the fibres by thermal reactive chemical vapour deposition (RCVD) either in pressure-pulsed (P-RCVD) mode at low pressure or at atmospheric pressure (AP-RCVD) with a H₂/TiCl₄ gaseous mixture. The conversion rate of C into TiC was studied as a function of the H₂/TiCl₄ pulse number for the P-RCVD method and as a function of the treatment time for the AP-RCVD method. Chemical and micro-structural characterisations of the coatings were carried out by X-ray photoelectron spectroscopy, Auger electron spectroscopy and scanning and transmission electron microscopies. Mechanical assessment was achieved by tensile tests at room temperature. For the P-RCVD method, the conversion rate increased when the number of H₂/TiCl₄ pulses increased from 20 to 100. Once 20 H₂/TiCl₄ pulses were performed, an interlayer made of TiC was observed at the carbon coating/fibre interface indicating that the H₂/TiCl₄ gas has diffused inside the porous carbon and has reacted in depth and more particularly at the coating/fibre interface. With 100 pulses, the carbon coating was totally converted. For the AP-RCVD method, the conversion rate increased when the treatment time increased from 30 to 60 min. The reaction of conversion began preferentially at the outermost surface of the carbon coating but several isolated TiC grains were also observed at the coating/fibre interface. At atmospheric pressure, the gaseous mixture was more reactive than at low pressure whereas the diffusion of the gaseous species was limited inside the carbon coating. The mechanical properties of the fibre decreased when the conversion rate of the carbon into TiC increased both in P-RCVD and AP-RCVD.     

Synthesis of Hybrid Materials Based on Iron Nanoparticle-Decorated Multiwalled Carbon Nanotubes

Fe-containing nanoparticles have been grown for the first time on the surface of multiwalled carbon nanotubes by metalorganic chemical vapor deposition using iron acetylacetonate, Fe(acac)₃, as a precursor. The resultant hybrid nanomaterial has been characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and thermogravimetric analysis. The results demonstrate that the synthesized material consists of multiwalled carbon nanotubes whose surface is decorated with iron nanoparticles.     

Fabrication of biomimetic super-hydrophobic surface on aluminum alloy

Inspired by microstructure characteristics of surfaces of typical plant leaves such as petal of red rose, the biomimetic super-hydrophobic surface of aluminum alloy has been successfully fabricated by laser processing and surface modification by DTS (CH₃(CH₂)₁₁Si(OCH₃)₃). The morphological features, chemical composition, and super-hydrophobicity of resultant surfaces were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and water contact angle measurements. The super-hydrophobic surface exhibited a microstructure consisting of myriad micro-scale crater-like pits. It is found that the super-hydrophobicity is synchronously governed by both the surface chemical composition and geometrical microstructure structures. The highest water contact angle of resultant surface reaches as high as 161.0°. Moreover, corrosion resistance property of these prepared films against NaCl solution is elucidated using electrochemical measurements; it is found that the corrosion resistance of aluminum alloy is also considerably improved.     

Electron field emitters based on multi-walled carbon nanotubes coated with conducting polymer/metal/metal-oxide composites

The present work describes the field emission properties of multi-walled nanotubes (MWNTs)-based conducting polymer/metal-oxide/metal/MWNTs composites (polyaniline (PANI)/SnO₂/Sn/MWNTs). MWNTs were synthesised by chemical vapour deposition technique. SnO₂/Sn/MWNTs were prepared by using chemical reduction followed by calcination. By in situ polymerisation method, surface of SnO₂/Sn/MWNTs were coated with PANI. PANI/SnO₂/Sn/MWNTs field emitters were fabricated over flexible graphitised carbon fabric substrate by spin coating technique. High-resolution transmission electron microscopy and scanning electron microscopy were used to characterise the field emitters. Field emission properties have been studied using an indigenously made facility. The fabricated PANI/SnO₂/Sn/MWNTs field emitters exhibited excellent field emission properties with a turn on field of 1.83 V µm^?1 and a field enhancement factor of 4800.     

Synthesis of carbon modified TiO<Subscript>2</Subscript> photocatalysts with high photocatalytic activity by a facile calcinations assisted solvothermal method

We demonstrate a simple and green synthetic pathway to prepare well crystalline carbon modified titanium dioxide (C–TiO₂). For the first step, the TiO₂ products were synthesized using the non-aqueous solvothermal route, and for the second step, the as-prepared TiO₂ was calcined to dope carbon. Such a method can avoid the incorporation of extra carbon sources but utilize the organic group in the alcohols instead. The structures, morphologies, and surface chemical states of the samples were characterized using X-ray diffraction, scanning electron microscope, Fourier-transform infrared spectroscopy, UV–Vis, photoluminescence spectra, thermal analyses, and X-ray photoelectron spectroscopy. The experimental results show that the obtained C–TiO₂ products composed of well crystalline TiO₂ coated with carbon species on their surfaces. The existence of the carbon can improve the adsorption of light and retard the recombination of photo-generated electron–hole pairs. Measurements of the photocatalytic degradation of Rhodamine B show that the photocatalytic activity of the C–TiO2 photocatalysts, especially TB15-300, is higher than that of other samples.     

Assessment of diffusion barriers for Ti–SiC composites

Abstract

The application of chemical vapour deposition and physical vapour deposition coatings, either singly or in combination, onto SiC fibres is discussed in terms of their ability to enhance the high temperature stability of Ti–SiC composites. The thermal stability and success of potential barrier layers was assessed by studying the fibre-matrix interdiffusion and measurement of the mechanical properties of individual fibres following coating and thermal exposure. Measurements of the level of strength retention have proved to be a reliable method of assessing the effectiveness of potential diffusion barriers. Failures may result from one of three sources. For high strength fibres failures are SiC–core reaction zone initiated, for intermediate strength fibres failures are surface defect (SiC) initiated and for low strength fibres, failures are fibre–matrix reaction zone or coating initiated. To ensure high strength (i.e. core failures) it is essential that a carbon layer is retained at the SiC surface. The most successful barriers have been shown to be TiB₂ and PtAl₂ coatings preventing outward diffusion of carbon and minimising the interaction with the titanium matrix. From these results a life prediction model has been developed based on the fibre–coating interaction, which will predict fibre strength as a function of time at a given temperature.

MST/3001     

Change in the chemical structures of carbon black and active carbon caused by CF4 plasma irradiation

Carbon black and active carbon were fluorinated by exposure to CF₄ plasma. Their surface chemical structures were studied by means of elemental analysis, X-ray photoelectron spectroscopy, and inverse gas chromatography as a function of treatment time. Fluorine is mainly introduced onto the carbon black and active carbon surfaces during the CF₄ plasma treatment. The amount and type of carbon-fluorine (C-F) functionality formed on the surfaces of the carbon materials depends on the C-C framework structure as well as the plasma treatment time. C1s chemical shifts caused by C-F bonds on the fluorinated active carbon and carbon black surfaces are slightly different from those reported on the various types of fluorinated organic polymers, and have a somewhat ionic character. For the fluorinated active carbon the C-F bond is relatively stable, whereas for the fluorinated carbon black the C-F bond is unstable and has a significant ionic character. In addition, CO₂ gas adsorption characteristics on the fluorinated active carbon can be controlled by the surface C-F functionality.