化学气相反应法制备不同碳基体表面SiC涂层组织结构分析

采用化学气相反应法, 以同种工艺分别在石墨和C/C复合材料表面制备了SiC涂层, 借助X射线衍射仪(XRD)、扫描电镜(SEM)及能谱分析等手段分析了涂层的微观结构, 研究了不同碳基体对SiC涂层结构和表面形貌的影响, 并初步对比考察了涂层的高温抗氧化性能. 结果表明: 制备的SiC涂层整体致密, 与基体结合良好, 但存在明显的结构差异. 石墨表面制得的SiC涂层呈梯度分布, 涂层主要由致密外层及过渡内层组成, 而C/C复合材料表面制得的SiC涂层仅由致密外层组成; 在1823 K的空气氧化氛围中, 与C/C复合材料SiC涂层试样相比, 石墨SiC涂层试样表现出更好的高温抗氧化性能, 经30 h氧化及7次循环热震实验后, 涂层试样的氧化失重率仅为0.182%.     

ARXPS-analysis of sputtered TiC, SiC and Ti0.5Si0.5C layers

Summary TiC, SiC and Ti_0.5Si_0.5C layers have been deposited by magnetron sputtering in Argon at bias voltages between 0 and 1500 V. AES and ARXPS analyses show that TiC and Ti_0.5Si_0.5C, at bias voltages below 1000 V, are C-rich (+20%) and contain TiC crystallites of diameter below about 10 nm and have a metal-like resistance of about mcm. The excess C segregates to the surface of TiC nanocrystallites showing an XPS C 1s level shift similar to Li-graphite or doped fullerenes. The doped carbon (carbidic) interface layer, higher deposition rate and better mechanical strength seem to be interrelated. Magnetron sputtered SiC is X-ray amorphous and insulating, grows more slowly, has reduced mechanical strength and does not contain excess C. The ARXPS analysis of Ti_0.5Si_0.5C layers allows the modelling of the TiC nanocrystallites embedded in interfacial carbon and defective SiC.     

TiN和TiC涂层对碳氢燃料裂解结焦的影响

采用化学气相沉积(CVD)法,在304型不锈钢管道内壁分别沉积了TiN和TiC涂层,并采用SEM、EDS、金相显微镜和热冲击等方法对其进行了性能表征和测试。结果表明,两种涂层均匀致密,TiN涂层厚度为7.24μm,TiC涂层为11.52μm,且均具有良好的结合强度。为评价涂层抑制结焦效果,选用某碳氢燃料A,采取程序升温法进行超临界裂解实验,当反应管前后压差超过1 MPa时停止实验,结果表明,304空白管由于严重结焦,在650℃只运行了180 s;而TiC和TiN涂层管分别在780℃运行了275和1560 s。通过压差、产气组成和积炭微观形貌的综合分析表明,TiN、TiC涂层均呈现出优良的抑焦效果,且TiN涂层抑焦效果更优。     

Fabrication of polytetrafluoroethylene- and graphite-containing oxide layers on aluminum and titanium and their structure

Stable aqueous electrolyte emulsions with negatively charged micelles containing dispersed particles of polytetrafluoroethylene (PTFE) or graphite are obtained using siloxane-acrylate emulsion as an emulsifier. The oxide coatings formed in such electrolytes contain carbon, polytetrafluoroethylene, or graphite. The coatings with PTFE particles are similar to monolithic polytetrafluoroethylene with respect to its hydrophobic characteristics. According to X-ray photoelectron spectroscopy data, the surface of the formed coatings predominantly contains aliphatic carbon (C-C and C-H bonds) and some fraction of oxidized (or, in the case of PTFE-containing electrolytes, fluorinated) carbon.     

Large-area highly-oriented SiC nanowire arrays: synthesis, Raman, and photoluminescence properties

Large-area highly oriented SiC nanowire arrays have been fabricated by chemical vapor reaction using an ordered nanoporous anodic aluminum oxide (AAO) template and a graphite reaction cell. Their microstructures were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy. The results show that the nanowires are single-crystalline beta-SiC's with diameters of about 30-60 nm and lengths of about 8 microm, which are parallel to each other, uniformly distributed, highly oriented, and in agreement with the nanopore diameter of the applied AAO template. The nanowire axes lie along the [111] direction and possess a high density of planar defects. Some unique optical properties are found in the Raman spectroscopy and photoluminescence emission from oriented SiC nanowire arrays, which are different from previous observations of SiC materials. The growth mechanism of oriented SiC nanowire arrays is also analyzed and discussed.     

Electrochemical and spectroscopic characterization of quinone functionalized exfoliated graphite.

Natural graphite was exfoliated by thermal decomposition of graphite-bisulfate intercalation compound. Oxidative/reductive pre-treatment of exfoliated graphite was subsequently carried out to introduce various functional groups on the graphite surface. The resulting material was covalently modified with redox active quinones. The covalent modification was effected through oxygen containing functional groups formed on the graphite surface. The modified exfoliated graphite was characterized by infra-red (FTIR) and X-ray photoelectron spectroscopy (XPS). Electrochemical characterization of the pressed pellets of the modified graphite showed that the modification occurred at the edge sites. These electrodes were found to be very stable and the surface renewal was simply accomplished by polishing the surface using SiC emery sheets. Application of the benzoquinone modified electrode for the electrocatalysis of ascorbic acid oxidation was demonstrated.     

Significantly enhanced photocatalytic activity of TiO2/TiC coatings under visible light

Journal of Solid State Electrochemistry - Rutile TiO2 forms on TiC coatings (TiO2/TiC coatings) during carbon-embedding heat treatment (cHT) for TiC coatings. The photocatalytic activity of...     

Investigation of multi-layer coatings on cemented carbide cutting tools by analytical electron microscopy

Multi-layer coatings on cemented carbide substrates have been investigated by analytical electron microscopy (AEM). The samples were taken from cross-sections through the coating thus enabling a study of individual layers and interfaces. Various phenomena are shown: (1) tungsten diffusion and graphite inclusions in TiC layers, (2) oxygen impurities in Ti(C, N) coatings and (3) the occurrence of titanium oxinitrides in the interface between the Al₂O₃ and TiN-layers.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Identification of selective oxidation of TiC/SiC composite with X-ray diffraction and Raman spectroscopy

Open cell 3D titanium carbide/silicon carbide (TiC/SiC) composite was oxidised to titanium oxide/silicon carbide (TiO₂/SiC) following different temperature profiles in a thermal gravimetric analysis (TGA) instrument in continuous air-flow and static air (oven) environments. The TiC oxidation to anatase, starting at temperatures over 450°C, was confirmed by Raman spectroscopy and X-Ray diffraction (XRD). By increasing the temperature, the mass fraction of anatase diminished, while the mass fraction of rutile increased. SiC oxidation started at 650°C when a mixture of TiO₂/SiO₂/SiC could be observed by Raman, XRD and HRTEM.     

Comparative study of microstructure and tribological behavior of TiC/a‐C:H and a‐C:H coatings in a sand‐dust environment

TiC/a‐C:H and a‐C:H nanocomposite coatings were prepared on AISI 440C steel substrates using magnetron sputtering process. A comparative study was made on their composition and microstructure by Raman spectroscopy and high‐resolution transmission electron microscopy (HRTEM). The tribological properties of two types of carbon‐based coatings were investigated by pin‐on‐disc tribometer under the sand‐dust conditions concerning the influence of applied load, amount of sand and sand particle sizes. The results show that these carbon‐based coatings exhibited high tribological performance with low friction coefficient and wear rate under the sand‐dust environments. However, the TiC/a‐C:H coatings exhibit relatively higher fluctuant friction coefficient as well as higher wear rate in comparison with the a‐C:H coatings under sand‐dust environments. The formation of nanocrystalline hard TiC phase distributed in amorphous carbon matrix decreased the residual stress but significantly increased the hardness and Young's modulus of TiC/a‐C:H coatings, and consequently caused a relatively higher abrasive and fatigue wear loss under the sand‐dust conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

Intercalating oleylamines in graphite oxide

Graphite oxide has been synthesized from raw graphite particles and been treated with various mass amounts of oleylamine as intercalants to form intercalation compounds. X-ray diffraction patterns reveal that the inter-sheet distances strongly depend on the graphite oxide to oleylamine mass ratios. The equilibrium-like behavior implies diffusion-dominated oleylamine adsorption on graphite oxide in solution and excluded volume intercalations among oleylamine-adsorbed graphite oxide during restacking. The intercalation compounds are soluble in organic solvents, and their applications in the fabrication of transparent and conductive coatings have been demonstrated.     

Organosilicon polymers with bis-acetylenic units: Conductivity and ceramisation studies

The transformation poly[(silylene)diacetylene] into ceramic have been studied and SiC obtained with a quantitative yield: all the silicon atoms present in the starting material are converted into SiC. The key step is the crosslinkage of C₄ units into a carbon matrix in which the R₁SiR₂ moieties are in the vicinity one to each other allowing the quantitative transformation into SiC. The carbon content of the resulting ceramic depends on the nature of R₁ and R₂ groups. The excess of carbon has been used for the carboreduction of oxides (TiO₂, ZrO₂, HfO₂, etc…) and mixed ceramics with interpenetrating network have been obtained: SiC / TiC, SiC / ZrC, etc… Under nitrogen atmosphere, the ceramisation leads to different systems such as SiC / TiN, SiC / AlN, etc…     

Low-temperature mechanochemical synthesis of nanosized silicon carbide

The methods of X-ray diffraction analysis, scanning electron microscopy, synchronous thermal analysis, and adsorption are used to study the mechanochemical synthesis of silicon carbide through the reaction Si + C → β-SiC. The reaction is found to take place in several stages. At the first stage, i.e., at activation doses below approximately 5 kJ/g, the powders of the components are independently ground to increase the specific surface area of the mixture to 145 m²/g, graphite is amorphized, and the sizes of the coherent-scattering regions of silicon drastically diminish. At the second stage (doses of 5–15 kJ/g), dense Si/C aggregates are formed and two fractions (coarse and fine) with different particle sizes arise in silicon crystallites. As the activation dose is enhanced, the amount of the fine fraction rises, while the sizes of coherent-scattering regions decrease to 2–3 nm. When samples are heated at 800°C, the fine fraction of silicon interacts with carbon to yield silicon carbide with crystallite sizes of 3–4 nm, whereas the coarse fraction of silicon recrystallizes. At the third stage, i.e., at doses of higher than 15 kJ/g, the mechanochemical synthesis of SiC occurs through the following scheme: fine fraction Si + C → amorphous SiC → crystallization of SiC.     

无压烧结合成高纯度Ti3SiC2粉体

本文通过优化混合方式将Ti、Si、石墨和Al等粉末按照一定配比混合后,在1 420℃氩气保护下合成了Ti3SiC2粉末。用XRD和SEM分别分析了样品中的相成分、微观形貌,计算得出其质量百分含量,高达96.7%,研究了烧结工艺中降温速率对Ti3SiC2微观形貌的影响,并讨论了其生长机理。本工艺原料混合简单有效,得到的产品纯度高,因而有助于实现Ti3SiC2粉末的批量生产。     

Site-resolved X-ray scattering studies,I investigations on plates from PP-graphite composites

Cross-sections cut from rectangular plates injection or compression-molded from composites of isotactic polypropylene and varying amounts (up to 40 mass%) of different grades of graphite were investigated by site-resolved wide-angle X-ray scattering (WAXS), using a two-circle goniometer and a specially adapted Kratky camera, respectively. The measurements yielded detailed information about the orientation of both the filler particles and the PP crystallites, in dependence on the position in the cross-sections. In the plates molded from composites, the graphite particles are preferentially oriented with their (002) planes parallel to the surface of the plates and the α-PP crystallites prefer the same orientation for their (040) planes. In plates devoid of graphite, the PP crystallites show a different orientation behavior, however, the presence of 0.2% graphite is already sufficient to change the orientation to the afore-mentioned mode. The observed parallelism in the preferential orientation of the graphite particles and the PP matrix suggests the assumption of hetero-epitaxial growth of α-PP crystallites on the (002) surface of oriented graphite particles. According to our results, the effects of the PP-graphite interaction are dependent on the nature and properties of the graphite particles and may be modulated by treating the graphite surface with different coatings.     

Surface characteristic and cell response of CVD SiC coating for carbon/carbon composites used for hip arthroplasty

SiC coatings were applied on carbon/carbon composites by chemical vapor deposition for potential application in hip arthroplasty. The surface morphology, roughness, and wettability of the coatings were evaluated by scanning electron microscopy, laser confocal scanning microscope, and video‐based contact angle measuring device, respectively. The bonding strength between the coatings and carbon/carbon composites was analyzed by scratch testing. The cell responses to coatings were studied by analyzing the cell morphology and cell proliferation. The results showed that SiC coatings showed spherical morphology with a roughness of R_a = 1.0 ± 0.2 µm and a contact angle of 64.7 ± 4.0°. The coatings had lower surface roughness and better surface hydrophilicity compared with those of the uncoated carbon/carbon composites. A strong shear strength averaging 120.0 MPa between the coating and carbon/carbon composites was achieved. The cell culture experiments showed that cell spreading was improved, and cell proliferation was increased with the SiC coatings. It was demonstrated that CVD‐SiC‐coated carbon/carbon composites were good candidates as artificial hip joint materials. Copyright © 2012 John Wiley & Sons, Ltd.     

Formation of carbon nanotubes from a silicon carbide/carbon composite

The reaction of a SiC/C composite powder in an arcing plasma forms carbon nanotubes in good yield. Besides carbon nanotubes, a Si/C composite composed of β SiC covered with a shell of graphite is formed. The graphitic carbon surface layers of the carbon shell of this composite reacts further to form carbon nanotubes when heated to 600 °C. This process seems highly effective since only a small overall low weight loss, indicative for a complete carbon shell oxidation is observed by thermal analysis. The formation of the carbon nanotubes from SiC is unlikely since no SiO₂ has been found when heating the SiC/C core shell composite to its reaction temperature of 600 °C under O₂. The CNTs formed are of good quality with 3 to 6 concentric walls and high aspect ratio. Occasionally even single walled carbon naotubes have been observed.     

负载型氧电极PtRuIr/TiC催化剂的制备、结构及CV研究

以TiC纳米粉作载体,超声波分散?共还原沉积方法制备以Pt、Ru和Ir为活性组分的负载型催化剂PtRuIr/TiC.BET比表面积、扫描电子显微镜(SEM)、X光衍射(XRD)及循环伏安(CV)等测试表明:该负载型催化剂活性组分Pt、Ru、Ir微晶(组成2.6%Pt,1.3%Ru,16%Ir和80%TiC,by mass)在载体TiC上趋于无定型化结构,主要分散在载体的外表面上,其析氧性能约是相同成分无负载催化剂的3倍,经过120次CV扫描,PtRuIr/TiC在电解质溶液中几乎不溶解.实验证实,这一电极具有良好的电化学催化性能和稳定性.     

Interaction between nuclear graphite and molten fluoride salts: a synchrotron radiation study of the substitution of graphitic hydrogen by fluoride ion

The interaction between nuclear graphite and molten fluoride salts (46.5 mol % LiF/11.5 mol % NaF/42 mol % KF) is investigated by synchrotron X-ray diffraction and C K-edge X-ray absorption near-edge structure (XANES). It is found that there are a large number of H atoms in IG-110 nuclear graphite, which is attributed to the residual C-H bond after the graphitization process of petroleum coke and pitch binder. The elastic recoil detection analysis indicates that H atoms are uniformly distributed in IG-110 nuclear graphite, in excellent agreement with the XANES results. The XANES results indicate that the immersion in molten fluoride salts at 500 °C led to H atoms in nuclear graphite partly substituted by the fluorine from fluoride salts to form C-F bond. The implications of these findings are discussed.     

Concentration conditions of formation of electrically conducting coatings from colloid-graphite dispersions

Concentration conditions under which electrically conducting graphite coatings can be formed on cardboard and polymeric dielectric substrates by deposition of graphite particles from colloid graphite dispersions were studied. It was found how the surface resistance of the samples varies, in the dc mode and in the microwave range, with the concentration and time conditions of formation of electrically conducting coatings. The transmittance and reflectance to microwave electromagnetic radiation were measured for samples coated with particles of colloid graphite from suspensions with various particle sizes.