In situ fabrication of carbon nanotube/mesocarbon microbead composites from coal tar pitch

Carbon nanotube/mesocarbon microbead composites have been synthesized from coal tar pitch with carbon nanotubes. How the carbon nanotubes affect the growth and the structure of mesocarbon microbeads are studied. The result shows that the size of beads decreases when more carbon nanotubes are added, and when the ratio of carbon nanotubes is set at 5%, we get the smallest sample with quite uniform shape. Carbon nanotubes exist both on the surface and inside of the samples and they will inhibit the growth and coalescence of these spheres. The addition of carbon nanotubes decreases the graphitization degree of the samples and makes their microtexture tend to be disordered.     

Interface enhancement of carbon nanotube/mesocarbon microbead isotropic composites

Carbon nanotubes (CNTs) are incorporated into mesocarbon microbead (MCMB)-derived isotropic graphite to improve their mechanical properties. CNTs are homogenously distributed on the MCMB surface by acid-treatment and mechanical mixing. The composites are prepared by cold isostatic pressing, carbonization, and graphitization. The mechanical properties and isotropy ratios of the CNT/MCMB composites are determined by four-point bend tests and thermal expansion measurements, respectively. The addition of CNTs improves the flexural strength by ca. 20%, while keeps a low isotropy ratio. CNTs dispersed on particle interfaces improve the interfacial strength, this reinforcing mechanism is confirmed by a fracture mode analysis with scanning electron microscope.     

Cerium silicates formation from mechanically activated oxide mixtures

Reactions of cerium silicate formation in mechanically activated oxide powders of CeO₂ and SiO₂ (quarz) were studied. Three different mixtures were prepared, the compositions of which corresponded to Ce₂Si₂O₇, Ce_4.67(SiO₄)₃O and Ce₂SiO₅. Oxide mixtures were mechanically activated in vibratory mill up to 120 min. X-ray analysis performed on activated mixtures showed that the CeO₂ crystallite size decreased with increasing activation time. However, CeO₂ lattice distortions passed through a maximum after 30 min of activation. The results obtained after heating showed that reactions proceeded via formation of intermediate compounds. Evidence of the existence of a liquid phase at 1550°C is given.     

Surface desublimation of carbon dioxide from binary gas mixtures

The results of an experimental investigation of the time evolution of the main characteristics of the process of surface desublimation of carbon dioxide from N₂-CO₂ and He-CO₂ gas mixtures are given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 6, pp. 965–970, December, 1986.     

Vapor phase synthesis of nanofibrous carbon materials from water-ethanol mixtures

We present a detailed study of the pyrolytic synthesis of nanofibrous carbon materials (NCMs) from ethanol and various water-ethanol mixtures on a nickel catalyst at temperatures from 400 to 700°C. In the synthesis from 96% ethanol, the initial deposition rate increases with temperature, but this is accompanied by a substantial decrease in catalyst life. The addition of water to the reaction system considerably increases the catalyst life. One possible reason for this is that water vapor prevents carbonization of the catalyst particles. At the same time, above 600°C the rate of NCM deposition from a 50% water-ethanol mixture is considerably slower. At 550°C and lower temperatures, the rate of NCM deposition from water-ethanol mixtures (based on ethanol consumption) changes insignificantly. Our results demonstrate that NCMs can be synthesized even from very dilute (down to 10 vol %) aqueous ethanol solutions. The participation of water vapor in chemical processes that take place in the reaction zone is discussed.     

膜接触器分离混合气中二氧化碳

以N-甲基二乙醇胺（MDEA）水溶液为吸收剂,采用疏水性聚丙烯中空纤维膜组件（HFPPM）作为膜接触器,研究了膜接触器分离CO2/N2混合气传质性能,主要考察了吸收剂浓度,液速,吸收温度,原料气浓度和气速等因素对CO2吸收性能的影响,比较了同一膜组件不同流程和不同膜组件及膜形态对分离效果的影响,并对膜组件运行的稳定性进行了初步考察,实验结果表明,采用MDEA溶液和HFPPM膜接触器分离CO2/N2混合气具有较快的传质速率和较高的分离效率．     

Mechanism behind the formation of self-assembled nano-sized clusters in diamond-like carbon nanocomposite

Many studies have shown that Diamond-like carbon (DLC) films with diversified material properties are obtainable through doping process but the presence of the dopants were reported to form independent nanoclusters within the carbon matrix. Using combined analysis from theoretical estimations (Saha's equation and coefficient of absorption, alpha(p)), Transport of Ions In Matter (TRIM) simulation and experimental results, this work examined the mechanism behind the formation of self-assembled nanoclusters in DLC nanocomposite. We showed that the presence of metal dopants increased the heat dissipation on DLC, which allowed the energetic metal species to diffuse and enhance the formation of nanoclusters that increased the surface roughness of the films. In addition, TRIM and X-ray Photoelectron Spectroscopy (XPS) hinted the presence of energetic species may force the carbon ions to react with the interface to form silicon carbide bonds, which may be a more dominant factor compared to internal stress reduction in improving the adhesion strength of DLC.     

Self-organized monolayer formation from binary mixtures of substituted alkyl chains studied by STM

The molecular assembly of p-iodo-phenyl octadecyl ether (I-POE), p-iodo-phenyl docosyl ether (I-PDE) and a binary mixture of these two molecules on graphite has been studied using a scanning tunneling microscope. Each molecular system self-assembles on the graphite surface to form a stable monolayer. For the binary system, the I-POE and I-PDE molecules do not mix on the surface, preferring instead to form isolated monolayer domains. Here, the I-POE molecules are preferentially adsorbed on the graphite surface, due to the effects of alkyl chain length and the functional group on the monolayer structure.     

Mechanical activation of calcium titanate formation from CaCO3—TiO2 mixtures

Complete CaTiO₃ formation has been found to occur in CaCO₃—TiO₂ (anatase or rutile) mixtures subjected to mechanical activation by high energy milling. Such formation has been demonstrated to occur by rapid heating (20 K/min) up to 1250°C. The first stage of the reaction takes place as CaO forms, the reaction, then, proceeds at higher temperatures reaching its maximum rate at about 1000°C. Alternatively CaTiO₃ formation can be effected by 12-h annealing of the activated mixtures at temperatures between 750 and 850°C. Partial CaTiO₃ formation was realized when starting from physical mixtures neither by rapid heating to 1250°C nor by 12-h annealing at temperatures as high as 1000°C.     

Stability of alginate microbead properties in vitro

Alginate microbeads have been investigated clinically for a number of therapeutic interventions, including drug delivery for treatment of ischemic tissues, cell delivery for tissue regeneration, and islet encapsulation as a therapy for type I diabetes. The physical properties of the microbeads play an important role in regulating cell behavior, protein release, and biological response following implantation. In this research alginate microbeads were synthesized, varying composition (mannuronic acid to guluronic acid ratio), concentration of alginate and needle gauge size. Following synthesis, the size, volume fraction, and morphometry of the beads were quantified. In addition, these properties were monitored over time in vitro in the presence of varying calcium levels in the microenvironment. The initial volume available for solute diffusion increased with alginate concentration and mannuronic (M) acid content, and bead diameter decreased with M content but increased with needle diameter. Interestingly, microbeads eroded completely in saline in less than 3 weeks regardless of synthesis conditions much faster than what has been observed in vivo. However, microbead stability was increased by the addition of calcium in the culture medium. Beads synthesized with low alginate concentration and high G content exhibited a more rapid change in physical properties even in the presence of calcium. These data suggest that temporal variations in the physical characteristics of alginate microbeads can occur in vitro depending on synthesis conditions and microbead environment. The results presented here will assist in optimizing the design of the materials for clinical application in drug delivery and cell therapy.     

Mullite formation from highly homogeneous mixtures of Al2O3 and SiO2

Mullite, 3A1₂O₃ · 2SiO₂, was synthesized by heat-treating homogeneous sol-gel-derived mixtures of A1₂O₃ and SiO₂ taken in stoichiometric amounts. To reduce the mullitization temperature, sols containing γ-AlOOH and SiO₂ nanoparticles (2 to 20 nm) were used in the preparation of the mullite precursors. A few samples were made using the products of hydrolysis of aluminum salts instead of the γ-AlOOH sol. The process parameters determining the homogeneity of the precursor mixtures were revealed. The preparation conditions ensuring mullite crystallization at temperatures between 1200 and 1250°C were found. The results are discussed in terms of the reaction between A1₂O₃ and SiO₂ during mullitization.     

Mechanism of factory-roof formation

Factory-roof (F-R) patterns produced by cyclic torsion loading of V-notched cylindrical steel specimens were investigated by means of experimental and theoretical methods. A three-dimensional model of F-R patterns was constructed by means of stereophotogrammetry in the scanning electron microscope and the basic geometrical rules of F-R formation were identified. The theoretical analysis revealed that the F-R initiates by elementary mode I branches of semi-elliptical surface cracks growing under mixed-mode II + III. The exact positions of such branches were analytically determined in terms of the maximum synergy of mode II and mode III loadings. An increasing density of the semi-elliptical surface cracks results in the refinement and the size reduction of F-R patterns. This effect, along with strong wear damage, explains the fact that the F-R patterns are usually not observed in the low-cycle fatigue region.     

Activated carbon catalyzing the formation of carbon nanotubes

Activated carbon (AC), a common carbon material, is employed as catalyst to synthesize carbon nanotubes (CNTs) through chemical vapor deposition (CVD) and detonation-assisted CVD methods. The results show AC can effectively catalyze CNT formation. From the microscopic observations on morphologies and structures of the formed intermediates, it is found that carbon-catalyzed CNT formation follows particle-wire-tube stepwise evolution mechanism, in which carbon nanoparticles first assemble into wire-like nanostructures, then evolve into nanotubes via particle-particle coalescence and structural crystallization.     

Diamond formation on carbon/carbon composite

A carbon/carbon composite was used as substrate for low-pressure diamond deposition. To enhanced diamond nucleation on carbon/carbon composites, a total of ten surface preparation methods have been investigated. These methods involved the use of atomic hydrogen etching, mechanical polishing, sonication, or coating. Diamond nucleation was found to occur on either the defects of the carbon/carbon composite substrates or diamond particulate left on the substrates. The defects were created primarily by atomic hydrogen etching during the coating process. Seeding with diamond powders was performed by dip coating, sonication, or spray-coating processes. It was found that these seeding processes resulted in excellent nucleation of diamond.     

Peculiarities of graphene layer formation from amorphous carbon and silicon-carbon films

Graphene layers on device structures have been formed from amorphous carbon and silicon-carbon films using a sequence of technological procedures, including thermodiffusion of carbon atoms, their accumulation at the heteroboundary between layers with significantly different diffusion coefficients, and subsequent phase transition from a carbon quasi-liquid to graphene layer.     

Critical parameters of mixtures of carbon dioxide and ethane

This paper deals with an evaluation of the critical parameters reported for mixtures of carbon dioxide and ethane. Equations are presented for the critical parameters as a function of the concentration.     

Ion-molecule reactions in mixtures of methane with carbon tetrafluoride

Ion-molecule reactions have been measured for methane-carbon tetrafluoride mixtures of different composition using a quadrupole mass spectrometer with a high-pressure ion source. Concentration of methane in these mixtures ranged from 10% to 90% (at 10% increment). Primary ions , , F⁺, CF⁺ and were produced by electrons with energy of 300 eV. Secondary ions , , , , and were observed as the result of ion-molecule reactions. Relative current intensities for primary and secondary ions are presented as a function of both total mixture pressure and concentration of methane in the mixture. Potential of repeller electrode inside the ion source collision chamber was fixed at 5 V for all measurements. Total mixture pressure was changed from 0.7 to 33.3 Pa. Schemes of ion-molecule reactions were proposed.     

Diamond formation from glassy carbon under high pressure and temperature conditions

The process of the formation of diamond from the glassy carbon with its characteristic bond nature was investigated in the diamond stable region at high pressures (up to 10 GPa) and temperatures (up to 3000° C), without any intentional addition of metals as solvent. The process of diamond formation was found to obey Ostwalds's step rule as follows: amorphous glassy carbon crystallized to form fully well-crystallized graphite prior to diamond formation and then the graphite crystals were converted to diamond by further heat treatment at pressures above 9 GPa. The many trigons formed are considered to be essentially a record of growth failure in the growth period. As a result of heat treatment for a longer time and/or at a higher temperature close to the diamond—graphite stability boundary, the diamond tended to grow with the (111)-face composed of the thin growth layers.     

Resonant laser-induced formation of double-walled carbon nanotubes from peapods under ambient conditions

The selective excitation of fullerenes encapsulated in single-walled carbon nanotubes (SWCNTs) is carried out by irradiating them using a UV laser, the wavelength of which corresponds exactly to their maximum of absorption. Under such conditions, fullerenes strongly absorb the laser energy, open, and break, while the containing SWCNT merely acts as both a nanoreactor and a mold which is only weakly heated by the laser. The containing tube confines the fullerene fragments, promotes their reconstruction into an inner tube, and protects them from air oxidation. This leads to the overall formation of double-walled carbon nanotubes (DWCNTs). The transformation is found to strongly depend on the laser irradiance and dose. This proves that the related mechanism is a multiphoton photolysis, different from the previous heat-induced transformation attempts found in the literature, whether the heat is produced by means of a thermostat, infrared laser, or nonresonant UV laser. The actual peapod-to-DWCNT transformation is monitored by Raman spectroscopy and high-resolution transmission electron microscopy.     

中间相碳微球(MCMB)素坯制备过程的研究

以Tween 80为分散剂,分别以丙烯酰胺和N,N'-亚甲基双丙烯酰胺为单体和交联剂,制备中间相碳微球(MCMB)浆料,采用凝胶注模工艺,制得高质量的素坯.研究了制备过程中的分散剂用量、成型温度的控制问题,并在理论上对这两个关键操作步骤进行简要的分析.