Effect of the addition of carbonaceous fibers on the tribological behavior of a phenolic resin sliding against cast iron

The tribological behavior of novolac phenolic resin matrix composites reinforced with three kinds of carbonaceous fibers was studied in sliding contact against cast iron. Slow pyrolysis was used to obtain carbonaceous fibers from Colombian plantain fiber bundles (crops residues from Urabá region). After the carbonization process the samples were heated up to either 1200 or 1400 °C ensuring that many morphological aspects of the natural fibers were retained. Then, novolac phenolic resin with HMTA as curing agent and the carbonaceous fibers were used to obtain a composite material by compression molding process. Samples with different type and volume fraction of carbonaceous fibers were prepared and tested in sliding contact against cast iron in a pin-on-disc wear testing machine. At the end of the tests, the worn surfaces and the debris were analyzed by SEM.A decrease in both friction coefficient and wear of composites was observed with the increase in fiber volume fraction, which was associated to a beneficial effect of the detachment of carbonaceous material from the worn surface. Under the tested conditions, this material remains at the interface between the composite and the cast iron and helps reduce the shear resistance of the interface. On the other hand, surface fatigue and adhesion wear was identified as the dominant wear mechanism of the phenolic resin matrix.     

骨科植入材料的研究现状及发展趋势

综述了目前临床使用的主要骨科植入材料的研究现状及发展趋势,详细介绍了各种材料的特点、优势和存在的问题,结合各种材料的特点,介绍了它们的主要用途。本文认为目前用于制造骨科植入器械的任何一种材料（无论是金属或合金、陶瓷、高分子材料或碳质材料）均不能同时满足人体生理环境（良好的生物相容性及稳定性、耐腐蚀性）和关节生物力学环境（良好的力学相容性及强韧性、高疲劳性能和耐磨性）的苛刻要求。现有骨科植入器械的有效使用寿命和功能尚不能完全满足患者的要求,有待材料研究专家和临床医学专家共同努力解决。最后,阐述了骨科植入材料的未来发展方向。     

PM2.5 chemical composition in Hong Kong: urban and regional variations

Chemically speciated PM2.5 measurements were made at roadside, urban, and rural background sites in Hong Kong for 1 year during 2000/2001 to determine the spatial and temporal variations of PM2.5 mass and chemical composition in this highly populated region. Annual average PM2.5 concentrations at the urban and rural sites were 34.1 and 23.7 microg m(-3), respectively, approximately 50-100% higher than the United States' annual average National Ambient Air Quality Standard (NAAQS) of 15 microg m(-3). Daily PM2.5 concentrations exceeded the U.S. 24-h NAAQS of 65 microg m(-3) on 19 days, reaching 131+/-8 microg m(-3) at the roadside site on 02/28/2001. Carbonaceous aerosol is the largest contributor to PM2.5 mass (explaining 52-75% of PM2.5 mass at the two urban sites and 32% at the background site), followed by ammonium sulfate (ranging from 23% to 37% at the two urban sites and 51% at the background site). Ammonium sulfate and crustal concentrations showed more uniform spatial distributions, while the largest urban-rural contrasts found in carbonaceous aerosol (likely due to emissions from on-road gasoline and diesel vehicles). Marine influences accounted for 7% of the mass at the background site (more than twice as much as at the two urban sites). Ternary diagrams are utilized to illustrate the different spatial patterns.     

碳质难处理金矿浸出工艺研究进展

碳质金矿属于难处理金矿的一种,当原生矿石中有机碳含量＞0.2%时,会严重干扰氰化提金,出现“劫金”现象。目前,碳质金矿的处理方法主要有氧化焙烧法、微波焙烧法、化学氧化法、生物氧化法和硫脲法等。其中,氧化焙烧法能够有效消除碳质的“劫金”作用,提高金的浸出率,但能耗大及环境污染严重等缺点制约着它的发展;微波焙烧法能够选择性地加热碳质,具有成本低、效率高及污染小的特点;湿法氧化预处理工艺避免了SO2污染的问题,特别是生物氧化法由于成本低、安全洁净和操作简便等独特优势,具有很大的发展前景。     

废弃碳材料对工业硅冶炼的影响研究

以一种废弃碳材料替代部分还原剂,在8MVA埋弧炉进行工业化试验。依行业经验对比实际生产现状及试验的前中后期的变化进行评估。结果表明,试验中期电耗降低,产品中Al、Ca、Cr、Ni含量明显降低,Fe、P、Ti 未得到改善。在碳排放方面,通过废弃碳材料的替代使用使得每吨工业硅生产过程的CO2排放较少了0.805t。     

INTEGRATED LINEAR AND NONLINEAR VISCOELASTICITY OF DISCOTIC LIQUID CRYSTALS

Theory and simulation of steady, small-amplitude, and large-amplitude oscillatory capillary Poiseuille flow of discotic mesophases are presented, discussed, and used to provide an integrated framework to characterize the rheology of precursors used in the manufacturing of carbon super-fibers. The underlying microstructural changes responsible for the non-Newtonian rheology are presented and discussed, taking into account dynamic couplings between orientation and velocity fields. Proper scaling of viscoelastic material functions leads to superposition and hence provides a better fundamental understanding of flow processes in steady and oscillatory flows. The relations between shear-thinning behavior in steady flow, elastic storage in small-amplitude oscillatory shear, and flow enhancement in pulsatile flow are established.     

An integrated approach to assess air pollution threats to cultural heritage in a semi-confined environment: The case study of Michelozzo's Courtyard in Florence (Italy)

An example of an integrated approach to assess air pollution threats to cultural heritage in a semi-confined environment is presented in this work, where the monitoring campaign carried out at the Michelozzo's Courtyard (in Palazzo Vecchio, Florence, Italy) is used as a case study. A wide research project was carried out, with the main aim of obtaining the first quantitative data on air quality and microclimate conditions inside the Courtyard, and, if possible, identifying the main causes of degradation and suggesting appropriate conservation strategies. The investigation adopted a holistic approach involving thermographic measurements on the wall paintings, microclimatic analysis, gaseous pollutant monitoring, atmospheric particles characterisation and dry deposition compositional analysis. Attention was focused on the wall painting depicting the city of Hall because of its anomalous and critical conservation conditions, which are visible at a glance, due to the contrast between a wide darker zone around the central subject of the painting and external lighter areas.     

石油沥青制备炭质催化剂载体的研究

研究了以沥青为原料制备炭质凝胶，由炭质凝胶制备中孔活性炭用作催化剂载体的影响因素及制备规律。试验结果表明：制备炭质凝胶的转化率与反应物配比、反应温度、反应时间及沥青原料性质有关。添加镍盐、铁盐和钴盐对炭的催化扩孔作用十分明显。制备的中孔活性炭可以用作催化剂载体，使用浸渍法制备的加氢催化剂具有较好的加氢脱硫效果。     

Carbon support hydrogenation in Pd/C catalysts during reductive thermal treatment

The resistance of the Pd/C samples towards hydrogenation of the carbon support was studied in the temperature-programmed and isothermal regimes. Carbonaceous graphite-like material Sibunit was used as a carbon support. Pristine Sibunit was additionally graphitized via high temperature treatment (1900 °C) in an inert atmosphere. Both initial and graphitized supports were subjected to oxidative treatment in order to increase the amount of surface functional oxygen-containing groups. Palladium (1 wt%) was supported using an aqueous solution of H₂PdCl₄. All the samples were characterized by a low-temperature adsorption of nitrogen, transmission electron microscopy, and Raman spectroscopy. The graphitization procedure was found to decrease significantly the specific surface area of the support, while the oxidative treatment affects this parameter negligibly. Testing the Pd-containing samples in a hydrogen flow revealed the following order in accordance with amount of methane released: Pd/iSib » Pd/iSib-ox > Pd/gSib > Pd/gSib-ox.     

Nanostructured C–Pd films for hydrogen applications

We propose nanostructured carbonaceous-palladium (C–Pd) films as promising material for covering different, big surfaces as improving hydrogen storing properties material. The C–Pd films were obtained by annealing of samples prepared by physical vapor deposition on fused silica substrates. Palladium nanocrystallites placed within the film volume and also on its surface enhanced absorption of hydrogen due to dissolution of H₂ molecules in the nanocrystallites. We studied structure, morphology and topography of these films by different methods (XRD, GIXRD, SEM and EDS). XRD measurements performed in situ under H₂/N₂ atmosphere showed that α phase and β phase of palladium hydride were formed.