Effects of crystallinity of starting carbons on diamond formation in presence of nickel under high pressure and high temperature condition

The processes of graphitization and diamond formation of several carbons in the presence of nickel were investigated under 8 GPa at temperatures up to 1800° C. Diamond was formed easily from graphitized pitch coke which had a well-developed graphitic structure and in less amount from glassy carbon preheated at about 3000° C which was partly graphitized. On the other hand, pitch coke and glassy carbon, preheated at about 2000° C and not graphitized, did not transform to diamond but remained graphitized even in the diamond stable region. Diamond from graphitized pitch coke and glassy carbon preheated at about 3000° C grew to form by direct bonding.     

Effect of high-pressure pre-treatment of starting carbon on diamond formation

Four starting carbons differing in crystallinity and grain size were pre-treated with or without nickel at 3 GPa and 1800° C or at 6 GPa and 1700° C. Diamond synthesis from carbons pre-treated and then further treated in vacuum was carried out at 8 GPa and 1700° C. Pre-treated carbons with or without nickel, which were fully or partly graphitized, changed a little or did not convert to diamond at 8 GPa and 1700° C. Diamond did form from the pre-treated carbons after treatment in a vacuum at 1000° C. Diamond formation, even from the graphitized carbons, was found to be inhibited mainly by gases adsorbed on the treated carbon during the pre-treatment under high pressure.     

中子辐照金刚石生成卡宾碳

金刚石在中子辐照下发生相转变,得到了线性结构的卡宾碳。所得产物为覆盖金刚石表面的黑色薄膜状物质,其拉曼光谱在2191cm-1处有强峰,归属于C≡C伸缩振动;同时,其俄歇电子谱的峰位与金刚石相比有5eV的位移,证实了卡宾碳的存在。在中子辐照条件下,金刚石向卡宾碳的转化可能是通过碳原子堆垛形式发生变化而实现的。     

沥青基球状活性炭对几种生理分子的吸附性能

考察了具有不同BET比表面积及不同孔结构的沥青基球状活性炭（PSAC）对溶液中尿毒症分子肌酐、有益分子α-淀粉酶和脂肪酶的吸附行为，测定了PSAC对肌酐的吸附等温线及吸附速度曲线，并根据Freundlich等温线方程对肌酐吸附等温线数据进行处理，检验了实验数据与方程的吻合度，确定了方程参数。结果表明：PSAC对α-淀粉酶及脂肪酶吸附选择性差，对肌酐的吸附选择性好。PSAC对肌酐分子的吸附平衡容量取决于溶液浓度、孔径和比表面积；吸附速率随孔径增大而增加。PSAC对α-淀粉酶及脂肪酶的吸附选择性取决于PSAC的孔结构，孔越大吸附选择性越好。因此，评价PSAC吸附性能时需要考虑比表面积、孔结构及吸附质分子的特性。     

Hydrothermal formation of diamond from chlorinated organic compounds

The unique properties of diamond are well known a long time ago and therefore are extensively used. However, the most general aspects of diamond origin are not yet clearly determined. Hydrothermal synthesis as any heterogeneous reactions occurring under the conditions of high-temperature–high-pressure (> 100 °C, > 1 atm) in aqueous solutions in closed system has a growing interest among the scientists in particular due to a possibility of synthesis of new phases or crystals growth. During this study the diamond particles or films were produced through hydrothermal interaction of 1,1,1-Trichloroethane and 10 M NaOH in the presence of diamond or cubic BN seeds at temperature 300 °C and pressure 1 GPa. Synthesized diamond was thoroughly characterized by TG–DTA, SEM (EDX) and had (220) preferable orientation according to XRD pattern. These results demonstrate that the hydrothermal growth of diamond in like manner with quarts and emerald is possible.     

Mask for micropattern formation on diamond films

A new technology of forming micropatterned masks for the etching of diamond films is proposed, which makes possible high-precision lithography on the samples with areas up to 10⁴ mm². A minimum element size that can be achieved is only determined by the level of lithography accessible for silicon-based integrated circuits. The proposed technology can be used in creating unique devices, including biosensor chips for human genome decoding.     

水蒸气辅助法制备LA-GA共聚物蜂窝状多孔膜

以D，L-丙交酯(LA)-乙交酯(GA)共聚物为膜材质，在高湿度气氛环境中使用溶液浇铸的方法在固体基板上制得具有蜂窝状孔结构的聚合物膜．发现不同组成比的LA—GA共聚物的亲水性对形成蜂窝状结构具有关键的影响，同时这种蜂窝状结构可以通过改变成膜条件加以有效控制．     

Low-frequency Raman and Brillouin spectroscopy from graphite, diamond and diamond-like carbons, fullerenes and nanotubes

Inelastic light scattering by acoustic phonons (Brillouin scattering) is a useful tool for probing material properties at the submicrometre scale. In media which are statistically homogeneous at this scale, it gives access to the acoustic properties and the elastic moduli. In nanostructures it probes the vibrational properties at the mesoscopic scale. Applications to carbonaceous materials are reviewed.     

金刚石膜的计算机虚拟制备技术中的分子动力学模拟

综述了近年来金刚石薄膜形成过程的分子动力学（Molecular Dynamics，简称MD）模拟研究，详细地阐述了原子间相互作用势的选取，总结了不同沉积条件下MD的计算模型和几种典型情况下的模拟结果。研究表明：在原子尺度上，MD方法能较全面地提供有关膜生长的信息，对进一步了解金刚石膜形成的微观机制以及为细观层次仿真提供基本信息均具有重要意义。     

Effects of starting carbon and solvent-catalyst on the reaction sintering of diamond

Polycrystalline diamond sintered compact was prepared under high pressure and temperature conditions (7 GPa, 1700° C, 10 to 15 min) from purified natural graphite (NG) or graphitized pitch coke (GPC) using iron, cobalt or nickel as the catalytic active metal and titanium or zirconium as the solvent metal. The effects of the combinations of starting carbon and solvent-catalyst on the transformation behaviour and morphology of the converted diamond were investigated in relation to the starting powder compositions. Diamond crystals converted from NG tended to have euhedral habits, when twin crystals were occasionally found due to a relatively rapid conversion and growth rate of diamond. On the other hand, a skeletal structure of diamond was easily formed by a mild conversion from GPC in the 15 to 30 vol% ( 40 to 60 wt%) nickel solvent-catalyst. The degree of catalytic action in the 8A group of 3d transition metals for the GPC system was in the order: Ni Co > Fe. The grain growth of the converted diamond was depressed by the addition of 4A transition metals (titanium or zirconium) which results in the fine-grained and homogeneous sintered microstructure.     

Influencing factors on gelatin matrix for chlorhexidine delivery

Objective: The objective was to evaluate the influencing factors in the fabrication of gelatin matrix (gelatin chips) for drug delivery. The attributes affecting drug release characteristics of the gelatin products were examined.

Significance: Understanding the attributes that affect drug release from gelatin matrix could provide the knowledge base for the development, manufacturing, and performance evaluation of gelatin-based drug products for sustained drug delivery.

Methods: Chlorhexidine (CHX) was the model drug in the gelatin-product testing. The gelatin products were fabricated by two methods: a single-pot mixing of all the components and a two-step gelatin crosslinking followed by drug loading. Different gelatin types (Type A porcine and Type B bovine), glutaraldehyde (GTA) crosslinking conditions, glycerin concentration, and CHX concentration in drug loading and loading time were used to fabricate the products. The cumulative amounts of CHX release from the gelatin products were determined using in vitro release testing (IVRT).

Results: The attributes affecting CHX release from the gelatin products were gelatin type, GTA crosslinking, and CHX loading concentration. The fabrication methods (two-step method of gelatin crosslinking and drug loading by equilibration vs. direct mixing of the components) also affected CHX release. Other attributes such as glycerin and CHX loading time did not show significant effects on drug release under the conditions studied. In addition, the results in the two IVRT methods employed in this study were comparable.

Conclusion: Gelatin products of qualitative (Q1) and quantitative (Q2) differences could lead to different drug release behaviors. Drug release was also affected by the ingredient mixing steps during gelatin chip fabrication.     

柠檬酸盐为碳前驱体制备介孔炭及其在电化学电容器中的应用(英文)

热解柠檬酸镁或柠檬酸钡,制备了两种介孔炭(MgC或BaC),并将其用作双电层电容器电极材料。采用氮气吸附、扫描电子显微镜和傅里叶红外光谱对所制介孔炭进行表征。结果表明:所制介孔炭孔结构与柠檬酸盐所含金属阳离子有关。其中,BaC呈典型的双峰孔径分布,最可几孔径分别为3.8nm和15nm;而MgC的孔道主要是小尺寸的介孔或微孔。通过循环伏安、恒流充放电法测试所制介孔炭作为电化学电容器电极材料时的电化学性质。测试表明,在离子液体中MgC和BaC都具有很高的比电容值,分别达到180F.g-1和171F.g-1。其中,BaC的倍率性能良好,能量密度可达到53.3Wh.kg-1,最大功率密度为20kW.kg-1。BaC优良的电容特性主要归因于其孔径双峰分布的孔结构和亲水性表面化学性质。     

Phase formation sequence of Cr2AlC ceramics starting from Cr–Al–C powders

The reaction process of Cr₂AlC ceramics was analyzed, in which the samples were prepared for composition Cr:Al:C = 1:1.2:1 by hot-pressing in argon in the range of 850–1450 °C using Cr, Al and graphite powders as the starting materials. X-ray diffraction (XRD), electron probe microanalysis (EPMA) and energy dispersive spectrum (EDS) were employed for identification of phase assembly and analysis of reaction route of the samples. The phase formation sequence of Cr₂AlC was finally analyzed based on phase diagram of the Cr–Al binary system combined with the results of differential thermal analysis (DTA) and XRD. It was found that Cr₅Al₈, Cr₂Al and Cr₇C₃ were the intermediate phases appearing in turn in the heating process. The amount of Cr₂AlC phase was gradually increased with increase in temperature by the reaction between Cr–Al intermetallic compounds, un-reacted Cr and graphite, and it became a pure phase in the sample with disappearance of intermediate phases above 1250 °C.     

Investigation of the process of diamond formation from SiC under high pressure and high temperature

SiC powder or graphite in contact with cobalt, nickel or a Ni₇₀Mn₂₅Co₅ alloy was treated at high pressure and high temperature in stable region of diamond. It was found that Ni₇₀Mn₂₅Co₅ alloy is more effective in the process of diamond formation from SiC than the others, but the difference was not apparent when graphite was used instead of SiC. Using the Ni₇₀Mn₂₅Co₅ alloy, diamond formed rapidly with the decomposition of SiC at a pressure of 5.4–6.0 GPa and temperature 1350–1570°C, and the growth tended to stagnate after 6 min, when SiC was completely exhausted. X-ray diffraction showed that the relative intensity of the diffraction lines of diamond and graphite was nearly constant in the samples synthesized under the same conditions for 2, 4 and 6 min. The results suggest that diamond and graphite may be formed directly and respectively from separated carbon atoms in a short time.     

Influencing factors for railroad-highway grade crossing accidents in Florida

Multiple regression was used to investigate the influence of physical factors on accident rates at 1,140 rail-highway grade crossings in Florida. Selection of the final model involved examination of residuals, transformation of variables. dummy variables and interaction terms. Variables in the final model were functions of average daily traffic, type of crossing protection, maximum train speed, trains per day. crossing speed limit, and number of lanes of traffic. Transformations were made to return estimates to the original scale of the data. Suggestions were made for improving the model and the data.     

Bimodal activated carbons derived from resorcinol-formaldehyde cryogels

Abstract

Resorcinol-formaldehyde cryogels prepared at different dilution ratios have been activated with phosphoric acid at 450 °C and compared with their carbonaceous counterparts obtained by pyrolysis at 900 °C. Whereas the latter were, as expected, highly mesoporous carbons, the former cryogels had very different pore textures. Highly diluted cryogels allowed preparation of microporous materials with high surface areas, but activation of initially dense cryogels led to almost non-porous carbons, with much lower surface areas than those obtained by pyrolysis. The optimal acid concentration for activation, corresponding to stoichiometry between molecules of acid and hydroxyl groups, was 2 M l^?1, and the acid–cryogel contact time also had an optimal value. Such optimization allowed us to achieve surface areas and micropore volumes among the highest ever obtained by activation with H₃PO₄, close to 2200 m² g^?1 and 0.7 cm³ g^?1, respectively. Activation of diluted cryogels with a lower acid concentration of 1.2 M l^?1 led to authentic bimodal activated carbons, having a surface area as high as 1780 m² g^?1 and 0.6 cm³ g^?1 of microporous volume easily accessible through a widely developed macroporosity.     

Bimodal cellular activated carbons derived from tannins

New cellular activated carbons mainly derived from tannins and furfuryl alcohol are introduced and suggested as adsorbents and catalyst supports. They present a bimodal porosity, based on a highly porous, reticulated vitreous carbon backbone, whose micro/meso-porosity was developed by steam activation. The macroporosity corresponds to the connected network of cells whose average diameter is close to 250 μm. In contrast, the micro/meso-porosity is located at the inner surface of the cells and is thus fully and easily accessible. Consequently, much higher adsorption kinetics than for usual granular activated carbons are expected. A burn-off close to 30% was shown to be optimal for getting a high proportion of microporosity without complete loss of mechanical resistance. In these conditions, the surface area is close to 850 m² g⁻¹, thus similar to that of many commercial carbonaceous adsorbents.