ON THE REACTIVITY OF C60 FULLERENE WITH DIENE RUBBER MACRORADICALS. II. THE REACTIVITY WITH CIS-1,4-POLYISOPRENE UNDER MILDER THERMAL CONDITIONS

Evidences about the reactivity of cis-1,4-polyisoprene (natural and synthetic origin) with C₆₀ are presented by TGA data and by FT-IR and UV-VIS spectroscopy. At 190°C under nitrogen C₆₀ fullerene causes the crosslinking cis-1,4-polyisoprene. The proposed resulting structure is a three-dimensional network where C₆₀ represents the knots and the rubber chain fragments the filaments connecting the knots.     

ON THE REACTIVITY OF C60 FULLERENE WITH DIENE RUBBER MACRORADICALS. I. THE CASE OF NATURAL AND SYNTHETIC CIS-1,4-POLYISOPRENE UNDER ANAEROBIC AND THERMOOXIDATIVE DEGRADATION CONDITIONS

C₆₀ fullerene has been studied as thermal stabilizer and as antioxidant of both natural rubber (cis-1,4-polyisoprene) and synthetic cis-1,4-polyisoprene. The study has been conducted respectively under nitrogen flow and under air flow by simultaneous thermogravimetric analysis and differential thermal analysis (TGA-DTA) on rubber samples containing known quantities of fullerene in comparison to a “blank” of pure rubber. The results show that C₆₀ fullerene (in absence of oxygen) is a thermal stabilizer of cis-1,4-polyisoprene because it reacts with the polyisoprene macroradicals formed by the thermally-induced chain scission reaction slowing down the degradation reaction. Conversely, under thermo-oxidative degradation conditions (in air flow) fullerene C₆₀ acts as an antioxidant for cis-1,4-polyisoprene, provided that the heating rate of the samples is slow (5°/min). At higher heating rates (20°C/min) C₆₀ does not show any antioxidant effect.     

ON THE REACTIVITY OF C60 FULLERENE WITH DIENE RUBBER MACRORADICALS. I. THE CASE OF NATURAL AND SYNTHETIC CIS-1,4-POLYISOPRENE UNDER ANAEROBIC AND THERMOOXIDATIVE DEGRADATION CONDITIONS

C₆₀ fullerene has been studied as thermal stabilizer and as antioxidant of both natural rubber (cis-1,4-polyisoprene) and synthetic cis-1,4-polyisoprene. The study has been conducted respectively under nitrogen flow and under air flow by simultaneous thermogravimetric analysis and differential thermal analysis (TGA-DTA) on rubber samples containing known quantities of fullerene in comparison to a “blank” of pure rubber. The results show that C₆₀ fullerene (in absence of oxygen) is a thermal stabilizer of cis-1,4-polyisoprene because it reacts with the polyisoprene macroradicals formed by the thermally-induced chain scission reaction slowing down the degradation reaction. Conversely, under thermo-oxidative degradation conditions (in air flow) fullerene C₆₀ acts as an antioxidant for cis-1,4-polyisoprene, provided that the heating rate of the samples is slow (5°/min). At higher heating rates (20°C/min) C₆₀ does not show any antioxidant effect.     

ON THE MECHANISM OF CARBON CLUSTERS FORMATION UNDER LASER IRRADIATION. THE CASE OF DIAMOND GRAINS AND SOLID C60 FULLERENE

It is shown by FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometry that carbon clusters considered to be the superior homologues of C₆₀ fullerene are formed by laser irradiation of both synthetic diamond grains or from pure C₆₀ fullerene crystals. The surfaces of the laser irradiated diamond or C₆₀ have been examined by Raman spectroscopy. In the case of diamond the Raman spectrum suggests the superficial formation of mixed carbon nanostructures consisting of disordered graphite, fullerenic nanostructures, onion-like carbon nanostructures and diamond-like carbon. Based on the Raman spectra of the surface and on data taken from the phase diagram of carbon, it is shown that the graphitization is needed in order to produce fullerenes from diamond under laser ablation conditions. In the case of C₆₀ fullerene, it is shown by Raman spectroscopy that the laser irradiation of the crystals causes initially their photopolymerization and after further irradiation their transformation into disordered graphite. Based on these results and on a literature survey on the formation of fullerenes from more than 15 completely different substrates, it is concluded that fullerenes are formed always when laser ablation leads to a graphitization of the laser-irradiated substrate. Some astrochemical implications of the conclusions have been discussed.     

ON THE MECHANISM OF CARBON CLUSTERS FORMATION UNDER LASER IRRADIATION. THE CASE OF DIAMOND GRAINS AND SOLID C60 FULLERENE

ABSTRACT

It is shown by FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometry that carbon clusters considered to be the superior homologues of C₆₀ fullerene are formed by laser irradiation of both synthetic diamond grains or from pure C₆₀ fullerene crystals. The surfaces of the laser irradiated diamond or C₆₀ have been examined by Raman spectroscopy. In the case of diamond the Raman spectrum suggests the superficial formation of mixed carbon nanostructures consisting of disordered graphite, fullerenic nanostructures, onion-like carbon nanostructures and diamond-like carbon. Based on the Raman spectra of the surface and on data taken from the phase diagram of carbon, it is shown that the graphitization is needed in order to produce fullerenes from diamond under laser ablation conditions. In the case of C₆₀ fullerene, it is shown by Raman spectroscopy that the laser irradiation of the crystals causes initially their photopolymerization and after further irradiation their transformation into disordered graphite. Based on these results and on a literature survey on the formation of fullerenes from more than 15 completely different substrates, it is concluded that fullerenes are formed always when laser ablation leads to a graphitization of the laser-irradiated substrate. Some astrochemical implications of the conclusions have been discussed.     

A STUDY ON THE THERMAL STABILITY OF THE PHOTOPOLYMER,THE OZOPOLYMER,AND THE PHOTOCHLORINATED DERIVATIVE OF C60 FULLERENE

The thermal stability of the C₆₀ photopolymer, the C₆₀ ozo-polymer, and photochlorinated C₆₀ was studied by thermogravimetric analysis (TGA) ultraviolet-visible (UV-vis) and TGA-differential thermal analysis techniques up to 950°C in comparison to graphite and pure C₆₀. The ozopolymer was found to be the least stable material followed by C₆₀Cl _x . The resulting residual carbonaceous matter formed by the decomposition of the photopolymer and the ozopolymer has been studied by Fourier transform-infrared (FTIR) spectroscopy and has been found to be completely comparable to carbon black. The thermal decomposition of the C₆₀ photopolymer prepared in solution yields negligible amounts of C₆₀. The main product is carbon black.     

A STUDY ON THE THERMAL STABILITY OF THE PHOTOPOLYMER, THE OZOPOLYMER, AND THE PHOTOCHLORINATED DERIVATIVE OF C60 FULLERENE

The thermal stability of the C₆₀ photopolymer, the C₆₀ ozo-polymer, and photochlorinated C₆₀ was studied by thermogravimetric analysis (TGA) ultraviolet-visible (UV-vis) and TGA-differential thermal analysis techniques up to 950°C in comparison to graphite and pure C₆₀. The ozopolymer was found to be the least stable material followed by C₆₀Cl_x. The resulting residual carbonaceous matter formed by the decomposition of the photopolymer and the ozopolymer has been studied by Fourier transform-infrared (FTIR) spectroscopy and has been found to be completely comparable to carbon black. The thermal decomposition of the C₆₀ photopolymer prepared in solution yields negligible amounts of C₆₀. The main product is carbon black.     

顺1,4—聚丁二烯和反1,4—聚丁二烯共混物相容性的研究

通过动态力学分析、结晶速率测定及透射电子显微镜对形态结构的观察等方法研究了顺1,4-聚丁二烯(顺1,4-PB)和反1,4-聚丁二烯(反1,4-PB)共混体系的相容性。结果表明,该共混体系是非均匀的相容体系,反1,4-PB晶片的聚集体可成为顺1,4-PB低温下结晶的晶核,线性地提高顺1,4-PB的结晶速率。     

橡胶热氧老化条件下不同预载的压缩机隔振脚垫动态特性研究

揭示热氧老化条件下不同预载的隔振脚垫动态特性机理是空调器压缩机隔振系统匹配的关键所在。该文引入Peck模型表征热氧老化因子,并运用包含热氧老化因子的分数导数Kelvin-Voigt摄动模型和Coulomb摩擦摄动模型分别描述其频率依赖性和振幅依赖性,建立了考虑变预载影响的隔振脚垫热氧老化-动态特性模型。进一步辨识了不同预载条件下的模型参数,通过试验数据验证了模型的正确性,创新提出了刚度转变点和刚度转变频率的概念以更好地描述服役后变预载、变振幅工况下橡胶隔振脚垫的软化效应。为深入研究空调压缩机与隔振脚垫的刚度匹配与橡胶配方的优化设计奠定理论基础。     

EFFECT OF STRESS STATE ON THE FAILURE MECHANISM AND FRACTURE OF AUSTENITIC STEEL UNDER THERMAL CYCLING CONDITIONS

Abstract This study was aimed at assessing the influence of stress state upon the life of specimens as well as on the failure mechanisms under thermal cycling. The experiments were carried out on thin-walled tubular specimens (made of austenitic steel). They were loaded in pure tension and in pure torsion as well as under complex loading. A constant value of an equivalent stress was obtained in each case. The influence of stress state on both the specimen life and the equivalent steady strain rate has been found. The Monkman—Grant failure criterion was used as a relationship between time to failure and equivalent steady strain rate. The analysis of the results obtained showed that the low proportion of the shear stress component in the equivalent stress does not change the values of constants in that failure criterion as is also the case for the Norton-Bailey law. The prevalence of the shear stress component is a cause of a significant change in the coefficient of the Monkman-Grant failure criterion while the exponent remains constant for all examined stress states. Initiation and propagation of cracks as well as their surface character were found to be affected by the stress state.     

INHIBITORY EFFECTS OF FULLERENE C60 DERIVATIVES ON ENDOTHELIUM-DERIVED RELAXATION IN RABBIT THORACIC AORTA

Inhibitory effects of newly synthesized fullerene C₆₀ derivatives 1 (C₆₀-bis(N,N-dimethylpyrrolidinium iodide)), 2 (C₆₀-proline-N-acetic acid) and 3 (C₆₀-ethylenediamine-N, N′-diacetic acid) on acetylcholine-induced relaxation in endothelium-intact rabbit thoracic aorta precontracted by phenylephrine (10^?6 M) were studied. Fullerene C₆₀ derivative 1 (3 × 10^?6 M), 2 (10^?5 M) and 3 (10^?5 M) reduced the maximum amplitude of the acetylcholine-induced relaxation without significantly changing the pD₂ values obtained from the concentration - response curves. In the presence of fullerene C₆₀ derivative 1 (10^?5 M) the acetylcholine-induced relaxation was eliminated and an acetylcholine-induced contraction was observed. These results suggest that fullerene C₆₀ derivative 1 strongly inhibits endothelium (nitric oxide)-dependent acetylcholine-induced relaxation in thoracic aorta of rabbit.     

INHIBITORY EFFECTS OF FULLERENE C60 DERIVATIVES ON ENDOTHELIUM-DERIVED RELAXATION IN RABBIT THORACIC AORTA

Inhibitory effects of newly synthesized fullerene C₆₀ derivatives 1 (C₆₀-bis(N,N-dimethylpyrrolidinium iodide)), 2 (C₆₀-proline-N-acetic acid) and 3 (C₆₀-ethylenediamine-N, N'-diacetic acid) on acetylcholine-induced relaxation in endothelium-intact rabbit thoracic aorta precontracted by phenylephrine (10^-6 M) were studied. Fullerene C₆₀ derivative 1 (3 × 10^-6 M), 2 (10^-5 M) and 3 (10^-5 M) reduced the maximum amplitude of the acetylcholine-induced relaxation without significantly changing the pD₂ values obtained from the concentration - response curves. In the presence of fullerene C₆₀ derivative 1 (10^-5 M) the acetylcholine-induced relaxation was eliminated and an acetylcholine-induced contraction was observed. These results suggest that fullerene C₆₀ derivative 1 strongly inhibits endothelium (nitric oxide)-dependent acetylcholine-induced relaxation in thoracic aorta of rabbit.     

不同负温条件下冻土导热系数的理论模型和试验验证

基于饱和冻土的三相组成和导热系数量纲定义,将冻土简化为由土柱、液态水、冰柱组成的混合物,进而建立了冻土导热系数的几何模型。考虑实际冻土中三相组成的含量随温度变化而不断变化的事实,给出了随温度变化的水柱和冰柱体积计算与演变规律。在此基础上,利用并联体系导热效果的叠加原理,给出了随温度变化的冻土导热系数计算模型。基于热流传递过程中并联与串联同时进行的耦合特性,建立了考虑固-液界面的导热系数计算模型。将预测值与瞬态探针法的实测结果和Johansen法的计算结果对比后发现,该类计算方法能有效模拟不同负温条件下冻土的导热系数,并且具有概念清晰、方法简单等特点。     

PHOTOPOLYMERIZATION AND THERMAL DECOMPOSITION OF POLYMERIZED PHASE IN C60 CRYSTALS UNDER STRONG LASER ILLUMINATION

We have investigated the photopolymerization and thermal decomposition of photochemical products with high density excitation (11–480 mW/mm²) by means of time-gated Raman scattering experiments in C₆₀ single crystal. The temperature of laser-illuminated area was measured by Stokes and anti-Stokes Raman scattering of C₆₀ Hg(1) mode, which shows the local temperature rise with increase of laser power density. The Raman intensity of Ag(2) mode rapidly decreases with irradiation time for I<170 mW/mm² indicating the rapid decrease in C₆₀ monomer density due to photopolymerization. For higher power densities, however, the Raman intensity increases after showing a minimum, which suggests a dissociation of photopolymers. The results are well explained by the rate equation model taking into account photochemical generation and thermal decomposition of photo-produced dimers. These results indicate the strong laser illumination simultaneously induces the photopolymerization and thermal decomposition.     

CFRPA1010等速降温结晶动力学的研究

将等温Ａｖｒａｍｉ方程推广应用于等速降温的非等温结晶过程，用ＤＳＣ法研究了ＣＦＲＰＡ１０１０的等速降温结晶行为和结晶动力学。结果表明，用此方法得到的动力学参数与文献报导的等温法结果有良好的一致性；ＣＦＲＰＡ１０１０中的ＣＦ使基体的结晶温度明显提高，使结晶峰呈不对称形态，结晶温度范围变窄。其结晶行为和动力学参数ｎ、ｋ、ｔ１／２等结果显示，ＣＦ具有诱导基体结晶作用，影响了ＰＡ１０１０结晶的成核和生长机     

THE INFLUENCE OF PRECRACKING TECHNIQUES ON FATIGUE CRACK GROWTH THRESHOLDS UNDER MIXED MODE I/II LOADING CONDITIONS

Abstract— The influence of precracking history on the subsequent fatigue crack growth thresholds for branch cracks has been studied for AISI 316 stainless steel and BS4360 50D under mixed mode I/II loading. The work has examined: (1) the influence of precrack length; (2) the influence of stress intensity factor range at the final stage of precracking; (3) the influence of precracking load R -ratio; and (4) the influence of precracking unloading schemes. A computer controlled precracking test system has been set up in the current investigation and comparisons have been made between the results of computer controlled work and those published previously using a manually controlled technique. The results show that a computer controlled precracking method generally gives more conservative and more repeatable growth threshold values for branch cracks than a manually controlled precracking procedure.     

不同边界条件下脱层对层合梁自然频率的影响

本文研究了层合梁的脱层现象对其自振频率的影响。文中详细分析了脱层对层合梁振动频率的敏感性及相互关系,特别对在不同边界条件下,脱层的特征对前8阶自振频率的影响进行了研究。计算与分析结果表明,脱层现象对第1、2阶自振频率具有较大的影响,其影响程度依赖于边界条件。而第3阶以后的频率则对脱层的敏感性较低。本文给出的关于层合梁自振频率变化规律和边界效应关系的结果,将对结构动力设计和无损检测提供理论依据和重要参考。     

低温工况下结霜对翅片管蒸发器性能影响研究

翅片管蒸发器的结霜将增加空气压降，增大传热热阻，从而直接影响到蒸发器的效率及空气侧平均换热系数，本文就低温工况下，结霜对蒸发器性能的影响进行了测试研究，为翅片管蒸发器的设计应用提供了重要依据。     

添加填料的聚乙烯和聚丙烯的热氧化和光氧化的研究

用红外光谱及力学性能测试方法研究了添加填料的聚乙烯和聚丙烯的热氧化和光氧化。发现碳酸钙可加速PE和PP的光氧化,但却抑制其热氧化。填料滑石粉对PP的热和光氧化有类似的作用。同时,添加经铁酸酯偶联剂处理的碳酸钙和滑石粉的PE和PP的热和光氧化速率都比添加未经处理的填料的PE和PP的相应速率大,表明铁酸酯偶联剂具有一定的促进PE和PP氧化的作用。     

桐油改性酚醛树脂的耐热性研究

本文对桐油改性酚醛树脂的一些性能进行了研究，并着重利用ＤＴＡ、ＴＧ热分析技术研究了这类改性树脂的耐热性能及其热分解动力学。实验结果表明，桐油改性酚醛树脂的热分解分为两个阶段：第一个分解峰为４５０～４９０℃，约分解３０～４５％；第二个分解峰为５７０～６７０℃，约分解３５～５５％。随着甲醛／苯酚摩尔比的增加，初始分解温度逐渐升高。这种经桐油改性的酚醛树脂耐热性能可达：初始分解温度３５９．４～３８３．７