Copolymerization of methylmethacrylate with styrene using triphenylbismuthoniumylide as radical initiator

Bismuthoniumylide‐initiated radical copolymerization of methylmethacrylate with styrene at 60 ± 0.2°C using dioxane as an inert solvent, follows ideal kinetics (R_p ∝ [ylide]^0.5 [MMA]^1.0 [sty]^1.0), and yields alternating copolymer as evident from NMR spectroscopy. The values of reactivity ratios r₁ and r₂, calculated from Finemann–Ross method are 0.48 and 0.45, respectively. The system follows ternary molecular complex mechanism. The radical mode of polymerization has been confirmed by ESR spectroscopy and the effect of hydroquinone. The value of activation energy and k/k_t are 65.0 KJ mol^?1 and 2.5 × 10^?5 l mole^?1 s^?1, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2774–2781, 2001     

Photoionization of Ferrocyanide at Various Wavelengths in Polar Glasses at 77°K

Solutions of potassium ferrocyanide in 10 N NaOH glass and in ethylene-glycol/water (3/1) glass at 77°K were irradiated with UV-light. The ratio of the yields of radicals in the two solvents, as well as the scavenging efficiency of an election scavenger (acrylamide) in 10 N NaOH, were found to change with the irradiation wavelength. From the experiments the conclusion is drawn that the ejection of electrons may occur from different electronic levels depending on the excitation wavelength and that the electrons ejected from a charge-transfer-to-solvent state have higher reactivity with a scavenger than electrons ejected from intramolecular singlet states.     

Ionization Processes in Polar Solution of Tryptophan at 77° K

The triplet absorption spectrum of tryptophan in ethylene-glycol/water glass at 77°K has been registered. It is demonstrated that light of wavelength 250 nm produces trapped electrons by a two-photon process in this system. In both UV- and X-ray-induced ionization the probability that an ejected electron will recombine with its mother ion is around 0.5. Bleaching with visible light causes the trapped electrons to react with the solvent and there is also a considerable degree of retrapping. The retrapping becomes more probable when the temperature increases.     

Ignition of a coal particle on a heated surface

With the use of high-speed (to 6 × 10⁵ frames per second) video recording facilities, the following three physicochemical transformation regimes were recognized on the induction heating of the single particles (4–6 mm in size) of D coal on a steel plate (at a temperature of no higher than 1000 K): thermal decomposition without ignition, smoldering, and ignition. The limiting (minimum) values of heat source temperatures necessary and sufficient for the initiation of combustion of coal particles were established.The effect of particle sizes on the integral characteristics of the test process was found. The particle-size dependence of the time of heating of a natural solid fuel particle to the intense development of an exothermic reaction was obtained. It was found that the characteristic times of the initiation of the ignition and smoldering regimes were no longer than 10 and 20 s, respectively, with variations in coal particle size.     

Toughening mechanisms of ZTA ceramics at cryogenic temperature (77 K)

ZTA ceramics containing 20 wt% ZrO₂ were fabricated at different sintering temperatures (1450, 1500 and 1550 °C) by SPS and HP processes, respectively. The influence of sintering process on the mechanical properties of ZTA ceramics at 298 K and 77 K was investigated. It can be seen that the bending strength and fracture toughness of samples prepared by the two processes both improved at cryogenic temperature. The stress-induced martensitic transformation toughening mechanism was confirmed by the in-situ Raman technique. The tetragonal ZrO₂ would be even more easy to transform because of the residual stress generated when temperature decreased from 298 K to 77 K. Therefore, the transformation toughening effect would become stronger, result in the increase of mechanical properties.     

Compositionally-tunable surface nanostructuration of microspheres obtained from a self-stabilizing copolymerization of methylmethacrylate and vinylpyrrolidone

The high differential reactivity of methylmethacrylate (MMA) and vinylpyrrolidone (VP) in standard radical copolymerization allows the one-pot preparation of stable methylmethacrylate (MMA)-based solid particles by a surfactant-free process. The copolymers obtained in methanol exhibit a high compositional heterogeneity and a phase separation at high conversion. Partitioning of copolymer chains between the phases as a function of their composition has been observed, being the dispersed phase rich in copolymers with high content of hydrophobic MMA monomer and the continuous phase rich in copolymers with high content of hydrophilic VP monomer. The addition of water under stirring leads to formation of solid particles. The particles have shown a hierarchical structure composed of micron-size particles decorated with nano-size structures on their surface. The size of the nanostructures depends on the initial MMA/VP feed molar ratio in the copolymerization.     

Experimental evidence of an upper limit for hydrogen storage at 77 K on activated carbons

An upper limit for hydrogen storage at 77 K on activated carbons was clearly observed in the present experimental work. Such a limit is around 6.4 wt.%, i.e., close to the theoretical limit of 6.8 wt.%. Results of hydrogen storage were obtained in three independent laboratories using volumetric and gravimetric devices. Lab-made activated carbons (ACs) were found to have higher capacities than those of the commercial material AX-21. A maximum excess hydrogen storage capacity of 6.0 wt.% at 77 K and 4 MPa was obtained. This maximum was reduced to 0.6 wt.% at 298 K and 5 MPa. ACs with surface areas (S_BET) as high as 3220 m² g⁻¹ were prepared from chemical activation of anthracites with alkali (Na and K) hydroxides. At 77 K and 4 MPa, excess hydrogen storage capacity was directly correlated with S_BET for ACs having S_BET values lower than 2630 m²/g. Hydrogen uptake at 77 K also correlated with micropore volume and strongly depended on average pore diameter.     

甲基丙烯酸甲酯的光引发聚合研究

本文探讨了光引发剂的种类与浓度、光照强度、光聚合组合物体系粘度及光聚合体系氛围对甲基丙烯酸甲酯(MMA)光引发聚合硬化时间、产率、重均分子量及分子量分布的影响。结果表明,体系初始粘度或引发剂含量的增加均有利于加快光聚合速度以及提高产率,产物具有良好的实用价值。PMMA的重均分子量Mw随着光引发剂浓度的增加而降低,但对紫外(UV)光强不敏感。     

Anomalies in standard gas adsorption isotherms of N2 and Ar on graphite at 77 K

Pronounced hysteresis due to pores, and a distinct step near a relative pressure of 0.4, appeared in the adsorption-desorption isotherms of N₂ and Ar at 77 K for both natural graphite and natural graphite subjected to various treatments. The step stems from the adsorption of a second layer. By applying the same method as that used to determine Point B, the amount of gas adsorbed up to the completion of a second layer was read from the isotherm and the relationship between the surface area of pores and the amount of surface oxygen was investigated.     

Pore size distribution model derived from a modified DR equation and simulated pore filling for nitrogen adsorption at 77 K

The Dubinin-Radushkevich (DR) equation has been used extensively to characterize microporous materials. However, it assumes a continuous pore filling mechanism and does not reduce to Henry’s law at low adsorptive pressures. In this study, we modify the DR equation by introducing adsorption density and the correlation between pore filling pressure and critical pore size for N₂ adsorption at 77 K. This modified DR equation is used as the local isotherm in the generalized adsorption isotherm (GAI) to interpret N₂ adsorption isotherm at 77 K. To solve the GAI, a modified normal distribution is developed and used as a distribution function of pore size on the domain [0, ∞). Pore size distribution (PSD) analyses of several adsorbent samples are carried out using this model. The results are found comparable with other popular PSD methods (e.g. MP, JC, HK and DFT).     

A grand canonical Monte Carlo study of hydrogen adsorption in carbon nanohorns and nanocones at 77 K

H₂ adsorption in carbon nanohorns and nanocones has been simulated at 77 K using the grand canonical Monte Carlo method. The models used for the solid adsorbents were nanosized curved graphene sheets of conical shape with five different apex angles, corresponding to the introduction of 1–5 pentagons to the hexagonal carbon network; nanohorns are a subclass of the carbon cone family (5 pentagons). Hydrogen molecules have been treated as Lennard-Jones spherical particles with quantum behavior. Details of the adsorption process have been revealed by studying carefully the cone–hydrogen interactions as well as the adsorption capacities and energies, in cones of different dimensions. Additionally, for comparison purposes similar studies have been carried out for carbon nanotube model structures and the effect of pore shape/size as well as elements of the role of confinement on sorption have been highlighted.     

Preparation of a coal surface for contact angle measurements

Coal specimens of different ranks were polished using silicon carbide abrasive papers (with a grit from #60 to #1200) and alumina powder of varying size (from 5 to 0.05 μm). The coal surface roughness and contamination (by alumina powder) were examined with both scanning electron microscopy and atomic force microscopy. The water advancing and receding contact angles were measured on such surfaces by varying the bubble size, using the captive-bubble technique. It was found that silicon carbide paper abraded all components of the coal surface, i.e. both organic and inorganic matter, to a similar depth. The roughness of the coal surface due to polishing with silicon carbide abrasive papers affected the contact angle hysteresis and the contact angle vs. bubble size relationship. Polishing of coal specimens with alumina powder reduced the microroughness of the coal surface but produced rough features at the macro level and caused mineral inclusions rising above the smooth organic matter. This phenomenon results from the heterogeneity of coal specimens consisting of minerals and macerals with different hardness values. The roughness at the macro level was easily distinguishable and had a significant impact on the measured contact angles when the coal surface was polished with coarse alumina powders, 5 and 1 μm in diameter. The effect of surface roughness on the advancing and receding water contact angles was significantly reduced (if not completely eliminated) when the coal surface was polished with a fibrous cloth (CHEMOMET) in the final step, after having been polished with 0.05 (0.06) μm alumina powder. Microscopic observation of the coal surfaces revealed that an appropriate ultrasonic treatment (8-10 min in an ultrasonic bath filled with water) and mechanical cleaning (polishing with a CHEMOMET cloth) of coal samples were required to remove the alumina particles left on the surface due to the previous polishing procedure. An improved methodology for coal surface preparation, prior to contact angle measurements, as proposed in this paper, includes polishing with a series of abrasive papers and 0.05 (0.06) μm alumina powder, polishing and cleaning with a fibrous cloth (e.g. CHEMOMET), and, finally, an extended cleaning in an ultrasonic bath filled with water.     

Phenomenology of surface failure of poly(methylmethacrylate) resulting from rolling contact fatigue

Results of phenomenological study into the forms of surface failure of poly(methylmethacrylate) (PMMA) are presented. Surface failure of the polymer resulted from rolling contact fatigue produced in a model configuration consisting of a PMMA disc with nominally flat surface loaded against three steel balls able to roll free over the surface of the disc. It was found that the performance of the polymer under the test conditions used is influenced by lubricating medium and the main form of failure is of surface fatigue type. © 1995 John Wiley & Sons, Inc.     

Luminescence studies in poly(ethylene terephthalate) films at 77 K. Investigation of emission centres in polymers

Optical luminescence of amorphous bright poly(ethylene terephthalate) (PET) films and the changes in luminescence due to certain morphological changes have been studies at 77 K to identify the luminescent centres in this polymer. The emission spectrum consists of both fluorescence and phosphorescence with distinct band peaks at 304, 326, 365 nm corresponding to fluorescence and at 426, 453, 476 nm corresponding to phosphorescence. Comparison of the PET emission spectrum with that one from dimethyl terephthalate microcrystals indicates that the emitter in the polymer is most probably the basic terephthalate unit. Polarized absorption and emission studies in oriented and unoriented PET films also support this observation. Change in the relative intensity distribution on changing the crystallinity of the film suggests that each of the 304, 326 and 365 nm fluorescence bands arises from different environments of the emitting centre. On γ-irradiation, a large increase in emission intensity is observed. This is explained on the basis of formation of a radical which in turn causes a large inductive effect on the benzene rings.     

Simulation on hydrogen storage properties of metal‐organic frameworks Cu‐BTC at 77–298 K

In recent years, many researchers have studied on the hydrogen storage properties of metal‐organic frameworks (MOFs) by grand canonical Monte Carlo (GCMC) simulation. At present, the GCMC studies of Cu‐BTC (BTC: benzene‐1,3,5‐tricarboxylate) which is a prototypical metal‐organic framework mainly adopt the classical force fields, the simulation temperatures are mainly focus on 298 and 77 K, and most researchers did not consider the effects of quantum effects at low temperature. Therefore, we used the quantum effects to correct the classical force fields and the force fields with more accurate simulation results were used to simulate the hydrogen adsorption performances of Cu‐BTC in the temperature range of 77–298 K and the pressure range of 1–8 MPa at each temperature. The results show that the effects of quantum effects on the hydrogen storage of Cu‐BTC cannot be neglected and the corrected Dreiding force field can simulate hydrogen adsorption performances of Cu‐BTC more accurately at low temperature. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1383–1388, 2018     

煤泥—煤矸石混烧技术在沸腾床锅炉上的应用

依据洗煤泥—煤矸石的混合特性 ,在沸腾床锅炉上进行了混合燃烧试验 ,探讨了沸腾床锅炉燃烧洗煤泥—煤矸石的机理 ,确定了沸腾床锅炉掺烧洗煤泥改造的最佳方式及应采取的有效措施 ,指出了煤泥—煤矸石混烧过程中存在的问题     

Effect of NaOH treatment on surface properties of coal

Surface properties of sub-bituminous Wyodak and bituminous Illinois coals were examined using sorption and immersion techniques, to elucidate the effects of aqueous NaOH treatment. Sorption of non-polar gases such as CO₂ and N₂ decreased significantly after the alkali treatment for the Wyodak coal; however, similar tests with the Illinois coal did not produce such dramatic results. Water sorption and heats of immersion into liquid water increased considerably for both coals following the NaOH treatment. It is concluded that treatment with aqueous NaOH affects the chemical and physical structure of the coal surface.     

气体与煤表面吸附作用的量子化学研究

选用褐煤、次烟煤、高挥发分烟煤、低挥发分烟煤和无烟煤5种煤表面结构模型,采用量子化学半经验方法INDO,从分子水平描述了CO、O₂、H₂O(g)、CO₂、CH₄和H₂等6种气体在煤表面的吸附作用,计算了气体在煤表面的吸附能、吸附距离、吸附作用键级和净电荷变化等微观参数,用Morse函数拟合了气体与煤表面的结合能曲线,得到了气体吸附作用强弱次序为：CO和O₂最强,H₂O和CO₂次之,CH₄和H₂最弱。