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排序方式: 共有63条查询结果,搜索用时 15 毫秒
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2.
Bogdan C. Simionescu Silvia Ioan Aurora Chiriac Cristofor I. Simionescu 《Polymer Bulletin》1987,17(5):439-443
Summary Temperature dependence of viscosity data was investigated on poly(butyl methacrylate) fractions in dilute solution. A discontinuity in intrinsic viscosity was observed in the 25°C–35°C temperature range. Sharp changes of unperturbed dimensions were visualized from this behaviour. The phenomenon can be accounted for by assuming conformational changes of the chain in different solvents. 相似文献
3.
An ammonia/water mixture can be used as an efficient working fluid in industrial-type heat recovery heat pumps and heat transformers. Several configurations of such systems are possible depending on the availability of the waste (thermal) and primary (thermal or electrical) energy sources. This article presents the configurations, the main thermodynamic and hydraulic parameters, and some design guidelines and operating experiences of a medium-temperature, ammonia/water-based compression/re-sorption heat recovery system for district domestic hot water production. In-field experiments have proven the advantages of the concept and its applicability limits in a particular economical environment, while hot water was produced at 55 °C with industrial cooling water at 36 °C as a waste heat source. 相似文献
4.
In the present work, we studied the effect of metal chlorides, MCl2, on the thermal decomposition of ammonia borane NH3BH3 (AB). Some metals from row n = 4 of the periodic table were chosen and used as MCl2: namely, FeCl2, CoCl2, NiCl2, CuCl2, and ZnCl2. In addition, three metals from column VIII of the periodic table were considered: NiCl2, PdCl2 and PtCl2. The AB decomposition was followed by TGA and DSC; the decomposition gases analyzed by μGC/MSD coupling, and the solid by-products identified by XRD, IR and XPS. We observed that the presence of CuCl2 in AB is beneficial, making the decomposition occur in much milder conditions than for pristine AB; for example, the dehydrogenation of CuCl2-doped AB started at 25 °C, with the sample losing about 14 wt% at 85 °C. However, MCl2 does not hinder the evolution of the undesired borazine; it only contributes to a decrease in its content compared to pristine AB. To rationalize the better performance of CuCl2, we propose that Cu offers an optimal doping activity with intermediate binding energies for the intermediates: i.e. with H not too strongly bonded but optimally bonded to the N of AB. The germ Cu?NH2–BH2, then formed, acts as a Lewis acid through B and has an optimized reactivity towards a new AB molecule (head-to-tail dehydrocoupling). This is discussed herein. 相似文献
5.
Loredana Elena Nita Aurica P Chiriac Sossio Cimmino Clara Silvestre Donatella Duraccio Cornelia Vasile 《Polymer International》2008,57(2):342-349
BACKGROUND: The possibility to use β‐cyclodextrin as biodegradable tensioactive and an electromagnetic field in order to improve the kinetic parameters of radical emulsion polymerization is of interest. Thus, the influence of different surfactants—sodium lauryl sulfate (SLS) and β‐cyclodextrin (CD)—on the pathway of emulsion polymerization of methyl methacrylate (MMA) and emulsion copolymerization of MMA with 2,3‐epoxypropyl methacrylate (GMA) performed with or without the presence of a continuous electromagnetic field (MF) was studied. RESULTS: The presence of the MF leads to a considerable increase of the conversion during the first part of the reaction if the classic surfactant (SLS) is used. The reactions performed without MF and with CD exhibit a decrease of the conversion and of the polymerization rate as compared with the variants using SLS. The swelling rate and the maximum degree of swelling vary with the surfactant nature and with the reaction conditions and MF presence. Data from thermogravimetry and differential scanning calorimetry evidence the dependences between the polymer characteristics and the preparation conditions. CONCLUSION: This research underlines the coupling possibilities of the influence of a MF—growth of the reaction rate and conversion explained through radical pairs mechanism—with a combination of the ‘cage’ effect and ‘conformational control’ afforded by CD. The presence of MF and CD during the syntheses leads to an increase of Tg and an increase of PMMA and P(MMA‐co‐GMA) thermal stability. Copyright © 2007 Society of Chemical Industry 相似文献
6.
Constantin I. Chiriac 《Polymer Bulletin》1986,16(2-3):143-146
Summary Aromatic polyureas and polythioureas are prepared from aromatic diamines and carbon dioxide or carbon disulfide, by a new direct polycondensation reaction with ethylene chlorophosphite as reagent in pyridine as solvent and acceptor for hydrochloric acid at 50–60° for 6–7 hours. 相似文献
7.
Constantin I. Chiriac 《Polymer Bulletin》1984,11(4):371-374
Summary Aromatic polyamides are prepared by a direct condensation reaction using phenyldichloropnosphite as reagent at 80–90°(2h) and 95–100°(4h) in N-methyl-2-pirrolidone and pyridine as acceptor for hydrochloric acid. 相似文献
8.
Nita LE Chiriac AP Nistor MT Tartau L 《Journal of materials science. Materials in medicine》2012,23(5):1211-1223
The study presents the possibility to use the 2-hydroxyethyl methacrylate--HEMA copolymer with a comonomer with spiroacetal moiety, 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane)-U, as polymer network for loading the indomethacin--INN as drug model, and also, the controlled release evaluation of the prepared bioactive system. The macromolecular compounds were prepared by radical dispersion polymerization in the presence of a pair of surfactants. The use of cyclodextrin as surfactant allowed the building of the host-guest complexes by inclusion of hydrophobic molecules. Also, the cyclodextrin supplemented the hydrogen bonds and the hydrophobic interactions responsible for the stability of the achieved complexes. The copolymers composition and the INN inclusion onto the polymeric matrix were confirmed by FTIR analysis. The porous structure of the lyophilized P(HEMA-U) samples was illustrated by SEM images. The swelling studies evidenced the interdependence between P(HEMA-U) network properties and the spiroacetal moiety amount. Thus, the copolymers presented the increase of the equilibrium swelling degree with pH and temperature. Also, the polymeric matrices manifested dual sensitivity with pH and temperature. The in vitro release of the INN drug from the polymeric network as well as the in vivo experimental studies evidenced the benefit consequence of the spiroacetal compound presence. The clinical observation of the experimental groups does not show any behavioral modifications to suggest a possible toxic effect of these polymeric formulations with and without INN. 相似文献
9.
Adrian BirtasIulian Voicu Cristian PetcuRadu Chiriac Nicolae Apostolescu 《International Journal of Hydrogen Energy》2011,36(18):12007-12014
Extensive studies have been dedicated in the last decade to the possibility to use hydrogen in the dual-fuel mode to improve combustion characteristics and emissions of a diesel engine. The results of these studies, using pure hydrogen or hydrogen containing gas produced through water electrolysis, are notably different.The present investigation was conducted on a tractor diesel engine running with small amounts of the gas—provided by a water electrolyzer—aspirated in the air stream inducted in the cylinder. The engine was operated at light and medium loads and various speeds.It was found that the addition of HRG gas has a slight negative impact, up to 2%, on the engine brake thermal efficiency. Smoke is significantly reduced, up to 30%, with HRG enrichment, while NOx concentrations vary in both senses, up to 14%, depending on the engine operation mode. A relative small amount of HRG gas can be used with favorable effects on emissions and with a small penalty in thermal efficiency. 相似文献
10.
M. Urse M. GrigorasN. Lupu F. BorzaH. Chiriac 《Materials Science and Engineering: B》2013,178(16):1019-1026
A series of Ta/NdFeB/Ta thin films with Mo and Mo–Cu additions embedded by alloying and by stratification have been prepared by r.f. sputtering. The influence of additions, their embedding mode, and annealing temperature on the structural and magnetic behavior of Ta/NdFeB/Ta thin films is presented. The use of additions of Mo and Mo–Cu leads to refined grain structure and improvement in the hard magnetic characteristics of Ta/NdFeB/Ta thin films. The Ta/[NdFeBMo(540 nm)/Ta films and Ta/[NdFeB(180 nm)/MoCu(dnm)] × n/Ta multilayer films present enhanced coercivities and Mr/Ms ratios in comparison with the Ta/NdFeB(540 nm)/Ta films. The stratification of Ta/NdFeB/Ta thin films with Mo–Cu interlayers leads to an oscillatory behavior of hard magnetic characteristics of the Ta/[NdFeB(180 nm)/MoCu(dnm)] × n/Ta multilayer films, when the thickness, d, of Mo–Cu interlayers varies by increments of 1 nm. When the thickness of Mo–Cu interlayers varies by increments of 2 nm the oscillatory behavior of the magnetic characteristics is not revealed. For a thickness of the Mo–Cu interlayer of 3 nm in the Ta/[NdFeB(180 nm)/MoCu(3 nm)] × 3/Ta thin films annealed at 650 °C, the c-axis of part of the hard magnetic Nd2Fe14B grains is oriented out-of-plane. 相似文献