Novel empirical correlation for ionanofluid PEC inside tube subjected to heat flux with application to solar energy

Journal of Thermal Analysis and Calorimetry - Ionic liquid-based nanofluids are a very novel group of fluids used for enhancing heat transfer in different applications, especially in solar energy...     

Effect of oxygen concentration and temperature on ignition time of polypropylene

The presented article deals with the assessment of combined impact of temperature and flow of oxidising atmosphere, its oxygen concentration and heat flux on the ignition time of isotactic polypropylene (PP). The ignition time was determined in a specially adapted hot air Setchkin furnace at temperatures (450 and 600?°C), density of heat flux (12.4 and?26.4?kW m^?2), flows of oxidation mixture (6 and 8?L?min^?1) and volume oxygen concentrations (3, 9, 15, 21, 27, 33, 39, 45 and 50?%). Obtained data allows us to assume that the temperature influence on PP induction period of ignition increases with decreasing flow rate of oxidising atmosphere. At the flow of oxidising mixture equal to 6?L?min^?1 and temperature of 600?°C, oxygen concentration had only a negligible impact on the the induction period of ignition in the analysed period. From the presented results, the induction period of ignition depends on the temperature and also on the flow rate of oxidising mixture and oxygen concentration in it. In addition, heat flux has a significant influence on the induction period. However, the quantification of the heat flux influence was not possible with the applied experimental device.     

ESR application to radiation chemistry of polymers

Important results obtained in our group in the field of ESR application to the study of irradiated polymers are summarized. They are the analysis of the decay reaction of the free radicals, spur-like trapping of the free radicals and the related discussions. A diffusion controlled bimolecular reaction scheme was a good way of analyzing the data of the decay reaction. Power saturation phenomenon of ESR spectra of the free radicals showed a circumstance of the spur-like trapping of the free radicals in irradiated polyethylene. The phenomenon of spur-like trapping was quite consistent with the interpretation of the decay reaction of the free radicals.     

Effect of organosilicon chain-transfer agents on the heat resistance of vinyl polymers

The effect exerted on the resistance of polymers to thermal oxidation degradation by organosilicon hydrides used as chain-transfer agents in polymerization of styrene, methyl methacrylate, and vinyl acetate was examined.     

A model for the prediction of the thermal degradation and ignition of wood under constant and variable heat flux

The ignition of combustible materials is an important aspect of the processes taking place in an unwanted fire. In this work, an experimental and theoretical study of the ignition process of wood has been carried out. Experiments of both spontaneous and piloted ignition have been performed. Constant and decreasing variable heat fluxes have been tested. A mathematical model has been used to predict the time to ignition of wood for the different operating conditions used. The solution of the model provides the temperature at each point of the solid, the local solid conversion and the time to ignition of the material. In general, a good agreement between experimental and theoretical results is obtained.     

A microcalorimetric study of crystallizable polymers subjected to severe plastic deformation

Differential scanning calorimetry has been used to investigate the evolution of the structural and thermophysical parameters of a number of semicrystalline polymers (high-density polyethylene, polyamide-6, polyoxymethylene) that is initiated by severe plastic deformation imposed through equal-channel multiple-angle extrusion. Thermograms of the deformed polymers have been found to exhibit an additional high-temperature melting peak. It has been shown that the onset, maximum, and end temperatures for both melting peaks increase with the strain buildup. The degrees of crystallinity and the thicknesses of crystallites increase as well. The magnitude of the effects is determined by the deformation route selected. It has been revealed that conformational transitions due to the formation of “double-triple” folds in macromolecular chains can occur during the course of equal-channel multiple-angle extrusion.     

Temperature dependence of radiation effects on polymers

Temperature dependence of radiation effect on various polymers including hydrocarbon and fluorocarbon polymers was investigated. Gas evolution and mechanical properties were measured in a wide range of temperatures. G-values of chain scission and crosslinking were estimated. It has been made clear from those experimental results that radiation effect be profoundly affected by temperature. Particularly, significant changes of radiation effect in the melting region were found out.     

The melting of high-pressure polyethylene subjected to stepwise heat treatment

Silver antimony oxide (Ag₂Sb₂O₆) having a defect pyrochlore structure has been synthesized by solid-state reaction between silver oxide and either Sb₂O₃ and Sb₂O₅. The reaction sequence has been shown by thermogravimetry, interdiffusion measurements on oxide pellets and electrical conductance measurements to involve the reduction of Ag₂O, followed by diffusion of silver and oxygen into the antimony oxide component. When the starting material is Sb₂O₃, initial diffusion of oxygen occurs, forming Sb₂O₄ into which silver and further oxygen subsequently diffuse. Comparison of the activation energies for diffusion and electrical conductance in the various oxide phases suggests that the rate of Ag₂Sb₂O₆ formation is controlled by the diffusion of oxygen rather than that of silver.

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Zusammenfassung Silber-Antimonoxid (Ag₂Sb₂O₆) von defekter Pyrochlorstruktur wurde durch eine Festphasenreaktion zwischen Silberoxid und entweder Sb₂O₃ oder Sb₂O₅ synthetisiert. Durch Thermogravimetrie, Interdiffusionsmessung an Oxidpillen, sowie elektrische Leitfähigkeitsmessungen wurde erwiesen, daß die Reaktionsfolge die Reduktion von Ag₂O mit darauffolgender Diffusion des Silbers und Sauerstoffs in die Antimonoxidkomponente enthält. Bei Sb₂O₃ als Ausgangsmaterial erfolgt eine Diffusion des Sauerstoffs wodurch Sb₂O₄ entsteht, in welches dann Silber und weiterer Sauerstoff diffundiert. Der Vergleich der Aktivierungsenergien der Diffusion und der elektrischen Leitfähigkeit in den verschiedenen Oxidphasen läßt vermuten, daß die Bildungsgeschwindigkeit des Ag₂Sb₂O₆ eher durch die Diffusion des Sauerstoffs als durch die des Silbers bedingt ist.

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Résumé L'oxyde d'argent antimonié (Ag₂Sb₂O₆) à structure pyrochlore imparfaite a été synthétisé par réaction en phase solide entre l'oxyde d'argent et Sb₂O₃ ou Sb₂O₅. La séquence de réaction étudiée par thermogravimétrie, par mesures d'interdiffusion sur pastilles d'oxyde et par mesures de conductibilité électrique consiste en la réduction de Ag₂O suivie par la diffusion de l'argent et de l'oxygène dans le composant d'oxyde antimonié. Quand le matériau de départ est Sb₂O₃, la diffusion initiale d'oxygène a lieu et donne Sb₂O₄ dans lequel l'argent et l'oxygène en excès diffusent ensuite. La comparaison des énergies d'activation pour la diffusion et la conductivité électrique dans les diverses phases d'oxydes suggère que la vitesse de formation de Ag₂Sb₂O₆ est contrôlée par la diffusion de l'oxygène plutôt que par celle de l'argent.

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ë (Ag₂Sb₂O₆), . . , . ë , Sb₂O₄ . , , Ag₂Sb₂O₆ , .

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We are grateful to Mr. M. Ahangarha for assistance with the diffusion experiments and to Mr. A. Nossoni for assistance with the thermogravimetric experiments.     

Temperature calibration of heat flux DSC's on cooling

The temperature calibration of a TA Instruments 3200-2920 DSC has been performed on cooling using the isotropic → nematic, isotropic → cholesteric and other liquid crystal → liquid crystal transitions of thermally stable, high purity liquid crystals. The thermal stability of these liquid crystals has been verified by measuring the temperature of the mentioned transitions during cyclic heating and cooling experiments. Correspondence has been established between the real and indicated temperature during cooling for all combinations of heating and cooling rates of practical interest: correction values were determined to the indicated temperature in order to obtain the real temperature on cooling. These correction values were calculated as the average from the temperatures of four or five different liquid crystal transitions for each heating-cooling rate combination. The accuracy of the temperature calibration on cooling is ca. 0.2?C for heating and cooling rates up to 20?C min^?1.     

Effect of annealing time on the self‐nucleation behavior of semicrystalline polymers

It is widely known that when a polymer is heated just above its melting point and is kept at a given temperature (denoted T_s) for a short time, when it is cooled down its nucleation density increases and its peak crystallization temperature shifts to higher temperatures, as detected for instance by differential scanning calorimetry (DSC). The T_s temperature range where the described process occurs has been named Domain II self‐nucleation (SN) because the selected T_s temperatures are high enough to melt the polymer without causing detectable annealing of any remnant crystals by DSC. Experimental results obtained by DSC, polarized light optical microscopy (PLOM), and rheology indicate that these techniques are unable to detect any remaining crystal fragments in Domain II. Our kinetic results demonstrate that Domain II SN is a transient phenomenon that can even disappear if enough time at T_s is allowed. Results of the study of the time dependence of the SN effect indicates two possibilities: (a) if crystal fragments are present (even if undetected by the employed techniques) their final melting is a very slow process (in the order of hours); (b) if all crystallites have melted in Domain II, then it may be more plausible to reinterpret self‐nuclei as arising from “precursors” whose detail nature has not been the subject of this investigation but that can be regarded as either a residual segmental orientation in the melt (i.e., a melt memory effect) or a mesophase in a preordered state. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1738–1750, 2006     

A probabilistic theory on the time to fracture of amorphous crosslinked polymers

The energy probability theory of fracture proposed by Valanis has been extended to apply to the global fracture of a large material region and has been generalized to take into account the probabilistic distribution among bonds of the free energy of the region. In contrast to the theory of fracture initiation of the first author, it is assumed, in the present paper, that global fracture is brought about by the fracture of a critical number N_cr of primary bonds. Whereas this condition alleviates some of the problems encountered in the application of the theory to fracture initiation and propagation—such as determination of the local energy field at the root of a developed crack—it introduces the difficulty that N_cr may, in general, depend on the geometry of the specimen and the directionality of the stress field, though it was found to be relatively insensitive to the rate of deformation, as corroborated in this paper. The theory is used in this work to predict the time of global fracture, under conditions of constant load, constant strain, and constant strain rate.     

Effect of heat and solvent treatment on radiation grafting of acrylic acid to poly(ethylene terpehthalate)

Direct radiation graft polymerization of acrylic acid onto oriented poly(ethylene terephthalate) films and fibers subjected to thermal treatment and treated with structure-active solvents, such as dichloroethane and dioxane, was studied. Based on the results of thermomechanical analysis, X-ray diffraction, sorption, and acrylic acid grafting, conclusions were drawn concerning the character of structural changes in poly(ethylene terephthalate) exposed to structure-active solvents. The physicochemical properties of the graft copolymers obtained were examined, including the resistance against γ-radiation.     

Computer plots of HOH normal modes depending on time

The combination of the antisymmetric and symmetric stretching vibrations of water is a decoupled OH vibration. It means the X₁₃ anharmonicity constant of HOH must be related with the X₃₃ anharmonicity constant of HOD. It is found that $\text{1}\text{2}$X₁₃(HOH)= X₃₃(DOH) = X(OH). Instead of the usual condition X_ik = 0 for i > k a new definition will be given for the anharmonicity constants: $\text{X}$_ik = $\text{X}$_ki. The X values of other molecules were compared with each other and it follows the general rule for a symmetric molecule m-M-m with m ? M: $\text{X}$₁₃ (mMm) = $\text{X}$₃₁ (mMm) = X (Mm).Computer plots of normal modes of the ν₁ + ν₃ combination depending on time show the rotation of the dipole moment derivatives vector. It is strongly different for H₂O and HOD and explains the different band intensities. We expect higher band intensities and X₁₃ values using IR light with rotating electric field vector.     

Modeling and calculation of thermal explosion time to ignition of cylindrical fireworks and crackers

To analyze the thermal safety of cylindrical fireworks and crackers in storage and transportation, this article establishes a physical model and a mathematical model of thermal explosion time to ignition of finite cylindrical fireworks and crackers. And in order to simplify the thermal explosion model, effective Biot number about boundary condition is deduced according to the theory of heat transfer. The partial differential equation of thermal explosion model are calculated with difference method in Matlab program, to obtain the time to ignition as well as the temperature–time history before explosion system explodes. The rationality of effective Biot number and calculation method is proved through comparison of calculation solution and literature solution. Being the first to solve the problem of two-dimensional thermal explosion unsteady-state model of fireworks and crackers, where the upper surface, lower surface, and side surface have different heat dissipation conditions. Meanwhile, calculation steps were shown about a type of fireworks.     

Effect of amorphous sequences on the longitudinal acoustic modes in partially crystalline polymers. I. Transfer matrix method

A novel theoretical scheme is developed which enables the determination of the LAM-like vibrations of polymer chains made up of crystalline and amorphous parts as they occur in partially crystalline structures. The boundary conditions effective at the junction points are formulated in terms of the compliances of the associated amorphous sequences. These compliances can be derived from their eigenfrequencies and eigenvectors in a disconnected state. The treatment uses a matrix formalism which can be extended to include bending and torsional motions in a general state of vibration of the crystalline stem. A first numerical example demonstrates that the LA mode of a crystalline stem can be strongly perturbed by the coupling to the adjacent amorphous sequences. Interpretation of frequencies and line shapes of observed LA modes should always include these coupling effects; their neglect can lead to considerable errors.     

Study on oxidation of polymers treated by high LET radiation

The oxidation of medical silicone rubber and segmented polyether urethane which were bombarded with 11.2 MeV Si⁺ or F⁺ at the dose of 5 × 10¹⁴ ions/cm² was studied. In XPS measurements, it was found that the oxygen concentration on the surface of the implanted polymeric membranes had been increasing in three months at least. ESR measurement showed that some free radicals existed in these membranes and their quantities decreased with time. Chemical analysis proved that peroxides were generated in the γ irradiated membranes. The reason for the increasing of oxygen concentration was that free radicals combined with oxygen in the air and produced peroxides on the membrane surface. Moreover, in order to demonstrate the radiation mechanism, low LET (γ rays) radiation of such polymeric membranes was carried out for comparison     

Advanced research work on radiation cross-linking of polymers in CIAC

Recent research carried out at the Chinese Institute of Applied Chemistry has contributed significantly to the understanding of the radiation chemistry of polymers. High energy radiation has been successfully used to cross-link fluoropolymers and polyimides. Here chain flexibility has been shown to play an important role, and T-type structures were found to exist in the cross-linked fluoropolymers. A modified Charlesby-Pinner equation, based upon the importance of chain flexibility, was developed to account for the solradiation dose relationship in systems of this type. An XPS method has been developed to measure the cross-linking yields in aromatic polymers and fluoropolymers, based upon the dose dependence of the aromatic shake-up peaks and the F/C ratios, respectively. Methods for radiation cross-linking degrading polymers in polymer blends have also been developed, as have methods for improving the radiation resistance of polymers through radiation cross-linking.