Anomalous heat capacity and phase transition of graphite-ICl intercalation compounds

By means of alternating current calorimetry and X-ray diffraction, a study has been made of the phase transition behavior of graphite-ICl intercalation compounds slowly heated from 290 to 340 K. The heat capacity vs. temperature plots exhibit λ-type anomalies at 305 ± 1, 312 ± 1 and 315 ± 1 K. X-ray diffraction indicates that abrupt expansion of the c-axis occurs also near 305, 311 and 315 K, when the first-to-second, second-to-third and third-to-fourth or fifth stage changes, respectively, occurring in the subsequent temperature ranges are initiated. Each λ-type anomaly seems to represent the two-dimensional order-disorder transition of ICl layers taking place prior to the stage change. In order to account for the repetition of the order-disorder transition at different temperatures, it is proposed that deintercalation and restabilization of ICl layers occur alternatively during the slowly proceeding stage changes.     

A specific heat anomaly in multiwall carbon nanotubes as a possible sign of orientational order-disorder transition

We present micro-calorimetric specific heat measurements on different multiwall carbon nanotubes of large outer diameter, as a function of temperature in the range 10-120 K. A clear anomaly at 60 K with the shape of a peak is present in two of the samples, and both the height and the characteristic temperature of the peak are independent of magnetic field and do not exhibit thermal hysteresis, discarding magnetic degrees of freedom related to Fe seeds or contributions from adsorbed gases. These features suggest that the anomaly may be caused by a structural change. As the anomaly is also unaffected by induced intertube disorder, it may be related with a melting of orientational dislocations of individual tubes within multiwall nanotubes, an effect that was theoretically predicted to occur in carbon nanotubes and represents a distinctive feature of asymmetric molecular systems.     

Pressure induced order-disorder transition in a diblock copolymer

Polymers are known to undergo order↔order and order↔disorder transitions, when subjected to a change of pressure, temperature, solvent, pH of the medium etc. The molecular processes, which alter the volume of the system, are found to be highly sensitive to the pressure. In the present communication Zimm and Bragg model of helix↔coil transition has been modified to interpret the experimental data of pressure induced phase transition in polystyrene-polybutadiene [PS-PB] at different pressurization rates, as reported by Migler and Han, utilizing the Birefringence and small angle neutron scattering technique. An expression for the degree of order is obtained from the grand partition function for the entire chain in terms of nucleation parameter, which controls the transition width. The nucleation parameter σ increases with the increase in the ODT temperatures of the system. The phenomenon of hysteresis has been discussed in relation to the pressurization rate, which increases/decreases with the corresponding increase/decrease in the pressurization rate. The theoretical transition curves are found to be in good agreement with experimental data.     

A deformation induced order-disorder transition in isotactic polypropylene

In this study, isotactic polypropylene (i-PP) has been deformed by uniaxial compression to draw ratios up to 16×, and at draw temperatures from 30°C to 140°C. An order-disorder transition in the crystals is observed at draw temperatures well above the stability limit, 70°C, reported for the disordered phase; Furthermore, this disordered phase (called smectic) is found to induce ductility and improve the efficiency of draw. The deformation induced smectic phase has been characterized using WAXS, DSC, and on-line compression load versus draw ratio measurements. In consequence, a set of process conditions are offered to optimize draw. A mechanism for plastic deformation of i-PP is also suggested, using the smectic phase as a probe.     

Monte-Carlo simulation of the order-disorder transition in the KDP-type structure

Monte Carlo simulations are presented for a model for the KDP-type structure, using a simplified pseudo-Ising model. Phase transitions occur for simulated temperatures that concur with analytical results in the limit of weak ordering fields. Significantly non-zero pseudo-spin correlations are found in the paraelectric phase only for the ordering on the PO₄ tetrahedra. Most of the computation is Boolean logic, making it ideal for the ICL Distributed Array Processor.     

Phonon spectrum in first stage graphite-lithium intercalation compound

Phonon dispersion relations have studied for the first stage graphite-lithium intercalation compound C₆Li using an angular force model approach. We have used the stacking sequence CαCαCα in the present case. A good agreement is seen when compared with the experimental results, suggesting that the angular forces play an important role in explaining the phonon spectra of layered structures. We obtain a satisfactory agreement for the elastic constants C₄₄ and C₃₃ when compared with experiment.     

Modeling volume changes due to lithium intercalation in a carbon fiber

Two different approaches were used to model the insertion of lithium ions into a single carbon particle fiber under potentiodynamic control. In the first approach, volume changes in the particle due to lithium intercalation/deintercalation were neglected (NVCP model) while in the second approach the volume changes were included (VCP model). Modeling discrimination techniques were used to determine the statistical significance of the different models when fitting experimental cyclic voltammetry data. It was found that the VCP model is a better fit of the experimental cyclic voltammetry data than the NVCP model. The VCP model predicts significant changes in the radius of the particle due to lithium intercalation/deintercalation. It is recommended to extend the application of the VCP model to a complete lithium ion cell. Incorporation of volume changes into the model along with the formation of the SEI layer may be the key to understanding and predicting capacity fade in a lithium ion battery during cycling.     

Predicting heat buildup due to the sun's energy

PVC building products such as siding, windows, and roofings are exposed to the sun. Absorption of the sun's energy leads to a temperature rise, which may cause dimensional control problems, such as expansion and, in severe cases, distortion of the PVC products. The amount of heat buildup in the product depends on the color and/or pigment system of the PVC compound. Generally, the darker the color, the more the sun's energy is absorbed and the higher the temperature heat buildup. Because of the growing demand for darker colors of PVC building products, a test for measuring temperature rise to predict performance of the product in actual use is needed. A laboratory test method for predicting maximum heat buildup due to the sun is described in this paper. The effects of the sample thickness and gloss, carbon black and titanium dioxide levels, and the distance of an infrared heat source from the sample on the heat buildup are also presented in the paper.     

Movement of hot loads due to their heat

Construction of a cooled container is presented with a detachable loading vessel and a sealed heat exchange cavity. With the aim of increasing the endurance of the end sealing under high temperature conditions and reducing air flow through the container the end seal it is made in the form of a circular collector with a steam generator with circular orifice, that is directed at an angle to the wall of the pipeline and in a direction opposite to container movement.     

Skin damage due to heat transfer by conduction

This study provides basic data with respect to pain and burns produced on short-term contact of bare skin with heated substances. The data may also be used to determine the thermal properties and thicknesses of fabrics or coatings required to prevent injury in such contacts. The maximum temperature any material might attain without causing injury on contact with bare skin was determined from measurements of pain threshold during contact with heated materials representing a wide spectrum of thermal properties form good conductors to good insulators. Pain threshold times were converted to blister times and the latter extrapolated to predict those temperatures at which blistering would result form ‘instantaneous’ (0.3 s) contact. The predicted temperatures were verified experimentally in contacts with four different materials. From these data, charts and equations were derived by which the maximum permissible temperature for safe contact could be determined for any material solely form a knowledge of its thermal conductivity, density and specific heat. Additionally, equations for transient heat flow in two-layer systems yield the thickness of coatings, fabrics or other thermal barriers of known properties which would be required to protect the skin form pain or burn on contact with materials at excessive temperatures.     

Order-order, lattice disordering, and order-disorder transition in SEBS studied by two-dimensional correlation infrared spectroscopy

The temperature-dependent transitions of polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene block copolymer (SEBS) at high temperature were studied using infrared spectroscopy combined with two-dimensional (2D) correlation spectroscopy. The order-order transition (OOT), the lattice disordering transition (LDT), and the order-disorder transition (ODT) of SEBS were explored with a linear temperature increment ranging from 100 to 220 °C. AFM was employed to study the surface morphology of SEBS and to identify the correlation intensity peaks in the MW2D spectra. The OOT was determined around 152 °C. The LDT appears around 170 °C. The ODT was also successfully determined around 202 °C. It is gained that the key driver of the OOT is the movements of -CH₂- in the main chains of EB blocks. In the LDT, the movements of groups are simultaneous and the SEBS molecular chains move as a whole. In the ODT, it shows the driver is the movements of -CH₂- in the main chains of EB blocks.     

调整过渡层配方 克服胎肩脱层内露丝缺陷

分析全钢载重子午线轮胎胎肩脱层内露丝产生原因。根据分析结果,采用两种过渡层胶料对轮胎肩部进行有限元分析,结果表明,不同胶料对轮胎肩部的受力分布有较大影响,两种胶料的动态力学分析结果也表明,轮胎肩部模量较高、蠕变小的过渡层胶料受力应变降低超过50%。过渡层胶料调整后全钢载重子午线轮胎的胎肩脱层内露丝现象明显减少。     

Changes in the structure of soybean triacylglycerols due to heat

Commercially refined soybean oil was heated at 180 C for 50, 70 or 100 hr with aeration. The triacylglycerol fractions separated from the oils by column chromatography on silica gel were fractionated further by silicic acid thin layer chromatography (TLC), and species compositions were determined by argentation TLC and lipase hydrolysis. There was a decrease in the absolute amounts of the triacylglycerols with longer heating periods, such as 21% for 50 hr and 42% for 100 hr. Relatively large changes occurred in the proportion of the molecular species of the triacylglycerols during heating; there was an increase in the more saturated species, 1–4 double bonds, and a decrease in species containing 5–7 double bonds. Although these changes occurred in the percentage of each triacylglycerol species, the positional distribution of the fatty acids in the 2-position remained virtually unchanged throughout heating. Oleic and linoleic acids were commonly found in the 2-position of the acylglycerol moiety, whereas most of the palmitic and stearic acids favored esterification in the 1- and 3-positions. The results indicate that unsaturated fatty acids located in the 2-position are protected significantly from thermal oxidative decomposition.     

Reduction of fractures in dried clay-like materials due to specific surfactants

The possibility of fracture reduction as a result of application of specific surfactants during intensive drying of clay-like materials was examined in this paper. The dodecyl sulfate sodium salt (SDS) and the fluoric (FC 4430) surfactants were used for the tests. Different amounts of these surfactants were mixed with distilled water and used for wetting a dry clay material before forming clay samples. The clay samples in the form of cylinders 44 mm in diameter and 50 mm high were extruded and after leveling the moisture distribution subjected to convectively drying in hot air at 120 °C. The acoustic emission (AE) method was used to monitor on line the development of crack formation in dried samples. It was stated that application of surfactants in a prescribed amount may significantly reduce the drying induced fractures in clay during its intensive drying and thus to obtain good quality products by high drying rates.     

Changes in oxyreactivity of carbons due to heat treatment and prehydrogenation

Evidence from deactivation due to heating chars at elevated temperatures supports the suggestion that impurities catalyse all oxidation reactions of carbons in similar ways. Data on deactivation by both thermal treatment and prehydrogenation how that the concentration of sites at which oxidation reactions proceed is dependent on the morphology of impurities and possibly their chemical type. The rate limiting step, or steps, during oxidation of chars and cokes are not redox reactions between the carbon and catalytic impurities. An assumption of steady reaction conditions during gasification of chars and cokes will not be valid generally. Impurities may be capable of catalysing the carbon-hydrogen reaction, but such catalytic activity will decay due to aggregation of impurities.     

Anomalous bexavior of fracture toughness of ferro-electrics in the phase transition region

Temperature dependences of fracture toughness of some ferroelectric crystals have been studied both experimentally and theoretically. It is argued that its anomalous behavior in the phase transition region may be related to the presence of the piezoeffect in the ferrophase.     

Anomalous thickness increase in crosslinked closed cell polyolefin foams during heat treatments

When crosslinked closed cell polyolefin foams are under a temperature above the melting point of the base polymer, a reduction of their size is expected due to the gas diffusion out of the foam. However, some kinds of crosslinked closed cell polyolefin foams present one direction (thickness direction) in which the foam size increases during the first minutes of the thermal treatment. The thickness of the foams after the thermal treatment can be higher than the thickness of the original foams. An experimental study is presented on the thickness increase, as well as on the changes in the dimensions and the properties of foams with different densities, which were obtained from different foaming processes and made of different base polymers, as a function of the treatment temperature and the treatment time. This investigation sought to discover the physics mechanisms that control the anomalous thickness increase. The experimental results show that the thickness increase of these materials is related to the anisotropic cellular structure of the original foams. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2825–2835, 1999     

Shear-rate dependence of first normal stress difference of poly(isoprene-b-styrene) in solution near the order-disorder transition temperature

Viscoelastic properties of poly(isoprene-b-styrene) in dioctylphthalate under steady shear flow were measured near the order—disorder transition temperature. In ordered states, first normal stress difference N₁ is proportional to shear rate at low region, but becomes proportional to at the high region, similar to the N₁ behaviour of polymer blends undergoing shear-induced homogenization. Because the existence of microdomains was confirmed at the high region by the flow birefringence method, it is concluded that the above N₁ behaviour is not caused by shear-induced homogenization, but is probably caused by the shear-induced alignment of the microdomain structure.     

板式换热器在复混(合)肥料生产中的应用

针对复合肥生产中对固体物料连续加热的要求,对普通板式换热器的板对结构形式进行了改进。介绍改进后的板式换热器的结构、工作原理和使用情况。用于高塔复合肥生产线粉状原料的加热和硫包缓释肥料生产中预热颗粒芯料,加热均匀,能耗小,无粉尘逸出,占地面积小,是较为理想的固体物料加热设备。