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排序方式: 共有324条查询结果,搜索用时 15 毫秒
41.
The undercooling of pure aluminum melt was in situ investigated by differential scanning calorimeter with flux processing technique in this study. The highest undercooling of pure aluminum with 17.8 K was obtained as the thermal treatment temperature of the melt being 1033 K and the cooling rate being 50 K min?1. When cooling rate is fixed, the undercooling depends on the melt processing temperature, and increases rapidly at the first stage. The effects of thermal treatment temperature and cooling rates on the undercooling are discussed in this article. 相似文献
42.
E. F. Vargas J. C. Moreno J. Forero D. F. Parra 《Journal of Thermal Analysis and Calorimetry》2008,91(2):659-662
A new solution-reaction isoperibol calorimeter was developed to measure enthalpies of solution and reaction. A new system
of sample cell was developed to avoid the breaking of glass ampoules, hence making the sample cell reusable. The system is
suitable for measuring molar enthalpies of solid-liquid and liquid-liquid interactions at different temperatures. The reproducibility
and accuracy of the apparatus were tested by measuring the enthalpy of solution of KCl in water at 298.15 K and the enthalpy
of protonation of THAM in HCl (0.1 M) at 298.15 K. The results showed the uncertainty taken as the reproducibility was ±0.3%
and the difference with the literature values was within ±0.5%. 相似文献
43.
A fully automated adiabatic calorimeter for heat capacity measurement between 80 and 400 K 总被引:1,自引:1,他引:0
Z. -C. Tan Q. Shi B. -P. Liu H. -T. Zhang 《Journal of Thermal Analysis and Calorimetry》2008,92(2):367-374
A fully automated adiabatic calorimeter controlled on line by a computer used for heat capacity measurements in the temperature
range from 80 to 400 K was constructed. The hardware of the calorimetric system consisted of a Data Acquisition/Switch Unit,
34970A Agilent, a 7 1/2 Digit Nano Volt /Micro Ohm Meter, 34420A Agilent, and a P4 computer. The software was developed according
to modern controlling theory. The adiabatic calorimeter consisted mainly of a sample cell equipped with a miniature platinum
resistance thermometer and an electric heater, two (inner and outer) adiabatic shields, two sets of six junction differential
thermocouple piles and a high vacuum can. A Lake Shore 340 Temperature Controller and the two sets of differential thermocouples
were used to control the adiabatic conditions between the cell and its surroundings. The reliability of the calorimeter was
verified by measuring the heat capacities of synthetic sapphire (α-Al2O3), Standard Reference Material 720. The deviation of the data obtained by this calorimeter from those published by NIST was
within ±0.1% in the temperature range from 80 to 400 K. 相似文献
44.
A phosphorus-containing flame retardant, 4-(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphorinan-2-yloxymethyl)-2,6,7-trioxa-1-phospha-bicyclo[2.2.2]octane-1-oxide (MOPO), was synthesized successfully and characterized. The flame retardancy and thermal behavior of a new intumescent flame-retardant (IFR) system for EVA, which was made of MOPO and ammonium polyphosphate (APP), were investigated by limiting oxygen index (LOI) test, vertical burning test (UL-94), cone calorimeter, and thermogravimetric analysis (TGA). An LOI value of 28.4 and UL-94 V-0 rating can be achieved when the total loading of MOPO and APP was 30 wt.%. The results from cone calorimeter indicate that both the heat release rate (HRR) and the total heat release (THR) of IFR-EVA decreased significantly compared with those of neat EVA. TG curves showed that the amount of residues increased significantly when intumescent additives were added; it also could be found that the LOI values increased with the increase in char residues. Meanwhile, morphology of the residues obtained from burning IFR-EVA in LOI test was studied through the SEM observations and rich compact char layers could explain the excellent flame retardance. 相似文献
45.
A.E. Elmughrabi 《Polymer Degradation and Stability》2008,93(10):1877-1883
A small-scale loading frame was used to apply tensile and compressive stresses to glass vinyl ester and glass polyester laminates in a cone calorimeter under a heat flux of 75 kW m−2. It was found, for the first time, that stress has a small but significant effect on the fire reaction properties. Increasing tensile stress increased heat release rate and smoke production while shortening the time-to-ignition. Compressive stress had the reverse effect. This was attributed to the fact that tensile stress promotes the formation of matrix microcracks, facilitating the evolution of flammable volatiles. This hypothesis is further supported by the observation that stress has the greatest effect on the early heat and smoke release peaks, with a lower effect on the final ‘run-out’ values.Stress rupture (time-to-failure) curves were produced for tension and compression. In tension, the behaviour was fibre dominated, with times-to-failure being roughly 10 times those in compression. Compressive failure involved resin dominated local fibre kinking, initiated near to the rear face of the specimen. The failure time was determined by a significant proportion of the specimen reaching its glass transition temperature. 相似文献
46.
47.
在298.15 K下利用等温环境溶解反应热量计测定了离子液体C3MIBF4(四氟硼酸1-甲基-3-丙基咪唑)和C5MIBF4(四氟硼酸1-甲基-3-戊基咪唑)不同浓度水溶液的摩尔溶解焓(ΔsHm). 借助Pitzer电解质溶液理论, 得到了它们的标准摩尔溶解焓 和Pitzer焓参数: 和 , 并计算了表观相对摩尔焓. 根据Glasser理论计算了离子液体晶格能, 进而估算了离子液体C5MIBF4和C3MIBF4中正离子的水化焓分别为-171 kJ•mol-1 (C5MI+)和-207 kJ•mol-1 (C3MI+). 相似文献
48.
P. Pardhasaradhi B.T.P. Madhav M. Venugopala Rao R.K.N.R. Manepalli 《Phase Transitions》2016,89(9):902-909
Characterization and phase transitions in pure and 0.5% BaTiO3 nano-dispersed liquid crystalline (LC) N-(p-n-heptyloxybenzylidene)-p-n-nonyloxy aniline, 7O.O9, com-pounds are carried out using a polarizing microscope attached with hot stage and camera. We observed that when any of these images are distorted, different local structures suffer from various degradations in a gradient magnitude. So, we examined the pixel-wise gradient magnitude similarity between the reference and distorted images combined with a novel pooling strategy – the standard deviation of the GMS map – to determine the overall phase transition variations. In this regard, MATLAB software is used for gradient measurement technique to identify the phase transitions and transition temperature of the pure and nano-dispersed LC compounds. The image analysis of this method proposed is in good agreement with the standard methods like polarizing microscope (POM) and differential scanning calorimeter (DSC). 0.5% BaTiO3 nano-dispersed 7O.O9 compound induces cholesteric phase quenching the nematic phase, which the pure compound exhibits. 相似文献
49.
50.
Tan Zhi-Cheng Zhang Ji-Biao Shang-He Meng 《Journal of Thermal Analysis and Calorimetry》1999,55(1):283-289
A computerized adiabatic calorimeter for heat capacity measurements in the temperature range 80–400 K has been constructed.
The sample cell of the calorimeter, which is about 50 cm3 in internal volume, is equipped with a platinum resistance thermometer and surrounded by an adiabatic shield and a guard
shield. Two sets of 6-junction chromel-copel thermocouples are mounted between the cell and the shields to indicate the temperature
differences between them. The adiabatic conditions of the cell are automatically controlled by two sets of temperature controller.
The reliability of the calorimeter was verified through heat capacity measurements on the standard reference material α-Al2O3. The results agreed well with those of the National Bureau of Standards (NBS): within ±0.2% throughout the whole temperature
region. The heat capacities of high-purity graphite and polystyrene were precisely measured in the interval 260–370 K by using
the above-mentioned calorimeter. The results were tabulated and plotted and the thermal behavior of the two materials was
discussed in detail. Polynomial expressions for calculation of the heat capacities of the two substances are presented.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献