Calorimetric study and thermal analysis of crystalline nicotinic acid

As one primary component of Vitamin B-3, nicotinic acid [pyridine 3-carboxylic acid] was synthesized, and calorimetric study and thermal analysis for this compound were performed. The low-temperature heat capacity of nicotinic acid was measured with a precise automated adiabatic calorimeter over the temperature rang from 79 to 368 K. No thermal anomaly or phase transition was observed in this temperature range. A solid-to-solid transition at T-trs = 451.4 K, a solid-to-liquid transition at T-fus = 509.1 K and a thermal decomposition at T-d = 538.8 K were found through the DSC and TG-DTG techniques. The molar enthalpies of these transitions were determined to be Delta(trs)H(m =) 0.81 kJ mol(-1), Delta(fus)H(m) 27.57 kJ mol(-1) and Delta(d)H(m) = 62.38 kJ mol(-1), respectively, by the integrals of the peak areas of the DSC curves.

THE RADIATION STABILITY OF PERFLUOROALKOXY RESIN

By examining the changes in melting temperature, heat of fusion, tensile strength and ultimate elongation at 150-degrees-C, and weight loss, radiation effects on perfluoroalkoxy resins (PFA) were investigated. The results show that at the temperatures used here the predominant effect caused by radiation on PFA is degradation of the molecular weight. The radiation stability is much better than that of polytetrafluoroethylene, however.

Conjugate Model for Heat and Mass Transfer of Porous Wall in the High Temperature Gas Flow

Heat and mass transfer of a porous permeable wall in a high temperature gas dynamical flow is considered. Numerical simulation is conducted on the ground of the conjugate mathematical model which includes filtration and heat transfer equations in a porous body and boundary layer equations on its surface. Such an approach enables one to take into account complex interaction between heat and mass transfer in the gasdynamical flow and in the structure subjected to this flow. The main attention is given to the impact of the intraporous heat transfer intensity on the transpiration cooling efficiency.

Effect of coal-over-coal reburn on furnace temperature and heat flux distributions in 1 MW tangentially fired furnace

The furnace temperature and heat flux distributions of 1 MW tangentially fired furnace were studied during coal-over-coal reburn, and the influences of the position of reburn nozzle and reburn fuel fraction on furnace temperature and heat flux distributions were investigated. Compared with the baseline, the flue gas temperature is 70–90 C lower in primary combustion and 130–150 C higher at furnace exit, and the variations of the flue gas temperature distributions along furnace height are slower. The temperature distribution along the width of furnace wall decreases with the increase of the relative furnace height. In the primary combustion zone and the reburn zone, the temperature and heat flux distributions of furnace wall are much non-uniform and asymmetric along the width of furnace wall, those of furnace wall in the burnout zone are relatively uniform, and the temperature non-uniformity coefficients of the primary combustion zone, the reburn zone and the burnout zone are 0.290, 0.100 and 0.031, respectively.

Effect of Heat Treatment Temperature on the Catalytic Performances of PtRu/C Catalysts for Methanol Electro-Oxidation

Non-ionic surfactant Triton X-100 was used as a stabilizer to prepare PtRu/C catalysts for methanol oxidation reaction (MOR). The cyclic voltammogram was used to investigate the catalytic activity for MOR of different PtRu/C catalysts. TG-DTA, EDX, XRD, XPS and TEM were Used to characterize the composition, structure and morphology of the as-prepared PtRu/C catalysts. It is found that the heat treatment plays a crucial role in the particles size, particles distribution of the PtRu/C catalysts and the oxidation state of platinum. The results show that 350 degrees C is an optimum heat treatment temperature. The as-synthesized catalyst heat-treated at this temperature exhibits the best catalytic performance for MOR.

Variation of crystallographic parameters in PEEKK with heat treatment temperature

Using the wide-angle X-ray diffraction method, the variation of crystallographic parameters of poly(aryl ether ether ketone ketone) (PEEKK) has been studied in different heat treatment temperatures. All the reflections and their intensities as well as their Miller indices are presented in detail according to an orthorhombic system. The investigation indicates that the unit cell parameters a, b, c and the unit cell volume V systematically decrease with increasing heat treatment temperature. This variation is interpreted by the change of conformation of polymer molecular chains during thermal treatment. The results calculated from the formula of degree of crystallinity (W-c,W-x) for PEEKK, which was derived based on X-ray scattering intensity theory and the graphic multipeak resolution method, are compatible with the density measurement (W-c,W-d) and calorimetry (W-c,W-h) values. (C) 1997 Elesevier Science Ltd.

Low temperature specific heat and thermal stability of Fe-B ultrafine amorphous alloy particles

Fe-B ultrafine amorphous alloy particles (UFAAP) were prepared by chemical reduction of Fe3+ with NaBHO4 and confirmed to be ultrafine amorphous particles by transmission electron microscopy and X-ray diffraction. The specific heat of the sample was measured by a high precision adiabatic calorimeter, and a differential scanning calorimeter was used for thermal stability analysis. A topological structure of Fe-B atoms is proposed to explain two crystallization peaks and a melting peak observed at T=600, 868 and 1645 K, respectively.

Energy conversion in shape memory alloy heat engine - Part II: Simulation

In this paper, a theoretical model proposed in Part I (Zhu et al., 2001a) is used to simulate the behavior of a twin crank NiTi SMA spring based heat engine, which has been experimentally studied by Iwanaga et al. (1988). The simulation results are compared favorably with the measurements. It is found that (1) output torque and heat efficiency decrease as rotation speed increase; (2) both output torque and output power increase with the increase of hot water temperature; (3) at high rotation speed, higher water temperature improves the heat efficiency. On the contrary, at low rotation speed, lower water temperature is more efficient; (4) the effects of initial spring length may not be monotonic as reported. According to the simulation, output torque, output power and heat efficiency increase with the decrease of spring length only in the low rotation speed case. At high rotation speed, the result might be on the contrary.

Effects of heat-treatment processes on the electroless Ni-B coating and its natural aging mechanism

A Ni-B coating was prepared with EN using potassium borohydride reducing agent. The as-plated micro-structure of the coating was confirmed from XRD to be a mixture of amorphous and supersaturated solid solution. Three kinds of phase transformation were observed from the DSC curve. Different from the previous works, the formation of Ni4B3 and Ni2B was found during some transformation processes. The key factors which influence the variation of micro-hardness and micro-structure in deposits are the formation, the size and amount of Ni3B, Ni4B3 and Ni2B. Aging of the deposits treated under some heat treatment conditions occurred at room temperature. Changes of the micro-hardness indicated aging phenomena evidently. the natural aging phenomena are concerned with various kinds of decomposition of borides, especially with Ni4B3 phase. The extent of natural aging depends on the formation and the quantity of Ni(4)B3 and Ni2B.

Heat-Transfer Study of External Superheater of CFB Incinerator

The heat transfer coefficients for horizontally immersed tubes have been studied in model internally circulating fluidized bed (ICFB) and pilot ICFB incinerators. The characteristics in the ICFB were found to be significantly different from those in a bubbling bed. In ICFB, there is a flowing zone with high velocity, a heat exchange zone, and a moving zone with low velocity. The controllable heat transfer coefficients in ICFB strongly depend on the fluidized velocity in the flowing zone, and also the flow condition in the moving zone. The heat exchange process and suitable bed temperature can be well controlled according to this feature. Based on the results of experiments, a formulation for heat transfer coefficient has been developed. These results were applied to an external superheater of a CFB incinerator with a 450 degreesC steam outlet in a waste-to-energy pilot cogeneration plant of 12 MW in Jiaxing City, China.

Determination of Proper Processing Conditions of Material Surface Heat Treatment Through Finite Element Method

A two-dimensional model has been developed based on the experimental results of stainless steel remelting with the laminar plasma technology to investigate the transient thermo-physical characteristics of the melt pool liquids. The influence of the temperature field, temperature gradient, solidification rate and cooling rate on the processing conditions has been investigated numerically. Not only have the appropriate processing conditions been determined according to the calculations, but also they have been predicted with a criterion established based on the concept of equivalent temperature area density (ETAD) that is actually a function of the processing parameters and material properties. The comparison between the resulting conditions shows that the ETAD method can better predict the optimum condition.

Three-Dimensional Modeling of Heat Transfer and Fluid Flow in Laminar-Plasma Material Re-Melting Processing

Modeling study is performed concerning the heat transfer and fluid flow for a laminar argon plasma jet impinging normally upon a flat workpiece exposed to the ambient air. The diffusion of the air into the plasma jet is handled by using the combined-diffusion-coefficient approach. The heat flux density and jet shear stress distributions at the workpiece surface obtained from the plasma jet modeling are then used to study the re-melting process of a carbon steel workpiece. Besides the heat conduction within the workpiece, the effects of the plasma-jet inlet parameters (temperature and velocity), workpiece moving speed, Marangoni convection, natural convection etc. on the re-melting process are considered. The modeling results demonstrate that the shapes and sizes of the molten pool in the workpiece are influenced appreciably by the plasma-jet inlet parameters, workpiece moving speed and Marangoni convection. The jet shear stress manifests its effect at higher plasma-jet inlet velocities, while the natural convection effect can be ignored. The modeling results of the molten pool sizes agree reasonably with available experimental data.