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Abstract
A method was devised to evaluate latent heats of vaporization from quasi-isothermal isobaric analysis data. The procedure requires the recording of at least two diagrams: one for the investigated liquid, and the other for a standard liquid with a known latent heat of vaporization. Use of the method to determine the heats of vaporization of some alcohols, with water as standard liquid, led to results close to those previously reported in the literature. The main advantage of the procedure consists in the fact that it requires only small amounts of sample (5–10 mg).
Abstract
The thermal analytical study of most hydrophobic and hydrophilic D/L amino acids reveals significant hydropathy index correlation between the presence of water and crystalline amino acids. The TG derivative mass profiles for arginine and lysine (hydrophilic acids) at various time intervals of atmospheric exposure, show two distinct peaks, one between 50 and 60°C (unbound water), and one close to 100°C (bound-like water). The DSC heat-cool profiles for lysine and arginine confirmed the presence of these multiple waters with two heats of vaporization. The absence of these patterns from the TG and DSC for cysteine and phenylalanine (hydrophobic acids) further supports the conclusions.
dipole moment. Water is a polar liquid that can form a hydronium ion (H 3 O + ) and is interactive with hydroxide ion (OH − ). The heat of vaporization, (Δ H v ), is the energy required to change a given quantity of water into its gas phase at
Thermal characterisation of cellulose based materials
Investigation of water content
Summary Natural polymers, as cellulose, with hydrophilic groups such as hydroxyl groups have various strengths of interaction with water. Cellulose is a structurally heterogeneous polymer, consisting of paracrystalline and amorphous domains. Water can interact with the amorphous domains, but it is excluded almost completely from the crystalline regions. The purpose of this study was to estimate the amount of bulk free water in cellulose based materials, as linen, cotton and paper, by measuring the heats of vaporisation. Moreover the amount of free water in oxidised and grafted samples has been determined by DSC and this quantity has been compared with that found in the corresponding native materials. In oxidised cellulose the water content increases with decreasing the degree of crystallinity; the oxidation, being a degradative reaction, modifies the amorphous content in the cellulose. In presence of acrylic grafted polymer, the free water content is reduced and this reduction is related to the grafting yields.
The cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and mercury(II) complexes of diethyldithiocarbamic acid were prepared and their thermal properties determined by TG, DTA, and high temperature reflectance spectroscopy. It was found that the copper(II), nickel(II), and zinc(II) chelates were completely volatile and thus represent a new class of volatile metal chelates. Vapor pressure measurements were made on four of the metal complexes; heats of vaporization ranged from 9.3±0.2 kcal/mole for Na[Co(DDC)3] to 24.2±0.6 kcal/mole for Zn(DDC)2.
. It shows the latent heat of fusion of 1.436 kcal/mol and latent heat of vaporization of 9.717 kcal mol −1 [ 1 ]. During the cooling, water is solidified to ice and the solutes are concentrated in the liquid phase. The ice usually forms
range is consistent, because the activation energy represents the energy required to promote a shift in the case of endothermic transformations and usually is larger than the heat of vaporization. Analysis performed in sealed
Reference diffusivity, m 2 s −1 Δ H st Heat of vaporization, kJ kg w −1 Δ H a Integral heat of adsorption, kJ kg −1
related through the equation: (1) where LHV corresponds to the lower heating value of the dry sample, HHV is the higher heating value, W is the moisture percentage content and H d is the hydrogen percentage of the dry sample. The heat of vaporization
1 Introduction Boiling heat transfer and two-phase flow plays a significant role in many heat exchange systems. Boiling heat transfer mode is an efficient mode among other heat transfer modes, and this is due to the latent heat of vaporization that
