Search Results

You are looking at 21 - 30 of 137 items for :

  • "Thermochemistry" x
  • Refine by Access: All Content x
Clear All

Abstract  

The flexibility of the internal structures of solids, both crystalline and amorphous, is a result of the freedom of the displacement of their elements, without disturbance of the continuity of the structure as a whole. This article discusses peculiarities of solids with flexible structures. The effects of flexibility in the thermal reactions of the creation of new compounds in the internal structure of solids, and the phase transitions, are considered. Flexibility is indispensable for random amorphous structure formation. The glass transition effect is a consequence of the high flexibility of the structure of glasses.

Restricted access

Abstract  

The copper(II) complex of 6-benzylaminopurine (6-BAP) has been prepared with dihydrated cupric chloride and 6-benzylaminopurine. Infrared spectrum and thermal stabilities of the solid complex have been discussed. The constant-volume combustion energy, Δc U, has been determined as −12566.92±6.44 kJ mol−1 by a precise rotating-bomb calorimeter at 298.15 K. From the results and other auxiliary quantities, the standard molar enthalpy of combustion, Δc H m θ, and the standard molar of formation of the complex, Δf H m θ, were calculated as −12558.24±6.44 and −842.50±6.47 kJ mol−1, respectively.

Restricted access

The hydrated rare earth orthophosphates LnPO4 ·xH2O (Ln=La-Dy) contain zeolitic water in the structural channels, which is released reversibly up to 300°. The thermal stabilities of the hydrates depend upon the nature of the Ln atom. The dehydration temperature decreases with decreasing ionic radiusr of Ln3+, according to the general equationθ=(r−a)/b (whereθ is the DSC and/or DTG dehydration peak temperature, anda andb are empirical constants depending on the experimental conditions).

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: V. Ovchinnikov, E. Sagadeev, L. Lapteva, L. Khasieva, M. Alikberov, E. Sitnikova, I. Antipin, I. Stoikov, and A. Konovalov

Abstract  

The enthalpies of vaporization of different classes of phosphorylated alcohols and amines were determined from their enthalpies of solution in hexane and carbon tetrachloride. The enthalpies of specific (hydrogen-bond) interaction with the solvents (chloroform and pyridine) of derivatives containing X-H groups (X=O or N) in the α-position to the P=O group were determined. The results were explained in terms of the spatial structure of such compounds.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: M. R. Bissengaliyeva, L. P. Ogorodova, L. V. Mel'chakova, and M. F. Vigasina

Abstract

Thermal and thermochemical investigations of natural hydroxyl-bearing copper sulfate Cu3SO4(OH)4—antlerite have been carried out. The stages of its thermal decomposition have been studied employing the Fourier-transform IR spectroscopy. The enthalpy of formation of antlerite from the elements Δf H m o (298.15 K) = (−1750 ± 10) kJ mol−1 has been determined by the method of oxide melt solution calorimetry. Using value of S m o (298.15 K), equal to (263.46 ± 0.47) J K−1mol−1, obtained earlier by the method of adiabatic calorimetry, the Gibbs energy value of Δf G m o (298.15 K) = (−1467 ± 10) kJ mol−1 has been calculated.

Restricted access

Abstract  

The mixing and melting enthalpy of the binary system nitrocellulose+2,6-dinitrotoluene was determined using the DSC method. The mixing enthalpy of the components was calculated. At the melting temperature the maximum value of the mixing enthalpy for the mole fractionx w26DNT=0.607 is equal H M max= −3.41 kJ mol−1. Measurements of the melting process (second measurement) were conducted after a storage period of several days at room temperature. Analysis of the melting peaks shows that the melting process of 26DNT takes place in pores of the micro-fiber and bulk outside the fibers. In the case of a mass fraction of x w26DNT>0.9 the melting process takes place in the bulk, which suggests that in the case of such concentrations separation of the micro-fibers occurs.

Restricted access

Abstract  

A method of gelation enthalpy determination of nitrocellulose (NC)+s-diethyldiphenylurea (Centralite 1, C1) binary system was elaborated using the change of Centralite 1 melting enthalpy in the mixture. The heats of C1 melting together with gelation and dissolution of NC fibres were determined by DSC calorimetric methods. A sharp maximum of the gelation enthalpy for C1 mole fraction x C1 max =0.555 suggests that the complex is very stable and one partly nitrated anhydroglucose ring is interacting with about 1.25 C1 molecules. The gelatinization enthalpy maximum equals
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\bar H_{max}^M$$ \end{document}
=−4.59 kJ mol−1.
Restricted access