An isothermal method was applied to measure the thermal
decomposition of reactive solids in a sensitive heat flux reaction calorimeter,
C80. This technique experimentally clarified the decomposition mechanisms
of unstable substances based on the shapes of the heat flow curves, from which
autocatalysis, first-order reaction or pseudo-autocatalytic reaction could
be recognized. Kinetic parameters were derived from the measured data.
In order to investigate relative reactivity of different oxidants in solid-state reactions of pyrotechnic mixtures, thermal
properties of Sn + Sr(NO3)2, Sn + Ba(NO3)2, and Sn + KNO3 pyrotechnic systems have been studied by means of TG, DTA, and DSC methods and the results compared with those of pure oxidants.
The apparent activation energy (E), ΔG#, ΔH#, and ΔS# of the combustion processes were obtained from the DSC experiments. The results showed that the nature of oxidant has a significant
effect on ignition temperature, and the kinetic of the pyrotechnic mixtures’ reactions, and the relative reactivity of these
mixtures was found to obey in the following order: Sn + Sr(NO3)2 > Sn + Ba(NO3)2 > Sn + KNO3.
Authors:B. Arias, C. Pevida, F. Rubiera, and J. Pis
Char particle combustion is the slowest step in the combustion of coal, therefore char reactivity and texture have an important
influence on this process. In this work, two coals were devolatilised in an entrained flow reactor and the chars obtained
were burned under different experimental conditions in order to achieve various degrees of burnoff. Char reactivity was determined
by means of non-isothermal thermogravimetric analysis, and the conversion-time data were evaluated by the random pore model
proposed by Bhatia and Perlmutter. Char texture was characterised by means of N2 and CO2 adsorption isotherms. The surface areas obtained were used to calculate intrinsic reaction rate parameters. It was found
that under chemical controlled conditions, the available surface area during combustion is best represented by the N2 surface area.
Authors:B. Randhawa, Anand Pal Singh, R. Sharma, and P. Bassi
The solid state reactions between ferrous oxalate dihydrate i.e. FeC2O4.2H2O and unsubstituted/ substituted aniline hydrochlorides have been studied. The products [FeCl/oxH/. AN-Cl] have been characterized by elemental analysis, infrared and Mössbauer spectroscopic techniques. The kinetic studies for the reactions have been performed at various temperatures for fixed particle sizes at constant compaction. The following order of reactivity has been observed: unsubstituted > p-substituted > m-substituted o-substituted.
The reactivity of the C6F5X (X=F, Cl, Br, I) molecules following low energy (0–15 eV) electron attachment is studied in the gas phase under single collision
conditions, free molecular clusters and condensed molecules by means of crossed beams and surface experiments. All four molecules
exhibit a very prominent resonance for low energy electron attachment (<1 eV, attachment cross section >10−14 cm2). Under collision free conditions thermal electron capture generates long lived molecular parent anions C6F5X−*. Along the line Cl, Br, I dissociation into X−+C6F5 and X+C6F5-increasingly competes until for X=1 only chemical fragmentation is observed on the mass spectrometric time scale. In free
molecular clusters chemical fragmentation is quantitatively quenched at low energies in favour of associative attachment yielding
undissociated, relaxed ions (C6F5X)−n,n≥1. A further dissociative resonance at 6.5 eV in C6F5Cl is considerably enhanched in clusters. If these molecules are finally condensed on a solid surface, one observes a prominent
Cl− desorption resonance at 6.5 eV. While the quantitative quenching of the chemical reactivity at low energies is due to the
additional possibilities of energy dissipation under aggregation, the enhanched reactivity at 6.5 eV is interpreted by the
conversion of a core excited open channel resonance in single molecules into a closed channel (Feshbach) resonance when it
is coupled to environmental molecules.
Modelingand experimental approaches to study reactive transport across chemical gradients in porous media are presented. Particular emphasis is placed on apurposeful experimental setup to obtain information necessary for model calibration and verification. As example, diffusion tube experiments on the layered acidic jarosite/alkaline coal fly ash system have been carried out using radiotracers 3H+, 22Na+, and 59Fe3+. Such radiotracer diffusion tube experiments provide modelers with reliable information incorporatingsome of the complexities observed in the environment such as local heterogeneities.
Authors:Lisardo Núñez-Regueira, M. Villanueva, and I. Fraga-Rivas
Differential scanning calorimetry was used to study the influence of
an epoxy reactive diluent, vinylcyclohexane dioxide, on the curing reaction
of a polymeric system composed of diglycidyl ether of bisphenol A (n=0) and 1,2-diaminecyclohexane (DCH). Heat evolution
and glass transition temperature, were measured in terms of the added diluent
percentage. Experimental results show that both the curing degree and the
glass transition temperature of the polymeric system decrease with an increase
in the diluent percentage.
Dynamic mechanical analysis of several
samples also showed that Tg
decreases with the increase of diluent percentage, thus corroborating DSC
Authors:Urszula Szeluga, Lidia Kurzeja, and H. Galina
This paper reports on the work carried out to evaluate the frequency dependent viscoelastic properties of epoxy/novolac compositons
modified with a liquid reactive rubber and carbon filler. For epoxy systems modified with elastomer, three typical transitions
were observed: the α-relaxation deeply related to the glass transition of epoxy, the β-transition of epoxy, and the glass
transition of rubber appeared near to the β-relaxation of epoxy resin. Considering an Arrhenius equation, the activation energies
of β-relaxation were estimated. In the region of glass transition and rubbery state the temperature dependence of the shift
factor (αT) was determined through Williams-Landel-Ferry (WLF) equation.
Authors:K. Vessalas, P. Thomas, A. Ray, J. Guerbois, P. Joyce, and J. Haggman
Thermogravimetric (TG) analysis was applied to the characterisation of the pozzolanic reaction in mortars containing the supplementary
cementitious materials (SCMs) pitchstone fines (PF) and fly ash (FA) as partial replacements for Portland cement (PC). TG
analysis was used to determine the proportion of calcium hydroxide (CH) present from the hydration of the PC based on the
dehydroxylation of the CH present in the blended PC-SCM mortars. The consumption of CH indicated that both SCMs underwent
the pozzolanic reaction and that PF was found to compare favourably in its pozzolanic reactivity of FA, the industry and globally
accepted standard artificial pozzolan.
Mixtures of methanol and isopropanol in a ratio (v/v) varying from 91 to 19 have been gamma-irradiated at 77 K and relative yields of trapped electrons have been measured. The reactivity of the trapped electrons towards acetone and uranyl nitrate has been studied at various methanol isopropanol ratios. On the basis of the results, an attempt has been made to assess the relative importance of the reaction of the electron with the solute prior to trapping with respect to the tunnelling reaction of the trapped electron with the solute.