Search Results

You are looking at 1 - 7 of 7 items for

  • Author or Editor: E. Karmazsin x
  • All content x
Clear All Modify Search

Abstract  

In a microwave study a program was designed for thermal regulation. This software allows different types of regulations: P, PI, PD or PID (proportional integration derivation). Results obtained with PID and PI regulation for different previous linear heating schedules (1 deg·s−1 and 0.15 deg·s−1) imposed on a polymer sample (DGEBA/3DCM) up to 280°C and more are reported. Mathematical resolution of thermal laws applied to the sample permits the regulation constants (T i,T d andG s) to be linked to the physical features of the polymer. A method used to calculate: the reflexion constant of the wave on the polymer, ρ and the diminution factor, α is presented.

Restricted access

The metal matrix composites (MMC) being of very high interest for the aerospace industry, particularly to build up thermal-structural components, it is important to have available methods which are easy and simple to conduct for characterization of the mechanical strength of the material.

Restricted access

Simultaneous measurements of variations in magnetic and dilatometric properties were successfully used to detect the phase transition occurring during the thermal treatment of iron(III) oxide microcrystals. The increase of the compacting pressure, i.e. the increase of the interparticular number, favours the irreversibleγα transition. An unusual phase of iron(III) oxide, different from theγ-phase, has been unambiguously demonstrated. Its stability seems to be improved by the surface energy excess due to the highly-divided state.

Restricted access

Abstract  

This work presents the modelling of heat transfer in a polymer sample submitted to a microwave field in the quartz column of a dilatometer surrounded by vacuum to avoid convection. The temperature rise is studied in transient state by the finite element method. It is assumed that a uniform and constant heat production is maintained in the entire volume of the sample. It is shown that it is possible to design the set composed of the sample and of the column to achieve a nearly uniform temperature in the whole volume of the sample while its temperature is raised from 20 to 250°C at a heating rate of 5 deg·min−1.

Restricted access

Abstract  

Molybdenum-dioxide samples were produced by reduction of MoO3 in flowing H2. The chlorination kinetics of the pure crystalline MoO2 and samples containing a mixture of Mo-oxides were studied by thermogravimetry, using gaseous CCl4 as chlorinating agent. The initial samples and the chlorinated residues were investigated by XRD and BET methods, as well. The pure molybdenum-dioxide sample was remarkably less reactive than the partially reduced non-stoichiometric molybdenum-oxides or MoO3. The characteristic sigmoid shape of the TG curves were explained by the difference in the reactivity of molybdenum-oxides and by the change of the specific surface area during chlorination. The observed reaction order ofn=0.5 suggests a fast, reversible dissociative adsorption of CCl4 before the volatilization step. For samples of low specific surface area activation energies of 123 and 97 kJ·mol−1 were obtained, and the kinetic curves could be well fitted by an Avrami-Erofeev equation. For sample of much higher specific surface area a diffusion controlled reaction (E a=52 kJ·mol−1) was supposed, and the kinetic model of contracting spheres could be applied.

Restricted access
Restricted access

The chlorination kinetics of pure vanadia was studied via isothermal thermogravimetric measurements, with CCl4, CoCl2 and Cl2 as chlorinating agents. At temperatures where chemical control was predominant, apparent activation energies of 77, 48 and 126 kJ: mol−1 were obtained for chlorination by CCl4, COCl4 and Cl2, respectively. For interpretation of the conversion vs. time curves in the whole conversion range, a non-uniform particle size distribution was assumed, where the reacting solid phase was considered to be composed of thin plates of different thicknesses. With this model, a fairly good correspondence was obtained between the measured and calculated kinetic curves. Selected thermodynamic calculation data on the V2O5 + CCl4, V2O5 + COCl2 and V2O5 + Cl2 systems are presented.

Restricted access