Search Results

You are looking at 1 - 8 of 8 items for :

  • "pulse thermal analysis" x
  • Refine by Access: All Content x
Clear All

Abstract  

Pulse thermal analysis (PTA) is based on the injection of a specific amount of gaseous reactant into a carrier gas stream. PTA provides the following advantages compared to conventional TA: (i) quantitative calibration of the mass spectrometric signals allows increasing the sensitivity of TA measurements; (ii) monitoring of gas-solid processes with defined extent of reaction i.e. the reaction can be stopped at any point between pulses, enabling elucidation of the relationship between the composition of the solid and the reaction progress; (iii) simultaneous monitoring of changes in mass, thermal effects, composition and amount of gaseous reactants and products under pulse conditions.

Restricted access

Abstract  

Thermal analysis combined with mass spectrometry was applied to radiocarbon dating procedures (age determination of carbon containing samples) to determine the optimal temperature range for the reduction of CO2 over metallic cobalt of various particle sizes. Experiments were carried out to show the different catalytic activities of cobalt of particle sizes 1, 1–45 and 44 m. The morphology of the cobalt samples and the deposited carbon were investigated. The quantification of CH4 and CO formed during the reduction of CO2 was done by means of pulse thermal analysis.

Restricted access

Abstract  

The formation of CF3-CH2F (HFC-134a) by catalytic hydrodechlorination of CF3-CCl2F (CFC-114a) has been studied utilizing the recent PulseTA technique. Instead of hydrogen as reactant, deuterium was used which facilitates the detection of the reaction products, i.e. the discrimination of various hydrofluorocarbons (HFC), by mass spectrometry. The product composition confirms a reaction mechanism via the carbene CF3-CF. Water traces which are retained in the channel structure of the catalyst interact with chemisorbed deuterium thus explaining the formation of hydrogenated fluorocarbons as well. The obtained results demonstrate the potential of the pulse technique for the investigation of solid state reactions.

Restricted access

Abstract  

The complexity of the processes occurring during cobalt oxalate dihydrate (COD) decomposition indicates that an interpretation of the mechanism based only on the TG curve is of little value. Mass change alone does not allow deeper insight into all of the potential primary and secondary reactions that could occur. The observed mass changes (TG) and thermal effects (DTA/DSC) are a superposition of several phenomena and thus do not necessarily reflect COD decomposition alone. Investigation of the mechanism of decomposition requires the application of different simultaneous techniques that allow the qualitative and quantitative determination of the composition of the gaseous products. Composition of the solid and gaseous products of COD decomposition and heats of dehydration and oxalate decomposition were determined for inert, oxidizing and hydrogen-containing atmospheres. Contrary to previous suggestions about the mechanism of cobalt oxalate decomposition, the solid product formed during decomposition in helium contains not only metallic Comet, but also a substantial amount of CoO (ca 13 mol%). In all atmospheres, the composition of the primary solid and gaseous products changes as a result of secondary gas-solid and gas-gas reactions, catalyzed by freshly formed Comet. The course of the following reactions has been investigated under steady-state and transient conditions characteristic for COD decomposition: water gas shift, Fischer-Tropsch, CO disproportionation, CoO reduction by CO and H2, Comet oxidation under rich and lean oxygen conditions.

Restricted access

, M , Emmerich , WD , Baiker , A 1999 Pulse thermal analysis–a new range of opportunities . J Therm Anal Calorim 56 : 627 – 637 10.1023/A:1010177300149 . 20. Maciejewski , M

Restricted access

Abstract  

Thermal analysis combined with mass spectrometry was applied to radiocarbon dating procedures (age determination of carbon-containing samples). Experiments carried out under an oxygen atmosphere were used to determine carbon content and combustion range of soil and wood samples. Composition of the shell sample and its decomposition were investigated. The quantification of CO2 formed by the oxidation of carbon was done by the application of pulse thermal analysis. Experiments carried out under an inert atmosphere determined the combustion range of coal with CuO as an oxygen source. To eliminate a possible source of contamination in the radiocarbon dating procedures the adsorption of CO2 by CuO was investigated.

Restricted access

Abstract  

Evidence of the existence of a high-limit degradation temperature for polymers is reported. At this high-limit temperature, the rate of polymer thermolysis exceeds the reaction rate predicted by the Arrhenius law by many orders of magnitude. An explanation is proposed for the observed behaviour, based on the disappearance of intermolecular interactions. For the study of degradation reactions under high-limit temperature conditions, new methods of fast (pulsed) thermal analysis are presented. The investigated samples, as very thin films, are brought into tight contact with a hot moving metal surface. Under these conditions, the heating rate exceeds 104 deg/s, allowing estimation of accompanying decomposition rates for heating times of the order of 0.01 s.

Restricted access

quadrupole mass spectrometer QMS 403 C Aeolos and the device for pulse thermal analysis PulseTA. The measurement technique included the following steps: preparation of a sample by the standard quartering method, placement of the 10–20 mg sample in

Restricted access