I.N. Beckman

STUDY OF NATURAL AND ION EXCHANGED VERMICULITE BY EMANATION THERMAL ANALYSIS, TG, DTA AND XRD

Emanation thermal analysis (ETA), thermogravimetry, DTA and XRD were used in thermal characterization of natural vermiculite (Santa Olalla, Huelva, Spain) and of Na+- and - exchanged vermiculite samples during heating in air in the range 25-1100°C. A good agreement between the results of these methods was found. Changes in the radon release rate measured by ETA, which reflected the decrease and collapse of the interlayer space after the release of water as well as the formation of new crystalline phases were evaluated using a mathematical model. The model used for the evaluation was found suitable for the quantitative characterization of microstructure changes during in situ conditions of heating of vermiculite samples.

Use of nonporous polymeric flat-sheet gas-separation membranes in a membrane-liquid contactor: experimental studies

Flat-sheet non-porous asymmetric poly(vinyltrimethylsilane) (PVTMS) membranes and composite membranes comprising a dense layer of polydimethylsiloxane/polyphenylsilsesquioxane (PDMS/PPSQ) block copolymer were evaluated for low-temperature bubble-free deoxygenation of water flowing in a two-channel countercurrent liquid-membrane contactor. A novel large-scale three-channel flowing-liquid-membrane module (selective membrane valve), designed for gas separation, is also described. The system comprised PVTMS or PDMS/PPSQ non-porous membranes which acted as gas-permeable barriers. A membrane system (SMV) in which pure water formed a flowing liquid membrane was evaluated to control hydrogen transfer rates. The liquid flowing along the turbulence-promoter spacers between the membranes reduced liquid-film resistance. The overall mass-transfer coefficients were found to be a function of the liquid flow rate. The liquid-film resistance controlled the rate of gas transfer in such membrane contactors.

Emanation Thermal Analysis: Ready to fulfill the future needs of materials characterization

The paper reviews the actual state of the development and use of emanation thermal analysis (ETA). Examples of its recent applications are presented. The advantages of ETA in the microstructure characterization of materials under in situ conditions of their heat treatment are outlined.

Theory of Emanation Thermal Analysis: XI. Radon diffusion as the probe of microstructure changes in solids

The theoretical background for the use of radon diffusion as a probe of microstructure changes in solids is given. The high sensitivity of the emanation thermal analysis (ETA) in the study of solid state processes especially interactions taking place on surfaces and in the near surface layers is described. The increasing sensitivity of the method towards bulk processes with rising temperature is theoretically shown. The background considerations to be used in the mathematical modeling of temperature dependences of the radon release from solids on heating (i.e. simulated ETA curves) are presented. Various models for radon diffusion and various functions describing the annealing of structure irregularities, which served as diffusion paths for radon, were used in the modeling. It was shown, that ETA is able to characterize microstructure changes in the surface layers of the thickness from several nanometers to several micrometers.

Gas separation processes in membrane absorber

Abstract The possibility of combining absorption and membrane gas separation processes in one integrated system is considered. Theoretical models for gas transport phenomena in membrane absorbers of different configurations are presented. A selectively factor higher than 3000 was observed in experiments on a CO 2 /CH 4 gas mixture separation, using a laboratory membrane absorber with polvinyltrimethylsilane asymmetric membranes and a solution of monoethanolamine in water as an absorbent.

Separation of gas mixtures in unsteady-state conditions

Abstract The prospects for the application of unsteady-state boundary conditions at the membrane inlet for increasing the selectivity of gas separation are discussed in this paper. The phenomena occurring upon passage of a concentration pulse and two-gas-component penetrant concentration waves through the membrane have been investigated. It has been shown that pulsed supply of the mixture to be separated at the membrane inlet increases the separation coefficients by a factor of several orders owing to differences in the diffusion coefficients of the gas mixture components in the membrane. Sinusoidal boundary conditions at the membrane inlet allow filtration of the amplitude of the total output oscillations from the signal of the component with a low diffusion coefficient (in this case the membrane acts as a frequency filter), which can be employed for increasing the selectivity of the sensors. The proposed techniques are exemplified by separation of the He/CO 2 gas mixture on a polymeric polyvinyltrimethylsilane (PVTMS) membrane.

Integrated membrane systems for gas separation in biotechnology: potential and prospects

Integrated non-porous membrane systems were applied for microbial combustible gas separation processes. Methane/CO2 mixtures of various concentrations from methane fermentation processes (biogas) were separated using a membrane-separation complex of permabsorber type into individual components of technical grade (more than 95% purity). In experiments with three-component mixtures, using a selective membrane valve with various liquid carriers, all the gases of interest (H2, CH4 and CO2) were obtained at greater than 90% purity in one separation step. The perspectives for the further application of non-porous membrane separating devices for various gaseous mixtures from different microbial processes are discussed.

Theory of emanation thermal analysis: IV. Influence of inertia of the apparatus on the form of the ETA curve and reconstruction of the true form of the ETA curve during thermally stimulated inert gas release

Abstract Factors influencing the response of the apparatus for emanation thermal analysis are discussed and the ETA computed curves accounting for the various factors are demonstrated. The influence of inertia of the ETA apparatus is demonstrated on model short time pulses as well as on ETA curves obtained during thermally stimulated inert gas release. Examples of the distortion of ETA curves when using different inert gases are given. A method for the reconstruction of the true ETA curve, based on the determination of the apparatus response to a “one second model pulse” is suggested. This method has other applications and may be used not only for ETA but also, for example, for evolved gas analysis curves. A practical example of the reconstruction of an ETA curve is given which was obtained with polypropylene foil at the following conditions: heating rate 4°C min−1, the temperature range from −196 to + 400°C.

Emanation thermal analysis study of synthetic gibbsite

Emanation thermal analysis (ETA) was used for thermal characterization of microstructure changes taking place during heating of synthetic gibbsite sample in argon in the range of 25–1200°C. Microstructure development and the increase of the surface area under in-situ conditions of the sample heating were characterized. The increase of the radon release rate from 130–330°C monitored the increase of the surface area due to the dehydration of Al(OH)3. During heating of the sample in the range 450–1080°C the ETA results characterized the annealing of surface and near surface structure irregularities of intermediate products of gibbsite heat treatment. The mathematical model for the evaluation of the ETA experimental results was proposed. From the comparison of the experimental ETA results with the model curves it followed that the model is suitable for the quantitative characterization of microstructure changes taking place on heating of gibbsite sample.

Thermal behaviour of silicagel investigated by emanation thermal analysis

Abstract The thermal behaviour of two different silicagel samples (PORASIL A, S = 300 m 2 g −1 , Waters, U.S.A., and PRAGOSIL, S = 600 m 2 g −1 , Nuclear Research Institute, Czechoslovakia) have been characterized by means of the emanation thermal analysis during heating in air at the constant heating rate. The temperature interval of the silicagel stability (950 – 1000 °C corresponds to the relaxation of the silicagel) was established.