Thermogravimetrische Methode zur Untersuchung der Gleichgewichte Festkörper/Gas und Schmelze/Gas in korrosionschemisch wichtigen Sulfatsystemen

Thermogravimetric method for investigating the solid/gas and melt/gas equilibria in sulphate systems of corrosion-chemical importance The authors describe a micro-thermogravimetric method which permits the determination of the phase zones of sulphate systems as a function of temperature and of the SO₃-partial pressure. At the Me₂SO₄ SO₃ (Me = Na, K) system, the existence limits of the bi-variant melt and the mono-variant equilibria Me₂SO₄(solid)-melt and Me₂SO₄(solid)-Me₂S₂O₇(solid) are determined. Water vapour is dissolved in the melt phases investigated because the existence limits of the latter are modified by the vapour.     

The alimentary ingestion, analysis and biological significance of thiocyanate

A survey is given of the alimentary ingestion, metabolization and elimination as well as of the biological significance of thiocyanate (SCN-) in the mammalian organism. SCN- is an important nutritional factor since it influences essential bodily functions, e.g. immune response. Its analytical determination in vegetable and animal foodstuffs may be considerably affected by the reversible binding of SCN- to protein molecules and by natural products, e.g. amino acids and cyanide, from glycosidic precursors, which interfere with the reaction with bromine. This will be combining paper chromatography with gas chromatography. Except Brassica species which are relatively high in SCN- in glycosidic combination, vegetable foodstuffs contain nearly 0.1-1.3 mg SCN-/kg fresh material; animal foodstuffs, e.g. beef, contains 0.5-0.7 mg SCN-/kg. Balances calculations have shown that in non-smokers the average alimentary ingestion ranges from 1.8 to 5.2 mg SCN-/d.     

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Development of stresses in concrete structures with alkali-silica reactions

The present paper, deals with the development in time of stresses and strains in concrete structures suffering from alkali-silica reaction (ASR). The properties of the concrete are combined with the dimensions of the structure in which the concrete is placed. A geometrical model that permits the determination of stresses and strains is established for concrete. This model is combined with a computer program which is able to calculate the moisture flow into a given structure, and this moisture flow is connected with the development of ASR. The resulting calculation takes into account the dimensions of the structure, the concrete quality, the content of reactive silica and the climate around the structure, as it predicts the strains and stresses developed in concrete structures suffering from ASR. It is shown that, cracks are developed locally around the reacting particles, and it is proposed that most of the cracks that become visible on the surface of a structure originate from the period of construction.

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Resume Cet article traite de la croissance des contraintes et des déformations dansle béton de structure où se développent des réactions silico-alcalines (ASR). Les propriétés du béton sont associées aux dimensions de la construction dans laquelle la béton est mis en place. On a établi un modèle géométrique du béton permettant de déterminer les contraintes et les déformations, combiné avec un programme informatique qui, pour une construction donnée, peut calculer la migration d’eau qui est liée au développement de réactions silico-alcalines. L’ensemble des calculs pour la prédiction, des contraintes et déformations dans les constructions en béton où se développent, ces réactions prend en compte la dimension de la structure, la qualité du béton, la teneur en silice réactive et les conditions ambiantes. On montre que des fissures se produisent localement autour des particules réactives, et on présume que la plupart de celles qui aparaissent à la surface d’une structure remontent à l’époque de la construction.

     

DUST STRANDS IN CYCLONE SEPARATORS AT LOW DUST CONCENTRATION

State of the art in calculating a cyclone separator is the application of the equilibrium theory and taking the formation of dust strands into account as well. The latter process does not depend on particle size mainly. An ideal flow pattern for the formation of dust strands is the so called Dean-vortex: it is being realized favorably in the axial flow cyclone. A dust strand can be produced down to a raw gas concentration C₀ ≈ 10^-5. Then, it is being exhausted through one or few holes in the mantle of the axial cyclone applying bleeding of about 10 % of the volume flow Separating its dust in a bin cyclone and recirculating the binflow gas to the main, axial cyclone completes this high performance cyclone separator. Dimensional analysis shows that the clean gas concentration c₁ mainly depends on the swirl W_tan/w_ax, the raw gas concentration c₀and on Reynolds number. For usual dust conditions a clean gas concentration c₁ ≤ 50 mg/m³ is feasible.     

Raman scattering studies of ultrathin-layer YBa2Cu3O7/PrBa2Cu3O7 superlattices

We present Raman scattering studies ofc-oriented ultrathin-layer superconducting (YBa₂Cu₃O₇) _m /(PrBa₂Cu₃O₇) _n superlattices. For the superlattice with (m=2,n=1) sequence, Raman spectra reveal a new line in the spectral region around 320 cm^?1. It is interpreted as a mode representing a combination of IR optical phonons of the Y-sublayers with an admixture of aB _1g type Raman active vibration in the Pr sublayers. This new line, which is similar to those from the interior of the Brillouin zone of the original lattice, does not exhibit superconductivity-induced self-energy effects, although its counterpart in the pure substance does. No additional line is found in the (m=1,n=2) superlattice in the same region, supporting our interpretation for the (m=2,n=1) sample.     

Effects of Flow Depth on Water Flow and Solute Transport in Furrow Irrigation: Field Data Analysis

Because of field-scale heterogeneity in soil hydraulic and solute transport properties, relatively large-scale experiments are now increasingly believed to be critical to better understand and predict the movement of water and dissolved solutes under field conditions. In this study, five field experiments were conducted on short blocked-end furrows to assess the effects of irrigation water level on water flow and solute transport in furrows. Three experiments were carried out, each of the same duration but with different amounts of water and solutes resulting from 6, 10, and 14 cm furrow water depths, designated as low, moderate, and high water levels, respectively. Two more experiments were performed with the same amounts of applied water and solute and, consequently, different durations, on furrows with depths of 6 and 10 cm of water. Results show that both the water level and the duration play an important role in transporting and distributing water and solutes in the soil profile. A positive correlation was found between water level and infiltrated amount of water or solute. Irrigation/solute application amounts increased with decreasing water level. Water and solutes were both distributed almost vertically (one-dimensionally) for the low water level and short application treatments, while they moved much more two-dimensionally with low and moderate water depths but longer application times. Irrigation with the 14 cm water level and short application time improved the distribution of water and solutes within the soil profiles, while also causing relatively less deep percolation of water and solutes as compared to low and moderate water levels and relatively long duration times.     

Time-dependent permeation of carbon dioxide through a polyimide membrane above the plasticization pressure

The time-dependent permeation behavior of a glassy polyimide is studied above and below the plasticization pressure with carbon dioxide as the permeating gas. The work particularly focuses on the quantification of the slow increase in permeability at feed pressures above the plasticization pressure. Significant differences in permeation behavior were found for membranes with and without permeation history. Introducing the quantity “conditioning time” allows one to compare the results obtained for membranes with different permeation history. The concept of conditioning time furthermore allows one to quantify the aging of a membrane plasticized during previous permeation. © 1995 John Wiley & Sons, Inc.