Der Einfluß des Kerbradius auf die Kollaps- und die Initiierungsgrenztemperatur schweißbarer Baustähle

Kollapsgrenztemperatur T_gy, Initiierungsgrenztemperatur T_i. Einfluß des Kerbradius bei verschiedenen Probengrößen, werkstoffmechanische Zusammenhänge. Einfluß des plastischen Spannungskonzentrationsfaktors, der Spaltbruchfestigkeit und der Streckgrenze auf T_gy. Abschätzung des Einflusses des Kerbradius und der Probengröße auf den plastischen Spannungskonzentrationsfaktor mit Hilfe der Fließlinientheorie und der Spannungen entsprechend dem HRR-Feld. Bedeutung der Ergebnisse für die Sicherheitsanalyse. T_i als Grenztemperatur für die Anwendung elastisch-plastischer Bruchmechanik hinsichtlich Initiierung und Wachstum stabiler Anrisse. Ermittlung von T_i mit gekerbten Proben, insbesondere bei Schweißverbindungen. Einfluß des Kerbradius auf Initiierungskennwerte.     

Zur zerstörungsfreien Prüfung des Holzes durch Schwingungsversuche

Ohne Zusammenfassung     

Switchable glazing with a large dynamic range in total solar energy transmittance (TSET)

Modern, energy-saving buildings incorporate large areas of highly insulating glazing. The resulting solar gains lead to major savings in heating energy during winter, but protection against overheating in summer is also needed. Usually this problem is solved by using mechanical shading devices, with the disadvantages of high cost and low durability.The work on switchable glazing at Fraunhofer Institute for Solar Energy Systems, in cooperation with industrial partners, aims to present new and viable alternatives. Two types of switching layers, which are quite different in their structure and function, but are similar in having a large dynamic range in TSET, are being investigated—gasochromic and thermotropic.Gasochromic windows are actively switched between a clear and a coloured (but image-preserving) state by alternately introducing strongly diluted O₂ and H₂ gases. In contrast to classic electrochromic configurations, only one tungsten oxide film with a very thin catalyst coating is needed. At present, prototype windows with an area of 1.1×0.6 m² are being produced by sputtering. Careful adjustment of the layer structure, the gas concentration and its flow velocity is needed to obtain the desired switching rate. Homogeneous colouring of the whole area within seconds has been achieved. In addition to information on the colouring kinetics, the paper also discusses system aspects of these windows.Thermotropic layers switch reversibly and automatically, from a clear state with high transmittance to a milky white state with high diffuse reflectance, when their temperature rises. Depending on the composition of the material, the switching temperature can be chosen in the range needed. The measured optical properties of glass laminates with a thermotropic layer are presented. These are combined with the measured values for further panes to calculate the characteristic data for thermotropic insulated glazing units. The results are compared with those measured on a 1.1×1.65 m² prototype window. Stability results are also included.The effect of the two different types of switchable glazing on building energy savings is explored for a residential building model, using the TRNSYS building energy simulation program.     

High-Yield Synthesis of B4C/BN Ceramic Materials by Pyrolysis of Polymeric Lewis Base Adducts of Decaborane(14)

Polymers of type [B₁₀H₁₂˙diamine]x (diamine=H₂NCH₂CH₂NH₂, (CH₃)₂NCH₂CH₂NH₂, (CH₃)₂NCH₂CH₂N(CH₃)₂, etc.) have been found to be useful ceramic precursors. In a stream of argon, their pyrolysis gives B4C/BN; in a stream of ammonia, BN.     

Determination of carboxyl endgroups and comonomers in poly(ethylene terephthalate) with hydrazine

On complete hydrazinolysis of poly(ethylene terephthalate), terephthalomonohydrazide is formed from carboxyl-end terephthaloyl residues in a quantity equivalent to the content of carboxyl endgroups in the polymer. The compound is separated from the reaction mixture by ion exchange and determined photometrically [epsiv;₂₄₀ in 0.1 N HCl = 16,700 (1000 cm²/mole)]. A COOH determination carried out in this way is endgroup specific and, unlike titration, is not subject to interference by ionogenic fiber additives. Aromatic comonomers with acidic substituents (e.g., 5-sulfoisophthalic acid) in chemically modified, cationically dyeable poly(ethylene terephthalate) are determined simultaneously with the carboxyl endgroups by the same analytical method. In this case, the terephthalamonohydrazide and 5-sulfoisophthalodihydrazide are separated by ion exchange, and the difference in their spectral behavior is used for quantitative determination with the aid of a two-component analysis: where c₁c₂ = concentration of terephthalomonohydrazide and 5-sulfoisophthalodihydrazide, respectively; and D₂₄₀ D₂₁₂ = optical density at 240 and 212 nm, respectively. The content of carboxyl endgroups in polyether esters poly(p-(2-ethyleneoxy)-benzoate), is determined on the basis of the p-(β-hydroxyethoxy)benzoic acid [epsiv;₂₅₈ in 0.1 N HCl = 16,100 (1000 cm²/mole)] liberated from carboxyl-end monomer units by hydrazinolysis. For copolyether esters with p-(β-hydroxyethoxy)benzoic acid as a comonomer, the contents of carboxyl-end terephthalic acid and p-(β-hydroxyethoxy)benzoic acid are determined simultaneously with the acid of a spectrophotometric twocomponent analysis: where c₂, c₂ = concentration of terephthalomonohydrazide and p-(β-hydroxyethoxy)-benzoic acid, respectively; and D₂₄₀, D₂₅₈ = optical density at 240 and 258 nm, respectively.     

Stereoisomeric flavour compounds LXXVI: direct enantioseparation, structure elucidation and structure-function relationship of 4-tert-butyl-α-methyldihydrocinnamaldehyde

 Using enantioselective gas chromatography and heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin (DIAC-TBDMS-β-CD) as the chiral stationary phase, the direct enantioseparation of 4-tert-butyl-α-methyldihydrocinnamaldehyde was achieved. The threshold values and odour characteristics of the enantiomers were investigated by enantioselective gas chromatography/olfactometry. In order to elucidate stereochemical features, the carbonyl-function was oxidized to the corresponding acid and diastereomeric amides were generated with (S)-2-amino-2-phenyl-ethanol [L(+)-α-phenylglycinol] as the enantiopure reagent. After separation and isolation by high-performance liquid chromatography, absolute configurations were deduced from X-ray structure elucidation of a pure stereoisomer. Amide cleavage, reduction and selective oxidation yielded the enantiomers of 4-tert-butyl-α-methyldihydrocinnamaldehyde. Received: 7 October 1996 / Revised version: 18 November 1996     

IDENTIFICATION,QUANTIFICATION AND DISTRIBUTION OF PAC-METABOLITES,HETEROCYCLIC PAC AND SUBSTITUTED PAC IN GROUNDWATER SAMPLES OF TAR-CONTAMINATED SITES FROM GERMANY

Four tar-contaminated sites in Germany (Lünen, Castrop Rauxel, Stuttgart and Wülknitz) were investigated and 42 polycyclic aromatic compounds (PAC) were detected in significant concentration ranges including polycyclic aromatic hydrocarbons (PAH), substituted PAC, heterocyclic PAC containing nitrogen, sulphur and oxygen as well as their metabolites. A similar composition and pattern of PAH heterocyclic PAC and metabolites were found in corresponding groundwater samples. Identification and quantification were performed using liquid-liquid extraction and analyses with gas chromatography – electron impact – mass spectrometry. Detailed investigation (in Castrop Rauxel, Germany) showed that the distribution of non-polar compounds can only be detected close to the source of contamination, whereas the distribution of more polar compounds and degradation products is more widespread downstream of an aquifer.