Efficient X-ray generation of Sm2+ in nanocrystalline BaFCl/Sm3+: a photoluminescent X-ray storage phosphor

Efficient X-ray generation of relatively stable Sm2+ centers is observed in nanocrystalline Sm3+-activated BaFCl, as prepared by a one-step wet chemical reaction. The conversion efficiency is approximately 50,000 times higher than that in microcrystalline BaFCl/Sm3+ prepared at 900 degrees C. The Sm2+ centers, and hence the radiation dose, can be directly monitored by the narrow photoexcited 5DJ-7FJ f-f luminescence lines. The relatively high efficiency of Sm2+ generation appears to be directly linked to the particle size.     

Investigation of stress-concentration factors in tensile strips

A photoelastic and a numerical investigation has been carried out to determine the stress-concentration factors at the edge of a central circular hole in a tensile strip for different ratios of hole diameter to width of the strip. The photoelastic data and the numerical results indicate that the stress-concentration factor at the minimum cross-sectional area tends to a value of two if the ratio of the hole diameter to the strip-width approaches a value of one.     

Adjustment of Heating Rate for Maximum Resolution in TG and TMA (MaxRes)

Conventional thermogravimetric analysis (TG) uses constant heating rates to determine decomposition rates of a material and compositional analysis. Often, the decomposition steps can not be separated clearly enough due to parallel or consecutive reactions. If the reaction rates and the respective activation energies are enough different the TG resolution can be much enhanced by lowering the heating rate during the decomposition steps. The automated discrete adjustment of the heating rate is controlled by a set of parameters, such as threshold values, waiting times and rate factors. This technique, called MaxRes, allows for faster compositional analysis without loss of resolution. The same technique is also applicable to thermomechanical analysis (TMA) if time/temperature dependent events such as softening are to be separated. This revised version was published online in July 2006 with corrections to the Cover Date.     

A new state of aggregation?

The DSC curve of succinonitrile shows a melting peak at approximately 60°C with the very small heat of fusion of 47 J/g. Further investigations in the low temperature range result in an additional exotherm at ?60°C. On heating there are the two corresponding endotherms repeatably. We postulate a so called plastic crystalline mesophase between the two thermal effects.     

Metal Complexes with Macrocyclic Ligands. Part XXVII. Cu2+-promoted hydrolysis of carboxylic- and phosphonic-acid esters in the side chain of tetraazamacrocycles

The X-ray structures of the Cu²⁺ complexes of 1,4,8,11-tetraazacyclotetradecane derivatives with an ethylpro-pionate and diethylphosphonate group, 5 and 6 , respectively, indicate that the metal ion is pentacoordinated by the four N-atoms of the macrocycle and one O-atom. In the case of 5 , it is the carbonyl O-atom of the carboxylate group, whereas for 6 it is the phosphonyl O-atom of the phosphonate group. The hydrolysis kinetics of the functional group in the Cu²⁺ complexes with the 1,4,8,11-tetraazacyclotetradecanes 3 – 6 have been measured by pH-stat and stopped-flow techniques. The rate law for the hydrolysis of the carboxylates 3 – 5 is proportional to the complex concentration and to [OH^?] up to pH 13, whereas that of the phosphonate 6 is proportional to [OH^?] up to pH 11.5, becoming independent of [OH^?] at pH > 11.5. The mechanisms of these two reactions are discussed, considering the possibility of an intra- or an intermolecular OH^? attack and the results of the X-ray structure analyses.     

Expansion and Shrinkage of Fibers: Load- and temperature modulated TMA measurements temperature calibration of fiber attachments

The thermal behavior of a drawn PET fiber has been investigated by thermomechanical analysis, TMA, and by differential scanning calorimetry, DSC. Above the glass transition temperature of 79°C, the fiber shrinks to a maximum of 8% of the initial length. Temperature modulated TMA enabled the separation of the thermal expansion from the overlapping shrinkage during the first heating and to calculate the expansivity, _e and the shrinkage coefficient, _s, independent of each other. Young's modulus, E, was measured by TMA with modulation of the tensile stress. Hence, it was possible to record the behavior of _e, _s and E during the structural changes by combining both modulations in a single measurement.A new technique was developed to calibrate the sample temperature. With this, accurate control of the modulated temperature of the specimen was achieved, independent of the changing heating rate.This revised version was published online in November 2005 with corrections to the Cover Date.     

Metal Complexes with Macrocyclic Ligands. Part XXVIII.. Structures and stabilities of the Cu2+ complexes with 1,4,7-triazacyclononane-1-acetic acid

The potentiometric study of the complexation of 1,4,7-triazacyclononane-l-acetic acid ( 1 ) with Cu²⁺ (I = 0.5 (KNO₃), T = 25°) indicates the presence of the species [Cu( 1 )], [Cu( 1 )OH], [Cu( 1 )₂], and [(Cu( 1 ))₂OH], the stability constants of which are determined. The two complexes [Cu( 1 )]ClO₄ and [(Cu( 1 )₂)OH]ClO₄ were also characterized by X-ray structure analysis. In both cases, the Cu²⁺ ion is in a distorted square-pyramidal arrangement, penta-coordinated by the three N-atoms of the macrocycle, an O-atom of the carboxylate, and an additional O-atom either from a second carboxylate or from an OH^?, acting as a bridge between two metal centres.