Aspects of reproducibility and stability for partial cure of epoxy matrix resin

Partial cure of thermosets is a promising approach to enhance manufacturing possibilities of reinforced and unreinforced polymers. If partial cure is taken into consideration as a genuine process parameter, novel manufacturing technologies can be developed by exploiting the specific properties of incomplete polymer networks. A main concern in this context is to control the kinetic reaction avoiding inhomogeneous or instable degrees of cure. Based on a combination of numerical simulations and experiments, a methodology is presented that enables a systematic assessment of the reproducibility and stability of partial cure. Special attention is paid to the interaction of thermal boundary conditions and the cure kinetic of thick samples as well as the storability of partially cured resin under different conditions. Guidelines for cure cycle selection, mold design, and storage are derived. The possibility to use complex multistep cure schedules and extended storage periods is demonstrated for an unmodified noninhibited epoxy resin. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals Inc. J. Appl. Polym. Sci. 2020 , 137, 48342.     

Structural response of A2TiO5 (A = La,Nd, Sm,Gd) to swift heavy ion irradiation

Different compositions of orthorhombic A₂TiO₅ (A = La, Nd, Sm, Gd) have been irradiated with swift Xe ions (1.47 GeV). Systematic analysis of the structural modifications induced by ion track formation was completed using transmission electron microscopy, synchrotron X-ray diffraction, and Raman spectroscopy. Significant radiation-induced amorphization occurred, but the size of the amorphous regions within the tracks decreased as smaller cations (higher Z) occupied the A-site. This decrease in the amorphous domain size is attributed primarily to epitaxial recrystallization of a disordered phase at the outer edge of the tracks, the stability of which is related to the ratio of the ionic radii of the A- and B-site (B = Ti) cations. While similar ion track recrystallization phenomena have been observed in pyrochlores of varying composition, A₂TiO₅ is unique in that the disordered phase is not a high-temperature polymorph, suggesting kinetic control of the radiation-induced transformation.     

Preparation and properties of B6O/TiB2-composites

B₆O/TiB₂ composites with varying compositions were produced by FAST/SPS at temperatures between 1850 and 1900 °C following a non-reactive or a reactive sintering route. The densification, phase and microstructure formation and the mechanical and thermal properties were investigated. The comparison to an also investigated pure B₆O material showed that the addition of TiB₂ in a non-reactive sintering route promotes the B₆O densification. Further improvement was obtained by sintering reactive B–TiO₂ mixtures which also results in materials with a finer grain size and thus in enhanced mechanical properties. The fracture toughness was significantly improved in all composites and is up to 4.0 MPa m^1/2 (SEVNB) and 2.6–5.0 MPa m^1/2 (IF method) while simultaneously a high hardness of up to 36 GPa (HV_0.4) and 28 GPa (HV₅) could be preserved. The high temperature properties at 1000 °C of hardness, thermal conductivity and CTE were up to 20 GPa, 18 W/mK and 6.63 × 10^?6/K, respectively.     

Gamma-induced Positron Spectroscopy (GiPS) at a superconducting electron linear accelerator

A new and unique setup for Positron Annihilation Spectroscopy has been established and optimized at the superconducting linear electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (Germany). The intense, pulsed (26 MHz) photon source (bremsstrahlung with energies up to 16 MeV) is used to generate positrons by means of pair production throughout the entire sample volume. Due to the very short gamma bunches (< 5 ps temporal length), the facility for Gamma-induced Positron Spectroscopy (GiPS) is suitable for positron lifetime spectroscopy using the accelerator’s radiofrequency as time reference. Positron lifetime and Doppler broadening Spectroscopy are employed by a coincident measurement (Age-Momentum Correlation) of the time-of-arrival and energy of the annihilation photons which in turn significantly reduces the background of scattered photons resulting in spectra with high signal to background ratios. Simulations of the setup using the GEANT4 framework have been performed to yield optimum positron generation rates for various sample materials and improved background conditions.     

Single Sampling Point Detection of Frequency Modulated Terahertz Waves

We present single sampling point detection of the amplitude and phase of frequency modulated continuous wave terahertz radiation. Employing a conventional photomixing setup with a precise wavelength control allows for rapid scan rates in the kHz regime. Two application examples demonstrate the potential of this approach for real time monitoring of samples’ thicknesses and transmittances.     

Full-text prior art and chemical structure searching in e-journals and on the internet – A patent information professional’s perspective

In depth analysis of non-patent literature prior art is a crucial step in checking patentability of new inventions and validity of competitor’s patents, since by patent law relevant subject matter disclosed in non-patent literature is as important as any patent document. E-journal articles, as well as any scientific and technical information published on the web are an important source of prior art that is very often insufficiently covered and indexed by commercial databases. This article reviews search and display capabilities of e-journal search sites of different publishers and hosts, as well as their value for full-text prior art analysis to enhance retrieval from commercial databases. Moreover, current developments and future prospects of chemical structure searching both in e-journals and on the internet are discussed.     

Driving concepts for bundled ultrasonic linear motors

Several positioning tasks demand translatory drive instead of rotary motion. To achieve drives that are capable, e.g., to drive the sunroof of a car or to lift a car’s window, multiple miniaturized motors can be combined. But in this case many other questions arise: The electromechanical behavior of the individual motors differs slightly, the motor characteristics are strongly dependent on the driving parameters and the driven load, many applications need some extra power for special cases like overcoming higher forces periodically. Thus, the bundle of motors has to act well-organized and at last controlled to get an optimized drive that is not oversized and costly.