Monitoring real‐time curing of epoxies in situ using single‐sided NMR

Automated optimization of spatial resolution for single-sided NMR

Single-sided NMR instruments utilize inhomogeneous magnetic fields with strong gradients to nondestructively probe physical properties of materials. The sensitive region of this type of magnet is often a thin slice above the magnet's surface; measuring planar samples with high spatial resolution requires coplanarity between the sensitive region of the magnet and the sample region of interest. We developed an algorithmic approach to position flat samples coplanar with the magnet's sensitive region. The efficient and objective positioning process utilizes an adjustable stage that offers control over three degrees of freedom, and the optimal position for each sample is found with a quadtree algorithm. We show this algorithm is effective for positioning samples with various relaxation behaviors. We report resolution values that describe position optimization, acquisition constraints, and final spatial resolution for each sample. Measurements after optimized positioning had appropriate spatial resolution to distinguish physical regions of layered samples with different physical properties, namely, relaxation behavior. Our algorithmic positioning process can be implemented for planar samples in research and industrial settings to enhance spatial resolution of single-sided NMR measurements.

A Study on Temperature Distribution within HVDC Bushing Influenced by Accelerator Content during the Curing Process

Power transmission technology plays an important role in energy sustainability. Bushing is an indispensable type of equipment in power transmission. In production, the accelerator changes the temperature distribution during the curing process, influencing the formation of defects and thus the safety output of renewable energy. In this study, uncured epoxy resin samples with different accelerator contents were prepared and measured by differential scanning calorimetry (DSC). The obtained heat flow curves were analyzed for curing kinetics. Then, the curing process of large length–diameter ratio bushings was simulated by using the finite element method combined with a curing kinetics model, transient Fourier heat transfer model, and stress–strain model. The study reveals that the curing system can be established by the Sestak–Berggren autocatalytic model with different accelerator contents. The overall curing degree and the maximum radial temperature difference of the capacitor core tend to increase and then decrease with the accelerator content. This is mainly attributable to the rapid exotherm excluding the participation of some molecular chains in the reaction, resulting in permanent under-curing. As the accelerator content increases, the strain peak decreases and then increases. This paper provides guidance for the comprehensive evaluation and manufacturing of the low-defect capacitor cores of large-size high voltage direct current (HVDC) bushings.

Perspectives in process analytics using low field NMR

Low field NMR is a powerful analytical tool which creates an enormous added value in process analytics. Based on specific applications in process analytics and perspectives for low field NMR in form of spectroscopy, relaxation, diffusion, and imaging in quality control, diverse applications and technical realizations like spectrometers, time domain NMR, mobile NMR sensors and MRI will be discussed.