Mechanical properties and densification mechanism of powder-in-tube BaxK1-xFe2As2 superconductors

BaxK1-xFe2As2 (BaK-122) iron-based superconductors (IBSs) have been considered to be promising for high-field applications. The transport J c performance of BaK-122 wires and tapes is continuously enhanced by introducing advanced fabricating methods. The mass density of BaK-122 superconducting core in wires and tapes is important to the transport J c performance and related to the mechanical behavior during preparation. In this work, the mechanical property parameters including Poisson's ratio-density, yield strength-density, and elastic modulus-density of BaK-122 IBS powder were examined via uniaxial compression experiments. The density-dependent mechanical constitutive of BaK-122 was obtained for the first time. The relationship function between density and Vickers hardness of BaK-122 was established as HV0.05=0.0249ρ5.332 based on the numerical simulation of hardness testing, and a method for characterizing the BaK-122 core density was developed. It had been found the sheath materials and preparation method have great influences on the stress state of the BaK-122 core, and then affect the density. The densification mechanism and corresponding improvement method were revealed to provide guidance for preparing high-density BaK-122 wires and tapes. Finally, the generalized relationship between density and the superconducting transport J c was established according to lots of experimental data from multiple BaK-122 samples, which has confirmed the positive correlation of ρcore and J c. We comparatively discussed the various cold-work and heat-treatment processes used in our team for preparing the BaK-122 wires and tapes, and the critical factors affecting the transport performance were summarized.

DEM PARAMETERS CALIBRATION OF MIXED BIOMASS SAWDUST MODEL WITH MULTI-RESPONSE INDICATORS

Taking hybrid biomass sawdust as the material, carry out the simulation calibration experiment with JKR contact model based on DEM principle. The Plackett-Burman factorial experiment is carried out by Design-Expert for 10 related factors. Combined with the steepest climbing test scheme, according to the Box-Behnken experiment, the parameter calibration of the multi-response Indicators is completed. The results are as follows: the Poisson's ratio of hybrid sawdust is 0.30, the density is 399.22kg·m-3, the recovery coefficient between sawdust particles is 0.47, the rolling friction coefficient between sawdust particles is 0.39, and the parameter of surface energy density between sawdust particles (JKR) is 0.29J·m-2. Through the comparative verification experiment, it can be seen that the relative error of the repose angle is 3.41%, and the relative error of the stress-time response curve is less than 6.36%, which verifies the reliability of the calibration method, and provides a theoretical reference for the study of the constitutive characteristics of biomass materials and the densification mechanism.

Densification of Carbon Nanotubes During Growth

Carbon nanotubes are highly attractive for research purposes due to their field emission properties. However, when the nanotubes are vertically aligned on a substrate to form a continuous film, screening effect is observed, which reduces the efficiency. To densify the tubes into bundles and eliminate this screening effect, costly lithography patterning of catalysts and post-growth chemical treatments have been previously reported. In this work, we report a novel, cheap, and reproducible technique of densifying the growth of carbon nanotubes by utilizing a colloidal catalyst and microwave plasma-enhanced chemical vapor deposition. A qualitative investigation was carried out, and a possible densification mechanism was proposed.