Microwave-hydrothermal synthesis and characterization of Co-VSB-5 microporous framework

The crystallization of cobalt metal incorporated microporous nickel phosphate framework, Co-VSB-5, with initial Ni/P gel ratio of about 1.0, 1.5 and 2.5, respectively, has been investigated under microwave-hydrothermal conditions. Attempts are made to incorporate metal ion in the range of 2.5–10 atomic % in the VSB-5 framework having varied Ni/P ratio by varying gel pH. The prepared samples were characterized by means of X-ray diffraction, scanning electron microscopy, UV-visible diffuse reflectance spectroscopy (UV-visible DRS), and nitrogen adsorption–desorption measurements at 77 K. The prepared samples are found to be crystalline in nature. The initial gel pH is found to be critical for crystallization of nickel phosphate framework with varied Ni/P ratio. Like wise, isomorphic substitution is favored with an increase in Ni/P gel ratio. The results for UVDRS demonstrated the incorporation of transition metal ions in the octahedral position for nickel sites in VSB-5 framework. The textural properties, such as surface area and micropore volume, of the Co-VSB-5 samples crystallized from initial Ni/P gel ratio of 2.5, were found to lower than those crystallized from initial Ni/P gel ratio of 1.5 at equivalent metal content level. Interestingly, crystallization of framework having micro-mesoporosity is favored with an increase in Ni/P gel ratio. Furthermore, scanning electron microscopy revealed the crystallization of samples with rod shaped morphology irrespective of the nature of metal ion and its concentration from gel comprising of Ni/P of 1.5 and 2.5. The results of UV-Vis DRS demonstrated the incorporation of transition metal ions in the octahedral position for nickel sites in VSB-5 framework.     

Powder Synthesis,Sintering Kinetics,and Nickel-Activated Pressureless Sintering of Ti3AlC2

This work aims to produce Ti₃AlC₂ powder via a new route that consists of two-step processes, and studies the sintering kinetics and effect of nickel addition on the pressureless sintering behavior of Ti₃AlC₂ powder. Ti₃AlC₂ powder of about 5 μm was produced using TiC_x and Al powder. Relative density of about 97.6% was achieved using 1 wt% nickel as a sintering aid. Ti₃AlC₂ powder shows two different activation energies (AE) of sintering, 347 ± 4 and 183 ± 8 kJ/mol at lower and higher temperature ranges, respectively. These AE were found to be matching closely with the AE of Al diffusion in the Ti–Al binary system reported in the literature, indicating that the sintering of ternary Ti₃AlC₂ ceramic was controlled by the diffusion of Al atoms. When nickel is added, Ni reacts with Ti₃AlC₂, tends to decompose it, and forms Ni-based compounds and liquid phase. Nickel was found to suppress the grain growth of Ti₃AlC₂ significantly. Sintered sample exhibited a Vickers hardness of 3.2 GPa at a load of 10 N.     

Deep learning-based hybrid reconstruction algorithm for fibre instance segmentation from 3D x-ray tomographic images

3D x-ray tomography is a powerful scanning technique used for generating images of complex fibre structures. A novel machine-learning algorithm to identify and separate individual fibres using 3D images is proposed in this article. The developed four-step hybrid 3D fibre segmentation algorithm involves deep-learning aided semantic segmentation that slices 3D images to create 2D images for fibre extraction, elliptical contour estimation combined with the marker-controlled watershed algorithm for separating fibres from the background area, identifying individual fibres through 3D reconstruction, and, lastly, the 3D object refining approach based on outlier object detection and replacement. The proposed methodology is implemented on a real-time sample of nylon fibre bundle under compression and its 3D x-ray image volume to validate the performance. The results show its superior performance compared to off-the-shelf image processing algorithms in terms of precision, that is, with a validation accuracy greater than 90%, and efficiency, that is, preventing the need for a huge data set and reducing the complexity.     

Laser Treatment of Sintered Silicon Carbide Surface for Enhanced Hydrophobicity

In this study, laser treatment of sintered SiC surfaces is carried out to enhance the surface hydrophobicity. Morphological and metallurgical changes of the treated surfaces are evaluated using optical and scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction (XRD). Microhardness and fracture toughness are measured using indentation tests. The residual stresses present are determined using the XRD technique. The wetting characteristics of the treated surfaces are assessed through contact angle measurements. It is found that the laser-treated surfaces consist of fine grooves and pillars and that the resulting surface roughness enhances the surface hydrophobicity. The fracture toughness of the treated surface is reduced possibly because of the microhardness increase at the surface. The residual stress formed in the surface region is on the order of 1.8 GPa, and it is compressive.     

Prediction of the plastic viscosity of self-compacting steel fibre reinforced concrete

Micromechanical constitutive models are used to predict the plastic viscosity of self-compacting steel fibre reinforced concrete (SCFRC) from the measured plastic viscosity of the paste. The concrete is regarded as a two-phase composite in which the solid phase is suspended in a viscous liquid phase. The liquid matrix phase consists of cement, water and any viscosity modifying agent (VMA) to which the solids (fine and coarse aggregates and fibres) are added in succession. The predictions are shown to correlate very well with available experimental data. Comments are made on the practical usefulness of the predicted plastic viscosity in simulating the flow of SCFRC.     

The Real Area of Contact in Polymeric Magnetic Media—II: Experimental Data and Analysis

Electrical-contact-resistance and two-beam optical-interference techniques were employed to measure the real area of contact of magnetic tapes. The former technique does not work well due to significant contributions from tunnel effect and multimolecular insulating films; the latter provides shape and size distribution of asperity-contact areas.

Experiments were conducted at a pressure range of 13.8 kPa and 1.38 MPa. Normal pressure had strong dependence on both the real area of contact and the number of contact spots, and weak dependence on the mean asperity-contact diameter. This is in agreement with the theory. In the case of the two tapes tested in the pressure range, the real area of contact varied from 0.5 to 25 percent. The mean asperity-contact diameter and number of contact spots ranged from 6 to 13 μm and 200 to 2300 per mm², respectively. The mean real pressure was in the range of 2 to 8 MPa. The real area of contact increased with an increase in the ambient temperature. Surface roughness had strong influence on the real area of contact, as expected. Tapes subjected to pressure and temperature for a period resulted in a growth of the real area of contact. When the tapes were unloaded, a significant portion of the deformation was not recovered.