Effect of High-Pressure Torsion on Texture,Microstructure, and Raman Spectroscopy: Case Study of Fe- and Te-Substituted CoSb3

Fe_0.05Co_0.95Sb_2.875Te_0.125, a double-element-substituted skutterudite, was prepared by induction melting, annealing, and hot pressing (HP). The hot-pressed sample was subjected to high-pressure torsion (HPT) with 4 GPa pressure at 673 K. X-ray diffraction was performed before and after HPT processing of the sample; the skutterudite phase was observed as a main phase, but an additional impurity phase (CoSb₂) was observed in the HPT-processed sample. Surface morphology was determined by high-resolution scanning electron microscopy. In the HP sample, coarse grains with sizes in the range of approximately 100 nm to 300 nm were obtained. They changed to fine grains with a reduction in grain size to 75 nm to 125 nm after HPT due to severe plastic deformation. Crystallographic texture, as measured by x-ray diffraction, indicated strengthening of (112), (102) poles and weakening of the (123) pole of the HPT-processed sample. Raman-active vibrational modes showed a peak position shift towards the lower energy side, indicating softening of the modes after HPT. The distortion of the rectangular Sb–Sb rings leads to broadening of Sb–Sb vibrational modes due to local strain fluctuation. In the HPT process, a significant effect on the shorter Sb–Sb bond was observed as compared with the longer Sb–Sb bond.     

Coupling effect of pond ash and polypropylene fiber on strength and durability of expansive soil subgrades: An integrated experimental and machine learning approach

This study explores the coupling effect of pond ash(PA) and polypropylene(PP) fiber to control the strength and durability of expansive soil. The PA is used to chemically treat the expansive soil and PP fiber is adopted as reinforcement against tensile cracking. The sustainable use of PA and PP fiber are demonstrated by performing mechanical(i.e. unconfined compressive strength, split tensile strength and ultrasonic pulse velocity), chemical(p H value, electrical conductivity and calcite content), and microstructural analyses before and after 2 nd, 4 th, 6 th, 8 th and 10 th freezing-thawing(F-T) cycles. Three curing methods with 7 d, 14 d and 28 d curing periods are considered to reinforce the 5%, 10%, 15% and20% PA-stabilized expansive soil with 0.25%, 0.5% and 1% PP fiber. In order to develop predictive models for mechanical and durability parameters, the experimental data are processed utilizing artificial neural network(ANN), in association with the leave-one-out cross-validation(LOOCV) as a resampling method and three different activation functions. The mechanical and durability properties of the PA-stabilized expansive soil subgrades are increased with PP fiber reinforcement. The results of ANN modeling predict the mechanical properties perfectly, and the correlation coefficient(R) approaches up to 0.96.     

Proton microbeam irradiation effects on PtBA polymer

Proton beam lithography has made it possible to make various types of 3D-structures in polymers. Usually PMMA, SU-8, PS polymers have been used as resist materials for lithographic purpose. Microbeam irradiation effects on poly-tert-butyl-acrylate (PtBA) polymer using 20 MeV proton microbeam are reported. Preliminary results on pattern formation on PtBA are carried out as a function of fluence. After writing the pattern, a thin layer of Ge is deposited. Distribution of Ge in pristine and ion beam patterned surface of PtBA polymer is studied using the optical and secondary electron microscopic experimental methods.