Wet‐Spun Stimuli‐Responsive Composite Fibers with Tunable Electrical Conductivity

Wet‐spun stimuli‐responsive composite fibers made of covalently crosslinked alginate with a high concentration of single‐walled carbon nanotubes (SWCNTs) are electroconductive and sensitive to humidity, pH, and ionic strength, due to pH‐tunable water absorbing properties of the covalently crosslinked alginate. The conductivity depends on the material swelling in humid atmosphere and aqueous solutions: the greater the swelling, the smaller is the electrical conductivity. The covalently crosslinked fibers reversibly deform during the swelling/shrinking. In the swollen state, the fibers are less conductive, while they return to the same level of conductivity after shrinking. This unique reversible change of electroconductivity of the SWCNT‐alginate fibers is due to the elastic deformation of the alginate network in the area of electrical contacts between SWCNT bundles arrested in the alginate matrix. Fibers of this kind can be used as a simple, robust, disposable, and biocompatible platform for electrotextiles, biosensors, and flexible electronics in biomedical and biotechnological applications.     

Hydrogenation-Disproportionation in Samarium–Cobalt Ferromagnetic Alloys Based on Sm2(Co,Fe, Cu,Zr)17

By methods of differential thermal analysis and X-ray phase analysis, we investigate the processes of hydrogenation, disproportionation, desorption, and recombination and solid hydrogenation, disproportionation, desorption, and recombination in Sm_18.6Co_46.1Fe_27.1Cu_5.9Zr_2.3 commercial ferromagnetic alloy in the temperature range 293–1175 K and in the pressure interval from 5 to 4 MPa. By the method of differential thermal analysis, in the interval 293–1175 K, we recorded phase transformations at 680 K (formation of hydride), 937 K (disproportionation), and 1034 K. Desorption-recombination takes place in four stages with maximum hydrogen release at 405, 640, 724–840, and 900 K. Conventional hydrogenation-disproportionation results in formation of samarium hydride, solid solution of cobalt-iron, and an unidentified phase. In the case of solid hydrogenation-disproportionation, we detected another unidentified phase showing itself only in one peak. We performed phase analysis of the intermediate products of interaction. Desorption-recombination leads to renewal of the main initial phase, and heating of the alloy in hydrogen under initial pressure 0.1 MPa results in homogenization of the material.     

Hydrogen-induced phase transformations in Sm-Co alloy under the action of ultrasound

By the method of X-ray phase diffraction analysis, we study specific features of the action of ultrasound with a frequency of 44 kHz on the interaction of an alloy based on SmCo₅ (SmCo₃ is an impurity) with hydrogen at pressures of 200–500 kPa and temperatures lower than 1223°K under the conditions of hydrogenation and disproportionation. It is shown that at 473 and 773°K, the impurity phase transforms into unidentified products. At 913°K, the alloy partially disproportionates into SmH_x and Co. The degree of disproportionation increases as a result of holding at 913°K. Above 1173°K, we identify SmCo₅, SmH_x, and Sm₂Co₁₇. The ultrasonic treatment accelerates the hydrogen-induced phase transformations. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 71–75, September–October, 2007.     

High hydrogen content super-lightweight intermetallics from the Li–Mg–Si system

The existence of Li-rich super-lightweight intermetallics in the Li–Mg–Si ternary system has attracted attention for high capacity hydrogen storage materials. The hydrogenation properties of the alloys were studied by thermogravimetric analysis, differential scanning calorimetry in H₂ atmosphere and X-ray diffraction. The Li-rich alloy absorbs the highest amount of hydrogen (8.8% w/w for Li₇₀Mg₁₀Si₂₀), while the Mg-rich alloy (Li₃₀Mg₄₀Si₃₀) absorbs 6.0% w/w H₂ and shows the first experimental evidence for LiMgH₃ formation with LiNbO₃-type structure during hydrogenation.     

A masked process for the industrial production of buried contact solar cells on multi‐crystalline silicon

This paper reports on the development of a masked process for the production of buried contact solar cells on multi‐crystalline silicon. The process results in high efficiencies, and only includes steps that would be feasible in an industrial environment. We report here on different mask candidates and on the importance of hydrogenation with the new process. Using the developed process, we produced 111 large area (12 × 12 cm²) cells and achieved an average cell efficiency of 16·2%. The best cell had an efficiency of 16·9%, a V_oc of 616 mV, a J_sc of 35·0 mA/cm² and a fill factor of 78·3%. Copyright © 2008 John Wiley & Sons, Ltd.     

Specific Features of Phase Transformations in Lanthanum–Nickel–Aluminum Alloys under the Action of Hydrogen

By the methods of differential thermal and X-ray phase diffraction analyses, we study the interactions in LaNi_{5 – x} Al _x –H₂ systems with x = 1.0 and 1.5 at temperatures varying from the room temperature to 920°C under an initial pressure of hydrogen of up to  5.0 MPa. The temperature of disproportionation is equal to 555 and 535°C for the compounds with aluminum content x = 1.0 and 1.5, respectively. The original phase decomposes into LaH _x and Ni₃Al. At temperatures above 800°C, we observe the onset of recombination of the original phase leading to the formation of a compound with double-spaced structure. The products of disproportionation of the LaNi₄Al compound, i.e., La(Ni, Al)₅, LaH _x , Ni₃Al, and an unknown phase, recombine in a vacuum at 215°C with hydrogen release and the formation of one or several unknown phases. The products of disproportionation of the LaNi_3.5Al_1.5 compound, i.e., LaH _x , Ni₃Al, and an unknown phase, recombine in a vacuum at 150, 230, and 580°C with hydrogen release and the formation of the original phase.     

HDDR Process and Hydrogen-Absorption Properties of Didymium–Aluminum–Iron–Boron (Dd12.3Al1.2Fe79.4B6) Alloy

We investigate the interaction of hydrogen with the alloy of the Dd–Al–Fe–B system containing (in wt. %) 28.6% Dd, up to 0.5% Al, 1.1% B, and the rest Fe. At an initial hydrogen pressure of 1.0 MPa, hydride with a hydrogen content of 0.5 wt. % is formed. Hydrogen adsorption is accompanied by an increase in the lattice constants (a grows by 1.4% and c does by 1.1%) under a total volume increase of 4.1%. According to the kinetics of hydrogen adsorption, the duration of a full saturation by hydrogen is 3–5 h at an initial gas pressure of 0.1–0.2 MPa. Under heating in the hydrogen medium, the alloy disproportionates at a temperature of 1003 K. X-ray diffraction data indicate that the ferromagnetic phase disproportionates into didymium hydride DdH _x [a = 0.5443(2) nm, -Fe (a = 0.2865(1) nm) and a = 0.5112(8) nm, c = 0.423(2) nm] and iron boride Fe₂B. Heating of the products of disproportionation in vacuum to a temperature of 1123 K results in the recombination of the initial ferromagnetic phase.