Search

An advanced and newly developed severe plastic deformation (SPD) method called accumulative fold-forging (AFF) was applied to produce layered nanostructured MgNi alloys exhibiting superior hydrogen storage capacity. Microstructural developments and storage properties were characterized in depth to correlate the structure and performance of this advanced material. The enhanced hydrogen storage performance of the magnesium-based layered composite material was investigated in comparison to the pristine state by conducting hydrogenation and dehydrogenation testing. It was also shown that the hydrogen uptake and release characteristics can be controlled by adjusting the layered structure or the Mg: Ni stoichiometry ratio. Refining the grain structure of the magnesium alloy down to the nano-scale range (∼400–900 nm) by applying high cycles AFF consolidation to promote creation of multi-million nanometric interfaces led to superior storage performance with a remarkable hydrogen absorption capacity of up to ∼1.425 wt%. X-ray diffraction (XRD) analysis of the hydrogenated products revealed the formation of MgH2 that indicates the dominance of the magnesium matrix for controlling the hydrogen storage behavior of the layered Mg/Ni composite material. Finally, the relationship between the directional hydrogen storage behavior and the induced structural features upon AFF treatment were also established using quantitative characterization and analytical tools.

In this work, MgNi26, MgNi26Mn10, MgNi26Co10 and MgNi26Nd10 alloys were prepared by mechanical alloying (MA) and subsequent spark plasma sintering (SPS). Mechanical alloying leads to a grain refinement and increases the concentration of lattice defects. SPS technology provides a compact material but with high porosity, consequently creating a high internal surface area within the volume of sample. The combination of the MA and SPS techniques produces a promising material in terms of fast hydriding kinetics and a high content of absorbed hydrogen. All samples were electrochemically hydrided in a 6 mol/L KOH solution at 80 °C for 480 min. The microstructures of the alloys were characterized by scanning electron microscopy and energy dispersive spectrometry. The phase compositions were characterized by X-ray diffraction, and the total hydrogen content in the hydrided pellets was measured using an inert gas fusion analyser. The dehydriding process was studied by thermogravimetry and mass spectrometry. The highest total amount of hydrogen was absorbed by the MgNi26Nd10 alloy, nearly 1.8 wt%. The main hydriding product was the binary hydride MgH2. The results of the mass spectrometry analysis reveal a significant reduction in the temperature of hydrogen evolution from magnesium hydride, probably due to the formation of fine microstructures of the hydrogenated alloys and catalytic effect of Ni. The decomposition temperature was reduced by more than 200 °C as compared to the commercial MgH2.

In this study, three binary Mg–Ni alloys were prepared by gravity casting (GC) and mechanical alloying combined with spark plasma sintering (SPS). All samples were subjected to electrochemical hydriding in 6 mol/l KOH at 80 °C for 480 min. The structures and phase compositions of the samples were studied by optical and scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. The concentration of absorbed hydrogen was determined using an optical emission spectrometer with glow discharge for the GC alloys and using a hydrogen analyzer for the SPS alloys. The process of hydrogen evolution was observed by mass spectrometry for SPS alloys. The highest total amount of hydrogen was absorbed by the MgNi26 alloy both for both the GC and SPS alloys. The only hydriding product was MgH 2 in the α- and γ-modification. Compared to commercial powder MgH 2, the decomposition temperature was reduced by more than 200 °C, which can be ascribed to the catalytic effect of Mg 2 Ni and namely to the nanostructured magnesium formed after SPS.

The MgNi26 alloy was prepared by three different methods of gravity casting (GC), mechanical alloying (MA) and rapid solidification (RS). All samples were electrochemically hydrided in a 6 mol/L KOH solution at 80 °C for 240 min. The structures and phase compositions of the alloys were studied using optical microscopy and scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. A temperature-programmed desorption technique was used to measure the absorbed hydrogen and study the dehydriding process. The content of hydrogen absorbed by the MgNi26-MA (approximately 1.3%, mass fraction) was 30 times higher than that of the MgNi26-GC. The MgNi26-RS sample absorbed only 0.1% of hydrogen. The lowest temperature for hydrogen evolution was exhibited by the MgNi26-MA. Compared with pure commercial MgH2, the decomposition temperature was reduced by more than 200 °C. The favourable phase and structural composition of the MgNi26-MA sample were the reasons for the best hydriding and dehydriding properties.

The contribution deals with synthesis and characterization of conductive polypyrrole (PPY), which should be suitable for depositions of thin layers by Matrix Assisted Pulsed Laser Evaporation (MAPLE) method. The samples of doped PPY containing various organic dopants – (i) p-toluenesulfonic acid, (ii) dodecyl-benzenesulfonic acid, (iii) dioctyl-sulfosuccinic acid and (iv) camphorsulfonic acid – were synthesized by polymerization of pyrrole in acidic or neutral solution. Solubility of synthesized PPY and settlement time of PPY particles in water and dimethylsulfoxide – parameters critical for MAPLE method – were investigated. The composition of prepared PPY was verified by FTIR spectroscopy. Conductivity of the polymer in solid state was determined to be in range from σ = 2.6 × 10 −6 S cm −1 to σ = 6.0 × 10 −2 S cm −1 . The optimal material for MAPLE deposition is PPY containing organic dopants (ii)–(iv), dissolved in DMSO matrix (solubility from 4.1% to 6.5% by weight and settlement time 140–240 h).

Thin sensitive layers of polypyrrole (PPY) are deposited onto alumina sensor substrates by matrix-assisted pulsed laser evaporation (MAPLE) technology. The depositions are carried out with the KrF excimer laser from dimethylsulfoxide (DMSO) matrix. After 1-month “ageing” period the complex impedance of prepared sensors is measured in the frequency range from 15 Hz to 10 MHz in following atmospheres: “pure” synthetic air and synthetic air with variable (23% or 90%) relative humidity. The general character of Nyquist diagrams, plots of complex admittance versus frequency, parameters of sensor equivalent circuit and phase-angle sensitivities are then evaluated from the obtained impedance data. While equivalent circuit capacity ( C ) of PPY-based sensors remains from 1.7 to 2.0 pF in all the above-mentioned atmospheres, equivalent circuit resistance ( R ) varies widely from 6 to 140 MΩ, mostly in dependence on surrounding atmosphere humidity. The differences in charge-transport mechanisms between PPY and tin dioxide sensitive layers and also influence of surrounding atmosphere to electric properties of PPY are discussed.

Complexes of metals with organic ligands are known to be widely used materials for active layers of chemical gas sensors. Among these materials especially those containing a system of conjugated double bonds in ligands have suitable properties for gas sensing. This article deals with deposition and characterization of three materials commonly used in detection of oxidizing gases: indium acetylacetonate (InAcAc), nickel phthalocyanine (NiPc) and copper(II) para -tetratolylmethylporphyrine (CuTTMP). The layers are deposited by a non-conventional matrix-assisted pulsed laser evaporation (MAPLE) method. The choice of a proper matrix and investigation of the deposition rate versus energy density dependence are made. Prepared layers are characterized by Raman spectra and also by measuring their responses to oxidizing gases. The best dc-gas-response was exhibited with an InAcAc layer ( S ∼ 10–100 ppb of ozone at 100–160 °C and S ∼ 8–1 ppm of NO 2 at 230 °C).

Thin layers of polypyrrole (PPY) were deposited by MAPLE (Matrix Assisted Pulse Laser Evaporation) technology. The deposition was carried out by KrF excimer laser from water and dimethylsulfoxide matrixes. Ablation thresholds (Fth) were determined to be Fth ~ 0.3 J.cm−2for dimethylsulfoxide matrix and Fth ~ 0.45 J.cm−2for water matrix. The roughness of deposited layers was measured by AFM and their chemical composition was characterized by FTIR spectroscopy. Finally, resistance of sensors with PPY active layer was measured in dependence on working temperature and relative humidity of surrounding atmosphere.

Native and acetylated B-starch was used in biodegradable films after blending with either poly-(e-caprolactone) (PCL) or ethylene vinyl acetate copolymer (EVA). The following mechanical characteristics of prepared films were derived from the stress-strain curves: Young modulus, yield stress, stress-at-break and strain-at-break. Acetylation of starch molecules in the composites reduced the degradation rate in compost. Optical microscopy, combined with the image analysis system NIS-Elements completed with extended depth of focus (EDF) module, was used to study the PCL/starch and EVA/starch films surface morphology during composting. Parameters of the compost used for film exposition were measured.