Papers by Alex A Volinsky
Coatings
Hydroxyapatite coatings were deposited for 1, 2, and 3 h on NiTi substrates using plasma-assisted... more Hydroxyapatite coatings were deposited for 1, 2, and 3 h on NiTi substrates using plasma-assisted radio frequency sputtering. The matrix consisted of NiTi B2 and NiTi B19’ phases and Ti2Ni, Ni3Ti, and Ni4Ti3 intermetallic compounds. The surface coating was monoclinic hydroxyapatite. Increasing the deposition time to 3 h made it possible to form a dense hydroxyapatite layer without visible defects. The phase contrast maps showed that the coating consisted of round grains of different fractions, with the smallest grains in the sample deposited for 3 h. The wettability tests showed that the coating deposited for 3 h had the highest surface energy, reflected in the proliferation density of the MCF-7 cell line.
MethodsX, 2015
Procedure to establish full contact between the sample and the 1 mm diameter cylindrical flat pun... more Procedure to establish full contact between the sample and the 1 mm diameter cylindrical flat punch tip to measure polydimethylsiloxane (PDMS) mechanical properties using the Hysitron TriboIndenter is described. This procedure differs from the standard automated indentation because each indent has to be performed manually after establishing full contact with the sample surface. Incomplete contact happens because of the sample tilt with respect to the flat punch surface and results in incorrect elastic modulus values. Automated indentation results in incorrect values of the elastic modulus due to initial incomplete contact between the flat punch and the PDMS sample surface, caused by the tilt, and using the unloading slope, which is affected by viscoelastic soft polymer deformation. Correct procedure requires establishing the full contact between the tip and the sample. This is achieved by moving the tip into the sample in 1-2 mm increments, up to 40-80 mm maximum combined displacement, until the loading stiffness no longer increases. The elastic modulus is calculated from the loading stiffness and the diameter of the flat punch, instead of the unloading stiffness, which is larger due to viscoelastic unloading. After establishing the full contact, other mechanical testing can be conducted.
Engineering Failure Analysis, 2020
Scanning and transmission electron microscopy was used to characterize quantity, pattern, size, a... more Scanning and transmission electron microscopy was used to characterize quantity, pattern, size, and distribution of microstructure and precipitated phases in T91 steel exposed to high temperature in the subcritical unit superheater of a specific power plant. The materials were mechanically and electrochemically tested using a universal testing machine and an electrochemical workstation. The structure and performance of the original material and after the long-term service time were compared. The hardness and strength of T91 steel initially increased before they decreased during long-term service. It took 4000 h for the T91 steel to transform from the original to the service state, forming (Cr, Fe, V, Mo) 23 C 6 multi-component mixed phase, which delayed or inhibited the growth of the M 23 C 6-type carbides during the long-term high-temperature service. The MX-type carbide formation would pin dislocations and increase the strength. When the service time was between 4000 and 130,000 h, the carbide coarsening was obvious, and the effect of solid solution strengthening was reduced, the dislocation density was decreased, reducing the material's strength below the original state level. Electrochemical tests showed that longer service time degraded corrosion resistance of the T91 steel.
International Heat Treatment and Surface Engineering, 2014
High-carbon-chromium bearing steel is often annealed in a sealed pot with a small amount of charc... more High-carbon-chromium bearing steel is often annealed in a sealed pot with a small amount of charcoal without physically contacting it. The charcoal is supposed to provide non-contact protection by simultaneously preventing oxidation and decarburisation during spheroidising. However, the actual effects of charcoal have not been thoroughly studied previously. In this paper, the effect of the non-contact charcoal protection is investigated. It remarkably reduces oxidation, but significantly increases decarburisation, compared with ambient air annealing. The oxide and decarburised layers with the non-contact charcoal protection are thicker than those after annealing in a sealed pot without charcoal protection and in ambient air. Experimental results have been analysed based on thermodynamics, and an improved spheroidising process for the bearing steel is suggested.
Journal of Alloys and Compounds, 2017
Magnetite (Fe 3 O 4) nanoparticles have been readily prepared via a one-step solution combustion ... more Magnetite (Fe 3 O 4) nanoparticles have been readily prepared via a one-step solution combustion synthesis (SCS) method by designing a simple airless device: a beaker with perforated rubber plug could not only separate the outside air but also release the gases generated during the combustion reaction, which could ensure an air free condition in the SCS process. The whole process did not involve any toxic or unavailable reagents, and could be finished in a few minutes by its self-generated energy derived from the redox reaction between glycine (fuel) and ferric nitrate (oxidizer). Innovatively, the combustion reaction mechanism, morphology and microstructure, phase composition and magnetic properties of SCS products in relation to the glycine have been systematically investigated. The results revealed that with the increasing molar ratio (f) of glycine to ferric nitrate, the combustion mode varied from selfpropagating combustion to smouldering combustion and the average grain size of SCS products increased in nanometer scale. On the contrary, the iron oxidation state of SCS products decreased with the increase of f value, and the oxide phase changed from a-Fe 2 O 3 to Fe 3 O 4 and then to FeO sequentially. It was noteworthy that when f ¼ 0.7, we could easily obtain pure phase Fe 3 O 4 nanoparticles with the highest saturation magnetization of 89.17 emu g À1 and small average grain size of 57.3 nm, which would have great potential for various applications, such as magnetic drug delivery, magnetic data storage and novel ferrofluids.
Physics Letters A, 2017
Edge effects on mechanical properties of armchair molybdenum disulfide nanoribbons were investiga... more Edge effects on mechanical properties of armchair molybdenum disulfide nanoribbons were investigated using first principles calculations. The edge eigen-stress model was applied to explain the relaxation process of forming molybdenum disulfide nanoribbon. Edge effects on surface atoms fluctuation degree were obtained from each fully relaxed nanoribbon with different width. Changes of the relaxed armchair molybdenum disulfide nanoribbons structure can be expressed using hexagonal perimeters pattern. Based on the thickness change, relaxed armchair molybdenum disulfide nanoribbons tensile/compression tests were simulated, providing intrinsic edge elastic parameters, such as eigen-stress, Young's modulus and Poisson's ratio.
Materials Science and Engineering: A, 2014
The effects of quenching and tempering on the microstructure evolution and bake hardening (BH) be... more The effects of quenching and tempering on the microstructure evolution and bake hardening (BH) behavior of both ferrite and dual phase steels were investigated. The C-Mn steels were heated to the soaking temperature, quenched in water and then tempered in the 100-500 1C range. After prestraining, the baking treatment (180 1C for 20 min) was carried out to measure the BH values. It was found that increased quenching temperature reduced the BH value. Furthermore, the BH value turned to be negative when the quenching temperature exceeded 670 1C and 710 1C for the steels annealed at 800 1C and 900 1C, respectively. The ferrite aging and the martensite tempering played key roles in the bake hardening behavior during the tempering process. In the present study, three stages were identified during tempering of the above steels: (1) the relief of residual stresses in the ferrite; (2) the precipitation of carbides in both ferrite and martensite; (3) the dissolution of carbides in the ferrite. The BH values of both ferrite and dual phase steels had a complex variation with the tempering temperature. After an apparent increment, the BH value reduced, and then was slightly enhanced when the tempering temperature increased from 25 1C to 500 1C.
Metallurgical and Materials Transactions A, 2017
Two-and three-dimensional pore evolutions along with nitrogen diffusion behavior in nuclear graph... more Two-and three-dimensional pore evolutions along with nitrogen diffusion behavior in nuclear graphite were studied using thermogravimetric analysis, X-ray computed tomography, scanning electron microscopy, and the Brunauer-Emmett-Teller method. Calculated nitrogen diffusion activation energy was approximately 2.5 kJAEmol À1 . Stable weight loss of graphite specimens increased with temperature, primarily due to more escaped nitrogen from the graphite matrix. Fewer nano-pores and more micro-pores were formed because of the nano-pore coalescence. At 873 K (600 °C), graphite microstructure evolution might be induced by temperature and mild oxidation. Before being placed into high temperature gas-cooled reactors (HTGRs), porous nuclear graphite should be subjected to vacuum at 573 K to 673 K (300 °C to 400 °C) to minimize 14 N in the pores and 14 C generated during operation of HTGRs.
Journal of Applied Polymer Science, 2014
A macroscopic compression test utilizing a simple custom-built instrument was employed to measure... more A macroscopic compression test utilizing a simple custom-built instrument was employed to measure polydimethylsiloxane (PDMS) elastic modulus. PDMS samples with varying crosslinking density were prepared with the elastomer base to the curing agent ratio ranging from 5 : 1 to 33 : 1. The PDMS network elastic modulus varied linearly with the amount of crosslinker, ranging from 0.57 MPa to 3.7 MPa for the samples tested. PDMS elastic modulus in MPa can be expressed as 20 MPa/PDMS base to curing agent ratio. This article describes a simple method for measuring elastic properties of soft polymeric materials. V
Procedia Materials Science, 2014
The surface topography and potential changes of the 2205 duplex stainless steel due to tensile de... more The surface topography and potential changes of the 2205 duplex stainless steel due to tensile deformation were investigated by the in situ scanning Kelvin probe force microscopy. The slip bands generated by tensile deformation could decrease the surface potential. The surface roughness and the work function increased with deformation in the elastic region and reached the maximum values at the yield point. In the plastic deformation stage, the surface roughness continued to increase, while the work function decreased and stabilized. The surface roughness is the major factor affecting the work function during elastic deformation, while dislocations and slip bands play the key role during plastic deformation.
Electrochimica Acta, 2014
Mesoporous Cr 2 O 3 with a high specific surface area of 162 m 2 g −1 is prepared by the solution... more Mesoporous Cr 2 O 3 with a high specific surface area of 162 m 2 g −1 is prepared by the solution combustion method. The mesoporous Cr 2 O 3 has a sheet structure, which consists of nanoparticles with an average size of 20 nm. As an anode electrode material for rechargeable lithium-ion batteries, the mesoporous Cr 2 O 3 nanoparticles display enhanced electrochemical performance. Stable and reversible capacity of 480 mA h g −1 after 55 cycles is demonstrated. The enhanced electrochemical performance of the Cr 2 O 3 can be attributed to the high surface area and morphological characteristics of mesoporous materials.
Bulletin of Materials Science, 2014
LaNi 4⋅7 Al 0⋅3 alloy was prepared by vacuum induction melting in high purity helium atmosphere, ... more LaNi 4⋅7 Al 0⋅3 alloy was prepared by vacuum induction melting in high purity helium atmosphere, and the ingot was pulverized into 200-400 mesh powder after annealing. X-ray diffraction (XRD) and scanning electron microscopies (SEM) were utilized to study the alloy morphology and phase structure. X-ray photoelectron spectroscopy (XPS) was used for surface analysis. The poisoned alloy was tested at 30 °C in the mixture gas by thermogravimetric and differential thermal analyses (TG + DTA). The hydrogen storage properties were studied by the pressure-composition-temperature test. The activated sample was completely deactivated after only 3 hydriding/dehydriding cycles in hydrogen containing 300 ppm CO at 30 °C, but hydrogen storage capacity did not degrade when tested at 80 °C. Additionally, two different steps appeared in the absorption processes. Combined with XRD, XPS and TG + DTA results, an explanation for this phenomenon is given. Keywords. LaNi 4⋅7 Al 0⋅3 hydrogen storage alloy; CO impurities gas; hydrogen purification; absorption/ desorption kinetics.
MRS Proceedings, 2003
ABSTRACTAluminum and copper are widely used for microelectronic interconnect applications. Interf... more ABSTRACTAluminum and copper are widely used for microelectronic interconnect applications. Interfacial oxides can cause device performance degradation and failure by significantly increasing electrical resistance. Interfacial oxide layers found in Al/Ta and Ta/Cu metal stacks were studied using Transmission Electron Microscopy (TEM) combined with Energy Dispersive Spectroscopy (EDS) and Parallel Electron Energy Loss Spectroscopy (PEELS). The analysis indicates that the observed interfacial oxide layers, Al2O3 and mainly Ta2O5, result from spontaneous reductions of Ta oxide and Cu oxide, respectively. Thermodynamics enables interpretation of the results.
RSC Adv., 2014
The catalytic effects of CoFe2O4 nanoparticles on the hydrogen storage properties of LiAlH4 prepa... more The catalytic effects of CoFe2O4 nanoparticles on the hydrogen storage properties of LiAlH4 prepared by ball milling were investigated.
Journal of Power Sources, 2014
h i g h l i g h t s CoFe 2 O 4 has strong catalytic effect on MgH 2 hydrogen storage based on its... more h i g h l i g h t s CoFe 2 O 4 has strong catalytic effect on MgH 2 hydrogen storage based on its strong oxidative activity. The final reaction products of MgH 2 and CoFe 2 O 4 are the ternary combinations: Co 3 Fe 7 , MgO and Co. Co 3 Fe 7 , MgO and Co combination has a great catalytic effect on MgH 2 hydrogen storage performance. MgH 2 hydridingedehydriding process depends on the methods of adding Co 3 Fe 7 , MgO and Co.
Ceramics International, 2015
Iron oxides were synthesized by solution combustion synthesis using glycine (fuel) and ferric nit... more Iron oxides were synthesized by solution combustion synthesis using glycine (fuel) and ferric nitrate (oxidizer) as raw materials. The effects of the fuel to oxidizer ratio, ϕ, on the combustion behavior, phase, morphology and surface area of the products were systematically studied. Pure hematite was synthesized directly by the combustion of the precursors under fuel-lean conditions in one step without further heat treatment, simply by selecting a proper fuel to oxidizer ratio, ϕ. The hematite has a highly mesoporous structure with specific surface area of 103 m 2 g-1 and an average size of about 20 nm, which was obtained at ϕ ¼0.3. The hematite displays a continuous absorption band in the visible region. The photocatalytic activity of the hematite was evaluated by degrading the methylene blue pollutant in water at ambient temperature. The synthesized mesoporous hematite is a promising visible light photocatalysts for organics decomposition.
The Journal of Physical Chemistry C, 2013
The effects of NiFe 2 O 4 nanoparticles addition on the dehydrogenation behavior of LiAlH 4 were ... more The effects of NiFe 2 O 4 nanoparticles addition on the dehydrogenation behavior of LiAlH 4 were investigated. The onset dehydrogenation temperature for LiAlH 4 +3 mol % NiFe 2 O 4 sample is 61°C, which decreased by 94°C compared with the as-received LiAlH 4 and released ∼7.2 wt % hydrogen when heated to 180°C. Isothermal desorption measurements show that the 3 mol % NiFe 2 O 4-doped sample releases ∼7.0 wt % of hydrogen in 91 min at 120°C, which is 6.3 wt % higher than the as-received LiAlH 4 under the same conditions. Through calculating the apparent activation energy of the LiAlH 4 samples with and without NiFe 2 O 4 for the first two dehydrogenation stages, the E a of the LiAlH 4 +3 mol % NiFe 2 O 4 sample is 54.3 and 70.8 kJ/mol, resulting in 52.5 and 59% decrease, respectively, compared with the as-received LiAlH 4. Analyzing the X-ray diffraction and Fourier transform infrared spectroscopy results, it is reasonable to believe that the remarkable improvement of dehydrogenation properties of NiFe 2 O 4-doped LiAlH 4 results from the in situ formed LiFeO 2 and Al−Ni compounds, providing the active sites for nucleation and growth of the dehydrogenation products.
Metals and Materials International, 2012
This paper presents a classic process-structure-properties approach for optimizing the magnetic p... more This paper presents a classic process-structure-properties approach for optimizing the magnetic properties of electrical steels. Cold-rolled non-oriented electrical steel (Fe; 0.001 wt% C; 0.2 wt.% Mn; 1.3 wt% Si) was subjected to extremely short 3-30 seconds annealing cycles in a range from 880°C to 980°C with a heating rate varying from 15°C to 300°C/sec. The resulting microstructure was studied by means of optical microscopy and X-ray orientation distribution function analysis. Recrystallized grains were refined with increased heating rate, caused by the nucleation rate increase, which is faster than the growth rate due to rapid heating. The optimal grain size of 60 to 80 mm in terms of magnetic properties was obtained by increasing the annealing temperature range to 920°C to 940°C with a higher heating rate of 300°C/sec and an annealing time of 6 to 9 seconds. With the heating rate increase, the characteristic {111} recrystallization fiber of cold-rolled steel was depressed, but the beneficial {110}<001> Goss texture component was significantly strengthened. The recrystallized grain size and texture were enhanced by rapid annealing, and, as a result, the magnetic properties of non-oriented electrical steel improved.
Materials Science and Engineering: A, 2012
Equal channel angular pressing of a fully pearlitic Fe-0.8C steel was carried out at 923 K. The m... more Equal channel angular pressing of a fully pearlitic Fe-0.8C steel was carried out at 923 K. The microstructure, before and after processing, was analyzed by scanning and transmission electron, and atomic force microscopy. After one pass of the equal channel angular pressing, the cementite lamellae is bent, kinked, and fractured, with its spacing significantly decreased. The shape of the local cementite is a short or elliptical bar. After four passes, an ultrafine microduplex structure (ferrite + cementite), with a grain size at the sub-micrometer level, was observed and the planar lamellae was converted to equiaxed threedimensional grains. The cementite lamellae was fully spheroidized, with the average diameter of the cementite particle being equal to about 150 nm. Equiaxed ferrite grains, with an average size of 400 nm, are developed due to the dynamic, continuous recrystallization during the equal channel angular pressing deformation.
Journal of Power Sources, 2013
h i g h l i g h t s MnFe 2 O 4 nanoparticles effect on MgH 2 desorption properties is studied for... more h i g h l i g h t s MnFe 2 O 4 nanoparticles effect on MgH 2 desorption properties is studied for the first time. MgH 2 þ 7 mol% MnFe 2 O 4 desorption temperature onset reduction is 140 C, compared with MgH 2. The apparent activation energy of the 7 mol% MnFe 2 O 4-doped sample is dramatically decreased. Mg 2 MnO 4 and Fe 0.872 O phases play an important role in improving MgH 2 desorption properties.
Uploads
Papers by Alex A Volinsky