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DOE OSTI2022

Calorimetry can detect the early onset of hydrolysis in hybrid supercapacitors with aqueous electrolytes

This study investigates the effect of cation species on the onset of electrolyte hydrolysis in hybrid supercapacitors with aqueous electrolytes using isothermal operando calorimetry. The cells consisted of a positive α-MnO 2 cryptomelane electrode and a negative activated carbon (AC) electrode with either 0.5 M K 2 SO 4 or 0.5 M Cs 2 SO 4 aqueous electrolytes. They were characterized using cyclic voltammetry and galvanostatic cycling. In addition, the instantaneous heat generation rate at each electrode was measured using a custom isothermal operando calorimeter. Heat generation associated with resistive losses (Joule heating) and reversible ion adsorption/desorption was clearly identified. For larger potential windows, an endothermic dip, attributed to the onset of hydrolysis, was observed at the positive α-MnO 2 electrode where K + and Cs + ions engaged in fast surface redox reactions. Interestingly, this endothermic dip appeared at 1.8 V and 2.0 V for K 2 SO 4 and Cs 2 SO 4 aqueous electrolytes, respectively. The difference in the stable operating potential window was attributed to thinner solvation shell around Cs + cation than for K + thus reducing the amount of water present near the electrodes as ions partially shed their solvation shells during adsorption. The early onset of hydrolysis could be observed by isothermal operando calorimetry before it could be observed with conventional electrochemical methods.

42 ENGINEERING↗

DOE OSTI2017

Effect of Er{sup 3+} ions on the phase formation and properties of In{sub 2}O{sub 3}nanostructures crystallized upon microwave heating

Regular sized nanostructures of indium oxide (In{sub 2}O{sub 3}) were homogeneously grown using a facile route, i.e. a microwave-hydrothermal method combined with rapid thermal treatment in a microwave oven. The presence of Er{sup 3+} doping plays an important role in controlling the formation of cubic (bcc) and rhombohedral (rh) In{sub 2}O{sub 3} phases. The samples presented broad photoluminescent emission bands in the green-orange region, which were attributed to the recombination of electrons at oxygen vacancies. The photocatalytic activities of pure bcc-In{sub 2}O{sub 3} and a bcc-rh-In{sub 2}O{sub 3} mixture towards the UVA degradation of methylene blue (MB) were also evaluated. The results showed that Er{sup +3} doped In{sub 2}O{sub 3} exhibited the highest photocatalytic activity with a photonic efficiency three times higher than the pure oxide. The improved performance was attributed to the higher surface area, the greater concentration of electron traps due the presence of the dopant and the possible formation of heterojunctions between the cubic and rhombohedral phases. - Graphical abstract: Photodegradation curves as a function of irradiation time of the samples obtained upon rapid microwave heating. - Highlights: • Efficient and rapid microwave heating to obtain Er{sup 3+} doped In{sub 2}O{sub 3} nanostructures. • Er{sup 3+} ions doping is fundamental to stabilizing the crystalline rhombohedral phase. • Symmetry breaking induced by vacancies in the lattice leads to photoluminescence. • Surface area of doped sample was two times higher than the surface of pure oxide. • The presence of defects in the lattice structure favors photocatalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

First-principles study lone-pair effects of Sb (III)-S chromophore influence on SHG response in quaternary potassium containing silver antimony sulfides

First-principles studies of the geometric structures, electronic structures and optical properties of non-centrosymmetrical (NCS) KAg{sub 2}SbS{sub 4}, K{sub 2}AgSbS{sub 4} and K{sub 2}Ag{sub 3}Sb{sub 3}S{sub 7} and centrosymmetrical (CS) KAg{sub 2}SbS{sub 3} and K{sub 3}Ag{sub 9}Sb{sub 4}S{sub 12} have been performed by means of density functional theory. It is indicated that although they have similarity in their anionic groups and, the electronic structures, prominent features of the optical anisotropy or second-order nonlinear optical (NLO) susceptibilities are apparently different. The calculated birefringences are 0.0537, 0.0343, 0.1324, 0.2217 and 0.0604 which are attributed to the different anionic groups [SbS{sub 3}] and triangles [AgS{sub 3}]. Also, the calculated NLO responses are about 0.5×, 1.0× and 2.0× times than that commercial AgGaS{sub 2} (AGS, d{sub 36}=11 pm/V) for K{sub 2}AgSbS{sub 4}, KAg{sub 2}SbS{sub 4} and K{sub 2}Ag{sub 3}Sb{sub 3}S{sub 7}, respectively. In comparison with the absolute magnitude of second harmonic generation (SHG) coefficients, the order K{sub 2}Ag{sub 3}Sb{sub 3}S{sub 7}>KAg{sub 2}SbS{sub 4}>K{sub 2}AgSbS{sub 4} is clearly established in the SHG response. Further analysis based on the real-space atom-cutting method reveals that the main sources of the SHG properties of these compounds are from the Sb-S group, especially K{sub 2}Ag{sub 3}Sb{sub 3}S{sub 7} is mainly attributed to the lone pair stereochemical activity of Sb (III)-S group. - Graphical abstract: Compounds K{sub 2}AgSbS{sub 4}, KAg{sub 2}SbS{sub 4} and K{sub 2}Ag{sub 3}Sb{sub 3}S{sub 7} exhibit second-order NLO response: 15×, 30× and 62× times than that KDP (KH{sub 2}PO{sub 4}, d{sub 36}=0.39 pm/V), respectively. First-principles methods reveal that the large SHG response of K{sub 2}Ag{sub 3}Sb{sub 3}S{sub 7} is dominated by the Sb-S chromophore with lone pairs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Fabrication of heterostructured BiOBr/Bi{sub 24}O{sub 31}Br{sub 10}/TiO{sub 2} photocatalyst by pyrolysis of MOF composite for dye degradation

The pyrolysis of metal-organic frameworks has emerged as a promising route to synthesize metal oxides with diverse phase compositions, morphologies, sizes and surface areas. The BiOBr/Bi{sub 24}O{sub 31}Br{sub 10}/TiO{sub 2} (BBT) heterostructures have been achieved for the first time by calcining BiOBr/MIL-125(Ti) composite at 500 °C in air. The BBT-2 composite exhibited the highest photocatalytic performance for degradation of RhB under visible light irradiation. The enhanced photocatalytic activity is attributed to narrower band-gaps and synergistic effect originating from the well-aligned straddling band-structures between BiOBr, Bi{sub 24}O{sub 31}Br{sub 10} and TiO{sub 2}, also result in an faster interfacial charge transfer during the photocatalytic reaction. This work could be conductive to the design of heterostructured photocatalysts contained metal oxide by pyrolytic conversion of metal-organic frameworks for significantly improved photocatalytic performance. - Graphical abstract: A novel BiOBr/Bi{sub 24}O{sub 31}Br{sub 10}/TiO{sub 2} heterostructure was achieved by calcining BiOBr/MIL-125(Ti) composite and exhibited the photocatalytic performance for degradation of RhB. Display Omitted - Highlights: • A novel BiOBr/Bi{sub 24}O{sub 31}Br{sub 10}/TiO{sub 2} heterostructure was achieved by calcining BiOBr/MIL-125(Ti) composite. • The heterostructure exhibited the photocatalytic performance for degradation of RhB. • The enhanced photocatalytic activity is attributed to synergistic effect between BiOBr, Bi{sub 24}O{sub 31}Br{sub 10} and TiO{sub 2}. • This work could be conductive to the design of heterostructured photocatalysts by pyrolytic conversion of MOF.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Solvothermal synthesis, electromagnetic and electrochemical properties of jellylike cylinder graphene-Mn{sub 3}O{sub 4} composite with highly coupled effect

Jellylike cylinder graphene-Mn{sub 3}O{sub 4} composite with highly coupled effect was successfully synthesized by a simple solvothermal process. Without using toxic reducing agent and expensive equipment, this method is environmental compatible and suitable for low cost mass production. High capacitance Mn{sub 3}O{sub 4} nanoparticles are homogeneously anchored on excellent conductivity graphene framework and a growth mechanism is hypothesized. Excellent electron conductivity and unique structure of Mn{sub 3}O{sub 4}-graphene composite give rise to various applications such as microwave absorber and electrode material. As a microwave absorber, the composite exhibits lowest reflection loss of −14.2 dB in the frequency range of 2–18 GHz. Good microwave absorption performance is due to the structure of the composite where conductive channels form between nano sized Mn{sub 3}O{sub 4} and high conductivity graphene with defects and dangling bonds. As for electrochemical property, Mn{sub 3}O{sub 4}-graphene composite with coupled effect shows excellent performance with highest specific capacitance of 246.7 F g{sup −1} in saturated K{sub 2}SO{sub 4} at a scan rate of 5 mV s{sup −1}. Good electrochemical property is also attributed to the structure with high utilization of Mn{sub 3}O{sub 4}, fast charge carrier transmission, and excellent electronic conductivity. This composite shows a promising application in absorbing materials and electrodes. - Graphical abstract: Graphene-Mn{sub 3}O{sub 4} composite. Display Omitted - Highlights: • Strongly coupled graphene-Mn{sub 3}O{sub 4} composite is synthesized by a solvothermal method. • Excellent microwave absorption property is ascribed to the composite structure. • Good capacitance performance is attributed to the structure and physical property. • The composite shows promising application in absorbing material, and electrode.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Growth mechanism of extension twin variants during annealing of pure magnesium: An ‘ex situ’ electron backscattered diffraction investigation

Pure magnesium was subjected to plastic deformation through CSM (continuous stiffness measurement) indentation followed by annealing at 200 °C for 30 min. Nucleation of no new grains was observed neither at the twin–twin intersections nor at the multiple twin variants of a grain after annealing. Significant growth of off-basal twin orientation compared to basal twin orientation was observed in the sample after annealing and is attributed to the partial coherent nature of twin boundary in the later case. Further, growth of twins was independent of the strain distribution between parent and twinned grains. - Highlights: • An ‘ex situ’ EBSD of pure Mg during annealing was investigated. • Nucleation of no new grains was observed. • Significant growth of off-basal twin orientation was observed. • Growth of twins may be attributed to the partial coherent nature of twin boundary.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Influence of differential speed rolling ratio on the ridging behavior of ultra purified 17%Cr ferritic stainless steel

Highlights: • Differential rolling process improves ridging resistance of ferritic stainless steel. • Texture orientation inhomogeneity were attributed to non-uniform deformation. • Shear bands results in homogeneous deformation and recrystallization nucleation. • Uniform recrystallization grains and random orientation grains were obtained. - Abstract: The effect of the differential speed rolling on the ridging resistance and the crystallographic texture evolution of ultra purified 17%Cr ferritic stainless steel was investigated in order to select the optimal procedure for improving the surface quality. In the present study, the three different cold rolling processes were carried out: a conventional cold rolling and two different speed ratios asymmetric rolling. In the conventional cold rolling, the ridging of ferritic stainless steel was pronounced due to the band-like clusters of grains with similar crystallographic orientations. For differential speed rolling, ridging depth decreased and ridging was less pronounced when a higher different speed ratio was applied. The results show that severe ridging is attributed to the presence of band-like clusters of γ-fiber (<111>//ND) oriented grains. The shear bands introduced by differential speed rolling can enhance the nucleation for recrystallization both in grain interiors and grain boundaries, which can fragment the band-like clusters of similar orientation effectively, promoting the random grain orientation and improving surface quality.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Evolution of microstructures and mechanical properties during solution treatment of a Ti–V–Mo-containing high‑manganese cryogenic steel

Highlights: • High-Mn cryogenic steels are getting the spotlight in the cryogenic market. • The grain size grew slowly and the yield strength remained almost stabilized with an increase of solutionizing temperature. • The Hall–Petch strengthening coefficient for yield strength was small, estimated to be 153 MPa μm{sup 0.5}. • The weakening effect of solutionizing temperature on grain size was attributed to the nano-sized (Ti, V, Mo)C precipitate. - Abstract: The effect of solution treatment on the microstructure and mechanical properties of a high‑manganese (Mn) twin-induced plastic (TWIP) cryogenic steel that was alloyed from elemental titanium (Ti), vanadium (V) and molybdenum (Mo) was investigated by a variety of techniques such as microstructural characterization, room tensile testing and − 196 °C impact testing. The austenite grain size grew slowly with an increase of the solutionizing temperature (ST). The relatively weak effect of the ST on the austenite grain size is attributed to the superior thermal stability and coarsening resistance of the (Ti, V, Mo)C precipitate, which hindered austenite grain growth. An increase in ST improved the low-temperature toughness (LTT) significantly and decreased the strain hardening rate (SHR), but had no significant effect on the yield strength. The Hall–Petch strengthening coefficient for yield strength was small, and was estimated to be 153 MPa μm{sup 0.5}. Undissolved large-sized chromium (Cr) carbide can deteriorate the LTT significantly. Because of its excellent mechanical properties, high-Mn steel that was alloyed by elemental Ti, V and Mo can be used to manufacture storage tanks for liquefied natural gas.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Effect of microstructure and crystallographic texture on mechanical anisotropy of Ti-Nb microalloyed hot rolled 800 MPa HSLA steel

Highlights: • Anisotropy in yield strengthis attributed to the relatively stronger {332} . • γ-fiber with counter-balancing {111} and {111} could not induce anisotropy. • The maximum CVN value at 0° is attributed to the higher fraction of {113} and {112} . • The large anisotropy in CVN value, ~ 100 J is observed due to a weaker {332} and {554} . - Abstract: The impact toughness of a Ti+Nb HSLA steel plate, conventionally hot rolled in the austenitic region, were measured at four different directions at 0 °C, −20 °C and −40 °C respectively. The microstructure was characterised using light optical microscope, scanning electron microscope (SEM) followed by evaluation of hot rolled texture using X-ray diffraction (XRD) and orientation distribution function (ODF) obtained from electron back-scattered diffraction (EBSD). The anisotropy in the yield strength (YS) and Charpy impact toughness (CVN) were examined in the light of orientation distribution function (ODF) obtained from EBSD. The skeleton lines, showing intensity distribution, f(g), of the fcc-to-bcc transformation texture, namely the α-fiber (<110>∥ RD), the γ-fiber (<111>∥ ND) and ε-fiber (<110>∥ TD) are considered to explain the observed anisotropy along with microstructural features. The major components like, {112}<110>, {113}<110>, {332}<113>, {111}<112> and {111}<110>, their relative intensity distribution, are found to cause the observed anisotropy in yield strength and impact toughness. A stronger presence of {113}<110> component of the α-fiber over relatively weaker {332}<113> component of the ε-fiber further augments the observed toughness anisotropy. In absence of any microstructural banding, strong the presence of {113}<110> and {112}<110> can also cause delamination in ductile fracture mode.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Effect of Ni content on the microstructure and mechanical properties of weld metal with both-side submerged arc welding technique

Highlights: • This manuscript primarily studied the effects of Ni content on the K65 weld metals; • Increase Ni content could significantly improve the strength and low temperature impact toughness of the weld metal. • The beneficial effect of Ni is attributed to its positive effect on phase transformation. • GBF keeps K-S or N-W relations only with one austenite and the variants belong to the same bain group are two reasons. • The M/A islands are considered to be another reason for the reduced toughness. - Abstract: The effects of nickel (Ni) content on the mechanical properties and microstructure evolution in the weld metals of commercial K65 oil and gas pipeline steel were studied. Increase Ni content could significantly improve the strength and low temperature impact toughness (−40 °C and −60 °C) of the weld metal. The above influences of Ni were attributed to the formation of predominant acicular ferrite (AF), at the expense of grain boundary ferrite (GBF), ferrite side plates (FSP) and martensite/austenite (M/A) constituent in weld metal. EBSD results indicated that GBF keeps K-S or N-W relations only with the prior austensite grain that belongs to one side of the grain boundary and the variants belong to the same bain group which always forms low angle boundary. Moreover, the retained austenite as one part of M/A constituent was mainly found in the weld metal with lower Ni content. It indicated that the transformation process could be promoted more completely by the increase of Ni content. The mechanism of the toughness improvement brought by Ni increasing was ascribed to the relatively uniform transformation to final microstructure, which reduces the appearance of GBF and M/A constituents.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Precipitation-hardening of superalloy 693 and modeling of initial stages of hardening

Highlights: • Isothermal Time-Temperature-Precipitation diagram of superalloy 693 established. • At 973–1173 K, increase in hardness up to 1.5 h of ageing followed by drop noticed. • Initial hardening of alloy at 973–1173 K is modeled by Johnson-Mehl-Avrami equation. • XRD, TEM but not SEM-EDS indicate formation of fine γ′ precipitates in aged samples. • Initial stages of hardening is attributed to formation of fine γ′ precipitates. - Abstract: Isothermal time-temperature-hardness behavior for Ni{sub 3}Al type phase in austenitic superalloy 693 was investigated by micro hardness measurements of the aged specimens. Ageing of the alloy between 973 K and 1173 K indicated an initial increase in micro hardness with ageing time attaining a peak at 1.5 h followed by a drop of its value. The early stages of hardening for the alloy was modeled by the expression: ΔH = (Kt){sup n}, where ΔH, t, n and K are increase in hardness, ageing time (h; in hour), time exponent and temperature-dependent rate constant (h{sup −1}) respectively. X-ray diffraction of solution-annealed and aged specimens indicated formation of Ni{sub 3}Al type precipitation-hardening (γ′) phase, while scanning electron microscopy with energy dispersive X-ray spectroscopy could not clearly reveal the formation of γ′ phase. Transmission electron microscopy on peak-aged (1.5 h at 973 K, 1073 K, 1173 K) samples revealed formation of fine, face centered cubic, Ni{sub 3}Al type (γ′) precipitates, while over-aged (3 h at 973 K, 1073 K, 1173 K) specimens indicated coarsening of precipitates. The initial stages of hardening for the alloy (at 973 K, 1073 K, 1173 K) are attributed to formation of fine Ni{sub 3}Al type precipitates.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Cyclic plastic deformation behaviour of a directionally solidified nickel base superalloy at 850 °C: Damage micromechanisms

Highlights: • Isothermal LCF life of CM 247 DS is reduced using R = 0 instead of R = −1. • Reduction in LCF life is significant at lower values of Δε/2. • Reduction in fatigue life is attributed to the development of sustained mean stress. • Sustained mean stress prevents the slip transfer from γ-channels to γ′-precipitates. • Sustained mean stress promotes dislocation network formation and looping. - Abstract: Dislocation based deformation micromechanisms during low cycle fatigue deformation of nickel base superalloy CM 247 DS LC at 850 °C was investigated by conducting fatigue tests employing constant strain amplitudes for strain ratio (R) values of 0, −1 and carrying out extensive SEM and TEM examinations. Cyclic life of the alloy reduces for all fatigue tests conducted employing R = 0 in comparison with R = −1 owing to sustained mean stress developed during fatigue at R = 0. TEM examinations confirmed that sustained mean stress developed during low strain amplitude fatigue test (Δε/2 = 0.5%) using R = 0 condition prevented slip transfer from γ-channels to γ′-precipitates and resulted in the formation of dislocation substructures such as networks, nodes etc. and also promoted dislocation looping around γ′-precipitates. Lower fatigue life at R = 0 is mainly attributed to the development of these types of substructures, which promotes strain localization in both intra as well intergranular regions. Whereas, in specimen fatigue tested (Δε/2 = 0.5%) using R = −1 condition, shearing of γ′-precipitates by APB coupled dislocation and formation of stacking faults were observed. The formation and nature of stacking faults were analysed using weak beam imaging technique. Stacking fault formed during fatigue tests using R = −1 condition matured to micro-twins when Δε/2 value was increased to 0.8%. The mechanism of formation of these microtwins is discussed in detail. SEM based microstructural and fractographic examinations revealed that mean stress induced creep effect resulted in intergranular crack initiation and grain boundary cavitation during fatigue tests under R = 0 condition and therefore verified the facts revealed in TEM studies.

36 MATERIALS SCIENCE↗

DOE OSTI2018

In-situ fabrication of graded material with the application of a horizontal magnetic field during directional solidification

Highlights: • The horizontal magnetic field caused the migration of primary grains and the formation of graded material. • TEMF play a major effect on the formation of graded material. • The magnitude of TEMF increases with the increase of magnetic field intensity. • This work initiates a new method to prepare the “graded material” via an applied horizontal magnetic field. - Abstract: The present paper proposes a method of graded materials preparation under a low horizontal magnetic field during directional solidification. The external horizontal magnetic field was applied to the mushy zone of the directionally solidified Al-10 wt% Cu and Al-18 wt% Si samples, which was perpendicular to the growth direction. Experimental results demonstrate that the applied horizontal magnetic field produces a gradient size distribution of the primary α(Al) grains in Al-10 wt% Cu alloys and a gradient fraction distribution of primary Si particles in Al-18 wt% Si alloys. 3D numerical simulations indicate that the formation of graded structure should be attributed to the migration of primary phase driven by the thermoelectric magnetic force (TEMF). The formation of segregation channel should be attributed to the TEM convection (TEMC) in the mushy zone. Further, in situ synchrotron X-ray radiography observations of the initial transient of directional solidification show that the primary α(Al) phases were migrated approximately along the direction perpendicular to the magnetic field. These results suggest that the TEM effects can greatly change the growth of primary grains and the solidification structure, and the application of an external horizontal magnetic field would be beneficial to fabricate the graded material during directional solidification.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Development of high Fe content squeeze cast 2A16 wrought Al alloys with enhanced mechanical properties at room and elevated temperatures

Highlights: • Applied pressure improved tensile properties at both room and elevated temperatures. • Experimental alloys meet the requirement of safety-critical component in automotive industry. • Increasing value of mechanical properties at elevated temperatures resulting from pressure decreases - Abstract: In this study, the evolution of iron-rich intermetallics and their effects on room and elevated-temperature tensile properties of gravity die cast and squeeze cast 2A16 wrought Al alloys with high Fe content of 0.5% after T7 heat treatment were investigated by various methods. Compared to gravity die-cast alloys, squeeze cast 2A16 wrought Al alloys showed superior tensile properties at both room and elevated temperatures, especially in terms of elongation. This can be attributed to refinement in grain size and iron-rich intermetallics, which decreased porosity and raised dispersoids in α(Al) matrix. However, the increase in mechanical properties at high temperature resulting from applied pressure was lower than that obtained at room temperature. The results were attributed to the refinement in grain size and the weakness of grain boundary at elevated temperature.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Control on the homogeneity and crystallinity of Zn0.5Cd0.5S nanocomposite by different reaction conditions with high photocatalytic activity for hydrogen production from water

Highlights: • The effects of the various reaction conditions are investigated. • Different photocatalytic activities attributed to the different homogeneity and crystallinity of the nanoparticles. • Combination of good crystallinityand homogeneityresulted in an excellent photocatalytic activity. - Abstract: Zn{sub 0.5}Cd{sub 0.5}S nanoparticles with phase homojunctions were prepared by a one-step hydrothermal method with thioacetamide as sulfur source. The effects of the various reaction conditions, such as initial concentrations of Zn and Cd ions, initial content of sulfur source in the reaction mixture, and the temperature rising rate, are investigated. The photocatalytic activities for H{sub 2} evolution from water in the presence of sacrificial reagents of these Zn{sub 0.5}Cd{sub 0.5}S nanoparticles were significantly affected by the reaction conditions. These differences on the photocatalytic activities can be attributed to the different homogeneity and crystallinity of the nanoparticles prepared at different reaction conditions. A faster reaction rate leads to the formation of Zn{sub 0.5}Cd{sub 0.5}S nanoparticles with bad crystallinity, but good homogeneity. On the contrary, a slow reaction rate results in a bad homogeneity, but better crystallinity. Combination of good crystallinity and homogeneity in a Zn{sub 0.5}Cd{sub 0.5}S nanocomposite resulted in an excellent photocatalytic activity. The highest rate of H{sub 2} evolution achieved for these phase-homojunctions materials under visible-light irradiation (λ ≥ 420 nm) reached 1252.7 μmol h{sup −1} with an apparent quantum efficiency of 21.46% at 420 nm. The H{sub 2} evolution rate did not reduce distinctively in a continuous 15 hour test for H{sub 2} evolution, indicating an excellent stability for this material. This work not only demonstrates a facile method to produce highly active phase-homojunctions containing Zn{sub 0.5}Cd{sub 0.5}S solid solutions for photocatalytic hydrogen production from the perspective of controlling various reaction conditions, but also provides new insights into understanding the importance of the homogeneity and crystallinity for enhancing photocatalytic activity and stability of Zn{sub 0.5}Cd{sub 0.5}S solid solutions. It is expected that the strategies of modifying the homogeneity and crystallinity by controlling various reaction conditions can be extracted and used when designing other efficient and robust photocatalysts in the future.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2018

The grain refinement mechanisms of various phases in shot-peened Nickel-Aluminum bronze (NAB) alloy

Highlights: • There exist two grain refinement mechanisms at the same time in the α phase. • The refinement of β' phase is attributed to the formation of dense and ordered nano twins. • The brittle strip-shape κ{sub iii} phases are fragmented after large deformation. • The κ{sub iv} and κ{sub ii} phases exhibit the twinning and dislocation deformation modes, separately. • The microhardness increases significantly owing to work hardening effect and grain refinement. - Abstract: In this study, coarse-grained Nickel-Aluminum bronze (NAB) alloy is subjected to shot-peening (SP) treatment, and the grain refinement mechanisms of various phases in shot-peened NAB alloy are investigated separately. The results show that severe deformation layers are produced on the surface. Meanwhile, refined grains with the average size below 100 nm are induced through SP treatment indicated by the results of X-ray diffraction (XRD) patterns. Various phases in NAB alloy including α, β' and three intermetallic phases (κ{sub ii}, κ{sub iii} and κ{sub iv}) display different grain refinement mechanisms. The grain refinement in the α phase involves dislocation segmentation in the precipitation-free zone and the twinning intersection in the precipitation zone. The formation of nanotwins by emitting partial dislocations at the grain boundary is found to be responsible for the grain refinement in the β' phase. As for the κ phases, the strip-shaped κ{sub iii} phases are fragmented after severe deformation, and the κ{sub iv} and κ{sub ii} phases exhibit the twinning and dislocation deformation modes, respectively. Also, the microhardness is significantly enhanced after SP treatment, which is mainly attributed to the work hardening effect and grain refinement.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Isothermal deformation and spheroidization mechanism of (TiB + La2O3)/Ti composites with different initial structures

Highlights: • Different initial microstructures were obtained through designed heat treatment. • Refined lamellar microstructures promoted dynamic recrystallization. • The spheroidization mechanism was attributed to dynamic recrystallization. • The micron TiB and submicron La{sub 2}O{sub 3} impeded dislocation movement. (TiB + La{sub 2}O{sub 3})/Ti composites with different initial structures were obtained through designed heat treatment. The isothermal deformation and spheroidization mechanisms of (TiB + La{sub 2}O{sub 3})/Ti composites with different initial structures were investigated. Initial structures were refined as the heat treatment temperature decreased. Simultaneously, the quenching and reheating resulted in finer α lamella colonies and α interlamellar spacing compared to the furnace cooling. The flow resistance of furnace cooled samples was lower than the quenched and reheated samples in terms of flow stress data. Following the deformation at 920 °C, the furnace cooled samples demonstrated lamellar α phase and partial spheroidized structure. Moreover, the spheroidization mechanism was similar to the boundary splitting model. Recrystallized grains of approximately 1 μm in diameter were obtained in the quenched and reheated sample following deformation at 920 °C. The spheroidization mechanism was attributed to the development of finer needles through quenching and reheating, as well as to subsequent dynamic recrystallization during the hot deformation. Additionally, the dislocation movement was blocked by the reinforcements on account of the composites with micron TiB and submicron La{sub 2}O{sub 3} during the hot deformation. Furthermore, the reinforcements could facilitate the dynamic recrystallization (DRX) of the α phase.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Mo-N-co-doped mesoporous TiO{sub 2} microspheres with enhanced visible light photocatalytic activity

Highlights: • The Mo-N-co-doped mesoporous TiO{sub 2} microspheres were synthesized via a solvothermal method and further nitriding treatment. • The properties of TiO{sub 2} microspheres can be tuned by Mo-N-co-doping. • Photocatalytic rate is much higher than Pure TiO{sub 2} catalyst powder and Mo doped TiO{sub 2} microspheres. • The higher activity is attributed to the large BET surface area, narrow band gap and intense light absorbance in visible region. - Abstract: Mo-N-co-doped mesoporous TiO{sub 2} microspheres were synthesized via a solvothermal method, followed by nitriding treatment under ammonia gas flow. The efficiency of the samples was investigated by monitoring the degradation of Rhodamine-B under visible light irradiation. The experimental results revealed that Mo-N-co-doped mesoporous TiO{sub 2} microspheres showed better performances than Mo-TiO{sub 2} microspheres. It was observed that; 0.1% molar quantity of Mo doped on TiO{sub 2} at 500 °C for 2 h under nitriding conditions gave highest photocatalytic activities. The nitridation under ammonia gas of Mo-TiO{sub 2} samples created oxygen vacant sites and led to incorporation of substitutional and interstitial Nitrogen. The enhanced visible light photocatalytic activities of Mo-N-co-doped TiO{sub 2} photocatalyst was attributed to the large surface areas, narrow band gap and intense light absorbance in visible region. This study may create a promising and eco-friendly method towards synthesis of metal and non-metals co-doped on semiconductor materials to improve their photocatalytic activities and applications.

36 MATERIALS SCIENCE↗