Showing papers on "Annealing (metallurgy) published in 2017"

Porous flower-like NiO@graphene composites with superior microwave absorption properties

Abstract: Novel porous flower-like NiO@graphene composites were prepared using a method involving a facile hydrothermal reaction and an annealing process. The precursor Ni(OH)2 was grown to a flower-like microsphere under weak basic conditions and was partly coated with graphene oxide flakes. The final porous composites were obtained after the annealing process. The structure of the flower-like NiO@graphene composites was characterized by XRD, Raman spectroscopy, XPS, SEM, TEM, and N2 adsorption–desorption. The influence of base strength on the morphology of the three-dimensional structure of NiO@graphene was investigated. The flower-like NiO@graphene is highly porous and has a large surface area of 107 m2 g−1. As an absorber, the composite with a filler loading of 25 wt% exhibited superior microwave absorption capacities owing to its special porous flower-like structure, polarization effect, good impedance matching, and synergistic action. The maximum reflection loss can reach −59.6 dB at 14.16 GHz, and the absorption bandwidths (RL below −10 dB) ranged from 12.48 GHz to 16.72 GHz with a thickness of only 1.7 mm. The results indicate that the lightweight NiO@graphene composites with high-performance microwave absorption properties are promising materials for Ku-band electromagnetic wave absorption.

Effect of heat treatment and hot isostatic pressing on the microstructure and mechanical properties of Inconel 625 alloy processed by laser powder bed fusion

Abstract: The effect of different heat treatments and hot isostatic pressing on the microstructure and mechanical properties of laser powder bed fusion IN625 alloy was studied. The heat treatments were: stress relief annealing, recrystallization annealing and low-temperature solution treatment. The resulting microstructure and crystallographic textures were studied using optical and scanning electron microscopy. The mechanical properties of the as-built and post-treated IN625 alloy were obtained after tensile testing at room temperature and at 760 °C (1400 °F), and compared to those of an annealed wrought alloy of the same composition.

Large ferroelectric polarization of TiN/Hf0.5Zr0.5O2/TiN capacitors due to stress-induced crystallization at low thermal budget

Abstract: We report on atomic layer deposited Hf0.5Zr0.5O2 (HZO)-based capacitors which exhibit excellent ferroelectric (FE) characteristics featuring a large switching polarization (45 μC/cm2) and a low FE saturation voltage (∼1.5 V) as extracted from pulse write/read measurements. The large FE polarization in HZO is achieved by the formation of a non-centrosymmetric orthorhombic phase, which is enabled by the TiN top electrode (TE) having a thickness of at least 90 nm. The TiN films are deposited at room temperature and annealed at 400 °C in an inert environment for at least 1 min in a rapid thermal annealing system. The room-temperature deposited TiN TE acts as a tensile stressor on the HZO film during the annealing process. The stress-inducing TiN TE is shown to inhibit the formation of the monoclinic phase during HZO crystallization, forming an orthorhombic phase that generates a large FE polarization, even at low process temperatures.

Thermal stability of WS2 flakes and gas sensing properties of WS2/WO3 composite to H2, NH3 and NO2

Abstract: We report on the fabrication and on the morphological, structural, chemical and the electrical characterization of WS2 thin films sensors prepared by drop casting a commercial solution of dispersed few-layers WS2 flakes on Si3N4 interdigitated substrates and annealing the films in air at 150 °C, 250 °C and 350 °C. Thermal stability of WS2 in air at different annealing temperatures has been investigated by X-ray photoemission spectroscopy, scanning electron microscopy, X-ray diffraction and by simultaneous thermal analysis techniques. We found that WS2 is not stable in air and partially oxidizes to amorphous WO3 in the annealing temperature range 25 °C–150 °C. The oxidation of WS2 in air at 250 °C and 350 °C yields a composite crystalline WS2/WO3 hierarchical structure characterized by the presence of surface oxygen and sulphur vacancies. The contribution of each phase of the WS2/WO3 composite to the overall chemoresistive gas response utilizing H2 (1–10 ppm), NH3 (1–10 ppm) and NO2 (40 ppb–1 ppm) gases in dry air carrier is presented and discussed. WS2/WO3 composite films show excellent gas sensing properties to reducing (H2, NH3) as respect to oxidizing (NO2) gases at 150 °C operating temperature. In this work we found low detection limits of 1 ppm H2, 1 ppm NH3 and 100 ppm NO2 in dry air carrier, among the smallest so far ever reported for transition metal dichalcogenides. Furthermore, the sensor doesn’t show any cross sensitivity effects to both H2 and NH3 when exposed to water vapor. Outstanding reproducibility responses, by exposing the 150 °C annealed film to dynamic and cumulative gas pulses where obtained utilizing H2 gas.

CsPbBr3 Solar Cells: Controlled Film Growth through Layer-by-Layer Quantum Dot Deposition

Abstract: All inorganic cesium lead bromide (CsPbBr3) perovskite is a more stable alternative to methylammonium lead bromide (MAPbBr3) for designing high open-circuit voltage solar cells and display devices. Poor solubility of CsBr in organic solvents makes typical solution deposition methods difficult to adapt for constructing CsPbBr3 devices. Our layer-by-layer methodology, which makes use of CsPbBr3 quantum dot (QD) deposition followed by annealing, provides a convenient way to cast stable films of desired thickness. The transformation from QDs into bulk during thermal annealing arises from the resumption of nanoparticle growth and not from sintering as generally assumed. Additionally, a large loss of organic material during the annealing process is mainly from 1-octadecene left during the QD synthesis. Utilizing this deposition approach for perovskite photovoltaics is examined using typical planar architecture devices. Devices optimized to both QD spin-casting concentration and overall CsPbBr3 thickness produce...

Disordered Atomic Packing Structure of Metallic Glass: Toward Ultrafast Hydroxyl Radicals Production Rate and Strong Electron Transfer Ability in Catalytic Performance

Abstract: Developing new functional applications of metallic glasses in catalysis is an active and pivotal topic for materials science as well as novel environmental catalysis processes. Compared to the crystalline materials with highly ordered atomic packing, metallic glass has a simply disordered atomic structure. Recent reports have demonstrated that the metallic glasses are indeed having many superiorly catalytic properties, yet the understanding of the mechanism is insufficient. In this work, the structural relaxation (α-relaxation) by annealing in an amorphous Fe78Si9B13 alloy is studied for unraveling the catalytic mechanism at the atomic scale. The volume fractions of the crystalline structures, such as α-Fe, Fe2Si, and Fe2B, in the as-received and annealed metallic glasses are fully characterized. It is found that the randomly atomic packing structure with weak atomic bonding in the as-received metallic glass has an efficient electron transfer capability, presenting advanced superiorities in the aspects of production rate of hydroxyl radicals (•OH), dye degradation rate (k), and essential degradation ability (KSA) for water treatment. The discovery of this critically important work unveils why using metallic glasses as catalysts has higher reactivity than the crystalline materials, and more importantly, it provides new research opportunities into the study of synthetic catalysts.

An ultrathin high-performance heat spreader fabricated with hydroxylated boron nitride nanosheets

Abstract: An ultrathin, highly thermally conductive heat spreader has been fabricated by layer-by-layer stacking of hydroxylated boron nitride nanosheets (HBNNS) for the first time. HBNNS were prepared by a molten hydroxide-assisted liquid exfoliation from hexagonal boron nitride powder. The as-prepared heat spreader of HBNNS exhibits a high thermal conductivity of 51.1 W m(-1) K-1 along the in-plane direction, and can be further enhanced 14% by annealing for de-hydroxylation. This heat spreader with 10-30 mu m in thickness possessed excellent thermal stability with negligible weight loss at wide temperature range up to 700 degrees C, resulting in promising applications for heat dissipation in electronic components operated at high working temperature.

Thermal engineering of FAPbI 3 perovskite material via radiative thermal annealing and in situ XRD

Abstract: Lead halide perovskites have emerged as successful optoelectronic materials with high photovoltaic power conversion efficiencies and low material cost. However, substantial challenges remain in the scalability, stability and fundamental understanding of the materials. Here we present the application of radiative thermal annealing, an easily scalable processing method for synthesizing formamidinium lead iodide (FAPbI3) perovskite solar absorbers. Devices fabricated from films formed via radiative thermal annealing have equivalent efficiencies to those annealed using a conventional hotplate. By coupling results from in situ X-ray diffraction using a radiative thermal annealing system with device performances, we mapped the processing phase space of FAPbI3 and corresponding device efficiencies. Our map of processing-structure-performance space suggests the commonly used FAPbI3 annealing time, 10 min at 170 °C, can be significantly reduced to 40 s at 170 °C without affecting the photovoltaic performance. The Johnson-Mehl-Avrami model was used to determine the activation energy for decomposition of FAPbI3 into PbI2. Processing is crucial to ensure material quality and stability in perovskite solar cells. Here, Poolet al. develop a scalable infrared annealing method and use in situXRD to map the processing phase space relative to the device efficiency. This provides a tool to determine processing requirements.

Synthesis and characterization of refractory TiZrNbWMo high-entropy alloy coating by laser cladding

Abstract: A novel refractory high-entropy alloy (HEA) coating with composition close to TiZrNbWMo was synthesized on 45 # steel by laser cladding. Constituent phases, microstructure, chemical composition and microhardness of the coatings before and after annealing were investigated by XRD, SEM, TEM, EDS and micro/Vickers hardness test, respectively. Results showed that the TiZrNbWMo coating was ~ 513 μm in thickness. The microstructure of the coatings exhibited typical dendritic and interdendritic structure. The coating was composed of a major body-centered cubic (BCC) solid solution and a small amount of β-Ti x W 1 − x precipitated phase due to high-entropy affect and laser rapid solidification. Apart from enhanced fraction of β-Ti x W 1 − x precipitation, the structure and BCC solid solution phases remained almost unchanged after annealing at 800 °C, 1000 °C, and 1200 °C for 20 h, indicating that the coating had high thermal stability. The microhardness of as-clad HEA coating reached around 700 HV 0.5 , which was three times of 45 # steel substrate. The coating microhardness increased significantly after annealing, which was due to the solid solution strengthening of BCC matrix and formation of β-Ti x W 1 − x precipitation. Notably, the highest value was up to 1300 HV 0.5 after heat treatment at 800 °C. Therefore, the HEA coatings showed high microhardness and resistance to softening.

Solution-processed SnO2 thin film for a hysteresis-free planar perovskite solar cell with a power conversion efficiency of 19.2%

Abstract: A hysteresis-free and high-efficiency planar perovskite solar cell was developed using a solution-processed SnO2 electron-transporting layer (ETL). Tin(IV) isopropoxide dissolved in isopropanol (IPA) was spin-coated on a fluorine-doped tin oxide (FTO) substrate in a nitrogen atmosphere. The effects of annealing temperature and precursor concentration on the photovoltaic performance were systematically investigated. The annealing temperature was scanned from 100 °C to 500 °C, whereby the 250 °C-annealed SnO2 film demonstrated the best performance along with negligible current–voltage hysteresis. The SnO2 film annealed at 250 °C was X-ray amorphous, while it was observed to be nanocrystallite from SnO2 annealed at 500 °C. The faster stabilization of the photocurrent and lower interfacial capacitance for the 250 °C-annealed SnO2 than for the 500 °C-annealed one were responsible for the markedly reduced hysteresis. The photovoltaic performance and hysteresis were influenced by the precursor concentration, where a concentration of 0.1 M showed hysteresis-free higher performance among the concentrations investigated ranging from 0.05 M to 0.2 M owing to a larger and faster photoluminescence quenching. The planar (HC(NH2)2PbI3)0.875(CsPbBr3)0.125 perovskite that was formed on the 40 nm-thick, 0.1 M-based and 250 °C-annealed SnO2 thin film delivered a power conversion efficiency (PCE) of 19.17% averaged out from the forward scan PCE of 19.40% and the reverse scan PCE of 18.93%.

Understanding the Role of Temperature and Cathode Composition on Interface and Bulk: Optimizing Aluminum Oxide Coatings for Li-Ion Cathodes.

Abstract: Surface coating of cathode materials with Al2O3 has been shown to be a promising method for cathode stabilization and improved cycling performance at high operating voltages. However, a detailed understanding on how coating process and cathode composition change the chemical composition, morphology, and distribution of coating within the cathode interface and bulk lattice is still missing. In this study, we use a wet-chemical method to synthesize a series of Al2O3-coated LiNi0.5Co0.2Mn0.3O2 and LiCoO2 cathodes treated under various annealing temperatures and a combination of structural characterization techniques to understand the composition, homogeneity, and morphology of the coating layer and the bulk cathode. Nuclear magnetic resonance and electron microscopy results reveal that the nature of the interface is highly dependent on the annealing temperature and cathode composition. For Al2O3-coated LiNi0.5Co0.2Mn0.3O2, higher annealing temperature leads to more homogeneous and more closely attached coati...

UV-Sintered Low-Temperature Solution-Processed SnO2 as Robust Electron Transport Layer for Efficient Planar Heterojunction Perovskite Solar Cells

Abstract: Recently, low temperature solution-processed tin oxide (SnO2) as a versatile electron transport layer (ETL) for efficient and robust planar heterojunction (PH) perovskite solar cells (PSCs) has attracted particular attention due to its outstanding properties such as high optical transparency, high electron mobility, and suitable band alignment. However, for most of the reported works, an annealing temperature of 180 °C is generally required. This temperature is reluctantly considered to be a low temperature, especially with respect to the flexible application where 180 °C is still too high for the polyethylene terephthalate flexible substrate to bear. In this contribution, low temperature (about 70 °C) UV/ozone treatment was applied to in situ synthesis of SnO2 films deposited on the fluorine-doped tin oxide substrate as ETL. This method is a facile photochemical treatment which is simple to operate and can easily eliminate the organic components. Accordingly, PH PSCs with UV-sintered SnO2 films as ETL we...

High-Strength Stereolithographic 3D Printed Nanocomposites: Graphene Oxide Metastability

Abstract: The weak thermomechanical properties of commercial 3D printing plastics have limited the technology’s application mainly to rapid prototyping. In this report, we demonstrate a simple approach that takes advantage of the metastable, temperature-dependent structure of graphene oxide (GO) to enhance the mechanical properties of conventional 3D-printed resins produced by stereolithography (SLA). A commercially available SLA resin was reinforced with minimal amounts of GO nanofillers and thermally annealed at 50 and 100 °C for 12 h. Tensile tests revealed increasing strength and modulus at an annealing temperature of 100 °C, with the highest tensile strength increase recorded at 673.6% (for 1 wt % GO). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) also showed increasing thermal stability with increasing annealing temperature. The drastic enhancement in mechanical properties, which is seen to this degree in 3D-printed samples reported in literature, is attributed to the metastable...

Microstructure and properties of a CoCrFeNiMn high-entropy alloy processed by equal-channel angular pressing

Abstract: A CoCrFeNiMn high-entropy alloy (HEA) was processed by equal-channel angular pressing (ECAP) for up to four passes at 673 K and the results show that the strength increases gradually with increasing straining up to ~ 1 GPa with an elongation to failure of ~ 35% after four passes of ECAP. In this condition, the microstructure is a single-phase ultrafine-grained (UFG) CoCrFeNiMn HEA with an average grain size of ~ 100 nm and a high dislocation density. This UFG HEA was subjected to post-deformation annealing (PDA) at temperatures of 673–1073 K for 60 min and it is shown that the hardness increases slightly due to precipitation to 773 K and then decreases to 1073 K due to a combination of recrystallization, grain growth and a dissolution of precipitates. The formation of brittle σ -phase precipitates improves the strength significantly but with a minor decrease in ductility. Annealing at the peak temperature of 773 K produces a very high yield strength of ~ 1015 MPa and an ultimate strength of ~ 1080 MPa together with an excellent elongation to failure of ~ 30%. An analysis of the data shows that grain boundary strengthening is the most important strengthening mechanism in these ECAP samples both before and after PDA.

Low-Temperature Atomic Layer Deposition of MoS2 Films

Abstract: Wet chemical screening reveals the very high reactivity of Mo(NMe2)4 with H2S for the low-temperature synthesis of MoS2. This observation motivated an investigation of Mo(NMe2)4 as a volatile precursor for the atomic layer deposition (ALD) of MoS2 thin films. Herein we report that Mo(NMe2)4 enables MoS2 film growth at record low temperatures—as low as 60 °C. The as-deposited films are amorphous but can be readily crystallized by annealing. Importantly, the low ALD growth temperature is compatible with photolithographic and lift-off patterning for the straightforward fabrication of diverse device structures.

Room-Temperature Processed Nb2O5 as the Electron-Transporting Layer for Efficient Planar Perovskite Solar Cells

Abstract: In this work, we demonstrate high-efficiency planar perovskite solar cells (PSCs), using room-temperature sputtered niobium oxide (Nb2O5) as the electron-transporting layer (ETL). Widely spread ETL-like TiO2 often requires high-temperature (>450 °C) sintering, which is not desired for the fabrication of flexible devices. The amorphous Nb2O5 (labeled as a-Nb2O5) ETL, without any heat treatment, can give a best power conversion efficiency (PCE) of 17.1% for planar PSCs. Interestingly, the crystalline Nb2O5 (labeled as c-Nb2O5), with high-temperature (500 °C) annealing, results in a very similar PCE of 17.2%, indicating the great advantage of a-Nb2O5 in energy saving. We thus carried out a systematical investigation on the properties of the a-Nb2O5 film. The Hall effect measurements indicate both high mobility and conductivity of the a-Nb2O5 film. Kelvin probe force microscopy measurements define the Fermi levels of a-Nb2O5 and c-Nb2O5 as −4.31 and −4.02 eV, respectively, which allow efficient electron extra...

Triple-cation mixed-halide perovskites: towards efficient, annealing-free and air-stable solar cells enabled by Pb(SCN) 2 additive

Abstract: Organo-metal halide perovskites have suffered undesirably from structural and thermal instabilities. Moreover, thermal annealing is often indispensable to the crystallization of perovskites and removal of residual solvents, which is unsuitable for scalable fabrication of flexible solar modules. Herein, we demonstrate the non-thermal annealing fabrication of a novel type of air-stable triple-cation mixed-halide perovskites, FA0.7MA0.2Cs0.1Pb(I5/6Br1/6)3 (FMC) by incorporation of Pb(SCN)2 additive. It is found that adding Pb(SCN)2 functions the same as thermal annealing process by not only improving the crystallinity and optical absorption of perovskites, but also hindering the formation of morphological defects and non-radiative recombination. Furthermore, such Pb(SCN)2-treated FMC unannealed films present micrometer-sized crystal grains and remarkably high moisture stability. Planar solar cells built upon these unannealed films exhibit a high PCE of 14.09% with significantly suppressed hysteresis phenomenon compared to those of thermal annealing. The corresponding room-temperature fabricated flexible solar cell shows an impressive PCE of 10.55%. This work offers a new avenue to low-temperature fabrication of air-stable, flexible and high-efficiency perovskite solar cells.

Three-dimensional porous MoNi4 networks constructed by nanosheets as bifunctional electrocatalysts for overall water splitting

Abstract: Non-noble bifunctional electrocatalysts for overall water splitting in alkali water solution are highly attractive. Herein, novel 3D porous MoNi4 networks constructed by nanosheets show superior catalytic activity and durability towards overall water splitting, rivaling state-of-the-art non-noble bifunctional electrocatalysts. The porous MoNi4 networks were prepared on porous Ni foam by the hydrothermal process and then with the annealing process in hydrogen. The porous MoNi4 networks annealed at 450 °C show high activity for both HER and OER. The superior catalytic performance is ascribed to not only being fully reduced into MoNi4 but also maintaining the original morphology as much as possible after annealing at 450 °C. NiOOH species were formed on the surface of the porous MoNi4 networks annealed at 450 °C after OER, and the in situ formation of NiOOH leads to excellent activity as well as stability in the OER. The 3D porous MoNi4 networks annealed at 450 °C need only ∼1.58 V to achieve 10 mA cm−2 for overall water splitting and exhibit excellent stability without loss of activity after 24 hours. A two-electrode device to split water with porous MoNi4 networks as bifunctional electrocatalysts can be driven by a single AA battery (1.5 V).

Defects and Surface Structural Stability of MoTe2 Under Vacuum Annealing.

Abstract: Understanding the structural stability of transition-metal dichalcogenides is necessary to avoid surface/interface degradation. In this work, the structural stability of 2H-MoTe2 with thermal treatments up to 500 °C is studied using scanning tunneling microscopy and scanning transmission electron microscopy. On the exfoliated sample surface at room temperature, atomic subsurface donors originating from excess Te atoms are observed and presented as nanometer-sized, electronically-induced protrusions superimposed with the hexagonal lattice structure of MoTe2. Under a thermal treatment as low as 200 °C, the surface decomposition-induced cluster defects and Te vacancies are readily detected and increase in extent with the increasing temperature. Driven by Te vacancies and thermal energy, intense 60° inversion domain boundaries form resulting in a “wagon wheel” morphology after 400 °C annealing for 15 min. Scanning tunneling spectroscopy identified the electronic states at the domain boundaries and the domain ...