Phase Equilibrium studies in the system “FeO”–SiO2–Al2O3–CaO–MgO at 1200 °C and Po2 10-8atm

Iron oxides and silica are the major components of copper smelting slag. The oxides of aluminum, calcium and magnesium are also present in the slag that is introduced through copper concentrate, flux and refractories. Liquidus temperatures of the copper smelting slags are usually controlled by Fe/SiO₂. The concentrations of Al₂O₃, CaO and MgO, and FeO/Fe₂O₃ in the slag can also affect the liquidus temperatures where FeO/Fe₂O₃ is a function of oxygen partial pressure. High temperature equilibration under controlled oxygen partial pressure followed by quenching and electron probe microanalysis were used to determine the compositions of the liquid and solid phases at 1200 °C and Po₂ 10^-8 atm. The experimental results are presented in the forms of pseudo-ternary sections “FeO”-CaO-SiO₂ at fixed 2, 4 and 6 wt pct MgO, and 2 + 2, 4 + 4 and 6 + 6 wt pct MgO + Al₂O₃. Spinel and tridymite are the major primary phases in the composition range investigated. In addition, CaSiO₃, pyroxene, olivine, and melilite are also present. The isotherms in the spinel and tridymite primary phase fields move towards higher SiO₂ concentration directions with increasing CaO, Al₂O₃, and MgO concentrations. The experimentally determined results are compared with the FactSage calculations.     

Experimental phase diagram study of the TiAl-rich part of the Ti–Al–Ni ternary system

Phase equilibria of the TiAl-rich part of the Ti–Al–Ni ternary system have been studied experimentally by scanning electron microscopy and electron probe micro-analysis of heat-treated alloys. Partial isothermal sections involving the liquid, β-Ti, α-Ti, α₂-Ti₃Al, γ-TiAl and τ₃-Al₃NiTi₂ phases were constructed between 1623 and 1273 K. Eight three-phase regions of the L + β + α, L + α + γ, L + β + γ, β + α + γ, L + β + τ₃, β + γ + τ₃, β + α₂ + τ₃ and α₂ + γ + τ₃ were derived. Extrapolations of these tie-triangles indicate the occurrence of three transition-type reactions; L + α = β + γ at around 1593 K, L + γ = β + τ₃ at around 1553 K, and β + γ = α + τ₃ at around 1393 K. The Ni solid solubility in the α and α₂ phase is extremely low, less than 1 at.% in all studied temperature ranges.     

Efficient organic light-emitting diodes with C60 buffer layer

Organic light-emitting diodes (OLEDs) with C₆₀ buffer layer were fabricated. The effect of C₆₀ buffer layer on the performance of the devices was investigated by inserting C₆₀ buffer layer at the interface between the electrode and organic layers. The device structures were (1) ITO/C₆₀ (0.0, 0.4, 0.7 and 1.0 nm)/NPB/Alq₃/LiF/Al and (2) ITO/NPB/Alq₃/C₆₀ (0.0, 0.4, 0.7 and 1.0 nm)/LiF/Al. The highest brightness and efficiency of the device (1) with 0.7 nm-thick C₆₀ layer reached 6439 cd/m² at 16 V and 1.80 cd/A at 6.4 V, respectively. The enhancements in brightness and efficiency are attributed to an improved balance of hole and electron injections due to C₆₀ layer blocking parts of the injected holes. On the contrary, the brightness and efficiency of the devices with the structure (2) had been hardly enhanced.     

An efficient and bright organic white-light-emitting device

A white-light-emitting device has been fabricated with a structure of ITO/NPB/BCP/Alq₃/LiF/Al. The hole blocking layer(BCP) result in a mixture of lights from NPB molecules (blue-light) and Alq₃ molecules (olivine-light), thereby producing white-light emission. The chromaticity can be readily adjusted by only varying the thickness of the BCP layer. The CIE coordinates of the device are largely insensitive to the driving voltages. The maximum brightness is 5740 cd/m², the EL efficiency is 2.12 cd/A at the applied voltage of 18 V.     

Development and performance analysis of a low-cost MEMS microphone-based hearing aid with three different audio amplifiers

In this paper, MEMS-based capacitive microphone and low-cost amplifier are designed for low-cost power-efficient hearing aid application. The developed microphone along with the associated circuitry is mounted on a common board in the form of pocket-type (body-worn) device. The designed microphone consists of a flexible circular silicon nitrite (Si₃N₄) diaphragm and a polysilicon-perforated back plate with air as dielectric between them. The incident acoustic waves on the sensor cause deflection of the diaphragm to alter the air gap between the perforated back plate (fixed electrode) and the diaphragm (moving plate) which causes a change in capacitance. The acoustic pressure applied to the microphone is from 0 to 100 Pa for an operating range of 100 Hz–10 kHz which corresponds to the audible frequency range in case of human beings. The main purpose of this work is to increase the longevity of battery used in conventional hearing aids. The designed MEMS microphone with Si₃N₄ diaphragm is capable of identifying acoustic frequencies (100 Hz to 10 kHz) which correspond to a specific change in absolute pressure from 0 to 100 Pa for 2-micron-thick diaphragm with a sensitivity of about 0.08676 mV/Pa. The design of the sensor and the characteristics analysis are performed in FEM-based simulation software, which are later validated in real time. The prototype is designed using MEMS microphone and low-cost amplifier ICs with biasing components in the form of pocket-type (body-worn) hearing aid. In order to study the performance of proposed device, three different market-available amplifiers with controllable gain are used. Finally, the performance of the hearing aid is studied through audio spectrogram analysis to choose the best-suited amplifier among the three.

     

Analysis of interface states of metal–insulator–semiconductor photodiode with n-type silicon by conductance technique

A metal–insulator–semiconductor photodiode (MIS-PD) as active layer with n-type silicon as interdigitated Schottky electrodes has been fabricated. The current–voltage characteristics, density of interface states and photovoltaic properties of the MIS-PD diode have been investigated. The diode has a metal–insulator–semiconductor configuration with ideality factor higher than unity. The electronic parameters (ideality factor, series resistance and barrier height) of the diode were found to be 1.94, 2.23 × 10⁴ Ω and 0.74, respectively. At voltages between 0.13 and 0.50 V, the charge transport mechanism of the diode is controlled by space charge-limited current mechanism. The interface state density of the diode was found to vary from 5.54 × 10¹² to 5.67 × 10¹² eV⁻¹ cm⁻² with bias voltage. The Au/SiO₂/n-Si/Al device shows a photovoltaic behavior with a maximum open circuit voltage V_oc of 97.7 mV and short-circuit current I_sc of 17.4 μA under lower illumination intensities. The obtained electronic parameters confirm that the Au/SiO₂/n-Si/Al diode is a MIS type photodiode.     

Cationic P⋯N interaction in XH3P+⋯NCY complexes (X = H,F, CN,NH2, OH; Y = H,Li, F,Cl) and its cooperativity with hydrogen/lithium/halogen bond

The geometries, interaction energies and bonding properties of cationic pnicogen bond (CPB) interactions are studied in binary XH₃P⁺⋯NCY (X = H, F, CN, NH₂, OH; Y = H, Li, F, Cl) complexes by means of MP2/aug-cc-pVTZ calculations. Interaction energies of these binary complexes span a large range, from −16.36 kcal/mol in (NH₂)H₃P⁺⋯NCF to −71.36 kcal/mol in FH₃P⁺⋯NCLi complex. The spin–spin coupling constant across P⋯N interaction depends considerably on the nature of X and Y substituents. The characteristic of CPB interactions is analyzed in terms of parameters derived from quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. The charge transfer from the nitrogen base to the cationic acid stabilizes these pnicogen–bonded complexes. For a given XH₃P⁺, the net charge transfer value increases as the interaction energy of the complex becomes more negative, i.e., NCLi > NCCl > NCH > NCF. Moreover, mutual influence between the CPB and hydrogen/halogen/lithium bond is studied in the ternary XH₃P⁺⋯NCY⋯NCH complexes. The results indicate that the formation of a Y⋯N interaction tends to strengthen CPB in the ternary systems.     

Piezo-tunneling strain sensors integrated on plastic by combining vacuum thin film coatings and 3D printing technologies

There is a growing demand for the integration of sensor functions on flexible substrates for wearable electronics, robotics or medical monitoring. For this, it is necessary to develop strain gauges both sensitive and integrable at low cost with a low thermal budget. The gauge factor of metal/insulator/metal piezo-tunneling strain sensors is first measured as a function of applied current and polarity, for different electrode materials (Al, Pt or Pd) and insulator (Al₂O₃) thicknesses. A maximum gauge factor of 90 is obtained with an Al/Al₂O₃ (10 nm)/Al junction and top electrode injection. Results are discussed based on the Fowler–Nordheim model and it is shown that the electron effective mass in Al₂O₃ most likely plays a major role in the observed mechano-sensitivity. Next, the feasibility of a low-pressure sensor demonstrator based on a 3D-printing process on a polymer substrate is shown with a sensitivity of 0.19 bar⁻¹ in the 0–450 mbar range.

     

Ab initio study of mono-layer 2-D insulators (X-(OH)2 and h-BN) and their use in MTJ memory device

The paper presents an ab initio study of the 2-D insulators and their effect on the performance of a magnetic tunnel junction memory (MTJ) device. MTJ devices has been considered as an alternate to the charge based data storage cells due to its spin-polarised operation and high scaling probability. The use of 2-D insulators like X-(OH)₂ (X: Ca and Mg) and h-BN (hexagonal-Boron Nitride) in such device would be interesting. The authors have calculated the band structures, density of states and effective mass of electrons and holes for the mono-layer of these three non-conventional 2-D insulators using the first principle calculations in density functional theory framework using Quantumwise ATK tool. The ab initio calculation yielded band gap (E_g) of 4.633, 4.685 and 4.249 eV for h-BN, Ca(OH)₂ and Mg(OH)₂, respectively. The effective mass of electrons was calculated as 0.621, 0.604 and 0.478 for single layer h-BN, Ca(OH)₂ and Mg(OH)₂, respectively. While for holes it is 0.834, 0.446 and 0.407, respectively for h-BN, Ca(OH)₂ and Mg(OH)₂. The MTJ device properties as tunneling-magneto resistance, differential TMR, parallel and anti-parallel resistance, differential resistance and spin transfer torque components (in-plane and out-of-plane) with these materials as composite dielectric has been reported in this paper using MTJ Lab tool. The performance of MTJ memory device with h-BN based composite dielectric is found better.

     

Phase equilibria of the Cu–Zr–Si system at 750 and 900 °C

Phase equilibria in the ternary Cu–Zr–Si system at 750 and 900 °C have been experimentally investigated via electron probe micro-analyzer (EPMA) and X-ray diffraction (XRD) analysis on the equilibrated alloys. The results show the presence of eight three-phase regions at 750 °C and seven three-phase regions at 900 °C. Four ternary phase: τ₁ (Zr₃Cu₄Si₆, tI26-Zr₃Cu₄Si₆), τ₄ (Zr₃Cu₄Si₄, oI22-Gd₃Cu₄Ge₄), τ₅ (ZrCuSi, oP12-Co₂Si), and τ₆ (Zr₃Cu₄Si₂, 2hP9-Fe₂P) were confirmed to exist in the Cu–Zr–Si ternary system at 750 and 900 °C. At 900 °C, the dark gray phase, the chemical composition of which is close to η-Cu₃Si, is confirmed to be the liquid phase. Moreover, the solubilities of Cu in ZrSi₂, SiZr and Zr₃Si₂ are considerably small. The solubility of Zr in η-Cu₃Si is determined to be negligible. The newly determined phase equilibria of the Cu–Zr–Si system in this work can provide important experimental data for the thermodynamic assessment of the Cu–Zr–Si system and to develop the Cu–Zr–Si alloys and related transition metal silicides.     

Characterization of Al–Ni intermetallics around 30–60 at% Al for TLPB application

Interest on the Al–Ni equilibrium diagram along the latest years is associated with the attractive properties of its intermetallic phases, such as high thermal stability, high corrosion resistance and high strength to density ratio. The Transient Liquid Phase Bonding (TLPB) is a technological process which can be applied to manufacture new pieces and to perform reparations. Morphology, composition profiles, growth kinetic and hardness as a function of temperature and composition of the Intermetallic Layers (ILs) were analyzed, especially focused on solid–solid interactions during isothermal annealing in reactive diffusion couples Ni/Al (800–1170 °C). The study yields to the following association of the Al–Ni Intermetallic Phases (IPs) to the ILs: L₁ (Al₃Ni), L₂ (Al₃Ni₂), L₃ (Ni-poor AlNi), L₄ (Ni-rich AlNi) and L₅ (AlNi₃). The composition ranges of L₃ and L₄ are 36–46 and 53–58 at% Al, respectively. Martensitic transformation was found in the half thickness of L₄ (L_4M and L_4S) at 1170 °C. Kinetics show diffusion controlled growth for L₂ and L₅ and interface reaction control for L₄ at 800–1170 °C, while L₃ revealed a mixed kinetic behavior: parabolic at 800–1000 °C and linear at 1170 °C. The growth rate constants presented temperature dependence according to the Arrhenius model. Vickers microhardness values decrease with annealing temperature and Ni concentration for ILs, and put in evidence different mechanical properties of L₃, L_4M and L_4S.     

Unlocking the potential of p-doped hole transport layers in inverted organic light emitting diodes

The MoO₃ doped N,N′-bis-(1-naphthyl)-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB:MoO₃ in 2:1 mass ratio) and 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO₃ in 2:1 mass ratio) as p-doped hole transport layers have been used in inverted organic light emitting diodes (IOLEDs). Compared to the NPB/20 nm NPB:MoO₃ structure, the NPB/10 nm CBP:MoO₃/10 nm NPB:MoO₃ structure showed increased device performance, mostly because the hole transport barrier from CBP:MoO₃ to NPB was smaller than that from NPB:MoO₃ to NPB; it also presented improved device performance than the NPB/20 nm CBP:MoO₃ structure, ascribed to the higher conductivity of NPB:MoO₃ than that of CBP:MoO₃. We provide a manageable way to unlock the merits of p-doped hole transport layers for markedly increasing the performance of IOLEDs.     

Theoretical study of the geometries and decomposition energies of CO2 on Al12X: Doping effect of Al12X

The adsorption and decomposition of CO₂ molecule on X-centered icosahedronal Al₁₂X clusters (doping atom X = Al, Be, Zn, Fe, Ni, Cu, B, C, Si, P) were investigated by the DFT methods of PW91 and PWC. Adsorption energies, chemisorption energies and energy barriers of physic- and chemisorptions for CO₂ were determined. It was found that the doping atoms and spin states have important influences on the Al₁₂X geometries, electronic properties and energies of the adsorption processes. CO₂ chemisorption on the Al₁₂C cluster is energetically and kinetically unfavorable. CO₂ decomposition on the metallic doping Al₁₂X (X = Fe, Ni, Cu) clusters has relatively low energy barriers. On contrary, the barriers are large when X = B, C, Si and P. The energy barriers for CO₂ chemisorption and decomposition on the Al₁₂Fe cluster are 5.23 kJ/mol and 38.53 kJ/mol, respectively. These values are the lowest among all the clusters being discussed. The adsorption and decomposition of CO₂ on the Al₁₂X cluster can be tuned by X doping.     

Modeling of phase relations and thermodynamics in the Mg(OH)2 + MgSO4 + H2O system with implications on magnesium hydroxide sulfate cement

Temperature-dependent thermodynamic models for Mg(OH)₂ + H₂O and Mg(OH)₂ + MgSO₄ + H₂O systems were developed using the CALPHAD approach. Six magnesium hydroxide sulfate (MHS) hydrates, i.e. 5-1-2, 3-1-8, 1-2-2, 1-2-3, 1-1-5, and 5-1-7, were included in the ternary model and their thermodynamic properties were determined as functions of temperature. The reliability of the solubility data, solubility products and thermochemical data of brucite were evaluated by considering the internally thermodynamic consistency of them. Ternary solubilities of brucite, 5-1-2 and 3-1-8 phases reported in literature were generally evaluated for the development a temperature-dependent ternary model. The models were applied to simulate the phase relations of the Mg(OH)₂ + MgSO₄ + H₂O systems and the hydration products of MHS cement. However, the model is limited due to the lack of reliable solubility and thermodynamic data in the system. Only with the appearance of sufficient and reliable experimental data, the model can really be adapted or evaluated. Provisionally, according to the simulations, brucite, MgSO₄·7H₂O, MgSO₄·6H₂O, MgSO₄·H₂O and the 5-1-2 phase were identified as stable MHS phases, while 3-1-8, 5-1-7, 1-1-5, 1-2-3 and 1-2-2 were metastable. A preferable proportion is MgO:MgSO₄:H₂O molar ratio 5:1:12, from which a cement stone with composition of 88.2 wt% ‘3-1-8’+11.8 wt% brucite or 100 wt% ‘5-1-7’ could be produced, respectively. However, it was noticeable that both of the two cement stones were thermodynamically metastable. The long-term performance of them would suffer from the phase transition to stable state. Moreover, thermodynamically stable 5-1-2 phase is also only stable in presence of MgSO₄-containing solution. Therefore, the poor weather resistant of the material as conventional cement is inherent.     

Phase equilibria study in the system “Fe2O3”-ZnO-Al2O3-(PbO+CaO+SiO2) in air

Phase equilibria studies have been undertaken first time in the system PbO-“FeO_x”-CaO-SiO₂-ZnO-Al₂O₃. Pseudo-ternary section of the phase diagram “Fe₂O₃”-ZnO-(PbO + CaO + SiO₂) with CaO/SiO₂ weight ratio of 0.93 and PbO/(CaO + SiO₂) weight ratio of 2.0 at fixed 4 wt% Al₂O₃ has been constructed by equilibration and quenching technique. Zincite, spinel, melilite and Ca₂SiO₄ are the major primary phases in the temperature and composition ranges investigated. It was found that, Al₂O₃ stabilizes the spinel and melilite phases and extents their primary phase fields. The liquidus temperatures are increased in the spinel primary phase filed and decreased in the zincite primary phase field with increasing Al₂O₃. Significant difference of the liquidus temperatures is observed between the experimental data and FactSage calculations. Accurate compositions of the solid solutions have been determined in the present study together with the accurate temperature and liquid compositions. This study can provide direct support for industrial practice and optimization of the thermodynamic database.     

Relationship between exciton recombination zone and applied voltage in organic light-emitting diodes

In this paper, the relationship between exciton recombination zone and applied voltage in organic light-emitting diodes (OLEDs) ITO/NPB (40 nm)/Alq₃(w nm)/rubrene(3 nm)/Alq₃(50−w)/Al, in which a 3 nm rubrene as sensing layer is inserted in Alq₃ layer at different depth, is studied. By comparing the electroluminescence (EL) spectra of device driven under different applied voltages, a conclusion can be drawn that the recombination zone shifts logarithmically with increasing applied voltages.     

Development of a continuous injection direct rolling imprint system for microstructure thin-plate

A prototype of a continuous injection direct rolling (CIDR) imprint system was developed and applied to CIDR tests to evaluate its feasibility for the large-area replication of an optical micro device. The developed system adopts the theories of injection compression and thermal imprinting and presents the capacity to fabricate a 200 mm-wide and over 10 m-long PMMA plate and to replicate ultra-precision structures on its surface at a rolling speed range of 1.1–11.5 mm/s. Under the given CIDR conditions (injection temperature, 280 °C; injection pressure, 6 MPa; rolling force, 13 MPa; roller temperature, 85 °C), complete fabricating of a 0.7 mm-thick Polymethyl methacrylate (PMMA) plate with 17.3 μm-deep and 35 μm-wide V-groove microstructures was achieved at a rolling speed of 3.4 mm/s. Finally, a light guide plate for a backlight panel was fabricated by CIDR. The light transmittance of this plate reached 90.8 %, the maximum birefringence was ~99 nm and its average haze was 0.51 %.

     

Single quantum dot-micelles coated with gemini surfactant for selective recognition of a cation and an anion in aqueous solutions

The synthesis of quantum dot coated with cetyltrimethyl ammonium bromide (CTAB) and gemini surfactant [C₁₂H₂₅N⁺(CH₃)₂(CH₂)₄(CH₃)₂N⁺C₁₂H₂₅]·2Br⁻ (C_12-4-12) in aqueous solution have been described. It is characterized by photoluminescent spectroscopy, UV–vis spectroscopy and transmission electron microscopy (TEM), etc. In comparison with CTAB-coated QDs, the QDs coated with C_12-4-12 respond selectively to both transition metal ion copper and fluoride ion in aqueous media. When Cu²⁺ is bound to C_12-4-12-coated QD micelles, the fluorescence intensity is quenched. Linear relationships are found between the relative fluorescence intensity and the concentration of Cu²⁺ in the range 0–500 μM, which is best described by a Stern–Volmer-type equation. Meanwhile, it is found that F⁻ enhanced the luminescence of the C_12-4-12-coated QD micelles in a concentration dependence that is described by a Langmuir binding isotherm equation in the range 0–300 μM. The limits of detection of Cu²⁺ and F⁻ are 1.1 and 0.68 μM, respectively. The possible mechanism is discussed.     

Investigation of surface roughness in the milling of Al7075 and open-cell SiC foam composite and optimization of machining parameters

In the present study, aluminum alloy 7075 (Al7075)-based open-cell silicon carbide (SiC) foam composite was fabricated and the machinability of both Al7075 and the open-cell SiC foam Al metal matrix composite was investigated during milling using an uncoated carbide tool. The machining trials were conducted using the Taguchi L₂₇ full-factorial orthogonal array, and the milling parameters were optimized for surface roughness. Analysis of variance was employed to determine the effect of the cutting variables on surface roughness. The experimental results were evaluated by signal-to-noise ratio, 3D surface graphs, artificial neural networks (ANNs) and main effect graphs. The analysis results show that the feed rate was the most significant milling parameter affecting surface roughness of both Al7075 and the open-cell SiC foam composite. Prediction models have been developed for the surface roughness through regression analysis and ANNs. Confirmation experiments were performed to identify the performance of mathematical models, and the surface roughness was predicted with a mean squared error equal to 1.6 and 0.24 % in the milling of Al7075 and open-cell SiC foam composite, respectively. The test result showed that the three-dimensional open-pore SiC foam network reinforcement was restricted the movement of the soft matrix and provided an acceptable surface quality in the milling of MMCs.