Effects of post-sinter annealing on microstructure and magnetic properties of Nd–Fe–B sintered magnets with Nd–Ga intergranular addition

We investigate the effects of post-sinter annealing on the microstructure and magnetic properties in B-lean Nd–Fe–B sintered magnets with different quantities of Nd–Ga intergranular additions. The magnet with fewer Nd–Ga additions can enhance 0.2 T in coercivity, with its remanences nearly unchanged after annealing. With the further increase of the Nd–Ga addition, the annealing process leads coercivity to increase 0.4 T, accompanied by a slight decrease of remanence. With the Nd–Ga addition further increasing and after annealing, however, the increase of coercivity is basically constant and the change of remanence is reduced. Microstructure observation indicates that the matrix grains are covered by continuous thin grain boundary phase in the magnets with an appropriate Nd–Ga concentration after the annealing process. However, the exceeding Nd–Ga addition brings out notable segregation of grain boundary phase, and prior formation of part RE6 Fe13 Ga phase in the sintered magnet. This prior formation results in a weaker change of remanence after the annealing process.Therefore, the diverse changes of magnetic properties with different Nd–Ga concentrations are based on the respective evolution of grain boundary after the annealing process.     

Ceramic synthesis of 0.08BiGaO_3–0.90BaTiO_3–0.02LiNbO_3 under high pressure and high temperature

In this paper, the preparation of 0.08BiGaO_3–0.90BaTiO_3–0.02LiNbO_3 is investigated at pressure 3.8 GPa and temperature 1100–1200?C. Experimental results indicate that not only is the sintered rate more effective, but also the sintered temperature is lower under high pressure and high temperature than those of under normal pressure. It is thought that the adscititious pressure plays the key role in this process, which is discussed in detail. The composition and the structure of the as-prepared samples are recorded by XRD patterns. The result shows that the phases of Ba TiO_3, BaBiO_(2.77), and Ba_2Bi_4Ti_5O_(18) with piezoelectric ceramic performance generate in the sintered samples. Furthermore, the surface morphology characteristics of the typical samples are also investigated using a scanning electron microscope. It indicates that the grain size and surface structure of the samples are closely related to the sintering temperature and sintering time. It is hoped that this study can provide a new train of thought for the preparation of lead-free piezoelectric ceramics with excellent performance.     

Effect of the annealing temperature on the long-term thermal stability of Pt/Si/Ta/Ti/4H–SiC contacts

The Pt/Si/Ta/Ti multilayer metal contacts on 4H–Si C are annealed in Ar atmosphere at 600°C–1100°C by a rapid thermal processor(RTP). The long-term thermal stability is evaluated by aging the annealed contact at 600°C in air. The contact's properties are determined by current–voltage measurement, and the specific contact resistance is calculated based on the transmission line model(TLM). Transmission electron microscope(TEM) and energy-dispersive x-ray spectrometry(EDX) are used to characterize the interface morphology, thickness, and composition. The results reveal that a higher annealing temperature is favorable for the formation of an Ohmic contact with a lower specific contact resistance, and causes the rapid degradation of the Ohmic contact in the aging process.     

Observation of selective surface element substitution in FeTe_(0.5)Se_(0.5) superconductor thin film exposed to ambient air by synchrotron radiation spectroscopy

A systematic investigation of oxidation on a superconductive Fe Te_(0.5)Se_(0.5)thin film,which was grown on Nb-doped SrTiO_3(001) by pulsed laser deposition,has been carried out.The sample was exposed to ambient air for one month for oxidation.Macroscopically,the exposed specimen lost its superconductivity due to oxidation.The specimen was subjected to in situ synchrotron radiation photoelectron spectroscopy(PES) and x-ray absorption spectroscopy(XAS) measurements following cycles of annealing and argon ion etching treatments to unravel what happened in the electronic structure and composition after exposure to air.By the spectroscopic measurements,we found that the as-grown FeTe_(0.5)Se_(0.5)superconductive thin film experienced an element selective substitution reaction.The oxidation preferentially proceeds through pumping out the Te and forming Fe–O bonds by O substitution of Te.In addition,our results certify that in situ vacuum annealing and low-energy argon ion etching methods combined with spectroscopy are suitable for depth element and valence analysis of layered structure superconductor materials.     

High thermal stability of diamond-cBN-B_4C-Si composites

Improving the thermal stability of diamond and other superhard materials has great significance in various applications. Here, we report the synthesis and characterization of bulk diamond–cBN–B_4C–Si composites sintered at high pressure and high temperature(HPHT, 5.2 GPa, 1620–1680 K for 3–5 min). The results show that the diamond, cBN, B_4C,B_xSiC, SiO_2 and amorphous carbon or a little surplus Si are present in the sintered samples. The onset oxidation temperature of 1673 K in the as-synthesized sample is much higher than that of diamond, cBN, and B_4C. The high thermal stability is ascribed to the covalent bonds of B–C, C–N, and the solid-solution of B_xSiC formed during the sintering process. The results obtained in this work may be useful in preparing superhard materials with high thermal stability.     

Fluctuations of optical phase of diffracted light for Raman–Nath diffraction in acousto–optic effect

The Raman–Nath diffraction in acousto–optic effect was studied theoretically and experimentally in the paper.Up to now,each order of diffracted light in Raman–Nath diffraction was still considered simply to be just frequency-shifted and to be a plane wave.However,we find that the phase and frequency shifts occur simultaneously and individually in Raman–Nath diffraction.The findings demonstrate that,in addition to the frequency shift,the optical phase of each order of diffracted light is also shifted by the sound wave and fluctuates with the sound wave and is related to the location in the acoustic field from which the diffracted light originates.As a result,the wavefront of each order of diffracted light is modulated to fluctuate spatially and temporally with the sound wave.Obviously,these findings are significant for applications of Raman–Nath diffraction in acousto–optic effect because the optical phase plays an important role in optical coherence technology.     

Corrosion behavior of high-level waste container materials Ti and Ti–Pd alloy under long-term gamma irradiation in Beishan groundwater

Titanium and titanium–palladium alloys are important potential materials for nuclear waste container, which will endure both intense γ-irradiation and groundwater erosion. Therefore, it is very important to investigate the corrosion behavior of the container materials. In this research, the cumulative dose effect of TA8-1 type titanium–palladium alloy(TA8-1) and TA2-type pure titanium(TA2) under γ-irradiation was studied based on the geological disposal of nuclear wastes. The irradiation experiments were performed at room temperature using60 Co gamma sources with a 5.0-k Gy·h-1 intensity for 40, 80 or 160 days, respectively. The p H value and conductivity of Beishan groundwater were investigated.The results showed that the p H value changed from alkaline(8.22) to acidic(2.46 for TA8-1 and 2.44 for TA2), while the un-irradiated solution remained alkaline(8.17 for TA8-1 and 8.20 for TA2) after 160 days. With the increase of irradiation dose, the conductivity increases rapidly and then tends to become stable, which indicates that the titanium dioxide corrosion layer formed on the surface of the sample surface effectively prevents further corrosion. Meanwhile, XRD and SEM–EDS analysis results show that the main components of corrosion products are Ti O_2 and Ti O. The titanium on the surface of the sample is oxidized, resulting in slight uneven local corrosion. The results show that TA8-1 and TA2 are suitable to be used as candidate materials for high-level waste(HLW) disposal containers due to their excellent performance under long-term and high-dose irradiation corrosion.     

Equilibrium between NO_3~- and NO_2~- in KNO_3–NaNO_2 melts:a Raman spectra study

We study ionic structure of KNO3–NaNO2 melts under air atmosphere by using Raman spectroscopy. Molar fraction of NO--3 and NO2 is obtained and thermal stability of this kind of melts system is then analyzed. The results show that when the temperature is increased to a certain value, equilibrium between the decomposition of NO-3 and the oxidation of NO-2 exists in KNO3–NaNO2 melts. When temperature is higher than 644 K, the molar fraction of NO-3 decreases a little with temperature increasing for the melts in which the initial fraction of KNO3 is 90 wt%, but for the melts in which the initial fraction of KNO3 is 10–80 wt%, the molar fraction of NO-3 increases with temperature, and the increasing rate is slower for a higher initial fraction of KNO-3. Molar fraction of NO3 increment increases linearly with initial fraction of NaNO2. The sample in which the initial fractions of NaNO2 are 11.3 and 14.5 wt% under air atmosphere shows the best thermal stability at 762 and 880 K, respectively.     

Effects of terbium sulfide addition on magnetic properties,microstructure and thermal stability of sintered Nd-Fe--B magnets

To increase coercivity and thermal stability of sintered Nd–Fe–B magnets for high-temperature applications, a novel terbium sulfide powder is added into(Pr_(0.25)Nd_(0.75))_(30.6)Cu_(0.15)Fe_(bal)B_1(wt.%) basic magnets. The effects of the addition of terbium sulfide on magnetic properties, microstructure, and thermal stability of sintered Nd–Fe–B magnets are investigated.The experimental results show that by adding 3 wt.% Tb_2S_3, the coercivity of the magnet is remarkably increased by about 54% without a considerable reduction in remanence and maximum energy product. By means of the electron probe microanalyzer(EPMA) technology, it is observed that Tb is mainly present in the outer region of 2:14:1 matrix grains and forms a well-developed Tb-shell phase, resulting in enhancement of HA, which accounts for the coercivity enhancement.Moreover, compared with Tb_2S_3-free magnets, the reversible temperature coefficients of remanence(α) and coercivity(β) and the irreversible flux loss of magnetic flow(hirr) values of Tb_2S_3-added magnets are improved, indicating that the thermal stability of the magnets is also effectively improved.     

Total ionizing dose effects in pinned photodiode complementary metal-oxide-semiconductor transistor active pixel sensor

A pinned photodiode complementary metal–oxide–semiconductor transistor(CMOS) active pixel sensor is exposed to ~(60)Co to evaluate the performance for space applications. The sample is irradiated with a dose rate of 50 rad(SiO_2)/s and a total dose of 100 krad(SiO_2), and the photodiode is kept unbiased. The degradation of dark current, full well capacity,and quantum efficiency induced by the total ionizing dose damage effect are investigated. It is found that the dark current increases mainly from the shallow trench isolation(STI) surrounding the pinned photodiode. Further results suggests that the decreasing of full well capacity due to the increase in the density, is induced by the total ionizing dose(TID) effect, of the trap interface, which also leads to the degradation of quantum efficiency at shorter wavelengths.     

Progress in recycling of Nd–Fe–B sintered magnet wastes

Significant efforts have been put into the recycling of bulk Nd–Fe–B sintered magnet wastes around the world in the past decade because bulk Nd–Fe–B sintered magnet wastes are valuable secondary rare-earth resources.There are two major facts behind the efforts.First, the waste magnets contain total rare-earth content as high as more than 30 wt.%, which is higher than most natural rare-earth mines.Second, the waste magnets maintain the physical and chemical properties of the original magnets even with deterioration of the properties on surfaces due to corrosion and contamination.In this review,various techniques for recycling bulk Nd–Fe–B sintered magnet wastes, the overall properties of the recycled Nd–Fe–B sintered magnets, and the mass production of recycled magnets from the wastes are reviewed.     

Chaotic analysis of Atangana–Baleanu derivative fractional order Willis aneurysm system

A new Willis aneurysm system is proposed, which contains the Atangana–Baleanu(AB) fractional derivative.we obtain the numerical solution of the Atangana–Baleanu fractional Willis aneurysm system(ABWAS) with the AB fractional integral and the predictor–corrector scheme.Moreover, we research the chaotic properties of ABWAS with phase diagrams and Poincare sections.The different values of pulse pressure and system order are used to evaluate and compare their effects on ABWAS.The simulations verify that the changes of pulse pressure and system order are the significant reason for ABWAS'states varying from chaotic to steady.In addition, compared with Caputo fractional WAS(FWAS),ABWAS shows less state that is chaotic.Furthermore, the results of bifurcation diagrams of blood flow damping coefficient and reciprocal heart rate show that the blood flow velocity tends to stabilize with the increase of blood flow damping coefficient or reciprocal heart rate, which is consistent with embolization therapy and drug therapy for clinical treatment of cerebral aneurysms.Finally, in view of the fact that ABWAS in chaotic state increases the possibility of rupture of cerebral aneurysms, a reasonable controller is designed to control ABWAS based on the stability theory.Compared with the control results of FWAS by the same method, the results show that the blood flow velocity in the ABWAS system varies in a smaller range.Therefore, the control effect of ABWAS is better and more stable.The new Willis aneurysm system with Atangana–Baleanu fractional derivative provides new information for the further study on treatment and control of brain aneurysms.     

Regulating element distribution to improve magnetic properties of sintered Nd–Fe–B/Tb–Fe–B composite magnets

Nd content was varied in Nd_(13.2-x)Fe_(80.8+x)B_6(x = 0, 0.5, 1, and 1.5) to optimize the magnetic properties of sintered Nd–Fe–B/Tb–Fe–B composite magnets, which were prepared by mixing 9 g of Nd–Fe–B with 1 g of Tb_(17)Fe_(75)B_8 powder.In conventional magnets, by reducing Nd content, the coercivity of 10.4 kOe in Nd_(13.2)Fe_(80.8)B_6 decreases to 7.2 kOe in Nd_(12.2)Fe_(81.8)B_6; meanwhile, in Nd–Fe–B/Tb–Fe–B magnets the coercivity does not decrease when reducing Nd content.In the intergranular phase, the Tb content increases owing to the reducing Nd content of the Nd–Fe–B alloy in the sintered composite magnets.Therefore, the excess Tb in Tb_(17)Fe_(75)B_8 enters the intergranular phase, and more Tb atoms can substitute for Nd at the grain boundary of the Nd–Fe–B phase, leading to a more significant increase in coercivity.The remanence increases with reducing Nd content, and the energy product of 39.1 MGOe with a high coercivity of 21.0 kOe is obtained in Nd_(12.2)Fe_(81.8)B_6/Tb_(17)Fe_(75)B_8 magnets.These investigations show that magnetic properties can be further improved by regulating the element distribution in sintered composite magnets.     

Effect of optimized aging processing on properties of the sintered Dy-doped Nd–Fe–B permanent magnet

We investigate the effect of the optimized aging processing on magnetism and mechanical property of the sintered Dydoped Nd–Fe–B permanent magnet. The experimental results show that the magnetism, especially intrinsic coercivity, of the optimized aged Dy-doped Nd–Fe–B magnet is more excellent than that of the sintered one, but the former's strength and hardness are lower than that of the latter. It was observed that the optimized aged Dy-doped Nd–Fe–B magnet have more uniform grain size, thinner(Nd, Dy)-rich boundary phase. By means of the EBSD technology, the number of larger angle grain boundaries in the optimized aged Dy-doped Nd–Fe–B magnet is more than that of the sintered one. The reasons for the increased intrinsic coercivity and decreased mechanical properties of the optimized aged Dy-doped Nd–Fe–B magnet are also discussed.     

Properties of passive nano films on zircaloy-4 affected by defects induced by hydrogen permeation

In this work, hydrogen absorption and the permeation behavior of the passive layer formed on zircaloy-4 are investigated. Potentiodynamic polarization, Mott–Schottky analysis, electrochemical impedance spectroscopy, and Raman scattering spectroscopy are employed to characterize the passive defects before and after hydrogen permeation. It is found that the nanoscale passive ZrO2 films play an important role in the resistance against corrosion; hydrogen impingement,however, reduces the passive impedance towards hydrothermal oxidation. The increase of defects(vacancies) in passive film is probably attributed to the degradation. We believe that this finding will provide valuable insight into the understanding of the corrosion mechanism of zircaloys used in light water reactors.     

Magnetic Microstructure of Sintered Nd-Fe-B Magnets Made from Casting Strips

The magnetic microstructures of two Dy-AI substituted sintered Nd-Fe-13 magnets with the different nominal compositions of Nd12.2Vy0.6Fe80.4Al0.7B6 (at.%) (composition-A,C-A) and Nd13.7Dy0.6Fe78.8Al0.7B6.2(at.%)(composition-B,C-13) prepared by strip casting technique have been revealed by using a magnetic force microscope. The magnetic properties of sintered C-B magnets are worse than that of C-A sintered magnets. In particular, the value of density products (BH)max for sintered C-A magnets is about 32% higher than that of C-B magnets, which is reflected by their quite different magnetic microstructures. We believe that for the C-B samples, the inappropriate composition and thus the redundant Nd2Fe17(B) phase of the casting strips make its final magnetic microstructures worse than the C-A, and then deteriorates the performance of the C-B magnets.     

A multicomponent multiphase lattice Boltzmann model with large liquid–gas density ratios for simulations of wetting phenomena

A multicomponent multiphase(MCMP) pseudopotential lattice Boltzmann(LB) model with large liquid–gas density ratios is proposed for simulating the wetting phenomena. In the proposed model, two layers of neighboring nodes are adopted to calculate the fluid–fluid cohesion force with higher isotropy order. In addition, the different-time-step method is employed to calculate the processes of particle propagation and collision for the two fluid components with a large pseudoparticle mass contrast. It is found that the spurious current is remarkably reduced by employing the higher isotropy order calculation of the fluid–fluid cohesion force. The maximum spurious current appearing at the phase interfaces is evidently influenced by the magnitudes of fluid–fluid and fluid–solid interaction strengths, but weakly affected by the time step ratio.The density ratio analyses show that the liquid–gas density ratio is dependent on both the fluid–fluid interaction strength and the time step ratio. For the liquid–gas flow simulations without solid phase, the maximum liquid–gas density ratio achieved by the present model is higher than 1000:1. However, the obtainable maximum liquid–gas density ratio in the solid–liquid–gas system is lower. Wetting phenomena of droplets contacting smooth/rough solid surfaces and the dynamic process of liquid movement in a capillary tube are simulated to validate the proposed model in different solid–liquid–gas coexisting systems. It is shown that the simulated intrinsic contact angles of droplets on smooth surfaces are in good agreement with those predicted by the constructed LB formula that is related to Young's equation. The apparent contact angles of droplets on rough surfaces compare reasonably well with the predictions of Cassie's law. For the simulation of liquid movement in a capillary tube, the linear relation between the liquid–gas interface position and simulation time is observed, which is identical to the analytical prediction. The simulation results regarding the wetting phenomena of droplets on smooth/rough surfaces and the dynamic process of liquid movement in the capillary tube demonstrate the quantitative capability of the proposed model.     

Formation of hydrogen atom in 2s state in proton–sodium inelastic scattering

The inelastic collision of protons with sodium atoms are treated for the first time within the framework of the coupledstatic and frozen core approximations. The method is used for calculating partial and total cross-sections with the assumption that only two channels(elastic and hydrogen formation in 2s state) are open. In each case, the calculations are carried out for seven values of the total angular momentum l(0≤ l≤ 6). The target is described using the Clementi Roetti wave functions within the framework of the one valence electron model. We use Lipmann–Swinger equation to solve the derived equations of the problem, then apply an iterative numerical method to obtain the code of computer to calculate iterative partial cross-sections. This can be done through calculating the reactance matrix at different values of considered energies to obtain the transition matrix that gives partial and total cross sections. The present results for total hydrogen(2s state)formation cross sections are in agreement with results of other available ones in wide range of incident energy.     

Degradation of current–voltage and low frequency noise characteristics under negative bias illumination stress in InZnO thin film transistors

The instabilities of indium–zinc oxide thin film transistors under bias and/or illumination stress are studied in this paper. Firstly, illumination experiments are performed, which indicates the variations of current–voltage characteristics and electrical parameters(such as threshold voltage and sub-threshold swing) are dominated by the stress-induced ionized oxygen vacancies and acceptor-like states. The dependence of degradation on light wavelength is also investigated. More negative shift of threshold voltage and greater sub-threshold swing are observed with the decrease of light wavelength.Subsequently, a negative bias illumination stress experiment is carried out. The degradation of the device is aggravated due to the decrease of recombination effects between ionized oxygen vacancies and free carriers. Moreover, the contributions of ionized oxygen vacancies and acceptor-like states are separated by using the mid-gap method. In addition, ionized oxygen vacancies are partially recombined at room temperature and fully recombined at high temperature. Finally, low-frequency noise is measured before and after negative bias illumination stress. Experimental results show few variations of the oxide trapped charges are generated during stress, which is consistent with the proposed mechanism.     

Room temperature damping correlated to the microstructures in Cu–20.4Al–8.7Mn

The damping capacity of the shape memory alloy Cu–20.4Al–8.7Mn(at.%) at room temperature is investigated by an internal friction technique.Results indicate that the alloy exhibits higher damping capacity in the Martensitic condition than that in the austenitic condition due to the latter having lower intrinsic damping capacity and pinning effect coming from the precipitate particles.The maximum damping capacity is obtained in the coexistence condition of Martensite and austenite.The condition can be achieved when processing an isothermal ageing for the as-cast sample at temperatures of 100°C–150°C.Three possible mechanisms are considered to account for the maximum damping capacity.They are listed as much increased interfaces between twin boundaries,owing to the thinning of martensitic plates,martensitic transformation induced by the applied stress during internal friction measurements,phase transformation itself based on the coexistence of martensitic and austenitic phases with a macroscopic amount.However,the contribution of the first mechanism is predominant.