Phase equilibria of slag systems“FeO”−SiO_(2)−CaO−Al_(2)O_(3)and“FeO”−SiO_(2)−CaO−MgO at 1200℃and p(O_(2))of 10^(−7)kPa

High-temperature experiments were carried out for the slag systems of“FeO”−SiO_(2)−CaO−Al_(2)O_(3)and“FeO”−SiO_(2)−CaO−MgO at 1200℃and p(O_(2))of 10^(−7)kPa.The equilibrated samples were quenched,and the phase compositions were measured by electron probe microanalysis(EPMA).A series of pseudo-ternary and pseudo-binary phase diagrams are constructed to demonstrate their applications in copper smelting process and evaluation of the thermodynamic database.Spinel and tridymite are identified to be the major primary phases in the composition range related to the copper smelting slags.It is found that the operating window of the smelting slag is primarily determined by w_(Fe)/w_(SiO_(2))ratio in the slag.Both MgO and Al_(2)O_(3)in the slag reduce the operating window which requires extra fluxing agent to keep the slag to be fully liquid.Complex spinel solid solutions cause inaccurate predictions of the current thermodynamic database.

Simultaneously enhancing coercivity and remanence of hot-deformed Nd-Fe-B magnets by flake copper powder assisted DyF_(3) interflake addition

It is still a challenge to simultaneously enhance coercivity(H_(cj))and remanence(J_(r))of hot-deformed Nd-Fe-B magnet due to the coercivity-remanence trade-off dilemma.Here,we achieved this balance between H_(cj)and Jr by flake Cu powder assisted DyF_(3)interflake addition.The Hcj increases from 1218 to 1496 kA/m and Jr increases from 1.32 to 1.34 T compared with the original magnet.Results show that the width of coarse grain layers reduces because of the introduction of flake Cu,which increases the contact areas of the adjacent grains at ribbon interfaces and suppresses the excessive growth of grains.The stronger degree of texture and higher density compared with the original magnet should take the responsibility for the increase of J_(r).Additionally,the aggregation regions of rare earth rich(RE-rich)phase reduce and the betterment of the microstructure is another reason for the enhancement of Jr in the flake Cu aided DyF_(3)hot-deformed magnet.This strategy of using flake powder additives provides a promising method for optimizing microstructure and enhancing magnetic properties of hot-deformed Nd-Fe-B magnets.

Fabrication and application prospects of Pr-Fe-B/Alnico nanocomposite alloys

The potentials of rare earth-based nanocomposite alloys have never been realized due to strict microstructural constraints.Owing to the easy demagnetization it is challenging to increase the soft magnetic phase content.To avoid the easy demagnetization,Pr-Fe-B/Alnico magnets were fabricated and reported in this manuscript.The content of the Alnico phase is increased from 0 to 25 wt%,while the content of Pr element is reduced to below the sub-stoichiometry of the 2:14:1 main phase.The maximum magnetic energy product,which is the figure-of-merit for permanent magnets,is increased from 122 kJ/m^(3) for the standard alloy to 146 kJ/m^(3) for the alloy with 15 wt% Alnico which shows a significant improvement considering the fact that the Curie point of the magnet is also increased by~66 K.The special microstructure contains distinctly and heterogeneously distributed 2:14:1 and Alnico phases.The dimensions of neither the 2:14:1 nor the Alnico phases meet the dimensional requirements of the nanocomposite magnets,but still the smooth demagnetization curves are noted for the alloys.The behavior of effective anisotropy,the performance of the magnets in applied magnetic field and the magnetic interactions among the various constituent grains were quantitatively studied by reversible susceptibility,irreversible susceptibility and re coil loop openness.This study may provide some guiding principles for the development of nanocomposite magnetic alloys with excellent magnetic properties by using much less RE elements.

Effects and regulation mechanisms of post-sinter annealing treatment on magnetic properties and microstructures of Nd-Fe-B sintered magnets with varying boron contents

In traditional Nd-Fe-B-based sintered magnets,the composition,role of each element and microstruc-tures have been extensively investigated globally since they were invented in 1983.However,the effects of boron(B)content and post-sinter annealing(PSA)on the microstructure and magnetic properties have been least studied so far and the relative mechanisms are not yet clear.In this paper,we investigated the influence of B on the magnetic performance and microstructure of Nd-Fe-B sintered magnets origi-nally containing copper(Cu),gallium(Ga)and titanium(Ti).It is shown that the intrinsic coercivity has a substantial increment of 2.86 kOe and the remanence has a slight reduction of 0.16 kGs when B content is reduced from 0.980 wt.%to 0.900 wt.%.Moreover,there is a coercivity increment of 27.3%and 65.3%for samples with 0.980 wt.%and 0.900 wt.%B content after PSA,respectively.It is shown that the im-pacts of B content and PSA are significant and their regulation mechanisms are worthwhile to be studied systematically.Furthermore,it is revealed by microstructural analysis that high coercivity of the sample with 0.900 wt.%B after PSA results from the uniform distribution of Ga,Cu,Nd,and the formation of RE 6(Fe,M)14(RE=Pr,Nd,M=Cu,Ga)compound in triple junction phases.The dilution of Fe content in grain boundary phases(GB phases)also plays an important role.It is found out that decrease of the re-manence is mainly due to reduction of the matrix phase and c-axis alignment degree.In this study,we explored a new path to develop Nd-Fe-B-based sintered magnets with high comprehensive properties by novel approaches through varying B content,PSA technique and co-adding trace elements.

Optimization of core-shell structure distribution in sintered Nd-Fe-B magnets by titanium addition

In view of the uneven distribution of the core-shell structure of sintered Nd-Fe-B magnets after grain boundary diffusion,this study proposes to use high-melting-point and reactive element titanium(Ti)as an additive to increase the diffusion channels and to enhance the diffusion of heavy rare earth elements along the grain boundary phase.By adding Ti element,the diffusion depth and hence the intrinsic coercivity of magnets are increased significantly.The addition of Ti increases the coercivity at two stages:initially from 16.07 to 16.29 kOe by addition effect,and then from 16.29 to 25.16 kOe by facilitating the diffusion of Tb element.The formation of TiB_(2) phase improves the periodic arrangement of the crystal structure in the surroundings of the grain boundary phase and enhances its activity.The improved grain boundary diffusion and better core-shell structure distribution provide a theoretical guidance fo r solving the problem of diffusion depth in bulk magnets.

Mechanism of ferrite nucleation induced by Y_(2)O_(2)S inclusion in low carbon steel

To reveal the mechanism of ferrite nucleation induced by Y_(2)O_(2)S inclusion in steel,the work of adhesion,interfacial energy,structure stability and electronic properties of Fe(111)/YY_(2)O_(2)S(001)interfaces with various terminations were first investigated using the first-principles calculations.Secondly,the steels with and without yttrium were prepared,while the rare earth yttrium-based inclusions in low carbon steel were characterized using an electron probe micro-analyzer,and the grain size of steel was analyzed using a scanning electron microscope with electron backscattered diffraction.The results show that the bonding strength of Fe/Y_(2)O_(2)S interfaces with S-and Y-terminations is stronger than that of the interface with O-terminations.The Fe-hcp-S interfaces with S-termination have the highest work of adhesion(4.01 J/m2)and the lowest interface distance(1.323A).The Fe-hcp-S interface exhibits the highest stability,and its interfacial bonding force is mainly attributed to the strong hybridization of Fe-3d and S-2p orbitals in the energy range of-7.5-0 eV.Moreover,the interfacial energy of Fe-hcp-S is substantially lower than those of the ferrite(s)/Fe(L)interface and the ferrite-austenite interface,suggesting that Y_(2)O_(2)S inclusions in steel can efficiently promote ferrite nucleation.The experimental observations demonstrate that the ferrite grain size of steel containing 0.03 wt.% Y is much more refined than that of the steel without yttrium,and the average grain size of steel with and without Y is 102 and 258μm,respectively.This indicates that the results of our calculations match with experimental findings.

Enabling efficient NIR-II luminescence in lithium-sublattice core–shell nanocrystals towards Stark sublevel based nanothermometry

The luminescence in the second near-infrared(NIR-II)spectral region(1,000–1,700 nm)has recently attracted great attention for emerging biological applications owing to its merit of deep tissue bioimaging and high spatiotemporal resolution.However,it still remains a challenge to achieve the highly efficient NIR-II emissions of lanthanides in nanomaterials.Herein,we report an ideal design of sensitizing lithium sublattice core–shell nanocrystals for efficient NIR-II emission properties from a set of lanthanide emitters including Er3+,Tm3+,Ho3+,Pr3+,and Nd3+.In particular,the typical NIR-II emission of Er3+at 1.5μm was greatly enhanced by further manipulating the energy transfer via Er3+–Ce3+cross-relaxation,and the quantum yield can reach up to 35.74%under 980 nm excitation(12.5 W·cm−2),which is the highest value to the best of our knowledge.The 808 nm responsive efficient NIR-II emission was also enabled at the single-particle level through rational core–shell–shell structure design.Moreover,the lithium-sublattice provides an obvious spectral Stark-splitting feature,which can be used in the ultrasensitive NIR-II nanothermometer with relative sensitivity of 0.248%K−1 and excellent thermal cycling stability.These results open a door to the research of new kinds of efficient NIR-II luminescent materials,showing great promise in various frontier fields such as deep tissue nanothermometry and in vivo bioimaging.