Source: China Rare Earth Website

Editor's note: The "2018 China Rare Earth Top 10 Science and Technology News", sponsored by the China Rare Earth Society and Baotou Rare Earth Research Institute, organized by the "China Rare Earth" website, and co organized by media such as "Rare Earth Information" and "Rare Earth", was recently announced. The selection results will be published on the website of the China Rare Earth Society, the China Rare Earth website, and the "Rare Earth Information" magazine. The top ten science and technology news selected this time were selected from over 100 rare earth technology news articles of 2018, which underwent two stages of initial review and evaluation.

Selected news ranking in no particular order

1. Rare earth single crystal fiber achieves mW level mid infrared laser output

Single crystal fiber is a new and efficient laser gain medium that can effectively overcome bottleneck problems such as thermal effects caused by bulk crystals and glass fibers. It will have significant application value in the field of high-power all solid state fiber lasers in the future. Based on years of experience in rare earth crystal design and growth technology development, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences has achieved mW level mid infrared laser output. This achievement constructs a fully innovative chain from the basic theoretical research of rare earth crystals and the design of new crystal structures, to the optimization of micro pulling growth technology and the output of single crystal fiber lasers. This marks another original breakthrough in the downstream application field of high value-added rare earth resources in China.

Researcher Xue Dongfeng, Director of the State Key Laboratory of Rare Earth Resource Utilization, has clarified the definition of "rare earth crystals" and constructed a micro pulling rare earth single crystal fiber growth model from the perspectives of crystallization thermodynamics and kinetics. Using this theoretical model, key parameters in the growth of rare earth single crystal fibers are obtained. In order to further clarify the chemical bonding mode at the growth interface, an orbital hybridization model was established to study the bonding behavior of rare earth ions, quantitatively correlate the coordination number, coordination structure, and outer orbital hybridization mode of rare earth ions, and use them to quantitatively calculate the growth rate of rare earth single crystal optical fibers. This work innovatively utilizes the chemical bonding mode at the growth interface to solve the cross scale problem between micro crystal composition and rare earth single crystal fiber block materials. It is used for the directional design of multi-scale rare earth single crystal fiber growth schemes, and successfully grows a series of rare earth aluminate, gallate, silicate and other single crystal fibers with diameters of 0.5-3 mm, obtaining mW level mid infrared laser output.

2. In situ construction of hollow core-shell structure rare earth upconversion nanocrystals by electron beam etching

Due to the upconversion luminescence properties of rare earth nanocrystals, which convert near-infrared light into short wavelength visible ultraviolet light, and the advantages of hollow core-shell structured nanocrystals, such as high specific surface area and rich adjustable pore structure, they have broad application prospects in biosensing and imaging, drug delivery, and medical diagnosis and treatment. The synthesis of hollow core-shell structure upconversion nanocrystals mainly utilizes the hard template method. However, the hard template method requires first coating the upconversion nanocrystals with silica or polymer, and then removing the template through selective corrosion or high-temperature calcination. The synthesis process is complex and cannot achieve in-situ construction of hollow core-shell structured nanocrystals on the substrate, greatly limiting its application range.

The uniform coating of homogeneous shell layers on the surface of rare earth nanocrystals through epitaxial growth is generally considered an effective strategy to reduce the density of surface defects on the original nanocrystals and improve the upconversion luminescence efficiency. However, there is still a lack of in-depth experimental research on fundamental issues such as whether interface defects are significantly suppressed in the conversion of nanocrystalline core-shell interface structures on homogenous coated core-shell structures. Supported by the Science Fund for Distinguished Young Scholars of the National Natural Science Foundation of China, the "973" Program of the Ministry of Science and Technology, the Chinese Academy of Sciences strategic leading science and technology project and innovation team, the Chen Xueyuan Research Group and Wang Yuansheng Research Group of the Key Laboratory for Functional Nanostructure Design and Assembly of Fujian Institute of Physical Structure of the Chinese Academy of Sciences cooperated to find that there are still a lot of crystal defects at the interface between the core and shell of homogeneous coated core-shell structure nanocrystals by electron beam irradiation of rare earth upconversion nanocrystals, and the concentration of the interface defects is even higher than the concentration of bulk defects in the core. On this basis, by utilizing this interface defect control, in-situ construction of hollow core-shell structure rare earth upconversion nanocrystals on carbon film substrates was achieved through electron beam etching. Under electron beam irradiation at a certain power density, the core-shell structured rare earth upconversion nanocrystals pre deposited on a carbon film substrate rapidly transform from solid spheres to hollow core-shell structures, and the entire process can be completed within 30 seconds, while the hollow core-shell structured nanocrystals still maintain their original crystal structure. Through in-situ transmission electron microscopy observation of the transition process of nanocrystals from solid to hollow core-shell structure, and combined with theoretical model analysis, researchers further revealed the microscopic mechanism of the formation of this hollow core-shell structure: when nanocrystals are irradiated with high-energy electron beams, Ln (rare earth atoms), F, and Na atoms in the nanocrystals gain kinetic energy during collisions with electrons and break free from lattice constraints to undergo atomic migration or sputtering, thereby forming pores in the nanocrystals. Due to the presence of numerous defects at the core-shell interface in core-shell structured nanocrystals, the probability of lattice atoms breaking free from lattice constraints and undergoing atomic migration or sputtering significantly increases when exposed to electron beam irradiation. Therefore, a spherically symmetric hollow structure is preferentially and rapidly formed at and near this interface, achieving the transition of nanocrystals from solid to hollow core-shell structure. The results of this study indicate that interface defect control based on core-shell structured nanocrystals using electron beam atomic scale etching of nanocrystals is an effective method for in-situ construction of hollow core-shell structured rare earth upconversion nanocrystals. This method will provide new ideas for in-situ construction of special structured functionalized nanocrystals in the field of nanodevice applications.

3. Progress has been made in resource-saving high-performance rare earth permanent magnet materials

On October 12, 2018, Academician Shen Baogen successfully passed the acceptance of the National Key Basic Research Development Program (973 Program) project "Design and Controllable Preparation of Resource saving High performance Rare Earth Permanent Magnet Materials" by the Ministry of Science and Technology. This project consists of three sub projects: "Scientific Basic Research on the Preparation Technology of High Performance Rare Earth Permanent Magnet Materials", "Research on the Mechanism of High Light Rare Earth Content and High Performance Rare Earth Permanent Magnet Materials", and "Design and Exploration of New High Performance Rare Earth Permanent Magnet Materials", respectively led by Professor Zhu Minggang, Academician Shen Baogen, and Researcher Rao Guanghui.

This project has made breakthroughs in the research of high performance and corrosion resistance of high abundance rare earth permanent magnet materials. When the Ce substitution amount is 35% of the total rare earth content, its magnetic energy product exceeds 40MGOe (laboratory level); When Ce accounts for 50% of the total rare earth content in the magnet, its intrinsic coercivity reaches 10.8 KOe; Obtained multiple innovative inventions such as "high corrosion resistance multi hard magnetic main phase Ce permanent magnet" and key industrial technologies, and prepared a dual main phase sintered magnet with comprehensive performance (BH) max+Hjc>63 for high-performance cerium magnets; It was found that magnets with high Ce content exhibited galvanic corrosion, where the main phase was corroded while the magnetic phase was not. By implementing the project and promoting technology, we aim to increase the national production of cerium (or cerium containing) magnets from 800 tons at the beginning of the project to over 30000 tons, accounting for one-fifth of the total production of rare earth permanent magnets.

The intrinsic magnetism of mixed rare earth iron boron was studied, and it was demonstrated that Ce contributes to the saturation magnetization. It was found that the co substitution of La and Ce facilitates the migration of Ce's valence state towards+3 valence. MMFeB has the necessary conditions for preparing permanent magnets; Revealed the exchange coupling effect and coercivity mechanism of rapidly quenched MM-Fe-B permanent magnet material.

The phase equilibrium of La-Fe-B, Ce-Fe-B ternary system and Nd2Fe14B-RE2Fe14B pseudo binary alloy system were determined, and thermodynamic parameters consistent with the phase equilibrium of rare earth RE Fe system and thermochemical experimental data were obtained. A phase diagram thermodynamic database of rare earth RE-Fe-B multi-component alloy system was constructed, providing important thermodynamic basis for studying the structure-activity relationship of rare earth permanent magnet alloy composition structure magnetic properties.

4. Industrialization of rare earth based SCR catalysts for diesel vehicles

On February 24, 2016, Baotou Rare Earth Research Institute and Hebei Huate Automotive Parts Co., Ltd. began joint research and development of SCR catalysts for diesel vehicles. In January 2018, the rare earth based SCR catalyst passed the bench test conducted by the China Automotive Technology Research Center, and its performance met and exceeded the National V emission requirements; In the vehicle PEMS test (including urban and non urban roads), the effective window pass rate of foreign brand vanadium based catalysts is 90% -92%, while the pass rate of rare earth based SCR catalysts is 100%. Through various test results, it can be seen that rare earth based SCR catalysts have successfully taken the "crown" of diesel vehicle rare earth based denitrification catalysts with independent intellectual property rights, breaking the technical barriers of multinational enterprises in China.

At the end of September 2018, a pilot line for powder synthesis of rare earth based SCR catalysts was successfully built, with a production scale of 2.5-3 tons of powder per month. In the same year, Northern Rare Earth, Hebei Huate, and Beijing Kaides jointly established Northern Rare Earth Huakai High tech (Hebei) Co., Ltd. to build a rare earth based SCR catalyst and post-treatment system project for diesel engines. The plan is to build a demonstration line with an annual production capacity of 100 tons of SCR catalyst powder (50000 sets/year) in 2019 and a production line with an annual production capacity of 1000 tons of SCR catalyst powder (250000 sets/year) in 2022. It is expected to achieve sales of 5 million liters of SCR catalyst and 2 million liters of DPF catalyst by 2023, with sales revenue of 381 million yuan.

During the rapid advancement from National V to National VI, catalysts containing light rare earth compounds such as lanthanum and cerium with special pore structures were synthesized, successfully breaking through the coating process of National VI catalysts. At present, the performance of rare earth based SCR catalysts has fully met the requirements of China's National VI emission standards.

5. Breakthrough progress in precise control of photon dynamics in rare earth upconversion nanomaterials

Kong Xianggui and Liu Xiaomin, researchers of the Changchun Institute of Optics, Precision Mechanics and Physics of the Chinese Academy of Sciences, innovatively combined the controllable "ion nanozone doping" technology and the delayed excitation control method of rare earth ions with the Monte Carlo simulation method, clearly described the dynamic process of the absorption, migration, transfer and recombination of photon energy in the multi nano layer region, vividly described the dynamic images of rapid single transient migration and "wandering" randomness of photon energy, realized the precise control of the photon dynamics process, and defined the direction for solving the challenging problem of low photon up conversion efficiency.

6. Achievements have been made in the application of rare earth electronic pastes

The performance of rare earth electronic pastes is far superior to traditional electronic pastes. It has the characteristics of intelligence, far-infrared, high efficiency, environmental protection, and green energy saving, and its electrical, thermal, magnetic, chemical, and mechanical properties are unparalleled.

Guangdong Fuchen Electronic Technology Co., Ltd. has further upgraded and applied rare earth electronic paste formulation technology based on previous research results, and developed PTCR rare earth thick film circuit controllable electric heating element products. This technology has been invented domestically, in the United States, Japan, and the European Union. The key technology involved in this intelligent chip heat source is mainly composed of a variety of high thermal conductivity substrate materials, which are used in the field of electric heat sources and have stable thermal performance. It is still in the early stage of research and development. In 2018, the modular modular combined intelligent collector system was successfully developed, and this technology was applied to the intelligent non tank electric boiler series. It heats up quickly, has high thermal efficiency, is energy-saving, safe, environmentally friendly, comfortable, compact in size, and easy to install. It is widely applicable in fields such as solar energy, wind energy, lithium-ion batteries, smart home appliances, industry, automobiles, energy, electricity, military, and various new energy fields.

7. Progress has been made in the research of extremely low field magnetic resonance imaging

Dong Hui, a doctoral team from the Superconducting Electronics Innovation Center of the Chinese Academy of Sciences, and the State Key Laboratory of Information Functional Materials of the Shanghai Institute of Microsystems and Information Technology of the Chinese Academy of Sciences, collaborated with Professor Krause of the Yulich Research Center in Germany to suppress power frequency noise interference within ± 500Hz bandwidth in extremely low field magnetic resonance imaging (ULF-MRI) images by more than 85%, solving the problem of inherent power frequency noise interference in unshielded or simply shielded ULF-MRI imaging, and taking a solid step towards realizing low-cost mobile MRI systems.

Magnetic resonance imaging (MRI) technology has become an indispensable tool for clinical medical diagnosis. At present, the typical field strengths of mainstream clinical MRI systems are 1.5 and 3.0 Tesla, which are expensive and have strict requirements for the usage environment. The working field strength of ULF-MRI is four orders of magnitude lower than traditional MRI, and it has the characteristics of simple system, low cost, insensitivity to metals, and can obtain the intrinsic T1 contrast between tumors and normal tissues without the need for contrast agents. In recent years, it has received widespread attention and research. However, power frequency harmonic noise from the power grid can introduce band artifacts in ULF-MRI images. These artifacts will cross the sample image, seriously damaging the imaging quality and affecting the signal-to-noise ratio. This study uses the ultra sensitive magnetic sensor - Superconducting Quantum Interferometer (SQUID) - as the signal detection probe. Based on the spatial correlation of power frequency harmonic noise, starting from the design of sensor hardware configuration and denoising algorithm, a dynamic suppression method for ULF-MRI power frequency harmonic interference is proposed. The proposal of this method helps to reduce the system's requirements for environmental magnetic fields, laying a solid foundation for future research on low-cost mobile MRI systems that can be used for daily routine examinations. This method has potential applications in fields such as ground magnetic resonance imaging and hyperpolarized magnetic resonance imaging that use traditional coil detection.

8. Successful development of multifunctional solid-state quantum memory with multiple degrees of freedom reuse

Guo Guangcan, an academician of the CAS Member and a professor of the University of Science and Technology of China, has made new progress in the field of quantum storage, developed a solid-state quantum memory with multiple degrees of freedom for parallel reuse, realized the reuse of quantum storage across three degrees of freedom, and demonstrated the function of arbitrary photon pulse operation with time and frequency degrees of freedom.

Due to insurmountable fiber channel losses, the current ground safe quantum communication distance is limited to the order of hundreds of kilometers. The quantum relay scheme based on quantum memory can effectively overcome channel loss and expand the working distance of quantum communication, so quantum memory is the core device of future long-range quantum communication and quantum networks. The key indicator for the practical application of quantum networks is communication speed, and multi-mode multiplexed quantum memory can greatly improve the communication speed of quantum networks. For classic storage devices such as hard drives or USB drives, each storage unit can only store one bit at a time. For quantum memory, due to its quantum coherence, one storage unit can store a large number of quantum bits at once, which is the concept of reuse. In principle, all degrees of freedom of quantum memory can be reused.

In recent years, Li Chuanfeng's research group has been dedicated to experimental research on multiplexed quantum storage based on rare earth doped crystals. In 2015, the spatial degrees of freedom of photons were utilized to achieve multiplexed quantum storage, with a storage dimension of 51 dimensions. Since then, solid-state quantum storage has maintained a high level of dimensionality. When multiplexed, each dimension can be treated as a mode, resulting in 51 spatial degrees of freedom modes. In the same year, by utilizing the temporal degrees of freedom of photons, deterministic single photon quantum storage with 100 modes was achieved, maintaining a high level of pattern reuse in solid-state quantum storage to this day.

In order to further enhance the reuse capability of quantum memory, the research group innovatively adopted a storage scheme of multi degree of freedom parallel reuse. For example, if there are M storage modes in the first degree of freedom, N modes in the second degree of freedom, and P modes in the third degree of freedom, then the total number of multiplexed modes in quantum memory is the product of the number of modes in each degree of freedom, i.e. MNP. The research team chose the time, space, and frequency degrees of freedom of photons for parallel multiplexing, and was the first to achieve multiplexed quantum storage across these three degrees of freedom. In the experiment, 2 time modes, 2 frequency modes, and 3 spatial modes were used, with a total of 2x2x3=12 modes. The experimental results demonstrate the feasibility of multi degree of freedom parallel multiplexing quantum storage. This new method of increasing the number of quantum storage modes will have important applications in the research of quantum networks and quantum USB drives.

In the long range quantum communication with multi-mode multiplexing, the working modes of two relay nodes may be different. In order to perform further entanglement swapping, different relay nodes must change their working modes to the same mode, which requires the mode transformation function. The research team ingeniously designed storage schemes and devices to demonstrate that their multi degree of freedom multiplexed quantum memory has arbitrary mode transformation capabilities in both time and frequency degrees of freedom.

The research team further demonstrated that their memory can achieve arbitrary pulse operations in both time and frequency degrees of freedom, with representative operations including pulse sorting, beam splitting, frequency division, cross frequency photon combining, and narrowband filtering. The experimental results indicate that during all these operations, the three-dimensional quantum states carried by photons maintain a fidelity of approximately 89%. This storage device can perform all the operations required for Knill Laflamme Milburn type quantum computing, so this achievement is expected to have more applications in fields such as linear optical quantum computing.

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9. China's permanent magnet direct drive electric locomotive goes offline

On November 1, 2018, the permanent magnet direct drive high-power AC drive electric locomotive with completely independent intellectual property rights was officially launched by CRRC Datong Company. This is a high-power AC drive electric locomotive in China that adopts permanent magnet and direct drive technology.

The permanent magnet direct drive electric locomotive is another breakthrough in the field of AC electric locomotives in China, following the "fast passenger electric locomotive" and "heavy-duty electric locomotive". The total efficiency of the locomotive will be increased by more than 3%, and it can save 200 kWh of electricity per hour. It also has significant features such as low maintenance costs, green environmental protection, and quietness. At the same time, the permanent magnet direct drive electric locomotive adopts direct drive wheelset technology, which eliminates the traditional transmission gearbox and has a simple structure. It not only effectively reduces mechanical energy consumption losses, but also has a maintenance cycle of about 2 million kilometers for the drive system components, saving users a lot of maintenance costs. The comprehensive economic benefits of the product are significant.

10. Isotropic heat-resistant adhesive magnetic powder has won multiple awards including the China Award

In 2018, the preparation technology and products of isotropic heat-resistant rare earth bonding magnetic powder developed by research on rare earths successively won the 20th China Award, the 5th Beijing Invention Second Prize, and the China Rare Earth Science and Technology Progress Second Prize.

Rare earth bonded magnetic materials are particularly suitable for the application of micro and special motors due to their high magnetic performance, high degree of shape freedom, and net forming characteristics, making the motors more energy-efficient and efficient. With the rapid development of downstream applications such as new energy vehicles, energy-saving appliances, and intelligent robots, there is an urgent need for isotropic bonding magnetic powders with high comprehensive magnetic performance and high thermal stability.

Based on this, a key preparation technology for isotropic heat-resistant rare earth bonded magnetic powder has been successfully developed by research on rare earths, which solves the thermal stability problem of existing nanocrystalline bonded magnetic powder in complex service environments and achieves simultaneous improvement of the comprehensive magnetic properties and thermal stability of magnetic powder. At present, the company has successfully developed more than ten high-performance isotropic rare earth bonding magnetic powder grades, and has an annual production line of 1000 tons of rare earth bonding magnetic powder. The products are supplied in bulk to domestic and foreign bonding magnet production customers.