PREPARATION AND CHARACTERIZATION OF NANOSTRUCTURED GRANULAR SUPPORT PARTICLES AND CATALYTIC MATERIALS

We have set up successfully two experimental systems during the past time of the project. The first system is sol-gel chemical method for preparing {gamma}-Al{sub 2}O{sub 3}, SiO{sub 2}, Cr{sub 2}O{sub 3} granular support particles. The second system is the laser-induced solution deposition (LISD) technique for nanoparticle catalysts containing Fe/Cu, and Co/Cu on the granular support. We have successfully deposited {gamma}-Al{sub 2}O{sub 3}, SiO{sub 2}, Cr{sub 2}O{sub 3} granular support particles by sol-gel method and Co and CoO nanoparticles by LISD novel fabrication technique. The characterization methods we have used include scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM) and X-Ray diffraction (XRD). The research toward to the proposed direction is in good progress. We have given three presentations in national and local materials meetings and have submitted another two papers in another two key national meetings in nanotechnology and American Physical Annual March Meeting 2002. A couple of papers are in preparation

Method For Depositing Rare-Earth Boride Onto a Substrate

Disclosed is a method for depositing rare-earth boride onto the surface of a substrate which is submerged in an organic solution of borane and a rare-earth halide. Application of electromagnetic radiation, preferably in the visible wavelength range, near the surface of the submerged substrate drives the formation and deposition of rare-earth boride onto a substrate

Interstitial effects of B and Li on the magnetic phase transition and magnetocaloric effects in Gd2In alloy

Interstitial effects of B and Li on the phase transition and magnetocaloric effect in Gd2In alloys had been studied. The antiferromagnetic (AFM) - ferromagnetic (FM) phase transition was found to be of first-order nature while ferromagnetic - paramagnetic (PM) phase transition was of second-order nature in B- or Li-doped Gd2In alloys. AFM-FM phase transition temperature was increased while FM-PM phase transition was decreased with more doping concentrations. During AFM-FM phase transition, the slope of temperature-dependent critical field (μ0Hcr) was increased by increased doping amounts. The magnetic entropy changes under small field change were enhanced by B and Li addition, which showed the beneficial effects of B and Li additions

Superior properties of LaFe11.8Si1.2/La65Co35 magnetocaloric composites processed by spark plasma sintering

A series of LaFe11.8Si1.2/La65Co35 bulk composites were fabricated by spark plasma sintering (SPS) followed by diffusion annealing. The effect of sintering temperature (1073–1223 K) on the magnetocaloric and other properties of LaFe11.8Si1.2/La65Co35 bulk composites were investigated. The 1:13 phase content in all the annealed samples was ∼90 wt%. The mechanical and magnetocaloric properties of these annealed bulk composites could be improved by tuning the sintering temperature. The Curie temperature (TC) and maximum magnetic entropy change (−ΔSM)max of the annealed samples varied in the range of 211–228 K and 5.56–9.33 J kg−1 K−1, respectively. Selected samples exhibited excellent mechanical and magnetocaloric properties. The (−ΔSM)max value was 9.33 J kg−1 K−1 at TC of 217.8 K. Its maximum compressive strength (σbc)max value was 540 MPa at a strain of 3.48%, which exceeded the mechanical properties of most La–Fe–Si based bulk composites prepared by hot-pressing sintering (HPS). Thus, La–Fe–Si based bulk composites with good comprehensive properties could be obtained by combining SPS and diffusion annealing

Near room temperature LaFe₁₁.₆Si₁.₄/PrₓCo₇ magnetocaloric composites with excellent mechanical and thermal properties

LaFe11.6Si1.4/10wt%PrxCo7 (x = 1, 2, 3, 5) magnetocaloric composites were prepared by spark plasma sintering (SPS) and diffusion annealing. The phase composition, microstructure, magnetic, mechanical and thermal properties were studied. The addition of PrxCo7 binder can be used to tune the phase fraction and magnetic properties. Pr2Co7 binder promoted the formation of 1:13 phase. LaFe11.6Si1.4/10wt%Pr2Co7 composites possess the highest 1:13 content (~ 89 wt%). The Curie temperature (TC) can be tuned in the technologically useful range of 280–347 K. Relatively large maximum magnetic entropy change (− ∆SM)max (2 T) of 1.45−3.16 J/kg K and refrigeration capacity (RC) (2 T) of 117–137 J/kg were obtained. These composites exhibit superior compressive strength of 1005–1250 MPa and excellent thermal conductivity of 17.68–27.77 W/m K. Thus, LaFe11.6Si1.4/10wt%PrxCo7 magnetocaloric composites possess excellent mechanical and thermal properties, with adjustable magnetic properties and have the potential application for near room temperature magnetic refrigeration.This work was supported by the Guangzhou Municipal Science and Technology Project (Grant No. 201904010030); the Natural Science Foundation of Guangdong Province (Grant No. 2022A1515012578, 2019A1515010970); the National Natural Science Foundation of China (Grant Nos. 51874143, 52066001); the Foundation of State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization (Grant No. 2020Z2218)

Effect of Ga addition on the valence state of Ce and magnetic properties of melt-spun Ce17Fe78-xB6Gax (x = 0-1.0) ribbons

The Ce17Fe78-xB6Gax (x=0-1.0) ribbons were fabricated by a melt-spinning technique in order to study the mechanism of the valence variation of Ce and their magnetic properties as well as improve the thermal stability of Ce-based rare earth permanent magnets. The systematic investigations of the Ce17Fe78-xB6Gax (x=0-1.0) alloys show that the room-temperature coercivity increases significantly from 352 kA/m at x = 0 to 492 kA/m at x = 1.0. The Curie temperature (Tc) increases monotonically from 424.5 K to 433.6 K, and the temperature coefficients of remanence (α) and coercivity (β) of the ribbons are better off from -0.56 %/K, -0.75 %/K for x = 0 to -0.45 %/K, -0.65 %/K for x = 0.75 in the temperature range of 300–400 K, respectively. The Ce L3-edge X-ray absorption near edge structure (XANES) spectrums reveal that there is more Ce4+ in ribbons under total electron yield than fluorescence yield as Ce has a high affinity with oxygen. The weight of Ce3+ increases while the weight of Ce4+ decreases in Ga-added alloys. The refined grain size and a more uniform microstructure are mainly attributed to the improved magnetic properties and thermal stability with Ga doping. This paper may serve as a reference for further developing the so-called gap magnets and the effective utilization of the rare earth resources

Microstructure evolution and coercivity enhancement in Nd-Fe-B thin films diffusion-processed by R-Al alloys (R=Nd, Pr)

Diffusion process by Nd-Al and Pr-Al alloys was compared and investigated in Nd-Fe-B thin films. Enhanced coercivity 2.06T and good squareness was obtained by using Pr85Al15 and Nd85Al15 alloys as diffusion sources. But the coercivity of diffusion-processed thin films by Pr70Al30 and Pr55Al45 alloys decreased to 2.04T and 1.82T. High ambient coercivity of 2.26T was achieved in diffusion-processed thin film by Nd70Al30 leading to an improved coercivity thermal stability because Nd2Fe14B grains were enveloped by Nd-rich phase as seen by transmission electron microscopy Nd-loss image. Meanwhile, microstructure-dependent parameters α and Neff were improved. However, high content of Al in diffusion-processed thin film by Nd55Al45 lead to degraded texture and coercivity

The magnetocaloric effect in the vicinity of compensation temperature of ferrimagnetic DyCo

The magnetic and magnetocaloric properties in ferrimagnetic DyCo4Al alloy are investigated in the vicinity of compensation temperature. A compensation temperature closed to room temperature is observed due to the spin-offset. On both sides of compensation temperature, the magnetization presents the abrupt change. As a consequence, two successive positive and negative magnetic entropy change peaks are obtained for this alloy. The appreciable magnetic entropy change values with a very wide refrigerant temperature interval (~200 K) corresponding to the positive magnetic entropy change peak would make this alloy suitable to be used in a magnetic refrigerator

Improved magnetic properties and thermal stabilities of Pr-Nd-Fe-B sintered magnets by Hf addition

Nd2Fe14B-type permanent magnets have been widely applied in various fields such as wind power, voice coil motors, and medical instruments. The large temperature dependence of coercivity, however, limits their further applications. We have systematically investigated the magnetic properties, thermal stabilities and coercivity mechanisms of the (Pr0.2Nd0.8)13Fe81-xB6Hfx (x=0, 0.5) nanocrystalline magnets fabricated by a spark plasma sintering (SPS) technique. The results indicate that the influence of Hf addition is significant on magnetic properties and thermal stabilities of the (PrNd)2Fe14B-type sintered magnets. It is shown that the sample with x = 0.5 at 300 K has much higher coercivity and remanent magnetization than those counterparts without Hf. The temperature coefficients of remanence (α) and coercivity (β) of the (Pr0.2Nd0.8)13Fe81-xB6Hfx magnets are improved significantly from -0.23 %/K, -0.57 %/K for the sample at x = 0 to -0.17 %/K, -0.49 %/K for the sample at x = 0.5 in the temperature range of 300-400 K. Furthermore, it is found out that the domain wall pinning mechanism is more likely responsible for enhancing the coercivity of the (Pr0.2Nd0.8)13Fe81-xB6Hfx magnets