Materials Science Forum Vols. 809-810

Abstract: Electroless plating was used to coat Fe layers on the hard magnetic Nd-Fe-B powders to fabricate Nd-Fe-B/α-Fe heterostructured magnetic powders. The heat treatment was performed to study the property evolution of the heterostructured magnetic powders. The results show that Fe coating was oxidized to Fe₂O₃ while drying; through the hydrogen reduction annealing, Fe₂O₃ was reduced to α-Fe. The coercivity of the heterostructured magnetic powders increased from 111.3 kA/m (1.4 kOe) to 524.7 kA/m (6.6 kOe) after annealing at 650°C. However, the demagnetization curve of powders presents a kink due to un-ideal coupling between hard and soft magnetic phases because of the aggregation of α-Fe. The magnetization processes of the heterostructured powders transferred from the dominant nucleation mechanism to domain wall pinning mechanism after the heat treatment.

Abstract: α-Fe/montmorillonite (MMT) magnetic material was successfully prepared by the in-situ pillared-reduction method. The composite material was characterized by X-ray diffraction (XRD), laser particle size analyzer and other instruments. The magnetic property was researched by saturation magnetization. The results showed that: when 0.1mol/L hydroxyl-Fe was added as pillared agent, hydroxyl-Fe and cation of the MMT exchanged, leading to the inter-layer spacing expanded to 1.41nm and reached saturated pillared point. MMT interlayer hydroxyl-Fe was completely restored to α-Fe grains of 116nm when reducing agent was 0.2mol/L and produced α-Fe/MMT composite material. The average particle size of the composite was 5.529μm, the specific saturation magnetization was 0.812emu/g (9×10³A/moutside magnetic field) and exhibited ferromagnetism.

Abstract: Ti(C,N)-based cermets were prepared by pressureless sintering using micron-sized TiC and TiN powders as main starting materials and Ni and Co as metal binders. The fracture micrographs of Ti(C,N)-based cermets were observed by SEM. The effects of metal binder phase content on porosity and mechanical properties of Ti(C,N)-based cermets were investigated. The results show that when sintering at 1450 °C for 50min, typical core/rim microstructure is observed in the cermets, which is compact and distributed homogeneously, the density and relative density are 5.9 g/cm3 and 95.6%, respectively. Intergranular fracture is the main crack propagation mode, with a few of the transgranular fracture, and there are more dimples and tearing ridges in the fracture surface. Using the same sintering process, Ti(C,N)-based cermets with metal binder content of 10%Ni5%Co has a compact microstructure and fine grains, the metal binder phase is dispersed more evenly, the best vicker hardness, bending strength and fracture toughness of Ti(C,N)-based cermets are 15.8 GPa, 885.5MPa and 9.7 MPa·m^1/2, respectively. However, Ti(C,N)-based cermets with Ni replaced of high Co content will generate some brittle intermetallic compound, its toughness is inferior to the metal binder phase, which reduces the strength and toughness of Ti(C,N)-based cermet materials.

Abstract: In this paper, the hydriding of La (Fe, Fe)₁₃ based alloys was realized by the electrolytic method and the effect of electrolytic temperature on the hydriding was investigated. The phase components and surface morphology were analyzed by XRD and SEM. The magnetic properties of samples were characterized using VSM. Results showed that the electrolytic hydriding process was enhanced by increasing the electrolytic temperature. The Curie temperature was increased from 196 K to 325 K. Through Arrot-plot analyses, it was found that the phase transition of samples tends to be a second order phase transition. The magnetic entropy change was reduced from 8.03 J/(kg•K) to 2.03 J/(kg•K) under a maximum external field of 1.5 T.

Abstract: A type of PTFE/MoS₂/glass fiber composite has been used as bearing cage material. To study the friction properties, the tests have been performed under various parameters on block-on-ring. The experimental results were as follows: Wear rate of the polymer composites was dramatically affected by test duration. With increase of test duration, the wear rate rapidly decreased. At the sliding velocity of 1.83m/s and load of 45N, the highest wear rate was 8.85×10^-15m³/N·m in the test of duration 0.5h, while the lowest was 0.88×10^-15m³/N·m in the test of duration 10h (the minimum and maximum times examined).

Abstract: Area-selectively liquid-phase sintering (AS-LPS) method was developed to control the coarsening of Si particles in Al/60vol.% Si composites with the help of sol-gel-derived interfacial modification, achieved by pre-coating discontinuous Al₂O₃ film on Si powders. The results show that due to the local presence of less than 1 μm-thick films, Si particles can approximately preserve their as-received size and morphology after being sintered at 950 °C. Whereas, for those prepared by use of the unmodified Si powders, Si phases evolve to several hundred-micron-sized flakes, being similar to the typical eutectic Si in Al-Si casting alloys. It is assumed that the Al₂O₃-film-coated areas at Al/Si interface control the dissolution of Si into Al liquid, while in uncoated areas Al matrix and Si particles bond together by LPS, thus realizing AS-LPS.

Abstract: Adopting laminated dry pressure molding process, the HH2 (mixing powder of (Zn_0.7, Mg_0.3)TiO₃(ZMT3) and (Ni_0.8Zn_0.12Cu_0.12)Fe_1.96O₄(NZC) in weight ratio of 1:1) and (Zn_0.9, Mg_0.1)TiO₃(ZMT1) were designed to be interlayer, which was co-fired with ZMT3((Zn_0.7, Mg_0.3)TiO₃) and NZC((Ni_0.8Zn_0.12Cu_0.12)Fe_1.96O₄) at 900°C to synthesize layer composition. The study of interfacial microstructure SEM and diffusion mechanism shows that the co-fired layer composition could alleviate the interfacial stress and eliminate warp defects resulting from the co-fired process. The interfacial diffusion behavior of co-fired layer composition was researched，which provide a promising solution of warp and distortion resulting from different materials co-fired process.

Abstract: The fluoride removal agents of SiO₂-Al₂O₃ spherical particles were prepared using aluminum powder and sodium silicate as the main raw material by sol-gel method. The samples were characterized by XRD analysis method, and several influencing factors of fluoride removal performances had been studied, such as the content of SiO₂, calcinations temperature, calcinations time, pH values, etc. The results showed that the adsorption capacity of SiO₂-Al₂O₃ increased with the content of SiO₂ increasing in the range of 0 to 12%. The best calcination temperature is 500 °C, and the best calcination time is 1 hour. The concentration of fluorine could reduce from 190 mg/L to 0.388 mg/L in the environment of pH 5.5 ~ 6, and the adsorption capacity could reach 9.48 mg/g, and the fluoride removal rate could reach 99%.

Abstract: The capacity of 10%, 30%, and 50% ammonium dihydrogen phosphate were replaced with an equal amount of three phosphate (potassium dihydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate) respectively. Magnesium phosphate cement was made by phosphate of replaced, which strength, setting time, fluidity, hydration temperature, and the hydration products was researched. The results show that: MPC was made that replaced with the equal amount of three kind of phosphate, which has good mechanical properties. Setting time and fluidity change along with the replacment. Three kind of phosphate replace ammonium dihydrogen phosphate, which change the hydration process of MPC. When ammonium dihydrogen phosphate was replaced by an equal amount of disodium hydrogen phosphate, the temperature of hydration is only 69.4 °C. XRD showed that the diffraction peaks of composite’s magnesium phosphate cement increases.

Abstract: Graphene oxide (GO) synthesized through a modified Hummers’ method was added into cement matrix to prepare GO/cement. The microstructure, mechanical properties, and the electromagnetic shielding effectiveness (SE) at 8.2–12.4 GHz of GO/cement composite were investigated. It has been observed that incorporation of GO in the cement matrix can regulate to form flower-like hydration crystals and distinctly enhance the flexural/compressive early stage strength of GO/cement composites. Furthermore, GO sheets played a vital role in effectively improve the shielding effectiveness with the dominant shielding mechanism of absorption of electromagnetic radiation.