Sintered Sm2(Co, Fe,Cu,Zr)17 magnets withlight rare earth substitutions

The effects of partial substitution of light rare earths for Sm in (Sm_1-xR_x)₂ (Co,Fe,Cu,Zr)₁₇ have been investigated where R=Ce, Pr, Nd, Pr_0.5Nd _0.5, Ce_0.2Pr_0.4Nd_0.4 and x=0-0.5. Experiments show that both remanence and maximum energy product are improved for x=0.1-0.2, depending upon compositions and heat treatments. For a composition Sm_0.8R_0.2(Co_0.633Fe_0.286 Cu_0.061Zr_0.020)_7.59 with R =Ce_0.2Pr_0.4Nd_0.4, the authors obtained B_r=11.57 kG, _MH_c =15.5 kOe, _BH_c=10.33 kOe, H_k=10.03 kOe, and (BH)_max=30 MGOe     

Analytical electron microscopy of Sm(Co,Fe,Cu, Zr)9

Electron microscopic studies of as-cast Sm(Co,Fe,Cu,Zr)₉ magnets revealed a hexagonal phase of the type Sm₂(Co,Fe,Cu,Zr)₁₇ with crystal lattice parameters of a=0.84 nm and c=3.2 nm. After a solid solution treatment, only rhombohedral (3R) and hexagonal (2H) grains were found. After an additional annealing treatment at 800°C, grains with a microcellular precipitation structure similar to the one found in Sm(Co,Fe,Cu,Zr)_7.5 magnets occurred. In addition, in the as-cast and after-aged samples, other, partly unidentified Cu- or (Co,Fe)-enriched phases were detected     

(Sm0.2Gd0.2Dy0.2Y0.2Yb0.2)3TaO7高熵陶瓷的制备及热物理性能

寻求具有良好热物理性能的新型陶瓷材料是热障涂层领域的研究热点之一.本研究采用固相反应法制备了(Sm0.2Gd0.2Dy0.2Y0.2Yb0.2)3TaO7高熵陶瓷材料,对其晶体结构、显微组织、元素分布、结构稳定性和热物理性能进行了研究.结果表明:制备的高熵陶瓷具有单一的缺陷萤石结构,元素分布均匀,晶粒尺寸在0.2～3μ...     

Structural and Magnetic Properties of Sm$_3$(Fe$_1-rm x$Co$_rm x$)$_27.7$Ti$_1.3$

The structure and magnetic properties of Sm₃(Fe_1-x Co_x)_27.7Ti_1.3 compounds, with x ranging from 0 to 0.4, have been investigated by means of X-ray powder diffraction and magnetic measurements. The main phase formed was that of Nd₃(Fe, Ti)₂₉-type structure (3:29) with a relatively small amount of the ThMn₁₂-type structure (1:12) as a secondary phase (7-13 wt.%). The lattice parameters and the unit-cell volume decrease with increasing Co content x. It is found that substitution of Co for Fe leads to a significant increase in the Curie temperature from 488 K for x=0 to 941 K for x=0.4. Saturation magnetization gradually increases with increasing Co. All compounds show easy cone-type anisotropy     

Consolidation behavior of L12 phase (Al + 12.5 at.% Cu)3Zr powder with nanocrystalline structure during CIP and subsequent sintering

The mechanically alloyed (Al + 12.5 at.% Cu)₃Zr powders were consolidated by cold isostatic pressing (CIP) and subsequent sintering. Effects of CIP pressure and sintering temperature on the stability of metastable L1₂ phase and nanocrystalline structure were investigated. Before sintering, the powders were CIPed at 138, 207, 276, and 414 MPa. The relative densities of the CIP compacts were not greatly affected by the CIP pressure. However, the L1₂ phase of the specimen CIPed at pressures greater than 276 MPa was partially transformed into D0₂₃. The optimum consolidation conditions for maintaining L1₂ phase and nanocrystalline microstructure were determined to be CIP at 207 MPa and sintering at 800 °C for 1 h for which the grain size was 34.2 nm and the relative density was 93.8%. Full density specimens could be prepared by sintering above 900 °C, however, these specimens consisted of L1₂ and D0₂₃ phases. The grain sizes of all the specimens were confirmed by TEM and XRD, and were found to be less than 40 nm. This is one of the smallest grain sizes ever reported in trialuminide intermetallic compounds.     

水热法制备纺锤型磷灰石相Y4.67(SiO4)3O微晶及其陶瓷的热学性能研究

采用水热法在温度为503 K,反应时间为12 h的条件下制备了纺锤型磷灰石相Y_4.67(SiO₄)₃O微晶,该微晶由粒径约为50 nm的颗粒组成。首次报道了纺锤型磷灰石相Y_4.67(SiO₄)₃O微晶的热性能,同时研究了其相组成,微观结构及合成机理。结果表明,水热温度对所制备粉体的相组成及形貌有较大影响。此外,对应的陶瓷具有较低的热导率和较高的热膨胀系数,有望用作热障/环障涂层材料。     

Complex Permittivity and Permeability of Co$_2$U (Ba$_4$Co$_2$Fe$_36$O$_60$) Hexaferrite Bulk and Composite Thick Films at Radio and Microwave Frequencies

We measured dielectric, magnetic, and microwave properties of Co ₂U hexaferrite (Ba₄Co₂Fe₃₆O ₆₀) polycrystalline bulk and composite thick film samples, and studied the effect of annealing temperature on phase formation and microstructure. We synthesized the bulk samples from a precursor prepared by the citrate method. The values of dielectric constant at radio frequencies (50 Hz-1 MHz) of the bulk Co₂U12 sample sintered at 1200degC are much higher, and the resistivities are lower, compared to M-type barium hexaferrites. Coercivity is also low, having a value of 5 G for the Co₂U12 sample, whereas the saturation magnetization value is 59 emu/g, which is comparable to that of M-type hexaferrites. We also measured the complex permittivity and permeability for Co₂U12 samples at microwave frequencies and found the values high compared to M-type barium hexaferrite at these frequencies. Thick composite films were prepared from a ferrite-polymer mix, and all the above properties were studied for these films. We observed that these thick films have lower values of dielectric and magnetic parameters both at low and microwave frequencies. We measured microwave-absorbing properties for the ferrite-polymer sample (ferrite to polymer ratio 70/30) which showed a maximum reflection loss of -37.5 dB at 11.5 GHz for the 3.5-mm-thick sample     

Magnetic properties of melt spun NdFe10Cr2-Nd0.67B0.33 pseudobinary alloys

The coercivity of the melt-spun pseudobinary (NdFe₁₀Cr ₂)_1-x (Nd₂B)_x alloys, in which Nd₂B represents a composition of Nd_0.67B_0.33, was systematically studied. It was found that significant coercivities are possible with optimal additions of the Nd-B composition at x=0.5-0.7. The as-spun (substrate velocity=10 m/s) coercivity increased from 0.1 kOe at x=0.0 to maxima of 7.0 and 7.5 kOe at x=0.5 and 0.7, due to the Nd₂ Fe₁₄B and a new Fe-Nd phase, respectively, as evidenced from thermomagnetic analysis and X-ray diffraction. Annealing the overquenched amorphous x=0.7 alloy led to the crystallization of the Nd₂Fe₁₄B phase, and a coercivity of 8.5 kOe was obtained     

Preparation of cobalt oxide nanoparticles and cobalt powders by solvothermal process and their characterization

Co₃O₄ nanoparticles and cobalt (fcc-Co) powders were successfully synthesized by solvothermal process from a single precursor. The reaction of Co(Ac)₂ with sodium dodecylbenzenesulfonate (SDBS) shows evident-dependent temperature effect. At 180 °C, Co(Ac)₂ reacts with SDBS to produce precursor CoCO₃ plate structures, which are assembled by small nanoparticles. At the temperature of 250 °C, the precursor CoCO₃ can be gradually decomposed to form Co₃O₄ nanoparticles with diameter of ca. 70 nm. While, at 250 °C, the reaction of Co(Ac)₂ with SDBS also produce precursor CoCO₃ nanoparticles/plates, but the CoCO₃ nanoparticles/plates would only decompose to give metal Co. In this process, SDBS acts as not only a surfactant but also a reagent. Magnetic measurements reveal that the as-prepared Co₃O₄ nanoparticles exhibit weak ferromagnetic properties and Co powders show ferromagnetic properties. In addition, a possible formation mechanism was elaborately discussed.     

多孔Co3O4纳米纤维用于锂-空气电池高性能正极催化剂

采用静电纺丝技术结合高温煅烧方法,以乙酰丙酮钴(Co(C₅H₇O₂)₃)为前驱物,制备了由Co₃O₄纳米颗粒组成的多孔纳米纤维(Co₃O₄ NFs),其比表面积高达83 m2·g?1,并将制得的多孔Co₃O₄ NFs用于锂-空气电池催化剂。多孔Co₃O₄ NFs为电池反应提供了充足的活性位点及反应物的传输通道,有利于电池反应的顺利进行,使电池的放电容量得到极大地提高。另外,Co₃O₄催化剂的加入提高了电极的催化活性,较大程度降低了电池的过电位。值得注意的是,Co₃O₄催化剂的加入同时调控了锂-空气电池放电产物Li₂O₂的形貌,得到的放电产物Li₂O₂尺寸更小,在电极表面分布更为均匀,该形态的Li₂O₂在充电过程中更容易被分解,有利于提高电池的充电效率,同时电极的体积效应也可得到极大缓解。得益于以上优势,基于多孔Co₃O₄ NFs/炭黑Super P (Co₃O₄ NFs/SP)正极的锂-空气电池的电化学性能得到较大提高,50 mA·g?1电流密度下Co₃O₄ NFs/SP的放电容量高达10600 mA·h·g?1,电池可实现100次的充放电循环。      

Fabrication of Lead-Free Piezoelectric (Na/sub 0.5/K/sub 0.5/)NbO/sub 3/Ceramics by a Modified Solid-State Reaction Method

Sodium potassium niobate, (Na_0.5K_0.5)NbO₃, fine powder has been successfully synthesized at the low temperature of 550degC through a modified solid-state reaction method, in which urea [CO(NH₂)₂] plays an important role. High-density (Na_0.5K_0.5)NbO₃ ceramics could be obtained by conventional sintering of the synthesized (Na_0.5K_0.5)NbO₃ fine powder with the addition of 0.03 mol% Co₃O₄ as a sintering additive. The crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The (Na_0.5K_0.5)NbO₃ ceramic showed a comparatively saturated P-E hysteresis loop. The (Na_0.5K_0.5)NbO₃ ceramic also displayed piezoelectricity with a piezoelectric constant d₃₃ of 126 pC/N and a planar electromechanical coupling factor k_p of 33%.     

Shielded magnetoresistive head for high density recording

The fabrication process and the head material properties for shielded magnetoresistive heads with planarized lower shields using a tri-layered MR element are described in detail. Applying the etch-back process with low molecular weight polystyrene and CF₄/O₂ reactive ion etching, the residual step height for a lower shield is dramatically decreased to less than 5% of the initial step height. The tri-layered MR element consists of an MR layer, a magnetic separation layer (MSL), and a soft adjacent layer (SAL). 40-nm thick Ni ₈₁Fe₁₉ (wt.%) films were deposited by evaporation for use as an MR layer. Evaporated Ti MSL thickness was experimentally determined to be 20 nm. Amorphous Co₈₂Zr₆Mo₁₂ SAL films exhibited preferable magnetic properties as an SAL material. The fabricated shielded MR heads, using the tri-layered MR element with these NiFe, Ti, and CoZrMo films, provide superior capability to realize high recording density     

粉末冶金(FeNiMnAl_(x))_(50)Cu_(50)中熵合金的微观组织与力学性能EI北大核心CSCD

对物理法制备的再生铜合金粉末进一步合金化,通过机械合金化(MA)结合放电等离子烧结(SPS)的方法制备了(Fe_(40)Ni_(40)Mn_(20))_(50)Cu_(50),(Fe_(38)Ni_(38)Ni_(38)Mn_(19)Al_(5))_(50)Cu_(50),(Fe_(36)Ni_(36)Mn_(18)Al_(10))50 Cu_(50)和(Fe_(32)Ni_(32)Mn_(16)Al_(20))_(50)Cu_(50)四种中熵合金块体,并研究了Al元素的含量对中熵合金微观组织与力学性能的影响。结果表明:在高能球磨60 h之后合金粉末完成合金化,四种中熵合金粉末均形成单一FCC相的过饱和固溶体且有微量WC杂质。经SPS烧结后,(Fe_(40)Ni_(40)Mn_(20))_(50)Cu_(50),(Fe_(38)Ni_(38)Mn_(19)Al_(5))_(50)Cu_(50)和(Fe_(36)Ni_(36)Mn_(18)Al_(10))50 Cu_(50)形成了由富Cu的FCC1相和富Fe-Ni的FCC2相组成的双相FCC结构,并具有超细晶+微米晶的多尺度结构;而(Fe_(32)Ni_(32)Mn_(16)Al_(20))_(50)Cu_(50)由富Cu的FCC主相和少量富Fe-Mn的FCC2相及富Ni-Al的BCC相(B2)组成。随着Al含量的提高,四种中熵合金的塑性逐渐降低,而强度和硬度逐渐提高。(Fe_(40)Ni_(40)Mn_(20))_(50)Cu_(50)合金的压缩屈服强度、抗压强度和维氏硬度分别为878 MPa,1257 MPa和248.5HV。与(Fe_(40)Ni_(40)Mn_(20))_(50)Cu_(50)相比,(Fe_(32)Ni_(32)Mn_(16)Al_(20))_(50)Cu_(50)的压缩屈服强度和硬度分别提高了50.1%和50.4%,断裂应变由19.55%下降至8.31%。     

Consolidation of Sm5Fe17 powder by spark plasma sintering method

Sm₅Fe₁₇ bulk materials, one of the newer permanent magnetic materials, were successfully produced by the spark plasma sintering method. The resultant bulk materials had high densities of 85–98%. When obtained by sintering at relatively lower temperatures, the Sm₅Fe₁₇ bulk materials consisted of the Sm₅Fe₁₇ and SmFe₃ phases, whereas they contained some -Fe phase together with the Sm₅Fe₁₇ and SmFe₃ phases when obtained by sintering at relatively high temperatures. High coercivity values, exceeding 2 MAm⁻¹, were found in the Sm₅Fe₁₇ bulk materials consisting of the Sm₅Fe₁₇ and SmFe₃ phases.     

Magnetic properties of melt spunSmFe11Ti-Sm2TM17 pseudobinary alloys

Several alloys in the SmFe₁₁Ti-Sm₂TM₁₇ (TM=Co/Fe/Cu/Zr) pseudobinary system containing O-90 wt.% Sm₂TM₁₇ were prepared by the melt spinning technique. A maximum as-spun coercivity of 4.6 kOe was obtained for the alloy containing 10 wt.% Sm₂TM₁₇ at a substrate velocity of 15 m/s. The coercivity is enhanced to 5.3 kOe after annealing at 800°C for 1 h. XRD (X-ray diffractometry) and TEM (transmission electron microscopy) were used to investigate the microstructure of the alloys. It is suggested that the grain refinement, doping of the 1-12 phase with Sm and other elements, and reduced free iron might be the main causes coercivity enhancement     

Co3O4纳米线阵列@活性炭纤维复合材料的水热合成及电化学应用

以Co(NO₃)₂·6H₂O为钴源, NH₄F和尿素作为添加剂, 通过水热法在粘胶基活性炭纤维(ACF)的表面生长了Co₃O₄纳米线, 制备了Co₃O₄@ACF复合材料并进行了结构形貌表征及电化学性能测试。结果表明: 针状的Co₃O₄纳米线阵列均匀地垂直生长在活性炭纤维表面, 形成了丰富的介孔结构。通过改变Co(NO₃)₂·6H₂O的用量, 可以获得不同负载量的Co₃O₄@ACF复合材料。当Co₃O₄负载量为47wt%时, Co₃O₄@ACF复合材料在1 A/g电流密度下的比电容高达566.9 F/g, 几乎是纯Co₃O₄的2倍; 在15 A/g的电流密度下, 其比电容仍可达到393.3 F/g, 表现了较好的倍率特性; 经过5000次循环充放电后, 其比电容仍可保持84.2%, 展现了优良的循环稳定性。     

酵母菌模板辅助合成Co3O4空心微球催化NaBH4水解制氢

预先在酵母菌模板表面沉积Co(OH)₃, 经高温煅烧后成功制得Co₃O₄空心微球, 并作为前驱体催化NaBH₄水解制氢。通过场发射扫描电镜(FE-SEM)和X射线衍射(XRD)进行样品的微观形貌和物相分析。研究结果表明, 当反应液中NaBH₄含量为10wt%时, 模板法制备的Co₃O₄空心微球催化产氢速率高达2140 mL/(min•g) (25℃), 约是同等条件下无模板制备Co₃O₄活性的9倍, 且所制备的Co₃O₄空心微球长期储存性能良好。     

Electrical transport and magnetic properties in La0.67Ca0.33MnO3 and CuFe2O4 composites

The (1 − x) La_0.67Ca_0.33MnO₃/xCuFe₂O₄ (x = 0, 0.04, 0.07, 0.10 and 0.15) composites have been prepared and investigated systematically for their microstructure, electrical and magnetic properties. The X-ray diffraction and scanning electronic microscopy analysis reveal that both La_0.67Ca_0.33MnO₃ (LCMO) and CuFe₂O₄ phases are distributed in the composites. Compared with pure LCMO, an obvious enhancement of magnetoresistance is observed over a wide temperature range for the composites. Under 3 T field, the magnetoresistance rises from a base value 44.5% for pure LCMO, to a maximum value of 66.7% for x = 0.1 composite. Meanwhile, a weak temperature-dependent MR platform is observed in the temperature range from 210 K to 240 K. The MR enhancement is discussed in terms of spin-polarized intergrain tunneling due to enhanced magnetic disorder and magnetic coupling near boundaries between LCMO and CuFe₂O₄ grains.     

稀土氧化物对SPS烧结AlN陶瓷电性能的影响

以AlN粉末为原料, 添加稀土氧化物(Sm₂O₃、Y₂O₃), 在氮气气氛下, 采用SPS烧结方法制备AlN陶瓷, 研究稀土氧化物的掺杂对AlN烧结试样相组成、微观结构和电性能的影响。实验表明: Sm₂O₃、Y₂O₃与Al₂O₃反应生成的液相稀土金属铝酸盐会提高AlN陶瓷致密度, 且在晶界处形成导电通路降低了AlN陶瓷电阻率。随着Sm₂O₃掺杂量的增加, 晶界相逐渐由Sm₄Al₂O₉过渡到SmAlO₃, 且Sm₄Al₂O₉对电阻率贡献最大。其中, 3wt% Sm₂O₃掺杂AlN陶瓷电阻率最低, 为      

Gd2Zr2O7陶瓷的高温热物理性能及Gd2Zr2O7-8YSZ双涂层制备

通过高温固相合成方法制备了烧绿石结构Gd₂Zr₂O₇陶瓷材料,研究了其高温相稳定性和热物理性能。采用电子束物理气相沉积方法制备了Gd₂Zr₂O₇-8YSZ(8%Y₂O₃-ZrO₂)双陶瓷层结构热障涂层,分析了涂层顶层的晶体结构和原子数量比。结果表明,Gd₂Zr₂O₇在室温至1500℃范围内具有良好的相稳定性,比第一代热障涂层8YSZ的高温相稳定区间提高250℃以上。Gd₂Zr₂O₇块材的热膨胀系数在100~1500℃范围内介于8.8×10^-6~11.0×10^-6 K^-1之间,与8YSZ接近; 在1000~1400℃高温区间,热导率约为1.0 W(m·K)^-1,比8YSZ降低一半左右。沉积制得的Gd₂Zr₂O₇涂层化学成分符合化学计量比,为烧绿石结构,涂层呈现典型的柱状晶结构。