氧化铝掺杂对Ba0.6Sr0.4(Zr0.2Ti0.8)O3陶瓷介电性能的影响

Zr4+取代Ti4+的Ba0.6Sr0.4(Zr0.2Ti0.8)O3固溶体在降低介电常数的同时,保持了BST固溶体优异的可调性。为降低BST材料的介电损耗和介电常数,以氧化铝为改性剂对Ba0.6Sr0.4(Zr0.2Ti0.8)O3材料(BSZT材料)进行了掺杂。随着氧化铝掺杂质量分数从1%到10%增加,BSZT材料的介电常数从5000降低到了1550(100kHz),介电损耗降低到0.001(100kHz)以下,而材料的介电可调性保持在35%左右(1.5kV/mm)。X射线衍射图谱表明,烧结后得到的BSZT材料具有典型的钙钛矿结构。扫描电子显微镜观察表明,氧化铝的掺杂使得陶瓷致密度较高,晶粒均匀。     

Disintegration and fine powder preparation of Nb75Si25 via hydrogenation

Hydrogenation of Nb₇₅Si₂₅ directly in an arc-melting chamber after arc-melting was investigated. A Nb₇₅Si₂₅ ingot absorbs hydrogen rapidly and simultaneously disintegrates into fine hydride powder. After dehydriding at 1073 K for 10.8 ks, fine Nb₇₅Si₂₅ particles with an irregular angular shape are obtained. The collecting efficiency of powder under 100 mesh is 56.1 wt.%.     

Kinetics and thermodynamics of hydrogen absorption in the Zr(Al0.1Fe0.9)2 intermetallic compound

Thermodynamic and kinetic characteristics of hydrogen absorption in Zr(Al_0.1Fe_0.9)₂ were investigated at pressures up to 80 atm of H₂ and temperatures between 248 K and 270 K. The heat and entropy of formation of the Zr(Al_0.1Fe_0.9)₂ hydride are estimated to be −24.7 kJ/(mole H₂) and −120 J/(K^*mole H₂), respectively. Small, well-defined samples were utilized for the kinetic research. The experimental kinetic data fit a shrinking core (sc) model, in accord with a visual examination of partly hydrided samples. The pressure dependence of the rate constants indicates an interface-controlled phase transition as the hydride formation rate-determining step. The activation energy for the hydriding process is estimated from Arrhenius plots of the reaction rates to be 0.30 eV/H atom. The kinetic data are discussed in view of similar results for additional intermetallic compounds.     

Kinetics and formation mechanism of amorphous Fe52Nb48 alloy powder fabricated by mechanical alloying

A single phase amorphous Fe₅₂Nb₄₈ alloy has been synthesized through a solid state interdiffusion of pure polycrystalline Fe and Nb powders at room temperature, using a high-energy ball-milling technique. The mechanisms of metallic glass formation and competing crystallization processes in the mechanically deformed composite powders have been investigated by means of X-ray diffraction, Mössbauer spectroscopy, differential thermal analysis, scanning electron microscopy and transmission electron microscopy. The numerous intimate layered composite particles of the diffusion couples that formed during the first and intermediate stages of milling time (0–56 ks), are intermixed to form amorphous phase(s) upon heating to about 625 K by so-called thermally assisted solid state amorphization, TASSA. The amorphization heat of formation for binary system via the TASSA, ΔH_a, was measured directly as a function of the milling time. Comparable with the TASSA, homogeneous amorphous alloys were fabricated directly without heating the composite multilayered particles upon milling these particles for longer milling time (86 ks–144 ks). The amorphization reaction here is attributed to the mechanical driven solid state amorphization. This single amorphous phase transforms into an order phase (μ phase) upon heating at 1088 K (crystallization temperature, T_x) with enthalpy change of crystallization, ΔH_x, of −8.3 kJ mol⁻¹.     

Hydrogen disproportionation by reactive milling and recombination of Nd2(Fe1−xCox)14B alloys

Stoichiometric Nd₂(Fe_1−xCo_x)₁₄B alloys (x=0, 0.25, 0.5, 0.75 and 1) have been disproportionated into NdH_2+δ and bcc–(Fe,Co) (0≤x≤0.75) or fcc–Co (x=1), respectively, by milling in hydrogen at enhanced temperatures. Reactive milling leads to the disproportionation of the thermodynamically very stable Nd₂Co₁₄B alloy. This reaction is not possible via the conventional hydrogenation disproportionation desorption and recombination (HDDR) process. Grain sizes of disproportionated and recombined Nd₂(Fe,Co)₁₄B materials were found to be <10 nm and 40–50 nm, respectively — approximately an order of magnitude smaller than those of conventional-HDDR processed alloys. The recombined Nd₂Co₁₄B alloy shows on average slightly smaller grain sizes than the Nd₂Fe₁₄B compound. A more effective exchange coupling leading to enhanced remanences, possibly due to the slightly smaller grain size, has been observed for Nd₂Co₁₄B powders recombined at 600–700°C.     

La_(0.6)Pr_(0.4)Fe_(11.4)Si_(1.6)B_(0.2)合金及其氢化物磁热性能研究

采用工业纯原料感应熔炼制备出公斤级La_(0.6)Pr_(0.4)Fe_(11.4)Si_(1.6)B_(0.2)合金,经退火后通过吸氢处理提高其居里温度到室温附近。研究了在1373~1473 K温度下经不同时间和温度退火对合金微观组织结构的影响。实验发现在1473 K经30 h退火样品的居里温度为202 K,在0~1.5 T变化磁场下的最大磁熵变达8.1~8.6 J/kg·K。在0.13 MPa氢气压力下,经553 K吸氢5 h氢化处理合金的居里温度为320 K,最大磁熵变达7.7~8.0 J/kg·K。     

铝合金细化相Al3(Zr,Sc)的能量和弹性性质的第一性原理研究

微合金化是强化铝合金的重要手段,Sc作为铝合金有效的细化剂而引起广泛关注。实验研究表明,在铝基体中同时添加Zr和Sc,在铝基质中形成Al3(Zr,Sc)细化相,可以实现更好的晶粒细化。本文基于密度泛函理论的第一性原理方法,系统地研究了不同Sc/Zr配比下形成的Al3(Zr,Sc)细化相的能量和弹性性质。结果表明,当Sc/Zr不高于1/3时,Al3(Zr,Sc)相具有较大的形成焓绝对值,细化相将优先于Al3(Zr,Sc)相析出。同时,Sc元素的加入有利于界面的形成,提高界面的结合强度和润湿效果,但高于1/3的Sc/Zr比对界面性能的提高并无积极作用。并且,Zr的加入可以有效提高细化相的弹性性能,并削弱Al3Sc的弹性各向异性特征。此理论研究指出,微合金化Zr和Sc的共同添加时Sc/Zr不高于1/3时,可以保证细化效果并大大降低合金的成本。     

Mechanical relaxations of a (Zr77.5Ti22.5)55(Ni48Cu52)21.25Be23.75 amorphous alloy studied using dynamic mechanical analysis

The dynamic mechanical properties of a (Zr_77.5Ti_22.5)₅₅(Ni₄₈Cu₅₂)_21.25Be_23.75 amorphous alloy were investigated by frequency-dependent elastic moduli and isothermal multi-frequency measurements. The frequency-dependent loss modulus showed a relaxation behavior resulting from a glass transition, and the variation of the peak frequency was related to the Arrhenius equation. Isothermal multi-frequency measurement data were used to construct the master curves of the elastic moduli and tan δ by applying the time-temperature superposition principle. The temperature dependence of the shift factor was found to follow the Arrhenius relationship, and the activation energies for the low temperature relaxation and glass transition were approximately 156.6kJ/mol and 554kJ/mol, respectively. The glass transition temperature (T _g) was manifested by the crossover region of the shift factor dependence, and from the relationship between the shift factors and the temperature aboveT _g), the fragility index of this alloy was estimated.     

Microstructural evolution of some MgO–TiO2 and MgO–Al2O3 powder mixtures during high-energy ball milling and post-annealing studied by X-ray diffraction

High-energy dry ball-mill and post-anneal processing were applied to synthesize MgTiO₃ and Mg₂TiO₄ single crystalline phases from the predetermined compositions of MgO–TiO₂ powder mixtures. Also, the experiments were performed to show that it is possible to prepare MgAl₂O₄ single crystalline phase from the predetermined composition of MgO–Al₂O₃ powder mixture only by employing high-energy dry ball milling, i.e. without post-annealing the milled samples. In contrast, fully developed single crystalline powders of MgTiO₃ and Mg₂TiO₄ were obtained after post-annealing the milled samples for 1 h at 900 and 1200 °C, respectively.     

Structural and magnetic properties of nanostructured Fe50(Co50)-6.5 wt% Si powder prepared by high energy ball milling

This work investigates the effects of 6.5 wt% Si addition and milling times on the structural and magnetic properties of Fe₅₀Co₅₀ powders. For this purpose, at first the elemental Fe and Co powders were milled for 10 h to produce Fe₅₀Co₅₀ alloy and then Si was added and the new product was milled again for different times. The microstructural and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results show that the minimum crystallite size of the as-milled powders (∼12 nm) has been achieved after introducing Si and milled for 8 h (total milling time of 18 h). Also an amount of 188 emu/g has been achieved for M_s. This amount of M_s is higher than most of those which have been already reported for M_s of different Fe-Si systems.     

Processing, microstructure, and properties of laser remelted Al2O3/Y3Al5O12（YAG） eutectic in situ composite

Laser remelting and rapid solidification were performed in preparing the high-performance Al2O3/Y3Al5O12（YAG） eutectic in situ composite. The microstructure characteristic and solidification behavior were studied using scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS）, X-ray diffractometry（XRD） and simultaneous thermal analysis（STA）. The hardness and fracture toughness were obtained using an indentation technique. The results show that the laser remelted Al2O3/YAG composite has a homogeneous eutectic microstructure without microcrack and pore. The component phases of Al2O3 and YAG are three-dimensionally and continuously reticular connected, and finely coupled without grain boundaries, colonies and amorphous phases between interfaces. The eutectic interspacing is greatly refined with increasing the scanning rate and average is only l μm. The synthetically thermal analysis indicates that the eutectic temperature of Al2O3-YAG is 1 824 ℃, well matching the phase diagram of Al2O3-Y2O3 system. The maximum hardness reaches 19.5 GPa and the room fracture toughness is 3.6 MPa.m^1/2.     

Trepanning of Al2O3 by electro-chemical discharge machining (ECDM) process using abrasive electrode with pulsed DC supply

Electro-chemical discharge machining (ECDM) of electrically non-conductive high-strength–high-temperature-resistant ceramics such as aluminium oxide (Al₂O₃) by trepanning method (i.e. orbital motion of tool) has shown the possibility of drilling large size holes by comparatively smaller electrodes efficiently and economically. However, at greater machined depth, the conventional electrode configurations and machining parameters show that machining performance gradually deteriorates with increase in tool depth and finally cause micro cracks on the machined surface due to thermal shocks at high voltage. To reduce this problem and to enhance the machining performance during trepanning operation of Al₂O₃, a spring fed cylindrical abrasive electrode of 1.5 mm diameter has been used under the effect of the three most influential parameters, namely, pulsed DC supply voltage, duty factor and electrolyte conductivity, each at five different levels to assess the volume of material removed, machined depth and diameteral overcut. The results obtained from this study revealed that pulsed DC has reduced the tendency of cracking at high supply voltage compared to smooth DC and the machining ability of the abrasive electrode was better than copper electrode as it would enhance the cutting ability due to the presence of abrasive grains during machining. In addition to this, trepanning provides the scope for drilling bigger holes.     

Magnetic properties of novel compounds R3(Fe,Cr)29Xy (R=Nd, Sm and X=N, C)

The novel ternary rare-earth iron-rich interstitial compounds R₃(Fe,Cr)₂₉X_y (R=Nd, Sm and X=N, C) with the monoclinic Nd₃(Fe,Ti)₂₉ structure have been successfully synthesized. Introduction of the interstitial nitrogen and carbon atoms led to a relative volume expansion ΔV/V of about 6% and an enhancement of Curie temperatures T_c about 268 K for the nitride and about 139 K for the carbide, respectively. The Nd₃Fe_24.5Cr_4.5X_y compounds have a planar anisotropy at room temperature. A first-order magnetization process (FOMP) with critical field B_cr=4.4 T and 3.1 T at room temperature were observed for the Nd-nitride and carbide compounds, respectively. The Sm₃Fe₂₄Cr₅X_y compounds were found to have a large uniaxial anisotropy of about 18 T at 4.2 K and about 11 T at 293 K. A FOMP with B_cr=2.3 T was also observed in the Sm-nitride compounds at 4.2 K. Magnets with coercivity of μ_OjH_c0.8 T at 293 K has been successfully developed from the Sm₃Fe₂₄Cr₅X_y (X---N and C) phases.     

The electrochemical hydrogen storage of CNTs synthesized by CVD using LaNi5 alloy particles as catalyst and treated with different temperature in nitrogen

The multi-wall carbon nanotubes (MWNTs) were synthesized by chemical vapor deposition (CVD) using LaNi₅ alloy particles as catalyst. The effect of 40–60 nm MWNTs treated with different temperature in nitrogen on the electrochemical properties of CNTs–Ni electrode were investigated. Three-electrode system was introduced for testing electrochemical hydrogen storage of the electrode. The CNTs–Ni electrodes were used as the working electrode, which were prepared by mixing MWNTs and Ni powder in a weight ratio of 1:10 (MWNTs:Ni). Ni(OH)₂/NiOOH worked as the counter electrode and Hg/HgO as the reference electrode. A 6 mol/L KOH solution acted as the electrolyte. MWNTs treated with different temperature in nitrogen ambient represented a great discrepancy in the electrochemical hydrogen storage capability under the same testing condition. The CNTs–Ni electrodes with 40–60 nm diameter CNTs which were treated in a temperature of 800 °C in nitrogen has the best electrochemical hydrogen storage capacity of 588.1 mAh/g and a corresponding discharging plateau voltage of 1.18 V. From 500 to 800 °C, the higher temperature the MWNTs treated, the better the electrochemical hydrogen storage property of them is. This shows that the temperature of treatment is an important factor that influences electrochemical hydrogen storage performance of MWNTs.     

Preparation of Cu(In,Ga)Se2 thin films by pulse electrodeposition

Cu(In,Ga)Se₂ thin films were prepared from aqueous solution by pulse electrodeposition. It was found that the co-deposition of the species occurred under a 3D growth with instantaneous nucleation. The morphology of the pulse-electrodeposited film can be improved by adjusting the duty cycle. The significant loss of indium and reduction of In-Se compound(s) accordingly were observed with decrease of duty cycle. Chalcopyrite structure Cu(In,Ga)Se₂ films with p-type behavior and enhancement in crystallinity were obtained after annealing treatment in Ar atmosphere.     

Improvement of the electrochemical performance of LiMn2O4 cathode active material by lithium borosilicate (LBS) surface coating for lithium-ion batteries

The LBS coating on the surface of spinel LiMn₂O₄ powder was carried out using the solid-state method, followed by heating at 425 °C for 5 h in air. The powder X-ray diffraction pattern of the LBS-coated spinel LiMn₂O₄ showed that the LBS coating medium was not incorporated in the spinel bulk structure. The SEM result showed that the LBS coating particles were homogeneously distributed on the surface of the LiMn₂O₄ powder particles. The effect of the lithium borosilicate (LBS) coating on the charge-discharge cycling performance of spinel powder (LiMn₂O₄) was studied in the range of 3.5-4.5 V at 1C. The electrochemical results showed that LBS-coated spinel exhibited a more stable cycle performance than bare spinel. The capacity retention of LBS-coated spinel was more than 93.3% after 70 cycles at room temperature, which was maintained at 71.6% after 70 cycles at 55 °C. The improvement of electrochemical performance may be attributed to suppression of Mn²⁺ dissolution into the electrolyte via the LBS glass layer.     

高速钢钻头电火花沉积 Ti( C, N) /Al2O3 复合涂层的组织及切 削性能

目的在高速钢钻头表面电火花沉积Ti(C,N)/Al2O3复合涂层,以提高其切削性能。方法利用电火花沉积技术,以Ti(C,N)/Al2O3作为电极材料,在高速钢钻头表面制备Ti(C,N)/Al2O3涂层,考察涂层的物相组成、组织形貌及横截面硬度分布,并进行切削试验。结果涂层组织均匀,厚度约32~36μm,物相主要为C0.3N0.7Ti,Al2O3,AlTi3,Fe7W6,Fe4N,TiN和AlN,平均硬度是基体高速钢的2.6倍。结论在高速钢钻头表面制备Ti(C,N)/Al2O3涂层可以提高刀具的切削性能,延长其使用寿命。     

Cathodic arc deposition of (Al,Cr)2O3: Macroparticles and cathode surface modifications

The present work investigates the microstructure and chemical composition of macroparticles incorporated in arc evaporated (Al,Cr)₂O₃ coatings. According to scanning and transmission electron microscopy analysis, two different types of macroparticles with a distinct difference in their shape and a noticeable variation in their chemical composition, i.e. the Al/Cr ratio, can be distinguished. In addition, the transformations on the surface of the corresponding Al-Cr compound cathodes during the evaporation process in O₂ atmosphere are studied by scanning electron microscopy and X-ray diffraction. Beside the virgin cathode material, a reaction layer consisting of various intermetallic Al_xCr_y phases with a fine-grained morphology and pillar-shaped Al₂O₃ islands was found. Correlations between the origin of the macroparticles and the observed modifications at the surface of the Al-Cr cathode are discussed.     

Preparation and characterization of polyelectrolyte multilayer films containing in-situ synthesized nanoparticles of Cu(OH)2

Copper ions-loaded polyelectrolyte multilayer films (PEMs) of poly(acrylic acid), coded as PAA, and poly(diallyldimethylammonium chloride), coded as PDDA, were constructed on silicon substrate via layer-by-layer (LBL) self-assembly, using CuCl₂ blended in the electrolyte solution as the source of Cu²⁺. Cu(OH)₂ nanoparticles were then in-situ synthesized in the multilayer films by immersion of the copper ions-loaded PEMs into 0.1 M NaOH solution. The Cu²⁺-loaded PAA/PDDA multilayer films and those doped with in-situ Cu(OH)₂ nanoparticles were characterized by means of ultraviolet-visible light (UV-vis) absorption spectrometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The friction and wear behaviors of the multilayer films sliding against 440C stainless steel counterparts were evaluated using a UMT-2 multifunctional micro tribometer. Results indicate that the Cu²⁺-loaded PAA/PDDA multilayers with a bilayer number of 2-8 show similar UV-vis absorbance features, and no noticeable accumulation in the amount of Cu²⁺ occurs during the fabrication of the multilayers, possibly owing to a weak bonding between Cu²⁺ and -COO⁻. The blue-shift of the absorption peak of -COO⁻-Cu²⁺ band, observed for PAA/PDDA multiplayer films, becomes more obvious after being doped with in-situ Cu(OH)₂ nanoparticles. The final Cu(OH)₂ nanoparticles-doped PAA/PDDA multilayer films have excellent friction-reducing and antiwear abilities, possibly owing to the modification and refining of their morphology and microstructure by the in-situ doped Cu(OH)₂ nanoparticles. The present approach could be extended to incorporate nanoparticles of other types of metal ions into the final PEMs to realize multifunctionalization.