Synthesis of the CaAl2O4 nanoceramic compound using high-energy ball milling with subsequent annealing

Monocalcium aluminate, CaAl₂O₄, is the main constituent of calcium alumina cements which have found wide applications in refractory industries. In the present work, CaAl₂O₄ nanoceramic compound was produced by high-energy ball milling of the oxide powders followed by annealing. The phase evolution and microstructural changes of the powders during the process were investigated by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that no CaAl₂O₄ was formed during ball milling even after 100 h. By subsequent annealing, the nucleation and growth of CaAl₂O₄ took place at 1000 °C after 2 h. Depending on milling time, the amount of CaAl₂O₄ increased with increasing annealing temperature. The CaAl₂O₄ single phase was obtained by milling the sample for 100 h and subsequently annealing at 1200 °C for 2 h. The quantitative phase analysis was used to measure CaAl₂O₄ phases in these processes. The average particle diameter of the sample milled for 100 h and annealed at 1200 °C was found to be less than 100 nm as measured by transmission electron microscopy.     

Synthesis of LiMn2O4 via high-temperature ball milling process

Spinel LiMn₂O₄ powder was prepared by a novel process of high-temperature ball milling. For comparison, the spinel LiMn₂O₄ powder was also synthesized by the traditional method of solid state reaction. It was found that high-temperature ball milling significantly decreased the synthesis temperature and time. LiMn₂O₄ with pure spinel phase could be successfully synthesized only by 2?h high-temperature ball milling at 500°C and 600°C. However, pure spinel LiMn₂O₄ could not be completely synthesized by 2?h solid state reaction at 800°C. The LiMn₂O₄ particles prepared by high-temperature ball milling are nano-sized (<100?nm) and much smaller than that prepared using solid state reaction. The electrochemical tests results indicated that the as-synthesized LiMn₂O₄ by 2?h high-temperature ball milling at 600°C showed a favorable initial discharge capacity of 124.2 mAh g^?1 at current rate of 0.1 C and still retained a capacity of 119.8 mAh g^?1 at 0.1 C after 80 continuous cycles from 0.1 to 2.0 C.     

Synthesis of nanocrystalline (Co, Ni)Al2O4 spinel powder by mechanical milling of quasicrystalline materials

In the present study, attempts have been made to synthesize the nano-crystalline (Co, Ni)Al2O4 spinel powders by ball milling and subsequent annealing. An alloy of Al70Co15Ni15, exhibiting the formation of a complex intermetallic compound known as decagonal quasicrystal is selected as the starting material for mechanical milling. It is interesting to note that this alloy is close to the stoichiometry of aluminum and transition metal atoms required to form the aluminate spinel. The milling was carried out in an attritor mill at 400 rpm for 40 hours with ball to powder ratio of 20 : 1 in hexane medium. Subsequent to this annealing was performed in an air ambience for 10, 20, and 40 h at 600 degrees C in side the furnace in order to oxidize the decagonal phase and finally to form the spinel structure. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of nano-sized decagonal phase after milling and then (Co, Ni)Al2O4 spinel type phase after annealing. The XRD studies reveal the lattice parameter to be 8.075 angstroms and the lattice strain as 0.6%. The XRD and TEM explorations of spinel phase indicate the average grain size to be approximately 40 nm.     

Synthesis of hydrophobic Ni-VN alloy powder by ball milling

This is the first report discussing the synthesis of hydrophobic alloy powders consisting of Ni and transition metal nitride (vanadium nitride (VN)) at different proportions through mechanical alloying. The milled alloy powder showed very good resistance to wetting when it was placed in a beaker containing water. The maximum contact angle of 150° with water was recorded for the alloy composition of Ni-75 (wt.%) VN when the powder was loosely sprayed on a glass slide. Few working examples also elucidated the hydrophobic nature of the as-prepared alloy powder. The optimised alloyed powder composition and its phase and morphology as well as the time of milling for maximum hydrophobicity were established with the help of X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) for phase and morphology analysis, respectively. The unique chemistry of toluene with elemental Ni and transition metal nitride VN as characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy led to the development of hydrophobicity in the ball milled powder.     

Enhanced photocatalytic performance of Cu2O nano-photocatalyst powder modified by ball milling and ZnO

In this paper, a ball milled Cu₂O-ZnO nano-photocatalyst with good photocatalytic performance in visible light range was prepared. Effect of ZnO presence and ball milling of Cu₂O on the structure, microstructure, optical properties and photocatalytic performance were studied. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), high resolution transmission electron microscopy (HRTEM), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) analysis and UV–Vis spectrophotometer were used as characterization techniques. FESEM results indicated that ball milling of Cu₂O changed the morphology of Cu₂O-ZnO composite. The uniform formation of ZnO particles with average size of 30 nm over the Cu₂O surface was observed. The formation of p-n heterostructure with good contact between Cu₂O and ZnO nanoparticles was found by HRTEM image. Ball milling of Cu₂O promotes visible light absorption and reduction band gap to 1.9 eV in Cu₂O-ZnO photocatalyst. Intensity of PL spectra for the ball milled Cu₂O-ZnO photocatalyst was obviously lower. Ball milled Cu₂O-ZnO photocatalyst shows the highest photocatalytic activity and degradation efficiency of 98% was obtained for 2 mg/L methylene blue (MB) solution after 240 min. The kinetics of the photodegradation was followed the Langmuir-Hinshelwood (L-H) model and degradation rates were decreased by increase of MB concentration. In the case of ball milled Cu₂O and presence of ZnO, the MB degradation kinetics was two times faster.     

Effect of annealing on the spectroscopy performance of YVO4:Ce3+ single crystals

In this study, 1.0 at.% YVO₄:Ce³⁺ single crystals were grown in the protective atmosphere by using the Czochralski method. The crystals were annealed in Ar and H₂ atmospheres at different temperatures. The absorption and fluorescence spectra of the samples before and after annealing were measured. Results showed that the luminescent efficiency of the crystals was significantly enhanced after annealing in H₂ than after annealing in Ar. This phenomenon can be attributed to the existence of some Ce⁴⁺ ions in the crystal lattice. These Ce⁴⁺ ions can be effectively reduced to Ce³⁺ via annealing in H₂. With a fixed annealing time in H₂, the luminescent intensity significantly increased with increasing annealing temperature. The possibility of the crystal as white light material was also discussed according to the luminescence properties.     

Synthesis of rutile TiO2 powder by microwave-enhanced roasting followed by hydrochloric acid leaching

In this paper, the preparation of rutile TiO₂ powder from titanium slag by microwave-assisted activation roasting followed by hydrochloric acid leaching was investigated. The effects of the additive Na₂CO₃ on the crystal form, cell, crystallinity, phase transformation, surface functional groups and micro-surface structure of the calcined product were systematically studied using X-ray powder diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The results confirmed that the strongest characteristic Raman bands of rutile TiO₂ and the weakest FT-IR bands of (CO₃)⁻² were found when the Na₂CO₃ mass ratio was 0.4. Accordingly, the crystallinity for the product, namely short rod structure rutile TiO₂ powder, reached its peak value of 99.21% with a corresponding average grain size of 43.5 nm. The excessive Na₂CO₃ was found to be disadvantageous for the crystallinity of the product, since it formed a coverage on the surface of titanium slag which prevented the oxidation reaction for the decomposition of anosovite.     

NiCo2O4/Co3O4纳米材料的球磨法制备及电化学性能

通过高能球磨碳酸镍、碱式碳酸钴的方法制备了NiCo2O4/Co3O4复合材料.系统研究了原料质量比、球磨参数以及退火温度等对材料的微观形貌、结构、组份以及反应活化能和电化学性能的影响.结果表明,在碳酸镍和碱式碳酸钴质量比为2:8,球磨时间为48 h,退火温度为300℃条件下制得复合材料在电位范围0～0.45 V,电流密...     

Synthesis of boron nitride nanotubes from boron oxide by ball milling and annealing process

Boron nitride nanotubes were synthesized from boron oxide by high-energy ball milling and annealing method. The diameter of the nanotubes is in the range of 20-200 nm. The nanotubes show a bamboo-like structure and cylindrical-like structure under low magnification. The shorter bamboo nodes with distinct knots were observed for the bamboo-like nanotubes with larger diameters and the knots can also occasionally be observed in the cylindrical-like BN nanotubes with smaller diameters under high magnification. Al and Si were found to be catalytic materials responsible for the formation of BN nanotubes besides the metallic particles containing Fe, Ni and Cr.     

Compositional variation of photoluminescence from Mn doped MgAl2O4 spinel

Spinel (MgAl₂O₄) crystals doped with 1.0% Mn have been grown by floating zone (FZ) technique with various Mg compositions, x = MgO/Al₂O₃, from 0.2 to 1.0. Compositional variations of photoluminescence are evaluated for a fluorescence thermometer application using crystals grown. Strong photoluminescence (PL) peak is observed at λ from 512 to 520 nm from the crystals grown from compositions, x, from 0.3 to 1.0. Peak wavelength of PL increases linearly from 512 to 520 nm with x. Weak PL peaking at λ = 750 nm is also observed from the specimens. Compositional variations of PL are considered to be due to the variation of crystal field surrounding the Mn²⁺ ions. The variation of crystal field strength agrees with the compositional variation of lattice constant.     

球磨合成Fe3Al金属间化合物及其固相反应机理

Fe3Al金属间化合物是一种新型耐高温材料,并因其电热和磁性能受到重视。本文研究由铁、铝元素混合粉末利用高能球磨工艺合成Fe3Al。通过对冷焊现象的分析,用适量的有机物有效地控制了机械合金化过程。利用X射线衍射研究了反应物在球磨过程中的结构演变。通过对Fe／Al固相反应热力学的分析,认为Fe／Al原子比相等成分附近,固相反应最容易进行。     

高能球磨锐钛矿型TiO2晶型转变的研究

应用机械力化学原理，研究高能行星磨粉磨锐钛矿型TiO2引起晶型转变的过程，采用XRD、SEM、TEM、FT－IR技术对粉体进行表征，探讨了机械力化学引起晶型转变的机制。研究发现：在一定操作参数（行星磨公转转速300r/min)条件下，粉磨初期（5h)为无定形形成期，颗粒出现团聚现象，晶粒尺寸减小，晶格畸变，转变为无定形，并形成金红石型TiO2晶核；粉磨中期（5－15h)为晶粒长大期，金红石型TiO2晶粒长大；粉磨后期（15h以后）为动态平衡期，晶粒长大与粉磨引起的晶粒减小处于动态平衡，研究表明；行星磨粉磨锐钛矿型TiO2可使晶型转变为金红石型TiO2，团聚的二次颗粒尺寸为1μm左右，并由颗粒尺寸为20－40nm团聚组成。     

高能球磨时间和退火温度对制备TiNi合金粉的影响

为获得高能球磨时间和退火温度对TiNi机械合金粉特性的影响机制,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能谱仪(EDS)、差示扫描量热法(DSC)等分析方法对TiNi合金粉进行了研究。结果表明,机械合金的相成分随着在氩气保护气氛中的球磨时间和退火温度的不同而发生变化。球磨22h的产物是非晶态TiNi合金、Ti的固溶体、Ni的固溶体,球磨27h的产物是非晶态TiNi合金粉和Ni固溶体相,球磨30h发生了明显的固相反应,生成了TiNi、Ni3Ti、Ti3Ni4等物相;在650℃/5h和1000℃/5h下的退火产物都是Ni3Ti、Ti2Ni、TiNi2、TiNi和TiC,但在上述2个退火温度下TiNi并不是主要物相,其中在650℃退火时TiNi的含量明显更低。     

Synthesis and characterization of MgAl2O4 spinel by PVA evaporation technique

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of ball milling time on the structural characteristics and mechanical properties of nano-sized Y2O3 particle reinforced aluminum matrix composites produced by powder metallurgy route

Mechanical milling presents an effective solution in producing a homogenous structure for composites. The present study focused on the production of 0.5 wt% yttria nanoparticle reinforced 7075 aluminum alloy composite in order to examine the effects of yttria dispersion and interfacial bonding by ball milling technique. The 7075 aluminum alloy powders and yttria were mechanically alloyed with different milling times. The milled composites powders were then consolidated with the help of hot pressing. Hardness, density, and tensile tests were carried out for characterizing the mechanical properties of the composite. The milled powder and the microstructural evolution of the composites were analyzed utilizing scanning and transmission electron microscopy. A striking enhancement of 164% and 90% in hardness and ultimate tensile strength, respectively, were found compared with the reference 7075 aluminum alloy fabricated with the same producing history. The origins of the observed increase in hardness and strength were discussed within the strengthening mechanisms' framework.     

Phase transformation behavior of porous NiTi alloy fabricated by powder metallurgical method

Nickel titanium shape memory alloys (NiTi-SMAs) were successfully produced from elemental Ni/Ti powders by powder metallurgical method and then subjected to age treatment. Microstructure was examined by SEM and XRD and phase transformation temperatures were measured by dilatometric method. The phase transformation temperatures increased with both duration and temperature of the age treatment. The porous product exhibited desirable shape memory effect.     

A comparative study of ZnNb2O6 nanoceramics synthesized by high energy ball milling and subsequent conventional and microwave annealing

Ball-milling and subsequent conventional and microwave assisted heating processes have been applied to synthesize ZnNb₂O₆ nanoceramic. X-ray diffraction, simultaneous thermal analysis, scanning electron microscope (SEM), transmission electron microscope (TEM) and BET techniques were utilized to characterize the as-milled and annealed samples. Characterization of synthesized powders revealed that in spite of the very short heating time in the microwave process without soaking time, the powder heated at 550 °C had all physical properties similar to powders synthesized in conventional heating at the 650 °C temperature with a heating rate of 10 °C/min and a soaking time of 1 h. In addition, SEM, TEM and BET observations of synthesized powders showed that the particle size of powders lies in the nano meter range.     

Effects of the annealing temperature on the structure and up-conversion photoluminescence of ZnO film

The up-conversion film is being tried to increase the photoelectric conversion efficiency of the silicon solar cell. To improve the efficiency of the photoluminescence film, the effects of the annealing temperature were investigated on the structure and photoluminescence of the ZnO up-conversion film, which was prepared using the sol-gel method and the spin-coating technique. The results show that the organic compounds and water in the ZnO film were completely eliminated when the annealing temperature reached 500?°C. The crystallinity of film is improved and the average grain size continuously increases as increasing the annealing temperature. The transmittance in the wavelength range of 400–2000?nm continuously increases as the annealing temperature increases from 500?°C to 700?°C, whilst it decreases first and then increases as the annealing temperature increases from 800?°C to 1000?°C. When the film is excited with a laser of 980?nm, there are two intense emission bands in the up-conversion emission spectra, 542-nm green light and 660-nm red light, corresponding to Ho³⁺: ⁵S₂/⁵F₄?→?⁵I₈?and ⁵F₅?→?⁵I₈ transitions, respectively. In addition, the intensity of up-conversion luminescence for the film increases first and then decreases with the increase of the annealing temperature. When the annealing temperature is at 900?°C, the film consists of small round compact particles with a high degree of crystallization, reaching maximum up-conversion intensity of the film.     

Effective removal of Zn (II) ions from aqueous solution by the magnetic MnFe2O4 and CoFe2O4 spinel ferrite nanoparticles with focuses on synthesis,characterization, adsorption,and desorption

In this study, the MnFe₂O₄ and CoFe₂O₄ spinel ferrites nanoparticles were synthesized via a practical co-precipitation route to investigate the zinc removal from aqueous solution. The synthesized magnetic adsorbents were characterized by XRD, VSM, FE-SEM, BET, EDS, and DLS analyses. The synthesized adsorbents had a diameter range of 20–80 nm. The specific surface areas of adsorbents were found to be 84.5 and 50.4 m²/g for MnFe₂O₄ and CoFe₂O₄, and the saturation magnetization were 61.39 and 37.54 emu/g, respectively. The effects of initial pH, contact time, metal ion concentration, and temperature on Zn (II) adsorption were precisely investigated. These nanoparticles could remove Zn (II) by following the Langmuir isotherm model at optimum pH = 6, with the high adsorption capacities of 454.5 and 384.6 mg/g for MnFe₂O₄ and CoFe₂O₄, respectively. The results of kinetics studies were well fitted by pseudo-second-order, with the determination coefficients of 0.999 for both adsorbents. The thermodynamics studies showed that the zinc (II) adsorption was an exothermic and spontaneous process. Furthermore, the reusability and the desorption capability of adsorbents were also investigated.     

Effect of annealing and hydrogen plasma treatment on the luminescence of hydrothermally grown bulk ZnO

The optical properties of hydrothermally grown bulk ZnO is investigated by low temperature photoluminescence (PL) spectroscopy. The effects of annealing in an argon atmosphere, as well as the influence of hydrogen plasma exposure, on the PL of as-grown material are studied. The 11 K PL spectrum of the as-grown ZnO shows different excitonic lines in the NBE region: several bound exciton lines are clearly visible. The origin of these bound excitons is discussed, as well as the influence of annealing on these lines. A shift in the deep level emission (DLE) is also observed with an increase in annealing temperature: a red shift is detected when the annealing temperature is increased up to 650 °C, while a subsequent blue shift is observed upon an increase in the annealing temperature. The involvement of Li and Cu in this phenomenon will be discussed and the effect of hydrogen on this DLE will also be studied.