高能球磨高温固相法制备尖晶石型铜铬黑颜料

以Cr2O3与CuO为原料,采用高能球磨高温固相法制备尖晶石型铜铬黑颜料;利用XRD、SEM和激光粒度仪等方法对制备颜料的结构、形貌及粒度进行了表征。系统研究了前体混料方式、球磨时间、煅烧温度、煅烧时间等条件对铜铬黑颜料晶型、粒度的影响;探讨了掺杂对铜铬黑颜料着色力的影响。研究表明,通过高能球磨可有效地控制颗粒大小及均匀性,NiO与CoO的掺入可显著提高其着色力。高能球磨10 min,煅烧温度900 ℃,保温时间3 h下制备出了粒径分布均匀着色力较好的铜铬黑颜料。     

Synthesis of CoFe2O4 Nanoparticles by a Low Temperature Microwave‐Assisted Ball‐Milling Technique

Well‐crystallized Cobalt ferrite nanoparticles with mean size of 20 nm and high saturation magnetization (82.9 emu/g) were synthesized at a low temperature (≤100°C) by microwave‐assisted solid–liquid reaction ball‐milling technique without subsequent calcination. CoC₂O₄·4H₂O and Fe powder were used as raw materials and stainless steel or pure iron milling balls with diameter of 1.5 mm were used. As a contrast, solid–liquid reaction ball milling without microwave assistance was also investigated. The results showed that this is a simple, environmentally friendly, and energy‐saving technique for ferrite nanocrystal synthesis.     

Effect of particle size of as-milled powders on microstructural and magnetic properties of Y3MnxAl0.8-xFe4.2O12 ferrites

Yttrium iron garnet ferrite using the chosen stoichiometry of (Y₃)(Mn_xAl_0.8-xFe_4.2)O₁₂ with x = 0.1 and different milling powder sizes were prepared through ball milling for various milling times to study the effect of powder size reduction on the resulting microstructural and magnetic properties. Sintered yttrium iron garnet ferrites were characterized by X-ray diffraction analysis and scanning electron microscopy. The particle size (D₅₀) of as-milled calcined powder was decreased using ball milling (from 3.682 μm for a 0.5-hour-long milling to 1.606 μm for a 2.5-hour-long milling). Scanning electron microscopy analyses confirmed that the sintered grain exhibited a crystal size that was increased from initial values (average crystal grain sizes of 3.5 ± 0.1 μm for 0.5 hour of milling) up to 6.2 ± 0.1 μm after 2.5 hour of ball milling and the subsequent sintering process. The same sintered specimen after 2.5 hour of ball milling exhibited an obvious increase in saturation magnetization (4πM_s), remanence (B_r), and squareness ratio (namely B_r/4πM_s); it also caused a notable decline in coercivity (H_c) and ferromagnetic resonance line width (∆H), which were attributed to the introduction of a smaller size of calcined powder after milling and subsequently resulted in a larger sintered grain. Furthermore, a sufficient spin-wave line width (∆H_k) and low insertion loss (|S₂₁|) were obtained for the operation of the microwave device. The aforementioned results are all beneficial to the use of yttrium iron garnet ferrite in microwave applications. A correlation between the calcined powder size after milling, grain crystal size after sintering, and magnetic properties was evident in this study. The strict control of calcined powder size after milling is critical in tailoring suitable magnetic properties for yttrium iron garnet ferrite manufacturing processes.     

高能球磨法制备铈锆铝复合氧化物的工艺

采用高能球磨法制备铈锆铝复合氧化物,运用XRD、SEM等方法研究CeO₂-ZrO₂-Al₂O₃复合催化材料分别在不同球磨时间、不同成分含量、不同焙烧温度和不同球磨工艺路线下的组织结构和稳定性能。结果表明：①随球磨时间的延长,各组元晶粒细化效果越来越明显,球磨30h,CeO₂晶粒约20nm,颗粒约200nm,但复合粉末一直未发生机械合金化。②经30h球磨的复合粉体,在1000℃以下具有良好的稳定性能,高温下有少量的ZrO₂溶入CeO₂中形成固溶体,CeO₂-ZrO₂和Al₂O₃之间表现出一定的协同稳定效应,而在1000℃以上相结构变化明显。③质量分数为18%的CeO₂和6%的ZrO₂的复合粉体颗粒比较细小,分布比较均匀,对γ-Al₂O₃的稳定化效果比较理想。④采用先将CeO₂和ZrO₂球磨30h,再添加Al₂O₃并继续球磨30h的高能球磨工艺,可制备出含大量CeO₂-ZrO₂固溶体的复合粉体,CeO₂-ZrO₂与γ-Al₂O₃相互改性作用更加理想。     

Abnormal grain growth in (K,Na)NbO3-based lead-free piezoceramic powders

Abnormal grain growth (AGG) is frequently observed in sintered (K, Na)NbO₃ (KNN)-based piezoceramics. However, in the present study, abnormal grain growth was unexpectedly discovered in calcined KNN-based powders. To explain the phenomenon, three well-established models that account for the AGG in sintered ceramics were discussed, including (a) liquid-phase-assisted grain growth, (b) two-dimensional nucleation grain growth, and (c) complexion coexistence. However, the AGG in calcined powders was concluded to be none of them, but a consequence of the A-site compositional inhomogeneity in the K₂CO₃-Na₂CO₃-Nb₂O₅ ternary system. Since repeated calcination and ball milling have low efficiency on solving AGG and the accompanied compositional inhomogeneity, abnormal grains were found to coexist with normal grains at a very high calcination temperature, that is, 1000°C. The compositional inhomogeneity is believed to be remaining even after sintering and consequently deteriorate the comprehensive performances, which might be a determinant for the unstable reproduction of KNN-based piezoceramics.     

Effect of high-energy ball milling on the microstructure and properties of ultrafine gradient cemented carbides

Planetary low-temperature high-energy ball mill was used for preparing the mixed powders with different particle sizes by adjusting the milling time. The ultrafine grain gradient cemented carbides were prepared by sinter-HIP treatment. The effects of milling time on the gradient formation, grain growth, and mechanical properties of ultrafine grain gradient cemented carbides were investigated. The results show that the high-energy ball milling cannot effectively reduce the particle size of mixed powder with short milling time. In addition, the particle size of the mixed powder is significantly reduced, while the specific surface area is significantly increased when the ball milling time exceeds 25 hours. The gradient layer thickness and the grain size increase at the beginning and then decrease when the mixed powder particle size was decreased. Simultaneously, the density, hardness, and fracture toughness of the alloy increase gradually. On the contrary, the number of WC with abnormal grain growth is significantly increased. The thickness of the gradient layer reached 32 μm, and the mean WC grain size is 314 nm. Based on the analyzed results, an optimized gradient layer thickness, grain size, density, and hardness can be obtained when the ball milling time is 35 hours.     

超细石英砂粉体的机械球磨工艺优化研究

利用长江沿岸低品位石英砂开发研制保温隔热砖,研究球磨参数对低品位石英砂粒径的影响,为制备高性能的保温隔热砖奠定原料基础。研究结果表明:随着球磨时间的延长,石英砂粒径减小;随着球磨转速的增加,石英砂粒径逐渐减小;随着球磨机装料量的增加,石英砂的粒径增加;随着球比的增加,石英砂粒径逐渐增加。综合考虑整个工艺过程性价比,确定最佳球磨参数为:球磨时间为60min,球磨转速为300r/min,球磨机装料量为200g/L,大小球质量比值为0.75。     

Anisotropic grain growth of mullite in high-energy ball milled powders doped with transition metal oxides

Dense mullite ceramics with anisotropic grains were derived from the high-energy ball milled mixtures of Al₂O₃ and amorphous silica with the presence of transition metal oxides (FeO_1.5, CoO and NiO). The mullitization and grain growth behavior of the unmilled mixture without the addition of the transition metal oxides and the undoped system of Al₂O₃ and amorphous silica with and without milling were also investigated and compared. The mullitization temperature was about 1200 °C in the milled systems, 100 °C lower than that required by the conventional solid-state reaction process. The lowered mullitization temperature, as well as the anisotropic grain growth, was attributed to the refined structure of the oxide powders, as a result of the high-energy ball milling. The experimental results have been explained by a dissolution-precipitation mechanism.     

机械力-微波活化对稀土尾矿NH3-SCR脱硝性能的影响

因为稀土尾矿中矿物复杂的连生关系,使其部分矿物在脱硝反应过程中并不能充分暴露发挥作用。本文采用机械力微波活化稀土尾矿,利用正交试验方法研究机械力微波活化参数对稀土尾矿NH₃-SCR脱硝性能的影响,借助XRD、SEM-EDS、H₂-TPR、NH₃-TPD、BET等表征手段分析了机械力微波活化对稀土尾矿性能的影响。实验结果表明,稀土尾矿对活化参数的敏感性为：球料比>转子转速>球磨时间=球直径比>微波焙烧时间=微波焙烧温度=微波焙烧功率,机械力微波活化最优参数为球磨2h、转子转速300r/min、球料比1∶1、球直径比1∶1∶1、微波焙烧温度250℃、微波焙烧时间20min、微波焙烧功率1100W,活化稀土尾矿脱硝效率最高提升了40%。活化后,稀土尾矿催化剂的比表面积、矿物分散度、表面酸性位数量和氧化还原性能均得到了提升,弱酸、中强酸和强酸活性中心均匀分布有利于脱硝反应。赤铁矿暴露程度越高,越有利于稀土尾矿脱硝反应过程。     

The Effects of Operating Conditions on the Milling of Microcrystalline Cellulose

There is little detailed work relating the physical process that occurs during milling to the mechanical properties and mechanism of particle breakage. Very often, the selection of an appropriate mill and subsequently the determination of its optimum operating conditions are by trial and error. This paper look into optimizing the operating conditions of a ball mill through statistical analysis and the effect of temperature on the milling behavior of a common pharmaceutical excipient, microcrystalline cellulose (MCC). In addition, the bulk milling behavior of MCC is compared to its single particle breakage behavior. In this work, milling is conducted in a Retsch single ball mill where a bed of powder is subjected to impact by a steel ball in a horizontal cylindrical container. The container is vibrated horizontally at a set frequency, causing the ball to impact on the bed of particles. It is found that the finest MCC product can be achieved by milling a 2 g batch of material using a 12 mm ball size and at a frequency of 18 Hz. Temperature is found to have insignificant effect on the extent of breakage of MCC in both bulk milling and single particle impact testing. Milling and single particle impact experiments have both shown that MCC is more susceptible to breakage with increasing strain rate. In conclusion, the single impact tests could be used successfully for predicting the bulk milling behavior of the material, as shown in the case of MCC.     

Anisotropic Grain Growth in Mullite Powders as a Result of High-energy Ball Milling

High-energy ball milling was applied to a commercial mullite powder, which had a particle size ranging from 2 to 10 μm, and was considerably refined to be <1 μm after milling for 10 h. Anisotropic grain growth of mullite was observed in the milled mullite powder, starting at relatively low temperatures (1200°C). The anisotropic grain growth was possibly attributed to the special anisotropic structure of mullite and refined mullite powder as a result of the high-energy ball milling, although other factors, such as lattice defects, localized stress of the milled powder, and impurities or contaminations caused by the high-energy milling also could be factors. This anisotropic grain growth of mullite might be useful in the fabrication of reinforced ceramics based on mullite and other materials.     

Process investigation, electrochemical characterization and optimization of LiFePO4/C composite from mechanical activation using sucrose as carbon source

LiFePO₄/C composite was synthesized by mechanical activation using sucrose as carbon source. High-energy ball milling facilitated phase formation during thermal treatment. TG-DSC and TPR experiments demonstrated sucrose was converted to CH_x intermediate before completely decomposed to carbon. Ball milling time, calcination temperature and dwelling time all had significant impact on the discharge capacity and rate performance of the resulted power. The optimal process parameters are high-energy ball milling for 2-4 h followed by thermal treatment at 700 °C for 20 h. The product showed a capacity of 174 mAh/g at 0.1C rate and around 117 mAh/g at 20C rate with the capacity fade less than 10% after 50 cycles. Too low calcination temperature or insufficient calcination time, however, could result in the residual of CH_x in the electrode and led to a decrease of electrode performance.     

Si/C composite lithium-ion battery anodes synthesized from coarse silicon and citric acid through combined ball milling and thermal pyrolysis

Silicon and related materials have recently received considerable attention as potential anodes in Li-ion batteries for their high theoretical specific capacities. To overcome the problem of volume variations during the Li insertion/extraction process, in this work, Si/C composites with low carbon content were synthesized from cheap coarse silicon and citric acid by simple ball milling and subsequent thermal treatment. The effects of ball milling time and calcination temperature on the structure, composition and morphology of the composites were systematically investigated by the determination of specific surface area (BET) and particle-size distribution, X-ray diffraction (XRD), O₂-TPO, and scanning electron microscopy (SEM). The capacity and cycling stability of the composites were systematically evaluated by electrochemical charge/discharge tests. It was found that both the initial capacity and the cycling stability of the composites were dependent on the milling and calcination conditions, and attractive overall electrochemical performance could be obtained by optimizing the synthesis process.     

Preparation of short carbon nanotubes by mechanical ball milling and their hydrogen adsorption behavior

Short multi-wall carbon nanotubes (MWNTs) with open tips were obtained by mechanical ball milling. The microstructure characteristics of MWNTs before and after ball milling were checked by transmission electron microscopy (TEM). The effect of ball milling on the hydrogen adsorption behavior of the MWNTs was studied. The hydrogen adsorption experiments were carried out at room temperature under a pressure of 8-9 MPa. The hydrogen adsorption capacity of carbon nanotubes milled for 10 h was 0.66 wt%, which was about six times that of MWNTs without milling. For the carbon nanotubes milled with MgO for 1 h, a hydrogen adsorption capacity of 0.69 wt% was obtained. The enhancement of hydrogen adsorption might result from the increase of defects and surface area of the MWNTs caused by ball milling.     

微波法制备纳米铁酸锌及其晶粒生长动力学

纳米铁酸锌广泛应用于催化和材料领域,为了避免传统焙烧法高耗能的缺点,本实验选用高效微波法制备纳米铁酸锌,并与常规焙烧进行对比,研究了铁酸锌晶粒生长动力学。采用FTIR、XRD和SEM对样品进行表征。结果表明,相同焙烧温度和焙烧时间下,微波法制备的铁酸锌比常规制备的样品结晶度高,颗粒大小更均匀。通过谢乐公式计算不同温度下铁酸锌粒径得出,焙烧温度低于500℃时,焙烧方式对铁酸锌粒径影响较大;纳米铁酸锌晶粒生长动力学研究显示,微波焙烧时晶粒的平均生长指数为9.66,低于常规焙烧生长指数(10.6),表明微波焙烧时晶粒的平均生长速率较高,有利于晶粒生长;同时,微波晶粒生长平均活化能为122.1kJ/mol,远低于常规焙烧平均活化能(179.4kJ/mol),说明微波可以降低晶粒生长活化能,且微波的“非热效应”影响晶粒的生长。     

Role of particle size on the magnetoresistance of nano-crystalline graphite

We report on microstructure and magnetotransport behavior of ball milled graphite to investigate the effect of particle size on magnetoresistance (MR) in graphite. The observed results show, large values of resistivity and a negative temperature coefficient of resistivity indicating non-metallic, semiconductor nature of the compacts. As the milling time increases, the resistivity value increase which is attributed to the particle size differences of the samples. Graphite exhibits the positive MR at room temperature as well as at low temperatures (4 K). 600 °C annealed samples exhibit less resistivity compared to as-milled samples due to the grain growth during annealing but show large MR values compared to as-milled sample.     

不同预处理工艺对磷石膏性能的影响

为研究不同预处理工艺对磷石膏性能的影响,通过X射线衍射、X射线荧光光谱、扫描电子显微镜、热重分析等手段表征磷石膏化学组分、微观形貌、晶型等特征,然后分别用普通煅烧法、微波煅烧法、水洗法、球磨法工艺对原状磷石膏进行力学性能、工作性能、凝结时间及需水量等指标的对比研究。结果表明：普通煅烧法、水洗法对可溶性五氧化二磷、氟类和有机质等杂质去除效果明显;微波煅烧法时间短,只需20 min左右;球磨法能细化颗粒,处理时间在20 min左右最佳。通过预处理制备的磷石膏物理化学特性都得到很大改善,抗压、抗折强度均优于GB/T 9776—2008《建筑石膏》指标,具有巨大的应用前景。     

Fabrication of low cost fine-grained alumina powders by seeding for high performance sintered bodies

The effect of seeding into commercial aluminum hydroxide on the α-alumina transition temperature, powder characteristics and properties of sintered bodies was investigated, with the purpose of obtaining high performance sintered bodies from low cost raw material. A small amount of fine α-alumina seed addition, which was worn from wet ball milling, drastically lowered the α-alumina transition temperature. The particle size of the low temperature transformed seeded powder was smaller than non-seeded powder. This powder could be sintered to full dense at lower temperature. The abnormal grain growth, which is often observed in high temperature sintered usual purity alumina, occurred at lower temperature in the sintered low temperature transformed seeded powder. However, the abnormal grain size was small and the number of the grains was high. The sintered bodies with these microstructures show high bending strength and very high fracture toughness.     

Polymerization of ethylene induced by fractured metallic oxides. III. Factors affecting the polymerization

Mechanochemical polymerization of ethylene was found to be induced by fracture of γ-alumina under quite low pressure and room temperature. The factors to control the polymerization yield, for example, calcination temperature of the alumina, spin concentration after ball milling, milling time, and changes of acidity before and after the fracture, were investigated in order to know the polymerization mechanism. It was found that the polymerization yield did correlate not with the spin concentration responsible to paramagnetic species produced by the fracture, but the calcination temperature of the γ-alumina and the milling time. The resultant polymeric material on the fractured alumina was extracted alumina was extracted with solvents, and the fraction extracted with petroleum ether was characterized using GC and GC mass spectrometer. The results indicated that odd-numbered linear hydrocarbons were produced, although the major products of this polymerization were even-numbered. It is concluded from the accumulated experimental results that a carbonium ion mechanism rather than radical mechanism is probable for the mechanochemical polymerization induced by fracture of γ-alumina.     

高能球磨对YAG陶瓷制备的影响(英文)

通过高能球磨法处理Y2O3-Al2O3(yttrium aluminum garnet,YAG)混合粉体,对球磨产物进行煅烧、成型以及烧结,并对固相反应中的物相变化、YAG粉体形貌以及YAG陶瓷密度、力学性能及显微结构进行表征和分析,确定了最佳的球磨时间和粉体煅烧温度.研究表明:经过40h高能球磨,得到的球磨产物具有良好的活性.采用传统固相法制备的YAG粉体,需要在1 500℃煅烧,该方法处理的YAG粉体在1 200℃煅烧2 h,可以得到活性较高的YAG粉体,使粉体的煅烧温度下降了300℃.利用常压烧结在1 550℃烧结坯体2h,得到致密的YAG陶瓷,明显改善了YAG陶瓷制备技术.