Fabrication and characterization of nanocrystalline Mg-substituted fluorapatite by high energy ball milling

The aim of this work was preparation and characterization of Mg-substituted nanostructured FA powders. Mg-substituted nanostructured FA powders were synthesized with a chemical composition of Ca_10?xMg_x(PO₄)₆F₂, with x=0, 0.5, 1, 1.5 and 2 by mechanical alloying method. Successful substitution of Ca²⁺ with Mg ions in the fluorapatite lattice was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The results showed that after 12 h of milling, pure nanocrystalline Mg-substituted FA powders with different Mg contents were synthesized. The incorporation of Mg ions into the fluorapatite caused the decrease of the lattice parameters. With increasing Mg content, the crystallinity of powder decreased while the degree of agglomeration of powder increased. SEM and TEM analysis showed that the powder was agglomerated and composed of nanocrystalline particles with the average particle size of less than 100 nm.     

Synthesis of nanosized gadolinium doped ceria solid solution by high energy ball milling

This paper reports the development of a new process for the synthesis of gadolinium-doped ceria (20GDC) solid solution nanoparticles, as a solid electrolyte for use in solid oxide fuel cells. It is based on high energy milling (mechanical alloying or MA) of CeO₂ and Gd₂O₃ powders containing 10 mol% Gd₂O₃. The samples, obtained after different milling times of 10 to 60 h, were characterized by X-ray diffraction (XRD), BET method of the specific surface area measurement, electron microscopy and Raman spectroscopy. The fluorite-structured Ce_0.8Gd_0.2O_1.9 solid solution nanopowder with the surface area of 16.86 m²/g and particle sizes below 50 nm was obtained by milling the oxide mixture for 30 h. Increase in the milling time beyond 30 h led to the smaller crystallite sizes and more agglomeration. The structural changes, as evidence for the formation of solid solution, which occurred during the course of the milling process, could be appropriately followed and discussed by Raman spectroscopy.     

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。     

高能球磨法制备纳米赤铁矿矿物颜料水分散体

以赤铁矿为原料,马来酸酐-醋酸乙烯酯共聚物PMV为分散剂,采用高能球磨法制备纳米级赤铁矿颜料水分散体,讨论了研磨时间、研磨介质以及分散剂用量等对分散体的粒径和Zeta电位的影响。结果表明,采用行星式球磨仪在球磨机转速为500 r/min,球磨时间为5 h,分散剂用量为0.25 g/g颜料,研磨介质为直径2 mm和0.5 mm锆珠的质量比为3∶2时,能获得粒径大小为230 nm的赤铁矿颜料水分散体,具有一定的粒径分散稳定性。     

高能球磨还原法对废水中邻氯苯酚的脱氯研究

在高能球磨条件下采用水合肼还原法对废水中邻氯苯酚进行脱氯研究。考察了还原剂用量、球磨时间、废水浓度等因素对脱氯效果的影响,并应用紫外光谱和高效气相色谱对脱氯产物进行了分析。研究结果表明,按水合肼与邻氯苯酚的质量比为1.4∶1,室温下球磨2min,处理邻氯苯酚的质量分数为1%的废水,脱氯率可达99.7%。该方法脱氯工艺简单,脱氯效果好。     

Synthesis of a nanocrystalline composite W-25 wt.%Ag powder by high energy milling

W-Ag pseudo-alloys are used in electric contacts of circuit breakers. They are produced by sintering of W-Ag powder mixtures followed by hot pressing or rolling to increase density. High energy milling (HEM) can enhance sintering of systems that present low sinterability because it improves dispersion, promotes refinement of the phases and produces composite particles. This work investigates the effect of HEM upon a W-25 wt.%Ag powder mixture. Phase dispersion, evolution of the shape and size of the particles during milling and the influence of strain on the crystal structure are investigated. The milled powders consist of composite particles that were formed in the first 25 h of milling. Longer milling times improve the distribution of phases inside the composite particles. The formation of the composite particles involves sequential steps of deformation, fragmentation, cold welding, work hardening and piercing of particles of the hard phase in the soft phase. The crystal lattice of W and Cu is damaged, but is not amorphized.     

Synthesis and dissolution behavior of nanosized silicon and magnesium co-doped fluorapatite obtained by high energy ball milling

Nanosized hydroxyapatite (HA) powders exhibit a greater surface area than coarser crystals and are expected to show an improved bioactivity. In addition, properties of HA can be tailored over a wide range by incorporating different ions into HA lattice. The aim of this study was to prepare and characterize silicon and magnesium co-doped fluorapatite (Si–Mg–FA) with a chemical composition of Ca_9.5Mg_0.5 (PO₄)_5.5(SiO₄)_0.5F₂ by the high-energy ball milling method. Characterization techniques such as X-ray diffraction analysis (XRD), Fourier transformed infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM) were utilized to investigate the structural properties of the obtained powders. Dissolution behavior was evaluated in simulated body fluid (SBF) and physiological normal saline solution at 37 °C for up to 28 days. The results of XRD and FTIR showed that nanocrystalline single-phase Si–Mg–FA powders were synthesized after 12 h of milling. In addition, incorporation of magnesium and silicon into fluorapatite lattice decreased the crystallite size from 53 nm to 40 nm and increased the lattice strain from 0.220% to 0.296%. Dissolution studies revealed that Si–Mg–FA in comparison to fluorapatite (FA), releases more Ca, P and Mg ions into SBF during immersion. 175 ppm Ca, 33.5 ppm P and 48 ppm Mg were detected in the SBF containing Si–Mg–FA after 7days of immersion, while for FA, it was 75 ppm Ca, 21.5 ppm P and 29 ppm Mg. Release of these ions could improve the bioactivity of the obtained nanopowder. It could be concluded that the prepared nanopowders have structural properties such as crystallite size (~40 nm), crystallinity degree (~40%) and chemical composition similar to biological apatite. Therefore, prepared Si–Mg–FA nanopowders are expected to be appropriate candidates for bone substitution materials and also as a phase in polymer or ceramic-based composites for bone regeneration in tissue engineering applications.     

Microwave synthesis and sintering of forsterite nanopowder produced by high energy ball milling

This paper reports the development of a new process for the synthesis and sintering of forsterite nanopowder via microwave-assisted high energy ball milling of a powder mixture containing silica gel and Mg(OH)₂. X-ray diffraction (XRD), FTIR spectrometer, BET, scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) techniques were utilized to characterize the as-milled and annealed samples. X-ray diffraction results showed that highly ordered forsterite can be obtained through the calcination of the as-milled powder over 900 °C. In addition, SEM and TEM observations of the synthesized powders showed that the particle size of the powder lies in the nanometer range, also being compared with the BET results (about 45 to 64.5 nm). Microwave sintering (MS) of the forsterite nanopowder produced with high energy ball milling and subsequent microwave heating resulted in remarkable enhancement in densification in comparison with conventional sintering (CS) at lower temperatures.     

Preparation and optical properties of dispersible ZnSe nanocrystals synthesized by high energy ball milling

ZnSe nanocrystals have been successfully synthesized by high energy ball milling method. X-ray diffraction patterns show a single zinc blende structure formed in the milling process. HRTEM images confirm that the formation of the ZnSe nanocrystals synthesized by high energy ball milling have a wide crystals distribution (3–20 nm). Using the aqueous solutions of Na₃PO₄, (NaPO₃)₆ and Na₄P₂O₇ to disperse the 40 h-milled samples, we have observed the gradual blue-shift of the absorption edge along with the different centrifuging speed. In PL spectras, two main bands peaked at about 1.95 and 2.35 eV are observed, the former band is related to the V_Zn defects emission; and the latter is related to the V_Se defects emission. The V_Se defects emission does not depend on the dispersants, but the V_Zn defects emission changes in different dispersants.     

高能球磨法制备ZrB2-Al2O3复合粉体

以金属Al粉(w(Al)=99%,粒度≤45μm)、ZrO2粉(w(ZrO2)=99%,粒度≤3.5μm)和B2O3粉(w(B2O3)=98%,粒度≤5μm)为原料,按n(Al)∶n(ZrO2)∶n(B2O3)=10∶3∶3混合后装入高能球磨罐中,在氩气保护条件下以560r.min-1的转速球磨2h后,取样进行XRD和SEM分析。结果表明:采用金属Al粉、ZrO2和B2O3为原料,在2h的较短时间内经高能球磨合成ZrB2-Al2O3复合粉体,其合成机理为机械碰撞诱发的自蔓延反应;所得到的复合粉体中,ZrB2为微米级,Al2O3为纳米级。     

高能机械球磨法制备高质量纳米β-SiC粉体

使用高能机械球磨法,首次以单质硅和石墨的混合粉体为初始原料,制备出了高质量的β-SiC纳米粉体.对球磨产物进行了XRD和TEM等表征,结果表明:球磨10h后,石墨粉完全非晶化,大部分硅粉也已经非晶化,而且已经有β-SiC纳米粉生成;球磨20h后,硅粉和石墨粉完全反应生成了单相的β-SiC纳米粉,平均晶粒尺寸约为20nm,但是团聚比较明显;球磨40h后的样品,平均晶粒尺寸约为12nm,而且样品分散性较好,为均匀的球形颗粒;继续增加球磨时间,虽然样品晶粒尺寸稍有减小,但是团聚又逐渐变明显,而且样品中混入铁的量逐渐增加.     

Characterization and comparison of gray cast iron powder produced by target jet milling and high energy ball milling of machining scraps

Target jet milling and conventional ball milling were used to produce powders from gray cast iron scraps. Powders of similar size distribution produced by the two methods were pressed at different compacting pressures. Green compacts were made at the compacting pressures of 500, 600, 700 and 800 MPa. Jet milled powder showed good compaction behavior while ball milled powder showed very poor compressibility. Also, balanced compacts composed of 50% Hoganas SC100.26 iron powder and each of the cast iron powders produced in this work were made at 500 and 800 MPa and their green properties were determined. Results showed that, green properties of the jet milled powder were acceptable and superior compared to ball milled powder. The jet milling process proved to be a much more efficient process compared to ball milling in terms of time and production capacity.     

Dense zircon (ZrSiO4) ceramics by high energy ball milling and spark plasma sintering

The addition of sintering additives has always been detrimental to the mechanical properties of sintered ceramics; therefore, methods to reduce or, as in this case, eliminate sintering additives are usually relevant. In this paper, dense zircon ceramics were obtained starting from mechanically activated powder compacted by spark plasma sintering without employing sintering additives.The high energy ball milling (HEBM) of starting powder was effective to enhance the sintering kinetics. The structural changes of the zircon powder introduced by the HEBM were evaluated. The phase composition and the microstructure of bulk zircon material were analyzed by SEM (EDAX) and XRD. The Vickers hardness and the fracture toughness were evaluated as well.Fully dense materials were obtained at 1400 °C with a heating rate of 100 °C/min, 10 min soaking time and 100 MPa uniaxial pressure. The zircon samples sintered at temperatures above 1400 °C were dissociated in monoclinic zirconia and amorphous silica. The dissociation was detrimental for the mechanical properties. Unlike conventional sintering methods (hot pressing, pressureless sintering) SPS permitted to overcome the dissociation of the zircon material and to obtain additive free, fully dense zircon ceramic with outstanding mechanical properties.     

Crystal defects and phase transitions of nanocrystalline yttria-stabilised zirconia induced by high-energy ball milling

Yttria-stabilised zirconia (YSZ) is a promising electrolyte for SOFCs and gas sensors. In this study, the particle size of a co-precipitated 5 mol% yttria-stabilised zirconia (5 YSZ) powder was refined from 10.47 μm to 130 nm via high-energy ball milling to improve its sinterability and ionic conductivity. The ball milling process increased the specific surface area of the 5 YSZ powder from approximately 11 to 22 m² g^?1. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) results indicated that the 5 YSZ crystallites decomposed into irregular shapes with the evolution of point, linear, and planar defects. An increase in the milling duration increased the number of oxygen defects in the 5 YSZ powder, as revealed by the X-ray photoelectron spectroscopy results. The tetragonal-to-monoclinic phase transformation occurring in the powder was investigated by X-ray diffraction, Raman spectroscopy, HRTEM, and selected-area electron diffraction pattern analyses. The ball-milled powders could be easily densified, but the presence of too many crystal defects and the large fraction of the m-ZrO₂ phase were detrimental to the further densification of the 5 YSZ powders. In spite of the high sintering temperature (1500 °C) used in this study, the maximum relative density of 99.67% could be achieved for the powder ball-milled for 60 min at the rotor speed of 1500 rpm. Moreover, the ionic conductivity of 5 YSZ was improved significantly from 20.6 to 36.2 mS cm^?1 (850 °C) after the high-energy ball milling process.     

Effect of high energy ball milling on compressibility and sintering behavior of alumina nanoparticles

The effect of high-energy ball milling on the textural evolution of alumina nanopowders (compaction response, sinter-ability, grain growth and the degree of agglomeration) during post sintering process is studied. The applied pressure required for the breakage of the agglomerates (P_y) during milling was estimated and the key elements of compressibility (i.e. critical pressure (P_cr) and compressibility (b)) were calculated. Based on the results, the fracture point of the agglomerates decreased from 150 to 75 MPa with prolonged milling time from 3 to 60 min. Furthermore, the powders were formed by different shaping methods such as cold isostatic press (CIP) and uniaxial press (UP) to better illustrate the influence of green compact uniformity and powder deagglomeration on the densification behavior of nanopowders.     

Incorporation of Mg-Al hydrotalcite into a biodegradable Poly(ε-caprolactone) by high energy ball milling

The technique of high energy ball milling (HEBM) was used to prepare nanocomposites of poly(ε-caprolactone) (PCL) and an organically modified Mg-Al layered double hydroxide. The amount of inorganic material was varied from 0 to 6 wt%, and the samples were melted and quenched in ice-water after milling. The molecular weight of PCL decreased and its distribution increased as a consequence of milling. The structural analysis of the milled samples, conducted by X-ray diffraction and infrared absorption techniques, showed that the 12 hydroxydodecanoates organic modifier was still attached to the inorganic lamellae even if a partial delamination of the layered compounds occurred. The mechanical parameters (modulus, stress at yield point, strain at break point and stress at break values) derived from the stress-strain curves, improved in the composite samples containing up to 2.8 wt% of inorganic filler, with respect to the pure polymer, in spite of the molecular weight decrease. The thermodynamic diffusion coefficient of water vapor in composite samples was lower than in pure PCL, indicating an improvement of the barrier effect.     

Polymer–nanofiller prepared by high‐energy ball milling and high velocity cold compaction

High‐energy ball milling using comilling in a solid state by low‐temperature mechanical alloying to prepare nickel‐ferrite (NiFe₂O₄) nanopowders and ultrafine poly(methyl methacrylate) (PMMA), dispersing nanoparticles in a polymer matrix, and a uniaxial high‐velocity cold compaction process using a cylindrical, hardened steel die and a new technique with relaxation assists have been studied. The focus has been on the particle size distributions of the nanocomposite powder during the milling and on the surface morphology of the nanocomposite‐compacted materials after compaction with and without relaxation assists. Experimental results for different milling systems are presented showing the effects of milling time and material ratio. It was found that a longer mixing time give a higher degree of dispersion of the nanopowder on the PMMA particle surfaces. Furthermore, with increasing content of NiFe₂O₄ nanopowder, the reduction of the particle size was more effective. Different postcompacting profiles, i.e. different energy distributions between the upper and lower parts of the compacted powder bed, lead to different movements of the various particles and particle layers. Uniformity, homogeneity, and densification on the surfaces in the compacted powder are influenced by the postcompacting magnitude and direction. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by reducing the expansion of the compacted volume and by reducing the different opposite velocities, giving the compacted composite bed a more homogeneous opposite velocity during the decompacting stage and reducing the delay time between the successive pressure waves. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers     

Synthesis,structural and magnetic characterization of nanocrystalline CuFe2O4 as obtained by a combined method reactive milling,heat treatment and ball milling

Nanocrystalline copper ferrite has been synthesized using a combined method which involves reactive milling, heat treatment and mechanical milling. After 4 h of reactive milling a solid solution between the starting oxides (CuO and α-Fe₂O₃) and a spinel phase is obtained. Increasing the milling time leads to a decomposition of those phases. After a heat treatment of the 30 h milled sample a single spinel CuFe₂O₄ phase is obtained. By mechanical milling the crystallite size of the copper ferrite is reduced down to 9 nm after 1 h of milling. For the CuFe₂O₄ samples milled between 2 and 4 h a decomposition of this phase is remarked and α-Fe₂O₃ is formed during milling. The spontaneous magnetization of the spinel decreases with increasing the milling time as results of the partial redistribution of the cations in the spinel and of spin canted effect. The magnetization of the milled samples does not saturate due to the presence of very fine ferrite particles which are superparamagnetic.     

Effect of high energy ball milling on strengthening of Cu-ZrO2 nanocomposites

In this paper, copper matrix nanocomposites reinforced by 5 and 10?wt% ZrO₂ particles were produced by mechanical milling technique at different milling times. The produced nanocomposite powders were investigated by X-ray diffraction technique and transmission electron microscopy. The effect of high energy ball milling on the morphology, microstructure and microhardness of the produced composites has been investigated. After that cold compaction was applied to the prepared powders under a pressure of 700?MPa and sintered at 950?°C for 2?h in hydrogen atmosphere. The results showed that increasing milling time improves microhardness of the prepared nanocomposites. The microhardness of Cu-10%ZrO₂ after 20?h milling is 3.76 times larger than pure Cu. This improvement is attributed firstly to the presence of ZrO₂ nanoparticles in addition to the improvement coming from the grain refinement and crystallite size reduction occurred due to mechanical alloying. So, in spite of the crystallite size of Cu-10%ZrO₂ nanocomposite is reduced to 10.75?nm compared to 105.5?nm for pure Cu, the presence of ZrO₂ nanoparticles plays a major role on mechanical properties improvement.