Microwave Permeability Change of FeCo Nanocrystalline During High Energy Ball Milling

The microwave magnetic properties of the ball milled FeCo panicles were investigated as functions of ball milling time （ t ） using microwave electromagnetic parameters analysis techniques. The results show that the imaginary part of intrinsic dynamic permeability （ ui ） of the ball- milled panicles is much bigger than that of raw powders. ui strongly depends on t and exhibits several slightly damped ferromagnetic resonances. These phenomena are in qualitative agreement with the formation of the corresponding microstructure or the Aharoni ＇ s model of non-uniform exchange resonance modes. The present microwave permeabilhy behavior indicates that nanocrystalline materials with the same grain size may exhibit different properties that depend upon the microstructure, which provides a possibility for manufacturing high performance microwave absorber.

NUMERICAL SIMULATION OF EXTRUSION OF COMPOSITE POWDERS PREPARED BY HIGH ENERGY MILLING

Based on the characteristic of high energy milling and the micromechanics of composite material, a plastic constitutive equation is implemented for milled composite powders. To check the equation, the extrusion of Ti/Al composite powders prepared by high energy milling was simulated. It was from the numerical analysis that the predicted extrusion pressure mounted up with milling time and extrusion ratio increasing, which was perfect agreement with experimental results.

Characteristics of Cr and Al Powders by High Energy Ball Milling

The variation of microstucture and phase structure of metal Cr and Al powders prepared by high energy mechanical milling was analyzed and investigated.The results show that with the continuous balling the average grain sizes of the brittle Cr powders are gradually decreased,and the diffraction peaks are widened and the peak values lower owing to the interrelation caused by both cold welding and breaking;the tough Al powders exhibit intense cold welding,and most of powders lead to adhesion to ball surface and pot wall,meanwhile,the Al powders subjected to intense deformation have led to many dislocation rings with non dislocation wind up found in the microstructure.

Preparation of MgTiO_3 Ceramics by High Energy Ball Milling

MgTiO3 precursor was mechanochemically synthesized by high-energy ball milling of MgO and TiO2 . The sinteting characteristic of the resulted MgTiO3 precursor was investigated. The experirneatal resalts indicate that particles of both MgO and TiO2 powders become smaller rapidly, and then the costalline structures of MgO and TiO2 change significantly. MgTiO3 was observed by XRD after 30 hours of ball milling. Strong diffraction peaks of MgTiO3 were observed after 50 hours of ball milling. HRTEM observation proves that dense MgTiO3 ceramics with a compact crystalline structure can be sintered from rnechanochemically activated MgTiO3 precursor, the volume density of the resulting ceramie is as high aa 95% of the theoretical density, the porosity and average pore diameter of the ceramic are measured as 4.95% and 50 nm respectively, and the transverse strength exceeded 500 MPa.

Evolution of structure and magnetic properties in PrCo_5 magnet for high energy ball milling in ethanol

High energy ball milling(HEBM) is employed to produce nano-sized grains and particles. In this paper, the structure and magnetic properties are investigated in PrCo5 alloy for HEBM in an ethanol milling medium. With the increase of milling time, the grain size reduces and the coercivity increases. For a milling time of less than 30 min, the hysteresis loop of the aligned sample is very different from that of the un-aligned sample and it does not show a large decrease in magnetization slope, indicating a relatively good alignment of easy axes in particles due to the fact that the texture is nearly well preserved. However, when the milling time is further prolonged, the textured structure deteriorates in the powders.Even though exchange coupling exists between grains within the particle, the magnetic properties are exchange-decoupled between particles and the dipolar interaction results in a negative value of δ m in the whole range of the magnetic field.

Structural Evolution of the Mn_(0.52)Sb_(0.48) Compound during High Energy Ball Milling

The structural transitions of the NiAs-type Mn0.52Sb0.48 magneto-ordered compound, ball milled to different periods, have been characterized by X-ray diffraction and DSC analysis. On the basis of lattice parameter results a structural evolution mode with three stages is proposed. In the first stage lattice parameters keep nearly unchanged with the refinement of grains and increase of lattice strain. In the second stage, microstrain shows a lowering tendency accompanying the successive decreases of grain size. The X-ray revealed internal strain is found to be strains inside the lattice, which can be relaxed with new grain formation. The change of Tc is shown to be affected by the dimension of c axis, however the overall magnetization is continuously decreased with milling, due to the disordering process occurred in milling. Correspondent disordering mechanisms have been tentatively postulated and discussed according to the changes of lattice para meters.

Overview of milling techniques for improving the solubility of poorly water-soluble drugs

Milling involves the application of mechanical energy to physically break down coarse particles to finer ones and is regarded as a“topedown”approach in the production of fine particles.Fine drug particulates are especially desired in formulations designed for parenteral,respiratory and transdermal use.Most drugs after crystallization may have to be comminuted and this physical transformation is required to various extents,often to enhance processability or solubility especially for drugs with limited aqueous solubility.The mechanisms by which milling enhances drug dissolution and solubility include alterations in the size,specific surface area and shape of the drug particles as well as millinginduced amorphization and/or structural disordering of the drug crystal(mechanochemical activation).Technology advancements in milling now enable the production of drug micro-and nano-particles on a commercial scale with relative ease.This review will provide a background on milling followed by the introduction of common milling techniques employed for the micronization and nanonization of drugs.Salient information contained in the cited examples are further extracted and summarized for ease of reference by researchers keen on employing these techniques for drug solubility and bioavailability enhancement.

Synthesis and Characterizations of Nanocrystalline WC-Co Composite Powders by a Unique Ball Milling Process

In order to explore the high efficiency of fabricating nanocrystalline WC-Co composite powders, this paper presented a unique high energy ball milling process with variable rotation rate and repeatious circulation, by which nanocrystalline WC-10Co-0.8VC-0.2Cr3C2 (wt pct) composite powders with mean grain size of 25 nm were prepared in 32 min, and the quantity of the powders for a batch was as much as 800 grams. The as-prepared powders were analyzed and characterized by chemical analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis (DTA). The results show that high energy ball milling with variable rotation rates and repeatious circulation could be used to produce nanocrystalline WC-Co powder composites with high efficiency. The compositions of the powders meet its specifications with low impurity content. The mean grain size decreases, lattice distortion and system energy increase with increasing the milling time. The morphology of nanocrystalline WC-Co particles displays dominantiy sphere shape and their particle sizes are all lower than 80 nm. The eutectic temperature of the nanocrystalline WC-10Co-0.8VC-0.2Cr3C2 composites is about 1280℃.

Spark plasma sintering of a high-energy ball milled Mg-10 wt% Al alloy

The influence of spark plasma sintering(SPS)temperature on microstructure,hardness and corrosion behavior of a high-energy ball milled Mg-10wt%Al alloy was investigated in this work.The holding time and sintering pressure for SPS were kept constant while varying the sintering temperature from 200 to 350℃.The grain size and microstructure were studied using X-ray diffraction analysis,scanning electron microscopy,energy dispersive X-ray spectroscopy,and Archimedes'based density measurement.Corrosion behavior was investigated using potentiodynamic polarization tests.The nanocrystalline regime(grain size<100nm)was maintained even after SPS up to 350℃.The density of the alloy increased with increasing the SPS temperature.Vickers'hardness and corrosion performance improved up to 300℃ followed by a decrease after SPS at 350℃.Possible reasons for densification,strengthening,and corrosion behavior have been discussed in the light of reduced porosity and microstructural changes.

Study on Nano-structured WC-Co Composite Powders Made by Mechanical Milling

Nano structured WC Co composite powders were prepared by high energy mechanical milling. The microstructure of as milled WC Co composite powders (including grain size, lattice strain, Co distribution and lattice defects) was investigated by X ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive X ray spectroscopy (EDS). Nano structured WC co vered and separated by cobalt thin layers with average grain size less than 10 nm was obtained by high energy mechanical milling. The morphology of WC grains is almost spherical. High energy mechanical milling could also bring about a large number of lattice defects in WC grains.

An Investigation on Hydrogen Storage Kinetics of the Nanocrystalline and Amorphous LaMg12-type Alloys Synthesized by Mechanical Milling

Nanocrystalline and amorphous LaMg_（12）-type LaMg_（11）Ni ＋ x wt% Ni（x = 100, 200） alloys were synthesized by mechanical milling. Effects of Ni content and milling time on the gaseous and electrochemical hydrogen storage kinetics of as-milled alloys were investigated systematically. The electrochemical hydrogen storage properties of the as-milled alloys were tested by an automatic galvanostatic system. And the gaseous hydrogen storage properties were investigated by Sievert apparatus and a differential scanning calorimeter（DSC） connected with a H_2 detector. Hydrogen desorption activation energy of alloy hydrides was estimated by using Arrhenius and Kissinger methods. It is found that the increase of Ni content significantly improves the gaseous and electrochemical hydrogen storage kinetic performances of as-milled alloys. Furthermore, as ball milling time changes, the maximum of both high rate discharge ability（HRD） and the gaseous hydriding rate of as-milled alloys can be obtained. But the hydrogen desorption kinetics of alloys always increases with the extending of milling time. Moreover, the improved gaseous hydrogen storage kinetics of alloys are ascribed to a decrease in the hydrogen desorption activation energy caused by increasing Ni content and milling time.

Study of Reactions Induced by Mechanical Milling in ZnO-α-Fe_2O_3 System

Spinel ferrite ZnFe 2O 4 powders were synthesized directly from ZnO and α Fe 2O 3 mixtures by high energy mechanical milling. X ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) were used to investigate the chemical reaction processing at different milling time. It has been found that the solid reactions between metal oxides are characterized by stages. Once the solid chemical synthesized reaction is initialized, it proceeds quickly and can be completed in very short time. Grain sizes of ZnFe 2O 4 are less than 10 nm.

Energy field-assisted high-speed dry milling green machining technology for difficult-to-machine metal materials

Energy field-assisted machining technology has the potential to overcome the limitations of machining difficult-to-machine metal materials,such as poor machinability,low cutting efficiency,and high energy consumption.High-speed dry milling has emerged as a typical green processing technology due to its high processing efficiency and avoidance of cutting fluids.However,the lack of necessary cooling and lubrication in high-speed dry milling makes it difficult to meet the continuous milling requirements for difficult-to-machine metal materials.The introduction of advanced energy-field-assisted green processing technology can improve the machinability of such metallic materials and achieve efficient precision manufacturing,making it a focus of academic and industrial research.In this review,the characteristics and limitations of high-speed dry milling of difficult-to-machine metal materials,including titanium alloys,nickel-based alloys,and high-strength steel,are systematically explored.The laser energy field,ultrasonic energy field,and cryogenic minimum quantity lubrication energy fields are introduced.By analyzing the effects of changing the energy field and cutting parameters on tool wear,chip morphology,cutting force,temperature,and surface quality of the workpiece during milling,the superiority of energy-field-assisted milling of difficult-to-machine metal materials is demonstrated.Finally,the shortcomings and technical challenges of energy-field-assisted milling are summarized in detail,providing feasible ideas for realizing multi-energy field collaborative green machining of difficult-to-machine metal materials in the future.

Induced dipole dominant giant electrorheological fluid

Traditional dielectric electrorheological fluid(ER)is based on the interaction of dielectric particle polarization,and the yield stress is low,which cannot meet the application requirements.The giant ER(GER)effect is caused by orientations and interactions of polar molecules adsorbed on the particle surfaces.Despite the high yield stress,these polar molecules are prone to wear and fall off,resulting in a continuous reduction in shear stress of GER liquid,which is also not suitable for application.Here we introduce a new type of ER fluid called induced dipole dominant ER fluid(ID-ER),of which the particles contain oxygen vacancies or conductor microclusters both prepared by high energy ball milling(HEBM)technique.In the electric field E,oxygen vacancies or conductor microclusters form induced dipoles.Because the local electric field E_(loc) in the gaps between particles can be two to three orders of magnitude larger than E,the induced dipole moments must be large.The strong interactions of these induced dipoles make the yield stress of the ID-ER fluid reaching more than 100 kPa.Since there are oxygen vacancies or conductor microclusters everywhere in the particles,the particles will not lose the function due to surface wear during use.The experimental results show that the ID-ER fluid possesses the advantages of high shear stress,low current density,short response time,good temperature stability,long service life,and anti-settlement,etc.The comprehensive performance is much better than the existing ER materials,and also the preparation method is simple and easy to repeat,thus it should be a new generation of ER fluid suitable for practical applications.

Effects of Doped Elements on Electrochemical Performance of Ni(OH)_2 Materials

High energy ball milling （HEBM） method was applied to synthesize Ni （OH）2 with different doped elements sub-stitution for Ni^2＋. The morphology, structure and electrochemical behavior of prepared powders were studied. The re-suits reveal that all the synthesized Ni（OH）2 particles were in sub-micron sizes and greatly agglomerated. Co-, Mg-,Fe- or Mn-doped Ni （OH） 2 was of β-phase with 0.400-0.500 nm crystal interlayer distance, while A1- and Zn-doped products displayed a-phase with larger crystal interlayer spaces. The electrochemical mechanisms of synthe-sized Ni（OH）2 electrodes were discussed by EIS spectra. The specific capacity of Co-doped Ni （OH）2 is 245 mA·h · g^-1, i. e. , 60 mA· h · g^-1 higher than that of Al-doped electrode, which has the highest discharging plat-form of a mid-voltage of 1.30 V.

Tuning the reactivity of Al-Ni by fine coating of halogen-containing energetic composites

In this paper,various core-shell structured Al—Ni@ECs composites have been prepared by a spray-drying technique.The involved ECs refer to the energetic composites(ECs)of ammonium perchlorate/nitrocellulose(AP/NC,NA)and polyvinylidene fluoride/hexanitrohexaazaisowurtzitane(PVDF/CL-20,PC).Two Al—Ni mixtures were prepared at atomic ratios of 1:1 and 1:3 and named as Al/Ni and Al/3Ni,respectively.The thermal reactivity and combustion behaviors of Al—Ni@ECs composites have been comprehensively investigated.Results showed that the reactivity and combustion performance of Al—Ni could be enhanced by introducing both NA and PC energetic composites.Among which the Al/Ni@NA composite exhibited higher reactivity and improved combustion performance.The measured flame propagation rate(v=20.6 mm/s),average combustion wave temperature(T_(max)=1567.0°C)and maximum temperature rise rate(γ_(t)=1633.6°C/s)of Al/Ni@NA are higher than that of the Al/Ni(v=15.8 mm/s,T_(max)=858.0°C,andγ_(t)=143.5°C/s).The enhancement in combustion properties could be due to presence of the acidic gaseous products from ECs,which could etch the Al_(2)O_(3)shell on the surface of Al particles,and make the inner active Al to be easier transported,so that an intimate and faster intermetallic reaction between Al and Ni would be realized.Furthermore,the morphologies and chemical compositions of the condensed combustion products(CCPs)of Al—Ni@ECs composites were found to be different depending on the types of ECs.The compositions of CCPs are dominated with the Al—Ni intermetallics,combining with a trace amount of Al_(5)O_(6)N and Al_(2)O_(3).

Synthesis of Ultrafine Mesoporous Tungsten Carbide by High-energy Ball Milling and Its Electrocatalytic Activity for Methanol Oxidation

Ultrafine mesoporous tungsten carbide （WC） was prepared from as-synthesized mesoporous WC using high-energy ball milling treatment. X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and nitrogen adsorption-desorption techniques were used to characterize the samples. Brunauer-Emmett-Teller （BET） surface areas of WC samples increased with the increasing ball milling time and kept constant at 10-11 mZog 1 for over 9 h. The electrocatalytic properties of methanol electro-oxidation at WC powder microelectrodes were investigated by cyclic voltammetry, chronoamperometry, and quasi-steady-state polarization techniques. The results reveal that ball-milled WC exhibits higher activity for methanol electro-oxidation than as-synthesized mesoporous WC. The suitability of ball-milled WC for methanol electro-oxidation is better than platinum （Pt） micro-disk, although the current peak is not as high as the Pt micro-disk. Moreover, increasing the methanol concentration and reaction temperature promotes methanol electro-oxidation on ultrafine mesoporous WC.

Microwave Absorbing Performance of RE-Fe Based Alloys

REI3Fes4Cr3（RE=Ce, Pr, Tb, Er） and Pr13_XFes4Cr3Ti（x=0, 2, 4, 6） alloy powders were prepared by are smelting method and high energy ball milling technique. The phase structure and the morphology of the alloy powders were investigated by X-ray diffraction （XRD） and scanning electron microscopy （SEM）, and their microwave absorbing properties were determined by a vector network analyzer. The results show that the alloys with light rare earths （Ce, Pr） have good low frequency absorbing property and those with heavy rare earths （Tb, Er） exhibit an improved high frequency absorbing property. The minimum refleetivity at the absorbing peak frequency of RE,FeuCr3（RE=Ce, Pr, Tb, Er） are -9.49 dB at 5.76 GHz, -22.38 dB at 7.92 GHz, -18.52 dB at 11.68 GHz and -17.59 dB at 10.24 GHz, respectively. The absorbing bandwidth under -10 dB of the Pr13FesaCr3 powder was widened from 1.91 GI-Iz to 3.89 GHz by adding 2% Ti, but the reflectivity of the alloy was increased from -22.38 dB to -14.91 riB.

EXPERIMENTAL RESEARCH ON CrAl MIXED POWDERS BY MECHANICAL ALLOYING

Thechangesof microstructure, phase? structureand microhardnessof Cr Al mixed powders in the processof mechanical? alloying ( MA) have? beeninvestigated by X ray diffractionanalysis , SEM examination and microstructure testing. The results show that the mi crostructure of Cr Al mixed powderssubjected? to mechanicalalloying for96 hoursexhibits super saturated solid solution of Cr andintermetalliccompound η AlCr2 .

XRD and HRTEM Analyses of the Ball Milled Nanocrystalline FeCo Alloy

The nanostractures of the ball milled FeCo particles were characterized as functions of the ball milling time （ t ） using quantitative X- ray diffraction （ XRD ）, high resolution transmission electron microscopy （HRTEM） analysis techniques. The results show that the nanocrystalliue bcc FeCo particles are available using carbonyl iron and cobalt powders as the start materials during the high-energy ball milling. At the early stage of ball milling, Co powders are easily mashed into nanocrystalllites, by which the surface of the larger Fe particles of about 80- 150 nm is coated. With t increasing, the refinement of grain size and the incorporation of defects including dislocations, disclinations and grain boundaries happen, and then FeCo alloy with a certain layered structure is formed, finally the layered stractare disappears with the formation of isotropic grains having a steadystate grain size in the nanometer regime after a certain period of t.