Jet-milled Powder Research Articles

High-coercivity SmFe12-based anisotropic sintered magnets by Cu addition

We achieved a record-high coercivity of 1.40 T in a SmFe12-based ThMn12-type anisotropic sintered magnet. This magnet was prepared by sintering jet-milled powder made from strip-cast alloys with a nominal composition of Sm8Fe73.5Ti8V8Al2Cu0.5, using the conventional process for anisotropic sintered magnet production. Detailed microstructural investigations conducted using scanning electron microscopy and transmission electron microscopy revealed that the formation of Fe-lean intergranular phases (with < 20 at.% of Fe) surrounding the fine SmFe12 phase grains resulted in the high coercivity. Nanobeam electron diffraction patterns showed that these Fe-lean intergranular phases (IGPs) exhibiting excellent wettability in this magnet are mainly composed of two phases: a hexagonal close-packed Mg-type Sm-based phase and a primitive cubic CsCl-type SmCu-based phase, which co-exist in the same intergranular region. Such Fe-lean IGPs minimize the intergranular exchange coupling in the SmFe12 main phase, which contributes to the high coercivity, as revealed by magneto-optical Kerr effect microscopy. Overall, this study provides detailed microstructure-coercivity correlations and insights for the future development of high-performance SmFe12-based sintered magnets.

Applicability of defatted soybean flours to 3D food printer: Effect of milling methods on printability and quality of 3D-printed foods.

Several particle sizes of defatted soybean powders were prepared by using a hammer mill and a jet mill, and their suitability for three-dimensional (3D) food printers was investigated. The particle sizes of the powders depended on the milling method, with cumulative volumes of 50% ranging from 6.1 μm in the jet mill to 93.3 μm in the hammer mill. Rheological properties of the pastes prepared by adding water varied with particle size, and jet-milled powders exhibited lower storage modulus, loss modulus and complex viscosity. These differences in rheological properties affect the printing performance, and the fine powders obtained from jet mill tended to have higher 3D printability in appearance in the range of 70–74% paste water contents. The milling method was found to have a significant effect on texture, and fine powders by jet mill was able to produce 3D-printed foods with a smooth surface structure.

Correlation between milling-induced strain, microstructure, and magnetic properties in anisotropic SrFe12O19 powders

Strontium hexaferrite (SrFe12O19) powders synthesized via conventional solid-state route are mechanically milled using air jet-mill and ball-mill techniques to produce anisotropic SrFe12O19 powders. Jet-milled and dry ball-milled powders showed higher strain (0.13%) compared to wet ball-milled powders (0.05%). On annealing, jet-milled powder exhibited better recovery of strain compared to the ball-milled powders. Enhancement in coercivity after annealing is maximum in jet-milled samples (1.7 kOe to 5.2 kOe). Angle-dependent magnetic hysteresis measurements suggest a difference in the nature of strain induced in jet-mill and ball-mill methods. Maximum remanence (0.81) is observed in both jet-milled and dry ball-milled powders, however, jet-milled powders showed a better retention of remanence (0.74) after annealing than the ball-milled powders (0.64). A stark contrast in the microstructure of jet-milled and ball-milled powders is revealed from SEM images. Particle size distribution curves confirm a considerable re-agglomeration in the ball-milled samples. The role of milling-induced strain and microstructure in obtaining anisotropic SrFe12O19 powders with optimum remanence and coercivity is discussed.

Effect of hydrogenation-disproportionation-desorption-recombination powder processing on the demagnetization process of Nd-Fe-B sintered magnets analyzed by soft X-ray magnetic circular dichroism microscopy

The demagnetization process of a variety of Nd-Fe-B-based magnets produced using different manufacturing techniques are studied by soft X-ray magnetic circular dichroism microscopy. The four magnets studied include a hot deformed magnet, sintered magnets produced from either a N2 jet-milled or a He jet-milled fine powder, and a magnet produced by hydrogenation-disproportionation-desorption-recombination (HDDR) followed by He jet-milling. The coercivity of the HDDR processed magnet is lower than the magnets produced with N2 jet-milled powder even though the size of the grains is smaller. By following the magnetic domain reversal behavior during the demagnetization process, it was found that, while the magnets produced with N2 jet-milled powder and the hot deformed magnet presents a predominance of the reversed magnetic domain propagation, in the HDDR processed magnet the nucleation of individual grains occurs before the reversed magnetic domains propagate. This behavior is associated with a decreased nucleation field of each grain.

Origin of coercivity in an anisotropic Sm(Fe,Ti,V)12-based sintered magnet

We have demonstrated an anisotropic bulk SmFe12-based sintered magnet with sufficiently large coercivity of μ0Hc=1.0 T and a remanence ratio (Mr/Ms) of 0.84 using conventional liquid sintering process of nitrogen jet-milled powders with the nominal composition of Sm8Fe73.5Ti8V8Ga0.5Al2 (at.%). The moderate saturation magnetization of μ0Ms =0.74 T is due to the dissolution of a large amount of stabilizing elements, Ti, V, and Al, in the 1:12 phase. The anisotropy field of the main 1:12 phase was determined to be µ0HA=10.2 T. Detailed multi-scale microstructure characterizations by scanning electron microscope (SEM) and scanning transmission electron microscope (STEM) showed the magnet consists of Sm(Fe,Ti,V,Al)12 grains with the ThMn12-type crystal structure with a size distribution of ~3 − 15 µm that are enveloped by ~3 nm thick Sm-rich amorphous intergranular phase. Secondary phases including metallic (Sm,Ga)-rich, SmOx, and Fe2(Ti,V) phases coexist with the 1:12 phase. Measured angular dependence of coercivity follows Kondorsky type magnetization reversal, suggesting the coercivity arises due to the pining of magnetic domain walls. Magneto-optical Kerr effect (MOKE) microscopy revealed magnetization reversal starts at the grain boundaries and interphase interfaces and thin amorphous intergranular phases act as the pinning sites against magnetic domain wall propagation. Small micromagnetic parameter α~0.164 estimated by fitting to the Kronmüllar equation suggest that the reduction of the grain size and engineering of the intergranular phase to an Fe-lean composition are necessary to improve the coercivity toward µ0HA/3 = 3.4 T. This work provides guidelines on an optimum microstructure to develop an anisotropic bulk SmFe12-based sintered magnet with a sufficiently large coercivity.

Mechanism of anomalous α-Fe formation from stoichiometric Sm2Fe17 jet-milled powder during post-pulverization annealing

Our research group developed a novel low-oxygen powder metallurgy process and succeeded in producing anisotropic Sm2Fe17N3 sintered magnets from finely pulverized high-performance powder without coercivity degradation, but the maximum energy product of the magnets was disappointingly low compared to the excellent performance of the powder. The performance degradation was attributed to some type of surface damage, and more specifically, poor crystallinity and randomly oriented nanocrystalline grains at the particle surfaces caused by the milling process. In this study, the current authors focused on Sm2Fe17 fine pulverized powder instead of Sm2Fe17N3 and explored the possibility of damage recovery to remove those microstructural defects by post-milling annealing/nitridation treatments. This treatment improved crystallinity to some extent but failed to remove the randomized nanocrystalline grains completely. In addition, it was found that α-Fe forms upon annealing of stoichiometric Sm2Fe17, which is inconsistent with the Sm-Fe binary phase diagram at a glance. The mechanism of this unexpected α-Fe formation was investigated by detailed microstructural analyses using transmission electron microscopy and three dimensional atom probe tomography.

Influences of microstructure on macroscopic crystallinity and magnetic properties of Sm-Fe-N fine powder produced by jet-milling

A variety of high performance Sm-Fe-N fine powders (the highest (BH)max = 43.6 MGOe (347 kJ/m3)) were produced by jet-milling technique under very low oxygen atmosphere. The particle size distribution, the crystallinity and the microstructure of those jet-milled powders were systematically investigated. It was confirmed that the macroscopic crystallinity (estimated from XRD peaks) was significantly deteriorated with the decrease of particle size and found that this is attributed to the formation of nanocrystalline regions and dislocations introduced by jet-milling. Careful analyses however clarified that those nanocrystalline regions play a very undesirable role in dominating the degree of alignment of a batch of aligned powder and consequently lead to degradation of saturation magnetization and (BH)max.

Inhalable Hydroxychloroquine Powders for Potential Treatment of COVID-19.

Background: Hydroxychloroquine (HCQ) is one of the repurposed drugs proposed for the treatment of coronavirus disease 2019 (COVID-19). However, all the published clinical trials involve oral administration of the drug, although the disease is primarily a respiratory one. Direct inhaled delivery could reduce the side effects associated with oral use and ensure a high concentration of the drug in the lungs. In this study, inhalable HCQ powders were prepared and characterized for potential COVID-19 therapy. Methods: Hydroxychloroquine sulfate (HCQ-sul) was jet milled (JM) followed by conditioning by storage at different relative humidities (43%, 53%, 58%, and 75% RHs) for 7 days. The solid-state properties, including particle morphology and size distribution, crystallinity, and vapor moisture profiles of HCQ-sul samples, were characterized by scanning electron microscopy, laser diffraction, X-ray powder diffraction, differential scanning calorimetry, thermogravimetric analysis, and dynamic water vapor sorption. The aerosol performance of the HCQ-sul powders was assessed using a medium-high resistance Osmohaler coupling to a next-generation impactor (NGI) at a flow rate of 60 L/min. Results: The jet-milled powder showed a volume median diameter of 1.7 μm (span 1.5) and retained the same crystalline form as the raw HCQ-sul. A small amount of amorphous materials was present in the jet-milled HCQ-sul, which was convertible to the stable, crystalline state after conditioning at 53%, 58%, and 75% RH. The recovered fine particle fraction (FPF)recovered and the emitted fine particle fraction (FPFemitted) of the HCQ-sul sample immediately after jet milling and the samples after conditioning at 43%, 53%, and 58% RH were similar at ∼43% and 61%, respectively. In contrast, the sample having conditioned at 75%RH showed lower corresponding values at 33% and 26% respectively, due to the formation of solid bridges caused by excessive moisture. Conclusion: Inhalable crystalline powders of HCQ-sul were successfully prepared, which can be used for clinical testing as a potential inhaled COVID-19 treatment.

In situ XRPD study of the ambient-pressure synthesis of nonstoichiometric Ag3O from Ag–Ag2O thin films: Phase abundance, unit-cell parameters, and c/a as a function of temperature and time

Ag3O was synthesized by jet-milling magnetron-sputtered Ag–Ag2O thin films. Heating the jet-milled powders in air and N2 from 40 to 148 °C at ambient pressure produced Ag3O-rich powders. The phase composition and unit-cell parameters of the jet-milled powders were measured as a function of temperature with in situ X-ray powder diffraction experiments from −186 to 293 °C. Ag3O was also produced by ball milling and sonicating jet-milled films at ambient conditions. The phase composition, unit-cell parameters, and thermal-reaction rates indicate nonstoichiometric Ag3O was produced from the reaction of metastable, nonstoichiometric Ag2O (cuprite structure) and ccp Ag. The thermal expansion of Ag3O is anisotropic; below 25 °C, the a-axis expansion is about twice the c-axis expansion resulting in a negative slope of c/a(T). The reversal of the sign of c/a(T) near 25 °C is dramatic. The thermal reaction is arrested when the temperature is rapidly increased from ambient to 130 °C. Ag3O is metastable and decreases its unit-cell volume during kinetic decomposition to Ag when heated above ambient temperature in air and nitrogen. The relative volume expansion of Ag3O is about 80% less than Ag at room temperature and below. The suite of nonstoichiometric Ag3O produced by heating displays a linear relation between c/a and unit-cell volume at room temperature. The c/a and unit-cell volume of a hydrothermally grown Ag3O single crystal reported in a published structure determination was the Ag-rich, low-volume end member of the linear series. The c/a and unit-cell volume are sensitive indicators of the oxygen content and state of disorder.

Selective laser melting of CP-Ti to overcome the low cost and high performance trade-off

In this study, commercially pure titanium (CP-Ti) parts were successfully fabricated by selective laser melting (SLM) using cost-effective hydride-dehydride (HDH) Ti powders for the first time modified by jet milling. Jet milling effectively improves the particle-shape sphericity, suppresses the impurity pick-up, and produces localized plastic deformation. The flowability of the jet-milled powders is tremendously improved to 29.7 s/50 g that satisfies the SLM processing well, while the oxygen content only increases by 0.02 wt.% (the raw oxygen level: 0.15 wt.%). The oxide layer in the powder surface is determined with the thickness of ∼8 nm and TiO being the predominant phase before and after jet milling. The SLM-made (SLMed) CP-Ti achieves dominant martensitic α’ phase with the fracture tensile strength up to 731.5 ± 5.7 MPa and elongation of 20.5 ± 1.1%, comparable with those using expensive atomized powders. Contrary to the conventional metallurgical mechanism for Ti which suffers the cost-performance dilemma, this work presents SLMed CP-Ti with excellent synergy of strength and ductility while using the cost-affordable HDH Ti powders.

A spark-plasma-sintering approach to the manufacture of anisotropic Nd-Fe-B permanent magnets

Sintered Nd-Fe-B permanent magnets are the first choice for electro-mechanical devices that rely on hard-magnetic materials to provide strong magnetic fields in a variety of operating conditions. However, the limitations of conventional powder-metallurgy methods regarding the complexity of the magnet’s geometry restrict the design freedom for electrical motors. Here, we propose a spark-plasma-sintering (SPS) approach to the waste-free net-shape manufacture of anisotropic Nd-Fe-B magnets. We investigated the effect of the SPS parameters on the density, magnetic properties and microstructure of disc-shaped samples prepared from a rare-earth-lean jet-milled powder. The absence of a grain-boundary phase and the presence of α-Fe in the as-sintered samples were identified as the main factors hindering the development of the intrinsic coercivity. The observed microstructural features were correlated with electrical effects specific to the rapid, non-equilibrium SPS. A post-SPS thermal treatment was found to be necessary for achieving the hard-magnetic properties. Our findings pave the way towards developing an SPS-based sintering procedure with great potential for the manufacture of complex- and net-shape permanent magnets for high-performance electrical devices.

Anisotropic, single-crystalline SmFe12-based microparticles with high roundness fabricated by jet-milling

Bulk sintered SmFe11Ti-based magnets with high energy density have not been realized yet despite three decades of research efforts. In order to move a step forward in this direction, in this work we demonstrate a process for producing fine, anisotropic, single-crystalline SmFe11Ti-based particles with high roundness by using jet-milling. Particle size of 2.7 ± 0.6 μm is realized in the case of Sm(Fe0.8Co0.2)10.5Cu0.5Ti composition. XRD results show that the ThMn12 phase is preserved during milling, whereas peaks from the intergranular phases vanish indicating partial removal and amorphization as confirmed by TEM studies. Increased roundness can be achieved by optimizing feeding rate and grinding gas pressure, which is beneficial for local demagnetization field reduction according to micromagnetic simulations. Grain boundary infiltration experiments using low-melting alloys enable liquid-phase sintering at a temperature as low as 500 °C. The resultant bulk samples are anisotropic and show full density, although coercivity remains only 0.32 T. The possible reasons are linked to defects in the microstructure, where formation of slip bands lead to Sm vacancies and can lower the local magnetocrystalline anisotropy and the coercivity. It was found that the volume fraction of the defects can be reduced by low temperature annealing of the jet-milled powders.

Preparation and characterisation of mechanically milled particles from waste alpaca fibres

In this work, a chemical free green processing route was followed to fabricate alpaca powders from waste alpaca fibres. The waste fibres were converted into powders with the average particle size of 2.5 μm without using any chemicals neither in pre-treatment nor in powder fabrication process. Despite visible morphological changes of the powder samples, Nuclear Magnetic Resonance Spectroscopy (NMR) and Fourier Transform Infrared (FTIR) revealed no chemical change or shift in the functional groups. The crystallinity of the powdered samples decreased with the reduction of particle size in different stages of the milling process. The differential scanning calorimetry (DSC) and thermogravimetric (TGA) test results revealed that the thermal stability of the alpaca powder was almost similar to that of alpaca fibre. The air jet-milled powder showed an increase in moisture regain and moisture content by around 38% and 33% respectively than that of alpaca fibres. The results suggest that alpaca powders have a great potential to be introduced to a wide range of new applications.

Origin of the coercivity difference in Nd-Fe-B sintered magnets processed from hydrogenation-disproportionation-desorption- recombination powder and jet-milled powder

Microstructures of Ga-doped ultra-fine-grained (UFG) Nd-Fe-B magnets processed from press-less sintering of He-jet-milled powder and hydrogenation-disproportionation-desorption-recombination (HDDR) powder have been investigated to understand the large coercivity difference in the two magnets with nearly the same grain size. While the sintered magnet processed from the jet-milled powder showed a very high coercivity of 2.14 T, the sintered magnet made from HDDR powder showed a low coercivity of only 1.31 T regardless of the similar grain size. Microstructure observations by scanning electron microscopy (SEM) and scanning transmission electron microscope (STEM) combined with energy-dispersive X-ray (EDS) analysis revealed that the Nd-rich grain boundary (GB) phase in the magnet produced from HDDR powder exhibits thickness of 1–2 nm with large variations in their chemical compositions, while the Nd-rich GB phase in the magnet made from He-jet-milled powder displays larger thickness variations (1–7 nm) along with significant increase of nonferromagnetic elements (Nd, Pr, Cu, Ga) in the GB phase after optimal annealing. The possible reasons for these differences in GB phases are discussed based on quantitative microstructure characterization results.

Production of CuSn10 bronze powder from machining chips using jet milling

In this study, an experimental target plate jet mill was designed and used to produce CuSn10 bronze powder from its machining chips. Taguchi method with an L9 orthogonal array was used as experimental design to determine the optimum conditions for the pulverization of the machining chips via jet milling. The effect of process variables including nozzle to target distance, impact angle, and air pressure were investigated. The optimum conditions were found to be 8 cm for nozzle to target distance, a 90° angle between nozzle and target, and an air pressure of 7 bar. Repeated impact cycles lead to the production of finer and more rounded particles, although the rate of size reduction was reduced. The jet-milled powder did not contain any contamination, and the amount of the surface oxide of the jet-milled powder was even lower than that of the initial machining chips. Investigation of the fragmentation of particles revealed that the initial machining cracks were the main sites for breakage during pulverization. In addition, the delta phase in the microstructure of the bronze alloy plays an important role in the propagation of pre-existing cracks as well as creating new cracks.

Hollow crystalline straws of diclofenac for high-dose and carrier-free dry powder inhaler formulations

ObjectiveTo crystallize diclofenac (DF) from diclofenac sodium (DFNa), to micronize DF and DFNa, and to evaluate in vitro aerodynamic performance of the jet-milled formulations Materials and methodsFrom the acidic titration of aqueous DFNa, DF crystals were formed and were identified using thermal analysis, spectroscopy, and X-ray powder diffraction. Following the micronization of the DF and DFNa powders, the recovered samples were imaged, and their particle size distributions were evaluated. Samples before and after jet millings were characterized, and in vitro aerodynamic performance testing was performed on the DF sample before jet milling and the DF and DFNa samples following jet milling. Results and discussionHollow needles of DF were precipitated. With similar particle size distributions, the jet-milled DFNa sample from the collection bag, and the DF sample from the cyclone were used for further characterization. Despite different deposition patterns in the Next Generation Impactor, the DF hollow needles had a comparable respirable fraction percentage to the jet-milled DF and DFNa particles. However, the jet-milled DF formulation had the best in vitro aerodynamic performance. ConclusionsHollow, crystalline needles of DF were formed and possessed promising aerosol performance in comparison with the jet-milled powders.

Investigation of the Changes in Aerosolization Behavior Between the Jet-Milled and Spray-Dried Colistin Powders Through Surface Energy Characterization

This study aimed to investigate the surface energy factors behind improved aerosolization performance of spray-dried colistin powder formulations compared with those produced by jet milling. Inhalable colistin powder formulations were produced by jet milling or spray drying (with or without l-leucine). Scanning electron micrographs showed the jet-milled particles had irregularly angular shapes, whereas the spray-dried particles were more spherical. Significantly higher fine particle fractions were measured for the spray-dried (43.8%-49.6%) versus the jet-milled formulation (28.4%) from a Rotahaler at 60 L/min; albeit the size distribution of the jet-milled powder was smaller. Surprisingly, addition of l-leucine in the spray drying feed solution gave no significant improvement in fine particle fraction. As measured by inverse gas chromatography, spray-dried formulations had significantly (p < 0.001) lower dispersive, specific, and total surface energy values and more uniform surface energy distributions than the jet-milled powder. Interestingly, no significant difference was measured in the specific and total surface energy values between the spray-dried formulation with or without l-leucine. Based on our previous findings in the self-assembling behavior of colistin in aqueous solution and the surface energy data obtained here, we propose the self-assembly of colistin molecules during spray drying contributed significantly to the reduction of surface free energy and the superior aerosolization performance.

Enhancement of Coercivity of Nd-Fe-B Ultrafine Powders Comparable With Single-Domain Size by the Grain Boundary Diffusion Process

Nd-Fe-B sintered magnets are widely used in many applications. However, for the use in motors for hybrid electric vehicles (HEV), the development of Dy-free or Dy-lean Nd-Fe-B sintered magnets with high coercivity is desirable. Decreasing grain size of the Nd 2 Fe 14 B phase is an established method for increasing coercivity of Nd-Fe-B sintered magnets. We decreased the size of jet-milled powder to around 1 mm by helium (He) jet-milling in Dy-free Nd-Fe-B sintered magnets and obtained high coercivity (μ 0 H cJ ) of 2 T with (BH) max of around 400 kJm−3 [1]. We also succeeded further decrease in the size to 0.3 μm by combining hydrogenation-disproportionation-desorption-recombination (HDDR), hydrogen decrepitation (HD) and He jet-milling [2, 3]. However, the effect of annealing on magnetic properties of the ultrafine powders was not clear. On the other hand, the grain boundary diffusion (GBD) process [4-6] is well known as an effective method for the enhancement of coercivity. However, the effect for the ultrafine powders has not been investigated. Therefore, in this investigation, we investigated the effects of annealing and GBD process on coercivity of the Nd-Fe-B ultrafine jet-milled powders prepared by our developed process which combined HDDR, HD and He jet-milling.

Study on Ultrafine-Grained Sintered Nd–Fe–B Magnets Produced From Jet-Milled HDDR Powders

One effective approach for obtaining high coercivity in sintered Nd-Fe-B magnets is to refine the grain size.[1] Recently, Sagawa and Une have developed He jet milling and pressless sintering technology for producing fine-grained Nd-Fe-B magnets with high coercivity of 2 T.[2] However, it is hard to refine the grain size further because that the size of lamellar structure consisting of Nd 2 Fe 14 B in conventional strip casting (SC) Nd-Fe-B alloys is as wide as 3 μm, which limits the refinement during jet milling process. Thus precursor alloy with fine grain size surrounded by homogeneous Nd-rich phase is a promising option. Nd-Fe-B alloys with a homogeneous micsturcture and an average grain size of about 0.3 μm can be produced by Hydrogenation-disproportionation-desorption-recombination (HDDR) process.[3] Therefore, more attention has been paid to HDDR powders as precursor alloys for jet milling.[4]

Applicability of the one-step DVS method for the determination of amorphous amounts for further different hydrophilic and hydrophobic drugs

In a former publication the authors showed that low amounts of amorphous content (LOQ of 0.5%) in a hydrophobic model API (Ciclesonide) can be measured with an individually adjusted one-step dynamic organic vapor sorption (DVS). In this investigation the applicability is tested on various APIs which differ in lipophilicity (poor water solubility) and hygroscopicity (absorption of water).The vapor sorption method proved to be applicable in almost all cases. Moisture sorption isotherms were determined for all five investigated crystalline and amorphous APIs. However, it was necessary to select the parameters individually for each API. The used solvents (water, methanol, isopropanol and methylene chloride) and the humidity-levels (0.05 p/p0 until 0.5 p/p0) were chosen carefully because otherwise the amorphous amounts switch to their crystalline counterparts and are not detectable. The production of fully amorphous samples (absence of crystalline material measured by DSC, mDSC and XRPD) was optimized over several trials. As successfully methods proved ball-milling, freeze-drying, spray-drying and/or quench cooling. In the next step these fully amorphous amounts were blended with crystalline starting material to calibration curves (Turbula blender, influence of electrostatic charge to homogeneity) for the calculation of amorphous content.In summary, the following presented methods were used to determine and quantify low amorphous amounts (between 1.5% and 17.0%) in jet-milled powders (grinding pressure of 8bar, 1–3 grinding cycles), respectively.