Jet Mill Research Articles

Influence of the Operating Temperature on the Ultrafine Grinding in Superheated Steam Jet Mill

Effects of operating temperature on the fineness and yields of the ultrafine circulating fluid bed fly ashes (CFBAes) have been studied. Results show that the temperature of selection zone increased faster than that of crushing zone. Introduction of secondary air decreased the temperature of crushing zone, which would make the classifier invalid. Also, ambient temperature and insulation measures have a great impact on the ultrafine grinding in superheated steam jet mill

Preparation and surface properties of cashmere guard hair powders

Cashmere guard hair, a by-product from the cashmere dehairing industry is used for low value applications because the guard hairs are not suitable for spinning as they are coarse, contain large medullation and lack crimp or curvature. To find new uses in high value-added applications, cashmere guard hairs were milled into fine particles using the processing sequence Chopping→Attritor milling→Spray Drying→Air Jet milling. The guard hairs were partially hydrolysed with hydrochloric acid which increased the pulverisation rate due to the deterioration in mechanical properties. The volume median particle size d(0.5) was reduced from 2.328μm, for untreated cashmere guard hair powder to 0.461μm for powder from the acid hydrolysed guard hairs. FTIR and XPS studies revealed the breakdown of the cashmere guard hair cuticle cells and the exposure of the cortex on the powder surface along with the oxidation of the cashmere guard hair during milling.

The integration of carborundum powder comminution and surface modification in an air jet mill

Surface modification of carborundum (SiC) particles with a modifying agent, with simultaneous ultrafine comminution in an air jet mill, was studied in this work. The production rate of SiC and the viscosity of the SiC-paraffin oil suspension were used to evaluate the performance of comminution and modification. The experimental results indicated that the modifying agent bonded onto the surface of the SiC to form an organic layer in the integrated process of modification and comminution. The types and content of modifying agents and the temperature of the compressed air have a great effect on the performance of ultrafine modified SiC, and there are some contradictory aspects between modification and comminution in the integrated process. According to the targets of both surface modification and ultrafine comminution, the optimum temperature of compressed air and feed rate of the modifying agent solution was 60 °C and 2 ml/min respectively, when the modifying agent A-151 was adopted to obtain the modified ultrafine SiC in one step.

Fabrication of uranium oxycarbide kernels and compacts for HTR fuel

Fabrication of uranium oxycarbide kernels and compacts for HTR fuel

Fragments spawning and interaction models for DEM breakage simulation

Particles breakage occurs in many industrial applications. During the last decade many works have been devoted for modelling and simulating such processes. A new and innovative procedure of empirical comminution functions for Discrete Element Method (DEM) simulations (Kalman et al. in Granul Matter 11(4):253–266, 2009) posed the question how to introduce the fragments of the broken particle back into the computational domain. Daughter particles (Fragments) spawning and interaction imposes several problems during DEM simulation. Some of the main problems are: seeding (allocating) daughter particles and their initial conditions i.e. fragments locations, velocities and physical properties. This work focuses on the daughter particles seeding and the interaction between “sibling” particles for spherical particles. Fragments spawning and interaction algorithm for particle breakage during DEM simulation was developed. The algorithm enables prediction of particle comminution/attrition processes using DEM applications. The new algorithm can utilize any breakage function allowing unlimited fragment size fractions. In the proposed model, sibling particles can overlap without increasing the energy of the system in the simulation. Particle-particle and particle-wall interactions are calculated using the standard DEM calculations. Daughter particles interactions were calculated using the developed temporary contact radius model. The model was utilized to predict particle comminution in jet milling and particle attrition during pneumatic conveying with great successes.

Electrochemical Features of LiFePO4 Nanoparticles Obtained by Grinding Ingot Synthesized in the Molten State

LiFePO4 nano-particles have been prepared by grinding ingot synthesized in the molten state. Formatting 25-nanometer particles was obtained by subsequent jet and wet milling. These primary particles tend to segregate to form secondary particles of size ∼100 nm, for which surface effects become increasingly important. Study of the electrochemical properties of Li//LiFePO4 cells showed that the cell performance appeared to be strongly dependant of the synthetic route used. The best electrode material formed by wet milling followed by 2 wt.% carbon coating delivered discharge capacity of 157 mAh g-1 at C/10 rate without capacity fading after 60 cycles.

Effects of grinding processes on enzymatic degradation of wheat straw

The effectiveness of wheat straw fine to ultra-fine grindings at pilot scale was studied. The produced powders were characterised by their particle-size distribution (laser diffraction), crystallinity (WAXS) and enzymatic degradability (Trichoderma reesei enzymatic cocktail). A large range of wheat-straw powders was produced: from coarse (median particle size ∼800μm) to fine particles (∼50μm) using sieve-based grindings, then ultra-fine particles ∼20μm by jet milling and ∼10μm by ball milling. The wheat straw degradability was enhanced by the decrease of particle size until a limit: ∼100μm, up to 36% total carbohydrate and 40% glucose hydrolysis yields. Ball milling samples overcame this limit up to 46% total carbohydrate and 72% glucose yields as a consequence of cellulose crystallinity reduction (from 22% to 13%). Ball milling appeared to be an effective pretreatment with similar glucose yield and superior carbohydrate yield compared to steam explosion pretreatment.

Effects of milling and surfactants on suspensibility and spore viability in Paenibacillus polymyxa powder formulations

Two milling methods and five surfactants were tested for their effects on the suspensibility of a wettable powder formulation of Paenibacillus polymyxa HY96-2 (P. polymyxa original powder or PPOP). Both hammer milling and jet milling significantly improved suspensibility of PPOP (from 8.1 to 26.4% and 58.3%, respectively), and did not decrease spore viability. Five surfactants (EFW®, D-425®, sodium dodecyl benzene sulfonate, tea saponin and sodium lignosulphonate) were each mixed with jet milled powder (JMP). The best results were obtained with sodium lignosulphonate and D425. These gave equal improvement in suspensibility. Sodium lignosulphonate had the best biocompatibility; spore viability values of JMP mixed with this at 1, 3, 5, or 10% (w/w) were all over 95.0%. Addition of sodium lignosulphonate to hammer milled powder (HMP) or JMP at 5% (w/w) increased suspensibility from 26.4 to 38.6% and from 58.3 to 81.1%, respectively. Our results suggest that jet milling and sodium lignosulphonate can synergistically improve the suspensibility of P. polymyxa wettable powder without adverse effects on spore viability. These findings will accelerate the commercialization of P. polymyxa wettable powder and provide a basis for the development of other biopesticides.

Parameter effects on dry fine pulverization of alumina particles in a fluidized bed opposed jet mill

The paper presents the experimental results on dry fine pulverization of alumina particles in a fluidized bed opposed jet mill. The effect of operating parameters (i.e., feed load, inlet air pressure and the distance between nozzle outlet and jet meeting point) on the grinding results was investigated in detail. The breakage behaviors of alumina particles with respect to the effects of different parameters were discussed via the selection and breakage functions calculated by the first Kapur function method. In addition, the product size distributions could be simulated by a proposed model.

Effects of brief milling and acid treatment on two ordered and disordered kaolinite structures

The structural characteristics of well-ordered kaolinite (K1) and poorly ordered kaolinite (K2) after the ¼ h milling procedures, continuing acid activation with 2 M hydrochloric acid and intercalation ability with urea were assessed. Kaolinite samples were examined by X-ray powder diffraction, thermogravimetry, infrared spectroscopy analysis and specific surface area measurement. Kaolinite K1 contained a slightly higher portion of particles <2 μm (38 vol.%) than K2 (31 vol.%) increasing after jet milling (to 92 vol.% and 54 vol.%, respectively), but decreasing slightly after ball milling (to the 37 vol.% and 26 vol.%, respectively). The acid treatment contributed to a narrower particle size distribution, increased value of the surface area and dehydroxylation temperature and improved the structural order of poorly ordered kaolinites. Maximum surface area SSA = 45 m 2g − 1 was measured for K2 after ball milling and treatment with hydrochloric acid. Treatment of kaolinites with hydrochloric acid supports their ability to intercalate urea and exfoliate, while the mechanical millings adversely affected intercalation urea. The SSA 9.8 and 20.5 m 2g − 1 of K1 and K2, respectively, changed after: (1) exfoliation to 21.0 and 34.1 m 2g − 1 , respectively, (2) jet milling and exfoliation to 38.0 and 42.0 m 2g − 1 , respectively, (3) ball milling and exfoliation to 20.3 and 34.4 m 2g − 1 , respectively, and (4) ball milling, acid treatment and exfoliation to 40.3 and 46.7 m 2g − 1 , respectively.

Influence of crushing equipment on the elementary composition of coke

The influence of grinding equipment on the contamination of the initial material is investigated. In particular, coke of different structure is ground using a drum-type ball mill, a roller mill, and a jet mill. Conclusions are stated regarding the strength of coke as a function of the microstructure (point score) and the increase in impurity content as a function of the equipment employed. Recommendations for reducing the impurity content are made when grinding coke of different structure.

Synthesis of Ultrafine Long Afterglow Phosphor with High Brightness via Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Coating Route

Long afterglow phosphor is a special energy-saving material, which can store the energy of light irradiation and release light slowly. Ultrafine aluminate long afterglow phosphor is commonly prepared by the jet milling method. This method results in weak brightness, which restricts its application in delicate printing or textiles. In this study, fine particle aluminate phosphor (5μm) was coated by alumina, and then re-reduced under a high temperature. The alumina film works as a barrier layer, which protects the particles from sintering. The re-reduced phosphor had double afterglow brightness, and the size of the particle retained original level. The influences of pH value and KOH adding speed were investigated, the optimized parameters are: pH = 5, KOH adding speed = 2 ml/min.

Development of a spiral-flow jet mill with improved classification performance

Our group has proposed a jet mill equipped with a particle-trap ring at the exit of the comminution zone to prevent the escape of large particles entrained by shortcut flow. The visualized swirl flow compares favorably with simulation results obtained by CFD. Experimental results reveal that a trap ring with a height of 4mm is the most effective for attaining high classification performance. Yet the classification efficiencies measured at various ring heights are much lower than the classification efficiencies calculated by the CFD. This discrepancy may be attributable to the particle-flow interaction and the change in particle size during the particle movement.

Effect of Particle Size Distribution of Calcined Diatomites on the Extinction Performance

Calcined diatomite was first investigated as matting agent for formulating high-performance coating. Jet milling and sieving or sedimentation methods were employed to obtain rational particle size distributions. It was found that the optimal size distribution of the particles with the diameters of D10 = 2.54 µm, D25 = 5.04 µm, D50 = 9.74 µm, D75 = 18.80 µm, and D90 = 31.66 µm showed the best extinction performance, with the gloss and extinction being 2.9 and 3.3 and 32.6% and 50.7% determined at incidence angles of 60° and 85°, respectively.

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.

Effect of crystallisation conditions and feedstock morphology on the aerosolization performance of micronised salbutamol sulphate

Salbutamol sulphate (SS) used in dry powder inhalers requires drug particles in the respirable size range of 1–5 μm to achieve a suitable therapeutic effect. The aim of this study was therefore to determine strategies for controlling drug substance characteristics pre and post-crystallisation to facilitate the production of micronised SS with desirable particle attributes for optimal delivery as an inhaled aerosol. SS batches were crystallised using an antisolvent method to produce a range of crystal morphologies. Air jet milling was then used to reduce the size of crystallised SS particles. Starting materials and micronised batches of SS were characterised in the solid state using a range of techniques with subsequent assessment of aerosol properties. Assessment of the aerodynamic characteristics of micronised SS delivered by DPI (without any carrier) indicated that fine particle fraction and emitted dose as a percentage of the total recovered dose were dependent on the quality attributes of the micronised SS, which were directly linked to the degree of imperfections and the morphology of the crystalline feedstock used in micronisation. Aerosolization performance of micronised SS can be optimised by manipulation of feedstock characteristics through crystal engineering and through definition of optimal processing conditions for micronisation.

Preparation of Ultrafine White Cement and its Hydration

The ultrafine grinding of white cement and its hydration were studied. The ultrafine grinding parameters, such as crushing pressure and feeding pressure of jet mill in a lab scale were optimized. The influence of the particle size distribution of ultrafine white cement and the usage of water reducer on the standard thickness and early age strength of white cement paste was investigated. The results indicated that the ultrafine white cement with d50=4.62 µm and d90=10.48 µm can be obtained when the crushing pressure was 0.7 MPa and the feeding pressure was 0.4 MPa. The standard thickness of white cement paste decreased from 30.5 % of the raw material to 26.0% of the ultrafine white cement (d50=4.42 µm, d90=10.26 µm). The use of 2% naphthalene-based water reducer can reduce 15.4% water consumption. The 3d compressive strength of pure ultrafine white cement sample reached 174% of that of raw white cement. The 28d compressive strength of ultrafine white cement with 3% naphthalene-based water reducer added was 22.9% of that of pure ultrafine white cement. A large number of needle-shape nanometer ettringite (AFT) was generated in the early stage of hydratration and layered C-H-S was formed with the decreasing of the amount of AFT in the later stage of hydratration. It’s supposed that the formation of the large number of needle-shape nanometer AFT was related to the reducing of the particle size of C3A during the ultrafine grinding and the no adjustment of the amount of the added gypsum, which resulted in the faster hydration of C3A.

Microstructure of fine-grained Nd–Fe–B sintered magnets with high coercivity

The microstructure of high-coercivity Nd–Fe–B sintered magnets with a grain size of about 1 μm, which was processed by helium jet milling and the pressless sintering process, was studied by scanning electron microscopy, transmission electron microscopy and atom probe tomography. The high coercivity can be attributed to a similar microstructure that is five times smaller than that of conventional sintered magnets. Initial magnetization curves showed a two-step magnetization process, suggesting that the grain boundary phase causes a pinning force.

Effect of Grinding Methods on the Performance of Ground Fly Ash

In this study, coarse fly ash was ground with laboratory ball mill, vibration mill and jet mill respectively. The powder characteristic of ground fly ash was tested by laser particle size analyzer and scanning electron microscope. And the performance of cement containing different ground fly ash was also studied. It was observed that the characteristic value of fly ash ground by ball mill, vibration mill and jet mill was 13.543 μm, 13.403 μm and 17.344 μm, respectively, when average particle size was about 25μm. And the uniformity coefficient of fly ash ground by ball mill, vibration mill, and jet mill was 1.26, 1.24 and 1.38, respectively. Specially, the mortar strength was increased when 10 to 20 percent of ground fly ash was added. And the highest fluidity of mortar was obtained when 30 percent of fly ash ground by jet mill was added.

Preparation of Nanocomposite Resistive Material with Modified Silicon Nanoparticles Si-C60 in Tin Metal Matrix

The paper describes the preparation of the nanocomposite resistive material formed of solid dispersion of fullerene-modified silicon nanoparticles Si-C60 tightly embedded in the Sn metal matrix. Nanoparticles of semiconductive silicon were manufactured top-down in a cavitation high-energy liquid jet disintegrator—the Water Jet Mill. They were further modified with fullerene C60 molecules in water dispersion and freeze dried in vacuum. After dry vibration milling with < 100 nm nanoparticles of metallic tin the output powder was cold pressed into tablets. These were further subjected to the pressure of 2.5 GPa at the temperature of 250 � C for 30 minutes. The solid resistive material prepared in this way consists of very fine metallic tin structure in between the nanoparticles. We expect that this complex nanostructure will substantially strengthen the interactions of conductive electrons with the structure defects of metallic tin. Our goal is to investigate if it is possible to reinforce the temperature-independent structure component of the composite resistivity with respect to its temperature-dependent phonon-electron interaction component. The resistivity of the nanocomposite material was measured in the temperature range from −50 � C to 160 � C. At the interval of approximately 75 � C to 110 � C it exhibits relatively flat minimum, where the resistivity is almost