Milling Intensity Research Articles

Economic Evaluation of Thermal and Mechanical Activation Energies in Gypsum Production

Plaster is among the most needed raw materials in the world. In this study, thermal activation provided by calcination and mechanical activation methods provided by intensive milling in the plaster production process were evaluated in terms of activation energy. In this context, the energies of laboratory-scale thermal and mechanical activation processes were calculated and these activation methods were evaluated economically and the ideal activation methods were determined. Although the mechanical activation method creates additional investment and operating costs, it reduces the calcination temperature by 13 °C, thus provides lower energy costs. Addition of a mechanical activator mill before thermal activation in plaster production as a more economical and more environmentally friendly method was proposed.

Processing of reactive Ni−Al powders via the LabRAM**

AbstractReactive Ni−Al materials have been developed using a variety of methods, with high energy ball milling (HEBM) being one of the most common means for tailoring reaction behavior. Powder production limitations associated with HEBM, including the addition of process control agents, have inspired the exploration of an alternate manufacturing technique: acoustic dry milling with the Resodyn Laboratory Resonant Acoustic Mixer (LabRAM). The influence of acoustic milling time, intensity, and media size with respect to microstructure and reactive behavior of Ni−Al powders were evaluated in this work. After just 20 min of milling, a reactive composite Ni−Al microstructure was produced. Milling intensity and media size were directly proportional to the formation of more homogeneous composite powders. The reaction onset temperature was decreased to 446 °C, or ≈200 °C lower than that of unprocessed material. The method shows promise for the production of reactive powder for a host of applications.

Novel Enhancement Opportunities in the Thermal and Electrical Conductivity of α-Al-CNTs+AgNPs Nanocomposites

In this study, effort was made to develop novel, cutting-edge composite materials consisting of conducting Al-CNTs and green synthesis silver nanoparticles (AgNPs). Spark plasma sintering (SPS) and very intense ball milling were used to develop the composites. The nanocomposites' microstructure, thermal and electrical conductivity were determined. Al-4%CNTs was refined into finer grains when AgNPs are present. The Al-4%CNTs+2%Ag.NPs composite produces a higher dislocation density because of the production of sub-grain. Al-AgNPs + CNTs can be used to make conductors with a high aspect ratio and lower contact resistance at the CNT junctions. It was established that enhanced electrical and thermal conductivity can be obtained using the developed AgNPs from sustainable materials to increase the dispersion of CNTs in Al for the production of high tensile conductors.

Formation, Stability, and Crystallinity of Various Tricalcium Aluminate Polymorphs.

Tricalcium aluminate is an important phase of Portland clinker. In this paper, three polymorphs of C3A were prepared by means of the solid-state synthesis method using intensive milling of the raw material mixture which was doped with various amounts of Na2O and sintered at a temperature of 1300 °C for 2 h. The final products were evaluated through X-ray diffraction using Rietveld analysis. The effect of the Na dopant content on the change in the crystalline structure of tricalcium aluminate was studied. It was proven that the given preparation procedure, which differed from other studies, was close to the real conditions of the formation of Portland clinker, and it was possible to prepare a mixture of different polymorphs of calcium aluminate. Fundamental changes in the crystal structure occurred in the range of 3-4% Na, when the cubic structure changes to orthorhombic. At a dosage of Na dopant above 4%, the orthorhombic structure changes to a monoclinic structure. There are no clearly defined boundaries for the existence of individual C3A phases; these phases arise at the same time and overlap each other in the areas of their formation at different Na doses.

An assessment of methods used for the generation and characterization of cryomilled polystyrene micro- and nanoplastic particles

There is a critical need to generate environmentally relevant microplastics (MPs) and nanoplastics (NPs) to better investigate their behavior in laboratory settings. Environmental MPs are heterogenous in size and shape, unlike monodisperse and uniform microspheres commonly used as surrogates. Cryogenic grinding, or cryomilling, was successfully utilized to transform polystyrene (PS) bulk material into heterogenous micro and nano fragments. Fourier-Transform Infrared (FTIR) spectroscopy confirmed that this approach did not alter polymer surface chemistry. The number of milling cycles (time of milling) and frequency of grinding (intensity of milling) were varied to investigate the role cryomilling parameters had on generated MP characteristics. The resulting particle size distributions of cryomilled samples were measured and compared. Coulter Counter and Nanoparticle Tracking Analysis (NTA) were used to measure the particle size distributions at the micro and nanoparticle size ranges, respectively. Microspheres were used to determine what camera settings yielded more accurate sizing and to reduce bias in the NTA analysis. Increasing milling cycles generally increased the number of smaller particles. The evolution of the measured size distributions indicated that small nanosized fragments broke off from larger MPs during cryomilling, steadily eroding larger MP fragments. The number of milling cycles was observed to more consistently impact the size distributions of fragments compared to the frequency of milling. This study offers both analysis of the cryomilling process and recommendations for generating more realistic PS MP/NPs for examining environmental fate and effects.

Tailoring the composition and microstructure of W-based coatings on metallic sheets by varying the type and combination of milling balls

W-based alloyed coatings with variable W content (90, 80, 75, and 55 wt%) were fabricated on Ti and steel substrates using a mechanically vibrated vial with different combinations of W milling balls. The resulting W-based coatings displayed heterogeneous nanocomposite structures; the composition and microstructures of which could be tailored through the selection of milling balls. The average size of the W grains ranged from 6 to 10 nm and increased with decreasing W content. The 90, 80, and 75 wt% W coatings exhibited amorphous matrix interphases; the 75 W coating also displayed amorphous and crystalline multicomponent oxide dispersions. The formation of these structures was governed by the intensity of milling and was driven by plastic deformation, deformation-induced intermixing, alloying, and atomic interactions. The 90 W coating exhibited the highest hardness value of 1200 HV, which decreased with an increasing fraction of the matrix phase. The W coatings greatly enhanced the wear resistance of the substrate surface with the wear rate value being seven times lower than that of an uncoated Ti surface. These results demonstrate the efficacy of using W milling balls to fabricate W-based coatings on various metallic substrates and the potential for tailoring their properties to specific applications.

Comparative Study on the Stiffness of Poly(lactic acid) Reinforced with Untreated and Bleached Hemp Fibers.

Composite materials containing natural reinforcement fibers, generally called biocomposites, have attracted the interest of both researchers and manufacturers, but the most environmentally advantageous combinations include a bio-based matrix, as well. With this in mind, a poly(lactic acid) (PLA) matrix was reinforced with natural fibers from hemp, both untreated strands (UHSs) and soda-bleached fibers (SBHFs). The preparation of the subsequent fully bio-sourced, discontinuously reinforced composites involved kinetic mixing, intensive single-screw extrusion, milling, and injection molding. Up to a fiber content of 30 wt%, the tensile modulus increased linearly with the volume fraction of the dispersed phase. Differences between SBHFs (up to 7.6 Gpa) and UHSs (up to 6.9 Gpa) were hardly significant (p = 0.1), but SBHF-reinforced composites displayed higher strain at failure. In any case, for the same fiber load (30 wt%), the Young's modulus of PLA/hemp biocomposites was greater than that of glass fiber (GF)-reinforced polypropylene (5.7 GPa), albeit lower than that of PLA/GF (9.8 GPa). Considering all the measurements, the contribution of each phase was analyzed by applying the Hirsch model and the Tsai-Pagano model. As a concluding remark, although the intrinsic tensile modulus of SBHFs was lower than that of GF, the efficiency of those natural fibers as reinforcement (according to the rule of mixtures) was found to be higher.

Potassium chloride recovery from mechanically activated microcline through the chlorination roasting and leaching route

In this study, effects of mechanical activation in the chlorination roasting and water leaching route known as CaCl2 process and developed for the production of potassium chloride (KCl) from potassium feldspar ores were studied. A microcline containing K-feldspar ore with 10.89% K2O was first intensively dry milled by a planetary ball mill and mixed with calcium chloride (CaCl2) and then roasted at temperatures up to 1000 °C to obtain KCl that will be finally dissolved by the water leaching. Potassium recovery by water leaching increased rapidly up to 800 °C. At higher temperatures, the recovery decreased fast due to the evaporation of KCl. According to the K recovery values per unit energy consumed, the optimum roasting temperature was determined as 750 °C and the milling time was 15 min. It was concluded that intensive milling causes mechanical activation of the microcline to reduce the chlorination roasting temperature, which triggers a rise in the K recovery by the water leaching.

Bagasse Electricity Potential of Conventional Sugarcane Factories

Sugar industries have huge potential to contribute to the sustainable energy transition through electricity generation and production of biofuels. Sugar-producing countries generate huge volumes of sugarcane bagasse as a byproduct of sugarcane production. In this study, the performance of an operating traditional sugar factory is analyzed for electricity generation and export potential. The study presents characteristics and energy potential of modern and traditional sugar factories. The challenges facing a traditional sugar mill are inefficient boilers, less efficient and back pressure steam turbines, and wasteful and inefficient use of steam turbine drives as prime movers instead of modern electric drives for the mills and cane knives. Others are the use of inefficient and energy intensive cane mill rollers instead of the diffusers which have low energy requirements. It was demonstrated that the cogeneration potential of sugar factory is quite significant but currently underutilized. Sugar factories can make significant contribution towards mitigation of greenhouse gas emission mitigation through supply of green electricity to the public grid. The study showed that the factory uses very old and inefficient boilers aged over 39 years which contributes to poor performance and low electricity generation capacity. Modernization is required to increase the generation and electricity export capacity through investment in new and modern high-pressure boilers, replacement of inefficient back pressure boilers (BPSB) with more efficient condensing extraction turbines (CEST), and reduction of factory steam consumption by electrification of mills and cane knife turbine drives among other measures. This study showed that the 3,000 TCD factory can invest in a 15 MW power plant based on current average factory performance indicators and more if the throughput and overall performance is close to design parameters.

Effect of milling intensity on the properties of chitin, chitosan and chitosan films obtained from grasshopper

To obtain high-quality insect products, milling was used as a modification tool and its effect on grasshopper chitin, chitosan and chitosan films was investigated. Three grasshopper powders were obtained and classified into coarse-milled powder (CMP, D90 = 956 μm), medium-milled powder (MMP, D90 = 492 μm), and ultrafine-milled powder (UMP, D90 = 79.1 μm). Fourier transform infrared spectroscopy illustrated that no drastic change due to milling was observed, but the crystallinity (X-ray diffraction) and thermal stability (Thermogravimetric analysis) of the chitin, chitosan and chitosan films reduced with increasing milling intensity. Besides, the purity of the chitin and the yield of chitosan obtained from UMP were improved. Chitosan prepared from UMP was also characterized by high degree of deacetylation (65.6 %) and solubility and rather low molecular weight (11.5 kDa), viscosity and water/fat binding capacity. The finer the powder used as the extraction material, the thinner the chitosan films and the more compact the structure. On the whole, the chitosan films prepared from the MMP had higher mechanical properties and better moisture-keeping ability on strawberries compared with CMP and UMP films. This study establishes the role milling intensity played in the modification of grasshopper products and provides a reference for practical applications.

Milling-Assisted Loading of Drugs into Mesoporous Silica Carriers: A Green and Simple Method for Obtaining Tunable Customized Drug Delivery

Mesoporous silica (MPS) carriers are considered as a promising strategy to increase the solubility of poorly soluble drugs and to stabilize the amorphous drug delivery system. The development by the authors of a solvent-free method (milling-assisted loading, MAL) made it possible to manipulate the physical state of the drug within the pores. The present study focuses on the effects of the milling intensity and the pore architecture (chemical surface) on the physical state of the confined drug and its release profile. Ibuprofen (IBP) and SBA-15 were used as the model drug and the MPS carrier, respectively. It was found that decreasing the milling intensity promotes nanocrystallization of confined IBP. Scanning electron microscopy and low-frequency Raman spectroscopy investigations converged into a bimodal description of the size distribution of particles, by decreasing the milling intensity. The chemical modification of the pore surface with 3-aminopropyltriethoxisylane also significantly promoted nanocrystallization, regardless of the milling intensity. Combined analyses of drug release profiles obtained on composites prepared from unmodified and modified SBA-15 with various milling intensities showed that the particle size of composites has the greatest influence on the drug release profile. Tuning drug concentration, milling intensity, and chemical surface make it possible to easily customize drug delivery.

Enhancing the ignitability of the Al–TiO2–B2O3 powder mixture through intensive vibratory ball milling (C:P12)

Alumina-TiB2 is a hard ceramic composite with applications in aviation, aerospace and wear resistant tools. It can be manufactured in-situ through a highly exothermic aluminothermic self-sustaining reaction from the starting materials of Al, TiO2 and B2O3. In this paper, the effect of vibration ball milling on the particle size reduction and the reactivity enhancement of the Al–TiO2–B2O3 powder mixture is examined by XRD, SEM, EDS, DTA and particle analysis techniques. Measures for combating the stoichiometric inconsistencies deriving from the tendency of B2O3 to absorb atmospheric water, giving boric acid H3BO3, are implemented. Characterisation of the milled samples display Al microparticles with d(0.9) below 64 μm, coated with nano-particles of TiO2 and B2O3, with particle sizes up to 600 nm. Differential thermal analysis reveals that ignition is feasible for all of the milled mixtures, unlike the un-milled one. It also presents that extensive milling results in a reduction in the ignition temperature of the reactant mixture to 925 °C for the 5 h-30Hz milled sample, from the previous 982 °C recorded for the 1 h–20Hz milled sample. The in-situ synthesised Al2O3–TiB2 matrix deriving from the 5 h-30Hz milled sample, gives less of the unwanted Al5BO9 phase and improved skeletal and bulk densities, by 0.15 g/cc and 0.1 g/cc respectively, compared to the respective composite deriving from un-milled reactants powder mixture.

Elaborating the crystal transformation referenced microhydrodynamic model and fracture mechanism combined molecular modelling of irbesartan nanosuspensions formation in wet media milling

In recent years, polymorphic transformation involved in media milling has become a key factor in inducing the instability of nanosuspensions (NSs). The variation trend of microhydrodynamic parameters, including milling intensity factor (F), can be observed under different milling conditions. Therefore, this study first referenced the microhydrodynamic model to explore how formulations and process parameters affect Irbesartan (IRB) form A crystallinity during wet media milling. As a result, the crystallinity of form A was affected by the intermolecular interactions between drug particles and stabilizers. The crystallinity of form A decreased with decreasing drug loading, increasing stirrer speed and bead loading, which depended on the role of F. Milling could promote the transformation from a 1H to 2H tetrazole ring with stabilizers containing –OH, and form B was changed to form A and finally to an amorphous state. Molecular modelling shows that forms A and B are ductile and fragile materials, respectively, and both present anisotropy. When milling beads hit both polymorphs paralleling to the (010) surface, the bead-bead collisions are more helpful in fracturing IRB particles. The results of this study may provide a foundation for controlling crystal transformation and obtaining ideal crystal forms.

Parboiled Germinated Brown Rice Improves Cardiac Structure and Gene Expression in Hypertensive Rats.

Hypertension leads to oxidative stress, inflammation, and fibrosis. The suppression of these indicators may be one treatment approach. Parboiled germinated brown rice (PGBR), obtained by steaming germinated Jasmine rice, reduces oxidative stress and inflammation in vivo. PGBR contains more bioactive compounds than brown rice (BR) and white rice (WR). Anti-hypertensive benefits of PGBR have been predicted, but research is lacking. The anti-hypertensive effects of PGBR were investigated in the downstream gene network of hypertension pathogenesis, including the renin-angiotensin system, fibrosis, oxidative stress production, and antioxidant enzymes in N-nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats. To strengthen our findings, the cardiac structure was also studied. PGBR-exposed rats showed significant reductions in systolic blood pressure (SBP) compared to the hypertensive group. WR did not reduce SBP because of the loss of bioactive compounds during intensive milling. PGBR also reduced the expression of the angiotensin type 1 receptor (AT1R), transforming growth factor-β (TGF-β), and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX4), which contribute to the renin-angiotensin system, fibrosis, and oxidative stress production, respectively. Losartan (Los, an anti-hypertensive drug)-treated rats also exhibited similar gene expression, implying that PGBR may reduce hypertension using the same downstream target as Los. Our data also indicated that PGBR reduced cardiac lesions, such as the cardiomyopathy induced by L-NAME. This is the first report on the anti-hypertensive effects of PGBR in vivo by the suppression of the renin response, fibrosis, and improved cardiac structure.

The effect of colloid milling on the microstructure and functional properties of asparagus dietary fibre concentrates

Dietary Fibre Concentrate (DFC) derived from vegetables side streams obtained during industrial processing can be exploited as a fibre-rich food ingredient. In this study, colloid milling was investigated as an environmentally-friendly physical method to improve the functional properties of asparagus DFC. Functional properties such as swelling capacity, water holding capacity and emulsifying activity of asparagus DFC showed significant improvement after intensive colloid milling. Scanning electron microscopic analysis showed that the microstructure of the freeze-dried samples consisted of an intertwined three-dimensional network containing highly branched micro-fibres. The fibre suspensions showed shear thinning behaviour, which could be explained by the network formation. An additional thermal pre-treatment appeared to further enhance the positive effect of colloid milling on the functional properties of DFC. This study shows that colloid milling is an effective process to functionalize asparagus DFC, which could broaden its application in fibre-rich food products.

Decreasing the degree of polymerization of microcrystalline cellulose by mechanical impact and acid hydrolysis

Depolymerization of cellulose is often used as a (pre)treatment protocol within the catalytic valorization strategies of cellulose. Typical depolymerization protocols yield polymerization degrees above 70 anhydroglucose units (AGU). However, shorter cellulose fibers are of interest in the search for accessible dietary fiber additives or renewable materials with distinct mechanical properties (bio-composites). In this work, short-polymer microcrystalline celluloses (SMCC) with an average polymerization degree between 29 and 70 AGU were produced with material yields of 95 % and above by combining a planetary ball mill pretreatment with mild acid hydrolysis. By first decreasing the levelling–off degree of polymerization (LODP) with an intensive ball mill treatment, a mild acid hydrolysis protocol was sufficient to ensure high yields of SMCC. Furthermore, the desired polymerization degree could be obtained by tuning the process parameters.

Understanding Poor Milling Behavior of Voriconazole from Crystal Structure and Intermolecular Interactions

The study investigated the milling behavior of voriconazole (VRZ) subjected to particle size reduction using air jet mill at differential air pressures of 5, 6, 7, and 8 bar for five cycles at each pressure. The crystal structure of VRZ was probed for understanding the fracture behavior from crystal packing and intermolecular interactions using molecular modeling tools of attachment energy (Eatt), density functional theory, and energy framework analysis. Upon milling for different cycles, VRZ showed that size reduction from (D90) 20 to 9 μm and 100% particles could not be milled to sizes below 9 μm, with the increase in either the milling intensity or cycle. The milled samples retained the original crystal lattice as evident from consistent melting endotherm (Tm = 130.75 °C); heat of fusion (ΔHf = 96.52 J/g) values; and the plate-shaped morphology. The powder X-ray diffraction pattern of milled samples consistently showed characteristic peaks of stable form B of VRZ. The crystallographic plane (001) was found to be the most prominent slip and the cleavage plane due to least Eatt and weak noncovalent interactions (6.996 kJ/mol) between 3'H and 4'F functional groups of the neighboring planes. The predicted indentation hardness value of 228.67 MPa further indicated toward the plastic nature of VRZ crystals. Corroborating outcomes from the different molecular modeling tools for VRZ, cleavage along the plane (001) was determined to be energetically favorable, whereas cleavage of isotropic 2D molecular sheets was energetically unfavorable. As milling proceeds and crystal reduces in size, contact surface area and overall interaction energy decrease contributing to plastic behavior of the crystal. It was concluded that crystal plasticity and isotropic 2D molecular sheets along with the orientation of particles to the direction of stress and attrition energy during air jet milling are contributing factors for nonuniform size reduction of VRZ particles.

DEM investigation of particle flow in a vertical rice mill: Influence of particle shape and rotation speed

The obscure milling mechanism, causing by diversity of rice grain shape, restricts appropriate selection of processing conditions for improving milling quality of different varieties. On this basis, the rice grain was represented as an axi-symmetric ellipsoid using discrete element method (DEM). Effects of particle shape and roller shaft rotation speed as well as the interplay of both on axial dispersion, radial exchange, spatial orientation and collision characteristics relating to the milling mechanism were analyzed. The results indicated that effects of aspect ratio on the milling uniformity depend on rotation speed, displaying the axial dispersion coefficient and mean effective collision rate increase with increasing aspect ratio in the lower rotation speed, whereas completely opposite in the higher rotation speed. Effects of aspect ratio on the milling intensity are independent of the rotation speed, showing radial ectopia number, variance of orientation distribution and mean collision energy all increase with increasing aspect ratio.

Robocasting of dense zirconia parts using commercial yttria-stabilized zirconia granules and ultrafine particles. Paste preparation, printing, mechanical properties

In this work, a commercial 3 mol% yttrium oxide partially stabilized zirconia spray-dried granules were used as such, and after intensive milling, for the production of dense samples by robocasting technique. The aim was to evaluate the suitability of using spray-dried granules instead of submicron particles in robocasting of ceramic parts. To this aim, robocasting pastes were produced from the as-received granules as well as from nanometric particles obtained from an effective ball milling of the granules. The formulation of the pastes was optimized in order to achieve optimal printability. The drying conditions were optimized as well, and the control of temperature and humidity either in the printing and drying chambers allowed to eliminate any warping issue. After sintering at 1450 °C, the monolithic dense parts were characterized by ultra-fine and highly sintered microstructures, with the highest density achieved by the sample produced from granules. This material not only did not show the typical defects of granules-derived ceramics but was also characterized by fewer and smaller defects than the sample produced by the fine particles. It seemed that the presence of large granules, and thus large intergranular space, favored the debinding process and limited the formation of the typical processing flaws. The ball-on-three balls test was used for the evaluation of the mechanical properties of the dense samples. Biaxial flexural strength values in the range from ∼100 to 500 MPa (with an average value of 255 ± 93 MPa) were determined for the samples made from granules while these values ranged from ∼100 to 300 MPa (with an average strength of 198 ± 52 MPa) for the samples prepared from the milled particles. In spite of low, these values are in line with literature data, obtained on 3 mol% Y 2 O 3 –ZrO 2 samples fabricated by the robocasting technique, and suitable to demonstrate the feasibility to use as-received granules as feeding material for robocasting parts.

Insights into remediation of acid cracked intensive real olive mill wastewater by electro-Fenton process in the presence of per-sulphate

ABSTRACT Olive mill wastewaters (OMW) have complicated pollutants that are hard to treat as it contains high concentrations of refractory and toxic compounds, which is looking for practicable and economical treatment options. In this work, the remediation of OMW was conducted using the electro-Fenton process (EFP) with iron electrodes in the presence of per-sulphate (PS) to chemical oxygen demand (COD) and total phenol (TP) reduction after acid cracking step. The system performance were COD, Colour, and TP per cent removal while initial pH, voltage, reaction time, H2O2 dosage, electrical conductivity (EC) and dosage of PS were independent variables. Acid cracking of wastewater in pH 2.5 was used to reduce disturbing parameters to provide suitable condition for reaction. Acid cracking leads to mean removal of turbidity, COD, TP, colour up to 80%, 18%, 17% and 30%, respectively. It was found that parameters such as H2O2, pH, reaction time, voltage and EC in an optimum value increase the process efficiency. The optimum condition by EFP was obtained at a pH 2, H2O2 0.2 M, voltage 10 V and conductivity of 11,000 µS/cm for removing over 70% of COD and TP at 60 min. However, after adding low concentration of PS there was not any enhance in the efficiency of COD and TP due to plenty presence of scavengers in OMW. It could be concluded that the remediation of pretreated OMW with acid cracking using EFP may be considered as reliable pretreatment method with further modifications.