Milled Samples Research Articles

Reactivity of fly ashes milled in different milling devices

Abstract The effect of two different milling devices, namely attrition mill versus vibration mill, on the reactivity of fly ash was studied. High calcium fly ash from 4th Thermal power station of Ulaanbaatar (Mongolia) was used for the experiments. The raw and processed samples were characterized by XRD, SEM, Particle size distribution, BET, Blaine surface area and density measurements. The efficiency of 1 hour milling was evaluated with the Blaine surface area set to be more than 5000 cm2/g. The physical and chemical properties of the attrition milled fly ash changed not much compared to the vibration milled samples. For example the d50 particle size became reduced from 29 µm to 6 µm by attrition milling and in vibration milled fly ash it was reduced to 7 µm. The density increased from 2.44 g/cm3 of raw fly ash to 2.84 g/cm3 and 2.79 g/cm3 in attrition and vibration milled samples, respectively. Mechanical milling revealed not only a particle size reduction but also the formation of a denser microstructure. As a result the vibration milled fly ash showed a weaker interaction with the alkaline solution (8 M NaOH used here) compared to the attrition milled fly ash. Consequently, compressive strength of the binder prepared using the attrition milled fly ash was higher, 61 MPa, while for vibration milled fly ash it was 49 MPa. For comparison unmilled fly ash, it was 21 MPa.

Variation of the milling conditions in the obtaining of nanocellulose from the paper sludge

This work aimed to evaluate three different milling conditions, seeking the optimization of CNS isolation process. The paper sludge was chemically treated with detergent and H2O2, by two steps, to remove the noncellulosic contents (hemicellulose and lignin). After these treatments, the sample was milled with the variation of a liquid medium. The three liquids milling medium were: i) dry medium (CNS-D); ii) moist with water and (CNS-W) iii) moist with ethanol (CNS-E). The CNSs were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), zeta potential and dynamic light scattering (DLS). The milled samples presented different behavior, depending on the medium applied. The CNS-W presented low efficiency due to the formation of agglomerates around the ceramic ball, resulting in larger fiber sizes (microsizes). Although, the samples CNS-D and CNS-E presented similar behavior of sizes distribution, with average size 340 nm and 373 nm, respectively, determined by DLS. The CNS-E sample presented higher yield and electrostatic stability in solution, besides not presenting loss of crystallinity, as occurred with CNS-D, observed by FTIR analysis. Thus, the isolation with ethanol showed more efficient process among the three processes studied. This work achieved the isolation of CNS; besides, it proposed an environmentally friendly isolation method, and this may add value in the paper sludge. Keywords: industrial residue, cellulose nanostructures, ball mill, cellulose characterization.

Fatigue life and Fracture Morphology of Inconel 718 machined by spark EDM process

Abstract Fatigue life of electric discharge machined and end milled samples of Inconel 718 alloy at high cycle fatigue mode was investigated. The objective of this work is to determine the influence of recast layer formed during the electric discharge machining on the fatigue life of Inconel 718. Data were generated in the fully reversed fatigue mode at ambient temperature using samples fabricated by following ASTM E606 standard. The specimens were machined on a spark electric discharge die sink machine. The specimens were subjected to fatigue, and the resulting fatigue lives and fracture morphology were compared with that of the end milled specimen. The surfaces of the specimens were examined under optical and scanning electron microscopes, and the roughness of the surfaces was measured using a standard surface profilometer. From the results of the investigation, it was concluded that the fatigue life of the samples fabricated by Spark Electric Discharge Machining decreased slightly when compared with that of the end milled sample. The results are explained using the data recorded on recast layer thickness, fracture mechanism observed because of the EDM process, and optical and scanning microscopy.

Structural Degradation of Layered Cathode Materials in Lithium-Ion Batteries Induced by Ball Milling

Layered LiNi0.4Mn0.4Co0.18Ti0.02O2 cathode powders were ball-milled for various lengths of time. The structural properties of the pristine and milled powders, which have different particle sizes were examined with X-ray diffraction, soft X-ray absorption spectroscopy, and transmission electron microscopy to determine the effect of milling on structure. Electrochemical testing in half-cells was also carried out and shows that milling plays an important role in the performance of these cathode materials; as milling time increases, there is a decrease in initial discharge capacity. The first cycle irreversible capacity also increases for milled samples, as does capacity loss upon cycling under some regimes.The electrochemical degradation is strongly correlated with damage to the lamellar structure of cathode particles induced by milling, and lithium carbonate formation.

A comparative study of the effects of milling and abrasive water jet cutting on flexural performance of CFRP

Machining of carbon fibre reinforced polymers is part of the production process that introduces several challenges due to inherent characteristics of CFRPs such as non-homogeneity of their mechanical properties. A comparative analysis of conventional milling and abrasive water jet (AWJ) cutting is performed to quantify the effects of machining induced damage on flexural strength of woven CFRP laminates. The machined surfaces quality is characterized using optical and scanning electron microscopy methods prior to flexural mechanical testing. High-speed Digital Image Correlation technique is also used to measure deformation evolutions and determine fracture mechanisms in relation to the applied machining operation and produced machined surfaces. The effect of machining induced damage on strength of milled samples was less than expected with the AWJ processed samples having the least mechanical properties. The surface morphology analysis revealed that the entry and exit point of the water jet introduced severe surface and subsurface damage across the full thickness. The failure initiation sites were determined by strain distribution maps indicating that machining induced damage promotes failure of the tested CFRPs away from maximum compressive stress observed under the loading points.

Enhancing lithium leaching by mechanical activation

The lithium (Li) bearing minerals lepidolite and spodumene were mixed with different mass ratios of Na2SO4 and mechanically activated by milling in a planetary ball mill for 5 h. The milled samples were studied using thermogravimetry under an air atmosphere up to 950 ºC. Isothermal heating of the milled samples was undertaken in a furnace at temperatures of 700 ºC and 800 ºC for 1 h. Hot water leaching of the calcines indicated that increasing the calcination temperature had a significant effect on the dissolution of lithium. The leaching of lithium from lepidolite was notably higher than that from spodumene.

An Efficient Approach to Optimize Wear Behavior of Cryogenic Milling Process of SS316 Using Regression Analysis and Particle Swarm Techniques

The present work is an endeavor to carry out a machining using LN2 in face milling operations and to produce the milling samples with excellent wear resistance property. The output response (wear rate) depends on appropriate choice of speed, feed, and depth of cut. The experimental data are conducted (collected) for SS316 as per central composite design. The present work exemplifies an employment of conventional and nonconventional strategies for optimizing the milling factors of cryogenically treated samples in face milling to achieve the desired wear (response). The results of nonlinear regression (desirability strategy) and nonconventional [particle swarm optimization, (PSO)] optimization techniques are compared, and PSO is found to outperform the desirability function approach. The present work even highlights the effect and results of LN2 on wear in contrast to wet condition.

ACTIVE-ILMENITE SURFACE STRUCTURE INFLUENCE ON ACID-ASSISTED BALL MILLING

Active-ilmenite powder derived from natural ilmenite sand was prepared by the ball milling process with acid-solution and Deionized (DI) water. Morphology and particle size of active-ilmenite product in acid/DI-assisted ball milling process were monitored by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). Surface atomic component and chemical bonding were investigated by X-ray photoelectron spectroscopy (XPS). Meanwhile, bulk chemical oxidation and fine structure of active-ilmenite were studied by X-ray absorption near edge structure (XANES) and extended X-ray absorption ne-structure spectroscopy (EXAFS) to confirm the oxidation state and local active species structure at surface. Active-ilmenite by acid-assisted ball milling process is a distinctive method for the preparation of active-ilmenite product with high active surface. Moreover, the distortion of TiO6and FeO6octahedral cluster on the sample surface was detected in all milled samples with acid-assisted ball milling process. The presence of Fe[Formula: see text], Fe[Formula: see text] ions and miniature sulfate was also detected on the sample surface by milled product with acid-assisted method.

Reflectance increase from broad beam ion milling of coals and organic-rich shales due to increased surface flatness

Broad ion beam (BIB) milling is useful in organic petrology because it can yield flat sample surfaces and avert the ‘smearing’ of organic matter (OM) that results from traditional mechanical polishing. This potentially makes BIB especially useful in the study of nano-porosity, where even minor mechanical disruption of the sample surface distorts the sample characteristic of interest—the pore structure. However, several studies have observed an OM reflectance increase after BIB milling, concluding that ion milling may cause thermal alteration to OM surfaces. To better understand ion milling effects on organic matter, coal (subbituminous, high volatile bituminous, medium volatile bituminous, anthracite) and shale [Bakken Formation, Ohio Shale-Huron Member (5), Kimmeridge Clay Formation, Alum Shale, New Albany Shale] samples were prepared using traditional mechanical polishing methods. Reflectance measurements (% Ro) were gathered on all maceral types present before BIB milling, followed by re-measurement of OM reflectance at the same locations after milling. Most OM increased in reflectance after BIB milling, with some exceptions in high maturity samples. Liptinite macerals in both coal and shale samples showed the greatest percent reflectance increase on average (+133%; n = 338), followed by solid bitumen (+49%; n = 313), vitrinite (+26%; n = 413), and inertinite (+9%; n = 220). Despite the increases to OM reflectance caused by BIB milling, no evidence was found for kerogen conversion (e.g., change in maceral abundances), or for migration of newly generated petroleum (e.g., pseudomorphic replacement of kerogen by solid bitumen). Such changes occur when samples are thermally altered from immature conditions into the oil window (e.g., by hydrous pyrolysis), and, if the increases in OM reflectance were thermally driven (by BIB milling), they should have been observed in the above experiments. Herein, we also used atomic force microscopy to document a decrease in surface roughness of correlative locations of OM on pre- and post-ion milled samples. This improved surface polish caused by BIB milling appears to be the root cause of increased OM reflectance, as no other supporting evidence of thermal alteration could be found. That is, the fraction of light formerly lost to oblique scatter in diffuse reflectance from a mechanically polished surface is converted to specular reflectance after BIB ion milling. Thus the light leaves the surface at a near normal angle and returns to the detector, resulting in increased OM reflectance.

Electromagnetic and absorbing properties of the composites based on iron, cobalt, B and rare earth Nd

In this paper, nanocomposite FeCoB alloy with low content of Nd were prepared by rapidly quenched technology and then treated with high energy ball milling for different milling time. The XRD spectra suggests that all samples only have the single ∝-Fe phase. Calculated by Scherrer formula, the grain size decreases with increasing ball milling time. The electromagnetic (EM) properties were investigated in the frequency range of 2–18 GHz by Agilent PNA 8363B. The permeability-frequency for all ball milling samples were increased at first and then decreased, while the permittivity-frequency were remained relatively a constant. It is found that the absorbing mechanism for as spun sample is natural resonance while that of the milled samples are eddy current effect. According to the transmission line theory, the reflection loss of samples has been significantly improved in the specific frequency range. The particles milled for 4 h presented a reflection loss of −9.8 dB at 3.8 GHz. It is noted that the appropriate milling time is the key of the excellent electromagnetic wave absorption properties in C-band.

Microstructure, optical and electrical characterizations of nanocrystalline ZnAl2O4 spinel synthesized by mechanical alloying: Effect of sintering on microstructure and properties

Nanocrystalline ZnAl2O4 spinel compound has been synthesized by mechanical alloying the stoichiometric mixture of ZnO and α-Al2O3 powders. Required phase is initiated within 1 h of milling and nanocrystalline ZnAl2O4 mixed spinel phase has been obtained after 4 h of milling. Phase transformation from mixed spinel to normal spinel structure occurs through redistribution of cations in tetrahedral and octahedral void spaces after 5 h of sintering at 1173 K. Structure and microstructure characterizations of all milled samples have been carried out by analyzing the respective XRD patterns employing Rietveld's refinement method and HRTEM images. The optical band gap of semiconducting ZnAl2O4 is blue shifted due to the sintering effect. All synthesized samples exhibit PL emissions primarily within the UV region. Both the dc and ac electrical conduction mechanisms have been explained respectively by the hopping transport phenomenon and frequency dependent conductivity behaviour, which obeys the Jonscher power law. A better optical property, enhanced electrical conductivity and low dielectric constant value make the synthesized semiconducting ZnAl2O4 compound suitable for optoelectronic applications.

Formation and occurrence of organic matter-hosted porosity in shales

Porosity within organic matter (OM) is considered to be the main site for gas storage (via fluid phase saturation of the pores and sorption on the pore walls) and thus its presence or absence is very critical for in-place gas assessment for organic-rich rocks. Numerous workers have suggested that OM-hosted porosity increases with thermal maturity mainly related to the process of bituminized organic matter cracking to gas. Comprehensive reviews of published literature enable us to conclude that organic porosity dominantly develops within bituminized organic matter (i.e., that portion that is petrographically identified, mainly based on its morphology, as solid bitumen (Mastalerz et al., 2018)) and primary (i.e, structured or amorphous) organic matter (kerogen) is mostly deficient in porosity. We show that in the same shale sample, structured kerogen shows no porosity whereas solid bitumen contains abundant porosity. It has been previously reported that sample preparation for SEM by ion milling may alter the organic matter. In this study, some adverse effects of ion milling have been observed by comparing SEM-visible pores of the same sample prepared by mechanical grind polish (MGP) and ion milling (IM) methods. Since solid bitumen is more labile, and probably more prone to chemical/physical alterations, we recommend that SEM observations of ion milled samples to be conducted with more attentiveness.We show that 1) MGP is a suitable sample preparation method for SEM observations, 2) the overwhelming majority of SEM-visible organic matter-hosted pores develop within solid bitumen and not in structured organic matter (kerogen), and 3) we reaffirm that shale mineral content is a key factor in preservation or destruction of solid bitumen-hosted porosity.Finally, we propose a conceptual model for the formation, preservation and destruction of OM-hosted porosity for shales. Accordingly, we suggest that, all other factors being equal, a quartz-rich brittle shale will preserve more SEM-visible solid bitumen-hosted (meso and micro) porosity compared to that of a clay-rich ductile shale. Therefore, gas storage capacity of a quartz-rich shale will be relatively high compared to that of a clay-rich shale.

Cyclic structural ordering induced by high energy ball milling in a Fe2.1Cr0.9Al magnetocaloric alloy

Abstract Current research on magnetocaloric materials (MCM) aims at developing low cost, environmentally friendly materials which can be manufactured by simple processes. We report the effect of high energy ball milling on the structural, magnetic and magnetocaloric properties of low cost Fe2.1Cr0.9Al alloys. The degree of structural order in the Fe-Cr sublattice was found to vary with milling time in a cyclic fashion at a milling speed of 600 rpm. This phenomenon was analyzed by a reaction rate model based on the stored energy during high energy milling. The sample possessed a B2 crystal structure before milling. Milling for 15 min. at 600 rpm induced structural changes to produce a L21 structure. Interestingly, the 15 min. milled sample exhibited ∼50% higher saturation magnetization (MS) compared to the value before milling. The relative cooling power (RCP) also increased to 300 Jkg−1 at 5 T, compared to a value of 244 Jkg−1 before milling. Extended X-ray absorption fine structure (EXAFS) studies revealed the emergence of short range order in the milled samples.

Fast preparation route to high-performances textured Sr-doped Ca3Co4O9 thermoelectric materials through precursor powder modification

This work presents a short and very efficient method to produce high performance textured Ca3Co4O9 thermoelectric materials through initial powders modification. Microstructure has shown good grain orientation, and low porosity while slightly lower grain sizes were obtained in samples prepared from attrition milled powders. All samples show the high density of around 96% of the theoretical value. These similar characteristics are reflected in, approximately, the same electrical resistivity and Seebeck coefficient values for both types of samples. However, in spite of similar power factor (PF) at low temperatures, it is slightly higher at high temperature for the attrition milled samples. On the other hand, the processing time reduction (from 38 to 2 h) when using attrition milled precursors, leads to lower mechanical properties in these samples. All these data clearly point out to the similar characteristics of both kinds of samples, with a drastic processing time decrease when using attrition milled precursors, which is of the main economic importance when considering their industrial production.

Sample edge effects on tensile properties and sheet formability

It is well known that the condition of the edge, whether sheared or milled, can affect the results in edge formability tests (i.e. a hole expansion test). In the current investigation, two experimental studies were performed to evaluate the effects of edge condition on the results of tensile tests and a laboratory formability test for sheet steels. The first study evaluated the tensile properties of a QP980 steel with samples prepared by four different machining methods: wire electro-discharge machine (EDM); mechanical milling; laser cutting; and waterjet cutting. It was found that the EDM and milled samples produced statistically similar values for yield strength, ultimate tensile strength, uniform elongation and total elongation. The yield strength and tensile strength from samples prepared by laser cutting were statistically different. Water jet cutting produced statistically different values for almost all four properties when compared to the EDM and milled samples. In the second study a DP600 steel was subjected to an angular stretch bend formability test with samples prepared by either shearing or milling. It was found that the sheared samples required higher forces but smaller displacements to reach the formability limit. Fracture for the sheared samples initiated on the edge of the sample whereas for the milled sample necking and fracture initiated in the center of the sample, close to the plane-strain condition. Results from both of these studies clearly show the importance of the edge condition on reported mechanical properties and on the formability of the sheet.

Development and characterization of nanocrystalline cobalt powder prepared via high energy ball milling process

This work investigated the influence of varied milling time and ball-to-powder weight ratio (BPR) at constant milling speed on micron-sized cobalt powder. Stainless steel balls of 2, 3 and 4 mm diameter were used to prevent cold welding of the charged powders and increase the collision energy available. Powder processing was performed in an argon filled chamber to avoid contamination of the powder. Detailed X-ray diffraction (XRD) studies were carried out to evaluate the lattice strain, crystallite size and the planes at different peaks using Williamson-Hall method. The morphologies of the as-received and milled samples were investigated with scanning electron microscope equipped with energy-dispersive spectroscope (SEM/EDS). The results indicated that the lowest crystallite size and highest lattice strain of 9.05 nm and 3.74 % respectively was achieved for powders subjected to 12 hrs milling at constant BPR of 20:1. A constant milling time of 2 hrs and varied BPR also yielded a crystallite size of about 13.73 nm and lattice strain of 0.79 % at BPR of 10:1. The XRD results show the influence of this process on the diffraction width and peaks. Hence, varying the BPR at constant milling time helps to save time, conserve energy and guarantee the economy of the operation.

Influence of Structural Features and Nature of Interaction between Minerals on the Selection of Methods for Lead-Bearing Ore Separation

The influence of structural characteristics and interaction parameters of minerals on separation method of lead-bearing complex ore in Russia is analyzed. Based on the studies of deep dissociation of minerals under disintegration using Mineral Liberation Analyzer (MLA), the quantitative distribution of mineral associations in grain-size categories is determined. From the data on mineral dissociation, the series of mineral associations, characteristic of complex ore from some deposits, are defined using milled samples of ore material. It is shown that galena associations with chalcopyrite, fahlore, secondary copper sulphides, sphalerite, pyrite and gangue mostly occur in finely dispersed aggregates with fahlore and, to a lesser degree, with other sulphides. The obtained series of mineral associations make it possible to determine the sequence of dissociation and separation of final-size minerals in the inter-cycle operations during flotation. The primary flotation concentrate contains fahlore, secondary copper sulphides, gold associations, galena and corroded pyrite.

Sinterability of 8 mol% Yttria Stabilized Zirconia

The sintering behaviour of low cost 8 mol% yttria stabilized zirconia powders has been studied. The effect of sintering holding time of the sintered granulated and milled 8YSZ were determined using density measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The elemental composition, particle size and morphology of the as-received 8YSZ powder and proceed for milling was investigated. 48 hours of ball milling on granulated 8YSZ resulted rises in specific surface area and sintered at 1550°C with the various period of time (4, 5, 6 and 7 hours). The milled 8YSZ sample with 5h sintering holding period coded as F5, sintering activity improved and the relative density came up to 98.3%. But then, granulated 8YSZ achieved only 62.7% with 5 hours holding time. Crystal structure analysis for milled 8YSZ powder consists of 59.6% of cubic ZrO2 phase, 40.1% of tetragonal ZrO2 and 0.3% of monoclinic ZrO2. Meanwhile, granulated 8YSZ indicated low content in cubic ZrO2 but high amount in monoclinic ZrO2 phase. In brief, low cost 8YSZ reached higher densification of 98% successfully.

Mechanochemically synthesized NiCo2O4/Vulcan/PANI nanocomposite and investigation of its electrochemical behavior as a supercapacitor

Wet-mechanical alloying was used to synthesize NiCo2O4 (Ni-Co) nanoparticles. XRD results showed that single phase nanoparticles were formed after 1 h of milling and a minimum crystallite size of ~ 3 nm was obtained for 3 h-milled sample. The 3-h-milled sample was mechanically alloyed with Vulcan (Vu) to fabricate NiCo2O4/Vulcan (Ni-Co/Vu). The Ni-Co/Vu sample was thoroughly mixed with aniline (ANI), and the mixture was then polymerized to polyaniline (PANI). The microscopic evaluations showed the change in shape of Ni-Co particles from spherical to worm-liked after the polymerization process. Their structure was evaluated using FT-IR and Raman spectroscopies. The electrochemical studies through cyclic voltammetry (CV) and chronopotentiometry (CP) showed the highest capacitance for the 3-h-milled Ni-Co, in comparison with other milled samples. The capacitance of 341 F g−1 of the 3-h-milled sample, was enhanced to 455 and 644 F g−1, upon introducing Vu and Vu/ PANI, respectively.

Investigations into the total antioxidant capacities of cultivars of gluten-free grains using near-infrared spectroscopy

Millet, buckwheat and oat are considered to be minor crops, hence chemical profiles for different cultivars are rare. The examination of a sum parameter, like the total antioxidant capacity (TAC) can thus be a first step to systematically assess the quality of different cultivars of mentioned gluten-free grains and thereby serve as an indicator for the selection of cultivars for food processing.TAC of 20 common buckwheat, 14 proso millet and six common oat cultivars was analysed using Folin-Ciocalteu assay and an optimized NIRS methodology. PLS regressions for milled and intact samples were established and yielded a R2(CV) of 0.892 and 0.929. The SEPs for milled and intact samples were approximately 1.7 and 1.6 mgGAE/g. Multivariate LOD and LOQ were also calculated. LODmax for intact and milled samples was 1.72 and 2.80 mgGAE/g.TAC varies considerably among cultivars of one species, emphasising the need for full chemical profiles. Values for LOD and LOQ show that established PLS-R models can be used to quantify TAC of buckwheat and oat cultivars. TAC of millet cultivars can be detected, however not quantified.