Unmilled Samples Research Articles

Investigation on electrochemical corrosion behavior and mechanical properties of Fe-nano particles produced by high-energy ball milling technique

Abstract This study focuses on converting iron particles from grinding sludge, after removing impurities, into Fe-nanoparticles using high-energy ball billing. The goal is to examine the corrosion behaviors and mechanical properties of these Fe-nanoparticles. Nanostructured Fe-powder was synthesized through a process involving 10 h of high-energy ball milling, followed by conventional hot pressing and sintering. Structural and microstructural properties were thoroughly examined using techniques such as X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and elemental diffraction spectroscopy. Upon sintering, SEM and TEM analyses unveiled the formation of a nanostructured alloy within the samples. Notably, the milled sample exhibited high hardness value, measuring at 155 HV. However, it is noteworthy that the un-milled sample demonstrated superior compression strength compared to its milled counterpart. Furthermore, the corrosion behavior of the samples was evaluated through electrochemical corrosion studies. Interestingly, the sample subjected to 10 h of milling (coin number 5) displayed a significantly lower corrosion rate, measuring at 1.3921 mm/year, suggesting enhanced corrosion resistance attributed to the nano structuring process.

Ionic conductivity of nanocrystalline γ-AgI prepared by high-energy ball milling

Abstract The compound AgI crystallizes, depending on temperature and pressure, with various crystal structures. While α-AgI is the stable form at elevated temperatures, the β and the γ forms exist at lower temperatures. Variants with stacking sequences different than in pure β-AgI and γ-AgI enrich the complex crystallographic situation for AgI. In the study presented here, we converted a mixture of β-AgI and γ-AgI into nanostructured γ-AgI by mechanical treatment, that is, by high-energy ball milling of such a mixture under ambient conditions. Our work extends an earlier study by Ahmad (Z. Naturforsch. 2015, 70b, 17). We used variable-temperature, potentiostatic conductivity spectroscopy as well as electric modulus measurements to characterize the electric transport parameters. For the case that the sample is heated to temperatures near and above 420 K, preliminary information on the “resistance” of the electric conductivity against healing of defects are also collected. As compared to the unmilled but mixed sample, whose Ag+ ionic transport is dominated by those ions residing in the γ-phase of AgI (0.25 eV vs. 0.46 eV in β-AgI), ball milling only leads to a small increase in overall electric conductivity (by a factor of 3–4) for nanocrystalline γ-AgI (0.25 eV). This observation is perfectly in line with a recent observation for the fast ion conductor Li10GeP2S12 (Hogrefe et al., J. Am. Chem. Soc. 2022, 144, 9597): In materials with already rapid diffusion pathways, nanostructuring and the introduction of defects and distortions do not lead to significantly enhanced ion transport. Here, a careful analysis of data from conductivity and modulus spectroscopy helps identify which dynamic parameters are mainly responsible for the change in the overall conductivity upon mechanical treatment of coarse-grained γ-AgI.

Comparison of fatigue test results of high-strength steel DED-Arc specimens with milled and unmilled surfaces

The surface characteristics of direct energy deposition (DED)-Arc specimens have been previously explored, revealing the dual effect of the surface topography on fatigue strength. This effect includes a reduction in the nominal load-bearing cross-section due to the waviness of the surface and the initiation of fatigue cracks at combined geometric and metallurgical notches from the surface. To complement these findings, this study focuses on the fatigue life and crack initiation of milled DED-Arc samples, e.g., after removal of the geometric notches. Fatigue tests on DED-Arc specimens validate the impact of surface topography on fatigue strength, emphasizing the significance of surface characteristics in determining structural integrity. The additional tests conducted on milled surfaces provide insights into the failure mechanisms specific to these samples. Fracture surface analysis, microstructure characterization, and hardness measurements are performed. For both surface conditions, cracks originate in the interlayer zone, where local hardness is reduced. In unmilled specimens, this is due to the stress concentration effect, and in milled samples, this is due to softened interlayer zones. The fatigue life of milled specimens is comparatively high, demonstrating the importance of optimizing surface characteristics for improved fatigue resistance.Highlights1. Both, unmilled and milled specimens, show crack origins in the interlayer areas. For unmilled specimens, this is because of the local stress concentration in the notch; for milled specimens, it was shown that soft zones between the layers act as the weakest link.2. The fatigue strength of unmilled test coupons is significantly lower than those of milled specimens.3. Unmilled samples exhibit multiple crack origins.

Sustainable SiO2 Nanostructures from Different Diatom Species As Anode Material for Future Generation Lithium-Ion Batteries

Energy harvesting and storage devices occupy a more prominent place in the 21st century than at any time in the past. Intensive efforts have been devoted to next-generation energy storage devices such as rechargeable lithium-ion batteries (LIBs) to develop high energy density and long cycle life electrode materials from sustainable sources. In the present anode, graphite is severely restricted by capacity and unavoidable solid electrolyte interface (SEI) formation. Besides, it has been listed as a critical material by the European Commission. Recently, silicon-based electrodes have been pinpointed as promising anode candidates due to their high theoretical capacity (~4200 mAhg-1 for Li4.4Si), low operating voltage (0.4V/Li/Li+), abundant resources, and environmental friendliness. Interestingly, nanostructures of Silica (SiO2) can be extracted from the frustules (exoskeletons) of a type of microalgae called diatoms. In this current work, SiO2 frustules were grown from two different diatom species, constituting a sustainable source for producing nanostructured Si-based materials. Scanning electron microscopy (SEM) images confirmed the highly nanoporous structure of diatom silica, which was retained even after ball-milling. The electrochemical performance of SiO2 was investigated as an anode material for LIBs. Herein, we have tested both species A & B milled and un-milled samples (denoted as SPAUM, SPAM, SPBUM, and SPBM). The diatom SiO2 un-milled species A (SPAUM) exhibited a high specific capacity of ~ 810 mAhg-1 with remarkable capacity retention and coulombic efficiency even after 100 cycles at 0.1 Ag-1 and delivered a high specific capacity of ~ 400 mAhg-1 even at high current density 3 Ag-1. For comparison and understanding, commercially available diatomaceous earth milled, and un-milled silica (denoted as EDAM & EDAUM) has been subjected to the same cycling protocol. Results clearly showed species A & B milled and un-milled displaying better electrochemical performance than diatomaceous earth milled and un-milled silica. Such improved electrochemical properties like cycle life, and rate capability of SPAUM are mainly ascribed to their highly porous nature which significantly facilitates fast Li ion diffusion, its unique morphology, which favors a faster kinetics and its complete lithiation/de-lithiation after the initial activation cycle. In view of the superior electrochemical properties, such sustainably sourced SiO2 materials can be considered a potential anode material for future LIBs. Figure 1

Effect of Milling on Dielectric Properties of PZT

In this study, we investigated the impact of high-energy milling on the structural and dielectric properties of Pb[Zr(1-x)Tix ]O3 [PZT] ceramics synthesized using the solid-state reaction process. The sample was milled for 2, 4 & 6 hours using a high-energy ball milling machine. The unit cell structure for all of the samples was observed to be monoclinic, according to x-ray diffraction measurements (space group: C1m1). A significant reduction in crystallite size was observed, from 132 nm to 46 nm after 6 hours of milling. The dielectric study indicated a classical ferroelectric type behaviour for the un-milled sample and diffused phase transition for all milled samples. However dielectric constant dropped from 940 to 487 after 6 hours of milling.

Performance of clinoptilolite zeolite after milling as a pretreatment on hydration kinetics, shrinkage, and alkali-silica reaction of cementitious materials

Natural clinoptilolite zeolite has been a popular supplementary cementitious material (SCM) due to its acceptable pozzolanic performance and the overall lower environmental footprint. Previous research established that milling is an effective pretreatment technique to further increase the pozzolanic reactivity of zeolitic tuffs leading to an increased specific surface area and amorphous contents. Therefore, the present study characterized the zeolite particles after ball milling for 1 and 3 h using phase analysis by X-ray diffraction (XRD), particle size distribution by laser diffraction, microstructural analysis by scanning electron microscopy (SEM), moisture absorption rate, and relative chemical dissolution. The performance of milled clinoptilolite zeolite as a SCM with the replacement of up to 20% portland cement was evaluated through hydration kinetics (heat of hydration, setting time, chemical shrinkage, degree of hydration), workability, compressive strength, autogenous shrinkage, drying shrinkage, and alkali-silica reaction (ASR). Results revealed that 1 and 3 h of milling led to an increased specific surface area, moisture absorption capacity, and relative dissolution of particles, but had no visible effects on the crystalline structure of zeolite particles compared to the unmilled zeolite particles. For the hydrated system, both 1 and 3-h milled zeolite increased the overall heat of hydration leading to an increased silicate and aluminate reaction along with the acceleration effects in the setting time. The compressive strength of up to 20% milled (1 and 3 h) zeolite samples was increased by about 20 to 25% compared to the unmilled zeolite samples at an early age which suggested an increasing pozzolanic response of milled zeolite particles in the system due to an increased volume of hydrated phases and degree of hydration. Milling slightly decreased the workability by demanding a higher content of fresh water which was released at a later age leading to a higher drying and autogenous shrinkage. In addition, milling reduced the internal curing capacity leading to damage to the porous structure of zeolite particles. The use of up to 20% 3-h milled zeolite reduced the deleterious expansion by about 80% due to ASR compared to the control sample and the overall performance of milled clinoptilolite zeolite as the SCM was satisfactory in the hydrated system.

Tailoring the Band Gap of Carbon Nanoparticles in Carbon Soot by Ball Milling

Carbon nanoparticles (CNPs) in carbon soot have been ball milled in air for time durations of 1, 3, and 5 hours. A reduction of the average height of CNPs, measured using atomic force microscopy, with increase in ball milling time has been observed with values about 22.54 nm, 11.09 nm, 9.48 nm, and 7.25 nm for un-milled and ball milled samples for durations of 1, 3, and 5 hours, respectively. The optical band gaps of the CNPs have been estimated from the optical absorption data with values of about 5.06 eV, 3.77 eV, 2.08 eV, and 1.55 eV for the as-synthesized CNPs and 1, 3, and 5 hours of ball milled CNPs, respectively. Such observations of reduction of height and decrease in band gap of the CNPs are due to the mainly increase in in-plane graphitic ordering in the CNPs and simultaneous attachment of oxygen from the air ambient. The ball milling provided the required energy to acquire the in-plane graphitic order in the CNPs reducing the disorders in it. Also changes in the functional groups (formation of carbon and oxygen bonds) in the surfaces of the in-plane graphite in the CNPs can lead to the formation of graphene oxide (GO) leading to change in the surface states which can result in decrease in band gap of the CNPs. With increase in ball milling time, amount of GO has been increased resulted in further decrease in the band gap of the CNPs.

Effect of the milling conditions on the decomposition kinetics of gibbsite

Synthetic gibbsite (Al(OH)3) was mechanically activated by attrition milling for 24h, with various grinding ball-to-powder weight ratios (0, 5, 10, and 20), and characterized by thermal analysis (TG-DSC). Further, we determined the corresponding kinetic parameters using the model-free and model-fitting methods from the Thermogravimetric Analysis (TG) data set. We found that the activation energies provided by both models agree very well. At temperatures higher than 350°C, the milled samples (GB5, GB10, and GB20) lose mass very slowly, while the unmilled sample (GB0) decomposes faster. In addition, we demonstrated that the decomposition mechanism of each sample engages multi-step reactions, and the corresponding activation energies change with the increasing milling conditions.

Effect of Post-synthesis Processing on the Electrochemical Performance of Y2W3O12

Lithium-ion batteries (LIBs) are enabling the uptake of electric vehicles and providing grid-scale storage solutions for renewable energy generation. However, it is vital to develop new and advanced electrode materials for lithium-ion batteries to meet various applied considerations such as cost, safety, toxicity, and performance. Here, solid-state synthesized Y2W3O12 is demonstrated as a high-rate active anode material in lithium-ion batteries, producing an initial discharge capacity of 637 mAh/g although with a very poor initial Coulombic efficiency of 35%. To improve the performance, simple post-synthetic milling and carbon coating are investigated. Carbon coating of the material leads to significant performance enhancement in both the unmilled and milled samples. For instance, the unmilled carbon coated electrodes maintained a high capacity of ∼140 mAh/g at 1600 mA/g after 2000 cycles with no capacity fading from cycle 200 to 2000. Such a remarkable rate performance and an excellent long-term cycling stability showcase the great potential of this unconventional electrode material in fast-charge and high-power applications. This facile post-synthesis process can be easily applied to other electrode material candidates to enhance their electrochemical performance.

High energy mechanical-milling induced modifications in structural and microstructural properties of Gd2Zr2O7

A polycrystalline sample of gadolinium zirconate (Gd2Zr2O7) was synthesized through a solid-state reaction route (unmilled sample) and then subjected to high-energy ball-milling for 6 hrs and 18 hrs duration (milled samples). Interestingly, elemental analysis of the samples indicates the gradual reduction in the atomic percentage of Gd and Zr cations while significant enhancement in oxygen atomic percentage with the milling process. Rietveld refinement of X-ray diffraction patterns suggests that all samples possess defect fluorite structure and the values of the goodness-of-fit parameter improve from 3.88 for the unmilled sample to 1.85 for 18 hrs milled sample. The diffraction pattern of 18 hrs milled sample showed reflections from the ordered pyrochlore phase. The formation of the disordered fluorite phase is owing to the preparation temperature and the ionic radius ratio, r(Gd3+)/r(Zr4+) = 1. 46. Transmission electron micrographs, and selected area electron diffraction patterns analysis confirm the nanophasic nature of the milled samples, and particle size is found to reduce with increasing milling time. It was found that BET surface area continuously increases from 1.99 m2/g for an un-milled sample to 17.79 m2/g for 18 hrs milled sample. The BET isotherms exhibited type-II hysteresis loop and suggested that all the samples are macroporous with pore width greater than 50 nm.

HSBM-Produced Zinc Oxide Nanoparticles: Physical Properties and Evaluation of Their Antimicrobial Activity against Human Pathogens.

This work examines the antibacterial and anticandidal activities of zinc oxide nanoparticles (ZNPs) synthesized by high-speed ball milling (HSBM), for short milling times: 0.5, 1, 1.5, and 2 h. First, ZNPs have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and the Zetasizer analyzer. The HSBM results in semispherical ZNPs with some local agglomeration. We found that nanoparticles decrease in size continuously with milling time until they reach about 84% of their original size after only two hours; at 1000 rpm, HSBM reduces ZNP's average size by 6 nm/min. As particle size decreases, the X-ray diffracted patterns become broader and less intense while confirming that no phase transformation has occurred, proving HSBM's effectiveness in synthesizing nanoparticles on a large scale within a short period of time. According to FT-IR analysis, as material sizes change, the polarization charge of the ZNP surface changes as well, creating discrepancies in vibrational frequency, as demonstrated by the shifting of the IR spectra in the 300-600 cm-1 frequency band. Raman responses have also been proven to depend on the particle size. Using the Agar well diffusion method, eleven microorganisms have been tested for the antimicrobial activity of ZNPs. Among the six Gram-negative tested bacteria, S. sonnei showed the largest inhibition zone of about 11.3 ± 0.6 mm with ZNPs measuring 148 nm in size (milled for 2 h), followed by E. coli ATCC 25922. Accordingly, S. aureus was the most susceptible Gram-positive bacteria, with inhibition zone size gradually increasing from 11.8 ± 0.3 mm to 13.5 ± 0.5 mm with decreasing nanoparticle size from 767 to 148 nm, while S. aureus ATCC 25923 was resistant to both milled and unmilled samples. Similar results were seen with candida, all milled ZNPs inhibited C. albicans, followed by C. tropicalis, whereas C. knisei was resistant to all ZNP sizes. In light of microorganism-ZNP interaction mechanisms, the obtained results have been discussed in depth.

Bioactivity enhancement by a ball milling treatment in novel bioactive glass-hydroxyapatite composites produced by spark plasma sintering

Hydroxyapatite (HA) and a lab-made bioactive glass (BGMS10) are combined (50/50 wt%) in this work, where the effect produced by a ball milling (BM) treatment (0–120 min) prior SPS consolidation on the characteristics of the resulting products is investigated. An extraordinary improvement of the apatite-forming ability during in-vitro test on SPS samples (800 °C/70 MPa/2 min) is obtained using the 30 min BMed mixture. Superior Young’s Modulus (122 GPa) and Vickers Hardness (675) were also found compared to unmilled samples (95 GPa and 510, respectively). Microstructural changes induced by BM, with 90 nm HA crystallites size in the bulk composite, and the intimate HA/BGMS10 interfaces established, are the factors mainly responsible for such result. When milling was prolonged to 120 min, samples with relatively lower density, mechanical properties, and in-vitro bioactivity, were produced under the same SPS conditions. The formation of crystalline SiO2 during SPS might be responsible for such behaviour.

Effect of mechanical milling on structural and photocatalytic properties of chemically synthesized ZnSnO3nanopowder

In this work, we report the structural and photocatalytic properties of chemically synthesized unmilled (0 hr) and mechanically milled (0.5 hr and 2 hrs.) ZnSnO3nano-powder. Samples were calcined at 700 °C after synthesis. Prepared samples were characterized by XRD, FESEM, EDX and UV–Vis spectroscopy. Rietveld refinement of x-ray diffraction was employed for microstructural analysis and this confirms successful synthesis of pure, single phase orthorhombic ZnSnO3 with space group Pnma. Grain size was also evaluated from FE-SEM micrographs using Image-J software. It was noticed that the optical band gap value (analyzed by UV–Vis spectroscopy) of the milled sample is greater than the unmilled sample indicating quantum confinement effect. Photocatalytic activity of ZnSnO3 catalysts was investigated using a model organic pollutant Congo red under visible light irradiation. Milled ZnSnO3 catalyst with lower grain size showed superior photocatalytic property in our studies. Attempt was made to correlate photocatalytic properties with variation of grain size and microstrain of the unmilled and milled sample.

The Art of Positronics in Contemporary Nanomaterials Science: A Case Study of Sub-Nanometer Scaled Glassy Arsenoselenides.

The possibilities surrounding positronics, a versatile noninvasive tool employing annihilating positrons to probe atomic-deficient sub-nanometric imperfections in a condensed matter, are analyzed in application to glassy arsenoselenides g-AsxSe100−x (0 < x < 65), subjected to dry and wet (in 0.5% PVP water solution) nanomilling. A preliminary analysis was performed within a modified two-state simple trapping model (STM), assuming slight contributions from bound positron–electron (Ps, positronium) states. Positron trapping in g-AsxSe100−x/PVP nanocomposites was modified by an enriched population of Ps-decay sites in PVP. This was proven within a three-state STM, assuming two additive inputs in an overall trapping arising from distinct positron and Ps-related states. Formalism of x3-x2-CDA (coupling decomposition algorithm), describing the conversion of Ps-decay sites into positron traps, was applied to identify volumetric nanostructurization in wet-milled g-As-Se, with respect to dry-milled ones. Under wet nanomilling, the Ps-decay sites stabilized in inter-particle triple junctions filled with PVP replaced positron traps in dry-milled substances, the latter corresponding to multi-atomic vacancies in mostly negative environments of Se atoms. With increased Se content, these traps were agglomerated due to an abundant amount of Se-Se bonds. Three-component lifetime spectra with nanostructurally- and compositionally-tuned Ps-decay inputs and average lifetimes serve as a basis to correctly understand the specific “rainbow” effects observed in the row from pelletized PVP to wet-milled, dry-milled, and unmilled samples.

Heavy metal contamination and health risk assessment of mechanically milled delicacy called fufu

Contamination of food by heavy metals is a concern as consumption of contaminated food is one of the most likely human exposure routes to metals. Fufu is a delicacy in Ghana consumed mainly by the Akans. Human exposure to some heavy metals (Cr, Fe, Zn, Mn and Ni) through mechanically processed fufu consumption was analysed by atomic absorption spectrophotometer and ascertaining consumer awareness of potential exposure by questionnaire administration. A total of 30 milled and un-milled fufu samples (cassava and plantain) were sampled from Bomso, Kotei, Ayeduase, Ayigya and Kentikrono, all within Kumasi. The results showed that Fe and Zn levels after milling were elevated in the range: 2.816–7.297 and 0.753–7.529 mg/kg, respectively. The concentrations of Fe and Zn were below the Food and Agriculture Organization/World Health Organization (FAO/WHO) permissible limits except Zn concentration at Bomso. Cr, Mn and Ni were below the detection limit (0.05). Hazard quotients and indices were less than the US Environmental Protection Agency’s permitted level of one, indicating no possible harm to consumers. Findings from the questionnaire administration indicated a complete lack of knowledge on consumer exposure due to the food processing method.

Dissolution of mechanically activated sphalerite in the wet and dry milling conditions

The aim of this work has been to examine the effect of intensive ball milling of sphalerite in the wet and dry modes on the microstructural changes and the subsequent effect on its dissolution rate. Sample characterization showed that the BET surface area and the amorphization degree were obtained to 18.2 m2/g and 78.92% in the wet mode and 7.72 m2/g and 90.35% in the dry mode milling after 180 min, respectively. The maximum extraction of Zn obtained 23.7, 67.12 and 85% in the unmilled, wet and dry milled samples, respectively. The ratio of kinetic rate constant has been increased by 37 and 67 times, respectively. Also, the activation energy was decreased with increasing of milling time. Selectivity of sphalerite leaching versus surface area was obtained higher than that of the wet milling. Leaching experiments indicated that structural disordering had a drastic effect on the reactivity of mechanically activated sphalerite.

Understanding of intriguing metal to semiconductor transition in Ni0.5Zn0.5Fe2O4 nanoparticulates

Temperature-dependent electrical transport characteristics of un-milled and high-energy ball-milled samples (3 h (70 nm), 6 h (55 nm) and 9 h (45 mm)) of Ni0.5Zn0.5Fe2O4 spinel ferrite were explored. A well-defined metal to semiconductor transition exhibited by all the samples has been construed in view of direct and superexchange cationic interactions and delocalization to localization of charge carriers on increasing temperature. The peak temperature (Tmax) was found to shift towards a higher temperature side on milling principally governs by the lattice vibration scattering and intrinsic excitation. The crystallite size reduction, enhancement in strain and sudden decrease in the formation and octahedral site occupancy of Fe 2+ ions on milling found responsible for the prodigious rise (~ 250 times) in normalized resistivity values for the sample comminuted for 9 h. The spectrum of energies corresponds to charge trapping centers that cause small bump (3 h milled sample) and sharp cusp (9 h milled sample) for T>Tmax. These materials may be found suitable for thermal cutoff switching applications.

Synthesis and Broadband Absorption of Fe-Based Nanoparticles in the Ku-Band

In this work, we propose a simple method to characterize the broadband absorption of different sizes of iron (Fe) nanoparticles. The absorption feature in the Ku-band (14–18 GHz) of paint/Fe nanocomposites with different Fe concentration is systematically investigated. The experiments confirm that the proposed samples can maintain a broadband absorption (with A > 60%) from 14.6 GHz to 18 GHz and from 15.2 GHz to 18 GHz for the as-milled Fe proportions of 5.0 g and 7.0 g, respectively, in a total thickness of only 2.0 mm. Furthermore, the absorption properties of the un-milled Fe nanoparticles samples are also characterized, which show lower absorption (A < 50%) than the as-milled nanoparticles. Our results contribute to the characterization of the next generation of wireless electronic devices based on thin layers of magnetic nanoparticles.

Evaluation of Structural and Electrical Properties of Ball-milled NaNbO3 Ceramic

This work reports the effect of milling on the structural, microstructural, electrical, and piezoelectric properties of NaNbO₃ (NN) ceramics synthesized using a solid-state reaction method. X-ray diffraction studies exhibited that the lattice structure of milled and un-milled NN samples is orthorhombic with a space group <em>Pmc</em>21. The average particle size and lattice strain were found to 203 nm and 0.05 un-milled samples whereas they were 37 nm and 0.2 for 10 h milled samples. FTIR spectra indicated a shift in peak position with milling time. SEM image showed the formation of small grains ~1.2 µm for 10 h milled NN samples which is advantageous for dielectric applications in high density integrated circuits. An increase in the values of dielectric constant from 377 to 698, <em>d33</em> from 29 to 37, and a drop in critical temperature from 426°C to 352°C at 1 kHz were registered for un-milled and milled samples. A negative temperature coefficient of resistance behaviour was noticed from the impedance and ac conductivity analyses. The correlated barrier hopping model successfully explains the charge transport mechanism in the present ceramic system and ac conductivity data obeyed Jonscher’s universal power law. A marked increment in <em>d33</em> with smaller particle size was observed with the increasing milling hour that could make NN a promising lead-free piezoelectric material for piezo-sensing/detection and energy harvesting applications.

Photocatalytic hydrogen production using FeTiO3 concentrates modified by high energy ball milling and the presence of Mg precursors

Ilmenite (FeTiO3) concentrates were modified by high energy ball milling (HEBM) at different times (1, 2, and 3 h) and in the presence of MgO or metallic Mg at different contents (0.5, 1.0, and 3.0 wt%), with the aim of obtaining a low-cost and highly available photocatalyst with enhanced performance towards H2 production. FeTiO3 concentrates were obtained from ilmenite-rich black sand by gravimetric concentration followed by wet electromagnetic and dry magnetic separation. HEBM was performed to insert Mg into FeTiO3 structure and to simultaneously reduce the particle size. The insertion of Mg intended to shift the conduction band of the materials to more negative potentials, in spite of the band-gap widening. XRD patterns of the milled samples showed a decrease in the intensity of ilmenite peaks without any displacement, indicating slight amorphization without significant changes in the crystalline structure. However, the increase in the intensity of hematite peaks suggests substitutional doping according to the proposed solid-state reactions. Although thermodynamic analyses showed that doping with metallic Mg should be more favorable, doping with MgO appears to be kinetically favored due to the physical characteristics of the precursor, as it was revealed by XRD, XPS, Raman spectroscopy, SEM–EDS, and UV–Vis DRS results. Deconvolution of high-resolution XPS spectra corresponding to Mg1s exhibited the presence of an additional component peak for the sample milled with metallic Mg, in comparison to that with MgO. This result evidenced the formation of a new phase, suggesting that part of the metallic Mg was not inserted into FeTiO3, as it was confirmed by Raman spectroscopy. UV–Vis DRS analyses showed an increase in the band-gap of the samples milled in the presence of Mg precursors (from 2.51 to 2.55–2.59 eV) which were attributed to slight modifications of the conduction band due to the insertion of Mg. The performance towards hydrogen production under UV irradiation was improved from 240.5 µmol g−1 h−1 (unmilled sample) to 255.3 µmol g−1 h−1 (2 h milled in the absence of Mg precursor), 296.0 µmol g−1 h−1 (2 h milled with 1.0 wt% MgO), and 265.2 µmol g−1 h−1 (2 h milled with 1.0 wt% metallic Mg). This improvement was attributed mainly to the insertion of Mg, and the consequent modification of the band structure, rather than the modification in the surface area.