Planetary Milled Research Articles

Size reduction via planetary milling and acid leaching effect on rice husk ash-derived nano-silica

Among the common sources of silica from agricultural waste are rice husk and rice husk ash (RHA). In this study, RHA used was prepared through the controlled burning of the rice husk. Two different RHA sizes were used in the synthesizing process via precipitation method: the original RHA (without planetary milling) and the planetary milled RHA. Prior to the precipitation method, RHAs were acid leached using hydrochloric acid (HCl) as the leaching agent and then subjected to heat treatment. This study strives to highlight the effect of planetary milling of RHA and acid leaching treatment on the acquired rice husk ash-based nano-silica properties. XRF analysis obtained show that leaching pre-treatment at two different temperatures had resulted in insignificant percentage of silica. Meanwhile, the XRF, XRD, FTIR and FESEM characterization confirmed that the obtained powders contain up to 99.7% of high purity amorphous silica particles in size less than 100 nm. FESEM micrographs indicated the insignificant difference in the resultant nano-silica particles size which suggest the physical alteration of RHA in the early stage might not have a significant role on producing nano-sized silica. The results of this study could suggest a convenient and reproducible method for the preparation of high-purity rice husk ash-derived nano-silica particles in an amorphous structure with a high potential to be used in a wide range of applications.

Synthesis by High-Energy Ball Milling of MgH<sub>2</sub>-TiFe Composites for Hydrogen Storage

The aim of this work is to investigate the influence of some processes variables on the microstructure and hydrogen absorption kinetics of MgH2 - X wt.% TiFe composites. Samples were synthesized by high-energy ball milling in a planetary (X = 40, 50, 60) and shaker mill (X = 40) under high-purity argon atmosphere. Commercial MgH2 instead of Mg powder was used in order to reduce adherence on the vial and balls. TiFe powder was previously produced by ball milling a mixture of TiH2 and Fe powders followed by a reaction synthesis at 600oC. Milled composites samples were characterized by XRD and SEM analysis. Milling time was preliminary investigated (X = 40) in the planetary ball mill (6 to 36h). TiFe particle size reduction was shown to be difficult since they are surrounded by MgH2 matrix. Strong particle reduction was obtained by using a shaker mill only for 2 hours and adding cyclohexane as process control agent. No reaction between MgH2 and TiFe compound was observed in any milled sample. Hydrogen absorption kinetics measurements of the as-milled samples were conducted on an Sieverts' type apparatus at room temperature after hydrogen desorption at 350oC under vacuum. The best hydrogen kinetics (3 wt% at the first hour) was attained by the planetary milled sample (36 h). Higher hydrogen capacity was observed for the sample milled in the shaker mill (4.0 wt.%), but only after 13h.

Effect of Milling Medium on Alumina Additivated with Niobia

Niobia has been successfully used as sintering additive to alumina in order to lower its sintering temperature. This effect can also be obtained by reducing the ceramic particle size. This work investigated the effect of the particle size on the ceramic final density of alumina with 4 wt% niobia. For that two milling media were used. The as-received powders were submitted to ball and planetary milling and then sintered at 1450°C. The planetary milling medium was more efficient in reducing particle size when compared to ball milling. However, planetary milling caused significant contamination in the niobia powder, from the alumina balls used as milling agents. It forced composition balance in order to keep the original proposed formulation. The planetary milled sintered samples showed better densification and lower grain size in comparison with ball milled ones. It could be concluded that the milling medium choice directly affected both microstructure and properties of the sintered alumina with 4wt% of niobia. .

Crystallization of high-strength nano-scale leucite glass-ceramics

ObjectivesFine-grained, high strength, translucent leucite dental glass-ceramics are synthesized via controlled crystallization of finely milled glass powders. The objectives of this study were to utilize high speed planetary milling of an aluminosilicate glass for controlled surface crystallization of nano-scale leucite glass-ceramics and to test the biaxial flexural strength. MethodsAn aluminosilicate glass was synthesized, attritor or planetary milled and heat-treated. Glasses and glass-ceramics were characterized using particle size analysis, X-ray diffraction and scanning electron microscopy. Experimental (fine and nanoscale) and commercial (Ceramco-3, IPS Empress Esthetic) leucite glass-ceramics were tested using the biaxial flexural strength (BFS) test. Gaussian and Weibull statistics were applied. ResultsExperimental planetary milled glass-ceramics showed an increased leucite crystal number and nano-scale median crystal sizes (0.048–0.055μm2) as a result of glass particle size reduction and heat treatments. Experimental materials had significantly (p<0.05) higher mean BFS and characteristic strength values than the commercial materials. Attritor milled and planetary milled (2h) materials showed no significant (p>0.05) strength difference. All other groups’ mean BFS and characteristic strengths were found to be significantly different (p<0.05) to each other. The mean (SD) MPa strengths measured were: Attritor milled: 252.4 (38.7), Planetary milled: 225.4 (41.8) [4h milling] 255.0 (35.0) [2h milling], Ceramco-3: 75.7 (6.8) and IPS Empress: 165.5 (30.6). SignificancePlanetary milling enabled synthesis of nano-scale leucite glass-ceramics with high flexural strength. These materials may help to reduce problems associated with brittle fracture of all-ceramic restorations and give reduced enamel wear.

Crystalline Al1 − x Ti x phases in the hydrogen cycled NaAlH4 + 0.02TiCl3 system

The hydrogen (H) cycled planetary milled (PM) NaAlH4 + 0.02TiCl3 system has been studied by high resolution synchrotron X-ray diffraction and transmission electron microscopy during the first 10 H cycles. After the first H absorption, we observe the formation of four nanoscopic crystalline (c-) Ti-containing phases embedded on the NaAlH4 surface, i.e. Al2Ti, Al3Ti, Al82Ti18 and Al89Ti11, with 100% of the originally added Ti atoms accounted for. Al2Ti and Al3Ti are observed morphologically as a mechanical couple on the NaAlH4 surface, with a moderately strained interface. Electron diffraction shows that the Al82Ti18 phase retains some ordering from the L12 structure type, with the observation of forbidden (100) ordering reflections in the fcc Al82Ti18 lattice. After 2 H cycles the NaAlH4 + 0.02TiCl3 system displays only two crystalline Ti-containing phases, Al3Ti and Al89Ti11. After 10 H cycles, the Al89Ti11 is completely converted to Al85Ti15. Al89Ti11, Al85Ti15 and Al3Ti do not display any ordering reflections, and they are modeled in the A1 structure type. Quantitative phase analysis indicates that the Al3Ti proportion continues to increase with further H cycles. The formation of Ti-poor Al1 − x Ti x (x < 0.25) phases in later H cycles is detrimental to hydrogenation kinetics, compared to the starting Ti-richer near-surface Al2Ti/NaAlH4 interface present during the first absorption of hydrogen.

Hydrogen absorption kinetics and structural features of NaAlH4 enhanced with transition-metal and Ti-based nanoparticles

The hydrogen cycled (H) planetary milled (PM) NaAlH4 + xM (x TiN > TiC > Ti, with rapid hydrogenation kinetics of ca. 23 wt.% H/hour for TiO2 enhanced NaAlH4, equivalent to TiCl3 enhanced NaAlH4. The TiN and TiC are partially reduced by ca. 7 and 22% respectively, and the TiO2 is completely reduced. The location of the reduced Ti cannot be discerned by X-ray diffraction at these minor proportions.

Hydrogen Absorption Kinetics of the Transition-Metal-Chloride-Enhanced NaAlH4 System

This study elucidates the role of transition metal (TM) additives in enhancing hydrogen (H) reversibility and hydrogenation kinetics for the NaAlH4 system. The isothermal hydrogen absorption kinetics of the planetary milled (PM) NaAlH4 + xTMCln (TM row 1 = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu; row 2 = Zn, Y, Zr, Nb, Mo, Ru, Rh Pd; row 3 = Pt; 2 < n < 5) and cryo-milled (CM) NaAlH4 + xTMCln (TM row 1 = Ti, V, Cr, Fe, Co, Ni, Cu; 2 < n < 3) systems have been measured at 140 °C and 150 bar system pressure. The variation in hydrogenation kinetics across the TM series for NaAlH4 + xTMCln is strongly dependent on the TM species and additive level, milling technique, and the type, structure, and morphological arrangement of nanoscopic Al1–xTMx phases that are embedded on the NaAlH4 surface. In the most interesting case, the surface-embedded Al1–xTix phases in the TiCl3-enhanced NaAlH4 system perform a dual catalytic function, where the outer Al1–xTix surface performs dissociation/recombination of molecular H2 and the inner Al1–xTix surface allows the distortion of a minor number of Al–H bonds from AlH4– tetrahedra in the vicinity of the subsurface Al1–xTix/NaAlH4 interface. The density of Ti atoms in the subsurface interface (which is Al:Ti composition- and H cycling temperature-dependent) shows the strongest effects on hydrogenation kinetics.

A structural review of nanoscopic Al1−xTMx phase formation in the TMCln enhanced NaAlH4 system

The twice hydrogen (H) cycled planetary milled (PM) NaAlH4+xTMCln (transition metal (TM)=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Pd, Pt; 2<n<4) and cryo milled (CM) NaAlH4+xTMCln (TM=Ti, V, Cr, Fe, Ni; 2<n<3) systems (x<0.1) have been studied by high resolution synchrotron X-ray diffraction. Face centred cubic (fcc) A1 crystalline (c-) Al1−xTMx (x<0.25) solid solutions are evident in PM samples for Sc, Ti, V, Cr, Mn, Zr and Pd while PM samples of Cu, Ni, Pd and Pt display mostly ordered and numerous crystalline Al1−xTMx phases. Very broad reflections in the 2Å d-spacing region for Cr, Mn, Co, and Pd are identified as partially ordered body centred cubic (bcc) A2 and B2 Al1−xTMx type structures. The amorphous (a-) Al1−xVx phase observed in the H cycled PM NaAlH4+xVCl3 system ranges in composition from a-Al90V10 (x=0.02) up to a-Al72V28 (x=0.1). Across the TM series, the Al1−xTMx particle size ranges as Sc-V 4-25nm, Cr, Mn, Co <5nm, Fe 5–15nm, Ni, Cu <50nm. A highly ‘compressed’ NaAlH4 phase is observed in the H cycled PM NaAlH4+0.1ScCl3 system, with unit cell dimensions of a=4.9995(2)Å and c=11.2893(1)Å, compared to the average dimensions of ‘normal’ NaAlH4 across the TM and rare earth (RE) series with a=5.0228(1)Å and c=11.3516(1)Å.

Amorphous Al1−xTix, Al1−xVx, and Al1−xFex phases in the hydrogen cycled TiCl3, VCl3 and FeCl3 enhanced NaAlH4 systems

The twice hydrogen (H) cycled planetary milled (PM) and cryo milled (CM) NaAlH4+xTMCl3 (transition metal (TM)=Ti, V, Fe) systems (x>0.1) have been studied by high resolution synchrotron X-ray diffraction, and high resolution transmission electron microscopy (TEM). Intense primary amorphous (a-) Al1−xTMx halos are evident in diffraction data of PM samples for V and Fe, and in CM samples for Ti, V, and Fe. Weaker primary amorphous Al1−xTix halos are evident in PM samples for Ti. The Ti poor a-Al1−xTix phase observed for NaAlH4+xTiCl3 (x>0.1) ranges in composition from a-Al86.5Ti13.5→a-Al92Ti8. High resolution TEM studies of the Al1−xVx phases in the H cycled PM NaAlH4+0.1VCl3 system demonstrates that a nanoscopic composite morphology can exist between face centred cubic (fcc) crystalline (c-) Al1−xVx and a-Al1−xVx phases, with the c-Al1−xVx/a-Al1−xVx composite embedded on the NaAlH4 surface. The amorphous Al1−xVx reaches ca. 28at.% V.

Functionality of the nanoscopic crystalline Al/amorphous Al 50Ti 50 surface embedded composite observed in the NaAlH 4 + xTiCl 3 system after milling

The NaAlH 4 + xTiCl 3 ( x < 0.1) system has been studied by a combination of X-ray synchrotron and neutron diffraction, and isotopic H 2/D 2 scrambling after the completion of the milling process, and the first thermal release of hydrogen (H). An in situ X-ray synchrotron diffraction study of the isochronal release of hydrogen from planetary milled (PM) NaAlH 4 + 0.1TiCl 3 shows that crystalline (c-) Al 1− x Ti x phases do not form until almost all H is released from the sample, demonstrating that the surface embedded nanoscopic crystalline Al/amorphous (a-) Al 50Ti 50 composite facilitates the release of H during the very first thermal desorption. Planetary milled (PM) NaAlH 4 + xTiCl 3 is observed to disproportionate at room temperature, with no NaAlH 4 remaining after ca. 200 days. A complete lack of ambient hydrogen release from PM NaAlH 4 + 0.1Al (80 nm) measured over 200 days suggests that the nanoscopic a-Al 50Ti 50 phase is entirely responsible for the hydrogen release during thermal desorption of milled NaAlH 4 + xTiCl 3. Isotopic H/D exchange has been observed by combined neutron and X-ray synchrotron diffraction on a PM NaAlD 4 + 0.04TiCl 3 sample, after exposing the milled sample to 20 bar H 2 at 50 °C for ca. 6 days. Under these pressure/temperature (P/T) conditions, disproportionation of NaAlD 4 is avoided, and ca. 32% of D atoms are exchanged with H atoms. Asymmetrically broadened reflections in the synchrotron data show peak splitting into two unit cell types, one expanded with H, the other remaining close to pure D based unit cell dimensions. The 2-phase model when fitted to the neutron data demonstrates that ca. 56% of D atoms in ca. 58% of all unit cells are exchanged with H, yielding a NaAl(H 0.56D 0.44) 4 composition for the expanded unit cells. HD scrambling (1 bar mixture of H 2 and D 2 at 23 °C) performed on desorbed H empty PM NaAlH 4 + 0.1TiCl 3 shows classic H 2 + D 2 ↔ 2HD equilibrium mixing, demonstrating that nanoscopic Ti containing Al 1− x Ti x surface embedded phases perform a H 2 dissociation/recombination function that unadulterated NaAlH 4 cannot.

The generation of toxic reactive oxygen species (ROS) from mechanically activated sulphide concentrates and its effect on thermophilic bioleaching

Two types of laboratory mills, planetary and vibratory, were used to activate sulphide mineral concentrates mechanically before thermophilic (bio)leaching. These samples were analysed in terms of particle size, surface area, density, SEM, XRD line profile analysis and reactivity. The product particle size distributions indicated different particle breakage mechanisms of the two mills. The surface area for pyrite milled with the planetary mill was three fold that milled in the vibratory mill for the same length of time. Planetary milled samples showed lower densities, up to 4% less for pyrite samples, compared to vibratory milled samples. Particle surface oxidation, observed by SEM, occurred post milling. Surface oxidation products were more prevalent with planetary milled sulphide samples. XRD line profile analysis showed more line broadening effects with the planetary mill. This indicated that more bulk particle-related structural defects were present in the planetary milled samples. The reactivity in acidic solution was measured in terms of the generation of toxic reactive oxygen species (ROS): hydrogen peroxide and hydroxyl radicals. The ROS generation from milled sulphides, normalised to constant surface area loading, increased with increased mechanical activation. The planetary milled samples generated greater ROS per sample surface area than vibratory milled samples, more than 4-fold for pyrite after 60 min of milling. Increased ROS generation was postulated to result from increased surface area defects, solubilisation of iron oxidation products and bulk particle-related defects. The effect of mechanical activation on performance on thermophilic leaching and bioleaching tests was investigated using milled samples at 2% (w/v) pulp density. Short mill times improved leach rates from both mills, up to 7-fold cf. unactivated feed leach rates. Poor bioleaching performance resulted following long periods of mechanical activation (20–60 min). Pyrite and chalcopyrite bioleaching performance decreased dramatically above surface area loadings of 25 and 125 m 2/L respectively. Planetary milled samples were less amenable to bioleaching. For pyrite milled for 20 and 60 min and chalcopyrite milled for 40 min, no viable cells were observed following inoculation via fluorescence microscopy, suggesting culture death supported by compromised ferrous iron oxidation. The generation of ROS was postulated to cause poor bioleaching performance under these conditions.

Effect of addition of planetary milled Gd-211 on the microstructures and superconducting properties of air-processed single grain Gd–Ba–Cu–O/Ag bulk superconductors

Planetary milling technique has been a very promising way to obtain bulk superconductors with very high critical current density, Jc, albeit a detail characterisation of milled secondary phase precursor powders in particular has not been reported to date. Hence we report systematic studies of the effect of addition of planetary milled Gd2BaCuO5 (Gd-211) on the final microstructures and superconducting properties of air-processed Gd–Ba–Cu–O/Ag bulk samples. Average size of Gd-211 precursor particles, which were planetary milled with 1.0mm ZrO2 beads, has been observed to decrease significantly from 1.03μm to 0.52μm with increasing milling duration. Besides the size distribution of milled Gd-211 was narrow compared to that of the reference powder. A small amount of Zr was detected, however, in the milled Gd-211 powder by the inductively coupled plasma-optical emission spectroscopy (ICP-OES) and its content was increased with increasing milling period, which led to an inhomogeneous bulk microstructure. Significantly, the average size of Gd-211 particles milled for 45min has been observed to decrease from 0.73μm to 0.48μm without severe contamination of Zr when the diameter of the beads were reduced from 1.0mm to 0.3mm. Trapped magnetic field of single grain Gd–Ba–Cu–O/Ag bulk sample with 32mm in diameter prepared from almost Zr free Gd-211 fine particles recorded over 1.5T at 77K, which was almost 1.3 times greater than that of the reference sample. Nevertheless the repulsive force of both bulk samples showed around 57N at a gap of zero between the sample surface and SmCo5 permanent magnet.

Mechanically Activated Combustion Synthesis of β‐Si6−zAlzOzN8−z (z=1–4)

Fine β‐sialon (Si6−zAlzOzN8−z, 1&lt;z&lt;4) was prepared by mechanical‐activated combustion synthesis (CS) using raw materials such as Si, Al, and SiO2 in a nitriding atmosphere of 1 MPa. Mechanical activation by planetary milling for only 18 min led to the formation of β‐sialon after combustion synthesis. Comparative experiments with ball milling showed that the relative amount of β‐sialon was considerably increased to 66% when planetary milled to 18 min after CS. The raw material Si was replaced by waste Si of 94.8 mass% in purity, and was combustion synthesized successfully under the same processing parameters for cost‐effective measures.

XRD Line Broadening Analysis with Ball Milled Palladium

Palladium powder was deformed by ball milling under an argon atmosphere in two types of mills for different milling times. Two methods for X-ray diffraction line profile analysis, the Williamson-Hall method and the Warren-Averbach method, yielded similar trends, but different quantitative results for crystallite sizes (column lengths) and microstrains. With both methods, from the anisotropic line broadening for planetary milled Pd smaller crystallite sizes and larger microstrains were obtained along the &lt;100&gt; direction than along &lt;111&gt;. Milling in a shaker mill causes microstrain higher by a factor of about two than milling in a planetary mill. The evolution of the crystallite size upon milling was discussed in terms of bimodal size distributions.

Fabrication of Nano-sized Titanate Powder via a Polymeric Steric Entrapment Route and Planetary Milling Process

Pure and nano-sized TiO₂ and CaTiO₃ powders were fabricated by a polymeric steric entrapment route and planetary milling process. An ethylene glycol was used as a polymeric carrier for the preparation of organic-inorganic precursors. Titanium isopropoxide and calcium nitrate were dissolved in liquid-type ethylene glycol without any precipitation. At the optimum amount of the polymer, the metal cations were dispersed in solution and a homogeneous polymeric network was formed. The dried precursor ceramic gels were turned to porous powders through calcination process. The porous powders were crystallized at low temperatures and the crystalline powders were planetary milled to nano size.

遊星ボールミル処理したアルミナ粉末のコンタミネーションと焼結性

The contamination of planetary milled alumina powder has been studied and correlated to sinterability. The powder contained Si-and N-contaminations caused by the wear from the grinding media and mill wall made of Si3N4. A part of worn-out Si3N4 was oxidized into Si(OH)4 by H2O contained in CH3OH used as the grinding liquid. The strong shear stress between the media generated during planetary milling promoted mechanochemical reactions among worn-out Si3N4, Si(OH)4 and Al2O3 forming an amorphous reaction layer on the alumina particles. This provided possibilities of planetary milling by applying the surface modification of ceramic powders despite the problem of contamination. The surface layer containing the contaminations resulted in the formation of the mullite phase at the grain boundary during sintering. The low diffusion coefficient of the mullite phase degraded sinterability even at a contamination as low as 400ppm-Si. When the contamination increased to 0.5wt%-Si, irregular grain growth and the formation of closed pores took place, suggesting the degradation of the mechanical properties.