Milling Jar Research Articles

Reliable Mechanochemistry: Protocols for Reproducible Outcomes of Neat and Liquid Assisted Ball-mill Grinding Experiments.

The equilibrium outcomes of ball mill grinding can dramatically change as a function of even tiny variations in the experimental conditions such as the presence of very small amounts of added solvent. To reproducibly and accurately capture this sensitivity, the experimentalist needs to carefully consider every single factor that can affect the ball mill grinding reaction under investigation, from ensuring the grinding jars are clean and dry before use, to accurately adding the stoichiometry of the starting materials, to validating that the delivery of solvent volume is accurate, to ensuring that the interaction between the solvent and the powder is well understood and, if necessary, a specific soaking time is added to the procedure. Preliminary kinetic studies are essential to determine the necessary milling time to achieve equilibrium. Only then can exquisite phase composition curves be obtained as a function of the solvent concentration under ball mill liquid assisted grinding (LAG). By using strict and careful procedures analogous to the ones here presented, such milling equilibrium curves can be obtained for virtually all milling systems. The system we use to demonstrate these procedures is a disulfide exchange reaction starting from the equimolar mixture of two homodimers to obtain at equilibrium quantitative heterodimer. The latter is formed by ball mill grinding as two different polymorphs, Form A and Form B. The ratio R = [Form B] / ([Form A] + [Form B]) at milling equilibrium depends on the nature and concentration of the solvent in the milling jar.

Comminution-amorphisation relationships during ball milling of lactose at different milling conditions

The purpose of the study was to investigate the relationship between comminution and amorphisation of α-lactose monohydrate particles during ball milling under different milling conditions, including ball-to-powder mass ratio, milling time and ball diameter. The results revealed that at a constant ball filling ratio, ball-to-powder mass ratio of 25:1 resulted in the lowest minimum particle diameter of ∼5μm and the highest degree of apparent amorphous content of 82%. The rate of comminution was high during early stage of milling whereas the degree of apparent amorphous content increased gradually at a slow rate. An increased ball-to-powder mass ratio during milling increased both the rate of comminution and the rate of amorphisation. Using a given ball-to-powder mass ratio, the ball diameter affected the degree of apparent amorphous content of the particles while the particle diameter remained unchanged. The relationship between comminution and amorphisation could be described as consisting of two stages, i.e. comminution dominated and amorphisation dominated stage. It was proposed that the rate constant of comminution and amorphisation are controlled by stress energy distribution in the milling jar and the stress energy distribution is regulated by the ball motion pattern that can be affected by the process parameter used.

Improved production efficiency of mesoporous silicon nanoparticles by pulsed electrochemical etching

The nanoparticles produced by top down methods possess typically considerably wide size distributions. However, monodispersive nanoparticle suspensions are essential for many applications. This is also true for mesoporous silicon nanoparticles, which can be produced by grinding the electrochemically anodized porous films in planetary ball mills. Herein, we report a method to control the particle size of porous silicon nanoparticles already prior to the milling. The method is based on fragile layers that are produced in the porous silicon film by repetitive pulsed electrochemical etching during porosification of silicon. The thin fragile layers separating the layers with normal porosity in the porous films guide the breakage of the films preferentially into the particle size corresponding to the distance of the adjacent fragile layers. The production method was evaluated in terms of the yield and particle size distributions. The distance of 173nm between the fragile layers increased substantially the yield of the corresponding nanoparticle sizes (122nm) with the short milling time of 2min. The milling was performed with an insert located in the normal milling jar so that glass vials could be used with smaller sample sizes. The present study paves the way for more effective production of mesoporous silicon nanoparticles which is applicable also for other corresponding nanomaterials.

Synthesis of tungsten nanopowders: Comparison of milling, SHS, MASHS and milling-induced chemical processes

Synthesis of tungsten nanopowders was studied using milling of micrometric tungsten, then using the WO3–Mg thermitic reaction, using SHS (Self-propagating High-temperature Synthesis), milling induced chemical reaction (MICR), and MASHS (Mechanically Activated SHS). Reactions are studied by measuring temperature and pressure inside the milling jar (during MICR), or by analyzing the temperature profile along the sample during the reaction propagation by infrared thermography (SHS, MASHS). After reaction, samples were analyzed by AFM or SEM, by XRD, and BET. MASHS seems to possess optimum conditions with a pre-milling before SHS of 10min, which yielded the highest tungsten purity, together with a grain size corresponding to our aim.

Advances in elucidating mechanochemical complexities via implementation of a simple organic system.

Mechanochemistry is becoming increasingly popular amongst both the academic and industrial communities as an alternative method for inducing physical and chemical reactions. Despite its rapidly expanding application, little is understood of its mechanisms, greatly limiting its capacity. In the present work the application of specialty devices allowed submission of the simple organic system, α-glycine + β-malonic acid, to isolated shearing and impact treatment. In doing so, unique products were observed to result from each of these major mechanical actions; shear inducing formation of the known salt, glycinium semi-malonate (GSM), and impact yielding formation of a novel phase. Correlation of these isolated treatments with a more common ball mill indicated two unique regions within the milling jar, each characterised by varying ratios of shear and impact, leading to different products being observed. It is widely accepted that, particularly when considering organic systems, mechanical treatment often acts by inducing increases in local temperature, leading to volatilisation or melting. A combination of DSC and TGA were used to investigate the role of temperature on the system in question. Invariably, heating induced formation of GSM, with evidence supporting a eutectic melt, rather than a gas-phase reaction. Shear heating alone is unable to describe formation of the novel phase obtained through impact treatment. By considering the formation and character of mechanically produced tablets, a model is described that may account for formation of this novel phase. This system and methodology for mechanochemical study offers intriguing opportunities for continued study of this widely used and exciting field.

Complexities of mechanochemistry: elucidation of processes occurring in mechanical activators via implementation of a simple organic system

There is, at present, a substantial lack of mechanistic-level understanding of mechanochemical processes, despite their current widespread use. The system α-glycine + β-malonic acid was previously shown to adhere to divergent reaction pathways under mechanical treatment. In the present study, this system's complexity was further amplified when mechanical treatment was observed to yield yet another divergent reaction path, producing either a known salt, glycinium semi-malonate (GSM), or what is at present an unidentified phase. Isolating the two major mechanical “actions” – impact and shear – it was observed that each of these treatments favours a different product; shear yielding GSM and impact inducing production of the novel phase. Combination of isolated treatments with milling studies demonstrated two distinct regions within the milling jar, the jar ends and the jar shaft. While sample located in the latter undergoes larger amounts of shear treatment, sample located in the former is privy to both shearing and impact, depending on both its ability to tablet and the geometry with which this tablet forms. Following tablet formation, in which the major stress appears to be shear, sample located in the milling jar ends is subsequently treated by pure impact. This study offers unique insights towards a mechanistic understanding of mechanochemistry and its processes.

A STUDY ON THE SYNTHESIS OF ULTRA-FINE IN SITUNi3Al–Al2O3/TiC COMPOSITE POWDER

Titanium carbide ( TiC ) has a low density, relatively high thermal and electrical conductivity. TiC is also very stable, with a melting temperature of 3100°C and does not undergo phase transformations. These properties have attraction to apply cutting tool extensively. Recently, in order to improve the properties of cermet tool materials, most researches have been carried out on the development of new binder. Ni3Al intermetallic is an interesting material because it has a great advantage of application for some structural materials, especially at the high temperatures. Ni3Al has low density, high strength and good corrosion resistance properties, which recommend them for the application of high temperature structural material. In this study, we had investigated the effects of mechanical alloying time and annealing temperature on the Ni3Al–Al2O3/TiC phase formation. Raw powders to fabricate Ni3Al–Al2O3/TiC composite powders were Ni , Al , TiH2 and activated carbon. These powders were ball-milled in planetary milling jar in argon atmosphere. Ball-milled powders were annealed up to 1200°C in Ar + 4%H2 atmosphere. The mean particle size of 300 nm was obtained after 10 h ball-milling. Ni3Al–Al2O3/TiC composite powders were formed by annealing for 1 h over 1100°C.

Effects of wet ball milling on lead stabilization and particle size variation in municipal solid waste incinerator fly ash

Water-extracted municipal solid waste incinerator (MSWI) fly ash was treated by a process of wet ball milling, using desalinated water as the milling solution. We investigated the influence of the milling process on the partitioning and leaching characteristics of lead (Pb) and the particle size distribution. The results show that 93.11% of the Pb was partitioned into the milled ash, 2.60% to the milling balls, and 0.17% to the inner surface of the milling jar, while amounts lower than the detection limit remained in the milled solution. As tested by the toxicity characteristic leaching procedure (TCLP), the leaching of Pb was inhibited after short-term grinding (from 5.2 to 1.2 mg/L after 1 h of milling), and further reduced by about 96% after 96 h of ball milling. The mobility of the heavy metal was analyzed after a sequential extraction procedure. The results also show that Pb tended to become more stable after milling. The size distribution of particles was analyzed by a laser particle diameter analyzer and their morphology during grinding was observed using scanning electron microscopy. The median size of the fly ash decreased significantly from 36 to 5 μm after 0.5 h of milling, but then only slightly, from 5 to 2 μm, with further milling from 0.5 to 96 h, due to the concurrent actions of fragmentation and/or agglomeration. The reason for the stabilization of Pb by ball milling was probably that Pb was sealed in the milled fly ash during the fragmentation and agglomeration of particles.

Extensive Dry Ball Milling of Wheat and Rye Bran Leads toin SituProduction of Arabinoxylan Oligosaccharides through Nanoscale Fragmentation

This study investigated the potential of ball milling as a dry process for in situ production of arabinoxylan oligosaccharides (AXOS) in arabinoxylan (AX)-rich wheat and rye bran. An extensive lab-scale ball mill treatment (120 h, 50% jar volume capacity) increased the wheat bran water-extractable arabinoxylan (WE-AX) level from 4% (untreated bran) to 61% of the wheat bran AX. Extractable AX fragments had an arabinose/xylose ratio (A/X ratio) of 0.72 and a molecular mass (MM) of 15 kDa. Ball milling of rye bran gave rise to similar results, with the A/X ratio of the extractable AX being considerably lower (0.51). Optimization of the ball mill treatment by varying the degree of filling of the milling jar permitted us to obtain equally high WE-AX levels (>70%) in wheat and rye bran within a 24 h ball-milling period. Ball milling at optimal conditions (24 h, 16% jar volume capacity) yielded wheat bran AXOS, with an A/X ratio of 0.65 and a MM of 6 kDa. Ball milling (24 h, 50% jar volume capacity) of pericarp-enriched wheat bran increased the WE-AX level from 1% (untreated pericarp) to 63%. The extractable material had a high A/X ratio (0.97) and a low MM (5 kDa). Fluorescence microscopy revealed that the extensive ball mill treatment led to the almost complete disappearance of discernible tissue structures in the ball-milled material, indicating bran particle size reductions down to the nanoscale level. It further visualized the aggregation of the treated material. These results show that AXOS can be produced in situ from wheat or rye bran in a single-stage dry milling process, rendering a wet extraction step redundant. The higher A/X ratio of the obtained AXOS than of enzymically produced wheat bran-derived AXOS offers perspectives for the production of a wide range of AXOS structures. Moreover, ball milling makes upgrading of the low-value pericarp layer feasible.

Synthesis of Titanium Carbide Nano Particles by the Mechano Chemical Process

Titanium carbides are widely used for cutting tools and grinding wheels, because of their superior physical properties such as high melting temperature, high hardness, high wear resistance, good thermal conductivity and excellent thermal shock resistance. The common synthesizing method for the titanium carbide powders is carbo-thermal reduction from the mixtures of titanium oxide(<TEX>$TiO_2$</TEX>) and carbon black. The purpose of the present research is to fabricate nano TiC powders using titanium salt and titanium hydride by the mechanochemical process(MCP). The initial elements used in this experiment are liquid <TEX>$TiCl_4$</TEX>(99.9%), <TEX>$TiH_2$</TEX>(99.9%) and active carbon(<<TEX>$32{\mu}m$</TEX>, 99.9%). Mg powders were added to the <TEX>$TiCl_4$</TEX> solution in order to induce the reaction with Cl-. The weight ratios of the carbon and Mg powders were theoretically calculated. The TiC and <TEX>$MgCl_2$</TEX> powders were milled in the planetary milling jar for 10 hours. The 40 nm TiC powders were fabricated by wet milling for 4 hours from the <TEX>$TiCl_4$</TEX>+C+Mg solution, and 300 nm TiC particles were obtained by using titanium hydride.

Effects of lifter bars on the ball motion and aluminum foil milling in tumbler ball mill

Effects of lifter bars on the ball motion during ball milling and characteristics of aluminum flake powders prepared by the ball milling of aluminum foil scraps were studied. When rotation speed of milling jar without lifter bar is below 75% of critical revolutions per minute (rpm), balls slide in the jar. As rotation speed of milling jar increases up to 93% and 140%, the mode of balls motion changes to cascading and cataracting type, respectively. By setting even one lifter bar in the jar, balls move as cascading mode and cataracting mode at 37% and 56% of critical rpm, respectively. As number of lifter bars increases, the necessary rotation speeds of milling jar for cascading mode and cataracting mode decrease drastically. The aluminum foils scrap was milled in the milling jar with four lifter bars and without lifter bar under the rotation speeds of jar corresponding to cascading and cataracting modes. That result shows that it is possible to achieve same quality of milled fine powder by using lifter bars even under the significantly lower rotation speeds of jar.