Physico-chemical aspects of grinding: a review of use of additives

In Situ Formation of Li2SiO3-Li-NaCl Interface on Si and Its Effect on Hydrogen Evolution

Silicon has emerged as a competitive candidate for hydrolytic hydrogen production due to its high theoretical hydrogen yield, low cost, and on-demand availability. However, the hydrolysis reaction is extremely restrained by passivated SiO₂, including the original one on the Si surface and the generated one during hydrolysis, and almost no hydrogen is produced in pure water. Herein, the original SiO₂ surface has been effectively removed by milling micro-Si mixed with a small amount of Li metal and NaCl. An artificial soluble interface on Si has been established containing Li₂SiO₃, Li, and NaCl. Once micro-Si is placed into water, fresh Si surface can be exposed and a weak LiOH solution can be generated due to the fast dissolution of the interface layer, resulting in the rapid liberation of hydrogen gas. Accordingly, the modified micro-Si displays a significantly enhanced hydrogen production in pure water at 30 °C (1213 mL g^-1 H₂ within 3.0 h), which is 2.0 and 4.7 times higher than that observed for ball-milled Si and raw Si in 0.06 M LiOH solution, respectively. In addition, it also exhibited an outstanding operation compatibility for practical uses. This work has proposed a green, effective, and scalable strategy to promote hydrogen production from the hydrolysis of Si-based systems.

Bhavana, an Ayurvedic Pharmaceutical Method and a Versatile Drug Delivery Platform to Prepare Potentiated Micro-Nano-Sized Drugs: Core Concept and Its Current Relevance

Scholars of ancient Ayurveda (Indian system of medicine) were extremely reasonable and had strong scientific rationality in fundamental concepts, which are also applied to drug manufacture and therapy. Bhavana is a unique traditional method of transformation of raw material/substances into the drug by levigation or wet grinding of powdered drugs with juice/decoction/solution of plant, animal, or mineral origin. This method adds the unique capability of affecting the physicochemical and biological properties of a drug, making the drug quicker, augmented, and persistent action with minimal dose. Despite the fact that Bhavana has a wide range of applications in Ayurvedic pharmaceutics, there is only a limited amount of knowledge of its fundamental notions. A comprehensive review was performed on the core concepts of Bhavana, alongside its possible pharmacotherapeutic effects and relevance in drug development, by probing Ayurvedic claims in light of published pharmaceutical, analytical, and pharmacological reports. Various processes, such as thermo- and photochemistry, physicochemical reactions, and mechanic chemical changes, appear to occur during Bhavana.

Study on Grinding Additives in Cassiterite–Polymetallic Sulfide Ore Grinding

To attempt a new approach to improve the grinding of cassiterite–polymetallic sulfide ores while simultaneously reducing cassiterite overgrinding and sulfide undergrinding, this article looked into the effects of grinding chemical additives on the distribution of grinding product size. Six chemicals, namely sodium hexametaphosphate, triethanolamine, ferric sulphate, aluminum chloride, polyaluminum chloride and polyacrylamide, were compared in terms of their influence on the grinding product size distribution. The results showed that the six chemicals changed the distribution results with varying orientations and degrees and that the addition of polyacrylamide achieved the most satisfactory effect by decreasing the production of both coarse and fine size fractions and increasing the production of qualified particles. The effect of the molecular weight of polyacrylamide on the grinding was also discussed. The polyacrylamides with molecular weights of about 3 × 106, 5 × 106, 8 × 106 and 12 × 106 could help to produce less of the coarse size fraction and more of the qualified size fraction, but only the polyacrylamides with molecular weights of 3 × 106 and 5 × 106 produced pronounced changes. Moreover, the polyacrylamides could slightly reduce the production of the fine size fraction. Polyacrylamide with a 5 × 106 molecular weight was better than that with a 3 × 106 molecular weight in aiding the grinding of the discussed ore. It was also found that the aid action of the polyacrylamide with a 5 × 106 molecular weight was related to grinding concentration and that a low grinding concentration of less than 70% solid mass was helpful in exerting its aid action. Using polyacrylamide could shorten the grinding time that is needed to achieve the same, or even improved, product size distribution.

Effect of Rotational Speed and Gap between Rotating Knives of the Grinder on the Yield Stress and Water-Binding Capacity of Fine Ground Chicken Bone

This article presents the results of the study of the dependence of yield stress (YS) and water-binding capacity (WBC) on mechanical processing of meat and bone raw materials when changing the rotational speed and the gap between the rotary knives of the grinder. It is revealed that the parameters of YS and WBC also increase when the rotational speed increases. Thus, the highest values of YS (943.29 Pa) and WBC (66.98%) are observed when the rotary knives’ rotational speed is 4000 min−1 and the clearance between knives is 0.16 mm, while the lowest values of YS (635.87 Pa) and WBC (63.83%) are observed when the knives’ rotational speed is 1000 min−1 and the clearance is 0.38 mm. The power consumption of the electric motor of the unit increases as the rotation speed of the working bodies increases and the gap between the knives decreases.

Energy Efficiency Analysis of Copper Ore Ball Mill Drive Systems

Milling is among the most energy-consuming technological stages of copper ore processing. It is performed in mills, which are machines of high rotational masses. The start of a mill filled to capacity requires appropriate solutions that mitigate the overloading. One method for increasing the energy efficiency of ball mills is to optimize their drive systems. This article looks at two variants of drive systems with efficiencies higher than the already existing solutions. The first variant is a low-speed synchronous motor with permanent magnets without a gearbox, and the second variant is an asynchronous high-efficiency motor with a gearbox and a fluid coupling. The energy performance analysis of the three solutions was based on the average energy consumption indicator per mass unit of the milled material and on the energy consumption per hour. The investigations required models of the drive systems and analyses with the use of the Monte Carlo methods. The highest energy efficiency is observed in the case of the solution based on the permanent magnet motor. However, the drive system with the high-speed motor offers a gentle start-up possibility owing to the fluid coupling.

An experimental assessment on the performance of different lubrication techniques in grinding of Inconel 751

The application of emulsion for combined heat extraction and lubrication requires continuous monitoring of the quality of emulsion to sustain a desired grinding environment; this is applicable to other grinding fluids as well. Thus to sustain a controlled grinding environment, it is necessary to adopt an effectively lubricated wheel-work interface. The current study was undertaken to assess experimentally the ​ effects of different grinding environments such as dry, minimum quantity lubrication (MQL) and Cryo-MQL on performance, such as grinding force, temperature, surface roughness and chip morphology on Inconel 751, a higher heat resistance material posing thermal problems and wheel loading. The results show that grinding with the combination of both liquid nitrogen (LN₂) and MQL lowers temperature, cutting forces, and surface roughness as compared with MQL and dry grinding. Specific cutting energy is widely used as an inverse measure of process efficiency in machining. It is found from the results that specific cutting energy of Cryo-MQL assisted grinding is 50–65% lower than conventional dry grinding. The grindability of Inconel 751 superalloy can be enhanced with Cryo-MQL condition.

Synthesis of nanoparticles from malleable and ductile metals using powder-free, reactant-assisted mechanical attrition

A reactant-assisted mechanochemical method was used to produce copious nanoparticles from malleable/ductile metals, demonstrated here for aluminum, iron, and copper. The milling media is intentionally degraded via a reactant-accelerated wear process, where the reactant aids particle production by binding to the metal surfaces, enhancing particle production, and reducing the tendency toward mechanochemical (cold) welding. The mechanism is explored by comparing the effects of different types of solvents and solvent mixtures on the amount and type of particles produced. Particles were functionalized with oleic acid to aid in particle size separation, enhance dispersion in hydrocarbon solvents, and protect the particles from oxidation. For aluminum and iron, the result is air-stable particles, but for copper, the suspended particles are found to dissolve when exposed to air. Characterization was performed using electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, solid state nuclear magnetic resonance, and X-ray photoelectron spectroscopy. Density functional theory was used to examine the nature of carboxylic acid binding to the aluminum surface, confirming the dominance of bridging bidentate binding.

Continuous production of drug nanoparticle suspensions via wet stirred media milling: a fresh look at the Rehbinder effect

Nanoparticles of BCS Class II drugs are produced in wet stirred media mills operating in batch or recirculation mode with the goal of resolving the poor water-solubility issue. Scant information is available regarding the continuous production of drug nanoparticles via wet media milling. Griseofulvin and Naproxen were milled in both recirculation mode and multi-pass continuous mode to study the breakage dynamics and to determine the effects of suspension flow rate. The evolution of the median particle size was measured and described by an empirical breakage model. We found that these two operation modes could produce drug nanosuspensions with similar particle size distributions (PSDs). A reduced suspension flow rate slowed the breakage rate and led to a wider PSD and more differentiation between the two operation modes. The latter part of this study focused on the roles of stabilizers (hydroxypropyl cellulose and sodium lauryl sulfate) and elucidation of the so-called Rehbinder effect (reduction in particle strength due to adsorbed stabilizers such as polymers and surfactants). Milling the drugs in the absence of the stabilizers produced primary nanoparticles and their aggregates, while milling with the stabilizers produced smaller primary nanoparticles with minimal aggregation. Using laser diffraction, BET nitrogen adsorption, scanning electron microscopy imaging, and a microhydrodynamic analysis of milling, this study, for the first time, provides sufficient evidence for the existence of the Rehbinder effect during the milling of drugs. Not only do the polymers and surfactants allow proper stabilization of the nanoparticles in the suspensions, but they also do facilitate drug particle breakage.