Centrifugal Ball Mill Research Articles

Analytical Evaluation of Wet and Dry Mechanochemical Syntheses of Calcium-Deficient Hydroxyapatite Containing Zinc Using X-ray Diffractometry and Near-Infrared Spectroscopy.

Calcium-deficient zinc-containing calcium phosphate (ZnAP), which has sustained zinc release properties that are effective for treating osteoporosis, can be efficiently synthesized as a biomaterial through wet grinding. To elucidate the physicochemical mechanism of these mechanochemical syntheses, ground products were obtained from the starting material powder (S-CP), consisting of calcium hydrogen phosphate dihydrate (CHPD), calcium oxide (CaO), and zinc oxide (ZnO), by wet and dry grinding for 0–3 h in a centrifugal ball mill. The ground S-CP products were analyzed using powder X-ray diffraction (XRD) and near-infrared spectroscopy (NIRS); the crystal transformations and molecular interactions of the ground products were kinetically analyzed. The XRD and second-derivative NIRS results indicate that the S-CP is primarily transformed into ZnAP via amorphous solid formation in wet grinding, and the reaction follows a consecutive reaction model. In contrast, in dry grinding, the ground product of CHPD and CaO is transformed into an amorphous solid following an equilibrium reaction model; however, ZnO is predominantly not transformed and remains crystalline.

Влияние механической активации порошка вольфрама на структуру и свойства спеченного материала SN-CU-CO-W

Introduction. One of the methods for improving the properties of sintered materials is mechanical activation of powders. It ensures milling the powders, changing its energy state, intensifying the sintering of powder materials, and forming a fine-grained structure in it. When tungsten powders are mechanically activated in planetary centrifugal mills, nanoparticles can be formed, which have a high reactive power. The objective of the paper is to study the effect of mechanical activation of tungsten particles on the structure and properties of the sintered Sn-Cu-Co-W powder material. Research technique: Mechanical activation of W16,5 grade tungsten powder is carried out in a planetary centrifugal ball mill AGO-2U for 5…120 minutes with carrier speeds of 400…1,000 rpm. The mixture of tungsten, tin, copper, and cobalt powders are compacted by static pressing in molds and then sintered in vacuum at 820 °C. The morphology and size of powder particles, as well as the structure of the sintered samples, are studied by scanning electronic microscopy, X-ray microanalysis, and optical metallography. Porosity of the sintered samples is identified by the gravimetric method. Microhardness of the structural constituents and macrohardness of the sintered materials are measured, too. Results: in the modes under study, mechanical activation is accompanied by the formation of tungsten nanoparticles with the minimum size of 25 nm. Alongside this, the powder is exposed to cold working, which hinders further milling. Tungsten nanoparticles, characterized by high surface energy, have a significant effect on the dissolution-precipitation of cobalt during liquid-phase sintering of Sn-Cu-Co-W powder material. Addition of nanodispersed tungsten into the material slows down the growth of cobalt particles during sintering and contributes to the formation of a fine-grained structure. The sintered Sn-Cu-Co-W material, containing mechanically activated tungsten, features higher hardness of 105…107 HRB, which is explained by cold working of tungsten particles and dispersion hardening. The results can be applied for improving mechanical properties of Sn-Cu-Co-W alloys used as metallic binders in diamond abrasive tools.

Influence of compaction pressure and Si3N4/ZrO2 reinforcement on the properties of aluminium hybrid composites

ABSTRACT In the present study, the aluminium hybrid composites (AHCs) are developed by the powder metallurgy method. Pure aluminium is reinforced with varying weight percentages of ceramic reinforcements (Si3N4 and ZrO2). Pure aluminium powder is mixed with 3 wt% Si3N4 and (0, 1.5, 3 and 4.5 wt%) ZrO2 powder in a centrifugal ball mill at a high speed of 600 rpm for 2.5 hours. The XRD results of the AHC powders shows that no interfacial reaction takes place during the ball milling process. The powder composites are then compacted at three different compaction pressure (340,420 and 500MPa) and sintered in a tube furnace at 500 °C for 30 minutes under an Argon environment. The SEM results of different composites show that the reinforcement and matrix particles are distributed uniformly with the accumulation of nano-size ZrO2 particles. The density and micro-hardness improve with high compaction pressure and weight percentages of the reinforcements but the porosity decreases. The maximum hardness value is found as 72 VHN for sample E (Al+3 wt% Si3N4 + 4.5 wt% ZrO2) at 500 MPa.

Analysis and prediction of the tensile strength of aluminum alloy composite using statistical and artificial neural network technique

In this research work, aluminum alloy (Al-20Fe-5Cr) matrix-based aluminum oxide (Al2O3) reinforced composites were developed through the powder metallurgy (P/M) process. Effect of compaction pressure (200, 250 & 300 MPa) and wt.% of Al2O3 (0, 10, 20 & 30 wt.) on tensile strength and percentage elongation has been analyzed through statistical and artificial neural network techniques (ANN). The mixture of Al-alloy powder particles and Al2O3 particles were synthesized in a centrifugal ball mill for 20 min. Compaction of synthesized powder was carried in the standard tensile die using a uniaxial hydraulic pressing machine. Sintering was performed at temperature 580 ± 20 °C for one hour in an argon gas environment using an electric tubular furnace. It was found that tensile strength enhanced significantly with the addition of Al2O3up to 20 wt.% and then declined sharply for the 30 wt.% of Al2O3at all compaction pressures. The highest tensile strengths were found for each wt.% of Al2O3 at compaction pressure 300 MPa compare to other compaction pressures. Tensile strength increased from 105 to 158 MPa with the addition of 20 wt.% Al2O3 and decreased to 142 MPa for 30 wt.% at 300 MPa compaction pressure. The improvement resulted from better compaction, leading to more plastic deformation, better packing, and high effective contact area. However, the percentage of elongation decreased from 23.2% to 2.2% with an increment of wt.% of Al2O3 for compaction pressure 200 MPa, while for 300 MPa, its value drops from 25.8% to 6.5%. This depreciation can be reasoned for the reduction in ductile matrix content and dilute flowability of the Al matrix, which occurred due to brittle Al2O3. The statistical analysis using ANOVA revealed that the compaction pressure is the primary control factor influencing tensile strength by 90.3%. The feed-forward network with a back-propagating gradient-descent error minimization training approach and mean squared error (MSE) as performance function was employed to model and predict tensile strength. The developed 3-layered multilayer perceptron (MLP) with 2–10–2 network architecture established a correlation between the inputs and outputs with minimum error (MSE) below 1% and maximum correlation coefficient (R) close to 1.

Synthesis of La2Zr2O7 by thermal treatment of mechanically activated salt mixture

A lanthanum zirconate La2Zr2O7 was synthesized by soft mechanochemical method using zirconium oxynitrate ZrO(NO3)2·6H2O and lanthanum carbonate La2(CO3)3·8H2O as reagents. Mechanical activation of the reagents was carried out in a centrifugal planetary ball mill. The processes occurring during calcination of the jointly and the separately mechanically activated salt mixture were studied using DSC, TG coupled with mass spectrometry, XRD analysis, and FTIR spectroscopy. It was shown that in the course of joint mechanical activation in the mill alongside with intimate mixing of the reagents and their amorphization exchange reaction occurred, producing lanthanum nitrate, basic lanthanum nitrate, basic zirconium carbonate, and hydrated zirconium oxide. The DSC curve of the jointly mechanically activated salt mixture showed a strong exothermic peak at 878 °C which was not associated with mass loss. This peak was attributed to La2Zr2O7 crystallization in agreement with XRD data. Nanocrystalline lanthanum zirconate synthesized by annealing of the jointly mechanically activated salt mixture was characterized using XRD analysis, scanning, and transmission electron microscopy.

Microstructure and properties of surface-modified tungsten powders mechanically activated in different media

The results of an experimental-theoretical study of the effect of thin-film coatings on residual microstrains, microstresses, and local microdistortions of the atomic structure of powder tungsten mechanically activated in the centrifugal ball mill have been presented. It has been shown that microdistortions of the crystal structure of different system-hierarchical levels arise in the surface-oxidized powders, which increase with an increase in the time of the activation process. It has been shown that this should lead to a significant increase in the reactivity of the mechanically activated powder tungsten. In contrast, the adsorption films that plasticize the near-surface layer of particles can decrease the efficiency of the mechanoactivation process of the tungsten powder.

Mechanically Activated Chemical Conversion of Gaseous Hydrocarbons

Propane-butane gaseous mixtures were subjected to mechanical treatment in centrifugal ball mill in the absence or presence of some mineral particles. It was found that the composition of gas mixture was changed significantly depending on duration of the mechanical coercion and solid or porous nature of mineral additives. The mechanical treatment of light hydrocarbons in the presence of quartz particles at the temperatures not exceeding 100 °C resulted at long last in complete conversion of initial organic compounds to methane, hydrogen and small amounts of carbon. The same alterations of gas composition were lesser profound when the mechanical treatment was carried out in the absence of minerals or in the presence of porous silica gel or aluminum oxide. It have been shown that direct transformation of mechanic energy to intramolecular energy of hydrocarbons is more responsible for their destruction during the process considered rather than catalytic properties of the minerals. The removal of heavier hydrocarbons from natural or casing-head petroleum gas by means of MA treatment permits to facilitate further gas transportation and to improve essentially its heat-physical properties, namely, to decrease gas average molecular mass and specific gravity and to increase its caloricity and Wobbe number' values.

Energy and Natural Resources Saving In The Production of Expanded Glass Granules

Two processes relating to the preparation section of recycled glass are described with reference to the complete process of manufacturing of foamglass granulates and to their application. The first process consists of crushing the glass from differentiated collection, with simultaneous separation of the extraneous elements mainly consisting of: plastic, aluminium, steel and cork. Implementation of this operation is performed with the Ehinger MUD patented crusher that is able to distinguish the grinding ability of the glass from that of other substances resulting in the fragmentation of the glass and not that of foreign bodies. It is interesting to note that during this operation, substantial frictional forces develop that are useful to reduce and to almost always remove the physical link that exists between glass and other materials. The second process described is that of final refining of the glass which is performed with an Ehinger Impianti vertical axis centrifugal ball mill named RM with a 15 % energy saving compared to traditional ball systems. [1] Recycling is efficient and sustainable, saves energy and natural resources. One kilogram of recycled glass replaces 1.2 kg of virgin raw materials. Therefore glass recycling reduces CO2 emissions and the demand for natural raw materials. This helps prevent the exploitation of natural resources. Due to technical reasons during the recycling process, a certain amount of glass cannot be recycled by the glass industry to manufacture new products. Poraver® utilizes this cullet and closes a gap in the recycling process. The production of expanded glass starts with ultra-fine grinding of the recycling glass. The preparation of the recycled glass and the fine grinding are crucial to the quality of the foamglass. Glass flower, binder and foaming agent are mixed and moulded into granules. After this the grain is sintered and foamed (expanded) in a rotary kiln. The result is a new product that is used as a raw material for high-quality building materials and industrial products. Expanded glass is used in dry mortar, panels and lightweight concrete as functional lightweight aggregate in construction chemical products and mineral casting. Future applications are becoming evident in the automotive sector and are magnetisable designed in biotechnology as a growth substrate for immobilizing micro-organ.

Preparation and Characterization of Multifunctional Chitin/Lignin Materials

Multifunctional chitin/lignin materials were synthesized. In order to combine mechanical milling of the biopolymers with simultaneous mixing, a centrifugal ball mill was utilized. The resulting materials, differing in terms of the proportions of precursors used, underwent detailed physicochemical and dispersive‐morphological analysis. On the basis of FT‐IR spectra and results of elemental analysis, the efficiency of the preparation of the materials was determined. The influence of the precursors on the thermal stability of the resulting systems was also evaluated. Zeta potential was determined as a function of pH to describe the electrokinetic stability of aqueous dispersions. This is important for evaluating the utility of the materials and indirectly confirms the effectiveness of the proposed method of synthesis of chitin/lignin products. Measurements were performed to determine basic colorimetric parameters, crucial in the production technology of multiple colored materials. It is expected that chitin/lignin materials will find a wide range of applications (biosorbents, polymer fillers, and electrochemical sensors), as they combine the unique properties of chitin with the specific structural features of lignin to provide a multifunctional material.

Preparation of copper–graphite composite particles by milling process

The fabrication of copper–graphite composites by a milling process was investigated using a centrifugal ball mill. The copper particles were homogeneously milled in a graphite vessel, and the reaction time was varied. Scanning electron microscopy images clearly revealed that a fragment of graphite ground by the copper particle adheres to the copper particle surface, indicating the formation of a copper–graphite composite. The composite graphite amount per 1 g of copper particles increased to 0.46 mg at the milling time 5 min, and subsequently decreased to 0.25 mg at 60 min, indicating the suitable milling-time for the interfacial adhesion. When using only the copper particles, the naturally oxidized layer on the surface decreased with milling. On the other hand, when using only the graphite, the characteristic graphite structure is disrupted and the defect structure increased with milling. Thus, the new copper surface generated by milling strongly reacts with the defect structure of the graphite. It is suggested that the interfacial bonding between the copper and graphite was attributed to a Van der Waals attraction and/or binding force due to oxygen atoms located at the interface.

Effect of humidity on solid-state isomerization of various kinds of lactose during grinding.

The effect of humidity on isomerization during grinding of alpha-monohydrate, alpha-anhydrate and beta-anhydrate of lactose was investigated. Samples were ground in an agate centrifugal ball mill at 270 rev min-1 at room temperature (21 degrees C) and at 5 and 60% relative humidity. Crystallinity of the ground lactose was measured by Hermans' method from the powder X-ray diffraction profiles. The alpha- and beta-lactose content of the ground lactose was measured by using angular rotation spectrophotometry. The crystalline lactose samples were transformed into noncrystalline solids by mechanical stress during grinding. After grinding, the adsorbed water content of all ground lactose samples increased, and the isomerized amount increased with increase of the water content during grinding at 5 and 60% relative humidity. The results suggest that the isomerization rate of alpha-monohydrate during grinding may depend on the crystallinity, but those of alpha- and beta-anhydrate depend on the content of adsorbed water.

Reaction between Carbon Dioxide and Mechanically Activated Metal Powder

A fundamental study on the reaction between CO2 and mechanically activated metal powders has been conducted. In this research, the behavior and mechanism of CO2 reaction under various grinding conditions were investigated to fix and reduce CO2. The powder used was placed inside a grinding vessel, and was ground together with the SUJ2 balls in CO2 atmosphere. It was found that only the adsorption of CO2 gas on the ground samples was observed, whereas the decomposition of CO2 was not occurred. The CO2 adsorption increased proportionally with the increase in the grinding speed, weight of sample and number of SUJ2 balls. Furthermore, the CO2 adsorption increased with the decrease in the standard free energy of formation of each metal oxide. The morphology of the sample observed by SEM showed that the samples were not crushed into finer particles, but were only grazed on the sample’s surface. Therefore, it can be said that the CO2 can be adsorbed on the mechanically activated samples by using the centrifugal type ball mill, but in order to enhance the amount of CO2 adsorption, another type of machine with higher grinding intensity should be considered.

Reaction between CO 2 and CaO under dry grinding

This study was carried out to investigate the reaction between CO 2 and materials that contain CaO under dry grinding. Chemical reagent CaO was used in this experiment, and waste concrete was also tested to examine the feasibility of CO 2 sorption into it. Samples were ground in a CO 2 atmosphere by a centrifugal ball mill. The reaction was measured with the constant volume method. The effects of amount of sample, the number and diameter of balls, the concentration of CO 2 in the mixture of CO 2 and air and the rotational speed on the CO 2 sorption were examined. The amount of the CO 2 sorption under grinding was larger than that without grinding. The grinding enhanced the reaction between CaO and CO 2. The CO 2 sorption steeply increased with time in the early stage of grinding. After that, it increased gradually. The CO 2 reacted with the CaO at the surface layer of the newly exposed surface of the CaO particles during the grinding. The initial sorption rate of CO 2 was related with the shear force. In the latter stage of grinding, the grinding process caused the CaO particles to agglomerate. As a result, the sorption of CO 2 became slow. It was found that the waste concrete had high potential for sorption of CO 2 by means of dry grinding.

Mechanochemical synthesis and physicochemical properties of La1 − x Ba x FeO3 − δ (0 ≤ x ≤ 1) perovskites

La1 − xBaxFeO3 − δ (x = 0–1) perovskites were prepared by the mechanical activation of mixtures of binary oxides in a centrifugal planetary ball mill for 3 min followed by calcination at 1100°C for 4 h, and their phase composition was determined by X-ray diffraction. All samples up to x = 0.8 are single-phase oxides with a perovskite structure. The x = 1 sample is a mixture of perovskite-and brownmillerite-type phases. An orthorhombic-to-cubic morphotropic transition is observed at x = 0.3. The catalytic activity of the perovskite samples in CO oxidation, chosen as a model reaction, depends nonmonotonically on the barium content of the catalyst. High catalytic activities are shown by the x = 0.8 and 0.3 samples.

Surface morphology and dispersity of europium heteroligand compounds subjected to mechanical activation

The methods of scanning electron and atomic-force microscopy were used to study the surface shape, size, and morphology of the particles in a reaction mixture (rare-earth salts with organic ligands) before and after mechanical processing in a centrifugal planetary ball mill. It was established that, after mechanical treatment, the luminescent europium and terbium heteroligand carboxylates and β-diketonates with neutral nitrogen-containing ligands turn into 10–12-μm globules composed of smaller particles with sizes 0.3–0.01 μm.

Investigation of mechanically stimulated solid phase polymorphic transition of zirconia

The effect of mechanical treatment of monoclinic zirconia in a high-energy centrifugal planetary ball mill and in a vibrating ball mill, with much less mechanical impact, on its crystallographic characteristics and texture was investigated as a function of the applied mechanical load and the treatment medium. Mechanical treatment in a high-energy planetary ball mill was shown to result in particle desintegration into small crystallites of less than 20 nm in size, accumulation of strains, and fast solid phase transition to metastable nano-structured tetragonal form. The rate of the phase transition depended on the treatment medium. The transition completed during 15 min with dry-powdered ZrO 2. The presence of water retarded the phase transition. Mechanical treatment in a vibrating mill resulted in particle desintegration into crystallites of 38–42 nm in size, accumulation of strains, and gradual amorphization of the crystalline structure; however, the transformation to the tetragonal form did not occur. The factors favored the solid phase polymorphic transition of a stable form of ZrO 2 into metastable one are discussed. A high-temperature and a high pressure, which are developed in local sites of the solid under pulse mechanical impact of high-energy, provide thermodynamically favorable conditions and kinetic acceleration of the phase transition. The effect of the metastable form of ZrO 2 stabilization originates from the small size of the crystallites as a result of particle desintegration.

Effect of mixing process on electromagnetic interference shielding effectiveness of nickel/acrylonitrile–butadiene–styrene composites

AbstractThis article reports the effect of the mixing process on the electromagnetic interference (EMI) shielding effectiveness of nickel/acrylonitrile–butadiene–styrene (ABS) composites. Nickel in either powder or filament form was used as the filler material. It was mixed with ABS by two mixing processes: one was the Brabender‐mixing method, in which nickel was mixed in the polymer melt by a strong shear at high temperatures, and the other was a simple dry mixing method performed in a centrifugal ball mill. Our results showed that the dry‐mixing method could produce EMI shielding effectiveness of 36 dB at the 3 vol % nickel filaments level. In contrast, we need 20 vol % nickel powder to exhibit some shielding effectiveness for the Brabender method. After the nondestructive X‐ray examination and four‐point probe resistivity measurements, we concluded that better EMI shielding effectiveness could be achieved when the mixing method provided a state of uniformity on the macroscale, but not on the microscale. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 128–135, 2005

Use of soda-lime scrap-glass as a fluxing agent in a porcelain stoneware tile mix

Abstract The study was directed towards determining the feasibility of using soda-lime scrap-glass as a fluxing agent in a porcelain stoneware tile mix. Both laboratory and industrial scale tests were carried out. Starting from a reference mix composition, different amounts (5–20 wt.%) of sodium feldspar were replaced with the same amounts of soda-lime scrap-glass. The soda-lime scrap-glass was added in the form of powder, prepared by wet grinding in a centrifugal ball mill. The rheological study of the resulting slips showed that increasing the amount of glass in the mix composition increased the viscosity but decreased the yield stress. Both the laboratory experiments and results of industrial trials showed that the only mix in which the soda-lime glass acted as a good fluxing agent, i.e. lowered the firing temperature, was the mix in which the scrap-glass replaced 10 wt.% of the sodium feldspar. This mix also showed better mechanical characteristics, attributed to enhanced microstructural homogeneity.

Fine grinding of aggregated powders

In many cases, including natural ores as well as synthetic powders, fine grinding involves the breakage of bound aggregates rather than solid particles. The characteristics of breakage in such systems have been investigated by experimental studies of grinding kinetics, in a model system of partially sintered alumina particles, ground in a laboratory centrifugal ball mill. The effects of aggregate strength (extent of sintering) and energy input (mill speed) on the breakage rates and breakage distributions have been evaluated. Breakage appears to occur primarily through splitting of the aggregated mass into two or three smaller aggregates accompanied by release of the primary particles, leading to strongly bimodal breakage distributions.

Ultra fast synthesis of metastable tetragonal zirconia by means of mechanochemical activation

Ultra fast solid-phase synthesis of nanostructured metastable zirconia of tetragonal modification from the amorphous hydroxide with no cation and anion promoters and from the zirconia of monoclinic modification was performed at the ambient temperature by mechanical stimulation of the reactions of dehydration, crystallisation and solid-phase transition in a high-energy centrifugal planetary ball mill. The process occurred by stages as the mechanical loading increased and crystallisation of metastable form from dry powder of precursors was accomplished in 15 min. Short-term mechanical activation of the amorphous zirconium hydroxide allowed also subsequent thermal crystallisation into the metastable zirconia to occur at low temperature (320 °C). The generation of nano-sized zirconia is suggested to be one of the factors favouring the formation of the metastable form.