Mechanical Activation Process Research Articles

Mechanical Activation of Diopside in CO2

The mechanical activation (MA) of diopside in a controlled CO2 atmosphere was studied using different grinding facilities. The results demonstrate that diopside may sorb CO2 by two mechanisms, depending on the nature of the MA process. If grinding is not accompanied by structure breakdown, the sorption process is similar to that reported for metal oxides, and the adsorbate consists of undistorted CO32- groups. If the MA process leads to diopside amorphization, CO2 is sorbed in the form of distorted carbonate groups, and the IR spectrum contains a split absorption band (1433 and 1522 cm–1) similar to the CO32- band in the spectra of carbonate-containing silicate glasses. After ball milling in an AL-1000 mechanical activator in CO2 for 580 min, diopside contains up to 15 wt % CO2 . Subsequent heating ensures partial or complete removal of the carbonate. Acid treatment of diopside after MA in CO2 leads to decomposition of the carbonate and almost complete leaching of the Ca and Mg cations.

Synthesis and processing of nanostructured WC-Co materials

In this study a novel approach, termed the integrated mechanical and thermal activation (IMTA) process, was used to synthesize nanostructured WC-Co powder. As a result of the integration of mechanical and thermal activation, nanostructured WC-Co powder was synthesized below 1000°C, starting from WO3, CoO and graphite powder mixtures. Furthermore, consolidation of the nanostructured WC-Co powder via high velocity oxy-fuel (HVOF) thermal spraying and solid state sintering was investigated. The results demonstrated the feasibility of converting the nanostructured WC-Co powder to coatings and bulk components, the properties of which are either comparable to or better than that of the conventional coarse-grained counterparts.

On the reaction sequence of WC–Co formation using an integrated mechanical and thermal activation process

A systematic study on the reaction sequence of WC–Co composite formation by annealing high energy ball milled WO 3, CoO and graphite powder mixtures in a hydrogen atmosphere has been conducted. X-ray diffraction has been used as the main tool to analyze the phase transformation of the powder mixture during processing. It was observed that WO 3 is reduced to W phase by passing through the intermediate W 20O 58 and WO 2 phases and the subsequent carburization sequence appears as W→Co 6W 6C→Co 3W 3C→W 2C→WC. The intermediate Co 3W has been found in the reduction stage, which can be subsequently carburized at higher temperatures.

MATERIAL PROCESSING VIA AN INTEGRATED MECHANICAL AND THERMAL ACTIVATION PROCESS

This paper reviews the recent progress in material synthesis and processing based on mechanical activation approaches. Material processing based on mechanical alloying and attrition has been widely used to prepare metastable phases, amorphous alloys, composites, and nanostructured materials. The most recent progress made in mechanical activation is the development of a new process that integrates mechanical activation and thermal activation to produce novel materials as well as conventional materials. The integrated mechanical and thermal activation (IMTA) process represents one of the most exciting recent advancements and holds great promise for commercial viability. Examples of enhanced reaction rates and synthesis of nanocrystalline materials are provided to illustrate the progress brought about by the IMTA process.

Processing of Nanostructured Carbides, Nitrides, and Their Composites

This article reports a newly-developed process, termed as the integrated mechanical and thermal activation (IMTA) process, for large-scale production of nanostructured carbides, nitrides and their composites. Comparisons with other existing processes for making nanostructured carbides and nitrides are presented. The study shows that the IMTA process possesses great potentials in producing large quantities of high quality nanostructured carbides, nitrides and their composites at low material costs, low energy consumption, and high production rates.

Processing of Nanostructured Carbides, Nitrides, and Their Composites

This article reports a newly-developed process, termed as the integrated mechanical and thermal activation (IMTA) process, for large-scale production of nanostructured carbides, nitrides and their composites. Comparisons with other existing processes for making nanostructured carbides and nitrides are presented. The study shows that the IMTA process possesses great potentials in producing large quantities of high quality nanostructured carbides, nitrides and their composites at low material costs, low energy consumption, and high production rates.

Leaching and dissolution of a pentlandite concentrate pretreated by mechanical activation

This paper describes the properties and leaching behaviour of a pentlandite concentrate mechanically activated by grinding in an attritor (stirring ball mill) in H 2O for 15–60 min. It appears that mechanical activation brings about an increase in specific surface area and a decrease in the content of crystalline phase of the mineral components pentlandite (Fe,Ni) 9S 8, chalcopyrite CuFeS 2 and pyrite FeS 2. These transformations are accompanied by mechano-chemical surface oxidation of individual minerals and the formation of water-soluble Ni, Cu and Co compounds. The process of mechanical activation in water and subsequent leaching in an acid solution (Fe 2(SO 4) 3) proceeds in two steps. In the first step (dissolution in H 2O), 46% of Ni, 29% of Cu and 29% of Co dissolve; and the rest can be extracted in the second step (leaching in Fe 2(SO 4) 3 solution). Mechanical activation affects the selectivity of extraction of individual minerals.

Mechanochemical synthesis of mullite

The specifics of mechanical activation processes in modifying synthetic corundum powder and gels by silicon alkoxide are considered. As Al2O3 is milled with a silicon alkoxide additive, Al2O3 and SiO2 reactants are activated with the formation of an intermediate self-organized complex, in which the mechanochemical interaction proceeds accompanied by the formation of mullite.

A research on detonation gun coating with Fe–SiC composite powders mechanically activated

Abstract The Fe–SiC composite powder prepared by the mechanical activation process has been used for coating on materials with the detonation gun (D-gun) machine in order to develop a new way for coating. It has been found that the coating layer has fine, homogeneous, dense structure and good wear resistance. The results of SEM and X-ray diffraction (XRD) show that some reactions happened between Fe and SiC during the D-gun coating, the Fe–Si compounds formed and SiC strength the coating layer. It has been proved that the technology combined mechanical alloying with D-gun coating is a new method for surface modification.

Synthesis of nanostructured chromium nitrides through mechanical activation process

High energy milling prior to nitriding chromium metals has led to the formation of nanostructured CrN. Furthermore, high energy milling has substantially enhanced the chromium nitridation process. Under the same nitridation condition, nearly 100% CrN is formed for Cr powder milled in NH 3 for 24 hours prior to nitridation, whereas little CrN is produced for Cr powder without milling. More nitrides are formed as milling time increases. The enhanced nitridation process is believed to be primarily related to the enhanced reaction kinetic of the milled powder due to the presence of the sorbed nitrogen (when milled in NH 3), the reduced crystallite size, large grain boundary areas associated with ultrafine grains, the reduced correlation length of ordered stacking, and possibly the increased defect concentration induced by high energy milling.

Mechanical-thermal synthesis of Al 2O 3-Cr composite powders

Three different approaches have been investigated to synthesize alumina-chromium composites by displacement reactions between aluminium and chromia. The reactions have been performed either by pure mechanosynthesis or pure thermal ignition or also by a combined mechanical and thermal activation process. Differential thermal analysis, dilatometry and high temperature X-ray diffraction have been used to show the various reaction mechanisms and chemical transformations. High-energy milling of the powder modifies the reactivity of the system. A partial pre-milling treatment not only reduces the reaction temperature but can also induce a different reaction path. It has been shown that an appropriate mechanical-thermal treatment leads to the synthesis of an alumina-chromia composite by a pure solid-state process: intermediate reaction stages exhibit little if any liquid phases.

Preparation of Fe/sub 3/O/sub 4/ and γ-Fe/sub 2/O/sub 3/ powders by magnetomechanical activation of hematite

Total phase transformation of hematite to magnetite was accomplished at room temperature by wet magnetomechanical activation of hematite. Low energy mechanical activation of the oxide surface is sufficient to effect the transformation. Oxygen bonds on /spl alpha/-Fe/sub 2/O/sub 3/ oxide surface are apparently broken during the mechanical activation process and oxygen is released (removed) to the dispersing polar liquid. The oxygen pressure during the process as well the nature of the dispersing liquid have a critical influence on successful and fast phase transformation. Thus, all preparations performed in air, dry conditions or with nonpolar hydrocarbons (benzene, anthracene) show that the process of hematite reduction is non existent or very slow. Normal air pressure and/or application of hydrocarbons suppress the transformation. >

Effect of mechanical activation on depression of quartz in flotation

1. The process of mechanical activation of quartz in a mill under conditions of self-abrasion has been studied. The physicochemical properties of the active surface formed in this process have been studied by ESR technique involving determination of the number of paramagnetic centers and by calorimetric technique involving determination of heats of wetting. These techniques show that the referred parameters are affected greatly by the conditions of mechanical and chemical treatment. 2. It has been shown that generation of surface defects upon mechanical impacts is an additional factor of depression of quartz flotability under the action of hydrofluoric acid, which makes it possible to reduce the consumption of the latter drastically.

Excitation of the nerve-muscle system in Crustacea

The nature of the action potential and the mechanical response of crustacean muscle is investigated. If electric shocks of sufficient intensity are applied to the muscle, graded local contractions occur at the cathode. If the intensity of the stimuli is further increased, propagated action potentials, up to 40 mV, are recorded, accompanied by vigorous twitches of the active fibres. The conduction velocity of the muscle impulse is about 20 cm./sec., at 20° C, and its wavelength about 2—3 mm. The mechanical and electrical responses of the muscle to motor nerve stimulation are local or propagated, depending upon the number and frequency of the nerve impulses. With single, or low-frequency, motor nerve impulses a negative potential change is recorded in the vicinity of the nerve endings. It spreads decrementally 2-3 mm. along the muscle fibres, and at 17° C rises to a peak in 3 msec, and falls to one half in about 6 msec. Because of its analogy to the junctional potential of curarized vertebrate muscle it will be referred to as 'end-plate potential’ (e. p. p.). The spatial characteristics of the e. p. p. provide evidence for a discrete ‘focal’ innervation of crustacean muscle fibres, similar to that in vertebrates. In many muscles, with repetitive stimulation, successive e. p. p.’s continue to grow in amplitude for 0⋅3-0⋅5 sec. The degree and time course of this ‘facilitation’ varies greatly in different muscles; depending upon initial size and rate of growth of successive e. p. p.’s, ‘fast’ and ‘slow ’ systems can be distinguished. At high frequencies (above 100 per sec.), e. p. p.’s sum to a plateau of several times their individual height. When the e. p. p.’s have grown or summed to a ‘threshold’ level, propagated spikes are set up. Spikes in individual fibres are usually asynchronous and occur at a lower rate than e. p. p.’s. If the e. p. p. is slightly below ‘threshold’, abortive spikes are observed. A prolonged series of e. p. p.’s is associated with a relatively slow maintained contraction of the junctional region. Propagated spikes, on the other hand, are accompanied by quick twitches of the active muscle fibres. This difference is seen clearly by direct inspection of the exposed muscle fibres, but not by recording the overall tension of the muscle. In many muscles, local junctional responses account for more than 50% of the maximum observed tension. Electric recording on the intact animal shows that a good deal of the normal limb muscle activity is based on e. p. p.’s and local contractions. Propagated muscle spikes were seen only during fast and powerful reactions. The rate of contraction varies with the frequency of motor impulses as a higher than second power function. This relation, and especially the origin of the very slow contraction at low frequency, is discussed. Recruitment of individual muscle fibres plays only a minor role; the main factor is the rate of summation of the local mechanical activation process at the junction. A further factor influencing the speed of contraction is the spatial spread of the active region, which controls the extent of internal elastic shortening of the muscle. The various links of the neuro-muscular transmission chain are discussed and compared with the analogous processes in vertebrates.