Junya Kano

Correlation of powder characteristics of talc during Planetary Ball Milling with the impact energy of the balls simulated by the Particle Element Method

Abstract Room temperature grinding of talc powder was conducted by a planetary ball mill using media balls of different sizes. The grinding behavior of the talc sample was investigated by X-ray diffraction (XRD) and particle size distribution analyses. The motion of the balls in the mill with talc powder was simulated by the Particle Element Method (PEM) under the same condition as that of the talc grinding. Within the size reduction range of the talc powder, the 50% passing particle size, D 50 , of the ground product is expressed by the equation, D 50.1 D 50.0 = (1 − D 50.1 D 50.0 ) exp (−K p t ) + D 50.1 D 50.0 , where K p is the rate constant and subscripts, 0, t and 1 denote the initial and arbitrary times, and the grinding limit. The amorphization process of talc powder during milling is expressed by ( I I 0 ) = exp (K S t) , where I denotes the representative peak intensity of the XRD pattern of the talc sample ground for arbitrary time, and subscript 0 the initial stage and K S the rate constant of the amorphization. Both K P and K S tend to increase with a decrease in the ball diameter, d , when the mill speed is high. A similar trend can be seen in the relation between the impact energy of balls, E 1 , and d . Therefore, both the size reduction and amorphization rates of talc correlate with E 1 .

A method for simulating the three-dimensional motion of balls under the presence of a powder sample in a tumbling ball mill

A method for simulating the motion of balls under the presence of a powder sample in a tumbling mill is proposed in this paper. The method is based on the particle element method and a coefficient of friction of colliding balls is the key to simulate the motion under powder filling. Four kinds of samples, i.e. glass beads, silica, aluminum hydroxide and kaolinite powders, were used for the milling. The movements of balls with and without a sample were observed visually by a video recorder and compared with the simulation results. The actual movement of balls in the mill is dependent on the kind of sample and the movement calculated by the present method can be simulated by choosing a suitable coefficient of friction for a given sample. The suitable coefficient of friction for the kaolinite sample is the highest value of all of the samples and is more than four times larger than that in grinding without sample. Suitable coefficients of friction for the samples are correlated with their angles of repose.

Application of dry grinding to reduction in transformation temperature of aluminum hydroxides

Abstract Dry grinding of gibbsite (α-Al(OH) 3 ) and pseudo (p)-boehmite (γ-AlO(OH)) powder samples separately, with and without fine α-alumina powder as a seed, was conducted using a planetary ball mill to investigate effects of grinding and addition of the seed on their transformation temperatures to α-phase during heating. The transformation temperatures of both samples reduced to below 1000°C with increasing grinding time as well as the amount of seed. The transformation temperatures depend on the grinding time and the amount of seed, and the minimum temperatures are about 910°C for gibbsite and about 950°C for p-boehmite when they are ground for more than 60 min with an equivalent amount of the seed powder. Combination of grinding with addition of the seed would be an effective operation for the reduction in the transformation temperature of both compounds to α-phase.

Correlation of grinding rate of gibbsite with impact energy in tumbling mill with mono-size balls

Abstract Dry grinding of a gibbsite powder was conducted in air using a tumbling ball mill with mono-size of media (balls) ranging from 4.8 to 31.7 mm diameter to investigate ball size effect on grinding rate. The impact energy of balls during grinding was calculated by the method proposed previously in order to correlate with the grinding rate. The grinding rate increases with an increase in the rotational speed of the mill, subsequently, it falls around the critical speed. The maximum grinding rate shifts toward higher rotational speed range as the ball size becomes large. In the range of rotational speed before the grinding rate falls, the grinding rate is improved when grinding with balls of 12.7 mm or less, while it is reduced when larger balls over 15.9 mm are used. A similar trend can be seen in the relation between the specific impact energy of balls and the rotational speed of the mill. The grinding rate is proportional to the specific impact energy of balls regardless of the ball size. Therefore, the specific impact energy of balls plays a significant role in governing the grinding rate in tumbling ball milling of the sample powder.

Ball mill simulation and powder characteristics of ground talc in various types of mill

Abstract Talc powder samples were ground by three types of ball mill with different sample loadings, W , to investigate rate constants of the size reduction and structural change into the amorphous state. Ball mill simulation based on the particle element method was performed to calculate the impact energy of the balls, E i , during grinding. Each rate constant correlated with the specific impact energy defined by E i / W on logarithmic coordinates with a high correlation factor.

Mechanochemical destruction of decabromodiphenyl ether into visible light photocatalyst BiOBr

In the present study, mechanochemical (MC) treatment of polybrominated diphenyl ethers (PBDEs), a kind of emerging persistent organic pollutant (POPs), was performed using a high energy ball mill. With Bi2O3 as co-milling reagent, deca-BDE was effectively destroyed and no hazardous intermediates or organic products were observed in the MC reaction. Meanwhile, BiOBr, a promising visible light photocatalyst, was proved to be the final product which could be utilized in further steps. Neither excessive Bi2O3 nor unreacted deca-BDE was left after the reaction as they were originally added at stoichiometric ratio for BiOBr formation. FITR and Raman analyses demonstrate the collapse of deca-BDE skeleton and the cleavage of C–Br bonds with the generation of inorganic carbon, revealing the mechanism of carbonization and debromination. The gaseous products at different reaction atmosphere were also analyzed, showing that mostly CO2 with a fraction of CO were released during the MC process. The reaction formula of deca-BDE and Bi2O3 was then proposed based on the identified final products. Besides, the photocatalytic activity of the generated BiOBr was evaluated using methyl orange as the model pollutant. A good degradation performance from BiOBr was achieved under both simulated sunlight and visible light irradiation, indicating the possibility for its further utilization.

Dechlorination of polyvinyl chloride by its grinding with KOH and NaOH

Abstract —Polyvinyl chloride (PVC) powder was ground with one of two dried alkaline additives, i.e. KOH and NaOH, pellets in air by a planetary ball mill to investigate the dechlorination reaction during the grinding. Grinding of the mixture causes the size reduction of PVC, with causing its mechanochemical reaction with the additive to form partially dechlorinated PVC and chloride (KCl or NaCl), respectively. In both reaction systems, the dechlorination yield increases with an increase in grinding time and amount of additive. The C C bonds in the PVC ingredient are created in its structure with decreasing molecular weight (MW). The MW of the polymer ground with KOH is higher than that ground with NaOH. The dechlorination speed of the polymer ground with KOH is faster than that ground with NaOH in the initial stage of grinding, but this is reversed during prolonged grinding.

Effect of the friction coefficient in the discrete element method simulation on media motion in a wet bead mill

In order to provide information on different sample materials to be ground by a bead mill under wet conditions, we have investigated the effect of the friction coefficient in the discrete element method (DEM) simulation on bead motion in the mill. This is also a joint attempt of simulation and experimental works — the former employs the DEM to simulate the bead motion in the mill and the latter is based on the observation of the bead motion in the same mill by a video recorder. Two kinds of sample, gibbsite and limestone, were used for the milling and they were suspended in water at solid concentrations from 2.5 to 10.0 wt%. The bead velocity simulated at different friction coefficients in the DEM was compared with the experimental data and the coefficient classified into two: one is the coefficient between bead and bead, μi, and the other between bead and wall, μw. The proper μi and μw are 0.2 and 0.25 for gibbsite and 0.2 and 0.3 for limestone according to the joint work, irrespective of milling conditions.

Amorphization of kaolinite and media motion in grinding by a double rotating cylinders mill — a comparison with a tumbling ball mill

Abstract Kaolinite powder was ground under atmospheric conditions by a co-axial double rotating cylinders mill [Ultra Fine (UF) mill] and tumbling ball mill to investigate the amorphization behavior of kaolinite. Motions of media balls in both mills were also numerically simulated by the particle element method. The UF mill lead to an amorphous state of kaolinite for a shorter time than the tumbling ball mill. The ball impact energy in the UF mill was about 5 times larger than that of the tumbling ball mill. The simulated total kinetic energy of media balls required for 80% amorphization of the sample by the UF mill was considerably lower than that using the tumbling mill. NMR analysis on 27 Al in the structure of kaolinite revealed that a pentagonal coordination remains in the amorphous state when ground by the UF mill, while it almost disappears in the sample ground by the tumbling mill for a prolonged time.

Chapter 11 Fine Grinding of Materials in Dry Systems and Mechanochemistry

Publisher Summary This chapter discusses recent development of fine grinding in relation to media motion simulated by the use of Discrete Element Method (DEM) and mechanochemistry. The DEM was invented in 1979 and it has been growing along with the advancement in computer performance. This enables to simulate particulate systems such as particle motion in mills, mixing devices and fluidized beds as well as the discharge behavior of powder in a bin. The science of mechanochemistry is related to the use of solid state reactions to produce useful compounds. This is applicable to separation and recovery of useful chemical species and components from minerals and waste materials and to dry coating of other components or metals on the surface of small particles or plate under ambient conditions. Milling induces mechanochemical effects such as phase transformation and solid state reaction. Some amount of powder is trapped between the two when two balls collide inside a mill pot, and particles deform plastically, and are repeatedly flattened, cold-welded, fractured, and rewelded.