Fumio Saito

Effects of rotational direction and rotation-to-revolution speed ratio in planetary ball milling

Abstract The rotational direction of a pot in a planetary ball mill and its speed ratio against revolution of a disk were studied in terms of their effects on the specific impact energy of balls calculated from the simulation on the basis of the Discrete Element Method (DEM) and structural change of talc during milling. The specific impact energy of balls is measured as a significantly large value, and the structure of talc is transferred into an amorphous state quickly when the mill pot is rotated in the counter direction against the revolution. In both rotation–revolution relationships, the specific impact energy increases with an increase in the rotation-to-revolution speed ratio in the initial stage and then falls around the critical speed ratio, which can be calculated by the balance equation based on the centrifugal forces acting on a ball due to the combination of the rotation and revolution. The highest value in the specific impact energy of balls during milling can be achieved effectively around this critical speed. This critical speed would, therefore, be a key condition in milling for designing suitable and optimum mechanical milling performance.

Mechanochemical dechlorination of polyvinyl chloride by co-grinding with various metal oxides

Abstract Polyvinyl chloride powder was ground with one of the oxide powders, i.e. CaO, Fe 2 O 3 , SiO 2 and Al 2 O 3 , in air by a planetary ball mill to investigate the mechanochemical dechlorination of PVC. Grinding causes the size reduction of the each component. The PVC powder sample is degraded by grinding with reduction of molecular weight, forming C=C bonds in its structure. The dechlorination occurs in all the ground mixtures, but its phenomenon is classified into two types. One is the solid-phase reaction to form chlorides, CaOHCl and FeCl 2 2H 2 O, when CaO and Fe 2 O 3 powders are used. The other is the release of HCl gas by degradation when SiO 2 and Al 2 O 3 powders are used. All the same, the dechlorination yield increases not only with an increase in grinding time, but also with excess of oxide powder.

Mechanochemical approach for preparing nanostructural materials

Several mechanochemical methods for synthesizing nanostructural materials have been introduced in this paper. The methods are three different routes; one is a direct synthesis method, the second is a combination method, which composes of grinding, heating and washing, and the third is a doping one. Dry grinding a mixture facilitates the solid-state reaction (MC reaction), to form a product of fine particles with nanostructure of grains and their boundaries in lattice configuration. The micro-structure of material depends mainly on grinding energy and the composition of starting mixture. Under the grinding energy enough for mechanochemical synthesis, the synthesized material tends to be aggregated, so that the specific surface area (SSA) is not large. In order to increase the SSA, the combination method is recommended. The doping method is another concept, enabling us to cause a partial MC reaction in the fine particles. The chemical form and structure of the material depend mainly on a mixing ratio of the starting samples. The authors have attempted to form different functional materials such as catalysts from various starting samples by using a planetary mill, and introduced some of them in the present paper.

Generation of high-purity hydrogen from cellulose by its mechanochemical treatment

Cellulose was mixed with the hydroxides of lithium and nickel and the mixture was milled, followed by heating to produce hydrogen. Several analytical methods of X-ray diffraction (XRD), thermogravimetry/mass spectrometry (TG/MS) and gas chromatography (GC) were used to characterize the samples. Hydrogen was emitted when heating the milled sample around 400 degrees C together with low concentrations of methane, carbon monoxide and carbon dioxide. It is understood that an interaction occurs between cellulose and lithium hydroxide to convert the carbon of cellulose into lithium carbonate and to emit hydrogen correspondingly. It is also found that nickel catalyst is required to facilitate the interaction and the behaviours of three different nickel compounds were compared. When high yield of hydrogen emission is available, the prepared samples can also serve the purpose of hydrogen storage.