Yuichi Ohira

Production of finely ground natural graphite particles with high electrical conductivity by controlling the grinding atmosphere

Abstract Natural graphite particles with high crystallinity sieved to obtain a particle size range of under 63 μm were ground with a ball mill, under various well-controlled grinding atmospheres such as N 2 , O 2 , He, H 2 , and vacuum. The ratio, X dif50 / X st50 , i.e. between the 50 wt.% Stokes diameter and the 50 wt.% laser diffraction diameter, of the ground particles, was used as an index of the flakiness of the particles. The specific resistance of films composed of the ground graphite particles was systematically measured. The rate of reduction in the size of the particles by grinding was slow under an O 2 -rich atmosphere such as 100% O 2 and dry air. On the other hand, it was relatively fast in vacuum, or under an N 2 or He atmosphere, and a gas mixture of 99% N 2 and 1% O 2 . The rate of size reduction by grinding under a H 2 atmosphere was intermediate. In our experimental conditions, the flakiness of the ground particles increased with the decrease in the particles’ sizes. The electrical conductivity of the ground particles, however, tended to decrease with the decrease in their sizes. Under the condition that the Stokes diameter of the ground particles remains constant, the electrical conductivity of films made from the ground particles increases with the increase in the flakiness of the particles. It was finally determined from our systematic grinding experiments that small flaky particles, which had a size, X st of ∼1 μm, with a high electrical conductivity can be produced by grinding in a gas mixture of 99% N 2 and 1% O 2 . In this case, the flaky shape of the ground particles was visually confirmed by scanning electron microscopy.

Classification Performance of a Low Pressure Differential Mobility Analyzer for Nanometer-sized Particles

Size distribution measurements and classification tests by a low pressure differential mobility analyzer (LPDMA) for nanometer-sized silver particles and cesium iodide particles under low pressure conditions (123–300 Torr) were performed using a transmission electron microscope (TEM) and the tandem DMA technique. When the ratio of the sheath gas flow rate and the aerosol gas flow rate was set at 5 : 1, the targeted sizes calculated from the classification voltage applied to the LPDMA at 160 Torr are found to be in good correlation with the count mean Feret diameter obtained from the TEM observation of the particles collected after a classification ranging from 6 to 25 nm, although the targeted sizes set by the LPDMA were approximately 15% greater than the count mean Feret diameter measured by the TEM after classification. The geometric standard deviations of DMA-classified particles measured by TEM and those obtained from the tandem DMA method ranged from 1.08 to 1.17 and from 1.05 to 1.13, respectively. They were slightly greater than the ideal geometric standard deviations (1.05) of the particles classified with the LPDMA, which was calculated by neglecting the broadening effects due to Brownian diffusion. We experimentally demonstrated the validity of our LPDMA system for size measurements and classification of the nanometer-sized particles under low pressure conditions.

Phase transformation of mesoporous calcium carbonate by mechanical stirring

We report a simple strategy to synthesize vaterite/calcite mesoporous calcium carbonate through collisions and organization of colloidal particles accelerated by mechanical stirring. Mechanically stirring the precursor colloidal dispersion can control the calcium carbonate polymorphs.

Association of Passive and Active Smoking with Elevated Blood Lead Levels Among Children and Adults Resided in a City of Japan

There were no previous reports assessing the effect of tobacco smoke on blood lead levels (BLLs) simultaneously in children and adults in Japan. We investigated the association of passive and active smoking with BLLs in children and adults among the general population in Hokkaido, Japan. One hundred seventy-seven persons (78 males, 99 females) participated in the survey in May, 2014. Age groups of subjects younger than 18 years (age group A) and subjects older than or equal to 18 years (age group B) were designated. The median value of the BLLs was used for us to divide into two groups, such as high and low BLL groups. Age and sex adjusted odds ratios (OR) and 95% confidence levels (CLs) were estimated with analysis of the logistic regression model. BLLs in age group B were significantly higher than age group A (p=0.023). In age group A, the proportion of subjects living with habitual smokers other than parents in the household was significantly higher in the high BLL group than in the low BLL group (p=0.019). In age group B, currently habitual smoking was significantly associated with increased risk being in the high BLL group (OR=3.17, 95% CL, 1.28-7.86). A duration of smoking longer than or equal to 20 years was significantly associated with increased risk of being in the high BLL group (OR=2.73, 95% CL, 1.07-6.94), BLL is higher in older persons than in younger persons. Active and passive smoking may be associated with high BLLs in adults and children, respectively.

Application of Correction Line in Floated Particle Size Distribution Measurement Using the Buoyancy Weighing-Pan Method

This study demonstrates that the buoyancy weighing-pan method is suitable for measuring the particle-size distribution of floating particle after correction line is applied to the obtained results. After the correction line is applied to the buoyancy weighing-pan method results, then these results agree with the laser diffraction/scattering method.