Executive Summary
Two kinds of spherical particle materials were manufactured on the demand of IFPRI. One is transparent and the other is opaque. The transparent particles are glass beads made from barium titanate glass or soda-lime-eilicate glass by use of a horizontal flow sintering furnace or a fluidized sintering furnace. The opaque particles are made from phenol-resin spheres and carbonized in vacuum or in nitrogen atmosphere. They are really black. These transparent or black particles are not monodisperse, but they have appropriate size distributions in the respective size range of 1 to 10µm, 3 to 30µm, 10 to 100µm, and 150 to 650µm.
The manufactured transparent particles are here denoted as MBP!-10, MBP3-30, MBP10-100, and LBP150-650, according to their size ranges. Also the corresponding black particles are denoted as GCP1-10, GCP3-30, GCP10-100, and GCP150-650. More than 95% in weight of these particles are respectively within the stated size range. The manufactured amounts of these particles are; MBP1-10:10kg, MBP3-30:10kg, MBP10-100:20Kg, LBP150-650:30kg, GCP1-10:10kg, GCP3-30:10kg, GCP10-100:20kg, GCP150-650:24kg, These particles were sent to AEA Technology, Winfrith Technology Centre, Dorchester Dorset DT2 8DH, England.
Particle density measured by liquid immersion method is about 4.1g/cm3 for MBP particles, about 2.5g/cm3 for LBP particles, and about 1.4g/cm3 for GCP particles. However, the particle density of GCP particles measured by gas compression method was scattered because of the surface open pores. Size distributions of these particles were measured by several methods including the laser scattering and diffraction method and found to be almost logarithmic-normal. Particle shape analysis was also carried out by use of an image analyzer based on photomicrographs. Particles are satisfactorily spherical and average aspect ratio is 1.05 both for the transparent particles and black particles.
These particles may, therefore, be applicable to the calibration of particle-size analysis instruments.
Further characterization of these particlea were carried out on the refractive index, particle strength, adheaive characteristics, and contact potential difference (electrostatic property). Refractive indices of transparent MBP and LBP particles were measured by a liquid immersion method with appropriate immersion liquids and found to be 1.93 for MBP particles and 1.52 for LBP particles. On the other hand, the refractive index of GCP black particles ws estimated based on the size measurement by use of a laser scattering and diffraction instrument. The particle strength was measured by a micro-compression testing machine and correlated with the particle size. The small black particles have a larger strength than the corresponding transparent particles, but the strength of them depends strongly on the particle size. The strength of the transparent particles is less sensitive to the particle size.
The adhesive force between a particle and stainless-steel surface was measured based on the particle reentrainment by high speed air flow. The black particle8 are less adhesive than the corresponding transparent particles. For both types of particles it was found that the adhesive force is proportional to the particle size below 30µm, while it increases with the particle size to the 3/2 power for larger sizes.
The contact potential difference between MBP-particles and gold( Au )-electrode is ranged from 0.038V to 0.265V depending on the particle size. It is 0.228V for LBP150-650. On the other hand, the contact potential difference of the black particles is almost constant in this size range. The estimated work function is about 5.0eV for black particles.
The size segregation of particle8 was also studied. In feeding the particles into a container, smaller particles are concentrated in the periphery of the bottom layer and in the central region of the upper layer. Also in vertical tapping of the container, the smaller particles are gathered in the bottom part and relatively large particles are floating near the surface region. Therefore, the size segregation may cause a problem in handling the standard materials, especially for larger particles such as LBP150-650 or GCP150-650. Complete mixing and careful splitting are very important before distributing them as small samples.
Statistical error caused by sample size has been studied by use of a computer simulation and the theory developed in our previous work has been confirmed. Therefore, the error caused by sample size or numbers of particles required in a measurement can be analytically estimated. Fairly large numbers of particles are required in order to get reliable data.