Tham khảo tài liệu 'volume 07 - powder metal technologies and applications part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Surface Area Density and Porosity of Powders Apparatus Lea and Nurse Ref 21 developed the apparatus shown in Fig. 4 to provide permeability measurements. The powder was compacted in the sample cell to a predetermined porosity. Air was permitted to flow through the bed and the pressure drop h1 was measured on the first manometer the air then passed through a capillary flowmeter across which another pressure drop was measured as h2 on a second manometer. Dry air Manometer Flowmeter Fig. 4 Lea and Nurse permeability apparatus with manometer and flowmeter The capillary permitted the system to operate under a constant pressure. The volume rate of flow through the flowmeter the pressure drop across the bed as measured by the manometer and the constants associated with the apparatus permitted determination of the specific surface area surface area per unit volume . Gooden and Smith Ref 22 added a self-calculating chart to a modified Lea and Nurse apparatus to enable direct readout of the specific surface. The commercial version of their modification is known as the Fisher subsieve sizer Fig. 5 . Fig. 5 Fisher subsieve sizer operation A simplified version of the air permeameter known as the Blaine permeameter Fig. 6 Ref 23 relied on a variable pressure technique Ref 24 . A vacuum was used to displace the oil in a U-tube connected in series with the powder cell. The resultant pressure caused air to flow through the powder bed and the time required for the displaced oil to fall back to its equilibrium position was measured. This method resulted in a measured specific surface area which decreased with porosity. Usui Ref 25 showed that log t and the void fraction exhibited a linear relationship and that a plot of these parameters gave a value for surface area. Filler paper Compacted bed Ị of powder Male or I Coupling to fit female top of manometer Perforated disk Coupling to fit Coupling to fit bottom of cell Male or female Etched line Measuring distance U-tube manometer .
