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An automated version of uniaxial powder flow testing has recently been developed and there is a need for experimental data from pharmaceutical powders.To compare the novel testing method with an annular shear cell using different pharmaceutical excipients. A particular aim was to gain an improved understanding of potential differences in the obtained flow results.Nine excipients were studied with both flow testers at different consolidation levels. Unconfined yield strengths were determined at similar major consolidation stresses. Finally, an anisotropic stress factor was calculated and the fractal character of the powders was assessed by means of image analysis in a rotating drum.Data correlated generally well; however, the unconfined yield strength from uniaxial testing resulted mostly in lower values compared to annular shear cell testing. Differences were specific for the given excipients and mannitol demonstrated the highest discrepancy of measured flow parameters. The differences were first discussed by considering wall friction, anisotropy of forces, brittleness as well as the fractal nature of the powder surface. This heterogeneity of the powder as well as the anisotropy of forces was also found to be important for the relative flow index.The automated uniaxial method demonstrated faster and more reproducible flow testing as compared to an annular shear cell. Therefore, the new method has a high potential in pharmaceutics for example in the quality-control of powders.

Percolation segregation in binary size mixtures for two particulate types, urea (spherical) and potash (angular), were studied. Materials chosen are major raw ingredients of blended fertilizer that represent two extremes based on shape and density. In this study, the coarse and fine particles were classified using particle sizes larger and smaller than 2,000 μm, respectively. Three coarse mean sizes (3,675 μm, 3,075 μm, and 2,580 μm) for both spherical and angular particles and three fines mean sizes (2,180 μm, 1,850 μm, and 1,550 μm) for angular particles and two fines mean sizes (2,180 μm and 1,850 μm) for spherical particles were selected for tests. Size ratio for binary size mixture is defined as the ratio of mean size of coarse to fine particles. Binary mixed samples of coarse and fine particles were placed into the shear box of the primary segregation shear cell (PSSC-II) very gently to avoid segregation. Percolation segregation was quantified using PSSC-II. Based on experimental results, the segreg...

Use of powder avalanches in the study of flow properties of pharmaceutical excipients has yet to be popularized even though it is rather simple to use and yields comparatively reliable results. Commonly employed flow assessment methods include compressibility studies and shear cell and repose angle measurements. Though widely accepted, these methods are not without limitations and inadequacies. More often than not, experimental and environmental conditions lead to a considerable amount of variability in the results obtained. The primary objective of this current work is to propose two new indices, avalanche flow index (AFI) and cohesive interaction index (CoI) based on the avalanche flow behaviors of powders. Not only were these two indices able to describe the ease of powder flow but they also provided a simpler means of quantifying the extent of cohesive interactions within the powder mass without elaborate mathematical functions.

Segregation occurs during most particulate materials-related unit operations including mixing, conveying, discharging, filling, and compaction. A redesigned second-generation primary segregation shear cell (PSSC-II) was fabricated to simulate and quantify percolation and sieving mechanisms-based segregation. Several binary mixtures were tested to quantify the effect of size ratios and absolute size. The constituents of binary mixtures studied were spherical glass beads. Three binary size ratios, 4:1, 6:1, and 8:1, were tested. For a given size ratio, three different absolute coarse (710–850, 1000–1200, and 1400–1700 μm) to fine particle sizes were studied. The experimental results showed that the PSSC-II was capable of quantifying segregation potential for various materials. Several physical parameters such as segregation rate (SR), phase of segregation rate (PSR), distribution of segregation rate (DSR), maximum segregation rate (MSR), and normalized segregation rate (NSR) were created to describ...

A flexible boundary-type cubical triaxial tester (CTT) was used to measure the flow parameters, i.e., cohesion and angle of internal friction, of Mohr-Coulomb model. The three test materials used in this study were BCR limestone, ground silica and wheat flour. Flow parameters for these materials have been reported in literature using different shear testers. A comparison between the CTT and published computer controlled shear cell (CCSC) results showed that for: 1) BCR limestone -- at low consolidation loads, the results were comparable; however, there were differences in cohesion at 12.5 kPa and cohesion and angle of internal friction at consolidation stress of 6.6 kPa, 2) ground silica -- flow parameter values were comparable at 2.8 and 8.4 kPa, and 3) wheat flour — cohesion values were different, however, angle of internal friction values were comparable. The differences between the CTT and published shear cell results were attributed to the differing initial bulk density values and lack of kn...

Many handling problems in industries dealing with particulate materials can be avoided by designing the handling systems and storage structures based on the flow properties of the materials stored or processed through them. Flow property data at low pressures are essential for design in several cases. The objectives of this study were: 1) to measure the flow properties of five test materials at low consolidation loads (1-6 kPa) using the computer controlled shear cell (CCSC) as a computer controlled Jenike tester (CCJT) and as a dynamic yield locus tester (DYLT), and 2) to evaluate further the DYLT which works on the constant volume concept. The five powders tested were: 1) BCR limestone, 2) glass fibers, 3) ground silica, 4) microcrystalline cellulose, and 5) wheat flour. Results showed that the flow properties, cohesion and angle of internal friction, measured using the CCJT and DYLT were statistically similar (p > 0.05) for BCR limestone, ground silica and glass fibers at all consolidation str...

The flow behaviors of granular materials in a shear cell were experimentally studied. Different masses of granular materials were put in an annular shear device with a stationary upper wall and a constantly rotated lower wall. The image processing technique and the particle tracking method were employed to measure average particle velocities and fluctuating velocities in the streamwise and transverse directions. The granular flows consisted of a low shear rate region with higher and more uniform velocities in the lower test section, and a high shear rate region in the upper part. The velocities decreased with the height, while the fluctuations, granular temperature and shear rate increased with the height. The velocity fluctuations were anisotropic and were greater in the streamwise direction. The slip velocity and the low shear layer thickness were greater for the case with greater total granular mass.

For the accurate measurement of diffusion coefficients, the shear cell method has been newly developed to overcome the disadvantages of the conventional long-capillary method for diffusion coefficient measurements in the large isothermal furnace of the MSL-l ( First Microgravity Science Laboratory) and the multipurpose furnace of TR-IA ( sounding rocket) [1] To achieve good accuracy, the thickness of the cell segments and the rotation rate of the cell ( shear process) are crucial. For estimating the depth of convection, a new concept of “isotope trace method in hydrodynamical simulation” is proposed by applying the idea of an isotope tracer experiment, and the mathematical model is appended to the Navier-Stokes equation and continuity equation. We suppose that the liquid used is a mixture of the sample and a kind of "isotope liquid," which has the same physical properties as the original in terms of density, viscosity, specific heat, etc. The redistribution of isotopes is caused by shear convection only, ...

The stickiness of adipic acid and alumina was tested in equipment for powder characterisation. Experiments covered various moisture contents at ambient temperature. Both wall adhesion and internal cohesion tests were carried out. The testers evaluated were the Jenike and Peschl shear cells, the Warren Spring Laboratory Cohesion tester, the unconfined yield strength tester, and the Teesside Laminated shear cell. In addition, the empirical tests put forward by Can (1) were carried out. The sticky-point temperatures of various amorphous materials were also tested. The Jenike shear cell and the Warren Spring Cohesion tesm gave the most consistent and repeatable results for cohesion. None of the equipment tested gave a simple and repeatable measure of adhesion. The tester developed by Howe et al (2) determined the sticky-point quickly and repeatably. Fluidisation tests were carried out in a small scale visualisation module. The results correlated well with the measured cohesion parameters.

The extensive use of powders in numerous industries has led to the need for a better understanding of their storage and flow properties. In order to design proper storage structures, it is essential to know the flow properties of powders under normal operating conditions. The objective of this research was to measure the flow properties of powders at low pressures (0.5-5 kPa) by using 1) the computer controlled shear cell (CCSC) as a dynamic yield locus tester (DYLT), and 2) the cubical triaxial tester. Five different powders were tested. The measured flow parameters, cohesion, and angle of internal friction were obtained using the three testers, and were statistically compared.

A number of methods of estimating ‘flowability’ of some direct compression vehicles have been evaluated as to their usefulness in predicting weight variation on tabletting. There was little or no inter-relationship between angle of repose, compressibility on tamping and flow rate values. In addition there was no correlation between any of these three values and tablet weight variation. In contrast cohesiveness and the reciprocal of the flow factor as determined from shear cell studies exhibited a fair correlation with weight variation of tablets produced on both a single punch and a rotary machine. It is suggested that the reciprocal of the flow factor is a direct measure of the tendency of the powder to arch or bridge during tabletting.

We describe a precise method for measuring the diffusion coefficient of solutes in liquid metals. A thin layer of a radioactive isotope of the solute is allowed to diffuse in capillaries which can be sectioned using a shear cell device. This method allows a precise measurement of the temperature and of the time duration of the experiment, and avoids any solute segregation when cooling the samples. The experimental results show that there is a negligible direct influence of the valence of a solute on its diffusion coefficient in tin