Uniformity Differentiation Analysis of Powder Deposition Characteristics in Circular and Rectangular Shallow Dies Using Feed Shoe with Square Cross-Section

The inhomogeneity of the pressure distribution after completion of the filling process might create tablet and compact quality issues. Generating a uniform precompaction powder deposition into a die would minimize one source of tablet quality issues. This article determines the characteristics of the deposition process into a rectangular die and a circular shallow die, using a feed shoe with a square cross-section tube. A series of experiments were performed that determined the cumulative influence of particle size, die geometry, and feed shoe speed on uniformity of pressure distribution at the end of filling process. For uniformity comparison, the profiles of pressure distribution at the end of filling process were displayed as contour plots. Symmetry analysis, variance metrics, and uniformity analysis were implemented to quantify the deposition characteristics. Feed shoe speeds of 20 and 100 mm/s were used to fill the die. Due to their differing particle characteristics and importance, a pharmaceutical powder filler (microcrystalline cellulose-Avicel PH102) and a battery powder mixture (BPM) were used as test materials. The results showed that (1) contour plot was the most reliable method for evaluating uniformity deposition characteristics in dies; (2) based on contour plot analysis, BPM deposition at 100 mm/s feed shoe speed for circular shallow dies resulted in the most uniform pressure distribution among all, that is, 64% uniformity at ±20 dm (decimeter) resolution and 14.7% coefficient of variation (COV); (3) Avicel deposition at 20 mm/s feed shoe speed for circular dies had the least uniformity (46%); (4) rectangular dies generally had lower symmetry index (61%) in comparison with circular dies, which was attributed to sharp edges of rectangular die, that is, particles trapped in corners generated higher stresses inside the rectangular die versus circular die.     

Uniformity Differentiation Analysis. Part 1: Powder Deposition Characteristics in Rectangular Shallow Die Using Feed Shoe with Circular Cross Section

The process of die filling is a significant unit operation in many industries. Inhomogeneity of distribution such as in mass, bulk density, and pressure might cause many tablet and compact quality issues, such as lamination, capping, and distortion. No systematic investigations have been done to evaluate pressure distribution characteristics in dies with small aspect ratios (ratio of fill height to characteristic cross section dimension <0.5). In order to evaluate pressure distribution during filling of shallow dies, a circular cross section feed shoe was used at two speeds. The deposition characteristics of two powders with differing particle characteristics were studied in this research. The second-generation pressure deposition tester (PDT-II) was used to measure the two powders' pressure distribution characteristics. A battery powder mixture (BPM) and microcrystalline cellulose (Avicel PH102) were used to fill a rectangular shallow die 32 × 30 mm in dimension and 6.5 mm deep. Feed shoe speeds of 20 and 100 mm/s were used to fill the die. Symmetry analysis, variance metrics, Gini coefficient, and uniformity analysis were used to quantify the deposition characteristics. The results showed that (1) the contour plot was the most reliable method for measuring powder deposition characteristics; (2) the leeward and forward pressure distrbution comparisons generated a larger symmetry index than the front and back pressure distribution; (3) based on contour plot analysis, BPM at 100 mm/s feed shoe speed resulted in the most uniform pressure distribution (64% uniformity at +/?20 dm (decimeter) resolution) among all; (4) feed shoe speed greatly influenced pressure distribution uniformity inside the die; and (5) the high stress zone was mostly observed in forward and back regions inside the die.     

Development of a Medium Pressure Flexible Boundary Cubical Triaxial Tester

ABSTRACT

A medium pressure flexible boundary cubical triaxial tester has been designed and fabricated. In this tester, air pressure up to 70 MPa can be applied to all six surfaces of a 50X50X50 mm cube-shaped powder specimen via flexible rubber membranes. Pressure in a vertical direction (top-bottom faces of the powder specimen) and the pressure in a horizontal direction can be controlled independently. This tester can handle displacements as large as 50 mm in each of the three principal directions. Hydrostatic triaxial compression (HTC) tests. conventional triaxial compression (CTC) tests, and mean effective stress (MES) tests will be conducted on three powders, including a pharmaceutical powder, a ceramic powder, and an aluminum oxide powder. HTC tests will be conducted at 0 to 20 MPa, with 3 loading-unloading cycles. CTC and MES tests will be conducted at several pressure levels from 0 to 20 MPa.     

Molecular identification of marine yeast and its spectroscopic analysis establishes unsaturated fatty acid accumulation

Marine microbes are competent organisms, some of which can accumulate large amounts of lipids. A yeast strain, Rhodotorula mucilaginosa AMCQ8A was isolated from the marine water of the Queenscliff region, Victoria, Australia. The yeast isolate was identified by sequencing 18s rDNA genes. Scanning electron microscopy images revealed scars on the surface of the yeast cells. The Fourier transform infrared spectroscopy microspectroscopy studies demonstrated the presence of unsaturated fatty acids by differential microscopic analysis. The sharp band at 1745?cm(-1) was represented by ν(CO) stretches of ester functional groups from lipids and fats, and therefore indicated the presence of total lipids produced by the cells. Over 65% of the fatty acids from the yeast strain were analyzed as C(16) and C(18:1) with omega-3 content from about 6% to 7%. Thus, this marine-derived yeast could be a potential source of lipids, including omega-3 fatty acids.     

Combustion-synthesized ferrites and ferroelectrics for microwave applications

The individual phases of Ni_{1 ? x} Cd _x Fe₂O₄ (x = 0.2, 0.4, 0.6) ferrite and Ba_0.8Sr_0.2TiO₃ ferroelectric (BST phase) were successfully prepared by autocombustion route. The oscillatory behavior of transmittance for the Ni-Cd ferrite was observed at about 0.44 at 8.2 GHz. The absorption study depicts the hopping phenomena of microwaves through the Ni-Cd phase. The dependence of microwave conductivity on ferrite content was discussed. The dielectric permittivity of Ni-Cd ferrites varied between 10 and 30. Compared to the Ni-Cd phase, the transmittance of the Ba_0.8Sr_0.2TiO₃ phase was found to be low. The dip in reflection loss for Ba_0.8Sr_0.2TiO₃ is equivalent to the minimum reflection or the maximum absorption of the microwave power for BST phase. The maximum microwave conductivity for Ba_0.8Sr_0.2TiO₃ was found to be about 0.459 S/cm. The high microwave permittivity for Ba_0.8Sr_0.2TiO₃ had a value of about 120.21.     

A THREE-DIMENSIONAL FINITE ELEMENT MODEL FOR POWDER COMPACTION—TIME-DEPENDENT FORMULATION AND VALIDATION

Many industrial powders have been documented to have time-dependent compression response. However, in the literature very few time-dependent formulations are reported for three-dimensional analysis of powder compaction. In the paper, a time-dependent constitutive model, based on the theory proposed by Adachi and Oka, was used in a three-dimensional finite element formulation suitable for PC or desktop environments. The finite element model (FEM) predicts both the stress and density distributions in the powder mass during compression, i.e., from no load to the maximum compression load. A user-friendly interactive GUI (graphical user interface) was developed for the 3-D FEM, making it easy to use. To validate the FEM, microcrystalline cellulose was compressed to form cylindrical pellets using a press. The pellet was used to obtain spatial density distribution using the sectioning method. Then, the measured density distribution was compared with the Adachi and Oka model-based FEM calculated values. The density distributions were predicted within the 95% confidence interval of measured values. In addition, the overall error between the measured and predicted density values throughout the pressed pellet was less than 10%     

MEASUREMENT OF COHESION AND ANGLE OF INTERNAL FRICTION USING CUBICAL TRIAXIAL TESTER AND COMPARISON WITH COMPUTER CONTROLLED SHEAR CELL

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 knowledge of the shear plane location in the CTT.     

Microstructure and mechanical behavior of die casting AZ91D-Fly ash cenosphere composites

The feasibility of incorporating fly ash cenospheres in die cast magnesium alloy has been demonstrated. The effects of fly ash cenosphere additions on the microstructure and some of the salient physical and mechanical properties of magnesium alloy (AZ91D) metal matrix composites were investigated. The control AZ91D alloy and associated composites, containing 5, 10, and 15 wt.% of fly ash cenospheres (added), were synthesized using a die casting technique. A microstructural comparison showed that microstructural refinement – occurred due to the fly ash additions and became more pronounced with an increase in the percentage of the fly ash added. The metal matrix areas nearer to the fly ash particles exhibited a greater degree of refinement than was observed in the areas further away from these particles. Both filled and unfilled fly ash cenospheres, and porosity were observed in the composite microstructures. The composite specimen densities decreased and the coefficient of thermal expansion did not change significantly as the volume percent of fly ash was increased within the range investigated. The hardness values of the composite specimens exhibited an increase in proportion to the increase in percentage of added fly ash. The tensile strength of the composites also increased as the concentration of fly ash cenospheres was increased. In contrast, the Young’s modulus of these composite samples, as measured by non-destructive pulse-echo method, decreased as the percentage of fly ash in the composite was increased. SEM micrographs of the tensile fracture surfaces showed broken cenospheres on the fracture surface and evidence of ‘pull outs’, where fly ash particles were previously embedded in the matrix. Compression testing results showed that the presence of 5 wt.% cenospheres decreased the compressive strength and compressive yield strength of the composite relative to that of the AZ91D matrix alloy. Surprisingly, a significant change in compression strength was not observed for the composites with 10 and 15 wt.% cenospheres in comparison to the AZ91D matrix alloy. In contrast to the tensile tests, no cenosphere remnants were observed on the compressive test fracture surface of the composites. This observation suggests that the fracture of the composite was initiated within the AZ91D matrix by normal void nucleation and growth, followed by crack propagation through the matrix, avoiding any of the cenospheres, leading to composite fracture of the matrix.