Function Of Compaction Pressure Research Articles

Formulation of a newly developed shale-swelling model as a function of compaction pressure and temperature

Formulation of a newly developed shale-swelling model as a function of compaction pressure and temperature

A powder tabletability equation

An equation describing tablet tensile strength as a function of compaction pressure was derived from the Ryshkewitch and Kuentz-Leuenberger equations. The equation was used to fit data from 11 powders, including single-component powders and mixtures, with a wide range of mechanical properties. Three fitted parameters are obtained directly from tensile strength-compaction pressure data, of which one describes the apparent bonding strength and another strongly correlates with the plasticity.

Investigation of Formation Behaviour of Al-Cu Intermetallic Compounds in Al-50vol%Cu Composites Prepared by Spark Plasma Sintering under High Pressure.

Al–Cu matrix composites with excellent mechanical and thermal properties are among the most promising materials for realising high performance in thermal management systems. However, intermetallic compounds (ICs) formed at the Al/Cu interfaces prevent direct contact between the metals and severely deteriorate the thermal conductivity of the composite. In this study, we systemically investigated the formation behaviour of Al–Cu ICs as a function of compaction pressure at a low temperature of 380 °C. The phases of the Al–Cu ICs formed during sintering were detected via X-ray diffraction, and the layer thickness and average area fraction of each IC at different compaction pressures were analysed via micro-scale observations of the cross-sections of the Al–Cu composites. The ICs were partially formed along the Al/Cu interfaces at high pressures, and the formation region was related to the direction of applied pressure. The Vickers hardness of the Al–Cu composites with ICs was nearly double those calculated using the rule of mixtures. On the other hand, the thermal conductivity of the composites increased with compaction pressure and reached 201 W·m−1·K−1. This study suggests the possibility of employing Al–Cu matrix composites with controlled IC formation in thermal management applications.

Microstructural Evolution, Powder Characteristics, Compaction Behavior and Sinterability of Al 6061–B4C Composites as a Function of Reinforcement Content and Milling Times

Al 6061100–x–x wt % B4C (x = 0, 5, 10, 20, 30 and 40) composites, prepared by mechanical alloying and compacted at room temperature, have been used for the present investigation. The effects of B4C content and milling time on the powder morphology, powder particle size, and other powder characteristics such as the apparent density, tap density, flow rate, cohesiveness, and hausner ratio are systematically investigated. The steady state of milling process is determined by observing the correlation between apparent densities and milling time explained by the morphological evolution of the powder particles during the milling process. The Hausner ratio (HR), estimated to evaluate friction between the particles, decreases with an increase in milling duration and B4C content due to the changes in morphology and hardness of the powders. The compressibility behavior of post-compacts as a function of compaction pressure and the B4C content was analyzed by using several linear and non-linear powder compaction equations. The linear Panelli and Ambrozio Filho, and non-linear Van Der Zwan and Siskens equations give the highest regression coefficients. The results are explained in terms of the plastic deformation capacity and plastic deformation coefficient of the powders, which are influenced by the hardness and the morphology of the powder. After compaction, the supersolidus liquid phase sintering was performed at various temperatures (585, 610 and 630°C) under high purity nitrogen atmosphere. The results revealed that the sinterability was degraded by increasing the reinforcement content, particularly above 10 wt % B4C. Neutron radiography measurements conducted on the rolled composite sheet have revealed the uniform distribution of B4C particles in the composite.

Analysis of soft magnetic materials by electron backscatter diffraction as a powerful tool

The current work demonstrates that electron backscatter diffraction (EBSD) is a powerful and versatile characterization technique for investigating soft magnetic materials. The properties of soft magnets, e.g., magnetic losses strongly depend on the materials chemical composition and microstructure, including grain size and shape, texture, degree of plastic deformation and elastic strain. In electrical sheet stacks for e-motor applications, the quality of the machined edges/surfaces of each individual sheet is of special interest. Using EBSD, the influence of the punching process on the microstructure at the cutting edge is quantitatively assessed by evaluating the crystallographic misorientation distribution of the deformed grains. Using an industrial punching process, the maximum affected deformation depth is determined to be 200 - 300 μm. In the case of laser cutting, the affected deformation depth is determined to be approximately zero. Reliability and detection limits of the developed EBSD approach are evaluated on non-affected sample regions and model samples containing different indentation test bodies. A second application case is the investigation of the recrystallization process during the annealing step of soft magnetic composites (SMC) toroids produced by powder metallurgy as a function of compaction pressure, annealing parameters and powder particle size. With increasing pressure and temperature, the recrystallized area fraction (e.g., grains with crystallographic misorientations < 3°) increases from 71 % (200 MPa, 800°C) to 90% (800 MPa, 800°C). Recrystallization of the compacted powder material starts at the particle boundaries or areas with existing plastic deformation. The progress of recrystallization is visualized as a function of time and of different particle to grain size distributions. Here, large particles with coarse internal grain structures show a favorable recrystallization behavior which results in large bulk permeability of up to 600 – 700 and lower amount of residual misorientations (>3°).

The impact of hot-melt extrusion on the tableting behaviour of polyvinyl alcohol

There is evidence that processing techniques like hot-melt extrusion (HME) could alter the mechanical properties of pharmaceuticals, which may impede further processability (e.g. tableting). The purpose of this study was to evaluate if HME has an impact on the tableting behaviour of polyvinyl alcohol (PVA)-formulations. Mixtures of partially hydrolysed PVA grades (with a hydroxylation degree of 75 and 88%) and sorbitol (0, 10 and 40%) were extruded, (cryo-) milled and compressed into compacts of 350±10mg. Before compression all intermediate products were characterized for their solid-state (Tg, Tm, crystallinity) and material properties (particle size, moisture content, moisture sorption). Because both PVA-grades required higher extrusion temperatures (i.e. 180°C), sorbitol was added to PVA as plasticizing agent to allow extrusion at 140°C. Compaction experiments were performed on both physical mixtures and cryo-milled extrudates of PVA-sorbitol. By measuring tablet tensile strength and porosity in function of compaction pressure, tableting behaviour was compared before and after HME by means of the CTC-profiles (compressibility, tabletability, compactibility). A higher amorphous content in the formulation (as a result of HME) negatively influenced the tableting behaviour (i.e. lower tablet tensile strength). HME altered the mechanical properties towards more elastically deforming materials, thereby increasing tablet elastic recovery during decompression. The lower tensile strengths resulted from a combined effect of less interparticulate bonding areas (because of higher elastic recovery) and weaker bonding strengths per unit bonding area (between glassy particles).

On development of hypoeutectic aluminium–silicon powder metallurgy alloy

Powder metallurgy allows for the rapid, automated and efficient production of many different types of automotive components. However, a drawback is the limited selection of readily available light alloy blends. Owing to the wide spread use of aluminium–silicon casting alloys for existing components it is logical to develop aluminium–silicon PM options. Therefore, an experimental hypoeutectic aluminium–silicon alloy was chosen for study and an optimum processing route developed. Tests were performed to determine the green strength and density as a function of compaction pressure. Sintering conditions were optimised based on sintered density, hardness and dimensional changes. Metallography, differential scanning calorimetry and energy dispersive X-ray spectroscopy analysis provided insight into post-sinter furnace cooling and heat treatment parameters. An appropriate T6 heat treatment was developed and samples were tested in tension. The alloy was able to achieve a high sintered density approaching 98% and a yield strength of 232 MPa under the T6 condition.

Evaluation of compaction equations and prediction using adaptive neuro-fuzzy inference system on compressibility behavior of AA 6061 100 − x –x wt.% TiO 2 nanocomposites prepared by mechanical alloying

Nanocrystallite/nanocomposite powders of AA 6061 100 − x –x wt.% TiO 2 (x = 0, 2, 4, 6, 8, 10 and 12) prepared by mechanical alloying and compacted at room temperature have been used for the present investigation. Compaction behavior of post-compacts as a function of compaction pressure and the nano titania content in the nanocrystallite matrix powder was investigated using several powder compaction equations (empirical form) including both linear and non-linear type. The non-linear equation proposed by Van Der Zwan and Siskens was the best fitting curve comparing other equations developed by Balshin, Heckel, Ge, Panelli and Ambrosio Filho, Kawakita, and Shapiro. The Van Der Zwan and Siskens compacting equation gives the regression coefficient very close to unity. Also, this paper focuses on the development of expert system based on an adaptive neuro-fuzzy inference system (ANFIS) on compaction behavior of the developed nanocomposite powder. This ANFIS model was accurately established to obtain the relationship between percentage of nano titania content in the nanocrystalline matrix and compaction pressure to get the required relative density. The predicted relative density obtained from ANFIS was compared with experimental data and also evaluated with the predicted relative density derived by multiple regression analysis (MRA). The comparisons indicated that the developed ANFIS achieved excellent accuracy and it was as high as 99.50%.

Evolution of fractal features of pores in compacting and sintering process

As an index of molding, the fractal dimension of pores can reflect system varying details as the density. Pores in the powder aggregates with a composition of Fe–2%Cu–0.5%C were researched. The change tendency of dimension of pores as a function of compaction pressure or sintering temperature was investigated. Result indicates that the dimensions of pores in this ternary system decrease both in the process of compacting and sintering. It is convenient to build up some theories by combining compacting and sintering based on the variation of pore dimensions.

Validity of a Power Law Approach to Model Tablet Strength as a Function of Compaction Pressure

Designing quality into dosage forms should not be only based on qualitative or purely heuristic relations. A knowledge space must be generated, in which at least some mechanistic understanding is included. This is of particular interest for critical dosage form parameters like the strength of tablets. In line with this consideration, the scope of the work is to explore the validity range of a theoretically derived power law for the tensile strength of tablets. Different grades of microcrystalline cellulose and lactose, as well as mixtures thereof, were used to compress model tablets. The power law was found to hold true in a low pressure range, which agreed with theoretical expectation. This low pressure range depended on the individual material characteristics, but as a rule of thumb, the tablets having a porosity of more than about 30% or being compressed below 100 MPa were generally well explained by the tensile strength relationship. Tablets at higher densities were less adequately described by the theory that is based on large-scale heterogeneity of the relevant contact points in the compact. Tablets close to the unity density therefore require other theoretical approaches. More research is needed to understand tablet strength in a wider range of compaction pressures.

Modeling and analysis of thickness gradient and variations in vacuum‐assisted resin transfer molding process

AbstractAs vacuum‐assisted resin transfer molding (VARTM) is being increasingly used in aerospace applications, the thickness gradient and variation issues are gaining more attention. Typically, thickness gradient and variations result from the infusion pressure gradient during the process and material variations. Pressure gradient is the driving force for resin flow and the main source of thickness variation. After infusion, an amount of pressure gradient is frozen into the preform, which primarily contributes to the thickness variation. This study investigates the mechanism of the thickness variation dynamic change during the infusion and relaxing/curing processes. A numerical model was developed to track the thickness change of the bagging film free surface. A time‐dependent permeability model as a function of compaction pressure was incorporated into an existing resin transfer molding (RTM) code for obtaining the initial conditions for relaxing/curing process. Control volume (CV) and volume of fluid (VOF) methods were combined to solve the free surface problem. Experiments were conducted to verify the simulation results. The proposed model was illustrated with a relatively complex part. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Validation of Macroscopic Attenuated Total Reflection-Fourier Transform Infrared Imaging to Study Dissolution of Swelling Pharmaceutical Tablets

Macroscopic attenuated total reflection (ATR) infrared imaging is applied to study the dissolution of realistically sized hydroxypropyl methylcellulose (HPMC) tablets. The water intake into in situ compacted tablets and pre-compacted tablets was studied as a function of compaction pressure. Rigorous analysis of the imaging datasets show that the speed of water intake into HPMC tablet is approximately 4 microm/min and is hardly affected by the studied range of compaction pressures or the type of ATR crystal used (diamond or ZnSe). This constant speed of water intake implies that leakage (''creeping'') of water into the space between the tablet and the ATR crystal does not occur. It is shown that the radius of the HPMC tablet initially expands to twice the original radius due to swelling.

Structure and properties of Al–Ni PM composites

Al–Ni powder mixtures containing 2, 4, 6 and 8 wt-% nickel were compacted at 125, 250, 375 and 500 MPa and sintered at 620, 630 and 640°C in a nitrogen atmosphere. The sintered density, sintered hardness and strength of composites thus produced were determined as a function of compaction pressure and sintering temperature. Wear rates of the composites were evaluated as a function of applied load and sliding velocity. Optical and scanning electron microscopy were used to reveal the morphology of powder and microstructures of green and sintered compacts. X-ray diffraction studies of the sintered compacts were made to confirm the phases formed on sintering. Sintered density, sintered hardness and strength increased with an increase in compaction pressure and nickel content. X-ray diffraction indicated the presence of Al3 Ni phase in the sintered alloy. The wear rate of the sintered Al–Ni PM composite was found to increase with increasing load and decrease with increasing nickel content.

Development and validation of a material-labeling method for powder process characterization using X-ray computed tomography

The material-labeling method presented in this paper, coupled with X-ray computed tomography (XRCT), allows in situ non-invasive 3D characterization of certain pharmaceutical processes using relevant materials and process geometry. Microcrystalline cellulose (MCC, Celphere) particles were used in experiments, and lead (II) acetate trihydrate was used to label the MCC particles because it has both high water solubility and high X-ray attenuation coefficient. A 0.5-M lead acetate solution was used to impregnate the Celphere particles, and thus to deliver sufficient contrast in the XRCT shadow images. Selected physical properties of the impregnated particles were examined and found to be similar to the as-received material. The mixture of Pb-impregnated and as-received Celphere particles constituted a model pharmaceutical system to investigate die compaction and blending. Lead impregnation allows particles of low atomic weight to become visually traceable on XRCT by enhancing their X-ray absorption. For the compaction study, the in-die positions of Pb-impregnated particles were monitored as a function of compaction pressure. For the mixing study, a linear correlation between the gray scale of the cross-section images and the percentage of Pb-impregnated particles in the mixture was demonstrated. Two different initial fill configurations were compared: column-filling and layer-filling. Results show that the layer-filled configuration leads to better mixing than the column-filled configuration.

Novel Synthesis of Nitride Powders by Microwave-assisted Combustion

A novel and simple microwave-assisted combustion procedure for the synthesis of a number of technologically important metal nitrides was demonstrated. The method involves the combustion reaction of a porous metal powder compact with N2 gas in the microwave field and provides phase-pure metal nitride products (consisting of fine particles, fibers, and whiskers) within minutes. The ignition and combustion temperatures of the reaction were found to vary as a function of compaction pressure. The microwave-prepared nitrides were characterized using x-ray diffraction, scanning electron microscopy energy dispersive spectroscopy, thermogravimetric analysis, and infrared spectroscopy. The present microwave-assisted hybrid-heating procedure allows the preparation of nitrides with good crystallinity, structural uniformity, and phase purity, and appears to have general applicability for the preparation of metal nitrides (using the respective metals or even their oxides).

Microstructure and mechanical properties relations for green bodies compacted from spray dried granules

Alumina granules from three binder systems were spray dried and pressed into bars at varied pressure. Granules are classified as strong, medium and weak as to reflect the different amount of poly(vinyl-butyral) binder and liquid paraffin plasticizer used in the binder system. Mechanical properties of the pressed bars were obtained from a four-point bend test and microstructures were examined using scanning electron microscopy SEM. Strengths and fracture toughnesses are found to increase as a function of compaction pressure, while the calculated effective flaw size is independent of the compaction pressure for all three granule types. Microstructural examination of fracture surfaces revealed that samples compacted at high pressure exhibited more transgranular fracture than samples compacted at low pressure. Evidently, higher pressure had increased the intergranular fracture resistance which correspondingly increased the fracture toughness of the pressed bars. For bars pressed from granules, green body strengths and toughnesses are strongly dependent on the cohesion between pressed granules and not on the effective processing flaw size.

Some pressing characteristics of molybdenum wire (fibers)

1. A study was made of the pressing behavior of molybdenum fibers in work-hardened and annealed conditions, as a result of which it was established that the residual porosity of compacts as a function of compaction pressure is described by an exponential relationship. 2. The apparent density of fibers was found to rise linearly with increase in their diameter and to fall with increase in their length.

Liquid Movement Through Kaolinite under Hydraulic, Electric, and Osmotic Gradients

Hydraulic, osmotic, and electro-osmotic conductivities of sodium kaolinite were measured as a function of compaction pressure ranging from 1 atm to approximately 600 atm. The data were used to estimate the relative importance of osmosis and electro-osmosis, compared with hydraulic flow, through confining beds at different depths of burial. The results indicate that Darcy's law is not a sufficient basis for predicting either the magnitudes or the directions of liquid movement through deep confining beds.

Dependence of the density of metal-powder compacts on compaction pressure

1. Formulas have been derived permitting determination of the mean relative volume of compacts and the variation in density over the compact length and diameter at a given compaction pressure or the required compaction pressure for a given mean compact density. 2. A technique has been proposed for determining the relative volume of compacts from multicomponent powders as a function of compaction pressure. 3. It is shown that, when σB and ψn values obtained in tensile tests on nonporous metals of the same composition and the recommended design values of the coefficient of external friction are substituted into the formulas proposed, the resulting calculated data are in good agreement with experimentally determined values reported by various authors.