Powder Mixing Process Research Articles

Effect of powder mixing process on the microstructure and thermal conductivity of Al/diamond composites fabricated by spark plasma sintering

Two powder mixing processes, mechanical mixing (MM) and mechanical alloying (MA), were used to prepare mixed Al/diamond powders, which were subsequently consolidated using spark plasma sintering (SPS) to produce bulk Al/diamond composites. The effects of the powder mixing process on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated. The results show that the powder mixing process can significantly affect the microstructure and the thermal conductivity of the composites. Agglomerations of the particles occurred in mixed powders using MM for 30 min, which led to high pore content and weak interfacial bonding in the composites and resulted in low relative density and low thermal conductivity for the composites. Mixed powders of homogeneous distribution of diamond particles could be obtained using MA for 10 min and MM for 2 h. The composite prepared through MA indicated a high relative density but low thermal conductivity due to its defects, such as damaged particles, Fe impurity, and local interfacial debonding, which were mainly introduced in the MA process. In contrast, the composite made by MM for 2 h demonstrated high relative density and an excellent thermal conductivity of 325 W·m−1·K−1, owing to its having few defects and strong interfacial bonding.

Quantitative Quasi-Simultaneous and Spatially Resolved Real-time Monitoring of Powder Mixing Processes with a Multiple NIR-Probe Setup

Diffuse reflectance near-infrared (NIR) spectroscopy is a non-invasive and widely used technology with the potential for a wide range of applications in the pharmaceutical industry, ranging from raw material identification to final product qualification. [...]

Optimization of Mixing Process of Polymer and Ceramic Powder by Ultrasound

Real-time, on-line, non-intrusive and non-destructive ultrasonic technology has been applied for mixing process in the internal mixer. Mechanical torque measurement, visual observation, and ultrasonic signatures (such as amplitude of transmission and reflection echoes, sound velocity and attenuation), were used for the diagnosis of the melting process of low density polyethylene (LDPE) and the mixing process of the melted LDPE with a calcium carbonate (CaC0 3 ) powder. Phenomena during the melting and mixing processes, including phase change from solid to melt, and distributing progress of CaC0 3 powder, were successfully monitored by ultrasound. Four ultrasonic parameters are compared for indicating the melting and mixing processes. The results showed that it was possible to determine when the polymer had melted thoroughly and mixed with CaCO 3 powder completely by using the peak value of ultrasonic L 2f echo. The presented ultrasonic technique can be utilized to optimize the melting and mixing processes.

Thermal, dielectric, and mechanical properties of SiC particles filled linear low‐density polyethylene composites

AbstractA thermally conductive linear low‐density polyethylene (LLDPE) composite with silicon carbide (SiC) as filler was prepared in a heat press molding. The SiC particles distributions were found to be rather uniform in matrix at both low and high filler content due to a powder mixing process employed. Differential scanning calorimeter results indicated that the SiC filler decreases the degree of crystallinity of LLDPE, and has no obvious influence on the melting temperature of LLDPE. Experimental results demonstrated that the LLDPE composites displays a high thermal conductivity of 1.48 Wm−1 K−1 and improved thermal stability at 55 wt % SiC content as compared to pure LLDPE. The surface treatment of SiC particles has a beneficial effect on improving the thermal conductivity. The dielectric constant and loss increased with SiC content, however, they still remained at relatively low levels (<102 Hz); whereas, the composites showed poorer mechanical properties as compared to pure LLDPE. In addition, combined use of small amount of alumina short fiber and SiC gave rise to improved overall properties of LLDPE composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Fabrication and dielectric properties of lead titanate nanocomposites

A simple powder mixing and pressure-less sintering process for fabrication of PbTiO 3 (PT) nanocomposites (micron-sized PT matrix reinforced with either PT nanoparticles or nanofibers) has been developed to enhance both densification and dielectric properties. The potentiality of a ceramic-nanocomposite technique as a low-cost and simple ceramic fabrication to obtain highly dense and pure PT/PT composites was demonstrated. It has been found that both densification and dielectric properties of the composites fabricated in this work were significantly enhanced, as compared to the two-stage sintering and the conventional PT ceramics.

Sintering mechanism of fine zirconia powders with alumina added by powder mixing and chemical processes

The present study examined the sintering behavior of fine zirconia powders (containing 2.9 mol% Y2O3) with and without small amounts of Al2O3 added by different ways: powder mixing (PM), homogeneous precipitation (HP), and hydrolysis of alkoxide (HA). The initial sintering behavior was examined by both measurement methods of a constant rate of heating and isothermal shrinkage. In the PM process, Al2O3 particles pinned the shrinkage of zirconia powder compact at the initial stage and diffuse toward zirconia surface to enhance the sintering. This initial sintering mechanism was explained by the grain-boundary diffusion for the Al2O3-free powder and the volume diffusion for Al2O3-added powder. When Al2O3 was added to zirconia powder by HP and HA processes, the densification rate was more stimulated compared to the PM process. The initial sintering mechanism did not change by the way for Al2O3 addition. The Al2O3 addition by chemical processes of HP and HA tended to enhance the grain growth of zirconia, while the uniform microstructure was achieved because of homogeneous addition of Al2O3 by those processes.

Characterization of continuous convective powder mixing processes

The Process Analytical Technology (PAT) initiative has encouraged the development of new technology to improve upon the current manufacturing paradigm. As a result substantial attention has recently focused on continuous processing due to the ability to control disturbances online, avoiding the loss of processing materials and enabling effective process scale-up. In this paper, a pharmaceutical formulation is blended using a continuous flow “high shear” mixer utilizing different operating and design parameters. The mixing efficiency is characterized by extracting samples at the discharge of the blender, and analyzing them using Near Infrared Spectroscopy to determine compositional distribution. Operational conditions such as the inclination angle of the mixer and impeller rotation rate were investigated and showed to affect the mean residence time. The effects of mixer angle, agitation speed, number of blades, blade angle, number of passes through the mixer on the mixing performance of a powder continuous convective mixer are also examined and shown to affect mixing performance whereas the cohesive properties of the material did not significantly affect the mixing operation.

Enhanced mechanical properties of machinable Si3N4/BN composites by spark plasma sintering

Abstract Si3N4/BN composites were fabricated by spark plasma sintering (SPS) through traditional powder mixing process and by a chemical route to Si3N4/BN composite powder, respectively. The SPS-processed Si3N4/BN composites maintain a considerably high bending strength, exhibiting some gradual decrease though with increasing BN content. Given the BN content, the bending strength is enhanced for the composites prepared by powder mixing relative to the chemical route counterparts. Differences in the α → β phase transformation of Si3N4 and grain growth during the SPS process play a key role in the variation of strength. Regardless of the preparation method, the Si3N4/BN composites with a BN content up to 30 vol.% can be well machined with WC tools.

Fabrication of Electronic Conductive Silicon Nitride Ceramics by Convenient Powder Metallurgical Process

Si3N4 ceramics with V2O5 based glasses as sintering additives were successfully fabricated by a powder mixing process and rapid sintering by the PECS method. The fabricated materials by Pulsed Electric Current Sintering (PECS) exhibited very fine microstructure with α and β grains. Electric conductivity for the Si3N4/(V2O5-B2O3) and the Si3N4/(V2O5-B2O3-Al2O3) at room temperature were four and six orders of magnitude higher at room temperature, and two and three orders of magnitude higher at 1000 oC than the conventional Si3N4, respectively

Characterizing powder mixing processes utilizing compartment models

Powder mixing has been the subject of substantial research due to its importance in a variety of industrial sectors, including pharmaceuticals, food, and polymer manufacturing. Although a number of different models have been proposed in the literature, most of them are either empirical or require computationally intensive calculations that make them difficult to implement for realistic systems. The aim of this paper is to develop a simplified framework, based on compartment modeling that efficiently and accurately captures the system behavior. Using the V-blender as a model system, the compartment modeling approach was used to illustrate the effects of vessel loading on mixing as well as the impact of sampling methods on the accuracy of mixing characterization.

Image processing and analysis for determination of concentrations of powder mixtures

The quality of the pharmaceutical powder mixing strongly influences the potency and properties of the tablets. Furthermore, in order to optimize powder mixing processes, fast and accurate methods are sought for determining the concentration of powder mixtures. This work describes an optical method based on an image processing system to determine concentration of powders in a mixture that can be sensed by its gray-level values. The methodology was developed utilizing univariate and multivariate gray image analysis. The effect of difference in mean gray value (DMGV) on the precision and accuracy of the vision system was determined. The results that were obtained from the vision system were compared to those obtained with near-infrared spectroscopy. The multivariate gray image analysis methodology using frequency of each gray-level value ( Φ) of gray scale as the independent variables obtained the best predictions. The vision system produced high precision with a standard deviation of about 1.7% w/w and a 2.6% relative standard deviation. The accuracy indicated by the root mean standard error of prediction (RMSEP) was around 1.7% w/w. The mixtures analyzed with the vision system and the near-infrared spectrometer yielded similar results. Analysis of all results confirms that the vision system is an adequate technology for determination of powder mixture concentrations.

Experimental study of the mixing kinetics of binary pharmaceutical powder mixtures in a laboratory hoop mixer

As increasingly commented by the literature during the last 5 years, estimating the homogeneity of a powder mixture and following powder mixing processes is not a simple task. In this paper, we present the development and statistical validation of a sampling methodology for defining the number of samples required to provide a reasonable estimation of the homogeneity attained in a laboratory scale tumbler mixer. This method is then used to follow the mixing kinetics of a dilute binary powder mixture in a hoop mixer. Special attention is paid to the statistical meaning of the values obtained and the influence of the physical characteristics such as particle size and shape. The role of the particle shape of the majority powder is particularly emphasised and it is quantitatively demonstrated that spherical particles are harder to mix and more ready to segregate than particles with irregular shapes. The different mixing mechanisms at play are identified; the practical limits of use of such tumbler mixers with pharmaceutical powders are discussed.

Denitrification of Ti(C,N) based cermet during powder mixing process

Changes in the nitrogen content of Ti(C,N)-based cermets during powder mixing and sintering processes were investigated and the denitrification mechanism was re-evaluated. The denitrification of N-containing cermets occurrs mainly during the powder mixing process, and is relatively small during sintering periods. Denitrification during powder mixing is caused by oxidation of the Ti(C,N) powders in contrast to denitrification during sintering, which is caused by the decomposition of the nitrides due to the high nitrogen partial pressure. It was concluded that the main source of oxygen for the powder oxidation was the water present in the ethanol solvent.

Real time and noninvasive monitoring of dry powder blend homogeneity

The primary goal of this research is to develop a method to implement both process and product verification in real time for blending of the dry active pharmaceutical ingredient with excipients. It is expected that success will facilitate process development and validation, open the possibility to reduce cycle time by eliminating the need for routine off-line analysis of blend homogeneity, and further assure product quality by measuring component homogenity in a way that avoids the possibility of sampling error. There is also the benefit of permitting better equipment utilization by shortening cycle time and reducing labor costs associated with this unit operation. Although this work described processing of pharmaceutical powders, this technology is applicable for all types of powder mixing process in other industries.

Microstructure and mechanical properties of SiC-platelet reinforced Al2O3/SiC-particle hybrid composites

SiC-platelet reinforced Al2O3/SiC-particle nanocomposites were fabricated by hot-pressing the mixture through the conventional powder mixing process. The mechanical properties of Al2O3/SiC-particle/SiC-platelet hybrid composites were evaluated. Fracture toughness and work of fracture were increased by the incorporation of SiC-platelets into Al2O3/SiC-particle nanocomposites. The typical rising R-curve was shown during crack growth for these hybrid nanocomposites, whereas Al2O3/SiC-particle nanocomposites showed the constant KR value and no rising R-curve. The further improvement of Al2O3/SiC-particle nanocomposites in the creep resistance was observed by the addition of SiC platelets. The relationship between the microstructure and mechanical properties for Al2O3/SiC-particle/SiC-platelet hybrid composites was discussed.

Structural Characterization and Electrical Properties of Lead Bismuth Zirconate Titanate (PbBi4ZrxTi4-xO15) Ceramics Prepared from Sol-Gel Derived Powders.

PbBi4ZrxTi4-xO15 (PBZT) ceramics were synthesized for the first time from sol-gel derived powders, and their electrical properties were investigated. The orthorhombic PbBi4Ti4O15 (PBT) structure was maintained in the Zr concentration (x) range up to x=2.0. However, in the range of 0<x≤0.5, monotonous changes in the lattice parameters were observed as well as the absence of a second phase. PBZT powders and ceramics were prepared by using both a conventional powder-mixing process and a sol-gel technique. The conventional powder-mixing process did not lead to PBZT phase formation under any conditions, even with x=0.5. The substitution of titanium by zirconium increased the Curie temperature (TC) from 554 to 563°C and decreased the relative permittivity at TC from 3003 to 1329 at x=1.0. A remarkable increase in ferroelectric properties was observed at a Zr concentration of x=0.5. 2Pr and 2Ec values at x=0.5 were 2.4μC/cm2 and 18.4kV/cm, respectively, at room temperature, and 9.9μC/cm2 and 28.1kV/cm, respectively, at 120°C, at an electric field of 40kV/cm.

ＳｉＣ粒子強化超塑性アルミニウム合金複合板の深絞り

Metal matrix composites to be plastically wrought under tensile load were developed, using superplastic aluminum alloy powder and SiC particles (5μm or 20μm diameter) as matrix and reinforcement material, respectively. We discussed the effects of powder mixing process, SiC particle size, hot pressing conditions and the local heating and cooling deep drawing on the characters of the MMCs (relative density, tensile strength and plastic workability, etc.). As an example of the results, drawing ratio of MMCs containing 20μm and 25% volume fraction SiC particles attained to 2.18 by the local heating and cooling deep drawing.

Drug-excipient interactions resulting from powder mixing. V. Role of sodium lauryl sulfate

The effect of sodium lauryl sulfate on the drug-excipient interactions resulting from prolonged powder mixing with magnesium stearate was evaluated. Two formulations, identical in their composition, with and without 0.1% sodium lauryl sulfate were compared under identical mixing conditions to study the drug-excipient interaction on prolonged mixing and its effect on in vitro dissolution from hand-filled, uncompacted capsules. The results of this study reveal that the addition of sodium lauryl sulfate in the solid state to magnesium stearate in 1: 5 ratio can offset the deleterious effects, such as the decrease in dissolution rate, associated with prolonged mixing of magnesium stearate. The results suggest that there is a strong physical interaction between the magnesium stearate flakes and sodium lauryl sulfate during the solid-state powder mixing process. The interaction between magnesium stearate and sodium lauryl sulfate frees the magnesium stearate flakes from the drug-excipient agglomerates. As a result, the capsule disintegration time and the drug dissolution rate are not adversely affected.

Flow and Mixing of Powder in the Vertical-Cylinder-Type Mixer

The flow pattern and the mixing process of powder in the vertical-cylinder-type mixer were investigated using photographic observation and measurements of the concentration profile of a tracer. Furthermore, using white glass particles as a tracer, the flow pattern in the mixer was studied by the model mixer, in which glass beads were made transparent by methylbenzoate, having same refractive index with glass beads.The flows of powder varied according to the local position in the mixer. Those characteristics were shown in term of the local rate coefficient of mixing.Desirable mixing states were observed under the condition of strong shear force and large rectangular velocity gradient in powder at the front edge of the paddle. In addition, many flowing circuits and mixing zones were found at the other regions.