Increasing Compression Pressure Research Articles

EFFECT OF PYROLYSIS TEMPERATURES ON COMPOSITION AND ELECTRICAL CONDUCTIVITY OF CARBOSIL PREPARED FROM RICE HUSK

The objective of this study was to evaluate the effect of pyrolysis temperatures on composition and electrical conductivity of carbosil produced from rice husk, by conducting pyrolysis experiments at three different temperatures of 200; 400; and 700 °C. The structure of the samples was characterized using Fourier Transform Infrared (FTIR) Spectroscopy and X-Ray Diffraction (XRD). The microstructure and elemental composition were characterized using Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), and the electrical conductivity was measured using four probe method. The FTIR analyses revealed the existence of Si-O-Si and Si-OH functional groups, but no functional groups associated with carbon, confirming the formation of carbosil. This formation of carbosil is also supported by the results of EDS analyses which show the presence of only three elements of C, O, and Si, respectively. The XRD results indicate that the carbosils are amorphous, suggesting that no transformation of carbon and silica into crystalline phase to the limit of the temperatures applied. The carbosil formation decreased with increasing of pyrolysis temperature. The microstructure of the carbosils indicates that the higher the temperature, the smaller the grain size of the samples. The values of electrical conductivity of the samples are in the range of 1.13 x 10-3 to 6.81 x 10-3/(Ω.m) with the application of 10 tones compression pressure, but the conductivities of the sample prepared at 200 °C were found to increase with increased compression pressure to six fold from 6.81 x 10-3 to 41.94 x 10-3/(Ω.m) by increasing compression pressure to 80 tones. Based on these conductivity values, the samples are considered as semiconductor, suggesting the potential use of the carbosil in semiconductor devices.

Energy Saving and Optimization for Compression and Liquefaction System in Power Plants CO<sub>2</sub> Trapping Project

Based on the data of 30000t/a CO2 capture & purification pilot scale test in Shengli power plant, the principle and method of CO2 compression and liquefaction were introduced, the calculation model of energy consumption for CO2 liquefaction process was built, the effection factors of CO2 purification power were analyzed, the ways to optimize energy saving were discussed. The results show that: (1) improving liquefaction pressure can effectively reduce the total power of CO2 compression and liquefaction, as the compression pressure increases, the compression power increases while the liquefaction power and total power reduce; (2) While the liquefaction pressure is less than 3.3MPa, compression power is less than liquefaction power, While the liquefaction pressure is greater than 3.3MPa, compression power is greater than liquefaction power; (3) While the liquefaction pressure of CO2 at the critical pressure 7.4 MPa, the theoretical total power is minimum.

The Influence of Micro Structure of the GDL and MPL on the Mass Transport in PEFC

The relationship between micro structures of the GDL/MPL and mass transport property was investigated through coupled visualization and numerical analyses. The electron transport resistance of the GDL was high with the increase in compression pressure, while the oxygen transport resistance was almost unchanged. The GDL structure obtained by micro X-ray computed tomography showed the decrease in large pores as well as porosity under compression. The random walk simulation based on the obtained GDL image suggested that the increase in the number of contact points between carbon fibers contributed to the reduction of electron transport resistance. In addition to GDL, the MPL structure was reconstructed by nano X-ray computed tomography. The porosity distribution was similar in all directions, indicating that the MPL had isotropic structure. These analyses revealed that the understanding of the transport properties based on more realistic structure is essential to provide the refined insights for improving cell performance.

Radial die-wall pressure as a reliable tool for studying the effect of powder water activity on high speed tableting

The effect of moisture as a function of water activity (Aw) on the compaction process is important to understand particle/water interaction and deformation. Studying powder/moisture interaction under pressure with radial die-wall pressure (RDWP) tool was never done. The aim of our study was to use this tool to study this interaction at high compression pressure and speed. Moreover, the effect of changing ejection cam angle (EA) of the machine on ejection force (EF) was investigated. Also, a new tool for prediction of tablet sticking was proposed. Materials with different deformation behaviors stored at low and high moisture conditions were used. Compaction simulation guided by modeling was applied. High Aw resulted in a low residual die-wall pressure (RDP) for all materials, and a high maximum die-wall pressure (MDP) for plastic materials, p < 0.05. This was due to the lubricating and plasticizing effects of water, respectively. However, microcrystalline cellulose showed capping at high Aw and compaction pressure. By increasing compression pressure at high Aw for all materials, effective fall time (EFT) was increased, p < 0.05, showing tendency for sticking. Increasing EA caused an increase of friction and EF for powders, p < 0.05. RDWP was a useful tool to understand particle/moisture interaction under pressure.

錠剤のスティッキングに及ぼす打錠圧力及び臼壁面圧力の影響

An eccentric-type tablet machine fitted with 8-mm-diameter flat-faced punches was used to measure the forces of upper and lower punches, die-wall pressure, tablet ejection force, and scraper pressure (SCR), a type of shear stress, to evaluate sticking behavior. The shear stress between the surfaces of the tablet and lower punch was determined using an SCR detection system. Mean surface roughness (R(a)) of tablets, measured by laser scanning microscopy, was used to estimate the magnitude of sticking. Tablet tensile strength tended to increase with compression pressure, which is consistent with previous reports. SCR decreased with increasing compression pressure for samples at all formulations (i.e., for different kinds and percentages of lubricant). R(a) associated with sticking increased with SCR, indicating that the adhesive force between the particles of the tablet surface and the lower punch surface plays an important role in sticking. Multiple linear regression analysis with SCR as the response variable was conducted. Upper and lower punch force, die-wall pressure, tablet ejection force, SCR, percentage of lubricant, and tensile strength of tablet were selected as explanatory variables. Results of this analysis indicate that the incidence of sticking decreased when either the lower punch force or die-wall pressure increased, where, of these two, increasing the lower punch force had a stronger effect on decreasing SCR.

Shock-wave synthesis of diamond nanofibers and their structure

Diamond nanofibers produced by high-temperature shock compression of graphite nanofibers in the presence of KCl at pressures of 25–35 GPa and temperatures of 3000–3500 K have been considered. The synthesized fibers have been shown to consist of randomly oriented nanograins of diamond with the amorphous phase impurity, whose content decreases as the impact compression pressure increases.

Fractal permeability models for the microporous layer and gas diffusion layer of PEM fuel cell

In this investigation, a series fractal permeability model is developed to predict the gas permeability for the microporous layer (MPL) and gas diffusion layer of proton exchange membrane fuel cells. In addition to macroscopic flow, the model also considers gas molecules using the Adzumi equation. Parameters such as the maximum pore size, porosity, fractal area dimension and fractal tortuosity dimension, and the thickness of the sample are used to predict the permeability. From scanning electron microscopic images, the two fractal dimensions are determined by the box-counting method. This model is validated by comparison with experimental measurement results. Effects of compression pressure and MPL baking time are studied. Results show that the gas permeability decreases with increasing compression pressure. Longer MPL baking time increases gas permeability, and cell performance.

FABRICATION OF MICRO GEARS BY MICRO-POWDER INJECTION–COMPRESSION MOLDING

Micro-spur gears were fabricated by powder injection–compression molding and micro-two-step gears were produced through stacking and sintering of the green parts. Shrinkage of micro-gears by sintering was larger in teeth and with increase of compression pressure, shrinkage was decreased due to increase of density in green parts. Surface roughness of sintered body was reduced to a few hundreds of nanometers by ultrasonic micro-polishing. The joining of green bodies by stacking and sintering was achieved using the pressurized sintering and insert of feedstock powders between both green bodies.

Influence of Compression Pressure and Velocity on Tablet Sticking

A rotary tablet machine fitted with 8-mm diameter flat-faced punches was used to measure scraper pressure (SCR), a type of shear stress, to evaluate sticking behavior. The shear stress between the surfaces of the tablet and lower punch was determined using an SCR detection system. Mean surface roughness (R(a)) of tablets, measured by a scanning laser-microscope, was used to estimate the magnitude of sticking. Tablet tensile strength tended to increase with compression pressure at either of the tablet production velocities tested, which was consistent with previous reports. SCR decreased with increasing compression pressure for samples at all compression velocities, and showed a tendency to increase with binder concentration. SCR also tended to increase with compression velocity for samples at all compression pressures, suggesting that the frequency of tablet sticking increased as compression velocity increased. R(a) associated with sticking increased with SCR, indicating that the adhesive force between the particles of the tablet surface and the lower punch surface plays an important role in sticking.

Uniformity of drug content during pharmaceutical dry granulating by roller compaction and tableting processes

Purpose : To evaluate the usefulness of dry granulation by roller compaction in pharmaceutical tableting processes. Methods: Acetaminophen (AAP) as a model drug, lactose, corn starch, microcrystalline cellulose as excipients and magnesium stearate (MgSt) as a lubricant were used. Granules were prepared with a roller compactor and a mill, and then tablets were compacted with a rotary tableting machine. Uniformity of drug content in flakes, granules and tablets was examined with HPLC. Hardness, weight and disintegration time of tablets were also examined. Results: Tablet hardness increased with increasing compression pressure and with decreasing content of AAP. With low AAP content, tablet hardness increased with increasing roll pressure. With high content of AAP, tablet hardness decreased with increasing roll pressure. Disintegration times were also affected by compression pressure, AAP content and roll pressure. High roll pressure prolonged the disintegration time with low AAP content, but did not prolong the disintegration time with high AAP content. The coefficients of variance for AAP content averages of granules were clearly lower than those for flakes, and those for tablets were lower than those for granules. The coefficients of variance for 0.1% AAP tablets were relatively higher than those for other formulations, although the values were still low enough. Conclusion: The uniformity of drug content was highest in tablet form, showing that uniformity progressed with granulating, milling, mixing with lubricant and tableting. The tableting process with roller compaction can produce AAP tablets with sufficient content uniformity.

Thermal Conductivity and Contact Resistance of Compressed Gas Diffusion Layer of PEM Fuel Cell

AbstractThis paper discusses the effect of compression pressure on the mechanical and thermal properties of gas diffusion layers (GDL). The stress–strain curve of the GDL revealed one nonlinear and two piecewise linear regions within the compression pressure range of 0–5.5 MPa. The thermal conductivity of the compressed GDL seems to be independent of the compression pressure and was determined to be 1.18 ± 0.11 W m–1 K–1 at room temperature. The thermal contact resistance between the GDL and graphite was evaluated by augmenting experiments with computer modelling. The thermal contact resistance decreased nonlinearly with increasing compression pressure. According to the results here, the thermal bulk resistance of the GDL is comparable to the thermal contact resistance between the GDL and graphite. A simple one‐dimensional model predicted a temperature drop of 1.7–4.4 °C across the GDL and catalyst layer depending on compression pressures.

Differential Scanning Calorimetry with Curve-Fitting Program Used to Quantitatively Analyze the Polymorphic Transformation of Famotidine in the Compressed Compact

Differential scanning calorimetry (DSC) combined with a curve-fitting program was utilized to quantitatively determine the polymorphic composition of famotidine in the compacts prepared by different compression treatments. Two types of famotidine compacts (compact I or II) were prepared by compressing a conical shape or a flattened shape of powder bed of famotidine form B. The compact I was constructed by a transparent region in the center with an opaque region surrounded outside, but the compact II was formed by a whole opaque region only. A drilled disc sample was prepared and then directly determined by DSC analysis. The Raman spectral results clearly indicate that all the compacts whether in any region before DSC determination were only of famotidine form B and independent of compression pressure applied. Under DSC determination, however, the curve-fitted relative compositions of form B in the drilled disc I sample were gradually reduced to 23–24% with the increase of compression pressure, whereas the curve-fitted relative composition of form A was slowly increased up to 76–77%. A transitional phase of famotidine form B (form B*) in the transparent region of the compact I after applying >150 kg/cm2 of compression pressure was easily detected, and then transformed to famotidine form A under DSC heating process. But this transitional phase and polymorphic transformation of famotidine could not be detected by other spectroscopic methods. This suggests that the DSC heating system was a preferred method not only to quantitatively analyze the polymorphic transformation of famotidine but also to find a newly transitional phase of famotidine in the compressed compact.

Influences of Gas Diffusion Layer Permeability on the Performance of Polymer Electrolyte Fuel Cells

In-plane air permeance of gas diffusion layers (GDLs) was measured under compression conditions typical of polymer electrolyte fuel cells (PEFCs). When the compression pressure increases, maximum and mean flow pore diameters of GDLs decrease, causing the permeability to be deteriorated. In the case of the GDL coated with a micro porous layer (MPL), through-plane permeance measured using the conventional Gurley method decreases significantly, however, in-plane permeance decreases slightly when compared to the GDL without MPL. The MPL thickness penetrated in the carbon paper substrate can be estimated by the comparison of in-plane permeances with and without MPL. The permeance increases in proportion to the value of porosity multiplied by squired mean flow pore diameter. This relationship provides effective means to evaluate the porosity of GDLs with MPL. Increasing thickness and porosity of the GDL substrate enhances in-plane permeability of GDLs with MPL. This is effective in reducing flooding, thereby improving the PEFC performance under high-humidity conditions.

Theoretical Analysis of Tablet Hardness Prediction Using Chemoinformetric Near-Infrared Spectroscopy

In order to clarify the theoretical basis of the variability in the measurement of tablet hardness by compression pressure, NIR spectroscopic methods were used to predict tablet hardness of the formulations. Tablets (200 mg, 8 mm in diameter) consisting of berberine chloride, lactose, and potato starch were formed at various compression pressures (59, 78, 98, 127, 195 MPa). The hardness and the distribution of micropores were measured. The reflectance NIR spectra of various compressed tablets were used as a calibration set to establish a calibration model to predict tablet hardness by principal component regression (PCR) analysis. The distribution of micropores was shifted to a smaller pore size with increasing compression pressure. The total pore volume of tablets decreased as the compression pressure increased. The hardness increased as the compression pressure increased. The hardness could be predicted using a calibration model consisting of 7 principal components (PCs) obtained by PCR. The relationship between the predicted and the actual hardness values exhibited a straight line, an R(2) of 0.925. In order to understand the theoretical analysis (scientific background) of calibration models used to evaluate tablet hardness, the standard error of cross validation (SEV) values, the loading vectors of each PC and the regression vector were investigated. The result obtained with the calibration models for hardness suggested that the regression vector might involve physical and chemical factors. In contrast, the porosity could be predicted using a calibration model composed of 2 PCs. The relationship between the predicted and the actual total pore volume showed a straight line with R(2) = 0.801. The regression vector of the total pore volume might be due to physical factors.

Impact of compression pressure on tablet appearance

The color of model tablets deepened and tablet gloss increased with increase in compression pressure regardless of colorant type. The possible reasons for these phenomena were examined. These observations could not be explained either by polymorphic transition of the colorant or by condensation of the colorant during compression. Instead, a change in surface roughness was assumed to be the most likely reason. The increase in compression pressure made the tablet surface smoother. With the increase in the surface smoothness, diffuse reflection decreased while specular reflection increased, indicating the opposite relation between diffuse and specular reflection as a function of surface roughness. A decrease in diffuse reflection results in a deepening of color. In contrast, an increase in specular reflection causes an increase in glossiness. Thus, the surface roughness seemed to govern gloss and color. The compression pressure seems to be one of the most important factors to control tablet appearance.

Direct measurement of through-plane thermal conductivity and contact resistance in fuel cell materials

An experimental study to determine the through-plane thermal conductivity of dry Nafion ®, various diffusion media, catalyst layer, and the thermal contact resistance between diffusion media and a metal plate as a function of temperature and pressure was performed. Dry Nafion ® thermal conductivity was determined to be 0.16 ± 0.03 W m −1 K −1 at room temperature, which decreases to 0.13 ± 0.02 W m −1 K −1 at 65 °C. Diffusion media thermal conductivity was found to be function of PTFE content and manufacturer, and was 0.48 ± 0.09 W m −1 K −1 for untreated and 0.22 ± 0.04 W m −1 K −1 for 20 wt.% PTFE treated SIGRACET ® diffusion media, respectively. Toray diffusion media thermal conductivity was measured to be 1.80 ± 0.27 W m −1 K −1 at 26 °C and decreases to 1.24 ± 0.19 W m −1 K at 73 °C. The thermal contact resistance between Toray carbon paper and aluminium bronze material was determined to vary from 6.7 × 10 −4 to 2.0 × 10 −4 m 2 K W −1 for an increase in compression pressure from 0.4 to 2.2 MPa. The equivalent thermal conductivity of a 0.5 mg cm −2 platinum loaded catalyst layer was estimated to be 0.27 ± 0.05 W m −1 K −1. A one-dimensional analytical model was also used to estimate the temperature drop in the fuel cell components. A maximum of 3–4 °C temperature drop can be expected for a 200 μm thick SIGRACET ® diffusion media at 1 A cm −2. The thermal properties characterized should be useful to help modelers accurately predict the temperature distribution in a fuel cell.

Comparative evaluation of bioactivity change of crystalline trypsin during compression by chemoinformatics and 2-D Fourier-transform infrared spectroscopy

The purpose of this study is to develop a method of evaluating the enzymatic activity of trypsin in a solid-state based on Fourier transform infrared (FT-IR) spectra using chemoinformatics and two-dimensional (2-D) correlation spectroscopy. Crystalline trypsin powders are compressed at 0-4000 kg cm-2 by a compression/tension tester. The enzymatic activity of trypsin is assayed by the kinetic degradation method. Spectra of 10 calibration sample sets are recorded 3 times with a FT-IR spectrometer. The maximum intensity of FT-IR spectra and enzymatic activity of trypsin decrease as the compression pressure increases. The FT-IR spectra of trypsin samples are subjected to a principal component regression (PCR). A plot of the calibration data obtained is made between the actual and predicted trypsin activity based on a two-component model with gamma2=0.909 (n=30). The regression vector is almost the same as the loading vector for PC1. On the other hand, a generalized two-dimensional (2-D) correlation spectroscopic method is applied to FT-IR spectra of compressed trypsin. The result is consistent with that of the chemoinformatics method. The FT-IR chemoinformatics method allows for solid-state quantitative analysis of the bioactivity of the bulk powder of a polypeptide drug.

Mechanical Properties of TiO&lt;sub&gt;2&lt;/sub&gt;-Kaolin FGM Produced by Progressive Lamination Method for NO&lt;sub&gt;x&lt;/sub&gt; Reduction

Mechanical properties of TiO2-Kaolin Functionally Graded Materials (FGMs) that combined TiO2 and Korean kaolin (Al2Si2O5(OH)4) in a graded distribution were experimentally investigated. TiO2 is an excellent photocatalysis material, however, it does not have the mechanical strength sufficiently. Therefore, FGMs were used as the photocatalysis materials with mechanical strength. To improve the mechanical properties, Korean kaolin was selected as a binder. Bulk FGMs were produced by vacuum filtration and compression involving wet filtration, mechanical compression and sintering. By this process, it is easy to control the thickness of FGMs. The porosity in FGM depends on the content of TiO2. The porosity in FGM decreases with increasing pressure of the compressor. The shrinkage decreases with increasing compression pressure at all ratios of TiO2 and kaolin. The materials have almost no shrinkage at 10 MPa. The bending strength and the Young’ modulus depends on content of TiO2. The bending strength of material was found to be approximately 2.5 MPa for 10 MPa compression pressure at TiO2 side. The bending strength and the Young’ modulus increases with increasing compression pressure. These results indicate that kaolin particles are useful to improve the strength of FGM. These properties of FGM, such as porosity, shrinkage, mechanical strength, etc., can be controlled by content of TiO2 and compression pressure. Based on an optimal design of production conditions, FGMs were developed for the nitrogen oxides (NOx) removal. The NOx reduction increases with increasing compression pressure. NO of 11.7 mg/m2h was removed under present conditions. The sintering temperature ensured the optimal removal of NOx was 800 oC. After NOx removal test, the FGMs were found to be free from erosion due to photocatalysis. And kaolin particles do not interfere in photocatalysis effect of TiO2. It can be concluded that TiO2-Kaolin FGM have a possibility for application to the air purification.

Electrical conductivity study of porous carbon composite derived from rice husk

The objective of this investigation is to evaluate the electrical conductivity of activated carbon derived from rice husk (RHAC) by a two-stage process. dc conductivity measurements by two-probe method were determined for RHAC samples prepared at 700, 800 and 900 °C. The samples were compressed in the pressure range 75.9–578.2 kPa in a hollow glass cylinder using two metal plungers connected to a Keithley ammeter. The conductivity at room temperature was found to increase from 3.28 × 10 −4 to 2.02 × 10 −3 S cm −1 for increase in compression pressure. Dense packing of the material, collapse of pores and decrease in air gap between the carbon particles could be the factors for the increase in conductivity with compression pressures. The temperature-dependent conductivity of RHAC samples were determined by compressing the sample within the metal plungers, followed by heating in a tubular furnace. A K-type thermocouple whose hot junction was located in close proximity to the specimen, was used to monitor the temperature accurately. The specimen inside the furnace was heated by a microprocessor-controlled programmer up to 250 °C. The temperature-dependent conductivity study conducted for the samples activated at 700, 800 and 900 °C, revealed that the energy gap value of the samples were 0.1023, 0.0745 and 0.052 eV respectively, determined from the linear plot of ln I versus 1/ T (K −1). The mesoporous RHAC samples were characterized using electron spin resonance, FT-IR spectroscopy and X-ray diffraction for quantitative evaluation of free electrons, functional groups and crystallites to support the mechanism of electrical conduction in mesoporous nonsinterable carbon samples.

Evaluation of Different Fast Melting Disintegrants by Means of a Central Composite Design

Fast-disintegration technologies have encountered increased interest from industries in the past decades. In order to orientate the formulators to the choice of the best disintegrating agent, the most common disintegrants were selected and their ability to quickly disintegrate direct compressed tablets was evaluated. For this study, a central composite design was used. The main factors included were the concentration of disintegrant (X1) and the compression force (X2). These factors were studied for tablets containing either Zeparox® or Pearlitol 200® as soluble diluents and six different disintegrants: L-HPC® LH11 and LH31, Lycatab PGS®, Vivasol®, Kollidon CL®, and Explotab®. Their micromeritics properties were previously determined. The response variables were disintegration time (Y1), tensile strength (Y2), and porosity (Y3). Whatever the diluent, the longest disintegration time is obtained with Vivasol® as the disintegrant, while Kollidon CL® leads to the shortest disintegration times. Exception for Lycatab PGS® and L-HPC LH11®, formulations with Pearlitol 200® disintegrate faster. Almost the same results are obtained with porosity: no relevant effect of disintegrant concentration is observed, since porosity is mainly correlated to the compression force. In particular, highest values are obtained with Zeparox® as the diluent when compared to Pearlitol 200® and, as the type of disintegrant is concerned, no difference is observed. Tensile strength models have been all statistically validated and are all highly dependent on the compression force. Lycatab PGS® concentration does not affect disintegration time, mainly increased by the increase of compression pressure. When Pearlitol 200® is used with Vivasol®, disintegration time is more influenced by the disintegrant concentration than by the compression pressure, an increase in concentration leading to a significant and relevant increase of the disintegration time. With Zeparox®, the interaction between the two controlled variables is more complex: there is no effect of compression force on the disintegration time for a small amount of disintegrant, but a significant increase for higher concentrations. With Kollidon CL®, the main factor influencing the disintegration time is the compression force, rather than the disintegrant concentration. Increasing both the compression force and the disintegrant concentration leads to an increase of the disintegration time.For lower Kollidon CL® percentages, the compression pressure increases dramatically the tablet disintegration. With the Explotab®, whatever the increase of compression force, the disintegrant concentration leads to an increase of the disintegration time. According to Student's t-test, only the compression force significantly and strongly influences the disintegration time when Pearlitol 200® is used. A slight interaction and some trends nevertheless appear: above 150 MPa, increasing the disintegrant concentration leads to a shortened disintegration time, below this limit the opposite effect is observed.