The effect of particle morphology on the physical stability of pharmaceutical powder mixtures: the effect of surface roughness of the carrier on the stability of ordered mixtures

The effect of particle morphology of the components on the physical stability of ordered mixtures was determined for a model system comprised of a mixture of micronized aspirin and a monodisperse carrier. Spray-dried lactose, crystallized lactose, microcrystalline cellulose, and dextrate were used as carriers. The surface texture of the carriers was quantified in terms of the ratio of the perimeter of the particles to that of an idealized shape at a constant magnification. Mixtures containing highly textured carriers segregated to a lesser extent than those containing smoother textured carriers. This was postulated to be due to the presence of a higher concentration of surface asperities on the coarse carriers that can constitute potentially strong adhesion sites for the fine component because of their higher energy relative to adjacent areas on the surface. The effect of the addition of a ternary component, magnesium stearate, on the stability of the above mixtures was studied. The observed differences in the segregation response were attributed to electrostatic charge effects.     

The effect of stirring rate on semisolid stirring brazing of SiCp/A356 composites in air

This paper explores the possibilities of joining SiC_p/A356 composites using semisolid Zn27Al filler metal with aid of mechanical stirring. Moreover, the effect of stirring rate on the macro-appearance, microstructure, bonded ratio, braze metal ratio of joints and the tensile strength of joints were investigated. Experimental results show that the bonded ratio of interface, braze metal ratio and the tensile strength of the joints is rise with increasing of stirring rate. It is indicated that increasing of stirring rate will promote the disruption of oxide film on surface of composites so as to enhance metallurgical bonds at joint interface. In addition, increasing of stirring rate will also promote formation to fine brittle η-Zn phase and its uniform distribution in bond.     

Polydisperse powder mixtures: effect of particle size and shape on mixture stability

The effect of the shape and size of the components on the stability of mixtures was evaluated in binary mixtures of drug and carrier. Aspirin was used as model drug; spray-dried lactose and microcrystalline cellulose were used as carriers. The coefficient of variation (CV) of the drug in the mixture at various time intervals during mixing was used as a measure of homogeneity. The stability of mixtures was assessed under conditions that were conducive to segregation—in this case, prolonged mixing. The pattern of change in CV with time was analyzed in terms of convective, shear, and diffusive mixing stages. The variation resulting from a change in the shape of the carriers was smaller than that resulting from size differences. The segregation rate constant, calculated on the assumption of a first-order mixing process, was found to be larger in mixtures having components of different shape than in mixtures having components of similar shape. In mixtures of micronized drug and carrier, the pattern of change in the CV of drug with mixing time was attributed to the distribution of agglomerates of micronized drug during convective mixing, followed by shearing of agglomerates and, finally, the distribution of the primary particles during diffusive mixing. Mixtures of non-cohesive powders of similar size and shape behaved like random mixtures of non-interacting components.     

Radioisotopic method of studying the effect of electromagnetic stirring on the dissolution of solid metals in liquid metals

A study was made of the effect which the flow of liquid metal has on the diffusive dissolution in it of solid metals. The dissolution of alloying elements was examined radioisotopically, along with the kinetics of mass transfer under conditions of lead alloy and aluminum alloy formation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 6, pp. 1002–1009, June, 1973.     

Solid state and dissolution rate characterization of co-ground mixtures of nifedipine and hydrophilic carriers

Co-ground powders of the poorly water-soluble drug nifedipine and a hydrophilic carrier, [partially hydrolyzed gelatin (PHG), polyvinylpyrrolidone (PVP), sodium dodecyl sulfate (SDS), hydroxypropyl methylcellulose (HPMC), polyethylene glycol (PEG), urea or Pluronic F108] were prepared in order to improve the dissolution rate of nifedipine. The effects of type of grinding equipment, grinding time, and type of hydrophilic carrier on the crystallinity of nifedipine (x-ray diffraction and differential scanning calorimetry) on the interaction between drug and carriers (differential scanning calorimetry), on the particle size and appearance (scanning electron microscopy), on the wettability (contact angle measurements), and on the drug release were investigated. Grinding nifedipine together with these carriers improved the dissolution rate. PHG-ground mixtures resulted in the fastest dissolution rate followed by PVP, SDS, HPMC, Pluronic, urea, and PEG. This effect was not only due to particle size reduction, which increased in the order PHG相似文献   

The effect of 2-hydroxypropyl-ß-cyclodextrin on the solubility,stability and dissolution rate of famotidine

Abstract

Famotidine was found to form an inclusion complex with 2-hydroxypropyl-ß-cyclodextrin (HPCD). Phase-solubility diagram was classified as type A_L with a stability constant for complex formation (K_st) of 100.50 M¹ at pH 7.4. Famotidine undergoes specific acid catalysis in strongly acidic solutions. Addition of HPCD to these solutions decreased the rate of drug degradation. The rate constant for degradation of complexed famotidine (k_c) and K_st were estimated from the relationship between the observed rate constant for overall drug degradation (K_obs) and HPCD concentration. An increase in ionization of famotidine resulted in a decrease in the magnitude of K_st. The dissolution rate of the prepared complex was significantly greater than that of the pure drug.     

The effect of mixtures of particle sizes on the minimum ignition temperature of a dust cloud

The ignition temperature in the air atmosphere at the separating line between an explosion and no explosion in a dust cloud, T_i^b, has been investigated for mixtures of fine and coarse dusts of the same material. The minimum ignition temperature, T_i^m, which is the lowest temperature at which an explosion is obtained has also been determined. Measurements were made in a Godbert-Greenwald Furnace apparatus. The results obtained indicated that the ignition temperature is dependent on the particle size, and an admixture of fine dust of 30% to coarse dust is sufficient to reduce the T_i^m values significantly.     

Laboratory study on the liquefaction resistance of sand-silt mixtures: effect of grading characteristics

The liquefaction susceptibility of saturated medium sand-silt mixture samples is evaluated by monotonic and cyclic undrained triaxial laboratory tests that were carried out on reconstituted specimens at various relative densities (D_r   =  20, 53 and 91%) and a constant confining pressure (s₃^￠=100{\sigma_{3}^{\prime}=100}  kPa). The test results were used to conclude on the effect of grading characteristics and other parameters on the liquefaction resistance of the sand-silt mixtures. The monotonic test results indicate that the undrained shear strength at the peak and the undrained residual strength can be correlated to the coefficient of uniformity (C_u) and the average diameter (D₅₀). Indeed, they decrease linearly with the increase of the uniformity coefficient and decrease of the average diameter. It is found that a relationship between the liquefaction resistance and any of the diameters (D₁₀ or D₅₀) and the coefficient of uniformity (C_u) would be more realistic than to build a relation between the coefficient of gradation (C_c) and the liquefaction resistance. Undrained cyclic triaxial tests indicate that the cyclic liquefaction resistance of the sand-silt mixtures decreases linearly with the decrease of the effective diameter (D₁₀) and mean size (D₅₀) and increase of the fines content for the fines content range tested (Fc  =  0–40%).     

The effect of HPMC particle size on the drug release rate and the percolation threshold in extended-release mini-tablets

The particle size of HPMC is a critical factor that can influence drug release rate from hydrophilic matrix systems. Percolation theory is a statistical tool which is used to study the disorder of particles in a lattice of a sample. The percolation threshold is the point at which a component is dominant in a cluster resulting in significant changes in drug release rates. Mini-tablets are compact dosage forms of 1.5–4?mm diameter, which have potential benefits in the delivery of drug to some patient groups such as pediatrics. In this study, the effect of HPMC particle size on hydrocortisone release and its associated percolation threshold for mini-tablets and tablets was assessed. For both mini-tablets and tablets, large polymer particles reduced tensile strength, but increased the drug release rate and the percolation threshold. Upon hydration, compacts with 45–125?μm HPMC particles formed a strong gel layer with low porosity, reducing hydrocortisone release rates. In comparison, faster drug release rates were obtained when 125–355?µm HPMC particles were used, due to the greater pore sizes that resulted in the formation of a weaker gel. Using 125–355?µm HPMC particles increased the percolation threshold for tablets and to a greater extent for mini-tablets. This work has demonstrated the importance of HPMC particle size in ER matrices, the effects of which are even more obvious for mini-tablets.     

Study of the effect of stirring on foam formation from various aqueous acrylic dispersions

Acrylic polymers in aqueous dispersions are very often used to prepare coating suspensions which contain insoluble particles. The mixing of the pigment suspension and the polymer dispersion is a very important step in the preparation of the liquid. The stirring can cause precipitation of the polymer and foam formation. Foam formation from different Eudragit dispersions was evaluated in this study. A high-speed mixer was applied and the foam and liquid phases formed were separated. The changes in concentration of the polymer in the two phases were studied by FT-IR with a horizontal attenuated total reflection (HATR) accessory. The presence of shape-holding foam can be detected at very different rates of stirring. The most intensive foam formation was detected for Eudragit FS 30 D. The Eudragit RL 30 D dispersion was the least sensitive to high-speed mixing. The relative content of the polymer in the foam was higher than that in the liquid. This is indicated by the accumulation of surface-active agent on the surface of the bubbles formed in the foam. This phenomenon differed considerably for the various dispersions. An exact knowledge of the foam formation from aqueous acrylic dispersions is very important in order to determine the parameters of mixing and the quantity of antifoaming agent.     

The impact of food components on the intrinsic dissolution rate of ketoconazole

To accurately predict the in vivo performance of drugs from an in vitro dissolution test, the dissolution conditions used are supposed to be similar to those present in the gastrointestinal milieu. Post-prandial gastric fluid contains partially digested food mixtures consisting of fat, protein and carbohydrate. Despite this, the compendia dissolution medium recommended to simulate the gastric fluid is still composed of a simple solution of hydrochloric acid and sodium chloride with or without the addition of pepsin. Therefore, in this investigation, biorelevant dissolution media were developed to evaluate the impact of food constituents; milk with different fat contents, egg albumin, gelatin, casein, gluten, carbohydrates and amino acids on the intrinsic dissolution behavior of ketoconazole. Most of the food additives that were evaluated enhanced the apparent solubility of the drug but to different extents. The greatest enhancement in dissolution was observed in media containing either neutral amino acids or media based on milk mixtures. The formation of complexes between the drug and the additives most likely accounted for the solubilizing effect and in milk-containing media, the effect was attributed to the whole complex structure of milk rather than simply its fat content. These results highlight the potential effect of the type of ingested meal on drug dissolution and subsequent bioavailability.     

Dissolution shapes ofY-rotated quartz plates andY sections derived from the polar diagram of the dissolution slowness

A study has been made of the rate at which variousY-rotated quartz plates are etched in a concentrated ammonium bifluoride solution. The changes in the surface texture of these differently oriented plates on repeated etching are systematically investigated. To obtain all the information needed for an analysis of the dissolution shapes in the framework of the tensorial representation of the dissolution slowness the profile graph of a deeply etchedY-cut plate is also reported. The polar diagramL _xz (θ) of the dissolution slowness associated with theY-rotated quartz plates is then derived using profile graph data. Numerical and graphical simulations of the dissolution shapes are used to verify the adequation of the lawL _xz (θ). The comparison of the theoretical etch profiles with the Z" etch profiles produced by repeated etching on someY-rotated quartz plates shows complete agreement. Excellent agreement is also found between the theoretical and experimental shapes of the magnified profile graph related to deeply etchedY sections. From the consistency between the observed dissolution shapes and the computed shapes deduced from the tensorial analysis of the dissolution we can conclude that the proposed polar diagramL _xz (θ) represents accurately the variations of the dissolution slowness with the angle θ in theXZ plane.     

The effect of ash and filter media characteristics on particle filtration efficiency in fluidized bed

The phenomenon of filtering particles by a fluidized bed is complex and the parameters that affect the control efficiency of filtration have not yet been clarified. The major objective of the study focuses on the effect of characteristics of ash and filter media on filtration efficiency in a fluidized bed. The performance of the fluidized bed for removal of particles in flue gas at various fluidized operating conditions, and then the mechanisms of collecting particles were studied. The evaluated parameters included (1) various ashes (coal ash and incinerator ash); (2) bed material size; (3) operating gas velocity; and (4) bed temperature. The results indicate that the removal efficiency of coal ash increases initially with gas velocity, then decreases gradually as velocity exceeds some specific value. Furthermore, the removal of coal ash enhance with silica sand size decreasing. When the fluidized bed is operated at high temperature, diffusion is a more important mechanism than at room temperature especially for small particles. Although the inertial impaction is the main collection mechanism, the "bounce off" effect when the particles collide with the bed material could reduce the removal efficiency significantly. Because of layer inversion in fluidized bed, the removal efficiency of incinerator ash is decreased with increasing of gas velocity.     

The effect of electromagnetic stirring on the microstructure of Al-7 wt %Si alloy

Abstracts are not published in this journal     

The effects of flow rate and particle shape on the convective diffusion to a solid catalytic particle

Summary The flow of a fluid, containing a reactant, past a solid catalytic particle on which a reaction takes place is considered for large Péclet number. The concentration of the reactant is given by the diffusion boundary-layer equation, and this is solved in the case when the rate of reaction on the particle surface and the rate of diffusion of reactant onto the surface are of the same order of magnitude.For a spherical particle, a series solution for the concentration is found for the case of Stokes flow, and numerical solutions are found for Stokes flow and for flow at higher Reynolds numbers (up to Re=10). To examine the effect of particle shape, numerical solutions are found for prolate and oblate spheroids in Stokes flow.     

Study on the thermal and mechanical properties of epoxy–nanoclay composites: The effect of ultrasonic stirring time

Epoxy–clay nanocomposites were synthesized with organophilic montmorillonite and diglycidyl ether of bisphenol A by using the in-situ polymerization under ultrasonic treatment. The clay layers were found to be separated further with the increase in the duration of ultrasonic stirring as measured from the X-ray diffraction measurements. Thermogravimetric analysis provided the fact that the maximum thermal decomposition temperatures increased with the increase in the duration of ultrasonic stirring. However, both the glass transition temperature and the storage moduli of the composites decreased with the increase of ultrasonic stirring time as measured from the dynamic mechanical analysis.     

An investigation into the effect of rate of stirring of bath electrolyte on the properties of electrodeposited CdTe thin film semiconductors

Electrodeposition (ED) has been recognized as a low cost and scalable technique available for fabrication of CdS/CdTe solar cells. Photovoltaic activity of these electrodeposited semiconductor materials drastically depends on the ED growth parameters namely; electrodeposition potential, concentrations and ratios of concentrations of precursors used to prepare the bath electrolyte, pH of the electrolyte, deposition temperature and rate of stirring of the electrolyte. In order to grow thin films with good photovoltaic properties, it is essential to maintain these variables at their optimum ranges of values during electrodepositions. Hence, this study was conducted to investigate the dependence of the properties of electrodeposited CdTe thin film material on the rate of stirring of the bath electrolyte. The CdTe material was grown on glass/FTO (2?×?3 cm²) and glass/FTO/CdS (2?×?3 cm²) surfaces in bath electrolytes containing 1.0 mol/L CdSO₄ and 1.0 mmol/L TeO₂ solutions at different rates of stirring within the range of 0–350 rpm while keeping the values of pH of the electrolyte, deposition temperature and cathodic deposition potential with respect to the saturated calomel electrode at 2.3, 65 °C and 650 mV respectively. After the heat treatment at 400 °C in air atmosphere, the deposited samples with a good visual appearance were selected and evaluated based on their morphological, elemental, structural, optical and electrical properties in order to identify the optimum range of rate of stirring for electrodeposition of CdTe thin film semiconductors. Results revealed that, rates of stirring in the range of 60–85 rpm in a 100 mL volume of electrolyte containing the substrate and the counter electrodes in the center of the bath with a separation of 2.0 cm between them can electrodeposit CdTe layers exhibiting required levels of morphological, structural, optical and electrical properties on both glass/FTO and glass/FTO/CdS surfaces.     

Kinetics of zeolite dissolution: Part 3. Dissolution of synthetic mordenite in hot sodium hydroxide solutions

The kinetics of dissolution of synthetic mordenite in 1 m NaOH solution at 338, 343, 348, and 353 K were studied by following the changes in the characteristics of the solid and the liquid phase during the dissolution. Various experimental techniques such as ICP spectroscopy, FTi.r. spectroscopy, X-ray diffractometry, and particle-size distribution measurement were used for this purpose. The results obtained were analyzed and discussed in accordance with the model of growth and dissolution proposed by Davies and Jones, taking into account the chemical and structural characteristics of synthetic mordenite.     

Dissolution of coated microbubbles: The effect of nanoparticles and surfactant concentration

The ability of solid particles to stabilise emulsions is a well known phenomenon which has recently been demonstrated for the stabilisation of gas bubbles. In this paper, a new theoretical model is developed which describes how an adsorbed layer of solid nanoparticles modifies the interfacial tension and diffusivity of a gas bubble in a liquid and hence its stability. In agreement with experimental observations on microbubbles coated with 15 nm diameter spherical gold particles, the results of simulations with the model indicate that the particles substantially decrease the rate at which bubble dissolution occurs and enables them to maintain a stable radius once a critical particle concentration has been reached.