Low Stirring Speed Research Articles

Influence of Processing Parameters on Microstructure of Casting Rolling Semi-Solid AZ91D Magnesium Alloy

Semi-solid AZ91D magnesium slurry was prepared by mechanical stirring method and the evolution of microstructure under different technological parameters such as casting temperature, standing time, stirring time and stirring speed et al were studied. The results show that the technological parameters have great influence on the microstructure of the semi-solid magnesium slurry. Neither too high nor too low stirring speed is a benefit to form the semi-solid state; stirring time is also not too long; higher casting temperature is unfavorable; with the increasing of standing time, the steady-state apparent viscosity of the slurry increases rapidly, the number of nucleation increases and the crystalline structure becomes finer.

Influence of Soil Characteristics and Formulation on Alachlor Dissipation in Soil

Alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)acetamide] is one of the most commonly found herbicides in surface and groundwaters of the United States and Europe, and it contaminates these environments even when it is used according to the manufacturer's instructions for conventional formulations. To determine how its persistence in soil is affected by herbicide formulation and soil type, alachlor was applied to several soils in different formulations: technical grade (AT), a commercial formulation (CF), and different ethylcellulose microencapsulated formulations (MEFs). The results show that MEFs provided a prolonged release of the herbicide into the soil solution and protected against its dissipation in soil more than AT or the CF. The half‐life in soil (t1/2) for the AT, CF, and MEFs was up to 2.7, 6.4, and 32.54 d, respectively. The lowest herbicide loss was observed in MEFs prepared using a lower stirring speed or a higher ethylcellulose viscosity during the microencapsulation process. As with AT and the CF, the microencapsulated alachlor persisted longer in the soils with low pH and high clay content. In the soil where alachlor showed the least persistence, MEFs reduced the herbicide loss by 54% compared with the CF. The use of MEFs extended the alachlor concentration in the soil, thereby avoiding the need for using high herbicide application rates and decreasing the risk of environmental contamination.

Tablet disintegration and drug dissolution in viscous media: Paracetamol IR tablets

An investigation into the influence of viscous media on tablet disintegration and drug dissolution was performed with the aim to simulate the potential formulation-specific food effect for a selected highly soluble model drug. Literature data on the in vivo drug absorption in fasted and fed state have been evaluated for in vitro–in vivo correlation (IVIVC) purposes. In vitro studies were conducted in simple buffer media with or without addition of HPMC K4M as a viscosity enhancing agent. Good IVIVC correlation ( r > 0.95) was obtained for paracetamol dissolution in viscous media at 50 rpm and fed state absorption profiles, while in vitro dissolution in simple media at lower stirring speed was predictable of drug products in vivo behaviour in the fasted state. The data obtained support the existing idea that relatively simple dissolution media and/or set of experimental conditions may be used to differentiate formulation-specific food–drug interactions. Such tests would be a useful tool in the development of formulations that would not be susceptible to the influence of co-administered meal and, furthermore, facilitate regulatory decision on the necessity to conduct food effect studies in vivo.

CaCO3 nanoparticle synthesis by carbonation of lime solution in microemulsion systems

Various aspects of nanoparticle precipitation in gas-reverse micellar systems have beenstudied. The experimental system chosen for investigation deals with the precipitation ofCaCO3 nanoparticles. The effect of operating variables, such as water-to-surfactant molar ratio,different continuous phases, surfactant concentration and stirring speed, have beeninvestigated experimentally. The results indicate that using low concentrations ofCa(OH)2 particles outside the micelles, low surfactant concentrations, low stirring speeds andwater-to-surfactant molar ratios lead to the formation of smaller nanoparticles ingas-reverse micellar systems.

Influence of stirring speed and stirring time on distribution of particles in cast metal matrix composite

In the present study, high silicon content aluminium alloy–silicon carbide metal matrix composite material, with 10%SiC were successfully synthesized, using different stirring speeds and stirring times. The microstructure of the produced composites was examined by optical microscope and scanning electron microscope. The Brinell hardness test was performed on the composite specimens from base of the cast to top. The results revealed that stirring speed and stirring time influenced the microstructure and the hardness of composite. Microstructure analysis revealed that at lower stirring speed with lower stirring time, the particle clustering was more. Increase in stirring speed and stirring time resulted in better distribution of particles. The hardness test results also revealed that stirring speed and stirring time have their effect on the hardness of the composite. The uniform hardness values were achieved at 600 rpm with 10 min stirring. But beyond certain stir speed the properties degraded again. An attempt is made in this study to establish the trend between processing parameters such as stirring speed and stirring time with microstructure and hardness of composite.

Improvement of lipase production at different stirring speeds and oxygen levels

Lipase production by a Brazilian wild strain of Yarrowia lipolytica at different stirring speeds and air flow rates was studied. The relationship among lipid consumption, cell growth and lipase production by this microorganism is presented. The most pronounced effect of oxygen on lipase production was determined by stirring speed. Maximum lipase activity was detected in the late stationary phase at 200 rpm and an air flow rate of 1-2 dm³/min (0.8-1.7 vvm) when the lipid source had been fully consumed. Higher stirring speeds resulted in mechanical and/or oxidative stress, while lower stirring speeds seemed to limit oxygen levels. An increase in the availability of oxygen at higher air flow rates led to faster lipid uptake and anticipation of enzyme release into the culture medium. The highest lipase production was obtained at 200 rpm and 1 dm³/min (0.8 vvm).

Ultra-porous hollow particles

Hollow particles with porous shells have been prepared by a simple modification to the surfactant-free polymerisation of styrene by the incorporation of water-soluble natural polymers and the use of high stirring speeds. The particle morphology has been characterised by scanning electron microscopy (SEM). When styrene is polymerised in the presence of either carboxymethyl cellulose (CMC) or sodium alginate at high stirring speeds, small homogeneous (solid) particles (diameter ~200 nm) and large porous particles (diameter~10 μm) are both formed. However, at low stirring speeds only the small homogeneous (solid) particles are formed. Further, only the small homogeneous (solid) particles are formed when non-adsorbing polymers such as starch and poly(vinyl alcohol) are present. In contrast, polymers that strongly adsorb onto polystyrene particles cause the polymerising mixture to flocculate. It is proposed that the porous character is a direct result of the polymerisation of a multiple emulsion in the presence of a depletion interaction. Moreover, addition of a high concentration of surfactant to the CMC system simply results in the spherical homogenous particles, suggesting that the surfactant removes the depletion effect.

Synthesis of Amorphous Calcium Carbonation in Ethanol and its Crystallization in the Aqeous Solution

ABSTRACT Amorphous calcium carbonate (ACC) was synthesized by reaction to the Ca(OH)2-C2H5OH-CH2OHCH2OH-CO2 systems. The ACC was then crystallized in aqueous solutions while observing the changes in crystal phases. Using lL/min of CO2 flow rate, 600rpm of stirring rate and various concentrations of Ca(OH)2 as the conditions, the reaction was divided into three stages according to changes of electrical conductivity that depends on Ca2+ concentration. ACC synthesized by these reactions was stabilized to calcite through vaterite according to time. When crystallizing the ACC in an aqueous solution, it was transferred to calcite by means of a low stirring speed regardless of temperature. However, a small amount of aragonite was obtained with higher stirring rate at high temperatures. Furthermore, the addition of NH4 + ions resulted in an irregular shape and size of the produced calcite, while Mg2+ ions enhanced aragonite production.

Engineering of a Dermal Equivalent: Seeding and Culturing Fibroblasts in PEGT/PBT Copolymer Scaffolds

The engineering of dermal skin substitutes, using autologous fibroblasts, requires high seeding efficiencies, a homogeneous cell distribution in the scaffolds, and optimal culture conditions. Dynamic seeding in spinner flasks was used to seed and subsequently culture fibroblasts in three-dimensional scaffolds. Several seeding and culture variables were investigated. Simulation of medium movement with microspheres showed that three different regions existed in medium (outer, middle, and inner), where overall particle movement was different. In the middle region the flow was turbulent and scaffolds were best placed in this region. After fibroblast seeding, methylene blue staining and scanning electron microscopy analysis of the scaffolds showed that at a low stirring speed (20 rpm) fibroblasts attached mainly onto the upper part of the scaffold, and at 40 and 60 rpm fibroblasts attached and spread throughout the scaffolds. Measurements of total DNA content per scaffold showed that lower stirring speeds (20 and 40 rpm) resulted in significantly higher cell-seeding efficiencies (20 rpm, 99.8 +/- 11.3%; 40 rpm, 93.8 +/- 10.5%) compared with 60 rpm (85.9 +/- 5.3%). Seeding kinetics were comparable for all three speeds investigated. In subsequent studies, 40 rpm was chosen for seeding. Using initial cell numbers ranging from 0.3 x 10(6) to 1.5 x 10(6) fibroblasts per scaffold, seeding efficiencies higher than 85% were consistently found (n = 4). The culture of fibroblast-seeded scaffolds at different stirring speeds (10-80 rpm) showed that stirring speeds higher than 10 rpm significantly stimulated fibroblast proliferation and glycosaminoglycan and collagen deposition as compared with 10 rpm. After 21 days, scaffolds cultured at 80 rpm showed significantly more collagen deposition as compared with those maintained at lower speeds. In conclusion, to achieve high seeding efficiencies, uniform fibroblast distribution and tissue formation in a three-dimensional scaffold, fibroblasts can be dynamically seeded at 40 rpm and subsequently cultured at a stirring speed of 60-80 rpm in spinner flasks. This flexible system shows that it is feasible to tissue engineer autologous dermal substitutes in a clinically acceptable time frame.

Effect of Dispersion Stirring Speed on the Particle Size Distribution and Rheological Properties of Carbomer Dispersions and Gels

ABSTRACT Studies on the influence of the stirring speed during the dispersion stage of Carbopol 5984 on the particle size distributions and rheological characteristics of the gel showed that increasing the stirring speed leads to a decrease in the particle size and in the polydispersity of the dispersion. These two characteristics have antagonist effects on the viscosity: a decrease of particle size leads to a decrease in viscosity while a decrease of polydispersity leads to an increase in viscosity. In this study, for low stirring speed, even if the particle size decreased, the viscosity remained constant because the polydispersity decreased also. For high stirring speed during the dispersion stage, the polydispersity remained constant and the particle size continued to decrease therefore the viscosity decreased. Therefore it is important to monitor the particle size and polydispersity of Carbopol 5984 dispersion during manufacturing to be able to ensure the rheological properties of the gels produced.

Kinetic Investigation of Reaction Between Metallic Silver and Nitric Acid Solutions

In this study, the reaction kinetics between metallic silver and nitric acid solutions was investigated by taking into consideration the parameters of temperature, solid-to-liquid ratio, stirring speed, nitric acid concentration, particle size and addition of sodium nitrite. It was determined that the dissolution rate of the process increased with decreasing particle size and solid-to-liquid ratio, and increasing nitric acid concentration, reaction temperature and the amount of the sodium nitrite in the solution. In addition, it was observed that the stirring speed had more effect on the dissolution rate at low stirring speeds than at high stirring speeds. In the present study, the examination of shrinking core models of fluid-solid systems showed that the dissolution of metallic silver in the nitric acid solutions was controlled by the reaction on the surface. A semiempirical model, which represented well the process, was developed by statistical methods. The activation energy of the process was found to be 57.66 kJ mol–1.

Kinetic Investigation of Reaction Between Metallic Silver and Nitric Acid Solutions

In this study, the reaction kinetics between metallic silver and nitric acid solutions was investigated by taking into consideration the parameters of temperature, solid-to-liquid ratio, stirring speed, nitric acid concentration, particle size and addition of sodium nitrite. It was determined that the dissolution rate of the process increased with decreasing particle size and solid-to-liquid ratio, and increasing nitric acid concentration, reaction temperature and the amount of the sodium nitrite in the solution. In addition, it was observed that the stirring speed had more effect on the dissolution rate at low stirring speeds than at high stirring speeds. In the present study, the examination of shrinking core models of fluid-solid systems showed that the dissolution of metallic silver in the nitric acid solutions was controlled by the reaction on the surface. A semiempirical model, which represented well the process, was developed by statistical methods. The activation energy of the process was found to be 57.66 kJ mol–1.

Formulation optimization of controlled release diclofenac sodium microspheres using factorial design

Diclofenac sodium is an ideal candidate for incorporation in a controlled release device to diminish its adverse effects after oral administration. Microspheres were prepared by using sodium alginate as a polymer and CaCl 2 as a cross-linking agent. In this investigation, 3 3 full factorial design was used to investigate the joint influence of three variables: the stirring speed ( X 1), concentration of CaCl 2 ( X 2) and % of heavy liquid paraffin in a blend of heavy and light liquid paraffin in the dispersion medium ( X 3) on the time for 80% drug dissolution ( t 80). Potential variables such as concentration of sodium alginate and drug: sodium alginate ratio were kept constant in the experimental design. A statistical model with significant interaction terms is derived to predict t 80. The results of multiple linear regression analysis and F-statistics revealed that for obtaining controlled drug release, the microspheres should be prepared using relatively lower stirring speed, higher concentration of CaCl 2 and higher percentage of heavy liquid paraffin in the dispersion medium. The X 1 X 2 and X 2 X 3 interactions were found to be statistically significant in nature. A response surface plot is presented to show the effects of X 1, X 2 and X 3 on t 80. The drug was released by diffusion of anomalous type. A model was validated for accurate prediction of drug release profile. Acceptable batches were identified in the experimental design with constraints on percentage drug released in 1, 6 and 8 h.

Instability mechanisms of supported liquid membranes in phenol transport process

This paper describes an investigation of instability mechanisms of supported liquid membranes (SLMs) in phenol transport system. It was observed that any factor facilitating the formation and stability of oil-in-water (O/W) emulsion, such as high HLB value, low electrolyte concentration and high stirring speed, was favourable to the loss of membrane liquid and the resulting SLMs were unstable. The formation of O/W emulsions accounts for the instability of SLMs in the present system. From a thermodynamics analysis, it is shown that emulsification can be realised with the supply of a suitable energy. The energy in the SLM processes can come from the forced flow of aqueous solutions and the hydrodynamic instability of the interfaces. Once loss of membrane liquid occurs, the vacated space is mainly filled with the membrane phase through the movement along the membrane capillaries and hence further loss can continue in the same way.

Process Performance of Continuous Inoculation and Acidification of Milk with Immobilized Lactic Acid Bacteria

Several parameters of a milk prefermentation process by immobilized lactic acid bacteria in a stirred bioreactor were investigated. This process was designed to acidify and inoculate skim milk continuously. Four strains of mesophilic lactic acid bacteria were entrapped separately in κ-carrageenan and locust bean gum gel beads. We studied the effect of four process parameters pH (5.8, 6.0, and 6.2), temperature (22, 26, and 30°C), stirring speed (90, 120, 150, and 180rpm), and ratio of gel to reactor volume (20, 25, 30, and 40%) on dilution rate, lactic acid productivity, fermentation time, and the composition of the prefermented milk and coagulum obtained after further fermentation to pH 4.7.Dilution rate increased with temperature, pH, gel ratio, and low stirring speed. Under the conditions used, the maximum reactor dilution rate was 30.6/h at pH 6.2, 30°C, 120rpm, and a gel ratio of 25%. The preacidified milk was inoculated with the four strains of lactic acid bacteria at 2 × 108 to 3 × 108 cfu/ml. Fermentation time was reduced by more than 50% with this prefermentation step, and the final coagulum contained about 109 cfu/ml. Citrate was entirely consumed during fermentation, and acetoin and diacetyl concentrations in the coagulum reached 2.8 and .014mM.

特集 粉末の成形・加工 粉末を応用したＳｅｍｉ‐Ｓｏｌｉｄ Ｄｉｅｃａｓｔｉｎｇの基礎的研究 Ａｌ‐Ｓｉ混合粉末の半溶融状態での撹はんの影響

In this work, influence of mechanical stirring on semi-solid state of Al-5mass%Si alloy prepared from elemental powders is examined to obtain an information about the semi-solid diecasting method using the powder. Viscosity of the slurry containing volume fraction of solid phase less than 40% is lower, but it remarkably increases when the volume fraction of the solid increased to more than 40%. In the case of low stirring speed, sizes of solid aluminum phase and eutectic silicon phase grow. The specimen solidified from the unstirred slurry has many blow holes, but they are disappeared by the stirring of low speed. As the stirring speed increased, the particle of aluminum solid in the slurry become to globular form and the grain size of silicon phase in the eutectic matrix decreases.

Hydrogenation of adiponitrile catalyzed by raney nickel use of intrinsic kinetics to measure gas-liquid mass transfer in a gas induced stirred slurry reactor

Three phase hydrogenation of adiponitrile (ADN) to hexamethylene diamine (HMD) proceeds via aminocapronitrile (ACN). In a first step it has been investigated in selected conditions of temperature, pressure, reagent and catalyst concentrations, avoiding external and intraparticle transfer limitations. Based on initial reaction rates, a Langmuir Hinshelwood model has been selected, involving limiting surface reaction between dissociate hydrogen and nitriles adsorbed on different sites. From concentration profiles different ACN adsorption coefficients depending on ADN concentration have been derived and explained by amine-nitrile interactions. Additional runs performed at lower stirring speeds have then been analysed using the intrinsic kinetic law to estimate the gas-liquid and liquid-solid mass transfer parameters. Comparison with parallel physical measurements performed in the same equipment but without reaction is discussed.

Exopolysaccharide production by Acremonium persicinum in stirred-tank and air-lift fermentors

Exopolysaccharide production by the fungus Acremonium persicinum was affected by the culture system used. The yields achieved in shake flasks were not obtained in a stirred tank reactor, except at very low stirring speeds (100 rpm). However when grown in an air-lift fermentor, exopolysaccharide levels were similar to those found with shake flask cultures. Results suggest that both dissolved oxygen tension and shear rate may determine the ability of this organism to synthesise this exopolysaccharide.

Effects of stirring on residual chlorine during chlorination of seawater containing ammonia nitrogen

Stirring affected the concentration and proportions of residual chlorine during the chlorination of seawater containing ammonia nitrogen. At high stirring speed, the residual chlorine level rose in direct proportion to the dose of chlorine, then decreased to a minimum. At low stirring speed, the residual chlorine level began to decline before the peak of the break-point curve, which was flatter than the one obtained with high stirring speed. Regardless of the speed of stirring, monochloramine was the predominant species in the residual chlorine that remained after 1 h and the break-point was at the same chlorine dose. The amount of monobromamine produced was inversely related to the speed of stirring. Residual chlorine loss occurred primarily via the disproportionation of monobromamine to form dibromamine and ammonia nitrogen. Later, dibromamine and bromochloramine disappeared on reacting with monochloramine, and only stable monochloramine remained. The degree of mixing of chlorine and seawater with ammonia nitrogen is of importance in evaluating the residual chlorine concentrations.

Mass transfer of acetylacetone, ethylene glycol mono- n-butyl ether and ethylene glycol monophenyl ether across water-carbon tetrachloride and water-chloroform interfaces

The interfacial mass transfer kinetics of acetylacetone (acac), ethylene glycol mono- n-butyl ether (EGBE) and ethylene glycol monophenyl ether (EGPE) across water-carbon tetrachloride (Ccl 4) and water-chloroform (CHCl 3) interfaces were studied by stirring the two phases at various speeds, maintaining a quiescent interface with a constant area. In the analysis of data, two rate-determining steps consisting of a diffusion toward the interface and a mass exchange between the interface and bulk phases are considered. It is shown that the transfer of EGBE and EGPE in both CHCl 3 and Ccl 4 systems is controlled by the diffusion step even at high stirring speeds, whereas the transfer of acac in Ccl 4 is controlled by the interfacial exchange step at high stirring speeds. An irreversible transfer has been also observed in the EGBE and EGPE systems at low stirring speeds.