Improvements in azithromycin recrystallization using ultrasound for size reduction

The primary motive of the current work is to achieve smaller mean particle size with narrow size distribution that can enhance the bioavailability of azithromycin (ARZ), an essential requirement due to its poor water solubility. Recrystallization of ARZ was evaluated using cooling as well as antisolvent crystallization approaches in the presence of ultrasonic irradiation with detailed study into effect of different parameters such as ultrasonic power, time and temperature. Ultrasound assisted antisolvent crystallization at low temperatures (<10℃) yielded best size reduction up to 80% with narrower distribution and also gave better yield of the product, that too within 5 min of sonication. With scale up considerations, recirculation mode of operation was also evaluated which offered promising results for the size reduction. Images captured using optical microscope and SEM revealed a nearly uniform rod/plate-shaped geometry. Increase in amorphous nature of ARZ was confirmed based on XRD analysis. FTIR analysis showed no significant changes in the functional groups when compared to the original sample. Overall, the work demonstrated an improved reprocessing approach based on the use of ultrasound with insights into effect of operating parameters and effect of ultrasound on various characteristics.     

Formulation of poorly water-soluble Gemfibrozil applying power ultrasound

The dissolution properties of a drug and its release from the dosage form have a basic impact on its bioavailability. Solubility problems are a major challenge for the pharmaceutical industry as concerns the development of new pharmaceutical products. Formulation problems may possibly be overcome by modification of particle size and morphology. The application of power ultrasound is a novel possibility in drug formulation. This article reports on solvent diffusion and melt emulsification, as new methods supplemented with drying in the field of sonocrystallization of poorly water-soluble Gemfibrozil. During thermoanalytical characterization, a modified structure was detected. The specific surface area of the drug was increased following particle size reduction and the poor wettability properties could also be improved. The dissolution rate was therefore significantly increased.     

Multiple size group analysis for transient radiative heating of particle polydispersions

The transient radiative heating of particle polydispersions initially at uniform temperature is numerically analyzed. Due to the different radiative heating characteristics between particles, the temperature evolution of particle changes with particle diameter. To take local thermal nonequilibrium between particles into consideration, the particles are discretized into several size groups. The radiative transfer equation in particle polydispersions and the transient energy equation for each particle group are solved by the discrete ordinates method and an implicit finite difference method, respectively. The effects of the standard deviation of particle diameter and the emissivity of particle surface on the thermal evolution of particle polydispersions are analyzed. The results show that, omitting thermal nonequilibrium of particles will result in significant errors in the calculation of radiative heat transfer, especially when the nonuniformity of particle diameter is large.     

The role of the particle size reduction and morphological changes of solid substrate in the ultrasound-aided enzymatic hydrolysis of cellulose

The contribution of ultrasound-aided particle size reduction to the efficiency of the subsequent enzymatic hydrolysis and the accompanying morphological changes of bleached cotton and linen powders were investigated. The aqueous suspensions of cellulosic powders were pretreated either with an ultrasonic bath (US-B) or with a horn-type reactor (US-H). Results revealed that the impact of US-H was more pronounced than that of the US-B. Clearly, the linen particles were more sensitive to ultrasonication than cotton. The US-H modified the particle size distribution differently for the cotton and linen powders and reduced the mean size of particles from 49 to 40 µm and from 123 to 63 µm, respectively. A significant increase in the water retention and water sorption capacity was also measured. The smaller particles with increased accessibility were preferably digested in the enzyme treatment, resulting in a considerably higher concentration of reducing sugars and an enrichment of the residual particles with a larger average size (cotton: 47 µm; linen: 66 µm).     

Dependency of percolation critical exponents on the exponent of power law size distribution

The standard percolation theory uses objects of the same size. Moreover, it has long been observed that the percolation properties of the systems with a finite distribution of sizes are controlled by an effective size and consequently, the universality of the percolation theory is still valid. In this study, the effect of power law size distribution on the critical exponents of the percolation theory of the two dimensional models is investigated. Two different object shapes i.e., stick-shaped and square are considered. These two shapes are the representative of the fractures in fracture reservoirs and the sandbodies in clastic reservoirs. The finite size scaling arguments are used for the connectivity to determine the dependency of the critical exponents on the power law exponent. In particular, the deviations of percolation exponents from their universal values as well as the connectivity behavior of such systems are investigated numerically. As a result, this extends the applicability of the conventional percolation approach to study the connectivity of systems with a very broad size distribution.     

Comparison of two different ultrasound reactors for the treatment of cellulose fibers

The pulp and paper industry is in continuous need for energy-efficient production processes. In the refining process of mechanical pulp, fibrillation is one of the essential unit operations that count for up to 80% of the total energy use. This initial study explores the potential and development of new type of scalable ultrasound reactor for energy efficient mechanical pulping. The developed reactor is of continuous flow type and based on both hydrodynamic and acoustic cavitation in order to modify the mechanical properties of cellulose fibers. A comparison of the prototype tube reactor is made with a batch reactor type where the ultrasonic horn is inserted in the fluid. The pulp samples were sonicated by high-intensity ultrasound, using tuned sonotrodes enhancing the sound pressure and cavitation intensity by a controlled resonance in the contained fluid. The resonant frequency of the batch reactor is 20.8 kHz and for the tube reactor it is 22.8 kHz. The power conversion efficiency for the beaker setup is 25% and 36% in case of the tube reactor in stationary mode. The objective is to verify the benefit of resonance enhanced cavitation intensity when avoiding the effect of Bjerkenes forces. The setup used enables to keep the fibers in the pressure antinodes of the contained fluid. In case of the continuous flow reactor the effect of hydrodynamic cavitation is also induced. The intensity of the ultrasound in both reactors was found to be high enough to produce cavitation in the fluid suspension to enhance the fiber wall treatment. Results show that the mechanical properties of the fibers were changed by the sonification in all tests. The continuous flow type was approximately 50% more efficient than the beaker. The effect of keeping fibers in the antinode of the resonant mode shape of the irradiation frequency was also significant. The effect on fiber properties for the tested mass fraction was determined by a low-intensity ultrasound pulse-echo based measurement method, and by a standard pulp analyzer.     

Use of a magnetic fluid for particle size analysis by a sedimentation method

A new method of particle size analysis of micrometer-sized particles is discussed. The improved method of sedimentation analysis with magnetic fluids has the potential and versatility to characterize polydisperse systems.     

The size of active bubbles for the production of hydrogen in sonochemical reaction field

The sonication of aqueous solution generates microscopic cavitation bubbles that may growth and violently collapse to produce highly reactive species (i.e. OH, HO₂ and H₂O₂), hydrogen and emit light, sonoluminescence. The bubble size is a key parameter that influences the chemical activity of the system. This wok aims to study theoretically the size of active bubbles for the production of hydrogen in ultrasonic cavitation field in water using a single bubble sonochemistry model. The effect of several parameters such as frequency of ultrasound, acoustic intensity and liquid temperature on the range of sonochemically active bubbles for the production of hydrogen was clarified. The numerical simulation results showed that the size of active bubbles is an interval which includes an optimum value at which the production rate of H₂ is maximal. It was shown that the range of ambient radius for an active bubble as well as the optimum bubble radius for the production of hydrogen increased with increasing acoustic intensity and decreased with increasing ultrasound frequency and bulk liquid temperature. It was found that the range of ambient bubble radius dependence of the operational conditions followed the same trend as those reported experimentally for sonoluminescing bubbles. Comparison with literature data showed a good agreement between the theoretical determined optimum bubble sizes for the production of hydrogen and the experimental reported sizes for sonoluminescing bubbles.     

Ultrasonic pretreatment of spodumene with different size fractions and its influence on flotation

The potential of ultrasonic pretreatment enhancing selective surface dissolution to improve the floatability of spodumene with different size fractions was verified and investigated. For coarse particles of −0.15 + 0.0385 mm, compared with traditional pretreatment methods, ultrasonic pretreatment could optimize the physicochemical properties of the surface, markedly increased the amount of NaOL adsorbed on the mineral surface, and improved the floatability of the spodumene. For fine particles of −0.0385 mm, both pretreatment methods (Ultrasonic and Traditional) could greatly increase the flotation recovery, but ultrasonic pretreatment had no obvious advantage compared with traditional method. ICP combined with XPS analysis were conducted to investigate the dissolution mechanism of spodumene surface in different pretreatment system. Si species on the surface of coarse particles were easily dissolved into the solution under the effect of ultrasound, which increases the relative content of Al and Li species on the surface. This was conducive to the adsorption of the collectors on the surface. However, the selective dissolution of the fine particle surface was weakened by excessive energy intake in the ultrasonic system, which neutralized the advantage brought by the large amount of dissolution, making the results obtained by the two preprocessing methods the same.     

Grain size reduction of copper subjected to repetitive uniaxial compression combined with accumulative fold

This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduction and microstrain variations of the high purity copper samples after different passes of compression and fold are investigated by scanning electron microscope and x-ray diffraction (XRD), respectively. Our results show that the average grain size of samples decreases from about 830nm to 127nm as the number of compression passes increases to 30. Microstrain in the compressed sample is found to increase for the first 20 passes, but to decrease at the last 10 passes. The variations of compressive yield strength and the shift of XRD peaks to larger diffraction angles are observed in the squeezed sample. Our experimental results demonstrate that the repetitive uniaxial compression combined with accumulative fold is an effective method to prepare bulk nanocrystalline metallic materials, in particular for soft metals such as Cu, Al and Pb.     

Determination of particle size in multiphase blends by different methods

Different methods for characterizing the morphology of multiphase blends were applied to a blend of thermoplastic polyurethane with 20 wt% polypropylene as the dispersed phase. Optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and light scattering were compared. The microscopy methods were evaluated with respect to their suitability for quantitative image analysis for determination of the particle size distribution. Comparison of the particle size distributions revealed that the dependence of the measured particle size on the method of preparation and technique was not very pronounced. The main difference resulted from cutting the particles outside their maximum diameter. The measured particle sizes determined with methods that analyze the whole particles, such as SEM on separated particles and laser light scattering, are larger than those measured on cut specimens. The factor 4/π valid in monodisperse systems for the ratio between the real particle size and that measured on sections was found also to be applicable to this polydisperse blend system. Although light micros-copy requires the least preparation efforts, it is a reliable method for this blend system.     

Anomalous diffraction approximation method for retrieval of spherical and spheroidal particle size distributions in total light scattering

Using total light scattering technique to measure the particle size distribution has advantages of simplicity in measurement principle and convenience in the optical arrangement. However, the calculation of extinction efficiency based on Mie theory for a spherical particle is expensive in both time and resources. Thus, a simple but accurate approximation formula for the exact extinction efficiency may be very desirable. The accuracy and limitations of using the anomalous diffraction approximation (ADA) method for calculating the extinction efficiency of a spherical particle are investigated. Meanwhile, the monomodal and bimodal particle size distributions of spherical particles are retrieved using the genetic algorithm in the dependent model. Furthermore, the spheroidal model in the retrieval of non-spherical particle size distribution is also discussed, which verifies the non-sphericity has a significant effect on the retrieval of particle size distribution compared with the assumed homogeneous isotropic sphere. Both numerical computer simulations and experimental results illustrate that the ADA can be successfully applied to retrieve the particle size distributions for spherical and spheroidal particles with high stability even in the presence of random noise. The method has advantages of simplicity, rapidity, and suitability for in-line particle size measurement.     

Inversion of visible optical extinction data for spheroid particle size distribution based on PCA

The problem of light scattering properties of spheroid particles is studied, and a general approach is presented for calculating the single particle light scattering of spheroids. In this approach, the extinction efficiency of spheroid particles can be calculated by combining the spline interpolation of T matrix method and ADA (anomalous diffraction approximation) theory. Furthermore, the retrieval of spheroid particle size distribution is performed in the dependent mode and a selection method about the optical extinction data is proposed based on PCA (principle component analysis) of first derivative corresponding to the raw optical extinction. By calculating the contribution rate of first derivative corresponding to the raw optical extinction, the optical extinction with more significant features can be selected as the inversion optical extinction data. In this way, the selected optical extinction has less information redundancy and higher capacity of resisting noise disturbance. Simulation experiments indicate that the spheroid particle size distributions obtained with the proposed method coincide fairly well with the given distributions, which provides a simple, reliable and efficient method to retrieve the spheroid particle size distribution using the optical extinction data.     

从散射谱反演颗粒尺寸分布的测试方法改进

针对从散射谱反演颗粒尺寸分布测量中,由于衍射近似要求近前向取值而带来的反演噪声问题,提出了一种改进的方法.在Chin-Shifrin(C-S)积分变换反演中,插入一种调节函数使得噪声基本消失,又不至于影响反演谱的分布峰位置.对理想单分散颗粒群的模拟效果说明了该法的可行性.对以线阵CCD为接受器件的实验测量和反演结果显示...     

The atomization current and droplet size of ethanol in two different small-scale electro-spraying systems

An experimental study on electro-spraying from small-scale combustors is carried out using liquid ethanol as fuel. Two systems of electro-spraying are employed in the present study; one is a nozzle system (without a ring electrode) and the other is a nozzle-ring system (with a ring electrode). The photos of electro-spraying at the cone-jet mode are taken by a digital camera. The voltage drop across the resistance in the loop is measured by a data acquisition instrument, and the atomization current is calculated according to Ohm's Law. The size and velocity of electro-spraying droplets are measured by a Phase Doppler Anemometer. A non-dimensional analysis on atomization current is completed to explain the electro-spraying phenomena of liquid at the stable cone-jet mode. The results show that, the lower atomization current and droplet velocity corresponds to smaller size of droplet. Based on the results of non-dimensional analysis, it is found that the dimensionless atomization current in both the nozzle system and nozzle-ring system obeys the scaling law as square root of the dimensionless flow rate. The charge density is of a −1.5 power dependence on droplet diameter. Both of the nozzle and the nozzle-ring systems show a good agreement with Rayleigh instability.     

Evaluation of a biological wastewater treatment system combining an OSA process with ultrasound for sludge reduction

Sludge production is an undesirable by-product of biological wastewater treatment. The oxic-settling-anaerobic (OSA) process constitutes one of the most promising techniques for reducing the sludge produced at the treatment plant without negative consequences for its overall performance. In the present study, the OSA process is applied in combination with ultrasound treatment, a lysis technique, in a lab-scale wastewater treatment plant to assess whether sludge reduction is enhanced as a result of mechanical treatment. Reported sludge reductions of 45.72% and 78.56% were obtained for the two regimes of combined treatment tested in this study during two respective stages: UO1 and UO2. During the UO1 stage, the general performance and nutrient removal improved, obtaining 47.28% TN removal versus 21.95% in the conventional stage. However, the performance of the system was seriously damaged during the UO2 stage. Increases in dehydrogenase and protease activities were observed during both stages. The advantages of the combined process are not necessarily economic, but operational, as US treatment acts as contributing factor in the OSA process, inducing mechanisms that lead to sludge reduction in the OSA process and improving performance parameters.     

Evaluation of the performance of high temperature conversion reactors for compound-specific oxygen stable isotope analysis

In this study conversion conditions for oxygen gas chromatography high temperature conversion (HTC) isotope ratio mass spectrometry (IRMS) are characterised using qualitative mass spectrometry (IonTrap). It is shown that physical and chemical properties of a given reactor design impact HTC and thus the ability to accurately measure oxygen isotope ratios. Commercially available and custom-built tube-in-tube reactors were used to elucidate (i) by-product formation (carbon dioxide, water, small organic molecules), (ii) 2nd sources of oxygen (leakage, metal oxides, ceramic material), and (iii) required reactor conditions (conditioning, reduction, stability). The suitability of the available HTC approach for compound-specific isotope analysis of oxygen in volatile organic molecules like methyl tert-butyl ether is assessed. Main problems impeding accurate analysis are non-quantitative HTC and significant carbon dioxide by-product formation. An evaluation strategy combining mass spectrometric analysis of HTC products and IRMS ¹⁸O/¹⁶O monitoring for future method development is proposed.     

Applicability of classical methods of pore size analysis for MCM-41 and SBA-15 silicas

Two most popular ordered mesoporous silicas, MCM-41 and SBA-15, exhibiting uniform mesopores of approximately cylindrical shapes, have been used as model adsorbents for verification, improvement and/or development of adsorption-based methods for characterization nanoporous materials. While the applicability of the classical methods for pore size analysis was widely examined by employing MCM-41 materials, the large-pore materials such as SBA-15 did not find adequate usage for this type of studies. The current work addresses the issue of applicability of classical methods such as Barrett-Joyner-Hallenda (BJH) and Broekhoff-de Boer (BdB) methods for pore size analysis of mesoporous silicas by using MCM-41 and SBA-15 materials as model adsorbents. In addition, the Kruk-Jaroniec-Sayari (KJS) method, which is based on the BJH algorithm and experimental relations for the pore width and statistical film thickness, is discussed too. While the MCM-41 materials cover the range of small mesopores (about 2-7 nm), the inclusion of SBA-15 materials allowed us to examine the range of the pore diameters up to about 12 nm. The high quality MCM-41 and SBA-15 samples are used to discuss the applicability and limitations of the aforementioned characterization methods and to propose some recommendations for pore size analysis of these materials.     

Method for independent control of particle size and distance in rhodium epitaxy on TiO2(110)-(1×2) surface An STM study

A method for independent control of the particle size and distance is presented for rhodium epitaxy on TiO₂(110)-(1×2) surface. The real space imaging of the surface morphology was performed by scanning tunneling microscopy. The amount of the deposited rhodium was checked by Auger electron spectrometry. The method consists of two steps: (i) evaporation of 0.001–0.050 ML equivalent of rhodium at room temperature with a post-annealing at 1100 K (“seeding”); (ii) post-deposition of rhodium for growing of the Rh nanoparticles formed in step (i) (“growing”). The mechanism of this procedure is based on the large difference of the surface diffusion coefficient between Rh adatoms and Rh nanocrystallites larger than 1–2 nm. In the first step the average distance between the metal particles is controlled in the range 5–200 nm, the second step determines the particles size (2–50 nm). This work demonstrates that the diffusion processes of metal nanoparticles of different sizes and the growing modes of the crystallites can be studied in detail by application of seeded surfaces.