Synthesis of spherical shape borate-based bioactive glass powders prepared by ultrasonic spray pyrolysis

Spherical shape borate-based bioactive glass powders with fine size were directly prepared by high temperature spray pyrolysis. The powders prepared at temperatures between 1200 and 1400 °C had mixed phase with small amounts of fine crystal and an amorphous rich phase. Glass powders with amorphous phase were prepared at a temperature of 1500 °C. The mean size of the glass powders prepared by spray pyrolysis was 0.76 μm. The glass powders prepared at a temperature of 1200 °C had two distinct exothermic peaks (T_c1 and T_c2) at temperatures of 588 and 695 °C indicating crystallization. The glass transition temperature (T_g) of the powders prepared at a temperature of 1200 °C was 480 °C. Phase-separated crystalline phases with spherical shape were observed from the surface of the pellet sintered at a temperature of 550 °C. Crystallization of the pellet was completely occurred at temperatures of 750 and 800 °C. The pellets sintered at temperatures below 700 °C had single crystalline phase of CaNa₃B₅O₁₀. The pellet sintered at a temperature of 800 °C had two crystalline phases of CaNa₃B₅O₁₀ and CaB₂O₄.     

Characteristics of nanosized Bi-based glass powders prepared by flame spray pyrolysis as transparent dielectric layer material

Bi-based glass powders with particle size of 34 nm were prepared by high-temperature flame spray pyrolysis. The glass transition temperature (T_g) of the powders was 442 °C. Dielectric layers fired at temperatures of 480 and 500 °C contained voids, while those fired at temperatures above 540 °C had clean surfaces and no voids. The dielectric layers sintered at temperatures of 560 and 580 °C had transmittances of 70% in the visible range. Further, it was observed that the dielectric layers formed from the nanosized glass powders obtained from spray solutions containing excess boron had higher transmittances (80% in the visible range at a sintering temperature of 580 °C) than the layers formed from spray solutions containing stoichiometric amounts of boron.     

Hydrodynamics of three-phase fluidized bed systems examined by statistical, fractal, chaos and wavelet analysis methods

Hydrodynamic studies were conducted in gas-liquid-solid systems (0.1 m ID, 2 m high) of 3.0 mm glass beads and of 2.1 mm polypropylene low-density particles, with particles densities of 2471 and 1290 kg/m³, respectively. Simultaneous measurement of differential pressure and bubble conductivity probe signals sampled at 500 Hz for 60 s enabled the investigation of the change in flow structure in relation to the flow regime transitions. Superficial gas velocities ranged between 0.010 and 0.052 m/s for polypropylene particles, and extended to 0.12 m/s for glass beads, while the superficial liquid velocities covered the ranges of 0.0007-0.045 m/s for polypropylene particles, and ranged up to 0.056 m/s for glass beads.Spectral analysis of the pressure fluctuations revealed a transition from dispersed to coalesced bubbling flow with decreasing liquid velocity for a given superficial gas velocity. The use of a conductivity probe facilitated characterization of the local flow structure in terms of bubble movement. The measurements were extensively analyzed using fractals and chaos, power spectra frequency analysis and wavelet decomposition in addition to the standard statistical analyses. The coefficient of variation of the bubble probe signals was found to be the most effective in deducing the transition velocity between coalesced and dispersed bubbling flow regimes, while wavelet energy confirmed the similarity in the distribution between two axial positions once operated in the dispersed flow regime. Comparison of the flow structure between glass beads and polypropylene particles showed that both the minimum liquid fluidization velocity and the transition velocity between the bubble flow regimes were much higher for the glass beads than for the lighter polypropylene particles. Furthermore, the standard deviations of the decomposed bubble probe signals through wavelet transformation successfully highlighted the difference between the two systems of particles.     

Powder formation by atmospheric spray-freeze-drying

Freeze-drying (lyophilization) has been one of the most useful methods for producing high quality powder from thermosensitive drugs. However, lyophilization has high capital and process costs. A new method for manufacturing powder has been developed in this work, with the aim of reducing drying time and increasing collection efficiency. Compared with other published atmospheric spray-freeze-drying technologies, the new technology combines the spray-freezing step and fluidization conveying of frozen powder using co-current flow to convey the frozen powder to the exit filter. This overcomes the difficulty of fluidizing and elutriating cohesive frozen powder from a substrate. In this process, a powder cake with uniform thickness builds up on the exit filter. Freeze-drying was then performed by continuously flowing a dry gas stream through the packed powder bed at a temperature below the eutectic point of water. The pressure in the chamber was monitored and the residual moisture of the powder was also measured vs time in the drying process. After the completion of drying, a loose powder cake was generated and a free-flowing powder was readily collected. Compared to lyophilization, the experiment indicates the content of α-helix of heat-sensitive protein (samples of bovine serum albumin) was essentially unchanged after drying (96.7% in 2.5 mM NaHCO₃ solution and 102.9% in 2.5 mM NaHCO₃ with trehalose protection (BSA:trehalose = 2:1)) and the powders show good aerosol dispersion for inhalation drug delivery (fine particle fraction FPF_< 5.6 μm was 62.1% ± 2.9% for a mannitol/ciprofloxacin powder). In addition, viability of bacteria (Bordetella pertussis avirulent strain) subjected to this powder processing method was more than 90% after drying, showing that this process has excellent potential for production of powdered biologics. The present process also offers greatly reduced process times i.e. drying was completed in 1-2 h vs 1-2 d with conventional lyophilization in a vacuum.     

Measuring the flow properties of small powder samples using an avalanche tester

The feasibility of using a small-scale avalanche tester to measure the flow properties of pharmaceutical lactose powders was examined. The modes of behavior observed in larger systems were displayed and showed a clear distinction between angular, free-flowing particles and more spherical particles of similar flow characteristics. Angular Lactohale LH100 particles showed slumping behavior at a rotational frequency of 0.33 Hz that disappeared at higher frequencies. Spherical lactose powder with a similar flow function to LH100 only showed rolling behavior under the same conditions, as did more cohesive powders LH200 and LH300. Further investigation of the LH100 data using fast Fourier analysis showed that the slumping frequency was one tenth of the rotational frequency.     

Favorable vibrated fluidization conditions for cohesive fine particles

The present study was performed to clarify the operational range for vibro-fluidization of fine cohesive particles (glass beads, d_p = 6 μm). Decreasing and increasing gas velocity methods were examined to clarify the favorable vibro-fluidization region. The upper limit of the gas velocity for intermittent channel breakage was higher in the case of the increasing gas velocity method than the decreasing gas velocity method. This was because the changes in the bed flow pattern from a favorable (intermittent channel breakage) to an unfavorable fluidization state (stable channels) were moderate in the case of the increasing gas velocity method. In the increasing gas velocity method, two kinds of cross-points were obtained from the relationship between the gas velocity and the bed pressure drop. At one of the gas velocities at these cross-points, the bed void fraction reached its maximum. In the present study, the above-mentioned gas velocity was defined as the upper limit of gas velocity for favorable vibro-fluidization, u_chu. A favorable vibro-fluidization region was determined by combining u_chu with u_chl, which is the lower limit of gas velocity for intermittent channel breakage obtained in a previous study. The value of u_chu was found to have a maximum corresponding to a certain vibration strength.     

The Flow Characteristics of High Explosives

A comparative study of flow properties of the explosive compound RDX is presented. The results were used to identify desirable free-flowing characteristics in the powders. Various static and free-flowing tests were conducted on the explosive powders. The results suggest that flow properties of the RDX powders tested were not influenced by particle size and surface roughness. However density, moisture content and cohesive strength between the particles had some effect on the flow properties. An increase in moisture content and cohesive strength of the particles reduced the flow rate. Whereas an increase in bluk density of the powders increased the flow rate.     

Influence of spray-drying operating conditions on Rhamnus purshiana (Cáscara sagrada) extract powder physical properties

The aim of this work was to study Rhamnus purshiana (Cáscara sagrada) extract spray-drying in order to obtain powders with good rheological properties for direct compression (DC) and stability attributes.The experiments were carried out in a Büchi B-290 Mini Spray Dryer using colloidal silicon dioxide as carrier agent. A 2^5 − 1 fractional factorial statistical design was used to find adequate spray-drying operating conditions to produce Cáscara sagrada powders with good flow, good compactability properties, high process yield, low moisture content, low hygroscopicity, and caking tendency. Morphology, size, structural and thermal properties of the particles were also evaluated. The operating variables studied were air inlet temperature, atomization air flow rate, pump feed rate, aspiration capacity, and feed solids concentration.The 2^5 − 1 factorial experimental design used was a good strategy to establish spray-drying operating conditions to produce Cáscara sagrada extract powders with good properties for direct compression and high process yields. Colloidal silicon dioxide was an effective drying adjuvant. Its use in relatively high concentrations together with low atomization air flow rates improved powder flowability, increased the product's glass transition temperature, and decreased its moisture content and hygroscopicity.     

Effect of chemical structure and crosslinking density on the thermo-mechanical properties and toughness of (meth)acrylate shape memory polymer networks

The objective of this work is to characterize and understand structure-mechanical property relationships in (meth)acrylate networks. The networks are synthesized from mono-functional (meth)acrylates with systematically varying sidegroup structure and multi-functional crosslinkers with varying mole fraction and functionality. Fundamental trends are established between the network chemical structure, crosslink density, glass transition temperature, rubbery modulus, failure strain, and toughness. The glass transition temperature of the networks ranged from −29 to 112 °C, and the rubbery modulus (E_r) ranged from 2.8 to 129.5 MPa. At low crosslink density (E_r < 10 MPa) network chemistry has a profound effect on network toughness. At high crosslink densities (E_r > 10 MPa), network chemistry has little influence on material toughness. The characteristic ratio of the mono-functional (meth)acrylates' components is unable to predict trends in network toughness as a function of chemical structure, as has been demonstrated in thermoplastics. The cohesive energy density is a better tool for relative prediction of network mechanical properties. Due to superior mechanical properties, networks with phenyl sidegroups are further investigated to understand the effect of phenyl sidegroup structure on toughness.     

Nanostructured Nd:YAG powders via gel combustion: The influence of citrate-to-nitrate ratio

Nanostructured neodymium doped yttrium aluminum garnet (Nd:YAG) powders were synthesized at low temperature by a gel combustion method with citric acid as fuel and nitrate as oxidizer. The method involves exothermic decomposition of an aqueous citrate–nitrate gel. The decomposition is based on a thermally induced anionic redox reaction. A variety of 1.0 at% Nd:YAG powders with different agglomerate structures were obtained by altering the citrate-to-nitrate ratio γ. The gel with γ = 0.277 yielded nanocrystalline Nd:YAG at 800 °C without the formation of any intermediate phase. For other gels nanostructured Nd:YAG powders were obtained at 850 °C. The gel with γ = 0.1 yielded nanostructured Nd:YAG powder with an average particle size of ∼40 nm. The stoichiometric citrate-to-nitrate ratio (γ = 0.277) gave the lowest amount of agglomeration. The decomposition of the gel was investigated by TG–DSC and FTIR. The produced ashes and calcined powders were characterized by XRD, BET and FETEM analysis.     

Mixing of pharmaceutical solids. I. Effect of particle size on mixing in cylindrical shear and V-shaped tumbling mixers

The mixing of a cohesive drug with a cohesive, non-cohesive and free-flowing excipient was studied using two types of mixers, cylindrical shear and V-shaped tumbling. Two mixing indices, one based on complete random mixing, s/σ_R, and the other based on standard specifications, s/σ_A, were used to evaluate the data. Both indices gave similar results for mixing cohesive drug with a free-flowing or non-cohesive excipient and were suitable for evaluating homogeneity. However, for mixing a cohesive drug with a cohesive excipient, s/σ_R was not a suitable index, while s/σ_A could be used. The ‘mixing margin’, a concept proposed by Hersey [3], is not a very useful tool in assessing mix-ability of powders having too large or too small particle size distributions. Because of electrostatic charging, preferential sticking of the drug to the walls of the mixer resulted in a lower mean value of the drug in the mixture. Although the mixing indices suggested that the desired mixedness was reached, it is proposed that the mean percent of the active ingredient should be checked in addition to the mixing indices for ensuring the uniformity and potency of the drug content in solid state mixtures.     

Fabrication and characterization of ZnO modified bioactive glass nanoparticles

Bioactive glass nanoparticles in the system (SiO₂-CaO-P₂O₅-ZnO) were synthesized following the sol-gel technique. The prepared glass nanoparticles of 1, 3 and 5 wt% of ZnO (coded: GZ1, GZ3 and GZ5, respectively) were characterized by TEM, FTIR, XRF, TGA and DSC. All glass powders had particle sizes less than 100 nm. Textural analysis revealed that for GZ1, GZ3 and GZ5, the average pore diameters, measured by the high-speed gas sorption analyzer, were 15.9, 15.4 and 15.2 nm, respectively, while the average pore diameters measured by the mercury intrusion porosimetry were 47, 50 and 63 nm, respectively. All glass powders were highly porous (75, 76 and 75%) with surface areas of 233, 94 and 118 m²/g for GZ1, GZ3 and GZ5, respectively. All glass powders induced an apatite layer on their surfaces upon immersion in simulated body fluid (SBF) as verified by SEM and TF-XRD.     

An investigation on flowability and compressibility of AA 6061100 − x-x wt.% TiO2 micro and nanocomposite powder prepared by blending and mechanical alloying

This work investigates the relationships between the components of powders, namely, the powder surface morphology, the flow characteristics and the compressibility of low-energy (microcomposite) and high-energy (nanocomposite) ball milled powders of Al 6061 alloy reinforced with TiO₂ particles. The morphology of the above powder as the function of reinforcement and the milling time was studied by using the scanning electron microscope (SEM). The changes in powder characteristics such as the apparent density, tap density, true density and flow rate were examined by the percentage of reinforcement and milling time. The cohesive nature of the powder was also investigated in terms of Hausner ratio and Kawakita plot. Further, the particle/agglomerate size of low-energy and high-energy ball milled powders was explained by the laser particle size analyzer. X-ray peak broadening analysis was used to determine structural properties of mechanically alloyed powders. The compressibility behavior was examined by the compaction equation proposed by Panelli and Ambrosio Filho to investigate the deformation capacity of the powder. The compressibility behavior, namely, the densification parameter (A) of the microcomposite powder (irregular morphology) was decreased significantly with increasing TiO₂ content due to the disintegration of TiO₂ particles and the cluster formation followed by its agglomeration. The compressibility behavior, namely, the densification parameter (A) of the nanocomposite powder (equiaxed and almost spherical) was decreased slowly with increasing TiO₂ content due to work hardening on the matrix powder. With increased milling time, the compressibility behavior of AA 6061-10 wt.% TiO₂ composite powders increased up to 30 h of milling due to embedding of TiO₂ particles with matrix and changes in powder morphology and finally decreased after 40 h due to work hardening effect.     

Flash grain welding in yttria stabilized zirconia

Self-standing samples made of isostatically pressed powders of ZrO₂:8 mol% Y₂O₃ were submitted to AC signals of 60 and 1000 Hz. At temperatures of around 900 °C, a current density exceeding approximately 100 mA/cm² starts an avalanche process with a fast increasing current under constant voltage. It lasts about 60 s and it is preceded by an induction period of the order of 30 s. After that, the material is sintered as confirmed by impedance diagrams. Relative densities of 94% could be obtained.     

Synthesis of nanocrystalline ytterbium-doped yttria by citrate-gel combustion method and fabrication of ceramic materials

Nanosized ytterbium doped yttria powders were prepared by citrate-gel combustion techniques. As-synthesized precursor and calcined powders were characterized for their crystalline structure, particle size and morphologies. Nanocrystalline Yb³⁺:Y₂O₃ powders with pure cubic yttria crystal structure were obtained by calcination of as-prepared precursors at 1100 °C for 3 h. Powders obtained were well dispersed with an average particle size of 60 nm. By using the obtained powders, nearly full dense Yb³⁺:Y₂O₃ ceramics were produced by vacuum sintering at 1800 °C for 12 h. The emission spectrum of the sintered ceramics under the excitation wavelength of 905 nm illustrates that there are three fluorescence peaks locating at 976 nm, 1030 nm and 1075 nm respectively, all corresponding to the ²F_5/2 → ²F_7/2 transitions of ytterbium ion.     

Uniaxial compaction behaviour and elasticity of cohesive powders

The compression and compaction behaviour of bentonite, limestone and microcrystalline cellulose (MCC) — three cohesive powders widely used in industry were studied. Uniaxial compression was performed in a cylindrical die, 40 mm in diameter and 70 mm high, for three selected cohesive powder samples. The initial density, instantaneous density and tablet density were determined. The influence of maximum pressure and deformation rate was examined. The secant modulus of elasticity E_sec was calculated as a function of deformation rate v, maximum pressure p and powder sample. After compaction experiments in hydraulic press at three pressures - p = 30, 45 and 60 MPa - and two different deformation rates, the strength of the produced tablets was examined in a material strength testing machine.From uniaxial compression tests performed on the universal testing machine for loading and unloading, the modulus of elasticity E was calculated on the basis of the first linear phase of unloading. The total elastic recovery of tablets was also obtained.     

High permeability Ni-Cu-Zn ferrites through additive-free low-temperature sintering of nanocrystalline powders

Nanocrystalline Ni-Cu-Zn ferrite powders Ni_0.20Cu_0.20Zn_0.62Fe_1.98O_3.99 were prepared by thermal decomposition of an oxalate precursor. The particle size is 6 nm and 350 nm, respectively, for powders obtained through calcinations at 350 °C or 750 °C. The shrinkage behavior significantly changes with particle size; the temperature of maximum shrinkage rate is T_MSR = 700 °C for particles of 6 nm size and increases to T_MSR = 880 °C for particles 350 nm in size. Dense samples with a permeability of μ = 780 are obtained by sintering at 900 °C for 2 h. Mixtures of nanocrystalline and sub-micron powders allow tailoring of the shrinkage behavior. A maximum permeability of μ = 840 is obtained after sintering of a 1:1-mixture at 900 °C. This demonstrates the potential of nanocrystalline ferrites for co-firing without additives at 900 °C and integration of ferrite inductors into LTCC modules.     

复杂流道结构料仓的下料流率预测

在实验室搭建的有机玻璃料仓下料平台上,分别以自由流动粉体玻璃微珠和黏附性粉体煤粉和聚氯乙烯为实验介质,针对无改流体(No-In)、封闭改流体(Con-In)和开放改流体(Ucon-In)三种情况所形成的不同流道结构,开展了粉体料仓下料及其流率建模研究,定量分析了改流体对粉体下料流率的促进作用,对比给出了玻璃微珠、煤粉和聚氯乙烯在不同流道结构料仓内的下料特性。研究表明,改流体的引入有利于提高料仓下料流率,Con-In促进流动效果最明显,对于流动性弱的煤粉,下料流率提升幅度达到最大的58%。基于剪切摩擦区的概念,提出流率校正因子F对最小能量理论方程进行了修正,将理想的料仓下料模型拓展至实际下料过程。进一步,对于Con-In,根据流道结构特征结合对粉体的受力分析,修正了模型中的锥角项;对于Ucon-In,基于粉体下料流动竞争机制,提出分阶段下料模式并关联了内层和夹层的下料流率,最终建立了复杂流道结构料仓的下料流率预测模型。该模型综合考虑了粉体物性、下料流型和流道结构的影响,可有效预测自由流动粉体和黏附性粉体流经传统料仓(No-In)和改流体料仓(包括Con-In和Ucon-In)的粉体下料流率,且预测偏差<10%。     

Size-controlled Bi-based glass powders prepared by spray pyrolysis as inorganic additives for silver electrode

Bi-based glass powders as additive for silver conducting pastes were prepared by spray pyrolysis. The glass powders formed from the spray solution with low concentration of 0.025 M had bimodal size distribution with nanometer and submicron sizes. However, glass powders with spherical shape and narrow size distribution were prepared from the spray solutions with concentrations of 0.05 and 0.5 M. The mean size of the glass powders increased from 0.34 to 0.7 μm when the concentrations of the spray solutions changed from 0.05 to 0.5 M. The glass transition temperature of the glass powders with the mean size of 0.34 and 0.70 μm were 382 and 396 °C, respectively. The glass layers fired at 450 °C had clean surfaces irrespective of the mean size of the glass powders. Silver conducting films were formed by melting of the silver powders irrespective of the mean sizes of the glass powders at firing temperatures between 400 and 500 °C. The specific resistances of the silver conducting films change from 3.13 to 4.03 μΩ cm according to the mean size of the glass powders at a firing temperature of 500 °C.