Particle Size Distribution Of Powder Research Articles

Experimental study of the influence of operational and geometric variables on the powders produced by close-coupled gas atomisation

The effect of several operational and geometric variables on the particle size distribution of powders produced by close-coupled gas atomisation is analysed from a total of 66 experiments. Powders of three pure metals (copper, tin and iron) and two alloys (bronze Cu-15 wt% Sn and stainless steel SS 316 L) have been produced. Nitrogen, argon and helium were used as atomising gases. It is shown that the gas-to-metal ratio of volume flow rates (GMRV) is more relevant than the ratio of mass flow rates (GMR) in order to analyse the effect of atomisation variables on the particle size. Kishidaka's equation, originally proposed for water atomisation, is modified to predict the median particle size in gas atomisation. The accuracy of the new equation is compared with that of Lubanska, and Rao and Mehrotra. Kishidaka's modified empirical correlation is the most accurate in predicting the median particle size of the powders produced in this work. The morphology of the produced powders is studied by scanning electron microscopy (SEM) and it is observed that the melt superheat can play an important role in the aggregation of fine particles (< 10 μm), which increases the fraction of large particles (> 100 μm).

Particle velocity measurement in powder gas jets of coaxial powder nozzles for laser material deposition

Laser material deposition (LMD) is a process in which a laser beam creates a melt pool on the surface of a substrate while a powder nozzle delivers a powdered additive into the melt pool, where the powder material then melts. A dense, metallurgically bonded layer forms once the melt solidifies. The velocity of powder particles in LMD is one of the key factors that influence the amount of particles’ energy absorption (along their individual trajectories) through the laser beam on the way between the powder nozzle and the substrate. The amount of energy that is absorbed by the powder particles above the melt pool determines the temperature on the substrate surface and, hence, influences the formation of the melt pool and the deposition of the powder material. Data about the particle velocity are, therefore, essential for modeling the LMD process—not only for physical simulation where a particle’s energy input can be integrated along its trajectory, but also in an experimental environment of process parameter studies, where understanding the interdependencies between the process parameters is crucial. In this study, a setup using a high-speed camera and an illumination laser is used to measure the velocity of powder particles in the powder gas jet of a coaxial powder nozzle. Several parameters that are known to influence the particle velocity are varied: Feed gas rate, shielding gas rate, nozzle geometry (width of annular gap), and powder mass flow rate. In this study, four different powder types are used. The influence of these process parameters on the particle velocity is measured. Four different methods for tracking individual particles and calculating the velocity distribution within the powder gas jet are used and compared: Manual frame-by-frame particle tracking and manual evaluation from multiple exposures in single frames, as well as particle tracking velocimetry and particle image velocimetry (PIV), which incorporate region-of-interest boxes into the algorithm. Sufficient accordance as to the measurement results is found in comparing the four methods. Further, using the highly automatable PIV method, the influence of main process parameters on particle velocity is measured. Out of the examined parameters, the feed gas rate is found to have the most immediate impact with a linear correlation to particle velocity. A correlation between different powder particle size distributions and measured particle velocities is shown as well.

The preparation of spherical metal powders using the high-temperature remelting spheroidization technology

In this paper, a novel technology to prepare spherical metal powder was proposed. Several spherical metal powders were fabricated successfully by using the high-temperature remelting spheroidization (HRS) technology. Among these powders, thorough research on copper powder spheroidization was conducted. The influence of feed rate and temperature on the properties of as-prepared HRS copper powder was investigated. The particle morphology, particle size distribution, oxygen content, bulk density, fluidity and spheroidization rate of copper powder were characterized. The results showed some unique advantages of the HRS technology in the preparation of spherical metal powders. When the temperature was 1623 K, the particles of HRS copper powder were perfect spheres with smooth surfaces and fully dense with no pores inside. The HRS technology can effectively avoid the defects in conventional methods such as satellite particle and hollow particle. The spheroidization rate of HRS copper powder was nearly 100%. The fluidity of HRS copper powder was 11.4 s/50 g, significantly increased compared to the 56.1 s/50 g of the raw powder. Regarding the settling process and heat exchange behavior of metal particles, we developed the HRS process analytical model. HRS technology is a promising method to prepare high-quality metal powder.

Determination of Cocoa Powder Particle Size Distribution by Using the Buoyancy Weighing-Bar Method

This study aims to examine the determination of the particle size distribution of cocoa powder by using the Buoyancy Weighing-Bar Method (BWM) with ethanol as a liquid medium. Laser diffraction and settling balance method are used as a comparison method in this study. The weighing bar used in BWM consists of cylindrical aluminium with a size of 10 cm x 210 cm. The measurement process is operated at ambient temperature and the measurement is carried out for 180 minutes. The results obtained indicate that the particle size distribution of cocoa powder can be measured by using BWM, and the results obtained are proportional to the measurement results by using the settling balance method, while laser diffraction is not suitable for measuring cocoa powder particle size distribution due to the shape of the cocoa powder that is not a sphere.

Визначення властивостей несферичних порошків сплаву ВТ20 для моделювання щільності упакування

The study of unfavorable titanium alloy powders of VT20 grades was carried out and the methods of computer analysis were applied to determine the parameters of their optimal packaging. Metallographic studies were performed on a scanning electron microscope EVO-40XVP, and elemental analysis was performed using an energy dispersion spectrometer OXFORD INCA Energy 350. Determination of particle size distribution of powders was performed using image analysis software ImageJ. The surface morphology of non-spherical particles of VT20 alloy powder was studied for three different fractions: 100 ... 160 μm, 160 ... 200 μm and 200 ... 250 μm. It is shown that the powder particles are characterized by a nonspherical shape and a small difference in size. There is a tendency according to which when the particle size of the powder of the investigated alloy decreases, their shape approaches spherical. According to the results of particle size analysis, it was found that the usual sieve analysis does not allow to fully assess the distribution of powder by fractions. It was found that for the fraction 200 ... 250 μm the dominant particles are with an average diameter of 226 μm, for the fraction 160 ... 200 μm - 177 μm and for the fraction 100 ... 160 μm - 114 μm, respectively. Thus, for the fraction of titanium powder of the BT20 brand 200 ... 250 the polydispersity is 6.4%, for the fraction 160 ... 200 - 8.3%, and for the fraction 100 ... 160 - 9.1%. It is established that the fluidity of titanium alloy powders of the BT20 brand is: for the fraction 200 ... 250 μm - 62.35 s, for the fraction 160 ... 200 μm - 65.44 s, and for the fraction 100 ... 160 - 68, 73 s. That is, the highest value of fluidity is characterized by the powder with the largest particle size. Simulation of the pre-defined volume filling was performed using the "Spheres test" program. The average radii of particles of VT20 titanium alloy powder particles and the probability of the sizes of each of fractions of powder which is necessary at filling of the set volume was calculatedthe possibility of their precipitation have been established. Based on the obtained results, the packing density of VT20 titanium alloy powders was calculated depending on their fractional composition. It is confirmed that as the particle size of the powder decreases, their packing density increases. The surface morphology of non-spherical particles of VT20 alloy powder of different fractional composition and their particle size characteristics were studied. It is shown that with decreasing fractional composition of powder fractions, their homogeneity and bulk density increase. It was found that finer fractions are characterized by poorer fluidity. The simulation results determine the optimal fractional composition of the powder to fill the pre-specified volume. It is shown that as the size of the test particles decreases, their packing density increases. Keywords: additive production, titanium, microstructure, particle size distribution, bulk density, fluidity, packing density modelingmodelling.

Dolomitic filler in self-compacting concrete: a review

The utilization of fine powders as fillers in self-compacting concrete (SCC) application is widespread, particularly in Europe. The incorporation of these fillers to attain the self-compatibility properties of SCC seems to be cheaper than the use of chemical admixtures. Among the wide range of potential fillers, dolomitic powders, particularly generated as by-products from quarry’s processing, are locally available and can be used to produce SCC. Few studies have shown that dolomitic powders can be incorporated in the SCC’s mix design, resulting in acceptable fresh and hardened properties of SCC. The particle size distribution and fineness of the dolomitic powder as well as the level of addition are the key factors affecting those properties. The influence of the chemical nature of the dolomitic powder on the properties of SCC, particularly the durability (e.g. alkali-carbonate reaction), is yet to be investigated. Furthermore, more efforts are still required to investigate the use of dolomitic by-products in the production of SCC.

Sand failure: effect of biocide on the geomechanical properties of outcrop carbonate rock under static condition

The effects of chemical interaction of a biocide with formation rocks on the rock geomechanical properties are examined. A combination of analytical tests (scanning electron microscopy/energy-dispersive X-ray analysis, X-ray powder diffraction and particle size distribution) and uniaxial compression test was used in this study. The particle size distribution in the effluent showed an increase in D50 with poor sorting for the chemically treated outcrop carbonate core samples. The XRPD shows evidence of altered minerals in the chemically treated samples. It was observed that the interaction led to precipitation of new materials that clogged the pore space of the samples leading to up to 150% increase in compressive strength of the carbonate following treatment with the biocide. The results give more insight into the limitations of existing sand production prediction models with respect to the effect of oilfield chemicals on the strength of the reservoir rocks.

Effect of Vacuum Contact Agitated Drying on Particle Size Distribution of Aspirin Powder and Aspirin Agglomerates

Experiments have been carried out to study the effect of agitation on particle size distribution of aspirin powder and aspirin agglomerates during vacuum contact agitated drying. Morphology G3 by Malvern was used to find the size distribution of the materials under investigation before and after the drying process at 0.1, 0.5 and 0.9 µm. It was found that due to agitation, aspirin powder portrayed from negligible to significant agglomeration dependent on the diameter of the material under investigation. While attrition and agglomeration compete together during the drying process of aspirin agglomerates, with attrition dominating at 0.1 and 0.5µm and agglomeration at 0.9 µm.

Experimental and Numerical Study on the Packing Densification of Metal Powder with Gaussian Distribution

In the additive manufacturing of metal materials, powder bed fusion 3D laser printing is the most widely used processing method. The density of the packed bed is another important parameter that can affect the part quality; however, it is the least understood parameter and needs further study. Aiming at addressing the problem of the powder packing density in the powder tank before powder spreading, which is neglected in the existing research, a combination of numerical simulation and experimental research was used to analyze the powder particle size distribution, powder stiffness coefficient, and vibration condition. Considering the van der Waals forces between the powders, a discrete element model suitable for fine metal powders for 3D printing is proposed. At the same time, a mathematical model that takes into account the vibration state is proposed, and the factors affecting the density of the powder were analyzed. A self-designed and manufactured three-dimensional vibration test rig was used to conduct physical experiments on spherical metal powders with approximately Gaussian distributions to obtain the maximum densities. The results obtained by the numerical simulation analysis method proposed in this paper are in good agreement with the experimental results. The influence of the amplitude and vibration frequency on the powder packing density is the same; that is, it increases with an increase in amplitude or frequency, and then decreases with a further increase in amplitude or frequency after reaching the maximum. It is unreasonable to discuss the packing densification only relying on the vibration intensity. Therefore, it is necessary to combine the amplitude and frequency to analyze the factors that affect the packing density of powders.

Highly Conductive Garnet-Type Electrolytes: Access to Li6.5La3Zr1.5Ta0.5O12 Prepared by Molten Salt and Solid-State Methods.

Tantalum-doped garnet (Li6.5La3Zr1.5Ta0.5O12, LLZTO) is a promising candidate to act as a solid electrolyte in all-solid-state batteries owing to both its high Li+ conductivity and its relatively high robustness against the Li metal. Synthesizing LLZTO using conventional solid-state reaction (SSR) requires, however, high calcination temperature (>1000 °C) and long milling steps, thereby increasing the processing time. Here, we report on a facile synthesis route to prepare LLZTO using a molten salt method (MSS) at lower reaction temperatures and shorter durations (900 °C, 5 h). Additionally, a thorough analysis on the properties, i.e., morphology, phase purity, and particle size distribution of the LLZTO powders, is presented. LLZTO pellets, either prepared by the MSS or the SSR method, that were sintered in a Pt crucible showed Li+ ion conductivities of up to 0.6 and 0.5 mS cm-1, respectively. The corresponding activation energy values are 0.37 and 0.38 eV, respectively. The relative densities of the samples reached values of approximately 96%. For comparison, LLZTO pellets sintered in alumina crucibles or with γ-Al2O3 as sintering aid revealed lower ionic conductivities and relative densities with abnormal grain growth. We attribute these observations to the formation of Al-rich phases near the grain boundary regions and to a lower Li content in the final garnet phase. The MSS method seems to be a highly attractive and an alternative synthetic approach to SSR route for the preparation of highly conducting LLZTO-type ceramics.

Impact of spray-drying conditions on physicochemical properties and rehydration ability of skim dromedary and cow's milk powders

The aim of this study was to evaluate the effect of air outlet temperature (75 and 85 °C) and milk type on proximate composition, water activity, particle size distribution, color, and rehydration ability of spray-dried skim dromedary and cow’s milk powders. While the water activity of powders was close to 0.4 when spray-dried at 75 °C air outlet temperature, it ranged from 0.2 to 0.3 for a production at 85 °C air outlet temperature. Skim dromedary milk powder had a lower water activity than skim cow’s milk powder after spray-drying at 85 °C air outlet temperature. Spray-drying yields were greater at the higher air outlet temperature (85 °C) for both skim milk powders. The particle size distributions of spray-dried skim milk powders were centered around 14–20 µm. The particles of skim dromedary milk powders were smaller than those of skim cow’s milk powders as skim dromedary milk was less viscous, leading to smaller sprayed droplets. No significant influence of spray-drying conditions on particle size distribution was observed for dromedary milk powders. Regardless of the spray-drying conditions and the milk type, the produced powders were very bright and had a low color saturation. Scanning electron microscopy images showed that spray-dried powders appeared as agglomerates of small particles with angular shapes rather than individual particles. All investigated spray-dried powders were considered non-wettable, hardly dispersible, and fairly soluble. Skim dromedary milk powder produced at 85 °C air outlet temperature showed a significantly higher solubility index than the same formulation spray-dried at 75 °C outlet air temperature. The opposite was obtained for skim cow’s milk powder. These results demonstrated that the outlet drying air temperature significantly influenced water activity, spray-drying yield and solubility of spray-dried dairy powders.

Multi-blade milling from log to powder in one step – Experimental design and results

This study investigated a new technique for obtaining wood powders from whole logs (Pinus sylvestris L.) in a single-step operation. The performance of a prototype multi-blade shaft mill (MBSM) was evaluated using a designed series of experiments including three input parameters, i.e., the moisture content of the log, milling blade speed and log feeding speed, combined with multilinear regression (MLR) analysis. The milling performance was characterised by specific milling energy, particle size distribution and bulk density of powder. For MBSM powders (80 to 95% particles <1.0 mm), the specific milling energy ranged from 99 to 232 kWh t−1 DM. The mass per cent of particles <0.5 mm in MBSM powders ranged from 55 to 80% compared to 41% from hammer-milled powders. Powder bulk density varied from 138 to 264 kg m−3 DM and the moisture content of the milled log was the only significant (p < 0.05) factor affecting the bulk density of resulting powders (dried). MLR models show that the milling energy is inversely proportional to the moisture content, which indicates that moisture influences MBSM milling in a similar way as in the sawing of wood and opposite to that of impact-based mills (i.e. hammer mills).

Dimensional Analysis of Powders Obtained by Electroerosive Dispersion of High-Chromium Steel in Kerosene

Purpose of reseach was to evaluate the dimensional characteristics of powders obtained by electrodispersion of high-chromium corrosion-resistant steel in lighting kerosene.Methods. When setting up experiments for electroerosive dispersion, wastes of high-chromium corrosion-resistant steel X17 were selected. Dispersing equipment - experimental setup (RF Patent No. 2449859). Lighting kerosene was used as a working fluid. In order to stabilize the process, the dispersion modes were selected experimentally and were as follows: voltage 100 V; pulse repetition rate 120 Hz; capacity 48 μF. The granulometric composition of the powders was studied using a laser particle size analyzer "Analysette 22 NanoTec".Results. It has been found that the average particle size is 28.66 pm and 95% of the total volume of particles in the powder have a size less than or equal to 57.36 pm. ,based on the conducted experimental studies aimed at studying the particle size distribution of electroerosive powders obtained from wastes of high-chromium corrosion-resistant steel X17 in lighting kerosene on an experimental setup (RF Patent No. 2449859) at a pulse repetition rate of 120 Hz, a voltage of 100 V and the capacity of the discharge capacitors is 48 μF.Conclusion. The conducted research will allow us to obtain new powder materials from wastes of high-chromium corrosion-resistant steel X17 in lighting kerosene with a guaranteed particle size distribution, through the use of progressive, environmentally friendly, low-tonnage and waste-free technology of electroerosive dispersion.

Granulometric composition of powders, obtained by electroerosive dispersion of high-chromium steel in kerosene

The results of a study of the particle size distribution of powders, obtained by electroerosive dispersion of high-chromium steel in lighting kerosene, are presented. When conducting experiments for electroerosive dispersion, we selected waste from high-chromium corrosion-resistant steel Cr17. Dispersion equipment - experimental setup (RF Patent No. 2449859). Lighting kerosene was used as a working fluid. In order to stabilize the process, dispersion modes were selected experimentally and were as follows: voltage 100 V; pulse repetition rate of 120 Hz; capacitance 48 uF. The particle size distribution of the powders was studied on a Analysette 22 NanoTec laser particle size analyzer. Studies have established that the average particle size obtained is 28.66 µm. The results of a study of the particle size distribution of powders, obtained by electroerosive dispersion of high-chromium steel in lighting kerosene, are presented. When conducting experiments for electroerosive dispersion, we selected waste from high-chromium corrosion-resistant steel Cr17. Dispersion equipment - experimental setup (RF Patent No. 2449859). Lighting kerosene was used as a working fluid. In order to stabilize the process, dispersion modes were selected experimentally and were as follows: voltage 100 V; pulse repetition rate of 120 Hz; capacitance 48 uF.The particle size distribution of the powders was studied on a Analysette 22 NanoTec laser particle size analyzer. Studies have established that the average particle size obtained is 28.66 µm.

Ultrafast synthesis of the nanostructured Al59Cu25.5Fe12.5B3 quasicrystalline and crystalline phases by high-energy ball milling: Microhardness, electrical resistivity, and solar cell absorptance studies

In this study, the Al59Cu25.5Fe12.5B3 nanoquasicrystalline alloy and related crystalline phases were synthesized through mechanical alloying using a high-energy ball milling and consolidated by a cold isostatic pressing apparatus. This paper focuses on the synthesis, structural and microstructural evolutions, thermal stability, microhardness, and electrical and optical properties of the Al59Cu25.5Fe12.5B3 nanoquasicrystalline alloy for solar selective absorber usages. The structural evolutions of the mechanically alloyed and heat-treated AlCuFeB powders were investigated by X-ray diffractometry. Accordingly, the effect of milling time and heat treatment on the formation of quasicrystalline and related crystalline phases were studied in the AlCuFeB alloy system. The microstructure, morphology, and chemical microanalysis of the un-milled and as-milled powders were examined by field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. The composition of the as-milled AlCuFeB powders was estimated employing inductively coupled plasma-atomic emission spectroscopy. The thermal stability of the AlCuFeB powders was recorded by differential thermal analysis, and the weight gain of the particles during annealing was investigated through thermogravimetric analysis. The nanostructured Al59Cu25.5Fe12.5B3 stable quasicrystalline phase and crystalline Al(Cu,Fe) solid-solution were synthesized by the ultrafast milling procedure in 1 h. The rationale behind using the term ultrafast synthesis is to synthesize the QC i-phase only by the high-energy ball milling procedure in short-term ball milling without subsequent annealing treatment. However, the single quasicrystalline phase could not be obtained even after the annealing treatment. The quasicrystalline size was calculated by the Williamson–Hall method and optimized by the Rietveld refinement procedure, and it was found that the size is varied between 53 and 61 nm. Furthermore, the particle size distribution of the as-milled AlCuFeB powders was measured using laser static light scattering, which ranges from 0.1 to 50 μm. The microhardness of the consolidated as-milled and heat-treated samples was estimated utilizing the Vickers microhardness indenter. At the same time, their electrical resistivity was assessed by the four-point probe method at room temperature. The spectral analyses of absorption on the consolidated as-milled samples were carried out in the ultraviolet, visible, and near-infrared regions. It was found that the presence of the quasicrystalline phase in the AlCuFeB alloy prominently improves the microhardness, electrical resistivity, and particularly sunlight absorptance.

A new strategy for strengthening additively manufactured cold spray deposits through in-process densification

Abstract In this study, a novel strategy for strengthening additively manufactured cold spray deposits is proposed, based on a rather under-explored niche of the processing parameters space. We have shown that a combination of two factors (a wide particle size distribution of the feedstock powder and low processing parameters) triggered a successful implementation of this strategy. At such conditions, a significant proportion of the particles (particularly those with a large size) fail to deposit and rebound after their impact instead, initiating the in-process densification effect: by accepting a small price increase trade-off (the wide range powders are inexpensive), the rebounds result in a severe accumulative plastic deformation of the deposited particles and further reduction in porosity. These, in turn, lead to mechanical properties comparable to those produced under high processing parameters (i.e., using N2 gas at high temperatures or using expensive and unsustainable He as the propulsive gas). As a welcome benefit, the detrimental thermal effects encountered in cold spraying using high-temperature processing gas (such as oxidation, nitridation and phase changes) can be effectively minimized using the new low parameters strategy. Overall, the aim of this study is to propose a new manufacturing strategy to fabricate high-performance cold sprayed deposits without the use of expensive and unsustainable He gas.

Effects of ultrafine grinding time on the functional and flavor properties of soybean protein isolate

Soybean protein isolate (SPI) powders were prepared at different ultrafine grinding time, and the functional and flavor properties of microparticulation SPI were evaluated. With extending ultrafine grinding time, a narrow and uniform particle size distribution in SPI powders was produced. The particle sizes of protein powders at grinding time 0, 2, 4, 6 and 8 h significantly reduced from 217 ± 16.5–137.5 ± 10.7 nm, while the absolute values of zeta-potential significantly increased from 25 ± 0.93–32.4 ± 117 mV (P < 0.05). The microstructure of SPI at grinding time 0–8 h changed from smooth to irregular. With prolonging the ultrafine grinding processing time, the solubility, foaming and emulsifying properties of SPI powders were improved, the content ofα-helix, β-sheet and random coils increased, while β-turn decreased. Furthermore, the ultrafine grinding time clearly influenced the volatile compounds of SPI powders. The main flavor compounds were aldehydes, alcohols, acids, ketones and alkanes. SPI powders for grinding time 2, 4, 6 and 8 h exhibited the higher total content of volatile compounds compared to that for 0 h. So the ultrafine grinding treatment at appropriate time could affect the functional and flavor properties of SPI.

Effect of Potassium Element Content and Crystal Form of Ammonium Tetramolybdate and Reduction Conditions on Properties of Molybdenum Powder

As the raw material for producing molybdenum products, the quality of molybdenum powder such as purity, microstructure, particle size and distribution, has great influence on the microstructure of molybdenum products, which will affect its performance. In this study, the effect of potassium element content and crystal form of ammonium tetramolybdate and reduction conditions on the properties of molybdenum powder was studied. The results show that under the same reduction conditions, the particle size of molybdenum powder obtained by the reduction of high potassium ammonium tetramebolybdate is larger than that obtained by the reduction of low potassium ammonium tetramebolybdate. The particle size distribution of molybdenum powder obtained by the reduction of ammonium tetramebolybdate with mixed crystal form (α-type and β-type) is wider, while that obtained by the reduction of ammonium tetramebolybdate with single crystal form (β-type) is narrower and the particle size is more uniform. The higher the reduction temperature is and the lower the hydrogen flow rate is, the larger the particle size of molybdenum powder will be. The agglomeration degree of molybdenum prepared by β-type ammonium tetramolybdate is lighter than that prepared by ammonium tetramolybdate with mixed crystal form (α-type and β-type), and its sieving rate is higher.

Numerical modeling of secondary breakup in molten metals gas-atomization using dimensionless analysis

Numerical modeling of secondary breakup in gas atomization of molten metals has been successfully performed by others to optimize the powder particle size distribution for various additive manufacturing techniques and metal alloys. The application of breakup analytical models has been tested and validated through experimental campaigns by several researchers. They have demonstrated the suitability of the models in predicting particle size distribution as a function of process parameters.The limit of these models is a lack of information about the particle shape. Assessing the particle morphology could be of great relevance for optimizing the gas atomization parameters of already produced or new alloys.To overcome this limitation, the method described in this paper resorts to the Volume Of Fluid (VOF) modeling approach. This method does not apply to gas atomization breakup because supersonic velocities bring to unaffordable computation times and lack of metal mass conservation. The new approach is conceived to scale down the high velocity flow towards much lower intensities. It makes use of a reference frame moving with the primary droplet and of the similarity theory. At present, the model has been validated through the comparison with DPM results. It demonstrated to be a reliable alternative model allowing to gain deeper insights. Heat transfer among gas and droplets is not simulated yet, thus the droplet deformation does not stop at the solidification time. Further developments are forecast to allow to freeze the particle shape at the time it is completely solidified.

Gum arabic/maltodextrin microencapsulation confers peroxidation stability and antimicrobial ability to pepper seed oil

In this study, pepper seed oil (PSO) was microencapsulated by spray drying at optimum conditions: oil/total solid material at 20% (w/w), gum Arabic/maltodextrin (GA/MD) at 1/5 (w/w), and air inlet temperature of 184 °C. Particle size distribution and morphology of the PSO powder (PSOP) were determined by a laser particle diameter analyzer and scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) were employed to identify the specific chemical groups of PSO, MD, and GA in the PSO-GA/MD complexes. The thermal stability of PSOP was evaluated by thermogravimetric (TGA) and differential thermal analysis (DTA). PSOP displayed inhibitory activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis although PSO had an antimicrobial activity against only Staphylococcus aureus. GA/MD microencapsulation resulted in significant preservation of PSO against oxidation during storage period.