Formation Of Fine Particles Research Articles

Numerical modeling of fine particle and deposit formation in a recovery boiler

In kraft pulp mills, black liquor is concentrated and burned in recovery boilers to produce steam and power and to recover pulping chemicals. Black liquor contains a large amount of alkali compounds, which form ash with low melting temperatures upon combustion. This causes many problems in recovery boiler operation, including fouling of the heat transfer surfaces, plugging of the flue gas passages, reduction of the heat transfer rate, and corrosion of the superheater tubes. This paper presents a model for simulating fine fume particles formed as a result of condensation of alkali compound vapors in the recovery boiler. The modeling method combines CFD modeling, equilibrium chemistry, and fine particle dynamics in a way that enables simulation of a full scale three-dimensional boiler environment. The model has been partially validated with measurements performed in an operating recovery boiler. The modeling results, particularly for the fume particle composition, agree well with the actual measurements.

Solubility of progesterone in supercritical carbon dioxide and its micronization through RESS

To investigate the formation of progesterone fine particles with rapid expansion of supercritical solution (RESS), it is vital to determine the solubility of progesterone under various equilibrium pressure and temperature conditions and to correlate the solubility data with a well-performed model. In this study, the solubility of progesterone in supercritical CO2 was measured using a dynamic apparatus at pressure ranging from 120 to 260bar, and temperature from 313.15 to 338.15K. The determined solubility in mole fraction is in the range of 5.3×10−5–8.9×10−4 and correlated with three empirical density-based models and the Peng–Robinson equation of state model. The latter model has better correlation effects than the other density-based models and provides an overall average absolute relative deviation of 11.6% between the calculated and experimental solubility. Then, the performances of RESS under different conditions are evaluated by analyzing the particle characteristics, and the effects of extraction temperature, extraction pressure, and nozzle diameter on the particle size and particle size distribution of the formed particles are discussed. The original progesterone has a particle size of about 150μm while the average particle size of the micronized particles ranges from 0.11 to 3.22μm based on different experimental conditions. The particles were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared analysis (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and in vitro dissolution measurements.

Preparation, Characterization and Effectivity of N, Fe-TiO<sub>2</sub> as a Visible Light Active Photocatalyst

Surface modification of the titanium dioxide by doping and co-doping with nitrogen and iron in order to make the photocatalyst active under visible light was investigated. Solgel method was adapted for the preparation of surface modified titanium dioxide, where tetra titanium isopropoxide, ammonium nitrate and ferric nitrate were used as precursors while maintaining the dopant concentration and calcination temperature at 0.75% and 600°C, respectively. The prepared photocatalyst samples were characterized by XRD, FE-SEM and FTIR in order to study their physical properties. The results from XRD confirmed that all prepared photocatalyst were of anatase phase. FE-SEM image analysis revealed the formation of fine particles and the FTIR analysis verified the presence of dopants. The effectivity of photocatalysts was tested by performing a standard batch photocatalytic degradation experiment with methylene blue as a model pollutant under visible light. The result showed that co-doped photocatalyst (0.75% N, 075% Fe-TiO2-600) yielded a maximum of 76% methylene blue degraded within three hours of irradiation time.

Synthesis, characterization of nickel aluminate nanoparticles by microwave combustion method and their catalytic properties

Abstract Microwave combustion method (MCM) is a direct method to synthesize NiAl 2 O 4 nanoparticles and for the first time we report the using of Sesame ( Sesame indicum L.) plant extract in the present study. Solutions of metal nitrates and plant extract as a gelling agent are subsequently combusted using microwave. The structure and morphology of NiAl 2 O 4 nanoparticles are investigated by X-ray diffraction (XRD), Fourier transforms infrared spectra (FT-IR), high resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray analysis (EDX), high resolution transmission electron microscopy (HR-TEM), diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectroscopy, Brunauer–Emmett–Teller (BET) analysis and vibrating sample magnetometer (VSM). XRD pattern confirmed the formation of cubic phase NiAl 2 O 4 . The formation of NiAl 2 O 4 is also confirmed by FT-IR. The formation of NiAl 2 O 4 nanoparticles is confirmed by HR-SEM and HR-TEM. Furthermore, the microwave combustion leads to the formation of fine particles with uniform morphology. The magnetic properties of the synthesized NiAl 2 O 4 nano and microstructures were investigated by vibrating sample magnetometer (VSM) and their hysteresis loops were obtained at room temperature. Further, NiAl 2 O 4 prepared by MCM using Sesame ( S. indicum L.) plant extract is tested for the catalytic activity toward the oxidation of benzyl alcohol.

Coercivity of Nd-Fe-B-Type Fine Particles Prepared by Mechanical Milling of HDDR Material

For bonded micro-magnet application, fine particles with high permanent magnetic performance are required. As the HDDR-treated Nd-Fe-B-type material consists of very fine grains (~0.3 μm), the fine particles prepared from the HDDR-treated material are expected to have high magnetic performance even in the form of fine particles. Fine Nd-Fe-B-type particles were prepared by mechanical milling of the HDDR-treated Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12.5</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80.6</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6.4</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> material, and coercivity of the fine particle was investigated. Coercivity of the HDDR-treated Nd-Fe-B-type material was radically reduced by mechanical milling. Surface oxidation was the major contributory factor for the radical coercivity reduction. Chemical etching of the oxidized surface led to significant recovery of the coercivity. Unlike the mechanically milled fine particles of sintered Nd-Fe-B-type magnet, which lose coercivity almost completely, the moderately milled and etched fine particles (20-80 μm) of HDDR-treated Nd-Fe-B-type material exhibited high coercivity over 12 kOe.

Synthesis and characterization of two cyanoxime ligands, their precursors, and light insensitive antimicrobial silver(I) cyanoximates

High-yield syntheses of N-piperidine-cyanacetamide (1), N-morpholyl-cyanacetamide (4) and their oxime derivatives N-piperidine-2-cyano-2-oximino-acetamide (HPiPCO, 2) and N-morpholyc-2-cyano-2-oximino-acetamide (HMCO, 5) were developed using two-step preparations. At first, the reactions of neat cyanoacetic acid esters and the respective cyclic secondary amines such as piperideine and morpholine afforded pure cyan-acetamides, which were converted into cyanoximes at room temperature using the nitrosation reaction with gaseous CH3ONO. The synthesized compounds were investigated by means of IR, 1H, 13C and UV–Vis spectroscopy. Crystal structures of two starting substituted cyan-acetamides and two target cyanoximes were determined. Silver(I) complexes of AgL composition (L=PipCO, 3; MCO, 6) were prepared in high yield. Both metal complexes are thermally stable above 100°C, and remarkably stable to high intensity visible light. The stability of dried AgL compounds towards short wavelength UV-radiation (a frequently used germicidal light) was examined using diffusion reflectance spectroscopy. Both complexes demonstrate slow photoreduction within ∼3h, observable as a gradual color change and darkening due to the formation of fine (nano-scale) particles of metallic silver. The complex Ag(MCO), 6, is about 2.6 times less stable towards UV-radiation than its more lypophyllic analog Ag(PipCO), 3. Antimicrobial and biofilm growth inhibition properties of the prepared solid acrylate-based polymeric composites containing embedded silver(I) cyanoximates were investigated using three human pathogens: Pseudomonas aeruginosa PAO1 (wound isolate), Staphylococcus aureus NRS70 (methicillin resistant respiratory isolate), and Streptococcus mutans UA159 (cariogenic dental isolate). Studies showed that both 3 and 6 compounds completely abolished the growth of PAO1 at 0.5 weight% concentration, and the growth of UA159 and NRS70 at 1% concentration. Thus, the data demonstrate that complexes 3 and 6 inhibit both planktonic and biofilm growth of Gram-positive and Gram-negative bacterial pathogens. The demonstrated thermal stability and pronounced antimicrobial activity of both silver(I) cyanoximates indicates the strong potential for the studied complexes to be used as light insensitive antimicrobial additives to light-curable adhesives that set indwelling devices in place.

Effect of co-modification by Ba and Sb on the microstructure of Mg2Si/Mg–Zn–Si composite and mechanism

Mg2Si/Mg–Zn–Si composite was in situ synthesized and modified by the addition of Ba and Sb; the microstructure and tensile properties of the resulting composites were investigated. Results show that the co-modification with Ba and Sb effectively refined the morphology of Mg2Si as follows: The primary Mg2Si particles were modified to fine polygonal particles <15μm; when the Ba content was 1.0wt.%, the average size of primary Mg2Si particles decreased with increasing Sb mass fraction. The ultimate tensile strength and elongation values of the composites increased with increasing Sb content. This was attributed to the formation of fine Ba2Sb particles that acted as the heterogeneous nucleation sites for the primary Mg2Si particles, resulting in a refined distribution of these precipitates. The dispersion of the refined Mg2Si particles strengthened the composite and improved the ductility.

Supercritical fluid assisted production of chitosan oligomers micrometric powders

Chitosan oligomers (O-chitosan) micrometric particles were produced from aqueous solution using a novel process, i.e. supercritical fluid assisted atomization introduced by hydrodynamic cavitation mixer (SAA-HCM). Hydrodynamic cavitation was introduced to enhance mass transfer and facilitate the mixing between SC-CO2 and liquid solution for fine particles formation. Well defined, separated and spherical microparticles were obtained, and the particles size could be well controlled with narrow distribution ranging from 0.5μm to 3μm. XRD patterns showed amorphous structure of O-chitosan microparticles. FTIR, TGA and DSC analyses confirmed that no change in molecular structure and thermal stability after SAA-HCM processing, while the water content was between 5.8% and 8.4%. Finally, tap densities were determined to be below 0.45g/cm3 indicating hollow or porous structures of microparticles. By tuning process parameters, theoretical mass median aerodynamic sizes lied inside respirable range of 1–2μm, which presented the potential of the O-chitosan microparticles in application as inhaled dry powders. SAA-HCM was demonstrated to be very useful in particle size engineering.

Seasonal variations in the chemical composition of particulate matter: a case study in the Po Valley. Part II: concentration and solubility of micro- and trace-elements

Size distribution (fine and coarse fraction) and solubility distribution (extracted and residual fraction) of 20 elements (As, Ba, Be, Cd, Co, Cu, Fe, Li, Mn, Pb, Ni, Rb, S, Sb, Se, Sn, Sr, Ti, Tl, V) in atmospheric particulate matter (PM) were determined during a 5-year field study carried out in the Po Valley (peri-urban area of Ferrara, in Northern Italy). By studying the contribution of the two size fractions and the two solubility fractions to the atmospheric concentration of each element, it was possible to obtain interesting information about the variability of PM sources, to assess the role played by atmospheric stability in determining pollution episodes, and to obtain an estimate of the bio-accessible fraction. Atmospheric stability is confirmed to be one of the main causes of atmospheric pollution in this area and is to be responsible for the pronounced winter increase in both PM and elemental concentration. Long-range transport of natural and polluted air masses caused temporary increases in PM and elemental concentration, while local industrial emission seemed to play a secondary role. Regulated elements were well below their concentration limit, but many toxic elements were in the form of fine particles and soluble chemical species, more accessible to the environment, and the human body.

Surfactant Assisted Ball Milling: A Simple Top down Approach for the Synthesis of Controlled Structure Nanoparticle

The unlimited applications of nanoparticles in human life are increasing day by day. Nanoparticles have drawn attention among researchers from academia to industry due to its large specific surface area, high chemical reactivity, physical affinity and interesting optical, electrical and magnetic properties. These properties of nanoparticles stimulate researchers to reduce particle sizes from few sub micrometers to nanometer levels. The successful application of nanoparticles depends on the simplicity of the methods for its cost effective synthesis. Since the very beginning of nanoscience, development of simple, low cost and high yielding methods has been a challenging task. Various approaches were proposed for the commercial production of nanomaterials from solid state. However, chemical method which is complicated and expensive showed limited success in the synthesis of controlled structure nanoparticles from rare-earth solid compounds. Among all the approaches, high energy ball milling with surfactant has been widely exploited for the synthesis of various nanomaterials, nanograins, nanocomposites from solid state. Self-assembled structures of surfactants provide a valuable tool for the controlled formation of nanostructure. In this process, the dispersion and enhanced grinding of particles are achieved in the reaction centers that reside in the microstructure of surfactants. In high-energy ball milling, plastic deformation, cold-welding and fracture are predominant factors which lead to a change in particle shape, size. These result in the formation of fine and dispersed particles. Stirred ball mill grinding is advantageous for nanoparticle production over other fine grinding techniques owing to its easy operation, simple construction, high size reduction rate and relatively low energy consumption. The aim of this systematic review is to represent the basic concept and applications of mechanical milling in the surfactant assisted synthesis of various nanomaterial, nanocomposite and nanocarbon materials.

Sequestration of Carbon Dioxide with Simultaneous Formation of Fine Calcium Carbonate Particles in Liposomes

Abstract1‐Palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine (POPC) liposomes containing CaCl2 were prepared in Tris solution. The optimal initial pH and temperature were determined based on the kinetics of bulk crystallization of CaCO3 and to depress the leakage of Ca2+ from liposomes. The CaCO3 particles were formed by mixing the liposome suspension and CO2‐saturated water, as analyzed with the scanning transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. The liposomal reaction system can be utilized for the formation of fine CaCO3 particles through sequestration of CO2.

A comparison study on airborne particles during haze days and non-haze days in Beijing

Airborne particles in Beijing during haze days and non-haze days were collected by an eleven-stage cascade impactor (MOUDI 110, MSP, USA), and the mass concentrations and water soluble inorganic ions of the size segregated airborne particles were quantitatively analyzed. PM10 concentrations during haze days ranged from 250.5 to 519.4μgm−3 which were about 3–8 times greater than those (ranged from 67.6 to 94.0μgm−3) during non-haze days, and PM1.8 concentrations during haze periods were in the range of 117.6–378.6μgm−3 which were 3–14 times higher than those (27.0 to 36.8μgm−3) during non-haze days. In comparison with non-haze days, all water soluble inorganic ions investigated in the airborne particles greatly enhanced during haze days. NH4+, NO3− and SO42− were found to be the dominant water soluble inorganic ions, accounting for 91–95% of the total inorganic ions in PM1.8 during haze days, and 73–81% during non-haze days. The size distributions of SO42−, NO3−, Cl−, K+ and Na+ exhibited bimodal types, while single mode was found for NH4+, Ca2+ and Mg2+. Only with exception of Ca2+ and Mg2+, all ions were concentrated in fine particles around 0.56–1.0μm of “droplet mode” during haze days, while 0.32–0.56μm of “condensation mode” during non-haze days. The extremely high mole ratio (>2) of [NH4+]/[SO42−] during haze days implied that the main form of ammonium in PM1.8 might be (NH4)2SO4 and NH4NO3. The mass ratio of NO3−/SO42− was >1 in PM1.8 during haze days and ~1 during non-haze days, indicating that NOx from the vehicle exhaust in Beijing is playing more and more important role on fine particle formation.

Experimental verification of segregation of carbon and precipitation of carbides due to deep cryogenic treatment for tool steel by internal friction method

This work presents an internal frictional behavior of cold work tool steel subjected to different heat treatment schedules to get insight related to segregation of carbon and refinement of carbide particles due to deep cryogenic treatment. The temperature dependence of internal friction was used to describe the variation of carbon concentration in solid solution of the martensite matrix in successive tempering steps. The results indicate that the carbon atoms segregated to nearby defects forming atomic clusters producing strong interactions, including interstitial carbon atoms themselves and between the interstitial carbon atoms with time-dependent strain field of dislocations because of lattice shrinking and thermodynamic instability of martensite during the deep cryogenic treatment. The clusters act as and grow into nuclei for the formation of fine carbide particle on subsequent tempering that was verified by analyses of TEM micrographs.

Catalytic Combustion‐Type Hydrogen Sensor Using BaTiO3‐based PTC Thermistor

A catalytic combustion‐type gas sensor using a positive temperature coefficient (PTC) thermistor, which shows a sharp resistance change around Curie temperature, was developed for the detection of hydrogen. La‐doped BaTiO3 (Ba0.998 La0.002 TiO3) was prepared through a solid‐state method and an oxalic acid method. La‐doped BaTiO3 obtained by the oxalic acid method showed improved PTC properties, due to the formation of fine particles, as compared to that prepared with the solid‐state method. The resulting sensor device showed a fairly high H2 sensitivity in the range of 100–1000 ppm. In addition, the H2 sensitivity and response speed were improved by coating a Pt/SiO2 catalyst on the sensor device because the catalytic combustion efficiency of H2 was improved by the catalyst coating.

Deferred action of illumination on the relaxation of a granular silver film when it is thermally annealed

It has been detected that UV radiation in the 300–400 nm wavelength interval affects the rate and final result of subsequent thermal annealing of a thin silver film on a sapphire substrate. Whereas the annealing of unirradiated films rapidly causes them to decay and causes the formation of individual fine particles of round shape, larger particles of irregular shape are formed when irradiated films are annealed, while the changes themselves occur significantly more slowly.

Effects of the growth and the charge of carbon nanoparticles on direct current discharges

The formation of fine particles in plasmas from sputtered carbon atoms and the consequences of their growth and charging mechanisms on sputtering DC discharges were investigated. Experiments were performed with a constant discharge current so that the coupling between the plasma and two successive generations of nanoparticles were studied through the evolution of the discharge voltage, proportional to the ionization rate and also through the plasma emission. The consequences of the formation of negative ionic molecular precursors of the first particle generation were established as well as the effects of a redistribution of the nanoparticle cloud in the inter-electrode gap, not similar to the void effects usually observed in RF discharges. The cathode heating during the sputtering mechanism was also considered to explain partly the evolution of the discharge voltage and the plasma emission during the growth of the second nanoparticle generation.

Size Distributions of Atmospheric Aerosol Compositions in Saitama, Japan

A survey of atmospheric aerosols in a suburban area near Tokyo, Japanwas conducted using an Andersen sampler. Significant amounts of Na+and Cl- collected were considered to be derived from sea salt. The difference between the Na+/Cl-ratio in the area and that in sea salt indicated a considerable loss of Cl-. This is assumed to be caused by the formation of NaNO3, which is one of the main nitrate species present. Most of the sulfate in the sample was found to be (NH4)2SO4 in the form of fine particles, which is different from the sulfate derived from sea salt and soil. The size distributions of K and Mg are also discussed in relation to particular sources.

Dry sliding wear behaviour of in situ Al–TiB2 composites

Aluminium matrix/titanium diboride reinforced (Al/TiB2) composites were fabricated by in situ process. The wear behaviour was studied by using a pin-on-disc wear tester at room temperature. The coefficient of friction and wear rate were calculated experimentally for the Metal Matrix Composites (MMC) prepared from the Al/TiB2 system. The wear properties of MMC has improved significantly as a result of formation of fine TiB2 particles which are more uniformly dispersed in the aluminium matrix. Furthermore, strong particle/matrix bonding in Al/TiB2 composites enables the in situ particles to be retained in the wear surface during sliding, thereby effectively resisting the shear deformation. The worn surface were analysed using Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS). This paper presents the relationship between various dominant mechanisms of wear that are observed to occur under different conditions as well as the anticipated rates of wear.

Effect of carbon particle and carbon fiber on the microstructure and mechanical properties of short fiber reinforced reaction bonded silicon carbide composite

Variation of microstructure and mechanical behavior was investigated with the content increase of carbon particles and carbon fiber in the reaction bonded silicon carbide composites. The composites were prepared by slip casting and liquid silicon infiltration. The bulk density is raised with the increase of carbon black due to the formation of fine β-SiC particles. The flexural strength increases for the reduction of residual Si and the formation of SiC framework; whereas a very high carbon content reduces the flexural strength. The fracture toughness is controlled by the contents of carbon particle and carbon fiber. Thus, fiber debonding, fiber pullout and crack deflection are considered as the main toughening mechanisms. Annealing treatment can effectively improve both the flexural strength and fracture toughness. An increase by 49% of fracture toughness is obtained. A series of structural models are proposed to illustrate the structure changes of carbon fiber.

Machinability of AISI 316 Austenitic Stainless Steel With Cryogenically Treated M35 High-Speed Steel Twist Drills

In this paper, machinability of AISI 316 austenitic stainless steel was investigated using cryogenically treated and untreated high-speed steel (HSS) twist drills. Machinability of AISI 316 austenitic stainless steel was evaluated in terms of thrust force, tool life, surface roughness, and hole quality of the drilled holes. Experimental results showed from 14% to 218% improvements for treated tool lives. Thrust force, surface roughness, and hole quality are better with treated drills when compared with untreated drills. These improvements were mainly attributed to formation of fine and homogeneous carbide particles and transformation of retained austenite to martensite. Microhardness and microstructure observations verified these formations.