Agglomeration Of Grains Research Articles

Antimicrobial Activity of CaO Nanoparticles

The high degree of microbial diseases and their multidrug resistant properties make the researchers to develop new class of antimicrobial agents. A modern and innovative approach of drug development is the use of metallic nanoparticles as new formulations of antimicrobial agents. In this study, microwave irradiated CaO nanoparticles (CaO-NPs) were used to determine their antimicrobial efficacy against gram negative and gram positive bacteria, as well as pathogenic yeast. The physiochemical properties of CaO-NPs were characterized by means of X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The nanoparticles consist of well dispersed agglomerates of grains with a narrow size distribution of 14-24 nm. The prepared CaO-NPs showed much higher antimicrobial activity against Pseudomonas aeruginosa (ATCC 27853) and Staphylococcus epidermidis (MTCC 435) in comparision to Candida tropicalis (NCIM 3110). The minimum inhibitory concentration (MIC) value of CaO-NPs was found within the range of 2-8 mM for all the above tested strains. This bioactive nanoparticle also inhibits the biofilm formation and may have future applications cheap and non toxic as antimicrobial drug for skin care product development.

Isoterma dan Termodinamika Adsorpsi Kation Cu2+ Fasa Berair pada Lempung Cengar Terpilar

Pillared Cengar clay have been synthesized by two methods, first clay suspension is directly mixed into aqueous solution of hydroxy-aluminum polycations (WK) and second by mixing the clay suspension into the solution of sodium acetate and hydroxy-aluminumpolycations (SAK) sequentially. Both clays were calcined in air on atmospheric condition. Diffraction pola, surface morphology and cationexchange capacity of the pillared clays were characterized using X Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) andvisible spectrophotometry methods, respectively. The pillared clays showed increases of basal spacing from 3.57 Å to 4.55 Å and smectiteas a new mineral. Morphology of SAK has more heterogeneous surface with small plates and agglomeration of grains compare with WKwhich small plates. Adsorption of aqueous cation of Cu 2+ were studied on various variables of initial concentration as well as temperatures.As the result, adsorption of cation Cu 2+ on pillared Cengar clay is corresponding to Freundlich isotherm, while the adsorption capacity ofWK on cation Cu 2+ is slightly lower than SAK. The thermodynamic aspect, the WK is reflected possessed exothermic processes withnegative entropy, increased in Gibbs energy and non spontaneous, while the SAK possessed endothermic processes having positive entropy,decreased in Gibbs energy and non spontaneous.

Effect of stirring time on size and dielectric properties of SnO2 nanoparticles prepared by co-precipitation method

Chemical co-precipitation method is employed to examine the effect of stirring time on particle size and dielectric properties of SnO2 nanoparticles. XRD patterns followed by Rietveld analysis revealed the as-prepared SnO2 samples to be pure tetragonal (P42/mnm) with rutile structure. The average crystalline size increases from 26nm to 32nm as the stirring time is increased from 5min to 20min and is confirmed from TEM measurements. The appearance of additional Raman peak at about 540, 574 and 696cm−1 is an indicative of the characteristic of crystal symmetry due to the nano-size and agglomeration of grains in nanocrystalline tin oxide. XPS analysis reveals that in SnO2 Sn exist in 4+ oxidation state. The dielectric constant and loss tangent of 5min stirred SnO2 sample is greatest as compared to samples prepared at increased stirring time.

Intense UV photoluminescence emission at room temperature in SnO2 thin films

Tin oxide thin films were prepared by sol–gel dip coating technique using Tin(II) chloride dihydrate (SnCl2·2H2O) as the precursor. X-ray diffraction pattern of SnO2 thin film annealed at 450 °C showed tetragonal phase with a particle size 8.2 nm. Scanning electron microscopy images showed crack free surface with agglomeration of grains. The electrical resistance decreased with increase in annealing temperature. The transmittance spectra gave transmittance greater than 80 % which found applications in anti-reflection coatings. The energy band gap values (3.78–3.87 eV) increased with the increase in annealing temperature, which was due to Moss–Burstein shift. Photoluminescence spectra gave an intense UV emission band at 396 nm. ‘‘Blue shift’’ of the films with annealing temperature originated from the formation of strain in the film due to lattice distortions. Nanocrystalline SnO2 thin film with wide band gap and short wavelength luminescence emission can serve as a better luminescent material for light-emitting devices.

Influence of Sn doping on structural, optical and electrical properties of ZnO thin films prepared by cost effective sol–gel process

Tin (Sn) doped zinc oxide (ZnO) thin films were synthesized by sol–gel spin coating method using zinc acetate di-hydrate and tin chloride di-hydrate as the precursor materials. The films were deposited on glass and silicon substrates and annealed at different temperatures in air ambient. The agglomeration of grains was observed by the addition of Sn in ZnO film with an average grain size of 60nm. The optical properties of the films were studied using UV–VIS–NIR spectrophotometer. The optical band gap energies were estimated at different concentrations of Sn. The MOS capacitors were fabricated using Sn doped ZnO films. The capacitance–voltage (C–V), dissipation vs. voltage (D–V) and current–voltage (I–V) characteristics were studied and the electrical resistivity and dielectric constant were estimated. The porosity and surface area of the films were increased with the doping of Sn which makes these films suitable for opto-electronic applications.

Synthesis, characterization and alcohol sensing property of Zn-doped SnO2 nanoparticles

The Zn-doped SnO2 nanoparticles synthesized by the chemical co-precipitation route and having dopant concentration varying from 0 to 4at%, were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) for structural and morphological studies. XRD analyses reveal that all the samples are polycrystalline SnO2 having tetragonal rutile structure with nanocrystallites in the range 10–25nm. The TEM images show agglomeration of grains (cluster of primary crystallites). A corresponding selected area electron diffraction pattern reveals the different Debye rings of SnO2, as analyzed in XRD. Alcohol sensing properties of all the Zn-doped samples were investigated for various concentrations of methanol, ethanol and propan-2-ol in air at different operating temperatures. Among all the samples examined, the 4at% Zn-doped sample exhibits the best response to different alcohol vapors at the operating temperature of 250°C. For a concentration of 50ppm, the 4at% Zn-doped sample shows the maximum response 85.6% to methanol, 87.5% to ethanol and 94.5% to propan-2-ol respectively at the operating temperature of 250°C. A possible reaction mechanism of alcohol sensing has been proposed.

Structural and spectroscopic modifications of nanocrystalline zinc oxide films induced by swift heavy ions

Structural and spectroscopic modifications of nanocrystalline (nc) ZnO films induced by Swift heavy ion (SHI) irradiation is reported. Films were irradiated at incremented ion fluences. Structural study reveals that the nanocrystals become more oriented at low fluences, while a release of strain and decrease in grain size is observed at high fluence. The surface morphology study also shows a decrease in crystallite size and agglomeration of grains at high fluence. On the other hand micro-Raman and Fourier transform infrared (FTIR) results show that the longitudinal optical (LO) mode is strengthened and red shifted, while the transverse optical (TO) mode get dampened at high fluence. But the amorphization of crystallites was not observed under the used irradiation conditions. The observed structural and spectroscopic modifications are explained in terms of high density of lattice defects and disorder created by dense electronic excitations induced by SHI irradiation.

Surface modified hydroxyapatite thick films for CO 2 gas sensing application: Effect of swift heavy ion irradiation

Swift heavy ion irradiation (SHI) is used to modify the structural and gas sensing properties of Hydroxyapatite (HAp) thick films. The HAp thick films, prepared by screen printing technique, are irradiated with a variable fluence (3×10 10 to 3×10 13 ions/cm 2) of Ag 7+ ions of 100 MeV energy. XRD shows gradual change in crystallinity of the matrix with increase in ion fluence. Atomic force microscopy reveals the agglomeration of grains with pronounced cluster type structure at relatively higher ion fluence. For confirmation of efficient gas sensing of pristine and irradiated HAp thick films, repeatability and reproducibility tests are conducted in a carbon dioxide atmosphere. The parameters responsible for device applications such as, gas uptake capacity, response to test gas and recovery time of HAp film sensor are also investigated. SHI modified HAp films show the maximum enhancement in the gas response and also in increased gas uptake capacity for the fluence 3×10 11 ions/cm 2. Moreover, SHI has resulted in modification of gas response and recovery time for CO 2 gas. The remarkable observation is to note that SHI irradiation improves the sensor characteristics of the HAp films without affecting the working temperature (165 °C) of gas sensor.

Reactive DC magnetron sputter deposited Ti–Cu–N nano-composite thin films at nitrogen ambient

Ti–Cu–N thin films have been grown on Si(111), KBr (potassium bromide), quartz and glass slide substrates using a TiCu (13:87 at. %) single multi-component target by reactive DC magnetron sputtering at nitrogen ambient. This study provides insight into the importance of nitrogen pressure on the characteristic of Ti–Cu–N thin films. Crystalline phases of these films are identified by X-ray diffraction (XRD) technique. The titanium atoms were inserted into the Cu 3N unit cell. The results from XRD show that the observed phases are nano-crystallite cubic anti-Rhenium oxide (anti-ReO 3) structure of Ti doped Cu 3N (Ti:Cu 3N) and nano-crystallite face centre cubic (fcc) structure of Cu. Formation of copper vacancies in Cu 3N cell substituted by titanium atoms and subsequent excess of interstitial nitrogen (N-rich) result in lattice constant expansion and optical energy gap widening. Surface morphology of the films studied by scanning electron microscope (SEM) indicates agglomeration of grains. Ti:Cu atomic ratio of Ti–Cu–N films, determined by energy dispersive X-ray (EDX) spectroscopy, is less than that of the original TiCu single multi-component target and nearly independent of nitrogen pressure. Optical study is performed by Vis-near IR transmittance spectroscopy. Film thickness, refractive index and extinction coefficient are extracted from the measured transmittance using a reverse engineering method. Absorption coefficient indicates that the nitrided films are direct semiconductor. The films electrically show quasi-metallic behavior. The effect of sputtering pressure on deposition rate is investigated. Compared with the Ti free Cu 3N film, the Ti:Cu 3N films possesses fine thermal stability in vacuum.

Generation of Nanosized Particles during Mechanical Alloying and Their Evolution through the Hot Extrusion Process in Bismuth-Telluride-Based Alloys

Our extensive studies of extruded alloys have shown that mechanically strong polycrystalline alloys also deliver surprisingly high thermoelectric performance with ZT > 1 for p-type material in the temperature range from 25°C to 90°C, which was traditionally attributed to the strong texture generated by the extrusion process. Optical and low-resolution scanning electron microscopy observations of the powder produced by mechanical alloying show a particle size distribution in the micrometric range. However, high-resolution transmission electron microscopy (HRTEM) observations of the powders obtained after milling clearly show nanosized crystal grains. The larger microparticles appear to be agglomerations of grains whose size goes down to 5 nm to 20 nm. Examination of bulk n-type and p-type materials using x-ray diffraction (XRD) combined with HRTEM shows that nanosized subgrains can also be found in materials after hot extrusion. In this article we present experimental evidence of the generation and evolution of nanocrystalline particles through the mechanical alloying and hot extrusion processes used to produce the thermoelectric alloys. We also discuss the possible influence of nanocrystalline inclusions on the thermoelectric performance of the produced material. The optimization of the hot extrusion process, in order to maximize the influence of the nanostructures, offers new opportunities to increase the thermoelectric performance of bulk materials.

Fabrication of MnBi/Bi composite using dilute master alloy solidification under high magnetic field gradients

By means of the application of a high gradient magnetic field during the solidification process of a dilute Bi–Mn master alloy, bulk MnBi/Bi composite magnets have been prepared. The observation on the microstructure indicates that MnBi grains aggregate at a specified end of the specimen with the local volume fraction of the MnBi phase above 40% and a high degree of orientation. This method avoids other unfavourable phases occurring in the solidified microstructure. The easy magnetization c axis of MnBi grains parallel to the imposed field is attributed to the rotation of magnetized MnBi grains under the effect of a high magnetic field, and the agglomeration of grains at the specified end results from the magnetization force induced by the field gradient. Simultaneously, the mutual action among magnetized grains makes the grain spacing uniform. Uniform orientation and the high degree of crystal ensure the improvement in the magnetic property of composite materials.

Effect of heating rate on the structure evolution of (K0.5Na0.5)NbO3–LiNbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)(K0.5Na0.5)NbO3–xLiNbO3 (abbreviated an KNLN) have been synthesized by traditional ceramics process. Effects of heating rate on the phase structure, microstructure evolution and piezoelectric properties of (1 − x)(K0.5Na0.5)NbO3–xLiNbO3 were investigated. Results show that the heating rate has no effects on the phase structures. However, the fracture surface of the 0.94(K0.5Na0.5)NbO3 −0.06 LiNbO3 ceramics transforms from intergranular fracture mode to a typical transgranular fracture mode with the increasing of the heating rate. This result is ascribed to the presence of agglomerates of grains which exhibit different sintering behavior at diverse heating rates. The 0.94(K0.5Na0.5)NbO3–0.06LiNbO3 ceramic sintered at 1080°C with heating rate of 5°C/min shows the optimum piezoelectric properties(d33 = 210 pC/N, kp = 0.403 and kt = 0.498).

The mantle, ink sac, ink, arm hooks and soft body debris associated with the shells in Late Triassic coleoid cephalopod Phragmoteuthis from the Austrian Alps

Fragmentarily preserved shells – mainly pro-ostraca, in several cases also phragmocones – occurring together with arm hooks and the ink sac of the Carnian (Late Triassic) coleoid cephalopod Phragmoteuthis bisinuata (Bronn) from Lunz (Austria) are examined with the scanning electron microscope and energy-dispersive spectrometer. The pro-ostracum bears black, shiny, pitch-like sheets. The black sheets, the ink sac content and the arm hooks have a granular ultrastructure of 0.1–1 μm grain size. The arm hooks and black sheets are micro-laminated; each lamina consists of fibres. The ink consists of an agglomerate of grains. On the ventral (internal) side of the pro-ostracum, the black sheets occasionally bear agglomerates of homogeneous, ink-like material along with heterogeneous structures. The pro-ostracum has crystal-shaped units with lamello-columnar ultrastructure of the inner layer and plate ultrastructure of the outer layer. This resembles the Late Triassic Lunzoteuthis [Doguzhaeva, L.A., Mutvei, H., Summesberger, H., 2005a. A Late Triassic coleoid from the Austrian Alps: the pro-ostracum viewpoint. In: Kostak, M., Marek, J. (Eds.), Proceedings of the 2nd International Symposium on Coleoid Cephalopods Through Time. Short Papers/Abstracts Vol. Prague, 26–29 September, 2005, pp. 55–59] and Early Jurassic Belemnotheutis [Doguzhaeva, L.A., Donovan, D.T., Mutvei, H., 2005b. The rostrum, conotheca and pro-ostracum in the Jurassic coleoid Belemnotheutis Pearce from Wiltshire, England. In: Kostak, M., Marek, J. (Eds.), Proceedings of the 2nd International Symposium on Coleoid Cephalopods Through Time. Short Papers/Abstracts Vol. Prague, 26–29 September, 2005, pp. 45–49]. The black sheets, the material on their inner surface, the ink and the arm hooks consist of carbon, occasionally with minor amounts of sulfur. The shell is of calcium carbonate. Based on their organic composition, position in the shell and lamello-fibrillar ultrastructure, the black sheets are considered to be remains of the mantle, sometimes with ink sac and soft body debris. The carbon composition and granular ultrastructure of arm hooks, ink, and soft tissue remains indicate that the non-mineralized structures are pseudomorphosed by carbon (carbonization), possibly due to C-accumulating bacteria.

Structural instability of Sn-doped In 2O 3 thin films during thermal annealing at low temperature

We report on observations of structural stability of Sn-doped In 2O 3 (ITO) thin films during thermal annealing at low temperature. The ITO thin films were deposited by radio-frequency magnetron sputtering at room temperature. Transmission electron microscopy analysis revealed that the as-deposited ITO thin films are nanocrystalline. After thermal annealing in a He atmosphere at 250 °C for 30 min, recrystallization, coalescence, and agglomeration of grains were observed. We further found that nanovoids formed in the annealed ITO thin films. The majority of the nanovoids are distributed along the locations of the original grain boundaries. These nanovoids divide the agglomerated larger grains into small coherent domains.

Room-temperature ferromagnetism in La2∕3Sr1∕3MnO3 nanoparticle assembled nanotubes

We present magnetic and transmission electron microscopy experiments on the double-exchange compound La2∕3Sr1∕3MnO3, nanostructured to form tubes with 700 nm of external diameter. Microscopy reveals that their walls are formed by a compact agglomerate of grains, whose sizes are around 20 nm. The study of magnetic properties of randomly oriented nanotubes shows that the transition from the ferromagnetic to paramagnetic state is at TC=320K, close to the bulk sample value. They exhibit hysteresis in magnetic field loops. The coercive field at 90 K is around 130 Oe, and estimated single-domain size is around 20 nm.

Titanium disilicide formation by rf plasma enhanced chemical vapor deposition and film properties

Titanium disilicide thin films have been deposited on Si(1 0 0) substrate by rf plasma enhanced chemical vapor deposition using TiCl 4 /H 2 gas mixture at different deposition temperatures. At low temperature of 650 °C excessive silicon substrate etching took place and silicide formation could not be confirmed. While at 700 °C Ti 5 Si 3 was the only detected phase as found by X-ray diffraction (XRD) analysis. As the deposition temperature increased from 750 to 900 °C, the polycrystalline C54-TiSi 2 phase deposited. Morphology of the film surface changed noticeably as the deposition temperature increased. At low temperature of 700 °C the film had a flake structure. Increasing the temperature up to 850 °C resulted in a continuous film with smoother grains, while at 900 °C agglomeration of grains took place resulting in coarse grains and discontinuous film. At the optimum experimental conditions it was possible to deposit a homogeneous film with smooth interface and suppressing silicon etching.

Chemical and morphological changes of millerite by mechanical activation

The chemical and morphological changes induced on the surface of millerite by mechanical activation have been studied by means of X-ray diffraction, electron microprobe, scanning electron microscopy and infrared spectra. Leaching tests in water, dilute nitric and hydrochloric acids have been carried out. The mechanical activation of millerite grains due to their disintegration is accompanied by an increase in the number of particles and generation of fresh previously unexposed surface. The agglomeration of grains and a partial oxidation of sulphide to sulphate ions were observed. The increase in leachability of the activated millerite may well be due to the combination of mechanically induced structural defects and chemical modification of millerite surface.

Synthesis and Characterization of Nanocrystalline RuO<SUB>2</SUB>-ZrO<SUB>2</SUB>

The nanocrystalline samples of zirconium oxide doped with ruthenium oxide (RuO 2 ) have been synthesized from chlorides as precursors by chemical precipitation method. The as-prepared and annealed powder samples were studied by XRD, TEM and Impedance Spectroscopy. With 7.5 mol% of RuO 2 , only a small percentage of ZrO 2 stabilizes in tetragonal form without stabilization in cubic form. With 9 mol% and above, ZrO 2 stabilizes in mixed phases having both tetragonal and cubic structure. On annealing, up to 1273 K the proportion of the cubic phase increases; however annealing at temperatures above 1273 K makes the sample to become monoclinic. Average grain size, as determined by Scherrer's formula using X-ray linewidth, increases with increase of annealing temperature. The same trend is observed in TEM studies. TEM studies show the agglomeration of grains. X-ray diffraction for various concentrations of RuO 2 shows the presence of small amount of RuO 2 as impurity. This implies that Ru 4+ goes to the interstitial position also in addition to its occupation of substitutional position of Zr 4+ due to its smaller ionic radius (0.062 nm) compared to that of Zr 4+ (0.084 nm). The impedance spectroscopy measurement shows that the conductivity decreases with an increase of grain size. The phase changes in the stabilization process with different concentrations and annealing temperatures, and growth of grain size in RuO 2 stabilized ZrO 2 will be presented. One of the salient points in this study is stabilization of ZrO 2 with RuO 2 alone without Y 2 O 3 as reported in the literature.

3. Condensation and Agglomeration of Grains

The thermodynamics of condensation from a cooling neutral gas of solar composition, have now been explored in great detail. Theories based on equilibrium condensation have had some striking successes, but there is still much to learn. There seems good reason to explore the condensation process experimentally, so far as it is possible to simulate the conditions usually assumed, to compare the results with what we see in the meteorites, and with the calculations. Preliminary results of this experimental investigation are being reported here.

9. Relationship between the Composition of Solid Solar-System Matter and Distance from the Sun

The chondritic meteorites have “solar” compositions, indicating that they have avoided fractionation in planetary processes such as partial melting or fractional crystallization. Since chondrites contain solar proportions of volatiles having nebular condensation temperatures ≤500 K, it follows that agglomeration of grains and accretion to parent bodies occurred after the nebula had cooled to such low temperatures, and, that models calling for simultaneous condensation and accretion of high-temperature minerals such as Fe-Ni metal or ferromagnesian silicates are implausible.Two independent intergroup fractionations have been recognized in chondritic materials; refractory element abundances (e.g., the Ca/Si ratio) and degree of oxidation measured by the FeO/(FeO + MgO) ratio decrease through the chondrite sequence: carbonaceous-ordinary-IAB-E. Hiatus between groups result from incomplete sampling by the Earth of the original spectrum. A plausible speculation is that this sequence reflects formation at different nebular pressures and temperatures, the fine-grained, oxidized, volatile-rich carbonaceous chondrites forming at lower temperatures >5 AU from the Sun, and the reduced enstatite chrondrites forming at higher temperatures near the Sun. The high fall frequency of the three groups of ordinary chondrites suggests an origin in the asteroid belt. The degree of oxidation of the IAB chondrites appears to be slightly lower than that of the Earth, suggesting an origin near or slightly less than 1 AU from the Sun. The O-isotope compositions of chondrites are consistent with this picture.Asteroids tend to be light or dark, with a hiatus in properties between these two classes. This can be understood if the light materials are ordinary chondrites originally formed at 2.2-3.5 AU, whereas the dark materials originated at >5 AU, and were deposited in the asteroid belt during a later period as a result of a major increase in the influx of cometary materials through the inner sc1ar system associated with the generation of the Oort cloud of comets.