Agglomeration Temperature Research Articles

A comparative study of C, N and Xe pre-amorphization implantation processes for improving the thermal stability of NiSi films

In this paper, a comparative study of C-, N- and Xe-based pre-amorphization implantation (PAI) processes is proposed. The impact of the use of such processes on the agglomeration resistance and physical properties of the final Ni(Pt)Si layer, as well as the formation mechanisms via solid-state reactions and electrical performances via the transfer length measurement (TLM) method, is evaluated. It is shown that although all species are able to increase the agglomeration temperature of Ni(Pt)Si layers (up to more than 100 °C), the underlying mechanisms are different. For C- and N-based PAI processes a strong chemical effect is observed, while for Xe-based processes the amorphization depth plays an important role. Consequently, the beneficial effect of stabilizing Ni(Pt)Si layers at high temperatures using C- and N-based PAI processes has to be balanced with an increased layer resistivity (up to 30%) combined with a strong deterioration of the associated specific contact resistivity (which is multiplied by almost a factor 10). In this sense, Xe-based PAI processes seem to be a better option as they could allow to combine both requirements.

Agglomeration behavior and mechanism of polybutadiene latex by nanocomposite emulsion particles

Polymer agglomeration method is an efficient way to enlarge the particle size of polybutadiene latex (PBL). However, thus far, the particle size of polymer agglomerating agent and agglomerated PBL could not been accurately regulated, and there is a lack of investigation of agglomeration mechanism. Herein, an efficient way for regulating the particle size of the agglomerating agent and PBL was proposed. It was found that the particle size of agglomerating agents can be obtained in the range of 69 nm to 143 nm by adjusting the monomer content and the amount of α-methacrylic acid in the emulsion polymerization process. Then, the effects of different agglomeration parameters on the particle size of agglomerated PBL were investigated, including the amount, the α-MAA content and the particle size of agglomerating agent, agglomeration temperature and agglomeration time. The results indicated that the particle size of agglomerated PBL first increased and then decreased to a stable state with the increase of the amount of agglomerating agent. This phenomenon was quite different from the results of existing studies, which show that the particle size of agglomerated PBL gradually increases with the increase of the amount of agglomerating agent. According to the investigation of agglomeration process of PBL, the PBL agglomeration mechanism of dispersion-adsorption-coalescence-shrinkage was proposed. This study not only provides theoretical support for the PBL polymer agglomeration process, but also provides a practical way to increase acrylonitrile–butadiene–styrene (ABS) production efficiency.

The Colloidal Stability of Apolar Nanoparticles in Solvent Mixtures

Solvent engineering is a powerful and versatile method to tune colloidal stability. Here, we link the molecular structure of apolar ligand shells on gold nanoparticles with their colloidal stability in solvent mixtures. The agglomeration temperature of the particles was measured with small-angle X-ray scattering. It depended on solvent composition and changed linearly for hexane-hexadecane mixtures, but nonlinearly for cyclohexane-hexadecane and hexanol-hexadecane mixtures. Molecular dynamics (MD) simulations indicate that agglomeration is dominated by temperature-dependent ligand order in the alkane mixtures and that the temperature at which the ligand shell orders depends on the solvent composition near the ligands, which can differ substantially from the bulk composition. Small-angle neutron scattering confirmed that, at intermediate solvent compositions above the agglomeration temperature, the fraction of cyclohexane near the ligands was larger than in the bulk. The enrichment of cyclohexane near the ligands stabilized their disordered state, which, consequently, led to the experimentally observed nonlinear trend of the agglomeration temperature. In contrast, hexanol was depleted from the ligand shell at all temperatures. This again stabilized the disordered state. Furthermore, we found that agglomeration at high hexanol fractions was driven by a solvophobic effect that exceeded the influence of ligand order. The results show that strong nonlinearities in the colloidal stability of nanoparticle dispersions in solvent mixtures are directly linked to the molecular details of ligand-solvent and solvent-solvent interactions, which can be used to precisely tune stability.

GaN Nanowire Growth Promoted by In-Ga-Au Alloy Catalyst with Emphasis on Agglomeration Temperature and In Composition.

The crystallographic orientation control of GaN nanowires (NWs) has been widely investigated by varying the V–III ratio. Here, we report the tuning of crystallographic orientation of GaN NWs by varying the composition of indium (In) in gallium–gold (Ga–Au) alloy catalyst using metal–organic chemical vapor deposition (MOCVD). The c-plane GaN thin film and sapphire substrate are used as growth templates. We found that the substrates of same orientation have a negligible influence on the orientation of the GaN NWs. The catalyst composition and the dimensions of alloy droplets determine the morphology of the NWs. The density of the NWs was controlled by tuning the droplet size of the alloy catalysts. With the constant V/III ratio, the crystallographic orientation of the GaN NWs was tuned from m- to c-axis by increasing the In composition inside alloy catalyst.

Experimental and model investigation on agglomeration of aluminized fuel-rich propellant in solid fuel ramjet

In order to gain insight into aluminum agglomeration behaviors and agglomeration processes, the aluminized fuel-rich propellants in solid fuel ramjet are investigated by using sampling method followed by scanning electron microscopy and laser scattering experimental technique on the small-scale combustion experimental system and connected-pipe experimental system. It is observed that the aluminum particles would break away from the burning surface after agglomeration, and interpocket agglomeration occurred. Under different ambient pressures, the microstructure of the combustion products and the aggregation behavior of aluminum particles are further analyzed. Based on the classical pocket theory and particle size analysis experiments, a new agglomeration size prediction model is established. It can be used to predict the agglomeration size on the burning surface. Compared with the empirical model and the typical pocket model, this model is in good agreement with the experimental results. A connected-pipe experimental system for solid fuel ramjet is established. The effects of inlet air temperatures on the combustion performance of ramjet, the microstructure and agglomeration size are studied. With the increase of inlet air temperature, the agglomeration size decreases, the pressure, temperature and thrust in the combustion chamber increase, which makes the propellant burn more fully. The characteristic velocity, specific impulse and combustion efficiency of the solid fuel ramjet increase.

Colloidal Stability of Apolar Nanoparticles: The Role of Particle Size and Ligand Shell Structure.

Being able to predict and tune the colloidal stability of nanoparticles is essential for a wide range of applications, yet our ability to do so is currently poor due to a lack of understanding of how they interact with one another. Here, we show that the agglomeration of apolar particles is dominated by either the core or the ligand shell depending on the particle size and materials. We do this by using small-angle X-ray scattering and molecular dynamics simulations to characterize the interaction between hexadecanethiol passivated gold nanoparticles in decane solvent. For smaller particles, the agglomeration temperature and interparticle spacing are determined by ordering of the ligand shell into bundles of aligned ligands that attract one another and interlock. In contrast, the agglomeration of larger particles is driven by van der Waals attraction between the gold cores, which eventually becomes strong enough to compress the ligand shell. Our results provide a microscopic description of the forces that determine the colloidal stability of apolar nanoparticles and explain why classical colloid theory fails.

Agglomeration and Properties of Ceramics Based on Partially Stabilized Zirconium Dioxide Containing Oxides of Aluminum and Iron

Agglomeration of ceramics of partially stabilized zirconium dioxide containing 5 wt % of aluminum oxide depending on the amount of additive (iron oxide) was studied. It was shown that introduction of an additive promotes a decrease in agglomeration temperature to 1400–1450°С and formation of a dense structure, as well as acquisition of high strength up to 450 MPa (after agglomeration at 1400°С).

Effect of Charge Fractional Composition and the Coke Amount on the Parameters of Manganese Ore Agglomeration

Under laboratory conditions, the method of mathematical planning of experiments was used to study the effect of charge fractional composition (in the range of 2 to 8 mm) and the amount of coke in the charge (in the range of 7 to 13 wt.%) on the agglomeration process characteristics of the “Mamatwan” manganese ore (South Africa). It was found that the main agglomeration parameters vary within the following limits: the initial vacuum under grate – 54...140 mm WC for the charge layer of 350 mm; the maximum temperature – 1365...1440 °С; linear burning speed – 13,4...26,2 mm/min; the charge length of stay at temperatures over 1300 °С (the width of the melting zone) – 2,4...4,8 minutes. Mathematical equations of the combined effect of charge fractional composition and the amount of coke on agglomeration temperature, linear burning speed, width of melting zone (in time), initial vacuum in reactor were calculated. It was found that a major factor in providing the optimum mode of agglomeration is not the amount of coke, but the charge piece size distribution. For example, increasing the charge piece size has an 3,5 times more effective influence on the agglomeration temperature than the amount of coke. For the dust-containing charges the moistening up to 4...6 wt.% H2O is only partially solves the problem of the aerodynamic resistance. Pre-granulation of the dust fraction is needed to improve the gas permeability of the charge.

The thermal evolution of Cu nanoparticles condensed from the gas phase: MD simulations

The gas-phase condensation of 85000 Cu atoms is examined by molecular dynamics simulation with a tight-binding potential. A detailed study of the evolution of the system cooled at a constant rate from 1000 K to 77 K is presented. The results are used to identify four distinct stages of the evolution from a hot atomic gas to a few synthesized particles. The effect of the subsequent thermal treatment on the shape and structure of synthesized particles was studied by simulating their gradual heating in a range of 100-1200 K. It is concluded that short-term heating leads to significant ordering of the internal structure in 70% of agglomerated nanoparticles with the predominant formation of spherical shapes. In order to explain this result, the main mechanisms of cluster formation from the gas phase have been analyzed and it is found that the agglomeration temperature plays the main role in the formation of clusters with unified shape and structure.

Changing of the shape and structure of Cu nanoclusters generated from a gas phase: MD simulations

The gas-phase condensation of 85,000 Cu atoms is examined by molecular dynamics simulation with a tight-binding potential. A detailed study of the evolution of the system cooled at a constant rate from 1000K to 77K is presented. The results are used to identify four distinct stages of the evolution from a hot atomic gas to a few synthesized particles. The effect of the subsequent thermal treatment on the shape and structure of synthesized particles was studied by simulating their gradual heating in a range of 100–1200K. It is concluded that short-term heating leads to significant ordering of the internal structure in 70% of agglomerated nanoparticles with the predominant formation of spherical shapes. In order to explain this result, the main mechanisms of cluster formation from the gas phase have been analyzed and it is found that the agglomeration temperature plays the main role in the formation of clusters with unified shape and structure.

Temperature-Switchable Agglomeration of Magnetic Particles Designed for Continuous Separation Processes in Biotechnology.

The purpose of this work was the synthesis and characterization of thermally switchable magnetic particles for use in biotechnological applications such as protein purification and enzymatic conversions. Reversible addition-fragmentation chain-transfer polymerization was employed to synthesize poly(N-isopropylacrylamide) brushes via a "graft-from" approach on the surface of magnetic microparticles. The resulting particles were characterized by infrared spectroscopy and thermogravimetric analysis and their temperature-dependent agglomeration behavior was assessed. The influence of several factors on particle agglomeration (pH, temperature, salt type, and particle concentration) was evaluated. The results showed that a low pH value (pH 3-4), a kosmotropic salt (ammonium sulfate), and a high particle concentration (4 g/L) resulted in improved agglomeration at elevated temperature (40 °C). Recycling of particles and reversibility of the temperature-switchable agglomeration were successfully demonstrated for ten heating-cooling cycles. Additionally, enhanced magnetic separation was observed for the modified particles. Ionic monomers were integrated into the polymer chain to create end-group functionalized particles as well as two- and three-block copolymer particles for protein binding. The adsorption of lactoferrin, bovine serum albumin, and lysozyme to these ion exchange particles was evaluated and showed a binding capacity of up to 135 mg/g. The dual-responsive particles combined magnetic and thermoresponsive properties for switchable agglomeration, easy separability, and efficient protein adsorption.

Effect of agglomeration and calcination temperature on the mechanical properties of yttria stabilized zirconia (YSZ)

Effect of azeotropic distillation after co-precipitation process of powder synthesis on powders morphology and mechanical properties of yttria stabilized zirconia was studied. The formation of hard or soft agglomerates during drying or calcination of co-precipitated powder can easily be prevented through azeotropic distillation. The powder prepared by direct co-precipitation and azeotropic treatment after co-precipitation process was calcined at different temperatures and was characterized through X-ray diffraction, transmission electron microscope and BET surface area measurement. The calcined powders were compacted uniaxially and sintered in two step sintering process. Sintered, polished and thermally etched samples were observed under scanning electron microscope. Vickers hardness and indentation fracture toughness were estimated. It is observed that reasonably higher density with better hardness and fracture toughness can be achieved for azeotroped samples in same sintering condition. Azeotropic treatment increases the surface area almost three times which helps to achieve better sintering. Pin on disc wear tests against alumina disc at 20N and 50N loads up to 3000m distance were carried out. The wear depth and coefficient of friction for both the material were compared.

Effect of temperature on wet agglomeration of crystals.

This study dealt with the wet agglomeration process in which a small quantity of binder liquid was added into a suspension of crystals, directly in the stirring vessel where the crystallization took place. The purpose of this investigation was evaluation of the effect of temperature on the agglomeration process in order to gain insight into the mechanism of the formation of the agglomerates. Carbamazepine was used as a model drug and water/ethanol and isopropyl acetate were used as crystallization system and binder liquid, respectively. The agglomeration of crystals was carried out at various temperatures and the agglomerates were characterized in terms of size, morphology, density and mechanical strength. Evaluation of the agglomerates along the course of agglomeration shows that the properties of the particles change gradually but substantially. Higher temperature of the system during agglomeration process favors the formation of more regular agglomerates with mechanically stronger and denser structure; this can be explained by the promotion effect of temperature on the agglomeration process. With optimized wet agglomeration temperature, spherical, dense, and strong agglomerates can be obtained.

Production of Nano NiO Particle with Chemical Precipitation Method and their Characteristics

Nano nickel oxide (NiO) particles were synthesized by a homogeneous precipitation method using NiCl2 as starting material and CO(NH2)2 as precipitant. Proper amount of NP-10 and appropriate organic solvent were added in the preparation process as dispersant. The chemical composition and properties were characterized by means of transmission electron microscope, X-ray diffractometer, and thermo gravimetry-differential thermal analyzer. The effects of reactant ratio, reaction temperature, reaction time, surfactant concentration, organic modifier concentration, agglomeration temperature as well as other reaction conditions on the appearances, size and dispersity degree of nano particles were investigated. The experiment results show that homogenous nano NiO particles were obtained by reacting nickel oxide and urea with a weight ration of 1:5 for 6 h at 80°C, then calcining for 2 h at 300°C. Adding surfactant NP-10 and organic solvent butanol to reaction system increases the dispersity and decreases the particle size of nano nickel oxide.

The effect of thermal treatment on the organization of copper and nickel nanoclusters synthesized from the gas phase

The condensation of 85000 Cu or Ni atoms from the high-temperature gas phase has been simulated by molecular dynamics with the tight binding potential. The efect of the subsequent thermal treatment on the shape and structure of synthesized particles was studied by simulating their gradual heating in a range of 100–1200 K. Some tendencies are revealed that are characteristic of the influence of heat treatment on the nanoparticles synthesized from the gas phase. It is concluded that short-term heating leads to significant ordering of the internal structure in 70% of agglomerated nanoparticles with the predominant formation of spherical shapes. In order to explain this result, the main mechanisms of cluster formation from the gas phase have been analyzed and it is found that the agglomeration temperature plays the main role in the formation of clusters with unified shape and structure. This opens the fundamental possibility of obtaining Cu and Ni nanoclusters with preset size, shape, and structure and, hence, predictable physical properties.

Improvement of the Thermal Stability of NiSi by Germanium Ion Implantation

The thermal stability of nickel monosilicide (NiSi) is one of the important research topics in the area of nano-complementary metal oxide semiconductor. This paper reports the effect of germanium (Ge) ion implantation on the thermal stability of the structure. High dose Ge ion implantation can improve the thermal stability of the structure. Ge ion implantation before NiSi formation results in a very smooth interface due to Ge atom pileup at the interface. This high concentration Ge layer reduces the interface energy so that the thermal stability can be improved. Both the phase-transformation temperature and agglomeration temperature are improved by . The effects of Ge ion implantation on the NiSi-contacted and shallow junctions are also examined. Although fast Ni diffusion via the ion implantation induced defects is observed, better thermal stability can still be observed on the junction.

Influence of germanium on thermal dewetting and agglomeration of the silicon template layer in thin silicon-on-insulator

We investigate the influence of heteroepitaxially grown Ge on the thermal dewetting and agglomeration of the Si(0 0 1) template layer in ultrathin silicon-on-insulator (SOI). We show that increasing Ge coverage gradually destroys the long-range ordering of 3D nanocrystals along the ⟨1 3 0⟩ directions and the 3D nanocrystal shape anisotropy that are observed in the dewetting and agglomeration of pure SOI(0 0 1). The results are qualitatively explained by Ge-induced bond weakening and decreased surface energy anisotropy. Ge lowers the dewetting and agglomeration temperature to as low as 700 °C.

Countermeasures against alkali-related problems during combustion of biomass in a circulating fluidized bed boiler

The purpose of this work was to study different ways to mitigate alkali-related problems during combustion of biomass in circulating fluidized beds. Wood chips and wood pellets were fired together with straw pellets, while the tendency to agglomerate and form deposits was monitored. In addition to a reference case, a number of countermeasures were applied in related tests. Those were addition of elemental sulphur, ammonium sulphate and kaolin to a bed of silica sand, as well as use of olivine sand and blast-furnace slag as alternative bed materials. The agglomeration temperature, composition and structure of bed-ash samples were examined. The flue-gas composition, including gaseous alkali chlorides, was measured in the hot flue gases and in the stack. Particles in the flue gas were collected and analysed for size distribution and composition. Deposits were collected on a probe in hot flue gases and their amount and composition were analysed. Addition of kaolin was found to be the best method to counteract the agglomeration problem. The deposition problem is effectively counteracted with addition of ammonium sulphate, while kaolin is too expensive to be used commercially against deposits, and sulphur is less effective than ammonium sulphate.

Ignition of Iron-Coated and Nickel-Coated Aluminum Particles Under Normal- and Reduced-Gravity Conditions

In aluminized solid propellants, the use of Al particles coated by certain transition metals may improve engine performance characteristics, owing to decreased agglomeration and lower ignition temperature of the particles. For this application, a detailed knowledge of particle ignition is required. Earlier, we reported the ignition mechanism of single ∼2.5-mm Ni-coated Al particles heated by a laser in Ar and CO 2 atmospheres. In the present work, using the same apparatus, we investigate the ignition mechanism of Fe-coated Al particles. The results show that intermetallic reactions contribute to the heating rate upon Al melting at 660°C, but the particles ignite at 1350-1500°C under normal-gravity conditions. The ignition mechanism includes the formation of a solid Fe 2 Al 5 phase at the interface between liquid Al and the coating, with subsequent melting of Fe 2 Al 5 , formation of a solid FeAl layer, and conversion of the Fe coating to a Fe-Al solid solution. Microgravity (10 -3 -10 -2 g) experiments with Fe-coated and Ni-coated Al particles were conducted to reduce convection inside the particles, which may influence phase mixing during ignition. In microgravity, both Ni-coated and Fe-coated Al particles ignited at 1250-1400°C. The significantly lower ignition temperature, compared with conventional oxide-coated Al, suggests that Fe-coated and Ni-coated Al particles are promising candidates for propulsion applications.

Kaolin Addition during Biomass Combustion in a 35 MW Circulating Fluidized-Bed Boiler

Kaolin addition to a 35 MW circulating fluidized-bed boiler, fired with forestry residues, was performed to study the effect on bottom and fly ash. Ash samples from a period of kaolin dosage were compared with ash samples without kaolin. The samples were analyzed for elemental composition, water solubility, and mineralogical composition. The cross-section of bed particles was examined for elements. The agglomeration temperature of the material from the particle seal was determined. The kaolin, in the form of a fine powder, was supplied to the particle seal. It was found to be carried by the flue gases to the electrostatic filter rather than staying in the bed. Despite this, alkali is removed from the furnace by the kaolin, and thereby, the agglomeration temperature of the bed material increases. The alkali ends up in the fly ash, in which the content of alkali increases and the solubility of alkali decreases, suggesting that alkali aluminum silicates have been formed. These compounds have high melting points and are therefore unlikely to become liquid and stick to the surface of superheaters. A small fraction of the kaolin stays in the furnace by forming a thin layer on bed particles. It is concluded that kaolin addition can significantly enhance the operation of a fluidized bed fired with biofuels both with respect to superheater deposition and corrosion and bed agglomeration. The results show that findings in small-scale reactors are also valid in large-scale combustors. However, under the present circumstances, most kaolin ends up as fly ash.