Suppression Of Agglomeration Research Articles

Aluminum particle agglomeration characteristics and suppression method during the combustion of aluminum‐based solid propellants: A review

AbstractAluminum is widely used in solid rocket propellants to improve the energy performance of the propellant. However, during propellant combustion, aluminum particles may agglomerate, resulting in slag deposition, incomplete combustion of metal particles, increased two‐phase flow losses, and reduced motor specific impulse. Therefore, it is of great scientific significance and engineering value to understand the agglomeration mechanism of aluminum particles and to explore the method of agglomeration suppression. Based on this, this paper firstly briefly introduced the agglomeration process of aluminum particles during propellant combustion. Subsequently, factors influencing the agglomeration of aluminium particles were analysed. The influencing factors can be roughly divided into two aspects: propellant‘s own formulation and external environment. Immediately afterwards, the existing agglomeration suppression methods were emphasized and summarized and analyzed. Presently, agglomeration suppression methods can be broadly classified into four categories, namely, conventional formulation optimization, use of aluminum nanoparticles, and modification of aluminum particles using fluorine‐containing compounds or alloy particles. Finally, several directions that need to be focused on in the future are proposed to address the problems in the study of aluminum particle agglomeration suppression methods.

Confined growth of NiCo2S4 on 2D/2D porous carbon self-repairing g-C3N4/rGO heterostructure for enhanced performance of asymmetric supercapacitors

In this work, porous carbon self-repairing g-C3N4 (pCCN) nanosheets were synthesised using a solvothermal technique followed by calcination and acid treatment. A facile hydrothermal process is employed for the confined growth of NiCo2S4 on porous carbon self-repairing g-C3N4/rGO heterostructure (pCRNCS) as hybrid material for supercapacitor electrodes. The improved electronic conductivity and activity of carbon self-repairing g-C3N4 (CCN) than g-C3N4 owing to the creation of extended delocalized π-electrons by the substitutional or interstitial C atoms in the structure and because of acid treatment, the larger planes of CCN are broken down into smaller segments, increasing the edge nitrogen and oxygen functional groups. The introduction of porous CCN led to the strong electrostatic interaction with GO and CCN which aided in the suppression of agglomeration of graphene sheets. The as-synthesised pCRNCS electrode showed remarkably high specific capacitance (1938 F/g at current density of 2 A/g). The excellent electrochemical activity is due to the 2D/2D heterostructure assembly of high surface area rGO and extended highly reactive region and defects in pCCN which facilitated the nucleation and confined growth of NiCo2S4 in the framework. The constructed pCRNCS//AC ASC exhibited remarkable electrochemical properties, including a specific capacitance of 211 F/g at 1 A/g, an exceptional capacitance retention of 93.6% after 6000 cycles, and the maximum energy density of 66 Wh/kg at a power density of 751 W/kg. The excellent capacitive behaviour of porous carbon self-repairing g-C3N4/rGO@NiCo2S4 assure the development of high-performance energy storage device.

Crystal Engineering in Antisolvent Crystallization of Rare Earth Elements (REEs)

Antisolvent crystallization is a separation technology that separates the solute from the solvent by the addition of another solvent, in which the solute is sparingly soluble. High yields are achieved by using higher antisolvent-to-aqueous ratios, but this generates higher supersaturation, which causes excessive nucleation. This results in the production of smaller particles, which are difficult to handle in downstream processes. In this work, the effect of varying the organic (antisolvent)-to-aqueous (O/A) ratio and seed loading on the yield, particle size distribution, and morphology of neodymium sulphate product, during its recovery from an aqueous leach solution using antisolvent crystallization, was investigated. A batch crystallizer was used for the experiments, while ethanol was used as an antisolvent. Neodymium sulphate octahydrate [Nd2(SO4)3.8H2O] seeds were used to investigate the effect of seed loading. It was found that particle sizes increased as the O/A ratio increased. This was attributed to the agglomeration of smaller particles that formed at high supersaturation. An O/A ratio of 1.4 resulted in higher yields and particles with a plate-like morphology. The increase in yield was attributed to the increased interaction of ethanol molecules with the solvent, which reduced the solubility of neodymium sulphate. Increasing the seed loading resulted in smaller particle sizes with narrow particle size distribution and improved filtration performance. This was attributed to the promotion of crystal growth and suppression of agglomeration in the presence of seeds.

Bottom-up holistic carrier management strategy induced synergistically by multiple chemical bonds to minimize energy losses for efficient and stable perovskite solar cells

The defects from electron transport layer, perovskite layer and their interface would result in carrier nonradiative recombination losses. Poor buried interfacial contact is detrimental to charge extraction and device stability. Here, we report a bottom-up holistic carrier management strategy induced synergistically by multiple chemical bonds to minimize bulk and interfacial energy losses for high-performance perovskite photovoltaics. 4-trifluoromethyl-benzamidine hydrochloride (TBHCl) containing –CF3, amidine cation and Cl− is in advance incorporated into SnO2 colloid solution to realize bottom-up modification. The synergistic effect of multiple functional groups and multiple-bond-induced chemical interaction are revealed theoretically and experimentally. F and Cl− can passivate oxygen vacancy and/or undercoordinated Sn4+ defects by coordinating with Sn4+. The F can suppress cation migration and modulate crystallization via hydrogen bond with FA+, and can passivate lead defects by coordinating with Pb2+. The –NH2–CNH2+ and Cl− can passivate cation and anion vacancy defects through ionic bonds with perovskites, respectively. Through TBHCl modification, the suppression of agglomeration of SnO2 nanoparticles, bulk and interfacial defect passivation, and release of tensile strains of perovskite films are demonstrated, which resulted in a PCE enhancement from 21.28% to 23.40% and improved stability. With post-treatment, the efficiency is further improved to 23.63%.

An ultra-dispersive, nonprecious metal MOF\u2013FeZn catalyst with good oxygen reduction activity and favorable stability in acid

Development of the more stable nonprecious oxygen reduction reaction (ORR) catalyst is of great significance nowadays. Herein, a high-performance iron-doped integral uniform macrocyclic organic framework (MOF–FeZn) catalyst is synthesized through a combined hydrothermal and pyrolysis process, showing favorable ORR activity and stability in acid. This as-synthesized MOF–FeZn catalyst displays high porous and graphitic structures with sufficient catalytic active dopants of pyridinic N, Fe–N, pyrrolic N, graphitic N, making it a promising ORR candidate catalyst with high electrochemical stability. The onset potential, half-wave potential and limited diffusion current density of MOF–FeZn are 0.93 V @ 0.1 mA cm−2, 0.768 V@ 2.757 mA cm−2 and 5.5 mA cm−2, respectively, which are comparable to the state-of-the-art nonprecious catalyst and commercial Pt/C. ORR catalysis on MOF–FeZn follows the nearly four-electron path. What is more, MOF–FeZn can sustain the 10,000 cycles electrochemical potential cycling process in acid with the half-wave potential changed only 21 mV, superior to the reduction of 149 mV for Pt/C. The well-developed integral uniform structures, homogeneously dispersed carbides and nitrides protected by the highly graphitic carbon layers and the better agglomeration suppression of nanoparticles by the confined graphitic carbon layers on catalyst can significantly enhance the catalytic activity and stability of MOF–FeZn.

Agglomeration Suppression of a Fe-Supported Catalyst and its Utilization for Low-Temperature Ammonia Synthesis in an Electric Field.

Fe-supported heterogeneous catalysts are used for various reactions, including ammonia synthesis, Fischer–Tropsch synthesis, and exhaust gas cleaning. For the practical use of Fe-supported catalysts, suppression of Fe particle agglomeration is the most important issue to be resolved. As described herein, we found that Al doping in an oxide support suppresses agglomeration of the supported Fe particle. Experimental and computational studies revealed two tradeoff Al doping effects: the Fe particle size decreased and remained without agglomeration by virtue of the anchoring effect of doped Al. Also, some Fe atoms anchored by Al cannot function as an active site because of bonding with oxygen atoms. Using an appropriate amount of Al doping is effective for increasing the number of active Fe sites and catalytic activity. This optimized catalyst showed high practical activity and stability for low-temperature ammonia synthesis in an electric field. The optimized catalyst of 12.5 wt % Fe/Ce0.4Al0.1Zr0.5O2-δ showed the highest ammonia synthesis rate (2.3 mmol g–1 h–1) achieved to date under mild conditions (464 K, 0.9 MPa) in an electric field among the Fe catalysts reported.

Synthesis of Sm2Fe17N3 compacts by mechanical milling with graphite powder and their magnetic properties

Abstract It is difficult to prepare Sm 2 Fe 17 N 3 sintered magnets because Sm 2 Fe 17 N 3 phase decomposes above 600°C, and the decomposition results in significant reduction of magnetic properties. To consolidate Sm 2 Fe 17 N 3 powder below the decomposition temperature, an increase of the filling fraction is expected to be one of the effective methods. In this study, an addition of graphite as well as Zn to Sm 2 Fe 17 N 3 powder was conducted by mechanical milling. The dispersion of graphite powder, which acted as a lubricant when compacting the powder, resulted in an increase in the filling fraction. The high relative density, 93.0%, of a sintered body was easily obtained by the addition of the most balanced amounts of graphite and Zn. The magnetization was increased with increase in the additive amount of graphite due to the reduction of the strain accumulated to crystal grains during the mechanical milling. The coercivity was not decreased even when the amount of Zn was reduced, because the Zn powder was dispersed more homogeneously due to the suppression of agglomeration among particles and adhesion of powder to the inside wall of pod during the mechanical milling by the addition of graphite powder.

Creation of Ni-B/Ni-P electroless coating on the WC particles without surface activator

One of the methods for improving metal-ceramic interface and suppression of agglomeration is the formation of a monolayer electroless coating on the particles. Investigations indicated that Ni-B monolayers should be first formed to develop in the next process an electroless Ni–P coating with the morphology of cauliflower. It was possible to produce a Ni-B layer on WC particles when a bath was heated at a temperature of 95 °C by using sodium borohydride and an appropriate stabilizer. Following this process, the Ni–P electroless coating was deposited on WC particles at 85 °C. In this way, two layers of electroless coating of Ni–B/Ni–P on the WC ceramic particles without using the surface activator were produced successfully. The coating morphology and surface analysis were performed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results showed that only the degreasing with acetone as a surface preparation of ceramic particles is sufficient to make a Ni–P or Ni–B coating. Electroless Ni–B coating with appropriate adhesion to the surface produces an acceptable surface for the electroless Ni – P coating formation.

Formation of epitaxial Ti-Si-C Ohmic contact on 4H-SiC C face using pulsed-laser annealing

Epitaxial Ti-Si-C Ohmic contacts on the 4H-SiC C-face for SiC power devices by pulsed-laser annealing were demonstrated. Titanium (Ti) is one of the carbon-interstitial type metals. In a conventional nickel silicide (NiSi) electrode on SiC, carbon agglomeration at the silicide/SiC interface occurs, and the contact resistance between NiSi and SiC substrates becomes larger. For the carbon agglomeration suppression, a nanosecond non-equilibrium laser annealing was performed, and also Ti was deposited for the formation of both silicide and carbide. As a result, the lowest specific contact resistance of 4.0 × 10−4 Ω cm2 was obtained for an Al/Ti-Si-C/SiC structure at a laser power of 2.5 J/cm2. The Ti-Si-C Ohmic electrode showed TiC and Ti5Si3 crystal phases, and these crystals were epitaxially grown on 4H-SiC at the interface.

Formation of amorphous alloys on 4H-SiC with NbNi film using pulsed-laser annealing

Amorphous alloys containing Ni-Si-Nb-C were formed on 4H-SiC creating a low resistance Ohmic contact electrode. In a conventional nickel silicide (NiSi) electrode on SiC, a carbon agglomeration at the silicide/SiC interface occurs, and contact resistance between NiSi and SiC substrate becomes larger. For carbon agglomeration suppression, nanosecond non-equilibrium laser annealing was introduced, and to form metal carbides, carbon-interstitial type metals Nb and Mo were introduced. Ni, Nb, Mo, Nb/Ni, Mo/Ni multilayer contacts, and NbNi mixed contact were formed on the C-face side of n-type 4H-SiC wafers. The electrical contact properties were investigated after a 45 ns pulse laser annealing in N2 ambient. As a result, with NbNi film, an amorphous alloy with Ni-Si-Nb-C was formed, and a low specific contact resistance of 5.3 × 10−4 Ω cm2 was realized.

Effects of rapid thermal annealing for E-beam evaporated Ag films on stainless steel substrates

There is significant interest in the development of flexible substrates for making electronic devices such as solar cells and organic light emitting diodes using roll-to-roll processes. Stainless steel (STS) is commonly used for flexible substrates. To explore the potential for new STS applications (e.g., optical scattering layers in opto-electronic devices) silver thin films of ~100nm thickness were deposited on STS substrates using the thermal evaporation technique. The films then underwent rapid thermal annealing (RTA) to create various sizes of silver particles. The RTA method was carried out at annealed temperatures from room temperature (RT) to 550°C for 20min. We investigated variation of the surface morphology caused by the interaction between Ag films and STS substrates after the RTA annealing. The grain size was studied by using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) methods. When the film was annealed at 250°C, particles started to separate and the gaps between particles enlarged. However, at the high temperatures (450 and 550°C), we observed that the gaps decreased when the annealing temperature was increased from 350 to 550°C. In particular, the surface of STS substrate was completely covered with Ag particles for the film annealed at 550°C. The results showed the suppression of the agglomeration of the Ag film. Secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS) was used to examine the movement of Fe and Cr atoms in silver film from STS substrates. These atoms observed with SIMS and XPS must be at the surface. It was found that Fe and Cr atoms play a critical role in suppressing Ag agglomeration.The optical properties of annealed Ag films were studied by spectrophotometer. Broader absorbance was found for films with 450°C annealing temperature. The total reflectance of the Ag films annealed at 550°C increased over the wavelength range of 400–800nm, compared with that at 450°C. This was due to suppression of Ag agglomeration.

Optimization of Surface Layers for Suppression of Agglomeration in Ag Films

We previously reported that Al, Ti, and Nb surface layers can effectively suppress agglomeration in Ag films, which is dominated by the surface diffusion of Ag atoms. In this study, Ag films with Pd, Ni, and W surface layers were prepared by RF magnetron sputtering, and the properties of these films were compared with previous observations of the effects of Ti and Nb surface layers. The most important properties of the appropriate surface layers for the suppression of agglomeration in Ag films are a high cohesive energy or a high Gibbs free energy of formation of the oxide, and a low solid solubility in Ag.

Effects of Nb Surface and Ti Interface Layers on Thermal Stability and Electrical Resistivity of Ag Thin Films

Nb/Ag, Ag/Ti, and Nb/Ag/Ti films were prepared by rf magnetron sputtering to investigate the effects of the Nb surface and Ti interface layers on the thermal stability and electrical resistivity of 100-nm-thick Ag thin films. The Nb surface layer, regardless of the chemical state of metal or oxide, prevented the migration of Ag atoms during annealing, which contributed to the agglomeration suppression of Ag films. Ti interface layers not only improved the adhesion of Ag films to SiO2 substrates but also impelled the overcoated Ag atoms to arrange along the close-packed plane (111); thus, Ag/Ti films exhibited relatively good thermal stability and low resistivity. By combining the roles of the Nb surface and Ti interface layers, Nb (5 nm)/Ag (100 nm)/Ti (3 nm) films showed the highest thermal stability and the lowest resistivity. Different materials of surface and interface layers might be more effective for improving the thermal stability and electrical resistivity of Ag films.

Effects of Nb Surface and Ti Interface Layers on Thermal Stability and Electrical Resistivity of Ag Thin Films

Nb/Ag, Ag/Ti, and Nb/Ag/Ti films were prepared by rf magnetron sputtering to investigate the effects of the Nb surface and Ti interface layers on the thermal stability and electrical resistivity of 100-nm-thick Ag thin films. The Nb surface layer, regardless of the chemical state of metal or oxide, prevented the migration of Ag atoms during annealing, which contributed to the agglomeration suppression of Ag films. Ti interface layers not only improved the adhesion of Ag films to SiO2 substrates but also impelled the overcoated Ag atoms to arrange along the close-packed plane (111); thus, Ag/Ti films exhibited relatively good thermal stability and low resistivity. By combining the roles of the Nb surface and Ti interface layers, Nb (5 nm)/Ag (100 nm)/Ti (3 nm) films showed the highest thermal stability and the lowest resistivity. Different materials of surface and interface layers might be more effective for improving the thermal stability and electrical resistivity of Ag films.

Effects of stabilizers on particle redispersion and dissolution from polymer strip films containing liquid antisolvent precipitated griseofulvin particles

Abstract In this work, we provide experimental evidence supporting the dual role of stabilizers on controlling growth and agglomeration of formed particles via liquid antisolvent (LAS) process and use this knowledge to demonstrate the feasibility of integrating these engineered particles into fast dissolving edible pharmaceutical strip films (PSF). A T-mixer was used to produce griseofulvin (GF) particles for incorporation into PSF in continuous mode, while the experiments crucial to elucidate the role of stabilizers were conducted in batch system. Stabilization was examined via addition of the non-ionic surfactant Pluronic F127 (PF 127), the polymer hydroxypropyl methyl cellulose (HPMC LV 15) and their combinations. Centrifugation was evaluated as a means to concentrate suspensions and minimize levels of residual solvent, while keeping the produced particles non-agglomerated. Laser diffraction, SEM imaging, Differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and Near-infrared Spectroscopy (NIR) were employed to characterize the particles and strip films. It was observed that the simultaneous evolution of particle growth and agglomeration is controlled if HPMC LV 15 and PF 127 are present before precipitation while only agglomeration is suppressed if added after precipitation. The addition of PF 127 along with HPMC LV 15 to GF suspensions results in controlling initial growth and suppression of agglomeration during downstream processing via synergistic effects. The optimal formulation results in faster and higher extent of dissolution than a poorly stabilized suspension, a film made from the unprocessed drug, a physical mixture or a compact of similar composition. Along with particle size data, cluster size analysis from NIR imaging emphasizes the role of wettability and re-dispersion in the particle dispersion in the film and recoverability of engineered particles to improve bioavailability.

Thermal stability and electrical properties of Ag–Ti films and Ti/Ag/Ti films prepared by sputtering

Ag–Ti (100 nm) alloy film, and Ti/Ag (100 nm) double-layer and Ti/Ag (100 nm)/Ti triple-layer films were prepared by rf sputtering to investigate the effect of Ti on suppression of agglomeration of the Ag thin film caused by thermal treatment. Scanning electron microscopy revealed that the Ag–Ti and Ti/Ag/Ti films had high thermal stability. X-ray photoelectron spectroscopy analysis showed that the surfaces of both kinds of films were covered with a TiO2 layer after annealing, which was considered to be the key factor for improvement of the thermal stability of the films. In addition, scratch tests indicated improvement of the adhesive strength of the Ti/Ag/Ti film to the SiO2 substrate due to the underlying Ti film layer, which effectively promoted suppression of Ag agglomeration. However, the resistivity of the Ag–Ti films increased abruptly with increasing Ti content due to the impurity scattering effect, and minimum usage of the alloying element was required to achieve low resistivity. In contrast, the Ti/Ag/Ti film exhibited both low resistivity and high thermal stability.

Agglomeration suppression behavior and mechanisms of Ag–Cu and Ag–Nb thin films

Agglomeration behavior of Ag–Cu and Ag–Nb thin films prepared by sputtering was investigated. The films were annealed at 400–600 °C in vacuum and their surface morphologies and resistivities were characterized. It was found that agglomeration was suppressed in both Ag–Cu and Ag–Nb films. The resistivity of Ag–Cu films remained low even when the Cu concentration was increased. However, the resistivity of the Ag–Nb films increased with Nb concentration. We found that 0.4 at% Nb and 2.1 at% Cu were optimum alloying concentrations from the standpoint of both morphology and resistivity. The mechanisms of agglomeration suppression for the Ag–Cu and Ag–Nb films appeared to be different. XRD measurements of the Ag–Cu films showed a marked preferential orientation for (111) in the case of as-deposited films. This suggested that the annealing-induced orientation change in the crystal grains of the Ag–Cu films was minimal. On the basis of XPS measurements, it is believed that the Nb oxides surrounding the Ag grains led to agglomeration suppression in the Ag–Nb film.

Thermal Immune NiGermanide for High Performance Ge MOSFETs on Ge-on- Si Substrate Utilizing $ \hbox{Ni}_{0.95}\hbox{Pd}_{0.05}$ Alloy

Highly thermally stable Ni germanide technology for high performance germanium metal-oxide-semiconductor field-effect transistors (Ge MOSFETs) is proposed, utilizing Pd incorporation into Ni germanide. The proposed Ni germanide shows not only the improvement of thermal stability but also the reduction of hole barrier height, which can improve the device on-current by reducing the Ni germanide to p+ source/drain contact resistance. The proposed Ni germanide showed a stable sheet resistance of up to 500degC 30-min postgermanidation annealing due to the suppression of agglomeration and oxidation of Ni germanide and the diffusion of Ni and Ge atoms by the incorporated Pd. Therefore, the proposed Ni0.95Pd0.05 alloy could be promising for the high mobility Ge MOSFET applications.

Thermally Stable Ag Thin Films Modified with Very Thin Al Oxide layers

Ag has long been of interest for use as a low-resistivity electrode material, but the problem of agglomeration caused by annealing must be resolved. One of the solutions is alloying Ag, but this often causes an increase in electrical resistivity. In this study, thermal stability of Ag thin films modified with thin Al oxide layers was investigated from the viewpoints of surface morphology and resistivity. It was found that agglomeration was suppressed in the multilayer films even after annealing at 600 °C, similarly to Ag(Al) alloy films, which were investigated previously. As a result, it was suggested that the presence of the Al oxide layers at the film surface and interface played a major role in suppressing agglomeration in Ag(Al) films. Moreover, the resistivity of the multilayer film was 1.8 µΩ cm, which was much lower than that of alloy films. Consequently, to achieve both agglomeration suppression and low resistivity, the structural modification of the Ag films using Al oxide layers is more useful than alloying the films.

Improvement of thermal stability of Ni silicide on N +–Si by direct deposition of group III element (Al, B) thin film at Ni/Si interface

The direct deposition of a thin Al or B layer at Ni/Si interface was proposed as a new method to solve a problem of degraded thermal stability of Ni silicide on heavily doped N +–Si substrates. Significant improvement of thermal stability evaluated by the sheet resistance vs. silicidation temperature properties was observed. The improvement is attributed to suppression of agglomeration of the silicide layers. The Al layer was effective only when it was located at the Ni/Si interface before the silicidation process. The deposited Al and B layers under Ni layer segregated at the surface after the silicidation process. The use of B layer was preferable to control the phase transition from NiSi to NiSi 2.