Microfluidic preparation of surfactant-free ultrafine DAAF with tunable particle size for insensitive initiator explosives

High purity and ultrafine DAAF(u-DAAF)is an emerging insensitive charge in initiators.Although there are many ways to obtain u-DAAF,developing a preparation method with stable operation,accurate control,good quality consistency,equipment miniaturization,and minimum manpower is an inevitable requirement to adapt to the current social technology development trend.Here reported is the microfluidic preparation of u-DAAF with tunable particle size by a passive swirling microreactor.Under the guidance of recrystallization growth kinetics and mixing behavior of fluids in the swirling microreactor,the key parameters(liquid flow rate,explosive concentration and crystallization temperature)were screened and optimized through screening experiments.Under the condition that no surfactant is added and only experimental parameters are controlled,the particle size of recrystallized DAAF can be adjusted from 98 nm to 785 nm,and the corresponding specific surface area is 8.45 m^(2)·g^(-1)to 1.33 m^(2)·g^(-1).In addition,the preparation method has good batch stability,high yield(90.8%-92.6%)and high purity(99.0%-99.4%),indicating a high practical application potential.Electric explosion derived flyer initiation tests demonstrate that the u-DAAF shows an initiation sensitivity much lower than that of the raw DAAF,and comparable to that of the refined DAAF by conventional spraying crystallization method.This study provides an efficient method to fabricate u-DAAF with narrow particle size distribution and high reproducibility as well as a theoretical reference for fabrication of other ultrafine explosives.

Application of Composite Ultrafine Particles in ER Fluids

Aim To obtain a kind of electrorheological (ER) flind with high comprehensive properties in order to satisfy the needs of engineering application. Methods A new type of dispersed phase── composite ultrafine particles (UFP) was obtained by the method of microemulsion, which was used to mix with silicon oil. aam electroinduced stress and apparent viscosity of the ER fluids with three different volume fractions were tested under the conditions of different temperatures, electric fields and shear rates. Results A series of systematic tests show that the new type of ER fluids with volume fraction of 30% possesses obvious ER effect. Conclusion The double layers polarization plays an important role in ER effect.

Preparation and hydrogen storage properties of ultrafine pure Mg and Mg-Ti particles

The ultrafine pure Mg and Mg-Ti particles were prepared through a direct current （DC） arc plasma method. The X-ray diffraction （XRD）, transmission electron microscopy （TEM）, pressure-composition-temperature （PCT） method and TG/DTA techniques were used to study the phase components, microstructure and hydrogen sorption properties of the powders before and after hydrogen absorption. It is revealed that most of the ultrafine Mg and Mg-Ti particles are hexagonal in shape with particle size in the range of 50-700 nm. According to the Van’t Hoff equation, the hydrogenation enthalpy of Mg-Ti powders is determined to be about -67 kJ/mol H2 based on the PCT curves of hydrogen absorption plateau pressures. This value is much higher than -78.6 kJ/mol H2 for pure Mg powders. TG/DTA analyses show that the onset dehydriding temperature of hydrogenated Mg-Ti powders is 386 °C, which is significantly lower than that of the hydrogenated Mg （423 °C）. The results prove that the addition of Ti into Mg through arc evaporation method can improve the thermodynamic properties of Mg for hydrogen storage.

PREPARATION OF WATERBORNE ULTRAFINE PARTICLES OF EPOXY RESIN BY PHASE INVERSION TECHNIQUE

Waterborne ultrafine particles of epoxy resin were prepared by phase inversion technique. The results of SEM revealed that the particles diameter was in the range of 50 to 100 nm and the effects on amount of water required at phase inversion point were also discussed.

Preparation and Characterization of CeO_2-ZrO_2 Solid Solution Ultrafine Particles Using Reversed Microemulsion

Ce0.6Zr0.4O2 solid solution ultrafine particle was prepared in the cyclohexane/water/OP-10/n-hexanol reversed microemulsion. The quasi-ternary phase diagram investigations showed that the system has narrow W/O type microemulison region, so it is the proper system to prepare Ce0.6Zr0.4O2 solid solution ultrafine particle. Some physical-chemical techniques such as TG/DTA, XRD, BET, and HRTEM are used to characterize the resultant powders. The results show that the fluorite cubic Ce0.6Zr0.4O2 solid solution is obtained at 400 ℃. The surface area is （146.7 m^2·g^-1）, which is higher than the surface area for sol-gel prepared sample （59.5m^2·g^-1）. HRTEM images indicated that the Ce0.6Zr0.4O2 solid solution ultrafine particle is well-crystallized, narrow size distribution, less agglomeration, within mean size of 5 -7 nm.

Preparation of Ultrafine γ-Al_2O_3 Particles in Non-ionic Water in Oil Microemulsions

Ultrafine γ-A12O3 particles are synthesized in Triton X- 10 0/n - hexanol/cycloh exan e/wat er water in o if(w/o )Inicroemulsion by mixing two separately prepared microemulsions containing Al(NO)3 and (Wb)ZCO, respectively.The ultrafine Al2O3 particles are characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD)and their size and distribution are measured. The effects of water, surfactallt and reactant concentrations on the particlesize and distribution are studied. The results show that the particle size and distribution can be changed by varying thepreparation conditions, and the size of the microemulsion droplets has a controlling effect on the size of the pafticles. A. possible mechanism of ultrafine particles (UFPs) prepared by microemulsions is proposed.

Sources,characteristics,toxicity,and control of ultrafine particles:An overview

Air pollution by particulate matter(PM)is one of the main threats to human health,particularly in large cities where pollution levels are continually exceeded.According to their source of emission,geography,and local meteorology,the pollutant particles vary in size and composition.These particles are conditioned to the aerodynamic diameter and thus classified as coarse(2.5–10μm),fine(0.1–2.5μm),and ultrafine(<0.1μm),where the degree of toxicity becomes greater for smaller particles.These particles can get into the lungs and translocate into vital organs due to their size,causing significant human health consequences.Besides,PM pollutants have been linked to respiratory conditions,genotoxic,mutagenic,and carcinogenic activity in human beings.This paper presents an overview of emission sources,physicochemical characteristics,collection and measurement methodologies,toxicity,and existing control mechanisms for ultrafine particles(UFPs)in the last fifteen years.

Studies on the Lanthanum-Modified Lead Titanate Ultrafine Particles by Raman Spectroscopy

Lanthanummodified lead titanate(PLT14) ultrafine particles were synthesized by means of stearic acid gel method. The structure of the samples was characterized using Xray diffraction(XRD) and TEM. The crystal graphic parameters of the samples were calculated. The Raman spectra of PLT14 powders at a high pressure as well as a high temperature reveal that the phase transition pressure or temperature shifts to a lower pressure or temperature with the decrease of grain size.

Morphology and Structure Analyses of SnO2 Thin Film Coated on Al2O3 Ultrafine Particles by Gas Phase Reaction in Fluidized Bed

Fluidized chemical vapor deposition (FCVD) technology was developed for coating SnO 2 thin film on ultrafine Al 2O 3 particles.Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) analyses demonstrated that SnO 2 films with different structures were deposited through controlling the coating temperature, reactant concentration, etc .. Nanocrystalline SnO 2 film was formed at 572.15K by gas phase reaction of SnCl 4 and H 2O.Electron probe microanalyser (EPMA) and energy dispersive spectrometer (EDS) analyses indicated that the distribution of nanocrystalline SnO 2 over inner and outer part of the Al 2O 3 agglomerates was homogeneous.

MICROSTRUCTURAL STUDIES OF ULTRAFINE IRON PARTICLES

The constitution,structure and surface state of the ultrafine iron particles prepared by gas evaporation technique have been investigated by means of X-ray analysis,high-reasolution electron microscopy(HREM)and electron spectroscopy for chemical analysis(ESCA).The results showed that the fine particles are spherical ones of～20 nm in diameter with α-Fe cores and covered by Fe_3O_4 fine crystalline layers of～4 nm thickness.

Mssbauer Effect in Ultrafine Particles with Fe-C Solid Solution,γ-Fe and Fe_3C Phases

Ultrafine particles prepared by evaporating pure Fe in CH4 atmosphere using arc-dischargeheating method, were found to consist of Fe-C solid solution, γ-Fe and Fe3C phases. EfFect of annealing temperature on phase transformation and hyperfine interactions has been investigated by Mossbauer spectroscopy, X-ray diffraction (XRD), differential thermal analysis and thermogravimetry (DTA-TG), transmission electron microscopy (TEM), oxygen determination and vibrating sample magnetometer (VSM) measurements. It was observed that phase transformation of γ-Fe to α-Fe occurs during annealing in vacuum. The mechanism causing the change of hyperfine interactions with annealing temperature differs for Fe-C solution and interstitial compounds. DifFerence of hyperfine interactions of Fe-C solid solution in the starting sample and its annealed samples is ascribed to the improvement of activation of interstitial carbon atoms. Stress-relieving in structure of annealed Fe3C particle can result in a weak influence on hyperfine interactions. Parameters fitted to the Mossbauer spectra show the existence of superparamagnetism in all the samples. Absorbed and combined oxygen on particle surface of the starting sample were determined.

Characterization and Growth Morphology of the Ultrafine Manganese Particles

In present work.the ultrafine manganese particles were prepared by gas evaporation method.The structure,size distribution,growth morphology and surface oxidation for the particles were investi- gated by using X-ray diffraction and electron microscopy.The results indicated that three types of the particles,with the structure of α-Mn,β-Mn and one unknown,respectively existed in the man- ganese particles.The growth morphology of the particles depended on the size and intrinsic structure.When exposed to air,the particles were slightly oxidized only in the surface layer and sta- ble in air.

STRUCTURE AND SURFACE CONDITION OF ULTRAFINE AI PARTICLES

The crystal habit,crystalline structure,surface condition and composition of the ultrafine Al particles prepared by inert gas evaporation method were studied in detail by means of high resolution transmission electron microscope,X-ray diffraction and X-ray photo-electron spectrum.The results indicate that the ultrafine Al particles prepared in high pure inert gas are of clear crystal habits,single crystal in a large majority and fcc crystalline structure with a_0=0.405 nm.It is also found on the surface of the Al particles that there is a layer of amor- phous Al_2O_3 with 2 nm average thickness,which could protect the particles against oxidizing further.Therefore,the ultrafine Al particles prepared by the inert gas evaporation method are very stable in atmosphere.

Preparation of γ-Al_2O_3 Ultrafine Particlesand Its Application in Hydrogen Peroxide Biosensor

In this article, we illustrated the preparation method of γ Al 2O 3 ultrafine particles. The particle size and morphology were decided by a transmission electron microscopy (TEM) and crystal patterns were determined by an X ray diffractometer (XRD). γ Al 2O 3 ultrafine particles have ultra characters in physics and chemistry, and the hydrogen peroxide biosensors based on it display not only fast response and high sensitivity, but also good stability.

Photoluminescence Studies on Ferric Oxide Ultrafine Particles

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Experiments and Modeling of the Preparation of Ultrafine Calcium Carbonate in Spouted Beds with Inert Particles

A novel reaction-drying process was carried out in a spouted bed reactor with inert particles and used to prepare ultrafine CaCO3 particles. Effects of concentrations of CO2 and Ca(OH)2, and reaction temperature on Ca(OH)2 conversion were experimentally investigated. The particle sizes and composition of CaCO3 produced were characterized with transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results indicated that ultrafine CaCO3 particles with mean size of 80 nm could be obtained with this novel process.By modifying the Arrhenius Equation and considering the Ca(OH)2 state, a kinetic model was established to describe the process in the spouted bed. The model parameters estimated from the reaction-drying experiments were found to fit well the experimental data, indicating the applicability of the proposed kinetic model.

NUCLEATION AND GROWTH OF ULTRAFINE PARTICLES AND CONDITIONS OF EPITAXY

The idea of free energy has been used in the discussion of physical conditions for nucleaton of clusters and or ultrafine particles on substrates.The physical picture of ultrafine particle growth are explained.,Conditions of epitaxial growth are also discussed.

The Magnetic Properties and Effective Magnetic Anisotropy of Fe-Ni Ultrafine Particles

Fe 100- x Ni x alloys of ultrafine particle with the average grain size of about 10 nm were synthesized by mechanically alloying process. The samples were investigated by X ray diffraction and measurements of the saturation magnetization and coercivity force. Both b.c.c and f.c.c phase exist within a wide range for Fe 100- x Ni x , while x ≤45. The effective magnetic anisotropy K e was measured by applying the law of approach to saturation. The value of K e decreases with an increase of Ni content. It is noticed that the strain anisotropy makes a large contribution to the magnetic anisotropy. The estimation of grain size leads to the determination of the single domain critical size and domain wall energy. The exchange stiffness and exchange integral deduced from the relationship between the effective magnetic anisotropy and domain wall energy are in agreement with that calculated by other methods.

Effect of Ultrafine Particles on Flow Field and Transport Properties near the Interface Around a Moving Bubble

Laser Doppler Anemometer has been used to measure the flow field characteristics near the interface around a moving bubble in the presence of ultrafine particles. In order to model a moving bubble, the bubble was fixed into the counter flow liquid by a metal mesh. Experimental materials are air and water, and the particles are complex oxidate powder. Experiments were carried out under the operating conditions: the liquid flow velocity u 0 is 12.6 cm/s, the equivalent diameter d e is 0.6 cm, the mass concentration of particle is 0.2 0 0 ,the average particle diameter is about 10 nm and the density is 2 g/cm 3. The velocity profiles of both frontal and tail vortex areas were measured respectively. The experimental results show that the velocity fields are obviously changed in the existence of particles. In the frontal area of the bubble, both tangential and normal velocities decrease due to the presence of particles, but in tail vortex area, the tangential velocities increase remarkably, and normal velocities rise gradually from the center towards the fringe in the opposite tendency to that of no particles. The influences of flow field change in the presence of particles on gas liquid mass transfer are analyzed and discussed.

Studies of Optical Nonlinearity Behaviors of Ultrafine PbS Particles in Perfluorocarboxylated Cation-exchanged Films

Ultrafine PbS particles with different sizes have been prepared in perfluorocarboxylated cation-exchanged films. The variation of PbS particle size was clarified by absorption spectra and TEM graphs. Time-resolved optical Kerr effects were measured by femtosecond pump-probe techniques. Optical Kerr effect response time was estimated to be less than 165 fs. A third-order optical nonlinearity of χ(3)10-12 esu for PbS particles was obtained and it was found that it increases with the decrease of particle sizes, showing the influence of quantum confined effect on optical nonlinear behaviour of ultrafine particles.