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.

High-Volume Mineral Admixtures Cement: The Effects of Particle Size Distribution

The effects of high-volume slag-fly ash cement with different particle sizes on hydration degree,microstructure and mechanical properties were systematically studied,by means of laser particle size(DLS),X-ray diffraction (XRD),comprehensive thermal analysis (TG-DTA),scanning electron microscopy(SEM) and mechanical properties tests.The results show that suitable particle size distribution of cementitious material has significantly promoting effects on hydration reaction rate and mechanical properties.Compared with slag without further grinding,the slag after ball milling for 4 h has an obvious improvement in reactivity,which also provides a faster hydration rate and higher compressive strength for the cementitious material.When the slag milled for 1 and 4 h is mixed at a mass ratio of 2:1 (i e,slag with D_(50) of 7.4μm and average size of 9.9μm,and slag with D_(50) value of 2.6μm and average size of 5.3μm),and a certain amount of fly ash is added in,the most obvious improvement of compressive strength of cement is achieved.

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.

Specific Property of Ultrafine Particle Classification

In the process of ultrafine particle classification,the separation curve,which reflects the characteristics of separating process,is frequently influenced by the characteristics of separation flow field and operating parameters,etc.This paper introduces the concept of system deviation and deduces the calculating method of the separation curves.Meanwhile,it analyses the influences of classification flow field's specific properties and some operating parameters on the separation curves.The results show that,in the process of ultrafine particle classification,the local vortex in the separation field improves the separation efficiency to a certain degree,but the accuracy will decrease;the coacervation action of particles will seriously influence the classification accuracy.

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.

Particle Size Distribution,Powder Agglomerates and Their Effects on Sinterability of Ultrafine Alumina Powders

An intensive study of the particle size distribution of four commercial ultrafine alumina powders to obtain information about the powder agglomeration and relate them to the compactibility and the sinterability has been made.

Studies on the Preparation and Catalyticproperties of Fe-C-Mn Ultrafine particle Catalyst in F-T synthesis

Based on the Fe/C ultrafine particle obtained by means of laser pyrolysis method, a series of Fe-C-Mn ultrafine particle catalysts for F-T synthesis were prepared by adding certain amounts of Mn organic compounds to the Fe/C UFP. XRD and TEM tests for the obtained catalysts showed that the active phases, α-Fe, Fe3Cand (Fe,Mn)O. were directly obtained. and that the particle size was in the range of 2-4 nm. The catalysts so obtained have stable structure, long life, high activity and selectivity for light olefins, especially for propylene. Testing of the crystal structure in the process of the reaction demonstrated the carbonide mechanism of FT synthesis and the presence of α-Fe, FexCy and (Fe, Mn)O, thus supporting the belief that these are the active phases.

Preparation of Ultrafine Starch Particle and its Application in Paper Coating

Despite its biodegradability, adequate cohesive strength and comparatively low cost, the use of cooked starch as a paper coating binder is limited due to its high viscosity and serious negative impact on the gloss. Starch-based bio-latex with size in the nanometer or sub-micrometer range has been developed recently to overcome these shortcomings. In this study, ultrafine starch particle(UFSP) was prepared by mechanical milling using a DYNO mill in combination with light chemical pretreatment. Model coating colors containing different dosages of UFSP were applied to base paper and the properties of the coated papers were evaluated. The results showed that the UFSP was disc-shaped with a median particle diameter of 167 nm. Water retention capacity of the coating colors was improved considerably with the addition of UFSP, i.e., the water retention value decreased by nearly 40% when styrene-butadiene latex was replaced by UFSP at a dosage of 3 pph(per hundred parts of pigment). The high shear rate viscosities of the coating colors containing no more than 2 pph of USFP were similar to that of the control coating color at shear strain rate higher than 2000 s^(-1). The properties and performances of the coated papers were comparable to the control coated paper with single synthesized latex binder. The gloss and the print gloss of paper samples with or without USFP were 59.7% and 58.2%, 79.0% and 78.8%, respectively. Surface strength of paper samples with or without USFP were 0.96 and 0.90 m/s, respectively, while the ink absorptivity values were 34% and 33%. This study demonstrates a promising approach to obtain submicrometer sized starch for paper coating.

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.

A MSSBAUER SPECTROSCOPIC STUDY ON THE STRUCTURE OF Fe-M ULTRAFINE PARTICLE CATALYSTS (M=Mn, Zn, Mg)

The structure of Fe-M ultrafine particle catalysts was investigated by in situ Mossbauer spectroscopy. Emphasis has particularly been put on the effect of the second metal component. It was found that the incorporation of second metal component hinders the reduction and carburization of iron- containing phase in the presence of H2 and CO, and the degree of hindrance is in the order of Mg】Mn】Zn due to the interaction between iron and the second metal component. Consequently, the formation of light olefinic products is in the order of Fe- Mg】 Fe- Mn】 Fe- Zn catalysts consistent with the F-T synthesis performance.

PREPARATION OF METALLIC ULTRAFINE PARTICLE FILM

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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.