Influence of Recycled Concrete Fine Powder on Durability of Cement Mortar

In this paper,the durability of cement mortar prepared with a recycled-concrete fine powder(RFP)was examined;including the analysis of a variety of aspects,such as the carbonization,sulfate attack and chloride ion erosion resistance.The results indicate that the influence of RFP on these three aspects is different.The carbonization depth after 30 days and the chloride diffusion coefficient of mortar containing 10%RFP decreased by 13.3%and 28.19%.With a further increase in the RFP content,interconnected pores formed between the RFP particles,leading to an acceleration of the penetration rate of CO_(2)and Cl^(−).When the RFP content was less than 50%,the corrosion resistance coefficient of the compressive strength of the mortar was 0.84-1.05 after 90 days of sulfate attack.But the expansion and cracking of the mortar was effectively alleviated due to decrease of the gypsum production.Scanning electron microscope(SEM)analysis has confirmed that 10%RFP contributes to the formation of a dense microstructure in the cement mortar.

Experimental investigation on micro-dynamic behavior of gas explosion suppression with SiO_2 fine powders

To study the effect of inert dust on gas explosion suppression mechanism,SiO_2 fine powders were sprayed to suppress premixed CH_4-Air gas explosion in a 20 L spherical experimental system.In the experiment,high speed schlieren image system was adopted to record explosion flame propagation behaviors,meanwhile,pressure transducers and ion current probes were used to clearly record the explosion flame dynamic characteristics.The experimental results show that the SiO_2 fine powders suppressed evidently the gas explosion flame,and reduced the peak value of pressure and flame speed by more than 40%.The ion current result shows that the SiO_2 super fine powders were easy to contact with and absorb free radicals near the combustion reaction region,which greatly reduced the combustion reaction intensity,and in turn influenced the flame propagation and pressure rising.

DYNAMIC RHEOLOGICAL BEHAVIOR OF POLYPROPYLENE FILLED WITH ULTRA-FINE POWDERED RUBBER PARTICLES

Dynamic rheological characteristics of polypropylene (PP) filled with ultra-fine full-vulcanized powdered rubber (UFPR) composed of styrene-butadiene copolymer were studied through dynamic rheological measurements on an Advanced Rheometric Expansion System (ARES). A specific viscoelastic phenomenon, i.e. 'the second plateau', appeared at low frequencies, and exhibits a certain dependence on the amount of rubber particles and the dispersion state in the matrix. This phenomenon is attributed to the formation of aggregation structure of rubber particles. The analyses of Cole-Cole diagrams of the dynamic viscoelastic functions suggest that the heterogeneity of the composites is enhanced on increasing both particle content and temperature.

AGGREGATE STRUCTURE OF FINE POWDER AND COMPACTION PROCESS

Compacting process of fine powder is greatly affected by the aggregate structure of particles. According to the experiment in which several kinds of silicon nitrides in different partical shape and size were compacted in uniaxialorientation, it is found that the volume compacting rate offorming body differs with the pressure. The aggregatestructure of each sample A, B or C was estimated by applying Cooper's equation to the analysis of the compacting process of each sample

Preparation of Strontium Bismuth Tantalum (SBT) Fine Powder by Sol-Gel Process Using Bismuth Subnitrate as Bismuth Source

Strontium bismuth tantalum (SBT) fine power was prepared by Sol-Gel method. Pentaethoxy tantalum, strontium acetate and bismuth subnitrate were used as raw materials, and were dissolved in proper order in ethylene glycol to form transparent sol. The mixed precursor was dried at 80℃ and annealed at 800℃ for 1 h. Crystallized nanometer sized SBT fine powder was obtained and characterized by XRD.

Three Techniques Used to Produce BaTiO₃Fine Powder

Homogeneous BaTiO3 fine powder has been synthesized at (80°C) by using three different chemical methods using the roots TiCl4, BaCl2 and NaOH or Oxalic acid. The resultant powders were characterized using x-ray diffraction (XRD) to estimate the crystal structure, lattice parameters and the crystallite size to investigate the favor method in producing BaTiO3 fine powder. The criteria that was dependent on considering the favor method that was given better results of XRD and demand a least time in preparation which tend to consume a lowest energy.

Crystal Structure of Ba_xSr_1-xTiO₃Fine Powder

Various compositions of the system BaxSr1-xTiO3 (BST) have been elaborated both as fine powders and ceramic monoliths, using the co-precipitation route within a warmed supersaturated solution of oxalic acid. The appropriate stoichiometry was determined from the mixtures of precisely titrated aqueous solutions of cations chlorides (SrCl2, BaCl2, and TiCl4). The reason of this process was to apply low sintering temperature in production of BST samples with ultra-fine powders. These powders primarily calcined at (850°C) for (5 hr) were used to elaborate ceramics after pellets sintering at (1200°C) during (8 hrs). Indeed, XRD patterns were confirmed that the samples are a pure phase and a perovskite cubic structural type at (x = 0, 0.5, 0.6). Whereas, (x = 0.7, 0.8, 0.9, 1) showed a tetragonal phase. There is agreement between the FTIR and XRD analysis, by the relation of the wave vector (K) and lattice constant. It was deduced a stimulated relation between (x) and (K). The results of TEM, they were clear that the lowest particle sizes investigated of BST powders nearly (36 - 50 nm).

Low-velocity pneumatic conveying in horizontal pipe for coarse particles and fine powders

First, the characteristics of low-velocity conveying of particles having different hardness are experimentally investigated in a horizontal pipeline in terms of flow pattern and pressure drop to show that the slug flow can be classified into two types depending on the settling of particles along the pipeline, and the period is small for slug flow without the settled layer, which is called solitary slug flow. The pressure drop for soft particles is shown to be larger than that for hard particles. Then, experimental results are presented on horizontal fluidized-bed conveying of fine powders to show that air release from the top surface of the conveying channel is an imnortant factor for high mass flow rate of particles.

FLUIDIZATION OF FINE POWDERS IN FLUIDIZED BEDS WITH AN UPWARD OR A DOWNWARD AIR JET

The hydrodynamic behavior of fine powders in jet-fluidized beds was studiednumerically and experimentally. The starting point of numerical simulation was the generalizedNavier-Stokes (N-S) equations for the gas and solids phases. The κ-ε turbulence model was used forhigh-speed gas jets in fluidized beds. Computation shows that a suitable turbulence model isnecessary to obtain agreement between the simulation and literature experimental data for ahigh-speed gas jet. The model was applied to simulating the fluidization of fine powders influidized beds with an upward or a downward air jet. An empirical cohesion model was obtained bycorrelating the cohesive force between fine particles using a cohetester. The cohesion model wasembedded into the two-fluid model to simulate the fluidization of fine powders in two-dimensional(2-D) beds. To study the fluidization behavior of fine and cohesive powders with a downward jet,experiments were performed in a 2-D bed. Agreement between the computed time-averaged porosity andmeasured data was obtained. With an upward jet in the bed center, the measured and computedporosities show a dilute central core, especially at very high jet velocities. Based on ourexperiments and computations, a downward jet located inside the bed is recommended to achieve bettermixing and contacting of gas and solids.

Optimal Conditions for Preparing Ultra-Fine CeO_2 Powders in A Submerged Circulative Impinging Stream Reactor

Cerium carbonate powders were produced in a submerged circulation impinging stream reactor （SCISR） from Ce（NO3）3· 6H2O. NH4HCO3 was used as a precipitant in the reaction. Cerium carbonate powders were roasted to produce ultra-fine cerium dioxide （CeO2） powders. The optimal conditions of such production process were obtained by orthogonal and one-factor experiments. The results showed that ultra-fine and narrowly distributed cerium carbonate powders were produced under the optimal flowing conditions. The concentrations of Ce（NO3）3 and NH4HCO3 solutions were 02,5 and 0.3 mol · L^-1, respectively. The concentration of PEG4000 added in these two solutions was 4 g · L^-1. The stirring ratio, reaction temperature, feeding time, solution pH, reaction time and digestion time were 900 r · min^- 1,80 ℃, 20 min, 5 - 6, 5 min and 1 h, respectively. The final product, CeO2 powders, was obtained by roasting the produced cerium carbonate in air for 3 h at 500 ℃. The finally produced CeO2 powders were torispherical particles with a narrow size distribution of 0.8 -2.5 μm. The crystal structure of CeO2 powders belonged to cubic crystal system and its space point 5 group was OH^5-FM3M. Under optimal conditions, powders produced by SCISR were finer and more narrowly distributed than that by Stirred Tank Reactor （STR）.

An investigation into flow mode transition and pressure fluctuations for fluidized dense-phase pneumatic conveying of fine powders

This paper presents the results of an ongoing investigation into the fluctuations of pressure signals due to solids-gas flows for dense-phase pneumatic conveying of fine powders. Pressure signals were obtained from pressure transducers installed along different locations of a pipeline for the fluidized dense-phase pneumatic conveying of fly ash （median particle diameter 30μm; particle density 2300 kg/m^3; loose- poured bulk density 700 kg/m^3） and white powder （median particle diameter 55 p.m; particle density 1600 kg/m^3 ; loose-poured bulk density 620 kg/m^3） from dilute to fluidized dense-phase. Standard deviation and Shannon entropy were employed to investigate the pressure signal fluctuations. It was found that there is an increase in the values of Shannon entropy and standard deviation for both of the prod- ucts along the flow direction through the straight pipe sections. However, both the Shannon entropy and standard deviation values tend to decrease after the flow through bend（s）, This result could be attributed to the deceleration of particles while flowing through the bends, resulting in dampened particle fluctua- tion and turbulence. Lower values of Shannon entropy in the early parts of the pipeline could be due to the non-suspension nature of flow （dense-phase）, i.e., there is a higher probability that the particles are concentrated toward the bottom of pipe, compared with dilute-phase or suspension flow （high velocity）, where the particles could be expected to be distributed homogenously throughout the pipe bore （as the flow is in suspension）. Changes in straight-pipe pneumatic conveying characteristics along the flow direction also indicate a change in the flow regime along the flow.

Ultrasound-assisted microfeeding of fine powders

Ultrasonic microfeeding of powders is a new and promising method for use in solid freeforming and pharmaceutical dosing. In this work, computer-controlled microfeeding systems using ultrasonic vibration of a capillary were built. A wide range of controlled, stable rates of flow and switching control were achieved in the acoustic vibration system and uniform powder doses were obtained in the ultrasonic system. Experimental results show that nozzle diameter, transmission fluid depth, waveform, voltage amplitude, frequency and oscillation duration all influence the dose mass. Among these factors, nozzle diameter, voltage amplitude and oscillation duration can be best used to control the dose mass. An artificial neural network （ANN） technique was applied to predict the dose mass. Based on these research results, four types of microfeeding were proposed.

IMPROVEMENT OF FLUIDIZABILITY OF FINE POWDERS--A COMPUTER STUDY

Simulations of the gas fluidization of a cohesive powder were performed usingthe Stokesian Dynamics method and an agglomeration-deagglomeration model to investigate methods ofimproving the fluidizability of fine powders. Three techniques (a) high gas velocity (b)vibration-assisted fluidization and (c) tapered fluidizer were used in the simulations whichprovided detailed information on the bed microscopy such as the motion of 100 particles in afluidizing vessel along with the formation and destruction of cohesive bonds during collisions.While all three techniques were found to effectively improve the fluidizability of a stronglycohesive powder, we suggest a combination of high velocity fluidization assisted by externalvibration of the fluidized bed to minimize entrainment of particles.

Flow properties of fine powders in powder coating

Three types of nanoparticles and their combinations were blended into a fine powder, which has been used in the powder coating industry. To study their effects on flow properties, the modified powder samples were characterized using a variety of techniques that tested the powder under different powder states ranging from dynamic to static. It was found that all three nanoparticles improved the flow properties of the powder to some degree, though the amounts of the nanoparticles needed were different depending on their physical properties. Secondly, inconsistency among these powder characterization techniques was also found. This is attributed to the different states of the powder samples during a measurement including dynamic, dynamic-static and static states. It was confirmed that characterization techniques which test the flow properties of a powder under all three states are needed to fully describe the flow properties of the powder. Finally, the effects of combinations of nanoparticles were explored, and it was found that combinations of nanoparticles can intensify, weaken or combine the effects of their component nanoparticles. The effects of nanoparticle combinations are not a simple summation of the effects of their comnonent nanoparticles.

Preparation and properties of Nd:YAG ultra-fine powders

Ultra-fine Nd：YAG powders with different doping concentrations were synthesized by sol-gel combustion method. The pure Nd：YAG could be prepared at the low temperature of 900℃. Ethanol could improve the dispersity of powders, and the average size of the ultra-fine powders was around 250 nm. The reflection spectrum showed that there were several apparent characteristic absorption peaks and the intensity of these peaks enhanced with the increasing concentration of Nd^3＋. The luminescence spectrum, which was excited by 808 nm wavelength, exhibited several obvious emission bands in the range of 900-1150 nm. The emission intensity of Nd：YAG powders increased until the Nd content was above 3 mol.% due to the fluorescent quenching effect.

Hydrogen Reduction:A Novel Method of Synthesizing Ultra-fine Chromic Oxide Powder

The ultra-fine chromic oxide powder was prepared by a novel gas-solid reduction reaction.Na2CrO4 was firstly reduced with hydrogen at 400-600 ℃.The obtained reduction products,mainly the mixture of NaCrO2 and sodium hydroxide（NaOH）,were converted into chromic oxide through hydrolysis followed by calcination.The obtained chromic oxide product was characterized by powder X-ray diffraction（XRD） and SEM.The results show that the hydrolysis process of sodium chromite is the key step and lower reduction temperature helps intensify the hydrolysis process.

Effects of Curing Systems on Properties of High Volume Fine Mineral Powder RPC and Appearance of Hydrates

The effects of different curing systems on the properties of high volume fine mineral powder RPC （reactive powder concrete） and the appearances of hydrates were studied. The experimental results show that dry-heating curing promotes the development of pozzolanic reactivity of fine mineral powder; due to low cement content, 0.20 water-bind ratio and high reactive fine mineral powder content, the strength of RPC increases by around 200% after steam curing and subsequent dry-heating curing. Scanning electron microscopy and energy spectrum diagram showed that： after the high volume fine mineral powder RPC with 0.16 water-bind ratio underwent steam curing and dry-heating curing, there was no significant change in the appearance of hydrates; after the RPC with 0.20 water-bind ratio, the cement content of 150 kg/m3 and more steel slag powder underwent dry-heating curing, there was a certain change in the appearance of C-S-H, the structure of gel was more compact and was uniformly distributed, and the Ca/Si of C-S-H gel decreased from 1.41 to around 1.20.

Influence of MnO_2 Mineralizer on the Crystal Structure,Properties of SiC Kiln Furniture Bonded with Fine Silicon Powder

The properties of SiC kiln furniture bonded with fine silicon powderare related to the bonder’s crystal structure. At high temperature, it will crystallize ina-cristobalite with great bulk effect. MnO2 mineralizer can make a-cristobalite convertto a-tridymite whose bulk effect is small. The crystal structure and its amount were investigated with XRD technique. The influence of different amounts of MnO2 on thecrystal structure and polycrystal transformation, and that of crystal structure on theproperties of kiln furniture were studied. The best proportion of MnO2 added was determined to be 2.0%.

Preparation of Ultrafine Tungsten Powder by Sol-Gel Method

Sol-gel method was employed for the preparation of nanoscale tungsten powder. The effects of different preparation conditions on particle size were discussed and the optimum preparation condition was found. The products were characterized by X-ray diffraction, scan electron microscopy and so on. The results show that the intermediate is monoclinic WO3, its particle shape is approximately spherical, and the particle size distribution is narrow. The average particle size is about 60 nm. After deoxidization, WO3 turns into cubic tungsten powder with small particle size （average particle size about 120 nm） and narrow size distribution.

Strengthening of HT250 by modified ultra-fine ceramic powders

In this study, three kinds of modified ultra-fine ceramic powders marked A, B and C, which were prepared by each of three different modifiers mixing with a commercial SiC, were added to HT250 cast iron, respectively, and the effects of the modified ultra-fine ceramic powders on microstructure, mechanical properties and wear resistance were studied. Metallographic examination, tensile test, scanning electron microscopy, and three-dimensional surface topography were applied to analyze and compare the samples containing modified powder with the original samples. The results showed that the most obvious modification effect among the powders was seen in the sample containing powder A, with the graphite and eutectic cells being refined, the tensile strength being increased by 36.9%, and the wear resistance being improved by 45.5% and 47.2% under loads of 150 N and 300 N, respectively. The improvements of mechanical properties and wear resistance in the HT250 cast iron with the modified ultra-fine ceramic powders were attributed to the synergistic effect of the grain refinement with the powder acting as a hard particle phase and the lubrication by the graphite.