Papers by Keyword: Fluidity

Abstract: In this work the Aluminum-LECA composite foam was fabricated using the molten method. First, the LECA pellets were sieved in to three different sizes. The sieved LECA was placed on a regular and irregular form in to the mold cavity and then the molten aluminum was poured. The effect of LECA pellets as like as using vacuum system on filling the mold were also studied. Optical microscopy and scanning electron microscopy were used to study the pour morphology and the bonding of LECA and aluminum. The results show that using vacuum system can improve the fluidity of molten aluminum as like as the bounding with the LECA pellet and the aluminum matrix. It is also illustrated that with increase in the pellet size, the fluidity was increased. It was while that the orientation of LECA pellets has a significant influence on the fluidity. Keywords: Aluminum-LECA composite, fluidity, Vacuum system

Abstract: Additions of trace elements such as Phosphorus (P) and Germanium (Ge) are common practice to improve the oxidation resistance in Tin-Copper (Sn-Cu) wave solder systems, however, little insights are available regarding their combined role. In this article, the effect of trace P (<100ppm), in the presence of Ge (<100ppm), on the phase composition and microstructure of Sn-Cu-Ni wave solder dross is studied using various techniques including Synchrotron XRPD, SEM, FIB and TEM. We find that P additions, in the presence of Ge, result in the formations of SnO, SnO₂ and Ni₂SnP intermetallic in the dross whereas only SnO is present in the P-free equivalent. The crystal structure of Ni₂SnP is identified as orthorhombic with the space group Pnma. Based on the findings, it is evident that P not only influences the oxidation state of tin oxides but also reduces the concentration of effective Ni in the alloys via the formation of Ni₂SnP intermetallic.

Abstract: This review research aims to discuss the results obtained researches on cement containing pure cement, pulverised fly ash, and nanoparticles, in order for eliminating negative side effects underlie the substitution of by–products for pure Portland cement. Nanoparticles (NP) used in these researches are nanoTiO2, nanoSiO₂, nanoCaCO₃, fibers of carbon nano tube (CNT), nanolimestone (nanoCaCO₃), nanoZrO₂, nanoclays, and nanometakaolin (nMK) for improving properties of cement systems. Published manuscripts explains two methods regarding on the usage of nanoparticles for cement system: blending and ultrasonication for dispersion of nanoparticles. However, differences between blending and ultrasonication methods suggested by various researchers are also discussed. Experiments reported these papers include the water demand, the density, the setting–times, the heat of hydration, the fluidity, the compressive strength and the flexural strength. According to these results, nanoparticles increase the water demand and heat of hydration of cement; it decreases the density and fluidity for cement mortars, evidently. The most effective nanoparticles on early compressive and flexural strengths are fibers of carbon nano tube and nanoCaCO₃. These papers also point effects of these nanoparticles on the strength gain of cement. This review paper inform us until Effect of nanomaterial on water demand and density section in this Part I. Second part of this review paper will explain Hydration properties of Portland pulverised fly ash cement section, Effect of nanomaterial on setting–time section, Effect of nanomaterial on heat of hydration section, Strength gain mechanisms for hardened Portland pulverised fly ash cement paste and mortar section, Effect of nanomaterial on compressive strength section, Effect of nanomaterial on flexural strength (Bending) section, and Conclusion section.

Abstract: It is not easy to disperse metakaolin in the cement concrete uniformly. The reunite phenomenon caused by lamellar structure and fine particles can reduce the properties of concrete. The fluidity of mortar were studied by recombining polyethylene glycol (PEG), sodium methyl-dinaphthalene sulfonate (NNO) and hydroxyethyl cellulose (HEC) with the metakaolin slurry, and then the internal structural properties of the different cement-based materials were analysed. The experimental results showed that when the ratio of MK and H₂O was 35 : 65, the metakaolin slurry could reduce the adverse effect of metakaolin on the fluidity of mortar to a certain extent. The slurry prepared by P1N2H2, P2N1H2 and P2N1H1 composite dispersant dispersed more uniformly in the mortar than other groups. The hydration caused by these types of slurry during cement formation consumed Ca(OH)₂ crystals sufficiently, which led to generating more dense C-S-H gel structure in the final cement-based materials.

Abstract: In order to raise up the the rate of multipurpose utilization of rich-silicon iron ore tailing (IOTP for short) and the preparation of ultra-high performance concrete(UHPC for short), the influence rules and mechanism of rich-silicon iron ore tailing powder replacing fly ash in UHPC were studied, the influences of different specific surface area and dosage of IOTP replacing fly ash on its strength and liquidity were tested. Moreover, the pore structure and hydration products morphology of UHPC were tested by MIP and SEM methods, respectively. The results show that when fly ash replaced by IOTP, the liquidity of UHPC will be increased. When alternative content of IOTP is less than 10%, proper specific surface area of IOTP can improve the strength and pore structure, it can get the best result when the alternative content is 5% and the specific surface area is 588m2/kg. However, when alternative content of IOTP is 15% or more, all of these properties of UHPC become worse. It proves that IOTP can be used in the preparation of UHPC and improve the properties of UHPC.

Abstract: Stir casting is a near net shape process that can cast the composite components directly. Fluidity is an important factor for mold filling in casting process, but the fluidity of composite slurry is poor due to the addition of SiCp. In this research, SiCp/A357 composites with 20wt.% SiCp were manufactured by mechanical stir casting. Effect of mechanical stirring and air pressure on the fluidity of SiCp/A357 composites were investigated with eight thin flow channels. The fluidity was compared at different rotating speed and air pressure. The results showed that the fluidity increased with rotating speed, which was more obvious in semi-solid interval. It was noticed that the fluidity decreased with air pressure, the gas involving and the cooling speed were aggravated with air pressure increasing, which reduced the fluidity.

Abstract: To assure the quality and required workability of mortar or concrete, various types of superplasticizers are used. There are many factors affecting the performance of superplasticizers explicitly, type and dosage of the superplasticizers, type of cement, temperature and mixing procedure, as well as the addition times of the superplasticizers. Some researchers investigated the effect of delaying the addition time of superplasticizer to mortar or concrete, but there is not enough data about the effect of external temperature on performance of superplasticizers and consequent influences on fresh properties of mortar or concrete. In this research the effect of delaying the addition time of superplasticizers and influence of external temperature, namely, heat stimulation of superplasticizers, on fluidity, fresh density and air content of fresh cement mortar was investigated. Two types of Precast and Ready-Mix of Polycarboxylic acid-based ether superplasticizers with Ordinary Portland Cement was used. Delaying the addition time of superplasticizers enhanced the fluidity, slightly decreased the fresh density and increased the air content of mortar in comparison with simultaneous addition time with both heated and non-heated Superplasticizers.

Abstract: This study investigated the influence of nanokaolin content on the behavior of cement mortar at various curing ages. The fluidity, chloride permeability, bending and compressive strength of cement mortar with various nanokaolin additives were examined. The addition of 0%, 1%, 2%, 3%, 4%, 5% and 6% nanokaolin were taken into consideration. The results showed that the addition of nanokaolin decreases the fluidity of cement mortar, and the fluidity the cement mortar decreases with the increase of nanokaolin additives. It is obtained that the addition of nanokaolin increases both the bending and compressive strength of cement mortar, and with the increase of nanokaolin additives, the bending and compressive strength of cement mortar increase. The addition of 4% nanokaolin can result in a significant low chloride permeability of cement mortar among the seven dosages. The chloride diffusion coefficient of the mortar with the addition of 4% nanokaolin was decreased by 18.93%, 12.68% and 31.05% at 7, 14 and 28 curing days, respectively.

Abstract: The current paper experimentally investigated the effect of different kinds re-dispersible polymer powers (RPP) on cement-based self-leveling mortars. The construction operation of mortar and its mechanical property was tested in accordance with the standard JC/T 981-2005. Besides, the micro-structure surface of self-leveling mortar was characterized by means of SEM to reflect the microscopic mechanism of the performance. The results showed the dispersible polymer powders could significantly improve performance of fluidity, adhesion property and abrasion resistance on cement-based self-leveling mortar; Meanwhile, there is no bad impact on its compressive strength and flexural strength. This study has guiding significance for the construction and application of cement based self-leveling mortar.

Abstract: The effect of melt superheat and oxide inclusions on the fluidity of a commercial A356 alloy has been investigated. Fluidity measurements have been performed by means of Archimedean spiral in sand moulds. The specific testing method and the experimental apparatus show a good reproducibility. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes and the amount of defects occurring at the tip of the spirals. The results reveal that oxide films increase the variability in the fluidity results obtained at the same apparent experimental conditions. A long permanence in the holding furnace and the introduction of some turbulence during sampling increase the oxide formation and entrapment in the molten bath, thus decreasing the repeatability of the fluidity results. The fluidity increases linearly with superheat and it extrapolates to zero at the temperature corresponding to a fraction solid of about 23%. The initial Ti content in the alloy produces an independent crystallization during freezing of the fluidity spirals.