Papers by Keyword: Rheological Behavior

Abstract: This paper presents the theoretical analysis and experimental results concerning the rheological behavior and mix design of a 3d printable cement paste as matrix for printing concrete. From the point of view of classical rheology of disperse systems, the application of 3D printing technology in construction has been analyzed. The general scientific concept for optimization of admixtures for 3D printable materials has been developed in terms of viscosity, consistency, and parameters of flocculation and structural built-up. The technological tools to control rheological behavior of visco-plastic admixtures are identified in all stages of 3D printing such as mixing, pumping, extrusion, multilayer casting and structural built-up in the printing layers. The relevant considerations include the concentration, size, morphology, chemical and mineralogical composition, the physical and chemical activity of the solid phase’s surface, and the ionic composition, viscosity, and density of the liquid phase. The squeezing test is used in this paper as a rheological behaviour identification tool of cement-based materials in order to evaluate the extrudability and buildability. It is shown that these properties are significantly influenced by the mix proportions such as W/C-ratio, concentration of plasticizer additives and viscosity modifier additives as factors of changes in the concentration of the dispersed phase and properties of the dispersion liquid.

Abstract: The apparent viscosity and rheological behavior of nanoSiC_P/Al-5Cu composites were studied by using a high temperature coaxial rotating cylinder viscometer. The results show that mass fraction of nanoSiC_P is an important factor for apparent viscosity of the nanoSiC_P/Al-5Cu composites, and there is a great enhancement of apparent viscosity of the slurry with the increase of nanoSiC_p content. It can attribute to the viscous force between nanoSiC_p and matrix alloy melt above the liquidus. The increased amplitude of apparent viscosity in semi-solid state is far less than those in liquid state with the increase of mass fraction of nanoSiC_p. The apparent viscosities of the composites reinforced with 0.5%, 1%, 1.5% and 2% nanoSiC_p at 700°C were 24.78%, 95.25%, 160.29% and 228.62% higher than that of Al-5Cu alloy, respectively. Besides, the rheological model of nanoSiC_P/Al-5Cu composites was established based on the fitting curve, which can precisely describe the relationship between the apparent viscosity of nanocomposites slurry and nanoSiC_p mass fraction.

Abstract: Calcium aluminate cement (CAC) and hydratable alumina (HA) are the most widely used binders for refractory castables. Nevertheless, CAC as the binder for refractory castable generates some low melting point phases when coupled with SiO₂, which deteriorate the high temperature performance of refractory castables. Although hydratable alumina (HA) bonded castables overcome the drawbacks of CAC bonded ones, they demand a longer mixing time and higher water contents due to HA's high specific surface area, as well as increasing the shear stress and viscosity of HA bonded castables. Therefore, in this paper, CAC combined with HA was used as the binder for corundum- spinel castables to obtain better performance. Sodium tripolyphosphate (STPP), dispersing alumina (ADS) and polycarboxylate ether dispersant (FS60) were used as dispersants, and their effects on the rheological behaviors of CAC-HA bonded corundum-spinel castables suspensions had been investigated. According to the viscosity-shear rate and stress-shear rate curves of suspensions with different dispersants, it was suggested that STPP, ADS, FS60 were all helpful for rheological performance of suspensions. Suspensions achieved much better rheological behavior with 0.3 wt.% of STPP, 1.0wt.% of ADS and 0.1wt.% of FS60, respectively. Suspensions with ADS and FS60 presented to be pseudo plastic fluid, which was helpful for the installation process of CAC-HA bonded corundum-spinel castables. And FS60 could simultaneously impart electrostatic and steric stabilization to the given suspension. Considering the actual rheological performance of CAC-HA bonded corundum-spinel castables, FS60 was much better than ADS.

Abstract: The abundancy of ball clay can be transform into more useful form. This study was conducted to investigate the effect of different amount of dispersant on ceramic system. Ball clay from Kampung Dengir, Besut, Terengganu was used as starting powder while sodium silicate was used as dispersant to produce good flow ability, minimum viscosity and controllable ceramic slurry. Ceramic slurry was prepared by adding additives such as binder, flux, filler and dispersant, casted onto POP mould to obtain ceramic body. Ceramic then cut into test pieces (8cm x 2cm) and mixed for 2 h and aged for 2 days before dried at 70 °C overnight and sintered at temperature of 800-1200 °C in furnace for 2 h with heating rate 5 °C/min. Slurries also tested for rheological properties using rheometer (brand Thermo Haake). Viscosity and shear stress were measured to investigate the rhoelogical behaviour of slip with different amount of dispersant (0.03 mL to 0.06 mL/200 mL of sample). Characterization of raw samples has been done using X-ray diffractometer (XRD) showing the presence of kaolinite and quartz. Effect of dispersant on rheological behavior, rate of shrinkage, water absorption, porosity and density were investigated It was found that increase in amount of dispersant added exhibit the best rheological behavior, and 0.05 mL dispersant was the optimum amount in term of rate of shrinkage, water absorption, porosity and density. As a conclusion, 0.05 mL was the optimum dispersant which gives best rheological behavior and almost fault-free ceramic bodies

Abstract: The apparent viscosities of the semi-solid SiCp/A357 composites with 0vol.%, 10vol.% and 20vol.% SiC particles manufactured by stir casting were investigated using a Couette type viscometer, and the composite fluidity was examined with a test casting. The results showed that, the viscosities of the semi-solid SiCp/A357 composites decreased with an increase in shear rate, but increased with the increasing of solid fraction, and apparent viscosity of 10vol.% SiCp/A357 composite was the lower than that of 20vol.% SiCp/A357 composite at the same solid fraction; and the composite fluidity results were in a good agreement with the viscosity ones.

Abstract: Fiber reinforced polymer composites are common materials used to produce parts for structural applications. The attractiveness of these materials is a result of the combined advantages of the fiber reinforcing effect and the high production rates achievable by technologies such as injection molding. The fiber orientation in short fiber reinforced thermoplastics depends on injection moulding technology parameters. The aim of this paper is to propose possibilities for comparing fiber orientation of the real sample and the result from simulation software.

Abstract: A novel rheological measuring apparatus was designed, which introduced an additional sinusoidal vibration in parallel on the extruding direction of polymer melt in this paper. Melt rheology of polypropylene filled CaCO₃ particles in various amounts of filler (i.e. with 3 and 20 wt%) during capillary melt-extrusion were investigated respectively. The effects of vibration parameters on rheological behaviors were studied. Compared with the steady extrusion, the apparent viscosity of filled system decreased remarkably with the increase of vibration frequency and amplitude. The apparent viscosity reached to the minimum value as vibration frequency was about 8 Hz. When the filled percentage of CaCO₃ was low, the response of apparent viscosity will be more distinct with the increasing vibration parameters.

Abstract: This paper proposes and tests new Fe-2.6wt%C-2.8wt%Cr-1.8wt%Si specially designed for thixoforming processing. Samples were heated to the semisolid state at 1195 °C and held at this temperature for 0, 30, 60 and 90s, and then subjected to compression tests. Two-platen compression tests were carried out in order to determine the semisolid behavior. The holding time in the semisolid range simulates the industrial heating process that is time-controlled rather than temperature controlled. Morphological characterization pointed to an as cast microstructure composed by pearlite matrix plus chromium based carbides and nodular graphite and heated conditions composed by pearlitic matrix plus chromium based carbides without free graphite. The semisolid behavior indicated that at 1195 °C the thixoforming procedure requires a maximum stress of 2.5 MPa and maximum apparent viscosity of 4.8x10⁵ Pa.s for the 0s soaking time condition, 2.0 MPa and 4.6x10⁵ Pa.s for 30 s, 1.7 MPa and 3.7x10⁵ Pa.s for 60 s and 1.2MPa and 3.3x10⁵ Pa.s for 90 s of holding time, best condition achieved.

Abstract: Using SiC particles and powder, the modified Si and α-Si₃N₄ powder as the main raw material, Si₃N₄-SiC composite materials have been fabricated by gelcasting. The Si₃N₄-SiC suspension with 75vol% (volume fraction) solid loading exhibits shear thinning rheological behavior under a shear rate from 10 to 160s^-1, which meets the requirement of the gelcasting process. The bulk density of the green bodies after solidification is 2.57 g·cm^-3 and the flexural strength 16 MPa, the green bodies have a dense and uniform structure. The bulk density and flexural strength of the Si₃N₄-SiC composites after nitriding are 2.67g·cm^-3 and 48 MPa respectively; the strength is higher than that of other industrial products without gelcasting. Well-developed intertwined fibrous Si₃N₄ crystals grow on the surface of the SiC particles to form a tight microstructure in the Si₃N₄-SiC composites after firing.

Abstract: Microencapsulated phase change materials (MPCM) slurries with high heat transfer and great latent heat can serve as both the heat transfer fluids and energy storage medias. Studies showed that the effective specific heat and heat transfer rate increased by 28.1% and 23.6% respectively as using MPCM slurries. The rheological behavior of slurries do not change as adding MPCM with low concentration, can be characterized by Newtonian fluid feature with mass fraction <0.25. MPCM particles have flow drag reduction effect under turbulent situation, which was applied to building energy efficiency and refrigeration, obtained remarkable energy conservation effect.