Papers by Keyword: Dispersion

Abstract: Yttria stabilized tetragonal zirconia (Y_0.08Zr_0.94O₂, YSZ) nanopowders were successfully synthesized by microwave solvothermal method (MSM). The synthesizing temperature, holding time and mineralizer concentration were optimized. The crystallization and particle distribution of as-prepared YSZ nanopowders were identified by DSC/TG, XRD, FESEM, TEM, FTIR, DLS, and BET. The dispersion of YSZ nanopowders dried by different methods and modified by polyethyleneimine (PEI) was analyzed and discussed. The results show that the PEI modified samples have the best dispersion, and the dispersion of freeze-dried samples is better than that of traditional dried ones. The particle size of the PEI modified samples calculated from the surface area determined by BET is 15.7 nm, which is consistent with that determined by TEM (16.5 nm), but slightly smaller than that calculated by the Scherrer formula according to XRD (22.3 nm). This may be attributed to the different testing principles in these methods.

Abstract: In this work, the characteristics of the cast structure formed under various conditions of slab casting and the micro-structure of hot-rolled sheets made from them are studied by a complex of chemical and metal-graphic analysis methods. This article presents the results on cast structure's dispersion studying of continuously cast slab that depend on the casting speed as well as hot rolled steel's the microstructure and mechanical properties produced from experimental slabs. A comprehensive study shows that continuously cast slab's solidification rate determines the dispersion of the dendritic structure and the microscopic inhomogeneity degree. It is established that the dendritic structure density is the degree indicator of cast steel’s microchemical homogeneity. In all structural zones and in the whole thickness of a continuous slab with a thickness of 105 mm, the dendritic structure density and the micro-chemical homogeneity increases with increasing crystallization rate. Using the methods of quantitative metallography, it is shown that with an increase in the crystallization rate, the resulting cast structure becomes significantly dispersed. The study revealed a pattern between the initial austenitic structure of a continuously cast slab obtained at different crystallization rates and the structure of hot-rolled rolled products obtained by direct rolling, when hot slabs are placed in a heating furnace before phase transformations γ→α in the steel structure.

Abstract: The loess produced in South Korea is an eco-friendly material with high gas adsorption performance. Korean loess, however, cannot be used as a structural material because it has a very low compressive strength compared to cement. However, even if it is recommended as an interior material, its large drying shrinkage during drying disturbs wet construction. Therefore, this study aimed to develop a method to reduce the amount of water added while maintaining the consistency required for the plastering work of Korean loess. The experimental results showed that the dispersion of clay particles was improved when Na+ and K+, which are monovalent cations, were added to the loess colloid; the reverse occurred, i.e., aggregation of clay particles, when Ca2+ and Mg2+, which are divalent cations, were added. In addition, the dispersion and aggregation of clay particles affect the consistency of loess. The dispersion allows the loess paste to obtain the required consistency using less water, but the aggregation may exhibit the opposite effect. Accordingly, based on the same consistency, the specimens with less water exhibited less drying shrinkage. The drying shrinkage decreased by 9.23% for the specimen fabricated with the 0.01 M Na2SiO3 aqueous solution.

Abstract: Free convective of nanofluid inside dispersive porous medium adjacent to a vertical plate under the effects of the zero mass nanoparticles flux condition and the thermal and solutal dispersions is studied. Buongiorno's model revised is used considering Darcy and non Darcy laminar flows, and isothermal or convective flux outer the wall. Dimensionless governing equations formulated using velocity, temperature, concentration and nanoparticle volume fraction have been solved by finite difference method that implements the 3-stage Lobatto collocation formula. The numerical data obtained with semi or full dispersions cases are compared to predictions made using the non dispersive porous medium. Taking into account the dispersions, the influence of the zero mass nanoparticles flux condition is examined to test the validity of the control active nanoparticle assumption. It is found mainly that the thermal transfers can reach more than 100% in connection with the case where of a semi-dispersion of the porous medium is applied. Realistic condition, i.e. zero mass flux should be addressed for the heat transfer rate rather than the mass transfer rate, discovered markedly different to the active condition. This signifies the importance of considering the zero nanoparticles mass flux and dispersions in the performance characterization of nanofluid flow in porous media.

Abstract: One of the critical physical and mechanical properties of metals and alloys is the suitability for abrasive machining. Machining by abrasive tools is the final operation that sets the desired macro-geometry parameters of processed blanks and microgeometry parameters of processed surfaces such as roughness and length of a bearing surface. Abrasive machining determines the most important physical and mechanical parameters of a blank surface layer, i.e. stresses, phase composition, structure. Machinability by abrasive tools depends on the machining performance affected both by the blank material properties and various processing factors. In our previous studies, we proved that during abrasive machining the metal microvolume affected by abrasive grains accumulates energy. This energy is used for metal dispersion and is converted into heat. According to the theoretical studies described herein, one may note the absence of a reliable and scientifically valid method as well as measuring instruments to determine the machinability of metals and alloys by abrasive tools. For this reason, we suggested a method simulating the effect the multiple abrasive grains produce in a grinding wheel, and enabling us to identify machinability of metals and alloys, select the most efficient abrasive materials for machining of the same, and form the basis for development of effective grinding operations.

Abstract: The effect of a magnetic source of variable strength has been studied on ferro-nanofluid incorporating nanoparticles of Cobalt ferrite (CoFe₂O₄) with water as a base fluid. Group method has been used to remodel the governing system to a system of ordinary differential equations. The recent study was motivated by inspecting the effect of four parameters including nanoparticles volume fraction, , Prandtl number, , magnetic field strength of the source,, and temperature difference ratio with respect to ambient temperature, . The results showed that the nanofluid velocity and shear stress increased as long as and increase. On the other hand, both are inversely related to the increment in Pr and Temperature distribution inside the boundary layer was noticed to increase due to the increment in Pr values and decrease due to the increment ratios. Contrarily, the heat flux throughout the boundary layer decreased and increased due to increasing respectively. Key words: Ferro-hydrodynamic; Nanofluids; Group Method

Abstract: The paper presents the results of studies of the effect of the concentration of binder components on the properties of cement alkaline stone. Formulations of clinker-free binders of alkaline activation with the level of filling the system of 20 and 40% have been developed, the properties of the cement paste of the binding binder "aspiration dust - mineral powder - liquid glass" have been studied, the dynamics of a set of strength indicators has been studied, both for bending and compressive forces. The received results allow to estimate uniqueness of properties of a binding binder "a mineral powder - Na₂SiO₃" and to create new materials on resource saving and energy saving technology. The results presented in this article were obtained within the framework of studies on the implementation of scientific project No. 05. 607.21.0320. "Development of technology for new building composites based on clinkerless cement of alkaline activation using substandard natural and secondary raw materials" supported by the Federal Target Program "Research and Development in Priority Areas of Development of the Scientific and Technological Complex of Russia for 2014-2020". The unique identifier for the agreement is RFMTFI60719X0320.

Abstract: Dispersion is one of the fate processes of oil spill. This research has been carried out on the numerical simulation of the dispersion of crude oil using the model obtained from the work of Hamam (1987). The model was solved with the explicit, implicit and Crank-Nicolson methods of solution of partial differentiation equations with the aid of MATLAB, and the concentration of the crude oil dispersed in water was obtained. The results obtained revealed that the three methods could be used to study the process because the profiles given by all of them were very similar. Also discovered from the investigations carried out was that the concentration of crude oil was decreasing with time for a particular spatial point while, for a particular time, it was increasing along the length of the water body. It was also discovered that experiments would be very necessary in order for the validation of the results obtained from the simulations.

Abstract: Nanocellulose (NC) has been successfully isolated from Oil Palm Empty Fruit Bunch (OPEFB) by using catalyst 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) through mediated oxidation process. For use as a reinforcing component in polymer bionanocomposites, NC has to be completely dried to avoid agglomeration in the non-polar solvent. In this research three types of approaches namely, oven drying (OD), freeze drying (FD) and solvent exchange (SE) were used to remove the water. Based on the dispersion stability results, the NC prepared from the OD technique gave longer stable suspension than that produced by FZ and SE. Besides, this method is also relatively simple and cost effective.

Abstract: At present, the products of polycarboxylate superplasticizer (PCE) mainly present liquid state. Compared with liquid PCEs, solid PCEs have not only high storage stability, but also high water-reducing rate. Based on acrylic acid (AA) and isobutenyl polyethylene glycol (IPEG) as the main materials, a series of solid PCEs were synthesized under anhydrous condition by employing ammonium persulfate (APS), benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN) and azobisvaleronitrile (ABVN) as initiators, and the effects of different initiators on the application performances of these solid PCEs were also investigated. The molecular characteristics of the synthesized products were determined by Infrared Spectroscopy (IR) and molecular weight measurements to confirm the expected structure. The fluidities, dispersions and micro-observations of cement pastes containing solid PCEs were evaluated. For both liquid PCE and PCE-ABVN, the average particle size reduced from 2373nm to 1147nm. The results showed that the paste fluidity, concrete slump and retentions were significantly enhanced when using ABVN as initiator, with the initial slump up to 225mm. This initiator had high initiating efficiency, exhibiting broad application prospects.