Papers by Keyword: Mixing

Abstract: This paper demonstrates the feasibility of ensuring radiation safety of solid substances that comprise environmental objects and have surfaces contaminated with radioactive substances. The identified problem is solved by utilizing the natural property of anti-radiation self-protection. To reintroduce structures and buildings contaminated with radionuclides into economic circulation, it is recommended to dismantle them, grind the materials, and mix the resulting mass. The proposed method is made possible by transforming the surface contamination of these objects into a uniform distribution of radionuclides throughout the mass of the contaminated substance. This uniform distribution will remain consistent in products made from the received raw materials. By implementing this approach, it is feasible to reintroduce large volumes of radioactively contaminated materials into the economic cycle and dispose of them in contaminated areas.

Abstract: In this study, the blast furnace slag (BFS) was used to replace 30% cement (weight replacement), freshwater, and saltwater (half, same, and twice the concentration of seawater) used to produce the cement mortar. Then, these four types of mixing water were used to cure the mortar till the test ages (7 days and 28 days). The test results show that, at 7 days, the compressive strength of saltwater (half concentration) mixing and curing mortar incorporating BFS is the highest (78 MPa). The freshwater mixing and curing control mortar has the lowest compressive strength (36.2 MPa). At 28 days, the compressive strength of saltwater (twice concentration) mixing and saltwater (half concentration) curing mortar incorporating BFS is the highest (90.2MPa). The strength of the control mortar is 53.0MPa under the same curing water, which is still relatively low. It can be seen from this that the mixing and curing of saltwater are beneficial to improving the compressive strength of cement mortar. The freshwater mixing and saltwater (twice concentration) curing cement mortar incorporating 30% BFS can have a higher strength at 28 days.

Abstract: For precise investigation of distribution for impurity or composition at SiO₂/SiC interface, dual-beam Time-of-flight Secondary ion mass spectrometry (TOF-SIMS) with low energy sputtering beam was available. In addition to the experimental profiles, simulation using MRI model, in which Mixing, Roughness and Information depth were employed as parameters, enabled to acquire a more authentic distribution at the SiO₂/SiC interface. Slight discrepancy on depth profiles between samples with different surface roughness was duplicated on the convoluted profiles in the simulation. Moreover, reconstructed profile of nitrogen indicated a real distribution with less impact of mixing and roughness, although that may contain uncertainty due to incompletion in the simulation model or variation of the distribution owing to detection species in the experiment. From the result of carbon profiles of both experimental and convoluted profiles, the relative discrepancy on the carbon distribution between samples was clarified, which suggested the possibility that a carbon thin layer at the SiO₂/SiC interface would be found in the future.

Abstract: This study investigates the effects of mixing condition on hardness, porosity, specific gravity, wear, and friction characteristics of automotive brake materials. In the experiment, mixing raw materials with three different conditions of impeller speed (3000, 4500, and 6000 rpm), mixing duration (up to 8 min) and mixture loading based on a mixer volume (35, 50 and 65 vol% ) were determined using the formulated mixture composition. Homogeneity in terms of density values including hardness, porosity, and specific gravity of the finished brake pads were determined. The surfaces and the distribution of friction material were studied using scanning electron microscopy (SEM). The correlation between various mixing conditions and physical and tribological properties of brake pads were discussed and reported.

Abstract: Mixing of nano-sized powders with soils (macro-sized powders) is a noteworthy issue for geotechnical projects. Thus, this study examined the horizontal ball mill mixing of nano-copper oxide with kaolinite. Ball milling parameters (rotation speed, weight ratio of balls to powder and milling time) of the planetary ball milling were optimized for proper mixing of nano-copper oxide and kaolinite powder. Results showed that increase in mixing time decreased the agglomeration of nano-copper powders and kaolinite and increased the homogeneity of nano-copper powder with kaolinite particles. The quality of mixing was assessed through intensity and scale of segregation using concentration data obtained through energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses. It was observed through these two tests that, increase in ball milling time after 6 hours resulted in grain size reduction. Field emission scanning electron microscopy analysis showed that nano-coppers were regularly found on the surface of kaolinite particles after 6 hrs. of horizontal milling at 4:1 ratio of balls to powder mixture. Furthermore, 24 hrs. mixing resulted in grinding of kaolinite particles and hence their size was reduced. Particle size analysis confirmed these results, as the highest size span value of 3.417 was observed after 6 hrs. milling with speed of 200 rpm.

Abstract: Nicrosil-nisil (NiCrSi-NiSi) thermocouples (Type N) have a high thermal EMF stability, radiation resistance, resistance to oxidation of the thermocouple wires and can be used as a universal means of measuring temperatures up to 1300 °C. However, when the traditional metallurgical method is used for the production of rod and wire materials of nicrosil and nisil from ingots of metals, it is difficult to ensure the homogeneity of the ingots and materials of the thermocouple. It is known that powder metallurgy methods can provide a greater homogeneity of the material compared to casting technology. The aim of this work was to study the possibility of using powder technology for the fabrication of rods of nicrosil and nisil thermocouple materials by extrusion and sintering of powders of source metals. Reduction in size and mixing of the raw powder components in a planetary ball mill was investigated. The regularities of pressing the prepared mixtures and microstructure of materials sintered from them were determined. Samples of nicrosil and nisil thermocouple materials in the form of cylindrical rods with a diameter of about 5 mm and a length of 200 mm with an uniform microstructure were also fabricated by extrusion of prepared mixtures followed by sintering. Experimentally determined specific differential thermal EMF of the thermocouple made from the sintered rods coincided with the theoretical value.

Abstract: This study focused on the mixing methods used in the manufacture of ultra-high molecular weight polyethylene (UHMWPE) reinforced by multi-walled carbon nanotubes (MWCNTs) and how these methods enhance the wear performance of the composite. Two mixing methods, ball milling and ultra-sonication, were used in this study, and the most effective forms of these mixing methods were analysed to allow an effective comparison. The performance of the mixing methods was evaluated through a comparison of wear volume loss, coefficient of friction, and hardness. The optimal power and mixing time for sonication in this study was determined and composites with 0.5% CNTs w/w concentration were conformed. It was evidenced that the mixing process influence the mechanical and wear performance of UHMWPE / MWCNTs composites and ultrasonication was identified as an effective mixing method that improves significantly the wear performance of the composite.

Abstract: This article deals with the ways of mixing method for concrete with extremely low water-cement ratio (w/c) typical for ultra-high performance concretes. For this purpose, the mixture with w/c ratio of 0.2 and amount 6% superplasticizers of cement weight was used. In total 6 various mixing methods was tested, which differed in application of superplasticizers, mixing order or mixing length. Workability, electricity consumption during mixing and compressive and flexural strength after 28 days were examined. The performed experiments showed that workability can be increased by, for example, separate doses of superplasticizers and water or other mixing methods. Strength of concrete was identical for all produced mixtures, even though the total mixing time was shortened in two cases.

Abstract: Wonorejo waters have a significant value, both economically and socially. One of ecosystem that have close relationships with Wonorejo waters is Estuary. Temperature and salinity have role in water circulation, where the water circulation have impact to some organism distribution and pollutant dispersion. The purpose of this study is to investigate the characteristic of temperature and salinity distribution in Wonorejo Estuary body’s water. Furthermore, it can be used for determining the type of Wonorejo Estuary. The observation has been done at Wonorejo Estuary in August 2015 to measure the vertical and horizontal temperature and salinity distribution. The measurement of temperature and salinity used Conductivity, Salinity, Temperature tool by YSI. The result show that commonly the temperature and salinity vertical profile are almost similar from surface layer until the bottom layer. But they have trend where the salinity increase, while the temperature decrease to the water depth. There is no thermocline layer due to the shallow water area, it is so from the upper layer until the bottom layer still influenced by dragforce and the vertical mixing between fresh water and sea water occurs. The horizontal temperature distribution in the open sea surface tend to zonation, which is not depend to longitudinal position. The salinity value in each depth are not change obviously indicate that there is a vertical well mixed between fresh water and sea water.

Abstract: This paper deals with a use of CFD modelling for optimization of supply of secondary combustion air in the two-chamber biomass boiler combusting very wet biomass (capacity ca. 200 kW). Objective of the analyse is to observe the impact of diameter of a secondary air supply pipe and air flow velocity on mixing of the secondary air with flue gas in the combustion chamber. The numerical model of the experimental boiler was build up for subsequent utilizing of CFD computation based on finite element method. The commercial code STAR-CD was used for carried out parametrical studies. Series of calculations were carried out for four different diameters of air distribution pipes and for 3 different air velocities in distribution orifice. Quality of air dispersion in flue gas flow was assessed in the vertical cross section lead in the end of the combustion chamber. The results of calculation were verified on the experimental installation of the boiler. Influence of secondary air mixing on emission production was measured and analysed. Emissions of pollutants for recommended air distribution comply with emission limits stipulated in the most stringent class 5 according to ČSN-EN 303-5 as well as with emission limits under Regulation No. 405/2012 Sb.