222 research outputs found
INVESTIGATION OF OFF-STATE VISCOSITY OF MAGNETORHEOLOGICAL (MR) FLUIDS
No full textBu çalışmada silikon yağ ve demir (Fe) bazlı manyetoreolojik (MR) akışkanlarının kapalı durum (off-state) viskozite özellikleri incelenmiştir.Farklı oranlardaki manyetik faz miktarı (hacmen %5, 10, 20, 30 ve 40) ile hazırlanan MR akışkanlarının rölatif viskozitesinin (ηrel)– manyetik faz miktarına (φ) olan ilişkisi deneysel olarak tespit edilmiştir. Elde edilen veriler Mooney ve Krieger-Dougherty modelleriylekarşılaştırılmıştır. Deneysel sonuçlar MR akışkanın viskozitesinin manyetik faz miktarı ile önemli ölçüde arttığını göstermiştir. Ayrıca viskoziteprofilleri Mooney modeli ile uyumlu bulunmuştur.In this study the off-state viscosity characteristics of silicone oil and iron (Fe) based magnetorheological (MR) fluids were investigated. The
relationship between relative viscosity (ηrel) and the amount of magnetic phase (φ) of MR fluids that were prepared with various concentrations
of magnetic phase (5, 10, 20, 30, 40 vol%) was determined experimentally. The data obtained from experimental study were compared
with Mooney and Krieger-Dougherty models. The experimental results showed that the viscosity had a shear thinning behavior and it increased
significantly with increasing magnetic phase. Besides, the viscosity profile was found to be in good agreement with Mooney model
Experimental Studies on Magnetorheological Fluids
No full textSmart materials are defined as the materials having properties that can be tuned or altered under externally applied fields. These materials
are usually polycrystalline or single crystal in their solid state. These smart materials exhibit properties such as ferroelectricity, pyroelectricity,
piezoelectricity, and magnetostriction. Another class of smart materials is known as the “field responsive fluids”. Magnetorheological (MR)
fluids, electrorheological (ER) fluids, ferrofluids, and some gels belong to this group. A common property of these fluids is that they are all
dispersions of particles in a carrier liquid and their properties are controlled by externally applied magnetic or electrical field.
MR fluid can be defined as ferromagnetic or ferrimagnetic particles dispersed in an organic or aqueous carrier liquid. MR fluid
has reversible and tunable ability to transform from liquid to viscoelastic solid in fractions of a millisecond when subjected to a
magnetic field. MR fluid has a consistency like paints in the “off-state” (B ¼ 0T) regime. In the “on-state” (B a 0T) regime the
magnetic particles line up, forming chain-like structure in the direction of the applied magnetic field in order to minimize the
magnetic dipole interactions between the particles. This chain alignment causes a considerable increase in the yield stress. This
increase is non-linear since the particles are ferro or ferrimagnetic. Depending on the composition, particle size, volume fraction,
magnetic saturation, and flux density, the yield stress can go up to 100 kPa (Genç and Phulé, 2002).
The ferromagnetic or ferrimagnetic magnetic phase is multi-domain with low coercivity and high saturation magnetization. The
diameters of the particles range from 0.01 to 20 mm. Due to its high saturation magnetization (Ms ¼ 203.7 emu/gr), carbonyl iron
(CI) produced by decomposition iron penta-carbonyl (Fe(CO)5), is the most commonly used magnetic material (Cullity and
Graham, 2010). Besides iron, cobalt, nickel, iron oxides (Fe3O4, Fe2O3), ferrites, and transition metal alloys are also used in the
synthesis of the MR fluid. Silicone oils, synthetic or semi-synthetic oils, lubricating oils and mineral oils, many other polar organic
liquid and water have all been reported to be used as carrier liquid (Genc and Derin, 2012).
Due to their field dependent rheology, MR fluid is used in automobile dampers, (Abu-Ein et al., 2010; Zeinali et al., 2016; Attia
et al., 2017), clutches (Hema Latha et al., 2017), and brakes (Kumbhar et al., 2015). They are also utilized in polishing devices (Jha
and Jain, 2009), loud speakers, vacuum sealing, cancer therapy (Liu et al., 2001).
Although iron having high saturation magnetization could be a good candidate for magnetic phase, its high density could be a
disadvantage. Mismatch between the density of the magnetic particles and carrier liquid causes sedimentation which deteriorates the MR
effect. To improve the sedimentation stability without sacrificing the MR effect is a challenge. One way to make a stable suspension is to
coat the magnetic particles with a surfactant in order to create steric stabilization (Phulé et al., 1999). The stability could also be
improved by using nanoparticles such as magnetite (Fe3O4), because thermodynamic forces can overcome the gravitation settling when
the particle size decreases to a critical value (Rosensweig, 2014). Microcrystalline cellulose, carbon nanotubes, silica, and graphene
oxide, nano-hollow Fe3O4 spheres are other additives that are investigated by various scientists (Ashtiani et al., 2015).
After the brief introduction of MR fluids, in the rest of the paper, the recent experimental studies of the MR fluids will be
discussed. These studies will include the improvement of MR effect and sedimentation stability, as well as the experimental
findings of the rheological and stability measurements
Experimental study on heat transfer of the magnetorheological fluids
No full textThermal conductivity of magnetorheological suspensions synthesized with iron powder and silicone oil is experimentally investigated for varying particle volume fractions (5, 20, and 40 vol%) of two different grades of iron (Fe) and magnetic field strengths. In order to determine the temperature range at which the thermal conductivity of MR fluids is more effective for different heat transfer applications, the experiments are done for three different temperature intervals in three different temperature ranges: from -20 to 0 degrees C, from 0 to 50 degrees C, and from 50 to 100 degrees C. In this study, ISO 8301 'Thermal insulation-determination of steady state thermal resistance and related properties-heat flow meter apparatus' is used. The thermal conductivity of the MR fluids shows an increase with increasing magnetic field and volume fraction in the temperature intervals from 0 to 50 degrees C and from 50 to 100 degrees C. In particular, there is a substantial enhancement in the thermal conductivity for the 50-100 degrees C temperature interval (enhancement ratio by almost 134% for 40SM at H = 150 G). However, the thermal conductivity shows a decrease in the lower temperature interval from 20 to 0 degrees C (a decrease by 42% for 40SM at 150 G), which could be due the effect of the thermal conductivity of silicone oil at lower temperatures. Although the heat transfer coefficient is higher for higher particle concentrations, the percentage increase is more pronounced for lower particle concentrations, especially in the 0 to 50 degrees C temperature interval (for the 40SM sample at 150 G 18% an enhancement for a 20 K temperature difference is observed, whereas for the 20% MR fluid sample, the enhancement is 34%)
Synthesis and rheology of ferrofluids: a review
No full textThere is no doubt about the potential technological significance of ferrofluids. The promising applications have been identified as dynamic sealing, heat dissipation, damping, and doping of technological materials. Ferrofluids are known as magnetic liquids that are colloidal suspensions of ultrafine, single domain magnetic particles in either aqueous or non-aqueous liquids. In this review article a general classification and the main properties of ferrofluids, description of their synthesis in terms of stability and rheology, and how it is understood in various parts of the science and technology are given. Then the structural changes and rheological properties of these smart fluids under an external stimulus together with a series of applications are presented
Field Responsive Fluids - a Review
No full textMagnetorheological (MR), Electrorheological (ER), and Ferrofluids are considered as a class of smart materials due to their novel behavior under an external stimulus such as a magnetic and electrical field. The behavior of these synthetic fluids offer techniques for achieving efficient heat and mass transfer, damping, drag reduction, wetting, fluidization, sealing, and more. Magnetorheological fluids are suspensions of non-colloidal, multi-domain and magnetically soft particles organic and aqueous liquids. Electrorheological fluids are suspensions of electrically polarizable particles dispersed in electrically insulating oil. Ferrofluids are known as magnetic liquids that are colloidal suspensions of ultrafine, single domain magnetic particles in either aqueous or non-aqueous liquids. In this review article a history of these fluids is given, together with a description of their synthesis in terms of stability and redisperibility and how it is understood in various parts of the science and technology. Then the structural changes and rheological properties of these smart fluids under an external stimulus together with a series of applications are presented
İttihât ve Terakkî Cemiyet
No full textFransız İhtilâlinden sonra ortaya çıkan ve 19. yy’da tüm dünyayı etkileyen “özgürlük, milliyet, bağımsızlık” gibi birçok fikir, kitleleri hareketlendirir ve devlet yönetimini, anayasal temellere oturtmagirişimleri dünya çapında başlar. Bu fikir akımlarının Osmanlı İmparatorluğu’na yayılmasında etkili olan ilk Osmanlı aydınları, Namık Kemal ve Şinasi’nin de aralarında olduğu Genç Osmanlılardır. Yeni (Genç) Osmanlılar’ın 1865’te İstanbul’da, 1867’de Paris’te bir cemiyet kurdukları görülür. II. Mahmud döneminde yapılan ıslahat faaliyetleri çerçevesinde kurulan müesseselerde yetişen devlet ve fikir adamları olan Genç Osmanlılar Batı’daki gelişmeler ve fikirlerden etkilenmelerine rağmen Osmanlı geleneksel değer yargılarını bir kenara bırakmamışlardır. Abdülaziz Döneminde faaliyetlerini yoğun olarak sürdüren Yeni Osmanlılar, 1867’de Bâb-ı Âli (Osmanlı Hükümeti) Baskınına kalkarlar, ancak baskın önceden önlenir ve kurucularının birçoğu
Avrupa’ya kaçar. II. Abdülhamid onları affedip ülkeye geri dönüşlerini sağlamışsa da 1877’den sonra grubu dağıtarak sürgüne göndermiştir
Production and microwave electromagnetic shielding effectiveness of polyaniline-La2Ti2O7:Er,Yb composites
No full textIn this research, La2Ti2O7 doped with erbium-ytterbium was produced by using solid state technique. A series of compounds with the chemical equation (La1-x-yREx-y)(2)Ti2O7 were doped with (Er3+, x = 0.025, 0.050) and (Yb3+ y = 0.02) rare earth ions prepared by conventional solid state reaction method at 1350 degrees C for 24 h. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were carried out for the structural analysis, which showed that second phase did not form in (La1-x-yREx-y)(2)Ti2O7. Additionally, the polyaniline- erbium, ytterbium doped La2Ti2O7 composites were fabricated via hot pressing using the compositions of (La0.955Yb0.02Er0.025)(2)Ti2O7, (La0.93Yb0.02Er0.05)(2)Ti2O7 and aniline. The weight ratios of erbium-ytterbium doped lanthanum titanate and aniline were 1:1 and 1:3 respectively, and epoxy resin was utilized to develop microwave shielding effectiveness composites. The microwave shielding effectiveness performances of polyaniline- La2Ti2O7: erbium-ytterbium composites were examined by shielding effect in 0-8 GHz using two-port vector network analyzer. A minimum of - 34.37 dB shielding effect performance was obtained in 6.27 GHz at the thickness of 2.0 mm. This shielding effect performance can be adjusted easily by managing the content of polyaniline in the composites for the needed frequency bands
Mechanical and electrical properties of Bi1.5-xLaxZn0.92Nb1.5O6.92 pyrochlore ceramics
No full textThe physical properties of Bi1.5-xLaxZn0.92Nb1.5O6.92 solid solutions are investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDS), and temperature dependent relative permittivity and electrical resistivity measurements. The La content which was varied from 0.10 to 0.60 is found to be solvable up to 0.21. Further increase in the amount of the La content caused the appearance of Bi0.4La0.6O1.5, LaNbO4, and ZnO minor phases in the pyrochlore matrix. While the lattice parameter and the theoretical, bulk and relative density are hardly affected by the increase in the La content, the strain, the dislocation density and the crystallite size are remarkably varied. The relative permittivity and temperature coefficient of relative permittivity are found to be sensitive to the La-Content. The electrical resistivity is observed to be temperature invariant below 390 K. It exhibits an insulator-semiconductor transition property at a critical temperature that increases with the increasing La content. Such observation is assigned to the increase in the dislocation density, which arises from the increment in the La content. The activation energies of the doped ceramics, which are determined from the electrical resistivity analysis are found to be similar to 1.12-1.00 eV
Evaluation of the Potential Use of Levan Polysaccharide in Paper Conservation
No full textConservation of paper-based materials, namely, manuscripts, includes repair of tears, gap filling, consolidation, and fixation, which requires the use of adhesives. The adhesive in use for these purposes should be compatible with the chemical and physical properties of paper and should present good aging characteristics. In this study, we conducted a set of experiments with paper samples on which fructan-based biopolymer Halomonas levan (Hlevan) was applied for the first time and compared with glucan-based adhesive starch. Adhesive-applied samples were initially prepared by the application of different historical recipes of sizing and ink. Then, they underwent accelerated thermal aging. Chemical and physical changes of paper samples (crystallinity, pH, and color) were analyzed. Finally, Principal Component Analysis was performed to identify dominating factors affecting sample behavior with applied adhesives. This study demonstrates the aging characteristics of Hlevan on cellulose-based materials. The results showed that there is a color shift from blue to yellow for all samples after aging, but it is more pronounced for some samples with Hlevan. In addition, Hlevan is slightly less acidic than starch in all cases and acted as a plasticizer for a specific kind of sizing material. The methodology of this research is also efficacious in terms of understanding the interaction of paper media with the adhesives and their effects on aging
- …
