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Irwan Nurdin - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation on thermal conductivity and viscosity of Maghemite (γ –Fe2O3) water-based nanofluids
IOP Conference Series: Materials Science and Engineering, 2018Co-Authors: Irwan Nurdin, M R Johan, Bee Chin AngAbstract:Thermal conductivity and kinematic viscosity of Maghemite nanofluids were experimentally investigated at a small volume fraction of Maghemite nanoparticles and temperatures. Maghemite nanofluids were prepared by suspending Maghemite nanoparticles in water as base fluids. Results show that the thermal conductivity of Maghemite nanofluids linearly increase with increasing particle volume fraction and temperature, while kinematic viscosity increase with increasing particle volume fraction and decrease with increasing temperature. The highest enhancement of thermal conductivity and kinematic viscosity are 18.84% and 13.66% respectively, at particle volume fraction 0.6% and temperature 35.
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The effect of particle volume fraction and temperature on the enhancement of thermal conductivity of Maghemite (γ–Fe2O3) water-based nanofluids
2017Co-Authors: Irwan Nurdin, SatrianandaAbstract:Thermal conductivity of Maghemite nanofluids were experimentally investigated at different Maghemite nanoparticles volume fraction and temperatures. Maghemite nanofluids were prepared by suspending Maghemite nanoparticles in water as base fluids. The thermal conductivity ratio of Maghemite nanofluids was linearly increase with increasing particle volume fraction and temperature. The highest enhancement of thermal conductivity is 42.5% which is obtained at particle volume fraction 2.5% and temperature 60 °C.
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Investigation on Electrical Conductivity Enhancement of Water Based Maghemite (γ-Fe 2 O 3 ) Nanofluids
International Journal of Materials Science and Applications, 2017Co-Authors: Irwan Nurdin, SatrianandaAbstract:The study of this research is to measure the electrical conductivity of Maghemite nanofluids. Maghemite nanofluids were prepared by dissolving Maghemite nanoparticles in water as base fluids. The investigation on electrical conductivity of Maghemite nanofluids have been performed at different particle volume fractions and temperatures. The electrical conductivity was measured by a 4-cell conductivity electrode meter. The electrical conductivity of Maghemite nanofluids was linearly increased as the particle volume fraction and temperature rises. The highest enhancement of electrical conductivity of Maghemite nanofluids due to the particle volume fraction and temperature are 160.49% and 22.55%, respectively. This condition obtained at a particle volume fraction of 2.5% and temperature 60°C. Significant effect of particle volume fraction and temperature were considered.
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Synthesis, characterization, and thermophysical properties of Maghemite (γ-Fe2O3) nanofluids with and without magnetic fields effect / Irwan Nurdin
2016Co-Authors: Irwan NurdinAbstract:Synthesis, characterization, and thermophysical properties of Maghemite nanofluids have been studied with and without magnetic fields effect. The objectives of study are to synthesize Maghemite nanoparticles and their characterization using various methods, to prepare stable Maghemite nanofluids, and measurement of thermophysical properties of Maghemite nanofluids with and without external magnetic fields effect. Maghemite nanoparticles were synthesized by chemical co-precipitation method with different concentrations of nitric acid. Maghemite nanofluids were then prepared and the stability of the nanofluids were characterized by zeta potential and dynamic light scattering at different pH and time of storage. Lastly, measurements of thermal conductivity, viscosity, and electrical conductivity of Maghemite nanofluids were taken at various particle volume fraction, temperatures, with and without strengths of magnetic fields. Results show that spherical shape of superparamagnetic Maghemite nanoparticles with good thermal and suspensions stability was successfully synthesized within the size range of 9.3 to 14.7 nm. The stability of Maghemite nanofluids show that the suspensions remain stable at acidic condition with zeta potential value of 44.6 mV at pH 3.6 and at basic condition with zeta potential -46.2 mV at pH 10.5. The isoelectric point of the Maghemite nanoparticles suspensions is obtained at pH 6.7. The Maghemite nanofluids remains stable after eight months of storage. The thermal conductivity of Maghemite nanofluids linearly increases with increasing of particle volume fraction, temperature, and magnetic fields strengths. The kinematic viscosity of Maghemite nanofluids increases with increasing of particle volume fraction and magnetic fields and decrease with increasing of temperature. Electrical conductivity of Maghemite nanofluids increases with increasing of particle volume fraction and temperature and no effect with magnetic fields.
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The Effect of Temperature on Synthesis and Stability of Superparamagnetic Maghemite Nanoparticles Suspension
Journal of Materials Science and Chemical Engineering, 2016Co-Authors: Irwan Nurdin, Ridwan, SatrianandaAbstract:Maghemite (γ-Fe2O3) nanoparticles have been synthesized using chemical co-precipitation at a different temperature. Characterizations of the sample were performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), alternating gradient magnetometry (AGM) and thermogravimetryanalysis (TGA). The stability of the Maghemite nanoparticles suspension was studied at different pH and time of storage by dynamic light scattering (DLS) and zeta potential measurements. The XRD patterns confirmed that the particles were Maghemite. TEM observation showed that the particles have spherical morphology with narrow particle size distribution. The particles showed superparamagnetic behavior with good thermal stability. The increasing of temperature in the synthesis of Maghemite nanoparticles produced smaller size particles, lower magnetization, better thermal stability and more stable Maghemite nanoparticle suspension.
Tianhu Chen - One of the best experts on this subject based on the ideXlab platform.
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reduction and transformation of nanomagnetite and nanoMaghemite by a sulfate reducing bacterium
Geochimica et Cosmochimica Acta, 2019Co-Authors: Yuefei Zhou, Qiaoqin Xie, Yang Gao, Jin Wang, Zhengbo Yue, Lin Wei, Yang Yang, Tianhu ChenAbstract:Abstract Magnetite and Maghemite are important components of iron oxides that determine the magnetic properties of rocks, soils, and sediments, and are also materials with broad industrial applications. We investigated the reduction and transformation of both phases with a strain of sulfate-reducing bacteria (SRB). SRB growth resulted in 28.1% and 7.1% sulfate to acid volatile sulfur conversion in magnetite and Maghemite, respectively. Transmission electron microscopy and X-ray photoelectron spectroscopy (XPS) analyses indicate that monosulfides (mackinawite and greigite) and polysulfides are the main secondary sulfides in the magnetite experiment, while the Maghemite experiment also contained a high proportion of pyrite. XPS analyses indicate the reduction of Fe(III) to Fe(II) on the surface of magnetite and Maghemite both by dissolved sulfides and SRB. Mossbauer spectroscopy measurements reveal the formation of superparamagnetic phases in microbial experiments, which indicates the dissolution and particle size decrease of the two minerals both by dissolved sulfides and SRB. X-ray diffraction and Mossbauer spectroscopy analyses suggest a complete transformation of nanoMaghemite to nanomagnetite under the mediation of SRB through solid phase Fe(III) reduction. This transformation controls the changing and different patterns of both magnetic susceptibility and magnetic hysteresis for the two minerals. It is suggested that the structural similarity between magnetite and Maghemite, and the conductivity of magnetite, constrain the unique solid phase transformation. Our findings indicate that the Maghemite–magnetite solid solution is a potential natural battery for the growth of anaerobic microbes in sulfidic environments.
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The kinetic and thermodynamic adsorption of Eu(III) on synthetic Maghemite
Journal of Molecular Liquids, 2016Co-Authors: Yuke Zhu, Haibo Liu, Zhongxiu Jin, Tianhu ChenAbstract:Abstract In this study, Maghemite (γ-Fe 2 O 3 ) nanoparticles were synthesized by calcining limonite under H 2 atmosphere. The adsorption of Eu(III) on Maghemite was studied by batch experiments under various experimental conditions. The kinetic adsorption processes were well described by pseudo-second-order model with high correlation coefficient. The macroscopic results showed that the adsorption of Eu(III) on Maghemite significantly decreased with increasing ionic strength, indicating that outer-sphere surface complexation predominated their adsorption of Eu(III). The adsorption isotherms indicated that the removal of Eu(III) adsorption on Maghemite were fitted by Freundlish models better than Langmuir and D-R models. The calculated thermodynamic parameters showed that the adsorption of Eu(III) on Maghemite was a spontaneous and endothermic process. According to XPS analysis, the high effective adsorption of Eu(III) was mainly attributed to oxygen-containing functional groups of Maghemite.
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Characteristics and genesis of Maghemite in Chinese loess and paleosols: Mechanism for magnetic susceptibility enhancement in paleosols
Earth and Planetary Science Letters, 2005Co-Authors: Tianhu Chen, Qiaoqin Xie, Jun ChenAbstract:Abstract Morphological characteristics and microstructures of magnetic minerals extracted from Chinese loess and paleosols were investigated using powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Our results indicate that Maghemite in loess–paleosol sequences was transformed from magnetite through oxidation of magnetite. Maghemite transformed from eolian magnetite during chemical weathering has low-angle grain boundaries among Maghemite nano-crystals. Some nano-crystalline Maghemites with nanoporous texture resulted from microbe-induced precipitation of magnetite or transformation of poorly crystalline ferric Fe (oxy)hydroxides in presence of Fe-reducing bacteria. Aggregates of euhedral Maghemite nano-crystals were transformed from magnetite magnetosomes. Both microbe-induced nanoporous magnetite and microbe-produced magnetite magnetosomes are directly related to microbial activities and pedogenesis of the paleosols. It is proposed that the formation of nano-crystalline Maghemite with superparamagnetic property in paleosol results in the enhancement of magnetic susceptibility, although the total amount (weight percent) of magnetic minerals in both paleosol and loess units is similar. Our results also show that nano-crystalline and nanoporous magnetite grains prefer to transform into Maghemite in semi-arid soil environments instead of hematite, although hematite is a thermodynamically stable phase. This result also indicates that a decrease in crystal size will increase stability of Maghemite. It is also inferred that surface energy of Maghemite is lower than that of hematite.
Bee Chin Ang - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation on thermal conductivity and viscosity of Maghemite (γ –Fe2O3) water-based nanofluids
IOP Conference Series: Materials Science and Engineering, 2018Co-Authors: Irwan Nurdin, M R Johan, Bee Chin AngAbstract:Thermal conductivity and kinematic viscosity of Maghemite nanofluids were experimentally investigated at a small volume fraction of Maghemite nanoparticles and temperatures. Maghemite nanofluids were prepared by suspending Maghemite nanoparticles in water as base fluids. Results show that the thermal conductivity of Maghemite nanofluids linearly increase with increasing particle volume fraction and temperature, while kinematic viscosity increase with increasing particle volume fraction and decrease with increasing temperature. The highest enhancement of thermal conductivity and kinematic viscosity are 18.84% and 13.66% respectively, at particle volume fraction 0.6% and temperature 35.
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Phase and surface area studies of Maghemite nanoparticles dispersed in silica gel
Materials Research Innovations, 2014Co-Authors: Bee Chin Ang, Iskandar Idris Yaacob, Yew Hoong WongAbstract:First, the superparamagnetic Maghemite nanoparticles were synthesised using Massart's procedure. Then, the nanocomposites of the synthesised Maghemite nanoparticles and silica were produced by dispersing the as-synthesised Maghemite nanoparticles into the silica xerogel prepared by sol–gel technique. The system was then heated for 3 days at 140°C. The phase analysis performed using X-ray diffraction confirmed that the as-synthesised nanoparticles and the nanoparticles within the silica gel were Maghemite. Surface characteristic of the nanocomposite was evaluated by N2 adsorption. The ‘pure’ silica gel and Maghemite nanoparticles showed high values of surface area (150–160 m2 g−1), while the surface area of nanocomposite was less than 40 m2 g−1. This was probably due to the formation of dense structures caused by incorporation of Maghemite nanoparticles within the pores of silica gel. The pore width increased with increasing content of Maghemite nanoparticles.
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effect of fe2o3 sio2 ratio on Maghemite silica particulate nanocomposites
Journal of Central South University, 2013Co-Authors: Bee Chin Ang, Iskandar Idris Yaacob, Irwan NurdinAbstract:Maghemite-silica particulate nanocomposites were prepared by modified 2-step sol-gel process. Superparamagnetic Maghemite nanoparticles were successfully produced using Massart’s procedure. Nanocomposites consisting of synthesized Maghemite nanoparticles and silica were produced by dispersing the as-synthesized Maghemite nanoparticles into the silica particulate form. The system was then heated at 140 °C for 3 d. A variety of mass ratios of Fe2O3/SiO2 was investigated. Moreover, no surfactant or other unnecessary precursor was involved. The nanocomposites were characterized using XRD, BET and AGM. The XRD diffraction patterns show the reflection corresponding to Maghemite nanoparticles and a visible wide band at 2θ from 20° to 35° which are the characteristics of the amorphous phase of the silica gel. The patterns also exhibit the presence of only Maghemite and SiO2 amorphous phase, which indicates that there is no chemical reaction between the silica particulate gel and Maghemite nanoparticles to form other compounds. The calculated crystallite size for encapsulated Maghemite nanoparticles is smaller than the as-synthesized Maghemite nanoparticles indicating the dissolution of the nanoparticles. Very high surface area is attained for the produced nanocomposites (360–390 m2/g). This enhances the sensitivity and the reactivity of the nanocomposites. The shapes of the magnetization curves for nanocomposites are very similar to the as-synthesized Maghemite nanoparticles. Superparamagnetic behaviour is exhibited by all samples, indicating that the size of the Maghemite nanoparticles is always within the nanometre range. The increase in iron content gives rise to a small particle growth.
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Effect of Fe2O3/SiO2 ratio on Maghemite-silica particulate nanocomposites
Journal of Central South University, 2013Co-Authors: Bee Chin Ang, Iskandar Idris Yaacob, Irwan NurdinAbstract:Maghemite-silica particulate nanocomposites were prepared by modified 2-step sol-gel process. Superparamagnetic Maghemite nanoparticles were successfully produced using Massart’s procedure. Nanocomposites consisting of synthesized Maghemite nanoparticles and silica were produced by dispersing the as-synthesized Maghemite nanoparticles into the silica particulate form. The system was then heated at 140 °C for 3 d. A variety of mass ratios of Fe2O3/SiO2 was investigated. Moreover, no surfactant or other unnecessary precursor was involved. The nanocomposites were characterized using XRD, BET and AGM. The XRD diffraction patterns show the reflection corresponding to Maghemite nanoparticles and a visible wide band at 2θ from 20° to 35° which are the characteristics of the amorphous phase of the silica gel. The patterns also exhibit the presence of only Maghemite and SiO2 amorphous phase, which indicates that there is no chemical reaction between the silica particulate gel and Maghemite nanoparticles to form other compounds. The calculated crystallite size for encapsulated Maghemite nanoparticles is smaller than the as-synthesized Maghemite nanoparticles indicating the dissolution of the nanoparticles. Very high surface area is attained for the produced nanocomposites (360–390 m2/g). This enhances the sensitivity and the reactivity of the nanocomposites. The shapes of the magnetization curves for nanocomposites are very similar to the as-synthesized Maghemite nanoparticles. Superparamagnetic behaviour is exhibited by all samples, indicating that the size of the Maghemite nanoparticles is always within the nanometre range. The increase in iron content gives rise to a small particle growth.
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Synthesis and characterization of Maghemite nanoparticles dispersed within silica matrix / Ang Bee Chin
2011Co-Authors: Bee Chin AngAbstract:Generally, this study comprises of 3 stages. Firstly, pure Maghemite nanoparticles were synthesized within 10nm size range. Secondly, the nanoparticles were encapsulated into the silica xerogel matrix to minimize agglomeration and aggregation by producing nanocomposites. Finally, the surface area of the nanocomposites was increased by modifying the matrix into silica particulate form. The nanoparticles and nanocomposites were characterized using XRD, TGA, TEM, BET, DLS and AGM. In stage I, the effects of varying the FeCl2 concentration on the properties of magnetic nanoparticles produced by Massart’s procedure were investigated. The lattice parameters of the samples obtained from XRD analysis revealed that the nanoparticles formed were Maghemites (γ-Fe2O3). The magnetization curves showed no hysteresis, indicating that the particles were superparamagnetic. The crystallite, magnetic and physical sizes were similar, indicating that the particles were monocrystals. When the FeCl2 concentration increased from 0.1 to 1.0M, the size of as-synthesized Maghemite nanoparticles decreased. However, when the FeCl2 concentration was increased further, the size of as-synthesized Maghemite nanoparticles increased. This indicates that a very low or a very high FeCl2 concentration leads to the formation of larger particles. In addition, agglomeration and aggregation occurred for most samples. Superparamagnetic Maghemite nanoparticles with the smallest size were chosen to proceed to stage II and stage III. Maghemite-silica xerogel nanocomposites were produced by dispersing the assynthesized Maghemite nanoparticles into silica xerogel by sol-gel technique. The phase analysis performed using XRD confirmed that the encapsulated nanoparticles were Maghemites. TEM micrographs showed that the Maghemite nanoparticles were spherical and homogeneously incorporated into the silica xerogel matrix. The surface area of the nanocomposites was less than 40m2/g. This was probably due to the fact that majority of the pores in the silica gel were filled by as-synthesized Maghemite nanoparticles. Reduction in average crystallite size of dispersed Maghemite particles was observed after the encapsulation process compared to as-synthesized Maghemite nanoparticles. However, increasing the weight ratio of Fe2O3/SiO2 in nanocomposites caused an increase in average crystallite size of embedded Maghemite nanoparticles. Maghemite-silica particulate nanocomposites were prepared by a modified solgel process. The purpose of changing the matrix from xerogel to particulate form was to increase the surface area and retain its properties. It is a promising alternative technique for fabricating nanocomposites because it is simple, manufacturable, inexpensive, fast, can be prepared at room temperature and its ability to control the composition, crystalline distribution and properties of Maghemite nanoparticles and nanocomposites. Moreover, no surfactant or other unnecessary precursor was involved. The HRTEM micrograph revealed that the embedded particle (core) was with the presence of atomic interspaces indicating that the particles were crystalline and covered with a noncrystalline material. The EELS result showed the presence of Fe-L3 signals, which proves that the embedded particles were iron-based compounds. In stage III, a very high surface area was attained for the produced nanocomposites (360 – 390 m2/g), compared with those of stage II. This enhances the sensitivity and the reactivity of the nanocomposites.
Iskandar Idris Yaacob - One of the best experts on this subject based on the ideXlab platform.
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enhancement of thermal conductivity and kinematic viscosity in magnetically controllable Maghemite γ fe2o3 nanofluids
Experimental Thermal and Fluid Science, 2016Co-Authors: Irwa Nurdi, Iskandar Idris Yaacob, Mohd Rafie JohaAbstract:The objective of this study is to investigate the thermal conductivity and kinematic viscosity enhancement of Maghemite nanofluids at various particle volume fractions (0.1%, 0.2%, 0.3%, 0.4%, 0.5% and 0.6%) under the influence of an external magnetic field in different orientations (parallel and perpendicular). The effect of magnetic field strength and orientation on these properties is investigated at two temperatures of Maghemite nanofluids (25 and 30 °C). The results show that the thermal conductivity enhancement of Maghemite nanofluids increases with an increase in the magnetic field strength. The highest thermal conductivity enhancement (39.09%) is attained at the following experimental conditions: (1) particle volume fraction: 0.6%, (2) magnetic field strength: 300 Gauss, (3) temperature of Maghemite nanofluid: 30 °C and (4) magnetic field orientation: parallel. The results also show that the kinematic viscosity enhancement of the Maghemite nanofluids increases with an increase in the magnetic field strength. Likewise, the highest kinematic viscosity enhancement (31.91%) is attained at the above-mentioned experimental conditions. Based on the results, it can be concluded that both the magnetic field strength and orientation has a significant effect on the thermal conductivity and kinematic viscosity enhancement of Maghemite nanofluids.
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Phase and surface area studies of Maghemite nanoparticles dispersed in silica gel
Materials Research Innovations, 2014Co-Authors: Bee Chin Ang, Iskandar Idris Yaacob, Yew Hoong WongAbstract:First, the superparamagnetic Maghemite nanoparticles were synthesised using Massart's procedure. Then, the nanocomposites of the synthesised Maghemite nanoparticles and silica were produced by dispersing the as-synthesised Maghemite nanoparticles into the silica xerogel prepared by sol–gel technique. The system was then heated for 3 days at 140°C. The phase analysis performed using X-ray diffraction confirmed that the as-synthesised nanoparticles and the nanoparticles within the silica gel were Maghemite. Surface characteristic of the nanocomposite was evaluated by N2 adsorption. The ‘pure’ silica gel and Maghemite nanoparticles showed high values of surface area (150–160 m2 g−1), while the surface area of nanocomposite was less than 40 m2 g−1. This was probably due to the formation of dense structures caused by incorporation of Maghemite nanoparticles within the pores of silica gel. The pore width increased with increasing content of Maghemite nanoparticles.
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effect of fe2o3 sio2 ratio on Maghemite silica particulate nanocomposites
Journal of Central South University, 2013Co-Authors: Bee Chin Ang, Iskandar Idris Yaacob, Irwan NurdinAbstract:Maghemite-silica particulate nanocomposites were prepared by modified 2-step sol-gel process. Superparamagnetic Maghemite nanoparticles were successfully produced using Massart’s procedure. Nanocomposites consisting of synthesized Maghemite nanoparticles and silica were produced by dispersing the as-synthesized Maghemite nanoparticles into the silica particulate form. The system was then heated at 140 °C for 3 d. A variety of mass ratios of Fe2O3/SiO2 was investigated. Moreover, no surfactant or other unnecessary precursor was involved. The nanocomposites were characterized using XRD, BET and AGM. The XRD diffraction patterns show the reflection corresponding to Maghemite nanoparticles and a visible wide band at 2θ from 20° to 35° which are the characteristics of the amorphous phase of the silica gel. The patterns also exhibit the presence of only Maghemite and SiO2 amorphous phase, which indicates that there is no chemical reaction between the silica particulate gel and Maghemite nanoparticles to form other compounds. The calculated crystallite size for encapsulated Maghemite nanoparticles is smaller than the as-synthesized Maghemite nanoparticles indicating the dissolution of the nanoparticles. Very high surface area is attained for the produced nanocomposites (360–390 m2/g). This enhances the sensitivity and the reactivity of the nanocomposites. The shapes of the magnetization curves for nanocomposites are very similar to the as-synthesized Maghemite nanoparticles. Superparamagnetic behaviour is exhibited by all samples, indicating that the size of the Maghemite nanoparticles is always within the nanometre range. The increase in iron content gives rise to a small particle growth.
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Effect of Fe2O3/SiO2 ratio on Maghemite-silica particulate nanocomposites
Journal of Central South University, 2013Co-Authors: Bee Chin Ang, Iskandar Idris Yaacob, Irwan NurdinAbstract:Maghemite-silica particulate nanocomposites were prepared by modified 2-step sol-gel process. Superparamagnetic Maghemite nanoparticles were successfully produced using Massart’s procedure. Nanocomposites consisting of synthesized Maghemite nanoparticles and silica were produced by dispersing the as-synthesized Maghemite nanoparticles into the silica particulate form. The system was then heated at 140 °C for 3 d. A variety of mass ratios of Fe2O3/SiO2 was investigated. Moreover, no surfactant or other unnecessary precursor was involved. The nanocomposites were characterized using XRD, BET and AGM. The XRD diffraction patterns show the reflection corresponding to Maghemite nanoparticles and a visible wide band at 2θ from 20° to 35° which are the characteristics of the amorphous phase of the silica gel. The patterns also exhibit the presence of only Maghemite and SiO2 amorphous phase, which indicates that there is no chemical reaction between the silica particulate gel and Maghemite nanoparticles to form other compounds. The calculated crystallite size for encapsulated Maghemite nanoparticles is smaller than the as-synthesized Maghemite nanoparticles indicating the dissolution of the nanoparticles. Very high surface area is attained for the produced nanocomposites (360–390 m2/g). This enhances the sensitivity and the reactivity of the nanocomposites. The shapes of the magnetization curves for nanocomposites are very similar to the as-synthesized Maghemite nanoparticles. Superparamagnetic behaviour is exhibited by all samples, indicating that the size of the Maghemite nanoparticles is always within the nanometre range. The increase in iron content gives rise to a small particle growth.
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Preparation of Maghemite-Silica Nanocomposites Using Sol-Gel Technique
Advanced Materials Research, 2010Co-Authors: Bee Chin Ang, Iskandar Idris YaacobAbstract:Superparamagnetic Maghemite nanoparticles were successfully produced using Massart’s procedure. Nanocomposites consisting of the synthesized Maghemite nanoparticles and silica were produced by dispersing the as-synthesized Maghemite nanoparticles into the silica xerogel, which was prepared by sol-gel technique. The system was then heated for 3 days at 140oC. A variety of weight ratios of Fe2O3/SiO2 was investigated. The nanocomposites were characterized using TGA, XRD, TEM and AGM. TGA thermogram showed one significant weight loss at around 250oC. It was caused by dehydration and evaporation of solvent from sol-gel process. XRD showed that the dispersed particles were still Maghemite. TEM micrographs showed that the Maghemite nanoparticles were in spherical shape and they were homogeneously incorporated in the silica matrix. The values of magnetization at 10kOe applied field were in the range of 1.79emu/g to 9.53emu/g depending of the Fe2O3/SiO2 ratio. Reduction of average crystallite size of dispersed Maghemite particles was observed after encapsulation process. Increasing weight ratio of Fe2O3/SiO2 caused increase of the average crystallite size of Maghemite nanoparticles.
Elizabeth Mcclelland - One of the best experts on this subject based on the ideXlab platform.
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the lepidocrocite Maghemite haematite reaction chain i acquisition of chemical remanent magnetization by Maghemite its magnetic properties and thermal stability
Geophysical Journal International, 2005Co-Authors: T S Gendler, Mark J. Dekkers, V P Shcherbakov, A K Gapeev, S K Gribov, Elizabeth McclellandAbstract:SUMMARY We report on the magnetic properties and the acquisition of a chemical remanent magnetization (CRM) in a field of 100 μT as a function of temperature and time during the lepidocrocite–Maghemite–haematite reaction chain. The development of CRM was monitored at a series of 13 temperatures ranging from 175 to 550 °C; data acquisition was done at the specific formation temperatures for durations of up to 500 hr. Up to acquisition temperatures of 200 °C it takes a considerable time (up to 7 hr) before the CRM is measurable. This time decreases with increasing temperature, reflecting the activation energy of the reaction to form the first Maghemite. During the lepidocrocite conversion, formation of two types of Maghemite is suggested by two peaks in the CRM versus time curves. Magnetic properties were analysed after various stages in the reaction. They indicate a mixture of superparamagnetic and single-domain Maghemite. The first reaction product (obtained after annealing at 200 °C) is a fine-grained yet crystalline Maghemite (labelled type A). Before massive Maghemite formation occurs, the coercive and remanent coercive forces go through a minimum at intermediate temperatures of 250–300 °C (annealing for 2.5 hr). This minimum lowers to 200–250 °C with increasing annealing time (500 hr). This is probably the result of two processes acting simultaneously—formation of superparamagnetic Maghemite particles of a second less crystalline Maghemite type (labelled type B) and removal of stacking faults in type A Maghemite. The second process is suggested by analogy to the behaviour of natural magnetite/Maghemite systems on annealing. Removal of stacking faults is reported to result in a magnetic softening of the grain assemblage. Annealing at 300–350 °C removes most of the lepidocrocite and the second Maghemite type, type B, becomes prominent. Haematite formation sets in at slightly higher temperatures, yet the type B Maghemite is in part thermally stable up to 600 °C enabling Thellier–Thellier experiments. This stability is also inferred from Arrhenius fitting that shows a comparatively high activation energy for the Maghemite to haematite reaction. In Thellier–Thellier experiments the CRM showed a markedly downward convex Arai–Nagata plot while a second thermoremanent magnetization (TRM) showed perfect linear behaviour as expected. This feature may be used to recognize CRM in natural rocks.
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The lepidocrocite–Maghemite–haematite reaction chain—I. Acquisition of chemical remanent magnetization by Maghemite, its magnetic properties and thermal stability
Geophysical Journal International, 2005Co-Authors: T S Gendler, Mark J. Dekkers, V P Shcherbakov, A K Gapeev, S K Gribov, Elizabeth McclellandAbstract:SUMMARY We report on the magnetic properties and the acquisition of a chemical remanent magnetization (CRM) in a field of 100 μT as a function of temperature and time during the lepidocrocite–Maghemite–haematite reaction chain. The development of CRM was monitored at a series of 13 temperatures ranging from 175 to 550 °C; data acquisition was done at the specific formation temperatures for durations of up to 500 hr. Up to acquisition temperatures of 200 °C it takes a considerable time (up to 7 hr) before the CRM is measurable. This time decreases with increasing temperature, reflecting the activation energy of the reaction to form the first Maghemite. During the lepidocrocite conversion, formation of two types of Maghemite is suggested by two peaks in the CRM versus time curves. Magnetic properties were analysed after various stages in the reaction. They indicate a mixture of superparamagnetic and single-domain Maghemite. The first reaction product (obtained after annealing at 200 °C) is a fine-grained yet crystalline Maghemite (labelled type A). Before massive Maghemite formation occurs, the coercive and remanent coercive forces go through a minimum at intermediate temperatures of 250–300 °C (annealing for 2.5 hr). This minimum lowers to 200–250 °C with increasing annealing time (500 hr). This is probably the result of two processes acting simultaneously—formation of superparamagnetic Maghemite particles of a second less crystalline Maghemite type (labelled type B) and removal of stacking faults in type A Maghemite. The second process is suggested by analogy to the behaviour of natural magnetite/Maghemite systems on annealing. Removal of stacking faults is reported to result in a magnetic softening of the grain assemblage. Annealing at 300–350 °C removes most of the lepidocrocite and the second Maghemite type, type B, becomes prominent. Haematite formation sets in at slightly higher temperatures, yet the type B Maghemite is in part thermally stable up to 600 °C enabling Thellier–Thellier experiments. This stability is also inferred from Arrhenius fitting that shows a comparatively high activation energy for the Maghemite to haematite reaction. In Thellier–Thellier experiments the CRM showed a markedly downward convex Arai–Nagata plot while a second thermoremanent magnetization (TRM) showed perfect linear behaviour as expected. This feature may be used to recognize CRM in natural rocks.
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Self Reversal of Chemical Remanent Magnetization On the Transformation of Maghemite to Haematite
Geophysical Journal International, 1993Co-Authors: Elizabeth Mcclelland, Catherine GossAbstract:SUMMARY Self-reversed chemical remanent magnetization (CRM) has been observed in haematite formed on heating Maghemite which has been produced by the dehydration of acicular crystals of synthetic lepidocrocite, 1 to 2 pm in length. Our experimental evidence suggests that self reversal of haematite remanence only occurs when the parent Maghemite is still blocked at the temperature of its transformation to haematite; when the transformation temperature is above the blocking temperature of the parent Maghemite and it is unblocked, the resulting haematite remanence is normally magnetized. It is suggested that the strong dependence on remanent state supports exchange control of the self-reversal process. We propose that the self reversal is probably a general feature of the Maghemite to haematite transition, and the significance of the source lepidocrocite in our experiments is that it produces Maghemite of a suitable grain size so that much of it remains blocked at the elevated temperatures required to make the transformation to haematite occur over the short time scale of the laboratory experiments. In nature, transformation of Maghemite to haematite will occur at much lower temperatures due to the much longer time scales involved, and self reversal of the resulting CRM may occur over a much less restricted grain size range of parent Maghemite.
