Dr. Mohammad Jellur Rahman has been working in this department since 27 June, 2007 and actively serving as an Associate Professor of Physics since 12 March, 2018. He has excellent academic background. He has established a Polymer Nanocomposites Laboratory for the postgraduate research of this Department. He has supervised 05 students to get their M.Sc. degree from this department and at present there are 04 Ph.D. students, 04 M.Phil. students and 05 M.Sc. students working under his supervision. He has shown outstanding performance in research work and so far he has contributed more than 27 papers in national and international referred journals with more than 325 citations. He has presented a number of conference papers and contributed to a book titled as ‘Carbon Nanotubes - Current Progress of their Polymer Composites’ for the Postgraduate Level and 02 books for the intermediate level (Physics Part I and II, Text Books for Higher Secondary Education).
Dr. Rahman is born in Tangail, Bangladesh in January, 1979. He obtained his B.Sc. (Honours) in 2001 (Held in 2004) and M. S. in 2002 (Held in 2006) in Physics from the University of Dhaka, Bangladesh. He joined the Bangladesh Bank (Central Bank of Bangladesh) as an Assistant Director in December, 2006. Later he joined the Department of Physics, Bangladesh University of Engineering and Technology (BUET), Dhaka in June, 2007 as a Lecturer. He completed his M.Phil. from BUET in 2011 and went to Japan in October 2011 for Ph.D. getting the MEXT (Monobukagakusho) scholarship. He got his Ph.D. on the Production, functionalization and applications of carbon nanotubes from Shizuoka University, Japan in September 2014. He became Assistant Professor in February, 2015 and Associate Professor in March, 2018. His present research interests are on Plasma Processing of Polymers and Carbon Nanomaterials. He is working on production of nanoparticles & nanocomposites, plasma polymerized thin films, and barium titanate based ceramics.
Optoelectronics and Nanostructure Science
GSST, Shizuoka University, Japan
Bangladesh University of Engineering & Technolog, Bangladesh
University of Dhaka, Bangladesh
University of Dhaka, Bangladesh
Got Ph.D. from Shizuoka University, Japan in 2014 getting the MEXT (Monobukagakusho) scholarship from Japanese Government for the period October 2011 to September 2014.
Enhanced Dielectric properties of Bismuth Doped Barium Titanate Ceramics with their Structural and Compositional Studies
Several strategies have been employed to tune the functional properties of environmentally friendly Barium titanate (BaTiO3). In this work, bismuth (Bi) doped BaTiO3 with a general formula Ba1-xBi2x/3TiO3 (where x = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05 and 0.06) were prepared by the conventional solid-state reaction method. The effect of Bi on the structure of BaTiO3; and their morphological and compositional studies were carried out by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) respectively. Furthermore, the effect of Bi on the transport properties of BaTiO3 was investigated. Our studies revealed that for x = 0.01, Bi doping gives rise to the highest tetragonality of the crystal with more homogeneous grains and pores distribution among all the doping concentration. Furthermore, the dielectric constant for x = 0.01 samples has been observed to be the highest, which is consistent with the structural and morphological studies. Also, the tetragonal to cubic phase transition temperature (Curie temperature) of the sample is found to increase with increasing Bi doping concentration. Our studies suggest that the higher value of the dielectric constant with higher Curie temperature can be obtained by a small amount of Bi doping (x = 0.01), which has potential applications in various electronic and energy storage devices.
Effect of Ce-Mn co-doping on the Structural, Morphological and Electrical Properties of the BaTiO3 Based Ceramics
Undoped, Cerium (Ce) doped, Manganese (Mn) doped and Ce-Mn co-doped Barium Titanate (BaTiO3) with the general formula Ba1-xCexMnyTi1-yO3 (where x = 0.00, 0.01, 0.02, 0.03, y = 0.00; x = 0.00, y = 0.01, 0.02, 0.03; and x = y = 0.01, 0.02, 0.03) were synthesized by conventional solid state reaction method and sintered at 1200 °C for 4 hr with an aim to study their structural and electrical properties. The grain size of the samples has been estimated using the Scanning Electron Microscopy (SEM). The X-ray Diffraction (XRD) analysis indicates that the structure of the Ce-doped and Ce-Mn codoped BaTiO3 is cubic. However, the undoped BaTiO3 and Mn-doped BaTiO3 confirmed the tetragonal-cubic mixed phase. With the change of doping concentrations, the positions of different peaks shifted slightly and the lattice parameter varied irregularly with increasing doping concentration, which is because of the changeable valance of Mn. EDX spectra confirmed the presence of Ba, Ti, Ce, and Mn contents in the co-doped samples with stoichiometric ratio. Crystallinity is observed to be clearly increased when Ce-Mn is co-doped in BaTiO3. J-V charecteristic curves indicate transition from conducting to semeconducting nature for the doped and co-doped samples with the increase in temperature. Dielectric constant of the samples increases upto 4500 with the doping concentration and the heigher values of dielectric contant is observed for the 2% Me doped and 1% Ce-Mn co-doped samples, incomparison of the other undoped samples. For the undoped and Mn-doped samples the values of dielectric constant increase with temperarute, but decrease for the Ce-doped and Ce-Mn co-doped samples. It is inferred that co-doping of BaTiO3 with Ce and Mn would be beneficial and economical for its applications.
Thickness Dependent Structural and Surface Properties of Plasma Polymerized N-benzylaniline Thin Films
Thickness dependent structural, surface morphological, topographical and compositional studies have been done on the plasma polymerized N-benzylaniline (PPNBA) thin films, where the plasma is obtained by a parallel plate capacitively coupled glow discharge system under AC of frequency 50 Hz. From the X-ray diffraction studies it is confirmed that the PPNBA thin films are amorphous in nature. The chemical structure of the PPNBA films is moderately changed from that of the monomer owing to the elimination of some benzyl groups, however become conjugated due to C=C stretching of the quinoid and benzenoid units. The PPNBA films contain mostly carbon and nitrogen, which is confirmed by the energy dispersive X-ray analysis. However, the presence of oxygen is considered to be incorporated from the reactor atmosphere. The surface morphologies of the PPBNA thin films of various thicknesses are mosaic-like structure, which are formed by the uniform distribution of unequal nanosized clusters over the smooth background of the film surface. The average roughness and root mean square roughness of the surface of the PPNBA thin films are found to be in the order of pm. The increase of the surface roughness is compatible with the increase of the cluster density, which is evidenced in the field emission scanning electron microscopy observations.
Bio-composites from Banana Tree Fibers Ambient with Multi-Walled Carbon Nanotubes: Manufacturing and Properties
A biodegradable composite fibers have been fabricated from easily available banana tree fibers (BTFs) using a simple dip-drying technique, where carbon nanotubes (CNTs) are used as reinforcing agent. A safe radio frequency oxygen plasma processing method is used to functionalize the surface of the CNTs with hydrophilic oxygen-containing group. The fibers are chemically treated with NaOH followed by oxygen plasma treatment to increase the heat conduction between the fibers in thermal contact. The implications of incorporating CNTs in the BTFs are observed by studying the surface morphology, structural, thermal, electrical and mechanical properties. The homogeneous CNT coverage on the BTFs surface is featured by the scanning electron micrographs of the CNT/treated BTF. The crystallinity index is exposed through X-ray diffraction analysis, which indicates the crystalline feature of the nanocomposites. The surface modification by CNT treatment has improved the thermal stability and flame retardancy of BTFs. A gradual decrease of resistivity of these composite fibers is observed from 5.69 to 0.0021 Ω.m by increasing the number of dip-drying cycle of BTFs in the CNTs solution. The electrical conductivity of the CNT/treated BTF becomes 163.75 S/m under the applied voltage of 100 V. The developed composite fib-ers exhibit an increase in the mechanical strength with the CNT coating. Therefore, the developed CNT-reinforced composite fibers affirm its aptitude as reliable reinforcement in electronic devices and as conductive fillers in composites industries.
Effect of M (Ni, Cu, Zn) doping on the structural, electronic, optical, and thermal properties of CdI2: DFT based theoretical studies
Structural, electronic, optical, and thermal properties of undoped and metal, M (Ni, Cu, and Zn), doped cadmium iodide (CdI2) were studied using a generalized gradient approximation of density functional theory. Lattice constants found from the theoretical studies of the structure of the undoped and doped CdI2 are in good agreement with those found in the available experimental and theoretical investigations. A strong mixing of I 5p and M 3d states is found after the doping of 3d M in CdI2, which alters the bandgap from positive to negative. Among all M (Ni, Cu, and Zn), Ni doped CdI2 with a narrow negative bandgap evolve the quantum dot level. Due to interactions between the Cd 4d and M 3d states, the measured optical and thermal properties of the doped system assessed with pure CdI2 indicate unusual behaviors, which suggest that the material can be used in different nano-electronic and electrochemical applications and in biological levels such as detection of COVID-19 pathogens.
Influence of Mg substitution on structural, magnetic and electrical properties of Zn-Cu ferrites
Studies on Mg substituted Zn-Cu ferrites with chemical formula of Zn0.6Cu0.4-xMgxFe2O4 were synthesized by solid-state reaction technique. The structural phase of all the samples is characterized by XRD, show single phased cubic spinel structure. Density of the samples increases with the increase of Mg quantity. Average grain diameter decreases with increasing Mg content. All samples show soft ferromagnetic behavior as confirmed from the M-H hysteresis loop obtained from the VSM analysis. Thesaturation magnetization decreases with increasing Mg quantity. Increasing and decreasing trend of coercivity with the increase of Mg quantityis observed, which led to the slightly hard magnetic phase. The high frequencies create more effective for the ferrite grains of advanced conductivity and minor dielectric constant for all the samples but the AC electrical resistivity and dielectric constant are initiate to be more operational at lower frequencies. The variation of resistivity, dielectric constant with the Mg concentration is completely related to the porosity and bulk density.
A wet chemical synthesis and characterization of mwcnt-starch biocomposites
MWCNT/starch composites were prepared by simple solution casting method by incorporating upto 1.0 wt. % of multi-walled carbon nanotubes (MWCNTs) as reinforcing fillers in the starch matrix. Gelatin was used as dispersing agent to disperse the MWCNTs into aqueous solution and glycerol was used as plasticizer to form composites. SEM images of the MWCNT/starch composite show the homogenous surface of the composite where CNTs are embedded into the starch matrices. XRD spectra of the composite show no characteristic peaks of CNTs in the starch matrix. FTIR spectra show peaks at around 3435 and 2927 cm-1 indicating that the covalent bonds between –OH groups and C-H groups of soluble starch and CNT were formed in the composite. Electrical conductivity of the composite was enhanced from 2.85×10-9 to 5.28× 10-8 S/m due to the addition of CNTs at room temperature and decreased with the increase of temperature. UV visible spectra showed increasing absorption with increasing CNTs content in the composite. TGA analysis demonstrated the stability of the MWCNT/starch composite.
Foot pressure sensor system made from MWCNT coated cotton fibers to monitor human activities
Highly sensitive pressure sensors have been developed from multiwall carbon nanotube (MWCNT) coated cotton fibers to utilize them in monitoring of human activities. The sensing mechanism is discussed through experimental and theoretical explanations. The principle of the sensing mechanism is related with the number of contacts among the MWCNT coated fibers and contact area among the fibers when a force is applied. Using the three sensors a foot pressure sensor system has been developed, which can detect the exerted force of human foot during standing, walking, running, jumping, and other activities. The locus of the center of gravity is also measured by these sensors during these human activities. The exerted force increases instantaneously when a person jumps from an upper step of a ladder onto a floor, which is clearly recorded. The foot pressure sensors can be used to monitor the real-time sporting performances. To prevent the ankle and knee injury of sportsmen and to monitor the activities of the patients, and old persons, the foot pressure sensors can be utilized.
Safely functionalized carbon nanotube–coated jute fibers for advanced technology
Biodegradable jute fibers become conductive when varying amounts of carbon nanotubes (CNTs) are incorporated onto it using a simple dip-drying technique. For uniform and efficient coating, CNTs have been functionalized safely by citric-acid-assisted oxygen plasma, and different properties of the fibers are investigated. The method is safe because no strong acids are used and the plasma is operative to the surface of the CNTs only, hence less destructive to the structure of the CNTs. Field emission scanning electron micrographs confirm uniform attachment of CNTs on the surfaces of jute fibers. Owing to coating, the crystallinity and mechanical strength of the composite fibers increase significantly. The thermal stability and flame retardancy are also observed to be enhanced especially for the treated jute fibers coated with functionalized CNTs. The resistance per meter of these fibers sharply decreases from 2.30 to 0.02 kΩ depending on the amount of CNTs integrated on to it. Current density through the samples increases 1000 times and conductivity increases up to 5 S m−1, which also increases with temperature. The activation energy is observed to be decreased from 330 to 68 kJ mole−1. Therefore, these fibers can be applied in different electrical and electronic devices as well as in polymer composites as conductive fillers.
Carbon nanotube-incorporated cellulose nanocomposite sheet for flexible technology
A flexible, electrically conductive and low-cost composite sheet has been prepared combining multi-walled carbon nanotubes (MWCNTs) and cellulose pulp using simple solution mixing method. The uniform attachment of MWCNTs on to the cellulose fibres of the composites lead to a gradual decline of the sheet resistance with an enhanced electrical conductivity. The crystallinity of the composites is also found to be increased. The composites remain thermally stable up to 550 K as well as demonstrate improved flame retardancy. The conducting CNT networks of the composites are not disrupted even after 600 bending cycles, indicating almost no loss of conductivity. This conducting and flexible composite sheet can be used in different energy storage devices.
Alternating Current Electrical Properties of Cerium Doped Barium Titanate below the Room Temperature
The alternating current (ac) electrical properties (dielectric constant, loss tangent and ac conductivity) of pure and cerium (Ce) doped barium titanate (BaTiO3) with a general formula Ba1-xCexTiO3 where x = 0.00, 0.01, 0.02, 0.03 and 0.04 were studied at the temperature range -25 to 30 °C. The samples were prepared by the conventional solid state reaction method and sintered at 1200 °C for 4 hours. The structural properties of BaTiO3 and Ce doped BaTiO3 were also studied. The scanning electron microscope micrographs for different doping concentration of Ce showed increase in grain size with doping concentration. Lattice constant and particle size of the sampleswereobserved to decrease slightly with Ce doping as obtained from the X-ray diffraction measurements. The dielectric constant of the sample increases with temperature and undergoes a transitionfrom orthorhombic to tetragonal at about 270 K. The value of dielectric constant sharply decreases with frequency up to 1 kHz and beyond that remains almost stable for all the samples at different temperatures. Dielectric loss at different temperatures showed a good agreement with frequency. The ac conductivity, sac of the samples increases with the increase in frequency reaches to a maximum value and then shows a decreasing trend. The frequencies of peak sacare observed to be shifted towards lower frequency with the increase in doping content.
Effects of Micro-Size Graphite-Flake to Reinforce the Performances of Poly (Lactic Acid) Thermoplastic Biocomposites.
Biocomposites of poly(lactic acid) (PLA) and micrometre-sized graphite (GP) flake powder with 0–30 wt% GP contents have been prepared using extrusion moulding followed by compression moulding. The pure PLA and PLA-GP composites (PGC) have been examined by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy (RS), X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), transmission electron microscopy (TEM), mechanical and micromechanical testing, differential thermal analysis (DTA) and thermogravimetric analysis (TGA). FTIR spectra confirm the physical bond formation between GP and PLA. RS distinguishes the D-band spectra of pure PLA and PGC. XRD shows a partially crystalline structure in the PLA. SEM and TEM exhibit a clear dispersion of GP particles in PLA matrix at lower loading and aggregates at higher loading. With an increase of filler content, the tensile and flexural strengths decrease, but the Young’s and tangent moduli are observed to increase by 58% and 77%, respectively. These increments represent an increase in the stiffness of the materials and are found to be consistent with the theoretical values. A decrease in microhardness with increase in filler content is also observed. Both the DTA and TGA reveal an increased thermal stability of the composites.
Enhanced Dielectric Properties of BaTiO3 Ceramics with Cerium Doping, Manganese Doping and Ce-Mn Co-doping
Ba1−xCexTi1−yMnyO3 (where x and y varies from 0.00 to 0.03) ceramic samples are synthesized by conventional solid state reaction technique. The samples are sintered at 1473 K for 4 h. The grain size is observed to increase with increasing dopant and co-dopant concentration. The X-ray diffraction confirmed the cubic phase of these BaTiO3 -based ceramics with a small amount of secondary phase. The current density shows a nearly linear relationship with voltage, and the AC resistivity of the samples is observed to decrease with increasing frequency and doping concentration. The dielectric constant and dielectric loss were observed to decrease with frequency in the lower frequency range (0.2–10 kHz), but remained almost the same at the high-frequency region (>10 kHz). Though Ce-doped samples shows better dielectric properties than Mn-doped samples, the Ce-Mn co-doped samples, having improved their dielectric properties, can be used to fabricate different optoelectric devices.
Development of Compact Load Cell Using Multiwall Carbon Nanotube/Cotton Composites and Its Application to Human Health and Activity Monitoring
Compact load cells have been developed using multiwall carbon nanotube/cotton (MWCNT/cotton) composites, whose performance has been optimized by varying the concentration of MWCNTs and the thickness of the composite. The sensitivity of the load cell, which is defined as the ratio of the change in the relative electric resistance to the change in applied pressure, is measured to be in the range of 180-0.20 kPa-1 for applied pressures of 8.84 Pa-884 kPa (F= 1.0 mN-100 N). The load cells show a rapid response in situations with a frequently changing force, with response times t1/2 of 4.5 and 5.0 ms for the application and release of load, respectively. The load cell demonstrates high reproducibility in tests involving more than 11,200 compression/relaxation cycles. It also has high reproducibility in different harsh environments and has a good electric-conductance recovery property. The load cell is successfully used to monitor the time-varying center of gravity of a human foot, which can be applied to the diagnosis of sick and healthy people. The MWCNT/cotton load cells can be used as wearable and flexible devices for monitoring human health.
AC Electrical Properties of Plasma Polymerized o-Methoxyaniline Thin Films.
Alternate current (ac) electrical properties of the plasma polymerized o-methoxyaniline (PPOMA) thin films synthesized in the glow discharge plasma using a capacitively coupled reactor are studied. Measurement revealed that the ac electrical conductivity varies with frequency ω as ωn , where the exponent n is less than unity in the range 0.1 to 2.0 kHz, indicating the Debye type conduction mechanism in the PPOMA thin films, while above this frequency range the exponent is become greater than unity indicating non-Debye type conduction. At low frequencies the conduction is considered to be due to hopping of carriers between the localized states. The PPOMA thin films of thicknesses 100−250 nm possesses dielectric constant <10, which remains static in the range 0.1−10 kHz, and decreases at higher temperature due to the orientation polarization. The dielectric loss increases with the increase in frequency having a peak around or above 10 kHz for all the PPOMA films of different thicknesses. Cole-Cole plot between the real and imaginary dielectric constant exhibits single relaxation mechanism in the PPOMA thin films.
Functionalization of Single-Walled Carbon Nanotubes by Citric Acid/Oxygen Plasma Treatment.
A safe and simple method of functionalizing single-walled carbon nanotubes (SWCNTs) has been developed, that significantly increases their dispersibility in water. SWCNTs in pure ethanol are treated with a supersonic homogenizer and dried. Then they are wetted with weak citric acid solution. Finally an RF (13.56 MHz) citric acid/oxygen plasma reaction is carried out under optimum conditions. As a result, hydrophilic functional groups attach onto the SWCNT surfaces, which enhance their dispersibility in water. The attachment of functional groups is identified by the FT-IR spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. The dispersibility and dispersion stability are studied by the precipitation tests, UV-visible spectroscopy, and transmission electron microscopy. These functionalized SWCNTs are expected to be used in various applications.
Conductive Cotton Textile from Safely Functionalized Carbon Nanotubes.
Electroconductive cotton textile has been prepared by a simple dipping-drying coating technique using safely functionalized multiwalled carbon nanotubes (f-MWCNTs). Owing to the surface functional groups, the f-MWCNTs become strongly attached with the cotton fibers forming network armors on their surfaces. As a result, the textile exhibits enhanced electrical properties with improved thermal conductivity and therefore is demonstrated as a flexible electrothermal heating element. The fabricated -MWCNTs/cotton textile can be heated uniformly from room temperature to ca. 100°C within few minutes depending on the applied voltage. The textile shows good thermal stability and repeatability during a long-term heating test.
Water-Dispersible Multiwalled Carbon Nanotubes Obtained from Citric-Acid-Assisted Oxygen Plasma Functionalization.
A new and safe method has been developed to functionalize multiwalled carbon nanotubes (MWCNTs) with fewer surface defects, which significantly increases their dispersibility in water. MWCNTs are pretreated in pure ethanol by a supersonic homogenizer. Then, the mixture is dried and soaked in weak citric acid solution. Finally, the MWCNTs in the citric acid solution are treated with radio frequency (13.56 MHz) oxygen plasma. As a result, many carboxyl functional groups are attached onto the MWCNT surfaces and stable dispersion of the MWCNTs in water is obtained. The treatment conditions are optimized in this study.
Structural and Optical Properties of Plasma Polymerized o-Methoxyaniline Thin Films.
Plasma polymerized o-methoxyaniline (PPOMA) thin films of different thicknesses were prepared in glow discharge plasma using a parallel plate capacitively coupled polymerization reactor. The PPOMA thin films are smooth, flawless and pinhole free. Fourier transform infrared spectra reveal a decrease of absorption intensity and disappearance of some absorption peaks for PPOMA as compared to those of OMA, indicating the formation of the thin film with modified/changed chemical structure. Analyses of the ultraviolet–visible spectroscopic results reveal that the allowed indirect (Egi) and direct (Egd) band gap energies have values in the range 1.68 to 2.08 eV and 2.90 to 3.08 eV, respectively for PPOMA thin films of thicknesses from 100 to 300 nm. The Egi of the experimental PPOMA thin films does not show any definite trend with film thickness, whereas the Egd shows weak dependence on film thickness.
Production of Single-Walled Carbon Nanotubes by Modified Arc Discharge Method.
Single-walled carbon nanotubes (SWNTs) are synthesized by the arc discharge method in He gas, where three directions of discharge current relative to gravity are selected and their production rates are compared. The soot production rate for the upward discharge current is larger than those for the horizontal and downward discharge currents. Also, the qualities of the produced SWNTs for the three cases are almost the same. The effect of a steady magnetic field (3.0 mT) perpendicular to the discharge current direction (J×B arc discharge) is also examined. This magnetic field increases the soot production rate for all three discharge current directions. The estimated ratio of the number of SWNT bundles to the number of carbon particles is higher for the upward discharge current in the case of B = 0. This ratio increases significantly for the horizontal and downward discharge currents when a magnetic field is applied.
Multiwalled Carbon Nanotubes-Reinforced Isotactic Polypropylene Nanocomposites: Enhancement of Crystallization and Mechanical, Thermal, and Electrical Properties
Multiwalled carbon nanotubes (MWCNTs)‐reinforced isotactic polypropylene (iPP) nanocomposites with low‐content of MWCNTs were fabricated using the melt‐cast techniques. The reinforced plastics were characterized by X‐ray diffraction (XRD) measurements, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, mechanical test, differential thermal analyses (DTA), and electrical tests. XRD studies exhibit the α‐crystal in the injection‐molded neat iPP with lamellar stacks having a long period of 150Å. Both the intensity of lamellar reflection and the thickness of long period increase with increasing the MWCNTs contents, indicating an enhancement of iPP crystallization by MWCNTs addition. This increase of lamellar thickness is analyzed to be consistent with that evaluated by DTA. SEM micrographs display larger MWCNTs aggregates with increasing amount of reinforcements and show a good adhesion between nanoparticles and iPP matrix. FTIR spectra reveal distinct chemical textures for the samples and confirm the existence of α‐crystal. Mechanical strengths, electrical conductivity, and dielectric constants are found to increase with increasing MWCNTs content, representing an improved performance of the nanocomposites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers
The Effect of Manganese Doping on the Grain Size and Transition Temperature of Barium Titanate Ceramics.
The structural and electrical properties of pure and manganese doped barium titanate (BaTiO3) with a general formula BaMnxTi1-xO3 (where x=0.00, 0.01, 0.02, 0.03, and 0.04) were investigated. For the observation of the surface morphology and estimation of grain sizes scanning electron microscopy (SEM) was employed. The grain size of BaTiO3 increased with an increase of the Mn doping. The Curie temperature (Tc) which indicates the tetragonal-to-cubic transition, of each sample was found from the resistivity versus temperature curve, and Tc of BaTiO3 increased linearly with an increase of the Mn doping. The Tc of un-doped BaTiO3 was lower than that of the doped samples. The Tc value of pure BaTiO3 was found to be 120 oC. It was found that the dielectric constant versus temperature curve also shows a similar type of Tc. The dielectric constant of BaMnxTi1-xO3 was found to decrease with an increase of Mn doping and the Tc of BaTiO3 increases with the addition of Mn.
Structural, Elastic and Thermal Properties of Titanium Dioxide Filled Isotactic Polypropylene, Polymer and Polymer Composites
Titanium dioxide (TiO2)-filled isotactic polypropylene (iPP) composites with various contents of TiO2 were prepared by a locally fabricated extrusion molding machine. The extrudates were melt-pressed at 180 °C and produced as plane sheets of nearly equal thickness by rapid cooling. X-ray diffraction studies reveal a decrease of crystallinity and crystallites size as well as a change of α-, β- and γ-crystalline phases of the neat iPP to the α-form due to filler inclusion. Scanning electron micrographs taken on the fractured surface of the samples show increasing amount of voids with increasing filler content. Tensile strength, elongation-at-break (%) and glass transition temperature of the samples are found to decrease considerably with the increase in TiO2 content, whereas microhardness decreases slightly with the filler content.
Effect of Cerium doping on microstructure and dielectric properties of BaTiO3 Ceramics
A solid state reaction method was used to synthesize barium titanate (BT) and barium cerium titanate (BCT) ceramics at sintering temperature of 1473 K for 4 h. The effect of cerium (Ce) on the structure, microstructure and dielectric properties of BCT was investigated. The scanning electron microscopy (SEM) investigations revealed that the grain size increases with increasing Ce content. The X-ray diffraction (XRD) patterns showed mostly the BT phase, where the lattice parameter decreased with the addition of Ce. The temperature dependence of dielectric constant showed decrease in the phase transition temperature with higher Ce content. The dielectric constant decreased slightly with increasing frequency. The direct current (dc) density-voltage characteristics of the ceramics showed ohmic behavior for both the BT and BCT. As the temperature increased, the dc resistivity of the ceramics decreased. The activation energy increased with increasing Ce content.
Study of Structures and performance of white-clay filled isotactic-polypropylene composites prepared by double-molding techniques.
Various contents of Bangladeshi white clay (WC)-filled Isotactic polypropylene (iPP) composites were fabricated by double-molding techniques. Scanning electron micrographs shows a good impact between iPP matrix and fillers. X-diffraction and IR spectroscopic measurements reveal that inclusion of fillers develops an additional γ-crystal along with the α- and β-crystals that are merely observed in the neat iPP. Young's modulus and microhardness are found to increase with increasing WC content. Thermal analyses represent a considerable increase of thermal stability of the composites with filler addition. Appearance of new crystalline phase by filler inclusion and performances of the composites are discussed in detail.
Improvedperformance of isotactic polypropylene/titanium dioxide composites: Effect of processing conditions and filler content
Titanium dioxide (TiO2) filled isotactic polypropylene (iPP) with various content of TiO2, which was used as filler, were first single-extruded by an extruder, and then double-molded by compression molding. Scanning electron micrographs show a better adhesion between iPP and filler in the extrusion cum compression-molded samples than the extrusion-molded ones. X-ray diffraction and IR spectral studies reveal a structural change from a three-phase (α, β and γ) crystalline system of the neat iPP sample to only α-form due to inclusion of fillers. Microhardness increases rapidly and then levels off with increasing filler content and also shows variations with respect to molding conditions. A slight decrease of melting temperatures and a considerable increase of degradation temperatures of the samples with addition of filler are also observed. The dc electrical resistivity is observed to decrease with increasing TiO2 content and temperature. Both the thermal and electrical properties are also found to affect by processing conditions. Based on these results, effect of processing conditions and filler content on changing morphologies and properties of the composites is described.
Study of Dielectric and Electrical Properties of Zirconium Doped Barium Titanate Perovskite
The microstructural and electrical properties of pure and Zirconium (Zr) doped Barium titanate (BT) samples with general formula Ba(Ti1-xZrx)O3 (where x=0.0, 0.1, 0.2 and 0.3), prepared by high temperature solid state reaction at a sintering temperature of 1250° C, were investigated. Dielectric and structural properties of BT ceramics is influenced significantly by small addition of ZrO2. Scanning Electron Microscope (SEM) observations revealed enhanced microstructural uniformity and retarded grain growth with increasing Zr content. The dielectric study with frequency at room temperature in the frequency range 75 kHz to 30 MHz shows that dielectric constant decreases with increasing frequency. The resistivity of the samples shows asymptotic behavior with the variation of frequency and was found to be of the order of ~103 Ohm-m. Loss factor of the grown materials decreased with increasing frequency but it became independent at higher frequency range.
Electrical Properties of Cerium Doped Barium Titanate
Effects of Magnetic Field and Gravity on Single-Walled Carbon Nanotube Production in Three Directions of Arc Discharge Current.
The effects of the discharge current direction with respect to gravity and a steady magnetic field on the production of single-walled carbon nanotubes (SWNTs) by the arc discharge method are examined. In the experiment, highly dense electrons in the arc plasma collide with He gas atoms at a frequency of ~3.5 × 1011 Hz, and the electron energy is effectively transferred to the gas atoms to accelerate them to a speed greater than that of the natural heat convection. The production rate of soot changes with the direction of the discharge current. When a magnetic field is applied, electrons in the arc plasma are accelerated in the J × B direction by the Lorentz force, resulting in an increase in the production rate of soot and the efficiency of SWNT production.
Physics Part I and II, Text Books for Higher Secondary Education Approved by NCTB.
Safer Production of Water Dispersible Carbon Nanotubes and Nanotube/Cotton Composite Materials.
Water-dispersible carbon nanotubes (WD-CNTs) have great importance in the fields of biotechnology, microelectronics, and composite materials. Sidewall functionalization is a popular method of enhancing their dispersibility in a solvent, which is usually achieved by strong acidic treatment. But, treatment under such harsh conditions deviates from green chemistry and degrades the structure and valuable properties of CNTs. Alternative safer and easier plasma method is discussed to produce functionalized CNTs (f-CNTs). The f-CNTs remain dispersed in water for more than 1 month owing to the attachment of a large number of carboxyl groups onto their surfaces. The WD-CNTs are applied to produce conductive cotton textile for the next generation textile technologies. Nonconducting cotton textile becomes electroconductive by repeatedly dipping into the f-CNT-ink and drying in air. The f-CNTs uniformly and strongly cover the individual cotton fibers. After several cycle of dipping into the f-CNT-ink, the textile becomes conductive enough to be used as wire in lighting up an LED. As a demonstration of practical use, the textile is shown as a conductive textile heater, where the textile can produce uniformly up to ca. 80°C within ca. 5 min by applying an electric power of ca. 0.1 W/cm2.
Physics Part I and II, Text Books for Higher Secondary Education Approved by NCTB.
The alternating current (ac) electrical properties (dielectric constant, loss tangent and ac conductivity) of pure and cerium (Ce) doped barium titanate (BaTiO3) with a general formula Ba1-xCexTiO3 where x=0.00, 0.01, 0.02, 0.03 and 0.04 were studied at the temperature range -25 to 30°C. The samples were prepared by the conventional solid state reaction method and sintered at 1200 °C for 4 hours. The structural properties of BaTiO3 and Ce doped BaTiO3 were also studied. The scanning electron microscope micrographs for different doping concentration of Ce showed increase in grain size with doping concentration. Lattice constant and particle size of the samples were observed to decrease slightly with Ce doping as obtained from the X-ray diffraction measurements. The dielectric constant of the sample increases with temperature and undergoes a transition from orthorhombic to tetragonal at about 270 K. The value of dielectric constant sharply decreases with frequency up to 1 kHz and beyond that remains almost stable for all the samples at different temperatures. Dielectric loss at different temperatures showed a good agreement with frequency. The ac conductivity, sac of the samples increases with the increase in frequency reaches to a maximum value and then shows a decreasing trend. The frequencies of peak sac are observed to be shifted towards lower frequency with the increase in doping content.
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He is working on the production, functionalization and applications of carbon nanotubes. His present research interests are on Plasma Science and Carbon Nanomaterials.
Dr. Mohammad Jellur Rahman
Department of Physics
Bangladesh University of Engineering and Technology
Bangladesh Journal of Physics (BJP)
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