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Abrupt change of dielectric properties in mullite due to titanium and strontium incorporation by sol-gel method

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Journal of Advanced Ceramics 2014年第4期3卷 278-286页

作者： Biplab Kumar PAUL kumaresh HALDAR Debasis ROY Biswajoy BAGCHI Alakananda BHATTACHARYA Sukhen DAS Physics Department Jadavpur UniversityKolkata-700032India

Highly crystallized mullite has been achieved at temperatures of 1100℃and 1400℃by sol-gel technique in presence of titanium and strontium ions of different concentrations:G_(0)=0 M,G_(1)=0.002 M,G_(2)=0.01 M,G_(3)=0.02 M,G_(4)=0.1 M,G_(5)=0.2 M and G6=0.5 M.X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),field emission scanning electron microscopy(FESEM),LCR meter characterized the *** formation was found to depend on the concentration of the *** dielectric properties(dielectric constant,loss tangent and AC conductivity)of the composites have been measured,and their variation with increasing frequency and concentration of the doped metals was *** the experiments were performed at room *** composites showed maximum dielectric constants of 24.42 and 37.6 at 1400℃of 0.01 M concentration for titanium and strontium ions at 2 MHz,*** to the perfect nature of the doped mullite,it can be used for the fabrication of high charge storing capacitors and also as ceramic capacitors in the pico range.

关键词： mullite sol-gel technique X-ray diffraction(XRD) dielectric properties field emission scanning electron microscopy(FESEM)

Structural and photoluminescence studies on europium-doped lithium tetraborate(Eu:Li2B4O7)single crystal grown by microtube Czochralski(μT-Cz)technique

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Chinese Physics B 2016年第5期25卷 429-433页

作者： A kumaresh R Arun Kumar N Ravikumar U Madhusoodanan B S Panigrahi K Marimuthu M Anuradha GRD Centre for Materials Research PSG College of TechnologyCoimbatoreIndia Department of Physics PSG College of TechnologyCoimbatoreIndia Radiation Safety Division Indira Gandhi Centre for Atomic ResearchKalpakkamIndia Department of Physics Gandhigram Rural UniversityDindigulIndia PSG Institute of Advanced Studies CoimbatoreIndia

Rare earth europium（Eu（3＋））-doped lithium tetraborate（Eu：Li_2B_4O_7） crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique（μT-Cz） for the first time. The grown crystals are subjected to powder x-ray diffraction（PXRD） analysis which reveals the tetragonal crystal structure of the crystals. UV–vis–NIR spectral analysis is carried out to study the optical characteristics of the grown crystals. The crystal is transparent in the entire visible region, and the lower cutoff is observed to be at 304 nm. The existence of BO_3 and BO_4 bonding structure and the molecular associations are analyzed by Fourier transform infrared（FTIR） spectroscopy. The results of excitation and emission-photoluminescence spectra of europium ion incorporated in lithium tetraborate（LTB） single crystal reveal that the observations of peaks at 258,297, and 318 nm in the excitation spectra and peaks at 579, 591, 597, 613, and 651 nm are observed in the emission *** chromaticity coordinates are calculated from the emission spectra, and the emission intensity of the grown crystal is characterized through a CIE 1931（Commission International d＇Eclairage） color chromaticity diagram.

关键词： crystal growth optical material growth from melt photoluminescence study

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Phase transformation and crystal growth behavior of 8mol%(SmO1.5, GdO1.5, and YO1.5) stabilized ZrO2 powders

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International Journal of Minerals,Metallurgy and Materials 2017年第7期24卷 842-849页

作者： R.Mahendran S.P.kumaresh Babu S.Natarajan S.Manivannan A.Vallimanalan Department of Metallurgical and Materials Engineering National Institute of Technology Tirchirappalli 620015 Tamil Nadu india

Nanocrystalline powders of ZrO_2–8mol%SmO1.5（8Sm SZ）, ZrO_2–8mol%GdO1.5（8Gd SZ）, and ZrO_2–8mol%YO1.5（8YSZ） were prepared by a simple reverse-coprecipitation technique. Differential thermal analysis/thermogravimetry（DTA/TG）, Fourier transform infrared spectroscopy（FTIR）, X-ray diffraction（XRD）, Raman spectroscopy, and high-resolution transmission electron microscopy（HRTEM） were used to study the phase transformation and crystal growth behavior. The DTA results showed that the ZrO_2 freeze-dried precipitates crystallized at 529, 465, and 467°C in the case of 8Sm SZ, 8Gd SZ, and 8YSZ, respectively. The XRD and Raman results confirmed the presence of tetragonal ZrO_2 when the dried precipitates were calcined in the temperature range from 600 to 1000°C for 2 h. The crystallite size increased with increasing calcination temperature. The activation energies were calculated as 12.39, 12.45, and 16.59 k J/mol for 8Sm SZ, 8Gd SZ, and 8YSZ respectively.

关键词： zirconia thermal analysis reverse coprecipitation activation energy

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Synthesis and characterization of AlCoCrCuFeZnx high-entropy alloy by mechanical alloying

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Progress in Natural Science:Materials International 2016年第4期26卷 380-384页

作者： M.Murali S.P.kumaresh Babu B.Jeevan Krishna A.Vallimanalan Department of Metallurgical and Materials Engineering National Institute of Technology

Equi-atomic and non equi-atomic multi-component systems were synthesized through different routes to form high-entropy single solid solution. One such high-entropy alloy（HEA） with hexanary composition AlCoCrCuFeZnxwas synthesized using mechanical alloying. The effect of zinc variation on the crystal structure and phase formation was characterized using XRD, FESEM with EDS and TEM. The synthesis resulted in both equi-atomic and non equi-atomic nano crystalline AlCoCrCuFeZn with a crystallite size less than 10 nm.

关键词： High-entropy alloy Mechanical alloying Crystallite size Lattice strain Selected area diffraction

Corrosion behavior of as-cast Mg–8Li–3Al+xCe alloy in 3.5wt% NaCl solution

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International Journal of Minerals,Metallurgy and Materials 2016年第10期23卷 1196-1203页

作者： S.Manivannan P.Dinesh R.Mahemaa Nandhakumaran MariyaPillai S.P.kumaresh Babu Srinivasan Sundarrajan Department of Metallurgical and Materials Engineering National Institute of Technology Tirchirappalli 620015 Tamil Nadu India TVS Sundaram-Clayton Limited Chennai 600050 Tamil Nadu India

Mg-8Li-3Al＋xCe alloys（x = 0.5wt%, 1.0wt%, and 1.5wt%） were prepared through a casting route in an electric resistance furnace under a controlled atmosphere. The cast alloys were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The corrosion behavior of the as-cast Mg-8Li-3Al＋xCe alloys were studied under salt spray tests in 3.5wt% NaC l solution at 35°C, in accordance with standard ASTM B-117, in conjunction with potentiodynamic polarization（PDP） tests. The results show that the addition of Ce to Mg-8Li-3Al（LA83） alloy results in the formation of Al_2Ce intermetallic phase, refines both the α-Mg phase and the Mg_（17）Al_（12） intermetallic phase, and then increases the microhardness of the alloys. The results of PDP and salt spray tests reveal that an increase in Ce content to 1.5wt% decreases the corrosion rate. The best corrosion resistance is observed for the LA83 alloy sample with 1.0wt% Ce.

关键词： magnesium lithium alloys cerium sodium chloride solutions corrosion rate polarization

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Investigation and corrosion performance of cast Mg-6Al-1Zn+XCa alloy under salt spray test(ASTM-B117)

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Journal of Magnesium and Alloys 2015年第1期3卷 86-94页

作者： S.Manivannan P.Dinesh S.P.kumaresh Babu S.Sundarrajan Department of Metallurgical and Materials Engineering National Institute of TechnologyTirchirappalliTamil NaduIndia National Institute of Technology TirchirappalliTamil NaduIndia

The corrosion behavior of cast Mg-6Al-1Zn+XCa(Where X=0.5,1.0,1.5 and 2.0 wt.%Ca)magnesium alloy,aged at different temperatures of 180 ℃,200 ℃,220 ℃ and 240 ℃ was investigated in accelerated corrosion test chamber according to ASTM-B117 Standard(salt spray test).The exposed alloys were characterized by X-Ray Diffraction(XRD),Optical Microscopy(OM)and Scanning Electron Microscopy(SEM)*** microstructural refinement due to calcium addition and ageing treatment results in the improvement of corrosion resistance of the experimental *** rate decreases due to fine precipitation of theβ(Mg17Al12)phase distributed along theα-grain boundaries during *** phases act as a barrier,which makes the alloy more resistant to *** found that better corrosion resistance of the alloy was observed in Mg-6Al-1Zn+1.5 wt.%Ca with 180 ℃ ageing *** corrosion behavior of Mg-6Al-1Zn+XCa alloy exhibited by ASTM B117 salt spray testing and electrochemical polarization measurements showed similar trends concluding that the calcium addition and ageing temperature decreases the corrosion rate.

关键词： AZ61 Calcium Precipitation Corrosion rate Polarization

Successful Resuscitation of Bone Cement Implantation Syndrome in a Patient with Pre-Existing Pulmonary Hypertension: A Case Report

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Open Journal of Anesthesiology 2020年第8期10卷 293-297页

作者： Yeo S. H. Lynn kumaresh Venkatesan Khoo Teck Puat Hospital/Woodlands Health Campus Singapore Khoo Teck Puat Hospital Singapore

Background: In patients with pre-existing pulmonary hypertension undergoing surgery, there is an inherent risk of decompensation and right ventricular failure. Cemented hemi-arthroplasty in patients with pre-existing pulmonary hypertension predisposes them even more to morbidity and mortality from bone cement implantation syndrome (BCIS) with worsening of pulmonary hypertension. This risk should be recognized and steps taken for increased awareness, risk counselling and minimization of adverse effects. Case: We report a case of successful resuscitation of a patient with pre-existing pulmonary hypertension who developed 2 episodes of cardiac arrests—Grade 3 BCIS, shortly after cement implantation. Learning Points: Patients with pre-existing pulmonary hypertension for cemented hemi-arthroplasty are at additional risks and should be identified. Adequate risk counselling needs to be undertaken prior to surgery. A multi-disciplinary team effort is required. Discussion should be undertaken with the orthopaedic surgeon about the risks and benefits of using cemented implants. The anaesthetist needs to be vigilant for signs of BCIS, especially at the time of cement implantation and institute immediate resuscitation. Supportive treatment is the mainstay of management.

关键词： Pulmonary Hypertension Bone Cement Implantation Syndrome

Reduced Activation Energy of Iron and Copper Ion Doped Mullite which Can Be Used as a Substrate in Electronic Industry

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Journal of Surface Engineered Materials and Advanced Technology 2013年第3期3卷 11-17页

作者： Debasis Roy kumaresh Haldar Biplab Kumar Paul Alakananda Bhattacharya Sukhen Das Papiya Nandy Physics Department Jadavpur University Kolkata India.

The crystallized mullite composite has been synthesized via sol-gel technique in the presence of transition metal ions such as iron and copper. The electrical resistivity and activation energy of the composites have been measured and their variation with concentration of the metal ion has been investigated. The resistivity of doped mullite decreases rapidly in the shorter temperature range and sharply in the higher temperature range. The decreasing resistivity is due to the 3d orbital electrons and the concentration of metal ions present. X-ray analysis confirms the presence of metal ions in mullite, which entered in the octahedral site. The Fe2+ and Cu2+ ions will substitute Al3+ ion in the octahedral site of mullite structure and most probably will be responsible for reducing the resistivity as well as the activation energy. Transition metal ion doped mullite-based ceramic can be considered as promising material as a substrate in the electronic industry, because of its reasonable atom density, its low activation characteristics, low thermal expansion coefficient and high mechanical strength. The present material we have developed has an activation energy of resistivity/band gap energy, Eg, 1.11 eV at 0.04 M concentration for Cu2+ ion.

关键词： Nanostructures Sol-Gel Growth X-Ray Diffraction Scanning Electron Microscopy (SEM) Electrical Conductivity

Influence of Microstructure and Experimental Parameters on Mechanical and Wear Properties of Al-TiC Surface Composite by FSP Route

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Journal of Minerals and Materials Characterization and Engineering 2012年第5期11卷 493-507页

作者： S. Jerome S. Govind Bhalchandra S.P. kumaresh Babu B. Ravisankar Department of Metallurgical and Materials Engineering National Institute of Technology Tiruchirappalli – 620 015 Tamilnadu India

Surface properties decide the fatigue, wear and corrosion behavior of a material. Hence their performance can be improved by surface modifications. Friction Stir Processing (FSP) is a promising technique to develop surface composite. The aim of the present study is to develop defect free surface composite of Al 5083 alloy reinforced with TiC particles and investigate the particle distribution in the matrix, mechanical properties and wear behavior of the composites. Microstructural observations were carried out by using optical and scanning electron microscopy (SEM). The microstructural studies revealed that distribution of particles were more uniform in samples subjected to double pass than the single pass FSP. The microhardness profiles along top surface and across the cross section of the processed samples were evaluated. The average hardness along the top surface was found to increase by 27.27%, as compared to that of the base metal (88Hv). The particles were incorporated maximum average depth about 250μm in the surface composite. The slurry erosion tests revealed that the wear rate was highly reduced in case of double pass FSP samples as compared to base metal and single pass FSPed

关键词： Al- TiC surface composite Friction stir processing Microhardness Wear resistance