Novel synthesis of hafnium oxide nanoparticles by precipitation method and its characterization

Ramadoss, Ananthakumar,Krishnamoorthy, Karthikeyan,Kim, Sang Jae Elsevier 2012 Materials research bulletin Vol.47 No.9

Modelling and Analysis of Elliptical Cantilever Device Using Flexure Method and Fabrication of Electrospun PVDF/BaTiO3 Nanocomposites

Ramadoss Tamil Selvan,W. A. D. M. Jayathilaka,Amutha Chinappan,Hilaal Alam,Seeram Ramakrishna 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2020 NANO Vol.15 No.02

Cantilever-based piezoelectric has been the most preferred technique for energy harvesting and sensing application due to its simple design. The energy conversion efficiency has been continuously improved by exploring alternative cantilever geometries by increasing the stress distribution on the beam surface. In this paper, we have introduced half elliptical and full elliptical profile modification in the cantilever structure to improve and uniformly distribute the stress at the beam surface. Stress distribution characteristics of the modified cantilever beams were investigated and compared using finite element analysis. Based on the theoretical and finite element analysis, cantilever beams were fabricated using 3D print technology. Fabricated cantilever beams were then used to investigate the piezoelectric performances of polyvinylidene fluoride (PVDF) in composite of barium titanate (BaTiO3) nanoparticles in the form of electrospun composite nanofibers. FTIR analysis shows successful conversion of alpha phase to beta phase of PVDF and PVDF/BaTiO3 nanocomposites. During 6Hz cyclic actuating experiment, maximum voltage output of 0.15 V and 1.5 nA current output were observed. The concept was proposed to replace MEMS-based sensor in hand tremor quantification to assist Parkinson disease management.

Realization of high performance flexible wire supercapacitors based on 3-dimensional NiCo2O4/Ni fibers

Ramadoss, A.,Kang, K. N.,Ahn, H. J.,Kim, S. I.,Ryu, S. T.,Jang, J. H. Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.13

<P>The rapidly developing electronics industry is producing miniaturized electronic devices with flexible, portable and wearable characteristics, requiring high-performance miniature energy storage devices with flexible and light weight properties. Herein, we have successfully fabricated highly porous, binder free three-dimensional flower-like NiCo2O4/Ni nanostructures on Ni-wire as a fiber electrode for high-performance flexible fiber supercapacitors. Such a unique structure exhibited remarkable electrochemical performance with high capacitance (29.7 F cm(-3) at 2.5 mA), excellent rate capability (97.5% retention at 20 mA), and super cycling stability (80% retention, even after 5000 cycles). The remarkable electrochemical performance is attributed to the large active area in the 3D porous architecture and direct contact between the active materials and 3D-Ni current collectors, which facilitate easy ionic/electronic transport. The symmetric fiber super-capacitor showed a gravimetric energy density of 2.18 W h kg(-1) (0.21 mW h cm(-3)) and a power density of 21.6 W kg(-1) (2.1 mW cm(-3)) with good flexibility and cycling performance, signifying potential applications in high-performance flexible energy storage devices. Further, performance in a self-powered system was demonstrated by charging these wire type NiCo2O4/Ni supercapacitors by serially wound DSSCs to drive commercial LEDs. These results suggest that the fabricated device has excellent potential as a power source for flexible, portable and wearable applications as well as self-powered systems.</P>

Enhanced activity of a hydrothermally synthesized mesoporous MoS₂ nanostructure for high performance supercapacitor applications

Ramadoss, Ananthakumar,Kim, Taehyun,Kim, Gui-Shik,Kim, Sang Jae The Royal Society of Chemistry 2014 NEW JOURNAL OF CHEMISTRY Vol.38 No.6

<P>In the present work, we have synthesized a mesoporous molybdenum disulfide (MoS<SUB>2</SUB>) nanostructure by a facile hydrothermal route for supercapacitor applications. FE-SEM and TEM images confirmed the mesoporous morphologies of the as-prepared samples. The electrochemical measurements showed that the as-prepared mesoporous MoS<SUB>2</SUB> electrode delivered maximum capacitances of 376 and 403 F g<SUP>−1</SUP> at a scan rate of 1 mV s<SUP>−1</SUP> in 1 M Na<SUB>2</SUB>SO<SUB>4</SUB> and KCl electrolyte solutions respectively, which indicated that the mesoporous MoS<SUB>2</SUB> nanostructure was a suitable electrode material for supercapacitor applications.</P> <P>Graphic Abstract</P><P>We have developed a facile route to synthesise a mesoporous MoS<SUB>2</SUB> nanostructure, which exhibited maximum specific capacitances of 376 and 403 F g<SUP>−1</SUP> at a scan rate of 1 mV s<SUP>−1</SUP> in 1 M Na<SUB>2</SUB>SO<SUB>4</SUB> and KCl electrolyte solutions, respectively. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3nj01558k'> </P>

Fully flexible, lightweight, high performance all-solid-state supercapacitor based on 3-Dimensional-graphene/graphite-paper

Ramadoss, Ananthakumar,Yoon, Ki-Yong,Kwak, Myung-Jun,Kim, Sun-I.,Ryu, Seung-Tak,Jang, Ji-Hyun Elsevier 2017 Journal of Power Sources Vol.337 No.-

<P><B>Abstract</B></P> <P>Realization of a highly flexible, lightweight, and high performance flexible supercapacitor was achieved using three-dimensional graphene on flexible graphite-paper. A simple and fast self-assembly approach was utilized for the uniform deposition of chemical vapor deposition (CVD)-grown high quality 3D-graphene powders on a flexible graphite-paper substrate. The fabricated paper-based symmetric supercapacitor exhibited a maximum capacitance of 260 F g<SUP>−1</SUP> (15.6 mF cm<SUP>−2</SUP>) in a three electrode system, 80 F g<SUP>−1</SUP> (11.1 mF cm<SUP>−2</SUP>) in a full cell, high capacitance retention and a high energy density of 8.8 Wh kg<SUP>−1</SUP> (1.24 μWh cm<SUP>−2</SUP>) at a power density of 178.5 W kg<SUP>−1</SUP> (24.5 μW cm<SUP>−2</SUP>). The flexible supercapacitor maintained its supercapacitor performance well, even under bent, rolled, or twisted conditions, signifying the excellent flexibility of the fabricated device. Our straightforward approach to the fabrication of highly flexible and lightweight supercapacitors offers new design opportunities for flexible/wearable electronics and miniaturized device applications that require energy storage units that meet the demands of the multifarious applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A fully flexible supercapacitor based on 3D-graphene/graphite-paper was fabricated. </LI> <LI> The 3D-porous architecture provided space for easy migration of electrolyte ions. </LI> <LI> Our device exhibited excellent electrochemical performance and flexibility. </LI> <LI> The present approach is simple, fast, scalable, and highly efficient. </LI> </UL> </P>

Analysis and prediction of ultimate strength of high-strength SFRC plates under in-plane and transverse loads

Ramadoss Perumal,S. Palanivel 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.52 No.6

Plates are most widely used in the hulls of floating concrete structures, bridge decks, walls of offshore structures and liquid storage tanks. A method of analysis is presented for the determination of loaddeflection response and ultimate strength of high-strength steel fiber reinforced concrete (HSSFRC) plates simply supported on all four edges and subjected to combined action of external compressive in-plane and transverse loads. The behavior of HSSFRC plate specimens subjected to combined uniaxial in-plane and transverse loads was investigated. The proposed analytical method is compared to the physical test results, and shows good agreement. To predict the constitutive behavior of HSSFRC in compression, a nondimensional characteristic equation was proposed and found to give reasonable accuracy.

Performance and modeling of high-performance steel fiber reinforced concrete under impact loads

Ramadoss Perumal 사단법인 한국계산역학회 2014 Computers and Concrete, An International Journal Vol.13 No.2

Impact performance of high-performance concrete (HPC) and SFRC at 28-day and 56-day under the action of repeated dynamic loading was studied. Silica fume replacement at 10% and 15% by mass and crimped steel fiber (Vf = 0.5%- 1.5%) with aspect ratios of 80 and 53 were used in the concrete mixes. Results indicated that addition of fibers in HPC can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths and toughness of HPC. Variation of fiber aspect ratio has minor effect on improvement in impact strength. Based on the experimental data, failure resistance prediction models were developed with correlation coefficient (R) = 0.96 and the estimated absolute variation is 1.82% and on validation, the integral absolute error (IAE) determined is 10.49%. On analyzing the data collected, linear relationship for the prediction of failure resistance with R= 0.99 was obtained. IAE value of 10.26% for the model indicates better the reliability of model. Multiple linear regression model was developed to predict the ultimate failure resistance with multiple R= 0.96 and absolute variation obtained is 4.9%.

Behavior of high-strength fiber reinforced concrete plates under in-plane and transverse loads

Ramadoss, P.,Nagamani, K. 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.31 No.4

The concrete plates are most widely used structural elements in the hulls of floating concrete structures such as concrete barges and pontoons, bridge decks, basement floors and liquid storage tanks. The study on the behavior of high-strength fiber reinforced concrete (HSFRC) plates was carried out to evaluate the performance of plates under in-plane and transverse loads. The plates were tested in simply supported along all the four edges and subjected to in-plane and traverse loads. In this experimental program, twenty four 150 mm diameter cylinders and twelve plate elements of size 600 × 600 × 30 mm were prepared and tested. Water-to-cementitious materials ratios of 0.3 and 0.4 with 10% and 15% silica fume replacements were used in the concrete mixes. The fiber volume fractions, Vf = 0%, 1% and 1.5% with an aspect ratio of 80 were used in this study. The HSFRC mixes had the concrete ompressive strengths in the range of 52.5 to 70 MPa, flexural strengths ranging from 6.21 to 11.08 MPa and static modulus of elasticity ranging from 29.68 to 36.79 GPa. In this study, the behavior of HSFRC plate elements subjected to combined uniaxial in-plane and transverse loads was investigated.

A new strength model for the high-performance fiber reinforced concrete

P. Ramadoss,K. Nagamani 사단법인 한국계산역학회 2008 Computers and Concrete, An International Journal Vol.5 No.1

Steel fiber reinforced concrete is increasingly used day by day in various structural applications. An extensive experimentation was carried out with w/cm ratio ranging from 0.25 to 0.40, and fiber content ranging from zero to1.5 percent by volume with an aspect ratio of 80 and silica fume replacement at 5%, 10% and 15%. The influence of steel fiber content in terms of fiber reinforcing index on the compressive strength of high-performance fiber reinforced concrete (HPFRC) with strength ranging from 45 85 MPa is presented. Based on the test results, equations are proposed using statistical methods to predict 28-day strength of HPFRC effecting the fiber addition in terms of fiber reinforcing index. A strength model proposed by modifying the mix design procedure, can utilize the optimum water content and efficiency factor of pozzolan. To examine the validity of the proposed strength model, the experimental results were compared with the values predicted by the model and the absolute variation obtained was within 5 percent.

Stress-strain behavior and toughness of high-performance steel fiber reinforced concrete in compression

P. Ramadoss,K. Nagamani 사단법인 한국계산역학회 2013 Computers and Concrete, An International Journal Vol.11 No.2

The complete stress-strain behavior of steel fiber reinforced concrete in compression is needed for the analysis and design of structures. An experimental investigation was carried out to generate the complete stress-strain curve of high-performance steel fiber reinforced concrete (HPSFRC) with a strength range of 52–80 MPa. The variation in concrete strength was achieved by varying the water-to-cementitious materials ratio of 0.40-0.25 and steel fiber content (Vf = 0.5, 1.0 and 1.5% with l/d = 80 and 55) in terms of fiber reinforcing parameter, at 10% silica fume replacement. The effects of these parameters on the shape of stress-strain curves are presented. Based on the test data, a simple model is proposed to generate the complete stress-strain relationship for HPSFRC. The proposed model has been found to give good correlation with the stress-strain curves generated experimentally. Inclusion of fibers into HPC improved the ductility considerably. Equations to quantify the effect of fibers on compressive strength, strain at peak stress and toughness of concrete in terms of fiber reinforcing index are also proposed, which predicted the test data quite accurately. Compressive strength prediction model was validated with the strength data of earlier researchers with an absolute variation of 2.1%.