MICROSTRUCTURAL ANALYSIS OF SINTERING BEHAVIOR OF INTRA - GRAIN PORES

Rajagopalan, Raj,Kim, Hern 한국화학공학회 1998 Korean Journal of Chemical Engineering Vol.15 No.6

A lattice-based Monte Carlo simulation approach has been developed for studying the behavior of intragrain pores during the intermediate and final stages of sintering. The changes of the microstructures and the resulting properties of intra-grain pores during sintering are easily examined. The sintering behavior such as pore size distribution, average pore size, etc. is in very good agreement with the experimental observations. In addition, the relationships between the number of pores and the average pore volume agree well with theory.

CHARACTERIZATION OF SIMULATED MICROSTRUCTURES IN POLYDISPERSE PARTICLE DEPOSITION

Rajagopalan, Raj,Kim, Hern 한국화학공학회 1994 Korean Journal of Chemical Engineering Vol.11 No.4

The deposition of polydisperse particles under the influence of gravity is examined using computer simulation. A parameter, σ, that represents the standard deviation of particle size is used for studying the effect of the variation in polydispersity on the resulting microstructures. Structural correlations are examined through contact networks, radial and angular distribution functions, and diffraction patterns. The results show that the onset of ordering appears near σ=0.05 as σ is decreased. The long-range ordering of the structures is not influenced by the introduction of a small amount of polydispersity, which may increase the uniformity of local density distribution in the angular direction. Polydisperse systems with small deviations in size display stronger positional order in some directions and this in turn contributes to the uniformity of overall packing structures.

SIMULTANEOUS EFFECTS OF ADHESION AND POLY - DISPERSITY ON MICROSTRUCTURES AND GEOMETRICAL PROPERTIES IN PARTICLE DEPOSITION

Rajagopalan, Raj,Kim, Hern 한국화학공학회 1994 Korean Journal of Chemical Engineering Vol.11 No.4

The simultaneous effects of adhesion and polydispersity on packing (or deposit) microstructures and their bulk properties are examined. The results show that the microstructures and bulk properties of the deposits vary sharply with the introduction of even small adhesion and polydispersity. A structural phase diagram is obtained as functions of adhesion and polydispersity. Increases in adhesion lead to noticeable or large fluctuations in packing fractions for polydisperse systems. However, the packing fraction can be stabilized and the fluctuations greatly reduced regardless of fhe magnitude of the polydispersity index by keeping the adhesion relatively low (i.e., s≤0.1).

Simultaneous Effects of Adhesion and Poly - dispersity on Microstructures and Geometrical Properties in Particle Deposition

Rajagopalan, Raj,Kim, Hern 한국화학공학회 1995 NICE Vol.13 No.1

The simultaneous effects of adhesion and polydispersity un packing(or deposit) microstructures and their bulk properties are examined. the results show that the microstructures and bulk properties of the deposits vary sharply with the introduction of even small adhesion and polydispersity. A structural phase diagram is obtained as functions of adhesion and polydispersity. Increases in adhesion lead to noticeable or large fluctuations in packing fractions for polydisperse systems. However, the packing fraction can be stabilized and the fluctuations greatly reduced regardless of the magnitude of the polydispersity index by keeping the adhesion relatively low(i.e., s≤0.1).

학술발표회 초록 -특강 - ( 재료 (4) ) : 세라믹 제조공정의 해석 및 설계용 전산실험 모델

김헌,Raj Rajagopalan ( Hern Kim,Raj Rajagopalan ) 한국화학공학회 1994 추계학술발표회 Vol.- No.-

입자침적시 미세구조 변화 분석용 전산모사 모델

김헌,Rajagopalan,Raj 한국화학공학회 1994 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.32 No.5

Hard-sphere입자들의 침적시 미세구조 및 부피분율과 같은 성질의 변화를 조사하기 위한 Monte Carlo 모사모델이 개발되었다. 다양한 입자계 및 공정조건의 영향을 분석하기 위한 주요 매개변수로서 Peclet수가 사용되었다. 침적물이 결정구조를 형성하는 최적조건, 동적 상거동, 초기 부피분율의 영향, 복합분산입자들의 분리 등이 검토되었다. 본 모델로 예측한 여러 결과들이 실험관찰과 정성적으로 잘 일치하는 것이 주목되었다. 본 모델은 여러 관련된 실험연구를 설계하는 간편하고도 효과적인 기구로서 사용될 수 있다. A Monte Carlo simulation model was developed to investigate the changes of microstructures and their properties such as packing fraction during the deposition of hard-sphere particles. As a major parameter Peclet number was used to analyze the effects of particulate systems and process conditions. The optimum conditions where the deposits form ordered structures, the dynamic phase behavior, the effects of initial volume fraction, the size fractionation of polydisperse particles, and so on were also examined. It was noted that a number of results predicted from the present model are in good qualitative agreement with experimental observations. The present model can be used as a simple and effective tool for designing a number of related experimental studies.

Novel Interfacial Bulk Heterojunction Technique for Enhanced Response in ZnO Nanogenerator

Pandey, Rajagopalan,Maria Joseph Raj, Nirmal Prasanth,Singh, Vipul,Iyamperumal Anand, Palani,Kim, Sang-Jae American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.6

<P>In this paper, a direct sustainable approach for the development of a n-ZnO:p-CuO heterojunction (ZCH) through a simple grinding is reported to be an effective technique to enhance the piezoelectric performance of ZCH/polydimethylsiloxane (PDMS) nanocomposite-based nanogenerators (ZP-PNGs). We have first optimized the best concentration for ZnO/PDMS nanocomposite for the realization of the piezoelectric nanogenerator. Later, with the same configuration, we implemented a novel, simple, facile, frugal, and inexpensive technique to fabricate ZCH. The heterojunction results in the improved charge transfer characteristics, low capacitance, and charge nullification contributing to the enhanced piezoelectric output. This reflects in the improvement of the peak-to-peak piezoelectric potential of the device from 2.7 to 9 V. The instantaneous max power density was found to be 0.2 mW/m<SUP>2</SUP>. The device can work as a force sensor with improved sensitivity of 1.7 V/N compared to 1.05 V/N of the intrinsic device. The device is being systematically studied for load matching and capacitor charging to demonstrate its practicability. Furthermore, we tested our device to harness the biomechanical energy from day-to-day life activities. Finally, the device was used to fabricate sustainable piezoelectric-based smart urinal systems for low-income group countries.</P> [FIG OMISSION]</BR>

Phase inversion enabled energy scavenger: A multifunctional triboelectric nanogenerator as benzene monitoring system

Khandelwal, Gaurav,Chandrasekhar, Arunkumar,Pandey, Rajagopalan,Maria Joseph Raj, Nirmal Prashanth,Kim, Sang-Jae Elsevier Sequoia 2019 Sensors and actuators. B Chemical Vol.282 No.-

<P><B>Abstract</B></P> <P>Mechanical energy harvesting using Triboelectric nanogenerator (TENG) based on the coupling of electrostatic induction and contact electrification is a cost-effective and straightforward process. TENG is well known for harnessing the waste energy at a large scale. Here, we demonstrated the fabrication of enhanced-performance TENG in contact-separation mode by utilizing the facile phase inversion process for only one triboactive layer. The phase inversion is a straightforward technique to achieve films with a porous structure and high crystallinity. The non-piezoelectric, semiconducting TiO<SUB>2</SUB> microparticle acts as charge trapping sites attributed to their high dielectric constant. The PVDF-10-TiO<SUB>2</SUB>/CA TENG showed 7 times and 10 times enhancement for voltage and short circuit current compared to the PVDF-TiO<SUB>2</SUB>/CA TENG prepared without phase inversion process. Furthermore, the device is a multifunctional energy harvester i.e. it can harvest biomechanical as well as wind energy. Finally, we demonstrated the use of TENG device for volatile organic compounds (VOCs) sensing. The device exhibits good response with the change in concentration as well as total flow rate. The voltage decreases with the increase in the benzene concentration. The sensitivity of as fabricated sensor is 0.0035 V/ppm concerning concentration and 0.29176 V/sccm concerning total flow rate. The sensor was integrated with the Arduino Uno for automatic detection of benzene giving the alarm warning for the presence of benzene in the environment. This work extended the application of TENG in the field of VOCs sensing, design and concept which can be applied in the future for the detection of other VOCs in the environment.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Phase inversion and semi conducting TiO<SUB>2</SUB> based TENG with enhanced performance. </LI> <LI> The TENG shows 7 times and 10 times enhancement for voltage and current. </LI> <LI> Fabricated TENG is multifunctional energy harvester. </LI> <LI> Demonstration of TENG as VOC’s sensor with good selectivity and sensitivity. </LI> <LI> Integration of TENG with Arduino for warning message and alarm to evacuate. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>