Synthesis of Calcium Phosphate Minerals from Biowaste Clam Shells Using Microwave Heating

Bramhe, Sachin,Ryu, Jae-Kyung,Chu, Min Cheol,Balakrishnan, Avinash,Kim, Taik Nam Materials Research Society of Korea 2014 한국재료학회지 Vol.24 No.12

Calcium phosphate minerals are biologically important because of their application in the fields of orthopaedics and dentistry. Herein we have tried to synthesize calcium phosphate minerals from biowaste clam shells. A simple microwave method was used to synthesize a mixture of calcium phosphate minerals such as hydroxyapatite, tri-calcium phosphate, and monetite. The microwave induces vibration of the dipole ions in the reagent. The heating and rearrangement of ions and atoms occurs during the process. The phases obtained in the final powder were ascertained by X-ray diffraction; the morphology of each sample was checked using a scanning electron microscope. We were able to obtain a mixture of calcium phosphate minerals using the microwave method; the calcined powder showed a brick like morphology, which is different from the rod shape morphology of the hydroxyapatite obtained using the hydrothermal process.

Facile Synthesis of Hydroxyapatite by Hydrothermal and Solvent Combustion Methods

Bramhe, Sachin N,Lee, Hyun Chul,Chu, Min Cheol,Ryu, Jae-Kyung,Balakrishnan, Avinash,Kim, Taik Nam Materials Research Society of Korea 2015 한국재료학회지 Vol.25 No.9

Hydroxyapatite (HA), which is an important calcium phosphate mineral, has been applied in orthopedics, dentistry, and many other fields depending upon its morphology. HA can be synthesized with different morphologies through controlling the synthesis method and several parameters. Here, we synthesize various morphologies of HA using two simple methods: hydrothermal combustion and solution combustion. The phase purity of the synthesized HA is confirmed using X-ray diffractometry. It demonstrates that pure phased hydroxyapatite can be synthesized using both methods. The morphology of the synthesized powder is examined using scanning electron microscopy. The effects of pH and temperature on the final powder are also investigated. At $140^{\circ}C$, using the hydrothermal method, nano-micro HA rods with a hexagonal crystal structure can be synthesized, whereas using solution combustion method at $600^{\circ}C$, a dense cubic morphology can be synthesized, which exhibits monoclinic crystal structures.

Conversion from biowaste Venerupis clam shells to hydroxyapatite nanowires

Bramhe, S.,Kim, T.N.,Balakrishnan, A.,Chu, M.C. North-Holland 2014 Materials letters Vol.135 No.-

The present study demonstrates a novel approach by which biowaste clam shells derived from Venerupis species can be processed into high aspect ratio one dimensional wires being an interesting candidate to biomedical applications. These nanowires were synthesized hydrothermally and exhibited an aspect ratio in the order of 10<SUP>2</SUP> with a surface area of 40m<SUP>2</SUP>g<SUP>-1</SUP> and narrowly distributed diameter size range from 40 to 130nm. Fast Fourier transform analysis during high resolution transmission electron microscopy showed the wires exhibiting growth along (300). X-ray diffractometry and Fourier-transform Infra-red spectroscopy showed that the nanowires produced were of high purity.

Synthesis of Yttria Stabilized Zirconia by Sol-gel Precipitation Using PEG and PVA as Stabilizing Agent

Bramhe, Sachin N.,Lee, Young Pil,Nguyen, Tuan Dung,Kim, Taik-Nam Materials Research Society of Korea 2013 한국재료학회지 Vol.23 No.8

There is increasing interest in zirconia as a dental material due to its aesthetics, as well as the exceptionally high fracture toughness and high strength that are on offer when it is alloyed with certain oxides like yttria. In recent years, many solution based chemical synthesis methods have been reported for synthesis of zirconia, of which the sol-gel method is considered to be best. Here, we synthesize zirconia by a sol gel assisted precipitation method using either PEG or PVA as a stabilizing agent. Zirconia sol is first synthesized using the hydrothermal method. We used NaOH as the precipitating agent in this method because it is easy to remove from the final solution. Zirconium and yttrium salts are used as precursors and PEG or PVA are used as stabilizers to separate the metal ions. The resulting amorphous zirconia powder is calcined at $900^{\circ}C$ for 2 h to get crystallized zirconia. XRD analysis confirmed the partially stabilized zirconia synthesis in all the synthesized powders. SEM was taken to check the morphology of the powder synthesized using either PEG or PVA as a stabilizing agent and finally the transparency was calculated. The results confirmed that the powder synthesized with 10 % PVA as the stabilizing agent had highest percentage of transparency among all the synthesized powder.

Yttria Stabilized Zirconia Synthesis via Hydrothermal Assisted Sol-Gel Method Using PVA as Stabilizing Agent

이용필, Bramhe Sachin N, 김택남 배재대학교 공학연구소 2013 공학논문집 Vol.15 No.1

Zirconia has many excellent mechanical properties which has helped it gain attention as a dental material. Sol-gel method is universally accepted as the best method for the synthesis of zirconia. Here we have tried to synthesize zirconia by combining hydrothermal and sol-gel method. NaOH is added as the precipitating agent who forms salt in the reaction mixture which can be easily separated from the final solution. Zirconium and yttrium salts are used as precursors and PVA is used to separate the metal ions. Finally the zirconia powder obtained is calcined at 900oC for 2hrs. XRD analysis was done on the samples to confirm the crystal structure of the synthesized zirconia. SEM was taken to check the morphology of zirconia. Finally transparency of the synthesized zirconia was checked which shows that 10% PVA shows highest percentage of transparency among all the synthesized powder.

Synthesis of 3 mol % yttria stabilized zirconia using precipitation and sol-gel method

사신 브람, 김택남 배재대학교 공학연구소 2012 공학논문집 Vol.14 No.1

There is increasing interest in zirconia as a dental material due to its aesthetics. Sol-gel method is considered to be the best for its synthesis. Here we have tried to synthesize zirconia by combining precipitation with sol-gel method. NaOH is the precipitating agent used in this method, which we think, is easy to separate from the final solution. Zirconium and yttrium salts are used as precursors and PEG is used to separate the metal ions. Finally the zirconia powder obtained is calcined at 900oC for 2hrs. XRD analysis was done on the samples to confirm the crystal structure which showed that 1M ZrOCl2 gave the best result.

Optical Properties of Opal Glass on the Various Contents of Chemical Composition

Nguyen, Tuan Dung,N., Bramhe Sachin,Kim, Ji Ho,Kim, Taik-Nam Materials Research Society of Korea 2013 한국재료학회지 Vol.23 No.1

Opal glass samples having different chemical compositions were synthesized and transparent glass was obtained after melting. The effects of $TiO_2$, $BaF_2$, and $CeO_2$ content on the color of the opal glass were studied by observing images of the opal samples and analyzing the results via ultraviolet visible spectroscopy and color spectrometry. The aesthetic properties of the opal glass were determined by studying the transmittance of visible light in the 400 nm to 700 nm range. The basic chemical composition of opal glass was $SiO_2$ 52.9 wt%, $Al_2O_3$ 12.35 wt%, $Na_2CO_3$ 15.08 wt%, $K_2CO_3$ 10.35 wt%, $Ca_3(PO)_4$ 4.41 wt%, $MgCO_3$ 1.844 wt%, $LiCO_3$ 2.184 wt%, and $TiO_2$ 0.882 wt%. The glass samples were prepared by varying the weight percentage of $TiO_2$, $BaF_2$, and $CeO_2$. The transmittance of visible light was decreased from 95 % to 75 % in the glass samples in which $TiO_2$ content was increased from 0 to 3.882 wt%. In the blue spectrum region, as the content of $TiO_2$ increased, the reflectance value was observed to become higher. This implies that $TiO_2$ content induces more crystal formation and has an important effect on the optical properties of the glass. The opalescence of opal samples that contained $CeO_2$ or $BaF_2$ is stronger than that in the samples containing $TiO_2$. Opal glass samples comprising $TiO_2$ had tetragonal lattice structures; samples including $CeO_2$ as an additive had cubic lattice structures (FCC, $CeO_2$).

Performance of Electric Double Layers Capacitor Using Activated Carbon Materials from Rice Husk as Electrodes

Nguyen, Tuan Dung,Ryu, Jae Kyung,Bramhe, Sachin N.,Kim, Taik-Nam Materials Research Society of Korea 2013 한국재료학회지 Vol.23 No.11

Activated carbon (AC) was synthesized from rice husks using the chemical activation method with KOH, NaOH, a combination of (NaOH + $Na_2CO_3$), and a combination of (KOH + $K_2CO_3$) as the chemical activating reagents. The activated carbon with the highest surface area (around $2000m^2/g$) and high porosity, which allows the absorption of a large number of ions, was applied as electrode material in electric double layer capacitors (EDLCs). The AC for EDLC electrodes is required to have a high surface area and an optimal pore size distribution; these are important to attain high specific capacitance of the EDLC electrodes. The electrodes were fabricated by compounding the rice husk activated carbons with super-P and mixed with polyvinylidene difluoride (PVDF) at a weight ratio of 83:10:7. AC electrodes and nickel foams were assembled with potassium hydroxide (KOH) solution as the electrolyte. Electrochemical measurements were carried out with a three electrode cell using 6 M KOH as electrolyte and Hg/HgO as the reference electrode. The specific capacitance strongly depends on the pore structure; the highest specific capacitance was 179 F/g, obtained for the AC with the highest specific surface area. Additionally, different activation times, levels of heating, and chemical reagents were used to compare and determine the optimal parameters for obtaining high surface area of the activated carbon.

Reliable and High Spatial Resolution Method to Identify the Number of MoS₂ Layers Using a Scanning Electron Microscopy

Sharbidre, Rakesh Sadanand,Park, Se Min,Lee, Chang Jun,Park, Byong Chon,Hong, Seong-Gu,Bramhe, Sachin,Yun, Gyeong Yeol,Ryu, Jae-Kyung,Kim, Taik Nam Materials Research Society of Korea 2017 한국재료학회지 Vol.27 No.12

The electronic and optical characteristics of molybdenum disulphide ($MoS_2$) film significantly vary with its thickness, and thus a rapid and accurate estimation of the number of $MoS_2$ layers is critical in practical applications as well as in basic researches. Various existing methods are currently available for the thickness measurement, but each has drawbacks. Transmission electron microscopy allows actual counting of the $MoS_2$ layers, but is very complicated and requires destructive processing of the sample to the point where it will no longer be useable after characterization. Atomic force microscopy, particularly when operated in the tapping mode, is likewise time-consuming and suffers from certain anomalies caused by an improperly chosen set point, that is, free amplitude in air for the cantilever. Raman spectroscopy is a quick characterization method for identifying one to a few layers, but the laser irradiation causes structural degradation of the $MoS_2$. Optical microscopy works only when $MoS_2$ is on a silicon substrate covered with $SiO_2$ of 100~300 nm thickness. The last two optical methods are commonly limited in resolution to the micrometer range due to the diffraction limits of light. We report here a method of measuring the distribution of the number of $MoS_2$ layers using a low voltage field emission electron microscope with acceleration voltages no greater than 1 kV. We found a linear relationship between the FESEM contrast and the number of $MoS_2$ layers. This method can be used to characterize $MoS_2$ samples at nanometer-level spatial resolution, which is below the limits of other methods.

Residue Free Fabrication of Suspended 2D Nanosheets for in-situ TEM Nanomechanics

Sharbidre, Rakesh Sadanand,Byen, Ji Cheol,Yun, Gyeong Yeol,Ryu, Jae-Kyung,Lee, Chang Jun,Hong, Seong-Gu,Bramhe, Sachin,Kim, Taik Nam Materials Research Society of Korea 2018 한국재료학회지 Vol.28 No.11

Two dimensional(2D) crystals, composed of a single layer or a few atomic layers extracted from layered materials are attracting researchers' interest due to promising applications in the nanoelectromechanical systems. Worldwide researchers are preparing devices with suspended 2D materials to study their physical and electrical properties. However, during the fabrication process of 2D flakes on a target substrate, contamination occurs, which makes the measurement data less reliable. We propose a dry transfer method using poly-methyl methacrylate(PMMA) for the 2D flakes to transfer onto the targeted substrate. The PMMA is then removed from the device by an N-Methyl-2-pyrrolidone solution and a critical point dryer, which makes the suspended 2D flakes residue free. Our method provides a clean, reliable and controllable way of fabricating micrometer-sized suspended 2D nanosheets.