• Biotechnology and Bioprocess Engineering:BBE
• /
• v.2 no.2
• /
• pp.109-112
• /
• 1997

Morphology of carbonate crystals grown on the surface of artificial cell membranes was controlled by changing the interfacial chemistry. For octadecyltriethoxysilane (OTE) films with terminal methyl groups interacting little with an aqueous calcium carbonate solution calcite (104) crystals were formed. Polymerized pentacosadiynoic acid (PDA) films with terminal carboxylic acid groups induced deposition of calcite (012) crystals aligned along with each other within a polymer domain. On the other hand, stearyl alcohol (StOH) films with terminal hydroxyl groups induced deposition of aragonite crystals. When PDA was mixed with StOH, the 8:1 PDA:StOH (molar ratio) film produced dominating calcite (012) crystals without any crystal alignment, and the 4:1 mixture film produced minor calcite (012) crystals and major aragonite crystals. For the 2:1, 1:1, 1:2, and 1:4 mixture films, aragonite crystals were dominating. Hence, it is found that the chemical composition at the interface plays a very important role in controlling the morphology of deposited carbonate crystals.

• Korean Journal of Materials Research
• /
• v.28 no.10
• /
• pp.578-582
• /
• 2018

ZnO crystals with different morphologies are synthesized through thermal evaporation of the mixture of Zn and Cu powder in air at atmospheric pressure. ZnO crystals with wire shape are synthesized when the process is performed at $1,000^{\circ}C$, while tetrapod-shaped ZnO crystals begin to form at $1,100^{\circ}C$. The wire-shaped ZnO crystals form even at $1,000^{\circ}C$, indicating that Cu acts as a reducing agent. As the temperature increases to $1,200^{\circ}C$, a large quantity of tetrapod-shaped ZnO crystals form and their size also increases. In addition to the tetrapods, rod-shaped ZnO crystals are observed. The atomic ratio of Zn and O in the ZnO crystals is approximately 1:1 with an increasing process temperature from $1,000^{\circ}C$ to $1,200^{\circ}C$. For the ZnO crystals synthesized at $1,000^{\circ}C$, no luminescence spectrum is observed. A weak visible luminescence is detected for the ZnO crystals prepared at $1,100^{\circ}C$. Ultraviolet and visible luminescence peaks with strong intensities are observed in the luminescence spectrum of the ZnO crystals formed at $1,200^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.16 no.1
• /
• pp.1-7
• /
• 2006

Some lead-based crystals show excellent ferroelectric, piezoelectric or scintillation properties and have attracted much attention in recent years. However, the erosion of the high temperature solution on platinum crucible and the evaporation of PbO component are the main problems often encountered during the crystal growth. In this paper, we reported recent progress on the Bridgman growth of lead-based functional crystals, such as novel relaxor ferroelectric crystals (PZNT and PMNT), scintillation crystals $(PbWO_4,\;PbF_2\;and\;PbClF)$ and piezoelectric crystals $(Pb_5Ge_3O_{11}\;and\;Pb_2KNb_5O_{15}),$ in Shanghai Institute of Ceramics, Chinese Academy of Sciences. The vertical Bridgman method has been modified to grow PZNT crystals from high temperature solution and as-grown crystals have been characterized. Large size lead-based scintillators, $PbWO_4\;and\;PbF_2$ crystals, have been mass-produced by the vertical Bridgman method in the multi-crucible fumace. These crystals have been supplied to CERN and other laboratories for high-energy physics experiments. The Bridgman growth of piezoelectric crystals $Pb_5Ge_3O_{11}\;and\;Pb_2KNb_5O_{15}$ are discussed also.

• Journal of the Korean Ceramic Society
• /
• v.24 no.5
• /
• pp.461-469
• /
• 1987

Single crystals of Mn-Zn Ferrite were grown by slow cooling method using Na2B4O7 as flux agent. The effects of flux content and cooling rate on the types of crystals, and the relation between supersaturation and growth mechanism were studied. As a result, the types of grown crystals occurred as plate, hopper and octahedral crystals. The occurrence of these crystal types was dependent on flux content. The habit was found to correlate with the growth rate and supersaturation. The lateral growth of a dendritic crystal is related to the twin layer. The growth of crystals from borax melts mainly occurred by the layer-spreading growth following corner and edge nucleation caused by high supersaturation in the melt. Especially, the plate crystals were produced on top of the melts. The hopper and octahedral crystals occurred at lower supersaturation than the plate crystals.

• Electrical & Electronic Materials
• /
• v.10 no.10
• /
• pp.989-994
• /
• 1997

In a Guest-Host cell the orientational ordering of dyes doped into liquid crystals has been investigated. To evaluate the influence of the host liquid crystals on the ordering of the dyes we have measured precisely the ordering parameters of the liquid crystals by using the dichroic ratio of the absorbances for infrared light polarized parallel and perpendicular to the diector. Our experimental results show that the ordering of the dyes can be expressed as a function of not only the molecular structure of the dyes but also the order parameter of the liquid crystals. These functions are dependent on the kinds of the liquid crystals and the dyes. Particularly the combination such as anthraquinone dyes doped into cyanobiphenyl liquid crystals show a very high ordering parameter. This is considered due to a strong intermolecular interaction between the dipoles of both liquid crystals and dyes.

• Proceedings of the Korea Crystallographic Association Conference
• /
• 2002.11a
• /
• pp.3-3
• /
• 2002

Many studies on crystal growth mechanisms of the hen egg-white lysozyme protein crystals have mainly performed by optical microscopy and atomic force microscopy (AFM). As results, two types of growth mechanisms, which are a two-dimensional nucleation mechanism and a spiral growth mechanism, were identified. However, there was no direct evidence of grown-in screw dislocations at the spiral sites. We first observed the screw dislocations in tetragonal lysozyme crystals using synchrotron X-ray topography. In addition, to confirm the characteristics of dislocations, we have observed some elastic constants in lysozyme crystals in terms of the sound velocity measurement by pulse echo methods. Tetragonal hen egg-white lysozyme crystals were grown by the concentration gradient method. The crystals were grown in test tubes, with an inner diameter of 8 ㎜ and 80 ㎜ in length, held vertically. The test tubes were kept at 23C for 2 weeks. The maximum size of crystals were 3×3×4 ㎟. The high quality crystals were examined by Laue topography with a water filter using synchrotron radiation. Figure is a X-ray topograph. Several straight screw dislocations were observed. We also determined Burgers vector to be a [110] direction. The measurement of sound velocity was performed by the digital signal processing method. the crystals were placed in stainless steel vessel, which was filled with lysozyme solution used for crystal growth. We observed the longitudinal sound velocity along the [110] direction in the tetragonal is obtained to be 1817 ㎧. Therefore, Young modulus and shear modulus were evaluated to be 2.70 Gpa and 1.02 Gpa, respectively, if we assumed Poisson ratio is 0.33. These results will be discussed at the meeting.

• Journal of Korea Foundry Society
• /
• v.14 no.6
• /
• pp.520-529
• /
• 1994

This study describes the influence of the trace amount of sulphur on the nucleation behavior of graphite crystals in high purity Fe-C-Si alloys prepared by levitation melting method. Detailed microstructural analyses of high purity(HP) and sulphur added(HP＋S) samples showed that the nucleation of graphite crystals was prevented by sulphur. With decreasing the sulphur content, the shape of graphite crystals tended to spherulitic, and below 2ppm S, that of graphite crystals was only nodular. The critical cooling rate for the nucleation of griphite crystals was calculated as $1.5{\times}10^3k/s$. It is obvious from this work that residual C-C clusters act as an effective nucleation site for graphite crystals and one of the important role of nodularizing elements is to act as scavenger which removes harmful impurities from the solution.

• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.268-273
• /
• 2004

Deformation of single crystals was studied using finite element analysis to investigate the orientation dependence of plastic deformation observed in NiAl single crystals. Investigation of mechanical properties of single crystals is closely related with the understanding of deformation processes in single crystals. Orientation dependence of material behavior in NiAl single crystals was studied by rotating loading directions from 'hard' orientation. The maximum nominal compressed stress in NiAl single crystals was ranged in a quite wide scope depending on the misalignment from 'hard' orientation. As the compressed axis set closer to 'hard' orientation, the maximum nominal compressed stress rapidly increased and made <100> slips difficult to activate. Therefore, non-<100> slips will be activated instead of <100> slips for 'hard' orientation.

• Journal of Mechanical Science and Technology
• /
• v.19 no.3
• /
• pp.802-810
• /
• 2005

Deformations of single crystals were studied using finite element analysis to investigate the localized modes and the orientation dependence of plastic deformation observed in single crystals. Investigation of mechanical properties of single crystals is closely related with the understanding of deformation processes in single crystals. Localized bands such as shear and kink were studied and the material and geometric characteristics that influence the formation of such localized bands were investigated. Orientation dependence of material behavior in NiAl single crystals was studied by rotating slip directions from 'hard' orientation. The maximum nominal compressed stress in NiAl single crystals was widely ranged depending on the misalignment from 'hard' orientation. As the compression axis was set closer to 'hard' orientation, the maximum nominal compressed stress was rapidly increased and made <100> slips difficult to activate. Therefore, non-<100> slips will be activated instead of <100> slips for 'hard' orientation.

• Current Optics and Photonics
• /
• v.2 no.1
• /
• pp.47-52
• /
• 2018

We systematically investigated the negative-refraction effect for both TE and TM polarizations in annular photonic crystals. Since two polarization waves are excited in different bands, they result in different refractive angles, and so polarization beam splitters can be made of annular photonic crystals. It was found that, in comparison to normal square-lattice air-hole photonic crystals, annular photonic crystals have a much wider common frequency band between TE-1 and TM-2, which is quite beneficial to finding the overlap between the negative-refraction regions belonging to TE-1 and TM-2 respectively. Further analyses of equifrequency surfaces and the electric-field distribution of annular photonic crystals with different parameters have not only demonstrated how the filling factor of annular cells affects the formation of the common negative-refraction region between TE-1 and TM-2, but also revealed some ways to improve the performance of a polarization beam splitter based on the negative-refraction effect in an annular photonic crystal.