Papers by Keyword: OPAL

Abstract: Natural opal, an amorphous, hydrous form of silica (SiO₂-n-H₂O), has been one of the favored precious gemstones for many centuries. Though beautiful, opal is very fragile and is damaged quite easily. Thus, opals of all varieties have been synthesized experimentally and commercially. The objective of this project was to synthesize and to compare crystalline opals. In this work, the development of powder sintered glass ceramics process based on soda lime silica glass waste with metal oxide powder enable jewelry applications. The substantial viscous flow of the glass led to dense products for rapid treatments at relatively low temperatures (900–1,000°C), whereas glass/metal powder interactions resulted in the formation of color agent crystals, provide enhancing optical properties. Several techniques were applied for characterization of the ingots. The chemical analysis was performed by Energy Dispersive X-ray Fluorescence (ED-XRF). The mineralogical compositions of the samples were determined by X-ray diffraction analysis. Raman spectroscopy was applied for optical characterization. The results were compared with a natural common opal. The present investigation demonstrated that the common opal with both color and colorless appearance can be synthesized by the technique, as the crystalline phase of opal structure was identified by XRD measurement. There is a great potential for such materials with novel functionalities for artificial gemstone application, i.e. opal forming.

Abstract: The bottom-up colloidal synthesis of photonic band gap (PBG) materials or photonic crystals (PC) has attracted considerable interest as compared to so-called top-down lithographic approaches due to the simple processing steps involved and the prospect of the economically viable production of complex 3-dimensional optical materials from simple colloidal particles. To date self-assembly techniques constitute the most popular approach to fabricate 3D photonic crystals from colloidal particle suspensions. Based on the natural tendency of monodisperse colloidal particles to organise into ordered arrays, this method represent the best option due to the ease of fabrication, ability to produce larger area samples and cost. Here we report on the fabrication of long range three-dimensional (3D) ordered poly (methyl methacrylate) (PMMA)-silica PC structures and the subsequent fabrication of robust silica inverse opals using self-assembly methods. The optical properties of these materials are described and discussed in terms of potential applications of these materials.

Abstract: A nano-material named opal blended with polymer, then were added into slurry, after a series of special paper-making process, the rice paper releasing anion was successfully prepared by us. By test of SEM, we observed nano-structure morphology in the image of opal particle and rice paper sample. A series of mechanical properties had been tested as GB18739 or QB/T3515 standard. After testing of anion concentration, maximum of rice paper reached -9510cm^-3，meet the needs of human health. There is no doubt opal is a kind of environmental material for human health.

Abstract: In this study, Tin Oxide (SnO₂) inverse opal was fabricated by infiltrating SnO₂ sol-gel precursor solution into Poly Styrene (PS) spheres crystal template which was generated via evaporative deposition self-assembling, then was heat treating at 500°C for two hours in controlled atmosphere box furnaces. PS spheres crystal template was characterized by Scanning electron microscope and Ultraviolet-visible-near infrared absorption spectrometer. The SnO₂ inverse opal was characterized by Scanning electron microscope, Energy Diffraction Spectrum, X Ray Diffraction. The large-area, highly ordered SnO₂ inverse opal was achieved in this paper.

Abstract: Opal as a carrier, tetrabutyl titanate as a titanium source, TiO2 loaded on opal was prepared by sol-gel technique. The photocatalysts were characterized by XRD, TEM and UV-VIS absorption spectrum. Their photocatalytic activities were examined by the photocatalytic decolorization of methylene blue solution under UV light irradiation. The effects of calcination temperature, the amount of TiO2 loading and pH on photocatalytic activities were discussed. The results show that TiO2 supported on opal induced enhancement of photocatalytic decolorization rant and TiO2 doping is about 30 wt. % with 92.15% of decolorization rate at 700°C.

Abstract: All over the world the investigations of nanophotonic structures called photonic crystals (PCs) are performed. These crystals have potential applications in optoelectronics, e.g. optical filters, antireflective surface coatings, lossless frequency selective mirrors. In Institute of Physics at Silesian Technical University the opal photonic crystals consisting of monodisperse spherical particles, that have diameters of several hundred nanometers, are produced using colloidal self-assembly technics. The main aim of this work is the comparison between pieces of information on morphology of photonic crystals that can be obtained from electron microscopy and from the angular characteristics of optical transmittance and reflectance. The morphology of the samples is characterized by scanning electron microscopy (SEM). Nanosphere diameters are established from statistical analysis of SEM images. The optical properties, which are determined by the photonic band structure, are studied by means of light transmission and reflection measurements. There is a relationship between the wavelength position of transmittance minimum or reflectance maximum and the diameter of the nanospheres. The size of nanospheres obtained from optical measurement results were compared with data obtained from SEM images.

Abstract: In the study, porous amorphous silica minerals including Porous Silicon (PS), Diatomite Filter Aid (DFA) and Opal (Op) were chosen as carriers or supports to prepare TiO₂/PS, TiO₂/DFA and TiO₂/Op composites by chemical co-precipitation method. The compound materials were characterized by SEM, TEM, and the photo-catalytic property of the prepared composites was investigated by degradation of Rhodamine B (RhB). Characterization showed that nanoTiO₂ was coated on the surface of porous amorphous silica minerals. The crystal form of TiO₂ was mainly anatase, and the size of which was nanoscale. Through comparative analysis, the photo-catalytic efficiency of TiO₂/PS composite was the best, followed by TiO₂/ DFA, and then TiO₂/Op.

Abstract: By mimicking the fine structures of butterflies wings and peacocks feathers, we have successfully brought structural color to silk fabrics. The three-dimensional (3D) face centre cubic (FCC) opal or inverse opal structure was constructed on the surface of the silk fabrics by materials assembly. The diversified colors were achieved by precisely controlling the lattice constants of the photonic crystals.

Abstract: Results of optical properties investigations of photonic crystals, filled by ferrites, are presented. The photonic crystals consist of amorphous SiO2 spherical nanoclusters. Pores of the crystals were filled by ferrites , where . Reflectance spectra were studied in visible range. It was shown that the reflectivity of the fabricated magnetophotonic crystals increases up to 80% under magnetization.

Abstract: ASTM (American Standard Testing and Materials) C 618 prohibits use of biomass ash in concrete. This paper systematically investigates mitigation of Alkali Silica Reaction (ASR) expansion of concrete by three biomass ashes (cement: biomass ash = 65: 35 by weight), and the ASR expansion is triggered by high alkali cement and opal (1-9% weight of quartz replacement). The three biomass ashes come from switchgrass or sawdust cofired with Powder River Basin coal and they cut the ASR expansion significantly below 50% of the control level; however, all three biomass ashes doubled the available alkali of the cement they replaced. Therefore, the exclusion of biomass ash in concrete by ASTM C 618 seems impropriate and more quality research on its role in mitigating ASRs expansion should be conducted.