scholarly journals Microstructural and Optical Properties of MgAl2O4 Spinel: Effects of Mechanical Activation, Y2O3 and Graphene Additions

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7674
Author(s):  
Nina Obradovic ◽  
William G. Fahrenholtz ◽  
Cole Corlett ◽  
Suzana Filipovic ◽  
Marko Nikolic ◽  
...  
Keyword(s):  
Optical Properties ◽  
Mechanical Activation ◽  
Spinel Phase ◽  
High Hardness ◽  
Rietveld Analysis ◽  
High Mechanical Strength ◽  
Low Dielectric ◽  
Oxide Powders ◽  
Spectral Selectivity ◽  
Α Al2o3

Magnesium aluminate and other alumina-based spinels attract attention due to their high hardness, high mechanical strength, and low dielectric constant. MgAl2O4 was produced by a solid-state reaction between MgO and α-Al2O3 powders. Mechanical activation for 30 min in a planetary ball mill was used to increase the reactivity of powders. Yttrium oxide and graphene were added to prevent abnormal grain growth during sintering. Samples were sintered by hot pressing under vacuum at 1450 °C. Phase composition and microstructure of sintered specimens were characterized by X-ray powder diffraction and scanning electron microscopy. Rietveld analysis revealed 100% pure spinel phase in all sintered specimens, and a decrease in crystallite size with the addition of yttria or graphene. Density measurements indicated that the mechanically activated specimen reached 99.6% relative density. Furthermore, the highest solar absorbance and highest spectral selectivity as a function of temperature were detected for the mechanically activated specimen with graphene addition. Mechanical activation is an efficient method to improve densification of MgAl2O4 prepared from mixed oxide powders, while additives improve microstructure and optical properties.

ELECTRONIC STRUCTURE AND OPTICAL PROPERTIES OF CRYSTALLINE C60

1992 ◽  
Vol 06 (06) ◽  
pp. 309-321 ◽  
Author(s):  
W.Y. CHING ◽  
MING-ZHU HUANG ◽  
YONG-NIAN XU ◽  
FANQI GAN
Keyword(s):  
Optical Properties ◽  
Electronic Structure ◽  
First Principles ◽  
Optical Spectrum ◽  
Local Density ◽  
Low Dielectric Constant ◽  
Experimental Measurements ◽  
Absorption Bands ◽  
Low Dielectric ◽  
Good Agreement

The electronic structure and optical properties of crystalline C 60 and their pressure dependence have been studied by first-principles local density calculations. It is shown that fcc C 60 has a low dielectric constant and an optical spectrum rich in structures. The spectrum shows five disconnected absorption bands in the 1.4 to 7.0 eV region with sharp structures in each band that can be attributed to critical point transitions. This is a manifestation of the localized molecular structure coupled with long range crystalline order unique to the C 60 crystal. At a sufficient high pressure, the structures in the optical spectrum start to merge due to the merging of the bands. These results are in good agreement with some recent experimental measurements.

Optical properties of zinc oxide powders

1979 ◽  
Vol 30 (1) ◽  
pp. 91-93
Author(s):  
M. M. Malov ◽  
V. P. Kutepova
Keyword(s):  
Zinc Oxide ◽  
Optical Properties ◽  
Oxide Powders

scholarly journals Application of Mechanical Activation in Synthesizing Multiferroic Pb(Fe1/2Nb1/2)O3 Powders

2011 ◽  
Vol 56 (4) ◽  
pp. 1015-1020 ◽  
Author(s):  
D. Bochenek ◽  
G. Dercz ◽  
D. Oleszak
Keyword(s):  
Structural Analysis ◽  
Mechanical Activation ◽  
Mossbauer Spectroscopy ◽  
High Energy ◽  
Partial Synthesis ◽  
Oxide Mixture ◽  
High Energy Milling ◽  
Oxide Powders ◽  
Simple Oxide ◽  
Powder Samples

Application of Mechanical Activation in Synthesizing Multiferroic Pb(Fe1/2Nb1/2)O3 Powders In the study, the method of high-energy powder milling - mechanical activation (MA) was used for synthesizing Pb(Fe1/2Nb1/2)O3 (PFN) powders. For the purpose of comparing the influence of high-energy milling on PFN synthesis, two groups of powder samples were used. The first mixture consisting of simple oxide powders; the second one consisting of compound oxide powders. The obtained powders were subjected to structural analysis with the use of XRD and Mőssbauer spectroscopy. Tests revealed that during the process of high-energy milling of initial constituents a partial synthesis of PFN material phases occurs. By comparing the two methods of PFN synthesizing it may be stated that mechanical activation in the case of a simple oxide mixture (PFN1) is equally effective as for a compound oxide mixture (PFN2).

scholarly journals Effect of Ti doping on mechanical and optical properties of super-hard I2d-CN2 materials

RSC Advances ◽  
2017 ◽  
Vol 7 (60) ◽  
pp. 37943-37951 ◽  
Author(s):  
Ze-Cheng Zhao ◽  
Chuan-Lu Yang ◽  
Mei-Shan Wang ◽  
Xiao-Guang Ma ◽  
Li-Bo Zhan ◽  
...  
Keyword(s):  
Optical Properties ◽  
Solar Energy ◽  
Visible Light ◽  
Formation Energy ◽  
High Hardness ◽  
Light Response ◽  
Energy Harvest ◽  
Visible Light Range ◽  
Ti Doping

The Ti-doped I2d-CN2 structures are favorable solar energy harvest or light-response materials due to their lower formation energy, high hardness and large absorption in the infrared and visible light range.

Modeling the optical properties of sapphire (α-Al2O3)

1998 ◽  
Vol 157 (1-6) ◽  
pp. 72-76 ◽  
Author(s):  
Aleksandra B. Djurišić ◽  
E.Herbert Li
Keyword(s):  
Optical Properties ◽  
Α Al2o3

Rietveld analysis of mechanically activated BaCO3–TiO2 system

2008 ◽  
Vol 23 (S1) ◽  
pp. S13-S17 ◽  
Author(s):  
Márcio de Sousa Góes ◽  
José Arana Varela ◽  
Carlos de Oliveira Paiva-Santos ◽  
Biljana D. Stojanovic ◽  
André Vitor Chaves de Andrade
Keyword(s):  
Mechanical Activation ◽  
Diffraction Data ◽  
Rietveld Analysis ◽  
Milling Process ◽  
X Ray Diffraction ◽  
Calcination Time ◽  
Calcination Process ◽  
X Ray ◽  
Weight Percentage ◽  
Crystallite Shape

BaTiO3 powders were prepared through mechanical activation chemistry and analyzed by Rietveld refinement with X-ray diffraction data. Raw BaCO3 and TiO2 powders were dry milled for 5 and 20 h and then calcinated for 2 and 4 h at 800 °C. The milling process was found to have broken up the BaCO3 and TiO2 crystals into smaller crystals and formed only small amounts (<1.5 wt%) of BaTiO3. Subsequence calcinations for 2 and 4 h at 800 °C successfully produced large amounts (>97.7 wt%) of BaTiO3 crystals. The calcination process also generated microstrains and crystallite-size anisotropy in BaTiO3. An increase in the calcination time from 2 to 4 h increased the BaTiO3 weight percentage and the crystallite-shape anisotropy, but decreased the tetragonal distortion anisotropic microstrains in BaTiO3 crystals.

Structural and optical properties of SnO2 films grown on α-Al2O3(0001) by MOCVD

2008 ◽  
Vol 310 (2) ◽  
pp. 295-298 ◽  
Author(s):  
Xianjin Feng ◽  
Jin Ma ◽  
Fan Yang ◽  
Feng Ji ◽  
Caina Luan ◽  
...  
Keyword(s):  
Optical Properties ◽  
Structural And Optical Properties ◽  
Α Al2o3

Effects of SiO2 and ZrO2 Additives on Microstructure and Properties of Al2O3 Ceramic

2013 ◽  
Vol 745-746 ◽  
pp. 523-527
Author(s):  
Yi Hua Li ◽  
De Chang Jia ◽  
Zhi Hua Yang ◽  
Yu Zhou
Keyword(s):  
High Hardness ◽  
Composite Ceramic ◽  
High Tech ◽  
Composite Ceramics ◽  
High Mechanical Strength ◽  
Mullite Phase ◽  
Good Corrosion Resistance ◽  
Alumina Composite ◽  
Resistance Performance ◽  
Silicon Sol

Alumina ceramic, with high mechanical strength, good electric insulation, high hardness and good corrosion resistance performance, has been widely used in machinery, electronic and electrical, chemical, medicine, construction and other high-tech areas. In this study, both silicon sol and zirconia particles are incorporated into the system and dense alumina composite ceramics were prepared by cold isostatic processing and pressureless sintering at 1550 . The influence of additives on phase composition, microstructure and mechanical properties were investigated. The XRD results show that mullite phase was generated in the composite ceramic. The composite ceramic has excellent comprehensive performance. For example, the sample with 3wt.% SiO2 and 5wt.% ZrO2 has density of 3.87g·cm-3, Vickers hardness of 17.6GPa, flexural strength of 369.0MPa, youngs modulus of 374.2GPa and fracture toughness of 3.57MPa·m1/2.

Optical Properties of Low Dielectric Constant Polyimides and Effects of Orientation

1993 ◽  
Vol 323 ◽  
Author(s):  
David C. Rich ◽  
Peggy Cebe ◽  
Anne K. St. Clair
Keyword(s):  
Dielectric Constant ◽  
Refractive Index ◽  
Optical Properties ◽  
Fluorine Content ◽  
Polymer Chains ◽  
Low Dielectric Constant ◽  
Refractive Indices ◽  
Electronic Polarizability ◽  
Low Dielectric ◽  
Preferential Alignment

AbstractControl of the refractive index in low dielectric constant polyimides through modification of chemistry and structure was investigated. The optical refractive indices of several low dielectric constant polyimides were measured, and the effects of orientation on optical anisotropy were determined. Refractive index in these polyimides was found to decrease with increasing fluorine content due primarily to the low electronic polarizability of the fluorine-carbon bonds. In zone drawn polyimides, refractive index was found to increase substantially in the direction of the draw, but decrease substantially normal to the draw direction. This was explained in terms of the preferential alignment of the polymer chains.

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