Study of Nanophase TiO2 Grain Boundaries by Raman Spectroscopy

1989 ◽  
Vol 153 ◽  
Author(s):  
C. A. Melendres ◽  
A. Narayanasamy ◽  
V. A. Maroni ◽  
R. W. Siegel
Keyword(s):  
Raman Spectroscopy ◽  
Grain Size ◽  
Grain Boundaries ◽  
Raman Spectra ◽  
Elevated Temperatures ◽  
Annealing Treatment ◽  
Average Diameter ◽  
Defect Structures ◽  
Rutile Structure ◽  
Grain Sizes

AbstractRaman spectra have been recorded for as-consolidated nanophase TiO2 samples with differing grain sizes and on samples annealed in air at a variety of temperatures up to 1273 K. The nanophase samples with the smallest grain size, about 12 nm average diameter, could have 15-30% of their atoms in grain boundaries; nevertheless, the strong Raman-active lines representative of the rutile structure were found to dominate all of the observed spectra, independent of grain size and annealing treatment. These lines were quite broad in the as-consolidated nanophase samples, equally in 12 nm and 100 nm grain-size compacts, but sharpened considerably upon annealing at elevated temperatures. The Raman data give no indication of grain-boundary structures in nanophase TiO2 that are significantly different from those in conventional polycrystals. However, defect structures within the grains, which anneal out at elevated temperatures, are evidenced by changes in the Raman spectra.

Raman spectroscopy of nanophase TiO2

1989 ◽  
Vol 4 (5) ◽  
pp. 1246-1250 ◽  
Author(s):  
C. A. Melendres ◽  
A. Narayanasamy ◽  
V. A. Maroni ◽  
R. W. Siegel
Keyword(s):  
Raman Spectroscopy ◽  
Grain Size ◽  
Grain Boundary ◽  
Raman Spectra ◽  
Short Range ◽  
Elevated Temperatures ◽  
Isochronal Annealing ◽  
Related Factors ◽  
Atomic Structures ◽  
Grain Sizes

Raman spectra are reported for consolidated nanophase TiO2 particles in their as-compacted state and after annealing at a variety of temperatures up to 1273 K. The Raman-active bands normally observed for the rutile form of TiO2 were present in as-compacted samples having average grain sizes in the range from about 10 to 100 nm. However, significant broadening of these bands was found, which was uncorrelated with initial grain size, but not necessarily with other synthesis-related factors. This broadening decreased upon isochronal annealing at elevated temperatures in air. Based upon these observations, it is concluded that nanophase TiO2 in the as-consolidated state contains significant defect concentrations within the rutile grains and that these intragrain defects and the grain-boundary regions as well have local atomic structures with the rutile symmetry, albeit with some short-range displacements. Some sporadic sample regions containing small amounts (<5%) of the anatase form of TiO2 were also found; these traces of anatase transformed to rutile upon annealing in air at temperatures above 883 K.

scholarly journals Effect of Grain Size on Carburization Characteristics of the High-Entropy Equiatomic CoCrFeMnNi Alloy

Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7199
Author(s):  
Hyunbin Nam ◽  
Jeongwon Kim ◽  
Namkyu Kim ◽  
Sangwoo Song ◽  
Youngsang Na ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Grain Sizes ◽  
Fine Grain ◽  
Cast Specimen ◽  
Vacuum Carburization ◽  
Cold Rolled ◽  
Face Centered

In this study, the carburization characteristics of cast and cold-rolled CoCrFeMnNi high-entropy alloys (HEAs) with various grain sizes were investigated. All specimens were prepared by vacuum carburization at 940 °C for 8 h. The carburized/diffused layer was mainly composed of face-centered cubic structures and Cr7C3 carbide precipitates. The carburized/diffused layer of the cold-rolled specimen with a fine grain size (~1 μm) was thicker (~400 μm) than that of the carburized cast specimen (~200 μm) with a coarse grain size (~1.1 mm). In all specimens, the carbides were formed primarily through grain boundaries, and their distribution varied with the grain sizes of the specimens. However, the carbide precipitates of the cast specimen were formed primarily at the grain boundaries and were unequally distributed in the specific grains. Owing to the non-uniform formation of carbides in the carburized cast specimen, the areas in the diffused layer exhibited various carbide densities and hardness distributions. Therefore, to improve the carburization efficiency of equiatomic CoCrFeMnNi HEAs, it is necessary to refine the grain sizes.

Simulation of the interaction of plastic zone dislocations with the grain boundary at brittle-plastic transition temperatures in molybdenum

2021 ◽  
Vol 2021 (3) ◽  
pp. 77-85
Author(s):  
K. M. Borysovska ◽  
◽  
N. M. Marchenko ◽  
Yu. M. Podrezov ◽  
S. O. Firstov ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Grain Boundary ◽  
Plastic Zone ◽  
Grain Boundaries ◽  
Crack Tip ◽  
Dynamics Simulation ◽  
Density Of Dislocations ◽  
Grain Sizes ◽  
Pile Up

The (DD) method was used to model the formation of the plastic zone of the top of the cracks in polycrystalline molybdenum. Special attention was paid to take into account the interaction of dislocations in the plastic zone with grain boundaries. Structural sensitivity of fracture toughness was analyzed under brittle-ductile condition. Simulations were performed for a range of grain sizes from 400 to 100 μm, at which a sudden increase in fracture toughness with a decrease of grain size was experimentally shown. We calculated the value of K1c taking into account the shielding action of dislocations. The position of all dislocations in the plastic zone at fracture moment was calculated. Based on these data, we obtained the dependences of dislocation density on the distance from the crack tip thereby confirming significant influence of the grain boundaries on plastic zone formation. At large grain sizes, when the plastic zone does not touch the boundary, the distribution of dislocations remained unchanged. As grains reduce their size to size of the plastic zone, they start formating a dislocation pile – up near the boundaries. Dislocations on plastic zone move slightly toward the crack tip, but the density of dislocations in the middle of the grain remains unchanged, and fracture toughness remains almost unchanged. Further reduction of the grain size leads to the Frank-Reed source activation on the grain boundary Forming dislocation pile-up of the neighbor grains. Its stress concentration acts on dislocations of the first grain and causes redistribution of plastic zone dislocations. If the reduction in grain size is not enough to form a strong pile-up, density of dislocations on plastic zone increases slightly and crack resistance increases a few percent. Further reduction of grains promotes strong pile-up, dislocations move to crack tip, and its density on plastic zone increases. Crack is shielded and fracture toughness increases sharply. The calculation showed that the fracture toughness jump is observed at grain sizes of 100—150 μm, in good agreement with the experiment. Keywords: dislocation dynamics simulation, molybdenum, fracture toughness, grain size, plastic zone, brittle-ductile transition.

Dielectric Properties of Nanograined BaTiO3 Ceramics Fabricated by Aerosol Deposition Method

2011 ◽  
Vol 485 ◽  
pp. 183-186 ◽  
Author(s):  
Tsutomu Furuta ◽  
Saki Hatta ◽  
Yoichi Kigoshi ◽  
Takuya Hoshina ◽  
Hiroaki Takeda ◽  
...  
Keyword(s):  
Grain Size ◽  
Room Temperature ◽  
Annealing Treatment ◽  
Aerosol Deposition ◽  
Dielectric Measurement ◽  
Deposition Method ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Aerosol Deposition Method ◽  
Polarization Electric Field

Freestanding BaTiO3 ceramics films were fabricated using the aerosol deposition (AD) method and the size effect of nanograined BaTiO3 ceramics was demonstrated. Dense BaTiO3 thick film fabricated by the AD method was crystallized and detached from substrate by an annealing treatment at 600 °C, and then the grain size was controlled by a reannealing treatment at various temperatures. As a result, freestanding BaTiO3 thick films with various grain sizes from 24 to 170 nm were successfully obtained. Polarization–electric field (P–E) measurement revealed that BaTiO3 ceramics with grain sizes of more than 58 nm showed ferroelectricity, whereas BaTiO3 ceramics with an average grain size of 24 nm showed paraelectricity at room temperature. Dielectric measurement indicated that the permittivity decreased with decreasing grain size in the range of 170 to 24 nm.

Effect of Grain Size on Carbide Precipitation and Intergranuiar Corrosion in AISI Type 201 Stainless Steel

CORROSION ◽  
1965 ◽  
Vol 21 (10) ◽  
pp. 332-336 ◽  
Author(s):  
C. P. DOSHI ◽  
W. W. AUSTIN
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
Elevated Temperatures ◽  
Austenitic Steels ◽  
Grain Sizes ◽  
Aisi Type ◽  
Sensitization Behavior ◽  
Acid Test ◽  
Sensitization Time ◽  
Carbide Particles

Abstract The grain size of the austenitic stainless steel affects the rate of intergranular attack at high temperatures. While the effect of grain size has been studied for 18-8 chromium-nickel austenitic steels, little work has been done on chromium-nickel-manganese austenitic steels. It is the purpose of this investigation to correlate intergranuiar attack with grain size in these steels. A commercially available alloy (AISI Type 201) was selected for study. Effect of four different grain sizes (ASTM Grain Size Numbers 1, 2, 3 and 5) at four different sensitization times and four temperatures was studied. Results obtained in terms of weight loss in the boiling nitric acid test and through photomicrography were used to correlate intergranuiar attack with grain size. Best resistance to corrosion was obtained at a sensitization temperature of 800 F (426 C) for all grain sizes. At elevated temperatures [1000 and 1200 F (537 and 649 C)] corrosion rate increased with increasing sensitization time. Upon comparison of sensitization behavior at 1400 F (760 C) for all grain sizes it was found that exposure for 48 hours produced less severe corrosive attack than did the 16-hr exposure. This was explained in terms of increase in size of carbide particles.

Electroplated Cu Recrystallization in Damascene Structures at Elevated Temperatures

1999 ◽  
Vol 564 ◽  
Author(s):  
Qing-Tang Jiang ◽  
Michael E. Thomas ◽  
Gennadi Bersuker ◽  
Brendan Foran ◽  
Robert Mikkola ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Grain Size ◽  
Film Thickness ◽  
Grain Growth ◽  
Elevated Temperatures ◽  
Retardation Effect ◽  
Cu Films ◽  
Grain Sizes ◽  
Geometrical Constraints ◽  
The Difference

AbstractTransformations in electroplated Cu films from a fine to course grain crystal structure (average grain sizes went from ∼0.1 µm to several microns) were observed to strongly depend on film thickness and geometry. Thinner films underwent much slower transformations than thicker ones. A model is proposed which explains the difference in transformation rates in terms of the physical constraint experienced by the film since grain growth in thinner films is limited by film thickness. Geometrical constraints imposed by trench and via structures appear to have an even greater retardation effect on the grain growth. Experimental observations indicate that it takes much longer for Cu in damascene structures to go through grain size transformations than blanket films.

Experimental Investigation of Grain and Specimen Size Effects During Electrical-Assisted Forming

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Michael S. Siopis ◽  
Brad L. Kinsey
Keyword(s):  
Grain Size ◽  
Current Density ◽  
Stress Reduction ◽  
Elevated Temperatures ◽  
Pure Copper ◽  
Electrical Current ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Grain Sizes ◽  
Reduction Effect

Alternative manufacturing processes such as hot working and electrical-assisted forming (EAF), which involves passing a high density electrical current through the workpiece during deformation, have been shown to increase the potential strain induced in materials and reduce required forces for deformation. While forming at elevated temperatures is common, the EAF process provides more significant improvements in formability without the undesirable effects associated with forming at elevated temperatures. This research investigates the effect of grain size and current density on annealed pure copper during the EAF process. The flow stress reduction effect of the process was shown to decrease with increasing grain sizes. A threshold current density, required to achieve a significant reduction in the flow stresses, becomes more apparent at larger grain sizes, and the value increases with increasing grain size. The effects increase with increasing strain due to dislocations being generated during deformation. Therefore, the dislocation density, related in part by the grain size, appears to be a factor in the EAF process.

Raman Spectroscopy Analysis of Nitrogen Ion Implantation in Silicon and Correlation with Transmission Electron Microscopy

1992 ◽  
Vol 279 ◽  
Author(s):  
A. PéRez-Rodríguez ◽  
A. Romano-Rodríguez ◽  
J. R. Morante ◽  
J. Esteve ◽  
J. Montserrat
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Raman Spectroscopy ◽  
Raman Spectra ◽  
Annealing Treatment ◽  
Structural Features ◽  
Spectroscopy Analysis ◽  
Subsurface Region ◽  
Transmission Electron ◽  
Nitrogen Ion

ABSTRACTIn this work Si samples implanted with nitrogen (N+ or N2+) at a dose of 1017 cm−2 are characterized by Raman spectroscopy and cross section transmission electron microscopy (XTEM). The correlation between the Raman spectra obtained with different excitation wavelengths and XTEM observations allows to determine the structural features related to the layers contributing to the total spectra. The evolution of these features with the annealing treatments (up to 1150°C) is studied. The results obtained show, after the annealing treatment at the highest temperature, the presence of silicon nitride precipitates in the silicon subsurface region, and the formation of a nitrogen rich polycrystalline Si layer with Si3N4 grains. The Raman spectra from the subsurface region show a remaining shift of -0.15 cm−1 when compared to the spectra from unimplanted Si. This shift, together with the similar shape of both Raman lines, suggests the presence in this region of an average tensile stress of 37.5 MPa.

Experimental Investigation of Grain and Specimen Size Effects During Electrical-Assisted Forming

2009 ◽  
Author(s):  
Michael S. Siopis ◽  
Brad L. Kinsey
Keyword(s):  
Grain Size ◽  
Current Density ◽  
Stress Reduction ◽  
Elevated Temperatures ◽  
Pure Copper ◽  
Electrical Current ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Grain Sizes ◽  
Reduction Effect

Alternative manufacturing processes such as hot working and Electrical-Assisted Forming (EAF), which involves passing a high density electrical current through the workpiece during deformation, have been shown to increase the potential strain induced in materials and reduce required forces for deformation. While forming at elevated temperatures is common, the EAF process provides more significant improvements in formability without the undesirable affects associated with forming at elevated temperatures. This research investigates the effect of grain size and current density on annealed pure copper during the EAF process. The flow stress reduction effect of the process was shown to decrease with increasing grain sizes. A threshold current density, required to achieve a significant reduction in the flow stresses, becomes more apparent at larger grain sizes and the value increases with increasing grain size. The effects increase with increasing strain due to dislocations being generated during deformation. Therefore the dislocation density, related in part by the grain size, appears to be a factor in the EAF process.

Structure-property relationships of Au films electrodeposited on Ni

2004 ◽  
Vol 821 ◽  
Author(s):  
C. San Marchi ◽  
N.R. Moody ◽  
M.J. Cordill ◽  
G. Lucadamo ◽  
J.J. Kelly ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Gold Films ◽  
Structure Property ◽  
Plastic Properties ◽  
Grain Sizes ◽  
Structure Property Relationships ◽  
Microelectronics Industry

Thin gold films and coatings on metal have long constituted an important technology for the microelectronics industry and will continue to be important for microdevices such as contact springs. The properties of these materials may be highly processing dependent, particularly when the gold is deposited by electrochemical means. In this study, we characterize gold electrodeposited on Ni substrates from two bath chemistries: hard Au sulfite with proprietary hardening additive and soft Au cyanide. TEM and SEM show that the bath chemistry alters the microstructure and the resulting surface of the electrodeposits. Nanoindentation techniques were used to determine the elastic and plastic properties of the Au electrodeposits as a function of the specifics of processing. Soft Au electrodeposits have a grain size of on the order of 300 nm and a hardness of about 1 GPa. Hard Au electrodeposits produced from the sulfite bath feature grain sizes as small as 30 nm, some twinning, and fine porosity uniformly distributed both within the grains and at grain boundaries. The hardness is about 2 GPa, approaching the hardest values reported for sputtered gold films. The effect of the hardening agent on the microstructure of electrodeposits from the Au sulfite bath was also investigated and found to significantly refine the grain size at concentrations of at least 4 mL/L, although little additional refinement was found at higher concentrations.

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