Synthesis, characterization, and properties of nanophase TiO2

1988 ◽  
Vol 3 (6) ◽  
pp. 1367-1372 ◽  
Author(s):  
R. W. Siegel ◽  
S. Ramasamy ◽  
H. Hahn ◽  
L. Zongquan ◽  
L. Ting ◽  
...  
Keyword(s):  
Sintering Temperature ◽  
Positron Annihilation Spectroscopy ◽  
Sintering Aids ◽  
Gas Condensation ◽  
Grain Sizes ◽  
Transmission Electron ◽  
Ultrafine Grained ◽  
Conventional Sintering ◽  
Hardness Values

Ultrafine-grained, nanophase samples of TiO2 (rutile) were synthesized by the gas-condensation method and subsequent in situ compaction. The samples were studied by a number of techniques, including transmission electron microscopy, Vickers microharness measurements, and positron annihilation spectroscopy, as a function of sintering temperature. The nanophase compacts with average initial grain sizes of 12 nm were found to densify rapidly above 500 °C, with only a small increase in grain size. The hardness values obtained by this method are comparable to or greater than those for coarser-grained compacts, but are achieved at temperatures 400 to 600 °C lower than conventional sintering temperatures and without the need for sintering aids.

scholarly journals Processing and Properties of Nanophase Oxides

1989 ◽  
Vol 155 ◽  
Author(s):  
J. A. Eastman ◽  
Y. X. Liao ◽  
A. Narayanasamy ◽  
R. W. Siegel
Keyword(s):  
Ultrafine Particles ◽  
Sintering Behavior ◽  
Sintering Aids ◽  
New Materials ◽  
Air Exposure ◽  
Gas Condensation ◽  
Grain Sizes ◽  
20 Nm ◽  
Reduced Scale

ABSTRACTNanophase oxides (Al2O3, MgO, ZnO and TiO2), with typical grain sizes in the range 2–20 nm, have been synthesized by the condensation of ultrafine particles in a convective inert gas followed by their collection and in-situ consolidation in vacuum at ambient temperature. These new materials, owing to the reduced scale of their grains along with the enhanced cleanliness of their grain boundaries, are found to have significantly improved properties relative to those of their coarser-grained, conventionally-prepared counterparts. Nanophase rutile (TiO2) with an initial mean grain diameter of 12 nm, for example, has been found to sinter at 400 to 600°C lower temperatures than conventional rutile powders, without the need for compacting or sintering aids, while retaining a small grain size. Additionally, the importance of the extremely clean surfaces obtained with the gas condensation method has been demonstrated by comparing the sintering behavior of powders with and without air exposure prior to consolidation. The research completed on the processing and properties of nanophase ceramics is reviewed, and the potential for engineering advanced ceramics using the nanophase processing method is discussed.

Pressureless Sintering of Boron Carbide-Based Superhard Materials

2010 ◽  
Vol 159 ◽  
pp. 145-148 ◽  
Author(s):  
Dimitar D. Radev
Keyword(s):  
Transition Metal ◽  
Boron Carbide ◽  
Sintering Temperature ◽  
Liquid Phase Sintering ◽  
Vacuum Furnace ◽  
Pressureless Sintering ◽  
Metal Carbides ◽  
Sintering Aids ◽  
Transition Metal Carbides

Boron carbide-based materials B4C-MexBy were densified by pressureless sintering in a vacuum furnace. Some transition metal carbides (TiC, ZrC, HfC, Cr3C2 and WC) from groups IV-VI were used as sintering aids. The optimal sintering temperature in the range 2220-2250oC was used for any composition. Here we show the possibilities to activate the mass transport of the B4C by the mechanism of liquid phase sintering. The method of reactive sintering of B4C in the presence of additives of some transition metal carbides allows in situ synthesis of dense B4C-MexBy materials. Structural properties and fracture toughness of the B4C-based composite materials were discussed. The properties of some of these materials and the possibilities for their application are also discussed.

In-Situ Growth and Polygonization of Epitaxial Passive Oxide Films on Nanoparticles of Iron

2001 ◽  
Vol 7 (S2) ◽  
pp. 1234-1235
Author(s):  
K.K. Fung ◽  
X.X. Zhang ◽  
Y.S. Kwok ◽  
Boxiong Qin
Keyword(s):  
Shell Morphology ◽  
Iron Core ◽  
X Ray Diffraction ◽  
X Ray ◽  
Gas Condensation ◽  
Transmission Electron ◽  
Image Position ◽  
Convergent Beam ◽  
Oxidation And Corrosion

Over the years, the study of the oxidation of nanoparticles of iron by transmission electron microscopy (TEM), Mossbauer spectroscopy and X-ray diffraction has established that nanoparticles of iron have a core-shell morphology in which the iron core is enclosed by shell of polycrystalline shell of ultrasmall γ-Fe2O3 and Fe3O4 crystallites. Recently, passivated nanoparticles of iron prepared by gas condensation of plasma evaporated vapor in Tianjin University exhibit remarkable resistance to further oxidation and corrosion in air and water. We have showed by TEM that these nanoparticles of iron are protected by a 4 nm epitaxial shell of γ-Fe2O3. The epitaxial orientation relationship, established by convergent beam electron diffraction from a nanoparticle, is as follows:The [001] diffraction pattern of the oxide is rotated by 45° about a cubic axis relative to that of iron.

scholarly journals Synthesis, Characterization, and Properties of Nanophase Ceramics

1988 ◽  
Vol 132 ◽  
Author(s):  
R. W. Siegel ◽  
J. A. Eastman
Keyword(s):  
High Vacuum ◽  
Synthesis Method ◽  
Ultra High Vacuum ◽  
Vacuum Consolidation ◽  
Fracture Characteristics ◽  
Gas Condensation ◽  
Ultrafine Grained ◽  
20 Nm ◽  
Reduced Scale

ABSTRACTUltrafine-grained ceramics have been synthesized by the production of ultrafine (2–20 nm) particles, using the gas-condensation method, followed by their in-situ, ultra-high vacuum consolidation at room temperature. These new nanophase ceramics have properties that are significantly improved relative to those of their coarser-grained, conventionally-prepared counterparts. For example, nanophase rutile (TiO2) with an initial mean grain diameter of 12 nm sinters at 400 to 600°C lower temperatures than conventional powders, without the need for compacting or sintering aids. The sintered nanophase rutile exhibits both improved microhardness and fracture characteristics. These property improvements result from the reduced scale of the grains and the increased cleanliness of the particle surfaces and the subsequently-formed grain boundaries. Research completed on the synthesis, characterization, and properties of nanophase ceramics is reviewed and the potential for using the nanophase synthesis method for engineering new and/or improved ceramics and composites is considered.

scholarly journals TEM observation of precipitates and their role to mechanical properties in Ti-5553 alloy heated to some temperatures up to 923 K

2020 ◽  
Vol 321 ◽  
pp. 11035
Author(s):  
E. Sukedai ◽  
E. Aeby-Gautier ◽  
M. Dehmas
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Hardening Mechanism ◽  
Transmission Electron ◽  
The Matrix ◽  
Higher Temperature ◽  
Shearing Mechanism ◽  
Hardness Values ◽  
Measured Hardness

A Ti-5553 specimen was continuously heated to 923 K and simultaneously in-situ HEXRD profiles were taken. In addition, specimens heated at the same rate to several temperatures up to 923 K and further quenched were observed by transmission electron microscopy. Based on both results obtained, transformation sequence was clarified, precipitations of ω-, α”iso- and α-phases were confirmed, and size and density of these precipitates were measured. Hardness values of those specimens were also measured. The hardening mechanism was considered as shearing-mechanism for specimens aged at lower temperatures and by-pass one for specimens aged at higher temperature. An attempt of distinction between α”iso - and α-precipitates was also tried. Both precipitates were in needle-like shape and a possibility was suggested by measuring angles between two needle-shape precipitates on {110} of the matrix and comparing with each other.

scholarly journals Synthesis, Characterization and Mechanical Properties of Nanocrystalline NiAl

1996 ◽  
Vol 457 ◽  
Author(s):  
M. S. Choudry ◽  
J. A. Eastman ◽  
R. J. DiMelfi ◽  
M. Dollar
Keyword(s):  
Room Temperature ◽  
Dark Field ◽  
Inert Gas ◽  
Coarse Grained ◽  
Gas Condensation ◽  
Grain Sizes ◽  
Room Temperature Ductility ◽  
Cast Alloys ◽  
Bend Tests

ABSTRACTNanocrystalline NiAl has been produced from pre-cast alloys using an electron beam inert gas condensation system. In-situ compaction was carried out at 100 to 300°C under vacuum conditions. Energy dispersive spectroscopy was used to determine chemical composition and homogeneity. Average grain sizes in the range of 4 to 10 nm were found from TEM dark field analyses. A compression-cage fixture was designed to perform disk bend tests. These tests revealed substantial room temperature ductility in nanocrystalline NiAl, while coarse grained NiAl showed no measurable room temperature ductility.

Microstructural Characterization of In Situ TiB Whiskers in Ti MMCs Fabricated by SPS

2007 ◽  
Vol 336-338 ◽  
pp. 1310-1312
Author(s):  
Hai Bo Feng ◽  
De Chang Jia ◽  
Yu Zhou ◽  
Qing Chang Meng
Keyword(s):  
Electron Microscopy ◽  
Spark Plasma Sintering ◽  
Sintering Temperature ◽  
Microstructural Characterization ◽  
Average Diameter ◽  
Matrix Composites ◽  
Plasma Sintering ◽  
Transmission Electron ◽  
Spark Plasma

The in situ TiB whisker reinforced titanium matrix composites were prepared by mechanical alloying followed by spark plasma sintering. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were used to characterize the microstructure of the TiB whiskers. The effect of sintering temperature on morphologies of in situ TiB whiskers was evaluated. With the increase of spark plasma sintering temperature, the average diameter of in situ TiB whiskers increased. The in situ TiB whiskers exhibited a hexagonal shape with (100), (101) and (10 1 ) planes at the transverse section and a growth orientation of [010]TiB direction.

scholarly journals Unique transition of yielding mechanism and unexpected activation of deformation twinning in ultrafine grained Fe-31Mn-3Al-3Si alloy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yu Bai ◽  
Hiroki Kitamura ◽  
Si Gao ◽  
Yanzhong Tian ◽  
Nokeun Park ◽  
...  
Keyword(s):  
Grain Refinement ◽  
Twip Steel ◽  
Deformation Twinning ◽  
Ultrafine Grain ◽  
Yield Drop ◽  
Grain Sizes ◽  
Deformation Twins ◽  
Ultrafine Grained ◽  
The Mean

AbstractTensile mechanical properties of fully recrystallized TWIP steel specimens having various grain sizes (d) ranging from 0.79 μm to 85.6 μm were investigated. It was confirmed that the UFG specimens having the mean grain sizes of 1.5 μm or smaller abnormally showed discontinuous yielding characterized by a clear yield-drop while the specimens having grain sizes larger than 2.4 μm showed normal continuous yielding. In-situ synchrotron radiation XRD showed dislocation density around yield-drop in the UFG specimen quickly increased. ECCI observations revealed the nucleation of deformation twins and stacking faults from grain boundaries in the UFG specimen around yielding. Although it had been conventionally reported that the grain refinement suppresses deformation twinning in FCC metals and alloys, the number density of deformation twins in the 0.79 μm grain-sized specimen was much higher than that in the specimens with grain sizes of 4.5 μm and 15.4 μm. The unusual change of yielding behavior from continuous to discontinuous manner by grain refinement could be understood on the basis of limited number of free dislocations in each ultrafine grain. The results indicated that the scarcity of free dislocations in the recrystallized UFG specimens changed the deformation and twinning mechanisms in the TWIP steel.

Kinetic and Thermodynamic Properties of Nanocrystalline Materials

1989 ◽  
Vol 153 ◽  
Author(s):  
R.S. Averback ◽  
H. Hahn ◽  
H.J. Hö;fler ◽  
J.L. Logas ◽  
T.C. Shen
Keyword(s):  
Thermodynamic Properties ◽  
Nanocrystalline Materials ◽  
Kinetic Properties ◽  
Gas Condensation ◽  
New Class ◽  
Nanocrystalline Ceramics ◽  
Grain Sizes ◽  
Metal Vapors ◽  
Kinetics Of

AbstractA new class of materials with ultra small grain size has recently been synthesized by combining the methods of inert gas condensation of metal vapors and in situ powder compaction. These ‘nanocrystalline’ materials, with grain sizes of 5-10 nm, can have over 30% of their atoms lying in the highly disordered interfaces or grain boundaries. Because of their unique atomic structure, nanocrystalline materials often have properties far different from their bulk counterparts. In addition, kinetic processes can be rapidly accelerated due to the short diffusion distances between grains. In this review, we will report on the thermodynamic properties and reaction kinetics of nanocrystalline metals and on such kinetic properties as sintering and grain growth in nanocrystalline ceramics.

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