On the influence of various pre-ageing treatments on the structure changes taking place at elevated temperatures in alloys of the type AlZn5Mg1

1985 ◽  
Vol 20 (3) ◽  
pp. 391-392
Author(s):  
E. Korngiebel
Keyword(s):  
Elevated Temperatures ◽  
Structure Changes

Significance of α-crystallin heteropolymer with a 3:1 αA/αB ratio: chaperone-like activity, structure and hydrophobicity

2008 ◽  
Vol 414 (3) ◽  
pp. 453-460 ◽  
Author(s):  
P. N. B. S. Srinivas ◽  
P. Yadagiri Reddy ◽  
G. Bhanuprakash Reddy
Keyword(s):  
Elevated Temperatures ◽  
Tertiary Structure ◽  
Small Heat Shock Protein ◽  
Molar Ratio ◽  
Eye Lens ◽  
Structural Perturbation ◽  
Structure Changes ◽  
Activity Structure ◽  
Structural Perturbations ◽  
Optimal Protection

The small heat-shock protein α-crystallin isolated from the eye lens exists as a large (700 kDa) heteropolymer composed of two subunits, αA and αB, of 20 kDa each. Although trace amounts of αA-crystallin are found in other tissues, non-lenticular distribution of α-crystallin is dominated by the αB homopolymer. In most vertebrate lens, the molar ratio of αA to αB is generally 3:1. However, the importance of this ratio in the eye lens is not known. In the present study, we have investigated the physiological significance of the 3:1 ratio by determining the secondary/tertiary structure, hydrophobicity and chaperone-like activity of αA- and αB-homopolymers and heteropolymers with different ratios of αA to αB subunits. Although, under physiologically relevant conditions, the αB-homopolymer (37–40 °C) has shown relatively higher activity, the αA-homopolymer or the heteropolymer with a higher αA proportion (3:1 ratio) has shown greater chaperone-like activity at elevated temperatures (>50 °C) and also upon structural perturbation. Furthermore, higher chaperone activity at elevated temperatures as well as upon structural perturbation is mainly mediated through increased hydrophobicity of αA. Although homopolymers and heteropolymers of α-crystallin did not differ in their secondary structure, changes in tertiary structure due to structural perturbations upon pre-heating are mediated predominantly by αA. Interestingly, the heteropolymer with higher αA proportion (3:1) or the αA-homopolymer seems to be better chaperones in protecting lens β- and γ-crystallins at both normal and elevated temperatures. Thus lens might have favoured a combination of these qualities to achieve optimal protection under both native and stress (perturbed) conditions for which the heteropolymer with αA to αB in the 3:1 ratio appears to be better suited.

Symmetry Changes At The Surface Of Al70Pd20Mn10

1998 ◽  
Vol 553 ◽  
Author(s):  
B. Bolliger ◽  
M. Erbudak ◽  
A. Hensch ◽  
A.R. Kortan ◽  
D.D. Vvedensky
Keyword(s):  
Room Temperature ◽  
Elevated Temperatures ◽  
Surface Composition ◽  
Structural Phase ◽  
Bulk Composition ◽  
Icosahedral Quasicrystal ◽  
Icosahedral Symmetry ◽  
Structural Phase Transitions ◽  
Structure Changes ◽  
Different Temperatures

AbstractSputtering with Ar+ ions induces structural phase transitions at the pentagonal surface of the icosahedral quasicrystal Al70Pd20Mn10. Sputtering at different temperatures changes the surface composition, thereby stabilizing different structures. At room temperature, the structure changes to body-centered cubic but, at elevated temperatures, it displays decagonal symmetry. In both cases, annealing the sample restores both the bulk composition and the icosahedral symmetry of the original surface.

Microstructure and Mechanical Property of Nano-Duplex Materials Produced by HRS Process

2006 ◽  
Vol 503-504 ◽  
pp. 227-232 ◽  
Author(s):  
Hiroshi Fujiwara ◽  
Ryota Akada ◽  
Yuki Yoshita ◽  
Kei Ameyama
Keyword(s):  
Mechanical Properties ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Surface Region ◽  
Hybrid Structure ◽  
Core Region ◽  
Grain Structure ◽  
Duplex Structure ◽  
Structure Changes ◽  
Conventional Material

An SUS316L and a Ti-6Al-4V alloy powders are treated by Mechanical Milling (MM) process, which is one of SPD processes, and then sintered by Hot Roll Sintering (HRS) process. The HRS process consolidates powder by hot rolling of an evacuated metal pipe filled with the powder at elevated temperatures. Those MM powders have a heavy deformed microstructure at the surface region and have a work hardened microstructure in the core region of the powder. In the surface region, a nano grain structure forms after the MM treatment in both materials. In case of the SUS316L powder, such a nano grain structure consists of an equiaxed nano ferrite (􀁄) grains which has transformed from nano austenite (􀁊) grains. Volume fraction of the 􀁄 phase decreases with distance from the surface of powder. During HRS the (􀁄 + 􀁊) nano-duplex structure changes to (sigma (􀁖) + 􀁊) nano-duplex structure by transformation of the 􀁄 to the 􀁖 phase. Thus, the SUS316L HRS material consists of a hybrid structure. That is, a (􀁖 + 􀁊) nano-duplex structure at the powder shell region, and a work hardened 􀁊 structure in the powder core region. In case of the Ti-6Al-4V MM powder, though no remarkable transformation occurs, a heavy deformed shell and work hardened core hybrid structure is also produced in the powder. By HRS the Ti-6Al-4V MM powder demonstrates a hybrid structure consists of an equiaxed nano grain structure and a coarse martensite structure. These two HRS materials indicate superior mechanical properties. Mechanical properties are improved by the HRS process. The proof stress and tensile strength in the SUS316L HRS material are x3.8 and x2.1 of the SUS316L conventional material, respectively. In the Ti-6Al-4V HRS material, they are x1.7 and x1.5 compared to the Ti-6Al-4V conventional material.

scholarly journals The impact of changes in pore structure on the compressive strength of sulphoaluminate cement concrete at high temperature

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
J.J.K. Tchekwagep ◽  
P. Zhao ◽  
S. Wang ◽  
S. Huang ◽  
X. Cheng
Keyword(s):  
Compressive Strength ◽  
Pore Structure ◽  
Elevated Temperatures ◽  
Nitrogen Adsorption ◽  
Cement Concrete ◽  
Constant Weight ◽  
Sulphoaluminate Cement ◽  
Structure Changes ◽  
The Impact ◽  
The Relationship

Abstract The internal pore structure of sulphoaluminate cement concrete (SACC) significantly affects its mechanical properties. The main purpose of this study was to establish the relationship between pore structure changes and compressive strength after exposure to elevated temperatures. SACC samples that had been cured for 12 months were dried to a constant weight and then exposed to different temperatures (100 °C, 200 °C and 300 °C), after which the compressive strength and pore structure were measured. The pore structure of SACC was quantitatively described by mercury intrusion porosimetry (MIP) and nitrogen adsorption results. The results showed that with increased temperature, the porosity of the SACC samples also increased and the pore structure was gradually destroyed. Moreover, the SACC’s compressive strength gradually decreased with increasing temperature. The relationship between compressive strength and porosity was in close agreement with the compressive strength–porosity equation proposed by Schiller. Therefore, after extensive exposure to elevated temperature, the changes in SACC’s compressive strength can be quantitatively described by the Schiller equation.

Characterization of Rare-Earth Fluoride Anti-Stokes Phosphors by Scanning arid Transmission Electron Microscopy

1971 ◽  
Vol 29 ◽  
pp. 142-143
Author(s):  
N. M. P. Low ◽  
L. E. Brosselard
Keyword(s):  
Electron Microscopy ◽  
Rare Earth ◽  
Elevated Temperatures ◽  
Stoichiometric Composition ◽  
Rare Earth Ions ◽  
Crystalline Solid ◽  
Precipitation Process ◽  
Rare Earth Fluoride ◽  
Earth Fluoride ◽  
Rare Earth Fluorides

There has been considerable interest over the past several years in materials capable of converting infrared radiation to visible light by means of sequential excitation in two or more steps. Several rare-earth trifluorides (LaF3, YF3, GdF3, and LuF3) containing a small amount of other trivalent rare-earth ions (Yb3+ and Er3+, or Ho3+, or Tm3+) have been found to exhibit such phenomenon. The methods of preparation of these rare-earth fluorides in the crystalline solid form generally involve a co-precipitation process and a subsequent solid state reaction at elevated temperatures. This investigation was undertaken to examine the morphological features of both the precipitated and the thermally treated fluoride powders by both transmission and scanning electron microscopy.Rare-earth oxides of stoichiometric composition were dissolved in nitric acid and the mixed rare-earth fluoride was then coprecipitated out as fine granules by the addition of excess hydrofluoric acid. The precipitated rare-earth fluorides were washed with water, separated from the aqueous solution, and oven-dried.

Observations oh Nucleation and Growth of Voids in Nickel

1970 ◽  
Vol 28 ◽  
pp. 414-415
Author(s):  
J. L. Brimhall ◽  
H. E. Kissinger ◽  
B. Mastel
Keyword(s):  
High Purity ◽  
Growth Stage ◽  
Elevated Temperatures ◽  
Early Growth ◽  
Nucleation And Growth ◽  
Pure Nickel ◽  
Different Temperatures ◽  
Total Fluence ◽  
Neutron Exposure ◽  
Growth Of Voids

Some information on the size and density of voids that develop in several high purity metals and alloys during irradiation with neutrons at elevated temperatures has been reported as a function of irradiation parameters. An area of particular interest is the nucleation and early growth stage of voids. It is the purpose of this paper to describe the microstructure in high purity nickel after irradiation to a very low but constant neutron exposure at three different temperatures.Annealed specimens of 99-997% pure nickel in the form of foils 75μ thick were irradiated in a capsule to a total fluence of 2.2 × 1019 n/cm2 (E > 1.0 MeV). The capsule consisted of three temperature zones maintained by heaters and monitored by thermocouples at 350, 400, and 450°C, respectively. The temperature was automatically dropped to 60°C while the reactor was down.

Voids in Irradiated Tungsten and Molybdenum

1969 ◽  
Vol 27 ◽  
pp. 190-191
Author(s):  
Robert C. Rau ◽  
Robert L. Ladd
Keyword(s):  
Melting Point ◽  
Fast Neutron ◽  
Neutron Irradiation ◽  
Elevated Temperatures ◽  
Irradiation Temperature ◽  
The Body ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Cubic Metals ◽  
Face Centered

Recent studies have shown the presence of voids in several face-centered cubic metals after neutron irradiation at elevated temperatures. These voids were found when the irradiation temperature was above 0.3 Tm where Tm is the absolute melting point, and were ascribed to the agglomeration of lattice vacancies resulting from fast neutron generated displacement cascades. The present paper reports the existence of similar voids in the body-centered cubic metals tungsten and molybdenum.

Mechanical Properties and Dislocation Structure of Single Crystal Cdte Deformed in Compression at 300°C

1976 ◽  
Vol 34 ◽  
pp. 592-593
Author(s):  
Ernest L. Hall ◽  
J. B. Vander Sande
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Dislocation Structure ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Strain Curve ◽  
Optical Devices ◽  
Semiconductor Compound ◽  
Wide Range ◽  
Sample Orientation

The present paper describes research on the mechanical properties and related dislocation structure of CdTe, a II-VI semiconductor compound with a wide range of uses in electrical and optical devices. At room temperature CdTe exhibits little plasticity and at the same time relatively low strength and hardness. The mechanical behavior of CdTe was examined at elevated temperatures with the goal of understanding plastic flow in this material and eventually improving the room temperature properties. Several samples of single crystal CdTe of identical size and crystallographic orientation were deformed in compression at 300°C to various levels of total strain. A resolved shear stress vs. compressive glide strain curve (Figure la) was derived from the results of the tests and the knowledge of the sample orientation.

Electron microscopy of crystalline structure in thermotropic random copolymers

1991 ◽  
Vol 49 ◽  
pp. 1054-1055
Author(s):  
Afzana Anwer ◽  
S. Eilidh Bedford ◽  
Richard J. Spontak ◽  
Alan H. Windle
Keyword(s):  
Electron Microscopy ◽  
Crystalline Structure ◽  
Liquid Crystalline ◽  
Elevated Temperatures ◽  
Random Copolymers ◽  
Molecular Characteristics ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Identical Monomer ◽  
Periodic Layer

Random copolyesters composed of wholly aromatic monomers such as p-oxybenzoate (B) and 2,6-oxynaphthoate (N) are known to exhibit liquid crystalline characteristics at elevated temperatures and over a broad composition range. Previous studies employing techniques such as X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) have conclusively proven that these thermotropic copolymers can possess a significant crystalline fraction, depending on molecular characteristics and processing history, despite the fact that the copolymer chains possess random intramolecular sequencing. Consequently, the nature of the crystalline structure that develops when these materials are processed in their mesophases and subsequently annealed has recently received considerable attention. A model that has been consistent with all experimental observations involves the Non-Periodic Layer (NPL) crystallite, which occurs when identical monomer sequences enter into register between adjacent chains. The objective of this work is to employ electron microscopy to identify and characterize these crystallites.

Generation of 4H and 6H Structures During the Hexagonal-Rhombohedral Transformation in Dy2Co17

1975 ◽  
Vol 33 ◽  
pp. 38-39
Author(s):  
C. W. Allen ◽  
D. L. Kuruzar
Keyword(s):  
Elevated Temperatures ◽  
Layer Structure ◽  
Transition Element ◽  
Temperature Structure ◽  
Allotropic Transformation ◽  
Layer Plane ◽  
Planar Defects ◽  
Topologically Close Packed ◽  
Transformation Mechanisms ◽  
Shear Transformation

The rare earth/transition element intermetallics R2T17 are essentially topologically close packed phases for which layer structure models have already been presented. Many of these compounds are known to undergo allotropic transformation of the type at elevated temperatures. It is not unexpected that shear transformation mechanisms are involved in view of the layering character of the structures. The transformations are evidently quite sluggish, illustrated in furnace cooled Dy2Co17 by the fact that only rarely has the low temperature rhombohedral form been seen. The more usual structures observed so far in furnace cooled alloys include 4H and 6H in Dy2Co17 (Figs. 1 and 2) . In any event it is quite clear that the general microstructure is very complicated as a consequence of the allotropy, illustrated in Fig. 3. Numerous planar defects in the layer plane orientation are evident as are non-layer plane defects inherited from a high temperature structure.

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