Comparison of high-temperature three-phonon resistivities from different theoretical models

Pramana ◽  
1976 ◽  
Vol 7 (4) ◽  
pp. 236-244 ◽  
Author(s):  
G P Srivastava
Keyword(s):  
High Temperature ◽  
Theoretical Models

scholarly journals Temperature dependence of hardness prediction for high-temperature structural ceramics and their composites

2021 ◽  
Vol 10 (1) ◽  
pp. 586-595
Author(s):  
Ruzhuan Wang ◽  
Dingyu Li ◽  
Weiguo Li
Keyword(s):  
High Temperature ◽  
Temperature Dependence ◽  
Material Design ◽  
Theoretical Models ◽  
Ceramic Composites ◽  
Basic Material ◽  
Experimental Measurements ◽  
Control Mechanisms ◽  
Oxide Ceramics ◽  
Structural Ceramics

Abstract Hardness is one of the important mechanical properties of high-temperature structural ceramics and their composites. In spite of the extensive use of the materials in high-temperature applications, there are few theoretical models for analyzing their temperature-dependent hardness. To fill this gap in the available literature, this work is focused on developing novel theoretical models for the temperature dependence of the hardness of the ceramics and their composites. The proposed model is just expressed in terms of some basic material parameters including Young’s modulus, melting points, and critical damage size corresponding to plastic deformation, which has no fitting parameters, thereby being simple for materials scientists and engineers to use in the material design. The model predictions for the temperature dependence of hardness of some oxide ceramics, non-oxide ceramics, ceramic–ceramic composites, diamond–ceramic composites, and ceramic-based cermet are presented, and excellent agreements with the experimental measurements are shown. Compared with the experimental measurements, the developed model can effectively save the cost when applied in the material design, which could be used to predict at any targeted temperature. Furthermore, the models could be used to determine the underlying control mechanisms of the temperature dependence of the hardness of the materials.

scholarly journals A Review on the High Temperature Strengthening Mechanisms of High Entropy Superalloys (HESA)

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5835
Author(s):  
Malefane Joele ◽  
Wallace Rwisayi Matizamhuka
Keyword(s):  
High Temperature ◽  
Configurational Entropy ◽  
Extended Period ◽  
Theoretical Models ◽  
Intermetallic Phases ◽  
Processing Route ◽  
Strengthening Mechanisms ◽  
High Entropy ◽  
Use Of Resources ◽  
The Impact

The studies following HEA inceptions were apparently motivated to search for single-phase solid solution over intermetallic phases, accordingly made possible by the concept of high configurational entropy. However, it was realised that the formation of intermetallic phases in HEAs is prevalent due to other criterions that determine stable phases. Nonetheless, recent efforts have been directed towards attributes of microstructural combinations. In this viewpoint, the techniques used to predict microstructural features and methods of microstructural characterisation are elucidated in HESA fields. The study further analyses shortcomings regarding the design approaches of HESAs. A brief history is given into how HESAs were developed since their birth, to emphasize the evaluation techniques used to elucidate high temperature properties of HESAs, and the incentive thereof that enabled further pursuit of HESAs in the direction of optimal microstructure and composition. The theoretical models of strengthening mechanisms in HEAs are explained. The impact of processing route on the HESAs performance is analysed from previous studies. Thereafter, the future of HESAs in the market is conveyed from scientific opinion. Previous designs of HEAs/HESAs were more based on evaluation experiments, which lead to an extended period of research and considerable use of resources; currently, more effort is directed towards computational and theoretical methods to accelerate the exploration of huge HEA composition space.

Experimental Study of High Temperature Performance of Steel Suspension Bridge Wires

2019 ◽  
Author(s):  
Jumari A. Robinson ◽  
Adrian Brügger ◽  
Raimondo Betti
Keyword(s):  
Elastic Modulus ◽  
High Temperature ◽  
High Strength Steel ◽  
Cold Working ◽  
High Strength ◽  
Suspension Bridge ◽  
Theoretical Models ◽  
Test Results ◽  
Single Wire ◽  
Steel Wires

<p>The performance of suspension bridges exposed to fire hazards is severely under-studied – so much so that no experimental data exists to quantify the safety of a suspension bridge during or after a major fire event. Bridge performance and safety rely on the integrity of the main cable and its constituent high-strength steel wires. Due to the current lack of experimental high temperature data for wires, the theoretical models use properties and coefficients from data for other types of structural steel. No other structural steel undergoes the amount of cold-working that bridge wire does, and plastic strains from cold-working can be relieved at high temperature, drastically weakening the steel. As such, this work determines the elastic modulus, ultimate strength, and general thermo-mechanical profile of the high-strength steel wires in a range of elevated temperature environments. Specifically, these tests are conducted on a bundle of 61-wires (transient), and at the single wire level (steady-state) at a temperature range of approximately 20-700°C. The test results show an alarmingly high reduction in the elastic modulus and ultimate strength with increased temperature. The degradation shown by experiments is higher than predicted by current theoretical models, indicating that use of high-temperature properties of other types of steel is not sufficient. The test results also show scaling agreement between the single wire and the 61-wire bundle, implying that a full material work up at the single- wire level will accurately inform the failure characterization of the full cable.</p>

scholarly journals The Effects of Aluminum-Nitride Nano-Fillers on the Mechanical, Electrical, and Thermal Properties of High Temperature Vulcanized Silicon Rubber for High-Voltage Outdoor Insulator Applications

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3562 ◽  
Author(s):  
Chang Liu ◽  
Yiwen Xu ◽  
Daoguang Bi ◽  
Bing Luo ◽  
Fuzeng Zhang ◽  
...  
Keyword(s):  
Contact Angle ◽  
Thermal Properties ◽  
High Temperature ◽  
High Voltage ◽  
Breakdown Strength ◽  
Electrical Breakdown ◽  
Theoretical Models ◽  
Dielectric Constants ◽  
Silicon Rubber ◽  
Electrical Breakdown Strength

AlN nanoparticles were added into commercial high-temperature-vulcanized silicon rubber composites, which were designed for high-voltage outdoor insulator applications. The composites were systematically studied with respect to their mechanical, electrical, and thermal properties. The thermal conductivity was found to increase greatly (>100%) even at low fractions of the AlN fillers. The electrical breakdown strength of the composites was not considerably affected by the AlN filler, while the dielectric constants and dielectric loss were found to be increased with AlN filler ratios. At higher doping levels above 5 wt% (~2.5 vol%), electrical tracking performance was improved. The AlN filler increased the tensile strength as well as the hardness of the composites, and decreased their flexibility. The hydrophobic properties of the composites were also studied through the measurements of temperature-dependent contact angle. It was shown that at a doping level of 1 wt%, a maximum contact angle was observed around 108°. Theoretical models were used to explain and understand the measurement results. Our results show that the AlN nanofillers are helpful in improving the overall performances of silicon rubber composite insulators.

Electrical and Dielectric Spectroscopic Characterization of Polycrystalline Dy2Si2O7

2012 ◽  
Vol 510-511 ◽  
pp. 194-200 ◽  
Author(s):  
Shahid Ameer ◽  
Asghari Maqsood
Keyword(s):  
High Temperature ◽  
Electrical Transport ◽  
Ac Conductivity ◽  
Orthorhombic Phase ◽  
Theoretical Models ◽  
Spectroscopic Characterization ◽  
Dielectric Parameters ◽  
Triclinic Phase ◽  
Electrical Conductivities ◽  
Phase Type

The compound Dy2Si2O7exists in two polymorphs, the low temperature triclinic phase (type B) and a high temperature orthorhombic phase (type E).The dc and ac electrical conductivities of E-Dy2Si2O7are measured in the temperature range 290-510 K and frequency range 1 kHz to 1 MHz . The dc electrical transport data are analyzed according to Motts variable-range hopping model. The disorder parameter (To) and density of states at fermi level are obtained. The ac conductivity σac(ω) is obtained through the dielectric parameters. The ac conductivity can be expressed as σac(ω) =B ωs, where s is slope and it decreases with increase in temperature. The conduction mechanism in the compound is discussed in low and high temperature regions in the light of theoretical models.

scholarly journals The Effects of Trace Metal Cations on the High Temperature Reactions of an Halloysite Mineral

2021 ◽  
Author(s):  
◽  
Susan Margaret Maciver
Keyword(s):  
Experimental Data ◽  
High Temperature ◽  
Rate Constants ◽  
Theoretical Models ◽  
Solid State Reactions ◽  
Free Energies ◽  
Reaction Sequence ◽  
X Ray ◽  
Sodium Calcium ◽  
High Temperature Reactions

<p>This thesis describes a kinetic study of the high temperature solid state reactions of a well characterized halloysite mineral and five of its cation-saturated forms, the cations used being sodium, calcium, manganese, copper and iron (Ill). The reaction sequence may be represented by the idealised equations: The formation of mullite from metakaolinite has been studied in the temperature range 1020° - 1200°C, by X-ray analysis. Comparison of the experimental data with several theoretical models suggests that up to 90% conversion the reaction takes place by exponential nucleation followed by crystal growth. There is, however, some evidence for diffusion occurring as a rate controlling process, especially at high degrees of conversion to mullite. The rate constants and experimental thermodynamic functions have been evaluated for all halloysite samples. The free energies of activation (111-128 k cal.mole-1) and the rate constants are independent of the starting materials, but the enthalpies of activation (51-118 k cal.mole-1) and the entropies of activation (0 to -50 cal.deg.-1 mole-1) are not.</p>

Manufacturing of High-Temperature Polymer Electrolyte Membranes—Part II: Implementation and System Model Validation

2009 ◽  
Vol 7 (1) ◽  
Author(s):  
Tequila A. L. Harris ◽  
Daniel F. Walczyk ◽  
Mathias M. Weber
Keyword(s):  
High Temperature ◽  
Polymer Electrolyte ◽  
Manufacturing System ◽  
Flow Behavior ◽  
Polymer Electrolyte Membrane ◽  
Theoretical Models ◽  
Polymer Electrolyte Membranes ◽  
Dynamics Modeling ◽  
Free Film ◽  
Electrolyte Membranes

In this paper, a complex system of theoretical models, which predicts flow rate as a function of pressure drop, formulated previously by Harris et al. (2007, “Manufacturing of High-Temperature Polymer Electrolyte Membranes—Part I: System Design and Modeling,” ASME J. Fuel Cell Sci. Technol., 7, p. 011007), are validated through a case study. Specifically, the flow behavior of a power law polymer electrolyte membrane solution, as it flows through a novel manufacturing system, is investigated. It is found that a strategic design methodology can be used to develop a complete manufacturing system to fabricate a defect free film. Moreover, the casting method offers significant improvements for the thickness uniformity of the membrane film, compared with film that is fabricated using scaled laboratory processes. The pressure losses predicted throughout the system are validated accordingly, not only from experimental results but also from computational fluid dynamics modeling.

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