scholarly journals Material properties and structure of natural graphite sheet

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Martin Cermak ◽  
Nicolas Perez ◽  
Michael Collins ◽  
Majid Bahrami
Keyword(s):  
Material Properties ◽  
Coefficient Of Thermal Expansion ◽  
Electrical Contact ◽  
Sheet Thickness ◽  
Electronics Cooling ◽  
Forming Process ◽  
Electrical Contact Resistance ◽  
Natural Graphite ◽  
Graphite Sheet ◽  
Thermally Conductive

Abstract Natural graphite sheet (NGS) is compressible, porous, electrically and thermally conductive material that shows a potential to be used in fuel cells, flow batteries, electronics cooling systems, supercapacitors, adsorption air conditioning, and heat exchangers. We report the results of an extensive material characterization study that focuses on thermal conductivity, thermal diffusivity, electrical conductivity, coefficient of thermal expansion (CTE), compression strain, and emissivity. All the properties are density-dependent and highly anisotropic. Increasing the compression from 100 to 1080 kPa causes the through-plane thermal and electrical conductivities to increase by up to 116% and 263%, respectively. The properties are independent of the sheet thickness. Thermal and electrical contact resistance between stacked NGS is negligible at pressures 100 to 1080 kPa. In the in-plane direction, NGS follows the Wiedemann-Franz law with Lorenz number 6.6 $$\times $$ × 10$$^{-6}$$ - 6 W $$\Omega $$ Ω K$$^{-2}$$ - 2 . The in-plane CTE is low and negative (shrinkage with increasing temperature), while the through-plane CTE is high, increases with density, and reaches 33 $$\times $$ × 10$$^{-6}$$ - 6 K$$^{-1}$$ - 1 . Microscope images are used to study the structure and relate it to material properties. An easy-to-use graphical summary of the forming process and NGS properties are provided in Appendices A and B.

Characterization of Thermal Contact Resistance in Metal Micro-Textured Thermal Interface Materials Using Electrical Contact Resistance Measurements

2010 ◽  
Vol 297-301 ◽  
pp. 1190-1198 ◽  
Author(s):  
R. Kempers ◽  
A.J. Robinson ◽  
A. Lyons
Keyword(s):  
Contact Resistance ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Electrical Contact ◽  
Applied Pressure ◽  
Thermal Interface Material ◽  
Metal Foil ◽  
Electrical Contact Resistance ◽  
Thermal Interface ◽  
Thermally Conductive

A novel Metal Micro-Textured Thermal Interface Material (MMT-TIM) has been developed to address a number of shortcomings in conventional TIMs. This material consists of a thin metal foil with raised micro-scale features that plastically deform under an applied pressure thereby creating a continuous, thermally conductive, path between the mating surfaces. One of the difficulties in experimentally characterizing MMT-TIMs however, is distinguishing the bulk thermal resistance of the MMT-TIM from the thermal contact resistance that exists where it contacts the test apparatus. Since these materials are highly electrically conductive, this study attempts to employ electrical contact resistance measurements to estimate their thermal contact resistance. Tests using flat silver and gold specimens of known bulk thermal conductivity were used to develop a correlation between electrical and thermal contact resistance. This relationship was then employed to estimate the thermal contact resistance of a prototype silver MMT-TIM and indicates the thermal contact resistance accounts for approximately 10% of the measured thermal contact resistance. A number of issues related to this technique are discussed as well as its future outlook.

PROCESS OPTIMIZATION AND SENSITIVITY INVESTIGATION IN LASER FORMING WITH FINITE ELEMENT ANALYSIS

2007 ◽  
Vol 04 (04) ◽  
pp. 653-670 ◽  
Author(s):  
H. C. JUNG ◽  
S. KRUMDIECK
Keyword(s):  
Thermal Conductivity ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Process Optimization ◽  
Material Properties ◽  
Coefficient Of Thermal Expansion ◽  
Laser Forming ◽  
Bend Angle ◽  
Forming Process ◽  
Element Analysis

Laser forming is a flexible sheet metal manufacturing technique capable of producing various shapes, without hard tools and external forces, by irradiation across the surface of the metal piece. A three-dimensional thermal-elasto-plastic (TEP) finite element model for a straight line laser forming process has been developed during the course of this study, which simulates bend angles and temperature distributions. Laser forming process optimization and material sensitivity are investigated. In order to seek the optimal process conditions to generate a desired bend angle in the multi-scan laser bending process, an optimization algorithm based on the approximation of objective function and state variables is integrated into the numerical model. An optimal set of process parameters such as laser power, scan speed, beam diameter and the number of scans are obtained with optimization procedure. In order to assess process sensitivity to material roperties, associations between bend angle and material properties are statistically determined using the Pearson product-moment correlation coefficient via Monte Carlo simulations, for which a large number of the finite element simulations are carried out. The material properties of interest include the coefficient of thermal expansion, thermal conductivity, specific heat, modulus of elasticity, and Poisson's ratio. Results show that the process optimization coupled with finite element analysis can be used to determine processing parameters, and that the material properties of primary importance are the coefficient of thermal expansion, thermal conductivity and specific heat.

Electrical Contact Fabrication and Measurements of Metals and Alloys to Thermoelectric Materials

2007 ◽  
Vol 1044 ◽  
Author(s):  
Jonathan James D'Angelo ◽  
Edward J Timm ◽  
Fei Ren ◽  
Bradley D Hall ◽  
Eldon Case ◽  
...  
Keyword(s):  
Contact Resistance ◽  
Thermoelectric Materials ◽  
High Efficiency ◽  
Coefficient Of Thermal Expansion ◽  
Electrical Contact ◽  
Michigan State University ◽  
State University ◽  
Electrical Contact Resistance ◽  
Contact Data ◽  
P Type

AbstractLow electrical contact resistance is essential for the fabrication of high efficiency thermoelectric generators in order to convert heat to electricity. These contacts must be stable to high temperatures and through thermal cycling. A ratio of the contact resistance to the leg resistance below 0.1 is the goal for fabrication of a high efficiency thermoelectric power generation device. Here we present the fabrication procedures and characterization of contacts of metal alloys to Pb-Sb-Ag-Te (LAST) and Pb-Sb-Ag-Sn-Te (LASTT) compounds. Contacts were fabricated and measured for both ingot and hot pressed materials. Stainless steel 316 has shown a low resistance contact to these thermoelectric materials when the proper bonding conditions are used. Different time-temperature-pressure conditions for bonding to n-type and to p-type legs are presented. Contact resistances below 10μΩcm2 have been measured. In addition, break tests have shown bond strengths exceeding the semiconductor fracture strength. One of the considerations used in selecting iron alloys for electrical interconnects is the similarity in the coefficient of thermal expansion to the LAST and LASTT materials which is 18 ppm/°C and relatively temperature insensitive. Contacts to the thermoelectric materials were accomplished by diffusion bonding in a furnace developed in our lab at Michigan State University. The furnace is capable of reaching temperatures of up to 1000°C with a controlled atmosphere of a reducing gas. Fabrication procedures and contact data are presented in this paper.

scholarly journals High Performance NbMoTa–Al2O3 Multilayer Composite Structure Manufacturing by Laser Directed Energy Deposition

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1685
Author(s):  
Hang Zhang ◽  
Zihao Chen ◽  
Yaoyao He ◽  
Xin Guo ◽  
Qingyu Li ◽  
...  
Keyword(s):  
Smart Materials ◽  
Composite Structure ◽  
Composite Structures ◽  
High Performance ◽  
Energy Deposition ◽  
Coefficient Of Thermal Expansion ◽  
Multilayer Composite ◽  
Forming Process ◽  
Directed Energy Deposition ◽  
Directed Energy

The conventional method of preparing metal–ceramic composite structures causes delamination and cracking defects due to differences in the composite structures’ properties, such as the coefficient of thermal expansion between metal and ceramic materials. Laser-directed energy deposition (LDED) technology has a unique advantage in that the composition of the materials can be changed during the forming process. This technique can overcome existing problems by forming composite structures. In this study, a multilayer composite structure was prepared using LDED technology, and different materials were deposited with their own appropriate process parameters. A layer of Al2O3 ceramic was deposited first, and then three layers of a NbMoTa multi-principal element alloy (MPEA) were deposited as a single composite structural unit. A specimen of the NbMoTa–Al2O3 multilayer composite structure, composed of multiple composite structural units, was formed on the upper surface of a φ20 mm × 60 mm cylinder. The wear resistance was improved by 55% compared to the NbMoTa. The resistivity was 1.55 × 10−5 Ω × m in the parallel forming direction and 1.29 × 10−7 Ω × m in the vertical forming direction. A new, electrically anisotropic material was successfully obtained, and this study provides experimental methods and data for the preparation of smart materials and new sensors.

scholarly journals The Route for Ultra-High Recording Density Using Probe-Based Data Storage Device

NANO ◽  
2015 ◽  
Vol 10 (08) ◽  
pp. 1550118 ◽  
Author(s):  
Lei Wang ◽  
Jing Wen ◽  
CiHui Yang ◽  
Shan Gai ◽  
YuanXiu Peng
Keyword(s):  
Phase Change ◽  
Data Storage ◽  
Electrical Contact ◽  
Crystal Nucleation ◽  
Access Time ◽  
Storage Device ◽  
Electrical Contact Resistance ◽  
Low Energy Consumption ◽  
Modeling Techniques ◽  
Second Period

Phase-change probe memory using Ge2Sb2Te5 has been considered as one of the promising candidates as next-generation data storage device due to its ultra-high density, low energy consumption, short access time and long retention time. In order to utmostly mimic the practical setup, and thus fully explore the potential of phase-change probe memory for 10 Tbit/in2 target, some advanced modeling techniques that include threshold-switching, electrical contact resistance, thermal boundary resistance and crystal nucleation-growth, are introduced into the already-established electrothermal model to simulate the write and read performance of phase-change probe memory using an optimal media stack design. The resulting predictions clearly demonstrate the capability of phase-change probe memory to record 10 Tbit/in2 density under pico Joule energy within micro second period.

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