Electrical Contact Resistance Research Articles

Ultralow Contact Thermal Resistance between Bismuth Selenide Nanoribbons Achieved by Current-Induced Annealing.

Thermal resistance at interfaces/contacts stands as a persistent and increasingly critical issue, which hinders ultimate scaling and the performance of electronic devices. Compared to the extensive research on contact electrical resistance, contact thermal resistance and its mitigation strategies have received relatively less attention. Here, we report on an effective, in situ, and energy-efficient approach for enhancing thermal transport through the contact between semiconducting nanoribbons. By applying microampere-level electrical currents to the contact between Bi2Se3 nanoribbons, we demonstrate that the contact thermal resistance between two nanoribbon segments is reduced dramatically by a factor of 4, rendering the total thermal resistance of two ribbon segments with a contact approximately the same as that of the corresponding single continuous nanoribbon of the same length. Analysis suggests that the ultralow contact thermal resistance is due to enhanced phonon transmission as a result of enhanced adhesion energy at the contact, with marginal contributions from direct electron-phonon coupling, even for ohmic contacts. Our work introduces a broadly applicable electrical treatment approach to various contacts between conducting and semiconducting materials, which has important implications for the design and operation of nanoelectronic devices and energy converters.

Preparation and Properties of Mo/Ti/Sn Conductivity Conversion Coatings on 6063 Aluminum Alloy

ABSTRACTConductivity chromium‐free conversion coatings on aluminum substrates were achieved by utilizing Na2SnO3 and Mo/Ti solutions. The composition and morphology of the coatings were characterized using XPS, SEM, EDS, AFM, and Raman spectroscopies. The corrosion behavior of the coatings in 3.5‐wt% NaCl solution was investigated through a dynamic potential polarization method and EIS analysis. Mott–Schottky and UV–Vis analyses were used to determine the semiconductor properties of the coatings, including carrier concentration and band gap. The results revealed that the main components of the coating were Al2O3, SnO2, MoO3, and MoO2 and the coating presented a double‐layer structure, including a transition layer close to the substrate and a compact layer on the surface. The coating also exhibited the properties of a p‐type semiconductor. The electrical contact resistance value of adding Na2SnO3 decreased from 0.4331 to 0.1343 Ω/in2 (in 200 psi), while the band gap decreased from 2.281 to 2.232 eV.

Chaotic dynamic analysis of electrical contact resistance measured in sliding current-carrying friction

This work explores the dynamic laws of electrical contact resistance (ECR) signals measured in the sliding current-carrying friction tests based on chaos theory. It is found that ECR time series have a chaotic nature, strongly verified by the positive largest Lyapunov exponent λ1. The chaos may originate from the combined friction effects on short and long timescales. Phase space analysis indicates that the ECR phase trajectory adheres to the “convergence–stability” evolution law over time, which pertains closely to energy dissipation. Hence, the chaotic attractor exists during current-carrying friction. Strikingly, wear surfaces confirm that the ECR phase trajectory evolution process corresponds to the stages of “formation–keeping” of the chaotic attractor, and also agrees with the electrical wear stages of “running-in–steady-state”. Further, the chaos quantifier variation is consistent with the phase space analysis results to identify wear transition quantitatively.

Investigating laser and ultrasonic welding of pouch cell multi-foil current collectors for electric vehicle battery fabrication

The escalating necessity for more efficient and defect-free joining of ‘ultra-thin foil collectors-to-tabs’ in electric vehicle (EV) Li-ion pouch cells motivates this study. The prevalent ultrasonic welding (USW) method for these joint types, faces limitations such as design constraints and access requirements, laser welding (LW) emerges as a promising alternative offering flexibility, one-side access and faster speeds with efficient heat input. This study aims to investigate the feasibility of LW as a viable alternative to USW for joining current collectors-to-tab joints. It compares the mechanical, metallurgical, electrical and thermal analysis of the joints to evaluate both welding techniques for joint defects. The comparison of solid-state material mixing during USW and the intermixing of aluminium (Al) and copper (Cu) during fusion LW using EDX analysis presents interesting observations in the study. The USW generates a thin transition layer with intermetallic compounds (IMCs) attributed to the diffusion of Cu into the Al matrix during joining, which is comparatively lower as in the case of LW with higher material mixing with brittle IMCs like Al2Cu and Al4Cu9. However, the joint strength of LW is comparatively lower than the USW joint attributed to the reduced fusion zone area. Furthermore, from the electrical contact resistance and the joint temperature analysis, it was found that the resistance and temperature vary by as much as 13% and 6%, respectively, for the 50 A and 75 A passing currents when the USW is replaced with the LW process.

The novel Auricularia-like MoS2 as binder-free electrodes for enhanced capacitive deionization

Molybdenum disulfide (MoS2) has been proven to be an effective and promising electrode material for capacitive deionization (CDI) due to its unique architectures and excellent electrochemical activity. However, MoS2-based electrodes still suffer from the high contact electrical resistance between MoS2 and the current collectors because of the necessity of adding binder during their fabrication. In this work, a flexible MoS2-based electrode with no binders was successfully fabricated. It was found that the frameworks of stainless-steel mesh with surface treatment could serve as an ideal substrate to provide plenty of active nucleation sites for the growth of MoS2. Consequently, a novel morphology of MoS2 with Auricularia-like architectures was produced. Based on electrochemical impedance spectroscopy (EIS), the charge transfer resistance was reduced to nearly zero after the treatment, highly increasing the transportation of charges inside the electrodes compared to the common MoS2-based electrodes. As a result, the binder-free MoS2-based electrodes demonstrated a superior desalination performance of 28.76 mg g-1 (1.2 V) for NaCl solution, which was superior to that of common MoS2-based and many other advanced materials-based electrodes. The novel MoS2-based electrode not only facilitates the utilization of MoS2 in CDI but also paves the way for its application in other electrochemical domains.

Printed Lateral p–n Junction for Thermoelectric Generation

Printed thermoelectric generators (TEGs) show promising potential for converting waste heat into useful electricity at a low cost but fall short of exhibiting a conversion efficiency anticipated from materials’ properties. The output power of conventionally printed TEGs in the “π‐type” geometry suffers due to low thermal voltage and low current because of high thermal and electrical contact resistance, respectively. Herein, a type of printed p–n junction TEGs (PN‐TEGs) as a possible remedy is explored. Two printed PN‐TEGs with different thicknesses are fabricated using printed p‐type Bi0.5Sb1.5Te3 and n‐type Bi2Te2.7Se0.3 materials. The PN‐TEGs show a promising way to minimize the influence of thermal and electrical resistance in printed TEGs. In the experimental and simulation results, the significant impact of PN‐TEGs’ dimensions on their power outputs is revealed. Also, a conventional “π‐type” printed TEG is fabricated and its performance is studied. The optimized PN‐TEG with a single thermocouple yields ≈14 times higher power output density of 5.3 μW cm−2 at a ΔT of 25 K compared to “π‐type” printed TEGs.

Analysis and Improvement of Characterisation Methods for Transport Properties of Gas Diffusion Layers (GDL) for Pemfcs

Target of the presented work is to determine absolute values of GDL parameters with high accuracy, analysing and avoiding error sources caused by both test equipment and measurement methodology to the highest possible extent. The focus is on electrical, thermal and gas transport. Error sources are examined and identified. Specific attention is paid to identify inherent, inevitable measurement uncertainties. As an example, stacking of GDLs as a method to separate the contact and bulk through-plane electrical resistance of the material under compression will be reviewed in detail. In addition, the influence of the sample dimension, the sample orientation and the sample preparation is shown in examples.The results presented are acquired within the project QM-GDL (GDL quality assurance for the market run-up), which is funded by the German Federal Ministry for Digital and Transport under grant agreement number 03B11016C.

Coating Titanium Transport Layers for Enhanced Short and Long Term Performance in PEM Water Electrolysis Cells

The ageing of titanium porous transport layers (PTL) affects the longevity of polymer electrolyte membrane water electrolysis systems by the formation and thickening of a weakly conductive oxide layer. The evolving oxygen on the anode in combination with the high electrical potential provides a challenging environment in which a low electrical contact resistance to the catalyst layer (CL) needs to sustain over a long period. One previous approach is a precious metal coating of the PTL with platinum or iridium [1], which can prevent oxidation of the titanium. A cost-effective alternative is a hydrochloric acid treatment, which forms titanium hydride (TiH). [2] Titanium nitride (TiN) promises better electrical conductivity with similar corrosion resistance, but has not yet been tested as a coating. The same is true for niobium, which performed well as a coating for stainless steel bipolar plates. [3] In our studies, all these candidates face the same conditions aside an untreated PTL in one unique series of measurements. All types are repeated three times to ensure reproducibility. The mean polarization curves (figure 1 left) show that the two precious metals, iridium and platinum, significantly improve the cell voltage at a current density of 2A/cm² by 80mV and 95mV, respectively. Titanium hydride achieves an even higher reduction of 100mV without the use of precious metals. The high frequency resistance plots in figure 1 right determine that the improvement of up to 20% or 30mΩ∙cm² is attributable to a reduced contact resistance to the CL. This assumption is proven by the fact that a PTL that is only coated with iridium on the side facing the CL behaves identically to a PTL that is coated on both sides. The ohmic losses in contact with the BPP are therefore negligible in these experiments. Titanium nitride and niobium coated PTLs behave in the same way as the reference measurement. In addition to the measurements shown, long-term experiments (>1000 hours) are currently running for all types of coating, and corrosion measurements in sulphuric acid are being carried out in parallel. The joint results will determine the suitability of the various coatings for long-term use in electrolysers.[1] Liu, C., Shviro, M., Gago, A. S., Zaccarine, S. F., Bender, G., Gazdzicki, P., Morawietz, T., Biswas, I., Rasinski, M., Everwand, A., Schierholz, R., Pfeilsticker, J., Müller, M., Lopes, P. P., Eichel, R.-A., Pivovar, B., Pylypenko, S., Friedrich, K. A., Lehnert, W., Carmo, M., Exploring the Interface of Skin-Layered Titanium Fibers for Electrochemical Water Splitting. Adv. Energy Mater. 2021, 11, 2002926. https://doi.org/10.1002/aenm.202002926[2] Bystron, T., Vesely, M., Paidar, M. et al. Enhancing PEM water electrolysis efficiency by reducing the extent of Ti gas diffusion layer passivation. J Appl Electrochem 48, 713–723 (2018). https://doi.org/10.1007/s10800-018-1174-6[3] Stiber, S., Hehemann, M., Carmo, M., Müller, M., Ayers, K.E., Capuano, C., Danilovic, N., Morawietz, T., Biswas, I., Gazdzicki, P., Heger, J.-F., Gago, A.S. and Friedrich, K.A. (2022), Long-Term Operation of Nb-Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Water Electrolyzers. Adv. Energy Sustainability Res., 3: 2200024. https://doi.org/10.1002/aesr.202200024 Figure 1

Contact pressure in the proton exchange membrane fuel cell: Development of analytical models based on experimental investigation and a posteriori design of experiments

To understand the link between the physical properties of the Gas Diffusion Layer (GDL) and the overall performance of a Proton Exchange Membrane Fuel Cell (PEMFC), it is essential to investigate the impact of compressive loading on the physical parameters of the component, focusing on its electrical properties. This paper's experimental results obtained in the team's previous research are classified and analysed using a posteriori Design of Experiment (DoE). It allows us to determine the influential parameters on the component behaviour. Two analytical models are developed through regression analysis, allowing for predicting the output variables as a function of the input ones. The results are evaluated with statistical tools. The first model predicts the electrical Contact Resistance (CR) variation of the GDL as a function of mechanical compression and component type. The analytical results show that cycling compression has a negligible effect due to the lower number of applied cycles. The Micro Porous Layer (MPL) presence increases the CR, while the polytetrafluorethylene (PTFE) decreases it slightly. The GDL thickness is the most influential geometrical parameter. For this reason, a second analytical model is developed and predicts that CR is reduced primarily by increased mechanical compression and thicker GDLs.

Dual conductive network enables mechanically robust polymer composites with highly electrical and thermal conductivities

Thermally and electrically conductive polymer composites (CPCs) have been widely used in smart and flexible electronics; however, huge challenges remain in simultaneously improving the electrical and thermal conductivity of CPCs while maintaining the satisfactory mechanical properties including sufficient strength and toughness. In this study, we propose an effective interfacial regulation approach to fabricate CPCs with a dual conductive network through decoration of Ag nanoparticles (AgNPs) onto the polyurethane (PU) nanofibers containing graphite nanoplatelets (GNPs), followed by hot-pressing. Rigid GNPs expand the PU nanofiber network, facilitating Ag precursor adsorption, while subsequent hot-pressing eliminates the big channels and pores inside nanofiber composite membranes and hence greatly enhance their mechanical properties. After hot-pressing, the synergistic dual conductive network with greatly reduced thermal and electrical contact resistance leads to significant improvements in both thermal and electrical conductivity (up to 27.71 W (m K)−1 and 1.87 × 106 S/m, respectively). Moreover, the mechanically robust CPCs with exceptional durability possess superior Joule heating performance at low voltages and heat dissipation capability. This study provides inspiration for designing highly thermally and electrically conductive CPCs with potential applications as flexible thermal interface materials.

The State of Health of Electrical Connectors

For modern machines, factories and electric and autonomous vehicles, the importance of vreliable electrical connectors cannot be overstated. With an increasing number of connectors being used in machines, factories and vehicles, ensuring their reliability is crucial for comfort and safety alike. One of the key indicators of reliability is the lifetime of connectors. To evaluate the lifetime of electrical connectors, a testing method and a model for calculating their lifetime based on the test data were developed. The results from these tests were compared to failure analysis data from long-term field operations. The findings indicate that the laboratory tests can accurately reproduce the main failures observed in the field. However, such lifetime tests can be time- and labor-intensive. To address this challenge, a data-driven method is proposed that predicts the lifetime of electrical connectors using statistical analysis of electrical contact resistance data collected from short-term tests. The predictions from this method were compared to actual results obtained from long-term tests. A strong correlation was observed between the contact resistance development in short-term tests and the number of failures in later stages of testing. Thus, apart from predicting the lifetime of connectors, this method can also be applied for failure prognosis in real-time operations.

High corrosion-resistance and electrical-conductivity phytic acid/permanganate composite coating on AZ31 magnesium alloy

A composite coating based on phytic acid and permanganate was developed on AZ31 magnesium alloy via two-step chemical conversion process, exhibiting high corrosion resistance and low contact resistance. The morphology, composition, anti-corrosion properties and electrical properties of the composite coating were characterized. The composite coating was mainly composed of magnesium phytate, MnO2 and Mn2O3. The corrosion protective efficiency of the composite coating is 80.25 %, which is higher than that of the phytic acid coating and potassium permanganate coating. Furthermore, the composite coating shows low electrical contact resistance around 0.083 Ω cm2, which is close to the potassium permanganate coating but much higher than the phytic acid coating. The high corrosion resistance and electrical conductivity of the composite coating can be attributed to the growth of conductive manganese oxide at the cracks or pores of the anti-corrosion phytic acid coating.

Local and quantitative measurement of mechanical properties by electrical-nanoindentation in situ SEM: Application to a multi-phase AgCuPd alloy

Nanoindentation has now become the key technique for measuring the mechanical properties of materials at small scales. However, the quantitative and accurate processing of nanoindentation data relies on a physical quantity that is not directly available: the contact area (Ac) between the indenter tip and the sample under test. In complex systems, determining Ac is challenging due to the limitations of standard methods: analytical models have restricted validity domains (sample homogeneity and rheology), and post-mortem observations of residual imprints are time-consuming, do not appraise property gradients and cannot be applied to materials with significant elastic recovery.In this paper, a comprehensive methodology is proposed to continuously measure contact area during indentation. The proposed methodology, referred to as electrical-nanoindentation (ENI), is based on real-time monitoring of the electrical contact resistance (ECR). The protocol only requires mechanical and electrical calibrations of the indenter tip on reference materials, leading to one-to-one relationship between ECR and contact area. An original approach is also proposed to deal with the presence of surface passivating layers that generally disturb ECR measurements. As an illustration, the methodology is applied to the characterization of a multi-phase alloy (MPA) composed of silver, copper and palladium. This alloy raises the same challenges as those usually faced by nanoindentation in advanced metallurgy: heterogenous distribution of individual phases at the micro-scale, composite response of a complex mixture of hard/stiff and ductile/soft phases, … In addition, the ohmicity of contact is disturbed by surface passivating layers. Despite these numerous hindrances, the proposed methodology is successfully applied to this material. The evolution of contact area is compared with standard methods: an impressive accuracy of <2% standard-deviation is achieved when compared to post-mortem observations. The elastic moduli and hardnesses of individual phases are then accurately extracted. In addition, in order to gain in spatial definition, the ENI set-up is integrated into a scanning electron microscope (SEM), enabling indent positioning with a precision close to 100 nm.Two challenges are successfully met with the ENI methodology. On a mechanical point of view, the response of individual phases can be identified despite the complex rheology of heterogeneous materials, proving the approach applies to all mechanical behaviors (sink-in or pile-up rheologies, homogeneous or heterogeneous materials, with or without elastic recovery, …). On an electrical point of view, even if contact ohmicity is the only requirement of the methodology, it is possible to identify and overcome deviations from contact ohmicity induced by surface passivation. In particular, the non-linear resistive contribution of insulating layers fades during indentation thanks to its dependence as the reciprocal of the square of contact radius. The present work provides the keys to monitoring the contact area on any metallic sample, whether oxide-free or oxidized, making this methodology a promising alternative to standard methods.

Understanding interfacial compounds induced by Ag diffusion on improving interface electrical contact resistivity between the Cu electrode and Bi2Te3 thin film

It has been reported that introducing Ag interlayer at the Cu/Bi2Te3 interface can achieve ultra-low electrical contact resistivity. However, there is no consensus on the influence of Ag diffusion induced by Ag interlayer on electrical contact. Thus, the impact of Ag diffusion on electrical contact conductivity for Cu/Ag/Bi2Te3 multilayers was investigated. The generation of interfacial compounds induced by Ag diffusion was analyzed and the contact resistivity was measured in Cu/Ag/Bi2Te3 multilayers with different Ag interlayer thickness before and after annealing. It was found that Ag diffusion induced interfacial compounds Cu4Ag3Te4 at the Cu/Ag interface before annealing, which could decrease contact resistivity to 3.728×10−12 Ω∙m2. After annealing, the relative amount of Cu4Ag3Te4 at the Cu/Ag interface slightly decreased, and the Ag2Te was found to appear at the Ag/Bi2Te3 interface, which could further decrease contact resistivity to 3.187×10−12 Ω∙m2. With Ag interlayer thickness increasing from 50 nm to 300 nm, the contact resistivity decreased from 3.726×10−10 Ω∙m2 to 3.728×10−12 Ω∙m2 before annealing because the relative amount of Cu4Ag3Te4 increased about 5 times, after annealing the contact resistivity further decreased by 10.27∼41.7 % because the relative amount of Ag2Te increased about 1.1 times. In addition, we had optimized the ultra-low contact resistivity test method by redesigning the structure of test samples and modifying the formula of contact resistivity to eliminate two errors. One is caused by Cu electrode short-circuit resistance due to the test current being short-circuited by the middle electrode between two test electrodes. The other is caused by the increased electrical resistance of Bi2Te3 thin film due to Te atom volatilization after annealing. The results showed that the errors of the test results were reduced by at least 21.50 %. Our work provides guidance for further optimizing electrical contact of thin-film thermoelectric devices.

An investigation of the electrical contact failure of JPT electric connectors used in automobiles under multiple stresses

The primary mode of failure in electric connectors is contact failure, one of the reasons is which occurs as a result of external vibrations in the environment. This failure arises due to the reduction in positive pressure on the electric connector terminal caused by the vibration, leading to fluctuations in the electrical contact resistance (ECR). When both vibrational stress and plug/pull stress is simultaneously present, the contact area of electric connectors experiences fretting wear and shear stress, resulting in a more intricate failure mechanism for the electrical connector. Thus, this study presents an accelerated degradation testing method designed to investigate the reliability of the junior power timer (JPT) electric connector employed in automobiles. A temperature resistance test, plug/pull test (sliding wear) and vibration test (fretting wear) were conducted for the JPT electric connector. The electrical contact failure mechanism of the JPT electrical connector was analyzed, with specific focus on its correlation with the concentration of oxides in the contact area.

The effect of electrical current on lubricant film thickness in boundary and mixed lubrication contacts measured with ultrasound

This work explores experimentally the effects of DC electrical currents on lubricant film thickness alteration in lubricated sliding steel contacts in the boundary and mixed regime as measured by ultrasound. The experiments were performed in a two-electrode cell-based pin-on-disk tester instrumented with ultrasonic transducers. Unelectrified and electrified tribological tests were conducted on steel flat-on-flat contacts under various speeds and loads using both a mineral base oil and a gear oil. Film thickness, coefficient of friction (CoF), and electrical contact resistance (ECR) were measured during short experiments (30 s) in unelectrified and electrified (1.5 and 3 A) conditions. The results suggest that film thickness, CoF, and all ECR are altered by passing DC currents through the contact. In particular, film thickness increased and decreased, respectively, by applying electricity at the different speeds and loads tested. These alterations were majorly ascribed to oil viscosity decrease by local heat and surface oxidation caused by electrical discharge and break down at the interface.

Investigation of the enhancement in current-carrying friction performance with internal “copper network structure” constructed by pre-oxidized carbon fibers of the carbon skateboard

The increased speed requirements for high-speed rails necessitate the enhancement in specifications for carbon skateboard properties. The main challenges faced by carbon skateboards are their limited ability to withstand severe impacts and their high resistance levels. Hence, a new and innovative approach is utilized to create a novel carbon skateboard material. The key technique involved in this approach is the creation of a "copper network structure" within the carbon skateboard by using pre-oxidized carbon fibers. The matching performance of the carbon skateboard was examined through a current-carrying friction wear test conducted at various currents. The dynamic friction coefficient of the contact pair was less than 0.51 and the electrical contact resistance remained at most 15.89 mΩ. In addition, while the temperature rises of the contact interface increased, it remained less than 108 °C. This work represents a breakthrough in the preparation of a high-performance carbon skateboard, which has significant value for guiding the optimal design of carbon skateboards used in the pantographs of high-speed trains.

Experiment-Validated multiphysics modeling, generalizable deep learning and interpretable global sensitivity analyses for thermoelectric generators

Despite extensive studies on thermoelectric materials in a thermoelectric generator (TEG), the inverse design of TEG operating conditions remains challenging. Recent efforts in deep learning of TEGs using artificial neural network (ANN) lack global sensitivity analyses and interpretation of the connection-weights, leading to unknown coupling between input parameters and errors in importance ranking. This work reports a deep learning framework for TEGs using generalizable ANN, interpretable local (LSA) and global sensitivity analyses (GSA). Sensitivity analyses are applied to determine how energy conversion efficiency (η) under the practical Neumann and Robin thermal boundary conditions is affected by TEG operating conditions, including hot-side heat flux (qh), cold-side convective heat transfer coefficient (hf), temperature of the cooling medium (Ta), load resistance (RL), electric contact resistance (Rc), and thermal contact resistance (Kc). First, multiphysics TEG simulation results based on 3D finite element method (FEM) are validated by our experimental measurements using a self-built TEG performance evaluation system. The partial derivative-based LSA is done on a 1D theoretical TEG model to obtain the trend in sensitivity factors. Then, an ANN model is trained and validated based on the FEM simulation results and applied to the GSA process, aiming at reducing the computational load. Variance-based GSA is applied on the ANN model to determine the importance ranking and reflect the coupling between input parameters. The variance-based GSA ranks the importance as qh>hf>RL>Ta≈Rc≈Kc, and reflects the coupling between qh and hf. Finally, to interpret the ANN and the hidden deep learning process, a method combining the connection-weights algorithm and neural interpretation diagram (NID) is proposed to extract the hidden information in the connection weights. The ANN model is proven generalizable towards larger ranges of operating conditions. This work provides a framework to design TEG operating conditions towards higher energy conversion efficiencies.

Design and optimization of three segmented thermoelectric generator for nuclear reactor application

With the scientific exploration in deep space and deep sea, traditional fossil energy and solar energy cannot supply energy for deep space aircrafts and deep sea vehicles continuously, new energy power systems with the features of long endurance, high reliability and high energy density are imperative. Small nuclear reactor has become one of the best solutions for deep space energy demand in the future due to its strong environmental adaptability and long-life time. To improve the reliability of the static heat pipe reactor, the thermoelectric generators (TEGs) are utilized to convert fission heat into electrical energy. Focusing on the demands of improving the conversion efficiency, a new three segmented TEG is proposed based on the Bi2Te3, CoSb3 and Half-Heusler thermoelectric materials in this paper. Combined with the application requirements of heat pipe reactor, the geometric configuration such as different heights and the cross-sectional area of the three different materials in the PN legs is designed and optimized under different heat flux boundary conditions. The influences of contact electrical resistance and contact thermal resistance on the conversion efficiency have been investigated. When the contact electrical resistivity increases from 0.01 μΩ cm2 to 1000 μΩ cm2, the conversion efficiency loss increases from 2.6% to 80.1%. As the surface roughness rises from 0.1 μm to 100 μm, the conversion efficiency loss increases from 0.9% to 42.7%. Based on the heat flux boundary conditions provided by the heat pipes, the thermoelectric conversion performances of three segmented TEG under different external loads are investigated. Through the geometric optimization of the three segmented TEG with total height 20 mm, the thermoelectric conversion efficiency improves from 6.9% to 15.34%. For the simulation heat flux density conditions of 70 kW m−2, 75 kW m−2, 80 kW m−2, 85 kW m−2 and 90 kW m−2, the maximum output power of a thermoelectric generator can reach 8.56W, 9.71W, 10.85W, 12.00W, and 13.11W, respectively. The output characteristics of the three segmented TEGs meet the design demands of the static conversion system.

Electrically conductive and corrosion resistant coating on Mg[sbnd]Li alloys, Part I: Chemical conversion coating

MgLi alloys are one of the lightest structural materials, but suffer from severe corrosion due to the hyperactivity of Mg and Li. In this work, an electrically conductive and corrosion-resistant chemical conversion coating was fabricated on a duplex MgLi alloy LA103Z by two different routes: the first route using a conventional immersion treatment (Im-PCCs); and the second route using a brushing conversion treatment (Br-PCCs). Results demonstrate that chemical composition of conversion coatings remained, but surface morphology was altered. The Im-PCC depicts many lamellar CaHPO4 when the immersion time was longer than 60 s. The Br-PCC shows no lamellas on surface till a treatment time of 120 s. These lamellar crystals are detrimental to the electrical contact resistance (ECR), and the ECR for the Br-PCC was one order of magnitude lower than that for the Im-PCCs. Corrosion resistance for Br-PCCs, however, was slightly lower than Im-PCCs.