Enhancement of Arc Erosion Resistance in AgCuO Electrical Contact Materials through Rare Earth Element Doping: First-Principles and Experimental Studies.

To investigate the stability and electrical and physical properties of undoped CuO and CuO doped with rare earth elements, electronic structures and elastic constants were calculated using first-principles density functional theory. Additionally, experimental verification was carried out on AgCuO and AgCuO-X (La, Ce, Y) electrical contacts, which were prepared using sol-gel and powder metallurgy methods. The contacts were tested under an 18 V/15 A DC resistive load using the JF04D contact material testing system. Arc parameters were analyzed, and three-dimensional surface profilometry and scanning electron microscopy were used to study the altered erosion morphology of the electrically contacted materials; moreover, the potential mechanisms behind their arc erosion behavior were investigated in depth. The results demonstrate that the doping of rare earth elements can improve the electrical conductivity and physical properties of the contacts, optimize the arc parameters, and enhance their resistance to arc erosion. Notably, AgCuO-Ce exhibited the highest electrical conductivity and the least amount of material transfer; moreover, it had excellent arc time and energy parameters, resulting in the best resistance to arc erosion. This study provides a theoretical basis for the screening of doping elements to enhance the performance of AgCuO contact materials and offers new ideas and scientific references for this field.

Factors Influencing Early Diagnosis and Poor Prognosis of Dysphagia After Senile Ischemic Stroke.

Dysphagia is often a long-term problem after ischemic stroke, which are often accompanied by complications and results in poor outcome. This study aimed to investigate the influencing factors associated with the prognosis of dysphagia after senile ischemic stroke and evaluate the diagnostic performance of crucial factors. A total of 192 elderly ischemic stroke patients (96 patients without dysphagia with average age of 69.81 ± 4.61 years and 96 patients with dysphagia with average of 70.00 ± 6.66 years) were enrolled in the retrospective study. The clinical factors of the patients were collected and recorded for chi-square analysis and logistic analysis. The receiver operating characteristic (ROC) curve was performed to evaluate the diagnostic performance of international normalized ratio (INR) and homocysteine (Hcy) in senile ischemic stroke patients. The age, cough reflex, history of stroke, mechanical ventilation, eating posture, insufficient elevation of the larynx, standard swallowing assessment (SSA) score, Hcy value, and INR were closely related to endpoint events of patients with dysphagia. The joint model (combined INR and Hcy value) can increase the area under the curve (AUC) value (0.948) with higher sensitivity and specificity for predicting patients with dysphagia occurred endpoint events. The influencing factors for older ischemic stroke patients with dysphagia include age, cough reflex, history of stroke, mechanical ventilation, eating posture, insufficient elevation of the larynx, SSA score, Hcy value, and INR. INR and Hcy were independent risk factors for prognosis and diagnostic markers for patients with dysphagia after senile ischemic stroke.

Electrical Properties of In Situ Synthesized Ag-Graphene/Ni Composites.

Ag/Ni composite contact materials are widely used in low-voltage switches, appliances, instruments, and high-precision contacts due to their good electrical conductivity and processing properties. The addition of small amounts of additives can effectively improve the overall performance of Ag/Ni contact materials. Graphene has good applications in semiconductors, thermal materials, and metal matrix materials due to its good electrical and thermal conductivity and mechanical properties. In this paper, Ag-graphene composites with different added graphene contents were prepared by in situ synthesis of graphene oxide (GO) and AgNO3 by reduction at room temperature using ascorbic acid as a reducing agent. The Ag-graphene composites and nickel powder were ball-milled and mixed in a mass ratio of 85:15. The Ag-graphene/Ni was tested as an electrical contact material after the pressing, initial firing, repressing, and refiring processes. Its fusion welding force and arc energy were measured. The results show a 12% improvement in electrical conductivity with a graphene doping content of approximately 0.3 wt% compared to undoped contacts, resulting in 33.8 IACS%. The average contact fusion welding force was 49.49 cN, with an average reduction in the fusion welding force of approximately 8.04%. The average arc ignition energy was approximately 176.77 mJ, with an average decrease of 13.06%. The trace addition of graphene can improve the overall performance of Ag/Ni contacts and can promote the application of graphene in electrical contact materials.

Study on Simulation and Experiment of Cu, C-Doped Ag/Ni Contact Materials.

Ag/Ni contact material with greenery and good performance is a cadmium-free silver-based contact material that has been vigorously developed in recent years. However, Ag/Ni contact material has poor welding resistance. Based on the first principles of density functional theory, the interface model of Cu, C-doped Ag/Ni was established. The work of separation and interfacial energy of interface models showed that doping can improve the interfacial bonding strength and interfacial stability, with C-doped Ag/Ni having the strongest stability and interfacial bonding strength. It can be seen from the population and density of state that covalent bonds exist between Ag and Ni atoms of the Ag/Ni phase interface at the electronic structure level. Finally, the doped Ag/Ni contact material was prepared by the powder metallurgy method. Through the arc energy and welding force in the electrical contact experiment, it was obtained that the welding resistance of C-doped Ag/Ni was better than Cu-doped Ag/Ni contact material, which verified the correctness of the simulation results. Overall, the present study provides a theoretical method for the screening of doping elements to improve the performance of Ag/Ni contact material.

Properties of AgSnO2 Contact Materials Doped with Different Concentrations of Cr.

As an important component carrying the core function and service life of switching appliances, the selection and improvement of electrical contact materials is of great significance. AgSnO2, which is non-toxic, environmentally friendly and has excellent performance, has become the most promising contact material to replace AgCdO. However, it has deficiencies in machinability and electrical conductivity. The property of AgSnO2 contact material was improved by doping element Cr. The relationship between the mechanical and electrical properties of AgSnO2 contact materials and doping concentrations were investigated and analyzed by simulation and experiment. Based on the first principle, the elastic constants of supercell models Sn1-xCrxO2 (x = 0, 0.083, 0.125, 0.167, 0.25) were calculated. The results show that the material with a doping ratio of 25% is least prone to warp and crack, and the material with a doping ratio of 12.5% has the best toughness and ductility and the lowest hardness, which leads to molding and is subsequently easier to process. The Cr-doped AgSnO2 contacts with different doping proportions were prepared by the sol-gel and powder metallurgy method. Additionally, their physical performance and electrical contact properties were measured in experiments. The results show that the doped SnO2 powders prepared by the sol-gel method realize integration doping, which is consistent with the crystal model constructed in the simulation calculation. Sn0.875Cr0.125O2 has lower hardness, which is beneficial to process and form. Doping helps to stabilize the arc root, inhibit the ablation of contact by arc, reduces arc duration and arc energy, improves the resistance to arc erosion of AgSnO2 contact material, and makes electrical contact performance more stable. The contact material with a doping concentration of 16.7% has the best arc erosion resistance.

Effect of Cu F Co-doping on the Properties of AgSnO2 Contact.

The crystal structures, mechanical properties, and electrical properties of Cu doped SnO2, F doped SnO2, and Cu F co-doped SnO2 were studied by using the first-principles method. Meanwhile, AgSnO2, AgSnO2-F, AgSnO2-Cu, and AgSnO2-Cu-F contacts were prepared by using the sol-gel method for a series of experiments to verify the theoretical analysis. According to the XRD patterns, the doping does not change the structure of SnO2, but increases its lattice constant and volume. Compared with the single-doped system, the doping formation energy of Cu F co-doped system is the smallest and the structure is more stable. Among the three groups of doping systems, the Cu F co-doped system has the highest shear modulus, Young's modulus, hardness, and Debye temperature, and its mechanical properties and wear resistance are relatively best, and the melting point is also the highest. Cu F co-doping can further narrow the band gap of SnO2, reduce the electron effective mass and donor ionization energy, increase the electron mobility, and further enhance the conductivity of SnO2. The wetting angle of SnO2-Cu-F sample with Ag liquid is 1.15°, which indicates that Cu and F co-doping can significantly improve the wettability of SnO2 and Ag liquid. AgSnO2-Cu-F contact has a hardness of 82.03 HV, an electrical conductivity of 31.20 mS⋅m-1, and a contact resistance of 1.048 mΩ. Cu F co-doping can improve the shortcomings of AgSnO2 contact properties.