Flame-Retarded Rigid Polyurethane Foam Composites with the Incorporation of Steel Slag/Dimelamine Pyrophosphate System: A New Strategy for Utilizing Metallurgical Solid Waste

Rigid polyurethane (RPUF) was widely used in external wall insulation materials due to its good thermal insulation performance. In this study, a series of RPUF and RPUF-R composites were prepared using steel slag (SS) and dimelamine pyrophosphate (DMPY) as flame retardants. The RPUF composites were characterized by thermogravimetric (TG), limiting oxygen index (LOI), cone calorimetry (CCT), and thermogravimetric infrared coupling (TG-FTIR). The results showed that the LOI of the RPUF-R composites with DMPY/SS loading all reached the combustible material level (22.0 vol%~27.0 vol%) and passed UL-94 V0. RPUF-3 with DMPY/SS system loading exhibited the lowest pHRR and THR values of 134.9 kW/m2 and 16.16 MJ/m2, which were 54.5% and 42.7% lower than those of unmodified RPUF, respectively. Additionally, PO· and PO2· free radicals produced by pyrolysis of DMPY could capture high energy free radicals, such as H·, O·, and OH·, produced by degradation of RPUF matrix, effectively blocking the free radical chain reaction of composite materials. The metal oxides in SS reacted with the polymetaphosphoric acid produced by the pyrolysis of DMPY in combustion. It covered the surface of the carbon layer, significantly insulating heat and mass transport in the combustion area, endowing RPUF composites with excellent fire performance. This work not only provides a novel strategy for the fabrication of high-performance RPUF composites, but also elucidates a method of utilizing metallurgical solid waste

Effect of Y2O3 on the Electrical Contact Behavior of Al2O3-Cu/MoTa Composites

With the massive penetration of electronics into human life, higher demands are placed on electrical contacts. Among them, the lifetime of electrical contacts and safety are the most concerning. In this research, Al2O3-Cu/25Mo5Ta and 0.5Y2O3/Al2O3-Cu/25Mo5Ta composites were prepared by using ball milling and powder metallurgy methods. The two composites were subjected to 10,000 contact opening and closing electrical contact experiments and the arc duration and arc energy were analyzed. The results show that the addition of Y2O3 has a slight effect on the mechanical properties of the Al2O3-Cu/25Mo5Ta composites but has a significant effect on the electrical contact performance. Y2O3 can reduce the mass loss of the electrical contacts during the electrical contact process, which prolongs their service life. The addition of Y2O3 decreased the average arc duration and arc energy of the electrical contact material by 21.53% and 18.02%, respectively, under the experimental conditions of DC 30 V, 10 A. TEM results showed that nanoscale YTaO4 with excellent thermal stability was generated during the sintering process, which has a positive effect on the electrical contact performance of the composites

Microstructure and electrical contact behavior of Al2O3–Cu/30W3SiC(0.5Y2O3) composites

The aim of this study is to observe the organization and properties of Al2O3–Cu/WSiC–Y2O3 composites and to investigate the effect of Y2O3 incorporation on the electrical contact properties of the composites. Preparation of Al2O3–Cu/30W3SiC(0.5Y2O3) composites by rapid hot-pressing sintering technique. The conductivity of the composites is 59.3 %IACS and 58.3 %IACS, respectively. Hardness is 179 HV and 183 HV, respectively. Thermal conductivity is 108 W/(m·k) and 275 W/(m·k), respectively. The dense structure of the composites and the homogeneous distribution of reinforcing phases give the composites excellent overall performance. The addition of Y2O3 increases the resistance of the materials to arc erosion. The amount of material transfer and loss is significantly reduced, and the arc ablation phenomenon is reduced. The arc duration was significantly reduced from 4.48 ms to 0.44 ms, 5.72 ms–4.68 ms, 6.23 ms–5.52 ms, and 12.5 ms–8.59 ms, respectively; and the melt force was significantly reduced to 58.9%, 81.4%, 87.5%, and 89.4% of the original