Low-temperature soldering process of AlN/Cu enhanced by Ti addition

Aluminum Nitride(AlN)ceramics were soldered to Cu substrate using active metallized Sn0.3Ag0.7Cu-x%Ti(wt.%,where x=2,4,6,8)at 250℃.This process yielded a robust and closely integrated metallized layer on the AlN ceramic’s surface.Employing SnAgCu solder paste within an air atmosphere,joints were formed for durations of 60s and 300 s.Through meticulous microscopic analysis,optimal metallization parameters were identified,resulting in the successful connection between metallized AlN ceramics and Cu substrate at a low temperature.The microstructure interface investigation further elucidated the impact of connection time on the low-temperature soldered joint of metallized AlN ceramics.

Characteristics of alumina particles in dispersion-strengthened copper alloys

Two types of alumina dispersion-strengthened copper（ADSC） alloys were fabricated by a novel in-situ reactive synthesis（IRS） and a traditional internal oxidation（IO） process. The features of alumina dispersoids in these ADSC alloys were investigated by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. It is found that nano-sized γ-Al2O3 particles of approximately 10 nm in diameter are homogeneously distributed in the IRS-ADSC composites. Meanwhile, larger-sized, mixed crystal structure alumina with rod-shaped morphology is embedded in the IO-ADSC alloy. The IRS-ADSC composites can obtain better mechanical and physical properties than the IO-ADSC composites; the tensile strength of the IRS-ADSC alloy can reach 570 MPa at room temperature, its electrical conductivity is 85% IACS, and the Rockwell hardness can reach 86 HRB.

无监督机器学习揭示金属表面本征反应性

The reactivity of metal surfaces is a cornerstone concept in chemistry,as metals have long been used as catalysts to accelerate chemical reactions.Although fundamentally important,the reactivity of metal surfaces has hitherto not been explicitly defined.For example,in order to compare the activity of two metal surfaces,a particular probe adsorbate,such as O,H,or CO,has to be specified,as comparisons may vary from probe to probe.Here we report that the metal surfaces actually have their own intrinsic/eigen reactivity,independent of any probe adsorbate.By employing unsupervised machine learning algorithms,specifically,principal component analysis(PCA),two dominant eigenvectors emerged from the binding strength dataset formed by 10 commonly used probes on 48 typical metal surfaces.According to their chemical characteristics revealed by vector decomposition,these two eigenvectors can be defined as the covalent reactivity and the ionic reactivity,respectively.Whereas the ionic reactivity turns out to be related to the work function of the metal surface,the covalent reactivity cannot be indexed by simple physical properties,but appears to be roughly connected with the valence-electron number normalized density of states at the Fermi level.Our findings expose that the metal surface reactivity is essentially a two-dimensional vector rather than a scalar,opening new horizons for understanding interactions at the metal surface.

Incorporating Sulfur Atoms into Palladium Catalysts by Reactive Metal–Support Interaction for Selective Hydrogenation

Developing highly active and selective catalysts for the hydrogenation of nitroarenes,an environmentally benign process to produce industrially important aniline intermediates,is highly desirable but very challenging.Pd catalysts are generally recognized as active but nonselective catalysts for this important reaction.Here,we report an effective strategy to greatly improve the selectivity of Pd catalysts based on the reactive metal–support interaction.