Ultrasonic-Assisted Surface Finishing of STAVAX Mold Steel Using Lab-Made Polishing Balls on a 5-Axis CNC Machining Center.

The inconvenience of conventional wool ball polishing is that the surface finishing process should be equipped with a slurry container. The main objective of this research is to develop an ultrasonic-assisted surface finishing process for STAVAX mold steel on a 5-axis CNC machining center, by using new lab-made rubber polishing balls containing the abrasive aluminum oxide instead of the traditional wool ball polishing. In total, five types (type A to type E) of new rubber-matrixed polishing balls with a composite of nitrile butadiene rubber (NBR), an abrasive of aluminum oxide, and an additive of silicon dioxide have been developed. The performance of the composites with different grain sizes (0.05 µm to 3 µm) and concentrations of the abrasive of aluminum oxide have been investigated. The effects of multiple polishing passes on the surface roughness improvement for the lab-made polishing balls have also been investigated in this study. A surface roughness of Ra 0.027 µm on average was achieved by using the multiple polishing process of E-C-B-A. The volumetric wear of the lab-made polishing balls, using ultrasonic vibration-assisted polishing, can be improved from about 12.64% (type A) to 65.48% (type E) compared with the non-vibration-assisted polishing. The suitable combination of the ultrasonic vibration-assisted polishing parameters were an amplitude of 10 µm, a frequency of 23 kHz, a spindle speed of 5000 rpm, a feed rate of 60 mm/min, a stepover of 20 µm, a penetration depth of 180 µm, and a polishing pass of E-C-B-A, based on the experimental results. The surface roughness improvement on a test carrier with a saddle surface has also been presented by using the ultrasonic vibration-assisted polishing with the lab-made polishing balls.

Hydrogen Bubble-Directed Tubular Structure: A Novel Mechanism to Facilely Synthesize Nanotube Arrays with Controllable Wall Thickness.

Nanowire arrays can be conveniently fabricated by electrodeposition methods using porous anodized alumina oxide templates. They have found applications in numerous fields. Nanotube arrays, with their hollow structure and much enhanced surface-to-volume ratio, as well as an additional tuning parameter in tube wall thickness, promise additional functions compared with nanowire arrays. Using a similar fabrication method, we have developed a facile and general method to fabricate metallic nanotubes (NTs). Using Ni NTs as a model system, the mechanism of the hydrogen-assisted NT growth was postulated and confirmed by controlling the hydrogen formation with conductive salts in an electrodeposition solution, which improves the H2 concentration but prevents the large H2 bubbles from blocking the nanochannel of a template. The controlled hydrogen generation forces the growth along the wall of nanochannels in the templates, leading to the NT formation. The magnetic properties can be controlled by the NT wall thickness, making these NTs useful for various applications.

Twisted molecule-based hyper-crosslinked porous polymers for rapid and efficient removal of organic micropollutants from water.

Organic micropollutants have become serious threats to human health and the environment over the past years. Novel materials and technologies are urgently needed to remove environmental contaminants. Herein, spirobifluorene (SBF) and triptycene (TP) were crosslinked to produce four hierarchically porous organic polymers (NHCPs). The twisted spatial structures of the monomers endow the NHCPs with high surface areas and abundant pores, which make them suitable for removal of pollutants in aqueous solution through adsorption. According to the results from adsorption experiments, the NHCPs exhibited high removal efficiency and adsorption capacities for pollutants in solution. Particularly, NHCP-3 could remove 99.4% of bisphenol A (BPA) in a few seconds with a maximum adsorption capacity of 562 mg g-1. Furthermore, the NHCPs could be easily recovered by immersion in ethanol and recycled at least five times without a loss in efficiency.

High Gas Uptake and Selectivity in Hyper-Crosslinked Porous Polymers Knitted by Various Nitrogen-Containing Linkers.

By introducing various N-containing compounds as efficient linkers, a series of hyper-crosslinked porous polymers with high surface areas and gas-uptake values were synthesized by using the Friedel-Crafts alkylation reaction. Structural characterization indicated the presence of nitrogen atoms, and gas-sorption experiments revealed that the high gas uptake benefitted from the high surface areas and the incorporation of N-containing linkers as Lewis basic sites. Among these porous polymers, HCP-4 had the highest H2 uptake of 9.29 mmol g-1 at 77 K and 0.1 MPa and the highest C2H2 uptake of 6.69 mmol g-1 at 273 K and 0.1 MPa, whereas HCP-3 showed the best CO2 uptake of 4.42 mmol g-1 at 273 K and 0.1 MPa. To understand better the important role played by nitrogen in these polymers, the isosteric heat of adsorption and adsorption selectivity of CO2 over N2 were calculated. The results showed that the triazine-based polymer HCP-1 had the highest CO2 over N2 selectivity of 75.4 at 295 K and 0.1 MPa, which makes it the most potential candidate for CO2 capture.