The first solid-state route to luminescent Au(I)—glutathionate and its pH-controlled transformation into ultrasmall oligomeric Au10–12(SG)10–12 nanoclusters for application in cancer radiotheraphy

There is still a need for synthetic approaches that are much faster, easier to scale up, more robust and efficient for generating gold(I)–thiolates that can be easily converted into gold–thiolate nanoclusters. Mechanochemical methods can offer significantly reduced reaction times, increased yields and straightforward recovery of the product, compared to the solution-based reactions. For the first time, a new simple, rapid and efficient mechanochemical redox method in a ball-mill was developed to produce the highly luminescent, pH-responsive Au(I)–glutathionate, [Au(SG)]n. The efficient productivity of the mechanochemical redox reaction afforded orange luminescent [Au(SG)]n in isolable amounts (mg scale), usually not achieved by more conventional methods in solution. Then, ultrasmall oligomeric Au10–12(SG)10–12 nanoclusters were prepared by pH-triggered dissociation of [Au(SG)]n. The pH-stimulated dissociation of the Au(I)–glutathionate complex provides a time-efficient synthesis of oligomeric Au10–12(SG)10–12 nanoclusters, it avoids high-temperature heating or the addition of harmful reducing agent (e.g., carbon monoxide). Therefore, we present herein a new and eco-friendly methodology to access oligomeric glutathione-based gold nanoclusters, already finding applications in biomedical field as efficient radiosensitizers in cancer radiotherapy

The role of different high energy ball milling conditions of molybdenum powder on the resulting particles size and morphology

High energy ball milling is a powder processing method in which the powder particle size can be decreased to micrometer size in a relatively short period of time. This method is based on the friction and the high energy kinetic collisions between the balls and the trapped powder particles. The milling process is influenced by many process variables such as mainly the rotational speed, ball to powder weight ratio and processing time. In the present study, high energy ball milling process was performed for molybdenum powder using a high energy ball mill under different milling conditions varying the: (i) rotational speed from 600 to 800 rpm, (ii) ball to powder weight ratio of 100:3 and 100:6, (iii) milling time in the range of 10 to 60 minutes, (iv) process control agent using polyethylene glycol, and (v) milling atmosphere under air or nitrogen. The used initial molybdenum powder was of globular morphology and 100 µm in particle size. The powders after milling were characterized by a scanning electron microscope (SEM) and a laser diffraction size analysis. The particle size of milled powders was decreased down to 1.1 µm. As the most effective ball to powder weight ratio was found 100:6 with the milling speed of 800 rpm. The milling time played a crucial role for the refinement of particles up to 45 min, where the further milling had negligible effect on the overall trend of particle size evolution

Effect of powder milling on sintering behavior and monotonic and cyclic mechanical properties of Mo and Mo–Si lattices produced by direct ink writing

Molybdenum is a refractory metal regarded as a promising basis for producing high-temperature components. However, the potential of manufacturing molybdenum-based structures by direct ink writing (DIW) has not been explored. In this study, three-dimensional porous molybdenum (Mo) and molybdenum-silicon (Mo–Si) composite lattices were fabricated using DIW with non-milled and milled powders. The effects of Mo powder morphology (resulting from milling) and chemical composition (alloying Mo with 3 and 10 wt% of Si) on the microstructure, phase composition, and static and cyclic compression properties at room temperature were investigated. Lattices fabricated from commercial spherical Mo powder exhibited the highest intra-filament porosity. Conversely, lattices fabricated from milled Mo powder were denser and had higher compressive strength, offset stress, and quasi-elastic gradient. Alloying Mo with Si during sintering resulted in composite lattices with Mo + Mo3Si microstructure. A low content of Mo3Si slightly decreased monotonic compression properties but did not affect the cyclic compression response compared to Mo lattices made from milled powder. In contrast, a high content of Mo3Si produced quasi-brittle lattices with reduced compressive strength and increased damage accumulation during cyclic loading. The cyclic behavior of all lattices was characterized by a ratcheting-dominated stress-strain response. Lattices fabricated from milled Mo and milled Mo-3 wt.%Si powders demonstrated superior performance compared to those fabricated from commercial spherical Mo and milled Mo-10 wt%Si powders. The results suggest that using milled powders can enhance the mechanical reliability and promote the use of DIW as preferred additive manufacturing technology for the fabrication of Mo–Si composite lattices