Herein, we report for the first time the successful preparation of a gold(III) nitrate [Au(NO3)3] water‐based precursor for use in a bottom‐up ultrasonic spray pyrolysis (USP) process. Due to its limited solubility in water, the precursor was prepared under reflux conditions with nitric acid (HNO3) as the solvent and ammonium hydroxide (NH4OH) as a neutralizer. This precursor enabled the USP synthesis of gold nanoparticles (AuNPs) and the in situ formation of low concentrations of NO2 − and NO3 − ions, which were caught directly in deionized water in a collection system. These ions were proven to act as stabilizers for the AuNPs. Investigations showed that the AuNPs were monodispersed and spherically shaped with a size distribution over three groups: the first contained 5.3 % AuNPs with diameters (2 r) <15 nm, the second contained 82.5 % AuNPs with 2 r between 15 and 200 nm, and the third contained 12.2 % AuNPs with 2 r>200 nm. UV/Vis spectroscopy revealed the maximum absorbance band of the AuNPs at λ=528 nm. Additionally, scanning transmission electron microscopy (STEM) observations of the smallest AuNPs (2 r<5 nm) revealed atomically resolved coalescence phenomena induced by interaction with the electron beam. Four stages of the particle‐growth process were distinguished: 1) movement and rotation of the AuNPs; 2) necking mechanism; 3) orientated attachment at matching facets; 4) reshaping of the AuNPs by surface diffusion. This provided important insight into the formation/synthesis process of the AuNPs.

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Ultrasonic Spray Pyrolysis (USP) possesses a great potential for production of higher quantities of gold nanoparticles (AuNPs), thus overcoming the problem of batch-to-batch variations in their properties. Recently, we demonstrated that USP with an additional evaporation chamber (modular USP) led to a better size control of AuNPs. However, their morphology, stability, toxicity, and immunomodulatory properties have not been investigated completely. Here, two types of spherical AuNPs were produced by using different USP parameters, followed by their stabilization in Na-citrate solution. No significant changes in their size, agglomeration, andz-potential occurred 3 months after their initial production in citrate solution. However, the conditioning of AuNPs in serum-containing cell culture media for 24 h induced an increase in the AuNPs’ hydrodynamic size and a red shift in their Surface Plasmon Resonance, pointing to their instability in biological media. Cytocompatibility tests showed that the produced AuNPs were internalized by L929 cells and primary human monocytes and were not cytotoxic at the concentrations lower than 200 μg/mL, but they exhibited antiproliferative and anti-inflammatory effects, respectively. AuNPs reduced the percentage of CD14+CD16+but not CD14lowCD16+monocytes in vitro and reduced the expression of CD86, HLA-DR, TNF-α, and IL-12/IL-23 by these cells. These results indicate that the anti-inflammatory effects of citrate-capped AuNPs produced by modular USP could be beneficial for their application in the treatment of inflammatory conditions.

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SummaryNowadays friction surfacing (FS) has become a popular solid state surface coating technology suitable for a range of substrates. The technology has the ability to produce coatings with marginal dilution and good metallurgical bonding. The present study has aimed at producing a single-track and a three-track overlapping coatings on high-speed steel substrates using an AISI 316 consumable rod. Microhardness of coatings was examined by a Vickers micro hardness tester. Coatings of all the friction surfaced samples in as-deposited condition showed significant hardness. The infrared thermography showed that the peak temperature achieved by the AISI 316 coating was about 1020 ͦ C. The coatings, thus attained, were further analysed for their microstructural features and interfacial characteristics by using FE-SEM. The EDX analysis showed the presence of nickel, chromium and oxygen, which indicates the formation of oxide compounds. The formation of AISI 316 deposits on the HSS substrate and the effect of coating overlapping are discussed in this article.

Background: The bulk production of Gold Nanoparticles (AuNPs) and their concentrated ink, with desirable properties such as morphology, purity, stability and final Au concentration, remains a challenge. Objective: (i) Synthesis of AuNPs through Ultrasonic Spray Pyrolysis (USP) from different precursors. (ii) Preparation of their concentrated ink and (iii) Test their feasibility for ink jet printing onto a glossy paper substrate. Method: Initially, two different start materials were used - precursor: Gold Chloride with its nanoparticles as C-AuNPs, and Gold Acetate with its nanoparticles as A-AuNPs stabilised with PVP40 in deionised water. The concentrated ink was prepared from both AuNPs, and filtered up to the [Au] of 1000 ppm. Ink-jet printing was performed, and the obtained patterns were analysed through SEM. Results: The [Au] in the obtained solutions, determined through ICP-OES analysis, was, for CAuNPs, about 100 ppm, and 150 ppm for A-AuNPs. In the case of C-AuNPs the solution was rose, and for A-AuNPs violet. TEM investigation revealed that C-AuNPs dominated in a circular shape with size about 18 nm; contrary to this, A-AuNPs were mostly in ellipsoid shape, with size in the longitudinal direction of about 36 nm. EDX analyses detected 99.9 wt. % of Au in both AuNPs, which is evidence that these were of high purity. Due to different AuNPs` sizes and [Au], the colloidal solutions showed maximum absorbance wavelength of 532 nm for C-AuNPs and 528 nm for A-AuNPs. SEM results showed that A-AuNPs were significantly better for printing on the paper substrate than C-AuNPs, due to their ellipsoidal shape, as the flow behaviour had been much smoother through the nozzle as compared to the circular shape. The printed area with A-AuNPs reflected in better incorporation of nanoparticles on the paper surface and high-density connectivity among AuNPs. Conclusions: C-AuNPs and A-AuNPs were synthesised successfully under optimum parameters of evaporation temperature, reaction temperature and gas flow rates. The spherical shape of C-AuNPs as compared to the ellipsoidal nature of A-AuNPs was due to the rapid sintering of Gold Chloride at a higher temperature of 300ºC as compared to Gold Acetate.

In the present work, the scientists were successful in obtaining a friction surfaced coating of mild steel over mild steel, mild steel over stainless steel (AISI 304) and stainless steel over stainless steel using a low-cost conventional milling machine. A 22 factorial method with three replications was used to design the experiments. The influence of variation in rotational speed (1400 rpm and 1000 rpm) and table feed rate (4.17 mm/s and 2.67 mm/s) on coating width, thickness and interface temperature of the coating and substrate was investigated. Multi-response optimization was performed and the developed model was validated by confirmatory experiments. The results showed that, with an increase in rotational speed and table feed rate, width and thickness of the coating decreases, while temperature increases. An infrared (IR) camera provided thermographs that elaborated the distinct stages of heat dissipation during the process of coating formation. The bond integrity and strength of the coating was analyzed by bend tests and Vickers micro hardness test. The results revealed that a higher hardness value was obtained at the interface of the coating as compared to coating and interface.

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