Long-term transients in fluidization of oxide nanoparticle agglomerates

Nanopowders are frequently fluidized for research during the last two decades. Interestingly, it was believed for a long time that nanopowders cannot be fluidized since they are classified as group C, very cohesive powders, in the Geldart diagram. For these powders the acting adhesion forces are too strong to allow fluidization. However, many studies showed that nanoparticles can be fluidized as micron-sized fractal agglomerates with very low densities and very high porosities [1]. The high porosities of the agglomerates are very attractive because most of the particle surface is accessible for mass transfer and reaction. The formation of the agglomerates in the fluidized bed is a dynamic process which includes collision, unfolding, breaking, and reagglomeration. This makes it likely that the agglomerate size distribution will change over time. On the other hand, long-duration fluidization of nanopowders is required for possible industrial applications such as coating or catalysis. Therefore, a better understanding of, the influence of time on the properties of fluidized nanoparticle agglomerates is crucial. Here we present a detailed analysis of the agglomerate size distribution over time during long-time fluidization of oxide nanoparticles. A settling tube set-up is used to investigate the agglomerate size distributions (see Fig. 1) as well as X-ray tomography which suggest stratification of the bed during long time fluidization (see Fig. 2). Further, the influence of the acting contact forces on the arising agglomerate size distributions was investigated. The results show that microscopic properties such as agglomerate size distribution can directly be linked to macroscopic properties as the bed expansion and that the time is a very important factor for the fluidization of nanopowders, because the bed dynamics changes strongly over time. Please click Additional Files below to see the full abstract

Fluidization of graphene nanoplatelets for atomic layer deposition

Graphene is an ideal catalysis support: it has a high surface area, is chemically and thermodynamically inert, and has high carrier mobility. A special type of graphene nanoparticles are graphene nanoplatelets. They consist of small stacks of graphene giving them a thickness of 1 – 15 nm while their diameters can range up to a few micrometres. However, for catalysis these nanoplatelets have to be provided with catalyst materials such as platinum or titania. One very promising technique for such a modification is Atomic Layer Deposition of nanoparticles on the graphene, which can provide a fast, highly controlled and scalable process. However, to separate the carbon nanoplatelets and achieve free large accessible surfaces in the reactor nanoplatelets have to be fluidized. While fluidization of carbon nanotubes is already well established, fluidization of nanoplatelets is a completely new research topic and was, to the best of our knowledge, not investigated so far. Based on the size of the carbon nanoplatelets they are treated as very cohesive (Geldart group C) powders which are hard to fluidize. Nevertheless, homogenous fluidization could be achieved by using assistance methods such as mechanical vibration. Here we present a detailed analysis of the fluidization behaviour of carbon nanoplatelets for atomic layer deposition. We analysed the bed expansion behaviour of the nanoplatelets depending on the gas velocities. Since the Atomic Layer Deposition process can be run at different temperatures, depending on the used precursors, we further analysed the influence of the temperature on the fluidization behaviour. Finally, we investigated the reproducibility of our results by an statistical analysis of our results. Please click Additional Files below to see the full abstract

Size distribution prediction of nanoparticle agglomerates in a fluidized bed

Nanoparticles have acquired considerable attention from academia and industry due to their unique properties arising from the large surface area to volume ratio. A promising method to process these particles is fluidization. Furthermore, it is worth knowing that nanoparticles fluidize as clusters called agglomerates, formed by the relatively strong adhesion forces among the individual particles (1). These agglomerates are large, highly porous fractal structures; thus, easy to access but extremely fragile. During fluidization, agglomerates move, collide, break, reform, deform, and combine, which make them suitable for a wide range of applications. Nanopowders can fluidize with bubbles or uniformly, which show different dynamics that might affect the morphology of the fluidized agglomerates. In order to better understand the dynamic behaviour of the system, it is crucial to know the agglomerate size distribution within the fluidized bed. Therefore, we developed a model based on a simple force balance to predict the agglomerate size distribution, which enables the optimization of processing methods. Please click Additional Files below to see the full abstract

Advances in scalable gas-phase manufacturing and processing of nanostructured solids: A review

Although the gas-phase production of nanostructured solids has already been carried out in industry for decades, only in recent years has research interest in this topic begun to increase. Nevertheless, despite the remarkable scientific progress made recently, many long-established processes are still used in industry. Scientific advancements can potentially lead to the improvement of existing industrial processes, but also to the development of completely new routes. This paper aims to review state-of-the-art synthesis and processing technologies, as well as the recent developments in academic research. Flame reactors that produce inorganic nanoparticles on industrial- and lab-scales are described, alongside a detailed overview of the different systems used for the production of carbon nanotubes and graphene. We discuss the problems of agglomeration and mixing of nanoparticles, which are strongly related to synthesis and processing. Finally, we focus on two promising processing techniques, namely nanoparticle fluidization and atomic layer deposition

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised

Contact behavior of size fractionated TiO2 nanoparticle agglomerates and aggregates

The size dependent contact behavior of nanoparticle agglomerates was studied. Size fractionated TiO2 nanoparticle agglomerates were synthesized with a combination of a flame spray reactor and a differential mobility analyzer resulting in four different agglomerate sizes (median values from 78 to 161nm). Contact behavior of the fractionated agglomerates was investigated using atomic force microscopy. A model of the contact behavior of agglomerates under tensile stress was established in which the aggregates within the agglomerates rearrange and form chains before breakage. Force curves show that the length of the chains and the amount of rearrangements depend on the agglomerate sizes. Larger agglomerates require more work for their aggregate rearrangement before the final breakage is induced. © 2014 Elsevier B.V.status: publishe

Nature–Inspired self–cleaning surfaces

| openaire: EC/H2020/725513/EU//SuperRepelNature-inspired self-cleaning surfaces have attracted considerable attention from both fundamental research and practical applications. This review adopts a chemical-engineering point of view and focuses on mechanisms, modelling, and manufacturing (M3) of nature-inspired self-cleaning surfaces. We will introduce six nature-inspired self-cleaning mechanisms: The Lotus-effect, superhydrophobic-induced droplet jumping, superhydrophobic-induced unidirectional movement of water droplet, underwater-superoleophobic-based self-cleaning, slippery-based self-cleaning, and dry self-cleaning. These mechanisms of nature self-cleaning examples are popular and well-known as well as have been widely applied or exhibited potential applications in our daily life and industrial productions. The mathematical and numerical modelling of the identified self-cleaning mechanisms will be carefully introduced, which will contribute to the rational design and reproducible construction of these functional self-cleaning surfaces. Finally,we will discuss how these materials can be produced, with a focus on scalable manufacturing. We hope this review will strengthen the understanding on nature-inspired self-cleaning surfaces and stimulate interdisciplinary collaboration of material science, biology and engineering.Peer reviewe