Predicting the average size of blasted rocks in aggregate quarries using artificial neural networks

The prediction of the average size of fragments in blasted rock piles produced after blasting in aggregate quarries is essential for decresing the cost of crushing and secondary breaking. There are several conventional and advanced processes to estimate the size of blasted rocks. Among these, the empirical prediction of the expected fragmentation in most cases is carried out by Kuznetsov’s equation (Sov Min Sci 9:144–148, 1973), modified by Lilly (1986) and Cunningham (1987). The present research focuses on the effect of the engineering geological factors and blasting process on the blasted fragments using a more powerful, advanced computational tool, an artificial neural network. In particular, the blast database consists of the blastability index of limestone on the pit face, the quantities of the explosives and of the blasted rock pile, assessing the interaction of these parameters on the blasted rocks. The data were collected from two aggregate quarries, Drymos and Tagarades, near Thessaloniki, in the Central Macedonia region of Greece. This approach indicates significant performance stability, providing the fragmentation size with high accuracy.

     

Signatures of Quantized Energy States in Solution‐Processed Ultrathin Layers of Metal‐Oxide Semiconductors and Their Devices

Physical phenomena such as energy quantization have to‐date been overlooked in solution‐processed inorganic semiconducting layers, owing to heterogeneity in layer thickness uniformity unlike some of their vacuum‐deposited counterparts. Recent reports of the growth of uniform, ultrathin (<5 nm) metal‐oxide semiconductors from solution, however, have potentially opened the door to such phenomena manifesting themselves. Here, a theoretical framework is developed for energy quantization in inorganic semiconductor layers with appreciable surface roughness, as compared to the mean layer thickness, and present experimental evidence of the existence of quantized energy states in spin‐cast layers of zinc oxide (ZnO). As‐grown ZnO layers are found to be remarkably continuous and uniform with controllable thicknesses in the range 2–24 nm and exhibit a characteristic widening of the energy bandgap with reducing thickness in agreement with theoretical predictions. Using sequentially spin‐cast layers of ZnO as the bulk semiconductor and quantum well materials, and gallium oxide or organic self‐assembled monolayers as the barrier materials, two terminal electronic devices are demonstrated, the current–voltage characteristics of which resemble closely those of double‐barrier resonant‐tunneling diodes. As‐fabricated all‐oxide/hybrid devices exhibit a characteristic negative‐differential conductance region with peak‐to‐valley ratios in the range 2–7.     

The Effect of Thermal Reduction on the Water Vapor Permeation in Graphene Oxide Membranes

In the present study, the influence of the thermal reduction on the water vapor transmission properties of thin graphene oxide (GO) membranes is evaluated. The macroscopically measured property of the Water Vapor Transmission Rate (WVTR) exhibits step like dependence contrary to the gradual microscopic structural alterations identified by several techniques (XPS, FTIR and XRD) applied in situ during the thermal annealing process. Three distinct regions of WVTR‐values associated with distinct interlayer distances i.e., >7.5 Å, ∼6 Å and <6 Å are essentially observed which may be compared to the findings of the recently reported first principle calculations. Our experimental results enable the understanding of the water vapor unimpeded transmission through the layers of the oxygen rich GO nanostructured membranes and consequently facilitate the design of functional membranes for separation applications.     

Electrochemical oxidation of alcohols on Pt–TiO2 binary electrodes

In this study Pt–TiO₂ binary electrodes were prepared by means of thermal decomposition of chloride precursors on Ti substrates, characterised by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), electrochemical techniques and CO stripping and used as anodes for alcohol oxidation. The minimization of the Pt loading without electrocatalytic activity losses was also explored. TiO₂ was chosen due to its chemical stability, low cost and excellent properties as substrate for Pt dispersion. It was found that TiO₂ loading up to 50% results in Electrochemically Active Surface (EAS) increase. The EAS of Pt(50%)-TiO₂(50%) was found to be almost one order of magnitude higher than that of pure Pt while the EAS of samples with Pt loading lower than 30% was negligible. The above conclusion has been confirmed both by following the charge of the reduction peak of platinum oxide and by CO stripping experiments. All samples have been evaluated during the electrochemical oxidation of methanol and ethanol. In both cases the Pt(50%)-TiO₂(50%) electrode had better electrocatalytic activity than the pure Pt anode. The observed higher performance of the binary electrodes was mainly attributed to the enhanced Pt dispersion as well as the formation of smaller Pt particles by the addition of TiO₂.     

Tungsten oxides as interfacial layers for improved performance in hybrid optoelectronic devices

Tungsten oxide (WO₃) films with thicknesses ranging from 30 to 100 nm were grown by Hot Filament Vapor Deposition (HFVD). Films were studied by X-Ray Photoemission Spectroscopy (XPS) and were found to be stoichiometric. The surface morphology of the films was characterized by Atomic Force Microscopy (AFM). Samples had a granular form with grains in the order of 100 nm. The surface roughness was found to increase with film thickness. HFVD WO₃ films were used as conducting interfacial layers in advanced hybrid organic-inorganic optoelectronic devices. Hybrid-Organic Light Emitting Diodes (Hy-OLEDs) and Organic Photovoltaics (Hy-OPVs) were fabricated with these films as anode and/or as cathode interfacial conducting layers. The Hy-OLEDs showed significantly higher current density and a lower turn-on voltage when a thin WO₃ layer was inserted at the anode/polymer interface, while when inserted at the cathode/polymer interface the device performance was found to deteriorate. The improvement was attributed to a more efficient hole injection and transport from the Fermi level of the anode to the Highest Occupied Molecular Orbital (HOMO) of a yellow emitting copolymer (YEP). On the other hand, the insertion of a thin WO₃ layer at the cathode/polymer interface of Hy-OPV devices based on a polythiophene-fullerene bulk-heterojunction blend photoactive layer resulted in an increase of the produced photogenerated current, more likely due to improved electron extraction at the Al cathode.     

Reduction of Tungsten Oxide: A Path Towards Dual Functionality Utilization for Efficient Anode and Cathode Interfacial Layers in Organic Light‐Emitting Diodes

Here, we report on the dual functionality of tungsten oxide for application as an efficient electron and hole injection/transport layer in organic light‐emitting diodes (OLEDs). We demonstrate hybrid polymer light‐emitting diodes (Hy‐PLEDs), based on a polyfluorene copolymer, by inserting a very thin layer of a partially reduced tungsten oxide, WO_2.5, at the polymer/Al cathode interface to serve as an electron injection and transport layer. Significantly improved current densities, luminances, and luminous efficiencies were achieved, primarily as a result of improved electron injection at the interface with Al and transport to the lowest unoccupied molecular orbital (LUMO) of the polymer, with a corresponding lowering of the device driving voltage. Using a combination of optical absorption, ultraviolet spectoscopy, X‐ray photoelectron spectroscopy, and photovoltaic open circuit voltage measurements, we demonstrate that partial reduction of the WO₃ to WO_2.5 results in the appearance of new gap states just below the conduction band edge in the previously forbidden gap. The new gap states are proposed to act as a reservoir of donor electrons for enhanced injection and transport to the polymer LUMO and decrease the effective cathode workfunction. Moreover, when a thin tungsten oxide film in its fully oxidized state (WO₃) is inserted at the ITO anode/polymer interface, further improvement in device characteristics was achieved. Since both fully oxidized and partially reduced tungsten oxide layers can be deposited in the same chamber with well controlled morphology, this work paves the way for the facile fabrication of efficient and stable Hy‐OLEDs with excellent reproducibility.     

Assessment of Novel Long‐Lasting Ceria‐Stabilized Zirconia‐Based Ceramics with Different Surface Topographies as Implant Materials

The development of long‐lasting zirconia‐based ceramics for implants, which are not prone to hydrothermal aging, is not satisfactorily solved. Therefore, this study is conceived as an overall evaluation screening of novel ceria‐stabilized zirconia–alumina–aluminate composite ceramics (ZA₈Sr₈‐Ce11) with different surface topographies for use in clinical applications. Ceria‐stabilized zirconia is chosen as the matrix for the composite material, due to its lower susceptibility to aging than yttria‐stabilized zirconia (3Y‐TZP). This assessment is carried out on three preclinical investigation levels, indicating an overall biocompatibility of ceria‐stabilized zirconia‐based ceramics, both in vitro and in vivo. Long‐term attachment and mineralized extracellular matrix (ECM) deposition of primary osteoblasts are the most distinct on porous ZA₈Sr₈‐Ce11_p surfaces, while ECM attachment on 3Y‐TZP and ZA₈Sr₈‐Ce11 with compact surface texture is poor. In this regard, the animal study confirms the porous ZA₈Sr₈‐Ce11_p to be the most favorable material, showing the highest bone‐to‐implant contact values and implant stability post implantation in comparison with control groups. Moreover, the microbiological evaluation reveals no favoritism of biofilm formation on the porous ZA₈Sr₈‐Ce11_p when compared to a smooth control surface. Hence, together with the in vitro in vivo assessment analogy, the promising clinical potential of this novel ZA₈Sr₈‐Ce11 as an implant material is demonstrated.     

The role of phosphoric acid in the anodic electrocatalytic layer in high temperature PEM fuel cells

The poisoning effect and the role of H₃PO₄ (PA) at the anodic electrocatalytic layer of a high temperature polymer electrolyte membrane (HT PEM based on ADVENT TPS^®) fuel cell are discussed under the light of cyclic voltammetry, CO stripping, and X-ray photoelectron spectroscopy (XPS) experiments. The catalytic layer was based on both the pyridine-modified multi-wall carbon nanotubes, 30 wt% Pt/(ox.MWCNT)–Py, and on commercial 30 wt% Pt/C, with varying PA loadings on the electrode. At low PA loadings (<3 gPA/gPt), the electrochemically active surface area of Pt decreases significantly under H₂ anode long-term operation, approaching surface Pt utilization <10 %. This degradation is attributed to the formation of pyrophosphoric or triphosphoric acid as well as catalytically H₂ reduced PA species, which block the Pt surface area. As was explicitly detected by means of XPS PA species were displaced from the Pt surface under H₂ or CO exposure. The poisoning effect is reversible as these species can be hydrated back to orthophosphoric acid. The reduced species can be reoxidized into PA at 750 mV versus RHE. On the other hand, the electrochemical interface is stable at PA loadings exceeding 3 gPA/gPt, thus approaching Pt surface utilization >80 % in the long term. This is believed to be a consequence of the more uniform distribution of PA, thus eliminating the PA displacement from the Pt interphase. It is hypothesized that the minimization of the PA poisoning effect at PA > 3 gPA/gPt, may also be a result of more efficient hydration of the catalytic layer that is being achieved through the hydration of the PA in the membrane and in the catalyst layer by the cathodically produced water vapors.