Recently, we have shown that the protecting layer of nanosize can be produced by means of ion beam mixing (IBM) of a Si/C multilayer system. The corrosion resistance of the layer correlated with the ...SiC amount and distribution, determined by Auger electron spectroscopy depth profiling. It has also been shown that the IBM of the Si/C system can be well described by TRIDYN simulation. By combining these two findings, it is possible to design protective layers for various arrangements of layer structure and irradiation conditions. Three different multilayer structures (with individual layer thicknesses falling in the range of 10–20 nm) have been irradiated by Ar+ and Xe+ ions at room temperature in the energy and fluence ranges of 40–120 keV and 0.25 × 1016 to 6 × 1016 ion/cm2, respectively. The carbon and silicon depth distributions have been calculated by TRIDYN simulation. From these profiles applying a simple rule for compound formation, the SiC in-depth distributions were calculated. The resulting corrosion resistance has been measured by potentiodynamic corrosion test in 4 M KOH solution. Excellent correlation between these results and the in-depth distribution (calculated by TRIDYN simulation) of SiC has been found. Thus, the design of a protective SiC coatings operating in harsh environments is possible by applying fast and cheap simulation techniques.
Ion beam mixing has been used to produce a silicon carbide (SiC)-rich nanolayer for protective coating. Different C/Si/C/Si/C/Si(substrate) multilayer structures (with individual layer thicknesses ...falling in the range of 10–20 nm) have been irradiated by Ar+ and Xe+ ions at room temperature in the energy and fluence ranges of 40–120 keV and 1–6 × 1016 ion/cm2, respectively. The effects of ion irradiation, including the in-depth distribution of the SiC produced, was determined by Auger electron spectroscopy depth profiling. The thickness of the SiC-rich region was only some nanometers, and it could be tailored by changing the layer structure and the ion irradiation conditions. The corrosion resistance of the layers was investigated by potentiodynamic electrochemical test in 4 M KOH solution. The measured corrosion resistance of the SiC-rich layers was orders of magnitude better than that of pure silicon, and a correlation was found between the corrosion current density and the effective areal density of the SiC.
Ti50Cu25Ni20Sn5 (at.%) powder was subjected to high-energy ball milling at room temperature and -78 ?C. As a function of the milling time, evaluation of phases, morphology, and the refinement of ...grain size were investigated by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and laser-diffraction particle size analysis (PSA). The transformation of the crystalline structure into an amorphous structure and then the transformation into a nanocrystalline structure during further milling was detected. The stress-induced martensitic transformation occurred after 30 min milling time at both temperatures, the cubic Cu(Ni,Cu)Ti2 phase transformed into the orthogonal structure. The hardness value of powders after 150 min milling time increased from 506 to 780 HV0.01. The milling temperature did not significantly influence the amount of amorphous fraction (33-36 wt.%), however, the composition of amorphous content was more influenced by temperature. The interval of crystallite size was between 1.2 and 11.7 nm after 180 min of milling. The amount and the cell parameters of the Sncontaining phases were different for the two milling experiments because the diffusion coefficients of the Sn atom differed to a large extent.
In this paper we report on a novel, large area method to produce SiC nano- and micro patterns at room temperature where the compound and pattern formation happens in one step. We have previously ...demonstrated that SiC can be produced by noble gas irradiation of a Si/C multilayer system utilizing the ion beam mixing (IBM) taking place at the interfaces. Here we show that by applying IBM in samples masked in any desired way patterned SiC surfaces, micro and nanostructures, result. Two different masking layers were applied to demonstrate the capabilities of the method; a Langmuir-Blodgett (LB) film of 590 nm silica nanoparticles and a lithographic grid, of 2 μm periodicity, mounted to the surface of a Si/C multilayer system. The systems were irradiated by Xe+ ions of 120 keV. The samples before and after IBM have been analyzed by AFM, SEM and AES depth profiling, proving that patterning occurred: the non-covered areas became SiC rich regions, while the covered areas remained untouched. As a possible application for the patterned samples, the gold-coated LB patterned nanostructure was used for surface enhanced Raman spectroscopic detection of an organic dye molecule (R6G) demonstrating the efficiency of IBM for producing SERS substrates consisting of a very stable compound like SiC.
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•A novel method was demonstrated for the production of SiC micro and nanopatterns.•Patterning and SiC compound formation happened in one step at room temperature.•The SiC formation was proved by AES depth profiling.•Two different structures were presented.•The method can be considered as a possibility to fabricate SERS substrates.
Recent implementations of QSAR modelling software provide the user with numerous models and a wealth of information. In this work, we provide some guidance on how one should interpret the results of ...QSAR modelling, compare and assess the resulting models, and select the best and most consistent ones. Two QSAR datasets are applied as case studies for the comparison of model performance parameters and model selection methods. We demonstrate the capabilities of sum of ranking differences (SRD) in model selection and ranking, and identify the best performance indicators and models. While the exchange of the original training and (external) test sets does not affect the ranking of performance parameters, it provides improved models in certain cases (despite the lower number of molecules in the training set). Performance parameters for external validation are substantially separated from the other merits in SRD analyses, highlighting their value in data fusion.
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•WC coating layers with excellent corrosion resistance were produced by IBM.•The corrosion resistance depends on the effective areal density of WC.•The effective areal density shows ...sharp changes as a function of irradiation fluence.•The effective areal density can be predicted by TRIDYN simulations.
Tungsten carbide (WC) belongs to the class of protective coatings due to its good mechanical properties and corrosion resistance. Herein WC-rich coating layers have been produced by irradiating C/W multilayers with noble gases at room temperature. The in-depth concentration distributions after ion irradiation have been measured by Auger electron spectroscopy depth profiling. The corrosion resistance of the formed layers has been tested in 3.5 wt% NaCl solution. It has been shown that the growth of the WC-rich layer started at the interfaces and with increasing fluence the separately growing layers coalesced. With the coalescence of the layers the corrosion resistance of the system suddenly increased. To describe this phenomenon the term effective areal density has been introduced. If the effective areal densities of WC were lower and higher than 550 (1/nm2) and 1200 (1/nm2), the corrosion current densities were 0.5 and 0.08 (µA/cm2), resp. The in-depth distribution of the WC-rich layer and thus the corrosion resistance could be tailored by varying the projectiles, fluences, energies and initial layer structure. The maximum corrosion resistance found was better than that of stainless steel and WC cermet. The effective areal densities could be predicted by TRIDYN simulations allowing the design of corrosion resistive coatings.
A concise account of the physicochemical properties of morphine and its derivatives of therapeutic interest is provided. Such properties include macroscopic and microscopic acid/base parameters, ...lipophilicity, solubility, permeability that all influence the fate of drugs in the body. The dependence of these parameters on pH is discussed and subsequent implications in drug administration and formulation are presented.
Prediction performance often depends on the cross- and test validation protocols applied. Several combinations of different cross-validation variants and model-building techniques were used to reveal ...their complexity. Two case studies (acute toxicity data) were examined, applying five-fold cross-validation (with random, contiguous and Venetian blind forms) and leave-one-out cross-validation (CV). External test sets showed the effects and differences between the validation protocols. The models were generated with multiple linear regression (MLR), principal component regression (PCR), partial least squares (PLS) regression, artificial neural networks (ANN) and support vector machines (SVM). The comparisons were made by the sum of ranking differences (SRD) and factorial analysis of variance (ANOVA). The largest bias and variance could be assigned to the MLR method and contiguous block cross-validation. SRD can provide a unique and unambiguous ranking of methods and CV variants. Venetian blind cross-validation is a promising tool. The generated models were also compared based on their basic performance parameters (r
2
and Q
2
). MLR produced the largest gap, while PCR gave the smallest. Although PCR is the best validated and balanced technique, SVM always outperformed the other methods, when experimental values were the benchmark. Variable selection was advantageous, and the modelling had a larger influence than CV variants.
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