Synthesis and sintering of Cu-Al2O3 nanocomposite powders produced by a thermochemical route

By hydrometallurgy and powder metallurgy along with prognosis of physical-chemical properties, a synthesis of new improved materials can be successfully performed with in advance pre-set properties which is conditioned by a quality of starting powders i.e. by improving their structure. In accordance with that, this paper presents synthesis of the nanocomposite Cu-Al2O3 powder by thermochemical method and sintering with a comparative analysis of the mechanical and electrical properties of obtained solid samples. Nanocrystaline Cu-Al2O3 powders were produced by thermochemical method through following stages: spray-drying, oxidation of precursor powder, reduction by hydrogen and homogenisation. Characterization of powders included differential-thermal and thermo-gravimetric analysis (DTA-TGA), X-ray-diffraction (XRD) and analytical electron microscopy (AEM) coupled with energetic dispersive spectroscopy (EDS). Size of produced powders was 20-50nm with noticeable presence of agglomerates. Composite powders are characterized with A12O3 homogenous distribution in copper matrix. Powders were cold pressed with pressure of 500 MPa and sintered. Sintering of the obtained samples was performed in the hydrogen atmosphere in isothermal conditions at temperature range from 800 to 900°C and time up to 120 minutes. Characterization of Cu-Al2O3 sintered system included examination of density, relative volume change, electrical and mechanical properties, examination of microstructure by SEM analysis, as well as by EDS. The obtained nanocomposite, which structure is with certain changes preserved in final structure, has provided sintered material with homogenous distribution of dispersive in copper matrix, with exceptional effects of reinforcing and excellent combination of mechanical and electrical properties

Algal assemblages in springs of different lithologies (ophiolites vs. limestone) of the Konjuh Mountain (Bosnia and Herzegovina)

The biodiversity of algal communities and environmental conditions were investigated in the springs of Mt. Konjuh. The assemblages of 20 springs emerging from different lithologies (limestones and ophiolites, respectively) comprised 234 algal taxa. Diatoms and cyanobacteria were the most species-rich groups. The most common alkaliphilic, circumneutral, and eutraphentic diatoms were represented by the genera Gomphonema, Nitzschia, Navicula, Cymbella, and Achnanthidium, and by the cyanobacterial genus Phormidium. Hierarchical clustering and SIMPROF analysis based on relative algal abundance clustered springs into six groups, separating them mainly according to spring type and lithology. Indicator species for groups and springs on different lithological substrata were singled out, revealing 33 taxa with preferences for ophiolites, and 20 taxa with preferences for carbonates. The values of the Shannon-Wiener diversity index were moderately high per spring location, and similar for the two groups of springs on different lithologies. A higher similarity in species composition was noted between springs on ophiolites and limestones than between springs on ophiolites and other types of siliceous substrata. The present study suggests that algal assemblages in springs emerging from ophiolites, even those made up by a preponderance of silicates, should be analyzed separately from those related to springs on other siliceous substrata. The results obtained showed that most of the springs studied are affected by anthropogenic impacts and morphological alterations leading to the dominance of highly competitive meso- and eutraphentic algal species, thus emphasizing the importance of further investigation and conservation of these habitats

Photographs of Cu-As-Sn binary and ternary metal pellets as supporting material for the article: "Experimental design of the Cu-As-Sn ternary colour diagram"

The dataset supports the article: Radivojević, M., Pendić, J., Srejić, A., Korać, M., Davey, C., Benzonelli, A., Martinón-Torres, M., Jovanović, N., and Kamberović, Ž. (2017). Experimental design of the Cu-As-Sn ternary colour diagram. Journal of Archaeological Science, https://doi.org/10.1016/j.jas.2017.12.001. Abstract: The aesthetic appearance of metals has long been recognised in archaeometric studies as an important factor driving inventions and innovations in the evolution of metal production. Nevertheless, while the studies of ancient gold metallurgy are well supported by the modern research in colour characteristics of gold alloys, the colour properties of major prehistoric copper alloys, like arsenical copper and tin bronzes, remain either largely understudied or not easily accessible to the western scholarship. A few published studies have already indicated that alloying and heat treatment change the colours of copper alloys, although they are mainly based on the examples of prehistoric tin bronze objects and experimental casts. Here we present the procedure for building the Cu-As-Sn ternary colour diagram, starting with experimental casting of 64 binary and ternary alloys in this system. We used two types of information to produce two different ternary colour diagrams: one, based on photographs of the samples, and the other, established on the colorimetric measurements. Furthermore, we developed the procedure for creating a graphic representation of colours in the Cu-As-Sn ternary diagram using QGIS. As an initial case study, we plotted the composition of the world’s earliest tin bronze artefacts; the graphic representation further supports claims about the importance of golden hue for their invention and demand, c. 6,500 years ago. We argue that the presented colour diagrams will find wide use in future investigations of aesthetics of prehistoric copper alloys.AH/J001406/1 D.M.McDonald Awar

Clinico-microbiological profile of urinary tract infection in south India

The knowledge of etiology and antibiotic resistance pattern of the organisms causing urinary tract infection is essential. This study was taken up to determine the presentation and risk factors associated with community-acquired urinary tract infection (CA-UTI). The distribution of bacterial strains isolated from these patients and their resistance pattern were also studied. This multidisciplinary prospective observational study was conducted in M. S. Ramaiah Hospital, Bangalore, between January and December, 2008. Patients who had CA-UTI confirmed by positive urine culture reports were included in the study. Statistical analysis was done using the SPSS version 16. Symptomatology and others risk factors for CA-UTI were studied in these patients and the causative organisms and their resistance patterns were recorded. Of the total 510 patients included, 57% belonged to the elderly age group (50–79 years). Fever and dysuria were the most common clinical presentation, but were not specific in predicting CA-UTI. Escherichia coli (66.9%) was the most common organism causing CA-UTIs with extended spectrum beta lactamase (ESBL) resistance seen in nearly two-thirds of these cases (42.2%). The organisms recorded least resistance against carbapenems (3.9%). A high resistance rate was seen for fluoroquinolones (74.1%). In conclusion, a high rate of ESBL-positive organisms and their resistance to commonly used antibiotics brings a concern for future options in treating these conditions

Characterization of PCBs from computers and mobile phones, and the proposal of newly developed materials for substitution of gold, lead and arsenic

In this paper, we have analyzed parts of printed circuit board (PCB) and liquid crystal display (LCD) screens of mobile phones and computers, quantitative and qualitative chemical compositions of individual components, and complete PCBs were determined. Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) methods were used to determine the temperatures of phase transformations, whereas qualitative and quantitative compositions of the samples were determined by X-ray fluorescence spectrometry (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES), and scanning electron microscopy (SEM)-energy dispersive X-ray spectrometry (EDS) analyses. The microstructure of samples was studied by optical microscopy. Based on results of the analysis, a procedure for recycling PCBs is proposed. The emphasis was on the effects that can be achieved in the recycling process by extraction of some parts before the melting process. In addition, newly developed materials can be an adequate substitute for some of the dangerous and harmful materials, such as lead and arsenic are proposed, which is in accordance with the European Union (EU) Restriction of the use of certain hazardous substances (RoHS) directive as well as some alternative materials for use in the electronics industry instead of gold and gold alloys

A European map of groundwater pH and calcium

Water resources and associated ecosystems are becoming highly endangered due to ongoing global environmental changes. Spatial ecological modelling is a promising toolbox for understanding the past, present and future distribution and diversity patterns in groundwater-dependent ecosystems, such as fens, springs, streams, reed beds or wet grasslands. Still, the lack of detailed water chemistry maps prevents the use of reasonable models to be applied on continental and global scales. Being major determinants of biological composition and diversity of groundwater-dependent ecosystems, groundwater pH and calcium are of utmost importance. Here we developed an up-to-date European map of groundwater pH and Ca, based on 7577 measurements of near-surface groundwater pH and calcium distributed across Europe. In comparison to the existing European groundwater maps, we included several times more sites, especially in the regions rich in spring and fen habitats, and filled the apparent gaps in eastern and southeastern Europe. We used random forest models and regression kriging to create continuous maps of water pH and calcium at the continental scale, which is freely available also as a raster map (Hájek et al., 2020b;). Lithology had a higher importance than climate for both pH and calcium. The previously recognised latitudinal and altitudinal gradients were rediscovered with much refined regional patterns, as associated with bedrock variation. For ecological models of distribution and diversity of many terrestrial ecosystems, our new map based on field groundwater measurements is more suitable than maps of soil pH, which mirror not only bedrock chemistry but also vegetation-dependent soil processes

Correlation of microstructure with the wear resistance and fracture toughness of white cast iron alloys

The objective of this investigation was to set down (on the basis of the results obtained by the examination of white cast iron alloys with different contents of alloying elements) a correlation between chemical composition and microstructure, on one hand, and the properties relevant for this group of materials, i.e., wear resistance and fracture toughness, on the other. Experimental results indicate that the volume fraction of the eutectic carbide phase (M3C or M7C3) have an important influence on the wear resistance of white iron alloys under low-stress abrasion conditions. Besides, the martensitic or martensite-austenitic matrix microstructure more adequately reinforced the eutectic carbides, minimizing cracking and removal during wear, than did the austenitic matrix. The secondary carbides which precipitate in the matrix regions of high chromium iron also influence the abrasion behaviour. The results of fracture toughness tests show that the dynamic fracture toughness in white irons is determined mainly by the properties of the matrix. The high chromium iron containing 1.19 wt% V in the as-cast condition, showed the greater fracture toughness when compared to other experimental alloys. The higher toughness was attributed to strengthening during fracture, since very fine secondary carbide particles were present mainly in an austenitic matrix