Clay mineralogy, chemistry, and diagenesis of late devonian K-bentonite occurrences in northwestern Turkey

Thin beds of tephra (K-bentonites) formed by the diagenesis of volcanic ash are exposed within the limestone-dolomitic limestone successions of the Yilanli formation at Zonguldak and Bartin in northwestern Turkey. They were deposited on the Middle Devonian-Lower Carboniferous shallow carbonate platform of the Zonguldak terrane. In this study, K-bentonite samples collected from Gavurpinari and Yilanli Burnu limestone quarries are investigated in order to reveal their mineralogical and geochemical characteristics and diagenetic evolution. Illite is the major clay mineral in the studied K-bentonites. Additionally, kaolinite and mixed-layer illite-smectite are identified in some samples. The nonclay minerals calcite, dolomite, quartz, gypsum, feldspar, pyrite, and zircon are also found. Crystal-chemical characteristics (Kiibler index, d060 values, and polytypes of illites) from two different sampling locations do not show significant variations. Kiibler index values for the Yilanli Burnu and Gavurpinari sampling locations, 0.47-0.93 (average: 0.71 A°29) and 0.69-0.77 (average: 0.72 A°29), respectively, indicate that illites were affected by high-grade diagenetic conditions. The swelling (or smectite) component (~5%), crystallite size (N = 10-20 nm), and polytype (2M1 > 1Md) data of illites support the same conditions. Illite d060 values of 1.491-1.503 A correspond to a range of octahedral Mg+Fe values of 0.27-0.51 atoms per formula, indicating a composition between end-member muscovite and phengite unit. Trace and rare earth element-based chemical classification of the K-bentonite samples revealed that composition of original volcanic ash is basaltic. Illitization took place by fixation of K from volcanic minerals and ash, and diffusion of elements (Mg+Fe) into and out of the beds during diagenesis. Mineralogical-chemical data point out that these K-bentonites evolved in high-grade diagenetic conditions (approximately 100-150 °C) from the products of volcanic eruptions of disputed sources and distances during the Late Devonian time. © 2015 TÜBİTAK

Predicting the tensile strength, impact toughness, and hardness of friction stir-welded AA6061-T6 using response surface methodology

In this research, an attempt has been made to develop mathematical models for predicting mechanical properties including ultimate tensile strength, impact toughness, and hardness of the friction stir-welded AA6061-T6 joints at 95 % confidence level. Response surface methodology with central composite design having four parameters and five levels has been used. The four parameters considered were tool pin profile, rotational speed, welding speed, and tool tilt angle. Three confirmation tests were performed to validate the empirical relations. In addition, the influence of the process parameters on ultimate tensile strength, impact toughness, and hardness were investigated. The results indicated that tool pin profile is the most significant parameter in terms of mechanical properties; tool with simple cylindrical pin profile produced weld with high ultimate tensile strength, impact toughness, and hardness. In addition to tool pin profile, rotational speed was more significant compared to welding speed for ultimate tensile strength and impact toughness, whereas welding speed showed dominancy over rotational speed in case of hardness. Optimum conditions of process parameters have been found at which tensile strength of 92 %, impact toughness of 87 %, and hardness of 95 % was achieved in comparison to the base metal. This research will contribute to expand the scientific foundation of friction stir welding of aluminum alloys with emphasis on AA6061-T6. The results will aid the practitioners to develop a clear understanding of the influence of process parameters on mechanical properties and will allow the selection of best combinations of parameters to achieve desired mechanical properties

Invited review: Adaptive numerical modelling and hybrid physically based ANM approaches in materials engineering - a survey

Many adaptive numerical modelling (ANM) techniques such as artificial neural networks, (including multi-layer perceptrons) support vector machines and Gaussian processes have now been applied to a wide range of regression and classification problems in materials science. Materials science offers a wide range of industrial applications and hence problem complexity levels from well physically characterised systems (e.g. high value, low volume products) to high volume low cost applications with intrinsic scatter due to commercial manufacturing processes. We review a number of recent examples in the literature, with the aim of identifying best practice in the use of these techniques as part of a multi-strand modelling approach. The importance of understanding the basic principles of these modelling techniques and how they can link with other modelling strategies is emphasised. In particular we wish to identify the importance of hybrid physically based-ANM in taking the field forward, which can range from, at the most basic level, careful data selection and data pre-processing to a full integration of physically based models with advanced ANM. A number of case studies are presented to illustrate the main points of the paper

Discovery of an earliest Triassic, post-extinction foraminiferal assemblage above the Permian-Triassic boundary, Strandzha nappes, north-west Turkey

A new foraminiferal fauna from Early Triassic (Induan) strata of the Çaglayik section on the “Strandzha Massif”, north-west Turkey, comprises five species precisely determined and five species in open nomenclature belonging to ten genera. They belong to the post-extinction foraminiferal assemblage of the Permian-Triassic crisis, characterized by the presence of both disaster taxa (Earlandia and Postcladella kalhori) and Lazarus taxa (Diplosphaerina inaequalis, Rectostipulina quadrata, Arenovidalina sp. and Glomospira sp.). The present study at Tütünlüktepe Formation identified for the first time the Permian foraminifers on the Strandzha Massif as relict members of a post-extinction foraminiferal assemblage

Plant growth regulator effects on in vitro propagation and stevioside production in Stevia rebaudiana bertoni

Stevia rebaudiana is of great importance due to its steviol glycosides (SGs) which are natural sweeteners used by the food industry as well as having medicinal purposes. In the present study, the effect of plant growth regulators (PGRs) and explant types on in vitro propagation and shoot growth of S. rebaudiana were studied, the effect of PGRs on SGs production was determined. For this purpose, nodal explants and shoot tip explants were cultured on woody plant medium (WPM) supplemented with cytokinins [6-benzyladenine (BA), kinetin (Kn), or thidiazuron (TDZ)] or cytokinins + auxins combinations [BA + indoleacetic acid (IAA); BA + naphthaleneacetic acid (NAA); Kn + IAA; Kn + NAA]. Although, the best shoot proliferationwas obtained onWPMsupplementedwith BA+ NAA combinations, shoots grown on PGR-containing media produced callus at the base of the shoots and showed chlorosis and necrosis. Additionally, shoots showed at all concentrations of TDZ, and at higher concentrations of BA, morphological changes such as malformed leaves and poor shoot growth. In contrast to PGR-containing media, on the PGR-free control medium, the development of shoots and roots occurred simultaneously and healthy and well-developed plantlets were obtained. Thus, we developed an economical viable means of in vitro propagation byminimizing themicropropagation steps and removing the requirement of PGRs. According to the high-performance liquid chromatography (HPLC) results, PGR-free control medium (WPM) led to considerably higher stevioside content in the leaves compared with the PGR(s)-containing media and the highest stevioside [34 mg·g-1 dry weight (DW)] and rebaudioside A content was only detected on the control medium without PGRs. Steviolbioside, rubusoside, and dulcoside A were detected qualitatively in the leaves of shoots grown on WPM supplemented with 2.27 µM TDZ, 4.54 µM TDZ, 2.22 µM BA + 2.69 µM NAA, 2.22 µM BA + 5.37 µM NAA, 2.32 µM Kn + 5.71 µM IAA, or 2.32 µM Kn + 2.69 µM NAA. © 2016, American Society for Horticultural Science. All rights reserved

Development and directed energy deposition of high strength Hf5Mo15Nb35Ta25Ti20 refractory high entropy alloys

In this study, a novel HfMoNbTaTi refractory high entropy alloy was designed by empirical calculations and CALculation of PHAse Diagram (CALPHAD) method by using ThermoCalc software. Directed energy deposition (DED) based additive manufacturing process was used to produce the alloy. After the process parameter determination studies using single-track productions, cuboids were produced. The microstructural investigations showed that while the central region of cuboids has large grains, the outer region has a dendritic structure with some unmolten Mo powders. Although columnar grain formation, which is the general characteristic of directional solidification, was observed at some points, irregularly shaped grains were dominant in the structure. Moreover, there were micron to nano-sized Hf-Ti-O particles inside the grains and especially around the grain boundaries. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses confirmed the formation of disordered body-centered cubic (BCC) Hf5Mo15Nb35Ta25Ti20 alloy with ∼6 vol% of Hf-Ti-O particles. Electron backscatter diffraction (EBSD) analyses indicated that there is a slight texture in the building direction along 〈111〉. In order to determine the stability of these alloys, ex-situ heat treatments coupled with XRD studies were conducted. As opposed to CALPHAD calculations it was not observed any HCP phase formation. Compression test results showed that Hf5Mo15Nb35Ta25Ti20 alloys have high strength (σy = ∼1300 MPa) and high compressive ductility with good strain-hardening ability. Theoretical calculations revealed that the strength of the alloy mainly originated from solid solution strengthening