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The aim of this work was to study the influence of quenching and partitioning temperatures combined with various levels of Mn and Ni contents on the austenite stabilization along the quenching and partitioning (Q&P) cycle. Three steels with 2 wt.%, 4 wt.% and 6 wt.% manganese and one steel with 2 wt.% nickel content were investigated. Phase transformation temperatures and critical cooling rates were obtained experimentally using dilatometer for each alloy. Q&P cycles with different quenching and partitioning temperatures were also done in dilatometer, thus, allowing monitoring of the expansion/contraction during the whole Q&P cycle. Microstructure characterization was performed by means of a Scanning Electron Microscope and X-Ray Diffraction to measure retained austenite content. It was found that, strongly depending on the Q&P conditions, austenite stabilization or decomposition occurs during partitioning and final cooling. In case of high partitioning temperature cycles, austenite reverse transformation was observed. Certain cycles resulted in a very effective austenite stabilization and interesting microstructure. This research has been carried out in the framework of the HIGHQP project, which has received funding from the Research Fund for Coal and Steel under grant agreement No 709855.

Difficulties found when manufacturing and forging two low density steels in different scales are described in this work. Austenitic and duplex low-density steels have attracted a lot of interest due to their good combination of mechanical properties and density reduction. In this work, the fabrication of 1.3 C30Mn10Al austenitic low-density steel and 0.65 C12Mn10Al duplex low-density steel have been studied. The scaling up of the manufacturing process from 1 Kg to 35 Kg ingots of both materials and the subsequent hot forging of the ingots is described, showing the difficulties encountered during the production and transformation of these steels. Only the small ingots were successfully forged, but not the larger ones, showing the important differences in the forging properties depending on the geometry and dimensions of the final part to be forged, and the homogenization temperatures. The possible causes of this scale dependence are proposed from the experimental results obtained, as well as from the hot axial compression tests and the thermodynamic simulations carried out. This work was supported by the Basque Government under ELKARTEK Research Program[KK-2016/00029-ABADE] and [KK-2018/00016- COFADEN].

In recent decades, highly alloyed low-density steels are being developed to reduce the weight of different automotive parts. Dilatometry can be a very useful experimental technique to understand phase transformations during heating or cooling of new low-density steel alloys. When performing dilatometry measurements some assumptions are made such as the homogeneity of the sample material tested during the experiment. In this study, dilatometry tests were performed for two different low-density steels, and the variations of the composition between the surface and the inner part of the sample were analyzed. The migration of manganese by diffusion from the interior of the samples and finally its evaporation on the surface under vacuum were observed. This compositional gradient generated in the samples may influence the veracity and interpretation of the results obtained in dilatometry when working with high manganese steel alloys. The detachment of surface grains created by this compositional change near the surface of the samples is also investigated. This research was funded by the Basque Government under its ELKARTEK Research Program, KK-2016/00029-ABADE project and KK-2018/00016-COFADEN project

In the last decades, low-density steels for forging have increasing interest in the automotive industry, and good mechanical properties are required for their real application. This paper describes the results obtained for a 0.66C11.4Mn9.9Al duplex austenitic low-density steel after applying a set of isothermal treatments at different combinations of time and temperature, aimed to promote kappa carbide precipitation, and improve the mechanical properties obtained with a water quenching treatment. The effects of the different isothermal treatments on the microstructure and on the mechanical properties have been analyzed and compared to those obtained from a quenching heat treatment. We found that isothermal treatments in the range temperature between 550–750 °C promoted the profuse precipitation of coarse kappa carbides at grain boundaries, which dramatically reduced the ductility of the alloy, whereas a traditional quenching treatment resulted in a better combination of ductility and mechanical strength. This research has been carried out with a financial grant of the Basque Government under its ELKARTEK Research Program, KK-2016/00029-ABADE project and KK-2018/00016-COFADEN project.

In this work, four low carbon steels with different contents of Mn and Ni were heat treated by quenching and partitioning (Q&P) cycles where high partitioning temperatures, in the range of 550 °C-650 °C, were applied. In order to elucidate the effect of applying these high partitioning temperatures with respect to more common Q&P cycles, the materials were also heat treated considering a partitioning temperature of 400 °C. The microstructure evolution during the Q&P cycles was studied by means of dilatometry tests. The microstructural characterization of the treated materials revealed that austenite retention strongly depended on the alloy content and partitioning conditions. It was shown that the occurrence of austenite reverse transformation (ART) in the partitioning stage in some of the alloys and conditions was a very effective mechanism to increase the austenite content in the final microstructure. However, the enhancement of tensile properties achieved by the application of high partitioning temperature cycles was not significant. This research was carried out in the framework of the HIGHQP project, which has received funding from the Research Fund for Coal and Steel under grant agreement no. 709855. This study reflects only the author’s views and the European Commission is not responsible for any use that may be made of the information contained therein.

In the last years numerous works have been done to try to reduce car weight in order to decrease CO2 emissions. In this line, Low Density Steels can be considered as one alternative in the lightweight approximation strategy [1-2] for the automotive industry. Generally, in low density steels, a considerable amount of Aluminum is added in order to reduce the overall steel density, but high Aluminum contents lead to processing drawback, that make it difficult to bring these new/lighter steel grades into the market. In the literature, different low density steel grades can be found but most of them are aimed at structural parts of the car, whereas almost none of them is aimed at forged components. In this research, different compositions of the three families of low density steels (ferritic, duplex and austenitic) were fabricated at low scale in order to try to understand the phenomena taking place in these steels, and try to find the best candidate for getting a low density steel suitable for forging in the upcoming research.

This paper develops a new low-cost construction material made of pH-adjusted fluorogypsum, class C fly ash, and type II Portland cement. The proposed fluorogypsum-based blend is durable in water and has a lower weight and lower cost than ordinary concrete. A preliminary investigation of strength and durability properties of this new construction material is also presented. A series of compressive strength tests and volumetric expansion measurements were conducted on specimens after 28 days of curing. The experimental results were used to develop response surface models. These models can be used to predict accurately compressive strength and volumetric expansion as functions of the relative content, in dry weight, of different components. The response surface models were employed to determine ranges of dry components of the system with sufficient strength and limited volumetric expansion. A composition with 62% pH-adjusted fluorogypsum, 35% fly ash, and 3% Portland cement was selected based on strength and volumetric expansion properties to conduct additional experimental studies to quantify its modulus of elasticity, Poisson’s ratio, setting times, density, void contents, and curing time effects on strength and volumetric expansion. The investigation results suggest that the proposed fluorogypsum-based blend is a promising low-cost concrete-like material for use in outdoor and underwater construction applications.

This study investigates the mechanical and durability properties of blends made of fluorogypsum (FG) with the pH adjusted by using controlled amounts of circulating fluidized bed combustion ash (CFBCA) and denoted as C-FG, class C fly ash (FA), and type II Portland cement (PC). A series of pH tests was conducted on samples of C-FG to develop an analytical relationship between acidity and CFBCA content, which can be used to determine the optimal amount of CFBCA needed to obtain a specified pH value. Two compositions of C-FG-based blends were investigated in detail to identify the effects of CFBCA content on compressive strength, modulus of elasticity, Poisson’s ratio, relative volumetric expansion, unit weight, and setting times. The obtained properties were compared with those of FG-based blends having the same composition and made using FG with the pH adjusted by using uncontrolled amounts of CFBCA (U-FG). Results suggest that the amount of CFBCA can have significant effects on the properties of C-FG-based blends, depending on the composition. In addition, C-FG-based blends generally achieve a higher compressive strength and initial stiffness than the corresponding U-FG-based blends.

The sulfate release from solidified/stabilized fluorogypsum was measured to develop the effective diffusion coefficients (De) as a parameter to assess the dissolution potential in aquatic a...

Tin(IV) sulfide (SnS2), as a mid-band-gap semiconductor shows good potential as an excellent photocatalyst due to its low cost, wide light spectrum response and environment-friendly nature. However, to meet the demands of large-scale water treatment, a SnS2 photocatalyst with a red-shifted band gap, increased surface area and accelerated molecule and ion diffusion is required. Doping is a facile method to manipulate the optical and chemical properties of semiconductor materials simultaneously. In this work, SnS2 photocatalysts with varied Ag doping content are synthesized through a facile one-step hydrothermal method. The product is characterized by XRD, SEM, TEM and UV-Vis spectrometry. The photocatalytic activity of the as-prepared Sn1−xAgxS2 is studied by the degradation of methylene blue (MB) dye under solar light irradiation. It is found that increasing the Ag dopant concentration can effectively increase the solar light adsorption efficiency of the photocatalyst and accelerate heterogeneous photocatalysis. The optimal concentration of Ag dopant is found to be 5% with the highest rate constant being 1.8251 hour−1. This study demonstrates that an optimal amount of Ag doping can effectively increase the photocatalytic performance of SnS2 and will promote the commercialization of such photocatalysts in the photocatalytic degradation of organic compounds.

Graphical abstractDisplay Omitted A simple fluorescent sensor was developed using light emitting diodes (LEDs), a photodetector, and optical filters.Microalgae concentration was successfully measured utilizing fluorescence of chlorophyll a in microalgal cells.Consistent and reliable fluorescent detection was demonstrated even with turbid sample solutions. This work reports the development of a portable and low cost fluorescent sensing system with a disposable microfluidic chip for on-site detection of a microalgal sample and its concentration. The sensor system has multiple light emitting diodes (LEDs) for excitation and a photodetector for measuring a fluorescent signal from a microalgal sample. The concentration of a microalgal sample is determined by measuring the fluorescent signal emitted by chlorophyll a. A dichroic filter and a color filter are also added to allow only the fluorescent signal from chlorophyll a to pass through the photodetector. The microfluidic chip consists of a glass slide and a PDMS channel with a vacuum pump, which collects a small volume of the microalgal sample (

In the present work, we report enhanced photocatalytic degradation of methylene blue dye in aqueous solution by using ultra-thin anatase TiO2 nanosheets (NSs) combined with graphene oxide (GO) as a photocatalyst. The two-dimensional ultra-thin anatase TiO2 NSs are fabricated via chemical exfoliation. By completely delaminating a lepidocrocite-type layered protonic titanate HxTi2� x/4□x/4O4 � H2 O( x ¼0.7, □: vacancy) into individual layers through ion exchange with tetrabutylammonium (TBA þ ) cations, well-dispersed ultrathin colloidal Ti0.91O2 NSs with a lateral size up to a few micrometers are obtained. Subsequent acid treatment induces colloidal Ti0.91O2 to reassemble and precipitate into a gelation form, followed by thermal annealing to convert the Ti0.91O2 gelation into anatase TiO2 nanosheets as photocatalyst for methylene blue degradation. TiO2 NSs show a high photocatalytic degradation efficiency of 53.2% due to the ultra-thin thickness for facile electron transfering and large surface area for methylene blue absorption. Moreover, photocatalytic effect can be further improved by simply adding GO suspension to achieve colloidal self-assembly of GO and TiO2 NSs. An optimal GO content of 3 wt% further increases the photocatalytic degradation efficiency to 91.2% due to faster electron–hole seperation and improved surface area provided by GO. This work provides a simple but effective approach by combing graphene oxide with TiO2 nanosheets synthesized via the exfoliation method for methylene blue degradation.

This paper presents a portable fluorescent sensing system that utilizes different light emitting diode (LED) excitation lights for multiple target detection. In order to identify different analytes, three different wavelengths (385 nm, 448 nm, and 590 nm) of excitation light emitting diodes were used to selectively stimulate the target analytes. A highly sensitive silicon photomultiplier (SiPM) was used to detect corresponding fluorescent signals from each analyte. Based on the unique fluorescent response of each analyte, it is possible to simultaneously differentiate one analyte from the other in a mixture of target analytes. A portable system was designed and fabricated consisting of a display module, battery, data storage card, and sample loading tray into a compact 3D-printed jig. The portable sensor system was demonstrated for quantification and differentiation of microalgae (Chlorella vulgaris) and cyanobacteria (Spirulina) by measuring fluorescent responses of chlorophyll a in microalgae and phycocyanin in cyanobacteria. Obtained results suggest that the developed portable sensor system could be used as a generic fluorescence sensor platform for on-site detection of multiple analytes of interest.

Polyhydroxybutyrates (PHB; a bacterially produced biodegradable plastic) was used as a carbon source for biological denitrification of water. The use of a solid, nonwater soluble bioplastic in the denitrification process reduces the need for monitoring and dosing of the carbon source. Denitrification rates at four different salt concentrations (0, 5, 15 and 30 ppt) using synthetic salt water were determined. The mean denitrification rates varied from 2.4 to 3.2 kg-NO3N/m 3 -day, with the highest rate in water with a salinity of 15 ppt. While differences in denitrification rates were observed, they were not statistically significant. Additionally, denitrification rates were higher at higher nitrate concentrations. The denitrification rates had no significant differences with PHA of different molecular weights. Hydrogen sulfide production was not observed in any of the studies, even 45 days after the depletion of nitrates. The mean bioplastic consumption was 2.92 ± 2.70 mg/mg of NO3-N reduced.