Analysis of porosity and pore connectivity of soil microaggregates by intrusion of the molten alloy Wood´s metal

<p>The limited exchange of dissolved matter with the interior of soil microaggregates (SMA) due to narrow pores of high tortuosity result in spatial biogeochemical gradients from outer towards inner SMA surfaces. The goal of our study was to analyze pore space characteristics in SMA by visualization and quantification of connected “open” versus closed pore structures in each of the pore size classes <10, 10-100 and >100 µm². SMA ranging in size between 20 and 250 µm were isolated along a soil clay content gradient (19-35%) and investigated by using a porosimetry technique with a molten alloy, called Wood´s metal, which solidifies below 78°C. The alloy was pressed into connective pores of SMAs by applying an Ar pressure of 55 MPa, allowing an intrusion of pores with a diameter below ~20 nm. After alloy solidification, polished sections of intruded SMA were analyzed by confocal laser scanning microscopy (Keyence, VK-9700) and the ImageJ software was used to quantify open and closed pores by segmenting grayscale histograms. The SMA typically consisted of two different sections, where particle arrangements are loose or dense. Coarse-sized aggregate-forming materials were observed in sections with loose particle arrangements, where pores appear well connected. Part of the coarse SMAs >100 µm show large circular structures with dense particle arrangements in the edge region. These dense arrangements contain high shares of layer silicates and reveal closed pore structures. The total SMA porosity was up to 40 area-%. The share of closed pores <20 nm in diameter ranged typically from 20 to 40 % of total porosity. Pore systems >100 µm² had the highest share within the open pores, while pore system <10 µm² showed the largest share of closed pores. The proportion of closed pores to total porosity decreased for SMA sizes < 50 µm. Our results show that, in addition to an extended connective pore system, SMA also exhibit sections with high contents of clay minerals, where the pore size distribution is narrow (<20 nm) and tortuosity high. Here, element transport and habitation by microorganisms might be impaired, resulting in larger conservation potential for organic matter.</p>

Influence of Manufacturing Conditions on Inclusion Characteristics and Mechanical Properties of FeCrNiMnCo Alloy

Three CoCrFeMnNi high-entropy alloys (HEAs) were produced by vacuum induction melting, induction melting under inert gas atmosphere, and melting under inert gas atmosphere followed by air exposure, respectively. The different manufacturing conditions for the three investigated alloys resulted in different levels and types of inclusions. The alloys melted under vacuum or inert gas contained Al2O3 inclusions formed by impurity Al, due to its high oxidation tendency. The molten alloy exposed in air showed an excessive oxidation. During oxidation of the molten alloy in air, impurity Al was initially oxidized, and fine MnCr2O4 inclusions were formed rather than pure Al2O3 inclusions. This difference was analyzed based on thermodynamic calculations. Specifically, the influence of impurity content on the inclusion characteristics was investigated for the three HEAs. Moreover, the inclusion characteristics were found to have an influence on mechanical properties of the alloys also. In air-exposed HEA, smaller inclusions were formed, resulting in a higher dislocation density at the matrix/inclusion interface and thus strengthening of the HEA. Thus, it is proposed that atmospheric conditions could be an important factor to control the inclusion characteristics and to form fine inclusion particles, which could improve the mechanical properties of HEAs.

The effect of testing procedure on DSC measurements of Gd-Ti-Zr alloy using ZrO2 container

Differential Scanning Calorimetry (DSC) was applied to determine the critical temperatures of phase transformations in the Gd40Ti30Zr30 alloy (wt%). The comparative measurements were carried out using three types of measuring devices at a temperature RT- 1650?C in the same flowing gas (Ar, 99.9992%) but applying different testing procedures, which allowed obtaining dissimilar oxygen contents in the surrounding atmosphere. The high temperature interaction and reactivity taking place between molten alloy samples and ZrO2 container during DSC tests were evaluated by structural analysis of the resulting interfaces using alloy samples solidified inside the ZrO2 containers. The conducted research has demonstrated methodological difficulties accompanying measurements of the thermophysical properties of Gd-rich alloys by the container-assisted DSC method, particularly when the tests are performed in flowing argon atmosphere with significantly reduced oxygen content. Under non-oxidizing conditions, the degradation of ZrO2 container can take place during DSC testing because the selected Gd40Ti30Zr30 alloy reacts with the ZrO2 to form a continuous interfacial reaction product layer. Under slightly oxidizing conditions, the gadolinium oxide formed in situ on the alloy surface, plays the role of a barrier for direct contact between molten alloy and container and thus may suppress or even prevent the degradation of the container and its subsequent strong bonding with the holder.

Effect of CeO2 addition in the slag on inclusions of FGH96 superalloy during electroslag remelting

The FGH96 superalloy was electroslag remelted by utilizing CeO2 containing slag. CeO2/Al2O3 ratio and atmosphere are found to be the main factors that control the oxide inclusion contents during electroslag remelting (ESR). The reaction between CeO2 in the molten slag and Al in the molten alloy leads to the increased dissolved Ce in the molten alloy, which is effective to remove oxide inclusions. Dissolved Ce reacts with MgO in the inclusions, leading to the transformation of Al2O3–MgO inclusion in the electrode to Al2O3–MgO–Ce2O3 and Al2O3–Ce2O3 inclusions in the ESR ingot. In case of low CeO2/Al2O3 ratio of 0.263, oxygen content decreases to as low as 8 ppm after ESR under vacuum, and the number density of oxide inclusion decreased by an order of magnitude in comparison to the electrode. In case of high CeO2/Al2O3 ratio of 5.0, oxygen content decreases further to 6 ppm no matter what the condition is.

Monolithic integration of InP on Si by molten alloy driven selective area epitaxial growth

We report a new approach for monolithic integration of III–V materials into silicon, based on selective area growth and driven by a molten alloy in metal–organic vapor phase epitaxy.