Manufacturing pure metals on Mars is challenging due to limited energy resources and unavoidable contamination of raw materials and production equipment with the Martian dust (regolith) resulting in impure materials. Understanding the effect of contamination on material properties is crucial for establishing materials manufacturing on Mars. This study investigates the influence of regolith contamination on its processability, and properties of the Fe-based material manufactured via laser powder bed fusion (L-PBF) for potential extraterrestrial applications. To simulate a contamination, water-atomized iron powder was mixed with 1 wt% Martian regolith simulant and processed by L-PBF. It was found the regolith is uniformly distributed within the iron matrix transforming from contaminant to reinforcement material. The crack-free interface between iron and regolith systematically studied using STEM reveals segregation of some elements but absence of notable reaction between matrix and particles. The Fe-regolith composite demonstrate moderate strength and large plastic deformability. The results suggest that unavoidable regolith contamination during production on Mars can be rethink as in-situ resource utilization for manufacturing of regolith reinforced iron matrix composites.

Ferrihydrite (Fe10O14(OH)2), an iron oxide/hydroxide, is found in a variety of terrestrial and extraterrestrial environments. This study presents a novel approach that combines bio-mineralization and electrolysis for the efficient mining of low-grade iron resources. Iron-reducing Carboxydothermus ferrireducens bacteria converted an iron oxide/hydroxide Fe(III)-mixture to magnetite. This ferrimagnetic phase was magnetically extracted and subsequently electrolyzed at 363 K in an alkaline medium to produce metallic iron. Integrating a heat treatment step increased the iron yield to 67%. This resulted in a high current efficiency of 63% and an energy consumption of 19.1 MJ/kg, which is competitive with current pyrometallurgical practices. Heat-induced morphological and chemical changes facilitated iron reduction and suppressed parasitic hydrogen evolution.Furthermore, improved reducibility of the biomineralized material was observed. This method could facilitate the exploitation of marginal iron reserves, particularly in areas where no rich ores are available. The process also promises adaptation to extraterrestrial sources such as the Martian regolith.

Inverse opal structures are of interest for various applications, as they exhibit high surface areas in conjunction with unique structure-specific properties such as the possibility to create photonic band gaps, e.g., for photocatalytic applications. An established synthetic pathway to prepare these nanostructures is to infiltrate the voids of a template comprised of close-packed spheres with a metal oxide and to remove the template subsequently by pyrolysis. To this end, polymer spheres are typically used which are produced by a water-based emulsion polymerization process. In this work, we present an improved and extended approach of that kind in case of PMMA spheresfeaturing narrow size distributions and mean diameters that can be varied over a large range between 170 up to 800 nm by properly adjusting the synthesis temperature and the ionic-strength of the water phase. By using reflux conditions, advanced experimental techniques requiring protective gas atmospheres are dispensable and comparatively short synthesis times can be realized. Time-resolved experiments reveal a two-step growth process occurring at temperatures below ∼400 K. It consists of a first phase, during which initial particles are formed, followed by a time-delayed second phase, where their diameter increases by roughly a factor of 2, most likely due to coalescence processes. At higher temperatures, both processes increasingly overlap so that only a single growth phase is observed.

An extension of the Debye–Einstein–anharmonicity (DEA) model has been addressed to describe the lattice thermal expansion up to a temperature‐dependent phase transition. By using an intrinsic anharmonicity (A) term in the DEA model only, it is not possible to describe the continuous changes of the lattice thermal expansion leading to anomalies originating from second‐order phase transitions. Therefore, an extended formalism is empirically developed to model these anomalies of the lattice thermal expansion based on temperature‐dependent X‐ray powder diffraction data. Inspired by Landau's theory of second‐order phase transitions, a gliding function (G) that considers the excess energy above the DEA terms, necessary to drive the phase transition, is introduced. The G‐function has been considered as an additive constituent of the DEA model, leading to the DEA + G model that describes the temperature‐dependent internal energy of the unit cell implemented in the first‐order Mie‐Grüneisen zero pressure equation of state (MG‐EoS). The extended approach allows to describe the soft‐mode‐driven anharmonic internal energy contribution and to determine the critical temperature of both nuclear and magnetic phase transitions.

We report on temperature-dependent structural and spectroscopic properties of two new members of the mullite-type ceramics SnAlBO4 and SnGaBO4. In-situ X-ray powder diffraction (XRPD) demonstrates positive thermal expansion behavior for all orthorhombic lattice parameters between 13 and 840 K. The lattice thermal expansion is modeled by Gr & uuml;neisen first-order approximation, where the vibrational energy is calculated by the Debye-Einstein-anharmonicity (DEA) approach. Although the thermal changes of the metric parameters do not show any discontinuity, the double-Debye model and low-temperature thermal analysis leave hints for subtle displacive changes. Splitting of the tin-doublets of the 119Sn M & ouml;ssbauer spectra at low temperature is assumed to be associated with structural modulation although the temperature-dependent Raman spectra could not support these findings. The modulation could either be dynamic which requires much longer thermal equilibration than the speed of the data collection for XRPD and Raman spectroscopy. Selective Raman mode frequencies are analyzed using a modified Klemens model, which helps to understand the thermal anharmonic behaviors of the SnO4, MO6, and BO3 polyhedra as a function of temperature.

Stereochemically active lone electron pairs (LEPs) draw research attention in designing materials for given crystal-physico-chemical properties. While the 5s2 LEP-containing schafarzikite (FeSb2O4) exhibits interesting properties, we report a new compound (PbBi)MnO4 which is isostructural to schafarzikites, where the stereochemical activity of 6s2-LEP is served by both Pb2+ and Bi3+ cations located in a single crystallographic site. The phase pure sample has been prepared in a sealed quartz tube with a low pressure of about 1 Pa at 923 K. Both Xray and neutron power diffraction data Rietveld refinements confirm (PbBi)MnO4 to be crystallized in the space group P42/mbc. The Wang-Liebau eccentricity parameter that measures the strength of the stereochemical activity of the LEPs of the associated Pb2+ and Bi3+ cations was found to be 3.41(2)& sdot;10- 5. Temperature dependent DC magnetic susceptibility suggests that (PbBi)MnO4 is antiferromagnetic at TN of 43(1) K, and the magnetic structure follows a G-type configuration determined by neutron diffraction at low-temperature. Thermogravimetric analysis demonstrates the thermal stability of the tetragonal phase. The lattice thermal expansion has been modeled for the low-temperature neutron data using a single Debye term, leading to a Debye temperature of 378(20) K. Temperature-dependent changes of some selective Raman frequencies are mainly dominated by the quasiharmonic effects over the isochoric anharmonicity below room temperature.

Plagioclase feldspars draw intensive research attention in planetary sciences because of their abundance in the Martian regolith. Crystal chemical studies on plagioclase feldspars would be of crucial importance for possible in situ resource utilization for future human settlement on Mars. This study focuses on the synthesis of representative plagioclase feldspars followed by simulation of mechanical weathering using ball milling. A series of (Ca1-xNa x )(Al2-xSi2+x)O8 plagioclase feldspars is synthesized perfoming the solid-state method, where the endmembers are the anorthite (CaAl2Si2O8) and albite (NaAlSi3O8). The bulk chemical composition, particularly the Al/Si ratio, of each member is determined from energy-dispersive X-ray spectroscopy, which is supported by X-ray powder diffraction data Rietveld refinements. Selective plagioclase members (x = 0.0, 0.4 and 1.0) are mechanically weathered using high-energy ball milling, leading to significant changes of microstructural features such as average crystallite size and micro-strain. Total scattering data are collected using in-house X-ray facilities and analyzed by pair distribution function refinements. The vibrational modes of the samples are evaluated by Raman spectroscopy, complementing the local structural description.

The susceptibility of either oxidation into Sn(IV) or disproportionation into Sn(IV) and Sn(0) limits the study of metal tin-(II)-borate ceramics. We report mullite-type SnCrBO4 and SnVBO4 synthesized in sealed quartz tubes by conventional solid-state method. X-ray powder diffraction data Rietveld refinements confirm that both compounds are isostructural to PbMBO4 phases for M = Al, Ga, Cr, Mn, and Fe. The end-members show a complete miscibility within the Sn(Cr1-xVx)BO4 solid solution. Both the microstructural (average crystallite size, microstrain, and degree of crystallinity) and crystal structural (metric parameters, bond lengths, polyhedral volume, and polyhedral distortion) parameters are observed with respect to the compositional x-value. The stereochemical activity of the 5 s(2) lone electron pairs of Sn2+ cations has been measured by using the Wang-Liebau eccentricity parameter. The structural features are complemented by Sn-119 M & ouml;ssbauer, Raman, and Fourier-transformed infrared spectroscopy. The Sn-119 M & ouml;ssbauer isomer shifts and the quadrupole splitting values confirm the SnO4 coordination and an Sn(II) valence state. The electronic band gap has been calculated from the UV/Vis diffuse reflectance spectra, which slightly increases with successive decrease of the cationic radius from V to Cr. Temperature-dependent inverse DC magnetic susceptibility suggests that SnCrBO4 and SnVBO4 are antiferromagnetic and ferromagnetic (FM) with a N & eacute;el temperature of 17.2(1) K and a Curie temperature of 29.8(1) K, respectively. Alike the end-member SnVBO4, Sn(Cr0.5V0.5)BO4 is also found to be a rare FM insulator. The thermal stability decreases with increasing vanadium content in the solid solution.

Over the past few years, the international space industry has focused extensively on advancing technologies to enable prolonged human space exploration missions. The primary limiting factor for these endeavors is the spacecraft's capacity to transport and store essential supplies from Earth to support human life and mission equipment throughout the mission's duration. In-situ resource utilization (ISRU) is the preferred solution for this challenge. Previous lunar missions have identified the presence of oxygen within the lunar regolith, which is an important resource for human space exploration missions. Oxygen is present in many different minerals within the lunar regolith out of which, ilmenite provides the highest yield of oxygen per unit mass using hydrogen reduction. However, the distribution of ilmenite is neither high nor uniform throughout the lunar surface and therefore, needs beneficiation, which is an important intermediate step for ilmenite-based oxygen production. A regolith beneficiation testbed was developed at DLR Bremen which is a TRL 4 level representation of the technology. The testbed has multiple process parameters that can be adjusted to produce the desired feedstock. This work focuses on the optimization of this testbed to produce a feedstock with higher ilmenite content than the input regolith. The testbed comprises three beneficiation techniques, viz. gravitational, magnetic and electrostatic beneficiation that work sequentially to produce the desired feedstock. The optimized parameter configuration achieved up to three-fold increase in the ilmenite grade relative to the input with about 32 wt% of the total ilmenite being recovered in the enriched output. These experiments have highlighted other underlying factors that influenced the experimental research such as the design of testbed components, system residuals and limited availability for Off-the-shelf components. The observations made from these experiments have also provided insights into the further development of the technology. The work has thus produced evidence for the effectiveness of the beneficiation testbed in producing an enriched feedstock while outlining avenues for future improvements.

Aerogels with noble metals have a wide range of applications such as sensing and catalysis, but research needs to be done to improve the integration of these materials in µ-channels. We realize silica aerogels without shrinkage and with high specific surface area (~600 m2/g) inside of closed channels. Further, Pt nanoparticles are deposited via capillary forces, into the complete network.

A procedure is presented to exactly obtain the apparent average crystallite size (ACS) of powder samples using standard in-house powder diffraction experiments without any restriction originating from the Scherrer equation. Additionally, the crystallite size distribution within the sample can be evaluated. To achieve this, powder diffractograms are background corrected and long-range radial distribution functions G(r) up to 300 nm are calculated from the diffraction data. The envelope function f env of G(r) is approximated by a procedure determining the absolute maxima of G(r) in a certain interval (r range). Fitting of an ACS distribution envelope function to this approximation gives the ACS and its distribution. The method is tested on diffractograms of LaB6 standard reference materials measured with different wavelengths to demonstrate the validity of the approach and to clarify the influence of the wavelength used. The latter results in a general description of the maximum observable average crystallite size, which depends on the instrument and wavelength used. The crystallite site distribution is compared with particle size distributions based on transmission electron microscopy investigations, providing an approximation of the average number of crystallites per particle.

Regolith draws intensive research attention because of its importance as the basis for fabricating materials for future human space exploration. Martian regolith is predicted to consist of defect-rich crystal structures due to long-term space weathering. The present report focuses on the structural differences between defect-rich and defect-poor forsterite (Mg2SiO4) - one of the major phases in Martian regolith. In this work, forsterites were synthesized using reverse strike co-precipitation and high-energy ball milling (BM). Subsequent post-processing was also carried out using BM to enhance the defects. The crystal structures of the samples were characterized by X-ray powder diffraction and total scattering using Cu and synchrotron radiation followed by Rietveld refinement and pair distribution function (PDF) analysis, respectively. The structural models were deduced by density functional theory assisted PDF refinements, describing both long-range and short-range order caused by defects. The Raman spectral features of the synthetic forsterites complement the ab initio simulation for an in-depth understanding of the associated structural defects.

Nanoporous gold (npAu) attracted increasing attention over the last 20 years as a highly active and selective oxidation catalyst in particular at low temperatures. Previous research mainly focused on npAu that was fabricated by corrosive dealloying of AuAg parent alloys. Yet, the use of other binary alloys, such as AuCu, promises interesting variations of the catalytic properties, when considering that residual amounts of the less noble metal were shown to be co-catalytically involved. Aiming at providing a platform for systematic studies in this direction for Cu, we not only dealt with strategies for a reliable and reproducible preparation of npAu(Cu) catalysts from AuCu, but also with their potential for CO oxidation in comparison to npAu(Ag). We were able to develop an approach based on thermally quenched Au0.3Cu0.7 alloys, providing distinct synthetic advantages as a starting material for the catalyst fabrication versus the thermodynamically more stable AuCu3 intermetallic compound. Using PCD (potentiostatically controlled dealloying), well-defined pore structures with ligament diameters of similar to 40 nm and variable residual Cu concentrations in the range between similar to 0.6 at % and similar to 1.2 at % could be straightforwardly obtained. After activating such catalysts at 150 degrees C, they reproducibly showed catalytic activity for aerobic CO oxidation in a broad temperature window between 40 degrees C and 250 degrees C. As opposed to npAu(Ag), the activity increased with decreasing residual Cu content, outperforming the former at temperatures above similar to 60 degrees C not only with respect to CO2 formation rates but also with respect to thermal stability. Based on X-ray photoelectron spectroscopic and transmission electron microscopic results, it was possible to conclude that Cu segregates to the surface and, with rising Cu bulk content, increasingly occurs in form of Cu2+ species at the surface. While the latter are expected to be catalytically inactive, Cu and Cu+ species are likely candidates for the activation of oxygen being not possible on pure Au. Nanoporous gold has emerged as a highly active oxidation catalyst, especially at low temperatures. While in the past it was predominantly synthesized from AuAg alloys, this study explores AuCu as starting material. Since residues of the less noble metal are co-catalytically involved, deviating properties are expected and were indeed observed. image

Metal tin-(II)-borates are rarely studied mainly due to the susceptibility of either oxidation into tin(IV) or disproportionation into elemental tin(0) and tin(IV). We report mullite-type SnAlBO4 and SnGaBO4 ceramics produced by conventional solid-state synthesis in sealed quartz tubes at low pressure of 10(-7) MPa. Both compounds are isostructural to PbAlBO4 as confirmed by Rietveld refinements of powder X-ray data. The crystal structures are highly influenced by the stereochemical activity of the 5s(2) lone electron pair of the Sn2+ cation measured by the Wang-Liebau eccentricity parameter. To further consolidate the structural features Sn-119 Mossbauer, solid state NMR, Raman, IR and UV/vis spectroscopic measurements are performed. The Sn-119 Mossbauer isomer shifts and the quadrupole splitting values confirm the SnO4 coordination and Sn(II) valence states. Solid state B-11, Al-27 and Sn-119 NMR spectra provided insights into the local crystal-chemical environment. The vibrational properties are discussed from group theoretical analysis to mode assignments. SnAlBO4 and SnGaBO4, respectively, possess an electronic band gap of 3.73(9) and 3.21(4) eV calculated from the diffuse reflectance UV/Vis spectra.

To fabricate metals from the base materials for future Mars exploration, synthesis of representative olivine phases and their structural and spectroscopic characterizations are of crucial importance. Using mechanochemical technique that mimics the mechanical weathering, a complete solid solution of (Mg1-xFex)(2)SiO4 has been synthesized to investigate the associated crystal chemical properties. X-ray powder diffraction data Rietveld analysis confirms that each polycrystalline sample crystallizes in space group Pbnm. The average crystallite size ranges between 80(1) nm and 223(4) nm. Each lattice parameter increases with increasing Fe-content due to the larger Fe2+ radius than that of Mg2+, following Vegard's rule. For a given nominal chemical composition, substitution of Mg with Fe at the M1-site (4a: 0,0,0) is preferred to the M2-site (4c: x,y,1/4). As a consequence, the average Fe-content lies slightly below the equivalence line for x = 0.2-0.8, indicating that the Fe/Mg ratio in the amorphous scattering content is most likely greater than unity. Characteristic Raman spectral features of the olivines have been explained in terms of the chemical composition (x). Simple regression models are demonstrated based on both X-ray diffraction and Raman spectroscopic data for the calculation of Mg/Fe in olivines. Diffuse reflectance UV/Vis spectra RATD analysis shows each olivine phase possesses direct band-gap between 3.38(3) eV and 4.90(3) eV. This study could keep valuable information to relevant databases for future human missions on Mars, in particular, for precise estimation of the representative olivines from the remote X-ray diffraction and spectroscopic data.

The crystal structures of both Pb2PbO4 (Pb3O4) and Pb2SnO4 at room temperature can be described using mullite-type setting in the space groups P4(2)/mbc and Pbam, respectively. At what chemical extend the crystal structure prefers either of the space groups would be an excellent playground in the Pb-2(Pb1-xSnx)O-4 solid solution. Members of the solid solutions have been prepared by solid-state reactions carried out in sealed quartz tubes. Each sample has been found to be phase pure confirmed by X-ray powder diffraction data Rietveld refinement. Samples with higher tin content require higher synthesis temperatures, and controlled decomposition of Pb3O4 serves as the source for both Pb2+ and Pb4+ cations. Since the Pb4+ cation is larger than Sn4+, the MO6 polyhedral volume decreases with increasing Sn-content. As such, each metric parameter shows a linear trend following Vegard's rule. The concomitant contraction of the MO6 octahedra and the high stereo-chemical activity of the 6s(2) lone electron pairs of lead in the Pb2+O4 distorted pyramid results in symmetry reduction. DFT suggests dynamical instability of the tetragonal Pb3O4 while Pb2SnO4 keeps orthorhombic symmetry at low temperatures, which agrees well with the experimental findings. The global blue shift of the vibrational mode frequencies is explained by the quasi-harmonic approach. The indirect band-gap linearly increases from 2.1(1) eV (x = 0) to a maximum value of 2.5(1) eV for x = 0.8 followed by a sharp drop towards Pb2SnO4. Thermogravimetric analysis demonstrates higher thermal stability with increasing Sn-content, which is explained in terms of higher bond strength of Sn-O than that of Pb-O in the MO6 octahedra.

The presence of ns(2) stereo-chemical active lone electron pairs (LEPs) causes asymmetric atomic environments around a given p-block cation, leading to change the crystal chemistry of a respective system. Here we report a series of mullite-type compounds to understand at what extend Sr2+ replaces the stereochemical active Pb2+ cation in (Pb1-xSrx)MnBO4. Each member of the solid solution has been synthesized by conventional solid-state method. The polycrystalline samples are characterized using X-ray powder diffraction followed by Rietveld refinement. Substitution of Pb2+ with Sr2+ leads to contraction of the a lattice parameter with slight elongation in the b and c direction. For a difference of 1 pm of the ionic radius between Sr2+ and Pb2+, the cell volume contracts about 4 % between the end members as the spatial requirement of the LEP activity in the MBO42- channels significantly decreases. Within the solid solution, two distinct Pb/Sr-O-2 bond distances significantly differ, which gradually decreases with increasing strontium content leading to a more symmetric coordination around strontium. The calculated BVS of Pb2+/Sr2+ exhibits a linear correlation with the Wang-Liebau eccentricity parameter, indicating to an increased bonding ability cation. The vibrational properties are characterized by both Raman and FTIR spectroscopy, complementing the XPRD results. Electronic band gaps of selected (Pb1-xSrx)MnBO4 samples were obtained from diffuse reflectance spectroscopy data. Additionally, the Sr containing samples show higher thermal stability than the Pb containing counterparts.

Polycrystalline double perovskite-type Sr2(Co1-xFex)TeO6 with various stoichiometric compositions (x = 0, 0.25, 0.5, 0.75, and 1) were synthesized by solid-state reactions in air. The crystal structures and phase transitions of this series at different temperature intervals were determined by X-ray powder diffraction, and from the obtained data the crystal structures were refined. It has been proven that for the compositions x = 0.25, 0.50, and 0.75, the phases crystallize at room temperature in the monoclinic space group I2/m. Down to 100 K, depending on the composition, these structures experience a phase transition from I2/m to P21/n. At high temperatures up to 1100 K their crystal structures show two further phase transitions. The first one is a first-order phase transition, from monoclinic I2/m to tetragonal I4/m, followed by a second-order phase transition to cubic Fm3̄m. Therefore, the phase transition sequence of this series detected at temperatures ranging from 100 K to 1100 K is P21/n → I2/m → I4/m → Fm3̄m. The temperature-dependent vibrational features of the octahedral sites were investigated by Raman spectroscopy, which furthermore complements the XRD results. A decrease in the phase-transition temperature with increasing iron content has been observed for these compounds. This fact is explained by the progressive diminishing of the distortion of the double-perovskite structure in this series. Using room-temperature Mössbauer spectroscopy, the presence of two iron sites is confirmed. The two different transition metal cations Co and Fe at the B sites allow exploring their effect on the optical band-gap.