Gert Kloess

Ni-struvite - a new biomineral formed by a nickel resistant Streptomyces acidiscabies.

Biomineralization dependent on bacterial activity has been described for struvite which is formed in soils, guano, putrescent matter and sediments. A new biomineral containing nickel instead of magnesium, Ni(NH4)(PO4) . 6H2O, has been identified. It was formed by nickel resistant Streptomyces acidiscabies E13, and putatively named nickel struvite. The mineral formation is dependent on biological activity since non-viable bacterial cells are not capable to induce formation of Ni-struvite under identical conditions. Formation of Ni-struvite was observed on colony surfaces upon prolonged incubation of solid minimal or complex media containing elevated concentrations of 8-15mM NiCl2. The formation of magnesium containing crystals was not observed although Mg2+ is present in the medium. However, the process was not depending on desiccation since small crystals attached to the mycelial biomass of the bacteria were observed microscopically also in liquid cultures of nickel supplemented minimal and complex media after two weeks of incubation. The capacity to induce biomineralization of a nickel containing mineral is postulated to constitute a resistance factor, allowing the soil bacterium to withstand high nickel concentrations. The strain shows nickel resistance as an adaption to its habitat, since this bacterium was isolated from a former uranium mining site in Eastern Thuringia, Germany, where nickel concentrations of up to 2000ppm (translating to appr. 30mM) occur as a result of former mining activities.

Identification of a possible superconducting transition above room temperature in natural graphite crystals

Measuring with high precision the electrical resistance of highly ordered natural graphite samples from a Brazil mine, we have identified a transition at

Shocked quartz in Sahara fulgurite

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Theoretical and experimental study of the vibrational spectra of sarkinite Mn2(AsO4)(OH) and adamite Zn2(AsO4)(OH)

350~K with

Comparative Study between Direct and Pseudomorphic Transformation of Rice Husk Ash into MFI-Type Zeolite

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Moldavite porosity: a 3-D X-ray micro-tomography study

40~K transition width. The step-like change in temperature of the resistance, its magnetic irreversibility and time dependence after a field change, consistent with trapped flux and flux creep, and the partial magnetic flux expulsion obtained by magnetization measurements, suggest the existence of granular superconductivity below 350~K. The zero-field virgin state can only be reached again after zero field cooling the sample from above the transition. Paradoxically, the extraordinarily high transition temperature we found for this and several other graphite samples is the reason why this transition remained undetected so far. The existence of well ordered rhombohedral graphite phase in all measured samples has been proved by x-rays diffraction measurements, suggesting its interfaces with the Bernal phase as a possible origin for the high-temperature superconductivity, as theoretical studies predicted. The localization of granular superconductivity at these two dimensional interfaces prevents the observation of a zero resistance state or of a full Meissner state.

Fractal Dimension and Maximum Roughness Applied as Sculpture Descriptor for Tektites

Comparative strain analyses were performed on quartz crystals within a Sahara fulgurite using neutron diffraction experiments. Besides, 3D-μXRCT (three-dimensional micro X-ray computed tomography) studies of the fulgurite were implemented in order to quantify the fusion behaviour, the expansion of the fulgurite as well as the distribution of the stressed quartz crystals. The study of the neutron diffraction pattern was carried out by applying an integral breadth method, more precisely a Rietveld and a LeBail strain–size evaluation with the software FullProf. The absorption contrast of the neutron diffraction pattern shows a concentration of the shocked quartz crystals in the outer shell of the Sahara fulgurite, while the inner part of the fulgurite is mostly glassy. On the basis of the diffraction results, the quartz crystals in the fulgurite can be assigned to a stage of deformation for which the causal shock pressure reaches about 25 GPa, as compared to a melting threshold pressure for quartz of about 50 GPa. Comparing the average density of the fulgurite with the average bulk density of quartz-based sand, it can be concluded that the fulgurite expanded by more than 35 % during its formation.

Structure and optical properties of PbS-SnS mixed crystal thin films

The arsenate hydroxyl-bearing minerals sarkinite and adamite were studied with vibrational spectroscopic (IR and Raman) and quantum theoretical methods. The observed IR bands in the higher (1100-600 cm(-1)) and especially lower (600-450 cm(-1)) frequency region of AsO4 vibrations could clearly discriminate between the studied analogues. The differences between their crystal structures are much pronounced in both IR and Raman OH-stretching regions. Namely, a single strong band is found in the case of orthorhombic adamite compared to four weaker bands observed in corresponding IR and Raman spectral regions of monoclinic sarkinite. Essentially all bands in the experimental spectra, collected at both room and liquid nitrogen temperature, were tentatively assigned. To support the tentative assignment of bands in the vibrational spectra of the mentioned minerals, periodic pseudopotential plane wave density functional theory calculations were carried out. Geometry optimizations of the 3D periodic systems included both optimizations of the atomic positions within the unit cell and of the unit cell itself. In most cases, the assignments were either supported or implied by the obtained theoretical data. It is worth mentioning that this is the first experimental and theoretical study of the vibrational spectra of the very-rare sarkinite mineral.

Effect of acid treatment on the chemical composition and the structure of Egyptian diatomite

Pre-shaped mesoporous amorphous rice husk ash (RHA) and MCM-41 derived from RHA as a silica source were transformed into MFI-type zeolites using two different structure-directing agents. Tetrapropylammonium hydroxide (TPAOH) was utilized as an alkali source for silica dissolution and structure control during the direct transformation of RHA into zeolite. A monopropylamine (PA)-containing alkaline solution (NaOH) was used for the pseudomorphic transformation of RHA or MCM-41 into zeolite. The hydrothermal conversion of RHA or MCM-41 into MFI-type zeolites was investigated as a function of reaction time at 175 °C. With PA as template, the crystallization took place inside and on the outer surface of RHA or MCM-41 without losing the original shape of the initial silica sources, while TPAOH led to the formation of conventional MFI-type zeolite crystals due to the complete dissolution of RHA. The final products were characterized by X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and optical emission spectroscopy.

Miscibility of NiSi2, FeSi2 and Cu3Si

Moldavites are natural glasses formed by distal ejection of meteorite-impact melts; they occur in several shapes ( e.g ., teardrops, lenticular, dumbbells, spheres) and all contain pores in different sizes. The aim of this study is to describe the distribution of pores in the interior of the scanned objects. The X-ray micro-tomography (μ-XRCT) measurements were utilized to create three-dimensional semi-transparent images of tektites in order to receive information about their porosity. Optimal data interpretation requires the use of proper software programs. For the visualization of the μ-XRCT-data, VG Studio Max 2.0 (Volume Graphics) and ImageJ were utilized. Four tektite samples from the Central European strewn field with different shapes were scanned. The μ-XRCT data depict relations between the distribution of the detected pores and the shape of the tektites. Total volumes, total porosity, number of pores, and pore sizes throughout the tektite samples vary. The evaluated porosity volume of the Bohemian moldavites ranges between 0.024 and 0.085 vol.%. The smallest detected pore has a volume of 0.0003 mm 3 , whereas the biggest has a volume of 0.35 mm 3 .