Dry reforming of methane (DRM) enables an efficient utilization of two abundant greenhouse gases by converting them into syngas, a versatile feedstock for chemical synthesis. Aiming for high catalyst performance and enhanced coke resistance, different preparation techniques of La-promoted Ni/γ-Al₂O₃ catalysts for DRM were compared facilitating structure–performance correlations. The studied synthesis techniques comprehend incipient wetness impregnation and co-precipitation as well as alternative techniques such as spray drying. All catalysts were fully characterized before and after reaction by N₂-physisorption, XRD, H₂-TPR and STEM-EDX elemental mapping. Additionally, a thorough investigation of carbon deposits has been carried out by TGA/DSC and STEM-EDX, respectively. The different preparation techniques led generally to very different physical properties, structure, chemical species and anti-coking properties of the catalyst. However, some catalysts with similar physicochemical characteristics differed in catalytic performance and coking resistance. Superior catalytic performance could be reached for catalysts prepared by spray drying and related to excellent Ni dispersion, strong metal–support interaction and very low coke formation of only 2.7% of the catalyst weight. After 6 h time on stream only minor sintering occurred, with few Ni nanoparticles up to 10 nm.

Thermal conductivity of NbO is studied experimentally and theoretically. Sputtered NbO samples, slightly overstoichiometric in oxygen, are x-ray amorphous with a combined NbO and NbO ₂ short-range order, which is consistent with the quantum mechanical data. Upon annealing, NbO ₂ crystallites form in the amorphous matrix due to an energetic preference of 44 meV atom ⁻¹ over NbO counterparts. The measured thermal conductivity at room temperature using time-domain thermoreflectance is 6.9 W m ⁻¹ K ⁻¹ , followed by a continuous increase due to electronic contributions, and it yields a total increase of 40 W m ⁻¹ K ⁻¹ at 650 K partly due to crystallisation. Phonon–phonon scattering can be induced by introducing Ni _0.75 Ta _0.25 O layers in NbO. These multilayers exhibit a thermal conductivity of 5.4 W m ⁻¹ K ⁻¹ at room temperature and a monotonic drop upon increasing temperature. It is thus feasible to modulate the high-temperature thermal conductivity of amorphous NbO by an order of magnitude. Hence, amorphous NbO may be of interest for thermoelectric devices, sensors and thermal insulation applications.

In cold extrusion of aluminum alloys adhesive wear can be prevented by an excessive lubrication of the process. While this causes additional process steps also environmental risks have to be addressed. Hence, dry metal forming, i.e. avoiding lubrication by means of coatings and topography modifications is highly desirable. In this paper first results concerning the behavior of tailored surfaces under dry metal forming conditions for pure aluminum are presented. Different surface treatments (laser polishing and Mo₂BC coating) of the tool steel AISI H11 are tested in a compression-torsion-tribometer under conditions adapted from cold extrusion. Normal stresses six times higher than the initial yield stress of the tested workpiece material pure aluminum (AA1050-O) are applied. Furthermore, a strategy for the characterization of aluminum adhesions to the tool is introduced. The influences of different topographies and the presence of a coating on the loss of material due to adhesive wear are investigated.

The authors demonstrate that functionalizing tool steel die surfaces with an octadecylphosphonic acid molecular monolayer decreases friction during Al cold forming. Specifically, molecular functionalization leads to a 1.9-fold decrease in time-averaged torque during tribological compression-torsion wear tests. Electron spectroscopy suggests that weak van der Waals interaction between aluminum and the distal CH3 termini of the phosphonic acid molecules anchored to the steel surface via P–O bridges lubricate the aluminum–steel interface. The observation of this effect at contact-pressures of ≥75 MPa underscores the tremendous potential of molecular functionalization for devising industrial metal forming processes without the use of liquid lubricants.

Liquid lubrication guarantees high precision and surface quality of workpieces in industrial forming processes. In the case of aluminum cold extrusion, wear and cold welding due to direct contact of tool and workpiece are usually prevented by the extensive use of lubricants. Since the use of lubricants is economically and ecologically unfavorable, surface treatments of tools by, e.g. laser polishing and/or coatings are in the focus of current investigations to substitute these lubricants and establish so called “dry metal forming” processes. The material AISI D2, a ledeburitic 12% chromium steel which is known to have a significant amount of chromium carbide precipitations, is widely used in cold extrusion for forming tools. The large fraction of chromium carbide precipitations, however, hinder the formation of a dense self-assembled monolayer (SAM) that is necessary to avoid direct contact of reactive aluminum with surface oxides of the tool. Therefore, a homogeneous distribution of the chemical elements with a smaller fraction or no chromium carbides in the steel matrix, particularly in the tool surface, is aimed for. Using laser polishing, the surface layer is molten by continuous or pulsed laser radiation. Within the melt pool, the elementary distribution is homogenized as a result of thermal convection and diffusion processes, as well as a smoothed surface and a grain refinement are achieved. Consequently, the effects of the surface treatment by laser polishing on the area coverage of self-assembled monolayers are investigated. Thus, a combined surface treatment by laser polishing and functionalization with a dense self-assembled monolayer shall reduce overall adhesive wear. For this investigation, several specimens of conventional manufactured and powder metallurgical molten AISI D2 are laser polished using continuous or pulsed laser radiation or a combination of both. The resulting surfaces are investigated by microscopy and spectroscopic techniques to analyze the surface topography and the elemental distribution near to the surface. These results are compared to those of conventionally hand-polished specimens. Furthermore, the influence of the element homogenization and grain refinement on the area coverage of self-assembled monolayers is explored. First results show that laser polishing of AISI D2 is suitable to achieve a reduction of grain size and a more homogeneous distribution of chromium carbides within the surface layer.

Cold extrusion processes are characterized by large relative contact stresses combined with a severe surface enlargement of the workpiece. Under these process conditions a high risk for galling of workpiece material to the tool steel occurs especially in processing of aluminum and aluminum alloys. In order to reduce adhesive wear lubricants for separation of workpiece and tool surfaces are used. As a consequence additional process steps (e.g. preparation and cleaning of workpieces) are necessary. Thus, the realization of a dry forming process is aspired from an environmental and economic perspective. In this paper a surface functionalization with self-assembled-monolayers (SAM) of the tool steels AISI D2 (DIN 1.2379) and AISI H11 (DIN 1.2343) is evaluated by a process-oriented tribological test. The tribological experiment is able to resemble and scale the process conditions of cold extrusion related to relative contact stress and surface enlargement for the forming of pure aluminum (Al99.5). The effect of reduced relative contact stress, surface enlargement and relative velocity on adhesive wear and tool lifetime is evaluated. Similar process conditions are achievable by different die designs with decreased extrusion ratios and adjusted die angles. The effect of surface functionalization critically depends on the substrate material. The different microstructure and the resulting differences in surface chemistry of the two tested tool steels appear to affect the performance of the tool surface functionalization with SAM.