3 results
Search Results
Now showing 1 - 3 of 3
- ItemNitrogen-Doped Carbon Nanotube/Polypropylene Composites with Negative Seebeck Coefficient(Basel : MDPI, 2020) Krause, Beate; Konidakis, Ioannis; Arjmand, Mohammad; Sundararaj, Uttandaraman; Fuge, Robert; Liebscher, Marco; Hampel, Silke; Klaus, Maxim; Serpetzoglou, Efthymis; Stratakis, Emmanuel; Pötschke, PetraThis study describes the application of multi-walled carbon nanotubes that were nitrogen-doped during their synthesis (N-MWCNTs) in melt-mixed polypropylene (PP) composites. Different types of N-MWCNTs, synthesized using different methods, were used and compared. Four of the five MWCNT grades showed negative Seebeck coefficients (S), indicating n-type charge carrier behavior. All prepared composites (with a concentration between 2 and 7.5 wt% N-MWCNTs) also showed negative S values, which in most cases had a higher negative value than the corresponding nanotubes. The S values achieved were between 1.0 µV/K and −13.8 µV/K for the N-MWCNT buckypapers or powders and between −4.7 µV/K and −22.8 µV/K for the corresponding composites. With a higher content of N-MWCNTs, the increase in electrical conductivity led to increasing values of the power factor (PF) despite the unstable behavior of the Seebeck coefficient. The highest power factor was achieved with 4 wt% N-MWCNT, where a suitable combination of high electrical conductivity and acceptable Seebeck coefficient led to a PF value of 6.1 × 10−3 µW/(m·K2). First experiments have shown that transient absorption spectroscopy (TAS) is a useful tool to study the carrier transfer process in CNTs in composites and to correlate it with the Seebeck coefficient.
- ItemLocal Structure Investigation of Cu Precipitates in Modified 18CrNiMo7-6 Steels by Synchrotron X-ray Absorption Spectroscopy(Tōkyō : ISIJ, 2022) Suwanpinij, Piyada; Bambach, Margarita; Bootchanont, Atipong; Sailuam, WutthigraiThis paper studied the copper precipitation in an 18CrNiMo7-6 martensitic steel (0.19 mass% C) with copper addition and its resulting improved mechanical behavior. The development of nano-precipitates in two modified alloys with 1.0 and 1.5 mass% copper addition was investigated by means of synchrotron X-ray absorption spectroscopy. The first-principles calculation has enabled the modeling of the unavailable copper standards: solid solution, B2, BCC, 2H, 9R and 3R, for calculating the XAS spectra and successfully identified the unknown phases after aging for the first time in this steel group. The samples alloyed with 1.5 mass% copper yielded the semi-coherent 9R structure when aged at 500°C between 166 to 360 minutes. The ones containing 1 mass% copper formed the B2 ordered structure after aging at 480°C for 50 minutes and revealed the co-existence of the 9R after 240 minutes. The analysis reveals the precipitation kinetics of copper in low carbon martensitic steel and helps determine the optimum tempering parameters to adjust peak strength.
- ItemMechanochemical Ionization: Differentiating Pressure-, Shear-, and Temperature-Induced Reactions in a Model Phosphate(Cham : Springer International Publishing, 2022) Sukhomlinov, Sergey V.; Kickelbick, Guido; Müser, Martin H.Using density-functional theory-based molecular dynamics simulations, we study stress and temperature-induced chemical reactions in bulk systems containing triphosphoric acid and zinc phosphate molecules. The nature of the products depends sensitively on the imposed conditions, e.g., isotropic and even more so shear stress create (zwitter-) ionic products. Free ions also emerge from thermal cycles, but the reactions are endothermic rather than exothermic as for stress-induced transitions and zinc atoms remain four-coordinated. Hydrostatic stresses required for reactions to occur lie well below those typical for tribological micro-contacts of stiff solids and are further reduced by shear. Before zinc atoms change their coordination under stress, proton mobility increases, i.e., hydrogen atoms start to change the oxygen atom they are bonded to within 10 ps time scales. The hydrostatic stress for this to occur is reduced with increasing shear. Our finding suggests that materials for which number, nature, and mobility of ions are stress sensitive cannot have a well-defined position in the triboelectric series, since local contact stresses generally depend on the stiffness of the counter body. Moreover, our simulations do not support the idea that chemical reactions in a tribo-contact are commonly those that would be obtained through heating alone.