Untersuchung von implantierten Schichten (N2+, CO+) von Werkzeugst?hlen mit dem AES-Verfahren

Summary The paper deals with the depth distribution of implanted elements from the surface, i.e., the concentration profile, studied by means of Auger electron spectroscopy. Results obtained in low carbon CrMoV tool steel implanted with N ₂ ⁺ or CO⁺ ions have been correlated with theoretical curves which were calculated by the LSS method for pure -iron.Low doses of implanted nitrogen (1.5 and 2.0 · 10¹⁷ ions/ cm²) exhibit no differences between measured concentration profiles and theoretical distribution, while a high dose (4.0 · 10¹⁷ ions/cm²) induced profile deformation together with sputtering of the material surface. By bombardment with carbon monoxide (1.5 – 4.0 · 10¹⁷ ions/cm²), these molecular ions are split after their incidence and carbon as well as oxygen atoms can move independently within the material. The position of the oxygen concentration profiles correspond to the theoretically found curves (the true heights of the profile being substantially lower), whereas the concentration profiles of carbon are very flat and of asymmetrical shape.     

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A comparison between plane wave and Gaussian-type orbital basis sets for hydrogen bonded systems: formic acid as a test case

The formic acid molecule, its dimers, and its molecular crystal are adopted as test systems to compare results obtained with plane wave (PW) basis sets and norm-conserving pseudopotentials to all-electron Gaussian-type orbital (GTO) calculations. The CPMD and CRYSTAL06 codes, respectively, are applied with the PBE, PW91, and BLYP density functionals. Hydrogen bonding is the leading interaction in the dimers and the crystal. In the latter, dispersive and weak C-H...O interactions are also relevant. Irrespective of the adopted functional, for all considered structures PW and GTO results converge smoothly as a function of the quality of the adopted basis sets to the same values for structures, energies of interaction, and harmonic vibrational features. To achieve a high level of mutual agreement the use of GTO basis sets of at least of triple-zeta quality including one set of polarization functions and PW basis sets with a kinetic energy cutoff higher than 110 Ry is recommended. Pros and cons of both approaches for studying molecular crystals are also discussed.     

Small scale adiabatic dewar techniques to determine exothermic onset temperatures

The heightened focus on safety in the chemical process industry has resulted in a growing trend to provide reliable thermochemical information before process scale-up. The exothermic onset temperature of compounds is of key concern. The small scale adiabatic dewar age (SSAD) test, developed at Merck Research laboratories, is used to determine exothermic onset temperatures. These tests are conducted under nearly adiabatic conditions using specially designed dewar sample cells and commercially available programmable calorimeters. The dewar cell method offers a rapid and accurate method to enhance standard test procedures and allows measurement of auto catalytic behavior using small samples.The SSAD technique is applicable to both solids and liquids and has the following advantages: 1) small sample size, 2) ability to handle compounds in which exothermic activity is accompanied by large pressure increases without damaging experimental equipment, 3) accurate determination of exothermic onset temperature, 4) ease of experiment set-up, 5) ease of data interpretation and 6) rapid experimental turn around time.The determination of the exothermic onset temperature using the SSAD technique will be presented and compared to data obtained using standard and isothermal age techniques.