Simultaneous determination of oxygen, nitrogen and hydrogen in metals by pulse heating and time of flight mass spectrometric method.
The inert gas fusion and infrared absorption and thermal conductivity methods are widely used for quantitative determination of oxygen(O), nitrogen(N) and hydrogen(H) in metals. However, O, N and H cannot be determined simultaneously with this method in most cases and the sensitivity cannot meet the requirement of some new metal materials. Furthermore, there is no equipment or method reported for determination of Argon(Ar) or Helium(He) in metals till now. In this paper, a new method for simultaneous quantitative determination of O, N, H and Ar(or He) in metals has been described in detail, which combined the pulse heating inert gas fusion with time of flight mass spectrometric detection. The whole analyzing process was introduced, including sample retreatment, inert gas fusion, mass spectral line selection, signal acquisition, data processing and calibration. The detection limit, lower quantitative limit and linear range of each element were determined. The accuracy and precision of the new method have also been verified by measurements of several kinds of samples. The results were consistent with that obtained by the traditional method. It has shown that the new method is more sensitive and efficient than the existing method.
Three-dimensional hydrogen distribution and quantitative determination of titanium alloys via neutron tomography.
Thermohydrogen processing (THP) is an attractive technique that uses hydrogen as a temporary alloying element to modify the microstructure and properties of titanium alloys. However, the hydrogen diffusion behavior during THP is not fully understood owing to limited scope of methods to detect hydrogen distributions. Herein, we introduce neutron tomography as an efficient tool for three-dimensional (3D) hydrogen distribution analysis and quantitative determination in hydrogenated titanium alloys after THP. Thus motivated, a series of calibration samples of Ti-6Al-4V alloys with varying hydrogen contents were prepared and elaborated neutron tomography experiments and image data processing were performed. In this way, the 3D hydrogen distribution of the hydrogenated samples was obtained and the quantitative relationship between the hydrogen contents and the tomographic images was determined. To the best of our knowledge, this enabled for the first time the direct 3D visualization and characterization of the hydrogen distribution and concentration in titanium alloys after THP. It was deduced that hydrogen diffused from the surface to the interior of the hydrogenated sample in all directions during THP. In addition, the feasibility of neutron tomography for 3D quantitative hydrogen distribution was validated using continuous sample segmentation and the traditional heat conductivity method. Consequently, neutron tomography can be efficient for determining the hydrogen distribution and concentration in bulk metals and shed light on the hydrogen diffusion behavior and the mechanism of hydrogen-related materials and processing.
The Invariance of the Vacuum is the Invariance of the World
The following theorem is demonstrated: If the vacuum is invariant under the group generated by the space integral of the time component of a local vector current, then the Hamiltonian is invariant also. A similar theorem holds for the group generated by the space integral of a space component of a local axial-vector current.