J. Mass Spectrom. Soc. Jpn., 47(1), 2-9, 1999
We present a combined experimental and theoretical study on the nature of hypervalent bonding in such molecules as Li2CN, Na2CN, K2CN, and Li2OH. The molecules M2CN (M=Li, Na, K) were observed in the vapor over a mixture of alkali metals and sodium cyanide by high-temperature Knudsen effusion mass spectrometry and Li2OH was detected by time-of-flight mass spectrometry for a molecular beam generated by laser ablation of slightly oxidized lithium metal. Despite their unusual stoichiometries, these molecules were confirmed to be thermodynamically more stable than the corresponding octet molecules (MCN, LiOH). Computational geometry optimization gives four possible structural isomers to each M2CN molecule; i.e., two planar structures with Cs symmetry and two linear structures with C
v symmetry. The planar M2CN molecules are favored and best described as a complex of the CN- anion with the M+2 cation. The extra valence electron in SOMO contributes to M--M bonding to form the M+2 unit. The linear M2CN molecules are electronomers" described as M+(CN)-M· and M·(CN)-M+. The Li2OH molecule with C2v symmetry comprises the Li+2 and OH- units, and the electrostatic attraction affords the stable molecule, similar to the planar M2CN.
J. Mass Spectrom. Soc. Jpn., 47(1), 10-15, 1999
The atmosphere controlled high temperature mass spectrometer has provided vapor pressure data for lithium-based oxide ceramics under condition of low pressure hydrogen introduction. The measured vaporization behaviors under hydrogen addition of Li4SiO4, LiAlO2, Li2TiO3, and Li2ZrO3 are summarized. From the experimental data, sum of the partial pressures of lithium containing species was estimated for each oxide. It was pointed out that hydrogen addition seemed to cause the formation of a nonstoichiometric layer at the surfaces of Li4SiO4 and Li2ZrO3. Work function measurement was employed as a new method for investigation of such oxygen deficient layers. The results of the work function measurements showed the formation of an oxygen deficient surface layer for Li4SiO4 and for Li2ZrO3, whereas such was not the case for Li2TiO3.
J. Mass Spectrom Soc. Jpn., 47(1), 16-22, 1999
For analysis of fission products release and transportation in severe accidents of nuclear reactors, vaporization behaviors of BaUO3, SrUO3, Cs2UO4, and Cs2U4O12 were investigated by using a Knudsen effusion high temperature mass spectrometer. To simulate water vapor and hydrogen environments in severe accident conditions of nuclear reactors, the environmental conditions inside the Knudsen cell were controlled by introducing proper amounts of gases, such as D2(g), D2O(g), O2(g), or their mixtures from outside reservoirs. To maintain dynamic equilibrium being established inside the Knudsen cell, however, the amount of input gas can not be too large. So the experimental result from the mass spectrometry can only apply for a small range of environmental conditions compared to those in a real severe accident of nuclear reactors. A calculation was made by using computer code Chemsage for other possible environmental conditions, such as wet condition with high H2O(g)/H2(g) ratio, reducing condition with low H2O(g)/H2(g) ratio, high temperatures up to 2500 K and high pressures up to 1 MPa. Both the experimental results and the calculation showed that environmental conditions have a great influence on vaporization properties of these compounds.
J. Mass Spectrom. Soc. Jpn., 47(1), 23-26, 1999
Thermodynamic activities of rare earth alloys such as La-Ce, La-Nd, and La-Gd alloys obtained with a mass-spectrometer by the present authors were summarized together with other reported values of Pr-Nd and Sm-Gd. Gibbs energy of mixing, which was calculated from the thermodynamic activity values, was compared to each other. The minimum regions of Gibbs energy of mixing in all La-Ln (Ln = Ce, Nd, Gd) alloys seem to be attained in almost equal molar compositions. The Gibbs energies of mixing and interaction parameters of the alloys were compared to each other and discussed with the Miedema's model. The difference in the electron density for elements was recognized as the important term for rare earth alloys.
J. Mass Spectrom. Soc. Jpn., 47(1), 27-31, 1999
An isotope exchange technique is introduced as a method for measuring the nitrogen dissolution rate into molten metal, and the results [H. Ono et al., Metall. Mater. Trans. B, 26, 991 (1995); ibid., 27, 848 (1996)] (refs. 1 and 2) for molten iron-M (M: Ti, Zr, V, Cr, O, Se, and Te) alloys at temperatures from 1873 to 2023 K are summarized.
The rate of nitrogen dissolution into molten iron is shown to increase by adding an element with a stronger affinity for nitrogen than Fe, such as Ti, Zr, V, and Cr. Among these elements, Ti increases the reaction rate most strongly and the rate constant for an Fe-0.08 mass pct Ti alloy is 1.5 times as large as that for pure iron at 1873 K. On the other hand, the addition of surface active elements, such as O, Se, and Te, retards the nitrogen dissolution into molten iron, and the degree of the retarding effect is in the order of Te, Se, and O.
For the addition of non-surface active elements, the correlation of rate constant with thermodynamic interaction parameter with nitrogen has been observed, and this effect is discussed in terms of the change in the activity of the vacant site on the surface of the molten alloy. In case of the addition of surface active elements, the adsorption coefficients of each elements are estimated by fitting the concentration dependence of the nitrogen dissolution rate constant. It can be suggested that surface active elements and nitrogen are adsorbed on the same site at the interface and that the dissociation reaction of nitrogen molecule on the site represented by the equation, Nad2 + 
= 2Nad, is the rate determining on the assumption that all sites at the metal surface have a uniform adsorption energy for each solute.
J. Mass Spectrom. Soc. Jpn., 47(1), 32-37, 1999
Diffusion coefficients of oxide ion and cations in alkaline-earths doped lanthanum chromites were determined by secondary ion mass spectrometry (SIMS). The contribution of grain boundary as a fast diffusion path was quantitatively evaluated by analyzing the depth profiles. The grain boundary diffusion coefficients were 104 times higher than the bulk diffusion coefficients for oxide ion, and 105 times higher for cations. For A-site cation diffusion, the diffusion mechanism at grain boundary has been found to be closely related with the valence state of chromium ion, which will play a main role of determining the vacancy concentration at A-site in the vicinity of grain boundaries. The oxygen partial pressure dependence of oxide ion diffusion coefficient was determined by annealing in Ar-18O2 and Ar-H2-C18O2, and the results revealed a good agreement with the data of oxygen permeation fluxes which were measured in steady state under a large gradient of oxygen partial pressure.
J. Mass Spectrom. Soc. Jpn., 47(1), 38-41, 1999
Born of necessity in the metallurgy of the reactive metals, vacuum technology is now being applied to the steel-making resulting in excellent quality control and properties not otherwise realizable. To provide an insight into the selection and evaluation of the experimental data, the authors have considered it advisable to present a systematic review of the principles and theories on evaporation phenomena. This article contains the basic aspect of the free evaporation under perfect vacuum, the vapor transfer through the thermal boundary layer under poor vacuum, the enhancement of evaporation, the restriction evaporation and the selective evaporation from multi-component bulk.
J. Mass Spectrom. Soc. Jpn., 47(1), 42-45, 1999
A mass-spectrometric Knudsen effusion method isused for measuring partial pressures of CsBO2(g) and Cs2(BO2)2(g) over melts in the CsBO2-SiO2 system. From the partial pressures, thermodynamic activities and partial molar Gibbs energies of the CsBO2 and SiO2 components, molar Gibbs energies of mixing, and excess molar Gibbs energies of mixing are determined in the whole composition range at 1000 K. Thermodynamic activities of both the CsBO2 and SiO2 components show negative deviation from Raoult's law. The melts in the CsBO2-SiO2 system are concluded to be thermodynamically more stable than those in the RbBO2-SiO2 system caused by the lower excess molar Gibbs energies of mixing.
J. Mass Spectrom. Soc. Jpn., 47(1), 46-48, 1999
Vaporization behavior of BaPuO3 was investigated by high-temperature mass spectrometry with a Pt Knudsen cell in the temperature range from 1, 673 to 1,873 K. The vapor species of Ba(g) and BaO(g) were iden-tified over BaPuO3 with the second phase of PuO2.It was suggested from the experimentalresults that thede-composition of BaPuO3 was expressed as the following equation;
BaPuO3(s)=PuO2(s)+BaO(g)
2BaO(g)=2Ba(g)+O2(g).
The second- and third-law standard molar enthalpies of formation of BaPuO3 were evaluated to be -1,661 and -1,673 kJ mol-1, respectively, which almost agreed with the calculated values previously reported.
J. Mass Spectrom. Soc. Jpn., 47(1), 49-52, 1999
The vapor pressures of Si(g) and Si2(g) over Si(l) were measured with a time-of-flight mass spectrometer equipped with a boron-nitride Knudsen cell. The equations for the vapor pressure of Si(g) and Si2(g) obtained by the least squares treatment were given as follows:
log(PSi/Pa)=(-2.08±0.10) x 104K/T+(10.84±0.53)
log(PSi2/Pa)=(-2.46±0.09) x 104K/T+(10.93±0.47)
The vaporization enthalpy of Si(g) at the standard state (409.2±2.3 kJ mol-1) calculated based on the third law was in good agreement with the second law one (407.4±19.1 kJ mol-1). The third law value of the vaporization enthalpy of Si2(g) at the standard state (493.7±1.9 kJ mol-1) was also in good agreement with the second law one (491.5±15.7 kJ mol-1). The dissociation energies of Si2(g) calculated from the vaporization enthalpy of Si(g) and Si2(g) at the standard state were 323.3±31.2 kJ mol-1 (the second law value) and 324.7±3.8 kJ mol-1 (the third law value).
J. Mass Spectrom. Soc. Jpn., 47(1), 53-57, 1999
A new mixed gas inlet system for a Knudsen cell was developed for the introduction of a H2-O2 mixture and other mixed gases into a Knudsen cell of a high temperature mass spectrometer from outside reservoirs. Pressure of the gases as introduced into the Knudsen cell is controlled by the gas flow rates through low conductance capillary tubes connected to the outside reservoirs. The experimentally obtained gas flow rates agreed fairly well with the calculated ones for room temperature. However, the measured temperature dependence of the gas pressure in the Knudsen cell showed a negative departure from that of the theoretical values, which became especially large above about 1400 K. It was confirmed that, compared to the case of using the conventional direct H2O introduction method, water vapor can be supplied much promptly into a Knudsen cell in mass spectrometer from the outside by introducing H2 and O2 gases separately through the mixed gas inlet system developed in this study.
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