S. Nalini

Investigation of the vaporization of boric acid by transpiration thermogravimetry and knudsen effusion mass spectrometry.

The vaporization of H3BO3(s) was studied by using a commercial thermogravimetric apparatus and a Knudsen effusion mass spectrometer. The thermogravimetric measurements involved use of argon as the carrier gas for vapor transport and derivation of vapor pressures of H3BO3(g) in the temperature range 315-352 K through many flow dependence and temperature dependence runs. The vapor pressures as well as the enthalpy of sublimation obtained in this study represent the first results from measurements at low temperatures that are in accord with the previously reported near-classical transpiration measurements (by Stackelberg et al. 70 years ago) at higher temperatures (382-413 K with steam as the carrier gas). The KEMS measurements performed for the first time on boric acid showed H3BO3(g) as the principal vapor species with no meaningful information discernible on H2O(g) though. The thermodynamic parameters, both p(H3BO3) and Delta sub H degrees m(H3BO3,g), deduced from KEMS results in the temperature range 295-342 K are in excellent agreement with the transpiration results lending further credibility to the latter. All this information points toward congruent vaporization at the H3BO3 composition in the H2O-B2O3 binary system. The vapor pressures obtained from transpiration (this study and that of Stackelberg et al.) as well as from KEMS measurements are combined to recommend the following: log [p(H3BO3)/Pa]=-(5199+/-74)/(T/K)+(15.65+/-0.23), valid for T=295-413 K; and Delta sub H degrees m=98.3+/-9.5 kJ mol (-1) at T=298 K for H3BO3(s)=H3BO3(g).

Vapor Pressure Measurements by Mass Loss Transpiration Method with a Thermogravimetric Apparatus

Thermobalances are used for equilibrium vapor pressure measurements based on both effusion and transpiration methods. In the case of the transpiration method, however, despite the numerous advantages a thermogravimetric apparatus can offer, it is not as widely used as is the conventional apparatus. In this paper, the difference that can exist in the vapor phase compositions in an effusion cell and in a transpiration cell is shown first with two examples. Subsequently, how a commercial thermobalance was utilized to perform transpiration experiments that conform to the basic principle of the transpiration method and yield vapor pressures consistent with the Knudsen effusion mass spectrometric method is described. The three systems investigated are CsI(s), TeO(2)(s), and Te(s), each known to vaporize congruently, but in different manner. A critical analysis was performed on the information available in the literature on transpiration measurements using thermogravimetric apparatuses, and the salient findings are discussed. Smaller plateau regions than with conventional transpiration apparatuses and the lack of evidence for perfect transpiration conditions in some transpiration thermogravimetric investigations are shown with a few examples. A recommendation is made for the use of the rate of mass loss versus flow rate plot to ascertain that the usual apparent vapor pressure versus flow rate plot corresponds to a meaningful transpiration experiment.

Vaporisation studies on tellurium dioxide: A Knudsen effusion mass spectrometric study

Abstract The vaporisation of TeO 2 (s) was studied by Knudsen effusion mass spectrometry. The vapour phase was found to consist of (TeO 2 ) n (n = 1−3)(g), (TeO) n (g) (n = 1−3) and Te 2 (g). The p − T relations of TeO 2 (g), (TeO 2 ) 2 (g) and (TeO 2 ) 3 (g) were derived to be log( p /Pa) = (−13534 ± 78)/ T + (14.241 ± 0.09) (750–950 K), log( p /Pa) = (−14823 ± 212)/T + (14.373 ± 0.242) (825–950 K) and log( p /Pa) = (−19074 ± 540)/ T + (17.337 ± 0.606) (850–921 K) respectively. From the partial pressures, Δ r H 298.15 0 of n TeO 2 (s) = (TeO 2 ) n (g) ( n = 1–3) were evaluated by second and third law methods. Also, enthalpy of the pressure independent reaction TeO 2 (s) + TeO 2 (g) = (TeO 2 ) 2 (g) has been evaluated. Using the Δ f H 298.15 0 of TeO 2 (s), Δ f H 298.15 0 of (Te0 2 ) n (g) ( n = 1–3) were calculated. The partial pressure and enthalpy data for (TeO 2 ) 3 (g) have been obtained for the first time.

Mass spectrometric studies on irradiated (U, Pu) mixed carbide fuel of FBTR

Mass spectrometry was employed to characterise the irradiated mixed carbide fuel of fast breeder test reactor (FBTR) for assessing its performance: thermal ionisation mass spectrometry to determine the isotopic composition, concentrations of U, Pu and Nd in the dissolver solutions and to deduce the burn-up, and a quadrupole mass spectrometric system to obtain the percentage release of fission gases (Kr + Xe). A summary and analysis of the results obtained with the fuel at 25,000 and 50,000 MWd/t in these studies is given in this paper.

A ternary phase diagram of the Mn-Te-O system at 950 K

A ternary phase diagram of the Mn-Te-O system at 950 K has been established in the composition range in and around the MnO-TeO 2 pseudo binary line. Various preparation methods were employed to confirm the co-existence of different ternary phases. The results of these phase equilibration studies were revalidated by the invariancy of partial pressures at constant temperature during high temperature mass spectrometric vaporization experiments. The following three-phase regions have been identified: MnO + Mn3O4 + Mn6Te 5O16 (phase region 1; PH1), Mn3O4 + Mn6Te 5O16 + MnTeO3 (phase region 2; PH2), Mn3O4 + MnTeO3 + Mn3TeO6 (phase region 3; PH3), and MnTeO3 + Mn2Te 3O8 + Mn3TeO6 (phase region 4; PH4). The complex nature of the Mn-Te-O ternary system was revealed by the interesting results obtained by us with regard to preparation of samples and mass spectrometric vaporization experiments.

Study of vaporization of sodium metaborate by transpiration thermogravimetry and Knudsen effusion mass spectrometry.

The vaporization of solid sodium metaborate NaBO(2)(s) was studied by transpiration thermogravimetry (TTG) and Knudsen effusion mass spectrometry (KEMS). The transpiration measurements, performed for the first time on NaBO(2)(s), involved use of argon as the carrier gas for vapor transport and derivation of vapor pressure of NaBO(2)(g) (by assuming it as the sole vapor species) through many flow-dependence runs and temperature-dependence runs in the temperature range 1075-1218 K. The KEMS measurements performed in the temperature range 1060-1185 K confirmed NaBO(2)(g) as the principal vapor species over NaBO(2)(s), in accord with the previously reported KEMS studies. The values of p(NaBO(2)) obtained by both TTG and KEMS are consistent within the uncertainties associated with each method and so are the second- and third-law values of enthalpy of sublimation, the latter aspect consistently missing in all previous vaporization studies. The results of both TTG and KEMS were combined to recommend the following thermodynamic parameters pertinent to the sublimation reaction, NaBO(2)(s) = NaBO(2)(g): Log{p(NaBO(2))/Pa} = -(17056 ± 441)/(T/K) + (14.73 ± 0.35) for the temperature range 1060-1218 K; Δ(r)H°(m)(298.15 K) = (346.3 ± 9.4) kJ·mol(-1); and Δ(r)S°(m)(298.15 K) = (210.2 ± 6.8) J·mol(-1)·K(-1).