Thermal Analysis of Solid Compounds Coupled with Mass Spectrometry of Gaseous Decomposition Products
Abstract Generated abstract
This paper describes a simple apparatus for coupling thermal analysis of solid compounds with mass spectrometric analysis of gaseous thermolysis products. The authors present a reaction vessel that functions as part of the mass spectrometer inlet system and can be used during either isothermal decomposition measurements or differential thermal analysis, with pressure monitoring and controlled heating. The design avoids some complications of sealed ampoules and ion source modifications, permits small gas samples to be taken without substantially disturbing kinetic measurements, and is reported to be reliable and sensitive in differential thermal analysis. Its operation is illustrated by ammonium perchlorate decomposition, including a thermogram and mass spectra of gases sampled at two stages.
Full Text
THERMAL ANALYSIS OF SOLID COMPOUNDS COUPLED WITH MASS SPECTROMETRY OF GASEOUS DECOMPOSITION PRODUCTS
R. N. Isaev, Yu. A. Zakharov, V. V. Bordachev
(Presented by the scientific seminar of the Department of Radiation Chemistry and the KhTT Laboratory)
Mass-spectrometric analysis carried out in the course of thermolysis of solids (in an isothermal or a nonisothermal regime of the latter) makes it possible to obtain diverse information on the specific features and mechanism of thermolysis. Depending on the tasks posed, devices are designed for systems of admission or introduction of the analyzed sample into the instrument.
A number of such devices have been described in the literature [1—4]; however, their use is often hampered by methodological complications. For example,
Fig. 1. Schematic of the setup for carrying out DTA or isothermal decomposition:
1, 2 — MChR-3 mercury manometer; 3 — Kamovsky pump; 4 — Bourdon manometer scale; 5 — stopcocks; 6 — Bourdon manometer; 7 — stopcock connecting the vessel with the ampoule system of the MX-1302; 8 — gate for lowering the weighed sample; 9 — cooling finger; 10 — suspension; 11 — cups for DTA; 12 — glass cup with the weighed sample; 13 — furnace; 14 — thermocouple; 15 — position regulator of the EPD-52 potentiometer; 16 — TRR relay; 17 — EPD-52 potentiometer.
the use of sealed-off ampoules containing the gas to be analyzed requires the creation of designs for opening them, filling them, and sealing them off, and at the same time does not permit continuous analysis of the products throughout the entire decomposition process. In works [2, 3], for introducing the sampl...
Table 1
Mass spectrum of gaseous decomposition products of \(\mathrm{NH_4ClO_4}\) in the DTA mode.
Ionizing voltage 70 V, emission current 2 mA
| m/e | Possible ions | Peak intensity, mV, I sampling | Peak intensity, mV, II sampling |
|---|---|---|---|
| 12 | \(\mathrm{C^+}\) | 46 | 30 |
| 14 | \(\mathrm{N^+}\) | 62 | 130 |
| 15 | \(\mathrm{N^{15+}}, \mathrm{NH^+}\) | — | 10 |
| 16 | \(\mathrm{O^+}, \mathrm{NH_2^+}\) | 111 | 190 |
| 17 | \(\mathrm{OH^+}, \mathrm{NH_3^+}\) | 12 | 21 |
| 18 | \(\mathrm{H_2O^+}\) | 45 | 70 |
| 28 | \(\mathrm{N_2^+}, \mathrm{CO^+}\) | 700 | 872 |
| 30 | \(\mathrm{NO^+}\) | 728 | 845 |
| 32 | \(\mathrm{O_2^+}\) | 415 | 1095 |
| 35 | \(\mathrm{Cl^+}\) | — | 145 |
| 36 | \(\mathrm{HCl^+}\) | — | 509 |
| 37 | \(\mathrm{Cl^{37+}}\) | — | 44 |
| 38 | \(\mathrm{HCl^{37+}}\) | — | 156 |
| 44 | \(\mathrm{CO_2^+}, \mathrm{H_2O^+}\) | 810 | 720 |
| 45 | \(\mathrm{C^{13}O_2^+}\) | 8 | 10 |
| 46 | \(\mathrm{NO_2^+}\) | 9 | 10 |
| 51 | \(\mathrm{ClO^+}\) | traces | — |
| 52 | \(\mathrm{HClO^+}\) | —»— | — |
| 53 | \(\mathrm{Cl^{37}O^+}\) | —»— | — |
| 70 | \(\mathrm{Cl_2^+}\) | 8 | 60 |
| 72 | \(\mathrm{Cl^{35}Cl^{37+}}\) | 5 | 39 |
| 74 | \(\mathrm{Cl_2^{37+}}\) | — | 10 |
…resorted to a design modification of the ion source, which is not always expedient.
We have assembled, and describe below, a very simple scheme that makes it possible to analyze thermolysis products in parallel with the study of the kinetics of isothermal decomposition or DTA of compounds. The reaction vessel, which at the same time is part of the inlet system, is shown schematically in Fig. 1. It is a cylindrical vessel made of molybdenum or quartz glass. Decomposition of the substance in the DTA mode or under isothermal heating is monitored, with an accuracy of 0.01 mm Hg, by the pressure of the evolved gases using a Bourdon membrane manometer (6), used here as a null instrument and operating with an MChR-3 high-precision mercury manometer (2). The use of a membrane manometer makes it possible to neglect the aggressive properties of the evolved gases, such as \(\mathrm{Cl_2}\), nitrogen oxides, etc.
Preliminary evacuation of the vessel (to a pressure of about \(10^{-3}\) mm Hg) is carried out with valve (7) open, using the pumping system of the MX1302 mass spectrometer. Thermostating of the vessel or linear temperature programming (in the DTA mode) is carried out by a massive furnace (13). Its operating mode is controlled by a thermostating system based on an EPD-52 regulating potentiometer (17), or is produced by a system for linear temperature programming of the Kurnakov pyrometer. The accuracy of temperature regulation in the isothermal-heating mode in the range 200–450°C is \(\pm 0.5^\circ\mathrm{C}\).
When isothermal decomposition is carried out, the weighed portion of substance is placed in cup (12), lowered by gate (8) into the previously heated part of the reaction vessel. When the cell is operated in the mode…
For DTA, the substance under study and the reference standard are placed in small cups sealed into the bottom of the vessel; the thermocouples are thereby separated from the samples by the thin glass bottom of the cups.
Gas samples for analysis are taken through valve (7) by filling one of the ampoules of the comb with the gas being analyzed; the comb is connected to the inlet system of the MX-1302 mass spectrometer [5]. Owing to the small volume of the samples taken, these operations do not interfere with the study of the kinetics of thermolysis.
The cell described was operated in both of the above modes and, while very simple to manufacture and operate, proved sufficiently reliable and sensitive in the DTA mode.
Fig. 2. Thermogram of ammonium perchlorate recorded at an initial pressure of \(2\cdot10^{-2}\) mm Hg
Figure 2 shows a thermogram of ammonium perchlorate recorded at an initial vacuum of \(2\cdot10^{-2}\) mm Hg and a sample heating rate of \(\simeq 10\) deg/min; points I and II denote gas sampling. The corresponding mass spectrum is given in Table 1.
REFERENCES
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- G. A. Heath, I. R. Majer. Trans. Farad. Soc. 60, No. 502, 783–91 (1964).
- A. M. Alekseev et al. Izv. Vuzov—Khimiya i khim. tekhnologiya, 9, No. 4, 604–608 (1966).
- R. S. Gohlke, H. G. Langer, Anal. Chem., 37, No. 10, 25A–28A (1965).
- Ya. A. Yukhvidin. Zavodskaya laboratoriya, No. 1, 35 (1957).
ERRATA NOTED
| Page | Line | Printed | Should read |
|---|---|---|---|
| 4 | Table 4 | Splitting | Splitting, gauss |
| 8 | Fig. 2 | 1000 Å | 10000 Å |
| 19 | 1st from bottom | V. M. Likhin DaN SSSR |
V. M. Lykhin DAN SSSR |
| 22 | 24 from top | \(O^{-}=\square+2e+1/2O_2\) | \(O^{-}=\square^{-}+e+1/2O_2\) |
| 23 | 13 from top | Due to electrons | Due to capture of electrons |
| 23 | 16 from top | Crystals constant | Crystals constant |
| 28 | 7 from bottom | \(A^{-}A \rightleftarrows {}^{0}_{\tau}+e^{-}\) | \(A^{-}\rightleftarrows A_{\tau}^{0}+e^{-}\) |
| 36 | 12 from bottom | Zoumeine | Roumeine |
| 40 | 3 from top | at the exit | at the entrance |
| 44 | 5 from bottom | (II) | (I) |
| 47 | 3 from top | and surrounding | into surrounding |
| 51 | Table 1 | \(NH^{3}+\) | \(NH_3+\) |
| 51 | Table 1 | \(HCl_{37}+\) | \(HCl^{37}+\) |
| 54 | Fig. 2 | \(t\) (sec) | \(\lg t\) (sec) |
| 64 | 5 from top | in crystals makes it possible to obtain with a controlled magnitude of the surface |
in crystals with a controlled magnitude of surface makes it possible to obtain |
| 69 | 8 from top and 13 from bottom |
PP–Sh | PP–III |
| 70 | Table 1 | \(0.99+1.06\cdot 10^{13}\) | \(0.99+1.06\cdot 10^{13}\) |
| 70 | 3 and 6 from bottom | A. D. Uobbe D. A. Zakharov |
A. D. Yoffe Yu. A. Zakharov |
| 71 | authors | \(0.5\%\) | \(0.05\%\) |
| 71 | 7 from bottom | \(\lg \sigma\) | |
| 74 | caption under Fig. 4 | \(N_3^{--}\rightsquigarrow^{\lg \delta} N_3^{0}+1\) | \(N_3^{-}\rightsquigarrow^{\lg \sigma_{\gamma}} N_3^{0}+e\) |
| 77 | caption under Figs. 1 and 2 | HO | \(H_0\) |
| 79 | 5 and 6 from top | ClO | \(ClO_3^{-}\) |
| 81 | 17 from bottom | \(Cl_4^{--}\rightsquigarrow Cl_4,1,[ClO_4^{-}]^{*}\) | \(ClO_4^{-}\rightsquigarrow ClO_4,e,[ClO_4^{-}]^{*}\) |
| 88 | 8 from top | % 1168 | No. 1168 |
| 91 | 2 from bottom | \(NH_3\) | \({}^{15}NH_3\) |
| 91 | 11 from bottom | \(I_{18}\) \({}^{14}N_{15}N^{+},{}^{12}C^{16}O^{+}\) |
\(I_{18}\) \({}^{12}C^{16}O^{+},{}^{14}N^{15}N^{+}\) |
| 111. | 1 from bottom | Kadelatsy | Kadenatsi |
| 126 | 7 from top | Kj | Kl |
| 128 | 1 from bottom | \(G=g+J\) | \(G=g+\gamma\) |
| 132 | 11 from top | \(V\) | \(V_k\) |
| 146 | 5 from bottom | spectrometry | spectroscopy |