Thermogravimetric Apparatus
Thermogravimetric Apparatus
E. Robens, K.K. Unger
Institute for Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg University, Duisbergweg 10-14, D – 55099 Mainz, Germany
Abstract
Thermogravimetric apparatus today are equipped with electromagnetic balances and in one case with a magnetic suspension balance. Sometimes vacuum aggregates are appended with gas supply for protecting gases. Automatic sample changers are optional. The survey covers composited thermogravimetric apparatus and thermobalances as its essential part. Instruments and manufacturers are compiled in tables.
In 1984 and 1987 we published a survey on vacuum microbalances and thermogravimetric apparatus [1,2,3]. Since that time this measuring technique was developed to a commonly used standard analytical method widely used in industrial and scientific laboratories. Only modest development could be observed in balance construction but handling of the apparatus was remarkably facilitated and the evaluation of results by means of computers in real time improved. Some companies stopped producing thermogravimetric apparatus and thermobalances whereas new ones begun with new designs. So it seems useful to present a renewed survey in order to facilitate the choice f the apparatus.
2. Historical remarks
Balances were used already in Old Egypt and other Mediterranean countries to proportion of the components of alloys [4]. First Marcus Vitruvius Pollio [5] reports on a gravimetric observation of a chemical reaction about 27 BC: "Whatever weight the limestone possessed when it is thrown into the kiln, it cannot answer to that when it is taken out; but when it is weighed, the bulk remaining the same, it is found to lose about one third of its weight" [6].
The history of chemical balances has been written in the ample work of Jenemann [7,8,9] and also the history of electromagnetic compensation [10,11]. Concerning microbalances we dispose on the detailed reviews of Emich [12], Gorbach [13] Cunningham [14] and Behrndt [15]. The history of
thermogravimetry and thermobalances we find in Duval\’s book [16] and ones by Iwata [17] and Keattch [18,19] and tabular surveys by Eyraud, Robens and Rochas [20,21,22]. The invention of thermogravimetry, however, must be antedated, as discovered by Eyraud [23,24,25]. In 1833 Talabot at Lyon equipped a laboratory with thermobalances for quality control of Chinese silk. 1895 Angström constructed a microbalance with electromagnetic compensation. The first thermogravimetric assembly seems to have been described by Nernst and Riesenfeld in 1903: a quartz balance with electric oven. In 1915 Honda was the first to use the expression "thermobalance" for his instrument [26,27]. Soon afterwards such instruments were used to investigate the metabolism of plants. Further developments on thermogravimetry were made in particular in France by Guichard, Dubois, Chevenard and Duval and also in Japan. The first vacuum microbalance both of spring and beam type, already with electromagnetic compensation, was made 1912 by Emich [28]. Later, MacBain and Bakr [29] reported on a series of sorption measurements by means of coil spring balances. In 1953 the company A.R.A.M. brought C. and I. Eyrauds electrodynamic recording balance on the market. In 1953 de Kaiser developed the differential thermogravimetric method. The most progressive concept for mass determination in vacuo is realised using electromagnetic suspension of the sample, the balance being outside the sample vessel.
Another line of development was started as a consequence of the application of gravimetry to sorption measurements. A prerequisite for such measurements was the development of sensitive microbalances, the first one attributed to Warburg and Ihmori in 1886 (Figure 9.14). Petterson published very sensitive observations of adsorption in 1914 further important developments were made by Rhodin, Gulbransen, McBain and Bakr, Gregg and Wintle, Cahn and Gast. One of the most essential steps forward in this development was the introduction of vacuum, which affected the construction of the balances.
3. Thermobalances
Today the balances built into commercial thermogravimetric instruments are electromagnetically compensating beam microbalances with sensitivity down to the nanogram range. Deflection sensors operate either according to a photoelectric or an electromagnetic method. Self constructed helical quartz spring balances are found occasionally in labortories. They are cheap and favourable in corrosive atmosphere. Advantageous, but expensive, is the magnetic suspension balance where the sample is freely suspended without connection to the measuring system and thus, can be placed in a separated vessel. For special tasks oscillating mass sensors are used: quartz crystal oscillator, vibrating band or tapered element. Such instruments are favourably used in corrosive environment and also in the gravittion-free space.
Thermobalances are usually designed for maximum loads beween 1 mg and 500 g. The relative sensitivity amounts to 10-8, and that for spring balances and other types whcih do not take advantage of mass difference measurements in the gravitatinal field is 10-5. Thermobalances are available for ultrahigh vacuum as well as for pressures up to 500 bar. Sample temperatures down to 4 K have been realised, using a liquid helium cryostat and temperatures up to 3000 K using resistance heaters with temperature transmission by radiation or by induction heating of the pan or the sample, respectively. Programmed temperature increase is typically between zero and about 0,5 K s-1, in scanning experiments up to 105 k s-1.
Table 1. Manufacturer of thermobalances
manufacturer
V
T
S
M
Beckman Instruments, Fullerton, CA 82834, USA
·
Cahn Instruments, 16207 South Carmenita Rd., Cerritos, CA 90701 USA
·
·
CI Electronics Ltd. Brunel Rd. Churchfields Salisbury, Wilts. SP2 7PX, U.K.
·
·
Linseis GmbH, Viellitzer Str. 43, 95100 Selb
·
Mettler-Toledo AG, CH-8606 Greifensee, Switzerland
·
·
Perkin-Elmer, 761 Main Ave, Norwalk CT 06859-0012, USA
·
·
Rheometric Scientific, Surrey Business Park, Weston rd. Kiln Lane, Epson, Surrey KT 17 1JF, U.K.
·
Rubotherm, Universitätsstr. 142, D-44799 Bochum, Germany
·
SETARAM, 7 rue de l’Oratoire, F-69300 Caluire, France
·
·
Sartorius AG, D-37070 Göttingen, Germany
·
TA Instruments, 109 Lukens Drive, New Castle, DE 19720-2795, USA
·
V = vacuum balance, T = thermo balance, S = suspension balance, M = micro balance
4. Thermogravimetric instruments
With thermogravimetric techniques the desorption is measured of volatile species set free from the solid sample at increasing temperature. Sometimes this process is performed in vacuum but mostly in air or in a protecting gas. In each case the partial pressure of the vaproising component is low. In other words: desorption isobars are measured at low pressure. The mass curve as a function of time or temperature gives a characteristic "fingerprint" of the material. Meanwhile data banks are available for identification of materials by comparison with typical curves. Attempts to calculate from the thermogram the surface and pore structure, however, failed [30]. Often thermogravimetric analysis (TGA) is combined with differential thermal analysis (DTA). In principle TGA apparatus could be used also for the measurement of sorption isotherms when equipped in addition with vacuum pumps, thermostats or cryostats, respectively. Constructive details, however, make conversions difficult.
Table 2. Manufacturers of thermogravimetric instruments
manufacturer
balance
Bähr Thermoanalyse, Altendorfstr. 12, D-32609 Hüllhorst, Germany
Bähr
Beckman Instruments, Fullerton, CA 82834, USA
Beckman
Cahn Instruments, 16207 South Carmenita Rd., Cerritos, CA 90701, USA
Cahn
Linseis GmbH, Viellitzer Str. 43, D-95100 Selb
Linseis
MC2 Thermal Systems, 667 Pinewood Ave., Troy, NY 12180, USA
Mettler-Toledo AG, CH-8606 Greifensee, Switzerland
Mettler
Netzsch Gerätebau, Wittelsbacher Str. 42, D-95100 Selb, Germany
Perkin-Elmer, 761 Main Ave, Norwalk CT 06859-0012, USA
Perkin-Elmer
Rheometric Scientific, Surrey Business Park, Weston rd. Kiln Lane,
Epson, Surrey KT 17 1JF, U.K.
Rheometric Scientific
Rigaku, Segawa Bldg., 2-8 Kandasurukadai, Chiyoda-ku, Tokyo, Japan
Rigaku
Seiko, Oyama Plant, Japan
Seiko
SETARAM, 7 rue de l\’Oratoire, F-69300 Caluire, France
Setaram
Shimadzu Corporation, 3 Kanda-Nishikicho 1-chome, Chiyoda-ku, Tokyo 101, Japan
Shimadzu
Stanton Redcroft, Copper Mill Lane, London SW17 OBN, U.K.
CI
TA Instruments, 109 Lukens Drive, New Castle, DE 19720-2795, USA
TA Instruments
5. Future aspects
The state of the art of thermobalances seems to have reached a high end level [31] and only some progress in electronic components is observed. It is, however, possible to read conventional balances much faster [32,33,34]. Developments are centered on handling (sample changer, automatic operation) and on evaluation by means of computers and print out of results in real time. On the one hand scanning methods are developed in order to resolve fast reactions, on the other hand by means of very low, quasi-isothermal measurements thertmodynamic parameters can be determined. Thus, the potentialities of the method are by far not exhausted.
References
1. M. Escoubes, C. Eyraud, E. Robens: Vacuum microbalances and thermogravimetric apparatus. Part I: Commercially available instruments. Thermochimica Acta 82 (1984) 1, 15-22.
2. E. Robens, C. Eyraud, M. Escoubes: Vacuum microbalances and thermogravimetric apparatus. Part II: Types of recording instruments. Thermochimica Acta 82 (1984) 1, 23-41.
3. C. Eyraud, M. Escoubes, E. Robens: Thermogravimétrie. Techniques de l\’ingénieur (1987) 7, P 1 260-1 - 10.
4. James, T.G.H.: An Introduction to Ancient Egypt. Revised ed., British Museum 1979, p. 221.
5. Marcus Vitruvius Pollio: De Architectura II v.3.
6. Mackenzie, R.C., Thermochimica Acta 75 (1984) 251-306.
7. Jenemann, H.R.: Die Entwicklung der mechanischen Präzisionswaage. In: Kochsiek, M. (ed.).: Handbuch des Wägens, 2. ed. Vieweg, Braunschweig 1985, p. 547-587.
8. Jenemann, H.R.: The Development of the Determination of Mass. In: M. Gläser, M. Kochsiek (eds.): Comprehensive Mass Metrology, Wiley-VCH, Berlin 2000., p. 119-163.
9. Jenemann, H.R.: Die Waage des Chemikers - The Chemist\’s Balance. Translated in English by A. Basedow DECHEMA, Frankfurt am Main 1997.
10. Jenemann, H.R.: Die frühe Geschichte der Waagen mit elektromagnetischer und elektrodynamischer Kraftkompensation. "Wägen und Dosieren" 26 (1995), 12-18.
11. Jenemann, H.R.: The early history of balances based on electromagnetic or electrodynamic force compensation. In: L Grossi (ed.): La massa e la sua misura - Mass and its Measurement - Proceedings of International Congress; Modena (Italy), 15 - 17 September 1993. CLUEB, Bologna 1995, p. 9-20.
12. Emich, F.: Einrichtung und Gebrauch der zu chemischen Zwecken verwendbaren Mikrowaagen. In: E. Abderhalden (ed.): Handbuch der biochemischen Arbeitsmethoden, Bd. 9, Urban & Schwarzenberg, Berlin 1919, pp. 55-147.
13. Gorbach, G., Mikrochemie, N.F. 14 (1936) 254.
14. Cunningham, B.B., Nucleonics 5 (1949) 62.
15. Behrndt, K.H.: Die Mikrowaagen in ihrer Entwicklung seit 1886. Z. angew. Phys. 8 (1956) 9, 453 - 472.
16. Duval, C.: Inorganic Thermogravimetric Analysis. 2. ed., Elsevier Amsterdam 1963, S. 3 - 24.
17. Iwata, S.: Über die Entwicklung der Thermowaage, besonders in Japan. Vortrag am Chemischen Institut der Universität Bonn, 6. Juni 1961.
18. Keattch, C.J.: The History and Development of Thermogravimetry. Thesis, Salford (U.K.) 1977.
19. Keattch, C.: An Introduction to Thermogravimetry, Heyden/Sadtler, London 1969.
20. C. Eyraud, E. Robens, P. Rochas: Some comments on the history of thermogravimetry. Thermochimica Acta 160 (1990) 25-28.
21. E. Robens, C. Eyraud, P. Rochas: Some comments on the history of vacuum microbalance techniques. Thermochimica Acta 235 (1994) 135-144.
22. W.-D. Emmerich, R.C. Mackenzie, W. Hemminger, C.J. Keattch, H.R.Jenemann: Comments on the papers: "Some comments on the history of vacuum microbalance techniques" and "Some comments on the history of thermogravimetry" by C. Eyraud, E. Robens, P. Rochas. Thermochimica Acta 254 (1995) 391-392.
23. Eyraud, C., Rochas, P.: La thermogravimétrie à la condition des soies de Lyon, une aventure méconnue. Vortrag zur "International Microbalance Techniques Conference", 20. April 1987, Rabat. Thermochimica Acta (1990).
24. Eyraud, C., Rochas, P.: Thermogravimetry and Silk Conditioning in Lyons. A Little Known Story. Thermochimica Acta 152 (1989) 1-7.
25. Hemminger, W., Schönborn, K.-H.: A Nineteenth Century Thermobalance. Thermochimica Acta 39 (1980) 321-323.
26. Honda, K., Science Reports of the Tôhoku Imperial University, Sendai Series I, 4 (1915) 97-105, 2610.
27. Honda, K., Kinzoku no Kenkyu 1 (1924) 543.
28. Emich, F.: Ein Beitrag zur quantitativen Mikroanalyse. Monatshefte für Chemie 36 (1915) 404-440.
29. McBain, J.W., Bakr, A.M., J. Am. Chem. Soc. 48 (1926) 690-695.
30. J. Goworek, W.Stefaniak: The investigations of the porous structure of solids by thermogravimetric analysis. Thermochimica Acta 1994.
31. Th. Gast, T. Brokate, E. Robens: Vacuum Weighing. In: M. Gläser, M. Kochsiek (eds.): Comprehensive Mass Metrology. Wiley-VCH, Weinheim 2000, p. 296-399.
32. C.H. Massen, C.H.W. Swüste, E. Robens, J.A. Poulis: Computer simulation of balance handling. Journal of Thermal Analysis and Calorimetry 55 (1999) 2, 367-370.
33. C.H. Massen, C.H.W. Swüste, E. Robens, J.A. Poulis: Optimizing of balances of the second generation. Journal of Thermal Analysis and Calorimetry 55 (1999) 2, 449-454. ISSN 1418-2874.
34. C.H. Massen, J.A. Poulis, E. Robens, R. Roverato: Method for subsecond mass determination with a conventional balance. 6th International Workshop on Subsecond Thermophysics, Leoben, Austria, September 26-28, 2001. International Journal of Thermophysics (2002) in the print.
Related articles::