Andersen, E.B.

Fenger, J.

The construction and performance of a thermostat of the "Gas-Stream" type are described. It was developed for Mossbauer measurements, but can equally well be used in connection with other types of spectrometrv. In the present form it has been used in the temperature range -150 - +250°C, with a regulating sensitivity of ±0.5°C

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Downloaded from orbit.dtu.dk on: Dec 19, 2017A simple thermostat based on a temperature-regulated gas streamForskningscenter Risø, Roskilde; Fenger, J.Publication date:1974Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Andersen, E. B., & Fenger, J. (1974). A simple thermostat based on a temperature-regulated gas stream.  (Risø-M; No. 1694).Riso-M - 1*94 Danish Atomic Energy Commission 5 Research Establishment Riso '-O & CHEMISTRY DEPARTMENT A Simple Thermostat Based on a Tempera ture- regula ted Gas Stream by E.B. Andersen and J. Fenger March 1974 Available on request from: Library of the Danish Atomic Energy Commission {Atomenergikommissionens Bibliotek), Riso, DK-4000 Roskilde, Denmark, Telephont: (03) 355101, telex: 1072 A. E. K.Risø Risø-M-QE Title and author(s) A Simple Thermostat Based on a Temperature-regulated Gas Stream by E.B. Andersen and J. Fenger 6 pages -\- 0 tables -f- 2 illustrations Date March 197H Department or group Chemistry Department Group's own registration number(s) Abstract The construction and performance of a ther-mostat of the "Gas-Stream" type are described. It was developed for Mossbauer measurements, but can equally well be used in connection with other types of spectrometrv. In the present form it has been used in the temperature range -150 - +250 C, with a regulating sensitivity of ±0.5°C. Copies to Library 10 0 Standard distribution Abstract to Available on request from the Library of the Danish Atomic Energy Commission (Atomenergikommissionens Bibliotek), Risø, Roskilde, Denmark. Telephone; (03) 35 51 01, ext. 334, telex; 5072. Introduction Cryostats for use in Mossbauer spectrometry, [e.g. 1 j can roughly be divided into two types: In 'Cold-finger cryostats' a heat-conducting rod connects the sample holder with a cold reservoir, e.g. a bath of liquid nitrogen; the temperature can be regulated with an electrical heater placed near the sample, [e.g. 2]. This type of cryostat is easy to build and it has a low consumption of nitrogen; the temperature stability can in advanced versions,[e.g. 3] be ±0.1 C. On the other hand it it not well suited for work in ""arge temperature ranges extending above room temperature. In 'Gas cryostats' the sample holder is in thermal contact with a temperature-regulated gas. Different temperatures can be obtained by various means, e.g. by mixing two gases of differ-ent temperatures [ 4 ] or by heating a cold gas appropriately. 'Gas cryostats' are generally more complicated and expensive than 'cold-finger cryostats', but they are well suited in ex-periments which require measurements both at low and high tem-peratures in an unchanged geometry. The present report describes the construction of a cryo-thermostat based on the gas-stream principle. It was intended for determinations of formal Debye temperatures in the mineral arfvedsonite [5]; this determined the temperature range -150 -+250 C, which can, however, easily be extended by minor modi-fications. In the design mechanical stability has been stressed more than accuracy in the temperature regulation. Although the set-up was built for Mossbauer measurements, it may also be used in other types of spectroscopy. Design The principle in the cryo-thermostat is shown in fig. 1. A cold nitrogen gas is produced by boiling of liquid nitrogen in a 5 0 1 Dewar vessel (Siegtal type TS50), in which is immersed a heater made from five 20 £2/4 W resistors in serier. To protect against over-pressure the Dewar vessel is equipped with a safety valve. The cold nitrogen gas is passed through an insulated quartz tube wit; a hea^r coil In :•! der to give the desired temperature. A safetv switch., activated by a thermocouple, protects against overheating in case of failure in the temperature regulation; this heating system (Varian type V-4547) was borrowed from an ESR-spectrometer. The gas is then led to a T-tube, which on one branch has a modified Edwards union for introducing a platinum resistance thermometer (Degussa type P7, 100 3 at 0 C). The other branch goes to the sample holder. The resistance thermometer, connected in series with a variable resistor (10 turns, 100 \ l ) , forms one branch in a Wheatstone bridge, the other three branches being 220 Q pre-cision resistors. The error signal is passed through a polarity-sensitive amplifier and used to trigger a relay which 'on-off regulates the voltage to the transformer in the heating system. The resistance of the resistance thermometer varies between about 40 Q at -150°C and about 200 £2 at +250°C; a desired tem-perature is obtained by adjusting the variable resistor to a value which makes the total resistance in the regulating branch of the bridge 22 0 Q. The accuracy of the temperature regulation of the gas stream Is essentially determined by two factors: (1) the temperature dependence of the resistance thermometer, (2) the sensitivity of the amplifier and the relay. The resist-ance of the thermometer increases by the order of 0.4 Q per deg. C; the sensitivity of the detecting system was determined at fixed temperatures, by varying the variable resistor, to be about 0.2 Q; therefore the sensitivity of the regulating system itself is about 0.5 deg. C. A vacuum insulating chamber made of brass with a sample holder for Mossbauer absorbers is shown in fig. 2. The sample is a thin powder layer clamped in a perspex box; it is placed in the middle of a thick-walled brass tube around which is wound a cobber tube (i.d. 4 mm; o.d. 6 mm). Through this tube the ther-mostat ed nitrogen gas is passed; in order to allow transmission of the radiation through the vacuum chamber, this is furnished with two 50 u mylar windows. The temperature is monitored with a thermocouple. Performance The temperature range which can be covered by the set-up is in the lower end determined by the quality of the insulation. Be-cause of the relatively high Debye temperature of the sample [5] verv low temperatures were not essential. With a primitive in-sulation oartly made of available vacuum tubes, partly of rubber from hoses (Armaflex) temperatures down to -150 C could be ob-tained with a liquid-nitrogen consumption of about 100 1/d. At -100 C the nitrogen consumption is about 2 0 1/d. The electrical effect necessary to evaporate these amounts is ?50 and 50 watts respectively; it can be adjusted via the voltage over the heater in the Dewar. For temperatures above room temperature, the cold nitrogen stream can be replaced by pressurized atmospheric air; a limit to the temperature which can be obtained is only set by the capacity of the heater and the stability of materials used in the construction. Surprisingly the perspex box containing the sample could, under the experimental conditions, stand temper-atures up to 250 C; this corresponds to a heater effect of about 30 watts, with a flow of about 10 1/min. References 1) M. Benczer-Koller and R.H. Herber. In: Chemical Applica-tions of Mcssbauer Spectroscopy. Edited by V.I. Goldanskii and R.H. Herber (Academic Press, New York, 1968) 134-158. 2) L.A. Frees and J. Fenger, A Simple Mossbauer Cryostat Based on the "Cold-Finger" Principle. Risø-M-1662 (1973) 8 pp. 3) F. van der Woude and G. Boom, Precision (0.1 C) Vacuum Cryostat and Furnace for Mossbauer Experiments. Rev. Sci. Instrum. 3JL (1965) 800-802. 4) J. Fenger, A Temperature Regulating System for Use with an Electron Spin Resonance Spectrometer. J. Sci. Instrum. 4_2_ (1965) 904-905. 5) K.B. Andersen, J. Fenger, and J. Rose-Hansen, Determination of Fe2+/Fe3+-Ratios in Arfvedsonite by Mossbauer Spec-troscopy, to be published. - S -15V = POWER 220V~ GALVAN-OMETER JF REFERENCE JUNCTION SAFETY VALVE Fig. 1. Simplified diagram of the temperature regulat ing and measuring system. The various par ts are not drawn to sca le . GAS OUTLET VELOCITY DRIVE AND SOURCE MYLAR T WINDOW- rsi SAMPLE HOLDER GAS INLET RESISTANCE THERMOMETER ; COUNTER \ THERMOCOUPLE TO VACUUM PUMP - 4 — • — + - -4—4—I I—I-0 1 2 3 4 5 6 7 8 9 10 cm Fig. 2. A cut through a vacuum chamber with sample holde signed for Mossbauer measurements. Typical positions of c source and counter are drawn in dashed line. Collimators, mechanical supports, etc. are omitted. ISBN 87 550 0245 3 

A simple thermostat based on a temperature-regulated gas stream

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A simple thermostat based on a temperature-regulated gas stream

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