Topics in..
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Chemical Instrumentation Edited by GALEN W. EWING, Seton Hall University, So. Orange, N. 1.07079
These articles are intended to serve the reodets of THIS JOURNAL by calling attentim to new developments in the theory, design, or availability of chemical laboratory instrumenlalion, or by presenting useful insights and ezplanations of topics that are of praclical importance lo lhose who use, or teach the use of, m o h instrumentatim and instrumental techniques. The editor invites correspondence from prospective cmlributors.
LXVII. Thermal Analysis Techniques: Part I. Thermobalances W. W. Wendlandt. De~ortmentof Chemistry, University of Houston, Houston, Texos 77004' Introduction
The fint thern,obala~>cewas prohahly the instrument described by Honda (1) in 1915. This instrument, as shown in Figure 1, consisted of a balance with a quartz beam. The bample was placed in a porcelain or magnesia crucible, G, which was suspended in an electrically heated furnace, J. At,taehed t o the opposite end of the balance beam was a. thin steel wire helix, E, which was immersed in oil contained in a Dewar flask, H. The Dewar flask-helix assembly was adjusted by a screw mechanism to maintain the balance beam in a null position. A rather slow heating rate was employed as it took 10-14 hr t o attain a temperature of 1000°C. However, Handa used a quasiisothermal heating cycle in that during a mass-lass transition, the furnace was maintained s t a constant temperature until the transition was completed. This procedure alone sometimes required 1 4 hr. Convection currents were evident above 300aC, as might be expected from the furnace-sample ssrangement. A sample
ngurc 1. Hondo ( 1 ) .
The thermobdonce as dercribed by
mass of about 0.6 g was normally employed. The TG curve of MnS04.4H*0, as determined bv Honds, (1). is shown in Figure 2. ~"eh~dration' tbok in two steps; the fimt three moles of water were evolved in the 70-110°C range, while the fourth mole came off at 230-260°C. Anhydrous MnSO, hegau to decompose to Mn30, starting a t about E20"C. Honda could also determine the rate of mass-loss a t various temperatures in grams per hour. The work of Honda. did indeed lay the foundation for practically all of the future work in thermogravimetry. His thermabalance enabled the investigator to continuously weigh the sample as it was heated and employed the feature of quasiisothermal heating. The latter technique cannot he carried out automatically by p m n t - d a y thermohalances. He modestly concludes his paper by saying, "All of the results above given are not altogether original; the present investigation with the thermohalance has however revealed the exact positions of the change in structure ilnd also the velocity of the change in respective temperatures. The investigation also shows the great convenience of using such a balance in similar investigations in chemistry." Numerous other Japanme workers modified the Honde. thermohalmee and also developed new instruments. The results of their studies have been summarized in a monograph by Saito (3). The French school of thermogravimetry was started by Guichard ( 5 ) in 1923. He apparently was unaware of Honda's work but then he never claimed to be the d i e coverer of thermogrwimetry. He improved the technique, brought it t o a high state of development for that time, and critically examined each phase of it. His original thermobalance (4) contained 8. garfired furnace in which gas wss metered to the burner via a collstant level device
Dr. Wesley W. Wendlandt is a native of La Crosse, Wisconsin. He attended and graduated from high school in La Crosse, Wisconsin, in 1945; he received the B.S. degree in chemistry and mathematics a t Wisconsin State University (River Falls) in 1950; and his M.S. and Ph.D. degrees in inorganic and analytical chemistry from the University of Iowa in 1952 and 1954, respectively. He was on the f ~ c u l t ya t Texas Technological College from 1954 to 1966; Chairman of the Department at the University of Houston from 1966 to 1972; and Professor of Chemistry at the latter institution since 1972. The iummers of 1954 and 1955 were spent nt the Argonne National Laboratory md he was Visiting Professor at New Mexico Highlands University during thesummer of 1961. He is the founder and Editor-in-Chief if Thermochirnica Aeta and is on the Editorial Boilrds of the Journal of Z'hwmal Analysis and the Chemical Series of John Wiley-Intersoience. In 1970, he received the Mettler Award in iynamic t h a m a l analysis. He has ,uhliihed 220 research papers, 22 book :hapters, and 5 hooks. His research nterests are in thermal analysis, .eflectance spectroscopy, analytical instrumentation, and the thermal proper;ies of coordination compounds. Dr. Wendlandt is a member of the lmerican Chemical Society, the :hernial Society (London), Internaional Confederation of Thermal Analy;is, North American Thermal Analysis h i e t y , Sigma Xi, Phi Lambda Spsilon, Alpha Chi Sigma, and is a ellow of the AAAS. consisting of a. valve with an attached float on it. The float rested on the surface of a tank filled with water. This water drained into snothe? container via an adjustable valve, thus causing a slow but gradual opening of the gas metering valve and hence, increasing the furnace temperature. Equally interesting is the manner in which the weight-change of the sample was detected by the balance. (Continued on page A676)
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Chemical Instrumentation This was achieved with a hydrostatic device in which small amounts of oil were added to a "U" tube t o exactly compensate for the weight change. A loss of mass of 100 mg corresponded t,o the addition of 9 ml of oil. Mass-loss curves recorded on this balance agreed well with the r e sults obtained by D u v d (5) some 40 years later. Guichard's work wa? followed by the investigations of Vallet (6), Dubois (7), and others (5). Perhaps the greatest impetus to the French school of thermogravimetry was due to the development of the Chevenard (8) recording thermobalance. This balance was under development since 1936 and became commereidly available in 1945; i t was the first automatic (photographically) recording instrnment. In the hands of Duval and co-workers (5, 9),it became the standard instrument for work in this field. This thermobalance will be described in s later section. Two other important milestones in the development of the modern thermobalance occurred in 1958 and 1964, respectively. Amultifunct,ionalinstmment, called the Derivatograph, was described by Paulik (ll), et al. in 1958. Not only could the T G curve be recorded but also its first derivative (DTG), and the differential thermal analysis (DTA) curve. I n 1964, Weidemann (1%) described the Mettler system, which is perhaps the most sophisticated thermobalance available today. Both instruments will he described later on in this review. Duval (5) stated that no less than fifty thermobalances had been described by 1961, and that ten of these were commercially available. Msny of these instruments have been descrihed in a. comprehensive review by Gordon and Campbell (10) in 1960. Modern thermohalancs have been descrihed by Duvd (5, !I Wendlmdt ), (IS), Keattch (14), and others (16, Ifi), while reviews of com-
mercisl instruments have been given by Wendlandt (17.18).. At the mesent time rhcrc ire alroltt eiphtwrt msnufnvtwrr\ and or di5trihutor- of rornmercnl thermubalances.
.
The Modern Thermobalance The thermohdance is an instrument which permits the continuous weighing of a sample as a function of temperature. The sample may he heated or cooled although the former is the usual mode of operation. The mass-change curve (usually mass-loss) so obtained is useful for the evaluation of the sample thermal stability, the stability and composition of the intermediate compounds formed (if any), and the composition of the residue. This technique finds wide application in all of the fields of chemistry and in many of the other sciences as well. A schematic diagram of the modern thermobalance is shown in Figure 3. I t consists basically of the following components: (a) recording balance; ( b ) furnace; (c) sample holder and temperature detector; (d) furnace temperature programmer; and ( e ) recording system. Each component of the thermoh&nce has been discussed in detail in well known text hooks (5, 13, 15, 16) and elsewhere (10, IS, 17). The furnace and/or sample t,empemture is generally detected with a thermocouple although a resistive element may also be employed. In most cases the temperature detector is not in contact wibh the sample and this can create problems in reaction kinetics or other studies where s knowledge of the exact sample temperature is necessary. The location of this detector thus becomes an important factor. A large number of recording ha.llsnees have been described (10) hut as far as commercial thermobalauces are concerned, about onehalf of them now use one model of the Cahn Electrobdances (19). These halances were accepted because they are accurate and reproducible yet inexpensive enough for general use. They are based upon a null-balance principle in which the bdance beam displaoement is detected by
Figure 3. Schematic diogram of lbsrmobdense system.
o modem
a light beam-shutter-photocell arrangement and the restoring force is by a. magnetic torque motor. Other balance mechanisms include helix and beam deflection types in which displacements are detected by linear voltage differential transformers (LVDT) or other transducers. Individual recording balances will be discussed with each commercial instrument. The furnace temperature ranges vary over wide limits with the usual maximum temperature limit of 1000 or 1200°C. However, furnaces with a maximum temperature of 1600 or 2400°C are also available. Provision is also made in each of t,he furnace arrangements to maintain a controlled atmosphere around the sample holder. A choice of either flowing (dynamic) or static gaseous atmospheres can usually be made a t pressures from atmospheric t o tom. The gases normally employed are the inert types such as Na, AT, He, 01, COX, and so on although corrosive gases can he used in some thermahdsnees. The choice of sample holders depends upon the sample under investigation and the maximum temperature draired. The usud geometrical configuration is s small crucible or cup but platelike or multi-phte holders are also employed. Materials of construction include platinum, Inconel, aluminum, quartz, graphite, dumina, and so on. Recording systems unua.lly consist of a. two or more channel strip-chart potentiometric or X-Y recorder. The former is perhaps more useful because it also permits an evaluation of the linearity of the furnace heating rate since furnace temperature is always plotted as well as the mass-change curve. There have been many thermobalances described in the Literature. Each instrument varies somewhat in the type of massdetection transducer, recording balance, sample holder configuration, and furnace arrangement. I t is beyond the scope of this review to discuss the features of each of these instruments. However, as a. look into the future of TG instrumentst,ion, the automated instrument of Bradley and Wendlandt (SO, $1) should be mentioned.
Commercial Thermobalances
10V
Figure 2.
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roo
xxr
TG curve of MnS01.4Hz0 Ill.
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am
rm
wa
Morr of rample.0.629 g.
Journal o f Chemicol Education
x*,
,m
z ,
mrl.
Commercial thermobalances fall into two categories, depending upon the type of recording balance employed. They are: (a) Cahn-type thermohalanees, which employ one of the Cahn Eleetmbalances; ( C o n h u e d on page A5741
Chemical lns~umentation and (b) non-Cnho balance type instnlments. I n most cases s modular approach is used in the instrumentation, in that the thermobalance is hot one module in the thermal analysis system. A central recording system, bemperatnre programmer, and other controls are common t o all of the modoles, which may include differential thermal analysis (DTA), differential scanning calorimetry (DSC), dilatometry, and so on. The Cahn Electrohalmces will be discussed first since these recording balances are used in ahont one-half of the commercial thermohalances. Each commercial instrument employing this balance will then he di3cossed only in terms of special features that it may contain. The non-Cahn type inst,n~mcnt~ will be discussed in more detail, especially the f e e tures of the recording balance. Thermobalances which recprd both the T G and DTA curves will be discussed in a separate section. Cahn Electrobalances
The Cahn balances used in commercial thermobalances are the Models RG, RH, RTL. and 16100. Bv far tthe most DODII-
extensive use becrwise of the many features it contains which are naL available in the other models. The principle of the Cahn Model TG balanceis shown in Fieure4. The balanee is bmed on the md-principle, which i generally accepted being the most accnrate and reliable method of measurement. .Changes in sample mass cause the beam to deflect, changing the photocell ~~~~~
Figure 6.
Figure 5. Cohn Model RH controls not shown.
Eledmbalonce;
current, which is then amplified and applied to the coil attached t o the beam. This coil is in a magnetic field so that, current flowing through it. exerts a moment on the beam restoring it to a null position. Thecoil current is thus an exact measure of sample mass. The balance enclosure c m be pumped down to pressure3 as low as 1 0 F torr and even 1 0 P tom has beerr reported. The prineipd difference between the Models ILG and HH balances (the latter is shown in Figure 5 ) is the sample loop capacity; it is 2.5 g on the R G and 100 g on the R H model. Sensitivity is, of course, greater on the RG, 5 X lo-' g, compared t o 1 X g for the latter. The balances will record exceptionally smell mass changes, down t o 20 s g lull scale on the recording system. With zero suppression, 1% of the sample mass chanxe . caibereeorded. The Cahn Model RTL Electrobalmce is illustrated in Figure 6. The balance has a. top-loading sample configuration which aids in its conversion to R thermohalance. Balance capacity is 10.0 g with s sen& t i d y of 0.01 mg. The three full-scale ranges of mass-change are: 0-10, 0-100 and 0-1000 mg, with an analog ontpnt voltage of 0-10 V dc for each range.
Cahn Madol RTL Elestrobalonee.
The Cahn Uodel R-100 Electrohalance is a new generation electrobalanee employing the electromagnetic weighing principle. The balance, as shown in Figure 7, h a a capacity of 100 g with a mechanical tare of 100 g and electrical tare of 50 mg. There are six mass ranges of 10 g, 1 g, 100 mg, 10 mg, 1 mg, and 100 fig. It contains many an autonovel electronic features such matic range expander, noise filter, output signal directly in percent mass-loss and so on.
I. Thermobolonces Employing Cahn Electrobalances
I.
Cohn Division, Ventron Instruments
Conversion of the Cahn Model RG balance into t,he thermohalance can be acchmplished by use of one of the two thermohalance kits from Cahn. The "Little Gem" TGA Kit, as shown in Figure 8, adapts the balanee far thermogravimetry in an sir a,tmosphere for uae n p t o a. maximum temperature of 650DC. The kit includes a ~ t a n dlor the balance, a micro furnace, Chromel-Alumel thermocouple, four disposable Pyrex hangdown tohes, Nichrome hsngdawn wire, and a micro sample pan. The sample pan is about 5 mm in diametel. and will contain about 15 mg of sample. The Deluxe System, aq shown in Figure 8, consists of a Cahn Model llG halance in a vacuum bottle enclosure, a fnrnace, balance stand, hmpdown tnbe and sample pans, temperalure proglammer, nrtd an X-Y recordel..
2. Columbio Scientific Industries, Premco Model 1000 Thermogrovimetric Anolysis Instrument
The Premeo Model 1000 thermobalance, as shown in Figure 10, includes the follow-
lbl Cohn Model RG Electrobolonce; (a) schematic, (b) photogroph,
Figure 4.
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Figure 7.
Cahn Model R-100 Electrobalance.
(Continued on page A.570)
Figure 12.
Fisher TGA occesrory, Model 120.
6. Perkin-Elmer Corporation, Model TGS- 7 Thermobolonce Figwe 10. bolonce.
w Cahn "Little Gem" TGA kit.
Figwe 8.
ing items furnished by the manufactorer: cabinet, temperature programmer, gas control system, icejunction bottle, and recorder cable. To complete the system, the nser furnishes either the Cahn Model RG or R H balance and x recorder. The photograph shows the instrument with a Model RG Cahn Electrobdance installed. Maximom temperature of the furnace is 1200°C.
3. Deltotherm (Technical Equipment Corp.) TGA System The Deltatherm Thermobalance, which
CSI Prernco Model 1 0 0 0 thermo-
channel strip-chert recorder is required. Maximum temperature of the furnace is 1200°C. Measurements can be made in static or dynamic gaseous atmospheres or itt pressure to 10 torr.
5.
Harrop Loborotories
The Hsrrop Totalab Series, incorporating the TGA module, is shown in Figure 13. Designed for use t o 1500PC, the TGA module can be operated using air, vacuum or controlled gaseous atmospheres. The furnace is mounted on a rack and pinion far easy operation. A programmer-recorder console operates the UTA. TGA or dilstometer modules.
is used with the Deltatherm Basic Unit, is
The Perkin-Elmer TGS-1 T h e r m e balanee combine5 the Cahn Model RG balance with a. unique low-mass, high speed internal furnace. The low-mass furnace, as shown in Figure 14, permits programming the bemperature to lO00'C a t heating rates as high as 160°C/min and then cooling back to room temperature in as little as 5 min. The module uses the control unit of the Perkin-Elmer DSC-1B but it has its own power supply and readout electronics. I t may be operated in the integral (direct weight) or derivative (DTG) mode, selectable by a. front panel switch. A permanent magnet on a pivoting mount is provided so that the sample may be placed in a magnetic field for magnetic susceptibility measurements or for the novel Curie point temperature scale calibration technique.
7. T B T Confrols
illustrated in Figure 11. The system uses a Cahn Model R G balance coupled t o a furnace which is counterbalanced on roller bearings for easy positioningof the thermal zone about the sample. Sample pan alignment, a critical adjustment at times, is aided by a light source and quartz light pipe. Maximum temperature limit of the furnace is either 1250 or 160O0C.
Two different TGA modules are available, each of which employ the use of Cahn balances. The Model 16A-TGA uses the Cahn Model RG balance while the Model Thermit 10-B TGA module uses the Cahn Model RTL balanee. The latter instrument, as shown in Figure 15, is a low-cost model designed for less sophisticated or routine TG messurements.
4. Fisher Scientific Co., Fisher TGA Accessory, Model 7 20
8.
The Model 120 is composed of modular components that are designed t o permit thermogravimetry measurements in conjunction with a Cahn Model RG balance. The accessory, as shown in Figure 12, includes a linear temperature programmer, furnece, and balance stand. A 1 mV two-
Tem-Pres
The Tem-Pres Thermal Grwbnetric Analysis System module k part of their Modular Thermal Analysis System. I t consists of a Cahn Model R G eleetrobalance coupled l o s. furnsce c&pahle of operation up t o 1200 or 1600DC. The control console features a. digital temperature display and an S-Y recording system.
11.
Non-Cahn Type Thermobalancer 7 . A.D.A.M.E.L., The Chevenard Thermobolonce
Figure 9. Cahn Deluxe System for thermogrovimetw.
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Figure 1 1.
Deltatherrn thermobolonce.
The principle and mechanisnl of the Chevenard thermohalance is illustrated in Fignre 16a. The sample is placed a t the end of support rod, T, which is suspended s t one arm, F, of ssensitivebalanee. The other end of the arm contain8 a counterweight, Cp; the arm can rot&t,ein a. verti(Continued on p a p A678)
Chemical Instrumentation
furnace, recorder, and furnace atmosphere (vacuum use, etc.). The Chevenard TH59, Model C, is shown in Figure 16b.
e d pplne hy means of two suspension wires, and r2. For recording the mass change curve, asmall mirror, If,is attached to one end oi the balance arm, F. A light beam from source, S, is reflected from this mirror and convergw t o form a spot, S'. Any change in the sample mass, m, result3 in a changein position of the arm, F, and hence movement of light spot, S', in a. vertical direction. Dependingupon the particnlar model of thermoballance, the displacement of this m o t will either be recorded directlv
The Aminco Thermo-Grav, in contra3t t o electronic null-type balances, .uses a helix to measure changes in mass. The sample is placed in a crucible supported by a precision helix suspension syst,em which hangs freely within a. Pyrex-quart,%g l a ~ s enclosure. Coil windings of a displacement transducer (LVDT) are mounted outside the elassware enclosure. concentric
available with variations in the type of
massduring heating muses acorresponding vertical displacement of the suspension
rt
2. American Instrument Co., Inc., Aminco Modular Thermo-Grov
Figure 14. Furnace of thermobmlmce.
Perkin-Elmer TGS-1
and generates an a x . voltage proportiond to it. A demodulator converts the signal to d.c. which is then recorded on an X-Y recorder. This thermobdance is illustrated in Figure 17.
3. Delfotherm Ill Thermogrovimetric Analyzer An interchangeable plupin module t o the Deltatherm I11 system, the T h e r m e gravimetric Analyzer, as shown in Figure 18, combines an electronic null balance, a flat-pan sample holder mounted above the balance, with a 1 2 0 0 T Ksnthal wound furnace. This balance ha- a Nichrome ribbon suspension which yields a sensitivity oi 0.4 mglin. Sample masses up to 10 g can hestudied. Figure 13.
Horrop Totolab thermal onoiyrir system, incorporating the TGA module.
4.
DuPont Instruments, Model 951 Thermogrovimetric Analyzer
The Thermogravimetric Analyaer, illustrated in Figure 19, is one of a series of individual modules which plug into the DuPont 900 Thermal Analyzer system. I t contains n. null-balancing (similar t o the Cahn Model RG Electrobalance), tautband electric meter movement with an optically actuated servoloop. The sample is placed in a container which is suspended direct.ly on the bdlanee beam. In normal operation, the temperature sensing thermocouple is positioned within 1 mm of the sample, hence, indicates very close t o the sample temperature. Mass-changes of t,he sample are plotted as a function of temperature on an internal X-Y recorder. Balance sensitivity is reported t o he 2 pg. The beam-in-furnace design and position of the sample container permits axial flushing oi the f ~ l r n s c etube with various inert gases. The sample presents minimum cross section to the gss flow which results in a negligible torque perpendicnlar to the bertm. Hence, there is n minimum
Figure 15. T 8. T Controls M o d e l Thermite 10.0 module.
(Conlinu~don page A5801
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Chemical instrumentation
temperatures (up t a 2200DC)are possible in the vertical position than horiaont.4 ((to 1100°C onlv); each position has its advantages and disadvant,ages. The halance is of the null-seeking type in which the deviat,ion ir detected by an inductive pickup and the restoring farce applied electrcmagnetically. The current required to rebalance the beam is proportional to the mass change. By use of the proper samole holder and electronic accessories. it is iossible to ohtam TG-DTA or TGDTG-DTA data.
6.
Netzsch Thermobobnces
Several different models of thermcbalances are available in which t,he Nodel 400 is the standard insbrument while the Xodel 419 can he used for high vacuum studies as well as at aatrnospheric pressure. The Model 409 consits of a three knifeedged balance in which the beam deviation is detected by a. light beam-photocell system. Rebalancing of the beam is affected by varying the length of a chain, attached t,o the beam, by means of aservcmotor. A second chain is used to m a n ally tare the balance. A Kanthal furnace element for operation to 1320'C or silicon carbide element for use up t o 1550°C may be selected.
Ibl Figure 16. The A.D.A.M.E.L. Chevenord thermobalance: (a) basic mechanism, (bl Series TH-59, Model C. Calibration ir achieved b y placing known small weight on plotform P; A is a dorhpot for damping out vibration,.
of turholence and noise in the hslnnce. A maximum furnace temperature of 1200°C is st,tainahle.
5.
Linseis, Thermobalonce 1 7 2
The Linseis thermoh~l.lanee permits operation wilh the furnace either in a horizontal or vertical position. Higher
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(bl thermoFigure 17. Aminco Thermo-Grav balonce: lo) boric TGA unit, Ibl complete instrument including TGA, DTA, and EGD.
101 Figure 20.
Stanton thermobolonce.: -
18. analyzer. Figure
(0)
(bl marrflow model, (b) rtmdord model.
(Continued on page A686)
Deltathem Ill lhermogravimetric
7. SETARAM The SETARAM system is a. multifunction instrument capable of measuring the TG, DTG, DTA, and EGA simoltaneously on the same sample. An Ugine-Eyrand B60 balance is used t o obtain the T G curve. This bdsnce is a beam-type instrument in which the beam unbalance is detected by a light beamshutter-photocell circuit. A restoring force is applied by a magnet-solenoid coil combination. Maximum furnace temperature is 1000 or 1600DC, depending upon the type of furnace.
8.
Sfanton lnsfrumenfs, Lid., Stanfon Thermobdance
There are 14 models of the Stanton thermobalance, each differing in maximum furnace temperature, heating rate specifications, recording weight change and so on. The principal instrrments are the Standard and Mass flow thermobalances, as illustrated in Figure 20. Each thermobalance contains a precision airdamped analytical balance and a. bifilar-wound vertical ttube-type furnace. The standad furnace is Nichrome wire wound and is useable up to 1000°C. Alternate models are available with Pt/Rh wire windings for use up t o 1350 or 1550°C. Furnace temperature and mass-change are recorded simultaneously on a two-pen recorder located above the balance and in front of the furnace. The two recorder pens are power-driven by servomotors which re-
Figure 19. DuPont Model 951 thermogrovimetric onolyrer.
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the furnace makes it suitable for connection t o gas analysis systems inchtding mass spectrometry. hIaximum temperature of the furnace is 1000°C.
9. Volond Corporofion, Series T-1 Modular Thermoanalyzer All of t,he models in this series have a common console, balance mechsnkm, furnace, temperatnre controller, and recorder. By adding one or more plug-in modules, DTA, TG, and DTG curves can be recorded. This instrument is shown in Figure 22. The balance mechanism, which consists of a titanium beam with ruby knives andsapphire bearings, is of the null-type, force-balance system. The mass of the sample is detected and a restoring force in the form of an electric current is applied t o re-balance the beam. A portion of t.he balancing current is measured t o indicate sample ma-s. As in the DuPont or Linseis instruments, a horizont,al ffomace configuration is employed. Maximum fwnsce temperature is 1000-1200°C while 1.500"C can be ohtained by use of a. special furnace. Figure 21. Stenton Redcroft Model TG-750 thermobalonce.
ceive their signals from a Pt,, Pt-Rh thermocouple and s. capacitance follower plate over the balance beam. The latter plate follows the movement of the beam yet has no direct mechanical conbact with it. A sensitivity of either 0.1 or 1 mg m w he obtained. Full scale mws changes of 1 1 0 0 mg or & 1 g can he recorded dependibgupon the balancesensitivity.
Stanton RedcroR TG-750 Thermobalance The Model TG-750 Lhennobalance, as
Because ift.he furnace design, there is sopposed to be no rrotieeable "buoyancy effect" over the entire temperature range even when operating at maximum sensitivity. Provision is also made for the control of the furnace atmosphere and low pressure operation. The small volume of
Literature Cited (1) HONDA,K.. Sci. R e p . Tahoku Uniu., 4 , 97 (1915). (2) SAITO. H., "Thermobslsnee Analysis," Gijitsu Shoin. Tokyo. 1962. (3) Garcxmo, M., Bull. Soc. Chim. Fr., 33, 258 (1923). (4) GVICHARII, M.. Bull. Soc. Chim. Pr., 37, 62 (1925). (5) DUYAL.C., .'Inorpanic Thermogravimetrie Analyais" (2nd ed.). Elrevier, Amsterdam, 1963, D. 9. (6) VALLET. P.. Bull. Soe. Chim. P i . . 3. 101 (1936). (7) Dunora. P.. Bull. Sor. Cliim. PI.,3, 1178 (1936). (8) C n ~ v ~ ~ a P., n o ,IVAcne, X.. A N D DE L A T~L~AY R.,E .Bull. Soe. Chim. Fr.. 10, 41 (1944). (9) Dcvhz, C . . "Inorganic Thermogrevimetrio Analyais" (1st ed.), Elsevier. Amsterdam. 1953. (10) GORDON.6.. A N D CAMPBEL', C.. A n d . Chrm., 32,271R (1960). , A N D ERDET,L.. (11) PAULIX.F., P ~ L I KJ.. 2.Anal. Chem.. 160, 241 (1858). , G., Aehema Cono7sse paoer, (12) V l E n ~ m N t i H. Frankiort, Germany. June 26, 1964. W. W.."Thermal Methods of (13) WENDLANDT. Analysis," Viley-Interscience, New York, 1964. ( l a ) KEATTCH, C.. " I n I n t i o d l i ~ t i ~t n o Thermomavimetry," Heyden, London, 1969. ic~l (15) GARN,P. D.. " T h e r m ~ ~ n ~ l y t Methods oi Investigstion." Aesdemio Press. New York 1905. Chanter . 10. (16) ANDERBON. H. C . . in "Technique and Methods of Polymer Evsluation." S L ~ EP., E., and JENKINS. L. T., Eds.. Dekker. New York.. 1966. C h a.~ t e 3. r ~ (17) WENDLANDT.IV. T., Lea. Mnna#cmcnl, October. 1965, D. 26. (18) ITENDLANDT, m.W.. "Handbook oi Commeroid Scientific Instruments." Dekker. New York, in press. Vol. 2. (19) H m s c ~ R. . F.. J. Cma. E m c . , 44, A1023 (1967); 45, A7 (1968): Renrinted in "Topics in Chemical Instrumentation,'' EWINO,G. W., Ed., Chem. Eduo. Publ. Co.. Easton, 1971, p. 269. (20) BRADLEY, W. S., A N D \VEI(DLANDT, W. W., A n d . Chem., 43,223 (1971). (21) IVENDLINDT,1V.W.,Chimio. 26, l(1972). (Port I will br concludad m the Noucmaer iaaue.)
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