Topics in..
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Chemical instrumentation Edited by GALEN W. EWING, Seton HoII University, So. Orange, N . J. 07079
These articles are intended to serve the readers O ~ T H EJOURNAL by calliny attention to new developments in the theory, design, or availability of chemical laboratory instrumentation, or by presenting useful insights and explanalions of topics that are of practical imporlance lo those who use, or teach the use of, modern inslrumatatia and instrumental techniques. The editor invites correspondence from prospective contribulors.
LXVII. Thermal Analysis Techniques: Part II. ~ifferentiaiThermal dnalysis and Differential Scanning Calorimetry
(Continued)
W . W . W e n d l a n d t , Deportment of Chemistry, University o f Houston, Houston, Texas 7 7 0 0 4 6 . Du Pont Instruments
The 1)u Pont RIodnlar Thermal Analyzer Syslem is perhaps the most cprnpre hensive system available commercially. Built around the Xodel 090 Thermal Analyzer basic unit, a variety of plug-in modules are available. These include modules for DTA, TG, thermomechanical analysis, and others. For DTA, there are fom standard furnaces ~ l u two s DSC furnaces; the latter will be discussed under DSC instruments. The Model 0!K1 Thermal Analyaer basic unit is shown in Figwe 35. I t conthins the X-Y recorder, furnace temperat,ure programmer, AT amplifier, and ocher controls. The plng-in module type UTA furnace and sample holder cells cover the following temperat,ure ranges: (a) Standard IITA Cell (to 500°C) is a general purpose, block-type sample holder. Samples are placed in dispossble glass cqA1sl.y tubes into which are inserled the ChromelAlumel thermoconples. (b) The Inter-
mediate Temperatlire DTA Cell (to 850°C) is similar t o (a) except that it uses quartz tubesin place of glass and attains a higher temperature. ( c ) The High Tempera, ture DTA Cell (two available with maximum temperat& of 1 2 0 F or 1600'C) uses a law-mass, quick-cool furnace. Samples are contained in small platinum crucibles.
feature furnace jacket, sealed sample chamber for measurements in vacuum and supraambient pressures, and a gas flow and mixing system. Standard maximum furnace temperature is 1200°C. 1 0 . Linseis
There are a wide variety of DTA instruments availahle which cover the temper* tnre range from -200' t a 1700'C. Sample holders are of the block or crucible type; both types have their specific advantages and disadvantages depending upon the nature of the application. For DTA studies from -200" to 500°C, the unit shown in Figwe 37 may he employed. I t consists of a sample chamber in which the sample and reference materials are contained in quartz tubes. For very small samples, the Micro-DTA sample holder may he used which consists of a crucibl&ype holder, or, if the samples are less than 1 mg, cavitiw drilled into the thermojunetion itself. N ~ ~ , ~ , . ~ ~ ~ are avail,ilahle ingsystems and A~ depending upon the DTA instrument and theapplication.
7 . Eberbach Corporation
The Eherbsch DTA apparatus is classified as a oortzhle field-tvoe instznment although it requires a source of 115-120 VAC to power the furnace. I t is designed for approximate, qualitative measure ments with the data being hand recorded and plotted. The sample and reference materials, contained in a metal block-type sample holder, is inserted into a preheated furnace. Manna1 AT and T readings are then taken and plotted on chart paper furnished wit,h the apparatus. Maximum temperature of the furnace is ahout 900°C.
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Figure 36. Fisher Therrndyrer.
Model
260
Differential
8. Fisher Scientific; Model 2 6 0 Differential Thermalyzer This is a low-cost DTA apparatus designed for educational, research, and industrial laboratories. The instrument, as shown in Figure 36, consists of three separate units: (a) sample holder, which has provision for two sets of reference and sample thermocouple and crucible; (b) furnace, capable of use up t o 1200°C;
fier if needed
,
,
r
Figure 35. Du Pont Anolyrer boric unit.
-I Model
990 Thermot
9. Harrop Laboratories A number of different DTA instmments are available from this manufacturer. The Model UTA-A1 is a hlock-type IITA instrument which includes 8. water-cooled
Figure 37. Linreir Model L 6 1 / 8 DTA system for use from -200' to +500DC.
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Table I.
Chemical Instrumentation Sample Holder
Netzsch Sample Holders
Q p e No.
Thermocouples P t Rh-Pt P t Rh-Pt P t Rh-Pt P t Rh-Pt P t Rh-Pt Pd-Pt P t Rh-Pt Ni02-Ni P t Rh-Pt NiOn-Ni
Standard Vacuum Protective gas type Standard Ni block DDK
Figure 38. Menler DTA 2000 3yrtem: lo) DTA cell; I, crucible; 2, differentid temperature senror; 3, furnace housing with heating coil; 4, purging gas conditioning; 5, platinum resistance sensor; 6, fan; 7, vacuum-tight singlelever rapid closure; 8, connection for purging gas and vacuum. Ib) AT meowring senmr; I, gloss disk with vapor-deposited fivefold thermopiles; 2, crucible; 3, centering hales for crucible positioning.
pile disc and guide pius on the crucibles. The temperature range of the instrument is -20" to 500°C. The DTA cell and temperature sensor are shown in Figure 38.
7 2. Netzsch Geratebau GMBH
Figure 39.
Nehrch DTA romple holders.
Netzsch, l i e Linseis, has a large number of models of DTA instruments. As an example of this multiplicity of instrumentation, the Netzsch DTA sample holders that may he selected are shown in Figure 39. These sample holders, or "measuring heads" as they are described by the manufacturer, are tabulated in Table I. Materials of construction range from alumina t o platinum; all of the holders are interchangeable and can he used with any Netzsch system. Selection of the apprw priste semple holder depends upon the system under investigation. The Model 404 DTA apparatus is shown in Figure 40. The apparatus consists of a furnace and furnace frame, one sample holder, furnace temperature controller, and the recording unit. For the recorder, a choice can he made between an electric compensation type or a photographic recording device.
Netzrch Model 404 DTA opparotur.
Figure 41. Analyzer.
Rigaku Denki Differential Thermol
1 7 . Mefiler Instrument Corporation; Mettler DTA 2000 System The Mettler DTA 2000 system is designed for high calorimetric sensitivity and precision and also accurate temperature measorement. Contrary to other DTA instruments, the sample cell temperature is measured by a plstinnm resistance thermometer rather t,han B thermocouple. Differential temperature is detectid with 8. thin-film fivejunction thermopile which is covered with a. protective coating. Exact positioning of the sample crucible is assured by centering holes on the thermw
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1 1
1 1 0.25 0.2 1 1 0.2 1
1600 1600 1600 1000 1000 1000 1600 450 1000 900
There are several,different DTA instruments availehle from this manufacturer; however, only the Model 20B micro-DTA system, as illustrated in Figure 42, will be discussed here. This instrument has a. rsther interesting sample holder which consists of small mela1 cups positioned on a "dumbbell" shaped thermoelectric disc. This type of detector has high sensitivity and a good baseline under most conditions. Maximum temperature of the furnace is 600°C and it is designed so that the temperature distribution is very uniform throughout the sample area. Measurements csn be made in air, inert or reactive gases s t atmospheric pressure, or in a vacuum down to 10 torr. A somewhat more elaborate system, the Model DT-2B, is capable of operation t o temperatures of 1000' or 1500°C. The standard sample holder consists of a thin platinum alloy cell which is placed in a beryllium oxide block.
The Differential Thermal Analyzer is s. modular, tabletop mounted DTA instrument. Another DTA instrument, which simultaneously records the TG-DTA curves, is discussed in the section on simultaneousTG-DTAinstruments. The former instrument is illustrated in Figure 41. I t is a rather compact instrument which uses a s m d thermal capacity furnace which permits rapid cooling. The modular design accepts different attachments for measurements on a variety of samples. Measurements can he made in air, vacuum, or flowing gas atmosphere. Maximum furnace temperatures are l l O O s or 1500PC. There is also available 8. lowtemperature furnace capable of operation from -150°C t o 800°C.
Figure 42.
Max. Temp. ('C)
14. Shimadzu Seisakusho Ltd.
13. Rigaku Denki; Differential Thermal Analyzer
Figure 40.
Capacity (ml)
The standard DTA instrument, the Standata 6-25 and 5-50, are floormounted units while the newer Model 671 is designed for tabletop use. Only the latter instrument will be described here. The Model 671 is designed for DTA st~tdies covering the temperature range from -180' t o 450°C. This instrument, as illustrated in Figure 43, features an integral heating coil and liquid nitrogen cooling. Sample and reference materials can be subjected to ten switch-selected heating or cooling rates between 1" and 2O0C/min. Cooling from 4 5 0 T t o room temperature is possible in ahout 10 minutes. The instrument is a compact table-top unit which consists of s. sample block and furnace, furnace programmer, amplifier, and recorder. The dwign permits easy connection to a mass spectrometer or other gay-monitoring accessory as well as direct microscopic observation of the sample during the heating or cooling cycles.
Shimadru Model 208 Micro-DTA system.
(Conlinued on page A674)
Chemical Instrumentation
Figure 43.
Stonton Model 671 DTA opporotur.
16. T&T Controls The Model 16A DTA system, which is capable of operating in the temperature range from -200' t o 160f1°C, is shown in Figure 44. I t consists of an electronics console, recording system, furnace platform, and a iurnaee and sample holder assembly. A wide selection of type of recording system, filmace, and sample holders are available. For example, three furnaces may be chosen: (a) subambient model for \me from -150" t o 450°C; ( b ) mid-range model for use from 26' t o 1200°C; and (c) high-temperabure model for use from 25" to 1600°C. Ges pressures from ambient atmospheric pressure t o 7 s t m may be employed. A number of sample holders, from block t o crucible types, and eonstrocted fmm stainless steel, boron nitride, alumina, and platinum alloy, are available. The Thennit-1OB IITA apparatus was designed t o fill t h e needs of 8 laboratory requiring aless sophisticated instrument or one where ease of operation, low cost, and high performance are primary considerations. Tho instrument consists of a furnace assembly, control console which features a continuous display of operating modes, and a strip-rhnrt recorder which displays both 1' and AT. The furnace temperature programmer is s closed-loop Lhermocouple feedback type with SClt propoxtion$ output,-power coott~ol. The furnace is designed for atmospheric pressure only with a maximum tempel.ntnre of 1000°C. A variety of sample holder eonfigwations, conslroeted from aluminum, stainless steel, and boron nitride, permit the examination of s wide range of sample sizes m d types.
Figure 44. system.
T & T Control. Model 16A DTA
(Continued on page A676)
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Figure 45. Tem-Prei DTA fvrnoce module ond contr01 conrde.
17. Tem-Pres The Tem-Pres Differentid Thermal Analysis system consists of s control eonsole and a DTA module. The console includes the temperature programmer, the temperature controller, and the X-Y r e corder. I n the DTA module are included the furnace, furnace stand, and sample holder-thermooonple assembly. Interchangeable furnace modules are available for maximum temperatures of 500°, 1200°, and 1600°C. Platinum sample cups have capacities from 50 to 200 mm5 and are readily accessible in the sample holder compartment. The DTA apparatus is shown in Figure 45.
18. Theto Industries The Theta Thermal Analyzer Model DTA 802, as shown in Figure 46, is a simple yet versatile instrument which permits measurements to be made in the temoerature ranee from -60" t o 900°C.
of 0.350 ml and is constructed of quarto.
DIFFERENTIAL SCANNING CALORIMETERS The distinction between differential scanning calorimetry (DSC) and the technique of DTA has become quite confused the past several years. Many of the instruments that use the name "ditTerentis1 scanning calorimeters" are in reality DTA type instruments. I t is hoped that this ambiguity will he resolved in the near future.
Figure 46. Analyzer.
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The term differential scanning calorimetry was coined by Perkin-Elmer in 1963 t o describe their Model DSC-1 instrument, which is not a DTA instrument. Their
is compensated for by adding or removing an equivalent amount of electrical energy
Delfatherm D5500 dynamic adiabotic embrimeter.
Figure
47.
to s. heater located in the sample holder. In practice this is achieved by comparing the signal from s platinum resistance thermometer in the sample holder with that from an identical sensor in the reference holder. The continuous and automatic adjustment of heater power (in energy units per unit time) necessary to keep the sample holder temperature identical to the reference holder provides a varying electrical signal opposite hut eouivalent to thevarvine thermal behavior
obtained in power units, expressed in millicdories per second. The peak area is a true electrical meruurement, the magnitude of which does not depend on any of the thermal constants of the sample or apparatus. The calibration constant, E, t o convert measured DSC dsta. t o millicalories or culorie.~i, idepcudrnr of t h e rwnper:uurr. In the I'erki~~-I~:lu~ec Ih
