Anal. Chem. 1982, 54, 97R-105R
Thermal Analysis W. W. Wendlandt Department of Chemistry, University of Houston, Houston, Texas 77004
An iterative, multiple regression analysis of these values yields an accurate determination of the mole fraction of the major component, the melting point, and the partition coefficient (187). Polymers. 4,4'-Diethylnylphenyl ether was synthesized and its thermal polymerization, beginning at approximately 150 °C, was studied by DSC, NMR, and IR (189). The heat of polymerization was 53 ± 2 kcal mol'1. The melting point of polyethylene terephthalate) crystalline and/or annealed at elevated pressures was studied by DSC at atmospheric pressure (95). DTA was found to give satisfactory results as a method for detecting the reactivity of cold- and heathardenable epoxy resins (193). The dehydration of cellulose in the presence of TiCl3 at 170-220 °C was confirmed by DTA and IR. As the temperature was increased to 250 °C, a sharp decrease occurred in the degree of order of the polymer (56). DSC and constant temperature calorimetry were used to determine the enthalpy of reaction occurring in the sulfur vulcanization of natural rubber, butadiene rubber, and butadiene-styrene rubber in the presence of tetramethylthiuran monosulfide accelerator (22). Homogeneous blends of incompatible polystyrene and poly(methyl methacrylate) were shown by DSC to have a single glass transition intermediate between those of the components (202). The phase diagram of PTFE was enlarged by DSC to include the concentration of CF3CF:CF2 comonomer units. The two solid-solid crystal transition temperatures apparently become one at small concentrations (231). Crystallinity determinations obtained by DSC on neck fibers formed by constant uniaxial tensile loading of high-density polyethylene at temperatures of 298-353 K confirmed a previous suggestion that the density decrease in the fibers is a result of void formation (73). The binary phase diagram determined by DSC for p-phenylenebis(4-methoxybenzoate) systems was similar to the typical phase diagram for mixtures of two small molecular nematogens. The nematic nature of the polymers was confirmed (81). For accurate and reproducible inducation times in determining the oxidation resistance of polyethylene by DTA, the temperature should be maintained at 200 °C and the heating times in N2 and 02 standardized (4). The intensity of the glass transition in semicrystalline polycarbonate, as determined by DSC and thermally stimulated discharge, is governed by the extent of primary crjrstallization and is a linear combination of intensities from two noncrystalline regions, bulk and within spherulites (241). During isothermal DSC treatments at 25-150 °C, the observed increase in weight-average molecular
Dr. Connie Murphy, after 22 years (1958-1980) of editing this review (160), has decided to turn the job over to another author. It is with a deep sense of responsibility and dedication that I hereby accept this challenge. The workers in the field of thermal analysis, as well as myself, should be eternally grateful to Dr. Murphy for his devoted and accurate reporting of thermal analysis activities as they occurred through the years. I only hope that I can continue this tradition in the manner and spirit that he did. As usual, this review covers the almost 2-year period from January 1980 through November 1981. Unfortunately, not all of the thermal analysis papers can be described here, due to their magnitude. An attempt has been made, however, to include representative studies in all of the thermal analysis areas as well as, in my judgement, new and novel ideas and developments. Due to space limitations, very few review articles (of which there are many), books, and meetings are included here. In an attempt to find out which thermal analysis experimental techniques are currently in use, a survey was made over a several year period in papers appearing in Thermochimica Acta (TCA) and the Journal of Thermal Analysis (JTA) (235). As expected, TG, DTA, and DSC accounted for the majority of these techniques. In TCA, TG was used in 29.1% of the papers published over the period 1978-1979. Likewise, DTA-DSC accounted for 23.5% of the experimental techniques in this journal. In JTA, 33.0% of the papers used DTA-DSC while 22.0% employed TG, for the time period 1975-1978. Thus, approximately 50% of the papers published in these journals used these three techniques. It is felt that this number will decrease in the future as new and more sophisticated thermal analysis techniques become available. A new report on symbols for thermal analysis was made by the ICTA Nomenclature Committee (142). A partial listing of these recommendations for the techniques of TG, DTG, DTA, and DSC are as follows: (a) The SI units should be employed, (b) Use of superscripts such as T should be avoided, (c) The use of double subscripts such as Ts„ and Tpj should be avoided, (d) The symbol T should be used for temperature whether expressed in °C or K. (e) The symbol t should be used for time (in s, min, or h). (f) The heating rate can be expressed as ATJAt or as fi in K min'1, (g) The symbols m for mass and W for weight are recommended, (h) The symbol a is recommended for fraction reacted, (i) The ordinate in DTA should be expressed in terms of AT, the difference in temperature between the sample and reference material, (j) The ordinate in DSC should be expressed in terms of AQ/AT or AQ/At rather than AH/AT or AH/At, since Q represents quantity of heat or electricity whereas H represents enthalpy.
DIFFERENTIAL DIFFERENTIAL
purity determinations.
weight of poly(p-isopropylstyrene) arose primarily from interchain linking between the longer radical-bearing chains. At 315 °C, the molecular weight increased (143). The glass transition temperatures of poly(diethylene glycol terephthalate) ranged from 275 K for a fraction with Mn of 2500 to 262 K for fraction with Mn 22000 (82). Natural rubber-polyisoprene rubber blends were characterized by DSC at 400-500 K. Addition of a small amount of one to the other produces a significant effect on the shape and position of the oxidation exotherm (77). Initial rate studies of the styrene homopolymerization were conducted by DSC and found to agree favorably with values in the literature (199). DSC showed that in high-density polyethylene, the internal surface layer of the thermally oxidized pipes had a lower melting temperature and lower crystallinity compared with the material in a similar position in unoxidized pipes (72). The DTA curves of polyethylene terephthalate samples, drawn near the Tg and not annealed, supply information about morphology, especially by analyzing the crystallization behavior, which cannot be obtained by measuring draw ratio, birefringence, or density (208). DTA was used to study the thermal behavior of unfractionated polyethylene at Co > Cu. It was not possible to make the Zn chelate (20). TG and DSC measurements showed that the decomposition of [Co(NH3)5H20][Cr(NCS)6] involves the loss of H20 and NH3 to yield [(NH3}3Co(SCN)3Cr(NCS)3] (101). The reaction of the rare earth oxides of Y, La, Gd, and Lu with NH4Br and of Y203 with NH4X, where X = F, Cl, Br, and I, were studied by TG, DTG, and DTA (97). Also, the thermal stability of the rare earth oxybromides of La, Pr, Nd, Sm, Gd-Lu, and Y were determined in air and compared with the RE oxyfluorides and oxychlorides (96). The thermal decomposition of the rare earth oxysulfides (excluding Sc, Ce, and Pm) were studied in air by TG (134,136). Final products of the thermal decomposition of Eu2(S03)3-3H20 in a CO atmosphere are EuS and Eu202S. The optimum temperature range for the production of the latter is 700-850 °C (135). Instrumentation. A new temperature programmer was developed for use in thermobalances, DTA, DSC, and other TA techniques. Temperature rate control is based on two sensors, which may be thermocouples or resistance thermometers (65). An automatic data acquisition system was described by using two Mettler thermoanalyzers, Model TA-1, and a Hewlett-Packard 9825S calculator. The system permitted data from the thermobalances to be simultaneously collected and stored on a magnetic cartridge (243). Isothermal studies of the reaction of S02 with limestone and dolomite were carried out on a pressurized TG system (225). Another higher-pressure thermobalance in which sample heat-up to an isothermal steady-state condition was reduced to less than 20 s has been designed and constructed (192). A combination of simple baffles and appropriate size for the hangdown tubes was found to reduce the noise of a microbalance in flowing gases up to 1700 K (203). A method was developed in which the oxidation and autoignition of oils could be determined, using a TG technique. It employed a commercial insulation wetted with the oil, a condition similar to that which could occur in a real plant situation (28). The identification and quantitative correction of experimental errors in isothermal TG were discussed in detail. Variations in gas flow rate, buoyancy, pressure, and convection effects were among the factors examined (164).
MISCELLANEOUS THERMAL ANALYSIS TECHNIQUES New Techniques, Miscellaneous Techniques. The derivatograph was used for the measurement of flash ignition and self-ignition temperatures of solid materials and for the combination of these with TG, DTG, and DTA (205). An ignition test for plastic films >6 mm thick used an apparatus consisting of a burner with a controlled pilot flame upon which a sample support plate and movable heat shield was fastened (104). The delay times for Plexiglass, polystyrene, nylon, and others were measured. A new thermal analysis technique, thermodenuder, for the determination of atmospheric H2S04, was described (161). The acid droplets are thermally decomposed in a heated glass tube and the small fragments formed are collected at the walls of the tube by diffusioncontrolled deposition. The tube is then rinsed with water and the dissolved matter is analyzed for sulfate by isotope dilution analysis. Polarizing microscopy and DSC showed that the relative stability of the smectic and cholsteric mesophases of cholesteryl esters of acyl chain length >20 carbons depends on the length of the acyl chain and its degree of unsaturation (76). DTA coupled with rheometry offers a new method for studying the utilization of vulcanizing agents, particularly after the optimum vulcanization time has been reached (212). A method was devised for temperature scanning with a vibrating-U-tube density meter. By use of this instrument, the volume expansion-melting curves of lipid dispersions have been obtained. The curves are similar in shape and resolution to the DSC excess heat-capacity curves (5). A new apparatus which permitted the simultaneous determination of both the thermally stimulated light emission (LE) and DTA of a compound was described. LE-DTA curves were reported for a selected number of coordination compounds, each containing vigorous oxidizing and reducing ligands (234). A new apparatus was described consisting of a DTA apparatus, a Zr02(Y203) solid electrolyte emf cell, and a stereoscopic microscope (61). An automated apparatus for the DSC 102 R
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ANALYTICAL CHEMISTRY, VOL. 54, NO. 5, APRIL 1982
and thermoacoustimetry of oil shales was described in detail (157,186). By use of thermosonimetry and DTA-TG, four different kaolins were studied (94). Two regions of pronounced thermosonimetry were found: (1) at 500-600 °C, corresponding to the dehydroxylation; and (2) the region of 980-985 °C, corresponding to the solid-solid phase transition. Emanation thermal analysis (ETA) was discussed as a tool for characterization of solid phases arising during treatment of the uranyl gel microspheres up to the final V02 product (7). Thermomagnetometry was found to be useful to indicate the distribution of the major impurities, Mg and Mn, in the thermal decomposition of three siderite samples. These impurities affect the extent of oxidation and stabilize a spinel phase, even in oxygen (68, 69). A new thermomagnetic analyzer, developed for the investigation of the thermochemical reactions of metal complexes, was used for the kinetic studied
the reduction of Co(III) — Co(II), of nitrosylpentaamminecobalt(III) chloride, and the transformation reaction, polymer to monomer, of bis(IV-phenylsalicylideniminato)nickel(II) (155). TG in the presence of an external magnetic field (thermomagnetometry) was used to detect the presence or absence of magnetic intermediates and products during the thermal decomposition of siderite samples (70). Phenomenological softening points Were measured on 13 anionic atactic polystyrene samples using a DuPont 943 thermomechanical analyzer in a penetration mode (116). Dynamic mechanical techniques and DSC were used to study sulfonated polypentenamers containing 1.9-17.6 mol % pendant S03Na groups (183). A two-phase morphology was shown in segmented polyurethane, based on an OH-terminated butadiene rubber soft segment and containing 20-60% hard segments, by dynamic analysis and other techniques (23). Evolved Gas Analysis. A new apparatus which permits the DTA and EGA of a sample was described (223). The EGA part of the apparatus was said to be quantitative. EGA was found to be the most suitable method for the detection of etheral-oil-/3-cyclodetrin complexes, while DSC was best for studying paracetamol (216). A simple EGA method was developed to determine the thermal stability of oil in N2 or 02 (48). A 0.2-2 sample is heated in a stream of N2 or air. The volatiles are oxidized over CuO at 850 °C, giving C02 which is determined every 3.7 min by gas chromatography. It can be used to study lubricant bases, perfumery oils, and other hydrocarbon liquids. From the gas content, the degassing rate, and the temperature of the maximum degassing rate, one can get useful information about the bonding of volatile compounds and the history of glasses (86). The EGA curves from natural glasses show that the mechanisms of degassing is quite different from that of artificial glass. EGA found that with the exception of poly(amyl methacrylate) and poly(octyl methacrylate), thermal degradation of poly (alkyl methacrylates) with primary substituents gives monomers as the primary products (99). The thermal decomposition of Co(N03)2-6H20 (174) and Nd2(C2O4)3-10H2O (195) was studied by EGA along with other thermal analysis techniques. The use of a Fourier transform IR spectrometer (FTIR) for analyzing the gaseous decomposition products evolved during TG was described (35). The Fourier transform IR evolved gas analysis described previously was expanded both with respect to data processing options and to application areas (132). With this technique, the thermal decomposition of kraft lignin was examined (57). Carbonate minerals can be routinely detected in the hundreds of ppm concentration range by using a nondispersive IR C02 detector linked to a DTA furnace (152). Modifications to the technique permit detection of certain minerals at
