Thermal Analysis C. 6. Murphy, Xerox Corporation, Rochester, New York 14644
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the major trends in thermal analysis throughout the period covered from the previous review (831) to October 1971. Thermal analysis has reached the stage of maturity to have a well-established international organization, International Confederation for Thermal Analysis, and national organizations in North America (North American Thermal Analysis Society, NATAS), Japan, U.K., Italy, and many other countries. The third ICTA was held in Davos, Switzerland, in August 1971, and the fourth will be held in Budapest, Hungary, in 1974. NATAS has established annual meetings and the second Symposium on Analytical Calorimetry was sponsored by the American Chemical Society in 1970. Although firm bases exist for the standard instrumentation (DTA, DSC, TG), new instrumentation for thermal analysis and new applications for existing equipment are being reported. Berg's (69) hope, expressed in 1968, "that in the future these methods will find even wider application in science and technology" certainly has come true. HE REVIEW COVERS
DIFFERENTIAL THERMAL ANALYSIS
The fundamental aspects of DTA have been well covered in a recent book (194). Reviews have been published on the general use (37), on enthalpic and kinetic applications (294),and on microDTA, using the thermocouple as heating source and sample holder (309). A low-temperature apparatus, using an Al-Si block cooled by liquid NO, has been patented (167). Thermopiles have been incorporated into equipments to improve sensitivity (249, 267) and commercial equipment incorporating a thermopile is available from Mettler. High sensitivity also has been obtained with equipment incorporating a glass thermistor (332). Microequipment, using a dumbbell-shaped, disk differential thermocouple (chromel-alumel) has been developed (369), giving a peak height of 26 gV for the melting of 1.7 mg of In. A constantan disk system also has been disclosed (23) and has been patented (137). Sample exposure and subsequent DTA and T G in a glove box (103) ensured sample conditioning at desired R.H. It was interesting to note that DTA of porous glass conditioned a t various humidities permitted the generation of absorptiondesorption isotherms (103). Pressure DSC equipment, with a maximum working pressure of 1000 psig, has been de-
scribed (184) and was applied to the polymerization of diallyl phthalate and to motor oil among other things. The applicability of this equipment to Hz reduction of aromatic nitro compounds has been demonstrated (66). Apparatus for pressures up to 4000 bar and 500 "C has been constructed (176) and was applied to S polymerization. Another high pressure equipment, operable to 100 kbar and 1100 "C, has been applied to the H20-D20 and H20-Bi systems (28). Equipment for the DTA determination of solubility curves and stability fields of refractory materials in molten solvents has been described (634) and has shown nickel ferrite crystallizing from a BaO-Bi20a-B208 flux between 1240 and 1140 OC. Serious base-line drift was encountered. To avoid nonhomogeneity in liquid samples resulting from inadequate mixing, a rocking equipment was developed (121) using a sealed Ni block sample holder having ca. bgram capacity. Chopped pyrometric sensing was used for differential temperature measurement in induction heated equipment capable of being operated to a temperature of 3000 "C (14). Applicationof this equip ment to ThC2 exemplified the marked advantage of DTA and derivative analysis (DA) over thermal analysis. DA, temperature derivative DS. time, was stated not to be a replacement for DTA, but had the advantage of eliminating the reference material, the complicated chopping device, and electronic circuitry for synchronization and amplification. High-frequency dielectricheated DTA equipment capable of treating samples up to 100 grams has been described (338) and mathematical treatment of the resultant thermograms given. It hag been applied to curing kinetic studies of rubbery materials (339). Simultaneous X-ray dflraction-DTA equipment has been applied to a number of clay minerals and inorganic hydrates (609). DTA equipment, providing for the automatic introduction of eight individual samples in capillary tubes, has been developed (346) and demonstrated by successive treatment of cuso4. 5Hz0 samples. Another equipment has been described (166) that simultaneously records eight types of thermograms, including DTA. A glass capillary tube has been SUKgested for use in DSC for samples that react with conventional A1 sample cups (346); however, Au sample holders have been suggested (320) for the same purpose. DTA with sealed capillary
tubes has been suggested (go), and it d that problems of has been p ~ i ~ i t eout vaporization and sublimation have been avoided by this practice while still providing adequate sample for other methods of analysis (286). However, a sealed capillary in the DSC of CuS04.5Hz0 gave only two endothermic peaks, rather than the usual three (346). The Kessis (169) DTA sample holder gave improved performance with anhydrous myristate when the lower part was replaced by a brass section ($NO), increasing the thermal conductivity. Pt gauze crucibles have been prepared for TG and DTA (166), and their use in studies of UOZoxidation and CaCZO4. H20 decomposition has been demonstrated. DTA peaks were found to be intensified and T G weight losses occurred over a narrower temperature range. CO evolution a t -200 OC has undergone catalytic oxidation with the walls of Pt crucibles to the extent that it interfered with thermal investigations (261). Ammonia catalysis also was observed. However, neither effect occurred with corundum crucibles. A similar investigation, involving NH4NOa decomposition, showed the reaction to be violently exothermic in metal or metal oxide sample holders (106), while the reaction was endothermic in graphite or corundum sample holders. Effects of grinding samples have been studied by DTA, usually accompanied by X-ray diffraction, which shows increased amorphicity with grinding. Fluorite (243), kaolinite (%'go), and boehmite (260) have been so treated. Grinding of AgN03 (235) has increased the transition temperature 5.5 OC. NiO doped with Lis0 has been shown (6) by DTA to be more reactive than NiO or NiO doped with Crz03. Addition of KC103 to CaCn04.H20had no influence on its decomposition (166). DSC, DTA, and T G investigation indicated that particle size had an influence on the decoinposition of Mg(OH)z (141), shifting the temperature to lower values with particle size decrease. Sample packing has been reported (206) to be a factor involved in inconsistent results obtained by DTA and DSC. Packing influences two distinct effects: gaseous diffusion and particle to particle contact associated with heat transfer in the system. The former can influence peak temperatures, while the latter more generally affects base-line drift. Uniform sample preparation by a die technique and
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appropriate positioning of the pellet improved the calorimetric accuracy of DTA (44). While optimum pellet size was found to be 3-5 mm (&), pressed pellets of 3-mm diameter gave highly reproducible results in a StoneTracor ring microsample holder (325). A tamping device has been described (104) to ensure more uniformity of packing in the Du Pont Model 900 high temperature cell. The heat transfer coefficient, K , of a DSC cell can be affected by the use of static or dynamic gaseous atmospheres, and in the latter case by the nature of the dynamic gas (74). Differences are more pronounced with pressure (74). Where gases are involved, either as reactants or products, some type of control is required to ensure repeatability. DTA of MnO2 in N2, air, and 02 (327) resulted in significant changes in peak temperatures for all but the 1200 "C peak. Changes in ambient atmosphere have influenced the decomposition of ZnC2Ol.H20 (166), and FeSp heated in Ar and air leads to the formation of distinctly different products (284). In a study of 25 oxalates (sa), DTA was used to distinguish between three reaction types: (A) those forming metals in NI, (B) those forming the lowest valence state oxide in N2, and (C) those forming the same oxide product in N2 and 02. I n 0 2 , the first group produces the oxide and the second group forms a higher valence oxide. The temperature of zeolite dehydration decreases with decreased pressure (273). The dehydration of MgSOd.7H20 had been the subject of considerable conflicting data until DTA, TG, EGA, and X-ray diffraction were applied (186) over a wide range of conditions that permitted assessment of the influence of H 2 0 partial pressure. While the atmosphere can create problems, it has been suggested (21) that it can be used to promote, or inhibit, specific reactions to good advantage. Recommendations for reporting thermal analysis data have been republished (206) and their implementation is strongly recommended. While it is doubtful that universally accepted results (88) will ever be obtained, data reported in the recommended manner should eliminate ambiguity in the interpretation of results. The ICTA's efforts to evolve standards has been reported (207, 216) and has resulted in the availability of standard materials from the U.S. National Bureau of Standards. The distinction between standards and standardization has been addressed (118) and it has been pointed out that the technique should not be standardized. Each test must be designed to optimize the specific parameter being investigated. The preparation of the double salt, Na2C03. CaCOa, from simple materials has 514R
resulted in the suggestion to use its inversions in the 390-450 "C range as a DTA standard (808). Au, Ag, and Cu (8), and T1 and Bi (180) have been suggested for high-pressure standards. An electrical technique to measure sensitivity and response time of DTA sample holders has been described (85). The analysis of the calorimetric response of the Du Pont 1200 "C DTA has shown (222) calorimetric precision of +2y0 with proper attention to technique, with a larger deviation in accuracy of :t5%',. An analysis of the Perkin-Elmer DSC-IB (106) has shown that heats of transition within 1% accuracy can be determined when the base line is unambiguous. Transport of heat through the sample was not found to be a limiting factor for many materials, but correction for several instrumental time constants was found to be necessary, if temperatures of transition or kinetic parameters were to be determined. I n a general method for characterizing thermoanalytical data (96), it was found that the salient features of the peak could be characterized using its iatrinsic parameters, but will be subject to base-line placement error. It was noted that if a good model were available, then a physical interpretation of the parameters might be obtained. A simple mathematical model has been developed (27) which permitted good reproduction of the CdCOs peak and reproducible kinetic constants without total comprehension of phenomenological details. Another model (214) considers the effect of sample and block parameters on the area, shape, and peak temperature of a typical DTA peak. A computer program accounting for thermal lag and heat capacity differences between initial and final states also has been developed (145). It has been shown (31) that "nonideal" adjustment of equipment can provide quantitative data, provided experimental runs, without adjustment, are made with and without the sample, and with the sample diluted with a nonreactive diluent of kqown specific heat. Curves so obtained permit base-line correction, determination of the specific heat, and heat of transformation in that order. Values obtained for specific heats and heats of transformation were in good agreement with the literature, with the exception of NHdBr and NH4C1, where the significant variation made the literature values suspect. I n a subsequent paper (SB), the influences of sample weight, bulk density, thermophysical properties, and thermocouple position were discussed. It was concluded that, within the limits of experimental error, the calculated heat of transformation is independent of these variables. The preceding work was conducted with AT plotted as a
ANALYTICAL CHEMISTRY, VOL. 44, NO. 5, APRIL 1972
function of time (SO), which was recommended rather than AT plotted v&. temperature. In another study (214),a mathematical model was developed considering numerous factors influencing the thermogram peak, including conductivity, density, specific heat, sample radius, heat leakage through thermocouples, etc. Some conclusions from this work are cited below. The area under the peak is directly proportional to heat of reaction and sample mass and inversely proportional to thermal conductivity. Area, measured as AT us. time, is independent of heating rate. The temperature of a DTA peak increases with increasing sample radius, but less than that of the reference, so DTA curves should use sample temperature as the abscissa. With large sample radii, the reaction is governed by an equation which is heating-rate dependent and distorted peak shape results. The peak reference temperature increases with increasing density and specific heat, and decreasing sample conductivity. Heat loss through the thermocouples causes reduction in peak area and also lowers the peak temperature. A rigorous mathematical expression for the evaluation of heat of reaction has been developed (910). While its application to experimental data is laborious and complex, simplifications were offered. The determination of calibration coefficients for enthalpy measurements has been described (68). Provided corrections for thermocouples and heat leakage can be made, DTA has been found capable of obtaining rough values of thermal conductivity with small samples (112). A double junction thermocouple arrangement, bolh junctions protruding from the thermocouple sheathing, has been used, and mathematical expressions have been developed for its quantitative application to DTA in liquid media (42). Advantages cited for this system were: dependency on thermal conductivity i s eliminated; specific heat requirement is essentially that of the medium (97% of mass) ; thermocouple positioning is unimportant, but peak area is greatest when one junction is centered; and variations due to sample packing are eliminated. The technique was applied to the melting of Na2S04.10H20 and NazS203.5Hz0 in several solvents with measured heats of fusion agreeing extremely well with literature values. Enthalpy measurements have been made for transitions occurring in cholesteryl esters (75, 76, 97, 360), synand anti- [2,2](1,4)-naphthalenophane and djbenxoequine @IO), tetramethylsuccinonitrile and tetramethylsuccinic acid ($SI), and a series of dibenzazepine derivatives (122), typifying work with organic materials. Inorganic materials have included transformation enthalpy
measurements on Cu(OH)2 (989); HfOC12 and ZrOClz (9.86) ; A&, AsaSe, AszTea, and Sb& (917); CuSO4.5H20 (3.43); and NaBF4, RbBF,, and DsBF4 (197). Deuterated Rochelle salt was found to undergo DSC decomposition a t 50.0 "C, 0.5' lower than the temperature for hydrated Rochelle salt (123) and with an enthalpy of 15.2 kcal/mole, as opposed to 16.6 kcal/mole for the hydrate. These data confirm earlier work (117), where deuterates of CuSO4 and BaC12 were shown to be less stable than the corresponding hydrates. Heats of fusion have been measured for partially hydrolyzed ethylene-vinyl acetate copolymers (323), polyethylene brominate to various degrees ( I S @ , ethylene-propylene blends (90), polydimethylsiloxane (182), and polydiethylsiloxane and polydipropylsiloxane (183). The specific heats of 26 polyquinoxalines (354), and variations in the specific heat of amorphous polystyrene have been measured with particular reference to sample treatment (69). Sealed glass ampoules were used as sample holders in the measurement of the heats of polymerization of styrene, methyl methacrylate, and acrylonitrile (59). While the value for styrene agreed with most literature data, values obtained with the other two monomers were on the high side. Polymer crystallinities also have been determined calorimetrically (148). DSC has been applied to determination of heats of mixing and vaporization (224), sublimation (26), and vaporization (101, 189). Preconditioning of samples has been demonstrated (220) as a means of eliminating the difficulties associated with overlapping peaks in quantitative analysis. When a polymorphic transformation is used for quantitative work, interfering effects associated with decarbonization, dehydration, etc., can be eliminated by initially heating the sample beyond the temperature range of detection (269). Chart paper nonuniformity has been an impediment to the peak area paper weight technique of analysis. This problem was overcome by using a Xerox copier to transfer the area to a high quality vellum (268), a technique found to result in greater reproducibility than the planimeter method. Protection of thermocouples in thermal analysis of sulfide minerals prevents corrosive attack (34) that could lead to spurious results and has permitted identification of these minerals in 82 ore samples. DTA apparatus has been designed for purity determination in organic compounds (199) with an error of less than *0.001 mole yo. While most purity work has been confined to organic compounds (162, 291), the measurement has been applied to metals (19) to extend the technique. It
is interesting to note that in this work (19), the actual samples were subjected to atomic absorption analysis to eliminate errors associated with blending in large samples. Seven guidelines were established for this technique (19), including a sample size of less than 3 mg, which should make it possible to measure as little as 0.005 mole % I n in Pb. Low heating rates, or cooling rates, are not conducive to generation of analytical data based on phase transformations (282). A minimum heating rate of 3 O C was required to observe a continuous heat effect for the DTA determination of the monoclinic-tetragonal transformation in ZrOr and ZrOr based systems. The 915 "C transformation peak of tricalcium silicate was used for analysis of this material in portland cement (269), obtaining results in good agreement with X-ray data. Ca(OH)2, formed in the course of hydration of tricalcium silicate, was determined (968, 970) by area measurements of the dehydration peak. A statistical analysis of the thermograms of hydrated cement ( B l l ) , relating area, intensity, and temperature of peaks, has shown correlation between two (second and third) observed peaks of samples hydrated for various times. SiOz has been determined by the intensity of the 573 OC transformation, using three techniques (230): heating to 1000 OC and measuring intensity on cooling, heating in an auxiliary furnace and measuring the intensity on heating, and heating to 750OC and measuring the intensity on cooling. The last was preferred because the lower temperature minimized potential reaction with other materials. It has been demonstrated (342) that differences in quartz content of minerals by DTA and X-ray analysis can occur in both techniques depending upon the form present. Ground and explosively crushed quartz exhibit a 300 O C exothermic peak that has been associated with its reactivity (170). Assuming this peak results from crystallization, the phenomenon occurring lower than the 573 OC transformation would not interfere with analysis. DTA of alunite mixtures, particularly with carbonates, have been shown to undergo a number of solid state reactions that could influence analytical data derived by this technique (187). Peak height, peak width a t half peak height, and peak area were explored as methods for analysis of carbon in fly-ash, coke, char, coals, peat, etc. (316), and the area method was found most useful. DSC was applied to a-D-glucose to assess purity (66), and the apparent purity was dependent upon the duration of scanning, as was the melting point. Chromatographic examination of trimethylsilylated samples indicated anomerization occurring in the melt.
However, this change was not reflected in the apparent purity measurement. A DSC method has been evolved to determine 1-monopalmitin in a mixture with 2-monopalmitin (318). The quantitative analysis of polymer polyblends by DSC (13) has been based on the establishment of the ratio of the specific heat increase at T, for the blend to the parent material. Using this technique, the amount of styreneacrylonitrile copolymer mixed with polybutadiene was found to be 76%, compared with 77.9% by the phase separation technique. I n polyphenyloxidepolystyrene blends, a single T, was found (IS), which increased with increasing polyphenylene oxide, and allowed analysis of the polyblend. This work has been extended to analysis of polyvinylchloride polyblends (12). DSC was applied to the quantitative analysis of plasticizers in polymers (203) with good reproducibility. I n this work (,%?OS), a comparison of DTA and DSC resulted in the following conclusions: small sample size was required in DSC to avoid a large positive shift in the endotherm temperature region; DTA gives a more intense peak due to larger sample; and the endotherm is more diffuse and variable with DSC. Improved results were obtained by use of pressed samples, encapsulation (DSC) to improve pan contact, dilution with glass beads (DTA), thermal conditioning of the sample, normalizing procedures, and replication of samples for rejection of obviously atypical thermograms (203). The water binding index of proteins, defined as the ratio of the energy to remove 1 mg of H20 from a protein to the energy to evaporate 1 mg of H20, has been determined by DSC (167') with values of 1.09 obtained for soy protein, 1.16 for beef muscle tissue, and 1.45 for sodium caseinate. An extremely interesting application of DTA to the measurement of edama in rats following burns (146) showed three endothermic peaks in control skin samples and only two in burned tissue. After 24 hours, the return of the threepeak pattern suggested tissue healing. The coupling of this effort with the water binding technique would appear to offer a means of quantification of burns. Derivation of mathematical expressions for the rate constant has been made (310), and the mathematical treatment of non-isothermal crystallization kinetics has been presented (248). Simplified techniques have been employed, with relative rates for reaction of aromatic amines with epoxy resin being determined (321) using a ratio method for two different peaks, and a single peak technique (267, 268) being used to study the kinetics of gypsum hydration (229) and dehydration of a number of hydrates (273). An elegant
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method for determination of kinetics and thermodynamics by a n isothermal DTA method has been demonstrated (164). In this technique, samples were brought to temperature in an atmosphere of their decomposition product gas and, on removal of this atmosphere, decomposition is initiated. Areas obtained during the course of decomposition a t different temperatures remain the same, providing the basis for determination of A H , and the rate of reaction a t each temperature were determined from the length of time required for reaction. While restricted to processes involving gaseous reactants, the method appears to be the most satisfactory approach to kinetics by DTA. Isothermal DSC was applied to decompositions of N-aryl-N-tosyloxydiimide N-oxides (84) with reactant consumption being determined by the fractional area method. Arrhenius activation energies, obtained from a plot of the common log of the rate constant us. 1/T, were compared with those obtained from constant heating rate data (280) and from the common log of the maximum deflection during isothermal heating plotted us. 1/T. While there was no correlation with the former, there was with the latter. It has been pointed out (281) that the reaction order should be determined before any attempt is made to derive kinetic constants. An expression was derived (281) for the determination of the Arrhenius activation energy from a DSC curve and the procedure outlined for attaining kinetic parameters. The technique was applied to the thermal decomposition of RDX and differences in parameters were shown as a function of assumed and determined order. The classical Borchardt- Daniels (46) kinetic technique has been reviewed (303) and some difficulties with it were pointed out. Curve integration, coupled with Doyle's (86) method, permitted a graphical method to be evolved (303). Computer derived curves from nine different rate processes made graphical matching a relatively simple process (303). Typical of many other kinetic investigations are those on alkali metal picrates (313), trjs(oxa1ato) metal(II1) complexes ( S o l ) , and isothiocyanate complexes (168). Temperatures of solid state transformations have been determined in alkali metal stearates (277), alkali metal sulfates (%'74), K20 (328), rare earth aluminates (119), and alkali metal tetrafiuoroborates (196). An orderdisorder transition has been found in LiNHz a t 83 "C (108). Dehydration temperatures have been determined for a number of fluoroberyllates (11), alkali metal hexamolybdochromates ( l 7 9 ) , CoCI2.6H20 (964), and Sr(HzPO&.HzO (300). A study of the 516R
decomposition of MgCO:*3Hd under a CO1 atmosphere indicated that two routm were followed (81): decomposition occurred via MgC0,-2Hz0 a t 760 mm CO,; and, at 100 mm C02, the 232 "C peak separated into two, indicating MgCO,. 2H20 also was formed. Dehydration of chromium hydroxide was shown (33) to proceed through formation of Cr20,.3Hz0 and CrzOa*H10to form CrzOl. Compound decomposition has been exemplified by decarbonization of EuCOa (80) and thermolysis of Mg oxalates and chlorooxalates (340), silver carbamate (40), and alkali metal salts of salicylic acid and p-hydroxybenzoic acid (136). DTA has been shown (271) to be useful in identifying glass types and an aid in furnace design for sealing glasses. Low temperature exothermal effects have been associated with glass phase separation (223). A DTA study of drawn glasses (92) has given useful information on the process, Le., an exotherm at ca. 200 "C and simultaneous disappearance of the coalescencesintering effect appear to be related to a siliceous phase a t the surface and an exothermic trend beyond T , is associated with fiber toughness. Chalcogenide glasses have been studied by DTA and DSC techniques. Using the latter method, it was shown (218) that a constant T , existed in Bi-Se glasses, with Bi contents > 10 atomic %, resulting from the tendency for nonrandom association. It also was used to show that in the composition 2AsnSea-AszTea,neither phase separation nor crystallization was observed. DTA was used to show the glass forming region in the Ge-As-Te system (288), crystallization and T, temperatures in the Ge-Te system (SIT), and transition and devitrification temperatures in Ge-As-Te and Ge-As-Se systems (269). After examination of a number of glassforming systems, including the elements, oxides, and sulfides, it was found (286) that the empirical rule suggested for organic polymers, that the ratio of T , to melting temperature equals 2/3, holds for such systems. Phase equilibria have been studied for a number of varied systems. Oxide systems are exemplified by PbO-SnO and GeO,-SnOz (110), and M o o r BaO (333). I n the metals, Pu-Cu (98), Ge-Sr (297), and Pb-T1 (263) have been examined. Among the halide systems investigated have been MgC12MgFz, CaF,-MgF2, and NaC1-MgF2 (299); NaF-KF-BF3 (22); and T1FThF4 (10). While many of the phase studies indicate the formation of compounds, e.g., PbS in the Pb-S system (178) and KAg414CNin the KCN-AgI system (216),other investigations have been directed toward synthesis. Coprecipitated BaCOa and ZrO(0H)z were shown to form BaZrO, a t a lower tem-
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perature than a mechanical mixture of 210,and BaCO: (186). DTA has been used to study the formation of manganese-zinc ferritm from the hydroxides (66) and of magnesium-manganw femtea from precipitated carbonates (176). The preparation of several selenides by reaction of the respective oxide with Se was shown (30s) to occur with formation of Se02 and MSe. This was followed by reaction of the selenide with the oxide to give the selenate. It was stated that intermetallic compounds are best studied by DTA (839) rather than through the more usual mixing, heating, grinding, refiring, etc. DTA permits determination of temperatures of reaction and decomposition, establishing the regime for synthesis. DTA has been used to characterize polywater (7$, the thermogram indicating melting a t -30 "C and boiling, or decomposition, in excess of 300 "C. Values of T, of aqueous solutions of glycerol, ethylene glycol, and methyl alcohol were extrapolated to give a T, for amorphous water of -137 "C (272). While TI showed no marked changes, DTA indicated a 250 "C exotherm in irradiated chromium phosphate ion exchanger (364) which indicated that the polymeric structure had been ruptured by radiation. It has been shown by DTA and TG that mixtures of oxides autoclaved to the critical point with solvents such as ethanol, butanol-1, and CCh are made lyophobic through incorporation of alkyl and CC13radicals on their surfaces (334). Heats of desorption of n-alcohols, CTCS, from laminar silicates were found to be significantly higher than their heats of vaporization (133, 134), indicating a chemisorption process. A plot of the contact angle between a liquid and n-hexatriacontane, or the surface tension of the solid, us. temperature showed a sharp break which corresponded to the enantiotropic phase change observed by DTA (144). The results, which offer interesting surface chemistry possibilities, were explained on the basis of molecular rotation. Polymorphism of mesophase materials has been investigated (160) and factors influencing the results were discussed. Nematic compounds derived from cinnamic acid (149), aldonitrones (361), and Schiff bases (316) have been investigated. Decomposition temperatures for 19 amino acids have been determined (244) and polymorphism in several 8-substituted naphthalene derivatives was determined (237). Phase transitions were determined in ferrocene ( @ ) ,hexanitroethane ( l 7 4 ) , and anhydrous and hydrated ceryl alcohol (329). Fusion and transition temperatures and enthalpies of fusion and transition for several organosilicon compounds were determined (233). In the
latter investigation, i t was reported that transition temperatures were sharp, while fusion temperature were more di5cult to establish because of low heats of fusion and impurity temperature depression. Phase studies in organic systems have been exemplified by DTA application to triglyceride derivatives of palmitic and stearic acids (266) and by naphthalene-bsubstituted naphthalene binary system investigations (938). The T.'s of several organic glasses have been determined by DTA (168). Methanol release from the hydroquinone clathrate has been studied by DTA and T G (61) which indicated crystal fragmentation at ca. 120 "C, followed by methanol release between 120 and 160 OC. However, a small distinct peak a t 163 "C also was related to methanol release by GC, and this peak, unaffected by Ar or air, was related to the quantity of methanol originally released. This indicates two mechanisms of release. DTA was used to study the effects of nuclear reactor irradiation on several explosive materials by comparing thermograms of irradiated and non-irradiated samples (276), and the order of decreasing stability was found to be DATB, HMX/EXON, TNT, PETN, and nitrocellulose-based propellants. I n this work, an anomaly was found in irradiated DATB, the decomposition exotherm increasing with exposure rather than being lowered as was the case with the other explosives. A review of the applications of thermal analysis to explosives has been issued
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(204)
The determination of polymer T i s by DTA and DSC has become common practice. T i s have been determined for butadiene-acrylonitrile copolymers (67) and for nylons (186). I n the latter investigation, time-dependent anomalous effects were observed and explained on the basis of a slow-forming, hydrogen-bonded network. I n another investigation of several systems, the time dependency was related to the number of frozen-in holes (363). The influence of plasticizer (water, glycerine, and mixtures) on the T , of ionenes indicated the differences observed result from the solvent alternation of the nature of the polymer with which it interacts (96). T , of styrene-butadiene copolymers were determined by DSC and the data were found to be in good agreement with NMR results (162). Mathematical expressions have been developed relating sequence distribution to T , in butyl methacrylate-vinyl chloride copolymers (161). The T , of copolymers of tetrafluoroethylene with several fluorinated monomers also has been measured (61). I n the DSC examination of styrene-ethylene oxide block copolymers (247), T i s were associated with each block and their
variation was associated with segment molecular weight rather than copolymer composition. The T,values for 22 polyquinoxaliies, as well as heat capacity differences, were measured by DTA (566) and the data were discussed in relation to four possible motion modes associated with a flexible ribbon structure concept. I n this investigation (566),instrumentation for a new thermal analysis technique, dynamic scanning dielectrometry, was described which contained a test cell capable of being heated to 500 "C at linear rates from 0.5 to 30 "C per minute. Melting and crystallization of copolymers of nylon-6,6 and nylon-6,10 with polyhexamethylene teraphthalamide (nylon-6T) have been studied by DSC and hot stage microscopy (140). The microscopic melting temperatures, taken a t the disappearance of the last trace of birefringence, gave temperatures of the order of 4-9 "C higher than DSC results. An extensive investigation of &polyamide (168) indicated that quenching and tempering conditions could depict one or two DSC melting endotherms, that the a-structure was so unstable that melting points could not be determined, that the a-structure had a heat of fusion of 55 to 64 cal/gram depending on the crystal density used, and that exact determination of crystallinity was not possible from fusion measurements. Polyurethanes, with soft and hard segments, were subjected to DTA and DSC, and fusion peaks and enthalpies of fusion were determined for the respective segments (138). DTA was applied to block copolymers from polydiethylene glycol adipate and poly(o-bis [b-hydroxyethoxy ]phenylene adipate) and hexamethylenediisocyanate (368) and DSC used to examine p,p'diphenylmethane diisocyanate chain extended with butanediol (296). Copolymers of a-olefin-SOz, with even numbered a-olefines from CB-C~B, were prepared and their melting temperatures were determined by DTA, DSC, and Kofler melt bar (67). While the DTA and DSC results paralleled each other closely, the Kofler data did not follow the same trend when melting point was plotted us. a-olefin chain length. The thermal stability of oligomeric arylenes (38) and polymers containing aromatic isocyanuric rings (4) has been studied by DTA. The decomposition of stabilized polyoxymethene was studied in pressurized DTA equipment (366) where i t was found to be accelerated by the presence of small amounts of 0 2 . The melting temperature of polyethylene was found to vary with filler content (178) and thermal oxidative resistance was found to be improved by incorporation of car-
bon black, chemically precipitated chalk, and sulfochlorinated polyethylene plasticizer. Oxidative resistance was decreased by cross-linking (179). DTA has been incorporated into a system (64) developed to establish the relative potential of a chemical to release energy suddenly and to indicate the magnitude of that release. I n a DSC study of cellulose decomposition in N) (7), it was found that this material decomposes by two competitive reactions: (A) dehydration to anhydrocellulose as low as 210 "C, and (B) depolymerization of nonreacted cellulose to levoglucosan a t ca. 270 "C. The conditions of the experiment will determine the DSC scan of the latter reaction (7), i.e., endothermic if the levoglucosan volatilizes and exothermic if decomposition to char occurs in the cell. The degree of substitution of cellulose derivatives, substitution consisting of introduction of cyanoethyl, trityl, sodium carboxymethyl, hydroxyethyl, benzyl, benzhydryl, and 2-ethylhexanoate groups into the cellulose structure, has been studied by DTA (66). With a well-defined peak as a prerequisite, a calibration curve is established by plotting either peak area or peak height us. degree of substitution, with the latter determined by chemical analysis (66). THERMOGRAVIMETRIC ANALYSIS
A recording thermobalance for T G to 1400 O C at 8.5"/minute in dynamic He has been described (g46). An interesting feature of the equipment was the sample temperature monitoring by a 3-wire Pt/Pt-l3Rh/Pt thermocouple, with the grounded third (Pt) leg eliminating random noise above 1000 OC. A microbalance, employing a tungsten helix, has been employed (M7) with a vacuum system to determine the kinetics of Cu oxidation at low 02 pressures. A twin furnace microthermobalance has been reported (276) for operation in controlled 02 partial pressure. However, its operation was impaired by a limited hot zone. Stainless steel and quartz springs were incorporated into a microbalance operated in atmospheres of 0 2 , GO, and C02 (331). A silica torsion microbalance with a sensitivity of 1.37 X lo-' g/mm and a 60-mg capacity has been developed (113) for studying vacuum deposition processes. Low temperature vaporization rates of the order of 10 pg/min have been measured (78) with a vacuum microbalance monitored with a time derivative computer. An automated, top-loaded thermobalance has been described (49), which is capable of automatic positioning, heating to a preselected temperature, and removing eight successive samples. Such a system used with the
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devised electrical circuit that permits T G curves to be plotted aa per cent mass loss u8. time ( 3 4 ) would sign%cantly shorten the on-line TG analyses (I 30). Simultaneous DTA-TG measurements have been made (348), with evolved gases being measured by gas chromatography and mass spectrometry. In this work (38), both EGA techniques were considered analytically equivalent, but GC was the slower technique. The Derivatograph has had EGA incorporated through transport of gaseous products to an absorbing medium where titration occurred with an automatic buret (863). A review has been written ($78) on the disturbances in gravimetric measure ments from thermal gas flow and precautions for minimizing such effects. The phenomenon of initial weight increase in decomposition studies was investigated (349) and has been mathematically related to temperature and the nature of the gaseous atmosphere. I n a study of BaO condensation rate of evaporation products from a coated cathode ( S d l ) , electrostatic forces, causing errors of 50-100 pg, were eliminated by painting the system exterior with silver paint and grounding it. I n this work, magnetic forces were found to be the most serious source of error, only partial correction occurring by use of a Pt counterweight. It has been suggested (840) that magnetic transitions be adopted as TG temperature standards. Materials, with their magnetic transition calibration points, suggested were Alumel, 163 "C; nickel, 354 "C; Perkalloy, 596 "C; iron, 780 OC; and HiSat 50, 1000 OC. These offer an attractive temperature range. TG in self-generated atmospheres has been reviewed, several crucibles described for this mode of operation, and the technique applied to decomposition of PbO, PbC03, and Mn(OHc)2-4H20 (236). The evaporation of oil-solvent mixtures (188), the determination of the diffusion coefficient of vapors in gases (79), and enthalpies of sublimation (8) have been determined. BaOz decomposition temperatures were determined by TG in pure O2 and in 0z-N~ mixtures (326) and, from a plot of log ~ ( 0 % us. )1/T, enthalpies and entropies of reaction and the formation of BaOz were calculated. The difficult analysis of maleic and fumaric acids in the presence of each other has been shown (322) to be very simply accomplished by TG. Maleic acid evaporates, a t different rates from solid and melt, from the mixture by 200 "C, and, above 210 "C, fumaric acid starts to sublime, resulting in two welldefined TG steps. While pyrite and calcite decompositions are easily studied with the separate materials, it has been reported (293) that when they are to518 R
gether side reactions take place, introducing large negative errors. Procedures, together with correction tables evolved from synthetic mixtures, have made such a n analysis possible. TG to 600 OC can provide (898) the means of analyzing mixtures of CaHPO4.2H20 and CaHPO, with an error of =!=0.5%. The purity of Fe, Co, and Ni disulfides has been determined by T G (360),and the method has been suggested to be broadly applicable to the analyses the inorganic chemist faces in solid-state materials. A TG system has been developed (16) to determine the S content in the Cu-S system, but is considered generally applicable to sulfide systems. The system incorporates a gas manifold for regulation of H~S-HZmixtures, and a means of introducing dry NPthrough the support column to eliminate S deposition and corrosion of the electronics. Buoyance and volatilization correction techniques were applied. One of the most significant applications of TG is in the field of kinetics and a number of contributions have been made in this area ranging from the manner of plotting curves (384) to computer calculation techniques ($96, 336) to specific applications such as cellulose degradation (60) and cobalt(111) amine complexes (128). It has been pointed out that isothermal measurements give more information about reaction mechanism than the conventional T G trace (287) but the latter do have advantages in studying rapid reactions a t high temperatures and the temperature and fraction of material decomposed are well-defined with a constant heating rate. Tables have been developed for log g ( a ) (287) to simplify the use of the log g (a) - log B, Doyle's (86) expression for p(x) TG decomposition. I n addition, graphical plots have been given (287) for nine different kinetic expressions that permit a rational approach to best fit of the process. Iterative calculations of E , and t,, the apparent activation energy and the equivalent isothermal time in Doyle's (87) method comparing the TG curve to one obtained isothermally, eliminates the inaccuracies in these two values (363) and permits E , to be calculated with an accuracy of ca. + O . l kcal/mole. The Freeman and Carroll ( I l l ) , and the maximum point method (3,114) have been compared with a new ratio method (119). The difficulty with the Freeman-Carroll method was determined to be the necessity of measuring several slopes accurately, while the maximum point method has the disadvantage of determining kinetic parameters from a single point. The ratio method consists of taking the ratio of the log of the rate expressions a t two different conditions, which eliminates the frequency factor, and from a single plot the activation energy is determined
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by the slope and the reaction order from the intercept. Ratios selected near unity require accurate knowledge of the temperature and the slope of the thermogram if any straight line is to be expected (1.5 and 3 were used). The methods were applied to the decomposition of a urethane polymer prepared from 3,4-toluene diisocyanante with a polyol. Comparison of the FreemanCarroll method, Coats-Redfern method (63),and a differential method (1) has been made ($98)using the decomposition of CaCOs (pellet and powder) and mixed with A1208 and with a-FezOa. The Freeman-Carroll method gave significant scatter in plotted data, leading to uncertainty in the value of E . The other two methods yield substantially the same results and can lead to satisfactory kinetic analyses when experimental conditions minimize temperature gradients within the sample. The Coats-Redfern method involves less tedious calculations and avoids determination of tangents, while the differential method has the advantage of direct measurement of A from the intercept. Non-isothermal TG has been used to study the catalytic decomposition of NaClOa (367), CaC204.HzO (336),and reduction of UO, and UaOs (36). I n the reduction of UO8 to UOZJI,the activation energy calculated by Piloyan DTA method (268) was 49.8 kcal/mole, while that from TG gave a value of 80.1 kcal/ mole. More reasonable agreement was obtained for other reduction processes. Isothermal weight loss measurements also have been used to determine the kinetic parameters associated with CaCzO4 H20 dedomposition (83),UaOs decomposition (226), and of the reactions of MgS04 with CrzOa (160) and Ti02 with SrCOa (161). Sr(0H)z.8Hz0 decomposition has been studied (36) with two stable phases being encountered: Sr(OH)z.HzO stable from 140-150 "C, and Sr(0H) stable from 200 to the melting point, 450 "C. Z ~ ~ ( O H ) Z ( N O & . ~ Hwas ZO found to dehydrate in the range 65110 O C , and decomposition of the anhydrous compound to ZnO occurred over the range 130-240 "C (312). C o t ( O H ) Z ( S O ~ ) Z . ~ Hstudied ~ O , by DTA and TG (89), was found to dehydrate to CO~(OH)~(SO~)Z, and then form C o t 0(S04)z. Dehydration of a series of 8-hydroxyquinol celates (127), of oxalate hydrates (261), and of hydrated nitrates (26) have been studied. The investigation of CaS04.2HzO dehydration in the presence of pure water vapor at 1-100 Torr resulted in the conclusion that a solid solution of water of insertion in anhydrous CaS04 exists with a steric saturation corresponding to CaS04. 0.66H20, rather than the definite compound CaS04.0.5HzO (116). I t should be noted that the a- and ,%forms of
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CaSO1.0.5Hz0 are not distinguishable by IR (62) and, again, the suggestion made that H20 molecules in the hemihydrate, due to the loose manner of binding in the crystal lattice, were held in an interstitial manner. The thermal stability of a series of metal acetate ammines @9), and dimethyl sulfoxids and diethyl sulfide adducts of Rh2(OAc), (h4) have been determined. Isothermal weight loss studies of by conventional irradiated "&lo4 gravimetric techniques (107) have shown the instability induced in this material with irradiation. The more elegant thermal analysis route, DTA and TGA, was taken (213) to show that beta self-irradiation of 147Pm2(C204)3-3H20 results in the formation of a material with the apparent formula Pm2OzC03.3H20. T, in NZ has been used to study the formation of CdS-CdSe solid solutions from CdS and Sd (60), and reaction was shown to occur a t 250-350 "C with each 2 Se atoms required for the replacement of each S atom in the CdS lattice. Together with DTA and thermodynamic calculations, TG has been used to show that LiAlH4 2Al 3& decomposes to LiaAlHe (48). Decomposition of the group I1 metal acetates was studied by DTA and TG (208) and it was shown that the Ba and Sr compounds formed the carbonates, while the oxides were the products in the case of Mg, Cd, and Zn acetates. Isothermal weight studies have been conducted on aqueous MnS04 solutions and the kinetics of decomposition steps determined (116) and, in a related study, the kinetics of freeze-dried A12(Ej04)a andAlNH4 (SO4)pweredetermined (169). Cryochemically prepared AINHI(SO& and crystalline alum hydrate were subjected to DTA and T G (260) where it was observed that the cryochemically prepared material had only 5.5 moles of water associated with it and was highly amorphous. Above 320 OC, thermograms were identical. T G was used to show that a t 577 OC and above, F e was more strongly oxidized than Cu ( 1 7 l ) , but when coated with enamel, the reverse was true. DTA and T G were employed (9) to show that meconic acid is decarboxylated to comenic acid a t 240 "C. The tendency for this product to sublime did not permit further decarboxylation to be studied. Decomposition kinetics for malonic acid were determined by the Derivatograph (132) using the differential T G curve to calculate the activation energy. Simultaneous DTA and T G showed (319) that phenobarbital monohydrate loses water of orystallization a t 82 "C and undergoes a phase transition a t 171 OC. TG, coupled with mass spectrometry, has permitted identification of evolved gaseous products from polymers, estab-
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lishment of the mechanism of degradation, and another route to kinetic parameters (361). Preliminary T G data indicate that it is possible to characterize block and random copolymers of aamino acids when the temperatures of the maximum degradation rate of the constituent homopolymers are sufficiently far apart (46) T G of monocarboxycellulose (CC), 1:1 CC-polyacrylonitrile (PAN) mixture, CC-PAN graft copolymer (40% PAN), and PAN (302) showed these materials to be in the order of decreasing weight loss, indicating reaction of components took part in carbon whisker formation. Examination of several model polymers indicated that the presence of amide groups in polyimide chains lowered the polymer thermal stability (279), the presence of the amide group resulting in two distinctly different kinetic processes: one below 42540°C with low activation energy and one above this range with a higher activation energy. A series of polyamides and polyimides with various linkages between monomer units, e.g., ether, thioether, carbonyl, triasole, oxazole, etc., were subjected to T G (177) demonstrating the increased thermal stability induced by incorporation of hetero rings in the structure. A series of reports from Wright-Patterson AFB has exemplified the high temperature TG applications. Carbon and graphite cloth reinforced phenolic composites were investigated to 1400 OC (99), and similarly reinforced polyaromatic and polyheterocyclic resins were investigated to the same temperature (100), and the TRIM computer program used to derive empirical kinetic parameters from such T G work has been described (246). I n addition to assessment of the thermal stability of vulcanizates, it has been shown (201, 208) that T G also can be used to determine the oil, carbon black, and filler contents of such materials. Derivative TG has been shown (126) to exhibit a series of maximum and minimum rates which are related to decomposition of epoxy resin and curing agent. The variation in the latter can be used to assess the degree of mixing through an adhesive and provide insight into bonding failure. Correlation has been found between the dynamic TG temperature at 5% weight loss in 0 2 and the thermal life rating of magnet wire (6.9). Incorporation of a photoelectric sensor in T G equipment has extended the utility of the equipment beyond weight loss measurements, permitting elastomer ignition points to be determined reproducibly with 2 "C (266). Exposure of nylon to liquids, with subsequent T G of the exposed nylon, permitted (41) determination of the amount of liquid sorbed and the activation energy of desorption. The results with 39 liquids indicated those with hydrogen bonding I
potential had the greatest interaction potential. ELECTROTHERMAL ANALYSIS
Electrothermal analysis (ETA) of polymers been reviewed (292). A sample holder has been designed for concurrent DTA and ETA (72) and its applicability to detection of moisture, glass transitions, crystallization, melting, and oxidation demonstrated. High pressure opposed-anvil equipment, using electrical resistance sensing has been described (337) and applied to S-Ni composites. Peaks were observed in the pressure-resistivity plot corresponding to S transitions. End-loaded piston-cylinder equipment was described (142) which used electrical resistance to follow high-pressure phase changes in Bi. I n such equipment, it has been shown (120) that corrections are required. Dilatometry and ETA were used to show phase changes in Sm a t 310 "C, and 588 and 598 OC on cooling and heating, respectively (198). Dilatometry and electrical conductivity with DTA and X-ray analysis were employed (311) to study the ZrO2-Sc208 system. I n this case, electrical conductivity isotherms, plotted us. mole 7 0 Sc203, were shown to have different shapes resulting from polymorphic variations occurring in the system. Conductivity measurements have been used to study the In-Zn, In-Bi, (262); Rb2SO4AgZS04 (53); and KNOrCa(K0a) (47) systems. Conductivity measurements were used to measure T, in the As-Se-Te system (242) and electrical conductivity, measured a t 50 "C, gave a linear plot with crystallization with As2SeTez (304). A discontinuing in the conductivity curve of Eu3S4 at 168 O K was confirmed by DTA, and associated with a phase transition ( 7 7 ) . Plots of the log of dark conductivity us. 1/T shows a transformation of semiconducting dcamphor into a plastic cubic phase at 244 "C (173). DTA, ETA, and dilatometry have been used to study the decomposition of Ca(OH)2, Sr(OH)z, and Ba(OH)2 (164), and dehydration of kaolinite was investigated by electrical conductivity (283) where the conductivity showed a strong maximum between 550 and 600 OC due to dehydroxylation. DILATOMETRY
Dilatometers have been described for low-temperature applications based on the rotation of a mirror centrally positioned on doubly twisted beryllium copper (964) and was applied to the thermal expansion of Cu below 10 O K . Another, operating in vacuum or various atmospheres, has been described to
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study solid-liquid interactions (70), and a two-component system dilatometer, with mixing accomplished by rupturing a capsule with an enclosed magnet, has been shown to be applicable to the study of physical chemical reactions (368). The Perkin-Elmer Thermomechanical Analyzer high temperature furnace has been described (6) and application of this equipment to the determination of the quartz transition, T, measurement in an inorganic glass, deflection measurements of polymers, and transitions in drawn nylon fibers was shown. The technique was applied to several synthetic fibers (136) and the resulting thermogram changes were found to agree with those determined microscopically. Du Pont TMA equipment was used in an isothermal mode to determine rates of polymer swelling and dissolution (191) and to measure the rates of penetration of a polymer by a spherical indenter (192). I n the former, polymethylenethacrylate, a t 23 OC, the volume swelling by methanol was found to be 131%, while that of ethanol was found to 92%, and the extended time diffusion coefficient for methanol was 7.6 X lO-%m*/sec, while that for ethanol was 6.6 X 10-8cm*/sec. Using 3-gram samples, cubic expansion with Hg as the working fluid was applied to the measurement of the mesophase transition temperatures in cholesteryl myristate (866) and in cholesteryl acetate (866). Transformation kinetics were found to fit the Avrami equation. EVOLVED G A S ANALYSIS
The EGA method is far from standardized. This results from the varied techniques employed to detect and measure evolved gaseous products. Further, this facet of thermal analysis is one of the most abused in terms of proliferation of abbreviations. Some of the abbreviations used are TVA for thermal volatilization analysis (!?IS), PGC for pyrolysis gas chromatography (368),GED for gas evolution detection (347),DSC-MS for combined DSC and mass spectrometry (91), and DTGT for derivative of thermogas-titrimetric curve (963). The recommendations of the ICTA Committee on Nomenclature (193) were to keep abbreviations to a minimum to avoid confusion. The Committee also has recommended the generic expression EGA for evolved gas analysis (196) rather than development of abbreviations based on specific techniques of specific effluents. One form of EGA is that based on the detection of released radioactive inert gas. This technique recently has been reviewed (16), indicating methods of incorporating the gas into materials, equipment to detect emanating gas, and applications to thermal analysis. It 520R
has been applied to the determination of the reactivity of Fez08 derived from various iron salts (17). Another radiochemical technique has been reported (506) which is based on the detection of “COP from 14C-labeled CdCOs and NaHCOs. The applications of coupled gas chromatography and TG (68) have shown the utility of this approach. Mass spectrometry has been coupled with DTA and TG to show the evolution of HzO and Cot from clay (307); with DTA to study thermal analysis of complex inorganic and organometallic compounds (181);with DSC to analyze the thermal and oxidative decomposition products of rosins, dicumyl peroxide, and methyl parathion (91); and with TG to shaw desorption of HzO and COz from ZnO powder (145). As previously noted, gas chromatography and mass spectrometry were considered to give equivalent analytical data, but gas chromatography was slower (548). In the mass spectrometric analysis of NH&lOd decomposition (166), the decomposition products were found to be HzO, HCI, Clz, 02, Nz,Nt0, and NO. Different ratios of Nz0, Nz, and N O were observed as a function of temperature which was attributed to the catalytic effect of NHdClr on gas phase reactions. The use of a controlled dynamic gas atmosphere with DTA permits the incorporation of a thermal conductivity cell to detect compositional changes in the gas phase (18) which have been used to identify and quantify metallic inclusion oompounds. A gas chromatographic system, with thermal conductivity detection, has been used to determine the decomposition kinetics of KbFe(Cz04)8(71). Flame ionization detection (93, 94) can replace the thermal conductivity cell and individually constitute a thermal analysis system, useful with organic materials. The coulometric measurement of water electrolysis, the water being sorbed on PzOS, also has provided an EGA system which has been shown to be useful in the study of decomposition of hydrates formed during hydration of portland cements (109). Response of a Pirani gauge has been used to record polymer EGA traces in a vacuum system (218). Decomposition of poly(vinylch1oride) has been followed by the measurement of HCl evolution through a titration technique (131) and by a chloride selective electrode (314). Polyethylene sulfide decomposition (64) was studied by measurement of the total volume of gas evolved, supplemented by IR analysis of the gaseous products. OTHER METHODS
LITERATURE CITED
(1) Achar, B. N. N., Brindley, G. W., Sharp, J. H., Proc. Int. Clay Conf., Jerusalem, 1, 67 (1966). (2) Akella, J., Kennedy, G. C., J . Geophys. Res., 76, 4969 (1971). (3) Akita, K., Kase, M., J . Polym. Sci., Part A i , 5 , 833 (1967). (4)Alsminov, Kh., Andonova, N., Vysokomol. Soyed., Ser. A , 12, 2129 (1970). (5) Altham, J. A., McLain, J. H., Schwab, G. M., 2. Phys. Chem. (Frankfurt), 74, 139 (1971). (6)Anon., Instrum. News, 20(4),6 (1970). (7) ~, Aneneau. D. F.,Can. J . Chem., 49, 632 (1971).’ (8)Ashcroft, S. J., Thermochim. Acta, 2 , 512 (1971). (9) Atkinson, G. F., Itekovitch, I. J., Anal. Chim. Acta, 49, 195 (1970). (10) Avignant, D., Cousseins, J. C., C. R. Amd. Sci., Ser. C, 271, 1446 (1970). (11)Avinens, C.,Cot, L., Maurin, M., Ann. Chim. (Paris), 5 , 423.(1970). (12)Bair, H.E.,Anal. Calorzmetry, Proc. Symp. dnd, 2 , 5 1 (1970). (13) Bair, H. E.,Polym. Eng. Sci., 10, 247 (1970). (14) Baldwin, N. L.,Lsnger, S., Kester, F. L., Hancock, C., Rev. Sci. Instrum., 41, 200 (1970). (15) Bale, C. W., Toguri, J. M., J . Them. Anal., 3 , 153 (1971). (16) Balek, V., ANAL. CHEM.,42 (9), 16A (1970). (17) Balek, V., J . Appl. Chem., 20, 73 (1970). (18) Bandi, W. R., Buyok, E. G., Krapf, G., Melnick, L. M., Therm. Anal., Proc. Int. Conf.. 2nd. 1968, 2 , 1363 (1969). (19) Barrall, E. M.,11, Diller, R. D., Thennochim. Acta 1, 509 (1970). (20) Barrett, E. J., Hoyer, H. W., San _
An excellent review has been published (163)in which the Mettler light intensity, , DTA, microscopic, Kofler,
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and other melting point methods were discussed. Of particular interest are the comparison of methods with selected compounds and the variations encountered through national pharmacopoeia techniques. Equipment for simultaneous DTA and hot stage microscopy has been developed (336)and has been applied to the melting-freezing processes in organic compounds and low-melting metals. Automatic thermomicroscopy has been employed to study the polymorphic transformations of several high explosives (108). The a -c j3 transformation of pathalocyanine has been investigated in an optical cell with DTA (189)and a pressure cell has been devised (330) to permit changes in light intensity, visible and IR, to be measured a t pressures to 500 kg/cm and to 80 OC. A cell has been developed (841) to utilize the full range of the Cary 14 (W to IR) in the measurement of fixed wavelength transmittance as a function of temperature (0.5%/min). The equipment was operated to just in excess of 80 “C. Intensity changes in depolarized light was one of the techniques used to determine transition temperatures in sulfur (881). The use of ultrasonics to measure transitions is becoming more prevalent. It has been applied to determination of phase transitions in CsPbCb (147) and in SrTiOI (124,190).
I
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