Manganese Disulfide (Hauerite) and Manganese Ditelluride. Thermal Properties from 5 to 350°K and Antiferromagnetic Transitions

The heat capacities of manganese disulfide and manganese ditelluride were determined by adiabatic calorimetry in the range 5–350°K. Lambda‐type transitions are present in both compounds with maxima at 47.93°K for MnS2 and at 83.0°K for MnTe2. Entropies, enthalpies, and Gibbs energy function values are calculated and tabulated. At 298.15°K they are: S°  =  23.88cal/mole⋅°K,H° − H0°  =  3384cal/mole,− [(G° − H0°) / T]  =  12.258cal/mole⋅°KS°=23.88cal∕mole⋅°K,H°−H0°=3384cal∕mole,−[(G°−H0°)∕T]=12.258cal∕mole⋅°K for MnS2 and 34.66, 4416, and 19.847 for MnTe2. The clearly cooperative entropy increments are only 0.71 cal/mole⋅°K for MnS2 and 0.80 for MnTe2. Available magnetic susceptibility data are interpreted in terms of zero‐field splitting of the 6S5/26S5∕2 state of the manganese 3d53d5 electrons. The resulting contributions to the heat capacity are evaluated. At 298°K the combined λ‐transitional and Schottky contributions to the entropy are 2.6 and 2.4 cal/mole⋅°K for MnS2 and MnTe2, respectively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69763/2/JCPSA6-52-7-3820-1.pd

Recent thermophysical developments on nuclear materials

The current status of chemical thermodynamics of the actinide and lanthanide chalcogenides including high-temperature adiabatic calorimetry of these important compounds (with stress on their electronic, magnetic, order-disorder, disproportionation transitions), as well as the spin-wave magnetic contributions, is reviewed. Schottky anomalies (and the information they yield on crystal-field level splitting), definitive resolution of lattice and magnetic contributions for both first- and second-order phase transitions, and other unusual aspects of phase behavior are considered. Unpublished work on the uranium trioxides, the non-stoichiometric and metastable tetrauranium octaoxides, the uranates, etc. is included. The close parallel between actinide and lanthanide behavior evidenced by our recent unpublished thermal studies on the actinide and lanthanide trichlorides, and hexaborides is emphasized.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22358/1/0000804.pd

Schottky contributions in chemical thermodynamics

Cryogenic heat-capacity determinations provide a useful tool for the determination of the energetic spectrum of condensed phases and also reveal information on their discrete electronic level structures as well. We have been interested in applying these techniques to actinide elements and have in recent months been working up the techniques to unravel the corresponding data for the lanthanide compounds—where opposite trends in cationic masses and molar volumes provide an opportunity to test theories useful for the resolution of excess heat capacity from lattice contributions. As an important aspect of heat capacities—especially of compounds with d and f electrons—the Schottky contribution deserves to be much better known—by chemists, by physicists, and by students of thermodynamics. These remarks are designed to further that goal. Bestimmungen der kryogenen Wärmekapazität sind nützlich zur Bestimmung des energetischen Spektrums kondensierter Phasen und liefern zugleich Informationen über deren diskrete Elektronenniveaustrukturen. Wir waren an der Anwendung dieser Techniken auf Actinidenelemente interessiert und haben in den letzten Monaten Methoden zur Ordnung der entsprechenden Daten für die Lanthaniden-Verbindungen ausgearbeitet — wo entgegengesetzte Trends von Kationenmasse und molarem Volumen die Möglichkeit bieten, Theorien zu prüfen, die nützlich für die Absonderung der Überschußwärmekapazität von Gitterbeiträgen sind. Als ein wichtiger Aspekt von Wärmekapazitäten, besonders von Verbindungen mit d- und f-Elektronen, sollte der Schottky-Beitrag von Chemikern, Physikern und Studenten der Thermodynamik besser verstanden werden. Diese Bemerkungen sollen diesem Zwecke dienen. Данные измерения теп лоемкостей при низки х температурах являют ся полезными для определения энергет ического спектра конденсированных фа з, а также дают информа цию о дискретной структур е электронных уровне й. Ранее авторы применили это т метод к элементам актиноидного ряда, а с овсем недавно для объ яснения соответствующих дан ных для лантаноидов, где прот ивоположные тенденц ии величин катионов и молярных о бъёмов предоставляют удобн ый случай проверки те орий, используемых при выд елении избыточной теплоемкости, обусло вленной решеточными вкладами. Одним из важных аспек тов теплоемкостей, в особ енности для элементо в с d- и f-электронами, являетс я вклад дефектов Шоттки, заслуживающи х намного лучшего пон имания термодинамики химик ами, физиками и студентами.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43141/1/10973_2005_Article_BF01914288.pd

Heat Capacities and Thermodynamic Properties of Two Tetramethylammonium Halides

Heat capacities of tetramethylammonium chloride and bromide were determined by low‐temperature adiabatic calorimetry from 5° to 350°K. Derived thermodynamic properties were then calculated. Two transitions were found in the chloride: a sharp, apparently first‐order transition occurs at 75.76°K with an entropy of transition of 0.37 cal mole—1 °K—1 and a lambda‐shaped transition at 184.85°K with an entropy increment of 0.14 cal mole—1 °K—1. No anomaly has been observed in the bromide. Molal values of heat capacity, entropy, and free energy function at 298.15°K for the chloride and the bromide are: 37.51, 38.64, 45.58, 47.99, and —23.36, —25.36 cal mole—1 °K—1, respectively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69935/2/JCPSA6-36-9-2420-1.pd

The thermophysical properties of three globular molecules

The low temperature heat capacities of adamantane, hexamethylenetetramine and triethylenediamine have been determined from 5 to 350[deg]K by adiabatic calorimetry. A transition at 208.6[deg]K involving an entropy increment of 3.87 e.u. is associated with a slight modification of the crystalline arrangement and the molecular freedom in adamantane. Although a related transition also occurs in triethylenediamine at 353[deg]K, none has yet been detected in hexamethylene-tetramine.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32392/1/0000467.pd

Thermodynamics, handmaiden to science and technology

Generally, the only items of reference data with real economic impact are—except in a few instances—the basic values from which the standard enthalpy increment of reactions and the Gibbs energy of formation of the substances involved in the reaction. The energetic requirements of chemical processing mandate exact values here as well as for rather precise Gibbs energies needed for evaluation of equilibrium constants. Even here the contribution may lie less in the intrinsic value of that accuracy than in the implicit reliability and ready availability of the tables. CODATA's endeavors and scientific task groups dealing with fundamental constants, key values for thermodynamics, internationalization and systematization of thermodynamic tables to assist chemical industry are noted. Im allgemeinen kommt — von wenigen Ausnahmen abgesehen — von den Bezugsdaten nur denjenigen Grundwerten eine wirkliche ökonomische Bedeutung zu, aus denen die VerÄnderungen der Standardenthalpien der Reaktionen und die Gibbs'schen Bildungsenergien der an der Reaktion beteiligten Stoffe berechnet werden können. Die energetischen Erfordernisse der chemischen Verfahren müssen auf exakten Werten beruhen, ebenso wie die zur Berechnung von Gleichgewichtskonstanten benötigten Gibbs-Energien. Die Genauigkeit der individuellen Werte steht dabei weniger im Vordergrund als Vielmehr die ZuverlÄssigkeit und leichte ZugÄnglichkeit der Tabellen. Der Autor geht auf die Bestrebungen der CODATA (Committee on Data for Science and Technology) und derjenigen wissenschaftlichen Gruppen ein, die sich mit der Internationalisierung und Systematisierung der für die chemische Industrie zusammengestellten thermodynamischen Tabellen sowie mit grundlegenden Konstanten und thermodynamischen Werten befassen. жА ИсклУЧЕНИЕМ НЕкОт ОРых слУЧАЕВ, ОсНОВНы Е жНАЧЕНИь, Иж кОтОРых δ H v 0 И δ G f 0 Дль хИМИЧЕскИх РЕА кцИИ, ьВльУтсь тОлькО пУНктАМИ УпОМИНАЕМы х ДАННых пО ОтНОшЕНИУ РЕАльНОгО ЁкОНОМИЧЕ скОгО ВОжДЕИстВИь. ЁНЕРгЕтИЧЕскИЕ тРЕБ ОВАНИь хИМИЧЕскОИ ОБРАБОткИ тРЕБУУт тО ЧНых жНАЧЕНИИ, тОЧНО т АкжЕ тРЕБУУтсь тОЧНыЕ жНА ЧЕНИь ЁНЕРгИИ гУББсА Дль ОпРЕДЕлЕН Иь кОНстАНт РАВНОВЕс Иь. ДАжЕ жДЕсь ЁтОт ВклАД МОжЕ т НАхОДИтсь В МЕНьшЕИ стЕпЕНИ В сО БстВЕННОМ жНАЧЕНИИ Ё тОИ тОЧНОстИ, ЧЕМ В пОДРАж УМЕВАЕМОИ НАДЕжНОст И И пРИгОДНОстИ тАБлИц. CODATA пРИВОДИт пОпыткИ И Н АУЧНыЕ гРУппы жАДАЧ, кАсАУЩИ Есь ОсНОВНых кОНстАНт, кл УЧЕВых жНАЧЕНИИ Дль тЕРМОДИНАМИкИ, ИНтЕР НАцИОНАлИжАцИИ И сИстЕМАтИжАцИИ тЕР МОДИНАМИЧЕскИх тАБл Иц В пОМОЩь хИМИЧЕскОИ пРОМышлЕ ННОстИ.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43140/1/10973_2005_Article_BF01907333.pd

Molecular Freedom of the Ammonium Ion. Heat Capacity and Thermodynamic Properties of Ammonium Perchlorate from 5°–350°K

The heat capacity of NH4ClO4 has been determined by adiabatic calorimetry from 5°–350°K and found to be of simple sigmate character without thermal anomalies. The heat capacity (Cp)(Cp), entropy (S°)(S°), enthalpy function (H°−H°0) / T(H°−H°0)∕T, and Gibbs energy function (G°−G0°) / T(G°−G0°)∕T evaluated at 298.15°K from these data are 30.61, 44.02, 20.24, and −23.78 cal/(gfm °K). Combination of these values with aqueous NH4ClO4 thermochemical data suggests the absence of zero‐point entropy. Comparison with the heat capacity of isostructural KClO4 permits resolution of the molecular dynamics of the ammonium ions and leads to the conclusion that these ions are restricted rotators, prevented from freely rotating by comparatively low‐energy barriers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70216/2/JCPSA6-50-12-5083-1.pd

Methanol: Heat Capacity, Enthalpies of Transition and Melting, and Thermodynamic Properties from 5–300°K

Thermal properties of methanol were studied by adiabatic calorimetry. The first‐order nature of the phase transition at 157.4°K with an entropy increment of 0.97 cal mole−1⋅°K−1 was confirmed. The heat capacity of the crystalline phase stable just below the triple point was defined and shown to be extremely sensitive to impurity. No evidence for a second previously‐reported phase transition could be detected. The standard entropy (S°)(S°) and Gibbs energy function (− [G° − H°0] / T)(−[G°−H°0]∕T) for the liquid at 298.15°K are 30.40 and 15.18 cal mole−1⋅°K−1, respectively. The proposed classification of methanol as a plastic crystal on the basis of its small entropy of melting (4.38 cal mole−1⋅°K−1) is considered with respect to hydrogen bonding in the liquid phase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70007/2/JCPSA6-54-4-1464-1.pd

MnWO4, calorimetric study of the bifurcated antiferromagnetic anomaly

The heat capacity of a powdered MnWO4 sample has been measured from 5–350 K. The data show three anomalies below 20 K: a small peak at 6.8±0.1 K, then two large sharp peaks at 12.57±0.05 and 13.36±0.05 K. The magnetic entropy was measured as R ln 6. The data between 5 and 11.5 K obeys a power law dependence Cmag=ATB where B=1.73. The sharp double peak is similar to the bifurcated anomaly in MnCl2 which originates from two distinct antiferromagnetic phases, reported by R. B. Murray et al. The double anomaly is discussed in terms of the superexchange properties of MnWO4.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87559/2/445_1.pd

Low‐Temperature Thermal Properties of Calcium Tungstate

The heat capacity of a single crystal of CaWO4 was determined by adiabatic calorimetry from 5° to 350°K and found to be without transitions or thermal anomalies. Deviation of the curve from normal sigmate shape is shown to be due to internal vibrations of the WO4= ions. Apparent Debye θθ's for the lattice‐only heat capacity and for that of the acoustical spectrum show “normal” deviation from simple Debye theory. Values of the heat capacity (Cp)(Cp), entropy (S°)(S°), enthalpy function [(H°–H0°) / T][(H°–H0°)∕T], and Gibbs function [(G° / H0°) / T][(G°∕H0°)∕T] at 298.15°K are 27.28, 30.21, 16.02, and −14.19, in calories per gram formula mass⋅degree Kelvin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69875/2/JCPSA6-49-8-3374-1.pd