Paul D. Garn

Kinetics of thermal decomposition of the solid state: II. Delimiting the homogeneous-reaction model

Abstract Present evidence shows that many thermal processes can be described by the generalized rate equation −d x /d t = Z exp( E */ RT ) f ( x ) but many others cannot. Still others may be adequately describable by a modified equation. A small set of tests will enable the experimenter to determine whether or not the equation applies. These include change of sample size, change of sample geometry, and extended time of reaction.

Instrmental effects on glass transition temperatures

Abstract The testing and evaluation program leading to the certification of a selected batch of polystyrene as ICTA Certified Reference Material GM 754 is described. Defined points from the glass transition curve were obtained, first in a preliminary program, then in 24 laboratories with the use of ten kinds of apparatus. Data were obtained in four heating rate ranges, 4-6, 8-12, 16-24, and 30-50°C/min. The initial departure was rejected for certification because of its relative lack of reproducibility and the comparatively subjective nature of its determination. The two defined points, Tb and Tc, had unweighted mean values of 104.4 and 107.5°C, respectively, with standard deviations of 1.5 and 1.7°C, respectively. Data from individual investigators had a mean standard deviation of 0.53 ± 0.28°C. Separation of the data by heating rate, sample holder configuration, temperature sensor location and combinations of these disclosed that the reproducibility under a given set of conditions warranted certificatio...

Temperature Calibration in Thermogravimetry

Five magnetic materials have been tested and certified as temperature reference materials for thermogravimetry. Use of these materials will enable the relating of data from thermobalances of different designs.

Dynamic purity determinations. II. Some additional systems

Menadione and phenacetin systems were each prepared with a series of concentrations of materials of varying similarity to the host. The data indicate that the measured impurity is dependent upon not only the concentration but also the nature of the impurity. The determination of the actual beginning of melting by nuclear magnetic resonance results in more precise purity measurements.ZusammenfassungEs wurden Menadion- und Phenacetinsysteme mit je einer Konzentrationsreihe von Zusatzstoffen, der Matrix in verschiedentlichem Ausmaß ähnlich, hergestellt. Die Ergebnisse zeigen an, daß die gemessene Verunreinigung nicht allein von ihrer Konzentration, sondern auch von ihrer Natur abhängig ist. Genauere Reinheitsmessungen erfolgen aus der Bestimmung des wahren Schmelzanfangs mittels kernmagnetischen Resonanzmessungen.РезюмеМенадион и фенацетин были получены с различной концентра цией примесей, изменяющих их свойст ва. Данные показали, чт о измеренная чистота з ависит как от концент рации, так и от характера при меси. Определение с по мощью ЯМР истинного начала плавления дае т более точные измере ния чистоты.

Dynamic purity determinations. I. Location of the solidus by nuclear magnetic resonance

The error in purity determinations by differential scanning calorimetry has been studied on two different kinds of systems, metallic and organic, the latter with different types of impurities added. The organic systems have been corrected for solid-solubility error by a nuclear magnetic resonance technique.The impurities chosen for the organic systems were either quite dissimilar to the matrix or similar enough to render solid solution probable. This solid solution leads to deviations from the equation used for dynamic purity determinations. The nuclear magnetic resonance determination of the solidus establishes the proper starting temperature for area summation on a DSC curve.ZusammenfassungDer Fehler in Reinheitsbestimmungen mittels Differential-Scanning-kalorimetrie wurde an zwei verschiedenartigen Systemen untersucht, metallisch und organisch, wobei zu letzteren verschiedentliche Verunreinigungen zugefügt wurden. Der durch Feststoff-Feststofflöslichkeit verursachte Fehler in den organischen Systemen wurde mittels einer kernmagnetischen Resonanzmethode korrigiert.Die für die organischen Systeme gewählten Verunreinigungen waren entweder sehr verschieden von der Matrix, oder aber genügend ähnlich, um feste Lösungen wahrscheinlich zu machen. Diese festen Lösungen führen zu Abweichungen von der für dynamische Reinheitsbestimmungen angewendeten Gleichung. Die Bestimmung der kernmagnetischen Resonanz des Feststoffs ermöglicht die Bestimmung der richtigen Anfangstemperatur für die Flächen-summierung auf der DSC-Kurve.РезюмеС помощью ДСК была изу чена ошибка при определении чистоты двух различных систем: металлическо й и органической. При э том последняя система из учалась с различного рода при месями. С помощью мето да ЯМР для органических систем была учтена ошибка твердо тельной растворимос ти. Примеси, взятые для органичес ких систем, или полностью отлича лись от исходного орг анисеского вещества, или же были в такой степени подобн ы, что могли образовыв ать твердый раствор. Твердый раст вор вызывал отклонения о т уравнения, исыользо ванного для динамического опред еления чистоть. Определение солидуса методом ЯМР позволило установить начальну ю температуру для итоговой поверхн оти ДСК-кривой.

Slow Reversion of Potassium Nitrate

Potassium nitrate exists in several crystalline forms depending upon both the temperature and the pressure (1,2). The three easily observed forms are the orthorhombic KNO3II, stable under standard conditions, a trigonal form, KNOoI, staole above 127.7°C at atmospheric pressure (3), and a second trigonal form, KNO3III, which is typically formed when KNO3I is cooled. The persistence of this form varies with, among other things, its degree of confinement; that is, the expansion of the crystallites transforming from I?III may be unrestrained in a shallow pan, but in a sample cup or well the points of contact are under pressure, so a confined sample transforms more quickly to the orthorhombic phase (4).

Differential Thermal Analysis Furnace Using Dynamic Flow of Water Vapor

A modification of the Lodding‐Hammell furnace is described in which steam can be generated and passed through the sample and reference to supply a dynamic water vapor atmosphere at any easily controlled pressure.

RELATIVE THERMAL STABILITIES OF COPPER (II) SULFATE PENTAHYDRATE AND BARIUM CHLORIDE DIHYDRATE COMPARED TO THEIR DEUTERIUM OXIDE ANALOGS.

Study of the extant literature on hydrated salts and on the effect of isotopic substitution led to a hypothesis that crystalline hydrates would have thermal stabilities different from their deuterium oxide analogs, and that the hydrates might be either more or less stable than their heavy-water counterparts. Although the general isotope effect and heat of solution data would suggest that the heavy-water solvate should be more stable, the two cases tested did not behave in this manner. Barium chloride dihydrate and copper sulfate pentahydrate are more stable, thermally, than their deuterium oxide analogs.

Relation of the report by G. Willman to ICTA's Standardization procedures

The inference by Willman [1 ] that 1CTAs Committee on Standardization had proposed [2] a procedure for determining the temperature of a DTA effect is erroneous. Instead, the Committee proposed that certain batches of selected materials be used to relate results from one laboratory to another. These materials were known by coordinated experiments to provide clear and reproducible solidsolid or solid-liquid transitions [3]. Use of the same source of material is important because some transitions are quite sensitive to impurities, hence the use of the same compound from different batches could lead to mistaken conclusions regarding agreement or disagreement in temperature of thermal events observed in different laboratories. See, for example, the example given by Deshpande et al. [4] of the behavior of potassium nitrate from another source and the further explanations of the behavior of the SRM potassium nitrate by Garn et al. [3] and the ascription of some of the anomalous behavior to the slowness of the Ili ~ I1 reversion under certain circumstances [6]. The procedure recommended by the Committee on Standardization avoids the effects of the slow reversion by first heating through the transition before making the calibrating run. The Committee had agreed very early in its work that there were inherent errors in the measurement of the temperature of a thermal effect and these error were related to the type of furnace assembly and, to a lesser degree, upon the heating rate. In its work preliminary to the certification of a group of Standard Reference Materials it had ascertained that the variation due to heating rate was much less than that due to variation in instrument types. Willmans data show that the variation of Ton for lead is about 5 ~ over a ten-fold change in heating rate. This is less than the average standard deviation for the ten materials certified. For its Second International Test Program which led to this certification, a range of heating rates (4-10~ within ordinary practice was specified to the participants [3]. The extrapolated onset temperature and the peak temperature were chosen as the values to be reported. The initial temperature, corresponding to the departure temperature, Tab, reported by Willman to be the correct measurement, was dropped from consideration because the previous testing had shown that reported values were less reproducible than the measurement points adopted.

DTA using single particles

A DTA sample holder for single particles was constructed using three thermocouples to hold the sample and reference material, respectively. The arrangement can be used to multiparticle samples too by setting a spherical-section sample holder on the three thermocouple junctions.