Gas phase thermal diffusivities by a thermal lens technique

A simplified design of thermal lens apparatus is presented in which a chopped cw argon laser beam produces a transient thermal lens in a cylindrical gas cell. The axial intensity variation of a cw helium-neon laser probing this lens is analysed to yield the thermal diffusivities and thus the thermal conductivity coefficients of Kr, CO₂, CH₄, C₂H₆, C₃H₈, C₃H₆ and C₄H₁₀ as 9.4 × 10^?3 ± 4%, 1.6 × 10^?2 ± 3%, 2.98 × 10^?2 ± 4%, 2.03 × 10^?2 ± 4%, 2.05 × 10^?2 ± 7%, 1.6 × 10^?2 ± 8% and 1.9 × 10^?2 ± 8% respectively in W m^?1 K^?1 at 300 K. The method is rapid, requiring only that the sample be transparent at both laser frequencies used. A simplified mathematical analysis is shown to be adequate for this system. For the conditions specified, self-lensing of the argon laser beam is shown to be compensated by using an effective laser beam diameter.     

Tunable thermal lens spectrometry utilizing microchannel-assisted thermal lens spectrometry

A tunable thermal lens spectrometry system was developed for microchip analysis. The system utilized a Xe lamp as an excitation source, instead of a laser. The system can measure the absorption spectrum of a turbid solution without disturbance of the light scattering background.     

The thermal and initiated thermal decomposition of biacetyl-d6

The thermal and methyl radical initiated decomposition of biacetyl-d₆ were investigated at conversions 5% over the temperature range of 387-412°C and 251–292°C, respectively. The deuterated sample contained 10.5% biacetyl-d₅. The reaction products were analyzed by mass spectrometry. The following data could be determined from product ratios: where E is in kcal/mol With reasonable assumptions and literature data Arrhenius parameters for elementary steps were derived and discussed in particular with respect to isotopic effects in H/D-abstraction reactions.     

Constant rate thermal analysis for thermal stability studies of polymers

This paper explores the relationship between the shapes of temperature-time curves obtained from experimental data recorded by means of constant rate thermal analysis (CRTA) and the kinetic model followed by the thermal degradation reaction. A detailed shape analysis of CRTA curves has been performed as a function of the most common kinetic models. The analysis has been validated with simulated data, and with experimental data recorded from the thermal degradation of polytetrafluoroethylene (PTFE), poly(1,4-butylene terephthalate) (PBT), polyethylene (PE) and poly(vinyl chloride) (PVC). The resulting temperature-time profiles indicate that the studied polymers decompose through phase boundary, random scission, diffusion and nucleation mechanisms respectively. The results here presented demonstrate that the strong dependence of the temperature-time profile on the reaction mechanism would allow the real kinetic model obeyed by a reaction to be discerned from a single CRTA curve.     

Simultaneous thermal analyses for thermal dissociation studies on ZrO2

The behaviour of zirconium oxide ZrO₂ during its heating in the temperature range 300–2670 K under high-vacuum conditions and at different heating rates has been studied.The experiments were performed with a Swiss made Universal Mettler thermoanalyser equipped with a super-high-temperature furnace SHT. Volatile products were analyzed simultaneously by means of a Balzers QMG-101 mass spectrometer.An analysis of the TG, DTG, DTA and EGA curves recorded simultaneously has shown the complex character of the studied process. The elementary steps of the overall process were defined and taken into consideration. The mechanism of the thermal dissociation reaction of ZrO₂ as function of the hearing rate was discussed too.

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Zusammenfassung Im Temperaturintervall von 300 K bis 2670 K wurde im Hochvakuum und bei verschiedenen Aufheizgeschwindigkeiten das thermische Verhalten von Zirkoniumoxid ZrO₂ untersucht.Die Experimente wurden mit Hilfe eines schweizer Universal Mettler Thermoanalysators, ausgerüstet mit einem SHT Super-Hochtemperatur-Ofen, ausgeführt. Flüchtige Produkte wurden simultan dazu mit einem Massenspektrometer QMG-101 der Balzers-Company analysiert.Die Auswertung der durch aufgezeichneten TG-, DTG-, DTA- und EGA-Kurven zeigt den komplexen Charakter des untersuchten Prozesses. Die Elementarschritte der Gesamtreaktion wurden definiert und berücksichtigt. Weiterhin wurde der Mechanismus der Thermodissoziation von ZrO₂ auch in Abhängigkeit von der Aufheizgeschwindigkeit diskutiert.

     

Intercomparison of thermal conductivity and thermal diffusivity methods for plastics

An intercomparison of measurements of the thermal conductivity and thermal diffusivity of two poly(methyl methacrylates) is reported. A wide variety of methods were used: temperature wave analysis, laser flash, transient plane source (Hot Disk^®), transient line-source probe, and heat flux meter methods. Very good agreement of thermal conductivity results and, separately, of thermal diffusivity results was obtained. Similarly, good agreement between thermal conductivity and thermal diffusivity results, when converted using specific heat capacity and density values, was also obtained. Typically, the values were within a range of approximately ±10%. Considering the significant differences between the methods and the requirements on specimen dimensions, the level of agreement between results was considered to be good.     

Controlled-rate thermal analysis

Controlled-rate thermal analysis (CRTA) and differential scanning calorimetry (DSC) were used to investigate the adsorbed water layers and the surface properties of different commercial activated carbons. A simple method is proposed to obtain information on the properties of the adsorbed water film and the surface heterogeneity of the materials studied. This method utilizes TG mass loss and the first derivative of the DTG mass loss curves with respect to temperature and time, obtained during programmed liquid thermodesorption. The obtained TG mass loss curves, which reflect the energetic heterogeneity, consisted of steps and inflections which were associated with the mechanism of wetting of the solid surfaces. The heights of these steps and inflections depend on the adsorption capacity, the adsorption potential and the nature and number of the active centers of the carbon samples studied. The values of the total porosity and the surface phase capacity obtained by this method are in good agreement with those estimated on the basis of independent methods. The behaviour of water/carbon samples was studied by means of DSC at subambient and elevated temperatures. The experimental results provided novel data on the structural heterogeneity, the thermal stability of the water/carbon interface and its phase and structural transitions.Support from the Research Council of Kent State University (Ohio, USA) is acknowledged. The author is pleased to thank Drs M. Jaroniec, R. K. Gilpin, J. Choma and R. Dobrowolski for fruitful discussions and the active carbon samples.     

The thermal diffusivity and thermal conductivity coefficient of methanol vapour

The thermal diffusivity of methanol vapour is measured by the thermal lens technique giving values of 0.76, 1.02, 1.70 and 1.78 N s⁻¹ at 321, 341, 377 and 405 K respectively. These thermal diffusivities are shown to be pressure-independent, the pressure dependence of the thermal conductivity merely reflecting the pressure-dependent heat capacity caused by the presence of dimers and tetramers.     

Oxyreactive thermal analysis

The paper presents the applicability of Oxyreactive Thermal Analysis (OTA) for the investigation of different kinds of carbon matter. For comparative reasons and more precise interpretation, along with OTA some physico-chemical properties of analyzed materials were used as the methods commonly applied for the investigations. The carbon materials of both natural (anthracites, graphite and diamonds) and synthetic origin (active carbon, glass carbon, expanded graphite, soot and synthetic diamonds) were investigated. It was stated that there is close relationship between structure parameters and physico-chemical properties and the thermal reactivity within the investigated groups of carbon matters. The results show that OTA can be accepted as a good investigative way for such materials. This revised version was published online in July 2006 with corrections to the Cover Date.     

Emanation thermal analysis

A high pressure differential thermal analysis (DTA) apparatus is described which is capable of operation in the pressure range up to 500 MPa and at temperatures from 25 to 300°C. The requirements for quantitative DTA are examined. The apparatus enables the determination of heat of transition under high pressure by using small samples.     

Laser-induced thermal diffusion

Selective absorption of laser photons was studied for the separation of a gaseous mixture by laser-induced thermal diffusion. It was found that the separation factor depends on the gas pressure in a way similar to that for normal thermal diffusion processes.     

Dielectric-differential thermal analysis

A quantitative relation is given for the temperature function of the output voltage is thermodielectric analysis. Results obtained with zeolites show the validity of the equation.     

Laser thermal ablation

Continuous wave and pulsed laser ablation of tissue is described as an explosive event. A subsurface temperature maximum and superheated tissue produce high pressures that eject fragments from the tissue. Decreased water content due to dehydration and vaporization decreases thermal conductivity which reduces heat conduction. Also, a decrease in water content dramatically alters the local rate of heat generation of laser radiation above 1.3 microns since water is the primary absorber. In contrast, at UV wavelengths protein and DNA are the primary absorbers so destruction of tissue bonds is due to direct absorption of the laser light rather than heat transfer from water.     

Periodic thermal instability during the differential thermal analysis of pyrite

The cause of oscillations in high resolution DTA curves was investigated using simultaneous TG supported by microscopic and XRD examination of quenched samples. The latter techniques showed the instability resulted from the sequential ignition of individual or small groups of particles. This behaviour was different to that observed in our earlier isothermal tests where the oscillations were caused by periodic cracking of the oxide film.

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Zusammenfassung Die Ursache von Oscillationen in hochaufgelösten DTA-Kurven wurde durch TG und gleichzeitige Ausführung von mikroskopischen und XRD-Untersuchungen von abgeschreckten Proben erforscht. Die zuletzt genannten Techniken lassen eine Instabilität erkennen, die auf eine regelmässig aufeinanderfolgende Verbrennung von individuellen oder kleinen Gruppen von Partikeln zurückzuführen ist. Dieses Verhalten unterscheidet sich von dem, das in unseren früheren isothermen Testversuchen beobachtet wurde, bei denen die Oscillationen durch periodisches Zerreissen des Oxidfilms verursacht wurden.

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Effect oftrans-polyoctenamer on thermal stability of rubbers determined by thermal analysis

An effect of a cyclic low molecular-weight polymertrans-polyoctenamer rubber (TOR) on the thermal stability of diene rubbers and their vulcanizates was investigated. The investigation was carried out in the air and nitrogen atmospheres using thermogravimetry, DSC and simultaneous thermoanalytical methods. The thermal stability indexes:T ₅,T _max and activation energy of degradation (E), as well asT _g andT _m values, have been determined.It was found thattrans-polyoctenamer (TOR) increases of the thermal stability indices of raw diene rubbers and their vulcanizates. The results show that the thermal degradation of diene rubbers occurred at higher temperature if they were blended with TOR. In our opinion, intermolecular structures formed between the cyclic low-molecular weight polymer and some linear rubber molecules may be the reason for the higher thermal stability of these rubber blends.The work was supported by State Committee for Research, Poland. Grant No. 7.T08 E 032-08.     

Identificaiton of potential thermal runaways using small scale thermal analytical techniques

With industry's focus on the early identification of potential thermal runaways in chemical processes, it is important that these potential thermal hazards be identified early in a process' development. Thermal runaways can be initiated in several ways: through an uncontrolled heat of reaction, the initiation of an exothermic decomposition/oxidation, or a combination of these two. It is therefore critical that information on exothermic decomposition/oxidation and heat of reaction be easily obtainable using small scale laboratory reactions.A small scale thermal hazards identification program, using process samples from a 200 ml reaction and small scale thermal analytical techniques, identifies potential thermal runaways rapidly. The small scale thermal hazards identification program utilizes three small scale thermal analytical techniques developed at the Merck Research Laboratories. These include the use of specially designed DSC reusable metal crucibles to identify closed system exothermic activity in process samples, the Small Scale Isothermal Age Technique to accurately determine exothermic onset temperatures and Syringe Injection calorimetry to determine heat of reactions which occur at room temperature.     

Rapid thermal analysis of processes of thermal decomposition of mineral salts

Kinetic curves of thermal decomposition and synthesis of mineral salts are obtained in the conditions of rapid heating approaching the heating conditions in a low-temperature plasma flow. The kinetic characteristics are used in calculations of transformations in the path of a chemical plasma reactor.

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Zusammenfassung Für thermische Zersetzung und Synthese von Mineralsalzen wurden die kinetischen Kurven unter den Bedingungen schnellen Aufheizens in Annäherung der Aufheizbedingungen in einem Niedertemperatur-Plasmastrom ermittelt. Die kinetischen Eigenschaften wurden zur Berechnung der Umwandlungen bei einem chemischen Plasmareaktor verwendet.

     

Measurement of the thermal impedance of laser diodes via thermal transients

The thermal impedance of laser diodes was determined by the measurement of thermal transients. The parameters of an equivalent R-C network were synthesized from the transient response. The network was compared with the real layer structure of the device. The effects of structure, mounting and aging on the temperature distribution were investigated with this method.

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Zusammenfassung Mittels Messung thermischer Einschwingvorgänge wurde die thermische Impedanz von Laserdioden bestimmt. Auf Grundlage des Sprungverhaltens wurden die Parameter eines äquivalentenR-C-Gliedes ermittelt, das mit der wahren Schichtenstruktur verglichen wurde. Mittels dieser Methode wurde der Einfluss von Struktur, Aufbau und Alterung auf die Temperaturverteilung untersucht.

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Integrated circuit thermal analysis: A new thermal technique for polymer characterization

Polymer characterization has largely helped in the development of thermal analyzers and calorimeters, based mainly on the thermocouple technology, or more recently the semiconductor technology. With the use of an integrated silicon thermopile as a detector, a new thermal technique is appearing, to give more possibilities of investigations in the field of polymeric materials. Combining high sensitivity and use of small amount of sample, the originality of the new design comes from its low power consumption, giving rise to a portable version of the instrument. With such a concept, the thermal analysis technique is carried on the industrial site, to perform online measurements.Melting and crystallization, glass transition, control of reticulation are a promising field of applications for the characterization of polymeric materials on industrial sites.This revised version was published online in November 2005 with corrections to the Cover Date.     

The use of thermal analysis to study thermal processing effects on polypropylene

The thermal stability of a polypropylene copolymer has been examined at several stages during the processing of the material into its final product in order to obtain information on the influence of processing steps such as grinding and thermal heating on the expected lifetime of the material. Mass loss kinetics in an inert atmosphere were able to detect differences in thermal stability, but oxidative differential scanning calorimetry studies proved to be a more sensitive techiique. A comparative study of a specially prepared series of samples revealed the importance of additives on measured thermal stability and indicated that both mechanical and thermal processing can cause reduction in measured thermal stability.