Thermoanalytical Methods in Vulcanizate Analysis II. Derivative Thermogravimetric Analysis

1975 ◽  
Vol 48 (4) ◽  
pp. 661-677 ◽  
Author(s):  
D. W. Brazier ◽  
G. H. Nickel
Keyword(s):  
Preceding Paper ◽  
Limiting Factor ◽  
Inorganic Pigments ◽  
Thermal Stabilities ◽  
Pyrolysis Products ◽  
Exothermic Reactions ◽  
Temperature Range ◽  
Black Oil ◽  
Scan Rate ◽  
Tg And Dtg

Abstract We have shown in this and the preceding paper that fully compounded stocks can be analyzed for all main constituents by use of a combination of DSC, TG, and DTG. Further, this can be achieved on a time scale consistent with routine quality control. DSC gives information on cure characteristics, sulfur, and accelerator levels in approximately five minutes. Elastomer, elastomer ratio, carbon black, oil/plasticizer, and inorganic pigments are determined in about 35 minutes by TG/DTG, at a scan rate of 10°C/min. This time can be reduced by increasing the scan rate, but interference from highly exothermic reactions can be a limiting factor. Each compound must be treated individually to determine the maximum scan rate that can be used without impairing reproducibility. Clearly limitations exist for identification of unknown blends by DTG. The main problem is that many commercial elastomers have very similar thermal stabilities, which results in DTG peaks in the same temperature range. Further work is being undertaken with the DTG—gas chromatography interface to identify not only the pyrolysis products, but the temperature range over which they are evolved. In this manner, the DTG acts essentially as a thermal fraetionation unit and GC analysis of products from a given component in a blend can be achieved.

Antiferromagnetic exchange in triclinic crystals of tetra-u-benzoato- bits (4-methylquinoline) dicobalt II

1978 ◽  
Vol 360 (1701) ◽  
pp. 191-210 ◽  
Keyword(s):  
Cobalt Complex ◽  
Preceding Paper ◽  
Transverse Magnetic ◽  
Antiferromagnetic Coupling ◽  
Temperature Range ◽  
General Terms ◽  
Carboxylate Groups ◽  
A New Technique ◽  
Unambiguous Conclusion ◽  
Good Agreement

The magnetic susceptibilities of tetra- u -benzoato- bis (4-methylquinoline) dicobalt ii have been measured and interpreted within the theoretical model described in the preceding paper. Crystals of the title complex are triclinic, a circumstance which has lead to the development of a new technique for the measurement of triclinic crystal susceptibilities using a Faraday balance. The technique is discussed in general terms and is applicable with Faraday equipment employing either longitudinal or, as here, transverse magnetic fields. The magnetic tensor for this binuclear cobalt complex has been determined throughout the temperature range 20- 300 K. Good agreement between these results and those calculated from the quantum mechanical model have been obtained in the temperature range 90-300 K. At lower temperatures, a probable small paramagnetic impurity prevents useful theoretical treatm ent. There emerges an unambiguous conclusion that the antiferromagnetic coupling between the cobalt atoms is almost completely determined by interaction between metal xy orbitals, presumably via a superexchange process involving the delocalized n bonding framework of the bridging carboxylate groups.

scholarly journals Excellent Fireproof Characteristics and High Thermal Stability of Rice Husk-Filled Polyurethane with Halogen-Free Flame Retardant

Polymers ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1587 ◽  
Author(s):  
Huong T.Q. Phan ◽  
Binh T. Nguyen ◽  
Lam H. Pham ◽  
Chi T. Pham ◽  
Thi Vi Vi Do ◽  
...  
Keyword(s):  
Rice Husk ◽  
Flame Retardants ◽  
Standard Test ◽  
Solid Particles ◽  
Cone Calorimetry ◽  
Thermal Stabilities ◽  
Pyrolysis Products ◽  
Halogen Free ◽  
Flame Retardancy Mechanism ◽  
Thermal Stability Of

The thermal stabilities, flame retardancies, and physico-mechanical properties of rice husk-reinforced polyurethane (PU–RH) foams with and without flame retardants (FRs) were evaluated. Their flammability performances were studied by UL94, LOI, and cone calorimetry tests. The obtained results combined with FTIR, TGA, SEM, and XPS characterizations were used to evaluate the fire behaviors of the PU–RH samples. The PU–RH samples with a quite low loading (7 wt%) of aluminum diethylphosphinate (OP) and 32 wt% loading of aluminum hydroxide (ATH) had high thermal stabilities, excellent flame retardancies, UL94 V-0 ratings, and LOIs of 22%–23%. PU–RH did not pass the UL94 HB standard test and completely burned to the holder clamp with a low LOI (19%). The cone calorimetry results indicated that the fireproof characteristics of the PU foam composites were considerably improved by the addition of the FRs. The proposed flame retardancy mechanism and cone calorimetry results are consistent. The comprehensive FTIR spectroscopy, TG, SEM, and XPS analyses revealed that the addition of ATH generated white solid particles, which dispersed and covered the residue surface. The pyrolysis products of OP would self-condense or react with other volatiles generated by the decomposition of PU–RH to form stable, continuous, and thick phosphorus/aluminum-rich residual chars inhibiting the transfer of heat and oxygen. The PU–RH samples with and without the FRs exhibited the normal isothermal sorption hysteresis effect at relative humidities higher than 20%. At lower values, during the desorption, this effect was not observed, probably because of the biodegradation of organic components in the RH. The findings of this study not only contribute to the improvement in combustibility of PU–RH composites and reduce the smoke or toxic fume generation, but also solve the problem of RHs, which are abundant waste resources of agriculture materials leading to the waste disposal management problems.

Thermal Stability of GaAs/InGaP and InGaP/(In)GaAs Interfaces

1995 ◽  
Vol 405 ◽  
Author(s):  
F. Hyuga ◽  
T. Nittono ◽  
K. Watanabe ◽  
T. Furuta
Keyword(s):  
Thermal Stability ◽  
Quantum Wells ◽  
Annealing Time ◽  
High Performance ◽  
High Reliability ◽  
Half Maximum ◽  
Single Quantum ◽  
Thermal Stabilities ◽  
Temperature Range ◽  
Thermal Stability Of

AbstractThermal stabilities of GaAs/InGaP and InGaP/(In)GaAs interfaces are investigated using InGaP/(In)GaAs/InGaP single quantum wells. Annealing is performed at a temperature range between 600 and 900 °C for 10 min. Positions and the full widths at half maximum (FWHM) of photoluminescence (PL) peaks are almost identical to those of as-grown ones up to 800 °C. Blue shifts of PL peaks and increased widths of their FWHM observed after 900 °C annealing are suppressed by shortening the annealing time to 0.1 sec. Annealing at 900 ‘C for 0.1 sec is sufficient to activate Si ions implanted into (In)GaAs layers. As a result, these thermal stabilities are able to provide high reliability and high performance of InGaP/(In)GaAs heterostructure MESFET ICs.

scholarly journals Pyrolytic characteristics and kinetics of Guanzhong wheat straw and its components for high-value products

BioResources ◽  
2021 ◽  
Vol 16 (1) ◽  
pp. 1958-1979
Author(s):  
Bingtao Hu ◽  
Zhaolin Gu ◽  
Junwei Su ◽  
Zhijian Li
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Wheat Straw ◽  
Pyrolysis Products ◽  
Transportation Fuels ◽  
Temperature Range ◽  
Model Free ◽  
System A ◽  
Gas Products ◽  
Kinetics Of

Wheat straw produced annually in the Shaanxi Guanzhong region is a potential biomass feedstock for the production of transportation fuels and specialized chemicals through combustion, pyrolysis, or gasification. In this work, the pyrolytic characteristics, evolved gas products, and kinetics of Guanzhong wheat straw and its components were first investigated with a thermogravimetry-Fourier infrared spectroscopy (TG-FTIR) system. A comparative kinetic study was conducted using different model-free methods of Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Kissinger, and the Coats-Redfern methods. The main pyrolysis products identified by FTIR include H2O, CH4, CO2, and CO as well as aromatics, acids, ketones, and aldehydes. Kinetic results showed that the pyrolytic apparent activation energy of the straw is approximately 200 kJ/mol obtained via FWO and KAS methods at the conversion range of 0.4 to 0.75, which was 30 kJ/mol higher than the value 171.1 kJ/mol obtained by the Kissinger method. The apparent activation energy of cellulose in its main pyrolysis region is 135.5 kJ/mol and is about three times larger than that of hemicellulose (49.5 kJ/mol). The apparent activation energy of lignin at the temperature range of 45 to 116 °C was 34.5 kJ/mol, while that value at the temperature range of 120 to 252 °C was 6.64 kJ/mol.

Temperature Response of Whole-plant CO2 Exchange Rates of Magnolia (Magnolia grandiflora L.)

HortScience ◽  
1998 ◽  
Vol 33 (3) ◽  
pp. 511d-511
Author(s):  
Marc W. van Iersel ◽  
Orville M. Lindstrom
Keyword(s):  
Dark Respiration ◽  
Temperature Response ◽  
Net Photosynthesis ◽  
Co2 Exchange ◽  
Limiting Factor ◽  
Response Curves ◽  
Gross Photosynthesis ◽  
Temperature Range ◽  
Whole Plant ◽  
Increasing Temperature

Photosynthesis and respiration temperature-response curves are useful in predicting the ability of plants to perform under different environmental conditions. Whole crop CO2 exchange of two groups of magnolia `Greenback' plants was measured over a 26 °C temperature range. Net photosynthesis (Pnet) increased from 2 to 17% C and decreased again at higher temperatures. The Q10 for Pnet decreased from ≈4 at 6 °C to 0.5 at 24 °C. The decrease in Pnet at temperatures over 17 °C was caused by a rapid increase in dark respiration (Rdark) with increasing temperature. The Q10 for Rdark was estimated by fitting an exponential curve to data, resulting in a temperature-independent Q10 of 2.8. Gross photosynthesis (Pgross), estimated as the sum of Rdark and Pnet, increased over the entire temperature range (up to 25 °C). The Q10 for Pgross decreased with increasing temperature, but remained higher than 1. The data suggest that high respiration rates may be the limiting factor for growth of magnolia exposed to high temperatures, since it may result in a net carbon loss from the plants. At temperatures below 5 °C, both Pnet and Rdark become low and the net CO2 exchange of the plants would be expected to be minimal.

Effect of Ammonium Halides On the Combustion of Polystyrene

1983 ◽  
Vol 1 (2) ◽  
pp. 81-95 ◽  
Author(s):  
K. Kishore ◽  
K. Mohandas
Keyword(s):  
Thermal Analysis ◽  
Weight Loss ◽  
Burning Rate ◽  
Exothermic Reactions ◽  
Temperature Range ◽  
Accelerated Degradation ◽  
Degradation Temperature ◽  
Ammonium Halides ◽  
Low Concentrations ◽  
Tg Studies

Effect of NH4Cl and NH4Br has been studied on combustion and decomposi tion of polystyrene (PS). NH4Br, at low concentrations showed unfavourable ef fects on burning rate, which is surprising for an accepted fire retardent. NH4Br accelerated degradation and combustion of PS. Thermogravimetric (TG) studies of PS + NH4Br samples in N 2 showed that these samples degraded at lower temperatures and with faster rates compared to neat PS. In O2 atmosphere the sensitization of the degradation started after about 30-40% weight loss. The dif ferential thermal analysis (DTA) of these samples gave some additional informa tion : both NH4Cl & NH4Br shifted the degradation temperature to a lower value than PS and exhibited exothermic reactions in the temperature range 400- 450 °C (more exothermicity in NH4Br samples).

SOME FACTORS IN APOTHECIUM PRODUCTION OF CIBORIA ACERINA IN DARKNESS AND LIGHT

1965 ◽  
Vol 43 (6) ◽  
pp. 641-645 ◽  
Author(s):  
Mary E. Elliott
Keyword(s):  
Limiting Factor ◽  
Mature Fruit ◽  
Temperature Range

Many conditions affect the production of mature apothecia of Ciboria acerina in culture. In this investigation four factors were studied: age of isolate, temperature at which the cultures were grown, host from which the cultures were isolated, and the absence or presence of light. It was found that no apothecia were produced when the isolate was more than 18 months old. The temperature at which the stroma of C. acerina developed was significant in apothecium production. Stroma grown at 14 °C produced apothecia while stroma grown at 5 °C did not. However, apothecia matured over a temperature range of 5–22 °C. Apothecia were produced in cultures isolated from Acer, Alnus, and Populus. The quality of light received did not affect apothecium production. The absence of light at all stages of the growth of this fungus from the time of inoculation to the appearance of mature fruit bodies was not a limiting factor. Mature apothecia of Ciboria acerina were formed under artificial conditions in darkness.

scholarly journals Cyclic and square-wave voltammetry for selective simultaneous NO and O<sub>2</sub> gas detection by means of solid electrolyte sensors

2020 ◽  
Vol 9 (2) ◽  
pp. 355-362
Author(s):  
Anastasiya Ruchets ◽  
Nils Donker ◽  
Jens Zosel ◽  
Daniela Schönauer-Kamin ◽  
Ralf Moos ◽  
...  
Keyword(s):  
Cyclic Voltammetry ◽  
Solid Electrolyte ◽  
Square Wave Voltammetry ◽  
Limit Of Detection ◽  
Inert Gases ◽  
Cyclic Voltammograms ◽  
Square Wave ◽  
Temperature Range ◽  
Wave Voltammetry ◽  
Scan Rate

Abstract. Solid electrolyte gas sensors (SESs) based on yttria-stabilized zirconia (YSZ) are suitable to detect traces of redox components in inert gases. Usually, their signals are generated as a voltage between two electrodes at open circuit potential or as a current flowing between constantly polarized electrodes. In these rather stationary modes of operation, SESs often lack the desired selectivity. This drawback can be circumvented if SESs are operated in dynamic electrochemical modes that utilize the differences of electrode kinetics for single components to distinguish between them. Accordingly, this contribution is directed to the investigation of cyclic voltammetry and square-wave voltammetry as methods to improve the selectivity of SESs. For this, a commercial SES of the type “sample gas, Pt|YSZ|Pt, air” was exposed to mixtures containing NO and O2 in N2 in the temperature range between 550 and 750 ∘C. On cyclic voltammograms (CVs), NO-related peaks occur in the cathodic direction at polarization voltages between −0.3 and −0.6 V at scan rates between 100 and 2000 mV s−1 and temperatures between 550 and 750 ∘C. Their heights depend on the NO concentration, on the temperature and on the scan rate, providing a lower limit of detection below 10 ppmv, with the highest sensitivity at 700 ∘C. The O2-related peaks, appearing also in the cathodic direction between −0.1 and −0.3 V at scan rates between 100 and 5000 mV s−1, are well separated from the NO-related peaks if the scan rate does not exceed 2000 mV s−1. Square-wave voltammograms (SWVs) obtained at a pulse frequency of 5 Hz, pulses of 0.1 mV and steps of 5 mV in the polarization range from 0 to −0.6 V also exhibit NO-related peaks at polarization voltages between −0.3 and −0.45 V compared to the Pt–air (platinum–air) electrode. In the temperature range between 650 and 750 ∘C the highest NO sensitivity was found at 700 ∘C. O2-related peaks arise in the cathodic direction between −0.12 and −0.16 V, increase with temperature and do not depend on the concentration of NO. Since capacitive currents are suppressed with square-wave voltammetry, this method provides improved selectivity. In contrast to cyclic voltammetry, a third peak was found with square-wave voltammetry at −0.48 V and a temperature of 750 ∘C. This peak does not depend on the NO concentration. It is assumed that this peak is due to the depletion of an oxide layer on the electrode surface. The results prove the selective detection of NO and O2 with SESs operated with both cyclic voltammetry and square-wave voltammetry.

The adsorption of ethylene on silver(I) oxide. II. Adsorption equilibria

1967 ◽  
Vol 20 (3) ◽  
pp. 409
Author(s):  
JA Allen ◽  
PH Scaife
Keyword(s):  
Adsorption Process ◽  
Preceding Paper ◽  
Isosteric Heat ◽  
Kcal Mole ◽  
Reversible Adsorption ◽  
Temperature Range ◽  
Chromatographic Methods ◽  
Adsorption Equilibria

The adsorption of ethylene on silver(I) oxide in the temperature range 190-363�K has been studied by volumetric and gas chromatographic methods. A reversible adsorption process characterized by an isosteric heat of 8.4 kcal mole-1 extends over the whole range of temperature and coverage, and coexists at temperatures greater than 250�K with an activated adsorption process described in the preceding paper.

On the determination of the metastable miscibility gap in ternary alloys from small-angle measurements. II. Application to the system Al–Zn–Mg

1977 ◽  
Vol 10 (1) ◽  
pp. 28-31 ◽  
Author(s):  
V. Gerold ◽  
J. E. Epperson ◽  
G. Kostorz
Keyword(s):  
Small Angle ◽  
Preceding Paper ◽  
Ternary Alloys ◽  
Metastable Equilibrium ◽  
Approximate Determination ◽  
Background Intensity ◽  
Miscibility Gap ◽  
Limiting Factor ◽  
Zone Formation

The method described in the preceding paper [Gerold (1977), J. Appl. Cryst. 10, 25–27] has been applied to the system Al–Zn–Mg where the small-angle scattering has been measured from nine alloys having zinc and magnesium contents up to 5.4 and 2.5 at. %, respectively. The alloys were annealed at room temperature where the metastable equilibrium of GP zone formation is reached after about one month. From combined analysis of the X-ray and neutron results the slopes of the tie-lines have been evaluated in this region of the phase diagram. The further analysis leads to the approximate determination of the miscibility gap limits. The confidence limits of the determination were restricted by it not being possible to make measurements far enough out in the tail of the neutron scattering profile from the small GP zones (diameter less than 30 Å) to allow the background intensity to be separated completely satisfactorily. The ultimate limiting factor for this type of analysis may be the accuracy to which the mean atomic volumes are known.

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