Chemie Ingenieur TechnikVolume 78, Issue 9 p. 1254-1255 VortragFree Access Bestimmung der Volumenabhängigkeit der Selbstentzündungstemperatur mittels adiabatischer Messungen W. Wildner Dr., W. Wildner Dr. [email protected] Sicherheitstechnisches Prüfzentrum/AQura GmbH, Rodenbacher Chaussee 4, D-63457 HanauSearch for more papers by this author W. Wildner Dr., W. Wildner Dr. [email protected] Sicherheitstechnisches Prüfzentrum/AQura GmbH, Rodenbacher Chaussee 4, D-63457 HanauSearch for more papers by this author First published: 06 September 2006 https://doi.org/10.1002/cite.200650293AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. REFERENCES 1 D. A. Frank-Kamenetskii, Zhur. Fiz. Khim. 1939, 13, 738. CASGoogle Scholar Volume78, Issue9Special Issue:GVC/DECHEMA‐Jahrestagungen 2006 mit 24. DECHEMA‐Jahrestagung der BiotechnologenSeptember, 2006Pages 1254-1255 ReferencesRelatedInformation

AbstractVorgestellt werden Experimente, die auf adiabatischen und isoperibolen Versuchsreihen beruhen. Diese Untersuchungen dienen dem Zweck, durch eine bestimmte Auswertung in Verbindung mit der Theorie der Wärmeexplosion Stoffdaten und kinetische Parameter zu gewinnen. Diese Daten dienen als Eingabewerte für die numerische Simulation und für eine einfache Gebrauchsformel zur Berechnung von volumenabhängigen Selbstentzündungstemperaturen.

Many devices used in the chemical or petrochemical industry involve hazards because of the existence of flammable gases. Thus, the lean and rich flammability limits are very important characteristics of homogeneous gas mixtures. These data are documented and summarized in various reports, but there are discrepancies between the reported limits. Also, there is a lack of data for mixtures of flammable gases. To complement experimental measurements, the calculation of the flammability limits is of tremendous interest. This article reports a computational study of premixed CH3OH/air and CH3OH/CH4/air flames close to the flammability limits using detailed chemical models and transport properties and comparing the results with data from experiments. A comparison between the results and flammability limits calculated by the Le Chatelier principle is also performed. The deviations are stated, and the causes are explained on the basis of detailed reaction flow analyses.

The Camaquã Basin comprises a volcano-sedimentary succession, located in southernmost Brazil, and represents a molasse basin formed at the post-collisional stage of the Brasiliano/Pan-African orogenic cycle in the Neoproterozoic III to Ordovician period. This basin is one of the most well-preserved ancient volcano-sedimentary sequences undeformed and unmetamorphic in the world, dominantly developed on a continental setting under subaerial conditions. It is composed of five major stratigraphic units, four of them with a distinct volcanic character from the bottom to the top, as: (1) Maricá; (2) Bom Jardim; (3) Acampamento Velho; (4) Santa Bárbara; and (5) Guaritas Allogroups. A concise sight of geochemical and isotopic rock data is presented, as well as stratigraphic correlation and description of rock structures and textures that lead to the identification of their genetic processes, the aim of this paper, indicating a relation with a coeval plutonism, and volcanism that evolved from high-K calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, with a crustal component represented by peraluminous granites. Volcanic deposits from bottom to top are made mostly of volcanogenic sedimentary deposits, succeeded by basic to intermediate lava and pyroclastic flows of shoshonitic affinity, followed by intermediate and acid lava flows and ignimbrites of sodic alkaline affinity. The last volcanic event is represented by basalt pahoehoe flows, probably of mildly alkaline sodic affinity.

Single crystals and ceramics of BaTiO3 and SrTiO3 have been studied by Mossbauer spectroscopy. The materials were investigated as sources and absorbers, doped with Fe57 (Co57) and Sn119. In the preparation of the samples various parameters (temperature, atmosphere, impurity concentration etc.) have been changed. It turned out to be a difficult problem to incorporate Fe into BaTiO3 or SrTiO3 lattices at the Ti4+ site. Thermal doping of single crystals was unsuccessful, in this case a second phase was formed by the addition of Fe57 and Co57. In melt grown BaTiO3 crystals a few hundred ppm Fe could be incorporated in the lattice trivalently. In contrast, Sn is relatively easy to introduce into BaTiO3 and the Mossbauer spectrum of a melt grown single crystal shows a very sharp line. No effects of phase transitions on the hyperfine parameters or the Debye Waller factor could be detected.

Crystallizing and non-crystallizing polymers have been investigated by Brillouin spectroscopy in the liquid state. The temperature gradient of the sound velocity of crystallizing polymers shows a discontinuity at ∼60–110K above the melting transition. The non-crystallizing polymers investigated show no uniform behaviour. We interpret the phase between the melt temperature and the temperature of the additional transformation as a phase of locally nematic structure. This interpretation is also supported by a study of density, refractive index, viscosity and hypersonic attenuation.

Small particles of metallic Sn were embedded in a BN matrix. The Mossbauer effect was measured around the melting point. The main results are : 1) At the melting point the resonance signal drops to an unmeasurable small value in a very limited temperature interval. Line broadening by diffusion could not be detected, confirming Packwood and Longworth. The observation of line broadening by Boyle et al. must have been due to impurities. 2) The resonance effect shows a pronounced hysteresis behavior due to undercooling. From the analysis of this phenornenon in conjunction with the Sn particle size an interphase energy between liquid and solid phase could be deduced. The energy (48 ergs cm-2) is in reasonable agreement with results by other techniques. Mossbauer spectroscopy has been used previously to investigate the behavior of tin at the melting point [l-31. However, the results were contradictory. Deviating from earlier experimental arrangement we have prepared a sample where the tin was embedded as small particles. Specifically, Sn particles with a diameter of (5 2 1) p were mixed with boronnitride (BN) powder (2 p in diameter) and pressed. A volume ratio of Sn : BN equal to 1 : 6 was obtained. Optical microscopy of the sample indicates an homogeneous mixture of Sn and BN particles and furthermore, the Sn particles were to a great extent isolated from each other by the BN matrix as shown schematically in figure 1. Such an absorber is easy to handle in the temperature region of the melting point of Sn (505 K), particularly repeated variation in temperature above and below the melting point of Sn does not change the consistence of the sample in any way. For the Mossbauer measurements the absorber was placed into a furnace. The temperature deviation never exceeded 0.2 K over a period of many hours and over the entire sample at any measuring temperature. Two main results were obtained : -1) At the melting point the resonance signal d r o ~ s Fm. 1. Consistence of the BN-Sn absorber. Hatched circIes to an unmeasurable small value in a very small temindicate Sn particles, between them BN crystallites. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1974670 C6-382 W. WILDNER, H.-D. PFANNES AND U. GONSER 2) The resonance effect shows a pronounced hysteresis resulting from an undercooling behavior of the specimen as shown in figure 2. The intensity of the resonance line makes an hysteresis loop which is completely reversible and extends over a wide temperature range of 80 K. This undercooling behavior is mainly due to the consistence of Our specimen. Because the Sn particles are isolated from each other, the existence of a nucleus for solidification in one or a few Sn particles does not affect an instantaneous solidification of the whole Sn present in Our sample. A comparison of the intensities in the heating-up and cooling-down branches gives an estimate of the fractional parts of liquid and solid phase present. According to the theory of homogeneous nucleation [4, 51 the number of nuclei per unit volume and per unit time is given by perature interval whose width corresponds to the • nkT I(AT) = -exp -exp h i ? 3 A ~ ( A T ) ~ kT limitation in Our temperature resolution. Line broadening by diffusion could not be detected, confirming Packwood and Langworth [2] . The observation of 5 line broadening by Boyle et al. [I l must have been due to impurities. where Tis the temperature, To the melting temperature, AT = To T the actual undercooling temperature, k Boltzmann's constant, h Planck's constant, n the number of metal atoms per cm3, AGA the free energy of activation for transport of atoms across the liquid solid interface, a,, the interfacial energy per cm2 between solid and liquid, and  the latent heat of fusion of the metal per cm3. This equation indicates that I(AT) remains very small until AT reaches a critical value, then I(AT) increases very fast, in fact in metallic systems the increase is so fast that the actual nucleation rate can not be measured. For instance as can be seen from eq. (1) Z(AT) increases from about 10' to 106 nuclei per second and per cm3 when the temperature lowers from 1 K above the maximum undercooling temperature to 1 K below. This narrow range is often called nucleation temperature [4]. According to Turnbull [ 5 ] the factor exp(AGA/kT) is approximately IO-' over the whole temperature region O interest and the rate of nucleation at the maximum of O