The thermal decomposition of silver azide

1979 ◽  
Vol 369 (1736) ◽  
pp. 83-104 ◽  
Keyword(s):  
Crystal Surface ◽  
Molar Fraction ◽  
X Rays ◽  
Silver Azide ◽  
Exponential Factor ◽  
Rate Limiting Step ◽  
Transmission Electron ◽  
Valence Electrons ◽  
Electron Microscopes ◽  
Rate Limiting

The isothermal pyrolysis of single crystals ( ca . 5 x 0.1 x 0.1 mm 3 ) of silver azide has been investigated in the temperature range T ═ 513–558 K by using a thermobalance. The kinetic equation is found to be 1 – (1 – α ) ½ ═ t {2(1 – ∊) / B } u 0 exp (– E/kT) , where α is the molar fraction of decomposition, t the time, B the width of the crystal, ∊( ≪ 1) is an aspect ratio, u 0 ═ 10 2.5 –10 3.4 m s –1 , E ═ 1.23 ± 0.20 eV, and k is the Boltzmann constant. The reaction is topochemical, i. e. it is controlled by the movement of the phase boundary. The solid product (silver) has been examined with X-rays and with scanning and high voltage transmission electron microscopes. It is shown that silver aggregates in the form of ‘pebbles’ 7–14 μm in diameter, which protrude out of the decomposing surface, are randomly orientated but are probably monocrystalline. A mechanism based on Mott’s (1939) model is proposed. The rate-limiting step is the emission of valence electrons from silver azide into silver, and the decomposition is autocatalytic. The theoretical values of the activation energy and the pre-exponential factor are in general agreement with the experimental results. The mechanism has also been used to explain the effects of additives as observed by other workers. The topo­chemical and the autocatalytic characteristics of the reaction suggest that during pyrolysis a silver film covers the crystal surface.

APPLICATIONS OF STEM INSTRUMENTS FOR SURFACE STUDIES

1997 ◽  
Vol 04 (03) ◽  
pp. 567-575 ◽  
Author(s):  
J. M. COWLEY
Keyword(s):  
Surface Structure ◽  
Standing Wave ◽  
High Efficiency ◽  
Electron Holography ◽  
X Rays ◽  
Wave Fields ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Detector ◽  
Electron Microscopes

Scanning transmission electron microscopy (STEM) instruments have some particular advantages as compared with the more common transmission electron microscopes for some applications to surface research. Imaging of surfaces and mapping of the elemental distributions on surfaces with spatial resolutions approaching 1 nm are possible in an ultrahigh-vacuum STEM instrument when the low-energy secondary electrons or the Auger-emitted electrons are collected with high efficiency. In the imaging of surface layers on thin-film substrates, viewed in transmission, the use of a thin annular detector in STEM may greatly enhance the contrast, as illustrated by the case of the imaging of very thin nanocrystalline carbon layers on much thicker amorphous SiO2 films. The scanning reflection mode in a STEM instrument can provide some useful forms of contrast in images of surface structure. Standing wave fields can be formed on the surfaces of crystals with electrons, as with X-rays, one advantage of the electron case being that the standing wave fields may be imaged. Two new forms of electron holography, involving a STEM instrument and suitable for the study of surface structure, are proposed.

scholarly journals KINETIKA MIKRO DEKOMPOSISI METANA MENJADI KARBON NANOTUBE PADA PERMUKAAN KATALIS Ni-Cu-Al

REAKTOR ◽  
2011 ◽  
Vol 13 (3) ◽  
pp. 148 ◽  
Author(s):  
Praswasti Pembangun Dyah Kencana Wulan ◽  
Widodo Wahyu Purwanto ◽  
Yuswan Muharam
Keyword(s):  
Carbon Nanotube ◽  
Kinetic Model ◽  
Phase Transfer ◽  
Internal Diffusion ◽  
Exponential Factor ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Decomposition Of Methane ◽  
Rate Limiting ◽  
Kinetics Of

MICRO KINETICS OF DECOMPOSITION OF METHANE TO CARBON NANOTUBES OVER NI-CU-AL CATALYST. The main focus of this research was to obtain micro kinetics decomposition of methane producing carbon nanotube on the surface of the Ni-Cu-Al catalyst. Experimental kinetics data collected at a temperature range of 650-750oC and pressure of one atmosphere. The preliminary test was conducted to obtain the kinetics are not influenced by external and internal diffusion limitations as well as inter-phase transfer. Kinetics data were tested by micro kinetic model derived from the catalyst surface reaction mechanism. The most appropriate kinetic model becomes the rate-limiting step of methane decomposition reaction. Results of preliminary experiment showed that the kinetics of the external diffusion effect is negligible at flow rates above 150 mL/min. Internal diffusion can be ignored with a catalyst under 0.25 mm in diameter with a weight of 0.04 grams of catalyst and contact time 2.5x10-4. Rate equation analysis shows that the rate-limiting step is the adsorption which indicates that intermediate consumption (CH4I + I Û CH3I + HI) is faster than the formation of intermediate (adsorption of methane, CH4 + I Û CH4I). The activation energy obtained for 34.628 kJ/mol and pre-exponential factor of 6.583x106.  Fokus utama penelitian ini adalah memperoleh kinetika mikro dekomposisi metana yang menghasilkan Carbon Nanotube pada permukaan  katalis Ni-Cu-Al. Data kinetika eksperimen diambil pada rentang temperatur 650-750oC dan tekanan 1 atmosfer. Percobaan pendahuluan dilakukan untuk memperoleh daerah kinetika yang tidak dipengaruhi oleh limitasi difusi eksternal dan internal serta perpindahan antar fasa.  Data kinetika  diuji dengan model kinetika mikro yang diturunkan dari mekanisme reaksi permukaan katalis. Model kinetika yang paling sesuai menjadi tahap pembatas laju reaksi dekomposisi metana. Hasil percobaan pendahuluan kinetika menunjukkan bahwa pengaruh difusi eksternal dapat diabaikan pada laju alir di atas 150 mL/menit. Difusi internal dapat diabaikan dengan menggunakan katalis berdiameter di bawah 0,25 mm dengan berat katalis 0,04 gram pada waktu kontak 2,5x10-4. Analisis persamaan laju menunjukkan bahwa tahap pembatas laju adalah tahap adsorpsi yang menunjukkan bahwa konsumsi intermediate (CH4I + I Û CH3I + HI) lebih cepat dari pembentukan intermediate (adsorpsi metana,CH4 + I Û CH4I). Energi aktivasi yang diperoleh sebesar 34,628 kJ/mol dan faktor pre-eksponensial 6,583x106.

scholarly journals Study of catalase immobilized on a silicate matrix for non-aqueous biocatalysis

2005 ◽  
Vol 3 (2) ◽  
pp. 279-287 ◽  
Author(s):  
Elena Horozova ◽  
Nina Dimcheva
Keyword(s):  
Enzymatic Reaction ◽  
Energy Of Activation ◽  
Specific Rate ◽  
Uv Spectrophotometry ◽  
Silicate Matrix ◽  
Experimental Conditions ◽  
Exponential Factor ◽  
Rate Limiting Step ◽  
Entropy Of Activation ◽  
Rate Limiting

AbstractCatalytic activity of catalase (CAT) immobilized on a modified silicate matrix to mediate decomposition of meta-chloroperoxibenzoic acid (3-CPBA) in acetonitrile has been investigated by means of quantitative UV-spectrophotometry. Under the selected experimental conditions, the kinetic parameters: the apparent Michaelis constat (KM), the apparent maximum rate of enzymatic reaction (Vmaxapp), the first order specific rate constants (ksp), the energy of activation (Ea) and the pre-exponential factor of the Arrhenius equation (Z0) were calculated. Conclusions regarding the rate-limiting step of the overall catalytic process were drawn from the calculated values of the Gibbs energy of activation ΔG*, the enthalpy of activation ΔH*, and the entropy of activation ΔS*.

STEM microanalysis of precipitates in a nickel-base superalloy

1978 ◽  
Vol 36 (1) ◽  
pp. 512-513
Author(s):  
A.J. Craven ◽  
R.G. Menzies ◽  
R.H. Bricknell
Keyword(s):  
Analytical Techniques ◽  
Nickel Base Superalloy ◽  
X Rays ◽  
Metal Carbides ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Electron Microscopes ◽  
Nickel Base ◽  
Electron Energy Loss ◽  
Base Superalloy

In a powder compacted nickel-base superalloy used in high temperature applications, a group of metal carbides (MC) 200-600nm in diameter were observed. Many of these precipitates contained an inner particle (20-60nm in diameter) which will be referred to as the nucleus. In addition to the commercial interest in such a metallurgical system, the identification of the two types of particles provides an interesting problem in microanalysis. Currently two analytical techniques are available on the VG Microscopes HB5, scanning transmission electron microscopes (STEM); energy dispersive X-ray analysis (EDX) and transmission electron energy loss spectroscopy (TEELS).When analysing thinned foils there is the problem of interference from a layer of matrix on the precipitate or from the outer precipitate surrounding the nucleus. Even if the foil is thinned to the extent that layering effects are removed EDX still suffers two drawbacks; (i) Inadequate collimation leads to system peaks following general specimen illumination; (ii) X-rays and electrons leaving the area analysed generate characteristic peaks from adjacent regions.

High-temperature Dislocation-precipitate Interactions in Al Alloys: An in situ Transmission Electron Microscopy Deformation Study

2005 ◽  
Vol 20 (7) ◽  
pp. 1792-1801 ◽  
Author(s):  
B.G. Clark ◽  
I.M. Robertson ◽  
L.M. Dougherty ◽  
D.C. Ahn ◽  
P. Sofronis
Keyword(s):  
High Temperature ◽  
Al Alloys ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Rate Limiting Step ◽  
Transmission Electron ◽  
Deformation Processes ◽  
Temperature Interaction ◽  
Rate Limiting

The fundamental processes controlling the high-temperature interaction of dislocations with precipitates in Al-alloys were investigated in real time by deforming specimens in situ in the transmission electron microscope at elevated temperature. The observations support a bypass mechanism involving the interaction of lattice dislocations with the precipitate–matrix interface dislocations, where the rate-limiting step in the interaction is the release of the dislocation from the particle. These observations are discussed in relation to high-temperature deformation processes and models.

scholarly journals Kinetics of the exchange of water absorbed in silica hydrogel with ethanol: Modelling by brouers and sotolongo-costa fractal kinetics

2021 ◽  
Vol 86 (9) ◽  
pp. 819-830
Author(s):  
Borivoj Adnadjevic ◽  
Nebojsa Cvetkovic ◽  
Jelena Jovanovic
Keyword(s):  
Isothermal Kinetics ◽  
Exponential Factor ◽  
Silica Hydrogel ◽  
Dependent Rate ◽  
Rate Limiting Step ◽  
Proposed Model ◽  
Isothermal Kinetic ◽  
Parameter Values ◽  
Rate Limiting ◽  
Kinetics Of

Isothermal kinetics of the exchange of absorbed water in a silica hydrogel (SH) with ethanol was examined. The isothermal kinetic curves of absorbed water exchange with ethanol were measured at the temperatures: T = = 297, 306 and 316 K. The rate of the exchange was analysed as a function of time. The possibility of mathematical description of the kinetics of exchange by the Brouers and Sotolongo-Costa?s (BS) fractal?s kinetics model was examined. Parameter values (n, ?, ?) of the model and their changes with temperature were calculated. By applying the method of Ozao, it was determined that the rate limiting step of the process of exchange was the rate of exchange of the absorbed water with ethanol. Values of the fractal dimension of the SH-ethanol interphase were calculated. The dependences of the effective time-dependent rate coefficient, activation energy and pre-exponential factor on time and degree of exchange were calculated and discussed. The proposed model of the mechanism of the exchange of absorbed water with ethanol was discussed.

Characterization of small inclusions: SEM vs TEM, or is it even worth considering Sem?

1996 ◽  
Vol 54 ◽  
pp. 498-499
Author(s):  
Carl Blais ◽  
Gilles L’Espérance ◽  
Éric Baril ◽  
Clément Forget
Keyword(s):  
Chemical Composition ◽  
X Rays ◽  
X Ray ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Diffraction Patterns ◽  
Micro Alloyed Steel ◽  
Steel Welds ◽  
Scanning Electron Microscopes

Inclusions of technological importance are often in the size range from 0.1 to 1 μm, These inclusions are generally too thick for EEL-spectrometry and require the use of EDS to characterize their chemical composition. Recent Monte Carlo simulations indicated that scanning electron microscopes (SEM’s) equiped with a field emission gun (FEG) might challenge transmission electron microscopes (TEM’s) for the charaterization of small inclusions, In the light of these results, we investigated the possibility of using a FEGSEM to characterize inclusions found in micro-alloyed steel welds used for arctic applications. The main setbacks of using EDS for such a task are due to the presence of small phases of unknown thicknesses, non-homogeneity of the X-ray generation volumes, variation in absorption along the path length of the X-rays, etc., Even though these problems are encoutered in both the SEM and the TEM, the relative ease of imaging the very small inclusions in TEM confers a definite advantage to this technique. Furthermore, TEM allows to obtain convergent-bearn electron diffraction patterns (CBED) which complement the chemical composition characterization, thereby allowing the unambiguous identification of the phases present (chemistry and crystal structure).

Development of a New Quantitative X-Ray Microanalysis Method for Electron Microscopy

2010 ◽  
Vol 16 (6) ◽  
pp. 821-830 ◽  
Author(s):  
Paula Horny ◽  
Eric Lifshin ◽  
Helen Campbell ◽  
Raynald Gauvin
Keyword(s):  
Field Emission ◽  
Beam Current ◽  
Physical Parameters ◽  
X Rays ◽  
Experimental Conditions ◽  
X Ray ◽  
Stable Regime ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

AbstractQuantitative X-ray microanalysis of thick samples is usually performed by measuring the characteristic X-ray intensities of each element in a sample and in corresponding standards. The ratio of the measured intensities from the unknown material to that from the standard is related to the concentration using the ZAF or ϕ(ρz) equations. Under optimal conditions, accuracies approaching 1% are possible. However, all the experimental conditions must remain the same during the sample and standard measurements. This is not possible with cold field emission scanning electron microscopes (FE-SEMs) where beam current can fluctuate around 5% in its stable regime. Very little work has been done on variable beam current conditions (Griffin, B.J. & Nockolds, C.E., Scanning13, 307–312, 1991), and none relating to cold FE-SEM applications. To address this issue, a new method was developed using a single spectral measurement. It is similar in approach to the Cliff-Lorimer method developed for the analytical transmission electron microscope. However, corrections are made for X rays generated from thick specimens using the ratio of the characteristic X-ray intensities of two elements in the same material. The proposed method utilizes the ratio of the intensity of a characteristic X-ray normalized by the sum of X-ray intensities of all the elements measured for the sample, which should also reduce the amplitude of error propagation. Uncertainties in the physical parameters of X-ray generation are corrected using a calibration factor that must be previously acquired or calculated. As an example, when this method was applied to the calculation of the composition of Au-Cu National Institute of Standards and Technology standards measured with a cold field emission source SEM, relative accuracies better than 5% were obtained.

The Clinical, Roentgenological and Morphological Effects of an Acute Exposure of Phosgene on the Lungs of Dogs

1971 ◽  
Vol 29 ◽  
pp. 236-237
Author(s):  
R. F. Bils ◽  
W. F. Diller ◽  
F. Huth
Keyword(s):  
Latent Period ◽  
Chemical Industry ◽  
Toxic Substance ◽  
Lung Edema ◽  
X Rays ◽  
Beagle Dogs ◽  
Male And Female ◽  
Morphological Alterations ◽  
Before And After ◽  
Electron Microscopes

Phosgene still plays an important role as a toxic substance in the chemical industry. Thiess (1968) recently reported observations on numerous cases of phosgene poisoning. A serious difficulty in the clinical handling of phosgene poisoning cases is a relatively long latent period, up to 12 hours, with no obvious signs of severity. At about 12 hours heavy lung edema appears suddenly, however changes can be seen in routine X-rays taken after only a few hours' exposure (Diller et al., 1969). This study was undertaken to correlate these early changes seen by the roengenologist with morphological alterations in the lungs seen in the'light and electron microscopes.Forty-two adult male and female Beagle dogs were selected for these exposure experiments. Treated animals were exposed to 94.5-107-5 ppm phosgene for 10 min. in a 15 m3 chamber. Roentgenograms were made of the thorax of each animal before and after exposure, up to 24 hrs.

Two- or three-way observations of the identical cell elements within the same sections by LM, TEM and/or SEM

1978 ◽  
Vol 36 (2) ◽  
pp. 82-83 ◽  
Author(s):  
Nakazo Watari ◽  
Yasuaki Hotta ◽  
Yoshio Mabuchi
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Fine Structure ◽  
Light Microscopy ◽  
Thin Sections ◽  
Transmission Electron ◽  
Identical Cell ◽  
Electron Microscopes ◽  
Scanning Electron

It is very useful if we can observe the identical cell elements within the same sections by light microscopy (LM), transmission electron microscopy (TEM) and/or scanning electron microscopy (SEM) sequentially, because, the cell fine structure can not be indicated by LM, while the color is; on the other hand, the cell fine structure can be very easily observed by EM, although its color properties may not. However, there is one problem in that LM requires thick sections of over 1 μm, while EM needs very thin sections of under 100 nm. Recently, we have developed a new method to observe the same cell elements within the same plastic sections using both light and transmission (conventional or high-voltage) electron microscopes.In this paper, we have developed two new observation methods for the identical cell elements within the same sections, both plastic-embedded and paraffin-embedded, using light microscopy, transmission electron microscopy and/or scanning electron microscopy (Fig. 1).

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