Room temperature Mossbauer

Figure 2. Room temperature Mossbauer spectra of amorphous Fe2oNi8o sample, a) before heating b) after heating at 483 K for 10 h c) after heating at 693 K for 5 h...

Mossbauer Spectroscopy. Figure 1 shows room temperature Mossbauer emission spectra of two of the unsupported Co-Mo catalysts which we have studied in the present investigation. It is observed that the MES spectra of the two catalysts are quite different. For the catalyst with the low Co/Mo ratio (0.0625), a quadrupole doublet with an isomer shift of 6=0.33 mm/s and a quadrupole splitting of AE =1.12 mm/s are observed (spectrum a). These parameters are very similar to those observed previously for the Co-Mo-S phase in other catalysts (6-9). Furthermore, the spectrum of an unsupported catalyst with Co/Mo = 0.15 is found to be essentially identical to spectrum (a). The MES spectrum (b) of the catalyst with Co/Mo =... 

Figure 7. Room temperature Mossbauer spectrum of an indochinite after heating at various temperatures up to 900°C,...

Table III. Room Temperature Mossbauer Parameters of Ferric Metaphosphate (19)"...

Fig. 7.5 Room temperature Mossbauer spectra and distributions of magnetic hyperfine fields for four goethites, decreasing in crystallinity from a to d (Murad, 1982a, with permission).

Room-temperature Mossbauer data revealed that fast electron transfer (ti, < 10 s) is retained throughout the compositional range 0 < x < 0.8. Samples with x = 0.4 and 0.8 exhibited room-temperature neutron-diffraction data consistent with collinear FeA -ion spins below T, but with a significantly reduced moment (ca. 1 Hb vis a vis a saturated spin-only value) on the B sites. However, at 4.2 K, the spontaneous magnetization could be interpreted with a Neel ferrimagnetic model ... 

The room-temperature Mossbauer data show two broad peaks, and at least seven different interpretations have been suggested At 800 °C, a single broad peak indicates fast charge transfer between all the iron, including the interstitial Fe ions ... 

AT-Phcnyl-AT,-(2-thiazolyl)guanidine forms 2 1 complexes with Cu11 and Hg11 and 1 1 complexes with WV1 and Movl as indicated by absorption spectra, conductometric and amperometric measurements.171 Room temperature Mossbauer parameters have been tabulated for dehydro-A, A, A"-trialkylguanidinohexacarbonyldiiron(O) and related compounds.172... 

Flo. 37. Mossbauer spectra of small Fe304 particles exposed to air at room temperature and after C02/C0 treatment at 700 K. (a) and (b) are room temperature Mossbauer spectra of nonsupported magnetites exposed to air for 80 days (c) is sample (b) treated at 700 K with a C02/C0 mixture. Spectrum at room temperature. Zero velocity is with respect to a 57Co in copper source. Figure according to Tops0c el al. (237). 

Figure 3. Room temperature Mossbauer spectrum of several nontron-ites showing two kinds of octahedrally coordinated Fe3+ and a" small fraction of Fe3+ in tetrahedral coordination. (Adapted from <4)>.

Firsova et al. (122) reported that the room temperature Mossbauer spectrum of supported tin molybdate, which had been aged in vacuo at 723 K, showed the presence of tetravalent tin. Only after exposure to oxygen at 473 K did the sample act as an adsorbent for propylene. It then gave a Mossbauer spectrum that showed the reduction of the tetravalent tin to the divalent state. Reduction without exposure to oxygen was achieved at 673 K but supported tin in the absence of molybdenum was not reduced. The results were interpreted in terms of the proposals (123) for the synergistic oxidation-reduction during catalysis. 

Fig. 2.46. The Fe room-temperature Mossbauer spectrum of augite [ (Ca,Mg,Fe)2Si20J (after Williams et al., 1971).

Murad E. and Schwertmann, U. (1986) Influence of A1 substitution and crystal size on the room-temperature Mossbauer spectrum of hematite. Clays Clay Min. 34 1-6. 

Figure 10. Room temperature MOssbauer spectra of 20% Fe30VSi02 catalyst (a) untreated, (b) oxidized (773K), (c) reduced in CO2/CO (658K), (d) reoxidized (773K), and (e) rereduced (663K) (f) unsupported FeoO i. (g) metallic Fe. Reproduced from...

Figure 4.33 Low temperature (18-23.5°K) Mossbauer spectroscopy data on the same catalysts (samples B, C, D) used in obtaining the room temperature Mossbauer spectroscopy data in Figure 4.32 (3,41). (Reprinted with permission from Academic Press, Inc.)...

The similarity between the Mossbauer parameters of ferritin and a synthetic polymer derived from hydrolysed ferric nitrate have been pointed out previously (101) the polymer has a similar room temperature Mossbauer spectrum with isomer shift and quadropole splitting of 0.48 and 0.67 mm/sec. respectively. At very low temperatures the spectrum of the polymer is also closely similar to ferritin. 

The sample was a 0.0127 mm thick iron foil, of 99.99% purity, cut into disks (2.5 cm diameter). Room temperature Mossbauer spectra were taken in the initial state, after treatment at 800°C for 30 minutes in 1 atm. argon saturated with water at room temperature, and finally after reaction in 1 atm. acetylene at 750°C for 0.5 minute. Velocities were calibrated using the known Mossbauer parameters of metallic iron at 25°C, and zero velocity is with respect to this standard absorber. 

After the specimens were loaded into the furnace tube, they were heated in Nj to 700°C, prior to introduction of ethane. With the tube still maintained at 700°C, ethane was admitted at a flow rate of 94 cmJ/min and the reaction allowed to continue for periods of between 1.0 to 6.0 hours. The weight of deposited carbon was determined by difference of the starting and final specimen weights. In addition, the chemical state of iron in the FeO and f O ) precursors was determined by room temperature Mossbauer spectroscopy after 2.Oh of reaction in ethane at 700°C. 

Figure 8. Room temperature Mossbauer spectra of a metallic iron foil after treatments in steam and acetylene. Key A, metallic iron foil as received B, from foil after treatment in steam at 800° C and C, sample of B after treatment in acetylene...

Figure 10. Room temperature Mossbauer spectra of the Fe.fi, and FeO precursors after reaction in ethane at 700°C for 2 hours. Key A, Fefi, precursor ...

Fig. 10.4 The room-temperature Mossbauer spectra of a-Fe203 for different particle sizes (A) <10 nm (1 nanometre = 10 A), (B) 13-5 nm, (C) 15 nm, (D) 18 nm, and bulk material. The full hyperfine pattern is only seen for large particles. [Ref. 13, Fig. 3]...

Figure 3. Room temperature Mossbauer spectra of coal samples from the Pratt seam in Alabama (top) and from an anthracite deposit in Rhode Island (bottom). In the top spectrum, peaks indicated arise from iron in the common coal minerals pyrite (P), clays (C), siderite (S), and jarosite (J), In the bottom spectrum, peaks indicated arise from iron in clays (C), and in the rare coal minerals, ankerite (A), iron metal (I), and ferric oxide (H),...

The room temperature Mossbauer spectrvun of the above sample shown in Fig. 4 consists of a broad doublet with IS of 1.20-1.22 mm s" QS of... 

The room temperature Mossbauer spectra of the Fei cCO cS (x <0.15) can be explained by the simultaneous occurrence of the high-temperature IC-state besides the semiconducting low-temperature 2C-state [1982Wie, 1982Kra]. The transition 1C 2C is associated with a drastic volume expansion [1987Bar]. 

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