Structural transformations of Fe81B13Si4C2 amorphous alloy induced by heating

Thermal stability and crystallization of the Fe₈₁B₁₂Si₄C₂ alloy were investigated in the temperature range 25-700 °C by the XRD and Mössbauer analysis. It was shown that on heating the as-prepared amorphous Fe₈₁B₁₂Si₄C₂ alloy undergoes thermal stabilization through a series of structural transformations involving the process of stress-relieving (temperature range 200-400 °C), followed by a loss of ferromagnetic properties (Curie temperature at 420 °C) and finally crystallization (temperature range 450-530 °C). The process of crystallization begins by formation of two crystal phases: Fe₃B and subsequently Fe₂B, as well as a solid solution α-Fe(Si). With increase in annealing temperature, the completely crystallized alloy involved only two phases, Fe₂B and solid solution α-Fe(Si).XRD patterns established a difference in phase composition and size of the formed crystallites during crystallization depending on the side (fishy or shiny) of the ribbon. The first nuclei of the phase α-Fe₃Si were found on the shiny side by XRD after heat treatment even at 200 °C but the same phase on the fishy side of ribbon was noticed after heat treatment at 450 °C. The largest difference between the contact and free surface was found for the Fe₂B phase crystallized by heating at 700 °C, showing the largest size of crystallites of about 130 nm at 700 °C on the free (shiny) surface.     

Note on thermodynamic instability ofM 4C3-type carbides of gallium group metals

The paper deals with thermodynamic stability of hypothetical solid binaryM ₄C₃ carbides of gallium, indium and thallium. Heats of formation whose contribution to the stability of these compounds is dominant, were estimated by two independent methods: semiempirical theory ofMiedema and empirical trends in the heats of formation of nitrides and carbides of Group III elements. Entropies were calculated with the use of theCantor equation. The estimated values suggest thatM ₄C₃ carbides of gallium, indium and thallium are thermodynamically unstable with regard to their decomposition to elements.

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Über die Instabilität von Galliumgruppenkarbiden des TypsM ₄C₃

Zusammenfassung Es wird die thermodynamische Stabilität von hypothetischen Gallium-, Indium- und Thalliumkarbiden diskutiert. Zur Abschätzung von Bildungswärmen, deren Beitrag zur Stabilität dieser Verbindungen dominant ist, wurden zwei unabhängige Methoden verwendet: die semiempirischeMiedema-Theorie und empirische Trends der Bildungswärmen bei den Nitriden und Karbiden der Elemente der III. Gruppe. Die Entropiewerte wurden mittels derCantor-Gleichung berechnet. Aus den abgeschätzten Werten geht hervor, daß die Galliumgruppenkarbide bezüglich der Zersetzung in die Elemente thermodynamisch instabil sind.

     

Macropolyhedral boron-containing cluster chemistry. Ligand-induced two-electron variations of intercluster bonding intimacy. Structures of nineteen-vertex [(eta5-C5Me5)HIrB18H19(PMe2Ph)] and the related carbene complex [(eta5-C5Me5)HIrB18H19[C(NHMe)2]

Addition of PMe2Ph to fused-cluster syn-[(eta5-C5Me5)IrB18H20] 1 to give [(eta5-C5Me5)HIrB18H19(PMe2Ph)] 3 entails a diminution in the degree of intimacy of the intercluster fusion, rather than retention of inter-subcluster binding intimacy and a nido-->arachno conversion of the character of either of the subclusters. Reaction with MeNC gives [(eta5-C5Me5)HIrB18H19[C(NHMe)2]] 4 which has a similar structure, but with the ligand now being the carbene [:C(NHMe)2], resulting from a reductive assembly reaction involving two MeNC residues and the loss of a carbon atom.     

Determination of impurities in silicon carbide powders

Summary The analysis of SiC powders used for the production of high-performance ceramics was investigated by combined procedures as well as by a direct technique including atomic spectrometric detection. For the combined chemical procedure, SiC powders (0.25 g) were completely dissolved in a mixture of HNO₃, HF and fuming H₂SO₄ in an autoclave at 240°C within 8 to 20 h. In the final 0.5% w/v solution 13 elements were determined by electrothermal atomic absorption spectrometry (ETAAS) and by inductively coupled plasma atomic emission spectrometry (ICP-AES). With acid decomposition the detection limits for Ca, Cd, Cr, Cu, Mg, Mn and Zn were found to be in the range of 0.1–1 g/g; those for Al, B, Fe, Ni, Ti and V are at the 1–5 g/g level. With a Babingtontype nebulizer 1% slurries of SiC can be directly analyzed by ICP-AES. Calibration was performed by standard addition of aqueous solutions of the elements to be determined and the detection limits are close to those of ETAAS subsequent to pressure decomposition. The required analysis time was reduced from approx. 24 h to 30 min. First results for Ca, Cr, Cu, Mg, Mn, Ti and V as well as the needs to overcome systematic errors of this method, e.g. for Fe, are communicated.Part of this paper was presented at XI. International Symposium of Microtechniques, Wiesbaden, FRG, Aug. 28th–Sept. 1st 1989     

Identification and determination of organic acids in cultivation medium ofPenicillium vermiculatum dang

Summary [2E,7E]-4,9-dioxo-2,7-decadienoic, [2E,7E]-9-oxo-2,7-decadienoic and [2Z,4E]-2-methyl-2,4-hexadienoic acids were isolated from the filtrate ofPenicillium vermiculatum Dang. The presence of [2E,2E,7S,7E]-4,9-dioxo-7-(4,9-dioxo-2,7-decadienoyloxy)-2-decenoic acid was confirmed by chromatography. HPLC was used for the determination of these acids in the cultivation medium.

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Identifizierung und Bestimmung von organischen Säuren im Kultivierungsmedium vonPenicillium vermiculatum Dang

Zusammenfassung [2E,7E]-4,9-dioxo-2,7-decadiensäure, [2E,7E]-9-oxo-2,7-decadiensäure und [2Z,4E]-2-methyl-2,4-hexa-diensäure wurden aus dem Kultivierungsmedium vonPenicillium vermiculatum Dang isoliert. Die Anwesenheit von [2E,2E,7S,7E]-4,9-dioxo-7-(4,9-dioxo-2,7-decadienoyloxy)-2-decensäure wurde chromatographisch bestätigt, Im Filtrat vonP. vermiculatum wurden diese Säuren mittels HPLC analysiert.

     

Determination of trace metals in aluminium oxide by electrothermal atomic absorption spectrometry with direct injection of aqueous suspensions

Trace amounts (10^-5–10^-6% $\text{w}\text{w}$) of Ca, Cr, Cu, Fe, Na and Pb in aluminium oxide can be determined by graphite-furnace a.a.s. with injection of stirred sample suspensions into the tube. Calibration is possible either with Al₂O₃ standards for peak height and peak area measurements, or with standard solutions containing no aluminium for peak area measurements (except for copper). The analytical signals do not depend on the quantity of applied sample (0.02–1 mg Al₂O₃). Relative standard deviations are 2–6%.     

A convenient route to carbon-substituted derivatives of nido-5,6-C2B8H12

An alternative route to the parent nido-5,6-C₂B₈H₁₂ dicarbaborane is reported together with a convenient synthesis of its carbon-substituted derivatives. The method is based on reactions between 4-(Me₂S)-arachno-B₉H₁₃ and alkynes R¹R²C₂ (where R¹R²=H,H; Me, Me; Ph,H, and Ph,Ph) in toluene at reflux. The characteristic reaction mode is a dicarbon insertion into the 9-vertex arachno cluster to produce a series of the 5,6-R¹R²-nido-5,6-C₂B₈H₁₀ species combined with concomitant elimination of one {BH} vertex. The products were characterised by high-field ¹H and ¹¹B NMR spectroscopy and mass spectrometry associated with [¹¹B–¹¹B]-COSY and ¹H{¹¹B(selective)} measurements that permitted complete assignments of all resonances to individual cluster {BH} units.