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2.
Zusammenfassung Der Schnitt: Me 3Si (Me=Cr, W bzw. Mo, W) wird an Hand heißgepreßter und in Argon homogenisierter Legierungen untersucht; es läßt sich weder das metastabile W 3Si, noch eine W-reiche Mischphase von diesem Typ beobachten. Cr 3Si nimmt bei 1500°C etwa 20 Mol%, W 3Si auf, während Mo 3Si selbst bei 1900°C praktisch kein W 3Si löst (ev. wenige Mol%). Dagegen bestehen lückenlose Mischreihen zwischen den Me 5Si 3-Phasen mit W 5Si 3-Typ. Die grundsätzliche Aufteilung der Phasenfelder ist damit möglich.Mit 2 Abbildungen 相似文献
5.
Zusammenfassung Mit Hilfe röntgenographischer Messungen werden die Boride von Vanadin und Niob untersucht, wobei eine neue Phase der ungefähren Zusammensetzung V 2B identifiziert wird, welche mit der entsprechenden Nb-Borid-Phase isotyp ist. Dieselbe Kristallart tritt auch im System: Ta–B auf. Die in der Literatur angegebene -Phase im Zweistoff: Nb–B erweist sich als NbO.Im System: V–B–Si wird wie im analogen Mo-System die Existenz einer ternären T 2-Phase Me 5(Si 1/3, B 2/3) 3 nach-gewiesen 1; ihre Gitterkonstanten werden ermittelt.Im Schnitt Ta 2Si–Ta 2B besteht ein geringes Lösungs-vermögen der beiden Phasen ineinander. Durch Zusatz von 20 Mol-% Ta 2Si zu Ta 2B erhält man die oben erwähnte neue Kristallart.Bei den Borid-Siliziden der Metalle aus der 4 a-, 5 a- und 6 a-Gruppe werden die Stabilitätsbereiche der T 1-, T 2- und D 8 8-Phasen miteinander verglichen. 相似文献
6.
Ohne ZusammenfassungMit 3 Abbildungen 相似文献
7.
Mössbauer spectroscopy, X-ray diffractometry and microprobe analysis were used to study electrodeposited Fe?Ni?Cr (40–50% Fe, 40–47% Ni, 3–5% Cr) alloys isothermally aged at 500°C from 5 minutes to 100 hours in an inert argon gas atmosphere. The main phase of the as-deposited samples exhibits ferromagnetic microcrystalline behavior, whereas the thermally prepared samples of same composition are always paramagnetic. The dominant effect of ageing is an oxidation process which resulted in the formation of hematite and magnetite iron oxides in considerable amounts and which are attributable to the presence of oxygen inclusions in the as-electrodeposited samples. 相似文献
8.
Ohne ZusammenfassungMit 4 Abbildungen 相似文献
9.
Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C−H and C−Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C−H and C−Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C−H, C−N, C−S, and C−O borylation transformations and provides insights to where further developments are required. 相似文献
10.
A series of La1?x
Sr
x
Cr1?y
Ru
y
O3?δ
(0.1 ≤ x ≤ 0.5, 0.05 ≤ y ≤ 0.15) materials was prepared by the sol–gel method to develop alternative catalysts for propane steam reforming. Catalyst characteristics were evaluated using physicochemical methods including X-ray diffraction, Brunauer–Emmett–Teller methods, H2 temperature-programmed reduction, and thermogravimetry analysis (TGA). Effects of the amount of ruthenium (Ru) and strontium and the steam-to-carbon ratio (S/C) were investigated. An increase in Ru content led to increased propane conversion and H2 yield, especially below 700 °C. Dramatic enhancement of catalytic activity was observed with La0.8Sr0.2Cr0.85Ru0.15O3 under 600 °C, achieving propane conversion over 79% between 600 and 800 °C with maximum propane conversion and H2 yield of 98.3% and 63.3%, respectively. Also, good resistance to carbon formation for the La0.8Sr0.2Cr0.85Ru0.15O3 catalyst was confirmed by long-term testing and TGA analysis. 相似文献
11.
Abstract Chromatographic behaviour of eighteen anions on thin layers of alumina and alumina mixed with silica gel (1:1, 1:2 and 2:1) has been studied using mixed acidic organic solvent systems containing formic acid. Though the addition of silica gel to alumina enhances the mobility and clarity of detection of anions, but it causes the increased tailing for Fe(CN) 3- 6, Cr0 4 2- and Cr 2O 4 2-. Formic acid is responsible for the differential migration of anions. All the anions remained at the starting line (R F = 0) in pure organic solvents. Formic acid-Ketone systems gave better results compared to formic acid-alcohol systems. Development time increases with the increase of viscosity/mol. wt. of organic solvents. The mutual separation of C1, Br ?, Br ?, I ? and NO ? 2 and NO ? 3 were achieved on pure alumina using formic acid-acetone solvent systems. The effect of transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) on C1 ?-Br ?-I ? and NO ? 2-NO ? 3 separations has been studied. 相似文献
12.
Zusammenfassung Mn–Al–Si-Legierungen werden aus den Komponenten hergestellt und röntgenographisch untersucht. Es werden vier neue Verbindungen festgestellt und zwei davon kristallchemisch charakterisiert.MnAl 0,75Si 1,25 kristallisiert im CrSi 2-Typ: a=4,47 5 Å, c=6,42 7 Å, c/a=1,43 6; MnAl 1,3Si 0,7 im TiSi 2-Typ: a=7,88 9 Å, b=4,57 0 Å, c=8,50 6 Å.Mit 2 Abbildungen 相似文献
13.
The variations in geometry structure, IR spectra, as well as the molecular orbitals upon anion recognition for polyamide cryptand are explored with the hybrid density functional theory. The cavity generated by six amide NH groups shrinks upon F ? recognition because of the strong hydrogen bonds between the amide protons and F ? , while the cavity expands upon Cl ? binding because of the strong electron repulsion between the p electron of Cl ? and the lone pair electrons of the nitrogen atom of the pyridine moieties. The “electropositive field space” …Cl ? coupling exists when Cl ? is recognized. The strong anion binding energy with F ? indicates that the polyamide cryptand prefers F ? to Cl ? . 相似文献
14.
Zusammenfassung Es werden vier Methoden zur Analyse einer Gasmischung N 2–NO–NO 2–N 2O 4–N 2O 3–HNO 2 besprochen und ihre Bedeutung für die Bestimmung der einzelnen Molekelarten kritisch auseinandergesetzt. Nach keiner der Methoden kann man den Gehalt an Salpetriger Säure und Salpetersäure neben den Oxyden des Stickstoffes auffinden. Aus diesem Grunde ist die Analyse der genannten Gasmischung nach den vier Methoden allgemein nicht genau durchführbar.Mit 1 Abbildung.Herrn Prof. Dr. A. Skrabal zum 75. Geburtstag gewidmet. 相似文献
15.
Zusammenfassung Im System Mn–As wurde die Struktur der Phase Mn 3As bestimmt. Sie kristallisiert in einem eigenen Typ, der eng in Beziehung zum Gitter von Mn 2As steht. Die Elementarzelle von Mn 3As ist pseudotetragonal orthorhombisch mit den Achsen: a= b=3,780 und c=16,2 6
k X·E. Im charakteristischen Raumsystem D 2h
13 werden die Parameter ermittelt. Auf die strukturellen Zusammenhänge zwischen der Zelle von -Mn, Mn 3As und Mn 2As wird hingewiesen; die Bauprinzipien bei solehen Gittern werden erörtert.Im System V–Sb wurde die zu TiSb 2 isotype Verbindung VSb 2 mit C 16-Struktur gefunden. Überraschend ist die hohe Dichte dieser Kristallarten. Die Achsen der Elementarzelle sind: a=6,54 2 und c=5,62 4
k X·E. Der Bereich der C 16-Strukturen erfährt damit bezüglich des B_Partners eine Erweiterung. Die sich daraus ergebenden Folgerungen werden besprochen.Im System Ti–Sb wird das Bestehen der Phase Ti 4Sb nachgewiesen, die gemäß einer Formulierung Ti 3(Ti 0,2Sb 0,8) im DO 19-Typ kristallisiert.Mit 2 Abbildungen 相似文献
16.
Two [Cr(C 2O 4) 2(AB)] 2– type complexes, obtained from the reaction of cis-[Cr(C 2O 4) 2(H 2O) 2] – with the AB ligand, [AB = picolinic (pyac) or 2-pyridine-ethanoic acid (pyeac) anions], were converted into [Cr(C 2O 4)(pyac)(H 2O) 2] 0 and [Cr(C 2O 4)(pyeac)(H 2O) 2] 0 compounds, respectively via Fe III-induced substitution of the oxalato ligand. The aquation products were separated chromatographically and their spectral characteristics and acid dissociation constants determined. The kinetics of the oxalato ligand substitution were studied with a 10–40 fold excess of Fe III over [Cr III] at [H +] = 0.2 M and at constant ionic strength 1.0 M (Na +, H +, Fe 3+, ClO –
4). The reaction rate law is of the form: r = k
obs[Cr III], where k
obs = kQ[Fe III]/(1 + Q[Fe III]). The first-order rate constants ( k), preequilibria quotients ( Q) and activation parameters derived from the k values have been determined. The reaction mechanism is discussed in terms of a Lewis acid catalyzed (induced) ligand substitution. 相似文献
17.
Zusammenfassung Die Monokarbide: TiC–HfC und ZrC–HfC bilden lückenlose Mischreihen.Mit 1 Abbildung 相似文献
18.
Organic ligands play a key role in determining the shape and stability of the perovskite nanocrystals (NCs). However, the ligands often create poor stability and defects through imperfect attachment, in addition to the post synthesis detachment. We developed a novel route to synthesize the ligand?free ambient stable two?dimensional (2D) cesium antimony chloride (Cs 3Sb 2Cl 9) NCs. First, hexagonal shape NCs are synthesized through a fast one?step reaction at room temperature using a reprecipitation method. The shape of hexagonal NCs is further tuned into well?defined 2D plates through a solid-state temperature-driven crystal phase transition. In?situ variable temperature X?ray diffraction and differential scanning calorimetry cycles probe temperature-sensitive metastability and irreversibility of trigonal to orthorhombic crystallographic phase transition. Rietveld analyses quantify volume fractions and coherently diffracting crystallite domains that promote the growth of the two crystal phases. Both the hexagonal NCs and plates show ambient structural stability for over months. The proposed formation mechanism can guide to improve synthetic methods to realize ligand?free shape-controlled perovskite NCs. 相似文献
19.
The geometries of the Cl –NH 3, Cl –H 2O, F –NH 3 and F –H 2O clusters are optimized using the coupled cluster method. The four lowest ionization potentials are then calculated, leading to the ground and low excited states of the neutral species. The first three IPs describe ionization from the external p state of the halogen atom, whereas the fourth corresponds to ionization from the NH 3 or H 2O moiety, leading to charge transfer complexes. These complexes were recently observed in the photoelectron spectrum of Cl –NH 3, in full accord with our calculations.Supported in part by the U.S.-Israel Binational Science Foundation 相似文献
20.
The goal of this review is to collect the recent developments in asymmetric organocatalytic (aza)-Morita?Baylis?Hillman reactions reported since the beginning of 2013. It also includes the asymmetric organocatalysed transformations of racemic (aza)-Morita?Baylis?Hillman adducts, illustrating that they constitute synthetically important synthons in organic chemistry. It is divided into four sections, dealing successively with organocatalytic enantioselective Morita?Baylis?Hillman reactions, organocatalytic enantioselective aza-Morita?Baylis?Hillman reactions, asymmetric (aza)-Morita?Baylis?Hillman reactions of chiral substrates and asymmetric organocatalysed applications of Morita?Baylis?Hillman adducts. 相似文献
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