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231.
钇对Ti-1100高温钛合金热稳定性和蠕变行为的影响 总被引:3,自引:1,他引:3
量了Ti1100和Ti1100/01%Y(质量分数)高温钛合金在600℃/100h空气中暴露后的拉伸性能及在600℃/150MPa/100h条件下的蠕变性能,利用透射电镜观察了合金室温及蠕变后的组织。结果表明,Ti1100合金加入01%的Y后,由于原始β晶粒得到细化,明显改善了其热稳定性;固溶在基体中的硅原子阻碍位错滑移和攀移,使蠕变中的回复过程难于实现;稀土还抑制α2相的长大,所形成的氧化物也阻碍位错的运动。这些均有利于提高Ti1100合金的抗蠕变性能。 相似文献
232.
51VNMR研究磷钼钒系杂多酸的热稳定性 总被引:2,自引:0,他引:2
用NMR及IR、TG-DTA等手段研究具有Keggin结构的磷钼钒系杂多酸在空气中的热稳定性。实验结果表明:合成的杂多酸在各个Keggin单元中具有不同的钒含量。样品的热稳定性与其钒含量有关.随着钒含量的增加,keggin结构的热稳定性逐渐降低,但H_4PMo_(11)V_1O_(40)具有比H_3PMo_(12)O_(40)还要高的热稳定性。由于钒的取代,钼钒磷酸的热分解过程不同于钼磷酸。失去结构水使Keggin结构遭到破坏,但在室温下与水重新作用可使钼钒磷酸的Keggin结构恢复。 相似文献
233.
T. Woignier C. Fernandez-Lorenzo J. L. Sauvajol J. F. Schmit J. Phalippou R. Sempere 《Journal of Sol-Gel Science and Technology》1995,5(3):167-172
The structure of the silica aerogels was studied by Raman spectroscopy. The spectra of the solid network resembles that of bulk silica with additional bands related to organic groups and a large amount of OH groups.The typical bands due to ring breathing also called defect bands D
1 and D
2 located at 490 and 610 cm–1 are present. However, the evolution of the D
2 band compared to that of OH band (980 cm–1) seems apparently, in contradiction with the results previously reported in the literature. During heat treatments between 25 and 300°C the D
2 and the OH bands increase simultaneously. Generally, in silica glass the defect band D
2 grows at the expense of the OH groups.This result is explained by the oxidation of the organic compounds which, in this temperature range, leads to the formation of the both species (OH) and those related to siloxane rings. 29Si MAS NMR results are in agreement with the Raman study. 相似文献
234.
S. V. Kurbatova E. E. Finkelshtein E. A. Kolosova A. V. Kartashev S. N. Yashkin 《Journal of Structural Chemistry》2004,45(1):144-150
The potential of the structural analogy method in the topological studies of adamantane derivatives and analogs is demonstrated. The topological and structural characteristics of these compounds are calculated. Chromatographic retention indices were determined experimentally. Correlations between the topological indices and the physicochemical and chromatographic characteristics are investigated. 相似文献
235.
Alkyl ketene dimer (AKD) sizing of paper involves the redistribution of the wax over the fibre surface upon heating. The two
major mechanisms widely studied so far are the spreading of an autophobic precursor of molten AKD and AKD vapour transport
and re-deposition on the fibre surface. All previous work assumed that the transport of AKD vapour could be expressed by the
change of water contact angle with substrates that were exposed to the vapour. Information regarding the chemical composition
of the vapour phase above the AKD wax has not been found in the literature. In this work, a simple method for analysing the
chemical composition of the vapour is established. Our preliminary results indicated that the chemical composition of AKD
vapour in the temperature range of 75–80 °C is dominantly fatty acids. This suggests that the sizing effect by actual AKD
molecules via the vapour deposition mechanism is likely to be insignificant in this temperature range. This also implies that
fatty acids play a positive role in AKD sizing. The chemical stability of AKD in this temperature range is also studied. 相似文献
236.
Devendra Kumar Uday Razdan Alka D. Gupta 《Journal of polymer science. Part A, Polymer chemistry》1992,30(7):1477-1487
Various melt-polymerizable bisimido-bisphthalonitrile polymer precursors were synthesized by the reaction of 4-aminophthalonitrile (4-APN) with bis(3,4-dicarboxyphenyl) dimethylsilane dianhydride (SIDA), 4,4′-hexafluoroisopropylidene diphthalic anhydride (6FDA), bis(3,4-dicarboxyphenyl)ether dianhydride (ODPA), and 3,3′, 4,4′-tetracarboxylichenzophen+ne dianhydride (BTDA) in an aprotic solvent. The synthesized monomers showed crystalline melting at 269 and 271°C. Elemental analysis, differential thermal analysis (DTA), infrared (IR), nuclear magnetic resonance (1H-NMR) and mass spectral studies were carried out to characterize the synthesized monomers. Thermogravimetric analysis (TGA) of the synthesized monomers showed their thermal stability at 410–400°C. A detailed study and NMR investigation of the first step of condensation reaction was carried out and indicated the formation of a transient charge transfer complex. Thermal cyclization of the formed intermediate, however, gave the required monomers. A preliminary study demonstrated that melt-polymerization of the synthesized monomers gave thermallystable, tough polymers. 相似文献
237.
The dependence of the stability of SiO2 and Al2O3 sols on the pH of their medium has been studied. Vapor adsorption isotherms on powders were prepared from acidic and basic
sols, the immersion enthalpy (heat) of samples containing preadsorbed water have been determined and, also, the reversibility
of the sol ⇌ xerogel transformation, i.e. the peptizability of the powders, has been investigated.
Based on the flocculation values determined with KCl, the sols have been classified into three groups. The stability of highly
hydrophilic sols (acidic SiO2- and Al2O3-sols) is ensured by a thick continuous diffuse lyosphere formed around the particles, as the continuity principle by Ostwald–Buzágh
suggests. In this case, no electric charge is needed for ensuring stability. These sols are thermodynamically stable (group
1). Sols with medium stability are stabilized by the electrical double layer around the particles and by 1–2 layers of adsorbed
water. The flocculation value of these sols is determined by the electrostatic interaction, whereas the peptizability of the
flocs is related to formation of water layers. Such sols are the basic SiO2- and Al2O3-sols (group 2). Sols of low stability are of hydrophobic nature. Their flocculation value with 1:1 electrolytes is smaller
than 0.1 molkg-1. The transformation process sol ⇒ floccule ⇒ xerogel is mostly irreversible. There are a lot of such sols (group 3). The
existence of a hydrosphere is proved by the almost identical value of the hydration energy for both the acidic and the basic
SiO2 sols, in spite of an order of magnitude difference in the flocculation value. The remnants of adsorbed water after drying
hinders sintering of the particles and ensures the peptizability of powders.
The highly hydrophilic sols (sequence of hydrophilicity: SiO2> Al2O3>FeO OH ⋅ 0.5 H2O) are all oxides which are formed in acidic media.
Received: 25 May 1997 Accepted: 13 October 1997 相似文献
238.
O. M. Radul M. Z. Krimer O. N. Rebrova V. N. Biyushkin I. V. Feofanova A. A. Panasenko 《Russian Chemical Bulletin》1993,42(3):522-527
The rearrangement of enol acylates of aryl 1H-1, 2, 4-triazol-1-ylmethyl ketones at 140–150°C in acetic anhydride is studied. The migration of the acyl group to the C(5) atom of the heterocycle is found to be intramolecular. The characteristics of the original and final products are presented. X-ray structural studies of the enol acetates of 2, 4-dichlorophenyl 1H-1, 2, 4-triazol-1-ylmethyl ketone and 2, 4-dichlorophenyl 5-acetyl-1H-1, 2, 4-triazol-1-ylmethyl ketone are carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 560–564, March, 1993. 相似文献
239.
The overall stability constantsK
1 andK
2 of NdNO
3
2+
and Nd(NO3)
2
+
complexes were determined (K
1=1.77;K
2=1.28) using an extraction method with tri-n-butyl phosphate as the extractant. The ratio 1/2 of the stepwise stability constants is discussed. It was established that the Nd(NO3)
2
+
complex was an outer-sphere ion pair.
Die Assoziation von Nitrat-Ion mit Nd3+
Zusammenfassung Mittels einer Extraktionsmethode wurden die StabilitätskonstantenK 1 undK 2 von NdNO 3 2+ - und Nd(NO3)+-Komplexen bestimmt (K 1=1.77;K 2=1.28; Tri-n-butylphosphat als Extraktionsmittel). Das Verhältnis 1/2 der stufenweisen Stabilitätskonstanten wird diskutiert. Es stellte sich heraus, daß der Nd(NO3)+-Komplex als ein Outer-Shere-Ionenpaar vorliegt.相似文献
240.
I. M. Krukovskii M. S. Molchanova A. V. Evtushenko V. A. Shlyapochnikov 《Russian Chemical Bulletin》1998,47(7):1266-1273
The ratio between the numbers of structural formulas of C,H,N,O-containing energetic compounds belonging to the classes of
fuels (low values of the oxygen coefficientA), explosives (mediumA), and oxidants (highA values) was studied by a computer generation procedure. The number of the theoretically possible structural formulas was
found to decrease rapidly on going from fuels to explosives and then to oxidants; this observation agrees with the data on
the numbers of various energetic compounds currently used and proposed. The strategy of the search for new compounds with
the specified properties is described in brief, and its applicability to the search for explosives and oxidants with a small
(up to 12) number of atoms in a molecule is evaluated.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1304–1310, July, 1998. 相似文献