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41.
Rainer P. H. Garten 《中国化学会会志》1994,41(3):259-274
Selected prominent problems in the analysis of advanced ceramic materials are surveyed. The importance of reliability of results is discussed in the field of elemental trace- and microanalysis in view of its interaction with economy, power of detection, local resolution and speciation selectivity. Particular problems in the analysis of major constituents, trace components and microlocal distributions are based on the striking propertics of ceramics; they are exemplified. Analytical assistance must start from the beginning of the production processing, in the preparation of the powdered base materials. Determination of the stoichiometry requires high accuracy and differentiation of chemical species in bulk and surface analysis of ceramic base powders. Element trace determination by direct instrumental methods requires standard reference materials for calibration; these are currently inavailable in a sufficient variety. For optimum reliability and power of detection, element traces must be prepared in isolated form in a small excitation volume for analysis. A review on the state-of-the-art of wet-chemical combined procedures is presented. Decomposition position procedures are emphasized, due to their risk of contributing severe systematic error. Combustion in elementary fluorine is presented for decomposition of refractory materials. The performance of some direct procedures is discussed. Very efficient methods are available for element trace determinations in ceramic materials, offering high detection power. Several approaches for high-resolution local microanalysis in non-conductive ceramic materials are identified as the most promising development in the analysis of sintered compact ceramic products and devices. 相似文献
42.
Günter Eichberger Herfried Griengl Willibald Paar 《Monatshefte für Chemie / Chemical Monthly》1986,117(4):545-551
Reaction of 3-methyl-1,3-oxazolidine with phthalic anhydride in chloroform leads to ring opening and higher oligomers2 are formed. These are cleaved by addition of protic solvents and 2-methylaminoethyl hydrogenphthalate3 a is obtained. Other 1,3-oxazolidines and succinic anhydride behave similarly.
Herrn Prof. Dr. Dr. h. c.Karl Kratzl mit den besten Wünschen zum 70. Geburtstag gewidmet. 相似文献
43.
44.
《Arabian Journal of Chemistry》2020,13(1):1198-1228
Vanadate and vanadium compounds exist in many environmental, biological and clinical matrices, and despite the need only limited progress has been made on the analysis of vanadium compounds. The vanadium coordination chemistry of different oxidation states is known, and the result of the characterization and speciation analysis depends on the subsequent chemistry and the methods of analysis. Many studies have used a range of methods for the characterization and determination of metal ions in a variety of materials. One successful technique is high performance liquid chromatography (HPLC) that has been used mainly for measuring total vanadium level and metal speciation. Some cases have been reported where complexes of different oxidation states of vanadium have been separated by HPLC. Specifically reversed phase (RP) HPLC has frequently been used for the measurement of vanadium. Other HPLC methods such as normal phase, anion-exchange, cation-exchange, size exclusion and other RP-HPLC modes such as, ion-pair and micellar have been used to separate selected vanadium compounds. We will present a review that summarizes and critically analyzes the reported methods for analysis of vanadium salts and vanadium compounds in different sample matrices. We will compare various HPLC methods and modes including sample preparation, chelating reagents, mobile phase and detection methods. The comparison will allow us to identify the best analytical HPLC method and mode for measuring vanadium levels and what information such methods provide with regard to speciation and quantitation of the vanadium compounds. 相似文献
45.
Preparation and Crystal Structure of the Pnictide Oxides Na2Ti2As2O and Na2Ti2Sb2O Na2Ti2As2O and Na2Ti2Sb2O were synthesized in form of very easily hydrolysed metallic-grey powders by reaction of Na2O and TiAs resp. TiSb in sealed tantalum tubes under argon. The tetrahedral bodycentered crystallizing compounds from a modified anti-K2NiF4 structure type [1] (also called Eu4As2O-type [2,3]), space group I4/mmm (no. 139), with the lattice constants for Na2Ti2As2O: a = 407.0(2) pm, c = 1528.8(4) pm and for Na2Ti2Sb2O: a = 414.4(0) pm, c = 1656.1(1) pm. Magnetic measurements of powder samples of Na2Ti2Sb2O show antiferromagnetic interaction within the Ti—O-layers. Superconductivity was not found by ac-shielding method down to 4 K. 相似文献
46.
O. I. Arillo-Flores M. F. Ruiz-López M. I. Bernal-Uruchurtu 《Theoretical chemistry accounts》2007,118(2):425-435
We discuss the failure of commonly used AM1 and PM3 semiempirical methods to correctly describe acid dissociation. We focus
our analysis on HCl because of its physicochemical importance and its relevance in atmospheric chemistry. The structure of
non-dissociated and dissociated HCl – (H2O)
n
clusters is accounted for. The very bad results obtained with PM3 (and also with AM1) are related to large errors in gas-phase
proton affinity of water and gas-phase acidity of HCl. Indeed, estimation of pKa values shows that neither AM1 nor PM3 are able to predict HCl dissociation in liquid water since HCl is found to be a weaker
acid than H3O+. We have proposed in previous works a modified PM3 approach (PM3-MAIS) adapted to intermolecular calculations. It is derived
from PM3 by reparameterization of the core–core functions using ab initio data. Since parameters for H–Cl and O–Cl core–core
interactions were not yet available, we have carried out the corresponding optimization. Application of the PM3-MAIS method
to HCl dissociation in HCl–(H2O)
n
clusters leads to a huge improvement over PM3 results. Though the method predicts a slightly overestimated HCl acidity in
water environment, the overall agreement with ab initio calculations is very satisfying and justifies efforts to develop new
semiempirical methods. 相似文献
47.
Fluoridolysis of Diphosphoryl Compounds The behaviour of diphosphoryl compounds [X2(O)P]2Y in fluoridolysis reactions is decisively determined by the nature of the bridging group Y. In the cases of Y = NH and CH2 and X = Cl [F2P(O)]2N? and [F2P(O)]2CH2 are obtained quantitatively. For Y = NPh, O, and CH2 the formation of phosphorylated pentafluorophosphates [F5P? Y? POX2]? is observed. Amido and ester derivatives containing fluorine (see table 2) are obtained from the corresponding chloro compounds by Cl/F exchange. Fluoridolysis of the azadiphosphetidine 19 results in the formation of acyclic 19 a . 相似文献
48.
研究金属离子、EDTA、表面活性剂、碘乙酸等对黑曲霉HD-404酸性蛋白酶活力的影响的结果表明:Cu2+、Mn2+对酶有明显的激活作用;Cu2+、Mn2+和Al3+同时使用时,产生协同效应,显著提高酶活力;十二烷基磺酸钠(SDS)、西湖高效洗洁剂对酶有明显的抑制作用;在以酪蛋白为底物时.AgNO3是酶的不可逆抑制剂. 相似文献
49.
乙醛酸与水杨醛在Cu—Hg阴极上的电解合成 总被引:1,自引:0,他引:1
选用便于操作的固态Cu-Hg合金作阴极,对草酸与水杨酸进行恒电位电解。电解电流效率均达到55.0 ̄60.0%。 相似文献
50.
《Journal of Coordination Chemistry》2012,65(9):985-990
The crystal of pentaqua (catena-pyridine-3,5-dicarboxylato-O,O) calcium(II) contain zigzag molecular chains composed of Ca ions linked by two bridging oxygen atoms, each donated by one carboxylate group [Ca-O1 2.353(2) Å, Ca-O3III 2.334(1) Å]. The Ca ions, the ligand molecules and one water oxygen atom coordinated by each metal ion [Ca-O5 2.410(2) Å] are coplanar. The coordination of the Ca ion is completed by four other water oxygen atoms situated above and below the plane of the chain [Ca-O6 2.475(1) Å, Ca-O7 2.371(2) Å]. The coordination number of the calcium(II) ion is seven. The water molecules act as donors in a system of hydrogen bonds. 相似文献