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51.
The hydration of a 1:3 molar ratio of tricalcium aluminate, Ca3Al2O6, to gypsum, CaSO4·2D2O, was investigated at temperatures of 25, 50, and 80 °C using time-of-flight powder neutron diffraction combined with multiphase Rietveld structural refinement. It was shown that ettringite, Ca6[Al(OD)6]2(SO4)3·∼26D2O, was the first and only hydration product of the system, in contrast to a prior investigation which suggested the occurrence of a precursor phase prior to the formation of ettringite. Kinetics data showed that the hydration reaction is very sensitive to temperature: hydration at 25 °C was characterized by a single kinetic regime while hydration at higher temperatures consisted of two distinct kinetic regimes. The presence of two kinetic regimes was attributed to a change in either the dimensionality of the growth process or a change in the rate controlling mechanism in the hydration reaction. 相似文献
52.
一种新的磷酸根离子敏感电极研究 总被引:5,自引:0,他引:5
一种新的磷酸根离子敏感电极研究肖丹,俞汝勤,李军,袁孔铨(湖南大学化学化工系,长沙,410082)关键词磷酸根,离子选择电极,磷酸二氢根磷酸根离子浓度的测定在化学化工、环境保护、生命科学和临床医学等领域有着重要的意义。对磷酸根离子敏感电极的研究和探索... 相似文献
53.
Aránzazu Espina Enrique Jaimez Sergei A. Khainakov Camino Trobajo José R. García Julio Rodríguez 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(4):333-352
The intercalation of some amines (aniline, benzylamine, cyclohexylamine,piperidine, pyridine, pyrazine and piperazine) into -titaniumphosphate, Ti(HPO4)2×H2O,has been investigated by the batch method and/or by exposing the host to thevapour of the amines. The changes in the interlayer distance of the solidduring the intercalation process was followed by X-ray powder diffraction.The new intercalates were characterised by chemical and thermal analysis.Materials with a monolaminar and/or bilaminar arrangement of amine moleculesin the phosphate interlayer region are obtained depending on the nature ofthe amine. Due to steric hindrance, saturated phases are not obtained forall amines studied. The thermal decomposition of the intercalates (nitrogenatmosphere), takes place in three stages: dehydration, removal of amines andcondensation of the hydrogenphosphate to pyrophosphate groups. 相似文献
54.
55.
Thanner H. Krempl P. W. Selic R. Wallnöfer W. Worsch P. M. 《Journal of Thermal Analysis and Calorimetry》2003,71(1):53-59
Quartz-homeotypic gallium (ortho-) phosphate, GaPO4, is of special interest for resonator applications asking for temperature compensated cuts with higher electro-mechanical coupling than quartz and operational temperatures up to 970°C. The crystal microbalance technique, well known for quartz (QCM) which can be used only at moderate temperatures, can now be extended to much higher temperatures using GaPO4 crystals, benefiting from all three advantages mentioned above. Two different experiments were done to demonstrate the advantages of a crystal microbalance based on GaPO4. First, the GaPO4 resonator was used for film thickness determination and compared with a commercial QCM. This experiment demonstrated that the measuring range can be extended by using GaPO4 resonators instead of quartz. The second experiment demonstrates the possibility for thermogravimetric analysis up to 720°C by using a new concept for resonator mounting.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
56.
Precise conductance measurements are reported on dilute aqueous solutions of the sodium and potassium salts of orthophosphoric
acid at 25 ∘C. Conductance measurements on solutions of electrolytes such as these phosphate salts that exist in solution as complicated
mixtures of ions have previously proved difficult to interpret. To overcome this, a mathematical method has been developed
to calculate the concentrations of all the species in the aqueous system M3PO4/M2HPO4/M2HPO4/H3PO4 (M = Na or K) over a continuous range of stoichiometries. The Lee–Wheaton conductance equation has been used to interpret
the conductance of these multicomponent solutions in terms of the limiting ionic conductances and concentrations of all the
ions in the solution. The limiting molar conductances of the ions H2PO4
− and HPO4
2− and the ion-pair formation constants of these ions with sodium and potassium ions were determine
This work has enabled the accurate determination of solution parameters for the important hydrogenphosphate ions in water
and provides an excellent example of the use of an advanced conductance theory in the analysis of the conductance of multicomponent
electrolyte systems. 相似文献
57.
58.
Frey PA 《Chemical record (New York, N.Y.)》2001,1(4):277-289
Research on the mechanism of action of coenzyme B12, adenosylcobalamin, as a graduate student introduced the author to the field of organic free radicals in enzymology. Twenty years later, related work on S-adenosylmethionine (SAM) as a "poor man's coenzyme B12" was initiated in a detailed analysis of the mechanism of action of lysine 2,3-aminomutase (LAM). The interconversion of L-lysine and L-beta-lysine is catalyzed by LAM, which requires SAM, pyridoxal-5'-phosphate (PLP), and a [4Fe-4S] cluster as coenzymes. The mechanism of this reaction has been delineated as a radical isomerization, in which radical formation is initiated by the [4Fe-4S]-dependent cleavage of the SAM into methionine and the 5'-deoxyadenosyl radical. The mechanism of this process is discussed, together with the role of this radical in hydrogen abstraction from lysine to initiate the substrate radical isomerization. The chemistry underlying the functions of SAM, PLP, and [4Fe-4S] in the action of LAM is novel in all respects, except for the formation of a lysine-PLP aldimine at the active site. Of the four free radicals in the mechanism, three have been characterized by EPR spectroscopy. In the suicide inactivation of adenosylcobalamin-dependent dioldehydrase (DDH) by glycolaldehyde, the formation of cob(II)alamin and 5'-deoxyadenosine is accompanied by the conversion of glycolaldehyde to cis-ethanesemidione radical at the active site. The cis-ethanesemidione radical has been characterized by EPR spectroscopy. Its exceptional stability at the active site is the basis for the inactivation of DDH by glycolaldehyde. 相似文献
59.
对合肥市16671名1-12个月幼儿的发锌,钙含量进行了测定,并对测定值进行了统计分析。结果表明,锌,钙的含量随着月龄的增加呈直线递减。并给出了发锌,钙含量的趋势线方程,丰富了目前文献给出的发锌,钙的标准值,为及时准确判断周岁内幼儿微量元素锌,钙缺乏程度提出依据。 相似文献
60.