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1.
Renate Naumann Christine Alexander-Weber Friedrich G. K. Bauche 《Analytical and bioanalytical chemistry》1994,350(3):119-121
Thermogravimetric and X-ray powder diffraction analyses revealed that the pH reference material sodium tetraborate decahydrate (“borax”) is not a stable substance but, loosing some of its water of crystallization, transforms slowly into the pentahydrate. The connected pH changes of the solutions are opposite to and larger than, those expected according to the dilution value of the decahydrate as shown by differential potentiometric measurements. The transformation rate depends on the storing time in the closed original container, the time of and after the first exposure of the material to the atmosphere, the frequency of and the relative humidity during subsequent exposures, and the temperature. The transformation reaction is not understood in detail. However, the experiments showed that sodium tetraborate decahydrate is a reliable pH reference material, whose pH is constant within ΔpH=±0.005 within at least two years after preparation, even if occasionally exposed to the atmosphere. Further work will show whether this time limit can be somewhat extended. 相似文献
2.
3.
Ammar R Ball RC Banerjee S Bhat PC Bosetti P Bromberg C Canough GE Coffin T Dershem TO Dixon RL Fenker HC Ganguli SN Gensch U Girtler P Goshaw AT Grard F Gurtu A Hamilton C Henri VP Hernandez JJ Hrubec J Iori M Jones LW Kuhn D Knauss D Leedom ID Legros P Lemonne J Leutz H Liu X Malhotra PK Marraffino JM Mendez GE Miller R Naumann T Nguyen A Nowak H Pilette P Poirier J Poppleton A Raghavan R Rasner K Reucroft S Robertson WJ Roe BP Roth A Senko M Struczinski W Subramanian A Touboul MC Vonck B 《Physical review letters》1988,61(19):2185-2188
4.
Naumann W 《The Journal of chemical physics》2005,123(6):64505
Fluorescence quenching by excimer formation is studied on the assumption that the excimer formation and dissociation can be modeled as overdamped motion in an attractive potential (classical potential models). An approach to the zeroth-order, concentration-independent quenching constants is proposed which starts from a mean reaction-time ansatz and reduces the calculation essentially to the solution of the eigenvalue problem for the Smoluchowski operator which describes the excimer equilibration. For a square-well potential model it is shown that a quenching constant expansion in terms of relaxation modes, truncated at the kinetic level, gives a satisfactory approximation of the recently obtained exact zeroth-order result under defined conditions. It is demonstrated how this two-mode approach can be applied for a quenching constant estimation if the excimer formation and dissociation are modeled by more realistic interaction potentials, as for instance, Morse- or Gaussian-type ones. 相似文献
5.
Perfluoroalkyl iodine compounds: preparations and properties of CF3IO, CF3IOF2, and CF3IO2. The trifluoromethyl iodine compounds CF3IO, CF3IOF2, and CF3IO2 are formed from the reactions of CF3I, CF3IF2 or CF3IF4 with ozone or silicon dioxide respectively. Their preparartions, properties, 19F-nmr spectra, and ir spectra are described. 相似文献
6.
CF3I(OCOCF3)2 is formed from the reactions of CF3IF2 or CF3IO with trifluoroacetic anhydride at low temperature. During the reaction of CF3IF2 with (CF3CO)2O CF3IF(OCOCF3) is formed as an intermediate product. The preparation, the 19F-nmr spectra and the thermal decomposition are described. 相似文献
7.
Scanning calorimetric methods permit determination of heat capacities at high temperatures up to 1600°C. For disk systems
with power compensation application limits are in order of 700°C, and for cylindrical systems with electrical calibration
up to 1000°C. For the high temperature range above 1000°C DSC plates and a cylindrical calorimetric systems based on the CALVET
principle ('MULTI HTC’) are known. For cylindrical calorimetric systems the precision of the Cp data is between 2 and 5% even
at high temperatures without any requirements on the kind and shape of samples. These results are better than data provided
by DSC plate systems.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
E. Hartung K. Heide R. Naumann K. H. Jost W. Hilmer 《Journal of Thermal Analysis and Calorimetry》1983,26(2):277-284
In spite of numerous investigations the literature data on the thermal decomposition of borax are contradictory. On the basis of thermal, X-ray, gas analytical and optical investigations this fact can be attributed to the complex decomposition mechanism. After the release of about 8 mole water the reaction product is an X-ray amorphous phase, having the thermal behaviour of glass. From this glass sodium diborate (Na2O.2B2O3) crystallizes between 500–600? with further mass loss. Sodium diborate decomposes from about 700? incongruently yielding NaBO2 vapor and B2O3 glass phase. After evaporation of NaBO2 is completed the rate of evaporation of B2O3 increases considerably. 相似文献
9.
Raman Spectra of the Iodine (III) Nitrates CF3I(NO3)2, C6H5I(NO3)2, and I(NO3)3 The Raman spectra of the title compounds are recorded and discussed. 相似文献
10.
(CF3)4Te is formed from the reaction of (CF3)2TeCl2 with (CF3)2Cd·glyme in CH3CN at ?10°C via the intermediate (CF3)3TeCl as a yellow liquid and identified by n.m.r. and mass spectra. 相似文献