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- Author or Editor: Kai Xu x
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Abstract
An efficient and novel method to prepare KNO3/NaY solid base catalysts was developed. High selectivity for phenetole along with high conversion of phenol was obtained in the vapor phase O-alkylation of phenol with diethyl carbonate over KNO3 modified NaY zeolite. Experimental results showed that a large number of basic sites on KNO3/NaY were generated mainly during catalytic evaluation, which was responsible for the outstanding catalytic performance. Furthermore, the excess KNO3 loadings might lead to the blockage of the pores in the NaY zeolite and decrease the catalytic activity.
Abstract
The effects of non-isothermal and isothermal crystallization on the formation of α- and β-phase in isotactic polypropylene (iPP) with different content of β-nucleating agent are investigated by differential scanning calorimetry (DSC). On non-isothermal crystallization, the content of β-phase and regularity of its crystals are depended on both cooling rate and the content of β-nucleating agent. The faster cooling rate is, the lower of melting peak temperature (Tmp) and crystallization peak temperature (Tcp) of α- and β-phase are. The enthalpy of fusion (∆H) of β-phase increases with cooling rate in a certain range for the sample with 0.1 wt% β-nucleating agent (G1) and decreases for that with 0.3 wt% β-nucleating agent (G3). On isothermal crystallization, the enthalpy of fusion of β-phase in G1 is higher than in G3 which is related to the efficiency of nucleation in different concentration of nucleating center in two samples.
Abstract
Earthworms were collected from agricultural fields in Admont, Graz, Piber and Gumpenstein, Austria. Six earthworm samples were investigated with INAA and with ICP-MS in parallel for the element concentrations of As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Pb, Rb, Sb, Se and Zn. With both techniques 14 elements were analysed in a wide concentration range (ng/g to mg/g) GF-AAS and HG-AAS were used for verification of some element concentrations. A comparison of analytical results between INAA and ICP-MS was discussed. In general, good agreement between ICP-MS and INAA was obtained, the relative difference values of most of the elements are within ±20% range, however, a methodical error for the determination of Hg by ICP-MS was found.
Abstract
A highly accurate and precise method for the simultaneous detection of 18 neonicotinoids and their metabolites in meat was developed using liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). To improve the pretreatment step of the method, five different commercially available clean-up materials (including C18+PSA (primary secondary amine), Z-Sep (with Discover DSC-C18), EMR-Lipid, SHIMSEN QuEChERS, and Clean-up LPAS) were studied in the treatment of three meat matrices: pork, duck and yellow croaker. Based on the recovery data, we found that among the five purification materials, SHIMSEN QuEChERS was slightly more effective than the others for 18 neonicotinoids. Therefore, SHIMSEN QuEChERS was used as the purification sorbent, and the extraction solvents, extraction methods and chromatographic and mass spectrometric conditions were optimized. A matrix-matched calibration method was applied for quantification. In three different meat matrixes (pork, duck, and yellow croaker), all the target compounds showed good linearity, both with values of r 2 > 0.995. The average recovery of all neonicotinoids ranges from 63.4 to 114.2% (pork), 63.0–113.2% (duck), and 63.9–110.5% (yellow croaker). Relative standard deviations were all <15% for intraday and interday precision. The values of limit of detection (LOD) and limit of quantification (LOQ) were, respectively, ranging from 0.04 to 1.0 μg kg−1 and 0.10 to 2.0 μg kg−1. Compared with previous reports, this method has advantage in LOQs, indicating that it it may be a preferred choice for the detection of neonicotinoid pesticides in meat samples.
Abstract
The thermal decomposition behavior of 3,4,5-triamino-1,2,4-triazole dinitramide was measured using a C-500 type Calvet microcalorimeter at four different temperatures under atmospheric pressure. The apparent activation energy and pre-exponential factor of the exothermic decomposition reaction are 165.57 kJ mol−1 and 1018.04s−1, respectively. The critical temperature of thermal explosion is 431.71 K. The entropy of activation (ΔS ≠), enthalpy of activation (ΔH ≠), and free energy of activation (ΔG ≠) are 97.19 J mol−1K−1, 161.90 kJ mol−1, and 118.98 kJ mol−1, respectively. The self-accelerating decomposition temperature (T SADT) is 422.28 K. The specific heat capacity of 3,4,5-triamino-1,2,4-triazole dinitramide was determined with a micro-DSC method and a theoretical calculation method. Specific heat capacity (J g−1K−1) equation is C p = 0.252 + 3.131 × 10−3 T (283.1 K < T < 353.2 K). The molar heat capacity of 3,4,5-triamino-1,2,4-triazole dinitramide is 264.52 J mol−1 K−1 at 298.15 K. The adiabatic time-to-explosion of 3,4,5-triamino-1,2,4-triazole dinitramide is calculated to be a certain value between 123.36 and 128.56 s.
Abstract
The thermal decomposition behaviors of 1,2,3-triazole nitrate were studied using a Calvet Microcalorimeter at four different heating rates. Its apparent activation energy and pre-exponential factor of exothermic decomposition reaction are 133.77 kJ mol−1 and 1014.58 s−1, respectively. The critical temperature of thermal explosion is 374.97 K. The entropy of activation (ΔS
≠), the enthalpy of activation (ΔH
≠), and the free energy of activation (ΔG
≠) of the decomposition reaction are 23.88 J mol−1 K−1, 130.62 kJ mol−1, and 121.55 kJ mol−1, respectively. The self-accelerating decomposition temperature (T
SADT) is 368.65 K. The specific heat capacity was determined by a Micro-DSC method and a theoretical calculation method. Specific heat capacity equation is 
(283.1 K < T < 353.2 K). The adiabatic time-to-explosion is calculated to be a certain value between 98.82 and 100.00 s. The critical temperature of hot-spot initiation is 637.14 K, and the characteristic drop height of impact sensitivity (H
50) is 9.16 cm.
