赵芸
,
李峰
,
Evans D G
,
段雪
,
郝建薇
应用化学
doi:10.3969/j.issn.1000-0518.2002.10.009
将纳米尺寸水滑石加入到环氧树脂中制备成复合材料,测试了复合材料的氧指数及无焰燃烧条件下的烟密度,考察了纳米LDH对环氧树脂的阻燃及抑烟效果,并探讨了LDH的阻燃及抑烟机理. 结果表明,在每克树脂中纳米LDH的添加量在0.20～0.60 g范围内, 就可显示出显著的抑烟效果,并可使环氧树脂的氧指数略有提高;多孔性、大比表面的LDH分解产物,吸附了燃烧过程产生的碳烟,从而起到了抑烟作用.
关键词:
水滑石
,
环氧树脂
,
阻燃
,
抑烟
孙幼松
,
矫庆泽
,
赵芸
,
段雪
,
Evans D G
应用化学
doi:10.3969/j.issn.1000-0518.2001.10.004
以水滑石Mg4A12(OH)12CO3@4H2O为前体,以乙二醇为介质,用离子交换法制备了对苯二甲酸柱撑水滑石Mg4Al2(OH)12[C6H4(COO)2],并用XRD、FT-IR、DTA测试技术对样品进行了表征.结果表明,通过控制离子交换条件,[C6H4(COO)2]2-可以完全取代水滑石层间的CO2-3;柱撑水滑石具有良好的层状结构,由于离子交换温度的不同(70～150℃),其层间距略有变化(1.38～1.45 nm);柱撑水滑石层间的[C6H4-(COO)2]2-在553℃左右氧化分解.
关键词:
水滑石
,
柱撑水滑石
,
对苯二甲酸
,
制备
,
表征
Physica B-Condensed Matter
Similar to the cases of 3d(n) ions in 4-fold (or 8-fold) and 6-fold cubic coordinations, a simple and uniform method that calculates the spin-lattice coupling coefficients G11 and G44 for those ions in the more complex 12-fold cubic coordination from the derivatives of zero-field splittings in low symmetries with respect to the distinct structural parameters has been established. Through this method, the analytic expressions of G11 and G44 for 3d5 ions in this cubic coordination based on various mechanisms and models have been given. The results are rather different from those in 4-fold (or 8-fold) and 6-fold cubic coordinations. As an example, the coefficients G11 and G44 for Fe3+ in K+ site ( 12-fold cubic coordination) as well as Ta5+ site (6-fold cubic coordination) of KTaO3 crystal are studied from the important spin-orbit coupling mechanism. When we compare these results with the experimental findings, it appears that the Fe3+ ion is in a Ta5+ site, and not in a K+ site as shown by some researchers.
关键词:
s-6-state ions;symmetry;formulas
Communications in Theoretical Physics
By successively taking into account various interactions for d(2) ions in trigonally distorted cubic crystal fields, detailed analyses, derivations and calculations of the zero-field splitting (ZFS) and g factors of the ground state have been carried out; and their physical essentials and origins have been clearly revealed. The mistakes and shortcomings in some references have been corrected and improved. The calculated results are in excellent agreement with experimental data and much better than those of previous work. It is found that both the combined action of the trigonal field and spin-orbit interaction and the interaction between the ground state and excited states are quite necessary for causing ZFS of the ground state, and both the spin-orbit interaction and the admixture between the ground state and excited states are necessary for causing the deviation of g factors of the ground state from spin-only values.
关键词:
zero-field splitting;g factors;d(2) ions;crystal field;combined;action;admixture of wavefunction
Journal of Physics and Chemistry of Solids
The g-shifts Ag( = g-g(s), where g(s) approximate to 2.0023 is the free-ion value) of the isoelectronic 3d(3) series Cr3+. Mn4+ and Fe5+ in SrTiO3 crystals are calculated from the high-order perturbation formula based on the cluster approach for 3d3 ion in cubic octahedral site. The formula includes not only the contribution from the crystal-field (CF) mechanism, but also that from the charge-transfer (CT) mechanism (which is omitted in the CF theory). From the calculations, it is found that the contribution Delta g(CT) from the CT mechanism in sign is contrary to the corresponding Delta g(CF) from the CF mechanism and the relative importance of CT mechanism (characterized by vertical bar Delta g(CT)/Delta g(CF)vertical bar) increases with the increasing valence state (and hence the atomic number) of 3d(3) ion. The positive g-shift Delta g of SrTiO3:Fe5+ is due mainly to the contribution of CT mechanism. So, for the explanations of g factors of the high valence state 3d" ions (e.g. Mn4+ and Fe5+) in crystals, the contributions from both CF and CT mechanisms should be taken into account. (c) 2005 Elsevier Ltd. All rights reserved.
关键词:
oxides;crystal fields;electronic paramagnetic resonance;optical;properties;electron-paramagnetic-resonance;atomic screening constants;scf;functions;luminescence;parameters;spectra;temperature;manganese;lattices;csmgbr3
Physica B-Condensed Matter
The perturbation formula of g factor for 3d(7) ion in cubic octahedral crystals has been obtained from a cluster approach. In the formula, the parameters related to the configuration interaction and the covalency reduction effect can be obtained from the optical spectra of the crystal under study and so no adjustable parameters are applied. From the formula, the g factors for Co2+ in fluoroperovskites LiBaF3, KMBF3, KZnF3 and CsCdF3 are calculated. The calculated results are in agreement with the observed values. The g factor following the order of LiBaF3 : Co2+ < KMgF3 : Co2+ < KZnF3: Co2+ < CsCdF3 : Co2+ is also explained. (C) 2000 Elsevier Science B.V. All rights reserved.
关键词:
electron paramagnetic resonance;crystal- and ligand-field theory;Co2+;LiBaF3;KMgF3;KZnF3;CsCdF3;perovskite;transition;impurities;crystals
Zeitschrift Fur Naturforschung Section a-a Journal of Physical Sciences
This paper presents a cluster approach to the calculation of the g factors for 3d(7) ions in cubic octahedral crystals, in which the parameters related to the configuration interaction and the covalency reduction effects are obtained from optical spectra of the studied crystals, and so no adjustable parameters are applied. From the approach, the g factors for MgO:Co2+ and CaO:Co2+ are calculated. The calculated results show good agreement with the observed values. The experimental values of g < 4.333 (the first order value in absence of configuration and covalency interactions) for MgO:Co2+ and g > 4.333 for CaO:Co2+ are also explained.
关键词:
electron paramagnetic resonance (EPR);crystal-field theory;Co2+ ion;MgO;CaO
