NaP1 zeolite synthesized via effective extraction of Si and Al from red mud for methylene blue adsorption

NaP1 zeolite, using red mud (RM) as raw material, was successfully prepared via alkali fusion and hydrothermal method. NaP1 zeolite, which was a mesoporous material, had specific surface area and pore diameter of 79.3 m²·g⁻¹ and 7.26 nm, respectively. NaP1 zeolite had excellent adsorption properties. Under the optimum adsorption conditions, methylene blue (MB) was adsorbed through NaP1 zeolite, the adsorption capacity was 48.7 mg·g⁻¹ and the removal efficiency was 97.1%. The adsorbent was regenerated with sodium chloride as eluent. The adsorption capacity of the adsorbent regenerated three times still was satisfactory 34.53 mg·g⁻¹, which showed the excellent stability performance from NaP1 zeolite. The adsorption conformed to the pseudo second order kinetic and Freundlich isotherm model. Moreover, MB molecules were adsorbed by diffusion on the outer surface, diffusion on the inner surface, and adsorption on the inner surface of NaP1 zeolite. And, during the external diffusion, electrostatic attraction and hydrogen bonding created. Al and Si were extracted from RM to prepare NaP1 zeolite with excellent adsorption properties. This result provides an important example for the development of the potential value of RM.     

On the crystallization mechanism of zeolite ZSM-5: Part 1. Kinetic compensation effect for the synthesis with some diamines

Zeolite ZSM-5 was synthesized from the initial gel: 33 Na₂O: 44R: Al₂O₃: 100 SiO₂: 4000 H₂O: 25 H₂SO₄, where R is tetrapropylammonium bromide (TPA) and C₂, C₃, C₄, and C₆ diamines are in the temperature range 423–453 K. The kinetic analysis of the crystallization of ZSM-5 permits us to follow the role of the used templates during the consecutive steps of the process. The diminishing of the crystallization rate with the increasing of the linear dimension of the molecule is proved. A kinetic compensation effect (KCE) was established between activation energy and the preexponential factor. The obtained KCE is proof for the uniform mechanism of crystallization of zeolite with C₂, C₃, C₄, and C₆ diamines and for a different one for the synthesis with TPA.     

Crystallization study of (TiO2, ZrO2)-rich SiO2-Al2O3-CaO glasses Part II Surface and internal crystallization processes investigated by differential thermal analysis (DTA)

Controlled crystallization of (TiO₂-ZrO₂)-rich calcium aluminosilicate glasses led to zirconolite in the bulk, and titanite and anorthite on the surface. Such glass-ceramics can be envisaged for minor actinides immobilization. In this study, the crystallization of three glass compositions with increasing TiO₂, ZrO₂ and CaO amounts was followed by differential thermal analysis (DTA). The effect of glass particle size and of heating rate on DTA curves was studied in order to investigate nucleation mechanisms and to extract the corresponding crystal growth activation energies E _c for the different crystalline phases. Exothermic effects associated with the crystallization of a phase having a defect-fluorite structure in the bulk and its consecutive transformation into zirconolite were only detected for the highly TiO₂, ZrO₂ and CaO enriched glasses due to their higher crystallization rate. Using an Avrami constant n = 3 and a dimensionality of crystal growth m = 3, the activation energy of defect-fluorite crystal growth was found to be E _c = 440 kJ · mol^–1 (modified Kissinger method). Titanite and anorthite grow only from glass surface with activation energies of respectively 493 and 405 kJ · mol^–1 (n = m = 1, Kissinger method). DTA study of melt crystallization during cooling showed that baddeleyite (ZrO₂) crystals firstly crystallize but become unstable versus zirconolite for higher undercooling.     

聚羟基丁酸酯的等温与非等温结晶动力学

用差示扫描量热法(DSC)研究了聚羟基丁酸酯(PHB)的等温与非等温结晶动力学。采用Avrami方程分析了等温结晶动力学,Avrami指数n≈2,表明PHB以异相成核的二维平面晶体方式生长,等温结晶活化能为82.4 kJ/min。采用Jeziorny法和莫志深法分析了PHB的非等温结晶动力学,Avrami指数n≈3,表明PHB非等温结晶过程以异相成核的三维球晶方式生长。     

Kinetics of zeolite dissolution: Part 3. Dissolution of synthetic mordenite in hot sodium hydroxide solutions

The kinetics of dissolution of synthetic mordenite in 1 m NaOH solution at 338, 343, 348, and 353 K were studied by following the changes in the characteristics of the solid and the liquid phase during the dissolution. Various experimental techniques such as ICP spectroscopy, FTi.r. spectroscopy, X-ray diffractometry, and particle-size distribution measurement were used for this purpose. The results obtained were analyzed and discussed in accordance with the model of growth and dissolution proposed by Davies and Jones, taking into account the chemical and structural characteristics of synthetic mordenite.     

On the crystallization mechanism of zeolite ZSM-5: Part 2. MNDO calculations of basic characteristics of some diamines used as templates

The basic characteristics of the C₂, C₃, C₄, and C₆ diamines and TPA were calculated. The high dipole moment, the minimum ionization potential, and the short dimension of diaminoethane and diaminopropane are the reasons for the high effectiveness. The MNDO calculation of the C₂C₆ diamines and TPA can be used for predictions of the effect of templates in zeolite synthesis. The correlations were obtained between kinetic parameters of the crystallization of ZSM-5 and basic characteristics of the calculated molecules.     

Fe73.5Cu1Nb3Si13.5B9非晶合金的晶化动力学

用ＤＴＡ结合ＸＲＤ了Ｆｅ７３．５Ｃｕ１Ｎｂ３Ｓｉ１３．５Ｂ９晶合金的晶化动力学。表明，该事金在５００℃时析出α－Ｆｅ（Ｓｉ）相。晶化初期激活能最小为２４２ｋＪ／ｍｏｌ，它随晶化量的增加，在ＸＣ为０．４－０．８时，呈极大值为５２０ｋＪ／ｍｏｌ。在６２４℃时析出Ｆｅ２Ｂ相。     

Study of SAPO-5 obtained from surfactant-containing gels: Part 1. Crystallization parameters and mechanism of Si substitution

The hydrothermal crystallization of SAPO-5 in a biphasic water-hexanol system in the presence of surfactants has been studied. Large crystallite aggregates with a high organic content are obtained by using a high concentration of cationic surfactants in the synthesis. The Si content of crystals is much less affected. ²⁹Si MASn.m.r. also shows deep modifications of the mechanism of Si incorporation. Neutral or anionic surfactants are uneffective in promoting these changes.     

Ion exchange in zeolite EU-1: Part 2. The effect of the chemical nature of the exchange site

Ion-exchange isotherms for samples of EU-1 where the exchange sites are predominantly SiO⁻ and (GaOSi)⁻ have been determined. The observed differences in ion-exchange selectivities are explained in terms of the differences in interaction of the cations with the solution and zeolite phases.     

Experimental and Theoretical Study of Kinetics of Bulk Crystallization in Poly(Chlorotrifluoroethylene)

The rate of isothermal bulk crystallization of poly(chlorotrifluoroethylene), T_m=221° C, was measured from 170° to 200° C. The intrinsic bulk crystallization, which accurately followed an n = 2 law, was shown to be a result of the injection of primary nuclei sporadically in time, with one-dimensional growth of centers derived from these nuclei. The crystallites are exceedingly small. The one-dimensional growth process was isolated by nucleating specimens with seed crystals, and its temperature-dependence determined between 191° and 205° C. The seed crystal isotherms followed an n = 1 law. The temperature coefficients of the rate of nucleation and the rate of growth were both strongly negative.A theory of homogeneous nucleation that takes into account the segmental character of the polymer chains is developed in some detail. A cylindrical nucleus is assumed. In the temperature range near the melting point, region A, where the radius and length of the nucleus are unrestricted, the rate of nucleation is shown to be proportional to exp(−α/T³ΔT²). The nucleation rate is proportional to exp (−β/T²ΔT) in region B, which extends from somewhat below the melting point to considerably lower temperatures; the length of the nucleus has a constant value l₀ in this region, but the radius is unrestricted. (In the above expressions, α and β are constants). Finally, at sufficiently low temperatures, region C is entered. Under certain circumstances, the rate of nucleation in region C will be extremely rapid, and correspond to a “nucleative collapse” of the supercooled liquid state. A calculation of the one-dimensional growth rate shows that it is proportional to exp(−γ/T²ΔT) where β=γ.A careful analysis of the experimental data obtained between 170° and 200° C clearly showed that both the rate of nucleation and the rate of growth were proportional to exp(−β/T²ΔT), and not exp(−α/T³ΔT²). The primary nucleation event was thus of type B in this interval. A detailed analysis of the data is given, and surface free energies and the dimensions of the nuclei quoted. Quenching experiments, where the polymer was crystallized well below 170° C, gave a firm indication of the existence of region C.An experimental study was made of the extremely slow crystallization process that prevailed when the degree of crystallinity became high. The onset of this stage of the crystallization was interpreted as being the result of a massive degree of impingement. This interpretation is justified by the calculations of Lauritzen, who has given a theory of impingements that predicts a pseudoequilibrium degree of crystallinity.As indicated above, the growth process originating at homogeneous nuclei is not of a three-dimensional or spherulitic character in the region of study. Such stray spherulites as do appear in this region are shown to originate at heterogeneities. The possibility that the intrinsic growth process may become three-dimensional at crystallization temperatures sufficiently near T_m is discussed.     

CdO纳米晶的固相合成及晶化动力学研究

以CdCl2和Na2CO3为原料,NaCl为稀释剂,利用固相反应合成前驱体,再经焙烧合成CdO纳米晶.用x-射线衍射(XRD)分析了不同焙烧温度对合成CdO晶粒尺寸的影响.研究结果表明:按Scherrer公式计算合成CdO纳米晶的晶粒尺寸在30～44nm,焙烧温度越高,晶粒尺寸越大;根据前驱体不同升温速率下的差热(DTA)曲线,用Kissinger 和Ozawa法计算合成CdO纳米晶的活化能分别为164.7kJ/mol和175.6kJ/mol,差别不大;根据晶粒生长动力学理论计算CdO晶粒长大的活化能为12.2kJ/mol,表明热处理过程CdO纳米晶粒的长大主要以界面扩散为主.     

溶胶-凝胶法制备(Bi0.5Na0.5)1-xBaxTiO3陶瓷的性能

测量了使用溶胶-凝胶工艺制备的 (Bi0.5Na0.5)1- xBaxTiO3(x=0,0.02,0.04,0.06)系无铅 压电陶瓷的介电、压电和弹性参数.研究发现,该工艺制备的 (Bi0.5Na0.5)0.94Ba0.06TiO3陶瓷具有 此系列最强的压电性能, 与传统工艺制备的该类压电陶瓷相比, 溶胶-凝胶工艺制备的 (Bi0.5Na0.5)0.94Ba0.06TiO3陶瓷具有压电常数( d33=173× 10- 12C/N)、机电耦合系数( kt=56%, kp= 26%)、泊松比(ν =0.3)提高; 频率常数( Nt=2250Hz· m, Np=2810Hz· m)、退极化温度( Td= 75℃)降低以及介电常数(εTr33=820)、介电损耗( tgδ=3.9%)稍大的特点.     

标准化的地位和作用(下)

本文针对标准化地位和作用论述中存在的问题,从理性思维出发,深入研究了标准化的地位和作用关系,研究提出了标准化的地位,并给出了每个地位的内涵解释;研究提出了标准化的直接作用,给出了每个作用的理论依据和应用关系;论述了标准化作用的关系和特点。