直接置换插层法0.85 nm水合高岭石的制备

以高岭石/尿素插层复合物作为中间相,利用简单的直接置换插层法制备了d001=0.85 nm的水合高岭石。利用X射线衍射、红外光谱、扫描电镜表征处理前后高岭石结构与形貌的变化。结果表明:尿素插层后的高岭石层间距从d001=0.72 nm增大到d001=1.08 nm,经不同温度酸洗或水洗后,插层复合物转变成层间有水分子的水合高岭石(d001=0.85 nm),且高岭石晶粒厚度明显从约25 nm减小到约10 nm。在高温条件下形成的水合高岭石含量最高,90℃水洗时d001=0.85 nm水合高岭石的转化率接近70%,这种水合高岭石具有进一步的置换插层能力,是一种制备其他高岭石插层复合物很好的前驱体。与乙二醇形成d001=1.10nm乙二醇/高岭石插层复合物,其置换率达到100%。     

高岭石纳米卷的制备与表征

本文以层状茂名高岭石为原材料,利用二甲亚砜、甲醇、十六烷基三甲基氯化铵(CTAC)插层处理成功制备了高岭石纳米卷。利用X射线衍射、红外光谱、扫描电镜、透射电镜、N2吸附-脱附、29Si CP/MAS NMR表征插层前后高岭石结构与形貌的变化。分析表明,高岭石片层的卷曲和剥离同时进行,随着CTAC甲醇溶液浓度的增加以及反应时间的延长,高岭石纳米卷的外径增加,而内径基本保持不变。高岭石纳米卷形成机理与CTAC分子的插层减弱了高岭石层与层之间作用以及表面活性剂的模板效应有关。     

高岭土／羧甲基淀粉复合颗粒的制备及其协同电流变效应

通过二次插层取代法，以二甲基亚砜为前驱体，羧甲基淀粉二次插层取代制备 了高岭土/羧甲基淀粉纳米复合材料。结合XRD，FTIR，SEM和EDS等测试手段对复合 材料的结构进行了表征。研究结果发现，羧甲基淀粉经过二次插层取代引起了高岭 土片层之间的剥离，形成剥离型纳米复合材料。该复合材料制备成电流变液出现了 较大的协同效应，具有很好的电流变行为，并发现电流变性能与复合物中羧甲基淀 粉的含量有密切关系。     

丁苯三嵌段共聚物/改性纳米层状白泥复合弹性体的力学性能

热塑性弹性体;混杂纳米复合材料;丁苯三嵌段共聚物/改性纳米层状白泥复合弹性体的力学性能     

Spectroscopic studies on organic molecules intercalated into clays

An overview of clay structures and characterization methods is followed by a discussion of some adsorption reactions of organic molecules which have been studied spectroscopically. These can be divided into two main classes: adsorption with and without reaction.Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August 1995.     

Influence of the particle-size reduction by ultrasound treatment on the dehydroxylation process of kaolinites

Kaolinites from well-known sources (KGa-1 and KGa-2) were used to study the influence of the particle-size reduction on the dehydroxylation process. Size reduction of particles was obtained by ultrasound treatment to avoid the effect of the progressive amorphization of the structure, which takes place with the traditional grinding treatment.The particle-size reduction causes an increase of the mass loss between 140 and 390°C attributed to the loss of the hydroxyl groups exposed on the external surface of kaolinite; a shift to lower temperatures of the endothermic effect related with the mass loss between 390 and 600°C and a shift of the end of dehydroxylation to lower temperatures. The first modification can be explained by an increase of the number of hydroxyls exposed on the external surface of kaolinite which is proportional to the new surface generated in the particle reduction process, whereas the shift of the dehydroxylation to lower temperatures is related to the reduction of the dimensions of the particles which favour the diffusion controlled mechanisms.Comparing between the DTA curves to the TG curves of the studied samples shows that the observed modifications in the thermal properties induced by the particle-size reduction are greater for the low-defect kaolinite. The intensity of these modifications depends on the effectiveness of the ultrasound treatment.The authors are grateful to S. Yariv, I. Lapides and S. Shoval for carefully reviewing this paper and making helpful comments. This research has been supported by Research Project MAT 2002-03774 from the Spanish Ministry of Science and Technology and Research Groups FQM-187 and RNM-0199 of the Junta de Andalucia.     

Acid and thermal treatments of lateritic bauxites

H₂SO₄ and HCl processes accompanied by thermal treatments at different stages are described for the industrial extraction of alumina from lateritic clay minerals, especially from kaolinite, an important component of lateritic bauxites. The effects of calcination at high temperatures on the pretreatments of the raw lateritic materials, as well as on the thermal transformations of the products (salts) resulting from the acid treatments of lateritic bauxites are analyzed. Beside energetic considerations, separation methods of Al from Fe and from other lateritic-metallic components are emphasized in the extraction and purification processes. The mechanism of a controlled HCl-extracting treatment performed on iron-bearing kaolinite is described, as well as its characterization by IR and DTA ad hoc methods, enabling to distinguish between Al and Fe in the structure of lateritic kaolinite. The location and quantification of Al in the structure of lateritic goethite is also considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature effects on the point of zero charge and isoelectric point of a red soil rich in kaolinite and iron minerals

The effects of temperature (373–1373 K) on the point of zero charge (PZC) and isoelectric point (IEP) of a red soil rich in kaolinite and iron minerals were studied. PZC values of the soil treated at 373 and 573 K indicated the presence of iron oxide. The soil calcined between 773 and 1173 K shows a PZC almost coincident with the respective values of kaolinite. At 1373 K, the PZC of the soil is nearer to the value of iron oxide. In the entire temperature range studied the PZC values were lower than the IEP values. An approach of PZC and IEP values was observed after a partial removal of iron oxide by the dithionite-citrate-bicarbonate (DCB) method. The analyses of the PZC and IEP values, of electron probe micro analysis (EPMA) data and of specific surface areas evidence a specific adsorption of iron oxide on kaolinite. Finally, the dissolution sequence of iron and aluminium contained in soil was determined using hydrochloric acid.     

IR Spectroscopy in Determination of Enrichment of Low Quality Bauxites

It is shown that processes of enrichment of low quality bauxite can be as effectively monitored by IR spectroscopy next to other generally applied analytical methods, such as chemicals analysis, X-ray diffraction and atomic absorption spectrophotometry. Changes were followed of characteristic vibration bands of main bauxite constituents, boehmite, haematite and kaolinite, as the carries of aluminum (gamma-AlOOH), iron (Fe₂O₃) and silicon [Al₂SiO₅(OH)₄], respectively.     

Effect of Electrolytes and Polymers on the Thixotropy of Mg‐Al‐Layered Double Hydroxides/Kaolinite Dispersions

The effect of electrolytes (NaCl and CaCl₂) and polymers (CPAM and HPAM) on the thixotropy of Mg‐Al‐layered double hydroxide (LDHs)/kaolinite dispersions has been investigated. It was observed that the type of thixotropy in LDH/kaolinite dispersions may be affected by NaCl, but not by CaCl₂ in range of concentration of interest. The type of thixotropy in LDH/kaolinite dispersion with R=0 transformed from positive thixotropy to complex thixotropy and at last positive thixotropy again with the concentration of NaCl in range of 0.00–0.10 mol·L⁻¹; the type of thixotropy in LDHs/kaolinite dispersions with R=0.25 transformed from complex thixotropy to positive thixotropy and then complex thixotropy again with the concentration of NaCl in range of 0.00–0.10 mol·L⁻¹. The type of thixotropy in LDH/kaolinite dispersion with R=0 may be not affected by cationic polyacrylamide (CPAM) and hydrolyzed polyacrylamide (HPAM); but the LDHs/kaolinite dispersions with R=0.25 transformed from complex thixotropy to positive thixotropy with the both polymers concentration in range of interest, which indicated that the microstructure of the dispersion changed from weak folc sediments structure to steric network structure.