Detection of four different OH-groups in ground kaolinite with controlled-rate thermal analysis

The thermal behaviour of mechanochemically treated kaolinite has been investigated under dynamic and controlled rate thermal analysis (CRTA) conditions. Ten hours of grinding of kaolinite results in the loss of the d(001) spacing and the replacement of some 60% of the kaolinite hydroxyls with water. Kaolinite normally dehydroxylates in a single mass loss stage between 400 and 600°C. CRTA technology enables the dehydroxylation of the ground mineral to be observed in four overlapping stages at 385, 404, 420 and 433°C under quasi-isobaric condition in a self-generated atmosphere. It is proposed that mechanochemical treatment of the kaolinite causes the localization of the protons when the long range ordering is lost.This revised version was published online in November 2005 with corrections to the Cover Date.     

高岭石/聚丙烯酰胺插层复合物的制备与表征

The kaolinite-polyacrylamide intercalation compound was prepared first by the displacement reaction of the kaolinite-formamide intercalation precursor with 30% acrylamide ethanol solution, and then the polymerization under 140℃ for 15h with the catalysis of dibenzoyl peroxide. The XRD analyses showed that the basal spacings of kaolinite-acrylamide intercalation compound and kaolinite-polyacrylamide compound were 1.135nm and 1.144nm respectively. The kaolinite-polyacrylamide compound was able to resist to 30-min washing with water, but the kaolinite-acrylamide compound was unstable during washing. FT-IR proved that the hydrogen bonds were formed between kaolinite Si-O group and polyacrylamide NH group and between kaolinite inner surface hydroxyl and polyacrylamide C=O group, and that parts of NH group keyed into the kaolinite ditrigonal hole. TG and DTG analysis proved that kaolinite-polyacrylamide was stable under 350℃. A net weight loss of 16.63% between 370℃～500℃ is due to the removal of intercalated polyacrylamide from the interlamellar space of kaolinite. These results clearly indicate that acrylamide has been intercalated into the layers of kaolinite and was polymerized in-situ.Based on the TG data, the formula of the kaolinite-polyacrylamide intercalation compound, Al₂Si₂O₅(OH)₄?CH₂CHCONH₂?_0.736, can be calculated.     

Influence of pH on the thixotropy of magnesium aluminum hydroxide-kaolinite suspension

The influence of pH on the thixotropy of pure kaolinite suspension and magnesium aluminum hydroxide (Mg-AI-MMH)-kaolinite suspension was studied. The results show that the thixotropic type of pure kaolinite suspension was not affected by pH studied in the range of 3.60-12.00. The thixotropic type of Mg-AI-MMH-kaolinite suspension with mass ratio (R) value of MMH to kaolinite 0.029 transformed from complex thixotropy into positive thixotropy with increasing of pH in the range of pH 3.83-12.00, and the type of thixotropy of Mg-AI-MMH-kaolinite suspension with R = 0.129 transformed from positive thixotropy into complex thixotropy with increasing of pH in the range of pH 3.70-11.96.     

高岭石插层效率评价

用基于X射线衍射分析(XRD)的插层率、基于热重分析(TGA)的热失重率和基于红外光谱分析(FTIR)的3 600 cm^-1谱带与3 700 cm^-1谱带强度比值对高岭石/二甲基亚砜(DMSO)插层复合物和高岭石/N-甲基甲酰胺(NMF)插层复合物的插层效率进行了综合评价。结果表明,当插层反应进行到1、6和25 d,高岭石/DMSO的插层率分别为5%、52%和89%;而高岭石/NMF的插层率则分别为93%、94%和95%。与此同时,高岭石/DMSO的热失重率分别为1.06%、8.06%和17.46%;而高岭石/NMF的失重率分别为6%、6.5%和14.2%。在红外光谱图中,高岭石/DMSO复合物的3 600与3 700 cm^-1带强度比分别为1.03,1.141和1.628,而高岭石/NMF复合物分别为1.403,1.433和1.612。3种评价方法显示很好的一致性,相对而言,在插层作用的初期,XRD方法比较灵敏,而在插层作用的后期,TGA和FTIR方法则显得更为灵敏和有效。     

Thermal Behaviour of Kaolinite Intercalated with Formamide, Dimethyl Sulphoxide and Hydrazine

The thermal behaviour of kaolinites intercalated with formamide, dimethyl sulphoxide and hydrazine has been studied by simultaneous TG-DTG-DTA-EGA and TG-MS techniques. The complexes can be decomposed completely without dehydroxylating the mineral. It was found that the amount of intercalated guest molecules per inner surface OH-group is close to unity for the formamide and dimethyl sulphoxide intercalates. For the intercalation of hydrazine it was found that hydrazine is locked in the expanded mineral as hydrazine hydrate and its amount is somewhat higher than that obtained for the other two reagents. The thermal evolution patterns of the guest molecules revealed that all the three reagents are bonded at least in two different ways in the interlayer space. This revised version was published online in August 2006 with corrections to the Cover Date.     

New Data on Thermal Effects of Kaolinite in the High temperature Region

DTA study of an Indian Kaolinite has been performed by varying packing density and rate of heating. Both these two parameters influence the intensities of both endothermic and exothermic peaks related to the dehydration, dehydroxylation and then crystallizations of Al-Si spinel, mullite and cristobalite phases. Significantly, the study reveals that mullitization takes place by two separate reactions as indicated by two exotherms in the 1200-1400°C range of DTA trace. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mg-Fe-HTlc/高岭土悬浮体流变性研究

研究了Mg-Fe类水滑石(HTlc)/高岭土(kaolinite)悬浮体的质量比(R)对其流变性和触变性的影响, 发现控制剪切速率(D)得到的屈服应力(τ_y)和控制剪切应力(τ)得到的临界剪切应力(τ_c)皆随R的增大先降低后升高. 小幅振荡剪切实验发现随R的增大, 体系由正触变性转化为复合触变性, 其中用小幅振荡剪切法在线性粘弹区发现复合触变性体系还是首次. 恒剪切速率(D_L)实验发现了震荡现象, 即粘度随时间发生周期性升高和降低的变化. 震荡现象与D_L和R有关, 较高的D_L和R可使震荡现象消失. 测定粘度随时间变化时采用的低剪切速率(D_L)影响体系的触变性类型. 根据HTlc和kaolinite粒子间的相互作用对实验结果的机理进行了探讨.     

Flash calcination of kaolinite studied by DSC,TG and MAS NMR

The structural changes occurring during the dehydroxylation of kaolinite have been followed using flash calcination to produce kinetically frozen calcines. The percentage of dehydroxylation was varied by changing the furnace residence time or temperature and/or heating speed. These calcination conditions affected the reaction kinetics, but the products depended only on the extent of dehydroxylation.Changes in the position and enthalpy of the endothermic transformation to metakaolinite and the high temperature exothermic reaction of metakaolinite have been followed using Differential Scanning Calorimetry of the flash calcines and related to Thermogravimetry. ²⁷Al magic-angle-spinning NMR spectra, at high magnetic fields and spin rates, enabled the reaction of kaolinite to be monitored and provides new information on the nature of the species formed in the course of dehydration.We thank the Science and Engineering Council for supporting our studies of mineral transformations and. R. Meinhold thanks N.Z. D.S.I.R. chemistry, and H Atakul thanks Istanbul Technical University, for leave to undertake these studies. We thank Bruker Analytische for access to NMR spectrometers in their Karlsruhe laboratory.     

高岭土磁性复合材料表面印迹聚合物选择性吸附分离环丙沙星

以氨基改性的磁性高岭土为基质材料,利用电子转移产生催化剂的原子转移自由基聚合法制备磁性高岭土表面印迹聚合物(MMIPs)。通过FTIR、TEM、TGA、XRD和VSM等方法对其物理化学性质进行表征,其比表面积112 m2·g-1,且具有较好的热稳定性、超顺磁性(Ms=13.365 emu·g-1)。吸附性能研究表明,准二级动力学模型能较好地描述MMIPs对环丙沙星(CIP)吸附动力学行为,Langmuir等温模型能较好地拟合MMIPs对CIP的吸附平衡数据,25℃时MMIPs的单分子层吸附容量为89.36 mg·g-1。选择性实验研究表明,MMIPs对CIP具有较好地选择识别性。结合高效液相色谱分析技术,MMIPs已成功应用于鲜鱼样品中痕量CIP的分离、富集和回收,CIP的回收率为92.15%。     

高岭石-硬脂酸插层复合物的制备及结构模型的提出

以张家口高岭土为原料,通过直接插层与取代相结合的方法制备高岭石-硬脂酸插层复合物。利用X射线粉末衍射、红外光谱、热重及透射电子显微镜对制备产物进行表征。结果表明:硬脂酸插入到高岭石层间,高岭石层间距d001值由0.72 nm增加到4.05~4.37 nm,插层率达到86.9%;反应时间和溶液p H值会对高岭石-硬脂酸插层复合物的层间距及插层率产生影响;甲氧基嫁接在高岭石表面,与硬脂酸分子同时存在于高岭石层间。高岭石经甲醇改性后脱羟基温度明显降低,高岭石羟基活性提高;高岭石-硬脂酸插层复合物的稳定温度在160℃以下。经过硬脂酸插层改性后的高岭石片层,从边缘开始出现卷曲现象,并且部分长条状片层形成类似埃洛石相的纳米卷;对硬脂酸插层高岭石的作用机理进行分析,结合结构计算,提出高岭石-硬脂酸插层复合物的结构模型,该模型可以解释高岭石-硬脂酸插层复合物在不同条件制备产物层间距变化的原因。