Electric-field-induced structuring and rheological properties of kaolinite and halloysite

Electric-field-induced structuring of kaolinite and halloysite particles was studied in respect to their electrorheological (ER) response in silicone oil and in paraffin dispersions. The structural and morphological properties of both clay minerals were studied by XRD, FTIR, SEM, TEM and TGA techniques. The dipolar arrangement induced under application of an electric field was investigated by 2D-WAXS and optical microscopy techniques. The ER response of the samples was measured by both the shear rate controlled method and bifurcation tests. Kaolinite particle dispersions were found to have an improved ER response relative to dispersions of halloysite particles. Finally, the electric currents of these ER fluids were measured and the results revealed differences in the current-magnitude between halloysite- and kaolinite-based silicone oil dispersions.     

Synthesis and characterization of Sb–SnO2/kaolinites nanoparticles

In this paper, we reported the synthesis of composite conductive powders of antimony-doped tin oxide (Sb–SnO₂) coated onto kaolinite. Structure and morphology of the samples were systematically characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transform infrared (FTIR) and X-ray photoelectron spectrum (XPS). The results showed that Sb–SnO₂ nanoparticles (< 10 nm) were successfully coated as thin layers on the surface of kaolinite. The antimony-doped tin oxide/kaolinite (ATK) composites retained the flake morphology like the original kaolinite and had a resistivity of 273.2 Ω·cm. Sb–SnO₂ layers were proved to attach to the kaolinite surface via the Sn–O–Si or Sn–O–Al bonds. The growth mode of Sb–SnO₂ layers onto the kaolinite was investigated.     

Mechanochemical intercalation of low reactivity kaolinite

Complete urea-intercalation of a low reactivity kaolinite from Birdwood has been carried out by co-grinding with urea in the absence of water (mechanochemical intercalation). The effectiveness of mechanochemical intercalation was compared to solution intercalation by X-ray diffraction (XRD), thermal analysis (TG, DTG), diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy and scanning electron microscopy (SEM). In aqueous solution of urea the Birdwood kaolinite was intercalated with difficulty and only 12% intercalation was achieved. After 2 h of co-grinding with solid urea, complete (100%) intercalation was attained. The possible explanation of complete intercalation is that co-grinding of Birdwood kaolin with solid urea can remove the high-defect kaolinite coating, which prevents the intercalation of the low-defect kaolinite particles. The mechanochemical treatment increased the degree of intercalation and in parallel reduced the amount of the crystalline kaolinite phase.     

Relationships between chemico-mineralogical composition and color properties in selected natural and calcined Spanish kaolins

A total of 21 raw, washed and ground Spanish kaolins were studied. Kaolinite, mica, quartz, feldspars and occasionally anatase and analcime were present. Calcined samples in which the kaolinite had been transformed into metakaolinite (650 °C, 3 h), as shown by X-ray diffraction and observed using SEM were also studied. These samples featured particles with openings and a lateral loss of laminar continuity, generated spaces, joined crystal edges and superficial coatings which appeared to be fused to the surface of the aggregates.Whiteness and tint indices (W₁₀, T_w,10), revealed that only nine kaolins could be considered white (limits of CIE Colorimetry, 1986. 2nd ed. CIE Publication No.15.2. Vienna: Central Bureau of the CIE), though upon calcination, this number is reduced to three. Calcinating also produced coloring and reddening of the samples. The CIELAB color parameters significantly correlated with compositional properties such as mineralogy, the chemical analysis of elements, the free oxide contents (Al₂O₃, SiO₂, Fe₂O₃) extracted with ammonium oxalate and with citrate–dithionite–carbonate, and trace elements. In the non-calcined kaolins: C_ab* is positively related to SiO₂ and negatively to the percentage of kaolinite; L* is negatively related to K₂O; h_ab is negatively related to K₂O and MgO; and W₁₀ is positively related to the percentage of kaolinite and negatively to the percentages of mica, K₂O, MgO, MnO and free Fe₂O₃. The calcined samples showed correlations of h_ab and L* (positive) and of C_ab* (negative) with the proportions of both elemental Al and the Al extracted as free oxides. There are nonsignificant differences between the L* of calcined and non-calcined kaolin samples, meaning that both samples fulfill the requirements of high lightness for use in the paper industry.     

Structural alterations in kaolinite by acid treatment

Structural changes that kaolinite underwent when leached with H₂SO₄ were studied through IR, XRD and electron microscopy. The evolution of IR bands and XRD spectra were analyzed as a function of Al³⁺ extraction, similar behavior in the (001) plane integrated intensity and the IR absorbance of bands assigned to bonds in which Al³⁺ takes plane was found. Electron microscopy shows that the extensively attacked mineral (x=95%) presents a structure retaining the geometrical features of the original crystals.     

Heteroepitaxial growth of TiN film on MgO (100) by reactive magnetron sputtering

TiN thin films were deposited on MgO (100) substrates at different substrate temperatures using rf sputtering with Ar/N₂ ratio of about 10. At 700°C, the growth rate of TiN was approximately 0.05 μm/h. The structural and electrical properties of TiN thin films were characterized with x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Hall measurements. For all deposition conditions, XRD results show that the TiN films can be in an epitaxy with MgO with cube-on-cube orientation relationship of (001)_TiN // (001)_MgO and [100]_TiN // [100]_MgO. TEM with selected-area electron diffraction pattern verifies the epitaxial growth of the TiN films on MgO. SEM and AFM show that the surface of the TiN film is very smooth with roughness approximately 0.26 nm. The minimum resistivity of the films can be as low as 45 μΩ cm.     

Effects of synthesis conditions on the morphology of hydroxyapatite nanoparticles produced by wet chemical process

Nanoparticles of hydroxyapatite (HAP) were synthesized by means of wet chemical precipitation method, under atmospheric pressure. HAP powders with various morphologies, such as sphere-, rod-, needle-, wire- and bamboo-leaf-like, were obtained by controlling the synthesis conditions. It was found that the solvent systems, dispersant species and drying methods had effects on the particle size and dispersibility. The initial pH values and reaction temperatures both played important roles in the morphology of HAP, as well as the phase formation and degree of crystallinity. The possible influence process of initial pH values and reaction temperatures was discussed in details. The crystal morphology and particle size were analyzed by transmission electron microscopy (TEM) and scanning electron microscope (SEM), and the compositions and chemical structures were identified by X-ray diffractions (XRD) and Fourier transform infrared spectroscopy (FTIR).     

氨水改性高岭土/NR复合材料微观结构的研究

采用透射电子显微镜、扫描电子显微镜、能量色散谱仪和动态粘弹谱仪分析氨水改性高岭土／NR复合材料的微观结构。结果表明，与采用凝聚法简单共混制备的高岭土／NR复合材料(CKNR)相比，采用凝聚共沉法制备的氨水改性高岭土／NR复合材料(NKNR)中高岭土粒子分布更均匀．平均粒径较小；NKNR的拉伸断面布满了直径约为50nm的拉丝，这些拉丝是高岭土NR界面附近的NR与高岭土表面凝胶的分子水平复合物；NKNR中的NR具有多种聚集态，包括NR基体、远程NR与高岭土表面凝胶复合物以及高岭土／NR界面附近的NR与高岭土表面凝胶复合物。     

Thermal annealing effects on the structural and electrical properties of PMN–PZ–PT ternary thin films deposited by a sol–gel process

Thin film samples of 0.15PMN–0.45PZ–0.40PT (PMN–PZ–PT) three-component system were prepared on Pt-coated Si substrates by a sol–gel process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS) show that the above films can be formed in a single-phase perovskite structure at 800 °C. This was further confirmed by the dielectric and ferroelectric properties of the samples annealed at different temperatures. It was demonstrated that the morphology and microstructures of the PMN–PZ–PT films were quite sensitive to their annealing conditions, which strongly affects their electrical properties.     

Synthesis and characterisation of novel titania impregnated kaolinite nano-photocatalyst

Nano-sized titanium dioxide (TiO₂) has received a great attention in the field of research and development as a promising photocatalyst to promote the degradation of organic contaminants in water. One of the key technical challenges involved in separation and recovery of the photocatalyst particles from the water treatment system makes this technology unviable as an industrial process. A novel titania impregnated kaolinite (TiO₂/K) photocatalyst was synthesized by a modified two step sol–gel method: hydrolysis of titanium(IV) butoxide and heterocoagulation with pre-treated kaolinite (K) clay. The TiO₂/K photocatalysts were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and BET specific surface area measurements (BET). The photocatalytic activity was evaluated by the degradation of Congo red in aqueous solution. The TiO₂/K photocatalyst had a rigid porous layer structure and promising nano-size properties, and demonstrated an enhanced adsorption and photocatalytic ability for the removal of Congo red. The TiO₂/K photocatalyst can be easily separated and recovered from the water treatment system. The TiO₂/K photocatalyst is expected to deliver a true engineering solution for an industrial water/wastewater treatment process.     

Synthesis and intercalation of silver nanoparticles in kaolinite/DMSO complexes

Ag nanoparticles were synthesized in the interlamellar space of a layered kaolinite. Disaggregation of the lamellae of the nonswelling kaolinite was achieved by the intercalation of dimethyl sulfoxide (DMSO). The kaolinite was suspended in aqueous AgNO₃ solution and the adsorbed Ag⁺ ions were reduced on the surface of kaolinite lamellae with NaBH₄ or UV light irradiation. The silver nanoparticles formed were characterized by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). We studied the effects of the two reduction methods on the size and the size distribution of Ag nanoparticles and how clay mineral structure is altered as a consequence of particle formation. It was established that the size of Ag nanoparticles depends on both silver content and the reduction method. Photoreduction of silver led to the formation of relatively large Ag nanoparticles (diameter 8–14 nm).     

Preparation and characterization of epoxy/kaolinite nanocomposites

Epoxy/kaolinite nanocomposites were prepared by adding the organically modified layered kaolinite to an epoxy resin [biphenyl phenol novolac epoxy resin (BPNE)] with 4,4′‐diamino biphenyl sulfone (DDS) as a curing agent. The dispersion state of the kaolinite within crosslinked epoxy‐resin matrix was examined by X‐ray diffraction (XRD) and transmission electron micrograph (TEM). The effects of kaolinite on thermal properties were investigated and discussed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Experimental results show that BPNE/kaolinite nanocomposites exhibit improved thermal than pure BPNE. When the kaolinite content is 5 wt %, the BPNE/kaolinite nanocomposites show the best thermal properties. These results indicate that nanocomposition is an efficient and convenient method to improve the thermal properties of BPNE. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Feasibility of recycled newspaper as cellulose source for regenerated cellulose membrane fabrication

An environmental friendly regenerated cellulose membrane (RCM) was successfully prepared via NaOH/urea aqueous solution system by utilizing recycled newspaper (RNP) as the cellulose source. The morphological and chemical structure of resulting membrane were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD) spectroscopy, and thermogravimetric analysis (TGA). Results from FTIR and XRD verified that the transparent RCM possesses cellulose II structure. SEM observation revealed that the transparent RCM consist of homogeneous dense symmetric membrane structure and composed of a skin layer with mean roughness parameter R_a, obtained from AFM analysis of 29.53 nm. Pure water flux, water content, water contact angle, porosity, and pore size of the resulting membrane were also measured. This study promotes the potential of the cellulose‐based membrane obtained from low cost cellulose source for application in filtration and separation system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42684.     

Template-directed hydrothermal synthesis of dandelion-like hydroxyapatite in the presence of cetyltrimethylammonium bromide and polyethylene glycol

A template-directed synthetic method, using surfactant cetyltrimethylammonium bromide (CTAB) as a template and co-surfactant polyethylene glycol (PEG600) as a co-template under hydrothermal conditions, has been applied to obtain dandelion-like HAp. The morphology, size, crystalline phase, chemical composition, physical characteristics, and thermal behavior of the product were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Fourier ransform infrared spectroscopy (FTIR), induced coupled plasma spectroscopy (ICP), BET (Brunauer, Emmett, and Teller) method, and simultaneous thermal analysis (STA). SEM and TEM observations showed in the presence of CTAB and a certain concentration of PEG600 (30%) HAp crystals have a uniform dandelion-like morphology with a diameter of about 80–150 nm and aspect ratio of about 20 for each tooth. Dandelion-like HAp crystals have a high surface area of 88 m² g⁻¹ showing potential applications. The template action of CTAB and co-template action of PEG600 are also discussed.     

Morphology and mechanical properties of Nylon 6/MWNT nanofibers

Aligned nanofibrous nanocomposites of Nylon 6 and surface-modified multiwalled carbon nanotubes (MWNTs) were successfully synthesized via electrospinning, using a rotating mandrel. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM) and dynamic mechanical analysis (DMA) were done to characterize the morphology and properties of the nanofibrous mats. DSC and XRD observations suggested the presence of MWNTs and the high speed take-up facilitated the transformation of Nylon 6 from γ phase crystals to a mixture of α and γ phase crystals. TEM and WAXD were used to characterize the nanotube and molecular orientations, respectively. The storage modulus of the fibers increased significantly although the concentration of MWNTs was relatively low (0.1 and 1.0 wt%). Thus the combination of carbon nanotubes and nanoscale processing results in structural and mechanical enhancements of Nylon 6.     

The geology and mineralogy of a range of kaolins from the Santa Cruz and Chubut Provinces, Patagonia (Argentina)

In the Santa Cruz and Chubut provinces, Patagonia, Argentina, kaolin deposits were formed by “in situ” alteration of volcaniclastic rocks, such as the Bajo Grande, Chon Aike or Marifil Formations, or by erosion, transportation, and deposition of residual clays in small basins. This paper describes the genesis; geology; mineralogy; major, minor, and trace element geochemistry; grain size distribution; and specific surface area of natural and washed kaolins in an attempt to understand their behavior in the ceramic process. The sedimentary clays of the Baqueró Fm Lower Member, related to the Bajo Grande basement, are kaolinitic–smectitic, very fine-grained, and with a very high specific surface area. The clays related to the Chon Aike or Marifil Fms are kaolinitic, showing intermediate values of specific surface area and a coarser particle size distribution, associated with quite a fine-grained texture. The Baqueró Fm Upper Member received a considerable pyroclastic supply, fostering the development of a fine-grained clay in which kaolinite (± halloysite) with higher values of kaolinite crystal order prevailed. Primary kaolins – derived from weathering of pyroclastic sequences of Chon Aike and Marifil Fms – are coarse-grained, composed of kaolinite + quartz ± halloysite and exhibit a very low specific surface area. Alteration of mostly crystalline pyroclastics yielded ordered kaolinite and illite (+ halloysite) with a fine particle size distribution and intermediate values of specific surface area. Alteration of mainly vitreous pyroclastics produced halloysite (+ kaolinite) with a fine-grained texture and moderately high values of specific surface area. A supergene origin of primary kaolins is inferred on the basis of palaeoclimatic and geochemical evidence that corroborates stable isotopic data. The mineralogy, grain size, and textural characteristics of clays are controlled by parent rock composition (primary kaolins) or by provenance and proximity to source areas (sedimentary kaolins).     

Crystal morphology of rapidly cooled isotactic polypropylene: A comparative study by TEM and AFM

The morphology of crystals, formed at the surface and in the bulk of rapidly cooled and subsequently at elevated temperature annealed films of isotactic polypropylene (iPP) was analyzed by transmission electron microscopy (TEM) and by atomic force microscopy (AFM). Both techniques show a lamellar crystals after melt-crystallization at 12 K s^-1, and a nodules after melt-crystallization at 750 K s^-1. The morphology of crystals is independent on the position of the investigated film of thickness of 100 μm, suggesting (a) that the crystallization at the surface is not affected by the use of a glass substrate for preparation, and (b) that the temperature-gradient during primary crystallization is sufficiently small to ensure identical structure at the surface and in the bulk. AFM suggests a larger size of crystals than TEM, in particular if the absolute size of objects approaches the dimensions of the used tip of the AFM. If the absolute size of objects is distinctly larger, then AFM and TEM yield nearly identical dimensional information.     

Time-resolved powder neutron diffraction study of the phase transformation sequence of kaolinite to mullite

Mullite formation from kaolinite was studied by means of high-temperature in situ powder neutron diffraction by heating from room temperature up to 1370 °C. Neutron diffractometry under this non-isothermal conditions is suitable for studying high-temperature reaction kinetics and to identify short-lived species which otherwise might escape detection. Data collected from dynamic techniques (neutron diffraction, DTA, TGA and constant-heating rate sintering) were consistent with data gathered in static mode (conventional X-ray diffraction and TEM). The full process occurs in successive stages: (a) kaolinite dehydroxylation yielding metakaolinite in the ∼400–650 °C temperature range, (b) nucleation of mullite in the temperature range ∼980–992 to ∼1121 °C (primary mullite) side by side with a crystalline cubic phase (Si-Al spinel) detected in the ∼983–1030 °C temperature interval; (c) growth of mullite crystals from ∼1136 °C, (d) high (or β) cristobalite crystallization at T > ∼1200 °C and (e) secondary mullite crystallization at T > ∼1300 °C. The calculated activation energy for the kaolinite dehydration was 115 kJ/mol; for the mullite nucleation was 278 kJ/mol and for the growth of mullite process was 87 kJ/mol; finally for cristobalite nucleation the calculated apparent activation energy was 481 kJ/mol.     

链状结构TS-1分子筛的合成

采用3种合成方法制备链状结构的钛硅分子筛(TS-1),并用X线衍射仪(XRD)、扫描电子显微镜(SEM)、红外光谱仪(FT-IR)和紫外可见分光光度计(UV-VIS)等手段对试样进行表征。研究结果表明:在常规水热合成条件下,TS-1晶体具有沿着[010]面层状堆积生长形成链状结构的趋势。合成温度越高,越容易获得与微波合成相似的较好的链状结构,进入骨架的Ti诱导了分子筛晶粒之间表面羟基的缩合反应,从而导致晶体层状堆积生长,与加热方法无关。     

XRD microstructural analysis of mullites obtained from kaolinite–alumina mixtures

A microstructural study of mullite obtained by the reaction sintering of kaolinite–α–alumina mixtures in the range 1150–1700°C has been performed by using X-ray line profile analyses together with scanning and transmission electron microscopy equipped with microanalysis by energy dispersion (SEM-EDS, TEM-AEM). Two kinds of morphology corresponding to primary (elongated grains) and secondary (equiaxed grains) mullite have been observed. A bimodal crystallite size distribution has been detected through XRD microstructural analysis from 1300°C. The results obtained by this method are compared with SEM/TEM data.