Film Forming Nanohybrids Obtained with Polyethers

New hybrid materials based on polyether polyols were prepared by using a sol-gel reaction of alkyltriethoxysilanes, in the presence of propylenoxide-ethylenoxide trifunctional block copolymers. The resulting composites are transparent and have a filmogene behavior. Two types of filler systems were used: one based on silane precursors and one based on both the silane precursors and nanoclay (sodium montmorillonite). FT-IR spectra were evaluated to prove both the covalent interaction at the functional groups level and the presence of silica nanodomains formed by sol-gel process. The polarity changes were analyzed in the UV spectra, which shift according to the nature of different cationic dyes. Polyether hybrids were also obtained in the presence of some layered silicates. The X-ray diffraction reflects the changes in basal spacing of the Cloisite Na⁺, when it is added to different formulations. The modification of film morphology, depending on the reactants nature, can be observed in the SEM images.     

Phase, microstructure, and oxidation resistance of yttrium silicates coatings prepared by a hydrothermal electrophoretic deposition process for C/C composites

Oxidation-resistant yttrium silicates coatings for SiC precoated carbon/carbon composites were prepared by a novel hydrothermal electrophoretic deposition process. Sonochemical-synthesized yttrium silicates nanocrystallites, isopropanol, and iodine were respectively used as source materials, solvent, and charging agent during the deposition. Phase compositions, surface and cross-section microstructures of the as-prepared multilayer coatings were characterized by an X-ray diffractometer (XRD) and a scanning electron microscopy (SEM). The influence of deposition temperatures on the phase, microstructure, and oxidation resistance of the multilayer coated C/C composites was particularly investigated. Results show that the as-prepared outer coatings are composed of yttrium silicates crystallites with a main phase of Y₂Si₂O₇ and Y₂SiO₅. The thickness and density of the yttrium silicates coatings are improved with the increase of deposition temperature. Compared with SiC coating prepared by pack cementation, the multilayer coatings prepared by pack cementation with a later hydrothermal electrophoretic deposition process exhibit better antioxidation properties. The as-prepared multilayer coatings can effectively protect C/C composites from oxidation at 1773 K in air for 35 h with a weight loss of 0.32 × 10⁻³ g/cm².     

HYDROTHERMAL SYNTHESIS AND ION EXCHANGE PROPERTIES OF THE NOVEL FRAMEWORK SODIUM AND POTASSIUM NIOBIUM SILICATES

ABSTRACT

Two novel metastable sodium niobium silicates of the empirical formula: Na_l+x?yH_y(Nb_1?xSi_x)O₃ nH₂O, where x=0.33?0.38, y<l+x, n=0,7-l.l (NbSi-Na, 6.0 Å phase), and Na_3-x H_xNb₃Si₂O₁₃ nH₂O, where x<1.5, n=2.5?3.5 (NbSi-Na, 12.6 Å phase), and two novel potassium niobium silicates: K_4?xH_xNb₄SijO₂₂nH₂O, where x<l, n=3.5-4.0 (NbSi-K., 10.0 Å phase), and K_1?xH_xNbSi₄O₁₁nH₂O, where x<0.2, n=0.4-0.5 (NbSi-K, 6.05 Å phase), were synthesized in the homogeneous alkaline reaction system NbCl₅ - SiO₂ - NaOH (KOH) -H₂O₂ - H₂O under mild hydrothermal conditions. The compounds were characterized by elemental analysis, FTIR, TGA, MAS ²⁹Si NMR and X-ray diffraction. It was found that alkali metal niobium silicates have open framework structures. Their ion exchange affinity towards alkali, alkaline earth and some transition metal ions was studied. All alkali metal niobium silicates are moderately acidic ion exchangers. Both sodium niobium silicates show a distinct affinity for Cs⁺ ion among alkali metal ions, whereas potassium niobium silicate, the NbSi-K, 10.0 Å phase, exhibits affinity for Rb⁺ ion. The affinity of the sodium niobium silicate, NbSi-Na, 6.0 Å, toward strontium ion in neutral solutions is equal or superior to the best Sr-selective inorganic ion exchangers. The sodium niobium silicate (NbSi-Na, 12.6 Å phase) exhibits extremely high affinity for Pb²⁺ ion in acidic and neutral media, and both sodium niobium silicates also show a moderate affinity for Hg²⁺ ion in neutral and highly alkaline media. These exchangers could be promising for the treatment of some specific nuclear waste and contaminated environmental and biological liquors containing lead, mercury and radioactive strontium.     

57Fe Mössbauer spectroscopic studies of fly ash from coal-fired power plants and bottom ash from lignite-natural gas combustion

A series of four fly ashes, representing a variety of geological origins, and a bottom ash sample derived from the combustion of lignite-natural gas mixtures have been studied by ⁵⁷Fe Mössbauer spectroscopy. The ashes are separated into magnetic and non-magnetic fractions to facilitate a study of the chemical state of the iron contained in the ash. The bottom ash contains no magnetic fraction whereas the magnetic fractions of the fly ashes range from 1.1 to 7.3%. The magnetic fractions contained iron in the form of magnetite, Fe₃O₄. Iron in the non-magnetic fly ash fractions occur as Fe⁺¹ and Fe⁺² mullites, and Fe⁺³ and Fe⁺² silicates. Only Fe⁺³ silicates are found in the bottom ash.     

The preparation and characteristics of surface treated barium sulfate extender pigment

This article deals with the treatment of barium sulfate extender pigment with iron oxide and its phenomenological adsorption mechanism in the presence of H⁺ and OH^? ions in solution. The pH range taken in the present study is 5–6. By depositing a ferric oxide layer on barium sulfate particles a novel pigment with better optical and functional performance is obtained. This pigment in various coating systems improves physicochemical performance and acts as an active barrier. The treated pigments can be suitably used in different architectural and industrial coatings. The experimental techniques of surface treatment are discussed, along with the instrumental analysis by SEM, EDAX, XRD, etc.     

Preparation and investigation of anticorrosion properties of the water-based epoxy-clay nanocoating modified by Na+-MMT and Cloisite 30B

In this study the effect of using nanoclay particles in two different matrices on anticorrosive performance improvement of a novel water-based epoxy coating was investigated. For this purpose, Na⁺-montmorillonite (Na⁺-MMT) and organo-montmorillonite (Cloisite 30B) were introduced into water-based hardener (RIPI-W.B.H.) and epoxy resin matrices, separately. Nanoclays were added to polymeric matrices using direct mixing under an ultrasonic homogenizer. The coatings were analyzed to ensure the intercalation and distribution of layered silicates by means of X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses. The structure of products is studied by infrared (IR) spectrometer. The corrosion protection performances of the coatings were investigated using salt spray test and electrochemical impedance spectroscopy (EIS) in 3.5% sodium chloride solution. The results showed that using Cloisite 30B in water-based hardener had the best performance and its application in anticorrosion water-based zinc rich epoxy coating approved of it.     

Structure,properties and corrosion resistivity of polymeric nanocomposite coatings based on layered silicates

This paper reviews the recent research and development of polymeric nanocomposite coatings based on layered silicates. In the past few decades, extensive research activities have been conducted on clay minerals due to their unique layered structure, rich intercalation chemistry and availability at low cost, environmental stability, and good processability. One of the most important categories of layered silicates is nanoclays. The nanoclay is considered as reinforcement for polymers in the manufacture of low-cost, lightweight and high performance nanocomposite coatings. In this paper, we try to introduce the structure, properties, and surface modification of clay minerals. Different properties of polymer clay nanocomposite coatings consisting of different polymers are also reviewed. These coatings may consist of conductive and nonconductive polymers. The corrosion resistance of each type is discussed separately. Some novel properties can be observed from the interaction of two dissimilar chemical components at the molecular level that posses enhancements in corrosion inhibition on metallic substrates. Finally, the prospective problems of industrial usage of these materials are mentioned.     

Structure and electrochemical characterization of electrolytic Ni + Mo + Si composite coatings in an alkaline solution

Ni + Mo + Si coatings were obtained by nickel deposition from a bath containing suspension of molybdenum and silicon powders. These coatings were obtained in galvanostatic conditions, at the current density of j_dep = −0.100 A cm⁻². For determination of the influence of phase composition and surface morphology of obtained coatings on changes of corrosion resistance, these coatings were modified in argon atmosphere by thermal treatment at the temperature of 1100 °C during 1 h. A scanning electron microscope was used for surface morphology characterization of the coatings. Chemical composition of obtained coatings was determined by X-ray fluorescence spectroscopy method. Phase composition investigations were conducted by X-ray diffraction method. It was found that the obtained coatings are composed of three phase structures, i.e., nickel, molybdenum and silicon. Phase composition for the Ni + Mo + Si coatings after thermal treatment is markedly different. The main peaks corresponding to the Ni and Mo coexist with the new ones corresponding to new phases: Mo₅Si₃, NiSi, Mo₂Ni₃Si and Ni₆Mo₆C_1.06.Electrochemical corrosion resistance investigations were carried out in the 5 M KOH, using potentiodynamic and electrochemical impedance spectroscopy methods. On the basis of these investigations it was found that Ni + Mo + Si coatings after thermal treatment are more resistant in alkaline solution than Ni + Mo + Si as-deposited coatings. The reason of this is presence of silicides in the coatings.     

Photoexcitation-Based Nano-Explorers: Chemical Analysis inside Live Cells and Photodynamic Therapy

PEBBLEs (Probes Encapsulated By Biologically Localized Embedding) are submicron-sized optical sensors designed specifically for minimally invasive analyte monitoring in viable single cells, with applications for real-time analysis of drug, toxin, and environmental effects on cell function. PEBBLE nanosensor is a general term that describes a family of matrices and nano-fabrication techniques used to miniaturize many existing optical sensing technologies. The main classes of PEBBLE nanosensors are based on matrices of cross-linked polyacrylamide, cross-linked poly(decyl methacrylate), and sol-gel silica. These matrices have been used to fabricate sensors for H⁺, Ca²⁺, K⁺, Na⁺, Mg²⁺, Zn²⁺, Cu²⁺, Cl⁻, O₂, NO, and glucose that range from 20 nm to 600 nm in diameter. A number of delivery techniques have been used successfully to deliver PEBBLE nanosensors into mouse oocytes, rat alveolar macrophages, rat C6-glioma, and human neuroblastoma cells. PEBBLEs with several newly emerging directions in design and applications, going from intracellular imaging to in vivo actuating and targeting, are also described. They include photonic, magnetic, and stochastic control and modulation of photo-excitation, and also targeted nano-platforms for photodynamic therapy of brain cancers, as well as contrast enhancement of the MRI for monitoring such therapy.     

Effects of twin methyl groups insertion on the structure of templated mesoporous silica materials

In this paper, the effects of dimethyldiethoxysilane (DMDES) addition on the sol-gel process in preparation of mesoporous hybrid silicates containing twin methyl groups, were investigated. The materials were synthesized using tetraethoxysilane (TEOS) as silica source and DMDES as methyl groups precursor. All samples were prepared at low temperature in alkaline conditions using cetyltrimethylammonium bromide (CTAB) as a template. Obtained materials were characterized applying nitrogen adsorption/desorption, X-ray diffraction, HR TEM, FTIR, ²⁹Si MAS NMR and Raman spectroscopy methods. The influence of aging time (from 5?min to 24?h) on the structure of samples containing 12% (mol/mol) of organic modifier was examined. Duration of synthesis significantly affected the material structure. The effect of added organosilicate amount (12%, 25% and 38%) on morphology and structure properties of prepared samples was also studied. The dimethylsilyl groups were successfully incorporated in wide range in the silica surface using presented short time sol-gel method.     

The Structure of Pb+ Laser Centres in KMgF3 from Optically Detected Electron Spin Resonance and Electron Nuclear Double Resonance

Laser action of X-rayed lead doped KMgF₃ crystals from an unknown defect was recently reported by Hörsch and Paus.¹ By applying optical detection of ESR and ENDOR, the structure of two very similar laser active Pb centres could be determined from the selectively measured hyperfine and superhyperfine interactions. They consist of a Pb⁺ substituting for a K⁺ next to an F⁻ vacancy along <110> with a next nearest K⁺ vacancy for charge compensation in two different positions (Pb⁺(1) centres). The absorption band for the excitation of the laser emission at 1.4eV could be identified from the optical excitation spectra and from a special magneto-optical ESR technique. The structural properties, as well as the explanation of their laser properties within a crystal field model, are analogous to those of Tl⁰(1) centres in alkali halides and Pb⁺(1) centres in alkaline earth fluorides. A Pb⁺⁺ perturbed F_A centre was also observed.     

Transparent and thermally stable improved poly (vinyl alcohol)/Cloisite Na/ZnO hybrid nanocomposite films: Fabrication,morphology and surface properties

A series of poly(vinyl alcohol)/Cloisite Na⁺-Tyrosine/Zinc oxide (PVA/Cloisite Na⁺-Tyr/ZnO) bionanocomposites were prepared by dispersing ZnO nanoparticles in solution containing mixture of the PVA and modified Cloisite Na⁺. Structure of nanocomposite coatings was investigated by X-ray diffraction and Fourier-transform infrared spectroscopy. The thermal stability and optical properties of bionanocomposite were characterized by thermogravimetric analysis and UV–vis spectroscopy, respectively. The introduction of ZnO nanoparticles into PVA/Cloisite Na⁺-Tyr mixed solutions significantly increased the thermal stability of the obtained films. The results revealed that the high UV-shielding efficiency of the composites: for a film containing 6.0 wt% of ZnO nanocrystals, over 92% of UV light at wavelengths of 368 nm was absorbed while the optical transparency in the visible region was slightly below that of a PVA/Cloisite Na⁺-Tyr film.     

溶胶-凝胶法制备太阳光谱选择性吸收薄膜的研究进展

从太阳光谱选择性吸收薄膜的作用原理、吸收材料和膜系结构特点出发,结合实际工作,综述近年来溶胶-凝胶法制备的纳米颗粒-电介质复合材料型和尖晶石结构过渡金属氧化物型两类太阳光谱选择性吸收薄膜的研究进展,并探讨目前存在的问题及今后研究的方向。与以溅射为代表的现代气相沉积技术制备薄膜相比,溶胶-凝胶法制备的这两类薄膜具有与之相当的光学性能（吸收率α0.90,发射率ε〈0.10）和优异的湿热稳定性,同时还具有工艺简便、设备要求低以及易于大面积制膜等优点;但是溶胶-凝胶法引入了溶液中的化学反应,组分间的兼容性以及化学反应的特异性使得难以通过简单变换化学组分获得种类繁多的薄膜,因而目前溶胶-凝胶法制备的太阳光谱选择性吸收薄膜还局限在少数材料上。     

C3S and C2S hydration in the presence of Na2CO3 and Na2SO4

This study analyses the behavior of calcium silicates C₃S and C₂S hydrated in two alkaline media, Na₂CO₃ and Na₂SO₄. The silicates were synthesized with laboratory reagents and hydrated in water, to which solid‐state alkaline activators with 4 wt% Na₂CO₃ or 4 wt% Na₂SO₄ were added. Two‐ and 28‐day mechanical strength values were determined and the reaction products were characterized with XRD, SEM/EDX, and ²⁹Si and ²³Na MAS NMR. The findings showed that the presence of Na₂CO₃ hastened hydration kinetics and stimulated early‐age mechanical strength development in both silicates. The most significant effect of sodium sulfate, however, was observed in the 28‐day material in both silicates, in which it raised strength by stimulating the precipitation of C–S–H gels with a high percentage of Q² units.     

Revealing the inner secrets of intumescence: Advanced standard time temperature oven (STT Mufu+)—μ‐computed tomography approach

Intumescent coatings have been used for fire protection of steel for decades, but there is still a need for improvement and adaptation. The key parameters of such coatings in a fire scenario are thermal insulation, foaming dynamics, and cohesion. The fire resistance tests, large furnaces applying the standard time temperature (STT) curve, demand coated full‐scale components or intermediate‐scale specimen. The STT Mufu⁺ (standard time temperature muffle furnace⁺) approach is presented. It is a recently developed bench‐scale testing method to analyze the performance of intumescent coatings. The STT Mufu⁺ provides vertical testing of specimens with reduced specimen size according to the STT curve. During the experiment, the foaming process is observed with a high‐temperature endoscope. Characteristics of this technique like reproducibility and resolution are presented and discussed. The STT Mufu⁺ test is highly efficient in comparison to common tests because of the reduced sample size. Its potential is extended to a superior research tool by combining it with advanced residue analysis (μ‐computed tomography and scanning electron microscopy) and mechanical testing. The benefits of this combination are demonstrated by a case study on 4 intumescent coatings. The evaluation of all collected data is used to create performance‐based rankings of the tested coatings.     

The influence of the mixed alkaline earth effect on the structure and properties of (Ca,Mg)–Si–Al–O–N glasses

Alkaline earth oxynitride glasses of (Ca, Mg)–Si–Al–O–N with different CaO/(CaO + MgO) molar ratios (0, 0.25, 0.5, 0.75, and 1) were successfully prepared using the sol-gel method, and their structural compositions were characterised by Raman and FT-IR techniques. The glass dynamic properties of thermal expansion coefficient, glass transition temperature (T_g), and static properties of density, molar volume, Vickers hardness and compressive strength were systematically measured and analysed. The results showed that the static properties exhibited an overall regular change as the CaO/(CaO + MgO) ratio gradually increased, while the dynamic properties had an obvious mixed alkaline earth effect, which represented the appearance of an extreme value point in CaO/(CaO + MgO) mole ratios of 0.25 and 0.75, respectively. The typical thermal expansion coefficient and T_g of mixed alkaline earth oxynitride glasses deviated far from the linear connection between single alkaline earth oxynitride glasses. Raman spectra and infrared spectra revealed that the ratio value of the Q³/(Q²+Q⁴) decreased (Qⁿ: n = no. of bridging anions joining SiO₄ tetrahedra) in the mixed alkaline earth oxynitride glasses with increasing the amount of Ca, confirming that Ca decreased the crosslinking between individual tetrahedra via the transformation of Q³ species into Q² and Q⁴ species.     

THERMODYNAMICS OF ALKALI AND ALKALINE EARTH METAL ION - EXCHANGE ON CERIUM(IV) HYDROGEN PHOSPHATE

ABSTRACT

Thermodynamics of alkali and alkaline earth metal ions/hydrogen ions exchange on a fibrous cerium(IV) hydrogen phosphate have been investigated. Selectivities for alkali and alkaline earth metal ions increase in the order; Na⁺<<K⁺<Rb⁺<Cs⁺ and Mg²⁺<Ca²⁺<Sr²⁺<Ba²⁺, respectively. The enthalpy changes for alkali metal and Ba2+ ions/H⁺ exchange are negative, those for the other alkaline earth metal ions/H⁺ exchange are positive, indicating that the enthalpy changes for monovalent ions are more favorable than those for divalent ions. In comparison with ions of the same valency, the enthalpy change decreases with the atomic number of the metal ion corresponding to a decrease in the entropy change of dehydration in response to enthalpy-entropy compensation.     

Fabrication and characterization of new semiconducting nanomaterials composed of natural layered silicates (Na-MMT), natural rubber (NR), and polypyrrole (PPy)

An electrolytic admicellar polymerization was chosen for synthesizing new semiconducting nanomaterials composed of sodium montmorillonite (Na⁺-MMT), polypyrrole (PPy), and natural rubber (NR). The contents of the pyrrole monomer and the Na⁺-MMT were varied from 100 to 800 mM and 1-7 parts per hundred of rubber (phr), respectively. Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) were used to confirm the success of the synthesis. The morphological studies carried out by X-ray diffraction (XRD) and TEM pointed out the different states of dispersion of the layered silicates, whereas the study done by scanning electron microscopy (SEM) showed a great dependence of the nanocomposite morphology on the inclusion of the layered silicates. Thermal stability studies demonstrated the thermo-protecting and thermo-oxidative behaviors imparted by the layered silicates. The mechanical and DC electrical conductivity properties were significantly improved with the inclusion of the layered silicates, especially at a 7 phr loading.     

N+ ion implantation-induced cell attachment to CNx coating prepared by ion beam assisted deposition

Ion beam-assisted deposition (IBAD) was used to synthesize carbon nitride (CN _x ) coatings on Ti-6Al-4V alloy at room temperature at 100-eV NHn⁺ beam bombarding energy. Nitrogen ion implantation was also conducted on the prepared coatings. The effects of ion fluence on the chemical bonding structure of the coatings were characterized by XPS, and Raman and FTIR spectroscopic methods. The results showed that N⁺ ion implantation increased the N concentration of the prepared CN _x coatings. The cell attachment tests gave promising results that N⁺ ion-implanted CN _x coatings exhibited low macrophage attachment. The adhered fibroblasts showed normal cellular growth and morphology. Under a fluence of 5 × 10¹⁷ ion/cm², the CN _x coating exhibits more N concentration and sp³ bonds which may be responsible for the changes in the cell attachment.     

Analysis of optical emission spectroscopy in diamond chemical vapor deposition

We used optical emission spectroscopy (OES) to study the gas phase chemistry in hot filament chemical vapor deposition (HFCVD) diamond processes. The results show that the methane concentration strongly influenced the intensity ratios of CH, CH⁺ and H_γ to H_β, and the effects of the pressure and filament temperature on the relative concentrations of the species were also analyzed. Spatially resolved OES implied that a relative high concentration of atomic H existed near the substrate surface, which is favorable for diamond film growth. Although the relatively high concentrations of CH and CH⁺ to atomic H are beneficial to increasing diamond nucleation density, they are very harmful to the growth of diamond films.