Gel-like Precursor Research Articles

Multi-functional epoxides cross-linked collagen sponges for tissue engineering scaffolds

With the efficient cross-linking abilities and the flexible regulation abilities to the performances of cross-linked products, the multi-functional aliphatic epoxides were once widely used to cross-link the collagen-based materials in the last century. In present work, the multi-functional epoxides were used to construct and cross-link collagen sponges for tissue engineering scaffolds, which was hoped to board the theoretical system of epoxides and explore their potentials for modern applications. The bi- to tetra-functional epoxides were used to cross-link collagen solutions and establish the gel-like precursors, then using freeze-drying to form the final sponges. The SEM observed that the sponges had shown regular porous structures with a wide range of pore sizes from 160 to 440 μm. The sponges had presented the resistance to enzymatic degradation, shape-remaining ability, and reversible compressibility in aqueous environments, which all could be regulated through the functionalities of epoxides. The regulation abilities of multi-functional epoxides on the performances of sponges had been mainly achieved through the cross-linking degrees that the higher functionality of epoxides would bring higher cross-linking degree. Such higher cross-linking degrees could enhance the elastic behaviors of gel-like precursors, and improve the compressive strengths and thermal stabilities of sponges. Nevertheless, the multi-functional epoxides had barely affected the safety of collagen sponges at the cellular level according to the results of CCK8 assay and the SEM and CLSM images of L929 fibroblasts cultured on the cross-sections of sponges.Graphical abstract

A New Approach to Prepare LuFeMgO4

A new method for the production of LuFeMgO4 based on the combustion reaction of a gel-like precursor prepared from metal nitrates and fossil fuels has been proposed. The possibility to prepare this oxide from stoichiometric compositions of metal nitrates with polyvinyl alcohol (PVA) and glycine has been studied. The adiabatic combustion temperatures Tad have been estimated for the systems under consideration. The combustion products of PVA-nitrate and glycine-nitrate compositions before and after their heat treatment have been studied using X-ray diffraction analysis and IR spectroscopy. It has been established that the combustion reaction products of the PVA-nitrate composition are an X-ray amorphous powder, while those of the glycine-nitrate composition are a mixture of nanocrystalline oxides containing 52.5 wt % LuFeMgO4. According to X-ray diffraction and SEM data, 4-h annealing of this mixture at 1300°C leads to the formation of a single-phase LuFeMgO4 powder with a layered microstructure and a grain size of about 1–2 μm.

PH Dependance of Scorodite Formation in As(V) Solution Using Magnetite as the Solid Iron Source

Arsenic-containing wastewater, which is mainly generated in nonferrous metal-smelting plants, threatens the natural environment and human health owing to its high toxicity and mobility. A promising arsenic immobilization method to solve this problem is to immobilize arsenic as scorodite. In this study, the method of scorodite synthesis using magnetite as the iron source was investigated, which can be performed using low-cost materials under atmospheric pressure without using an autoclave. The generation and crystallization behaviors of the intermediate of the gel-like precursor of scorodite were investigated by monitoring the concentration of each iron ion in solution and characterizing the precipitate. By clarifying the effect of the solution pH for each reaction step, the mechanism and suitable conditions of this process are discussed.

Effect of Base Oil and Thickener on Texture and Flow of Lubricating Greases: Insights from Bulk Rheometry, Optical Microrheology and Electron Microscopy

The structure and flow behavior of lubricating greases depend on the base oil and the type and concentration of the dissolved thickener. In this study, the linear viscoelastic properties of greases were characterized by combining oscillatory shear and squeeze flow covering a broad frequency range (0.1–105 rad s−1). Multiple-particle tracking (MPT) microrheology and scanning electron microscopy (SEM) provided further insight into local viscoelastic properties and sample structure on a submicron-length scale. The type and viscosity of the base oil did not affect the absolute value of the complex viscosity and the filament shape formed by a given thickener. High-frequency shear modulus data, however, indicated that the thickener lithium 12-hydroxystearate formed stiffer networks/filaments in poly-α-olefins than in mineral oils. As expected, the viscosity increased with increased thickener concentrations, but microscopy and high-frequency rheometry revealed that the thickness, length, and stiffness of the individual filaments did not change. In mineral oil, the 12-hydroxystearate thickeners yielded higher viscosity than the corresponding stearates with the same metal ion. The filamentous lithium thickeners created stronger networks than the roundish aggregates formed by magnesium and zinc stearate. Network mesh sizes varying between approximately 100 nm and 300 nm were consistently determined from SEM image analysis and MPT experiments. The MPT experiments further disclosed the existence of gel-like precursors of approximately 130 µm at thickener concentrations far below the critical value at which a sample-spanning network resulting in a characteristic grease texture is formed.

Preparation of Precursor for Hydrothermal Synthesis of Alkaline Titanosilicates

The conditions for the preparation of framework titanosilicates with zorite and ivanyukite structures were studied. The preparation of a gel-like precursor for hydrothermal synthesis is preferably performed from solutions. An excess amount of silicon relative to titanium(IV) and an alkaline medium with pH 10.5–12.5 provide oversaturation of the salt mass in the Na2O–K2O–TiO2–H2SO4–SiO2–H2O system. This makes it possible to regulate phase formation, ensuring the stability of the structure and surface properties of the final products. To inhibit titanium(IV) hydrolysis, the reduction Ti4+ → Ti3+ is performed. This technique leads to the formation of a monophase precipitate.

Sol\u2013gel alumina coating on quartz substrate for environmental protection

Transparent γ-Al2O3 thin film can be utilized as an absorbent or protective layer in environmental protection. The aim of the present research work is to improve the structural and optical properties of γ-Al2O3 thin film. Al2O3 thin films were synthesized by various newly developed routes based on colloidal technique and sol–gel chemistry. Many types of starting materials (Al acetate, nitrate, isopropoxide, boehmite, and Al2O3 powders) and additives (acetic acid, HCl, HNO3, citric acid) were used in the experiments. Suspension and gel-like precursor systems were compared for layer creation. The layers were characterized by their morphology (GIXRD), surface and thickness (SEM), as well as transparency (UV–visible spectroscopy). The best quality of layer (∼90% transmittance, 50–60 nm thickness, perfect covering) has been obtained by sol–gel technique starting from Al nitrate or Al acetate.

Influence of cerium content and heat treatment on Ce:YAG@glass wool nanostructures

The paper reports the influence of cerium content and heat treatment on composition, structural features and optical properties of nanostructures constituted by a layer of Ce:YAG nanoparticles on glass wool (Ce:YAG@GW). The Ce:YAG@GW nanostructures were obtained embedding the glass wool (GW) in a gel-like precursor and calcining at 800 and 900 °C. Gel-like precursor of urea glass route (UGR) method has been used to prepare both nanostructures and Ce:YAG nanoparticles prepared as references. Structural properties were investigated by using X-ray diffraction (XRD) and infrared spectroscopy (IR). Results showed that the composition of the final products strongly depends both on the cerium content and temperature. Optical properties of best materials have been investigated in order to verify their suitability for lighting applications. Obtained results show relatively high quantum efficiency for Ce:YAG@GW treated at 800 °C comparing with the Ce:YAG nanoparticles obtained at the same temperature confirming the improved luminescence properties of the nanoparticles when they are applied on GW surface.

Gel-Like Calcium Carbonate Precursors Observed by in situ AFM.

The debate about crystallization processes is still ongoing and nonclassical crystallization mechanisms attract more and more attention. This work indicates that polymer induced liquid precursor (PILP) phases play a role for nonclassical calcium carbonate crystallization and growth processes. Here we report the observation of gel-like precursors for the crystal growth on a calcite surface by means of an in situ AFM study. These precursors spread out on the surface with time supporting their liquid character. This study will give new insights into biomineralization and crystallization processes in general.

Synthesis of magnesium aluminate spinel nano-powders by co-precipitation method

Magnesium aluminate spinel nano-powders were synthesised by the wet chemical co-precipitation method. First, the gel-like precursors were obtained by dropping ammonia into the mixed solution of magnesium chloride hexahydrate and aluminium chloride hexahydrate with different Mg2+/Al3+ molar ratios and concentrations. After drying, the precursors were calcined at 700°C, 800°C, 900°C, 1000°C and 1100°C for 1.5 hours, respectively. Finally, the obtained samples were characterised by X-ray diffraction, thermal gravimetric and differential thermal analysis and scanning electron microscopy. It was revealed that the pure phase of MgAl2O4 started to form when the calcination temperature exceeded 700°C, and MgAl2O4 spinel with the smallest average crystallite size could be obtained when the calcination temperature reached 900°C.

Hierarchical structure of CaCO3biominerals – mesocrystals and functionalization

Skeletal parts and teeth of marine organisms, avian eggshells, trilobite and isopod eyes, and many more biomineralized tissues consist of bio-calcite or bio-aragonite crystals. We explore the nano- to micro-scale architectures of these materials by electron backscatter diffraction (EBSD) and complementary techniques. In contrast to their inorganic cousins the biogenic "crystals" are hybrid composites with small amounts of organic matrix controlling morphogenesis and critically improving mechanical performance or other functions. For the biominerals meso-crystal-like structures are ubiquitous, consisting of co-oriented nano-blocks with a mosaic-spread of a few degrees, depending on the organism and on the size of the mesocrystal entity[1, 2, 3]. The nano-mosaic can be attributed to growth by nano-particle accretion from an amorphous or gel-like precursor, where relics of organic matrix cause misorientations between the crystallized nano-blocks. Recently we were able to reproduce this feature in gel-grown calcite [Nindiyasari et al., Crystal Growth and Design, in press]. The mesocrystal-co-orientation spreads on to the micro- and even millimeter-scale, frequently with a fractal nature of co-oriented hierarchical units [Maier et al., Acta Biomaterialia, accepted for publication]. The hierarchically structured morphology of the composite crystal or polycrystal is always directed by organic matrix membranes. Sea urchin teeth show a multiplex composite crystal architecture, where different subunits of engineered shapes, Mg-contents, and small misalignments are essential prerequisites for self-sharpening [1]. The figure shows an EBSD map of dendritic interdigitating calcite crystals in an avian egg shell (color coding for crystal orientation) with an misorientation profile along the grey line.

Transparent High‐Performance Thin Film Transistors from Solution‐Processed SnO2/ZrO2 Gel‐like Precursors

This work employs novel SnO(2) gel-like precursors in conjunction with sol-gel deposited ZrO(2) gate dielectrics to realize high-performance transparent transistors. Representative devices show excellent performance and transparency, and deliver mobility of 103 cm(2) V(-1) s(-1) in saturation at operation voltages as low as 2 V, a sub-threshold swing of only 0.3 V/decade, and /(on) //(off) of 10(4) ~10(5) .

Nanocomposite MFI-alumina and FAU-alumina Membranes: Synthesis, Characterization and Application to Paraffin Separation and CO2Capture

In this work, we report the preparation of thermally and mechanically resistant high-surface (24-cm2 ) nanocomposite MFI-alumina and FAUalumina membranes by pore-plugging synthesis inside the macropores of α -alumina multilayered tubular supports. The MFI membranes were prepared from a clear solution precursor mixture being able to easily penetrate into the pores of the support. The MFI membranes were evaluated in the separation of n-/i-butane mixtures. The synthesis reliability was improved by mild stirring. The most selective MFI membranes were obtained for supports with mean pore sizes of 0.2 and 0.8 μ m. The MFI effective thickness could be reduced to less than 10 μ m by impregnating the support with water prior to synthesis and by diluting the synthesis mixture. The best MFI membrane offered an excellent tradeoff between selectivity and permeance at 448 K, with separation factors for equimolar n-butane/i-butane mixtures up to 18 and n-butane mixture permeances as high as 0.7 μ mols-1 m-2 Pa-1 . Furthermore, a novel nanocomposite FAU membrane architecture has been obtained by an original synthesis route including in situ seeding using a cold gel-like precursor mixture, followed by growth of the FAU material by hydrothermal synthesis in two steps using a clear solution of low viscosity. This new membrane showed interesting performance in the separation of an equimolar CO2 /N2 mixture at 323 K, with CO2 /N2 separation factors and mixture CO2 permeances up to 12 and 0.4 μ mols-1 m-2 Pa-1 , respectively.

Thermo-sensitive hydrogels formed from the photocrosslinkable polypseudorotaxanes consisting of β-cyclodextrin and Pluronic F68/PCL macromer

To create thermo-sensitive supramolecular hydrogels with high mechanical strength, viscous gel precursors were first formed via block-selected inclusion complexation between β-cyclodextrin (β-CD) and Pluronic F68/poly(e-caprolactone) block copolymer terminated with acryloyl groups in aqueous media, and subsequently in situ photocrosslinking was employed in the presence of a photoinitiator. The supramolecular assembly in photocrosslinked hydrogels was revealed by wide-angle X-ray diffraction (WXRD) and thermogravimetric analysis (TGA). The rheological studies demonstrated that in situ photocrosslinking could greatly improve the mechanical strength of the gellike precursors. The swelling measurements showed that as-obtained hydrogel displayed a thermo-responsive property. The temperature dependence of the hydrogels decreased with the increase of the β-CD amounts introduced. The resultant hydrogels have the potential to use as carriers for drug delivery and tissue engineering scaffolds.

Synthesis of Non-Oxide Ceramic Fine-Powders from Organic Precursors

Synthesis of titanium carbide ceramic powders and control of particle size were tried by carbothermic reduction of a precursor, comparing synthesis of silicon carbide from a precursor. Metal alkoxides were used as a metal source and phenolic resin was done as a carbon source. Homogeneous sol-like mixture was obtained by mixing ethylsilicate and phenolic resin with alcohol. Gel-like precursor was formed by drying the sol-like mixture. Precipitation was formed by mixing titanium(IV) tetraisopropoxide and phenolic resin. The precursor was amorphous and ceramization occurred by heat treatment in argon flow. Growth of particles and phase formation were investigated.

Geochemistry and mineralogy of zeolitic tuffs from the Alaçatı (Çeşme) area, Turkey

AbstractSilicic vitric tuffs of the Alaçatı (Çeşme) area, west of Izmir (Turkey), are partly altered to authigenic zeolites and clay minerals. Mordenite and clinoptilolite-heulandite accompanied by smectite are the main alteration products of the tuffs. Scanning electron microscope examination indicates that mordenite forms mainly from a gel-like precursor and to a lesser degree from volcanic glass. Mordenite and clinoptilolite-heulandite have formed by the hydrolysis and dissolution of silicic vitric tuffs by thermal waters which circulated through the fracture zone into porous vitric tuffs. These thermal waters, which resulted from mixing of thermal (Na-Cl type) and groundwaters, provided the extra Na and Ca that are necessary for the formation of mordenite. Various percentages of calcite are present in the altered tuffs. The enrichment of calcite in the altered tuffs indicates that thermal waters supply Ca, sourced from dissolution of Triassic carbonate rocks.The alteration minerals in the Alaçatı (Çeşme) area do not seem to be laterally zoned. The occurrence of the zeolites seems to be related to inferred fracture zones trending NE—SW. These fracture zones are important because they provide porosity and permeability in the tuffs for zeolite formation. The large glass content and permeability of tuffs accompanied by the favorable hydrochemical condition resulted in zeolitization of the Alaçatı (Çeşme) area.

Formation of Metallic Nanocrystals from Gel-like Precursor Films for CVD Nanotube Growth: An in Situ TEM Characterization

The evolution of a continuous Fe(NO3)3 catalyst film was observed by in-situ annealing in a Transmission Electron Microscope (TEM). Such catalysts are routinely used in the catalytic growth of carbon nanotubes. The experiments reveal that crystalline particles form from the gel-like film already around 300C. At usual carbon nanotube growth temperatures of 700C, the particles are single-crystalline with a log-normal size distribution. The observations furthermore show that in spite of the crystalline structure of the particles there is a high mobility. The experiments allow to obtain detailed information about the chemistry and the crystallinity of the catalyst film, which provides valuable information for the interpretation of the carbon nanotube growth by chemical vapor deposition.

Deposition of thermal barrier coatings using the solution precursor plasma spray process

The solution-precursor plasma-spray (SPPS) process is capable of producing highly durable thermal barrier coatings. In an effort to improve the understanding of the deposition mechanisms in this novel process, a series of specific experiments, where the substrate is held stationary and the plasma torch is programmed to scan a single pass across the substrate, were conducted and the resulting deposits were carefully characterized. In addition to the deposition mechanisms identified previously in the stationary torch experiments, the deposition mechanisms of two other types of deposits, thin film and fine spherical particles, were identified in this study. The melting of inflight formed 7YSZ particles and their rapid solidification to form ultra-fine splats on the substrate was found to be the dominant deposition mechanism. The characterization of actual SPPS coatings confirmed that the various coating-deposition mechanisms identified in the model experiments occur in concert during the actual coating process. Adherent deposits (ultra-fine splats, deposits from gel-like precursor and film formed via chemical vapor deposition), unmelted particles (spherical particles, deposits from non-decomposed precursor) and porosity were estimated to constitute ∼65, ∼19 and ∼16 vol%, of the coating, respectively.

Preparation of Porous Alumina Ceramics by Using the Gelation of Ammonium Alginate

The gelation of ammonium alginate by hydrochloric acid was applied for the formation of gel-like precursor composed of alumina particles and alginic polymer. The porous alumina ceramics fired at temperatures from 1000° to 1600°C had very sharp pore size distributions. Their porosity ranged from 17 to 56%, which was 15 to 20% higher compared with that of porous alumina prepared by the slip casting method. Furthermore, the pore structure was more stable at high temperatures than that of the slip casting method. The optimum concentration of ammonium alginate for the uniform mixing of each raw material was 0.3 to 2.0wt%. The concentration of hydrochloric acid was over 0.1N for the sufficient gelation of the gel-like precursor.

Preparation and some properties of porous alumina ceramics obtained by the gelatination of ammonium alginate

This study was carried out to develop a new preparation process of porous alumina ceramics and to examine their porous properties. The gelatination of ammonium alginate by hydrochloric acid was used for the formation of a gel-like precursor composed of alumina particles and alginic polymer. By this simple chemical shaping process of green bodies, porous alumina ceramics with a very sharp pore size distribution and a porosity of 40 to 55% could be obtained after firing at 1000 to 1600°C. The porosity showed an improvement of 15–20% compared with that of porous materials prepared from conventional procedures such as the pressing and slip-casting methods. The optimum concentrations of ammonium alginate and hydrochloric acid were 0.3–2.0 wt% and over 0.1 n, respectively, from the standpoint of the mixing treatment of raw materials and the gelatination.