High contrast glasses for all-solid fibers fabrication

We present composition development of borosilicate glasses for fabrication of high refractive index contrast, all-solid photonic crystal fibers. An oxide system composed of SiO₂B₂O₃Al₂O₃Li₂ONa₂OK₂O was adjusted to match thermal properties of selected highly nonlinear, lead bismuth gallium silicate glass. A high difference of refractive index of 0.376 is achieved at a wavelength of 1550 nm. We proved experimentally that the developed pair of glasses enables to draw optical fibers, and we propose a design of a photonic crystal fiber structure for broadband supercontinuum generation.     

Surface modification on polyethylene terephthalate films with 2-methacryloyloxyethyl phosphorylcholine

In this study, the surface of polyethylene terephthalate (PET) was modified to improve the protein and cell adhesion behavior with low temperature ammonia plasma treatment followed by 2-methacryloyloxyethyl phosphorylcholine (MPC) grafting. The x-ray photoelectron spectroscopy (XPS) results showed that the COO^?, NCO and POH groups were successfully incorporated onto the sample surface after MPC grafting. Furthermore, formation of new bonds, N and NH on the sample surface grafted with MPC was recorded by Fourier transform infrared spectroscopy (FTIR). A large number of spherical particles at submicron to nanometer scale were also observed on the surface by atomic force microscopy (AFM). The cell adhesion experiments on PET film surfaces were evaluated and the highly hydrophilic surfaces could not promote cell adhesion and spreading. All results achieved in this study have clearly indicated that the method combining low temperature ammonia plasma treatment and MPC grafting is an effective way of producing a suitably hydrophilic PET surface with the capability of weakening the protein adsorption greatly.     

Phase constitutions of MoSiN anti-oxidation multi-layer coatings on CC composites by fused slurry

To improve the oxidation resistance of MoSi fused slurry coating fabricated in vacuum, MoSiN multi-layer coatings were synthesized on C/C composites in nitrogen atmosphere by fused slurry using same Mo and Si element powders. The phase compositions and microstructures were characterized by X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The results indicate that the MoSiN coating contains SiC inner layer and MoSi₂/Si main layer, which was similar with MoSi coating. Additionally, a thin outer layer with nano-filiform morphology has been found on the coating surface, which consists of SiC, Si₃N₄, AlN, Al₂O₃ and sialon phase. Oxidation experiments show that the MoSiN multi-layer coating exhibits excellent oxidation resistance at 1400 °C and anti-oxidizing potential ability at 1450 °C.     

Synthesis of micron-sized porous CeO2SiO2 composite particles for ultraviolet absorption

Micron-sized porous composite particles composed of CeO₂ and SiO₂ nanoparticles were prepared for a UV absorption application by an aerosol spray-drying process from as-prepared CeO₂ nanoparticles, commercial SiO₂, and a polystyrene latex template. The morphology, structure crystallinity and pore size distribution of the as-prepared porous CeO₂SiO₂ composite particles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Barrett-Joyner-Halenda (BJH) method, respectively. The porous CeO₂SiO₂ composite particles, with diameters of approximately 10 μm, showed a spherical morphology. As the contents of CeO₂ in the precursor was increased from 0.25 wt% to 1.5 wt%, we observed a change in the morphology of the composite particles from compactly packed porous particles to loosely packed porous particles. The as-prepared CeO₂SiO₂ composite particles were composed of meso- and macropores in the range of 3–200 nm. The effect of the CeO₂ content on the porous composite particles in terms of the UV absorption properties was also investigated by UV-visible spectroscopy. When the content of CeO₂ exceeded 0.75 wt% in the precursor, the particles showed higher UV absorption values compared to those of commercial TiO₂ nanoparticles. The as-prepared porous CeO₂SiO₂ composite particles can therefore be promising materials given their high UV absorption value.     

Characteristics evaluation of calcium carbonate particles modified by surface functionalization

Calcium carbonate (CaCO₃) particles were modified by a direct blending method using different coupling agents. The changes in the CaCO₃ particles were determined using different techniques. Compared with pristine particles, the modified CaCO₃ particles show good dispersion, particularly those modified by γ-methacryloxypropyl trimethoxy silane. Results of the thermogravimetric analysis indicated that the coupling agents were adsorbed or anchored on the surface of the CaCO₃ particles, thereby hindering aggregation. The formation of covalent bonds [CaOSi] or [CaOTi] was verified using Fourier transform infrared spectroscopy and X-ray diffraction. The modified CaCO₃ particles showed more stable colloidal dispersion in ethyl acetate than that of pristine CaCO₃ particles. Some silane or titanate coupling agents can be combined with CaCO₃ by covalent bonds, thereby changing the surface properties of CaCO₃ and enhancing dispersion in many organic media. The hydroxyl groups on the surface of CaCO₃ particles can interact with silanol groups or titanate coupling agents forming an organic coating layer.     

Poly (hydroxyethyl methacrylate-glycidyl methacrylate) films modified with different functional groups: In vitro interactions with platelets and rat stem cells

Copolymerization of 2-hydroxyethylmethacrylate (HEMA) with glycidylmethacrylate (GMA) in the presence of α-α′-azoisobisbutyronitrile (AIBN) resulted in the formation of hydrogel films carrying reactive epoxy groups. Thirteen kinds of different molecules with pendant NH₂ group were used for modifications of the p(HEMA-GMA) films. The NH₂ group served as anchor binding site for immobilization of functional groups on the hydrogel film via direct epoxy ring opening reaction. The modified hydrogel films were characterized by FTIR, and contact angle studies. In addition, mechanical properties of the hydrogel films were studied, and modified hydrogel films showed improved mechanical properties compared with the non-modified film, but they are less elastic than the non-modified film. The biological activities of these films such as platelet adhesion, red blood cells hemolysis, and swelling behavior were studied. The effect of modified hydrogel films, including NH₂, (using different aliphatic CH₂ chain lengths) CH₃, SO₃H, aromatic groups with substituted OH and COOH groups, and amino acids were also investigated on the adhesion, morphology and survival of rat mesenchymal stem cells (MSCs). The MTT colorimetric assay reveals that the p(HEMA-GMA)-GA-AB, p(HEMA-GMA)-GA-Phe, p(HEMA-GMA)-GA-Trp, p(HEMA-GMA)-GA-Glu formulations have an excellent biocompatibility to promote the cell adhesion and growth. We anticipate that the fabricated p(HEMA-GMA) based hydrogel films with controllable surface chemistry and good stable swelling ratio may find extensive applications in future development of tissue engineering scaffold materials, and in various biotechnological areas.     

Theoretical and experimental studies on molecular spectra of the silica hollow spheres

The IR and UV spectra of the silica hollow spheres (SHSs) have been investigated using semi-empirical PM3 method. The calculated results have been compared with those from experiments. A cluster model of porous silica containing up to 36 SiO₄ has been proposed to characterize the fine structure of the SHSs. Effects of model size on the spectra have been discussed. The theoretical IR absorption peaks caused by OSiO vibration have matched the experimental response well. The UV absorption has been observed to move to larger wavelengths as the number of cluster and the number of configuration interaction (CI) increase. The PM3 calculations can assist greatly in analyzing the structure and molecular spectra of complicated materials with special morphologies.     

Whether do nano-particles act as nucleation sites for C-S-H gel growth during cement hydration?

In this study, three modelling experiments were designed to investigate whether nano-particles incorporated in the cement paste act as nucleation sites for CSH gel growth during cement hydration. The nano-particles with (nano-SiO₂) and without (nano-TiO₂) pozzolanic reactivity were used. In the first experiment, both the cement and nano-particles were dispersed in water to prepare dilute cement paste, in which the cement and nano-particles can contact each other. In the second one, the cement particles were laid inside a filter paper funnel and immersed in tap and ultrapure water with nano-particles dispersed, in order to separate the cement particles with nano-particles by using the filter paper. In the third one, large clinker particle was embedded in resin, surface-polished and then exposed upside down in ultrapure water with and without nano-particles dispersed. After hydration for 7 days, the hydration products in the paste or the nano-particle dispersion were observed by using TEM and the hydrated surface of the embedded clinkers were detected by using SEM. Based on the experimental results and the detailed discussions by using the classic nucleation theory, it was found that there may have no nucleus function of the nano-particles for the CSH gel precipitation during cement hydration, at least in the hydrating system with nano-silica and nano-TiO₂ addition. It was proposed to more reasonably explain the observations in the three modelling experiments by using the topochemical reaction instead of the through-solution mechanism for the CSH gel formation.     

Sol–gel synthesis of tantalum oxide and phosphonic acid-modified carbon nanotubes composite coatings on titanium surfaces

Carbon nanotubes used as fillers in composite materials are more and more appreciated for the outstanding range of accessible properties and functionalities they generate in numerous domains of nanotechnologies. In the framework of biological and medical sciences, and particularly for orthopedic applications and devices (prostheses, implants, surgical instruments, …), titanium substrates covered by tantalum oxide/carbon nanotube composite coatings have proved to constitute interesting and successful platforms for the conception of solid and biocompatible biomaterials inducing the osseous regeneration processes (hydroxyapatite growth, osteoblasts attachment). This paper describes an original strategy for the conception of resistant and homogeneous tantalum oxide/carbon nanotubes layers on titanium through the introduction of carbon nanotubes functionalized by phosphonic acid moieties (P(O)(OH)₂). Strong covalent CP bonds are specifically inserted on their external sidewalls with a ratio of two phosphonic groups per anchoring point. Experimental results highlight the stronger “tantalum capture agent” effect of phosphonic-modified nanotubes during the sol–gel formation process of the deposits compared to nanotubes bearing oxidized functions (OH, CO, C(O)OH). Particular attention is also paid to the relative impact of the rate of functionalization and the dispersion degree of the carbon nanotubes in the coatings, as well as their wrapping level by the tantalum oxide matrix material. The resulting effect on the in vitro growth of hydroxyapatite is also evaluated to confirm the primary osseous bioactivity of those materials. Chemical, structural and morphological features of the different composite deposits described herein are assessed by X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission (TEM) electronic microscopies, energy dispersive X-rays analysis (EDX) and peeling tests.     

Luminescence and scintillation properties of BaF2Ce transparent ceramic

Cerium doped Barium Fluoride (BaF₂Ce) transparent ceramic was fabricated and its luminescence and scintillation properties were studied. The photoluminescence shows the emission peaks at 310 nm and 323 nm and is related to the 5d-4f transitions in Ce³⁺ ion. Photo peak at 511 keV and 1274 keV were obtained with BaF₂Ce transparent ceramic for Na-22 radioisotopes. Energy resolution of 13.5% at 662 keV is calculated for the BaF₂Ce transparent ceramic. Light yield of 5100 photons/MeV was recorded for BaF₂Ce(0.2%) ceramic and is comparable to its single crystal counterpart. Scintillation decay time measurements shows fast component of 58 ns and a relatively slow component of 434 ns under 662 keV gamma excitation. The slower component in BaF₂Ce(0.2%) ceramic is about 200 ns faster than the STE emission in BaF₂ host and is associated with the dipole-dipole energy transfer from the host matrix to Ce³⁺ luminescence center.     

CO2 reduction to CH4 with H2 on photoirradiated TS-1

CO₂ reduction on reduced titanium silicalite (TS-1) with photoirradiation in the presence of H₂ was investigated in a closed circulation system. CO₂ was reduced to give CH₄ under u.v. irradiation, which TS-1 absorbs. The amount of the carbon species on TS-1 after photoirradiation indicated that all Ti atoms in the framework may act as a photocatalytic site. Infrared spectrum of TS-1 after the reaction showed that CH₂ and CH₃ were left on TS-1.     

Cr5Si3B and Hf5Si3B: New MAB phases with anisotropic electrical,mechanical properties and damage tolerance

Through a combination of electronic structure,chemical bonding and mechanical property investigations,anisotropic electrical and mechanical properties,and damage tolerant ability of MAB phases Cr_5Si_3B and Hf_5Si_3B are predicted.The anisotropic electrical conductivity is due to the anisotropic distribution of Cr in Cr_5Si_3B and Hf in Hf_5Si_3B,which mainly contribute to the electrical conductivity.The anisotropic mechanical properties are underpinned by the anisotropic chemical bonding within the crystal structures of Cr_5Si_3B and Hf_5Si_3B.The high stiffness is determined by the strong covalent-ionic Cr1 B Cr1 and Cr1 Si bonds in Cr_5Si_3B and the ionic-covalent Hf1 B Hf1 and Si B bonds in Hf_5Si_3B;while the low shear deformation resistance is attributed to the presence of metallic Cr Cr,Hf Hf and Si Si bond.Based on the low Pugh’s ratio,Cr_5Si_3B and Hf_5Si_3B are predicted tolerant to damage.The possible cleavage plane is(0001)and the possible slip systems are1 100|{11 20}and11 20|{0001}for both Cr_5Si_3B and Hf_5Si_3B.     

The relation between zeolite framework structure and vibrational spectra

Using a general valence force field method, infrared and Raman spectra of pure silica zeolite crystals and molecular substructures of zeolites are calculated. Computed spectra of the substructures are directly compared with computed spectra of the crystal. Also, a comparison of the atomic displacement vectors of the vibrational modes is made. No general theoretical basis for a correlation between the presence of large structural elements and spectral features, sometimes reported, is found to exist. An extensive comparison between experimental and theoretical infrared and Raman spectra of the SiO₂ forms of sodalite and faujasite is made. Other applications of vibrational spectroscopy to zeolite structure research, such as the SiOSi angle distribution and the location of acid sites, are evaluated as well.     

Crystallization process of zeolite ZSM-5 and zeolite ZSM-35 in a special autoclave

By use of a special autoclave, the crystallization process of the dehydrated amorphous gels was studied in the Na₂OAl₂O₃SiO₂⁻ ethylenediamine (EDA) — triethylamine (Et₃N) — H₂O system. In one run, zeolites ZSM-5 and ZSM-35 can be simultaneously synthesized at different areas of the autoclave. The data demonstrate that Gabelica's hypothesis (Gabelica, Z., Blom, N. and Derouane, E.G.Appl. Catal. 1983,5, 227) could be correct at some conditions.     

Luminescence at 1.53 μm for a new Er3+-doped transparent oxyfluoride glass ceramic

Transparent 45SiO₂25Al₂O₃5CaO10NaF15CaF₂ glass ceramics doped with different levels of Er³⁺ were prepared. The spherical CaF₂ nanocrystals with 10–20 nm in size were verified to be homogeneously embedded among the glassy matrix. Room temperature absorption and emission spectra corresponding to ⁴I_13/2 ↔ ⁴I_15/2 transitions of Er³⁺ ions in precursor glasses and glass ceramics, respectively had been measured. For glass ceramics, with increasing of Er³⁺ content from 0.1 to 2.0 mol%, the FWHM values of the emission bands increased from 42 to 71 nm; meanwhile, the lifetime of ⁴I_13/2 level slightly reduced. However, both the values of FWHM and lifetime were larger than those of precursor glasses due to the change of ligand field of Er³⁺ ions.     

The effects of the SiOSi segment presence in BAPP/BPDA polyimide system on morphology and hardness properties for opto-electronic application

Recent technological advances demanded incorporation of SiOSi segment into polyimides (PI)s to improve versatility in terms of processing, morphology and optoelectronic properties. In order to study the role of SiOSi segment in the morphology and hardness properties of PI, the SiOSi segment have been introduced into the PI backbone through the conventional copolymerization and in PI matrix through sol gel method. The PI series were characterized by Fourier transform infra-red (FT-IR), nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, solution viscosity and gel permeation chromatography (GPC). Scanning electron microscope (SEM) analysis suggested a microphase separation between the two components. FT-IR spectra confirmed the presence of silicone segment, as well as a complete imidization of PI series. Micrograph suggested a homogeneous phase between the PI and silicone segment for copolymerization series while sol gel technique revealed the inorganic particles were distributed homogenously in PI matrix. It was also found that the presence SiOSi segment in PI backbone and PI matrix influenced the opto-electronic properties.     

Room temperature solid–solid reaction preparation of ironboron alloy nanoparticles and Mössbauer spectra

The amorphous ironboron alloy can be prepared very easily by a room temperature solid–solid reaction of the FeCl₃·6H₂O, CrCl₃·6H₂O and KBH₄ powders. The characterizations show that the product is mainly composed of amorphous ironboron alloy nanoparticles. ⁵⁷Fe Mossbauer spectra at 84 and 295 K show that there are three kinds of Fe-containing components in the sample. There are the superparamagnetic relaxation in Mössbauer spectra and the continuous distribution of internal magnetic field in the ironboron alloy.     

Fresnoite crystal structure in glass-ceramics

A glass-ceramic including a crystallite of fresnoite crystal phase was prepared by crystallization of glass with a composition of 2BaOTiO₂3SiO₂. The length of the a-axis of fresnoite in the glass-ceramic was shorter than that of the single crystal, and that of the c-axis was longer. Parameters of the crystal structure were refined using the Rietveld method, and the refinement was terminated to a profile reliability factor of 0.080. It was concluded that atomic displacements of the single crystal depended on the crystallization-induced stress formed in the crystallization process and the thermal contraction stress created in the cooling process after crystallization, and that these stresses were responsible for the expansion and contraction of the crystal lattice.     

Metakaolin-based inorganic polymer composite: Effects of fine aggregate composition and structure on porosity evolution,microstructure and mechanical properties

This paper examines the phase transformation, pore evolution, microstructural and mechanical changes that occur in inorganic polymer cement (IPC) in the presence of three different grade of fine aggregates (ф < 100 μm) of ladle slag, nepheline syenite and quartz sand. Experimental results indicate that polycondensation was enhanced in nepheline syenite based specimens, compared to quartz sand, due to the increase in HMAS phases in relation to the dissolution and interaction of amorphous/disordered fraction of aggregates. HCS and HCAS with HMAS phases were identified in the ladle slag based specimens. The formation of these new phases reduced both the cumulative pore volume and pores size. The apparent increase in volume of capillary pores in ladle slag based specimens was explained by the residual bubbles from the carbonates included in raw slag. The flexural strength of the inorganic polymer cement increases from 4 MPa to 4.2, 4.8 and 6.8 MPa with the addition of 20 wt% of quartz sand, nepheline syenite and ladle slag respectively. These values increase significantly between 28 and 180 days of curing (9.1 MPa for ladle slag and 10.0 MPa for nepheline syenite). It was concluded that fines can be used to remove the HM and poorly bounded alumina oligomers in metakaolin based inorganic polymer matrices and improve the interfacial zone for the design of an optimum grade and high-performance composites.     

Studies on optimization of silica nanoparticles dosage in cementitious system

Optimization of silica nanoparticles (SNPs) dosage in cementitious system was carried out analytically as well as experimentally by understanding the early stage hydration reaction of tricalcium silicate (C₃S). XRD and TGA results show the maximum nucleation effect of SNPs at 8 h, when the rate of product formation was higher than the control (∼66% additional CSH and ∼61% more CH with 10% SNPs addition). While at 24 h of hydration, ∼25% additional CSH was formed and CH content reduced by ∼32% with 10% addition showing the pozzolanic effect of SNPs. Further, FTIR results reveal that SNPs accelerate the polymerization in silicate chain and with 10% SNPs addition more crystalline (probably tobermorite like) structure is formed. This is responsible for the formation of highly compact and dense microstructure at 24 h as observed in electron micrographs, which may be responsible for the slow hydration rate at later age. XRD, FTIR and TGA studies on C₃S revealed that up to 5% addition of SNPs is beneficial, whereas higher dosages do not contribute significantly. Based on these investigations, studies were performed on cement paste, mortar and concrete samples, which revealed that 2–3% addition of SNPs is the optimum quantity for significant contribution in strength properties.