Examination of nanocrystalline TiC/amorphous C deposited thin films

The relationship between structural, chemical and mechanical properties of nanocrystalline TiC/amorphous C (TiC/a:C) thin films was studied. Thin films were deposited by DC magnetron sputtering on oxidized silicon (Si/SiO₂) substrates in argon at 25 °C and 0.25 Pa. The input power of the carbon target was kept at constant value of 150 W while the input power of the titanium target was varied between 15 and 50 W.It was found that all thin films consist of a few nanosized columnar TiC crystallites embedded in carbon matrix. The average size of TiC crystallites and the thickness of the carbon matrix have been found to correlate with Ti content in the films. The mechanical properties of the films have been strictly dependent on their structure. The highest values of the nanohardness (∼66 GPa) and Young's modulus (∼401 GPa) were observed for the film with the highest TiC content which was prepared at the largest input power of Ti target.     

The structural and mechanical characterization of TiC and TiC/Ti thin films grown by DC magnetron sputtering

The formation of TiC and Ti phases and their influence on their mechanical properties was studied in this work. Thin layers were deposited by DC magnetron sputtering at room temperature in ultrahigh vacuum from Ti and C targets.Cubic TiC phase (c-TiC) was formed from 58 to 86?at.% Ti content. First formation of hexagonal Ti (h-Ti) occurred from 86?at.% Ti content. The c-TiC disappears from 90?at.% Ti content. Films with 86?at.% Ti content the c-TiC structure can transform to h-Ti by sequential stacking faults. Dominance of c-TiC(111) texture with increasing Ti content was observed.The hardness of thin films agree with structural observations. The highest hardness value (～26?GPa) showed the c-TiC thin film with 67?at% Ti content. The nanohardness values showed decreasing character with increasing Ti content over 70?at.%. The lowest values of nanohardness (～10?GPa) was observed for thin films with only h-Ti phase.     

Ablation behavior and mechanism of SiCf/Cf/SiBCN ceramic composites with improved thermal shock resistance under oxyacetylene combustion flow

The ablation properties and mechanisms (under oxyacetylene combustion) together with thermal shock behavior of SiC_f/C_f/SiBCN ceramic composites were investigated. The solid ablation products are primarily amorphous SiO₂ and cristobalite. The primary ablation mechanisms include fiber and ceramic matrix oxidation, evaporation of B₂O₃ (l) and SiO₂ (l), and mechanical exfoliation. SiC_f/C_f/SiBCN has a significantly low mass ablation rate and a desirable linear ablation rate. The combination of crack deflection caused by SiC and carbon fibers, fiber pull-out and debonding improves thermal shock resistance and thus leads to the absence of surface macrocracks.     

Characterization of basaltic tuffs and their applications for the production of ceramic and glass–ceramic materials

Alkaline basaltic tuffs, from Southern Turkey were characterized and employed to obtain ceramic and glass–ceramic materials by combined sintering and crystallization process. The chemical and mineralogical compositions were analyzed by X-ray fluorescence spectrometry and X-ray diffraction analyses, respectively. The phase formation and the sintering behaviour were investigated by DTA, differential dilatometer and hot-stage microscopy. The micro-structure and residual porosity of the sintered samples were observed by SEM and evaluated by pycnometric techniques. Ceramic material, based on 50% basaltic tuff and 50% clay, was obtained at 1150 °C with 13% total porosity and 4% water absorption. Glass–ceramic materials were synthesized directly using the milled basaltic tuff by mean of the sinter-crystallization technique, in the range 900–1150 °C. The investigation has showed that, due to the high porosity and low crystallinity, alkaline tuffs could be a suitable raw material for ceramic application.     

Physicochemical,osteogenic and corrosion properties of bio-functionalized ZnO thin films: Potential material for biomedical applications

Nano-sized zinc oxide (ZnO) is well known for its antibacterial activity and biocompatibility, which make this material a promising candidate to tailor titanium (Ti) implant surfaces. In an optimized scenario, the antibacterial activity of ZnO and its biocompatibility can be envisioned as a good bio-functionalization strategy to increase osteointegration. Thus, in this work, it is proposed that the bio-functionalization of ZnO thin films with dentin matrix protein 1 (DMP1) peptides could function as an apatite crystal nucleator. Ti was coated with ZnO and functionalized with two different spacers, 3-(4-aminophenyl) propionic acid (APPA) or 3-mercaptopropionic acid (MPA) to facilitate binding with DMP1 peptides. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) results confirmed the presence of the peptides on the ZnO thin film surface through characteristic bands related to amine and carboxylic acid groups and by the incidence of N 1?s spectra, respectively. Atomic force microscopy (AFM) images indicated that a more uniform layer of DMP1 peptides is formed in the the presence of the APPA and MPA spacers. In general, the results obtained showed that the bio-functionalized ZnO thin films with APPA spacer, ZnO APPA P sample, presented enhanced wettability (17°), surface energy (72?dyn/cm), with an osteogenic surface and apatite nucleating properties. Furthermore, the electrochemical analysis showed increased corrosion resistance with noble E_OCP (?0.13?V), Ecorr (?0.46?V), and Icorr (8.91?×10^?7 A/cm²) values. These findings indicated promising applications of ZnO APPA P in biomedical devices once it can accelerate the osteointegration process and improve the corrosion resistance of implants.     

Characterization of La0.67Sr0.33MnOz thin films synthesized by metal-organic decomposition on different substrates

La_0.67Sr_0.33MnO_z (LSMO) thin films were synthesized by means of metal-organic decomposition on the substrates including amorphous quartz, (1 0 0) Si chip, (1 0 0) MgO single crystal and polycrystalline Al₂O₃ ceramic plate. The structure and magnetotransport properties of the films were characterized. X-ray diffraction spectra show that all samples are polycrystalline with (2 0 2) preferred orientation. All films present metal–insulator transition and enhanced magnetoresistance (MR) effect below metal–insulator transition peak temperature (T_p). At room temperature (RT) low-field magnetoresistance effect (LFMR) and linear change of resistivity under applied field are exhibited by all the films. These magnetotransport properties were first ascribed to the porous structural characteristics in the films observed by atomic force microscope. Furthermore, the LSMO film synthesized on (1 0 0) MgO substrate presents a bit different magnetic properties and magnetotransport from the other samples, including broad ferromagnetic–paramagnetic transition zone, lower T_p and weaker LFMR at RT. However, for the samples synthesized on the other substrates, the LFMR effect is very similar to each other and their MR ratio reaches near 5% under 10 kOe field. Thus the substrate effect of LSMO film on (1 0 0) MgO is more intensive than that of the other samples.     

SiCl3CCl3 as a novel precursor for chemical vapor deposition of amorphous carbon films

Amorphous carbon films, characterized by XRD, AFM, SEM and Raman, were deposited from SiCl₃CCl₃ on quartz substrates at 773-1273 K by low pressure chemical vapor deposition using a hot-wall reactor. XPS studies showed that the films grown at 773 K contained 90% C and 10% Cl, while the films grown at 1273 K contained 100% C. SiCl₄, CCl₄ and Cl₂CCCl₂ were detected by on-line FT-IR studies. The extrusion of dichlorocarbene, :CCl₂, from SiCl₃CCl₃ should provide the source of carbon in the reaction. On Si substrates, an etching process at the film-substrate interface assisted the lift-off of the films from the substrates. The C films curled and formed rolls.     

Three-dimensional porous amorphous SnO2 thin films as anodes for Li-ion batteries

Three-dimensional (3D) porous amorphous SnO₂ thin films were deposited on Ni foam substrates by Electrostatic Spray Deposition (ESD) technique as anodes for Li-ion batteries. These films display good capacity retention of 94.8% after 100 cycles at 0.5 C and rate capability of 362 mAh/g at 10 C. The improved performance originates from the fact that the 3D porous structure offers a “buffer zone” to accommodate the large volume change during cycling, and the foam-like substrate maximizes the contact area between electrode and electrolyte. The facile ESD method can be potentially extended to prepare other 3D porous functional materials.     

Oxidation behavior and microstructure evolution of SiC-ZrB2-ZrC coating for C/C composites at 1673 K

To protect carbon/carbon (C/C) composites against oxidation, a SiC-ZrB₂-ZrC coating was prepared by the in-situ reaction between ZrC, B₄C and Si. The thermogravimetric and isothermal oxidation results indicated the as-synthesized coating to show superior oxidation resistance at elevated temperatures, so it could effectively protect C/C composites for more than 221 h at 1673 K in air. The crystalline structure and morphology evolution of the multiphase SiC-ZrB₂-ZrC coating were investigated. With the increase of oxidation time, the SiO₂ oxide layer transformed from amorphous to crystalline. Flower-like and flake-like SiO₂ structures were generated on the glass film during the oxidation process of SiC-ZrB₂-ZrC coating, which might be ascribed to the varying concentration of SiO. The oxide scale presented a two-layered structure ~130 µm thick after oxidation, consisting of a SiO₂-rich glass layer containing ZrO₂/ZrSiO₄ particles and a Si-O-Zr layer. The multiphase SiC-ZrB₂-ZrC ceramic coating exhibited much better oxidation resistance than monophase SiC, ZrB₂ or ZrC ceramic due to the synergistic effect among the different components.     

Self-growth of nanocrystalline structures for amorphous Sr0.925Bi0.05TiO3 thin films with high energy density

Process of self-growth nanocrystalline structure was explored to improve the dielectric properties of amorphous Sr_0.925Bi_0.05TiO₃ (SBT) thin films through controlling the annealing temperature. The crystallinity of the material was 15% when annealed at 550?°C, and the resulting nanocrystalline particles were 14?nm in size as determined by XRD analysis. Therefore, the proposed process could produce a novel film of an amorphous matrix coating nanocrystalline particles. Finite element analysis results showed that the applied electric field was focused primarily in the amorphous matrix, which could effectively decrease the probability of low voltage breakdown of the nanocrystalline particles. Simultaneously, the nanocrystalline particles supplied more polarization charges, which helped to improve the dielectric constant of the inorganic composite. Combining the merits of amorphous and crystalline phases, the ultimate energy storage density of the modified sample was as high as 21.2?J/cm³, which represents an improvement of 5.1?J/cm³ compared with that of pure amorphous SBT thin film.     

Gel reactive melt infiltration: A new method for large-sized complex-shaped C/C components ceramic modification

To widen the applications of conventional reactive melt infiltration (RMI) in large-sized complex-shaped C/C components, an ingenious process of gel-RMI (GRMI) was proposed in this study. The arching C/CSiC composite was prepared successfully using GRMI method with polycarbosilane (PCS)Si90Zr10 (Si: 90 at.%; Zr:10 at.%) sol. The porosity rate of the C/C preform decreased from 18.5% to 2.9%, while the density was raised from 1.40 g·cm⁻³ to 2.05 g·cm⁻³ after GRMI. The reason why C/C preform has been significantly densified is as follow: the PCS in PCS-Si90Zr10 sol formed SiC aerogel skeleton after pyrolysis, and then the Si90Zr10 powders were melted and released from the SiC aerogel into the C/C preform body when the temperature reached the melting point of Si90Zr10 alloy. The obtained C/CSiC composite showed a pseudo-ductile rupture characteristic distinguished from that of the C/C preform, and its bending strength was significantly improved from 104.2 MPa of the C/C preform to 258.8 MPa. The C/CSiC composite had a far lower mass ablation rate of 0.75 mg·s⁻¹ than that of C/C preform, 23.30 mg·s⁻¹. Moreover, the GRMI was preliminarily applied in ceramic modifying nozzle-like C/C preform, and the result showed that the nozzle-like C/C preform was successfully densified from 1.3 g cm⁻³ to 1.96 g cm⁻³. The GRMI process has great potential in ceramic modifying large-sized complex-shaped C/C components.     

Carbon black/polystyrene composites as candidates for gas sensing materials

Amorphous polymer-based composites consisting of polystyrene and carbon black were developed in the current work as candidates for gas sensing materials. With the help of polymerization filling, i.e., in-situ polymerization of styrene in the presence of carbon black, the composites were provided with low percolation threshold. The experimental results indicated that the composites have selective sensitivity as characterized by high electrical responsivity to the vapors of non-polar and low polar solvents, and low responsivity to high polar solvent vapors as well. Besides conductivity of the composites, absorption characteristics of both the matrix and the fillers exert importance influence on the gas sensitivity of the composites. Therefore, composites’ performance can be tailored by changing filler concentration, molecular weight and molecular weight distribution of matrix polymer, etc. In regard to the fact that most conducting polymer composites as vapor sensing materials are based on crystalline polymer matrices, the approach reported by this paper provides another feasible way to develop new candidates.     

Reaction sintered zirconium titanate-zirconia bulk materials from 3Y2O3-stabilized zirconia and TiO2. Phase composition and their potential for thermal shock applications

This work evaluates the potential of zirconium titanate-zirconia composites for thermal shock. Materials with Zr_0.97Y_0.03O_1.985:TiO₂ molar ratios 50:50 (Z(Y)T50) and 70:30 (Z(Y)T70) were obtained from Y₂O₃ (3 mol%)-stabilized ZrO₂ and TiO₂ mixtures colloidal processed and reaction sintered at 1773 K with low cooling rate (2-5 K/min). The crystalline phases and their unit cell parameters were determined by Rietveld analysis of high resolution X-ray diffraction patterns. The zirconium titanate phase in these materials is o-TiZrO₄, being the major phase in Z(Y)T50 in which c-ZrO₂ is secondary phase. Z(Y)T70 has t-ZrO₂ as main phase, o-TiZrO₄ as secondary phase and c-ZrO₂ and m-ZrO₂ as minor phases. The Hasselman thermal shock resistance factors, calculated using the experimental values of the involved properties, Young's modulus, thermal expansion coefficient, and fracture strength, have demonstrated the high potential of zirconia-zirconium titanate composites for thermal shock applications in oxidizing atmospheres.     

Reduction of irreversible capacities of amorphous carbon materials for lithium ion battery anodes by Li2CO3 addition

Amorphous carbon materials for lithium ion battery anodes which contain a small amount of Li₂CO₃ were prepared by three methods. The obtained materials were characterized using X-ray diffraction (XRD) analysis, Raman spectroscopy and CO₂ adsorption experiments. Although the XRD profiles and Raman spectra of these materials were similar to those of carbon materials synthesized with no addition, the amount of CO₂ adsorbed was largely decreased by Li₂CO₃ addition. These results suggest that the micropores in these materials were plugged and/or filled with Li₂ CO₃. Galvanostatic lithium charging and discharging experiments showed that the irreversible capacity of the material can be significantly decreased by Li₂CO₃ addition, which is thought to be due to the plugging of the pore inlets by Li₂CO₃. Moreover, it was also found that the reversible capacities of the materials can be increased by adjusting both the amount of Li₂CO₃ addition and carbonization temperature.     

Structural characterization of bulk ZrTiO4 and its potential for thermal shock applications

Zirconium titanate, ZrTiO₄, is a well known compound in the field of electroceramics. Furthermore, it shows a large potential as structural material for thermal shock resistance applications, since it presents crystallographic anisotropy in thermal expansion. However, there is no information in the current literature about its thermomechanical behaviour. In this work, single phase zirconium titanate bulk materials have been prepared from well dispersed ZrO₂ and TiO₂ mixed suspensions, combining reaction and conventional sintering processes. The crystal structures of ZrTiO₄ have been studied by the Rietveld method for bulk samples. The structural evolution upon the cooling rate has been unravel, as the b-axis strongly decreases for slow cooled samples when compared to quenched materials. For the first time apparent Young's modulus (≈130 GPa) and Vickers hardness (≈8 GPa) values of a fully dense single phase zirconium titanate material have been evaluated and its potential for thermal shock applications has been analysed in comparison with other thermal shock resistant materials.     

MCM-41 supported CuO/Bi2O3 nanoparticles as potential catalyst for 1,4-butynediol synthesis

CuO/Bi₂O₃ (CuO/Bi₂O₃/MCM-41) nanoparticles supported on MCM-41 were synthesized by a facile impregnation method. The products were characterized by nitrogen adsorption/desorption, X-ray diffraction (XRD), H₂ temperature programmed reduction (H₂-TPR) and scanning electron microscopy (SEM). XRD patterns indicated the presence of crystalline CuO and Bi₂O₃ phase for CuO/Bi₂O₃/MCM-41 catalyst. TPR results revealed CuO nanoparticles were dispersed well on MCM-41. SEM results showed that the nanoparticles were located on the MCM-41. The activity of the catalysts towards ethynylation of formaldehyde for 1,4-butynediol synthesis was evaluated at atmospheric pressure. Compared with unsupported CuO/Bi₂O₃ and commercial Cu/Bi-based catalyst, CuO/Bi₂O₃/MCM-41 catalyst showed maximum conversion (51%) and selectivity (94%) towards 1,4-butynediol. The results show that CuO/Bi₂O₃ catalysts supported on MCM-41 have potential for 1,4-butynediol synthesis in industrial application.     

Electrochemical characterization of amorphous LiFe(WO4)2 thin films as positive electrodes for rechargeable lithium batteries

Amorphous LiFe(WO₄)₂ thin films have been fabricated by radio-frequency (R.F.) sputtering deposition at room temperature. The as-deposited and electrochemically cycled thin films are, respectively, characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectra techniques. An initial discharge capacity of 198 mAh/g in Li/LiFe(WO₄)₂ cells is obtained, and the electrochemical behavior is mostly preserved in the following cycling. These results identified the electrochemical reactivity of two redox couples, Fe³⁺/Fe²⁺ and W⁶⁺/W^x+ (x = 4 or 5). The kinetic parameters and chemical diffusion coefficients of Li intercalation/deintercalation are estimated by cyclic voltammetry and alternate-current (AC) impedance measurements. All-solid-state thin film lithium batteries with Li/LiPON/LiFe(WO₄)₂ layers are fabricated and show high capacity of 104 μAh/cm² μm in the first discharge. As-deposited LiFe(WO₄)₂ thin film is expected to be a promising positive electrode material for future rechargeable thin film batteries due to its large volumetric rate capacity, low-temperature fabrication and good electrode/electrolyte interface.     

Solvothermal synthesis and characterization of ytterbium/iron mixed oxide nanoparticles with potential functionalities for applications as multiplatform contrast agent in medical image techniques

A solvothermal route to prepare Glutathione capped hybrid ytterbium/iron oxide nanoparticles with potential applications as multiplatform contrast agent in medical image techniques has been developed. The influence of ytterbium/iron molar ratio used as precursor, as well as the degree of the autoclave filling on the structural and morphological characteristics of the obtained nanoparticles has been extensively studied. Although all nanoparticles present similar composition, with YbFeO₃ being the majority phase, size and morphology of the as synthetized nanoparticles are highly influenced by the critical temperature and by the over -saturation reached during the solvothermal process. We have demonstrated that glutathione properly functionalizes the hybrid nanoparticles, increasing their colloidal stability and decreasing their cytotoxicity. Additionally, they show good imaging in magnetic resonance and X-ray computerized tomography, thereby indicating promising potential as a dual contrast agent. This work presents, for the first time, glutathione functionalized ytterbium/iron oxide nanoparticles with potential applications in Biomedicine.