Haemocompatibility of DLC and TiC–TiN interlayers on titanium

An interlayer approach was adopted to achieve adequate adhesion between a DLC coating deposited by plasma-assisted CVD and a titanium substrate as part of a study to coat a bi-leaflet heart valve prosthesis. The interlayers (TiC and TiN) were deposited by d.c. ion plating. TiN was also deposited by reactive r.f. sputtering. The substrate, interlayers and DLC were assessed for haemocompatibility and thrombogenicity using a dynamic blood method and interactions with rabbit blood platelets, respectively. The adhesion, activation and morphology of the platelets were determined by stereological techniques using SEM. All surfaces were assessed topographically by stylus profilometry and AFM. Surface energies were compared by liquid drop goniometry. The structure and crystallographic orientation of the TiN interlayers were determined using XRD. The coatings produced no haemolytic effect, except in the case of TiN deposited by reactive r.f. sputtering, which showed a significant effect after longer assessment periods. In contrast to the DLC coating, all of the interlayers showed a slight tendency towards thrombus formation during the later stages of incubation. Platelet spreading correlated with the surface energy of the coatings.     

Microstructure and mechanical properties of TiC–TiN–Zr–WC–Ni–Co cermets

Cermet cutting tools are widely used for semi-finishing and finishing work on steel and cast iron. However, their brittleness is still an unavoidable limitation for their utilizations. Zirconium was added to improve the fracture toughness of Ti(C, N) based cermets. The microstructure and the fracture surfaces of cermets were studied by using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The experimental results reveal that Zr dissolved and formed solid solutions during the sintering process. The amount of grains with typical core/rim structure decreases and that of coreless grains increases with increasing Zr addition. Moreover, the fracture toughness is improved clearly due to the increased amount of the coreless grains, the spinodal decomposition in cermets, as well as the crack deflection and crack branching mechanisms. Additionally, hardness and relative density were also measured, respectively.     

Properties of AlN–TiN composite ceramics

Abstract

Results are presented of a study dealing with an AlN–TiN composite material for high temperature applications. Hardness, microhardness, compressive strength, electrical resistance, and thermal conductivity of the material were measured at room temperature and flexural strength was measured at temperatures from 20 to 1800°C. The composite material containing 40 wt-% AlN and 60 wt-% TiN and hot pressed at 1850–1950°C exhibits an increase in strength of 20% with a rise in temperature, which permits it to be used at elevated temperatures.     

cBN–TiN,cBN–TiC composites: chemical equilibria,microstructure and hardness mechanical investigations

This paper summarizes theoretical and experimental studies of cBN–TiN and cBN–TiC of cBN:TiN/TiC molar ratio 1:1 and 2:1. Theoretical calculations show that, at temperatures between 1000 and 1400°C, TiN reacts with BN forming one new phase, TiB₂, and that TiC reacts with cBN forming two new phases, TiB₂ and TiC_0.8N_0.2.. Experimental cBN–TiC/TiN composites were prepared by high pressure hot pressing and the samples were subsequently heat treated.After heat treatment, sinters of cBN–TiN/TiC were characterized using transmission electron microscopy and X-ray diffraction. The samples exhibited a dense polycrystalline structure, and a thin layer of fine TiB₂ was visible at the BN–binder interface. It was found that hardness decreased significantly after heat treatment.     

Preparation and characterisation of TiN by microwave-assisted carbothermic reduction–nitridation in air atmosphere

Titanium nitride (TiN) is prepared from ilmenite (FeTiO₃) powders by microwave-assisted carbothermic reduction–nitridation in air atmosphere followed by acid leaching treatment. The thermal analysis of the reduction–nitridation of FeTiO₃ powders is conducted by thermogravimetry/differential scanning calorimeter. The phase transition sequence of microwave carbothermal synthesis of TiN–Fe composite is: FeTiO₃?→?Fe?+?TiO₂?→?Fe?+?TiN. There is no any other oxygen-deficient titanium oxides detected. Particularly, FeTiO₃ can be transformed into TiN–Fe composite completely at 900°C for 60?min by microwave heating. The increase in both the reaction temperature and dwelling time is in favour of the transformation of FeTiO₃. The product morphologies are spherical about 2–5?μm in size. Then TiN is obtained with the removal of Fe and their oxides from TiN–Fe composite by acid leaching treatment. This method not only reduces the reaction temperature significantly through microwave heating but also can simplify the operation process effectively.     

Spark plasma sintering of TiN–TiB2 composites

TiN–TiB₂ composites were fabricated by spark plasma sintering at 1773–2573 K. Effects of TiN and TiB₂ content on relative density, microstructure, and mechanical properties were investigated. Above 2373 K, TiN–TiB₂ composites exhibited relative densities over 95%. A high density of 99.7% was obtained at 2573 K with 20–30 vol% TiB₂. Shrinkage of the TiN–70 vol% TiB₂ composite was the highest at 1573–2473 K. For the TiN–70 vol% TiB₂ composite prepared at 1973–2373 K, TiN grains were small, while at 2573 K, TiB₂ became a continuous matrix, in which irregular-shaped TiN dispersed. hBN was formed in the TiN–TiB₂ composite containing 50–60 vol% TiB₂ above 2373 K. The maximum Vickers hardness and fracture toughness obtained for the TiN–80 vol% TiB₂ composite sintered at 2473 K was 26.3 GPa and 4.5 MPa m^1/2, respectively.     

In situ synthesis of PcBN composites from Sialon–TiN–TiB2 binder and cBN under high temperature and pressure

Polycrystalline cubic boron nitride (PcBN) composites were synthesized in situ with TiB₂, TiN, and Sialon as binders under ultrahigh temperature (1550°C) and high pressure (5.5 GPa). X-ray diffractometry, universal testing machine, field emission scanning electron microscopy, and transmission electron microscopy were used to study the effect of Sialon content (0%, 20%, 40%, 60%, and 80% by mass of binder) on the phase composition, microstructure, and mechanical properties of PcBN composites. The results show that the main phases in the system are lamellar TiN, needle-rodlike TiB₂, and irregular long-rodlike Sialon. Some TiB₂ grows along the (1 0 −1 0) face, and Sialon grows along the (0 0 0 1) face. The density and mechanical properties of the sintered product are significantly improved due to the formation of Sialon. When the content of Sialon is 60%, the binder is uniformly distributed, the cBN interface is well bonded, and the density is the highest. At this time, the strength reaches the maximum 34.57 GPa, the fracture toughness is 6.82 MPa m^1/2, and the flexural strength reaches the maximum 870.79 MPa. On the whole, cBN composites have excellent prospects for future applications in cutting inserts due to their excellent mechanical properties.     

Enhancing the sinterability and fracture toughness of Al2O3–TiN0.3 composites

We introduce a new and effective method for improving the fracture toughness of Al₂O₃-based composites through the addition of a nonstoichiometric material. Al₂O₃–TiN_0.3 composites were sintered by spark plasma sintering with different TiN_0.3 content at temperatures between 1300 and 1600 °C for 10 min and a micro-region diffusion phenomenon was observed at the Al₂O₃–TiN_0.3 interface. Ti atoms from TiN_0.3 diffused into Al₂O₃ to occupy Al sites, which led to the formation of Al vacancies that enabled the transport of aluminum by a vacancy mechanism. The optimal densification temperature of the Al₂O₃–30vol% TiN_0.3 composite was approximately 1400 °C. The maximum fracture toughness measured was 6.91 MPa m^1/2, from the composite with 30 vol% TiN_0.3 sintered at 1500 °C.     

Densification and mechanical properties of cBN–TiN–TiB2 composites prepared by spark plasma sintering of SiO2-coated cBN powder

cBN–TiN–TiB₂ composites were fabricated by spark plasma sintering at 1773–1973 K using cubic boron nitride (cBN) and SiO₂-coated cBN (cBN(SiO₂)) powders. The effect of SiO₂ coating, cBN content and sintering temperature on the phase composition, densification and mechanical properties of the composites was investigated. SiO₂ coating on cBN powder retarded the phase transformation of cBN in the composites up to 1873 K and facilitated viscous sintering that promoted the densification of the composites. Sintering at 1873 K, without the SiO₂ coating, caused the relative density and Vickers hardness of the composite to linearly decrease from 96.2% to 79.8% and from 25.3 to 4.4 GPa, respectively, whereas the cBN(SiO₂)–TiN–TiB₂ composites maintained high relative density (91.0–96.2%) and Vickers hardness (17.9–21.0 GPa) up to 50 vol% cBN. The cBN(SiO₂)–TiN–TiB₂ composites had high thermal conductivity (60 W m⁻¹ K⁻¹ at room temperature) comparable to the TiN–TiB₂ binary composite.     

Examination of morphology,degradation and biocompatibility of fluorapatite–forsterite nanocomposite

This research has been done to study the characteristics and biocompatible evaluation of nano-biocomposite ceramic. Nanocomposites with the base of fluorapatite with 15, 25, 35 wt% of forsterite have been synthesized by the sol-gel method. Fluorapatite-forsterite nanocomposites have been characterized in terms of degradation by determining the weight change percentages and the pH changes in terms of bioactivity by checking the apatite layer formation using a solution of simulated body fluid (SBF). The release rate of silicon ions and fluorine ions are measured by ICP and fluorine selective electrode, respectively. This is the indication of desirable bioactivity in the synthesized nanocomposite and can be increased by adding the amount of forsterite in the samples and the higher solubility of the forsterite incompatible with fluorapatite. Compressive strength measurements indicate that the compressive strength of the nanocomposite increases by adding the forsterite percentages. The result of MTT assay indicates nontoxicity and decreases the cell viability in 7 days incompatible with the first day.     

New catalytic functions of Pd–Zn, Pd–Ga, Pd–In, Pt–Zn, Pt–Ga and Pt–In alloys in the conversions of methanol

Pd and Pt supported on ZnO, Ga₂O₃ and In₂O₃ exhibit high catalytic performance for the steam reforming of methanol, CH₃OH+H₂OCO₂+3HH₂, and the dehydrogenation of methanol to HCOOCH₃, 2CH₃OHHCOOCH₃+2HH₂. Combined results with temperature-programmed reduction (TPR) and XRD method revealed that Pd–Zn, Pd–Ga, Pd–In, Pt–Zn, Pt–Ga and Pt–In alloys were produced upon reduction. Over the catalysts having the alloy phase, the reactions proceeded selectively, whereas the catalysts having metallic phase exhibited poor selectivities.     

Densification,microstructure, and mechanical properties of ZrC–SiC ceramics

ZrC–SiC ceramics were fabricated by high-energy ball milling and reactive hot pressing of ZrH₂, carbon black, and varying amounts of SiC. The ceramics were composed of nominally pure ZrC containing 0 to 30 vol% SiC particles. The relative density increased as SiC content increased, from 96.8% for nominally pure ZrC to 99.3% for ZrC-30 vol% SiC. As SiC content increased from 0 to 30 vol%, Young's modulus increased from 404 ± 11 to 420 ± 9 GPa and Vickers hardness increased from 18.5 ± 0.7 to 23.0 ± 0.5 GPa due to a combination of the higher relative density of ceramics with higher SiC content and the higher Young's modulus and hardness of SiC compared to ZrC. Flexure strength was 308 ± 11 MPa for pure ZrC, but increased to 576 ± 49 MPa for a SiC content of 30 vol%. Fracture toughness was 2.3 ± 0.2 MPa·m^1/2 for pure ZrC and increased to about 3.0 ± 0.1 MPa·m^1/2 for compositions containing SiC additions. The combination of high-energy ball milling and reactive hot pressing was able to produce ZrC–SiC ceramics with sub-micron grain sizes and high relative densities with higher strengths than previously reported for similar materials.     

Electrical properties and microstructural evolution of ZrO2–Al2O3–TiN nanocomposites prepared by spark plasma sintering

Electroconductive ZrO₂–Al₂O₃–25 vol% TiN ceramic nanocomposites were prepared by spark plasma sintering at 1200 °C for 3 min. The electrical resistivity of the composites decreased from 4.5 × 10^?4 Ω m to 3 × 10^?5 Ω m as the Al₂O₃ content in the ZrO₂–Al₂O₃ matrix increased from 0 to 100 vol%. SEM images graphically presented the microstructural evolution of the composites and a geometrical percolation model was applied to investigate the relationship between the electrical property and the microstructure. The results indicated that the addition of Al₂O₃ to ZrO₂–TiN improved the electrical conductivity of the material by tailoring the structure from “nano–nano” type for ZrO₂–TiN to “micro–nano” type for ZrO₂–Al₂O₃–TiN.     

Modeling,Simulation, and Experimental Validation of Drying and Denaturation Behavior of Whey Protein Isolate–Based Coatings

Previous studies proved that heat-treated whey protein isolate (WPI)-based coatings can act as an adequate packaging material with sufficient barrier properties and producibility. These properties also depend on the degree of denaturation of the coating formulations used. This study focuses on the modeling, simulation, and experimental validation of drying and denaturation behavior of WPI-based coatings. Simulation according to existing models is able to describe denaturation and drying kinetics of WPI based coatings adequately. A degree of denaturation of about 13% was reached during coating production. Water vapor transmission rates were reduced up to 67%.     

Preparation, characterization, and antibacterial activity evaluation of collagen–Zn complex

The different kinds of collagen–Zn complexes were prepared by zinc acetate, zinc chloride, zinc nitrate, and zinc sulfate reacted with collagen protein. Their antibacterial activities have been investigated by MIC method. It was found that the antibacterial activity of collagen–ZnSO₄ complex is better than that of others. To obtain a better antibacterial activity, collagen–ZnSO₄ complexes with different zinc amount were prepared using zinc sulfate as starting material. These complexes were characterized by FT-IR, XRD, and atomic absorption spectrometry. The results showed that zinc ion could chelate with N–H, C–O, and C=O group in collagen to form the stable complex. Antibacterial activities of collagen–ZnSO₄ complexes containing different Zn amount were evaluated against Escherichia coli and Staphylococcus aureus. The results suggested that antibacterial activity increases with the increase of zinc amount.     

Synthesis,characterization, and electrical properties of polypyrrole–bimetallic oxide composites

In this study, polypyrrole (PPy) and its bimetallic oxide composites (PPy–V₂O₅–MnO₂) were synthesized via a modified chemical oxidation polymerization method in the aqueous medium with FeCl₃·6H₂O as an oxidant. The synthesized materials were characterized with various analytical techniques to investigate their structural, crystallographic, thermal, morphological, optical, and electrical properties. The Fourier transform infrared study confirmed the successful synthesis of the materials, whereas the X-ray diffraction analyses showed the amorphous and crystalline natures of the PPy and PPy–V₂O₅–MnO₂ composites, respectively. The bimetallic oxide content improved the thermal stability of the composites, as ratified by thermal analysis. The synthesized PPy had a globular and spongy nature, whereas the composites were mixtures of short and long rod-shaped particles. The bimetallic oxide blend enhanced the doping, surface area and semiconducting nature of composites, and lower electrical resistance compared with those of the PPy. The resistance of the synthesized materials depended on the V₂O₅–MnO₂ blend content in the composites and the temperature. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47680.     

Physical,mechanical and microstructural characterization of TiC–ZrN ceramics

This study aims to investigate the impact of zirconium nitride (ZrN) additive on the microstructural features and physical-mechanical characteristics of TiC. For this objective, two different samples, namely monolithic TiC and TiC-5 wt% ZrN, were produced by spark plasma sintering method at 1900 °C for 10 min under 40 MPa. X-ray diffraction, field emission scanning electron microscopy, and thermodynamical evaluations confirmed the formation of a single solid solution of (Ti,Zr)(C,N), along with a carbon-rich secondary phase in the doped ceramic. The monolithic TiC provided a higher relative density (95.5%) than the ZrN-doped sample. The fractographical assessment revealed a change in the fracture mode of TiC from transgranular to intergranular with introducing the ZrN additive. Reinforcing TiC with ZrN resulted in a Vickers hardness of 2640 HV_0.1 kg, a flexural strength of 444 MPa, and a thermal conductivity of 14.9 W/mK. Furthermore, the TiC–ZrN sample presented a higher coefficient of friction (0.37 on average) compared to the monolithic TiC (0.34 on average).     

Ohmic contact formation mechanisms of TiN film on 4H–SiC

The atomic structure, interfacial charge distribution, bonding nature, and interfacial electronic states of a 4H–SiC/TiN interface are systematically investigated to understand the Ohmic contact formation mechanisms of TiN to 4H–SiC. The experiment results clearly demonstrate that the well-arranged TiN (111)-oriented lattice planes are parallel to the (0001) SiC-oriented substrate, which is in line with the XRD results. In addition, the interface is coherent without any secondary phase layers, amorphous layers, or transition regions, which confirms the direct contact of TiN to SiC at the atomic scale, exhibiting a linear current–voltage relationship. Quantitatively, first-principle calculations reveal that the Schottky barrier height (SBH) is as low as 0.03 eV and that the band gap nearly vanishes at the interface, indicating an excellent Ohmic contact of TiN to 4H–SiC. Furthermore, the SBH is significantly reduced through the interfacial charge polarization effect and strong coupling of interfacial electronic states, enhancing the quantum electron transport. The present results provide insight into the complicated electronic effects of the Ohmic contact interface and indicate that TiN is a promising SiC Ohmic contact material for advanced next-generation power device applications.