Papers by Keyword: Nanoceramic

Abstract: Silicon nitride nanoceramics were prepared by hot press sintering amorphous Si₃N₄ and α-Si₃N₄ nanopowders. The microstructures as well as the effect of starting powders size on the mechanical properties and thermal fatigue properties were investigated. The results show that microstructure of sintered materials consists of spherical grains with approximate size of 100 nm. The mechanical properties and thermal fatigue resistance vary with the addition of α–Si₃N₄ powders. The maximum flexural strength and fracture toughness are obtained when the α–Si₃N₄ powders amount is 40wt.%. And the Si₃N₄ nanoceramic added 40wt.% α–Si₃N₄ powders has the best capability to suppress crack propagation and the highest critical temperature difference.

Abstract: Environmentally friendly anti-corrosion surface treatment reinforced by nano-ceramic metal oxide particles were developed as a protective layer for galvanized steel. The treatment bath is based on a nano-ceramic conversion coating composed of dilute hexafluorozirconic acid with small quantities of additive components containing H₂O₂. The corrosion resistance of treated substrate was compared to samples treated in phosphate conversion coating bath and in a hexafluorozirconic acid without the addition. The effect of other parameters such as pH solution and H₂O₂ concentration as oxidant on coating morphology were evaluated. Scanning electron microscopy/energy dispersive spectroscopy(SEM/EDS) was used to characterize the coating surface morphology. Utilizing DC polarization and salt spray test were performed on the treated substrate for studying the corrosion performance of the coatings. During surface examination, uniform distribution of Zr along the surface of all treated samples was observed. Results of corrosion tests showed that phosphate-free coating have a higher corrosion resistance than simple galvanized steel samples and provided long term corrosion performance comparable to that of phosphate.

Abstract: The dynamic changes of the friction properties of the oxide film are characterized by the dynamic changes of the ELID grinding force. The tangential force and normal force are used to represent the friction coefficient in order to obtain the accurate real-time friction coefficient of oxide film. Therefore, the friction coefficient of various grinding wheels with different bonding agents, various grinding parameters, various grinding materials (nano- Al2O3 ceramic, nano ZrO2 ceramic and ordinary ZrO2 ceramic), and ELID grinding and ordinary grinding can be further studied. The results show that: the friction coefficient of the oxide film on the bronze-based grinding wheel is greater than that composed by iron; the friction coefficient of the oxide film decreases with the increase in grinding depth and feeding speed; the friction coefficient of the oxide film and nano-materials is smaller than that of the oxide film and ordinary materials; the transformation from γ-Fe2O3 to α-Fe2O3 in oxide film and the elastic deformation of the oxide film caused by the high-temperature of grinding may make the friction coefficient of ELID grinding greater than that of ordinary grinding, so the oxide film contains better property of friction and polishing. Therefore, excellent surface quality is easier to be obtained by it compared with the ordinary grinding technology.

Abstract: The composite of methoxy polyethylene glycol (mPEG) and poly(lactic-co- glycolic acid) (PLGA) thermosensitive hydrogel mixed with different mass raio of hydroxyapatite and β-tricalcium phosphate (β-TCP) were used as bone graft substitutes. The physical properties of a series of composite gels, including the critical micelle concentration (CMC), particle sizes, zeta potential, rheological behavior, morphology of composite gels, and sol–gel transition, were characterized in vitro. These composite gels could form a gel at body temperature and could be controlled easily at room temperature. During the in vitro degradation process, composite gels demonstrated a slight decrease in pH value, a slower degradation rate, less toxicity, and a higher cell survival rate. The biocompatibility of the composite gels was validated by hemolysis test. In vivo animal studies demonstrated both radiographic and gross bone union when the ratio of HAP/ β-TCP was 7:3.

Abstract: Different mole ratios of sebacic acid (SA) and 1,6-bis(p-carboxyphenoxy) hexane (CPH) were used to make copolymer. g-HAP, hydroxyapatite (HAP) nanopowder surface-modified by polycaprolactone (PCL), was added with the copolymer to enhance the mechanical strength. Because of surface erosion, polyanhydride sustained the mechanical properties with time. The degradation of copolymer did not cause obvious decline in pH, and was thus less harmful to the osseous tissue. HAP is the main components of human bone and a good osteoinductive substance to help bone mineralization. The result of our study showed that CPH:SA = 7:3 added with10 wt% g-HAP was the best condition with maximum compress strength of 103 MPa. With slow degradation rate and durable mechanical strength, the novel biomaterial was suitable bone repair in future clinical application.

Abstract: Porous ceramics filter was prepared by sintering of hydroxyapatite (HA) and silica composite nanopowder. Silica nanopowder of 50 wt% are incorporated into HA nanopowder. The mixing powders are uniaxially compact and then sintering at 900°C-1050°C in air. The characterization of the porous was carried out by scanning electron microscopy (SEM). Filtration studies using porous ceramic were performed for agricultural wastewater. The studies of the water filtration and flow through these porous showed that the sintered ceramic filter at all temperatures reduced the TDS, TS, conductivity, and arsenic (As) content. The water permeated through porous ceramic composites could be compared to drinking water quality.

Abstract: Silicon nitride nanoceramics were fabricated by hot press sintering two kinds of Si₃N₄ nano-sized powders. The effect of starting powders on microstructure, mechanical properties and thermal shock resistance were investigated. The microstructure of sintered materials consists of spherical grains and the addition of α–Si₃N₄ to starting powders does not affect the grain morphology. The flexural strength, fracture toughness and thermal shock resistance increase with the increase in amount of α–Si₃N₄ starting powders, and the maximum mechanical properties are obtained when the amount of α–Si3N4 powders is 40wt.%. The hardness values decrease with the increase of α–Si₃N₄ amount.

Abstract: Features of the optical properties of nanostructured samples of cupric oxide CuO prepared by shock wave loading (SWL) and by high pressure torsion (HPT) methods have been investigated by means of spectroscopic ellipsometry in the range of 0.5-5.0 eV. The results for nanostructured samples are discussed in comparison with the measurement data of the CuO single crystal. Dispersion of the components of the complex permittivity in nanostructured CuO samples is significantly different from that for the single crystal. The optical spectral density of the nanostructured CuO is redistributed from the energy region above the fundamental absorption edge to the region below the edge. The shift is unexpected strong for samples prepared by the HPT method. The intensity of the optical spectra is suppressed in the range above the fundamental absorption edge and increases in low-energy one. It has been shown that the energy positions of the main electronic transitions in nanostructured samples on the whole are the same as in the single crystal; at the same time, intensity of the low-energy transitions increases. The possible causes of this increase and resolution of the fine absorption structure of the nanostructured CuO are discussed.

Abstract: The brittleness, plasticity, super-plasticity and the removal mechanisms of critical fragmentation of the nano ZrO2 ceramics were investigated. The formula of critical ductile grinding depth of the common engineering ceramics was inapplicable to the nano-ZrO2 ceramics. A new formula of critical ductile grinding depth of the nano ceramics was established. The ultrasonic vibration grinding experiments showed that the critical ductile grinding depth of the ceramics was 15μm by conventional grinding, but the increment of the critical ductile grinding depth was 60 percent by ultrasonic grinding. The critical ductile grinding depth increased to 25μm. Analyzed by means of SEM, it was transgranular cracking during its cracking process. The nano-ZrO2 ceramics have high toughness so the critical ductile grinding depth increased. The shape, length, width and thickness of the grindings differed greatly from which obtained by conventional grinding.

Abstract: Surface plastic deformation form and residual stress distribution of nano-ceramics machined by ordinary grinding and two-dimensional ultrasonic grinding respectively were investigated. The obtained results show that machined surface residual stress in the two grinding modes is extrusion stress, and it decreased with the increasing of grinding depth. But the decrease of residual stress under two-dimensional ultrasonic grinding is less than that under normal grinding. In addition, under the same grinding parameters, the surface residual stress on two-dimensional ultrasonic vibration grinding is larger than that on ordinary grinding, and if other parameters unchanged, it is increased with the increase of wear particle granularity in the two grinding modes. It is produced by the reason that ductile regime of ceramic grinding become larger under ultrasonic grinding, so that material is still removed by plastic form at great depth. Plastic removal mode will produce greater surface extrusion stress, so with the increasing of grinding depth, the decreasing of residual stress under two-dimensional ultrasonic vibration grinding is less than that under the normal grinding. At the same time, the regular separating between wear particle and work piece improves the heat emission condition, which is also one of the reasons that the surface residual stress under two-dimensional ultrasonic grinding is larger than that under ordinary grinding.