Papers by Keyword: Nanoceramic

Abstract: The aim of this study was to optimize sintering aids and processing parameters for zirconia toughened alumina (ZTA) nano-ceramics with optimal properties as dental ceramics. Additive agents (TiO2, MgO, SiO2), dry pressing forces and sintering temperatures are very important for preparation of structural ceramics. In the present study, density and Vickers hardness measurement, SEM, and XRD analysis were employed to investigate the effects of these on the final products. The relevant results showed that higher pressing force led to an increase in the density and Vickers hardness of the sintered ceramics. Among the four groups of sintered nanoceramics with different ratios of alumina and zirconia, and combinations of additive agents, the best densification was achieved in the sample from Group 2# containing 1.05wt% MgO after sintered at 1450°C, as indicated by SEM observation. XRD analysis confirmed the formation of MgAl2O4 as an intermediate compound. The existence of TiO2 in the additive agents was in favor of the acquisition of high densification. The measured values for the density and Vickers hardness indicated that the sintered ZTA nano-ceramics would be a potential material for dental prosthetic applications.

Abstract: Nanostructured ceramic bulk materials were achieved from nano-Al2O3 ceramic powders via direct selective laser sintering (SLS). SLS as a non-traditional machining technology of Rapid Prototyping was introduced and compared with other ceramic forming technologies. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied to analyze the microstructure of the ceramic bulk materials. These results demonstrated that the nano-Al2O3 ceramic powders can be sintered into bulk materials maintained nanostructure with some technological parameters. It was found that the nanostructured ceramic bulk exhibited unique microstructure and was free formed rapidly by this sintering technology.

Abstract: The main semiconductor oxides for gas sensing have been examined, describing the synthesis processes and the morphological and structural properties. The powders have been deposited as thick films through screen-printing technique to achieve gas sensors. The sensing layers have been studied with regard to semiconductor behaviour, surface barrier potential heights and gas sensing properties. The interaction of humidity with semiconductor oxides has been considered with the aim to compensate, using an algorithm, its effect in gas detection. Finally, nitrogen oxides monitoring, contemporaneously performed in several sites of Italy, has been described.

Abstract: The fracture strength σf of ZrO2-based ceramics tends to increase with decreasing grain size d. As compared with the data for submicrometer-grain-sized material with d ≈ 350 nm, nano-crystallization of ZrO2 ceramics less than d ≈ 90 nm can improve σf by a factor of 2.0-2.5. The maximum strength reaches σf ≈ 2500 MPa, which is classed as the highest σf of oxide ceramic materials. The high σf can be associated with an increase in the critical t →m transformation stress and a decrease in the flaw size due to nano-crystallization.

Abstract: We were quite successful in demonstrating that two-dimensional inorganic compounds like anionic and cationic clays can be used as gene or drug delivery carriers, those which are completely different from conventional ones such as viral-based, naked, and cationic liposomes, those which are limited in certain cases of applications due to their toxicity, immunogenecity, poor integration, and etc. Since LDHs with positive layer charge have an anion exchange capacity, functional biomolecules with a negative charge can be intercalated into hydroxide layers of LDH by a simple ion-exchange reaction to form a bio-LDH nanohybrid. On the contrary, clays can uptake biofuctional molecules or drugs with positive charge in the interlayer space by cation exchange reaction. The possible roles of inorganic lattice as the gene and drug delivery carrier will be shown by demonstrating the cellular uptake experiments of FITC-LDH, with laser scanning confocal fluorescence microscopy as well as of radioactive isotope-labeled ATP-LDH hybrid. As the typical examples for gene and drug delivery systems, As-myc-LDH, MTX-LDH, and Itraconazol-clay nanohybrids will be demonstrated in detail.

Abstract: β-SiAlON nanoceramics were fabricated from β-SiAlON nano powder using the spark-plasma sintering (SPS) technique. The β-SiAlON nanopowder (Si4Al2O2N6) was synthesized from a mixture of SiO2 (QS-102, Tokuyama Co., Japan), AlOOH (Tomita, Japan) and C (Mitsubishi Chemical, Japan) using the carbothermal reduction nitridation (CRN) method. The heating rate for SPS was 50
/min. The β-SiAlON nanoceramics had high strength (500 MPa). TEM observation showed that the intergranular glassy phase was scarcely present at the grain boundary of the β-SiAlON nanoceramics. Aqueous corrosion resistance was evaluated by measuring the weight loss after soaking in 5 and 35 wt.% H2SO4aq. and 5 wt.% HNO3aq. at 80
for 100 h. It was found that β-SiAlON nanoceramics have much higher corrosion resistance than commercialized silicon nitride ceramics in acid solutions. Commercialized Si3N4 ceramics have an intergranular glassy phase created as a result of the sintering aids in them. Thus, they are easily corroded by acid solutions because the intergranular glassy phase is easily corroded under such conditions. The excellent corrosion resistance of the β-SiAlON nanoceramics stems from their glass-free grain boundaries, since the β-SiAlON nanoceramics were produced without using a sintering aid.

Abstract: According to the composition of nano ceramics, the paper firstly analyses mechanism of^nano ceramics materials surface machining in ultra precision grinding processes and gives a new critical grinding depth formulation. Then many grinding experiments have been done between the nano ceramics and the common ceramics in the same grinding parameters and grinding methods. Atomic force microscopy (AFM) images show that nano ceramics have outstanding machining performance. Its grinding processes is plastic material cutting like metal cutting, and nicks are clear and brittleness desquamated pits existing in common ceramics grinding surface have not found in nano ceramics grinding surface. Then, according to analyze microcosmic surface quality by AFM, the conclusion is that the nano ceramics surface quality is better than the common ceramics after grinding processes. Concretely, its surface roughness Ra tower above one or two degree than the common ceramics, and there is no crackle, no nick, and no obvious cutting defect. The research results provide experimental and theoretical guides for selection of grinding parameters and grinding methods.

Abstract: On the basis of analyzing the brittleness, ductileity, and the removal mechanisms of the^nano-ZrO2 Ceramics, the critical ductile grinding depth formula of the nano-ceramics was established. Due to superductileity of the nano-ZrO2 ceramics, it couldn’t apply the formula of the common engineering ceramic material according to experimental results. The value of material coefficient ζ has relations with not only the material characteristics but also the processing methods and the processing parameters. It was proved that ζ has great effects on the accuracy of theoretical calculation. Experimental results showed that the critical ductility grinding depth of the nano-ZrO2 ceramics is up to 12 µm in common grinding methods, while in ultrasonic grinding is up to 20µm. The grinding chips with and without ultrasonic vibration assistance were discussed.

Abstract: The preparation of transparent nanoceramics from nanocrystalline Y3Al5O12 (YAG) powders doped with rare-earth ions has been described and the results of investigation of the structure and morphology have been presented. Decomposition of YAG nanocrystals into YAlO3 (YAP) was observed. The temperature and pressure for the decomposition was much lower than that reported for larger crystals. The transformation was connected with grain coarsening. The influence of the method of preparation of the YAG nanopowders on the final transparency of the nanoceramic produced was determined. Preliminary results of the dependence of luminescence properties on the structural transformation of the nanograins are presented.