Papers by Keyword: Nanoceramic

Abstract: A high throughput combinatorial robot RAMSI (Rapid Automated Materials Synthesis Instrument) has been developed for nanoceramics synthesis. It can rapidly produce nanoparticle libraries that can be used for new materials discovery. The RAMSI robot has 3 motor-driven axes moving in X-Y-Z space and linking the synthesis, cleanup and printing sections. A High Throughput Continuous Hydrothermal (HiTCH) flow synthesis reactor is contained within RAMSI, and reaches significant production capability of 48 tubes of 50mL samples in 8 hours. Supported by the high throughput hardware design, the control system adopts parallel operations and multi-task assignments. Key strategies include intelligent supernatant detection, dot printing protocols and robot arm route schedule etc. The commissioning of RAMSI showed its high efficiency by producing samples of yttrium hydroxide doped with europium. In a 6-hour experiment, 8 unique 100mL samples were synthesized then cleaned and printed into 96 dots (100 minutes only for synthesis time). The ceramic dots were heat-treated at different temperatures up to 1200°C and affixed into a well-plate library. The brightest phosphors could be readily identified by illumination under UV light.

Abstract: The microwave heating allows sintering in a very short time which is useful to keep the materials nanostructure. Up to now the trial error method is commonly used to find the best experimental parameters. This method is time consuming and does not allow getting a high reliability. In this work, a specific optical based position sensing device has been used to record the shrinkage during hybrid microwave sintering. Owing to this particular device, the control of the nano-sized ZnO based powder sintering has been successfully achieved. Very fine microstructures were obtained and electrical properties of those nano-ceramics were determined.

Abstract: Y3Al5O12:Nd3+ nanoceramics were obtained by sintering nanocrystalline Y3Al5O12:Nd3+ powders at 450 oC under different pressures between 2 and 8 GPa. The structural purity, residual stress, strain, texture, and crystallite size of the products were analysed with X-ray powder diffraction. The results indicate that the average crystallite size remains unchanged at about 30 nm in spite of the heating and the pressure applied. No texture was observed. On the other hand, the microstrains increase with increasing pressure, while the residual stresses are at their maximum in the green body and the sample processed at 8 GPa. Increasing strains were observed to increase the width of the luminescence lines and to decrease the luminescence decay times.

Abstract: Nano-ceramics possessed ascendant mechanical property and physical characteristics contrast with traditional engineering ceramics, and its machining with ultrasonic assistance has been considered one of the most efficient methods. In the present paper a novel ultrasonic grinding vibration device has been developed and the theoretical model of grinding force has been created for ultrasonic vibration grinding. The influences of grinding parameters on grinding forces were tested with self-designd acoustic system based on local resonance. According to the test data, the effect of depth of cut and wheel velocity on the grinding force with/without ultrasonic assistance was analyzed. Both in common and ultrasonic grinding the normal grinding force and tangential grinding force descend against the wheel velocity, while ascend along with the depth of cut. In any case the grinding force in ultrasonic grinding was not more that that in common grinding.

Abstract: Several kinds of ceramic powders including SiC, TiO2 and Al2O3 were selected as fillers blending with epoxy resin, curing agent and other additives to prepare a heavy-duty and anti-wear coating. The effects of filler sort, powder size, dispersion homogeneity on the coating properties were investigated. The results showed that the wear resistance and corrosion resistance of the coating could be improved significantly after meliorating the dispersion of the ceramic particles in epoxy resin. Other mechanical properties were also studied in order to support the view on the positive effect of the nano-particles in the epoxy coating.

Abstract: The effect of nanocrystalization on superplastic flow was examined in ZrO2-30vol%spinel composite. The nanocrystalization can increase the strain rate by one order of magnitude or lower the deforming temperature by about 100 K. Irrespective of the lowered flow stress, however, the tensile elongation to failure of nanocrystalline composite is lower than that of submicrom-grain composite. The limited tensile elongation in nanocrystalline composite can be ascribed mainly to accelerating cavity damage accumulation.

Abstract: Research in nitrides and oxynitrides has experienced a significant downturn during the last 10 years – perhaps because there have been fewer new developments in the R. & D. field compared with the regular new initiatives reported in the 1980s and early 1990s, but also because the public perception is now very much that research issues associated with commercial nitride materials have been “worked out”. With the limited market (both in volume and price) for structural materials, funding bodies are tending to direct their resources into other research areas where it is perceived there are more opportunities and a larger market place. lnfluenced by these trends, new researchers at the start of their careers are tending to focus their research on other areas of ceramics or materials science, rather than striving to find new developments in what may be seen as a “worked-out” subject area. This is not to say that there is not still a considerable amount of research that can be done in the nitrides/oxynitrides field, but radical new ideas are needed, focused on topical and appreciably-sized market applications, in which the portfolio of properties offered by oxynitrides demonstrates clear advantages over cheaper and more easily prepared alternatives.

Abstract: Al2O3 particle dispersed 3Y-TZP nanoceramics doped with TiO2 was fabricated by the vacuum reduction of Ti(OH)4, Al(NO3)3 and 3Y-TZ powders at 873K for 2h and sintered in air at 1573K~1823K for 2-6h. The relation between Al2O3 and TiO2 content, sintering parameters, relative density and grain sizes were studied. Microstructural investigations revealed that, in comparison with direct powder mixing, the reduction method is more efficient in achieving a homogeneous dispersed fine alumina second phase, which results in the reduction of matrix grain size and the increase of the relative density of the 3Y-TZP ceramic. TiO2 addition facilitates the sintering process but may cause significant abnormal grain growth which can be offset by the homogeneity of the powder dispersion. A final 3Y-TZP-TiO2 ceramic matrix with grain size below 500nm dispersed with ultrafine second phase Al2O3 was obtained.

Abstract: In previous report, we succeeded in preparing dense nano-sized ceramics with the composition of Y- α-sialon (m=1.35, n=0.675) by high-energy mechanical milling followed by spark plasma sintering. The superplastic deformation of the obtained nano-ceramics was studied in this report. A good ductility of the nano-sized ceramics has been confirmed, which arised from the nano-sized grains and large amount of transient liquid phase. The effects of deformation on the phase and microstructural evolution were also studied. The nano-sized grains promoted the formation of elongated α-sialon grains during post-annealing at 1850oC for 3 h, which would strengthen and toughen the deformed ceramics.

Abstract: Fine grained and dense dielectric ceramics of the BaO-Nd2O3-TiO2 system have been fabricated by the most advanced Spark Plasma Sintering (SPS) technology, whose average grain size is about 100nm as determined by SEM. XRD showed that the diffractive peak of the sample was broadened clearly. The nano-ceramic microstructure formed by SPS is due to the high pressure up to 50 MPa, low temperature (1000°C) and fast sintering (1 minute). The BaO-Nd2O3-TiO2 ternary nanoceramic sample, which consists of the main phase Nd2Ti2O7 with perovskite-like layer structure (PLS) and the secondary phase BaNd2Ti4O12（Ba4.5Nd9Ti18O54）with perovskite-like tungsten bronze structure, was prepared for the first time by rapidly sintering nano-particles of the xBaO×(0.35-x)Nd2O3×0.65TiO2 compound. Those two phases are formed in BaO-Nd2O3-TiO2 micron-grained ceramics prepared by normal sintering of the nano-particles at 1300°C, resulting in good dielectric characteristics for microwave ceramics; however, dielectric characteristics are significantly degraded in the SPS-sintered samples probably due to the carbon contamination from the graphite SPS dies.