Dongliang Jiang

Preparation of silicon carbide reticulated porous ceramics

Commercial polyurethane sponges with cell size of ≈11 pores per inch were chosen to produce SiC-based reticulated porous ceramic (RPC) by the replication process. The dispersion of mixed powders (SiC, Al2O3, bentonite) in aqueous media using silica sol as a binder was studied by zeta potential and viscosity/rheological measurements. The pH value of the optimum dispersion was found to be around pH 10 for the mixtures. The optimum condition of the slurry suitable for impregnating the polymeric sponge was obtained. Effects of coating parameters including the separation between the rollers and the number of passes on the coating quality and macrostructure of RPCs were studied in detail. Flexural strength data of the sintered bodies were compared to a theoretical model. A statistical evaluation was carried out on the flexural strength data of the sintered bodies using Weibull statistics.

Controlled fabrication of silver nanoneedles array for SERS and their application in rapid detection of narcotics

Novel surface-enhanced Raman scattering (SERS) substrates with high SERS-activity are ideal for novel SERS sensors, detectors to detect illicitly sold narcotics and explosives. The key to the wider application of SERS technique is to develop plasmon resonant structure with novel geometries to enhance Raman signals and to control the periodic ordering of these structures over a large area to obtain reproducible Raman enhancement. In this work, a simple Ar(+)-ion sputtering route has been developed to fabricate silver nanoneedles arrays on silicon substrates for SERS-active substrates to detect trace-level illicitly sold narcotics. These silver nanoneedles possess a very sharp apex with an apex diameter of 15 nm and an apex angle of 20°. The SERS enhancement factor of greater than 10(10) was reproducibly achieved by the well-aligned nanoneedles arrays. Furthermore, ketamine hydrochloride molecules, one kind of illicitly sold narcotics, can be detected down to 27 ppb by using our SERS substrate within 3 s, indicating the sensitivity of our SERS substrates for trace amounts of narcotics and that SERS technology can become an important analytical technique in forensic laboratories because it can provide a rapid and nondestructive method for trace detection.

Characterization of nearly stoichiometric SiC ceramic fibres

A comparative study of the chemical composition and microstructure of Hi-Nicalon, Hi-Nicalon type S, Tyranno SA, Sylramic and Carborundum fibres has been conducted. This analysis has confirmed results already published but has also evidenced some original features. The Hi-Nicalon type S fibre has a near stoichiometric composition but it still contains some oxygen (≈1 at. %) and free carbon (≈2 at. %). The expected near stoichiometric composition of both the Tyranno SA and the Sylramic fibres is only effective near the edge region, while the core of the fibres contains some amount of free carbon (e.g., up to ≈14 at. % and ≈6 at. % respectively in large diameter fibres) as well as some residual oxygen (≈0.5 at. %). The composition of the Carborundum fibre is very close to stoichiometric SiC except rare and localised free carbon or B4C inclusions. The properties of the different fibres, some of them still beeing at a development stage, are discussed from a chemical and a phase composition point of view, on the basis of what is known about their respective preparation process.

Microstructure and mechanical properties of in situ produced Ti5Si3/TiC nanocomposites

Abstract The microstructure and mechanical properties of in situ produced Ti 5 Si 3 /TiC nanocomposites have been studied. Ti 5 Si 3 /TiC composites have been prepared by reaction hot pressing mixed powders of elemental Ti, Si and SiC. XRD, SEM, TEM were employed to characterize the structure of the composites. When no elemental Si is added, the resulting composite contains 65 vol.% Ti 5 Si 3 , with a small amount of carbon dissolved in it. The majority of the TiC particles are nanosized. A small fraction Ti 3 SiC 2 grains, with an average size 100 nm, are located in the TiC particles while other elongated Ti 3 SiC 2 grains in the Ti 5 Si 3 matrix. The highest bending strength of the Ti 5 Si 3 /TiC composites is 510 MPa at room temperature, which is approximately 6 times that of the monolithic Ti 5 Si 3 material. The fracture toughness of the composites exceeds that of pure Ti 5 Si 3 , and at 1100°C, the yield strength of Ti 5 Si 3 /35TiC reaches 800 MPa.

Preparation of porous carbon derived from mixtures of furfuryl resin and glycol with controlled pore size distribution

This paper describes the preparation and properties of porous carbon by a technique which consists of mixing a carbon precursor (furfuryl resin and furfural alcohol), a pore-forming agent and a solvent (glycol), polymerizing the resin mixture, and pyrolyzing the hybrid of resin and glycol. The properties of porous carbons have been systematically investigated as a function of composition and heat treatment, with emphasis on understanding and controlling their morphology and pore size distribution. The results seem to indicate that by varying the ratios of the constituents in the polymer system, porous carbons with a wide variation in pore size distribution and morphology can be obtained. Three types of morphologies were observed: interconnected carbon with secondary spherical pores, discrete carbon particulates, and a crosslinked carbon network. Porous carbons with a very narrow pore size distribution have been obtained and the average pore size was controlled between 5 and 0.008 μm. The microstructure of porous carbon formed as a result of phase separation of resin-rich phase and glycol-rich phase, rather than a result of the pyrolysis process. Heat treatment had little effect on the properties of the porous carbons.

The control of slurry rheology in the processing of reticulated porous ceramics

In this work commercial polyurethane sponges with open porosity of approximately 13 pores per inch were chosen as the templates to produce the SiC RPCs. Effects of the rheological behavior of the slurry on the coating quality and the properties of SiC RPCs such as strength, density, microstructure, were investigated in detail. The coating quality was found to depend strongly on the slurry viscosity and this was improved dramatically extremely as the viscosity increased. The SiC RPCs displayed a remarkable increase in the flexural strength as the solids content increased. In addition, the increase of the polymer content had also a little contribution to the improvement of the strength The optimum solids content and polymer content were found to be 80 and 0.20 wt.%. This study shows that the control of slurry rheology is very important for the processing of RPCs.

Effect of polyvinyl alcohol additive on the pore structure and morphology of the freeze-cast hydroxyapatite ceramics

Porous hydroxyapatite (HAP) ceramics with different morphologies were fabricated by the freeze casting method. The morphologies of HAP ceramics were modified by adjusting the concentration of polyvinyl alcohol (PVA) additive in the HAP slurries. HAP ceramics without PVA additive were composed of non-interconnected macroscopic lamellar pores and porous ceramic walls. With PVA additive, the HAP ceramics were made up of small lamellar pores or three-dimensional reticulate pores and porous ceramic walls. PVA additive had no effect on the phase composition of HAP ceramics. The open porosity and pore connectivity were improved because of the addition of PVA.

Tuning the phase and morphology of In2O3 nanocrystals via simple solution routes

By decomposing In(OH)3 under different reaction conditions, In2O3 nanocrystals with controllable phases and morphologies were synthesized. Metastable hexagonal In2O3 nanocrystals were obtained by an alcoholysis process in ethanol, and followed by decomposition in air. The well-defined cubic In2O3 nanocubes can be fabricated by treating In(OH)3 in methanol at 250??C for 25?h, whereas the replacement of the solvent by ethanol yields nanorods. The results indicated that the solvent, dopants, pressure, and reaction temperature are responsible for the variations of phases and morphologies. In addition, the photoluminescence properties of the products are strongly dependent on their phases, crystallinity, and morphologies.

Improvement in the strength of reticulated porous ceramics by vacuum degassing

SiC reticulated porous ceramics (RPCs) were fabricated from ceramic slurries by the replication process with polyurethane sponges as the templates. Vacuum degassing was adopted to remove air bubbles in the slurry. Effect of degassing on the rheological behavior of the slurry and the properties of RPCs was investigated. The slurry showed a slight increase in viscosity after degassing, which improved the loading of the slurry on the sponge. The large defects in the struts were significantly reduced by degassing, which was confirmed by scanning electron microscopy (SEM) observation and Hg porosimetry. Flexural strength of RPCs increases from 2.34 to 3.18 MPa after degassing. The results were discussed in terms of an available theoretical model on the mechanical behavior of open cell ceramics.

Synthesis of Dental Enamel-like Hydroxyapaptite through Solution Mediated Solid-State Conversion

An ordered dental enamel-like structure of hydroxyapatite (HAp) was achieved through a solution mediated solid-state conversion process with organic phosphate surfactant and gelatin as the mediating agent. Transmission electron microscopy (TEM) tests demonstrated uniform sizes in the obtained apatite nanorods which arranged in parallel to each other along the c-axis and formed organized microarchitectural units over 10 microm in size. The sizes of the synthetic hydroxyapatite nanorods were similar to that observed in enamel from human teeth. The formation and regulation of the orientation and size of HAp nanorods might lead to a better understanding of the biomineralization process for the preparation of high performance biomaterials.