Formulation of a ceramic ink for a wide-array drop-on-demand ink-jet printer

This paper describes the methodology for simulating a reprographic ink with a ceramic ink based on a commercially available zirconia powder for direct ceramic ink-jet printing. Of over-riding importance was matching viscosity and this was tested systematically by using a mineral oil–hexane binary system. Of secondary importance was adjustment of the pressure defect behind the nozzle to compensate for small differences in surface tension. The inks tested in the wide array print-head were based on low electrical conductivity liquids to avoid damage to the electroding system. The organic binder for the zirconia ink was paraffin wax and the dispersant was a hydroxystearic acid based polyester.     

Direct Ink-Jet Printing of Vertical Walls

Direct jet printing can assemble ceramic powder into a three dimensional shape by firing droplets of ink through a nozzle to build a multiple layered structure. As with stereolithography and selective laser sintering, the surface texture is expected to witness the layered assembly. The ability to create vertical walls by direct ink-jet printing was explored using a test piece based on a maze. The structure and topography are discussed in terms of droplet spreading and drying.     

Modelling the removal of organic vehicle from ceramic or metal mouldings: The effect of gas permeation on the incidence of defects

A shrinking undegraded core and a porous outer layer result, if the organic vehicle used for shaping ceramic or metal powder mouldings recedes in the interparticle space of the moulded body during pyrolysis. In the present work, a numerical model has been used which simulates the undegraded shrinking core situation and quantifies degradation of the organic vehicle and the diffusion of the resulting products in solution in the organic phase during pyrolysis of a ceramic moulding. This model is extended to include gaseous mass transport in the porous outer layer for a moulding in the shape of an infinite cylinder. The effect of resistance to gaseous mass transport in the porous outer region on defects originating in inner regions was estimated. It is shown that the greatest obstruction to mass transport is diffusion of degradation products in solution in the organic phase. However, the permeability coefficient for gas transport in the outer region begins to affect the critical heating rate required for avoidance of defects only when it is less than 10^–15m².Nomenclature C Concentration,C=C (r, t), based on the total volume of ceramic suspension - d Effective molecular diameter of alphamethylstyrene - D Diffusion coefficient,D=D (C, T) - e Porosity of powder - E Activation energy for thermal degradation - h Remaining weight fraction of polymer - H_vap Enthalphy of vaporization - i Node number - I Pre-exponential constant in Equation 13 - j Time step - K _p Permeability coefficient - K ₀ Specific rate constant - m Mass of monomer displaced - M Mass of one alphamethylstyrene molecule - P Monomer vapour pressure - P _s Monomer vapour pressure at outer surface of the cylinder - P ₁ ⁰ Vapour pressure of monomer over its pure liquid - Q Rate of production of monomer, based on the total volume of ceramic suspension - r Radius of the cylinder - r _j Distance from central axis to the inner surface of the porous layer at time stepj - r ₀ Initial radius of the cylinder - R Universal gas constant - S ₀ Specific surface area of powder per unit solid volume - t Time - T Absolute temperature - T _c Temperature at maximum vapour pressure of monomer and atZ _c - V Volume of monomer - V _c Ceramic volume fraction - V _p Polymer volume fraction - w Mass of monomer stored in the porous annulus - Z Heating rate - Z _c Critical heating rate - ₁ Volume fraction of monomer in the polymer-monomer solution - Viscosity of the monomer vapour - _p Density of the polymer - Polymer-monomer interaction constant     

Effect of operating conditions and liquid physical properties on the size of monodisperse microbubbles produced in a capillary embedded T-junction device

The aim of this study was to investigate the effect of operating parameters such as liquid flow rate, gas inlet pressure, and capillary diameter as well as the influence of the physical properties of the liquid, in particular viscosity, on the generation of monodisperse microbubbles in a circular cross section T-junction device. Aqueous glycerol solutions with viscosities ranging from 1- to 100 mPa s were used in the experiments. The bubble diameter generated was studied for systematically varied combinations of gas inlet pressure, liquid flow rate, and liquid viscosity with a fixed capillary inner diameter of 150 μm for the liquid and gas inlet channels as well as the outlet channel. In addition, the effect of channel geometry on bubble size was studied using capillaries with inner diameters of first 100 and then 200 μm. In all the experiments the distance between the coaxial capillaries at the junction was set to be 200 μm. All the microbubbles produced in this study were highly monodisperse (polydispersity index <1 %) and it was found, as expected, that bubble formation and size were influenced by the ratio of liquid to gas flow rate, capillary size, and liquid viscosity. The experimental data were then compared with empirical scaling laws derived for rectangular cross-section junctions. In contrast with these previous studies, which have found bubble size to be dependent on either the flow rate ratio (the squeezing regime) or capillary number (the dripping regime), in this experimental study bubble size was found to depend on both capillary number and flow ratio.     

Synthesis of silicon oxynitride from a polymeric precursor

Proton nuclear magnetic resonance (¹H NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and gas chromatography (GC) have been used to study the products of ammonolysis of dichloromethylsilane in diethyl ether at 0 °C. Results indicate that the major products are trimethylcyclotrisilazane and tetramethylcyclotetrasilazane. Hydrolysis of the cyclosilazanes has also been qualitatively investigated. A simple and useful method for the identification of cyclosilazanes has been developed using the ¹H NMR technique.     

Development of temperature-heating rate diagrams for the pyrolytic removal of binder used for powder injection moulding

A polypropylene-based binder system was used to injection mould test bars containing 65 vol% aluminium powder. Specimens, 3 and 6 mm thick, made from these bars were used for pyrolytic binder removal experiments in static air and nitrogen. The development of a carefully defined experimental procedure for the determination of the heating rate at which binder removal can be carried out at a given temperature without the creation of macro defects is fully described. The use of isothermal heat treatments during pyrolysis are also considered and results are presented as temperature-heating rate diagrams for each atmosphere and thickness investigated. These diagrams show a lower and an upper boundary. Defect formation occurs if the temperature-heating rate relationship lies between the boundaries. Near optimum binder removal schedules deduced from each diagram have been experimentally verified.     

Novel electrohydrodynamic preparation of porous chitosan particles for drug delivery

Uniform spherical chitosan particles of size <10 μm in diameter are important in drug delivery applications due to their excellent biocompability and biodegradability. A high concentration of chitosan in the particles can help to control the release of drugs and methods for processing high viscosity chitosan solutions are therefore required. In principle, any type of polymer, whether hydrophobic or hydrophilic, can be electrosprayed to obtain monodisperse particles of diameter <10 μm. In practice, however, electrospraying of biopolymers having viscosities of >100 mPa s results in particles >10 μm diameter. In this study, by reducing surface tension of a high viscosity chitosan suspension, it was found that smaller diameter particles could be prepared. Chitosan solutions were electrosprayed in the stable cone-jet mode to systematically study the relationship between particle diameter, viscosity and surface tension. Increasing viscosity resulted in larger diameter particles with a broad size distribution, but decreasing surface tension had the opposite effect. Results show that a chitosan solution having a viscosity of ~80 mPa s can be used to prepare chitosan particles of diameter ~2.5 μm which on drying reduced to particles of 500 nm.     

Gas Transport Parameters for Compacted Reddish-Brown Soil in Sri Lankan Landfill Final Cover

Gas exchange through the compacted final cover soil at landfill sites plays a vital role for emission, fate, and transport of toxic landfill gases. This study involved measuring the soil-gas diffusivity (Dp/Do, the ratio of gas diffusion coefficients in soil and free air) and air permeability (ka) for differently compacted soil samples (reddish-brown soil) from the final cover at the Maharagama landfill in Sri Lanka. The samples were prepared by either standard Proctor compaction or hand compaction to dry bulk densities of 1.60–1.94??g?cm-3. Existing and modified models for predicting Dp/Do and ka were tested against the measured data. The simple, single-parameter Buckingham model predicted measured Dp/Do values across compaction levels equally well or better than a dry bulk density (DBD) dependent model and a soil-water retention (SWR) dependent model. The measured ka values for differently compacted samples were highly affected by the compaction level and the sample moisture preparation method. Also, for air permeability, a single-parameter Buckingham-type ka model was most accurate in predicting ka in the differently compacted soil samples. Equivalent air-filled pore diameters (the effective diameter of the drained pores active in leading air through the sample) for gas flow, deq, were calculated from the measured Dp/D0 and ka values. The deq increased with compaction level, suggesting that a very high compaction level creates well-connected macropores in the reduced total pore space of the cover soil. This is an important consideration when designing cover soils for optimally low water and high oxygen exchange while minimizing climate and toxic gas emissions from the waste layer to the atmosphere.     

Selection of a powder for ceramic injection moulding

Ceramic suspensions were prepared from six alumina powders using the same high molecular weight organic vehicle. 18 mm diameter cylinders were compression moulded from four of these suspensions which were suitable for ceramic injection moulding. The organic vehicle in each cylinder was removed by thermal degradation according to the same temperature ramp. The defects present in the cylinders after removal of the organic vehicle are discussed in terms of the powder characteristics. Criteria for the selection of ceramic powders that could be used together with a high molecular weight organic vehicle for this shape-forming method, are deduced from the results obtained.     

Microfluorometric detection of catecholamines with multiphoton-excited fluorescence

We demonstrate sensitive spatially resolved detection of physiological chromophores that emit in the ultraviolet (<330 nm). An atypical laser source (a visible wavelength femtosecond optical parametric oscillator), and an unconventional collection geometry (a lensless detector that detects the forward-emitted fluorescence) enable this detection. We report the excitation spectra of the catecholamines dopamine and norepinephrine, together with near-UV emitters serotonin and tryptophan, in the range of 550-595 nm. We estimate the molecular two-photon action cross section of dopamine, norepinephrine, and serotonin to be 1.2 mGM (1 GM, or Goppert Mayor, is equal to 10(-58) m4 s(-1) photon(-1)), 2 mGM, and 43 mGM, respectively, at 560 nm. The sensitivity achieved by this method holds promise for the microscopic imaging of vesicular catecholamines in live cells.