Powder Slurry Research Articles

Sporicidal Kinetics of Bacillus subtilis Spores by Heated Scallop Shell Powder

Scallop shell powder heated at 1,000°C for 1 h exhibited sporicidal action against Bacillus subtilis spores. The sporicidal kinetics of this action were analyzed with the use of a nonlogarithmic model. Apparent death rate constants (k) were obtained under various conditions. The value of k increased with powder concentration but became constant beyond the concentration representing the solubility of Ca(OH)2. A linear inverse relationship between k and temperature was found, and from this relationship the activation energy required for the death of B. subtilis spores in the heated shell powder slurry could be determined.

Improved Model of Wafer/Pad Powder Slurry for CMP

Chemical mechanical polishing (CMP) is a key technique for wafer global planarization. Increasing demands for high uniformity and dimensional precision make previously discountable levels of asperity and particle effects significant. However, particle size and pad asperity have not been considered simultaneously in previous literature. This study presents a grain flow model which applies the average lubrication equation with partial hydrodynamic lubrication theory, thereby analyzing slurry flow between wafer and pad and taking into account both grain flow and roughness effects. This model predicts slurry flow film thickness with various convex wafer curvature radii under a variety of the CMP parameters, including applied load, rotation speed, dome height, particle size, and pad roughness. Furthermore, the influence of particle size and pad asperity on removal rate is investigated. The results compare well with experimental data in the literature. © 2003 The Electrochemical Society. All rights reserved.

Low-density open-cell foams in the NiTi system

It is shown that open-cell metallic foams having very low density, and that display martensite transformations required for shape memory and superelastic behavior, can be fabricated using a powder-metallurgy technique. Results are presented on experiments in which a polymeric precursor foam was coated with an equiatomic NiTi powder slurry and subsequently sintered to yield foams with relative densities as low as 0.039. Although contaminated with interstitial impurities, they displayed unambiguous calorimetric signature of the B2→B19′ transformation. The results are of considerable significance to potential applications requiring ultralightweight structures with the unusual dissipative and strain-recovery properties of NiTi shape-memory materials.

Kinetic Analysis of the Bactericidal Action of Magnesium Oxide Powder Slurry against Escherichia coli

The death of Escherichia coil in magnesium oxide (MgO) powder slurry was found to follow first-order reaction kinetics. The value of the apparent death rate constant (k) increased with the powder slurry concentration and the slurry temperature. The bactericidal action of the MgO powder slurry was greater than that of a NaOH solution of an identical pH. E. coil grown at lower temperatures (TG) became more sensitive to MgO. The Arrhenius plots of k for E. coil grown at 27, 37 and 45°C exhibited discontinuous points (Td) at approximately 13, 21 and 29°C, respectively, and the differences, TG-Td, were observed to be almost constant (14-16°C)

Evolution of Porosity by Freeze Casting and Sintering of Sol-Gel Derived Ceramics

Freeze cast of aqueous ceramic powder slurries is described as a versatile process to fabricate complex-shaped ceramic parts. Since freezing of aqueous sols or powder suspensions include the nucleation and growth of ice crystals the evolving microstructure in particular the pore characteristics which are left behind after elimination of the solvent can be controlled by the freezing process. The freezing kinetics have then to be used to manifest the conditions for the formation of the intended porosity. The temperature profile in the freezing slurry was measured and calculated, in particular the movement of the freezing front through the slurry was determined. The results show that a homogeneous microstructure is reached in the surface region of the consolidated part. Individual ice crystals are detected within a distance of some hundred micrometers from the surface. The final pores are dendritic in shape with an elliptical cross section. The pores can grow up to several millimeters in length under the process conditions used in this study. The limits of freeze-sensitive slurry compositions should be investigated in further studies and the approach should be followed to increase the porosity by additional foaming steps.

Experimental simulation of integrated optoelectronic sensors based on III nitrides

Reliable, miniature, multifunctional, real-time optoelectronic sensors can be fabricated by using III nitride materials that have several advantages over the conventional semiconductors. Recent advances in these materials allow integrated optoelectronic devices with tunable spectral characteristics. In addition, optically transparent sapphire substrates and commercially beneficial silicon wafers can be used for the device fabrication. Two concepts of the integrated optoelectronic sensor development are presented in this work. These concepts were investigated by fabrication and testing simulators based on III nitride and Si commercial components. The fabricated devices exhibit multifunctionality expressed by the ability to perform measurements of optical absorption (metallic salts solutions), reflection (interface with commonly used solvents), scattering (alumina powder slurries), and fluorescence (chlorophyll, fluorescein, pyrene, anthracene, and Escherichia coli strains carrying plasmids which encode fluorescent proteins). These measurements indicate the applicability of the III nitride and Si-based components and their layout according to the described concepts for the development of integrated multifunctional optoelectronic sensors.

Metals distribution and investigation of L'vov platform surface using principal component analysis, multi-way principal component analysis, micro synchrotron radiation X-ray fluorescence spectrometry and scanning electron microscopy after the determination of Al in a milk slurry sample

This work describes the use of different strategies/techniques, such as scanning electron microscopy (SEM), multivariate analysis (principal component analysis (PCA) and multi-way PCA) and micro synchrotron radiation X-ray fluorescence (μSRXRF), in order to extract information about platform morphology, metals distribution on its surface, and the performance of conventional and permanent modifiers after slurry analyses using electrothermal atomic absorption spectrometry (ET AAS). With multivariate analysis it was possible to select Zr (500 μg for each 50 heating cycles) as a permanent chemical modifier for the determination of Al in milk powder slurry samples. Employing multi-way PCA and SEM, it was possible to note the differences in morphology between platforms permanently treated with Zr and those conventionally treated with Mg(NO 3) 2. The use of PCA and SEM also allowed finding similarities between new platforms, and those with and without Zr treatment. Using the μSRXRF it was possible to establish metals distribution on the L'vov platform and compare the performance of conventional [Mg(NO 3) 2] and permanent (Zr) modifiers.

Tribological analysis on powder slurry in chemical mechanical polishing

Chemical mechanical polishing (CMP) is a key technique for wafer global planarization. Many studies have been conducted in recent years to analyse the slurry flow between a pad and a wafer due to its importance in CMP processing. In these studies, however, the grains in the slurry were not considered. Thus this investigation uses a grain flow model to analyse the slurry flow between wafer and pad. The proposed model predicts the film thickness of the slurry flow with various convex wafer curvature radius under a variety of the CMP parameters including load, rotation speed and grain size. The theoretical results compare well with experimental data in the literature. This study elucidates grain flow during CMP processing and further contributes to understanding of the CMP mechanism.

Silicon Nitride Joining Using Silica and Yttria Ceramic Interlayers

Dense hot‐pressed β‐Si3N4 blocks were joined using both SiO2 and SiO2‐Y2O3 powder slurries as bonding interlayers. The assembled specimens (Si3N4/interlayer/Si3N4) were heated in a flowing N2 atmosphere in the temperature range of 1500°–1650°C. The joining interlayer was clearly distinguished from the Si3N4 bulk. The microstructure and the reaction products found in the bonding interlayer were very different in both compositions. Reactions occurring between the Si3N4 and the ceramic joining compositions have been explained based on existing diagrams of the YN–Si3N4‐Y2O3‐SiO2 system.

Preparation, characterization and photocatalytic activity of nanocrystalline thin film TiO 2 catalysts towards 3,5-dichlorophenol degradation

Both opaque and transparent TiO 2 nanocrystalline thin films were developed on glass substrates by applying dip coating and doctor-blade deposition techniques, using titanium(IV) butoxide and Degussa P25 TiO 2 powder as precursor and starting material, respectively. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) evaluated the surface characteristics of the films. Results on their structure and crystallinity were obtained by means of X-ray diffraction and Raman spectroscopy. The catalytic activity of the films towards photodegradation of 3,5-dichlorophenol (3,5-DCP) pollutant was examined and their efficiency was compared to that of the TiO 2 powder (slurry) suspensions. Pseudo-first-order photodegradation kinetics were observed and the reaction constants were determined. It has been shown that the film photocatalysts can efficiently decompose the pollutant, although relatively higher decomposition rates were observed with the commercial starting powder. Differences in the film efficiencies can be attributed to differences in their grain size, surface roughness and fractal parameters. No altering on the doctor-blade films surface characteristics was observed for several hours of cyclic operation during which their photocatalytic efficiency remained remarkably stable.

Deposition of meso-porous γ-alumina coatings on ceramic honeycombs by sol-gel methods

Abstract The deposition of meso-porous γ-alumina coatings on multi-channeled cordierite honeycombs via sol–gel methods was investigated with the aim to correlate the deposition characteristics such as loading percentage, thickness and integrity of the coating to the support pore structure properties. Even though the mean pore size of the honeycomb supports was much higher than the size of the deposited particles, proper adjustment of sol viscosity prevented penetration of the sol into the support and led to the formation of a smooth coating of uniform, adjustable thickness. Sol viscosity was adjusted with the addition of poly-vinyl-alcohol (PVA) and with sol concentration by controlled evaporation, and fine-tuned in order to control loading percentage from 2 to 8 wt.% per impregnation, corresponding to coating thickness from 2 to approximately 10 μm respectively. The mean pore diameter of the support was found to affect the loading percentage. However, scanning electron microscopy observations have revealed that a very high loading percentage almost inevitably induces cracks on the coatings surface. The combination of sols and slurries of powders as coating media seems to be the optimum technical solution that can provide for satisfactory loading percentage per impregnation together with structural integrity of the coating.

Kinetic analysis of the bactericidal action of heated scallop-shell powder

Shell powder of scallop ( Patinopecten yessoensis) was exposed to heat treatment at between 200 and 1000 °C, and the bactericidal action of the powder slurry was investigated. Shell powder heated at 700 °C or higher exhibited bactericidal action against Escherichia coli, Salmonella typhimurium, Staphylococcus aureus and Bacillus subtilis (vegetative cells). The death of bacteria in the shell powder slurry followed first-order reaction kinetics, and the apparent death rate constant ( k) was determined. An increase in exposure temperature enhanced the bactericidal action. The bactericidal action is due to calcium oxide that is converted from calcium carbonate, which is the main component of the shell powder, by heat treatment. The slurry temperature is found to significantly affect the bactericidal action of the shell powder. The slope of the Arrhenius plot of k for E. coli and S. aureus that were grown at 37 °C exhibited a discontinuous point at approximately 22 °C, at which the values of activation energy for the death of bacteria in the powder slurry changed. This temperature corresponds to that of the phase transition of cell membrane lipids. The bactericidal action of the shell powder is greater than that of a NaOH solution of identical pH. Although the pH of the shell powder slurry is high, the slurry was considered to possess other antibacterial mechanisms in addition to that of alkalinity.

Effect of the Interparticle Pair Potential on the Rheological Behavior of Zirconia Powders: II, The Influence of Chem‐Adsorbed Silanes

The influence of two bifunctional aminosilanes, N‐(triethoxysilylpropyl)‐O‐polyethylen oxid urehtan (PEG‐silane) and N‐(3‐triethyoxsilylpropyl) gluconamid (Glucol‐silane), on the rheological behavior of aqueous zirconia (solid solution with 3 mol% Y2O3) powder slurries and consolidated bodies was investigated. Adsorption of the silanes was determined with viscosity measurements. The influence of tetramethylammonium (TMA) chloride added to dispersed slurries to produce weakly attractive particle networks, formulated with the aminosilane reacted powders was investigated. Bodies were consolidated by filtration at different applied pressures. Viscosity vs shear rate behavior, and consolidated body rheology, were determined for slurries formulated at different pH values and different salt contents. The Glucol‐silane coated powder had a different isoelectric point (pH ∼8.5) relative to the unreacted (pH ∼7.5) and PEG‐silane coated powders (pH ∼7). Dispersed slurries with Newtonian behavior could be formulated for the following conditions: unreacted powder = pH 11, PEG‐silane coated powder = pH 10, and Glucol‐silane coated powder = pH 6. Bodies with the highest relative density (∼51%) were produced from dispersed slurries (uncoated and coated); their relative density was nearly pressure insensitive. The relative density of consolidated bodies produced from slurries with an attractive particle network (formulated either at the isoelectric point or dispersed with added salt) was pressure sensitive. Bodies consolidated with the weakly attractive particle networks exhibited a critical relative density that separated the body's plastic and brittle behavior. The highest critical relative density (47%) was achieved for bodies consolidated with salt‐added, dispersed slurries formulated with the longest aminosilane molecule, which produced the weakest attractive particle network. Bodies that exhibited a claylike flow stress (∼0.1 MPa) could be formulated with the shorter aminosilane molecule, whereas the longer aminosilane molecule produced a fluidlike body without a significant yield stress.

Optimization of the rheological properties of alumina slurries for ceramic processing applications Part I: Slip-casting

Aqueous powder slurries are widely employed in ceramic manufacturing processes like slip-casting and spray-drying. The aim of the present work was to identify the conditions for the preparation of stable alumina slurries with high solids content for the production of slip-cast objects with improved properties, as well as to correlate the slurry properties to the final object properties. For slurry stabilization, three commercial dispersants were compared. It was found that for each dispersant there exists an optimum concentration range within which low viscosity is achieved for a slurry of high solids content. In addition to the slurry solids content, the choice of a particular dispersant also affects the slurry viscosity and through that the casting rate. The combination of high slurry solids content and slower casting rate results in objects with higher densities both in the green and fired state.

Kinetic analysis of death of bacteria in CaO powder slurry

The process of Escherichia coli and Staphylococcus aureus death in calcium oxide (CaO) powder slurry was assumed to follow first-order reaction kinetics. The apparent death rate constant ( k) was found to increase with increasing powder concentration and was higher than that for a NaOH solution having the same pH as the CaO powder slurry. The slurry temperature was found to significantly affect the bactericidal action of the CaO powder slurry against both E. coli and S. aureus. The slope of the Arrhenius plot of k for both bacteria changed at a slurry temperature of approximately 22°C, suggested to correspond to a change in the activation energy required to induce the death of bacteria in CaO powder slurry as a result of a phase transition of the cell membrane.

Colloidal processing of lead lanthanum zirconate titanate ceramics

Well-dispersed aqueous slurries of fine ceramic powders with high solids loading are often required for various shape forming techniques such as slip and tape casting in order to fabricate advanced ceramics with a dense and uniform microstructure. Colloidal processing of lead lanthanum zirconate titanate (PLZT) powders was conducted at various pH using ammonium polymethacrylate as a dispersant. Suspensions were characterized by viscosity and zeta-potential measurements. The effect of pH on polymer adsorption and the rheological behavior of the slurries were investigated and stabilization mechanisms discussed. Through optimization of the dispersant concentration and pH, solids loadings of the suspensions up to 50 vol.% with a relatively low viscosity were obtained.

An evaluation of the anti-bacterial action of ceramic powder slurries using multi-parameter flow cytometry

Multi-parameter flow cytometric techniques have been used to study the effects of three ceramic powders CaO, MgO and ZnO on the physiology of individual, exponentially growing E. coli cells. Whilst all three powders inhibited reproductive growth, depending on their concentration, the mechanism of action of CaO and MgO was different to that of ZnO as shown by fluorescent staining techniques developed in our laboratory.

Effect of Polymeric Flocculant on the Uniformity of Green Compacts Obtained from Heterogeneous Slurries.

The effect of polymeric flocculant on the uniformity of centrifugally formed green compacts was investigated. The compacts were obtained from heterogeneous ceramic powder slurries with different compositions and particle size distributions. When the content of cationic polymer, CP, was >10-3 (g/g-powder) in well-dispersed slurries containing aplite, alumina, and kaolin (with particle sizes in the range of 10-1-101μm in diameter), these powders flocculated but the particle dispersion in the green compacts became uniform. This flocculation process in heterogeneous slurries added with a polymeric flocculant was effective in order to prevent segregation in the green compacts for mixtures of powders with different particle size.

Effect of Al2O3 Raw Materials on Fluidity of Al2O3-Coated Graphite Powder Slurry.

Al2O3-coated graphite powder was prepared using ethyl acetoacetate aluminium diisopropoxide, aluminium tri-sec-butoxide and aluminium hydroxide lactate according to the sol-gel method. The effect of Al2O3 raw materials on fluidity of the Al2O3-coated graphite powder slurry was studied. The apparent viscosity of the Al2O3-coated graphite powder slurry depended on the selected Al2O3 raw material. The apparent viscosity of the Al2O3-coated graphite powder slurry prepared using aluminium hydroxide lactate was lower than that of other Al2O3-coated graphite powder slurries.

Kinetic modelling of binder burnout for optimisation of slurry–powder manufacturing process of Ti/SiC composites

A slurry–powder metallurgy method is currently under development as a low cost production route for Ti/SiC composites. One of the critical steps in the process is the complete removal of a fugitive binder used to form the powder slurry. A diffusion-controlled, shrinking-core model has been developed for the prediction of the binder burnout kinetics in a metal powder compact with relatively large particles. This model is suitable for a polymeric binder that decomposes mainly to a monomer. The model considers the degradation of the polymer and the diffusion of the monomer in the core that contains a powder structure filled with a liquid polymer–monomer solution. It is found that the dominant mechanism is the liquid diffusion of monomer and the burnout time increases significantly with the compact size. The model also predicts a longer burnout time for a larger particle volume fraction.