Fabrication and Tunable Dielectric Properties of (Ba0.7Sr0.3)TiO3-Glass-Based Thick-Film Capacitors

Ferroelectric glass–ceramics of composition 0.90 (Ba_0.7Sr_0.3) TiO₃–0.10(B₂O₃:SiO₂) (0.90 BST:0.10 BS) synthesized by sol–gel method have been used for the preparation of dielectric thick-film inks. The particle dispersion of the glass–ceramic powders in the thick-film ink formulations have been studied through rheological measurements for fabricating thick-film capacitors by screen printing technique. The thick films derived from such glass–ceramics are found to sinter at considerably lower temperatures than the pure ceramic, and exhibit good dielectric characteristics with a tunability of 32% at 1 MHz under a dc bias field of 35 kV/cm.     

Direct-Write Fabrication of Zinc Oxide Varistors

Zinc oxide (ZnO)-based pastes with tailored rheological properties have been developed for direct-write fabrication of thick-film varistor elements in highly integrated, multifunctional electroceramic devices. Such pastes exhibited pseudoplastic behavior with a low shear apparent viscosity of roughly 1 × 10⁴ Pa·s. Upon aging, the pastes attained printable, steady-state viscosities of approximately 3 × 10² Pa·s at 10 s⁻¹. Square and rectangular elements were patterned on dense alumina substrates and sintered at varying temperatures between 800° and 1250°C. Varistor elements fired at 900°C exhibited nonlinearity coefficients (α= 30) that were equivalent to high-density (>95%) varistors formed by cold isostatic pressing at 100 MPa (15 ksi) of a similar chemically derived powder heat-treated under analogous conditions.     

Rheological Behavior of Injection-Moldable Silicon Powder–Silicon Carbide Whisker Formulations

The rheological behavior of injection-moldable formulations for reaction-bonded Si₃N₄ toughened with silicon carbide whiskers was studied using capillary rheometry. The effects on rheology of the following parameters were examined: solids loading, powder/whisker volume ratio, particle size and type, and binder composition. Two important aspects of the flow behavior were delineated. First, corrections for end effects and slippage along the wall were made in order to interpret the experimental data properly. At high shearing rates (i.e., 10³ s⁻¹) slip may account for more than 50% of the total flow. Such slippage promotes flow into the smallest channels or corners of the mold and may appreciably facilitate molding. Consequently the careful study of slippage is an inherent requirement of the rheological characterization of these concentrated suspensions. Second, the suspension viscosities were delineated. An empirical equation for predicting relative viscosity was developed for formulations containing up to ∼30 vol% of silicon carbide whiskers (with more than 50 vol% total solids). Suspension viscosities generally increased with decreasing particle size and increasing whisker contents. Particle surface roughness appears to affect the shearing behavior. Binders of low molecular weight resulted in higher relative viscosities than higher molecular weight binders, indicating possibly better dispersion of solids when more viscous binders are employed.     

Processing and Properties of Screen-Printed Lead Zirconate Titanate Piezoelectric Thick Films on Electroded Silicon

The printing of lead zirconate titanate (PZT, Pb(Zr,Ti)O₃) piezoelectric thick films on silicon substrates is being studied for potential use as microactuators, microsensors, and microtransducers. A fundamental challenge in the fabrication of useful PZT thick-film devices on silicon is to sinter the PZT to high density at sufficiently low temperature to avoid mechanical or chemical degradation of the silicon substrate. The goal of the present study is to develop and implement suitable electrodes and PZT sintering aids that yield attractive piezoelectric properties for devices while minimizing reactions between the silicon, the bottom electrode, and the PZT thick film. A B₂O₃-Bi₂O₃-CdO sintering aid has been found to be superior to borosilicate glass, and the use of a gold/platinum bilayer bottom electrode has resulted in better thermal stability of the electrode/film structure. Films sintered at 900°C for 1 h have relative permittivity of 970 (at 1 kHz), remnant polarization of 20 μC/cm², coercive field of 30 kV/cm, and weak-field piezoelectric coefficient d ₃₃ of 110 pm/V.     

Tape Casting of Fine Alumina/Zirconia Powders for Composite Fabrication

Ceramic films, containing AI₂O₃, with up to 40 vol% ZrO₂, have been fabricated using the tape casting process. Finer powders (average mean diameter of 250–300 nm) than have generally been reported for tape casting were used in this study. The optimum formulation for tape casting is affected substantially by decreasing particle size. For example, the amount of dispersant needed is increased. Moreover, the amount of plasticizer/binder must be increased so as to maintain the solids content in the dried tapes below a critical level (about 55 vol% in this case), which decreases with particle size. Rheological studies on the effectiveness of menhaden fish oil and phosphate ester as dispersants show that phosphate ester can be used in lower concentrations, for the preparation of higher solids loading slurries, and was therefore selected for further study. The amount of dispersant required to obtain minimum slurry viscosity was found to be primarily dependent upon the effective particle surface area, defined as that available to the dispersant molecules. In the case of particles composed of agglomerated crystallites (such as the ZrO₂, powder used here), this may be considerably less than that measured by nitrogen absorption. Moreover, the porous internal structure of such powders is filled with solvent, which increases the effective solids loading of the slurry, and thus its viscosity. Particle morphology also influences the packing efficiency; i.e., the green density decreases as ZrO₂, is added.     

Powder Processing, Rheology, and Mechanical Properties of Feedstock for Fused Deposition of Si3N4 Ceramics

Fused deposition of ceramics (FDC) is a technique in which green parts are fabricated directly from CAD designs. The feedstock for FDC is a 1.778 mm diameter filament that requires a low viscosity and high column strength. This study explores the powder processing science, as well as the rheological and mechanical properties required for a successful FDC feedstock material. GS44 Si₃N₄ powders were dispersed in RU9 binder using oleyl alcohol (OA). The viscosity of the RU9/OA/Si₃N₄ mixture was measured as a function of temperature, solids loading, and OA concentration. The mechanical properties of the filament feedstock were evaluated in compression to establish FDC process limits. The feedstock material shows a shear thinning behavior with OA acting mainly as a plasticizer. The viscosity of GS44-filled RU9 decreases with temperature, and increases with solids content. At 185°C and 55 vol% loading, the viscosity was found to be in the range of 49–7 Pa·s for a corresponding shear rate of 70–1128 s⁻¹. This was sufficiently low for FDC. Based on pressure requirements for FDC extrusion (Δ P ), and maximum sustainable stress without buckling by the filament (σ_E), it has been found that for successful FDC of RU955, 1.1Δ P < σ_E.     

Cardanol: A New Dispersant for Alumina in Toluene

Cardanol, which is a naturally occurring C₁₅ unsaturated aliphatic chain-substituted phenol derived from cashew nut shell liquid, was used as a dispersant for alumina in toluene. Adsorption data, along with the results of sedimentation studies, green density, and slurry viscosity (as a function of dispersant concentration), suggest that cardanol adsorption initially proceeded through surface coverage by a phenolic group that lies flat on the surface and that the best powder dispersion occurred at surface saturation by more closely packed end-on adsorbed cardanol molecules. The alkyl-chain unsaturation significantly contributed to dispersion, such that the saturation by hydrogenation led to an increase in the slurry viscosity by a factor of ∼2.5. Concentrated slurries generally showed shear-thinning flow behavior, and the measured viscosity of a highly concentrated (53 vol%) slurry was <1 Pa·s at a shear rate of 93 s⁻¹.     

Alkoxide-Derived Titania Particles: Use of Electrolytes to Control Size and Agglomeration Levels

Methods of controlling the size and morphology of particles precipitated from the hydrolysis and condensation of tetraethyl orthotitanate (TEOT) in aqueous ethanol solutions through the addition of electrolytes are described. The precipitates display great sensitivity to agitation where, above a critical shear rate, agglomerated morphologies are observed. For reactions carried out at shear rates less than the critical value, narrow size distribution, spherical titania particles are formed under conditions where the particles have electrophoretic mobilities greater than 0.2 × 10⁻⁸ m²· V⁻¹· s⁻¹ for 0.05 M < [TEOT] < 0.2 M and 0.15 M < H₂O < 0.9 M . Addition of HCl and NaCl to the precipitation solution increases particle charge and expands the TEOT, H₂O concentration ranges where uniform particles are formed.     

粒度级配对CL-20基炸药油墨流变性能的影响

为了研究粒度级配对CL-20基炸药油墨流变性能的影响,制备了粒径分别为400nm和4μm的CL-20样品,以及7种不同粒度级配的CL-20基炸药油墨;采用博勒飞(CPS)流变仪对炸药油墨进行了黏度测试,得到了相应的流变数据,并计算出非牛顿指数、屈服值和触变指数。结果表明,炸药颗粒的粒度级配对炸药油墨的流变性能有着十分明显的影响;随着粒径为4μm的CL-20含量的增多,炸药油墨表观黏度出现先减小后增大的现象;同时,非牛顿指数出现先增大后减小的现象,屈服值和触变指数总体上呈现先减小后增大的现象;当炸药油墨中粒径分别为400nm和4μm的CL-20质量比为1∶2时,炸药油墨的非牛顿指数为最大值0.41,屈服值和触变指数均达到最小值,分别为26.73和8.74,表明在该粒度级配条件下,炸药油墨具有更好的流变性能。     

Shear Modulus and Yield Stress Measurements of Attractive Alumina Particle Networks in Aqueous Slurries

The shear modulus and yield stress of attractive alumina particle networks in aqueous slurries was determined as a function of volume fraction (0.1 to 0.5), pH (2, 4, 5, 6, and 9), and salt (NH₄l) concentration (0.25M to 2.34) using both vane and couette rheological tools. Consistent with previous observations concerning the relative strength of attractive particle networks, the shear modulus increased to a plateau value with salt concentration. In this work we have shown that the salt concentration at which this plateau value is achieved is a function of the pH, and thus, the surface charge density. The values of the shear modulus [G'], yield stress [τ_y], and yield strain [γ_y] of the attractive networks can be described with power law functions for particle volume fraction [φ] (G'∝φ^4.75, τ_y∝φ^3.6, and γ_y∝φ^−1.1) and salt concentration [c] (G'∝ [c]^2.0, τ, ∝ [c]^1.15, and γ_y∝ [c]^−0.85).     

Direct-Write Fabrication of Pb(Nb,Zr,Ti)O3 Devices: Influence of Paste Rheology on Print Morphology and Component Properties

Lead niobium zirconate titanate (PNZT) pastes with tailored rheological properties have been developed for direct-write fabrication of thick-film capacitor elements in highly integrated, multifunctional electroceramic devices. Such pastes exhibited pseudoplastic behavior with a low shear apparent viscosity of roughly 1 × 10⁶ cP. On aging, the degree of shear thinning and the low shear apparent viscosity decreased. Pastes prepared from as-received powders attained printable, steady-state viscosities of ∼2 × 10⁵ cP after 50 days of aging. In contrast, pastes prepared from dispersant-coated powders showed no measurable rheological changes after 1 day of aging. Square elements were patterned on dense alumina substrates or Teflon sheets. Leveling behavior as a function of time for single line prints, and the resulting surface topographies of dried PNZT films were measured by laser profilometry. PNZT layers sintered at varying temperatures between 950° and 1050°C for 5 h in either air or a lead-rich atmosphere yielded porous microstructures as revealed by scanning electron microscopy (SEM). Such layers exhibited dielectric constants ( K ) of 1400–1570 at 1 kHz with dissipation factors ( D ) of less than 4.1%.     

Synthesis of spherical lead zirconate titanate (PZT) nanoparticles by electrohydrodynamic atomisation

Abstract

This paper describes the production of spherical-shaped lead zirconate titanate (PZT) nanoparticles by the electrohydrodynamic atomisation (EHDA) process in order to make inks suitable for ink jet printing applications. PZT sols with different concentrations (0·1–0·6 M) were used as starting materials. Two different heating systems, gas heating and direct heating, were used in order to remove the solvent, reduce the particle size and stabilise the PZT particles. Several aspects have been considered, such as liquid flow rate, sol concentration and heat system temperature, and their influence on the particle dimension is determined. Using optimised processing parameters of direct heating at 520°C, 0·2 M precursor sol, flow rate of 0·2 mL h^?1 and field of 3 kV cm^?1, particles of 100–300 nm in diameter were synthesised. Following stabilisation at 300°C, the particles were suspended in a PZT sol to produce an ink suitable for ink jet printing.     

Piezoelectric Lead Zirconate Titanate Ceramic Fiber/Polymer Composites

Piezoelectric lead zirconate titanate (PZT) ceramic fiber/polymer composites were fabricated by a novel technique referred to as "relic" processing. Basically, this involved impregnating a woven carbon-fiber template material with PZT precursor by soaking the template in a PZT stock solution. Careful heat treatment pyrolized the carbon, resulting in a PZT ceramic relic that retained the fibrous template form. After sintering, the densified relic was backfilled with polymer to form a composite. Optimized relic processing consisted of soaking activated carbon-fiber fabric twice in an intermediate concentration (405-mg PZT/(1-g solution)) alkoxide PZT solution and sintering at 1285°C for 2 h. A series of piezoelectric composites encompassing a wide range of dielectric and piezoelectric properties was prepared by varying the PZT-fiber orientation and polymer-matrix material. In PZT/Eccogel polymer composites with PZT fibers orientated parallel to the electrodes, K = 75, d ₃₃= 145 pC/N, d _h= 45 ± 5 pC/N, and d _hg_h= 3150 × 10⁻¹⁵ m²/N were measured. Furthermore, in composites with a number of PZT fibers arranged perpendicular to the electroded surfaces, K = 190, d ₃₃= 250 pC/N, d _h= 65 ± 2 pC/N, and d _h g_h= 2600 × 10⁻¹⁵ m²/N.     

Factors Influencing Anisotropic Sintering Shrinkage in Tape-Cast Alumina: Effect of Processing Variables

The effect of the processing variables shear rate, solids loading, and sintering temperature on the anisotropy of sintering shrinkage of aqueous tape-cast alumina was studied. Higher shear rates and higher solids loading resulted in higher in-plane shrinkage anisotropy, whereas the shrinkage anisotropy in the thickness direction was higher for low solids loadings. The in-plane shrinkage anisotropy was found to be fairly constant above a certain critical shear rate (∼100 s⁻¹) independent of the solids loading. The shrinkage anisotropy through the thickness was higher than in-plane directions. A higher thickness direction sintering rate was observed and attributed to a greater number of interparticle necks in the thickness direction because of the platy nature of alumina particles and the greater thickness direction strains associated with binder removal. The binder did not significantly affect the in-plane sintering shrinkage but significantly affected the shrinkage in the thickness direction. It was suggested that emulsion binder particles occupy sites in between layers of particles in the thickness direction. The degree of anisotropic shrinkage was quantified using edge orientation polarograms and a direct correlation was obtained between the processing variables, shrinkage anisotropy, and the edge orientation index.     

Grain Boundary Diffusion of Magnesium in Zirconia

This paper reports the transport kinetics of Mg in cubic yttria-stabilized zirconia (containing 10% mol of Y₂O₃ (10YSZ)) involving the bulk and the grain boundary diffusion coefficients. The diffusion-controlled concentration profiles of Mg were determined using secondary ion mass spectrometry (SIMS) in the range 1073–1273 K. The determined bulk diffusion coefficient and the grain boundary diffusion product may be expressed as the following functions of temperature, respectively: D = 5.7 exp[(−390 kJ/mol)/ RT ] cm²·s⁻¹ and D 'αδ= 3.2 × 10⁻¹⁵ exp[(−121 kJ/mol)/ RT ] cm³·s⁻¹, where α is the segregation enrichment factor and δ is the boundary layer thickness. The grain boundary enhancement factor decreases with temperature from 10⁵ at 1073 K to 10³ at 1273 K.     

State of the Dispersant and Particle Surface During Wet-Jet Milling for Preparation of a Stable Slurry

Wet-jet-milled alumina slurries exhibited distinctly different stability behavior compared with ball-milled ones in terms of reflocculent efficiency and rheological properties. The distinction was attributed to the different behavior of the same dispersant (NH₄⁺ salt of poly(acrylic acid); PAA–NH₄⁺) in ball milling and wet-jet milling. Alumina particles after the wet-jet milling retained the initial surface conditions, although ball-milled alumina particles yielded more hydroxyl groups on the surface. Furthermore, degradation of dispersant on milling was investigated qualitatively. Infra-red analysis and isoelectric point measurements suggested that degradation of the dispersant occurred during ball milling, indicating neutralization of the dispersant due to formation of monodentate COOX groups. On the other hand, in the case of wet-jet milling, COO⁻ groups of PAA–NH₄⁺ were not degraded at all, indicating maintenance of the structures of dispersant with electrostatic repulsion. Change in the polymer size of the dispersant by different milling methods was confirmed using high performance liquid chromatography (HPLC) measurements. The HPLC results of the wet-jet milled samples showed that a dispersant with a larger molecular size was generated. Force measurement on approach via the colloid probe method in the centrifuged supernatant of the milled slurries confirmed that the interaction distance between an α-alumina colloid probe and c-sapphire surface was about two times larger in the wet-jet-milled slurry supernatant compared with the ball milled one. Thus, it was found that wet-jet milling process led to a stable slurry because of the maintenance of not only steric repulsion but also electrostatic repulsion.     

Thermally Induced Reversible Coagulation in Ceramic Powder-Polymer Liquid Suspensions

It was observed that slurries of oxide powders in oxidized polybutene fluids can be caused to change reversibly between fluid, nearly Newtonian behavior and plastic behavior by modest changes in temperature. This phenomenon was believed to result from changes in the dispersion vs association among the particles. The rheological effects of temperature, polymer oxidation, and particle size were observed for 30 vol% slurries of TiO₂, Al₂O₃, and ZrO₂ powders in polybutene fluids. Elasticity (in oscillation) and low-shear-rate viscosity (in steady shear) were observed to increase with increasing temperature for TiO₂ and Al₂O₃ particles in oxidized polybutene fluids. This behavior was attributed to the creation of interparticle structures. The attainment of this structure on heating was observed to be inhibited by increased oxidation of the polymer and increased particle size. It was concluded that the adsorption of oxidized molecules from the polymer liquid, along with the high viscosity of the bulk polymer, resulted in suspensions that were metastable against coagulation. Increased temperature resulted in lower viscosities of the liquid, allowing coagulation on a short time scale. The presence of the adsorbed polymer, however, prevented intimate contact among the particles so that the coagulated structure was easily destroyed upon subsequent cooling and shearing.     

Preparation of pigmented ink‐jet ink by a combination of surface treatments and synthetic dispersant

Drop‐on‐demand ink‐jet inks prepared from dyes usually show inadequate light and water fastness. Thus, in our previous paper, we studied black pigmented ink‐jet inks with the aim of overcoming the drawbacks of dye‐based ink by employing a variety of synthetic dispersants with gas black. In this study, pigmented ink‐jet inks were prepared by a combination of the synthetic dispersant and the surface treatments of a furnace black that is more common than gas blacks. The results of this study show that the surface treatment of the furnace black and the use of the synthetic dispersant are useful in the preparation of ink‐jet inks and endow them with properties that are comparable with those of commercial ink‐jet inks.     

Electrical Conduction in Single-Crystal Thallic Oxide: I, Crystals "As-Grown" from the Vapor in Air

Thallic oxide, "T1₂O₃," has been shown to be a degenerate n -type semiconductor with resistivity varying from 60 to 150 μΩ-cm over the range 4° to 900°K. The carrier concentration was 7 × 10²⁰ cm⁻³ and is temperature independent. Room-temperature Hall mobility was 105 cm² V⁻¹ s⁻¹, increasing to 130 cm² V⁻¹ s⁻¹ below 70°K. Donor states were shown to be native defects, probably oxygen vacancies.     

Effects of Temperature and Strain Rate on the Plastic Deformation of Fully Dense Polycrystalline Y1Ba2Cu3O7−x Superconductor

The knowledge of the steady-state stress for plastic deformation as a function of temperature and strain rate is essential for hot-forming superconducting material into commercially useful shapes. In this paper, results are presented on the experimental determination of the rheology of fully dense polycrystalline Y₁Ba₂Cu₃O_7−x superconducting material at temperatures ranging from 750° to 950°C and strain rates of 10⁻⁴, 10⁻⁵, and 10⁻⁶ s⁻¹. The data are best fitted by a power law: ε(s⁻¹)=8.9 × 10⁻¹⁷. (s⁻¹) σ^2.5 (Pa) exp [−2.01 × 10⁵(J·mol⁻¹)|RT]. X-ray analysis shows that the superconducting material retains its phase composition after nearly 70% total strain of the sample. A strong anisotropy in the resistivity of the deformed samples is observed because of the development of a preferred orientation of the a or b axis of Y₁Ba₂Cu₃O_7−x orthorhombic perovskite single crystals perpendicular to the principal maximum compressive stress.