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  • 1
    Electronic Resource
    Electronic Resource
    Comb Polymer Architecture Effects on the Rheological Property Evolution of Concentrated Cement Suspensions (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We have studied the rheological behavior of concentrated cement suspensions in the absence and presence of comb polymers comprised of a polyacrylic acid (PAA) backbone and charge-neutral, poly(ethylene oxide) (PEO) teeth. These species possessed a uniform backbone molecular weight and graft density, with varying teeth molecular weight. Both PAA, a linear polyelectrolyte, and PAA/PEO comb polymers imparted initial stability to concentrated cement suspensions above a critical weight fraction, w* of 4 mg/(g of cement). Cement–PAA suspensions, however, set prematurely. Their rapid, irreversible stiffening stemmed from deleterious interactions between PAA and multivalent counterions in solution. Interestingly, the presence of PEO teeth comprised of only a few monomer units in length mitigated such interactions. The rheological property evolution of concentrated cement–PAA/PEO suspensions exhibited complex behavior ranging from the reversible gel-like response observed at short teeth lengths to a remarkable gel-to-fluid transition observed during the deceleratory period for systems comprised of longer PEO teeth. At longer hydration times, all cement–PAA/PEO suspensions exhibited initial elastic modulus values, Gi′∼ exp(t/τc) before the onset of the acceleratory period, followed by initial set. Their characteristic hydration time, τc, and set time depended strongly on the concentration of “free” carboxylic acid groups [COO−] arising from non-adsorbed polyelectrolyte species in solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.01643.x
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  • 2
    Electronic Resource
    Electronic Resource
    Competitive Adsorption Phenomena in Nonaqueous Tape Casting Suspensions (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Competitive adsorption phenomena in alumina (α-Al2O3)–polyvinyl butyral (PVB)–Menhaden fish oil (MFO) suspensions are studied using diffuse reflectance Fourier transform infrared spectroscopy and thermogravimetric analysis. PVB and MFO commonly serve as binder and dispersant species, respectively, in nonaqueous tape casting systems. Adsorption isotherm measurements reveal that both PVB and MFO have an affinity for α-Al2O3 surfaces, with corresponding plateau coverages of 3.4 and 2.3 mg/m2, respectively. Sequential competitive adsorption of these species occurred during two-stage milling. MFO was fully adsorbed onto α-Al2O3 powder in the absence of PVB during first-stage milling. PVB was then introduced to the system during second-stage milling and found to displace preadsorbed MFO species from such surfaces. At the culmination of milling, PVB composed 25–35 wt% of the adsorbed organic layer. Complete displacement of MFO was not observed, which limited PVB adsorption on α-Al2O3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb01043.x
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  • 3
    Electronic Resource
    Electronic Resource
    Aggregation Effects on the Compressive Flow Properties and Drying Behavior of Colloidal Silica Suspensions (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The influence of aggregation phenomena on the compressive flow properties and drying behavior of nonaqueous and aqueous silica (SiO2) suspensions of varying electrolyte (NH4Cl) concentrations were studied. Compressive rheology measurements, including sedimentation and centrifugal consolidation, were first conducted to investigate consolidation behavior in the absence of solvent evaporation. The volume-fraction-dependent osmotic pressure and compressive yield stress were determined for dispersed and flocculated SiO2 suspensions, respectively. Consolidation behavior then was studied in situ by simultaneously measuring stress evolution and solvent loss as a function of drying time. The observed drying stress histories of the films were complex, consisting of several characteristic regions. First, there was an initial period of stress rise to a maximum drying stress. These measured stress values exhibited good agreement with the osmotic pressure and compressive yield stress at equivalent SiO2 volume fractions for the dispersed and flocculated systems, respectively. Beyond the maximum drying stress there was a subsequent region of stress decay, which coincided with the draining of liquid-filled pores. No residual drying stress was detected for films prepared from salt-free SiO2 suspensions, whereas salt-containing films exhibited residual drying stresses likely due to salt-bridging effects. Microstructural characterization of dried films prepared from aqueous SiO2 suspensions revealed nonuniformities in the spatial distribution of colloidal particles and precipitated salt, with the highest concentrations located at the outer edges of the films. Such features result from capillary-induced transport of these species during drying, and they have important implications on colloidal processing of ceramic thick films and bulk forms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02090.x
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  • 4
    Electronic Resource
    Electronic Resource
    Colloidal Processing of Ceramics (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Colloidal processing of ceramics is reviewed with an emphasis on interparticle forces, suspension rheology, consolidation techniques, and drying behavior. Particular attention is given to the scientific concepts that underpin the fabrication of particulate-derived ceramic components. The complex interplay between suspension stability and its structural evolution during colloidal processing is highlighted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01560.x
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  • 5
    Electronic Resource
    Electronic Resource
    Solid Freeform Fabrication of Aqueous Alumina–Poly(vinyl alcohol) Gelcasting Suspensions (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Solid freeform fabrication of aqueous alumina–poly(vinyl alcohol) (Al2O3–PVA) gel-casting suspensions was conducted using a computer-controlled extrusion apparatus fitted with a two-nozzle delivery system. The impact of casting parameters on the shear rate profiles experienced during deposition was evaluated via conventional flow analysis and computer simulations. In addition, the influence of these parameters on line resolution/uniformity, printability, and as-cast component properties was studied using laser profilometry, optical microscopy, and scanning electron microscopy. Continuous printablity was achieved for tip diameters ranging from 0.254 to 1.370 mm for all mixing rates and suspension compositions studied. Printed lines were uniform with good edge definition, and line dimensions were independent of mixing rate for these process conditions. The Al2O3 volume fraction (φAl2O3) in the as-deposited layers depended on casting conditions and cross-linking agent concentration, where (φAl2O3 increased with decreased tip diameter and increased cross-linking agent concentration. The free-formed Al2O3 components exhibited uniform particle packing, with minimal macrodefects (e.g., slumping or staircasing) and no discernable microdefects (e.g., bubbles or cracking).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01569.x
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  • 6
    Electronic Resource
    Electronic Resource
    Chemorheology of Aqueous-Based Alumina-Poly(vinyl alcohol) Gelcasting Suspensions (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new gelcasting system based on aqueous-based alumina-poly(vinyl alcohol) (PVA) suspensions cross-linked by an organotitanate coupling agent has been developed. The chemorheological properties of this system exhibited a strong compositional dependence. A sol-gel phase diagram was established, which yielded the critical titanium concentration ([Ti]c) required for gelation at a given PVA volume fraction as well as the minimum PVA volume fraction (φminPVA= 0.0245) and titanium concentration ([Ti]min= 9.984 × 10-4 g of Ti/mL) below which gelation was not observed irrespective of solution composition. The gelation time of suspensions of constant PVA volume fraction (φsolnPVA) decreased with increased cross-linking agent concentration, temperature, and solids volume fraction. The steady-state viscosity and elastic modulus of polymer solutions (φsolnPVA= 0.05) of varying [Ti] were well described by the percolation model, giving scaling exponents of 0.84 and 1.79, respectively. The steady-state elastic modulus of gelcasting suspensions, which provided a measure of their handling strength in the as-gelled state, increased with increased solids volume fraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb01796.x
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  • 7
    Electronic Resource
    Electronic Resource
    Directed Colloidal Assembly of Linear and Annular Lead Zirconate Titanate Arrays (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Lead zirconate titanate (PZT) arrays for ultrasonic sensing applications in the 2–30-MHz frequency range were fabricated by robocasting, a directed colloidal assembly technique. Both linear and annular arrays were produced by robotically depositing a concentrated PZT gel-based ink to create high-aspect-ratio PZT elements (thickness ∼ 130 μm and height ∼1–2 mm) of varying pitch (∼250–410 μm). The arrays were densified and infiltrated with an epoxy resin to fabricate PZT–polymer composites with 2–2 connectivity. Their dielectric and piezoelectric constants were measured and compared with values obtained for bulk PZT and those predicted theoretically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00293.x
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  • 8
    Electronic Resource
    Electronic Resource
    Cement Composition Effects on the Rheological Property Evolution in Concentrated Cement–Polyelectrolyte Suspensions (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We have studied the rheological property evolution and hydration behavior of white and ordinary portland cement (type I) pastes and concentrated cement–polyelectrolyte suspensions. Cement composition had a marked effect on the elastic property evolution (G′(t)) and hydration behavior of these suspensions in the presence of poly(acrylic acid)/poly(ethylene oxide) copolymer (PAA/PEO), even though their affinity to adsorb such species was nearly identical. Both white and ordinary portland cement pastes exhibited G′0 values of ∼104 Pa and fully reversible G′(t) behavior until the onset of the acceleratory period (t= 2 h), where the pastes stiffened irreversibly. In contrast, cement–PAA/PEO suspensions exhibited G′0 values of ∼1 Pa and G′(t) behavior comprised of both reversible and irreversible features. Interestingly, ordinary portland cement–PAA/PEO suspensions experienced a gel-to-fluid transition on high shear mixing at short hydration times (〈1 h), and the particle network did not rebuild until ∼24 h of hydration. In sharp contrast, white portland cement–PAA/PEO suspensions remained weakly gelled throughout the initial stage of hydration even after high shear mixing. At longer hydration times (〉1 h), both cement–PAA/PEO suspensions exhibited G′i(t) ∼ exp(t/τc) with τc values of 5.6 and 1.3 h for ordinary and white portland cement, respectively. Our observations suggest that hydration phenomena impact interparticle forces during early stage hydration and, ultimately, lead to initial setting through the formation of solid bridges at the contact points between particles within the gelled network.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06327.x
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  • 9
    Electronic Resource
    Electronic Resource
    Rheological, Structural, and Stress Evolution of Aqueous Al2O3:Latex Tape-Cast Layers (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The rheological, structural, and stress evolution of aqueous alumina (Al2O3):latex tape-cast layers of varying composition were studied by shear rheology, direct visualization, and a controlled environment stress measurement device. Their low shear viscosity was nearly independent of the alumina:latex ratio for binary mixtures whose particle size ratio (λ=D̄alumina:D̄latex) approached unity, but varied over an order of magnitude for systems with particle size asymmetry. Direct visualization of these mixtures revealed that particle flocculation occurred as their total solids loading increased. Their structure was characterized at intermittent points during the drying process by imaging freeze-dried samples using scanning electron microscopy (SEM). Their corresponding stress histories exhibited three distinct regions: an initial period of stress rise, followed by a stress maximum, and, finally, a period of stress decay. Pure alumina layers exhibited a maximum stress of ∼1 MPa and a residual stress below 0.01 MPa. Pure latex films exhibited a maximum stress of ∼0.1 MPa and only a slight stress decay. The ceramic phase dominated the initial period of stress rise, while the latex phase strongly influenced the residual stress of composite layers cast from alumina:latex suspensions. Their maximum drying stress increased with decreasing Al2O3 particle size, whereas their residual stress increased with increasing latex Tg.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00473.x
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  • 10
    Electronic Resource
    Electronic Resource
    Direct-Write Fabrication of Zinc Oxide Varistors (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00052.x
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