John Nychka
University of Alberta, Chemical and Materials Engineering, Faculty Member
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Purpose: The hydrophilicity of some elastomeric impression materials has not been fully established. The purpose of this study was to measure and compare the advancing contact angle of water on the surface of several set elastomeric... more
Purpose: The hydrophilicity of some elastomeric impression materials has not been fully established. The purpose of this study was to measure and compare the advancing contact angle of water on the surface of several set elastomeric impression materials. Materials and methods: We tested various consistencies of vinyl polysiloxane (VPS; Imprint 4) and vinyl polyether silicone (VPES; EXA'lence) with a polyether (PE; Impregum Soft) control. Impression discs (25.07 mm) were made using a metal die and ring. Deionized ultra-filtered water was placed on each disc and contact-angle measurements were made at 0, 15, 30, 45 and 60 s using a video contact angle drop shape analysis machine. The data were analyzed using repeated ANOVA and a post-hoc test with Bonferroni correction. Results: VPS contact angles reached a mean of 10.1° ± 0.2° at 60 s vs. 40.7° ± 0.1° for VPES. Overall, VPS contact angles were smaller than those for VPES at all measured times. However, heavy and super quick heavy VPS had much higher contact angles at 0 s compared with other VPS consistencies. There was a significant difference in contact angles between VPS and VPES (mean difference 33.9°, p < 0.05) and between VPS and PE (mean difference 32.8°, p < 0.05) but not between VPES and PE (P = 0.196). VPS heavy and super quick heavy were significantly different from other VPS materials (p < 0.05), but not from each other (p = 1.00). Conclusions: Set VPS is more hydrophilic than VPES. Contact-angle values of VPS indicated super hydrophilicity. VPES was hydrophilic, with measurements similar to the PE control. Thus, VPS impression materials may be excellent in terms of spreading and copying wet surfaces.
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Bone defects are treated with bone grafts, replacing damaged or diseased bone tissue with either natural bone or bone substitutes. This study investigates the structure, mechanical properties, and in vitro response of an all-ceramic... more
Bone defects are treated with bone grafts, replacing damaged or diseased bone tissue with either natural bone or bone substitutes. This study investigates the structure, mechanical properties, and in vitro response of an all-ceramic composite designed for use as a bone 'spackling' paste: a formable synthetic bone graft paste used to repair bone defects in place, reacting with CO2 gas in ambient conditions to become a void-filling, rigid scaffold. The composite is comprised of bioactive glass frit and a soluble liquid silicate precursor combined to form an air-setting, open porous scaffold with compressive strength within the low range for trabecular bone (1.3-4.4 MPa). Characterization of scaffolds, with varying amounts of binder, was executed in accordance with established design criteria of porosity, load-bearing capacity, and bioactivity. Bioactivity was assessed via morphological, structural, and chemical changes in surface mineralization that occurred during in vitro immersion in simulated body fluid. All phases of composite specimens were observed to form calcium phosphate minerals, indicating that a chemical change occurred between the bioactive glass and sodium silicate binder phase. Ion exchange between the two phases was likely, as sodium silicate (control) was not found to produce calcium phosphate in the absence of bioactive glass. Of the selected compositions, composites with 7.4 vol% sodium silicate binder were observed to possess the highest open porosity (44 vol%), highest rate of calcium phosphate mineralization, most uniform surface mineral distribution, and largest amount of hydroxycarbonate apatite formation. The structure, mechanical properties, and in vitro response of the composite scaffolds analyzed in this research signify their potential success as bone tissue scaffolds.
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... Information , E-mail The Corresponding Author , a , DR Clarke a , S. Sridharan b , E. Jordan b , M. Gell b , MJ Lance c , CJ ... peak proved problematic when performing the second derivative macro to find the peaks; the reference peak... more
... Information , E-mail The Corresponding Author , a , DR Clarke a , S. Sridharan b , E. Jordan b , M. Gell b , MJ Lance c , CJ ... peak proved problematic when performing the second derivative macro to find the peaks; the reference peak was orders of magnitude sharper than the ...
Research Interests: Materials Engineering, Condensed Matter Physics, Materials Science, Physical Vapor Deposition, Surface Coatings, and 10 moreSpectral analysis, Electronic Spectra, Luminescence, Comparative method, Surface and Coatings Technology, Curve fitting, Thermal Barrier Coating, Electron Beam, Round Robin, and Interim
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Ceramic sorbents based on combined perovskite/spinel structure have been investigated for their potential use in oxygen- enriched CO2 stream production. Oxides of strontium and barium doped with cobalt and iron were chosen for this study.... more
Ceramic sorbents based on combined perovskite/spinel structure have been investigated for their potential use in oxygen- enriched CO2 stream production. Oxides of strontium and barium doped with cobalt and iron were chosen for this study. X-ray diffraction studies revealed a dual-phase structure containing perovskite and spinel systems. Microstructure observed by SEM showed the spinel phase as intergrowth structure in the dominantly perovskite phase. Thermogravimetric studies show a higher desorption rate and sorption capacity compared to the similar perovskite sorbents which with a lower CO2 uptake can produce an optimum sorbent material for air separation in oxyfuel power generation. Sintering temperature also showed an effect on oxygen sorptive/desorptive properties. Improved properties can be explained based on the defect chemistry of the new structure.
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Research Interests: Engineering, Biochemistry, Materials Science, Chemistry, Inorganic Chemistry, and 15 moreMolecular Biology, Scanning Electron Microscopy, Medicine, Crystal structure, SEM, TGA, Ceramic Materials, CHEMICAL SCIENCES, Air Separation Unit, Oxyfuel Combustion, Oxygen, Chemical Looping, Chemical Looping Combustion, Surface chemical properties, and oxygen carriers
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ABSTRACT Oxygen production in an economic way is critical to oxy-firing combustion, a carbon capture technology. Oxygen-deficient oxides have been used for absorption of oxygen from air and desorption of oxygen in recycled flue gas for... more
ABSTRACT Oxygen production in an economic way is critical to oxy-firing combustion, a carbon capture technology. Oxygen-deficient oxides have been used for absorption of oxygen from air and desorption of oxygen in recycled flue gas for oxy-firing combustion. Cuprous/cupric oxide equilibrium with alumina can be used as an alternative for oxygen production and absorption. In this work, the effect of the spinel phase (CuAl2O4) content on oxygen sorptive/desorptive properties of CuO–CuAl2O4 sorbents has been investigated using thermogravimetric analysis. The desorption rate and oxygen sorption capacity were shown to be dependent upon the amount of alumina addition. The effect of SO2 and H2O in flue gas was investigated using FACTSage over a range of conditions. It was found that, at temperatures above 750 °C, CuO is inert to these species, making it a proper choice for oxygen carrier. Cyclic stability was also investigated using the same instrument. The molar CuAl2O4 content of 20% was observed to have the most positive cyclic stability effect. A stable morphology was observed in the scanning electron microscopy microstructure of the sorbent with this CuAl2O4 content. Sintering at a lower CuAl2O4 content and attrition because of second-phase agglomeration can destabilize the sorbents.
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Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Biomedical Engineering, Glass, and 15 moreMedicine, Ceramics, Composite Material, Hardness, Dissolution, Indentation, Residual Stress, Elastic Modulus, Bioactive Glass, Materials Testing, Bioactivity, Biocompatible Materials, Body Fluids, Driving force, and Mechanical Property
D engt l^iÉyff' BáJnLk Figure 7. Macrophotographs of water droplets (~3 mm in diameter) on the (a) top (adaxial) and (f) bottom (abaxial) leaf surfaces of the Elegant Dutchman's Pipe {Aristolochia Httoralis); scale markers ~1... more
D engt l^iÉyff' BáJnLk Figure 7. Macrophotographs of water droplets (~3 mm in diameter) on the (a) top (adaxial) and (f) bottom (abaxial) leaf surfaces of the Elegant Dutchman's Pipe {Aristolochia Httoralis); scale markers ~1 mm. Both leaf surfaces manage superhydrophobic behavior. ...
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Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Metallurgy, Optical microscopy, and 15 moreResidual Stresses, High Temperature, Nickel, Interface, Scaling, Alloy, Grain Boundary, Oxide, Room Temperature, Single Crystal, Spinel, Residual Stress, Oxidation, Fracture Toughness, and Spallation
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ABSTRACT Amorphous bioactive glasses such as 45S5 have been successfully used in bone‐filling therapy in non‐load bearing biomedical applications for decades. In this study, we challenge the predilection to amorphous over crystalline... more
ABSTRACT Amorphous bioactive glasses such as 45S5 have been successfully used in bone‐filling therapy in non‐load bearing biomedical applications for decades. In this study, we challenge the predilection to amorphous over crystalline ceramics by investigating the effect of synthesis route on surface texture, in vitro dissolution, and mineral formation on powders produced by sol–gel and glass melt‐casting methods. Many reports have indicated bulk crystalline bioactive glass‐ceramics to be less bioactive than their amorphous counterparts as measured by the onset time for mineral formation. Bioactive glass 45S5 was synthesized using the sol–gel method followed by heat treatment to produce a semi‐crystalline structure and was compared against commercially available amorphous melt‐cast 45S5 powder. Gel‐derived samples were stabilized at 700°C making more than 80% of the structure crystalline. Dissolution of 45S5 glass‐ceramic in powder form(particle diameter 12 μm) was studied by in vitro immersion in simulated body fluid solution for various periods of time. The immersed powders were then analyzed through X‐ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersive X‐ray analysis (EDS), Differential scanning calorimetry (DSC), and thermogravimetric analysis (DSC/TGA), and Fourier transform infrared spectroscopy (FTIR) to determine the onset time for surface mineralization, and were compared with the melt‐cast powder as a control. The rates of dissolution and onset time for mineral formation were similar for the gel‐derived powder as compared with the melt‐cast control; it is proposed that the higher surface area of the sol–gel powder overcame the penalty usually associated with lower dissolution rates of crystalline materials, implicating surface texture as a much more important determinant of dissolution and mineralization behavior than mere crystallinity.