Development of Thai lignite fly ash and metakaolin for pervious geopolymer concrete

The study was to use Thai lignite fly ash and metakaolin to produce geopolymer paste as binder material in pervious concrete. The proper ratio of fly ash to metakaolin were varied as 100:0, 70:30, and 50:50. Alkali solution to pozzolan (L/P) ratios viz., 0.5, 0.6 and 0.8 by weight were prepared. The mechanical and characterization of pervious geopolymer concrete (PGC) were carried out. The results presented that the particle of fly ash was sphere with smooth surface, while metakaolin was partly agglomerated and irregular shaped. The increase of fly ash in the ratio of fly ash to metakaolin affected the lower requirement of volume of alkali solution. The compressive strength and of pervious geopolymer concrete at 28 days were 3.7-5.4 MPa. The void ratio and water permeability were 28.5-30.7% and 1.9-2.1 cm/sec, respectively. Therefore, geopolymer paste from fly ash and metakaolin could be used for pervious concrete with satisfied properties according to standard of ACI 522R-10

The influence of yttria-stabilised zirconia and cerium oxide on the microstructural morphology and properties of a mica glass-ceramic for restorative dental materials

The addition of yttria-stabilized zirconia and cerium oxide to this mica glass ceramic was found to increase mechanical properties and decrease chemical solubility. They were also found to be able to control translucency. X-ray diffraction showed no significant change in phase formation with phlogopite-Ca mica, fluorapatite and tetragonal zirconia the main phases present with their addition. Scanning electron microscopy showed that the additives did affect the grain morphology significantly and this was the controlling factor in the observed changes in strength, hardness, and solubility. The microstructures consisted of mainly plate-like and interlocking crystals. The largest increased in strength and hardness and the largest decreased in chemical solubility can be attributed to the largest change in grain morphology by the addition of both the YSZ and CeO2. The values of hardness, biaxial flexural strength and chemical solubility were 3.5\u20136.2 GPa, 105\u2013120 MPa and 142\u2013732 \ub5g/cm2, respectively making them acceptable for dental materials according to ISO 6872:2015. The addition of YSZ increased the opacity, whilst the CeO2 improved translucency and influenced the color to a yellowish to yellow-brownish shade close to Thais\u2019 teeth

Relating type of mold materials to crystal morphology and properties of glass-ceramics with YSZ additions as a dental material

YSZ was added to glass frit in order to improve properties of the glass-ceramic dental materials by casting into a graphite mold and a cast iron mold and then crystallized via heat treatment. XRD results presented the similar crystalline phases of phlogopite-calcium mica and tetragonal zirconia in both molds. Microstructures by SEM showed the different crystal morphology due to casting molds. The slow cooling of graphite mold produced the equiaxed crystals whereas the fast cooling of cast iron mold promoted rod-like, and YSZ addition increased the number of crystals. The properties depended on the crystal morphology and crystallinity. The 5 wt% YSZ added glass-ceramic from graphite mold developed the equiaxed crystals to present the desirable properties of 147.15 MPa, flexural strength, 251.80 µg/cm2, chemical solubility and 9.26 × 10-6/°C CTE. The results were accepted by ISO 6872:2015 (Dentistry-Ceramic Materials) in type II class 2b as a partially and fully covered single substructure and matched with commercial porcelains

Tribology, mechanical properties and coloration of a mica glass-ceramic

The research employed pigments, Fe2O3 and CeO2, into the glass frit for adjustable mechanical properties and coloration. Disc samples were prepared to determine microstructures and mechanical properties in terms of tribology and nano-indentation hardness as well as biaxial flexural strength. The glass system presented the crystalline phases, by XRD, of phlogopite Ca-mica, fluorapatite, stishovite, anorthite and strontium apatite. Furthermore, SEM micrographs revealed rod-like microstructures and parent glass phase in all specimens 1) GC, 2) GC + 1wt% CeO2, 3) GC + 0.1wt% Fe2O3 and 4) GC + 1wt% CeO2 + 0.1wt% Fe2O3. For the tribology test, specimens were tested by a pin-on-disc tribometer with 10 N load and 1,000 wear cycles. The obtained values of wear rate and friction coefficient of GCF were better than those of others. The nanoindentation hardness results showed that GC exhibited 3.2 GPa which lower than those of GCC, GCF and GCCF, respectively. The addition of pigments affected reddish yellow color. After crystallization, the contrast ratio is around 0.72 for GC and decreases to 58-75% for the mica glass-ceramics that contain the pigments. The values of biaxial flexural strength of all were acceptable (≥100 MPa) according to ISO 6872:2015

Effect of the crystallisation time and metal oxide pigments on translucency and the mechanical and physical properties of mica glass-ceramics

Mica glass-ceramics tend to be opaque making them less desirable, from an aesthetic point of view, for dental materials. This research focuses on the development of a mica glass-ceramic for use as a restorative dental material with improved translucency. A ceria-based pigment and a zircon-based pigment consisting of Pr-ZrSiO4 and Fe-ZrSiO4 were added to glass-ceramic and the effect on translucency, phase development and morphology, strength, thermal expansion and chemical solubility were studied. The addition had no effect on the level of crystallinity obtained, the morphology of the crystals formed or the strength. The use of the pigments allowed for the control of the translucency and values of the translucency parameter similar to natural teeth were produced. The characteristic strength values and chemical solubility obtained to make these materials acceptable as dental ceramics type II class 2, for single-unit anterior or posterior prostheses adhesively cemented, according to ISO 6872

Comparison of shear bond strengths between a mica-based glass-ceramic and human dentin using three different resin cements

Three resin cements, RelyX\u2122 Ultimate, Panavia F2.0 and RelyX\u2122 U200, were evaluated for their bond strengths between a mica glass-ceramic and human dentin. This research shows that a self-etch dental cement resin system, Panavia F2.0 provided the best bond strength. The glass-ceramic was produced and phases analysed. Biaxial flexural strength and hardness were measured and found to be comparable to that of human enamel and dentin. Bond strength was measured before and after thermocycling. Thermocycling was found to reduce the bond strength. Thermocycling reduced the shear bond strengths of all adhesives by 50\u201360%. The two-way ANOVA test was used to analyse the data (p = 0.05). Failure modes were analysed, showing failure predominately at the cement/glass-ceramic and dentin/resin cement interfaces. Failure modes changed after thermocycling. The resin cement bond between the dentin and mica glass-ceramics interfaces was examined for failure by optical microscopy (OM) and scanning electron microscopy (SEM)