The corrosion behaviour of CoCrFeNi-x (x = Cu, Al, Sn) high entropy alloy systems in chloride solution

The corrosion properties in NaCl solution of four equiatomic HEAs of the CoCrFeNi system adding Al, Cu and Sn are investigated. These alloys are processed by vacuum arc melting and assessed via the Potentiostat method. The properties were compared with two standard stainless steels. The results indicate that CoCrFeNiSn possesses the best passivation in this solution, explained by the alloy phases and presence at the surface of elements in oxidation states corresponding to stable oxide films. The other systems show a range of behaviours attributable to their different microstructures and varying potential for stable oxide formation

Synergistic effect of metakaolin and fly ash on properties of concrete

© 2017 Elsevier Ltd This paper reports the effects of the interaction between metakaolin and fly ash on the microstructure and property development of concrete. X-ray diffraction analysis revealed unstable hemicarboaluminate and calcium monocarboaluminate compounds in most mixtures during 7–28 day curing periods, the relative amounts depending on the metakaolin to fly ash ratio. The mix with the highest peaks of the monocarboaluminate phase yielded the highest long-term strength. Significant improvements in terms of durability, abrasion resistance, chloride permeability and steel corrosion risk were observed. A proportion of cement:metakaolin:fly ash as 80:10:10 yielded marked improvements on slump, slump loss and long- term strength. Synergistic action in the ternary blend significantly improved the workability of fresh concrete and yielded a more uniform mix, denser microstructure and better performance of the hardened concrete

Machinable glass-ceramics forming as a restorative dental material

MgO, SiO2, Al2O3, MgF2, CaF2, CaCO3, SrCO3, and P2O5 were used to prepare glass-ceramics for restorative dental materials. Thermal properties, phases, microstructures and hardness were characterized by DTA, XRD, SEM and Vickers microhardness. Three-point bending strength and fracture toughness were applied by UTM according to ISO 6872: 1997(E). XRD showed that the glass crystallized at 892°C (second crystallization temperature+20°C) for 3 hrs consisted mainly of calcium-mica and fluorapatite crystalline phases. Average hardness (3.70 GPa) closely matched human enamel (3.20 GPa). The higher fracture toughness (2.04 MPa√m) combined with the hardness to give a lower brittleness index (1.81 μm-1/2) which indicates that they have exceptional machinability. Bending strength results (176.61 MPa) were analyzed by Weibull analysis to determine modulus value (m=17.80). Machinability of the calcium mica-fluorapatite glass-ceramic was demonstrated by fabricating with CAD/CAM

Development of thai fly ash blended with rice husk ash oeopolymers

Fly ash (FA) presented in the research is one of the by-products from combustion processes of lignite in electricity plants in Thailand. Generally, FA is exploited to mix with Portland cement to improve the mechanical properties of cement paste or mortar. In addition, FA is also claimed as an active pozzolanic material to synthesize geopolymers. The rice husk is used as fuel in rice mills and converted to ash called rice husk ash (RHA). The RHA in the research contains approximately 85% - 90% amorphous silica. RHA was chosen to blend with FA producing geopolymers to retard hardening time and develop good results of compressive strength of geopolymers. The mixed proportion of FA to RHA was prepared by variation as five ratios of 0: 100, 20: 80, 50: 50, 80: 20 and 100: 0 by weight. Sodium hydroxide of 8 Molar (8M NaOH) and sodium silicate (Na2SiO3) solution was used as alkali activators by mass ratio of Na2SiO3: NaOH at 3: 2. The suitable Si/Al molar ratio, the Na/Al molar ratio, pH and conductivity of experiment were studied and characterized. Finally, the specimens were investigated for compressive strength at 7, 14, 21 and 28 day ages and flexural strength and microstructures at 7 days of age

Development of Thai fly ash blended with rice husk ash geopolymers

Fly ash (FA) presented in the research is one of the by-products from combustion processes of lignite in electricity plants in Thailand. Generally, FA is exploited to mix with Portland cement to improve the mechanical properties of cement paste or mortar. In addition, FA is also claimed as an active pozzolanic material to synthesize geopolymers. The rice husk is used as fuel in rice mills and converted to ash called rice husk ash (RHA). The RHA in the research contains approximately 85%-90% amorphous silica. RHA was chosen to blend with FA producing geopolymers to retard hardening time and develop good results of compressive strength of geopolymers. The mixed proportion of FA to RHA was prepared by variation as five ratios of 0:100, 20:80, 50:50, 80:20 and 100:0 by weight. Sodium hydroxide of 8 Molar (8M NaOH) and sodium silicate (Na2SiO3) solution was used as alkali activators by mass ratio of Na2SiO3: NaOH at 3:2. The suitable Si/Al molar ratio, the Na/Al molar ratio, pH and conductivity of experiment were studied and characterized. Finally, the specimens were investigated for compressive strength at 7, 14, 21 and 28 day ages and flexural strength and microstructures at 7 days of age

Metakaolin-based porous geopolymer with aluminium powder

Porous concretes such as aerated and lightweight concretes are commonly used in construction fields. Lightweight construction materials are used to reduce either the weight or the budget of building structures. Aluminium (Al) powder was utilized to create bubbles in porous structure and giving information for porous geopolymer production. It was introduced by adding 0.05-1% Al-powder as the initiated materials of geopolymers to react with water in those materials and promote hydrogen gas inside specimens. The research, therefore, focused on the synthesis of porous geopolymer by metakaolin as a pozzolan and mixed with alkali solution consisting of 8M NaOH and Na2SiO 3 as well as Al-powder as a foaming agent. The highly porous geopolymers were produced with various Al-powders as 0%, 0.2%, 0.4%, 0.6% 0.8% and 1% by weight. After 7, 14 and 28 days age, the specimens were tested the mechanical properties, such as compressive strength. The water absorption, apparent porosity and bulk density were analyzed at 28 days age. The synthesis of metakaolin-based porous geopolymers with Al-powder presented good results. It showed that Al-powder content affected to degree of porosity of geopolymers and 0.2% Al-powder was the optimal Al-powder content for the porous geopolymer. © (2014) Trans Tech Publications, Switzerland

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

In vitro surface reaction in SBF of a non-crystalline aluminosilicate (geopolymer) material

Geopolymer is a non-crystalline material based on aluminosilicate reaction exhibiting ceramic-like properties. It showed the possibility to use geopolymer as biomaterials by soaking in SBF solution to induct carbonate apatite onto the surface of samples. Carbonate apatite possesses good biocompatibility and bioactivity. The aims of this research were to study the geopolymer synthesis as a biomaterial to replace bones and the effects of Ca/P ratio on bioactivity properties of metakaolin-based geopolymers. For in vitro bioactivity test, the samples were soaked in SBF to study the influence of Ca(OH)2 contents on the surface reaction. The 14, 28, and 90 day-soaked sample surfaces were investigated using SEM, XRD, and FTIR characterization. The compressive strength of samples was also tested. The SEM micrographs revealed that the increase of Ca/P ratio resulted in the increase of the carbonate apatite on sample surfaces. FTIR results confirmed that the formation of Ca10(PO4)3(CO3)3(OH)2 was investigated

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