Refractory Ceramics Synthesis by Solid-State Reaction Between CaCO3 (Mollusk Shell) And Al2O3 Powders

Calcium aluminate-based refractory ceramic was developed as an innovative refractory material, using garden snail (Helix aspersa) shells as a natural source of CaCO3. A 1:1 molar ratio mixture of CaC O3 from snail shells and commercial Al2O3 powder was prepared by means of high-energy mechanical milling. The mixed powder was compacted in cylindrical samples (disks) and consolidated by sintering at 1450°C and 1500°C for 1h. The density and porosity were evaluated using the Archimedes principle, while the mechanical properties (hardness, fracture toughness, and shear modulus) were determined by indentation and ultrasonic methods, respectively. The thermal shock resistance was tested by heating samples to temperatures between 900 and 1400°C and subsequent quenching in water at room temperature. X-ray diffraction patterns of sintered samples indicate the formation of different calcium aluminate phases, such as CaAl12O (krotite/monoclinic),CaAl4O7 (grossite/monoclinic) and CaAl2O (hibonite-5H/hexagonal). The fracture toughness and shear modulus values of materials sintered at 1450°C were higher (0.48 MPa•m1/2)) and 59 GPa, respectively than those of materials sintered at 1500°C (0.43 MPa•m1/ 2 and 55 GPa, respectively). Also changes in the bulk density, hardness and thermal shock resistance values were observed in materials sintered at 1450°C and 1500°C

An archaeometallurgical study of Mixtec silver gold alloy foils from Tomb No. 7, Monte Alban, Oaxaca, Mexico

This work evaluates four groups of silver gold alloy foil samples from Tomb No. 7 from Monte Alban, Oaxaca. These were classified as received according to coloration as LG1, LG2, LG3, and LG4. These samples were called silver gold alloy foils because of their main elemental composition. These were analyzed (without alterations) via optical microscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). It was necessary to prepare them by focused ion beam (FIB) cross section to know their real microstructure and finally to test their indentation hardness (HIT) and indentation modulus (EIT) to measure mechanical properties. The experimental results revealed that silver gold alloys were cold-worked and annealed using a mixed technique of hammering with intermediate annealing for grain-size refinement. These were modified in their mechanical properties. The LG2 sample was the thinnest (27 μm) and hardest foil (HIT ¼ 1781.7 MPa). It has the highest Au content (56.9 wt%) and the lowest Cu content (1.5 wt%) unlike LG4, which was the softest foil (HIT ¼ 325.1 MPa). This sample showed non-recrystallized grains: This was the major superficial damage and led to a deficient work metal

Physical, mechanical properties and antimicrobial analysis of a novel CaO·Al2O3 compound reinforced with Al or Ag particles

Ceramic-metal (CaO·Al2O3–Al and CaO·Al2O3–Ag) compounds were prepared by mechanical milling and consolidated through an in-situ sintering process. The aim of this work is to study the effects of the Al and Ag particles to ceramic-base compound, primarily in the microstructure, and its mechanical and antimicrobial properties. Chemical systems with a 1:1M ratio between CaCO3 and Al2O3 powder were formed, with the addition of 10 wt% Al or 10 wt% Ag, respectively. The compound material that consolidated were microstructurally characterized through X-ray diffraction, scanning electron microscopy, optic microscopy, and X-ray computed tomography. In addition, the hardness, the fracture toughness, the transversal elastic modulus, and the antimicrobial property were evaluated. The results of X-ray diffraction identified the formation of the calcium aluminate phases, such as CaO·6Al2O3 (hibonite:CA6), CaO·2Al2O3 (grossite:CA2), and CaO·Al2O3 (krotite:CA); as well as Al and Ag were identified in its respective system. In addition, the mechanical properties show changes compared to the reference material that was synthesized under the same conditions and, finally, these materials also have an antimicrobial effect, against the Staphylococcus bacterium that is common in the oral cavity, when studied in synthetic saliva

REFRACTORY CERAMICS SYNTHESIS BY SOLID-STATE REACTION BETWEEN CaCO₃ (MOLLUSK SHELL) AND Al₂O₃ POWDERS

Calcium aluminate-based refractory ceramic was developed as an innovative refractory material, using garden snail (Helix aspersa) shells as a natural source of CaCO₃. A 1:1 molar ratio mixture of CaCO₃ from snail shells and commercial Al₂O₃ powder was prepared by means of high-energy mechanical milling. The mixed powder was compacted in cylindrical samples (disks) and consolidated by sintering at 1450°C and 1500°C for 1h. The density and porosity were evaluated using the Archimedes principle, while the mechanical properties (hardness, fracture toughness, and shear modulus) were determined by indentation and ultrasonic methods, respectively. The thermal shock resistance was tested by heating samples to temperatures between 900 and 1400 °C and subsequent quenching in water at room temperature. X-ray diffraction patterns of sintered samples indicate the formation of different calcium aluminate phases, such as CaAl12O19 (krotite/monoclinic), CaAl₄O₇ (grossite/monoclinic) and CaAl₂O₄ (hibonite-5H/hexagonal). The fracture toughness and shear modulus values of materials sintered at 1450 °C were higher (0.48 MPa-m1/2 and 59 GPa, respectively) than those of materials sintered at 1500°C (0.43 MPa-m1/2  and 55 GPa, respectively). Also changes in the bulk density, hardness and thermal shock resistance values were observed in materials sintered at 1450°C and 1500°C