Synthesis of new Cr2O3/Fe2O3/glass composites from industrial wastes; from undesired to advanced optical products.

For the tendency toward cleaner production and safe conversion of undesired toxic wastes to highly priced advanced products, this work introduces new ceramics/glass composites of Cr2O3/Fe2O3/lead silicate glass (LSG) from industrial LSG wastes. Both chromia Cr2O3 and hematite Fe2O3 ceramics are added equally to the LSG wastes with different percentages (10, 20, and 30 wt.%) via the pressureless sintering method. The competitiveness of this work is dependent on the conversion of undesired waste materials into advanced/smart optical materials with a low cost and an environmentally friendly method. Hence, the influence of both Cr2O3 and Fe2O3 additions on the behavior and the different characteristics of the lead silicate wastes are comprehensively investigated. Evaluation of the final ceramics/glass composites was achieved through their phase composition, microstructure, optical, and magnetic characteristics. The results verified that the insertion of both chromia and hematite together into the glass waste had a key role in improving its morphological properties and optical and magnetic behaviors. Composite with 30% of Cr2O3/Fe2O3 gave the highest optical absorbance of 90%, the lowest and best band gap energy of 1.68 ev, and the highest refractive index of 2.85. Also, it recorded the best magnetic behavior with the highest saturation magnetization of 139.700 × 10-2A m2 kg-1 and the best coercivity of 190.0 Oe. These findings confirmed the successful clean conversion of the hazardous lead silicate waste into advanced products with promising optoelectronic characteristics.

Processing of high temperature alumina/aluminum titanate ceramic composites from clean sources.

Producing new technological materials with high performance from clean sources has become a global requirement. Alumina/aluminum titanate (Al2O3/Al2TiO5) composites are high-temperature portentous materials used in various advanced applications. In this work, different Al2O3/Al2TiO5 composites were obtained with high thermal and mechanical properties for high-temperature applications by a low-cost process. The targeted composites were produced from calcined alumina and, rutile ore extracted from the Egyptian black sands by pressureless sintering at a temperature of 1650 °C/2 h. Rutile was added to alumina with a different content (0-40 wt%) to promote its sinterability and thermo-mechanical response. Evaluation of the produced composites in terms of phase composition, densification, microstructural features, mechanical and thermal properties was investigated. The results indicated that the addition of small amounts of rutile (10 and 20 wt%) succeeded in forming a stable Al2O3/Al2TiO5 composite structure. However, higher content of rutile led to the formation of Al2TiO5 rich matrix composites. Moreover, highly dense composites with harmonic microstructure and enhanced mechanical strength were attained by increasing the rutile content. The composite with only 10 wt% rutile addition gave the highest density of 3.6 g/cm3 and the highest cold crushing strength and modulus of rupture values of 488.73 MPa and 106.19 MPa, respectively. Notably, the addition of rutile has a substantial effect on promoting the thermal properties and thermal stability of the obtained composites up to a high temperature of 1400 °C. The present study shows that addition of rutile ore to alumina is one economical way of improving the densification and thermal expansion of Al2O3 for high temperature applications. Using a clean source such as rutile ore that contains some thermal stabilizers as Fe2O3, Al2O3, SiO2, ZrO2, and MgO instead of pure TiO2 has played a noticeable role in improving the reaction sintering and resulting in a highly qualified material. Thus, sintered Al2O3/Al2TiO5 composites can be considered as a promising high-temperature material for advanced applications.

Optical, magnetic and electrical properties of new ceramics/lead silicate glass composites recycled from lead crystal wastes.

Nowadays, the disposal of industrial wastes is an ablaze issue worldwide, especially those containing hazardous materials. Lead silicate glass waste (LSG) produced during lead crystal glass manufacturing, which contains about 30% of toxic lead compounds, belongs to this category. This work aims to adopt an innovative clean method to convert this waste into novel advanced ceramic materials via an environmental friendly method. Chromia Cr2O3 and hematite Fe2O3 ceramics with different content (0, 5, 10, 15%) are added separately to the solid wastes of LSG recovered from national crystal glass industry to obtain various ceramics/LSG composites by pressureless sintering methods. Different properties of the produced composites are evaluated in terms of phase's identification and microstructural features. Optical properties in terms of absorbance, reflectance, band gap (Eg), refractive index (n) and photoluminescence (PL) are investigated. Magnetic and electrical properties are inclusively studied. Results indicated that, an addition of chromia and hematite as well as increasing their content to 15% has enhanced the microstructural features, optical, electrical and magnetic properties of the obtained composites. Cr2O3/LSG composites are considered as promising optical and electrical materials. However, Fe2O3/LSG composites showed the highest optical and magnetic properties. They are strongly recommended in optoelectronic and magneto-optical applications.

Combined effect of magnesia and zirconia on the bioactivity of calcium silicate ceramics at C\S ratio less than unity.

This paper describes the effect of magnesia in the presence of zirconia on the bioactivity, microstructure and physico-mechanical properties of calcium silicate composition adjusted at calcia/silica ratio(C/S) of 0.5. A mixture from calcium carbonate and silica was conducted at C/S of 0.5. 20wt.% of magnesia and 5-25wt.% of ZrO2 were added. Each mixture was mixed with ethanol in a planetary ball mill, dried, formed and fired at a temperature of 1325±5°C. Phase composition, FE-SEM, and physico-mechanical properties of the fired specimens were determined and explained. The in vitro bioactivities of these specimens were investigated by analysis of their abilities to form apatite in the simulated body fluid (SBF) for a short time (7days) using SEM-EDS. The findings indicated that the surface of the specimens containing 5 and 15wt.% ZrO2 were completely covered by single and multilayered hydroxyapatite (HA) precipitate typical to "cauliflower" morphology, respectively. The surface of the specimen containing 25wt.% ZrO2 did not cover, but there are some scattered HA precipitate. The differences among the results were rationalized based on the phase composition. Vickers hardness and fracture toughness of the specimens of highly promised bioactivity were 2.32-2.57GPa and 1.80-1.50MPa. m1/2, respectively. The properties of these specimens are similar to the properties of human cortical bone. Consequently, these composites might be used as bone implant materials.

Nano-alumina powders/ceramics derived from aluminum foil waste at low temperature for various industrial applications.

In this work, nanoscale single crystalline γ- and α-alumina powders have been successfully prepared from aluminum foil waste precursor via co-precipitation method using NH4OH as a precipitant. The obtained gel after co-precipitation treatment, was calcined at different temperatures (500,700, 900, 1050, 1100, 1300 and 1500 °C) and the products were characterized by XRD, FTIR and HRTEM. The results revealed that nano-γ-Al2O3 was fully transformed to nanometer-sized α-Al2O3 (36-200 nm) after annealing at temperatures as low as 1100 °C.The thermally preheated powder at 500 °C was further pressed under 95 MPa by the uniaxial press and the obtained bodies were found to have98.82% of the theoretical density, 1.18% porosity and 708 MPa compressive strength, when sintered at temperatures as low as 1600 °C without using any sintering aid. These excellent results proved that this work will contribute to finding a commercial source for preparing sub 100 nm α-alumina through the secondary resources management and even more so to synthesizing strong α-Al2O3 bodies which are promising in terms of their structure and compression. The α-Al2O3 bodies synthesized by the present work could be used as a feedstock for fabrication of various kinds of functional and structural materials that are extensively used in high tech.