Synthesis of mullite aggregates from fly ash: effect on thermomechanical behaviour of low cement castables
01 Aug 2004-British Ceramic Transactions (Maney Publishing)-Vol. 103, Iss: 4, pp 176-180
TL;DR: Refractory aggregates were synthesized from beneficiated fly ash by reaction sintering with calcined alumina at 1600°C, and 83% mullite yield was achieved as mentioned in this paper.
Abstract: Refractory aggregates were synthesised from beneficiated fly ash by reaction sintering with calcined alumina at 1600°C, and 83% mullite yield was achieved. The aggregates had low porosity, low thermal expansion and good refractoriness. To study compatibility in castable refractories, the aggregates were used in high alumina cement based low cement castables and their thermomechanical behaviour was studied. Microstructural characterisation revealed that the emergence of new bond phases such as mullite and calcium hexa-aluminate had a beneficial effect on the hot modulus of rupture and creep resistance of castables. An attempt was made to establish a structure-property relationship.
TL;DR: In this paper, a critical overview on fly ash utilisation with emphasis on mechanical activation of fly ash in developing processes for medium to high volume utilisation of fly Ash is presented.
Abstract: This paper is a critical overview on fly ash utilisation with emphasis on mechanical activation of fly ash in developing processes for medium to high volume utilisation of fly ash. Applications of mechanical activation that are particularly highlighted include blended cement containing high volume (50–60%) of fly ash, and geopolymer materials, such as high compressive strength (up to 120 MPa) geopolymer cements and self glazed tiles. The schemes for the utilisation of fly ash involving mechanical activation are worked out that have potential to evolve as sustainable solutions.
TL;DR: In this article, a fly ash-based radiopaque material (FARM) has been used for making X-ray radiation-shielding materials, which is a waste generated in power plants due to combustion of pulverized coal.
Abstract: For the first time the capability of fly ash to produce barium containing radiopaque materials has been demonstrated. Fly ash which is a waste generated in power plants due to combustion of pulverized coal, has been utilizeda for making X-ray radiation-shielding materials. A novel method for making radiation-shielding materials utilizing fly ash and barium compound has been developed by ceramic processing route using phosphate bonding. The fly ash based radiopaque materials (FARM), i.e. shielding materials are characterized for their X-ray attenuation characteristics. The shielding, i.e. half value thickness (HVT) for different energies of X-ray photons for FARM have been computed and compared with conventionally used shielding materials, namely concrete and lead, it is found that the HVT of the fly ash based shielding materials, in comparison to concrete, is significantly very less for the various energies of X-ray photons. The X-ray powder diffraction studies confirmed the presence of monoclinic and hexagonal celsian and sanbornite as the major shielding phases and potassium aluminosilicate, sodium aluminosilicate and silicophosphate as the binder phases in the FARM and are responsible for providing bonding to the ceramic matrix leading to the effective shielding and mechanical properties. Scanning electron microphotographs have revealed the compacted plate like particles with hexagonal morphological characteristics of the various barium silicate and barium aluminosilicate (BAS) shielding phases in the matrix of radiopaque materials. The mechanical properties, namely compressive strength and impact strength evaluation test showed that FARM meets the standard specifications laid down for radiation-shielding concrete and ceramic tiles. Based on the above studies, it is found that FARM, can preferably be used for the construction of X-ray diagnostic and CT-scanner room to provide adequate shielding against X-ray photons.
TL;DR: In this article, a lead free, non-toxic, X-ray radiation shielding glass possessing barium, boron substituted kornerupine crystallites in the glassy matrix has been developed.
Abstract: Conventionally lead based radiation shielding glasses find application in Diagnostic X ray room. However, the production and recycling of lead containing glasses posse’s health hazards and therefore there is an urgent need to develop lead free, non-toxic radiation shielding glasses useful for Diagnostic X-ray rooms and many other shielding applications. The major glass forming constituents includes oxide of alkali and alkaline earth metals etc. The simultaneous presence of glass forming and shielding imparting chemical constituents present in brine sludge (BS)—a waste generated in chloral alkali industries, enabling synergistic chemical reaction among other raw materials namely fly ash (FA) and Borax (B2O3), have been chemically formulated and designed for Developing shielding Kornerupine crystallites embedded in the developed lead free homogenous shielding glass by a novel process (The patent application has been filed in India Ref. No. 0059NF2016). Shielding glasses with composition xBS:(80-X)B2O3:20 FA, where (x = 35, 40, 45, 50 wt%) have been prepared using melt process followed by annealing method. The developed shielding glass has been characterized using complementary sophisticated instrumental techniques such as FESEM, EDS XRD, IR and TG/DSC and SEM for identifying shielding crystallites embedded in the developed glassy matrix. The X-ray attenuation test of the developed glass has shown that these glasses can find broad application spectrum ranging from diagnostic X-ray room to various functional accessories of shielding appliances being used in technical, medical and research applications. Graphical abstract of development of advanced, non-toxic, X-ray radiation shielding glass possessing barium, boron substituted kornerupine crystallites in the glassy matrix
TL;DR: In this paper, the authors discuss the potential of separating and recovering useful materials or elements from waste materials using sustainable recovery methods, which will not only decrease environmental pollution, but also provide an environmentally friendly and cost-effective approach for materials synthesis.
Abstract: Environmental pollution is one of the major concerns throughout the world. The rise of industrialization has increased the generation of waste materials, causing environmental degradation and threat to the health of living beings. To overcome this problem and effectively handle waste materials, proper management skills are required. Waste as a whole is not only waste, but it also holds various valuable materials that can be used again. Such useful materials or elements need to be segregated and recovered using sustainable recovery methods. Agricultural waste, industrial waste, and household waste have the potential to generate different value-added products. More specifically, the industrial waste like fly ash, gypsum waste, and red mud can be used for the recovery of alumina, silica, and zeolites. While agricultural waste like rice husks, sugarcane bagasse, and coconut shells can be used for recovery of silica, calcium, and carbon materials. In addition, domestic waste like incense stick ash and eggshell waste that is rich in calcium can be used for the recovery of calcium-related products. In agricultural, industrial, and domestic sectors, several raw materials are used; therefore, it is of high economic interest to recover valuable minerals and to process them and convert them into merchandisable products. This will not only decrease environmental pollution, it will also provide an environmentally friendly and cost-effective approach for materials synthesis. These value-added materials can be used for medicine, cosmetics, electronics, catalysis, and environmental cleanup.
TL;DR: In this paper, an interdisciplinary approach has been conceived to address environmental hazards of brine sludge and fly ash waste, from chloral alkali industry by developing non-toxic, geopolymeric (cement-free) materials for sustainable development.
Abstract: For the first time, an interdisciplinary approach has been conceived to address environmental hazards of brine sludge and fly ash waste, from chloral alkali industry by developing non-toxic, geopolymeric (cement-free) materials for sustainable development. The process enables the utilization of two industrial wastes, namely fly ash and brine sludge. The utilization of brine sludge in making geopolymeric (cement-free) paver blocks and bricks and its effect on the engineering properties of these products are discussed. The XRD, IR and SEM studies have also been presented. The compressive strength of geopolymeric mortar made using brine sludge could be achieved up to 20 MPa. These results clearly exhibit that brine sludge can be utilized for making geopolymeric (cement-free) paver blocks and bricks. The geopolymerization of brine sludge converts it into non-toxic material which is confirmed by leachability studies. The utilization of brine sludge in making geopolymeric (cement-free) paver blocks and bricks as construction materials could serve as an attractive approach to solve its disposal issue, thereby saving non-renewable natural resources otherwise required for making paver blocks and bricks.
TL;DR: Theoretischen Untersuchungen zufolge mus beim Aufbau eines Produkts aus losen Kornern, in dem die Korner ohne jegliche Ordnung vorhanden sind, die notwendige und hinreichende Bedingung fur die Konstanthaltung des Zwischenraums beim Zufugen grober and groberer Korner sein, das das Kornungsbild stets die Gleichung C(k
Abstract: Theoretischen Untersuchungen zufolge mus beim Aufbau eines Produkts aus losen Kornern, in dem die Korner ohne jegliche Ordnung vorhanden sind, die notwendige und hinreichende Bedingung fur die Konstanthaltung des Zwischenraums beim Zufugen grober und groberer Korner sein, das das Kornungsbild stets die Gleichung C(k) = kq befriedigt. Fur Produkte mit diesem Kornungsbild wird weiter der Zwischenraum symbat mit der Grose q wachsen. Es werden Untersuchungen uber Produkte aus zwei und drei Korngrosen vorgenommen, indem die Vorschriften Grun's und Kerkhof's fur die Erzielung des dichtest moglichen Produkts verglichen werden. Endlich werden Produkte mit dem obigen Kornungsbild, indem man q die Werte ∞, 2, 1, 2/3, 1/2 und 1/3 gegeben hat, samt ein Produkt nach der „Fullerkurve“ aufgebaut und auf Zwischenraum verglichen Bei allen Untersuchungen wird der Zwischenraum sowohl fur das lose eingefullte als auch fur das fest zusammengeschuttelte Produkt gemessen. Es wird gezeigt, das man eine grosere Dichte kaum erwarten darf bei Produkten aus wenigen, eventuell nacheinander abgepasten Korngrosen aufgebaut als bei Produkten, wo alle Korngrosen innerhalb gewisser Grenzen anwesend sind.
TL;DR: Stoichiometric mullite powder (3Al2O3·2SiO2) prepared by spray pyrolysis and sintered at 1650°C attained 95% of theoretical density as mentioned in this paper.
Abstract: Stoichiometric mullite powder (3Al2O3·2SiO2) prepared by spray pyrolysis and sintered at 1650°C attained 95% of theoretical density. The flexural strength was 360 MPa at room temperature and decreased slightly at 1400°C. A fairly high KIc value (2.8 MN/m3/2) was obtained. These mechanical properties can be attributed to the highly homogeneous stoichiometric composition of the raw powder.
TL;DR: In this paper, the effect of the mullite bond phase on the physico-mechanical and refractory properties of the castable castables was investigated after firing at different firing temperatures using X-ray diffractin analysis.
Abstract: In order to study the effect of the mullite bond phase on the physico-mechanical and refractory properties of the refractory castables, four castable samples were prepared; castable 1 contained 15 wt.% calcium aluminate cement (80% alumina) and 85 wt.% well graded tabular alumina . The other three samples (2, 3, 4) contained 10, 5 and 2% cement and 5, 10 and 13% of an alimina/ silica mixture (in the ratio 2.33:1, the molecular ratio of mullite). Their composition was investigated after firing at different firing temperatures using X-ray diffractin analysis. The physico-mechanical and refractory properties of such castables were determined according to standard specifications. Castable 4 that contained only 2 wt.% cement with 13 wt.% alumina/silica mixture and 85 wt.% well graded tabular alumina aggregate exhibited outstanding physico-mechanical and refractory properties after firing at 1500°C due to the presence of mullite in the bond phase with very little CaO. This enables their use in various refractory applications such as in steel, aluminium, copper, glass, cement, chemical and ceramic production.