This article aims to investigate the corrosion resistance of novel fly ash–based forsterite–spinel (Mg2SiO4-MgAl2O4) refractory ceramics to various corrosive media in comparison with reactive alumina–based ceramics. Because fly ash is produced in enormous quantities as a byproduct of coal-burning power stations, it could be utilized as an affordable source of aluminum oxide and silicon oxide. Corrosion resistance to iron, clinker, alumina, and copper was observed by scanning electron microscope with an elemental probe. The influence on the properties after firing was also investigated. Fly ash–based and reactive alumina–based mixtures were designed to contain 10%, 15% and 20% of spinel after firing. Raw material mixtures were sintered at 1550 °C for two hours. X-ray diffraction analysis and scanning electron microscopy were used to analyze sintered samples. The apparent porosity, bulk density, modulus of rupture, and refractory and thermo–mechanical properties were also investigated. The experimental results disclosed that the modulus of rupture, thermal shock resistance and microstructure were improved with increasing amounts of spinel in the fired samples. An analysis of the transition zones between corrosive media and ceramics revealed that all mixtures have good resistance against corrosion to iron, clinker, aluminum and copper.
Forsterite refractory ceramic is mostly used in the cement industry as the lining of a rotary kiln and as the lining of metallurgical furnaces due to its high refractoriness of up to 1850°C. Another significant property of forsterite is its coefficient of linear thermal expansion used in the electrotechnical industry for ceramic-metal joints. An addition of aluminium oxide to a raw-material mixture results in the creation of a magnesium-alumina spinel (MgO•Al2O3), which improves the sintering and mechanical properties of forsterite ceramics. An inexpensive source of aluminium oxide is fly ash. The utilization of fly ash, a secondary energy product of coal-burning power plants, is important for the environment and sustainable development. This paper evaluates the transformation of mullite (3Al2O3•2SiO2) from fly ash into a magnesium-alumina spinel, its influence during the synthesis and the resulting properties of a fired forsterite refractory ceramic body. Forsterite-spinel ceramics were synthesized from olivine, calcined magnesite and 0-20 % of fly-ash powders. XRD analyses were used to determine the mineralogical composition, thermal analyses were used to determine the formation of spinel and its behaviour during the firing, and scanning electron microscopy (SEM) was used to determine the morphology of crystal phases. The refractoriness of pyrometric cones, refractoriness under load, thermal-shock resistance, water absorption, porosity and mechanical properties of the fired test samples were also determined. The transformation of mullite resulted in small amounts of magnesium-alumina spinel in the forsterite ceramics. Test results showed that the presence of magnesium-alumina spinel improved the sintering, microstructure, thermal-shock resistance and mechanical properties in comparison with pure-forsterite refractory ceramics.
In this study, the potential use of waste diatomaceous earth from the production of diatomaceous earth for filtration purposes, as an alternative raw material for foam glass production, was explored. The chemical and mineralogical composition and the high temperature behavior of waste diatomite were studied to assess its suitability for foam glass production. Glass-ceramic foams were prepared using NaOH solution as a foaming agent, via a hydrate mechanism. The influence of different pretreatments and firing temperatures on the foam’s structure, bulk density and compressive strength was investigated. High temperature behavior was studied using TG/DTA analysis and high temperature microscopy. Phase composition was studied using X-ray diffraction analysis. Glass-ceramic foam samples of a high porosity comparable to conventional foam glass products were fabricated. The pretreatment temperature, foaming temperature and sintering holding time were found to have a significant influence on foam properties. With increased pretreatment temperature, pyrogenic carbon from the thermal decomposition of organic matter contained in the raw material acted as an additional foaming agent and remained partially unoxidized in prepared foams. The bulk densities of prepared samples ranged from 150 kg/m3 to 510 kg/m3 and their compressive strengths were between 140 and 1270 kPa.
This article examines the process for the synthesis of forsterite–spinel (2MgO·SiO2/MgO·Al2O3) refractory ceramics from fly ash and alumina as sources of aluminum oxide. Raw materials were milled, mixed in different ratios and sintered at 1500 °C for 2 h. Sintered samples were characterized by XRD, thermal analyses and SEM. Porosity, water absorption, bulk density, refractoriness, refractoriness under load and thermal shock resistance were also investigated. The impact of fly ash as a raw material was investigated in accordance with the resulting properties and microstructure of samples with fly ash and alumina as the raw materials. Due to the positive effect of flux oxides (iron oxides and alkalis) on sintering, the mullite contained in fly ash completely decomposed into silica and alumina, which, together with magnesium oxide, formed spinel. This led to improved microstructural and mechanical properties and thermal shock resistance. In particular, mixtures with 10 wt.% and 20 wt.% of fly ash had the most promising results compared to alumina mixtures. Both modulus of rupture and thermal shock resistance were improved, while the impact on refractory properties was minimal. The novelty of this research lies in the recycling of fly ash, a by-product from coal-burning power plants, into a raw material for the production of forsterite–spinel refractory ceramics.
The results described in this paper first demonstrate key differences between a plasma-exposed blanket porous dielectric sample and a patterned structure in terms of surface sealing induced by the patterning plasma using ellipsometric porosimetry characterization. While the blanket CVD organosilicate glass (nominal k-value = 2.4, ∼20% of porosity) surface was sealed by the C 4 F 8 /CF 4 -based plasma, the surface of the analogous patterned structure of 45 nm 1/2 pitch was found to be completely open after the same patterning plasma process. Second, the surface composition of the patterned feature, type of the residues generated during the plasma etch, and the effect of a subsequent wet clean step are presented. The experimental results demonstrate that the use of a relevant patterned test structure and its characterization represent an appropriate approach for the optimization of the etch and cleaning processes. The removal efficiency of various wet clean solutions, including dilute HF, citric acid, tetramethylammonium hydroxide:H 2 O 2 :H 2 O mixture, and a slightly alkaline formulated mixture, with regard to polymer residues, CFx, and metal-containing residues, TiFx, can be clearly distinguished using the patterned porous low-k stack. In back-end of line (BEOL) processing of advanced microelectronic CMOS integrated circuits, conductor lines are made using a damascene approach. For this, dielectric layers are locally etched through a patterned photoresist or metal hardmask layer using plasmas and followed by electroplating of Cu inside the etched patterns. In order to ensure accurate profile control, etching anisotropy, and minimize degradation of the exposed porous dielectric during the plasma etch, polymerizing plasma chemistries are employed to deposit a thin layer of polymer on the exposed surface.1-3 A good balance between the polymerization and the dielectric etch rate allows the polymer film to passivate the sidewalls without affecting the vertical etch rate, resulting in a vertical etch profile. The polymer formed during the dry etch process ("post-etch polymer residues" or PER), mostly fluorocarbon polymers for fluorocarbon-containing plasmas, must be removed prior to deposition of subsequent layers (metal) in the etched features to achieve high adhesion and good coverage. Removal of these polymers is usually performed by a combination of a short plasma treatment and wet clean using chemical solutions, or by wet cleans alone. It is known that this type of fluorocarbon polymer is chemically inert to many existing wet clean solutions, including aqueous solutions such as fluoride ion-containing or highly alkaline solutions, and solvent mixtures.4 A short plasma treatment carried out prior to the wet clean step enhances the polymer removal efficiency but also has a drawback of irreversibly damaging the porous dielectrics by material densification, carbon depletion, and increase of hydrophilicity. 1,2,5,6 An alternative approach for improving the residue removal efficiency involves structural modification o...
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