Issue No 3, December

Abstract

Viscous flow is the main sintering mechanism in glass matrix composites (GMCs) and ceramic glazes and bodies. The microstructural changes that occur in the sintering of these materials include continuous development of apparent and closed pore shape, size, and volume and of the relationship between apparent and total porosity, which determines the material’s final porosity. Final porosity is probably one of the major characteristics of these materials, as it determines many resulting material performance properties. This study examines the microstructural development and sintering of glass–zircon composites with different volume fractions of rigid inclusions: f=0, 0.05, 0.11, 0.17, 0.32, 0.43, 0.53, and 0.65. The test composite sintering curves and the variation of the above characteristics with temperature and zircon grain and crystallite size were experimentally determined. The parameters relating to zircon particle connectivity were theoretically estimated with a view to interpreting the sintering of the composites via particle rearrangement by viscous flow, using the percolation theory. The zircon solution–reprecipitation mechanism was verified to only occur at temperatures above 950 °C.

Abstract

Geopolymer foams are innovative materials synthetized at low temperature, resulting from the activation of an aluminosilicate source with an alkaline solution. The purpose of this study is to understand the role of additives, such as surfactants and fillers, on foam formation. Four different geopolymer foams were synthetized and analyses on their microstructure, density, mechanical resistance and thermal conductivity were carried out. Then, the reactive mixtures of dense geopolymers were studied by the means of FTIR, viscosity and surface tension measurements. The addition of surfactants leads to an increase in the volume expansion up to 4.03, in the porosity rate with a homogeneous microstructure and therefore the foam thermal conductivity and the compressive strength decrease to 57 mW/m.K and from 4950 to 52 kPa respectively. Besides, it modifies the polycondensation reaction by delaying the beginning of the reaction by up to 80 minutes. However, it appears the addition of silica fibers does not impact the geopolymer formation and improves the mechanical properties by 70%. This study also reveals that the ratio of surfactant (300) to metakaolin is crucial in order to stabilize the wet foam before its consolidation.

Abstract

Alkali activated materials (AAM) are obtained trough the reaction of aluminosilicate materials, preferably waste, with alkali activation solutions what results in materials with properties comparable to ceramic or concrete but at the same time with a  significant lowering of CO2 footprint. One such example which could consume a huge amount of waste is production of aggregate. Alkali activated aggregate (AAA) within this research was obtained from fly ash by granulation on a pelletization plate and curing at room conditions or elevated temperature. The density, porosity, compressive strengths, and alkali silica reactivity of so obtained AAA were determined. Density is below 2000 kg/m3, what classified this aggregate into lightweight aggregates (EN 13055-1:2002). Compressive strength depends greatly on the curing regime, and it amounts to 2.6 MPa if aggregate is cured at room conditions, by application of curing at 65 °C the compressive strength is 4.7 MPa. If aggregate is fired then the corresponding compressive strength increases up to 11.4 MPa. Alkali silica reactivity test confirmed that certain expansion is to be expected if such aggregate is used in concrete.

Abstract

The aim of this study was to validate the possibility of using the blast furnace sludge as raw material for the traditional ceramic industry. This validation occurred at the industrial level, in order to consider the maximum possible variables inherent to the industrial process, which are only possible to achieve with high production volume. For this purpose, the main focus was to determine the atmospheric pollution levels, as well as the potential leachability of hazardous components from the ceramic matrix. In addition, the main physical and mechanical properties of the products were also determined. The environmental tests showed that the investigated waste practically does not change the leaching and solubilization parameters of the ceramic product and also it brings benefit as the material particulate emission reduction due to the decrease of the combustible consumption. Additionally, the results indicated that the blast furnace sludge practically did not change the evaluated physical and mechanical properties.

Abstract

The partial masking followed by the chemical etching is a well-developed method in the fabrication of microelectromechanical systems (MEMS). When there is an anisotropic chemical etching demand, the aqueous solution tends to have extremely oxidizing compounds especially hydrogen fluoride (HF). Consequently, the traditional masking methods such as photolithography which is based on the photoresist polymers may fail to protect the substrate as polymers also become removed by such a harsh etching solution. In the current study, a two-step deposition and chemical etching method is developed to form micron-sized arrays of silicon micropillars. A set of <100> silicon wafers undergoes a physical vapor deposition (PVD) of a silicon carbide (SiC) thin film. Prior to the deposition, an extremely fine mesh made of woven thin stainless steel wires is used to partially cover Si substrates. As a result, an array of micron-sized patches of SiC is deposited underneath each opening of the mesh while the rest of the substrate remains uncoated. In the next phase, the substrate is immersed in a highly corrosive solution (a mixture of hydrofluoric acid, nitric acid, and acetic acid). After giving some minutes of chemical etching, the uncoated parts of the substrate suffer from the etching process while those micron-sized patches formed previously to protect the substrate against the severe corrosive solution. Consequently, the bare silicon exposed to the solution is corroded and leaves a micron-sized pillar beneath the protective SiC coat. The etched substrates are used latterly to receive a thin film of the hydrophobic material such as polytetrafluorethylene (PTFE). The AFM analysis shows the topography of the surface and the morphology of the etched surface is studied by using the scanning electron microscopy (SEM). The results demonstrate extremely high wetting contact angle of the mentioned surface. It is proved that there is an optimum corrosion time which leads to the highest contact angle.

Abstract

Phosphatization of waste gypsum (w-Gyp) was investigated in detail to search novel use for a recycling of waste gypsum boards as spherical beads composed of various calcium phosphates. The component of the w-Gyp powder was gypsum (CaSO₄·2H₂O) with some inorganic and organic impurities. The w-Gyp heated at 120 °C for 24 h was bassanite (CaSO₄·0.5H₂O) single phase as the same as the reagent gypsum. Mixture of heated w-Gyp and ion-exchanged water was successfully hardened as spherical gypsum beads in vegetable oil. The degree of phosphatization of w-Gyp and crystal phases of calcium phosphates formed were affected by treatment conditions, pH, temperature and reaction period. The w-Gyp was barely phosphatized in acidic pH with positively temperature depended increasing in reacted amounts. The phosphatization was completed in 6 to 24 h under neutral conditions and in 1 to 6 h under basic conditions. Dicalcium phosphate dihydrate (DCPD) could firstly be formed in all conditions and it changed into dicalcium phosphate anhydrous (DCPA) by dehydration of DCPD at over 60 °C. Under higher pH conditions, DCPA or DCPD was subsequently converted into hydroxyapatite, the most stable calcium phosphate in water. During the conversion, b-tricalcium phosphate (b-TCP) was also formed by the presence of Mg²⁺, a stabilizer of b-TCP. Spherical beads consisting of these calcium phosphates were prepared from spherical beads of the w-Gyp.

Abstract

Through collaboration between industry and government, we succeeded in blending synthetic seeds, evaluation seeds, and cosmetics needs and quickly established original products and sensibility studies. By controlling the average inter-surface distance in the liquid and the surface/volume precipitation in the droplet, it was possible to prepare composite particles, hollow granules and drug-encapsulating granules. Control of these microstructure improved UV shielding and optical sharpness and allowed obtaining several sustained release rates of the drug. Systematic verification of the direct shear testing method and organoleptic evaluation promoted the association between qualitative sensory parameters and physical properties and, furthermore, the standardization of the test method. Through collaboration among academia, industry and government in the powder technology field, authentication assessment (i.e., ISO, JIS) of the test methods was established.

Abstract

FIRE is committed to assist the education of young professionals and engineers of all horizons, to conceptualize, design, implement and organize efficient processes to manufacture the best refractory materials for all and specific users. FIRE education programs and the main accomplishments made since 2007 are at first briefly reviewed. In 2017, to enhance its educational mission FIRE members have undertaken the task to launch a second compendium series of books on the theme of Corrosion, to actualize the knowledge accumulated in the last three decades and to disseminate the main results for the benefit of the widest readership. The essential aspects of the 3 books to appear in 2018 are provided to illustrate the FIRE members’ role in such an endeavour.