Ta-Wui Cheng

Fire-resistant geopolymer produced by granulated blast furnace slag

This paper describes research into the use of granulated blast furnace slag as an active filler in the making of geopolymers. During this work it was found that geopolymer setting time correlates well with temperature, potassium hydroxide concentration, metakaolinite and sodium silicate addition. The physical and mechanical properties of the geopolymer also correlated well with the concentration of alkaline solution and the amount of metakaolinite that is added. The highest compressive strength achieved was 79 MPa. For fire resistance tests, a 10 mm thick geopolymer panel was exposed to a 1100 °C flame, with the measured reverse-side temperatures reaching less than 350 °C after 35 min. The products can be fabricated for construction purposes and have great potential for engineering applications.

On formation of CaO–Al2O3–SiO2 glass–ceramics by vitrification of incinerator fly ash

CaO-Al(2)O(3)-SiO(2) system glass ceramics of incinerator fly ash have been prepared by vitrification and then heat-treated in different conditions. The thermal molten process (TMP) was applied to heat treat vitrified samples at high temperatures whereas in the powder sintering process water-quenched vitrified samples were ground into powder and then sintered at high temperatures. Gehlenite was found present as the major phase in all treated samples. Treated samples in general exhibited good leachability characteristics as well as chemical durability, except in the HCl solution. Microstructure and physical properties varied with the treatment condition. Fine and relatively high dense structures with desirable properties were obtained for samples treated by the TMP. For both processes, higher temperature treatments caused crystal growth and thus poor properties were attained. Good physical and mechanical properties achieved at 900-950 degrees C in this study imply the treated samples have attractive potential for engineering applications.

Electromagnetic Shielding Effectiveness of the Twill Copper Woven Fabrics

Twill copper fabrics (3/1) were produced using a single cylinder handloom jacquard weaving machine. The effect of varying weft density, warp density, wire diameter, and lay-up angle on electromagnetic shielding effectiveness was studied. The electromagnetic shielding effectiveness (EMSE) of various copper woven fabrics was obtained using a coaxial transmission line holder in the frequency range of 144–3000 MHz. With an increase in the number of conductive fabric layers, warp density, and weft density, an increase in shielding effectiveness is observed. With an increase in wire diameter, a decrease in shielding effectiveness has been observed.

Combined glassification of EAF dust and incinerator fly ash.

Stainless steelmaking dust contains large amount of heavy metals, such as Cr and Ni. If these hazardous materials are not treated properly, they will cause detrimental secondary contamination. Preliminary study on recycling stainless steelmaking dust employed the thermal molten technology. Glass-ceramics were formed by combination stainless steel dust and incinerator fly ash with the ratio of 1:9. The major phases were Augite, Akermanite, and Donathite. It was found that the glass-ceramics shows the best characteristic at 900 degrees C after 5 h of heat treatment. This product can be used as building materials or refractory materials.

A study of synthetic forsterite refractory materials using waste serpentine cutting

Abstract There are more than 40 serpentine mines in Taiwan, and most of them are located in Hualien (Eastern Taiwan). Almost all the serpentine dimension stones produced from these mines are exported. Crushed serpentine is used as a flux material for iron-making. There are more than 0.54 million tons of serpentine waste produced per year during mining operation. This serpentine waste, at the moment, has no commercial value. The purpose of this research is to develop a process to manufacture synthetic forsterite refractory using serpentine waste with the addition of magnesium-based compounds by sintering technology. The test results show that, compared with MgO, the addition of Mg(OH) 2 or MgCO 3 can react with serpentine completely to produce better forsterite at lower temperature. The process is feasible and provides a potential usage of serpentine waste in the future.

The point of zero charge of monazite and xenotime

The point of zero charge (PZC) for monazite and xenotime reported in the literature has a wide range. Chemical modelling from this study shows that variation in the chemical composition of the monazite and xenotime samples can have detrimental effects on the chemical speciation of the mineral surfaces. It has been found that any slight variation of the chemical composition of the mineral surface would, therefore, cause a reversal of surface charge. This explains the wide variation of PZC of different rare earth mineral samples from different mines.

Effects of Nano-SiO2 on Setting Time and Compressive Strength of Alkaliactivated Metakaolin-based Geopolymer

This study presents a discussion on the effects of different solid-to-liquid (S/L) ratios (0.97 to 1.19) and nano- SiO2 (NS) percentages (0% to 3%) on some properties of metakaolin (MK)-based geopolymers. The setting time and compressive strength were investigated. Mercury intrusion porosimetry, fourier transform infrared spectroscopy, and scanning electron microscopy were used to determine the microstructure of the samples. The results show that a MK- based geopolymer sample added 1% NS with the S/L ratio of 1.03 exhibits more strength and less porosity. Applying NS to the geopolymer enhances compactness and increases strength. Therefore, nanotechnology can be used to improve geo- polymers.

Recycling of Solar Panel Waste Glass as a Partial Replacement of Meta-kaolinite in the Production of Geopolymers

This investigation elucidates the mechanical characteristics of geopolymer containing solar panel waste glass. With the SiO2/Na2O molar ratio (S/N = 0.75, 1.0, 1.25, 1.5, 1.75), the percentage of metakaolinite that is replaced by solar panel waste glass (040%), and the curing time of 1, 7, and 28 days as the study variables, the porosity, density, setting time, compressive strength, and flexural strength of the geopolymer were evaluated. The morphology of geopolymer was examined using Scanning Electron Microscopy (SEM), and its microstructural properties were examined through Fourier transform infrared spectroscopy (FTIR) analysis. The results demonstrate that the S/N molar ratio significantly influences the mechanical and morphological characteristics of geopolymers. The geopolymer containing solar panel waste glass with an S/N of 1.75 had the greatest compressive strength. The intensity of the peak that represented Si-O-Al bonding of the geopolymer containing solar panel waste glass increased with the S/N. Analysis of the sample morphology revealed that the microstructures of stronger samples were more homogeneous and appeared denser. Furthermore, solar panel waste glass has the potential to partially replace metakaolinite as a geopolymer material, and to exhibit favorable mechanical characteristics.

Utilization of Circulating Fluidized Bed Fly Ash as Pozzolanic Material

A circulating fluidized bed (CFB) boiler generates energy by burning petroleum coke. Because burnt petroleum coke has a high sulfur content, limestone is added to the boiler to reduce the emittance of sulfur dioxide through desulfuration. The residue collected from the boiler is called CFB ash. CFB boilers in Taiwan can produce 328,000 tonnes of CFB fly ash per year. In this study, the pozzolanic characteristics of CFB fly ash were investigated by blending CFB fly ash and ordinary Portland cement (OPC). The CFB fly ash was mainly composed of CaO, SO3, and SiO2 in concentrations of 37.8%, 9.2%, and 2.2%, respectively. The crystals of CFB fly ash contained 3CaO.SiO2, 2CaO.SiO2, Ca(OH)2, C-S-H (Tobermolite), and Ettringite. The results revealed that applying the toxicity characteristic leaching procedure to CFB fly ash renders it suitable for use in blended cement. At later curing ages (90 days), the pore volumes of both the OPC and the CFB-fly-ash-blended cement pastes (CFBFABCP) decreased as the curing time increased. A possible explanation is that C3S and C2S were consumed to form C-S-H gel, resulting in an increase in the Q 1 and Q groups identified by Si Nuclear Magnetic Resonance (NMR) spectroscopy. Furthermore, the peak of the Q group decreased, but those of the Q and Q peaks increased with an increasing curing time. The pozzolanic activity of the CFBFABCP containing 10% CFB fly ash indicates that it is a suitable substitute for OPC in blended cement.

The Purification of Crude Zinc Oxide Using Scrubbing, Magnetic Separation, and Leaching Processes

Physical separation and hydrometallurgical purification techniques, such as scrubbing, magnetic separation, leaching, and precipitation were used to convert crude zinc oxide into high purity zinc powder. Scrubbing was used to remove the soluble chloride on the crude zinc oxide surface. The solubility of metal oxides contained in the crude zinc oxide was simulated by DIASTAB software to determine the pH ranges for metals precipitation. Leaching under various conditions was conducted to determine optimum operating parameters. From the solubility diagram, the titration ends in the range of pH 5.78~6.1 and high purity (92.2%) zinc powder can be obtained with 82.04% recovery.