Key Engineering Materials Vol. 659

Abstract: In this work, the statistical analysis methods, including least square method and statistical hypothesis testing, were used to study the flexural strength and density of the specimens formed from mullite powder by powder injection molding (PIM). The feedstock for PIM consist of mullite powder and the composite binder consisting of 78 wt% polyethylene glycol (PEG), 20 wt% polyvinyl butyral (PVB), and 2 wt% stearic acid (SA). The PIM machine used in this work was the lab-scale plunger type. The compositions of the feedstock that could be injection molded by this machine were 50, 52, and 54vol% mullite. After molding, PEG in the green specimens was removed prior to sintering by soaking the specimens in the water at 60 °C for 24 hours while PVB and SA were removed during sintering. The sintering temperatures were 1300 to 1450°C. At significance level of 0.05, the least square method and the statistical hypothesis test showed that both feedstock compositions and sintering temperatures used in this work affected the densities of sintered specimens. However, the increasing of the flexural strength of sintered specimens was mainly by the increasing of the sintering temperature.

Abstract: Rising worldwide demands for energy encourages development of high-efficiency energy storage and capacitor components. Main requirements for dielectric materials employed in fabrication of high energy density capacitors include high dielectric constant, high dielectric breakdown strength, and low dielectric loss. Owing to its high dielectric constant and low dielectric loss [1], barium titanate is among common capacitor materials. Tailoring of dielectric properties of barium titanate can be achieved through controlled chemical composition, microstructure, and crystal structure. Synthesis and processing techniques, as well as doping of barium titanate, can be key factors to control the composition and structure, which consequently contribute to enhancement of dielectric constant in the material.

Abstract: The river sediments from the Chi River basin, including Chi River and Nam Phong River, are valuable to comprehend the brick process, physical and chemical properties which lead to its strength. Study areas cover three different regions in Maha Sarakham, Kalasin and Roi Et provinces nearby six brickyards which are separated in two areas Nam Phong and Chi River area. Mechanical property is referred to compressive strengths of a brick unit. These compressive strengths of the fired brick unit increase with increasing their densities. Elastic moduli of original fired brick at the ultimate stress and strain corresponding by time in submersion test show that any solutions filled in void or pore can enhance the apparent density of bricks. Thus, fired bricks are capable to resist compressive force than the normal condition. The ratio of modulus in submersion test for 4 hours, expressed in the original fired brick to water, acidic saline and saline is 1: 1.1: 1.2: 1.6, respectively. The stress level depends on the fracture plane over particular long space fabricating by manufacturing process. These results are related only to the linearity plot.

Abstract: The objective of this study is to improve the particle suspension stability of drinking water treatment sludge (DWTS) and comparable to other silicate powder which are bentonite, micro silica (micro-SiO₂), and nano-silica (nano-SiO₂). The main dispersion characteristic are related to particle size, and dispersion force. The representative samples of bentonite, micro-SiO₂, nano-SiO₂, and DWTS were dispersed at the same solid content in water. The particle size distribution and chemical composition of samples were analyzed. The suspended samples were measured for Zeta potential at the controlled pH value. Furthermore, turbidity of suspended samples were investigated at various sedimenting time. The results indicated that nano-SiO₂ has the highest Zeta potential value at pH 8-12. The stability of particle dispersion could be implied from turbidity of suspension at various sedimenting time. Bentonite suspension performed more stability than other samples for longer time. However, stability of DWTS particles can be improved by particle size controlling and treatment with dispersion agent to create repulsive force from the charge on the particle surface.

Abstract: The objective of this study is to investigate the effect of rice husk and rice husk ash which have the difference chemical composition and organic matter on porosity and properties of lightweight clay brick . Comparative adding between rice husk and rice husk ash were varied by 10, 20, 30, 40 % by weight. The results showed that more adding of rice husk and rice husk ash increase pore in microstructure and water absorption, while decrease bulk density. Porosity and water absorption are maximized when the rice husk are added at 40 %. The clay brick with 10, 20 and 30 % of rice husk or rice husk ash addition showed the required density and compressive strength followed the industrial standard of lightweight brick. The addition with 10 % of rice husk showed the best properties as 1.20 g/cm³ of bulk density and 4.6 MPa of compressive strength with 36.57 % of porosity. Whereas, the 10 % addition of rice husk ash showed 1.18 g/cm³ of bulk density and 5.97 MPa with 37.27 % of porosity.

Abstract: This study investigated the effect of silica to alumina ratio on the compressive strength of geopolymer. The high calcium fly ash (Class C, ASTM 618) wastes from Mae Moh Thailand power plant, which is SiO₂ (30.97%) and Al₂O₃ (17.16%)-rich materials was employed as the main solid part to prepare geopolymers, apart from kaolinite. The combination of sodium hydroxide (NaOH), sodium silicate (Na₂SiO₃) solution, and distilled water as 1:1:4 mass ratios were used as the liquid activator. The curing temperature in the oven was fixed at 75oC and varied curing time for 24, 48, 72 and 96 hours. Further curing was done at room temperature for 28 days before characterizations. XRD study of synthesized geopolymers showed a hump of not well-defined peaks and some major peaks of quartz, and unreacted kaolinite indicating the incomplete geopolymerization reaction. Infrared study showed the Al-O-Si and Si-O-Si bonds in all geopolymers samples. The compressive strength of geopolymer increased from 32 to 40 MPa when the ratio of SiO₂ : Al₂O₃ was increased from 2.60 to 2.65. However, the compressive strength was decreased after increasing the SiO₂ : Al₂O₃ ratio from 2.65 to 3.0. The highest compressive strength was found when the SiO₂ : Al₂O₃ ratio was 2.65 with the curing condition at 75oC for 96 h which the samples also possessed high density.

Abstract: Rice husk was used as a raw material to fabricate silicon carbide (SiC) ceramics. Carbothermal reduction was used together with in-situ reaction bonding as the preparation method. Rice husk was carbonized at the temperature around 700 °C in an incineration furnace. Carbonized rice husk was ground and treated with hydrochloric acid solution. After grinding, the sample powders were mixed with silicon metal powder and sintering additives (alumina (Al₂O₃) and magnesia (MgO)). The mixed powders were pressed and then pyrolyzed at various temperatures and pyrolysis patterns in argon atmosphere. Silicon carbide, as the main crystalline phase, was obtained in all pyrolized samples. Cristobalite was found together with silicon carbide in the samples which pyrolized only lower than 1500 °C. Amount of silicon carbide particle was increased at higher pyrolysis temperature while silicon carbide whisker was decreased. Weight loss, shrinkage and porosity of the pyrolized samples were investigated. Weight loss and shrinkage of the samples increased when increasing pyrolysis temperature while porosity decreased.

Abstract: This work focuses on the debinding conditions of the ceramic materials fabricated by powder injection moulding. Ceramic powder materials, including alumina and alumina-based composites were prepared as feedstocks and mixed with water-soluble polyethylene glycol (PEG) and polyvinyl butyral (PVB). The PEG/PVB binder mixture, with PEG to PVB ratio of 85:15 by weight and powder loading of 44 vol%, were thoroughly mixed and injected into the mould at the temperature of 190 °C to obtain rod-like specimens. Prior to sintering, the as-injected specimen was then leached in water, the temperature of which was varying from 30 (ambient temperature), 45 to 60 °C, in order to get rid of PEG and leave the specimens in shape by PVB. The rate of PEG removal according to different water temperatures was investigated. The experimental results suggested that PEG could completely be eliminated by 45 and 60 °C water without any dimensional disintegration in 5 hours whereas those leached in 30 °C water showed only 70% PEG removal. Higher water temperatures led to fast PEG removal rate at the beginning and then gradually decreased with elapsed times.

Abstract: PZTs can be classified into two types, i.e., soft and hard PZTs, which are categorized by the piezoelectric and ferroelectric properties such as coercive field, piezoelectric strain, mechanical quality factor etc. It is known that the combination effect of the soft/hard PZT composites can generate large strain/actuation compared to monolithic PZT ceramics. In this study, soft and hard PZT powders were co-pressed into bi-layer disks with various ratios between soft and hard PZT powders, ranging from 0:100~100:0 vol. % (with 10 % increments) and then they were co-sintered. Due to the difference in the planar shrinkage of the two layers and thermal expansion coefficient mismatch, dome-shaped bi-layer composites with various dome heights were obtained. It was shown that the constrained layer either soft PZT or hard PZT affected various properties including the dome geometry, the strain-E-field response, and the displacement hysteresis loop. The electromechanical properties and actuation performance of such bi-layer composite actuators have been investigated and compared to the soft and hard PZT single layer counterparts.

Abstract: The objective of this research is to study the feasibility of using fiber obtained from tobacco stalk as reinforcement fiber in the production of fiber cement through hydrothermal methods. The fiber cement samples are made of the mixtures of 50% of ASTM Type I ordinary Portland cement, 35% of milled sand, 10% of calcium carbonate powder and 5% of cellulose fiber (eucalyptus pulp and tobacco stalk pulp). This study include the morphological characterization of the fibers and the study of effects that the use of fiber has on the fiber cement suspensions and on the mechanical and physical properties of the final product. The flexural strength of fiber cement samples using tobacco stalk pulp after curing in an autoclave at 180 °C for 4 hours is 14.21 MPa which is slightly lower than that of the samples using eucalyptus pulp at 17.10 MPa. However, the results obtained in the tests confirmed the high potential of the tobacco stalk as a source of fiber for the fabrication of a fiber cement capable of meeting the requirements of demanding applications.