Halina Misran

Experimental and SPH study of cold spray impact between similar and dissimilar metals

Abstract In this study, the critical, maximum and optimum velocity of a single cold sprayed (CS) particle is estimated using the smoothed particle hydrodynamics (SPH) method by evaluating the impact shape coefficient of restitution, as well as the rebound and deposit energy ratio. The contact surfaces of the particle and the substrate are modelled as intersurface forces using the Dugdale–Barenblatt cohesive zone model. The application of SPH allows the simulation of the CS process without the use of mesh, thereby avoiding the disadvantages of the traditional numerical method in handling large deformations and tracing moving interfaces. The impact of CS particles is simulated using various powder and substrate materials. The influence of the materials on the optimum velocity and the coating quality is discussed. The reliability of the model is verified with CS experiments.

Effect of sintering holding time on low-temperature degradation of yttria stabilised zirconia ceramics

Abstract Effect of sintering holding time on low-temperature degradation of 3 mol-% yttria stabilised zirconia was investigated. Yttria stabilised zirconia samples were sintered using a two-step sintering cycle. The samples were initially heated to 1500°C with the heating rate of 10°C min−1, held for 1 minute before cooling down to 1200°C and kept at this temperature for varying holding times from 0 to 10 hours. The phase contents of the zirconia samples were measured using X-ray diffractometer, and the microstructural evaluation was evaluated by field emission scanning electron microscope. All the as-sintered samples exhibited 100% tetragonal phase and bulk density of about 6 g cm−3. The low-temperature degradation study was conducted under autoclave condition containing superheated steam at 180°C and 10 bar vapour pressure for periods up to 24 hours. The results showed that the tetragonal to monoclinic phase transformation decreased with increasing holding time up to 3 hours and thereafter it increased. The sample sintered with 3-hour holding time showed better aging resistance than other samples. It was found that the grain size of this sample was the lowest (0·29 μm) when compared to other samples.

Effect of calcination time on NiAl-Al2O3 using gel combustion synthesis method

This study was conducted in order to investigate the effect of calcination time on phase and microstructural characteristics of intermetallic matric composite (IMC), NiAl-Al2O3 powder. This powder was synthesized using gel combustion method with octyl alcohol as fuel. Upon completion of the combustion process, the loose powder was calcined at 1050°C for 1, 2 and 4 hours and characterized using XRD, FESEM and TEM. The crystallite size was calculated to be in the range of 29-30 nm. It was found that NiAl-Al2O3 exhibits high crystalline structure after calcination for 4 hours. Furthermore, longer calcination time also cause growth of the particle size. Findings indicate that high crystalline nanostructured NiAl-Al2O3 powder consisting of submicron particles can be successfully produced using gel combustion synthesis with longer calcination time.

Synthesis and Characterizations of SiO2-Ag Core-Shell Nanostructure Using Fatty Alcohols as Surface Modifiers

SiO2-Ag core-shell nanostructure with silica core (SiO2) and silver shell (Ag) nanoparticles with spherical morphology were successfully synthesized using a modified self-assembly sol-gel method. Ag nanoparticles at ca.10-50 nm were successfully attached on monodispersed silica spheres (SiO2) with diameter of ca. 450 nm. Renewable resources of palm oil, derived fatty alcohols (octyl-alcohol (C8), decyl-alcohol (C10) and dodecyl-alcohol (C12)) were employed as nonsurfactant surface modifiers prior to coating with Ag nanoparticles. X-ray diffraction (XRD) patterns of calcined SiO2-Ag core-shell nanostructure prepared with surface modifiers exhibited amorphous structure of SiO2 (core) and face-centered cubic (FCC) structure of metallic Ag nanoparticles (shell). The results obtained in the present work demonstrated the feasibility of employing fatty alcohols as potential nonsurfactant surface modifiers in synthesizing SiO2-Ag core-shell.

Sintering properties of zirconia-based ceramic composite

Abstract This study examines the effects of different ZrB2 content on various mechanical properties and electrical conductivity of ZrB2/Y-TZP composite. Composites with ZrB2 content of up to 20 wt-% were particularly beneficial at the lower sintering temperature range by achieving greater densification and better hardness than Y-TZP monolith. In contrast to the trends estimated from rule of mixture, the increment of ZrB2 content did not result in any significant improvement in the elastic modulus and hardness of the zirconia composites. Nevertheless, all composites showed tremendous improvement in fracture toughness compared with monolithic Y-TZP and thus, suggested that other toughening mechanisms were operative besides transformation toughening of zirconia. Incorporation of ZrB2 up to mass fraction of 20 wt-% into Y-TZP generally did not affect the tetragonal phase stability of zirconia. Significant reduction of electrical resistivity of the composites was achieved with ZrB2 content of 20 wt-% and sintering temperature of 1400°C.

Effect of NH3 on Structural and Optical Properties of SiO2-CuO Core-Shell Nanostructure

CuO nanoparticles at ca. 20-50 nm were successfully coated on monodispersed silica spheres prepared by modified sol-gel method. A renewable palm oil based decyl-alcohol (C10) was employed as nonsurfactant surface modifier prior to coating with CuO. Various amounts of ammonia (NH3) (0-1 ml) was as catalyst during the modification process to study the effect in homogeneous deposition of CuO on silica surfaces. The homogeneous depositions of CuO on silica were achieved with the addition of 0.9 ml of NH3. The optical absorption peak and energy band gap (Eg) values were at ca. 1.8-2.18 eV suitable for semiconductor and optical sensor materials.

Palm Oil Based Fatty Alcohols Templated Mesoporous Silica and Silica Spheres

Mesoporous silica xerogels with wormhole-like pore structure were successfully synthesized using a series of surfactantless oil-in-water emulsion at room temperature. The surfactantless emulsion systems consisted of palm-oil derived fatty alcohols having several carbon chain lengths to act as mesoporous templates in place of commercial surfactants in a direct base–acid catalyzed sol–gel method. This method allowed direct decomposition of fatty alcohols in situ during calcination process to create mesoporosity in the materials. The mesoporous silica xerogels exhibited relatively high surface area at ca. 505 m2/g and pore sizes at ca. 8 nm to 13 nm as the carbon chain lengths were varied. The pore size obtained in this study was larger than the conventional MCM-41 materials (at ca. 2 nm). The mesopores were generated from the interstices of the primary particles (framework-confined porosity) and secondary particles (textural porosity). Furthermore, by changing the co-solvent amount and oil/water ratio, surfactantless oil-in-water microemulsions were obtained. These microemulsions were useful in the synthesis of monodispersed silica spheres. The size of the silica spheres could be controlled at two different size clusters, ca. 50–200 nm and at ca. 500 nm.

CHARACTERIZATIONS OF CU-BASED COATED AL7075 VIA PLASMA-SPRAY METHOD — A WEAR CASE STUDY

Despite of its poor tribological properties (low hardness and low resistance to friction, wear and abrasion as well as poor seizure resistance), aluminum has become a potential material in automotives, particularly in the engine areas. To overcome these weaknesses and increase the engine lifetime, a good surface treatment can be one of the best options. In this work, Cu-Ni alloy that has such excellent properties like ductility, corrosion and wear resistance, good electrical and thermal conductivity as well as it can be easily joined or fabricated into useful shapes, was chosen. The work aims to study the wear behavior of Cu-Ni coatings deposited on Al7075 substrates using an atmospheric plasma spray (APS) with different level of plasma powers. Lubricated wear test were carried out on a pin-on-disc tester under an applied load of 100 N with a fixed sliding speed of 0.851 ms-1 at room temperature (~ 23°C). It was found that a decrease in plasma power from 40 kW to 30 kW promoted finer microstructures and higher hardness of the coatings, up to 39%. At 30 kW, the splats formation involved high degree of flattening and solidification without many splashes within the structure. At higher power (40 kW), both velocity and temperature of droplets were noted to be increased, resulting rougher coating structures which were most likely due to overlapped splats. In turn, this weakened the bonding strength between splats. In the case of wear, the resistance of Cu-Ni coated Al7075 was found to be increased from ~6 to 18 × 10-5 mm3/Nm, indicating a mild wear regime that was attributed to an increase in the coating hardness.

Long-term settlement prediction at open dumping area using Hossein and Gabr method for new development

In Malaysia, the most common method of disposal is landfill/open dumping. The soil at the dumping area are mixed with waste and soil. Thus, it was called as waste soil. Due to its heterogeneity properties, waste soil has a different settlement rate because different types of waste tends to settle differently. The Hussein and Gabr model which used empirical model was proposed to compute the long-term settlement. This Hussein and Gabr model is one of the soil settlement model that can be used to predict the long-term settlement at the dumping area. The model relates between the compression index and the time factor. The time factor are t1, t2, t3 and t4. The compression index is Cα1=compression index and Cβ is biodegradation index. The duration for initial compression, the compression, the biological compression and time creep are included in the model. The sample of waste soil is taken from closed dumping area in Lukut, Negeri Sembilan with the height of waste approximately 1 to 3 meters. The sample is tested using consolidation test for determining the geotechnical parameters and compressibility index. Based on the Hossein and Gabr model, the predicted long-term settlement for 20 years (ΔH) for the waste height of 1 to 3 meters are 0.21m, 0.42m and 0.63m respectively and are below the percentages of proposed maximum settlement for waste soil which is acceptable for new development to takes place.. The types of deep or shallow foundation are proposed based on the predicted settlement. The abandoned open dumping area can now be reused for the new development after the long-term settlement are predicted and some of the precaution measures has been taken as a safety measures.

Oxidation Behavior of NiAl Produced by Gel Combustion Synthesis

This paper presents the results of a study of the oxidation behavior of NiAl produced by gel combustion synthesis calcined at two different temperatures. The objective is to compare the oxide growth rates, oxide scale composition, morphology and elemental composition of the sample powder subjected to isothermal oxidation and calcined at 1050 °C and 1300 °C for 1, 2, 4 and 10 hours by means of mass gain measurements, X-ray diffraction (XRD), field emission scanning electron microsocopy (FESEM) and energy-dispersive spectrometry (EDX) in order to investigate the reliability of the gel combustion synthesis method and evaluate the effect of calcination temperature on the oxidation behaviour of the powder. It was found that for the sample calcined at 1300°C the sample was made up mainly of metastable and stable alumina before oxidation and stable alpha alumina after oxidation whereas for the powder calcined at 1050°C the sample was mainly composed of detrimental mixed oxides before and after oxidation. Overall findings indicate that the oxidation behavior of the powder calcined at 1300°C is more protective compared to the powder calcined at 1050°C.