Nik Akmar Rejab

An investigation of dielectric resonator antenna produced from silicon (100) enhanced by strontium doped-barium zirconate films

Dip-coated Ba1−xSrxZrO3 thick films with different Ba/Sr ratios (xxa0=xa00.0, 0.1, 0.3, 0.5, 0.7 and 0.9) were fabricated on Si (100-orient) substrate at a low temperature of 800xa0°C via the sol gel method. The experimental results show that dielectric resonator (DR) properties of Ba1−xSrxZrO3 films depend on the different Ba/Sr ratios. For structural characterization, the X-ray analysis revealed that phase transformation was affected by the increase in Sr concentrations for heat treatment at 800xa0°C. The films were crystalline and of single phase. The thickness of one BSZ film is around 1.259xa0μm when measured using the field emission scanning electron microscope. The BSZ film’s surface morphology as indicated by the atomic force microscopy showed the mean grain size to be in the range of 2.56 to 94.34xa0μm, and the surface roughness (RMS) was recorded to be between 2.35 to 19.64xa0nm. The dielectric resonator (DR) properties were measured using a network analyzer. By introducing Ba1−xSrxZrO3 (BSZ) films on the high dielectric Si (100-orient) substrate, better frequency stability was achieved i.e. within the range of 8–10xa0GHz. Measured results show that Si (100-orient) DRA has a 10xa0dB impedance bandwidth of 4.11% at 9.34xa0GHz and the BSZ improved this to 11.34% with xxa0=xa00.7 at 9.15xa0GHz. The radiation pattern was observed to be stable throughout the operating frequency and holds good potential for DR applications.

The Effects of Cr2O3 Addition on Fracture Toughness and Phases of ZTA Ceramic Composite

Fracture toughness and phases of ceramic composites produced from alumina, yttria stabilized zirconia and chromia oxide system was investigated. The Cr2O3 weight percent was varied from 0 wt% to 1.0 wt%. Each batch of composition was mixed, uniaxially pressed 13mm diameter and sintered at 1600 C for 4 h in pressureless conditions. Studies on on their mechanical and physical properties such as Vickers hardness and fracture toughness were carried out. Results show that an addition of 0.6 wt% of Cr2O3 produces the best mechanical properties. Results of the highest fracture toughness is 4.73 MPa.m1/2,

Preliminary Determination of Minerals in Mukah Coal

Coal is still one of the major energy sources. It is used as a reducing agent in the metallurgical industry, in the cement industry coal is a source of energy and it is still used in power generation. Mukah coal is characterized through chemical and mineralogical properties determinations. XRD pattern of the coal shows that it is amorphous in nature and dominated by quartz and kaolinite. Mukah coal has about total carbon 97.98 wt% with SiO2, Al2O3 and Fe2O3 present as the most predominant oxides. The oxides make up approximately 1.58 wt% of the coal samples. The SEM image shows basically depicts coal particles of various irregular shapes and sizes. The mineral matter was not clearly seen on the surface of the coal particle as it was supposedly embedded inside the bulk of carbonaceous matter.

Role of MgO nanoparticles on zirconia-toughened alumina-5 wt-% CeO2 ceramics mechanical properties

The poor hardness of zirconia-toughened alumina (ZTA) with 5u2005wt-% CeO2 (ZTA5CeO2) ceramic has limited its applications as a cutting insert. Therefore, in this work, the possibility of MgO nanoparticles (20u2005nm) as reinforcement to ZTA5CeO2 ceramics was investigated. Mgo nanoparticles with different weight percentages (0-2u2005wt-%) were added to ZTA5CeO2 ceramics. ZTA5CeO2 with 0.5u2005wt-%MgO showed the highest fracture toughness of 9.14u2005MPa.√m. The addition of 0.5u2005wt-%MgO nanoparticles showed the excellent role of MgAl11CeO19 grains as a crack deflector, which consequently produced a reasonable hardness value of 1591u2005HV and lowered the wear areas to 0.0528u2005mm2.

Role of Ce2Zr3O10 Phase on the Microstructure and Fracture Toughness of ZTA Composites

Despite the impressive development in understanding transformation toughening, tailoring the toughness of zirconia toughened alumina (ZTA) ceramics remained a major challenge. In our research, a simple route based on the powders mixing process of ZTA powders with varying CeO2 additions (0 - 10 wt.%) is developed to investigate this issue. The experimental results clearly reveal that the fracture toughness of ZTA ceramics can be tailored by mixing of ZTA starting powders.

Structural and Microstructure Relationship with Fracture Toughness of CeO2 Addition into Zirconia Toughened Alumina (ZTA) Ceramic Composites

The effect of CeO2 addition in zirconia toughened alumina (ZTA) was examined. The CeO2 addition in weight percent (wt %) was varied from 0 wt% to 15 wt%. The fabricated samples were sintered at a temperature of 1600°C. The sintered samples were characterized their properties such as fracture toughness and phase determination. X-ray diffraction patterns confirm the constituent phases present in the samples were alumina and zirconia. Fracture toughness for each sample in the range of 5.878.38 MPam1/2 respectively. It was observed that the addition of ceria increased the fracture toughness of the zirconia toughened alumina ceramic composites.