Narrow Results

The effect of metal particles (Mo) inclusion in an insulating matrix (Al₂O₃) has been investigated. The conducting phase (Mo) is dispersed in alumina in different amounts (00%, 5%, 10%, 20%, 25% in volume). Two types of Mo particles have been used: the first with an average particle size ≅0.56 μm, the other with an average particle size ≅10.0 μm. All specimens were fabricated by hot pressing. The bulk conductivities have been measured over temperatures ranging from 500°C to 900°C using two-probe impedance spectroscopy within the available frequency range (5 Hz–13 MHz). From the interpretation of the impedance spectra, it has been observed that the bulk conductivity for fine particles of Mo inclusion in alumina is higher than that for large particles of Mo inclusion in alumina. A microstructural study revealed that below 15 vol% of Mo inclusion in Al₂O₃ samples had no-contact random patterns. Samples with metal contents higher than 20 vol% of Mo consistently showed metallic conductivity due to percolation effect.

There are at present several applications where high strength ceramics have replaced metals that are subjected to high speed impact from projectiles. This requires an evaluation of behavior of ceramics under impact at high strain rates. This current study provides information on high strain-rate behavior of alumina tested in shear using torsional Hopkinson bar. Dynamic stress-strain curves were generated to investigate deformation behavior prior to fracture while fractography of the broken specimens was carried out to establish the mode of failure. The results of this investigation are similar to what is obtainable in metallic materials in which mechanism of damage is controlled by strain localization and formation of adiabatic shear bands.

The plate impact experiments have been conducted to investigate the dynamic behavior of alumina. Based on the experimental observations, the three-dimensional finite element models of flyer and alumina target are established by adopting ANSYS/LS-DYNA, several cases were performed to investigate the fracture behavior of alumina target under impact loading. By analyzing the fracture mechanism and damage process of the alumina target, it is concluded that the nucleation and growth of great number of radial and axial cracks and circumferential cracks play a dominant role in the fracture behavior of alumina target. The stress histories of alumina target are simulated. By the comparison of experimental results with the numerical predictions, a good correlation is obtained.

Nanostructured alumina ceramic templates have been fabricated by anodizing annealed high-purity aluminium foil. Pore diameter, pore separation and thickness in these alumina ceramics can be controlled using a range of acid electrolytes and anodizing voltage profiles. Thermal development of the structure of these robust and optically clear templates have been compared using XRD, thermal analysis and ²⁷Al MAS NMR techniques, showing that species substituted in the alumina lattice from decomposition of the acid electrolyte play a major role in determining the chemical and physical stability of the ceramic template at elevated temperatures. Deposition of ultrathin palladium films on the surface of these alumina templates creates robust membranes that enable hydrogen separation from mixed gas streams at elevated temperatures. Gas permeability measurements through these membranes as a function of temperature have demonstrated their very high selectivity for hydrogen.

Three types of low cement castables (LCC) were prepared from 5% reactive alumina (R₅), 5% calcined alumina (A₅) and equal proportions of 2.5% (AR). The nest of the composition was fine bauxite (0–1 mm, 57%), coarse bauxite (1–3 mm, 20%), calcined magnesia (5%), secar 71 refractory cemet (7%) and microsilica (1%). By the addition of 5% water, castables were moulded, aged, dried and fired to 1400°C for 2 h. XRD studies showed higher amount of in situ spinel formation in A₅. The lattice constants of spinels in A₅, AR and R₅ were, respectively, 8.0348, 8.0688 and 8.0847 Å. This accounted for respectively alumina rich, stochiometry and magnesia rich spinels. Since calcined alumina is cheaper, produce higher amounts of spinel with the aid of alumina from the aggregate of bauxite and the binder of cement, and alumina rich spinel has better corrosion resistance properties, use of calcined alumina is recommended in LCC.

The aim of this research is study the effect of polishing factors to the reduction ratio rate in surface roughness (%$\mathrm{\Delta }Ṙ)$ during the Magnetic Abrasive Finishing (MAF) process using Response Surface Methodology (RSM). The parameters studied were machining gap, rotational speed, abrasive size and magnetic abrasive particle (MAP) size. Quadratic models were developed by applying Box–Behnken Design (BBD). Also, experiments were carried out on the silicon wafer and results of surface roughness data were analyzed by using analysis of variance (ANOVA) and significant factors were identified. According to our findings, the maximum %$\mathrm{\Delta }Ṙ$ value and the best surface roughness of silicon wafer achieved 3.70 and 51 nm, respectively.

Alumina thin films deposited by electron beam (EB) evaporation are investigated with regard to their performance in high-temperature electrical insulators. The most important application is high-temperature sensors. The leakage behavior of EB-evaporated alumina thin films is investigated by analyzing the temperature dependence of the I–V characteristics of alumina thin films deposited on Pt/n-Si(100) substrates. The temperature is extending in the range from 300 K up to 1273 K. The results show that ln(J) increases linearly with the increasing electric field at high-temperature range, the trap depth of $q{\varphi }_B$ is 280 meV, the conductivity increases with the increasing temperature, while the resistivity decreases with the increasing temperature.

Thermal barrier coatings of Al₂O₃–ZrO₂ were prepared by air plasma spraying on the surface of 20G steel. Phase constitution, microstructures and elemental distributions of the coatings were studied by X-ray diffraction, scanning electron microscope and electron probe X-ray microanalysis. The results show that the plasma spray coating mainly consists of α-Al₂O₃, c-ZrO₂, and t-ZrO₂. The bond state of the interface between the top layer and bond layer is fine, and the bond layer has a good combination with the substrate. ZrO₂ and Al₂O₃ structures can closely integrate together and form compact top layer system.

Bayerite sol is spun onto single crystal Si substrate, after synthesis and optimization, to obtain films of thickness ~ 0.2 μm. The deposited films are room temperature dried and then heated up to a temperature of 350°C in order to obtain Al₂O₃. Surface and structural changes, during heating, are observed with optical microscopy. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used for post-treatment analyses/characterization. The as-deposited and heated samples' surfaces are smooth as seen with optical and scanning electron microscope in case of optimized conditions. XRD patterns show the change from amorphous to crystalline behavior of these films when heated under various conditions. The most stable form of aluminum oxide, i.e. α-Al₂O₃, is obtained when samples are heated up to a temperature of as low as 350°C. The thin films are also deposited onto sodalime glass substrates in order to confirm Al₂O₃ formation through band gap probing. Photoconduction is used to find the energy band gap, which comes out to be 4.7 eV; lower value is correlated to the defect induced states in the band gap.

Surface composites are developed on Mg RZ 5 alloy by friction stir processing. During FSP, hard reinforcements are introduced into the matrix of RZ 5 alloy and dispersed uniformly by mechanical stirring action. The reinforcements dispersed were boron carbide, carbon nanotubes (multi-walled) and an 80:20 mixture of zirconia and alumina particles. Dynamic recrystallization and grain boundary pinning action by reinforcement particles resulted in the generation of fine-grained surface composites. Corrosion characteristics of the base material and the surface composites are studied by potentiodynamic polarization technique. The corrosion rates estimated for the surface composites are found to be far lesser than the base material while their polarization resistances were higher than the base material. Among all surface composites, B₄C particle reinforced surface composites exhibited the lowest corrosion rate of $\sim$15 mpy. Reduction in the corrosion rate of the surface composites is influenced by fine-grained microstructure and presence of harder reinforcement particles.

The pure iron and aluminum powders were milled with 3wt.% and 7wt.% of alumina nanoparticles in planetary ball mill in order to produce iron aluminide by mechanical alloying technique. The resulting powder mixture was sintered after the formation of iron aluminide by spark plasma sintering (SPS) method to achieve specimens with the highest densification. SPS technique was utilized on specimens under the condition of 40MPa pressure at 950^∘C for 5min. The microstructures were analyzed after sintering using scanning electron microscopy and EDS analysis. The results indicated that the aluminide iron phase has been produced at high purity. The sintered specimens were treated under hardness and density tests, and it was characterized that the specimen included 3wt.% of alumina nanoparticles had the highest microhardness. Likewise, it was revealed that the unreinforced sample had a maximum relative density. The wear behavior of specimens was performed at 600^∘C. The results of weight loss showed after 1000m of wear test, the weight loss of unreinforced specimen was reduced up to 0.21g while the specimen with 3wt.% of alumina nanoparticle indicated the lowest weight loss about 0.02g. The worn surfaces were evaluated by scanning electron microscopy which indicated that the main wear mechanism at high temperature included adhesive wear and delamination.

The current development strategy of inorganic pigments is to develop technologies, such as high coloring ability, low oil absorption, easy dispersion, heat resistance, and nontoxicity. As the largest colored inorganic pigments, iron oxide pigments are widely used in building materials, coatings, rubber, plastics, paint, etc. In this paper, black iron oxide pigment was used as the carrier, and alumina substance was used as the support. Precipitation method was used to synthesize the aluminum oxide-coated iron oxide black composite pigment under different experimental conditions, and the coated iron was studied by XRD, SEM and TEM characterization methods. The structure of the black pigment, discuss the influence of the coating temperature, reaction pH, coating method, neutralizing acid and other factors on the microstructure of the composite material and the performance of the pigment. The experimental results show that, through co-current coating, the temperature of the reaction system of 80^∘C and the reaction pH of 10–11 are the best parameters for coating. The oil absorption, tinting power, hiding power and dispersion power of the coated iron black were tested, and the performance of the iron black pigment was greatly improved after the coating. The heat resistance and light fastness of iron black were tested through the color difference change experiment. The experimental results showed that the heat resistance and light fastness of iron black pigment showed good performance after coating.

The product’s surface quality and service performance depend on the surface integrity features formed by the machining process. Surface integrity consists of many features including surface topography and others. In this work, 3D (areal) surface topography features, particularly height variations, were investigated on the polycrystalline diamond (PCD) turning of alumina. Variations of the areal unevenness and height distribution parameters, namely arithmetic mean deviation (Sa), maximum peak height (Sz), skewness (Ssk) and kurtosis (Sku), with respect to turning parameters such as spindle speed (1000, 2000 & 3000 rpm), feed rate (0.05, 0.075 & 0.1 mm/rev) and depth of cut (1, 3 & 5 $\mu$m) were studied. The Taguchi technique was carried out in this study based on the L₉ standard orthogonal array for optimizing the turning parameters for the generation of better topography features. The error analysis was done with the experimental results and the error variations were noticed to be less than 10%. Based on the experimental results, the best surface figure combination of Sa 0.67 $\mu$m, Sz 3.18 $\mu$m, Ssk 0.0039 and Sku 3.06 was found at the employment of spindle speed of 1500 rpm, feed rate of 0.1 mm/rev, and depth of cut of 1 $\mu$m. The distribution of peaks and valleys formed over the PCD-turned alumina surfaces may influence the different functional properties such as fatigue, friction, wear, etc. Besides, the results were examined through means of responses and analysis of variance (ANOVA). The test results also reported that the depth of cut outperforms other hard turning parameters over the surface topography features of the turned alumina ceramics. At a lower depth of cut, the cutting tool is involved in the shearing action which causes the stable material removal of alumina ceramics through an appreciable chip formation.

The increase in demand for petroleum fuels attracted the attention of the research community to identify a control measure for petroleum source depletion. On the other hand, the heavy usage and burning of petroleum products cause environmental pollutants like oxides of nitrogen, carbon monoxide, hydrocarbons, etc. Therefore, it is important to control all the problems caused by the increasing use of petroleum products, such as diesel, petrol, Kerosene, fuel oil, etc. This investigation aims to reduce the usage of fossil-based petroleum diesel by producing an effective substitute bio-diesel from Juliflora seeds, which exhibit similar properties to diesel. Furthermore, the operational and emission behaviors of the biodiesel in the Reactive Controlled Compression Ignition (RCCI) engine are analyzed by including nanoadditives such as ZnO, ${\mathrm{\text{Al}}}_2{\mathrm{\text{O}}}_3$ and ${\mathrm{\text{CeO}}}_2$. Furthermore, the obtained performance and emission results are optimized using a hybrid deep neural network (DNN) using the Aquila optimization algorithm (AOA). The algorithm chooses the diesel-biodiesel blend with 75 ppm of alumina nanoparticle as the optimum blend. This considered blend provided better performance and emission results at 72.86% loading condition. The obtained results are 28.19% for brake thermal efficiency (BTE), 446.14 g/kWh for brake-specific fuel consumption, 0.105% for carbon monoxide emission, 19.82 ppm of unburnt hydrocarbon, 457 ppm of NO${}_x$ emission and 21.98% of smoke emission.

The influence of alumina addition on mechanical behavior and fracture properties of all-ceramics zirconia dental materials was evaluated. Samples containing 0, 5, 10, 15 wt.% Al₂O₃ particles were prepared by cold isostatic pressing (200 MPa) and sintered at 1500°C for 5 h. Commercial powders were investigated by bulk density and phase formation using Archimedes principle and X-ray diffraction (XRD). Bending strength and fracture load were determined at room temperature by three-point bending test. In order to study the fracture, we took points on the crack path under microscope, plotted points on coordinates and used software "Origin" to general fitting curves. Scanning electron microscopy (SEM) and atomic force microscope (AFM) were introduced to estimate the particle size of powders and observe the fracture surfaces. No density difference was observed for a given alumina content. The majority phases of ceramics were t-zirconia and α-alumina before breaking while m-zirconia, t-zirconia and α-alumina coexisted on the cross section of cracked samples. Zirconia containing 10% alumina had the best mechanical properties, the most tortuous crack propagation and the least obvious crack distribution. This observation may provide a reference for the materials selection, shape design and production process of all-ceramic crown and bridge.

A lot of research has been done to improve electric discharge machining (EDM) process to overcome the difficulties of lower material removal and surface finish. In the current study, magneto rheological (MR) fluid was used in place of conventional dielectric to develop a new variant of EDM process. A comparative study of MR fluid assisted EDM at the stationary and rotary conditions of the tool with M2 grade high-speed steel as workpiece has been presented. Investigations have been done to evaluate the effect of various process parameters such as percentage volume Al₂O₃, pulse on time, duty cycle and discharge current on material removal rate and surface roughness with surface morphology. Higher material removal rate and lower surface finish was obtained in rotary magneto rheological fluid assisted EDM as compared to magneto rheological fluid assisted EDM without rotation under the same processing condition at optimum process parameters.

In this paper, a comparative experimental analysis of die-sinking electric discharge machining (EDM) to two most exhaustively used aluminum metal matrix composites (AMMCs) has been performed using Copper and Tungsten as tool electrodes. AMMCs containing silicon carbide (SiC) and alumina (Al₂O${}_3)$ as reinforcement (10wt%) were fabricated by stir casting method. The Box–Behnken Design (BBD) approach of response surface methodology was used to develop experimental models for material removal rate (MRR) and surface roughness (SR). Effect of input parameters such as current ($I=4$–12A), gap voltage ($V_g=40-60$V), pulse-on time ($T_{\mathrm{\text{on}}}=100-200\mu$s), and duty factor ($\tau =4$–6) on the output responses has been investigated with response surface plots. Effectiveness of design of experiment (DoE) and evolutionary algorithm-based multi-objective optimization (MOO) technique have been compared to find the best feasible optimal solution. ANOVA analysis reveals that for alumina reinforced AMMC interaction between $I\times V$ has significant effect on both MRR and SR using Cu electrode. But for tungsten, electrode interaction between $I\times T_{\mathrm{\text{on}}}$, $I\times \tau$, and $V\times \tau$ have major role on MRR whereas SR is mostly influenced by interaction between $I\times V_g$ and $I\times T_{\mathrm{\text{on}}}$. The parametric analysis reveals that an increase of current from 4A to 12A at a higher pulse-ontime increases the MRR more significantly, and higher MRR occurs in cases of alumina-reinforced AMMC. Increase of pulse-ontime at low current (4A) reduces the MRR in AMMC/Al₂O₃. Good surface finish can be obtained by combining high voltage (60V) with either small current (4A) or small duty factor (4) for both AMMCs. Both DoE and metaheuristic-based MOO technique reveals that copper electrode should be preferred for die-sinking EDM of AMMC/SiC. Metaheuristic approach should be preferred for optimization of die-sinking EDM of AMMCs using different electrodes because it requires low current for effective machining of different AMMCs.

The development of novel nanomaterials has been in the fore front of research in recent years due to the unusually outstanding properties of such materials. Metallophthalocyanines are well known to be of very good use in a wide range of applications. Nanomaterials based on this class of compounds could potentially have better qualities than the "parent" molecules. The electrochemical synthesis of cobalt phthalocyanine nanowires and the characterization using scanning electron microscope are presented. This is the first step towards a move to harnessing the potential of this class of nanomaterials for a wide range of new possible applications.

The concept of elastic-modulus-graded ceramics for improved resistance to quasi-static contact damage (Hertzian-indentation), sliding-contact damage, and wear is reviewed. In these graded materials, the in-plane elastic modulus (E) is low at the contact surface and high in the interior (substrate) with a continuous, or step-wise continuous, E-gradation in-between. Processing strategies for fabricating such E-graded ceramic composites in the Al₂O₃-glass, the Si₃N₄-glass, and the Si₃N₄-SiC systems are described. The Hertzian indentation (quasi-static and sliding) behavior of these composites, along with some results from wear tests, are reviewed. Computational modeling (finite-element analysis or FEA) results are also reviewed, and are used to discuss the role of E-gradients in imparting contact-damage resistance to these materials. The use of calibrated FEA models as predictive tools for the design of next-generation graded materials is also discussed.

Electrospinning is a process in which solid fibers are prepared from polymer solution. In recent decades, studies have focused on improving the properties of electrospun nanofibers by exploring the possibilities of electrospinning different polymers. Two critical properties that have been studied in relation to this technique are thermal stability and mechanical properties. In this study, polyamide-6 (PA-6) nanofibers were prepared by embedding combinations of alumina and tungsten carbide particles. The morphology of the resulting hybrid nanofibers was analyzed using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC) and Thermogravimetric (TGA) techniques, and tensile tests were performed to evaluate their mechanical properties. The results showed that the sample containing tungsten carbide with a weight ratio of 4:10 had the highest melting standard enthalpy. The analysis also revealed that hybrid fibers containing equal ratios of alumina and tungsten carbide, each with a weight ratio of 2:10, had higher degradation temperatures and melting enthalpy compared to other nanofibers. Tensile testing showed that nanofibrous mats containing tungsten carbide had higher Young’s modulus, PA-6 fibers.