Alumina Blocks Research Articles

Dry sliding wear behavior of treated AISI 304 stainless steel by gas nitriding processes

The wear behaviour of AISI 304 stainless steel was investigated at consistent load. For gas nitriding the specimen were placed on top of alumina block and ammonia gas was allowed to flow through quartz tube at a flow rate of 100 ml/min, temperature of 570 °C and were treated at different nitriding timings like Gas nitriding 1 (GN1) 6 h, Gas nitriding 2 (GN2) 12 h, and Gas nitriding 3 (GN3) 18 h. After heat treatment wear test was done to find out the wear loss in the material. The pin of 40 mm length and 12 mm diameter was held on rotating disc of 150 mm diameter. The wear test for all specimens was conducted under the normal loads of 20 N and 30 N respectively. Metallographic tests like optical microscopic results, SEM is done to specimens for comparing physical characteristics before and after heat treatments. To compare the mechanical characteristics of the heat treated specimens before and after heat treatments they are subjected to pin on disc experiment and Vickers hardness test to determine wear resistance and hardness of the material. From SEM analysis, it was observed that a decomposition of CrN layer in the gas nitride specimen for 18 h. It was concluded that nitride distribution increases with increase in nitriding time. The hardness of gas nitride specimen3 (18 h) was found to be 1187 HV and the hardness for untreated specimen was found to be 330 HV.

Investigation of the surface integrity, flexural strength on the grinding of alumina for biomedical applications

This paper presents the analytical and experimental investigations on different factors such as surface integrity, flexural strength and grinding energy and cost of Alumina through the use of various diamond grinding wheels. For obtaining the analytical model for single-grit grinding, the effect of strain rate and grinding temperature are also included in the formulation. Moreover, the experimental tests are conducted with four different diamond grinding wheels to grind Alumina blocks. The applied force during grinding is measured. Then, the other important parameters, including surface roughness, wheel wear, and grinding cost are analyzed. According to the obtained results, a good agreement between the experimental and analytical results were achieved in all cases. Furthermore, it was found that controlling the grinding condition would be resulted in 11% reduction in the subsurface damages (SSD) according to the images of Scanning electron microscope (SEM) results at the distance of 150 μm under the ground surface. A converging improvement trend of the surface integrity and flexural strength was also observed. Also, approximately 29% improvement was attained for the flexural strength in optimum condition. In addition, the optimal condition for grinding was determined, in which 66% decrease in surface roughness and 75% decrease in grinding cost were accomplished.

Grinding performance by applying MQL technique: an approach of the wheel cleaning jet compared with wheel cleaning Teflon and Alumina block

Characterized by the high heat generation, grinding has great difficulty in dry machining. As an alternative, it is proposed to apply abundant cutting fluid (conventional method) or a minimum amount of lubrication, which in turn dispenses with disposal costs and drastically reduces the volume of cutting fluid application during machining compared with the conventional technique. Despite this, the application of cutting fluids in MQL can cause clogging of the grinding wheel, damaging the workpiece quality. Against this, one of the techniques explored in the literature is the application of grinding wheel cleaning jet (WCJ), removing part of the layer adhered to the surface of the grinding wheel. Also, the present work proposes the cleaning of the cutting surface of the grinding wheel through the mechanical contact between Alumina (WCAB), and Teflon (WCTB) blocks with the cutting surface of the CBN grinding wheel, during cylindrical grinding of AISI 4340 steel hardened. Feed rates of 0.25; 0.50; 0.75, and 1 mm/min were applied under the following lubri-refrigeration conditions: conventional, MQL, and MQL with WCJ, WCAB, and WCTB. The parameters studied were roughness, roundness deviation, diametrical wheel wear, grinding power, acoustic emission, and microstructural analysis. The results showed that the WCAB and WCTB could improve grinding conditions compared with MQL without cleaning, mainly when applied with Alumina block. However, WCJ is the better condition associated with MQL. However, the conventional flood lubricant application remains with better results, indicant that it is necessary more effort to improve the MQL technique.

Deposition of diamond-like carbon films on insulating substrates by plasma source ion implantation

Plasma source ion implantation (PSII) is a technique that is suitable for implantation as well as film deposition. Since it involves a high voltage that is applied to the sample holder to attract ions from the plasma to the sample, an influence can be expected in case that either the whole substrate or a part of it is nonconductive. Diamond-like carbon (DLC) films were deposited by PSII, using C2H2 as precursor. The substrates were silicon samples that were placed on a large, horizontally oriented conductive sample holder in three different ways: 1) directly on the holder, 2) with an alumina block of 5 mm height between holder and sample, and 3) with an alumina block of 12 mm height between holder and sample. A high voltage (pulse or DC) was applied directly to the sample holder. The plasma was generated by this voltage or, in some experiments, by an additional RF signal, which was applied to a plate that was oriented parallel to the sample holder in a distance of 100 mm. The investigation of the effect of the presence of the insulating alumina block on the film properties focused on the deposition rate, the hydrogen content and film structure, the surface roughness, the hardness and the friction coefficient of the films.

Self-enhanced electrical performance and less defective electrode/film structure for Al2O3 capacitor via interfacial anodic oxidation

Alumina (Al2O3) thin films derived from a sol-gel wet chemistry process were used to prepare capacitors with a simple MIM structure of Al/Al2O3/Pt. Driven by the external applied electric field, the phenomenon of anodic oxidation has been observed and confirmed at the Al/Al2O3 interface，resulting in the formation of a new alumina blocking layer (BL). Importantly, similar to the product of anodic oxidation of aluminum in liquid electrolytes, the blocking layer here exhibited excellent electrical characteristic and voltage-dependent growth mode as well, which endowed the capacitor with less defective electrode/film structure and self-enhanced electrical performance under the application of external voltage. Specifically, an ∼50% enhancement of the maximum working voltage and better capacitance characteristics of the thin film capacitor can be achieved. With the impedance and finite element analyses, the electrical characteristic of the BL and its corresponding effect on the alumina capacitor were explored in depth.

Effects of Post-Assembly Molecular and Atomic Passivation of Sensitized Titania Surface: Dynamics of Electron Transfer Measured from Femtoseconds to Seconds.

The dynamics of electron transfer at the dye-titania and titania-electrolyte interfaces is investigated in two post-sensitization processes: (i) atomic layer deposition of blocking alumina coating and (ii) hierarchical molecular multicapping. To measure the electron transfer dynamics, time-resolved spectroscopic methods (femtosecond transient absorption on the time scale from femtoseconds to nanoseconds and electrochemical impedance spectroscopy on the time scale from milliseconds to seconds) are applied to the complete dye-sensitized solar cells with cobalt-based electrolyte and champion ADEKA-1 dye (with silyl-anchor unit) or its popular carboxyl-anchor analogue, MK-2 dye. Both molecular capping and alumina blocking layers slow down the electron injection process (the average rate constant decreases from 1.1 ps-1 to 0.4 ps-1) and partial sub-nanosecond back electron transfer from titania to the dye (from ca. 10 ns-1 to 5 ns-1). Very small alumina layers (of 0.1 nm thickness) have the highest impact on reducing the rate constants of these electron transfer processes, and for the thicknesses greater than 0.3 nm the rate constants hardly change. In contrast, the electron recombination between titania and electrolyte, occurring on the millisecond time scale, starts to be significantly suppressed for the blocking layers of 0.3 nm or more in thickness (up to ca. 20 times for 0.5 nm thickness with respect to that for untreated sample), improving open circuit voltage and fill factor of the cells. The amplitude of the relative photocurrent (short circuit current per number of absorbed photons) is found to depend almost exclusively on the ultrafast and fast processes taking place in the first nanoseconds after dye excitation. The positive impact of coadsorbents on the solar cells performance for both ADEKA-1 and MK-2 is also studied.

Optimization and Application of Laser-Dressed cBN Grinding Wheels

Laser-dressing has been shown to be a promising method for overcoming some shortcomings of the conventional methods such as high wear of the dressing tool and its environmental concerns, high induced damage to the grinding wheel, low form flexibility and low speed. In this study, a resin bonded cBN grinding wheel has been dressed with a picosecond Yb:YAG laser. The efficiency of the laser-dressed grinding wheels has been compared with the conventionally dressed and sharpened grinding wheels through execution of cylindrical grinding tests on a steel workpiece (100Cr6). The conventional dressing and sharpening processes have been performed by using a vitrified SiC wheel and vitrified alumina blocks, respectively. By recording the spindle power values along with the surface topography measurements of the ground workpieces and the extraction of two roughness parameters (the average roughness Ra and the average roughness depth Rz), it is possible to provide an assessment of the cylindrical grinding process with different dressing conditions i.e. laser-dressing and conventional dressing. Accordingly, a strategy will be proposed to optimize the cylindrical grinding process with laser-dressed wheels regarding the forces and roughness values.

Optimization and Application of Laser-Dressed cBN Grinding Wheels

Laser-dressing has been shown to be a promising method for overcoming some shortcomings of the conventional methods such as high wear of the dressing tool and its environmental concerns, high induced damage to the grinding wheel, low form flexibility and low speed. In this study, a resin bonded cBN grinding wheel has been dressed with a picosecond Yb:YAG laser. The efficiency of the laser-dressed grinding wheels has been compared with the conventionally dressed and sharpened grinding wheels through execution of cylindrical grinding tests on a steel workpiece (100Cr6). The conventional dressing and sharpening processes have been performed by using a vitrified SiC wheel and vitrified alumina blocks, respectively. By recording the spindle power values along with the surface topography measurements of the ground workpieces and the extraction of two roughness parameters (the average roughness Ra and the average roughness depth Rz), it is possible to provide an assessment of the cylindrical grinding process with different dressing conditions i.e. laser-dressing and conventional dressing. Accordingly, a strategy will be proposed to optimize the cylindrical grinding process with laser-dressed wheels regarding the forces and roughness values.

The Reliability of Bonding between Alumina-Pure Metals Through Diffusion Mechanism

Bonding between dissimilar materials such as alumina to metals by diffusion mechanism was investigated in this work. Foils of high purity metals (Silver, Copper, Zinc, Aluminum, Lead and Tin) have been prepared with 1mm thickness and area of 1cm x 1cm. The foils have then be placed between two alumina blocks of similar area and 0.5cm thickness as a sandwich panel. Bonding has been achieved by using a suitable fixing under pressure of 0.3 MPa and then heated to about 90% of the melting point temperature of each investigated metals for 2 hours as a socking time in an atmospheric condition. For evaluation the bonding strength of fabricated joints, tensile test technique was used for this purpose. Three categories of bonding strength were obtained but the upper value of joint strength obtained is 86.5x10 4 Pa of the joint involved silver and tin metals. Obviously three types of fracture surfaces were obtained; fracture in alumina part, fracture in the interface region and fracture in metal part. Fracture surfaces were attempted by NDT (non destructive test) using optical microscope and x-ray techniques. Due to reduction of surface and bulk diffusivity an oxidation layers which covered the contact surfaces was found effected parameters caused to reduce the diffusivity and followed bonding strength of the fabricated joints.

Bond Strength of the Porcelain Repair System to All‐Ceramic Copings and Porcelain

The purpose of this study was to investigate the shear bond strength of the porcelain repair system on alumina and zirconia core ceramics, comparing this strength with that of veneering porcelain. Veneering ceramic (n = 12), alumina core (n = 24), and zirconia core (n = 24) blocks measuring 10 × 5 × 5 mm(3) were fabricated. Veneering ceramic blocks were used as the control. Alumina and zirconia core blocks were divided into 2 groups (n = 12 each), and a slot (2 × 2 × 4 mm(3)) filled with veneering ceramics was prepared into one of the alumina and zirconia core groups (n = 12). Followed by surface treatments of micro-abrasion with 30 μm alumina particles, etching with 35% phosphoric acid and silane primer and bond, composite resin blocks (2 × 2 × 2 mm(3)) were built up and light polymerized onto the treated surfaces by 3 configurations: (a) composite blocks bonded onto veneering ceramic surface alone, (b) composite blocks bonded onto alumina core or zirconia core surfaces, (c) a 50% surface area of the composite blocks bonded to veneering ceramics and the other 50% surface area of the composite blocks to alumina core or zirconia core surfaces. The shear bond strength of the composite to each specimen was tested by a universal testing machine at a 0.5 mm/min crosshead speed. The shear bond strength was analyzed by unpaired t-tests for within the configuration groups and ANOVA for among the different configuration groups. When the mean shear bond strength was compared within groups of the same configuration, there were no statistically significant differences. Comparison of the shear bond strength among groups of different configurations revealed statistically significant differences. The mean shear bond strength of composite onto 100% veneering ceramic surface and composite onto 50% veneering 50% all-ceramic cores was statistically higher than that of composite onto 100% all-ceramic cores; however, the differences of the shear bond strength of composite bonded only onto the veneering ceramic surface were not statistically significant from those of 50% surface area of composite bonded onto all-ceramic cores. No statistically significant differences in the bond strength of a porcelain repair system to alumina and zirconia copings were observed. Increasing the surface of veneering ceramics to a porcelain repair system improved the repair material's bond strength.

Cooperative effect of Ce and Mn in MnCe/Al2O3 environmental catalysts

Three samples, Mn/Al2O3, Ce/Al2O3 and MnCe/Al2O3 (containing 10wt.% metal) were prepared by impregnation and comparatively studied by means of FTIR spectroscopy, other characterization techniques and catalytic measurements. It was established that the active phase deposition led to (i) partial disappearance of all kinds of the alumina OH groups and (ii) blocking of part of the Al3+ Lewis acid sites. The results indicated that manganese was better dispersed on the MnCe/Al2O3 sample as compared to Mn/Al2O3. As a result, the bimetallic sample was the most active one in a series of catalytic reactions: NO decomposition, CO oxidation and CO+NO interaction.Interaction of all samples with CO leads to formation of carbonates and hydrogencarbonates increasing in amount with the temperature of interaction and in the sequence Al2O3<Ce/Al2O3<Mn/Al2O3≪MnCe/Al2O3. When the samples interacted with NO, different nitrogen oxo-compounds were formed and manganese nitrosyls appeared with the Mn-containing samples. In agreement with the higher Mn dispersion, the amount of the latter was larger with the bimetallic sample. Interaction between CO and NO results in formation of isocyanates, (hydrogen)carbonates and nitrogen oxo-compounds (nitrosyls, nitro-nitrito and nitrate species). When the interaction occurs at ambient temperature, the surfaces of the Al2O3, Ce/Al2O3 and Mn/Al2O3 are covered mainly by nitrates and nitro-nitrito species. With increase of the interaction temperature these species are gradually replaced by (hydrogen)carbonates. The temperature of this replacement decreases in the order Al2O3–Ce/Al2O3–Mn/Al2O3. With the MnCe/Al2O3 sample carbonates dominate even at 373K interaction. Consequently, the NO+CO catalytic conversion occurs in two regimes. The low temperature regime (the temperature interval depends on the catalyst) is associated with NOx precovered surface, while at higher temperatures the catalysts surfaces are precovered with (hydrogen)carbonates.

핵연료계장을 위한 정밀 드릴링장치 개발

When a new nuclear fuel is developed, an irradiation test needs to be carried out in the research reactor to analyze the performance of the new nuclear fuel. In order to check the performance of a nuclear fuel during the irradiation test in the test loop of a research reactor, sensors need to be attached in and out of the fuel rod and connect them with instrumentation cables to the measuring device located outside of the reactor pool. In particular, to check the temporary temperature change at the center of a nuclear fuel during the irradiation test, a thermocouple should be instrumented at the center of the fuel rod. Therefore, a hole needs to be made at the center of fuel pellet to put in the thermocouple. However, because the hardness and the density of a sintered UO<SUB>2</SUB> pellet are very high, it is difficult to make a small fine hole on a sintered UO2 pellet using a simple drilling machine even though we use a diamond drill bit made by electro deposition. In this study, an automated drilling mach ne using a CVD diamond drill has been developed to make a fine hole in a fuel pellet without changing tools or breakage of workpiece. A sintered alumina (Al<SUB>2</SUB>O<SUB>3</SUB>) block which has a higher hardness than a sintered UO<SUB>2</SUB> pellet is used as a test specimen. Then, it is verified that a precise hole can be drilled off without breakage of the drill bit in a short time.

핵연료 계장을 위한 천공조건에 대한 실험적 연구

To develop a new nuclear fuel, it needs to make a test fuel rod and carry out burn-up test in the test loop of a research reactor to check the irradiation characteristics of the nuclear fuel. At that time, several sensors such as thermocouples, LVDTs and SPNDs are needed to be attached in and out of the fuel rod and connect them with instrumentation cables. Then, the instrumentation cables deliver the signals measured by the sensors to the measuring device located outside of the reactor pool. In particular, to install a thermocouple in a fuel rod, it needs to drill off holes on the alumina blocks and sintered pellets. However, because the hardness of a sintered pellet is 700 Hv (or HRC 61) and that of an alumina block is 1480 Hv, a special drilling machine which adapts a diamond coated drill bit had developed. In this study, several case experiments have been carried out to find an optimal drilling condition of the drilling machine. And, using the optimal drilling condition, minimum numbers of the holes that a drill bit can drill off are verified.

Al2O3–MgO castables performance in an expansion constrained environment

The present work addresses the importance of considering the working structural conditions when evaluating the expansive behavior of alumina–magnesia castables under chemical corrosion. Slag resistance tests were conducted on spinel castables with different expansion levels, inserted in cement-bonded high alumina blocks, to limit their expansion, and compared to the results attained after performing the same experiments without any constraint. The results pointed out that in an expansion controlled condition, the penetration indexes were reduced as a result of the lower volume of pores in the castable microstructure. Moreover, this benefit was enhanced for the coarser MgO-containing materials, contradicting the trends usually observed when no structural constraint is considered.

Charge trapping in alumina and its impact on the operation of metal-alumina-nitride-oxide-silicon memories: Experiments and simulations

We investigate the electron/hole trapping phenomena in alumina blocking oxide and their impact on the program/erase operations and retention of TaN/Al2O3/Si3N4/SiO2/Si (TANOS) memory devices. For this purpose, we perform simulations using a physical model that reproduces the charge injection/trapping in TANOS devices, which is extended in order to account for the charge trapping phenomena in the blocking layer. We derive the electrical characteristics of both electron and hole traps in Al2O3 by reproducing the measured program, erase, and retention transients. Our results show that the amount of electron charge trapped in the alumina during a program operation strongly depends on the stack composition and program voltages and can account for up to 25% of the total threshold voltage shift, whereas hole trapping during erase is negligible. Finally, we investigate the degradation of retention caused by the electron trapping in the alumina blocking layer, which is shown to result in an accelerated charge loss.

Comparison of Bond Stability Between Dual-Cure Resin Cements and Pretreated Glass-Infiltrated Alumina Ceramics

To evaluate the bond stability of resin cements used for luting alumina-based all-ceramic dental restorations. Although different pretreatments may be applied on alumina to improve bond strengths, any previous study investigated the bond stability of resin-based cements luted to laser-irradiated alumina. 64 sintered, glass-infiltrated alumina blocks were sandblasted and randomly assigned to the following subgroups: 1. no additional treatment (NT); 2. Rocatec (Roc); 3. Nd:YAG laser (L); and 4. Nd:YAG laser plus Rocatec (LRoc). Composite samples were bonded to conditioned ceramics using two different resin based cements: a self-etching adhesive cement-Panavia F (PF) and a self-adhesive resin cement-RelyX Unicem (RXU). After 24 h, bonded specimens were cut into microtensile sticks (1 ± 0.1 mm(2)). One-half of the beams were loaded in tension until failure. The remaining one-half was immersed in 10%-NaOCl aqueous solution (NaOCl(aq)) for 12 h before testing. ANOVA and Student-Newman-Keuls tests were run (P < 0.05). Failure mode was recorded. Ceramic topography was SEM-analyzed. After 24 h, L-sticks achieved the highest MTBS despite the cement type, whereas NT-samples recorded the lowest values. After NaOCl(aq) immersion bond strengths decreased except for RXU luted to NT-alumina. PF luted to L- and LRoc-samples, and RXU luted to L-sticks attained the highest bond strength. Nd:YAG laser irradiation improved bond strength between alumina ceramics and resin cements (PF or RXU). Chemical challenging impaired adhesion, mainly through resin matrixes and silane coupling degradation. Laser-treated specimens remained with the highest bond strength.

Novel fabrication of pressure-less sintering of translucent powder injection molded (PIM) alumina blocks

A new method of fabricating translucent alumina brackets using powder injection molding (PIM) is reported. Alumina powder was mixed with MgO, La 2O 3, and Y 2O 3 to control grain size and porosity. The powders were mixed with a binder consisting of a mixture of paraffin wax and polyethylene in a 1:1 ratio to make feedstock for injection molding. The total amount of binder was limited to 14 wt% to minimize shrinkage and cracking after sintering. After injection molding, debinding was performed using the wicking method and samples were sintered in a vacuum at 1700 °C to achieve high density. Ultimately, translucent corundum was fabricated. The sintering additives resulted in a decrease in porosity and an improvement in translucency by promoting grain growth during pressure-less sintering. After sintering, Vickers hardness, bending strength, density, and transmittance of the fabricated parts were measured to show that those values were comparable to those of the commercially available dental brackets. Therefore, the translucent alumina block was successfully fabricated using PIM method to be potentially used as a dental bracket.

Influence of Different Ceric Oxide and Ferric Oxide Content on the Color of Alumina-Glass-Composites Restoration

This study aims to investigate the effects of ceric oxide and ferric oxide on the color of alumina-glass-composite (AGC). Uncolored glass and colored glass powder with 4% ceric oxide and 0.5% ferric oxide were fabricated. Primary mixture powder were made by mixing the two colored glass powder with 0.1g interval, and then 81 kinds of colored mixture powder were gained by mixing uncolored powder with the primary mixture powder. Molten glass was infiltrated into presintered alumina blocks. The colored AGC and VITAPAN-3D-MASTER shade guide were measured with spectrophotometer. Experiment results showed that the Yxy value of VITAPAN-3D-MASTER shade guide distributed from (185,0.378,0.340) to (121,0.443,0.341) and the Yxy value of colored AGC distributed from (227,0.352,0.343) to (102,0.489,0.364). There were 37 kinds of samples in the color range of shade guide. The color range of 81 kinds of AGC covered that of the VITAPAN-3D-MASTER shade guide.

Flexural strength of the joint between glass-infiltrated alumina frames and the alumina-magnesia modifier

The purpose of the present study was to evaluate the flexural strength of the joint between glass-infiltrated alumina frames and the experimental adjusting agent (MA modifier) that contains alumina and magnesia. A commercially available adjusting agent (Optimizer), a slurry of alumina powder (Alumina modifier), and a bulk specimen (joint-free alumina) were used as controls. Beam-shaped alumina specimens were machined from an alumina block. The ends of two alumina beams were positioned at an interval of 1.0 mm and joined with each adjusting agent. The joined specimens were subjected to sintering, glass infiltration firing, glass control firing, and then a three-point bending test was carried out to evaluate the flexural strength. The maximum flexural strength was observed in the joint-free alumina, followed by MA modifier, Optimizer and Alumina modifier. With the exception for joint-free alumina, the failure modes after three-point bending test tended to shift from adhesive failure at substrate material-adjusting agent interface to cohesive failure within adjusting agent as the flexural strength increased. The use of MA modifier significantly improved the flexural strength of joined glass-infiltrated alumina frame. The MA modifier could be applied for adjusting the margin as an alternative to Optimizer when fabricating crown and bridge substructures with In-Ceram Alumina system.

Fabrication of porous alumina ceramics by simultaneous thermal gas generating and thermal slurry solidification

In this study, porous alumina green bodies were formed from alumina slurries by simultaneous thermal gas generating and thermal slurry solidification. In order to cause simultaneous thermal gas generating and thermal slurry solidification, NH4HCO3 and potato starch were used as a gas generating agent and a gelatinizing agent, respectively. Alumina slurries containing NH4HCO3 and potato starch were heated in the 80°C oven, so that porous alumina green bodies were formed. With increasing the amount of NH4HCO3, the visible pore size of the porous alumina block and the number of visible pores in the alumina block increased. Additionally, the alumina slurry containing NH4HCO3 and potato starch was unidirectionally heated from the bottom side, so that a platy alumina green body with a number of through-holes was formed.