Improving the Quality of Laser Drilling by Assisted Process Methods of Static Solution and Mist Blowing

The use of static solution-assisted laser drilling can effectively improve hole roundness, decrease taper angle, and reduce recast layer thickness and hole wall slag adhesion. However, the enormous energy of the laser will evaporate the solution to form a suspension droplet and reduce the quality and efficiency of laser drilling. To deal with this defect, the mist-blowing method was used to reduce the influence of droplets on the taper angle and recast layer. In this work, the effect of wind speed on drilling quality was examined, and laser drilling in air, water, and NaCl solution was carried out to analyse the effect of solution composition on hole wall morphology. The results showed that a speed fan with a proper wind speed that disperses the droplets formed in the processing area can significantly reduce the refraction and scattering of the laser, and the taper angle and roundness of the drilling hole were also reduced by 15.6% and improved by 2.4%, respectively, under the wind speed of 2 m/s. The hole wall morphology showed a thicker recast layer and cracking in air, while it was thinner in water and there was little or no layer in the NaCl solution in the same current. When drilling in NaCl, the taper angle and roundness of the drilling hole were reduced by 4.13% and improved by 2.11%, respectively, compared to water. Due to the mechanical effect of the laser in the NaCl solution, the impact force on the material was much greater than that in water. The solution cavitation effect, generated by the absorption of laser energy, caused an explosive impact on the molten material adhered to the surface of the hole wall. Above all, drilling in the NaCl solution with a current of 200 A and a wind speed of 2 m/s was the optimal condition for obtaining the best processing quality.

Wireless High Temperature Sensing Chipless Tag Based on a Diamond Ring Resonator

A passive wireless sensor is designed for real-time monitoring of a high temperature environment. The sensor is composed of a double diamond split rings resonant structure and an alumina ceramic substrate with a size of 23 × 23 × 0.5 mm³. The alumina ceramic substrate is selected as the temperature sensing material. The principle is that the permittivity of the alumina ceramic changes with the temperature and the resonant frequency of the sensor shifts accordingly. Its permittivity bridges the relation between the temperature and resonant frequency. Therefore, real time temperatures can be measured by monitoring the resonant frequency. The simulation results show that the designed sensor can monitor temperatures in the range 200~1000 °C corresponding to a resonant frequency of 6.79~6.49 GHz with shifting 300 MHz and a sensitivity of 0.375 MHz/°C, and demonstrate the quasi-linear relation between resonant frequency and temperature. The sensor has the advantages of wide temperature range, good sensitivity, low cost and small size, which gives it superiority in high temperature applications.

Optimization of Alumina Ceramics Corrosion Resistance in Nitric Acid

The development of ceramic materials resistance in various aggressive media combined with required mechanical properties is of considerable importance for enabling the wider application of ceramics. The corrosion resistance of ceramic materials depends on their purity and microstructure, the kind of aggressive media used and the ambient temperature. Therefore, the corrosion resistance of alumina ceramics in aqueous HNO₃ solutions of concentrations of 0.50 mol dm^-3, 1.25 mol dm^-3 and 2.00 mol dm^-3 and different exposure times-up to 10 days-have been studied. The influence of temperature (25, 40 and 55 °C) was also monitored. The evaluation of Al₂O₃ ceramics corrosion resistance was based on the concentration measurements of eluted Al³⁺, Ca²⁺, Fe³⁺, Mg²⁺, Na⁺ and Si⁴⁺ ions obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES), as well as density measurements of the investigated alumina ceramics. The response surface methodology (RSM) was used for the optimization of parameters within the experimental "sample-corrosive media" area. The exposure of alumina ceramics to aqueous HNO₃ solutions was conducted according to the Box-Behnken design. After the regression functions were defined, conditions to achieve the maximum corrosion resistance of the sintered ceramics were determined by optimization within the experimental area.

Effects of Endoprosthesis Head Material on Acetabular Cartilage Metabolism: An Animal Study Using Crossbred Pigs

BACKGROUND

Hip endoprosthesis is one option for the treatment of displaced femoral neck fractures and avascular necrosis of the femoral head. Few reports are available describing acetabular cartilage metabolism after endoprosthesis surgery of the hip. The purpose of this study was to compare the biological effects on cartilage between cobalt-chrome (Co-Cr) and alumina ceramic heads wherein the cartilage articulates directly.

METHODS

We used the acetabular cartilage from six hips of three immature crossbred pigs to examine the effects on cytokines, the amount of hyaluronic acid (HA), and cartilage mRNA expression of ceramic head and Co-Cr head endoprosthesis. Mechanical loading of materials of Co-Cr and ceramic heads was performed on the acetabular cartilage in culture media as an organ culture model. Thereafter, protein levels of cytokines (MMP-1, 3, TNF-alpha (α), Interleukin (IL)-1 alpha (α), and IL-1 beta (β)) and the amount of HA were measured from the culture media. Cartilage RNA extraction was performed, and quantitative reverse transcriptase-polymerase chain reaction was performed with primer sets for type I, II, and III collagens; aggrecan; MMP-1, 3, 13; TNF-α; and IL-1 α, IL-1 β.

RESULTS

Protein level of IL-1 β and amount of HA in the Co-Cr group were significantly higher than those of the Ceramic group. Type II collagen mRNA expression in the Ceramic group was significantly higher than in the Co-Cr group. IL-1 β mRNA expression was significantly higher in the Co-Cr group than in the Ceramic group.

CONCLUSIONS

The present study showed that ceramic bipolar produces smaller adverse effects on cartilage cells compared to Co-Cr bipolar. These results could have significant implications for implant usage not only in hip joints, but also in other joints, including the shoulder, talus and radial head.

A Ceramic Diffusion Bonding Method for Passive LC High-Temperature Pressure Sensor

Alumina ceramic is a highly promising material for fabricating high-temperature pressure sensors. In this paper, a direct bonding method for fabricating a sensitive cavity with alumina ceramic is presented. Alumina ceramic substrates were bonded together to form a sensitive cavity for high-temperature pressure environments. The device can sense pressure parameters at high temperatures. To verify the sensitivity performance of the fabrication method in high-temperature environments, an inductor and capacitor were integrated on the ceramic substrate with the fabricated sensitive cavity to form a wireless passive LC pressure sensor with thick-film integrated technology. Finally, the fabricated sensor was tested using a system test platform. The experimental results show that the sensor can realize pressure measurements above 900 °C, confirming that the fabricated sensitive cavity has excellent sealing properties. Therefore, the direct bonding method can potentially be used for developing all-ceramic high-temperature pressure sensors for application in harsh environments.

Results of Total Elbow Arthroplasty with Cementless Implantation of an Alumina Ceramic Elbow Prosthesis for Patients with Rheumatoid Arthritis

We investigated the long-term clinical results of total elbow arthroplasty (TEA) by cementless fixation of alumina ceramic unlinked elbow prostheses (J-alumina ceramic elbows: JACE) for the reconstruction of elbow joints with rheumatoid arthritis (RA). Seventeen elbows in 17 patients (aged 44-72 years, average 54.8) replaced by JACE TEA without bone cement were investigated. The average follow-up period was 10.7 (range, 1.0-19.3) years. Clinical conditions of each elbow before and after surgery were assessed according to the Mayo Elbow Performance Index (MEPI). Radiographic loosening was defined as a progressive radiolucent line of more than 1 mm that was completely circumferential around the intramedullary stem. The average MEPI significantly improved from 46.8 points preoperatively to 66.8 points at final follow-up (p=0.0226). However, aseptic loosening was noted in 10 of 17 elbows (58.8%) and revision surgery was required in 7 (41.2%). Most loosening was observed on the humeral side. With radiographic loosening and revision surgery defined as the end points, the likelihoods of prosthesis survival were 41.2% and 51.8%, respectively, up to 15 years by Kaplan-Meier analysis. The clinical results of JACE implantation without bone cement were disappointing, with high revision and loosening rates of the humeral component.