Ceramic Spacers Research Articles

Mechanical performance evaluation and structural optimization of ceramic lined thin-walled vacuum chambers

Thin-walled vacuum chamber internally supported by ceramic spacers is a promising approach to provide sufficiently robust, ultra-high vacuum compatible and low gap vacuum devices for high energy, high current, heavy ions accelerators. The mechanical performance of the ring shaped ceramic spacers is a key factor in the structural design of these vacuum chambers. An extensive campaign was devoted to develop methodologies and equipment for evaluating the mechanical and structural properties of the ceramic spacers and to optimize the chamber design. To this aim, a force analysis on single ceramic rings was first conducted, and formulas for calculating the elastic modulus and bending strength of the ceramic rings were derived. The elastic modulus and critical position strength limits of alumina and zirconia ceramic rings were tested using a mechanical testing platform. Based on the test results of a single ceramic ring, a preliminary design and processing of ceramic lined thin-walled vacuum chamber test samples was finalized. A testing device capable to apply known water pressure values was then designed and built to test the chamber ability to withstand externally applied forces and measure the mechanical parameters of the ceramic spacers. Thanks to this, the acceptable stress limits of alumina and zirconia ceramic rings as the supporting components of the vacuum chamber were obtained. Knowing these values, through an iteration process, the whole design and properties of the ceramic lined thin-wall vacuum chamber was optimized. Finally, to reduce the impact of eddy current heat effect on ceramic strength and outgassing, a suitable cooling structure was designed and implemented.

Compact UHF Circularly Polarized Multi-Band Quadrifilar Antenna for CubeSat

This article presents a multi-band right-hand circularly polarized antenna designed for the Cube Satellite (CubeSat). Based on a quadrifilar structure, the antenna provides circular polarization radiation suitable for satellite communication. Moreover, the antenna is designed and fabricated using two 1.6 mm thickness FR4-Epoxy boards connected by metal pins. In order to improve the robustness, a ceramic spacer is placed in the centerboard, and four screws are added at the corners to fix the antenna to the CubeSat structure. These additional parts reduce antenna damage caused by vibrations in the launch vehicle lift-off stage. The proposal has a dimension of 77 × 77 × 10 mm3 and covers the LoRa frequency bands at 868 MHz, 915 MHz, and 923 MHz. According to the measurements in the anechoic chamber, antenna gains with the values of 2.3 dBic and 1.1 dBic are obtained for the 870 MHz and 920 MHz, respectively. Finally, the antenna is integrated into a 3U CubeSat that was launched by a Soyuz launch vehicle in September 2020. The terrestrial-to-space communication link was measured, and the antenna performance was confirmed in a real-life scenario.

Effect of Composite or Ceramic Thickness on the Polymerization Hardness of 5 Different Dual-cured Resin Luting Cements

Objective: The aim of the present study was to evaluate the influence of ceramic and composite thickness on polymerization hardness of five different dual-cure resin cements. Materials and Methods: A total of 100 disc-shaped spacer, 10-mm in diameter and five varying thicknesses (1.0mm, 2.0mm, 3.0mm, 4.0mm, 5.0mm) were fabricated from ceramic and composite materials. Dual-cure resin cement specimens with 8-mm diameter were prepared using metal brass mold and activated by light beneath the composite and ceramic disc shaped spacers. A total of 100 specimens of five different dual-cure resins (RelyX, Variolink, NX3, Calibra, Panavia F2.0) were prepared. Knoop hardness of each dual-cure resin cement was measured at five different point using a microhardness device with a 500 gm load, after 1 hr, 1 day, and 1 week polymerization. All data were statistically evaluated using one-way ANOVA. Results: Multivariate analysis of variance revealed significant differences in hardness of specimens dual-cured under composite resin or ceramic spacers and different time intervals (P<.001). Specimens cured through composite resin spacers showed less hardness values than ceramic spacers, with increasing thickness of the spacer. Also increasing the thickness of the composite or ceramic spacers produced a statistically significant decrease in microhardness of the dual-cure cements (P<.05). Conclusions: Hardness values significantly reduced when composite spacers were thicker than 2 mm and ceramic spacers thicker than 3 mm. Dual-cured resin cements are needed to be improved to achieve sufficient degree of hardening under composite and ceramic restorations. Different commercially available brands have different polymerization properties.

A Novel Approach for the Modeling of Electromagnetic Forces in Air-Gap Shunt Reactors

Shunt reactors are usually used in electrical systems to imbibe reactive powers created by capacitive powers on the lines when the system is operating on low or no loads. Moreover, they are also used to balance reactive powers and maintain the stability of a specified voltage. In general, the air gaps of a magnetic circuit shunt reactor are arranged along the iron core to reduce the influence of fringing and leakage fluxes. Therefore, non-magnetic materials made of ceramics or marbles are often used in air gaps to separate the iron core packets. The direction of the fringing flux is perpendicular to the laminations, so the core packets of the shunt reactor are generally made from radially laminated silicon steels. Due to the alternating electromagnetic field through the core, a periodically altered electromagnetic force is produced between the core packets, tending to compress the ceramic spacers. This electromagnetic force causes vibration and noise in the core. In this research, a finite element approach based on the Maxwell stress tensor was developed to compute the magnetic flux density and the electromagnetic forces appearing in a shunt reactor.

A Retrospective Comparative Study to Evaluate the Clinical Efficacy Using a Bioactive Glass Ceramic Spacer in Posterior Lumbar Interbody Fusion

A Retrospective Comparative Study to Evaluate the Clinical Efficacy Using a Bioactive Glass Ceramic Spacer in Posterior Lumbar Interbody Fusion

Measurement on the desorption yields of ceramic and Au-coated ceramic irradiated with Bi32+ and Xe23+

The Booster Ring (BRing) is the key part of the High Intensity Heavy Ion Accelerator Facility (HIAF). In order to reduce the eddy current effect, specifically developed stainless steel vacuum chambers with ultra-thin (0.3 mm) walls and ceramic spacers will be used. Desorption yields experiments were carried out on spacers made of zirconia ceramic, on zirconia ceramic coated with different Au thicknesses and coating processes, as well as on zirconia ceramic coated with getter films. A dedicated mass spectrometer was used to analyze the changes in the gas composition during the bombardment. The results show that Au-coated zirconia ceramic can effectively lower the desorption yields, the higher the Au coating thickness, the lower the desorption yield. When the beam impinges on the surface of the zirconia ceramic, the pressure randomly fluctuates, without showing any clear long term beam cleaning effect. As far as the coating process is concerned, samples coated by magnetron sputtering show higher desorption yields than those electroplated. However, the electroplating process is characterized by a low bonding force between the films and the ceramic substrate, which makes possible for the film to peel off under beam bombardment. Finally, TiN-coated zirconia ceramic has better static vacuum performances. However, due to its strong H2 absorption capacity, TiN coated samples will release more H2 under bombardment, thus providing a worse dynamic vacuum conditions. Practical consequences for the BRing vacuum system of the HIAF are given.

Quasi-static analysis of hip cement spacers

The use of temporary hip prosthesis made of orthopedic cement (spacer) in conjunction with antibiotics became a widespread method used for treating prosthetic infections despite the fact that this method makes bone cement (PMMA) more fragile. The necessity to incorporate reinforcement is therefore crucial to strengthen the bone cement. In this study, a validated Finite Element Modelling (FEM) was used to analyze the behavior of spacers. This FEM model uses a non-linear dynamic explicit integration to simulate the mechanical behavior of the spacer under quasi-static loading. In addition to this FEM, Extended Finite Element Method (XFEM) was also used to investigate the fracture behavior of the spacers reinforced with titanium, ceramic and stainless-steel spacer stems. The effect of the material on the performance of the reinforced spacers was also analyzed. The results showed that numerical modelling based on explicit finite element using ABAQUS/Explicit is an effective method to predict the different spacers' mechanical behavior. The simulated crack initiation and propagation were in a good agreement with experimental observations. The FEM models developed in this study can help mechanical designers and engineers to improve the prostheses’ quality and durability.

Temporal hemiarthroplasty for distal femoral osteosarcoma in early childhood: a case report

BackgroundProsthetic reconstruction for distal femoral osteosarcoma is challenging for younger children. We herein report a successful case of limb-sparing surgery for a younger patient with distal femoral osteosarcoma requiring osteo-articular resection.Case presentationA 5-year-old girl with high-grade conventional osteosarcoma in the left distal femur underwent a series of surgeries. After three cycles of neoadjuvant chemotherapy, limb-salvage surgery was planned because femoral rotationplasty had been refused. At 6 years and 2 months old, distal femoral resection and temporary spacer insertion using a 7-mm-diameter intramedullary nail and molded polymethylmethacrylate was performed. At 7 years and 8 months old, secondary surgery was performed because the first spacer had been dislocated and the residual femur became atrophic. The distal end of the residual femur was removed by 1 cm, but the periosteum and induced membrane around polymethylmethacrylate was preserved. In order to stabilize the spacer against the tibia, a custom-made ceramic spacer with a smooth straight 8-mm-diameter stem was utilized. The bone-spacer junction was fixed with polymethylmethacrylate and then covered with the preserved periosteum and induced membrane. After surgery, the bone atrophy improved. At 9 years and 7 months old, the second spacer was removed because it had loosened, and the knee joint was reconstructed using a custom-made growing femoral prosthesis with a curved porous 8.5-mm-diameter stem. Cancellous bone tips from the proximal tibia were grafted around the bone-prosthesis junction underneath the induced membrane. At 10 years and 5 months old, the patient was able to walk unsupported and a radiograph showed further thickening of the cortex of the residual femur without any stress shielding. Although having 5 cm of limb length discrepancy, the patient and her mother were satisfied with the function. The MSTS score was 24 out of 30 points. Repeated limb length extensions are planned.ConclusionsThis case report provides an example of limb-salvage surgery after distal femoral resection in a small child. The use of a temporary spacer utilizing partial cementation and preservation of the periosteum and induced membrane appears to afford a viable limb-salvage option after distal femoral resection for younger children.

Biological Responses of Ceramic Bone Spacers Produced by Green Processing of Additively Manufactured Thin Meshes.

Bone spacers are exclusively used for replacing the tissue after trauma and/or diseases. Ceramic materials bring positive opportunities to enhance greater osteointegration and performance of implants, yet processing of porous geometries can be challenging. Additive Manufacturing (AM) opens opportunities to grade porosity levels in a part; however, its productivity may be low due to its batch processing approach. The paper studies the biological responses yielded by hydroxyapatite with β-TCP (tricalcium phosphate) ceramic porous bone spacers manufactured by robocasting 2-layer meshes that are rolled in green and sintered. The implants are assessed in vitro and in vivo for their compatibility. Human bone marrow mesenchymal stem cells attached, proliferated and differentiated on the bone spacers produced. Cells on the spacers presented alkaline phosphatase staining, confirming osteogenic differentiation. They also expressed bone-specific COL1A1, BGAP, BSP, and SPP1 genes. The fold change of these genes ranged between 8 to 16 folds compared to controls. When implanted into the subcutaneous tissue of rabbits, they triggered collagen fibre formation and mild fibroblastic proliferation. In conclusion, rolled AM-meshes bone spacers stimulated bone formation in vitro and were biocompatible in vivo. This technology may give the advantage to custom produce spacers at high production rates if industrially upscaled.

Study on the electrochemical characteristics of porous ceramic spacers in a capacitive deionization cell using slurry electrodes

Many studies have been conducted on flow-electrode capacitive deionization (FCDI), by which the limited ion adsorption capacity per unit cell can be extended, and which can be applied to high-salinity water treatment. Especially, using low-cost ceramic filters as three-dimensional (3D) electrode structure for FCDI is possible, instead of stacking the unit cells for scale-up. However, using ceramic partition walls as spacer can affect water flow and ion transport due to their thickness and porosity. Furthermore, the integrated membrane-spacer-assembly (MSA) having a membrane-coated spacer is more suitable for 3D electrode structure than a separated MSA having a spacer sandwiched between membranes. Herein we investigated the effects of the thickness and porosity of plate-type porous ceramic spacers on the electrochemical properties of the cell and compared the electrochemical properties of separated MSA with those of integrated MSA. Spacer porosity was found to have a larger effect than spacer thickness. Integrated MSA had larger resistance and lower capacitance than separated MSA, leading to lower desalination performance. It was attributed to the change in physical properties of the spacer induced by coating and the difference in ion exchange capacity of the coated membrane itself.

Physico-mechanical properties of resin cement light cured through different ceramic spacers.

The purpose of this in vitro study was to compare the micro hardness, color stability/ΔE, and degree of conversion/DC of a resin cement light cured through different ceramic spacers. Lithium-disilicate ceramic samples were obtained from IPS E-max CAD blocks (HT A1) and IPS in-Ceram (transparent neutral); and divided in 7 groups (n = 8 for each test): CTR/control group; 06 M/0.6 mm monolithic; 12 M/1.2 mm monolithic; 20 M/2.0 mm monolithic; 06B/0.4 + 0.2 mm bilayered; 12B/1.0 + 0.2 mm bilayered; 20B/1.8 + 0.2 mm bilayered. The resin cement (Variolink veneer) was light cured through the ceramic spacers. The resin cement samples were evaluated for ΔE using a spectrophotometer after 24 h, 7days and after aging (24 h in water at 60 °C). Knoop microhardness and DC tests were conducted immediately after light curing, after 24 h and 7days. All experimental groups showed similar microhardness values, although being lower than CTR group. Similar results were observed after 7days. ΔE was similar between all groups after 24 h (except for 12B and 20B), and increased for all groups after 7days and after artificial aging, especially for thicker and bilayer groups. Only 06 M showed values similar to CTR group. DC values were similar to all groups immediately after light curing, increasing after 24 h and 7days. After 7days, only group 20B showed lower DC than CTR group. A tendency of higher DC could be observed for monolithic and thinner ceramics. All test results showed strong correlation (0.9987). Ceramic interposition can reduce mechanical and physical properties of resin cements, especially with thicker and bilayered ceramics. Group 06 M showed the best ΔE overtime.

Characterisation of a neutron diffraction detector prototype based on the Trench-MWPC technology

The Trench Multi-Wire-Proportional-Chamber is a new type of MWPC which has been designed to fulfill the requirements of the 2D curved neutron detector under development for the XtremeD neutron diffractometer, under construction at ILL. In this design, anode wires are mounted orthogonally to a stack of metallic cathode plates which are insulated from each other by ceramic spacers. A row of teeth is spark-eroded along the edge of the cathode plates so that anode wires appear to be stretched along trenches machined across a segmented cathode plane. This design was tested on a prototype detector module mounted in a vessel filled with a mixture of 3He-Ar-CO2 at 7 bar. The detector configuration as well as measurements performed on this prototype at ILL neutron test beam line are presented. Results show that the Trench-MWPC design provides uniform amplification gain across the detection area despite the absence of the top cathode wires used to balance the electric field in standard Cathode-Anode-Cathode MWPC configurations. The presence of cathode trench side-walls surrounding anode wires minimises the spread of neutron-induced charge across electrodes, allowing for detector operation at reduced amplification gain without compromising the signal to noise per electrode. Pulse-height spectra acquired under various neutron flux conditions demonstrated that the Trench-MWPC design minimises space-charge effects, thanks to its low amplification gain combined with the fast collection of ions by cathode trench side-walls surrounding anode wires. Measurements also showed that this space-charge effect reduction results in a high local count-rate of ∼100 kHz at 10% count loss when irradiating the detector with a small 5 mm × 5 mm neutron beam.

Preparing diopside nanoparticle scaffolds via space holder method: Simulation of the compressive strength and porosity

In the present study, diopside nanopowders were prepared via mechanical milling with eggshell as the calcium source. The space holder method (compaction of ceramic powder and spacer) as one of the most important methods to produce ceramic/metal scaffolds was used to produce diopside scaffolds. For the first time, the effect of the spacer size on mechanical properties and porosity of the obtained scaffolds was experimentally discussed. According to the results obtained, the NaCl particles (as the spacer) with the size of 400–600µm maintained their original spherical shape during the compaction and sintering processes. As a new work, the most important parameters including the spacer type, spacer concentration, spacer size, and applied pressure were considered, and their effects on mechanical properties and porosity of diopside scaffolds were simulated. Gene Expression Programming (GEP), as one of the most branches of the artificial intelligence, was used for simulation process. By using the GEP, two equations were introduced to predict the compressive strength and porosity of the obtained scaffolds with the lowest error values. The 3D diagrams extracted from the model were used to evaluate the combined effect of the process parameters on the compressive strength and porosity of the scaffolds. The GEP model presented in this work has a very low level of error and a high level of the squared regression for predicting the compressive strength and porosity of diopside scaffolds.

Clinical Application of Ceramics in Anterior Cervical Discectomy and Fusion: A Review and Update.

Study Design:Narrative review.Objectives:Anterior cervical discectomy and fusion (ACDF) is a reliable procedure, commonly used for cervical degenerative disc disease. For interbody fusions, autograft was the gold standard for decades; however, limited availability and donor site morbidities have led to a constant search for new materials. Clinically, it has been shown that calcium phosphate ceramics, including hydroxyapatite (HA) and tricalcium phosphate (TCP), are effective as osteoconductive materials and bone grafts. In this review, we present the current findings regarding the use of ceramics in ACDF.Methods:A review of the relevant literature examining the clinical use of ceramics in anterior cervical discectomy and fusion procedures was conducted using PubMed, OVID and Cochrane.Result:HA, coralline HA, sandwiched HA, TCP, and biphasic calcium phosphate ceramics were used in combination with osteoinductive materials such as bone marrow aspirate and various cages composed of poly-ether-ether-ketone (PEEK), fiber carbon, and titanium. Stand-alone ceramic spacers have been associated with fracture and cracks. Metallic cages such as titanium endure the risk of subsidence and migration. PEEK cages in combination with ceramics were shown to be a suitable substitute for autograft.Conclusion:None of the discussed options has demonstrated clear superiority over others, although direct comparisons are often difficult due to discrepancies in data collection and study methodologies. Future randomized clinical trials are warranted before definitive conclusions can be drawn.

Delayed Light Activation Improves Color Stability of Dual‐Cured Resin Cements

To evaluate the color change caused by post-irradiation conversion (ΔE24h and ΔE8days ) and artificial aging (ΔEAGING ) of resin cements light activated through ceramics of different opacities immediately and 6minutes after manipulating the material. Resin cement disks (Allcem and LuxaCore) were light activated through ceramics (without ceramic, e.max HT, LT, and MO) immediately and 6minutes after the manipulation (n = 10). Spectrophotometry was used to evaluate ΔE24h and ΔE8 days after 37˚C-dry-dark-storage for 24 hours and 8 days, and ΔEAGING after 60˚C-water-storage for 24 hours. Data were analyzed with three-way ANOVA and Tukey's HSD (α = 0.05). Regarding the post-irradiation color change, significant differences were found between the cements (p < 0.0001), light activation protocols (p = 0.037), and ceramics (p < 0.001). The immediate activation (16.2 ± 0.1) showed lower ΔE values than the delayed activation (16.5 ± 0.1). Ceramics influenced the ΔE values as follows: MO (14.0 ± 1.2) < LT (14.9 ± 1.2) ≈ HT (15.4 ± 1.2) < control (21.2 ± 1.2). Regarding ΔEAGING , significant differences were found between cements (p<0.001), light activation (p = 0.006), and ceramics (p < 0.001). The delayed activation (8.4 ± 0.1) showed lower values than the immediate activation (8.9 ± 0.1). Ceramic spacers influenced ΔEAGING as follows: control (5.6 ± 0.2) < MO (6.6 ± 0.2) < HT (11.0 ± 0.2) ≈ LT (11.5 ± 0.2). The delayed light activation resulted in increased color stability, while the ceramic interposition resulted in lower color stability.

Use of Miniplates and Local Bone Grafts to Prevent Spring Back in Laminoplasty for Cervical Spondylotic Myelopathy: 用金屬小綱板和骨移植來防止椎板回彈的技術在椎板成形術中的應用

Background/PurposeCervical spondylotic myelopathy/ossification of posterior longitudinal ligament can be treated by anterior or posterior decompression. For multiple levels, it is common to perform posterior decompression by laminoplasty. Hirabayashi described his open-door expansive laminoplasty in 1977, which soon became popular. Spring back of the lamina has always been a problem. Many methods including suturing to soft tissue, suture anchors, bone grafts, hydroxyapatite blocks, and ceramic spacers were used to prevent this problem, but with considerable failure. Recently, miniplates were used to prevent spring back. MethodsTwenty-nine consecutive patients who had underwent Hirabayashi open-door expansive laminoplasty in a single centre were recruited in this retrospective study. Miniplates were used to keep the laminae open. In addition, the spinous processes of lower cervical vertebrae were excised and used as local bone grafts to fill the gap between the cut laminae. Computerized tomography scans were performed postoperatively for all patients to assess bone union and spring back. ResultsA total of 126 levels of laminoplasty and 51 local bone grafts were studied. The minimal follow-up period was 12 months. Signs of bone union were demonstrated in 123 hinges (97.6%) and 51 bone grafts (100%). No spring back was detected. The clinical outcome in terms of Hirabayashi recovery rate was 47.2%. ConclusionMiniplates and local bone grafts are promising and effective tools for preventing spring back in cervical laminoplasty.

Effect of the variable cross-section channel on performance of a cusped field thruster at low power

The cusped field thruster has drawn much attention from many institutions due to its wide thrust range, high impulse, and long lifetime. However, lots of experimental results reveal that the cusped field thruster at low power has a poor performance. A cusped field thruster with a variable cross-section channel by putting a ceramic spacer in the channel is introduced in this paper, aimed at improving the thruster performance at low power. The DSMC results validate that the upstream atom density can be increased by a spacer, especially near the wall. Based on simulated results, spacers are put into different positions of the channel. The experimental results show that a suitable spacer can enhance thruster performance at low power, which can be confirmed by the results that the anode efficiency can achieve 40% at 400 V anode voltage and 20 sccm gas flow rate by contrast to 35% without a spacer under the same condition.

Modified Open-Door Laminoplasty Using a Ceramic Spacer and Suture Fixation for Cervical Myelopathy.

PurposeTo introduce a new simple technique using suture anchors and ceramic spacers to stabilize the elevated laminae in open-door cervical laminoplasty. Although ceramic spacers were placed in the opened laminae and fixed with nylon threads in this series, it was occasionally difficult to fix the nylon threads to the lateral mass.Materials and MethodsStudy 1: A preliminary study was conducted using a suture anchor system. Sixteen consecutive patients who underwent surgery for cervical myelopathy were prospectively examined. Study 2: The second study was performed prospectively to evaluate the feasibility of this new technique based on the result of the preliminary study. Clinical outcomes were examined in 45 consecutive patients [cervical spondylotic myelopathy (CSM)] and 43 consecutive patients (OPLL). The Japanese Orthopedic Association scoring system (JOA score), axial neck pain, and radiological findings were analyzed.Results1) In one case, re-operation was necessary due to dislodgement of the ceramic spacer following rupture of the thread. 2) In all patients, postoperative CT scans showed that the anchors were securely inserted into the bone. In the CSM group, the average JOA score improved from 9.5 points preoperatively to 13.3 at follow-up (recovery 51%). In the OPLL group, the average JOA score improved from 10.1 (5-14) points preoperatively to 14.4 (11-16) at follow-up (recovery 62%). There were no serious complications.ConclusionThe use of the suture anchor system made it unnecessary to create a hole in the lateral mass and enabled reliable and faster fixation of the HA spacers in open-door laminoplasty.

Influence of the interposition of ceramic spacers on the degree of conversion and the hardness of resin cements

This study evaluated: I) the effect of photo-activation through ceramics on the degree of conversion (DC) and on the Knoop hardness (KHN) of light- and dual-cured resin cements; and II) two different protocols for obtaining the spectra of uncured materials, to determine the DC of a dual-cured resin cement. Thin films of cements were photo-activated through ceramics [feldspathic porcelain (FP); lithium disilicate glass-ceramics of low translucency (e.max-LT), medium opacity (e.max-MO) and high translucency (e.max-HT); glass-infiltrated alumina composite (IC) and polycrystalline zirconia (ZR)] with thicknesses of 1.5 and 2.0 mm. DC was analyzed by Fourier transform infrared (FTIR) spectroscopy. Two protocols were used to obtain the spectra of the uncured materials: I) base and catalyst pastes were mixed, and II) thin films of base and catalyst pastes were obtained separately, and an average was obtained. KHN assessment was performed with cylindrical specimens. The results were analyzed by ANOVA and Tukey's test (α= 0.05). The light-cured cement showed higher DC (61.9%) than the dual-cured cement (55.7%). The DC varied as follows: FP (65.4%), e.max-HT (65.1%), e.max-LT (61.8%), e.max-MO (60.9%), ZR (54.8%), and IC (44.9%). The light-cured cement showed lower KHN (22.0) than the dual-cured (25.6) cement. The cements cured under 1.5 mm spacers showed higher KHN (26.2) than when polymerized under 2.0 mm ceramics (21.3). Regarding the two protocols, there were significant differences only in three groups. Thus, both methods can be considered appropriate. The physical and mechanical properties of resin cements may be affected by the thickness and microstructure of the ceramic material interposed during photo-activation.

A Fabry–Pérot Etalon with an Ultralow Expansion Ceramic Spacer

We have developed a Fabry–Pérot etalon with an ultralow expansion ceramic spacer and investigated the thermal properties of the ceramic. We found that the ceramic cavity has a “zero crossing temperature” at room temperature where the thermal expansion coefficient crosses zero. The sensitivity of the thermal expansion coefficient of the ceramic to temperature change is about five times greater than that of ultralow expansion (ULE) glass at around the zero cross temperature. Nevertheless, owing to the high specific rigidity and relatively low thermal expansion at room temperature, the ceramic should be an attractive material for long optical cavities that can reduce the effect of the thermal noise relatively.