Ceramic Polishing Research Articles

Process method of Si3N4 ceramic brazing sealed cavity for high-temperature application.

The process method of a Si3N4 ceramic sealed cavity is realized by vacuum brazing and chemical reaction at 1,100°C and 0.5 MPa pressure. Through the combination of Si3N4 ceramic polishing and thinning, inductively coupled plasma etching, and high-temperature metal filler (Ti-Zr-Cu-Ni) brazing process, a vacuum-sealed cavity suitable for high-temperature environments was prepared. The cross section of the bonding interface was characterized by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), which indicated that the two Si3N4 ceramic were well bonded, the cavity structure remained intact, and the bonding interface strength exceeded 5.13 MPa. Furthermore, it retained its strong bonding strength after in high-temperature environments of 1,000, 1,050, and 1,100°C for 1 h. This indicates that a brazed vacuum-sealed cavity can be used in high-temperature environments. Through the proposed method, pressure sensor that can withstand high temperatures can be developed.

Chemical mechanical polishing exploiting metal electrochemical corrosion of single-crystal SiC

A chemical mechanical polishing (CMP) method of single-crystal SiC is proposed based on metal electrochemical corrosion. The oxidation mechanism of SiC by electrochemical corrosion of metals and the mechanism of surface material removal are revealed by corrosion and polishing experiments. The metallic aluminum sheet that is in contact with single-crystal SiC was immersed in sodium sulfate (Na2SO4) electrolyte solution, and the morphological and elemental changes of single-crystal SiC surface were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Then, polishing experiments were conducted on single-crystal SiC using different metal polishing discs and different polishing solutions. The XPS and EDS results show that single-crystal SiC can electrochemically corrode to generate a silica reaction layer. The use of metal polishing discs in CMP significantly improved the material removal rate (MRR) of SiC, with the highest MRR of 1011.43 nm/h for aluminum polishing discs, followed by that for iron polishing discs, and the lowest MRR for copper and alumina ceramic polishing discs. When metal polishing discs were used, the addition of electrolyte solution significantly improved the MRR and reduced the surface roughness of the SiC surface. Polishing with Na2SO4 solution when the polishing disc was aluminum disc, the MRR was higher than that for using deionized water by 105%, and the surface roughness Ra decreased by 37.8% to 2.8 nm. The metal electrochemical corrosion reaction can promote the oxidation of single-crystal SiC and generate a soft SiO2 reaction layer on the SiC surface, thereby improving the polishing efficiency of single-crystal SiC.

Evaluation of Various Polishing Systems for Lithium Disilicate Glass-Ceramics.

The aim of this study was to investigate the surface roughness of lithium disilicates (LS2s) polished using various polishing systems. Two types of LS2 (A, Amber Mill and E, IPS e.max CAD) were polished using LS2-specific polishing systems (L-Edenta, L-Jota), a zirconia-specific polishing system (Z-Jota), and a conventional ceramic polishing system (P-Shofu) (n = 8 per group). The compositions of different polishing systems were analyzed using EDS. Surface roughness was measured using confocal laser scanning microscopy and analyzed using EDS and SEM. ANOVA and Tukey's tests were used for the statistical analyses (p = 0.05). The polishing systems were mainly composed of C, O, and Si. The L-Jota group exhibited rougher surfaces than the other groups. Amber Mill exhibited higher surface roughness than IPS e.max CAD (p⟨0.001). Among the polishing systems, the L-Jota group presented the highest roughness value (pp⟨0.001). The surface roughness of the AL-Jota group was higher than that of the other groups. A sufficiently smooth surface can be achieved without a LS2-specific polishing system. Further, the same polishing system can have different effects depending on the type of LS2.

Ceramic and Composite Polishing Systems for Milled Lithium Disilicate Restorative Materials: A 2D and 3D Comparative In Vitro Study.

Purpose: This study aims to evaluate the effectiveness of two ceramic and two composite polishing systems for a novel chairside computer-aided design/computer-aided manufacturing (CAD/CAM) lithium disilicate ceramic with three-dimensional and two-dimensional microscopy images. This ceramic material can be used for implant-supported or tooth-borne single-unit prostheses. Materials and Methods: Sixty flat samples of novel chairside CAD/CAM reinforced lithium disilicate ceramic (Amber Mill, Hass Bio) were divided into five groups (n = 15/group) and treated as follows: Group 1 (NoP), no polished treatment; group 2 (CeDi), polished with ceramic Dialite LD (Brasseler USA); group 3, (CeOp) polished with ceramic OptraFine (Ivoclar Vivadent); group 4, (CoDi) polished with composite DiaComp (Brasseler USA), and group 5 (CoAs), polished with composite Astropol (Ivoclar Vivadent). The polished ceramic surface topography was observed and measured with three-dimensional and two-dimensional images. Results: All polishing systems significantly reduced the surface roughness compared with the non-polished control group (Sa 1.15 μm). Group 2 (CeDi) provided the smoothest surface arithmetical mean eight with 0.32 μm, followed by group 3 (CeOp) with 0.34 μm. Group 5 (CoAs) with 0.52 μm provided the smoothest surface among the composite polishing kits. Group 4 (CoDi) with 0.66 μm provided the least smooth surface among all polishing systems tested. Conclusions: Despite the effectiveness of ceramic polishing systems being superior to composite polishing systems of the CAD/CAM lithium disilicate restorative material, both polishing systems significantly improved the smoothness.

Influence of Pulse Energy and Defocus Amount on the Mechanism and Surface Characteristics of Femtosecond Laser Polishing of SiC Ceramics.

SiC ceramics have excellent comprehensive properties and are typical hard and brittle materials that are difficult to process and are widely used in many fields. Laser polishing technology has developed into a new surface processing technology, and femtosecond laser polishing has become an important method for the precision machining of hard and brittle materials. In this paper, SiC ceramics were ablated and polished by infrared femtosecond laser, the laser ablation threshold of SiC ceramics was calculated and the influence of pulse energy and defocus amount on the surface morphology, surface roughness, polishing depth and oxidation degree of femtosecond laser polishing of SiC ceramics were investigated. The results show that when the laser repetition frequency f = 175 kHz, wavelength λ = 1064 nm and ablation time t = 9 s, the laser ablation threshold of SiC ceramics is 0.355 J/cm2. With the increase in pulse energy, the surface roughness first decreased and then increased, and the polishing depth showed an overall upward trend. The change of defocus amount will lead to the change of the laser spot diameter. With the increase of the defocus amount, the laser spot irradiated on the workpiece surface becomes larger, and the laser energy density decreases, which results in the decrease of the laser ablation ability and polishing depth and the increase of the polished surface roughness. Periodic nano-ripple structures appeared on the laser-induced surface. Through Energy Dispersive Spectrometer (EDS) elemental analysis, it was found that there was an oxidation phenomenon in SiC ceramics polished by femtosecond laser in an air environment, and the change of pulse energy and defocus amount had insignificant effects on the degree of oxidation.

Analysis of polishing waste ceramic foam packing in evaporative cooling

This paper proposes the use of ceramic polishing slag to make fillers for evaporative coolers. The experimental tests on the heat transfer performance of the ceramic foam packing are carried out by using the independent test bench, focusing on the effects of the packing's flow channel form, drench density, the inlet air volume and pressure drop on the heat, and the mass transfer performance of the packing. The experimental results show that the optimum drench density of the ceramic foam packing in the form of a folded runner and a linear runner is 10.0 and 6.7 kg/(m·h), respectively. The direct evaporative cooling efficiency of the ceramic foam packing in both runners tends to decrease with the decrease in the dry and wet bulb temperature difference of the inlet air and the increase of the air mass flow rate. Under the same experimental conditions, the direct evaporative cooling efficiency, optimum inlet air velocity, and pressure drop of the packing in the form of a folded flow channel are higher than those of the linear flow channel. The optimal inlet air velocities of the packing in the form of a folded runner under the conditions of Urumqi, Xi'an, and Guangzhou are 1.6, 1.4, and 1.0 m/s, respectively, and the direct evaporative cooling efficiency can reach 83.01%, 70.74%, and 66.41%. In comparison, the optimal inlet air velocity for all three conditions under the linear runner is 1.0 m/s, and the direct evaporative cooling efficiencies are 73.78%, 68.56%, and 63.28%, respectively.

Surface Morphology Evaluation and Material Removal Mechanism Analysis by Single Abrasive Scratching of RB-SiC Ceramics

Reaction-Bonded Silicon Carbide (RB-SiC) ceramics possessing excellent mechanical and chemical properties, whose surface integrities have an essential effect on their performance and service life, have been widely used as substrates in the core parts of aerospace, optics and semiconductors industries. The single abrasive scratching test is considered as the effective way to provide the fundamental material removal mechanisms in the abrasive lapping and polishing of RB-SiC ceramics for the best surface finish. In this study, a novel single abrasive scratching test with an increasing scratching depth has been properly designed to represent the real abrasive lapping and polishing process and employed to experimentally investigate the surface integrity regarding different scratching speeds. Three typical and different material removal stages, including the ductile mode, ductile–brittle transition mode and brittle mode, can be clearly distinguished and it is found that in the ductile material removal stage by increasing the scratching speed would inhibit the plastic deformation and improve its surface integrity. It is also found that in the ductile–brittle transition and brittle material removal stages, to increase the scratching speed would inhibit the plastic deformation due to the fast scratching speed that limits the time of plastic deformation on the target, but it also results in the increased length of lateral cracks with the increased scratching speed which can reflect that the size of brittle chips, like brittle fractures and large grain fragmentations, increases as the scratching speed increases. It can provide the references for the optimization of the abrasive lapping and polishing of RB-SiC ceramics with high efficiency and surface quality.

Study on the recycling of ceramic polishing slag in autoclaved aerated foam concrete by response surface methodology

In this study, the mechanical performance and thermal insulation properties of autoclaved aerated foam concrete (AAFC) with ceramic polishing slag (CPS) were investigated using chemical foaming technology at a density of 500 kg/m3. An orthogonal experimental array and the response surface methodology analysis were used to optimize the mix proportion of CPS slurry, cement, and lime content, and XRD, SEM, TG, and MIP were employed to study the microstructure and composition of the AAFC. The AAFC with the maximum compressive strength, minimum thermal conductivity, and cement consumption was obtained using the quadratic model of the response surface methodology analysis. The minimum thermal conductivity reached 0.1032 W/m·K, and a compressive strength value of 4.03 MPa was obtained for the mixtures with the CPS slurry, cement, and lime at 2804, 226.2, and 234 kg/model, respectively. The results of the microstructure development show that with an increase in CPS slurry, the compressive strength is significantly enhanced. This might be due to a sufficient hydration reaction with a proper water content. The Si and Al in the CPS react with the calcareous material and C–S–H gels to form tobermorite, thus promoting the compressive strength. In addition, the MIP indicates that the micropore (10–50 mm) content of the AAFC has a significant correlation with thermal conductivity, while macropores (>500 mm) have a significant relationship with compressive strength.

Preparation of the Nanodiamond@SiO2 Abrasive and its Effect on the Polishing Performance of Zirconia Ceramics

For the purpose of achieving the industrial requirement of efficient and high precision polishing of zirconia ceramics, nanodiamond@SiO2 abrasives were synthesized by a simple method using tetraethyl orthosilicate (TEOS) as raw materials. As observed in the transmission electron microscopy results, the composite abrasives showed a homogeneous and dense silica coating layer. It was confirmed by Fourier transform infrared spectroscopy and X-ray diffraction spectroscopy that the composite abrasives have a core–shell structure with a diamond core and a silica shell. According to the Zeta potential analysis, the dispersion stability of composite particles was improved compared to that of the pure nanodiamond particles. The chemical mechanical polishing (CMP) experimental results show that the polishing performances of composite abrasives on zirconia ceramics are better than that of the pure nanodiamond abrasives. The material removal rate of the composite particles is 2.184 μm h−1, and the surface roughness of the polished zirconia ceramics is 1.055 nm, which was 140% higher and 89% lower than that of pure nanodiamond abrasives, respectively. Furthermore, the polishing mechanism was explored by X-ray photoelectron spectroscopy (XPS), friction coefficient meter and dynamic contact angle test.

Rheological properties of magnetic field-assisted thickening fluid and high-efficiency spherical polishing of ZrO2 ceramics

Shear thickening polishing technology using non-Newtonian polishing fluids is a low-cost, low-damage polishing method for the ultra-precision machining of complex curved surfaces. However, the low polishing efficiency and poorly controlled viscosity of traditional shear thickening polishing fluids significantly limit their practical applications. In this study, a novel weak magnetic field-assisted shear thickening polishing fluid (WMFA-STPF) containing carbonyl iron particles, which utilized a weak magnetorheological effect to promote the shear thickening process, was developed, and its rheological characteristics were investigated. The obtained results revealed that WMFA-STPF exhibited good fluidity at low shear rates and enhanced thickening characteristics in the working shear rate range. To verify the high efficiency, high quality, and uniform polishing ability of WMFA-STP technology applied to the spherical surface of a zirconia ceramic workpiece, contrast polishing experiments were performed. After 75 min of polishing, the surface damage was effectively mitigated; the surface quality and uniformity were significantly improved; and the material removal rate increased by 156% up to 7.82 μm/h. Hence, the WMFA-STP method can be successfully utilized for the high-efficiency high-quality polishing of hard and brittle ceramics.

Investigation of performance and modification mechanism of ceramic-polishing-powder-modified asphalt mastic

In this study, ceramic polishing powder (PP) as an industrial waste product, was treated by a silane coupling agent (KH550) and an NaOH solution, and then it was used to prepare the PP-modified asphalts. The performance of the modified asphalts and their modification mechanisms were examined. The results showed that the optimal preparation process was pre-shearing 15 min, and then shearing 60 min at 145°C, 4000 r/min after adding PP. KH550-PP-modified asphalt exhibited the best high- and low-temperature performances, thermal-oxidative aging resistances and anti-water damage performance and the lowest temperature sensitivity. PP was evenly dispersed in the original asphalt, which increased the bee structure and the surface roughness of the asphalt. The surface modifier changed the surface physical properties of the PP particles, which is helpful to achieve co-melting and blending with the original asphalt. However, an effect on the chemical structures of the composite-modified asphalts was not evident.

Polishing of zirconia ceramics by chemically-induced micro-nano bubbles

This study introduces micro-nano bubbles (MNBs) in the process of polishing zirconia ceramics through sodium borohydride hydrolysis to assist in polishing yttria-stabilized zirconia (YSZ). Compared with conventional silica sol, the material removal rate using this MNB-assisted technology is increased by 261.4%, and a lower surface roughness of 1.28 nm can be obtained. Raman, X-ray diffraction, and X-ray photoelectron spectroscopy are used to study the structural changes and phase stability of the YSZ during different polishing periods. The results show that MNBs are the key factor promoting the transformation from the tetragonal phase to the monoclinic phase on the surface of the YSZ during polishing. The H2O molecules (or OH− ions) on the surface of the YSZ are driven by the thermal kinetic energy of the micro-jets formed by the collapse of micro-bubbles, and they permeate to occupy more oxygen vacancies in the crystal lattice. Atomic force microscopy and nano-indentation tests show that the micro-protrusions on the surface of the YSZ preferentially undergo phase transformation, and their hardness decreases. This promotes abrasives to preferentially remove rough spots on the surface and achieve more efficient polishing. We believe this work adds valuable insights regarding low-temperature degradation and ultra-precise machining of YSZ ceramic materials.

Effects of Grinding and Polishing on Surface Characteristics of Monolithic Zirconia Fabricated by Different Manufacturing Processes: Wet Deposition and Dry Milling.

To evaluate the effects of grinding and polishing on surface characteristics of monolithic zirconia fabricated by two different manufacturing processes. Two types of monolithic zirconia specimens, self-glazed zirconia (SZ) and conventional zirconia (CZ), were fabricated by wet deposition and dry milling, respectively. The specimens were randomly assigned into 4 groups (n = 10): as-sintered, ground, polished with a special zirconia polishing kit, and polished with a general-purpose ceramic polishing kit. Surface morphology and roughness (Ra ) were characterized, followed by one-way ANOVA analysis (α = 0.05). The as-sintered SZ exhibited a smooth surface with obvious different morphologies compared with the as-sintered CZ (Ra : 0.26 ± 0.05 μm versus 0.33 ± 0.10 μm). Ra of the ground SZ was significantly higher than that of the as-sintered SZ (p < 0.001) and the ground CZ (p = 0.011). For both SZ and CZ, Ra decreased significantly after polishing (p < 0.001), and there was no significant difference between the two groups with different polishing kits (SZ- p = 0.144; CZ- p = 0.322). Surface morphologies of SZ and CZ became similar after grinding and polishing. Monolithic zirconia SZ fabricated by wet deposition exhibited a smooth surface with specific patterns compared to the dry milled CZ. Grinding significantly changed the surface morphology of SZ and increased surface roughness of both zirconia specimens, which can be improved by polishing without being influenced by polishing kit selection.

Performance Evaluation of Rotational-Magnetorheological Glass–Ceramic Polishing (R-MRGP) Process Setups

Performance Evaluation of Rotational-Magnetorheological Glass–Ceramic Polishing (R-MRGP) Process Setups

Green-chemical-jump-thickening polishing for silicon carbide

An ultra-precision machining approach called green-chemical-jump-thickening polishing (GC-JTP) is explored to improve surface accuracy and to achieve high-efficiency polishing for silicon carbide (SiC) ceramics. A new concept of green-chemical-jump-thickening polishing slurry (GC-JTPS) is developed to be an environmentally-friendly fluid with including two essential capabilities: one is the chemistry-induced jump-thickening (JT) mechanism and the other is green-chemical-thickening to enhance removal efficiency. Based on Navier-Stokes's equation and flow continuity equation, the polishing pressure in the GC-JTP process is calculated. On the basis of the rheological dynamics and abrasive nano-indentation analysis, a predictive understanding model to assess material removal rate (MRR) is proposed for the machining controllability of GC-JTP. Under the GC-JTP verification experiments, the maximal proportional error between the testing results and the theoretical calculation stands at only ζ = 7.8%, which proves the accuracy and effectiveness of the new theory MRR in GC-JTP. Through the fitting error, the correction coefficient of α = 0.929 should be used in the MRR model in order to better guide the actual processing. The analysis of the maximal cutting depth and the threshold of ductile-brittle transition revealing subsurface damages might generate. Under the optimized polishing conditions of the shearing velocity v r = 2.0 m/s, the abrasive size D a = 2.0 μm, the gap depth δ 0 = 1.5 mm, the sodium bicarbonate W p = 15 wt%, the sorbitol W o = 20 wt% and the abrasive CeO 2 W a = 30 wt%, the SiC ceramics roughness is reduced from Ra 768 nm to Ra 32 nm and the subsurface damages depth can be controlled at the range of 2.5 μm–4.5 μm to achieve good surface integrity. The work demonstrates that the GC-JTP is a green and efficient processing method for the low-damage polishing of SiC ceramics.

41 - Effect of Polishing Technique on Flexural Strength of Glass-Ceramics

Aim of the study was to evaluate the influence of polishing on the flexural strength of dental glass-ceramic materials performed according to chairside techniques, laboratorial procedures or glazed. Specimens were produced of two dental ceramics (IPS e.max CAD/IPS e.max Press, both Ivoclar Vivadent, Schaan, Liechtenstein) as bars of 4 ×3 x 25 mm. Specimens were grinded wet with a rough diamond-copper wheel (D19) to standardize a rough surface (served as negative control, group 5). To simulate chairside conditions students of the 10th semester polished one side of the bars with either Diapro (two-step system, group 1) or Diapol (three-step system, group 2) (both from EVE Ernst Vetter GmbH, Keltern, Germany) dry with a KAVO handpiece. The positive control (group 3) was polished in laboratory with an automatic polishing machine (Buehler) with SiC papers up to 4000 grit under water-cooling. Group 4 was glazed (Crystal/Glaze Spray, Ivoclar) following manufacturers intructions. Afterwards all specimens were tested for flexural strength in a four-point-bending test. Stress at fracture was analyzed using Weibull statistics. The unpolished negative control group 5 showed the lowest mean flexural strength values for both materials. The chairside polishing groups (1/2) showed the highest mean flexural strength values. For e.max CAD those were significantly higher than in group 3 (lab polish), for e.max Press no significant difference between those groups could be found. Group 4 (glaze) reached similar mean flexural strength values to lab polishing (3) for e.max CAD; for e.max Press the values were significantly lower than in all polished groups (1-3). Polishing of dental ceramics increases flexural strength, independent if done dry chairside or in laboratory under water-cooling. Glazing can increase strength depending on material but is not more effective than polishing.

Experimental Study of Surface Roughness of Dental Ceramics After Polishing with Three Types of Polishing Systems.

This study evaluated the surface roughness of three dental ceramics after polishing with three types of extraoral ceramic polishing sets. One hundred and twenty specimens were fabricated from feldspathic porcelain, lithium disilicate, and zirconia ceramics. The specimens were randomly allocated into four subgroups (n = 10). Group one was glazed (control) and the other three groups were ground using fine diamond burs and then sequentially polished by two rubber wheels from three polishing sets: feldspathic porcelain, lithium disilicate, and zirconia sets. The surface roughness measurement was performed with a profilometer and the surfaces were analyzed using scanning electron microscopy. Elemental compositions of three polishing sets were examined using x-ray powder diffraction. The surface roughness values of three polishing systems were compared by one-way analysis of variance with Dunnett's T3 post hoc test. The significance level was set at p < 0.05. There was no significant difference in surface roughness when polishing ceramics with the lithium disilicate and zirconia polishing sets. In addition, those two sets provided lower roughness compared with the feldspathic porcelain polishing set and glazing. The main component of all polishing wheels was carbon, and only zirconia polishing wheel had more additional trace elements, which were titanium and silica. Lithium disilicate and zirconia extraoral polishing sets achieved superior results compared to feldspathic polishing set and glazing.

Optimization of Surface Modification for Additively Manufactured AlSi10Mg Using a Vibratory Polishing Surface Finisher

Surface morphology is a significant aspect of a solid material, whether for aesthetic or functional purposes and currently, through different surface modification methods, developments have been dedicated into advancing metallic materials to improved surface characteristics. Additively manufactured aluminium alloys have demonstrated an extensive choice of appropriate characteristics for different uses desired for the aviation and space industry. However, the surface hardness and tribological properties are insufficient in these materials due to the fact that when one property is enhanced one is compromised especially after thermal treatment. This makes the significant development and modification of the surface properties very imperative for existing and forthcoming engineering applications. There are many types of surface modification techniques used, in this paper an optimization of the barrel finishing that uses ceramic polishing media for commercially build SLM produced AlSi10Mg will be explored. Gloss value, surface roughness and other characteristics will be characterized.

Preparation of the rod-shaped SiO2@C abrasive and effects of its microstructure on the polishing of zirconia ceramics

This study aims to achieve higher-efficiency zirconia ceramic polishing demands, using a novel rod-shaped SiO2@C abrasive that was synthesized by a simple three-step method. The scanning electron microscopy and transmission electron microscopy results showed that composite abrasives were rod-shaped. As confirmed by Fourier transform infrared spectrometer and Raman spectra, the composite particle had a core-shell structure with a core of silica and a shell of carbon. According to the N2 adsorption-desorption results, this composite abrasive had a mesoporous structure. The material removal rate of 242.5 nm/h and the zirconia ceramic surface roughness of 1.86 nm are 70.4% higher and 27.9% lower, respectively, than those achieved with conventional silica abrasives. The improved polishing performance may be attributed to its line contact mode, the reduction of Young's modulus and the improvement of tribochemical reaction. This study highlights the interaction between the surface microstructure of abrasives and the surface planarization of ceramics.

Influence of Pulse Energy and Scanning Speed of Femtosecond Laser on Surface Roughness of SiC Ceramics

Laser polishing, as a novel surface processing technology, has been successfully employed for improving the surface smoothness and geometric accuracy of components for metals, glasses, fibers and ceramics. However, continuous wave and microsecond and nanosecond lasers leads to some undesirable defects of the polished surface, such as heat affected zone, debris redeposition and thermal stress induced microcracks, especially for hard brittle materials. To solve this issue, this article investigated femtosecond laser polishing of SiC ceramics. Influence of pulse energy and scanning speed on surface roughness and surface morphologies was studied. In addition, the relationship between laser parameters and surface roughness and removal depth of SiC ceramics has been revealed. The experimental results indicated that the polished surface without big voids and spalling was obtained through optimizing femtosecond laser parameters.