Ceramic Shell Research Articles

Co-extrusion of highly loaded feedstocks for fabrication of stainless steel-bioceramic core-shell structures

Co-extrusion of multi-materials structures shows technological challenges and opportunities. Filaments made of a metallic core and a ceramic shell are one example of how structural and functional features can be combined in a single component to provide a synergic effect. In this work, we focused on the fabrication of shell and core-shell scaffolds for potential applications as bone substitutes. Stainless steel 316L was selected for the core material, whilst in situ synthesized sphene (CaTiSiO5) bioactive ceramic was selected as a shell. The combination of a ductile core and a bioactive ceramic, so as scaffolds made of empty struts may represent a new generation of bone substitutes with mechanical properties closer to the ones of natural bone so as with improved bioactivity. Therefore, formulated inks were co-extruded in one step using a customized printing set-up. Microstructural and mechanical properties were investigated on shell and core-shell filaments and 3D structures. Shell bioceramics scaffolds possessed high porosity and target compression strength values. The sintering environment at the core-shell interface caused severe 316L oxidation thus compromising the ductility of the metallic part, however compression strength increased of 53% compared to shell structures.

Effects of surface-active elements on wettability and interfacial reaction between DD5 superalloy and Al2O3-based ceramic shell

The study investigates the effects of oxygen-sulfur content, holding temperature, and time on the wettability and interfacial reactions between DD5 superalloy and Al2O3-based ceramic shells through non-in-situ sessile drop experiments. Lowering the oxygen-sulfur content in the DD5 master alloy, as well as reducing the holding temperature and time, leads to an increase in the wetting angle and a mitigation of interfacial reactions. Improved wettability promotes interfacial reactions, while intensified interfacial reactions further spread the alloy melt, enhancing its wettability. The main products of the interfacial reaction between the DD5 alloy and Al2O3-based ceramic shells are Al2O3 and Si, with the process being influenced by the presence of Al. When the oxygen-sulfur content is controlled within 6 ppmw, the wettability will undergo a characteristic transformation, resulting in a sharp increase in the wetting angle. It demonstrates that the ultra-pure DD5 master alloy plays a crucial role in reducing wettability and interfacial reaction, as well as slowing down the tendency of the hetero-crystal formation. Therefore, it is of great engineering significance to further reduce the content of oxygen-sulfur impurity elements in DD5 superalloy.

Stress-strain state of ceramic shell mold during formation of spherical steel casting in it. Part 2

The paper presents the results of numerical calculations of the solution to the problem of modeling the process of possible cracking in a spherical shell mold when pouring liquid steel into it and cooling the solidifying casting. The numerical scheme of the axisymmetric problem and the algorithm for its solution were given in Part 1. The crack resistance is estimated by magnitude of the normal stresses in the ceramic shell during its co-cooling with a solidifying casting. The results detailed analysis considered: fields of displacement, stresses, and temperatures both on spherical surface and in growing crust of solidified metal. The solution took into account the change in the shear modulus of the mold material from temperature, and an assessment of this refinement was given. The problem was solved in two ways. The first – with a constant shift modulus of the shell mold; the second – with its temperature-dependent shift modulus. There is a significant difference between these variants in terms of magnitude of the normal stresses arising in the shell mold. The authors analyzed resistance of the shell mold spherical geometry to external influences from its support filler and filling funnel. The problem of determining the contact and free surfaces at the boundary of the shell mold and support filler was solved. The results are presented graphically in the form of diagrams of stresses and temperatures over the studied area in its different sections and time intervals for cooling of the growing metal crust. The role of compressive normal stresses σ22 , σ33 on the surface of contact of the shell mold with liquid metal at the initial moment of cooling on probability of cracking in a spherical mold is shown. The level of strain-stress state in a spherical shell mold when cooling a steel casting in it is significantly determined by dependence of shift modulus of the shell mold on temperature.

Injection 3D Printing of Doubly Curved Ceramic Shells in Non-Synthetic Particle Suspensions.

This paper examines the application of non-synthetic particle suspensions as a support medium for the additive manufacturing of complex doubly curved ceramic shells with overhangs between 0° and 90° using clay paste. In this method, the build-up material is injected within a constant volume of air-permeable particle suspension. As the used clay paste does not solidify right after injection, the suspension operates like a support medium and enables various print path strategies. Different non-synthetic suspension mixtures, including solid and flexible components such as quartz sand, refractory clay, various types of wood shavings, and cotton flocks, were evaluated for their ability to securely hold the injected material while allowing drying of the water-based clay body and its shrinkage. The balance between grain composition, added water, and the compressibility of the mixture during printing and drying played a pivotal role in the particle suspension design and assessment. Furthermore, the moisture absorption of the particle suspension and the structural integrity of the layer bond of the fired ceramics were also assessed. The examined additive manufacturing process not only enables the production of meso-scale doubly curved ceramic shells with average overhang of 56° but also introduces a new practice for designing specialized surfaces and constructions.

Enhanced comprehensive properties of alumina ceramic shells by a pennisetum fiber/AlF3•3H2O powder hybrid system

The strength and permeability to gas of ceramic shells are key factors affecting the quality of castings. This research aims to improve the properties of alumina-based ceramic shells (i.e., Al2O3 and SiO2) using a combination of pennisetum fiber and AlF3•3H2O powder. The pennisetum fiber can improve the green strength of ceramic shells, while AlF3•3H2O powder can improve the high-temperature strength of ceramic shells by inducing the generation of mullite (3Al2O3•2SiO2) whiskers at high temperatures. Meanwhile, the mixture of pennisetum fibers and mullite whiskers can also improve the permeability to gas of the ceramic shell. As a result, the modified ceramic shell shows a clear increase in the above-mentioned properties, including 43 % of the green strength, 100 % of the permeability to gas, and 30 % of the thermal diffusion coefficient. In addition, the high-temperature bending strength and deformation under the weight of the ceramic shells are also obtained.

Effect of Cr transition layer on the Al2O3/fe(ceramic/metal) interface microstructure based on binder jetting

Ceramic coating is a well-established method for enhancing the wear and corrosion resistance of metal components. Al2O3 coating has been extensively utilized in industrial applications. However, existing ceramic coating processes often yield coatings that are relatively thin with limited wear and corrosion resistance. Furthermore, achieving efficient and high-quality coatings on complex metal surfaces poses significant challenges. The poor wettability between ceramics and metals further complicates the bonding at their interface. Chromium (Cr), a commonly used alloying element in steel, exhibits excellent interfacial wettability with iron (Fe), making it an ideal transition material for the Al2O3/Fe interface. In this study, complex Al2O3-based ceramic shells were fabricated via Binder Jetting. The Cr coating was coated on the surface of the shell, and then the Fe-based metal liquid was poured into the Al2O3-based ceramic shell to achieve metallurgical bonding at the Al2O3/Fe interface by temperature control treatment. The performance of the Al2O3 ceramic matrix and the microstructure of the Al2O3/Fe interface with the Cr intermediate transition layer were investigated. The results indicate that when the solid loading of the Cr coating is 60 wt%, a uniform, and stable Cr coating can be formed on the surface of the sintered Al2O3-based ceramic. The bending strength of the Al2O3-based ceramic matrix increased from 113.79 MPa to 134.69 MPa. The Cr coating significantly improved the wettability between the Al2O3-based ceramic and the Fe-based metal, reducing the wetting angle from 98.9° to 78.4°. The interface between the Al2O3-based ceramic and Fe-based metal formed FeCr2O4 after infusion, resulting in a well-bonded interface without significant cracks.

Processing and properties of Al–Si microcapsules with a biomimetic-corrugated structure and corundum-mullite composite shell

The encapsulation of metal-based phase change materials using ceramics can realize safe and effective storage of high-temperature thermal energy. However, the use of a low toughness ceramic shell around the microcapsules cannot ensure the provision of a high latent heat and thermal cyclic stability. Here, we provide a new and effective design strategy for preparing biomimetic Al–Si microcapsules that are based on a sea-shell corrugated structure and a nano-scale corundum-mullite composite shell. The latent heat of the microcapsules was over 400 J/g, much greater than other metal-based microcapsules reported to date. The unique biomimetic-corrugated structure microcapsules obtained by a heat treatment at 1000 °C exhibited excellent thermal stability, achieving near zero heat loss after 5000 thermal cycles, whose latent heat of absorption and release reached up to 448.3 J/g and 451.8 J/g respectively. Furthermore, the microcapsules possessed a giant heat storage density of 945.8 J/g within 300–700 °C, and the performance figure of merit was 6384.2 × 106 J2·K–1·s–1·m–4, approximately 15 times higher than that of commercial solar salt. This new approach provides a pathway the practical application of Al–Si alloys as thermal storage materials for renewable energy applications.

Study of Ceramic Hollow Buoyant Balls Prepared Based on Slip Mold Casting and Brazing Process

In the domain of deep-sea buoyancy material applications, hollow ceramic spheres, known for their high strength and low mass-to-drainage ratio, contribute to increased buoyancy and payload capacity enhancement for deep submersibles, constituting buoyancy materials of exceptional overall performance. This study entails the brazing of two ceramic hemispherical shells, obtained through slurry molding, to form a ceramic float. This process, which integrates slurry molding and ceramic brazing, facilitates buoyancy provision. Further refinement involves welding a ceramic connector onto the ceramic shell, incorporating a top opening to create a ceramic float equipped with an observation window seat. The ceramic float maintains uniform wall thickness, while the observation window facilitates external environmental observation in deep-sea research. Two pressure-resistant spherical shells, produced using this process, underwent testing, revealing the wall thickness of the prepared alumina ceramic hollow spheres to be 1.00 mm, with a mass-to-drainage ratio of 0.47 g/cm3 and a buoyancy coefficient of 53%. The resultant ceramic hollow floating ball can withstand hydrostatic pressure of 120 MPa, while the pressure-resistant ball shell with an observation window seat can endure hydrostatic pressure of 100 MPa, ensuring safe operation at depths of 5000–6000 m. This process provides a production method for subsequent large-scale ceramic float manufacturing for the transportation of objects or personnel.

A novel method for evaluating thermal expansion forces during dewaxing of investment casting and 3D-printing waxes

This study proposes a novel method for the evaluation of expansion forces that occur during the heating of IC (investment casting) waxes with the help of a rheometer. Thermal expansion of the IC wax patterns is the main reason that causes ceramic shell failure during the dewaxing process. The technique is based on the measurement of normal forces that develop in the measuring system of the rotational rheometer during solidification of wax samples. These forces are created as a result of shrinkage of thermally expanded wax samples. To assess the efficiency of the proposed method, three types of commercially available waxes and one 3D-printable wax have been tested and compared. According to research findings, the proposed method can be prescribed as an efficient procedure for the evaluation of expansion forces that develop during wax heating, especially for waxes that have low viscosity properties. It was observed that machinable wax produced the highest value of normal load equivalent to 86 N while the IC and 3D-printing wax generated 18.8 and 36.3 N respectively. Moreover, it was discovered that additively manufactured wax patterns perform considerably better compared to their casted analogs during dewaxing processes

Improving Microstructural Homogeneity of Investment‐Cast Single‐Crystalline Ni‐Base Superalloys by Using Fluidized Carbon Bed Cooling

One impeding factor for faster solidification in typical investment casting processes is the limited heat removal capability. This study compares the classical Bridgman technique and the fluidized carbon bed cooling (FCBC) casting method. In particular, the influence of the thermal design is investigated in terms of microstructural and compositional homogeneity in single‐crystalline CMSX‐4. These investment casting processes mainly differ in the baffle type used to insulate the hot and cold zones inside of the casting vessel. While the Bridgman process is based on radiation cooling, the FCBC casting process relies on a dynamic baffle made of expanded graphite that is buoyant on fluidized bed of glassy carbon beads. Such a dynamic insulation layer can adapt to the cross‐sectional variation of ceramic shell molds and provide a better thermal insulation, which results in more uniform solidification conditions. This enables a reduction in the primary dendrite arm spacing by up to 26%, an increase in the homogeneity of the microstructure and composition, as well as a reduction in overall porosity and mean pore size of 41%.

Stress-strain state of ceramic shell mold during formation of spherical steel casting in it. Part 1

Stress-strain state of ceramic shell mold during formation of spherical steel casting in it. Part 1

Effect of sintering temperature and silicone resin content on in-situ formed SiC nanowire reinforced ceramic shells

The silicone resin was used to modify ceramic shells for investment casting. SiC nanowires were in-situ formed by the carbothermal reduction method. The pyrolysis of silicone resin and the formation mechanism of SiC nanowires were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results showed that the shells had the maximum sintering bending strength of 7.35 MPa when the silicone resin content and the sintering temperature were 20 wt% and 1300 °C, respectively. The phase of β-cristobalite during the transformation from amorphous SiOC to fused SiO2 after the pyrolysis of silicone resin impacted the bending strength. In addition, the iron oxide in corundum sand was used as the catalyst in the VLS mechanism to form the ball-stick-shaped SiC nanowires at 1000 °C–1100 °C. However, the necklace-like and rod-like SiC nanowires were formed at 1200 °C–1300 °C in the VS mechanism, which replaced the VLS mechanism.

Electromagnetic wave absorption mechanism and wear corrosion characteristics of Ti3SiC2 MAX phase-doped Ni/AlN composite coating with core-shell structure based on laser cladding-induced pitaya-like multi-level heterogeneous interface

To satisfy the service requirements of wave-absorbing materials in harsh environments, it is important to design and manufacture corrosion-resistant composite-absorbing materials. According to the strategy of impedance matching and the dissipation behaviour of nickel-based alloys, AlN ceramics, and MAX-phase Ti3SiC2 multicomponent composite-regulated materials were studied. As an additive manufacturing technology, multilevel heterointerface composites with core–shell structures were obtained by laser cladding. The construction of a unique core–shell structure of a metal–ceramic and ceramic (core)–ceramic (shell) multi-level heterogeneous interface increased the interfacial relaxation and multiple dissipation and improved the impedance matching. The results enabled the N20M3 cladding coating to exhibit excellent microwave absorption characteristics, with a reflection loss of −32.84 dB at the ultra-thin thickness of 1.8 mm. Additionally, the composites exhibited excellent corrosion resistance, high hardness, and relatively good resistance to erosion wear. This work promotes the durability of wave-absorbing materials under severe conditions, as well as the integration of the efficient manufacturing of wave-absorbing materials.

Penelusuran sisa-sisa Kerajaan yang hilang dibalik Letusan Gunung Tambora di Situs Doro Bente

The archaeological research in the Tambora Peninsula was initiated by the National Archaeological Research Center in 2006, and from 2008 onwards, it was continued by the Archaeological Office in Denpasar-Bali until 2021. Numerous archaeological pieces of evidence have been successfully excavated from Mount Tambora's pyroclastic material. Recent research has been focused on the Doro Bente Site on the Teluk Saleh Peninsula. The research aims to understand the sequence of historical events on settlement centers based on artifact evidence resulting from the eruption of Mount Tambora in 1815. The study employs qualitative, descriptive methods, and a geoarchaeological approach. Data acquisition involves excavation, surveys, and literature studies. Stratigraphic analysis is conducted to identify sediment matrices and understand the deposition sequence. Excavation activities have uncovered significant artifacts such as ceramic fragments, pottery, animal bones, and shell fragments. Micro-scale deposition chronology in excavation box B28U18 indicates that the three lower layers, the oldest, were deposited in a marine environment, followed by five layers of pyroclastic material from the 1815 eruption of Mount Tambora. The geographical factors and available natural resources make Sumbawa Island a focal point for Chinese and European attention from the 13th to the 19th centuries AD.

Novel Sodium Chloride/Aluminum Oxide Powder-Composite Structure with High Shape-Retention Performance for the Encapsulation of a High-Temperature Phase-Change Material

Inorganic phase-change materials (PCMs) with high melting points have great potential for thermal energy storage systems. Sodium chloride (NaCl) has a high melting point (801 °C) and high latent-heat-storage density (482 kJ/kg). However, it is difficult to encapsulate NaCl using a sintered ceramic shell because of its good wettability against ceramics and high volume-expansion capacity during melting. In this study, a novel NaCl/Al2O3 powder-composite structure was developed as highly stable PCM core material for highly stable encapsulation. The shape-retention performance and the mechanism of NaCl/Al2O3 powder-composite structure during melting were investigated. We have successfully fabricated a NaCl/Al2O3 powder-composite structure, which has a higher NaCl volume ratio of 80 vol% than conventional techniques. The gel-like network structure of Al2O3 particles in molten NaCl was a key structure to keep the shape of the composite ball and to prevent the evaporation of molten NaCl.

Segregation of chemical elements in the volume of powder particles during it's treatment as a method for the production of structurally graded powder materials

The paper deals with the examples of the use of microsegregation of chemical elements in powder particles of the Inconel 718 heat-resistant alloy for synthesizing on it's basis the “core-shell” type composite metal-ceramic particles in the inductively coupled plasma. A laboratory plasma treatment plant having a quartz plasmatron with a power of 40 kW and a frequency of 5.2 MHz was used. The spheroidization and degassing of the starting material were performed. It was established that, as the powder moved in the plasma flow, the explosive degassing of its particles, with the internal gas pores, took place first, and then the powder melted and spheroidized. It was shown that during the plasma treatment of the Inconel 718 powder in the presence of oxygen, microsegregation of the chemical elements contained in this alloy took place, with the formation of “core-shell” type composite metal-ceramic particles. The metal core consists predominantly of nickel, while the composition of the ceramic shell includes chromium and iron oxides, as well as spinels of the NiCr2O4 and NiFe2O4 types. By varying the oxygen concentration in the plasma, the shell thickness and the core diameter of the composite particle can be changed. The method makes it possible to synthesize metal-ceramic composite powders of the “core-shell” type for additive manufacturing.

Coaxial 3D printed Al2O3 ceramic continuous-flow fixed-bed reactor with bionic core-shell structure

Continuous-flow fixed-bed reactors (CFBR) have attracted considerable attention owing to their high efficiency and low energy consumption; however, the integrated fabrication of CFBR with core-shell structures remains a great challenge at present. Herein, a facile coaxial three-dimensional (3D) printing strategy was developed for the first time to rapidly and efficiently construct a CFBR with Al2O3 powder and aluminum dihydrogen phosphate (AP) as the outer shell ink, and Al2O3 powder, AP, and polymethyl methacrylate as the inner core ink that is extruded through a customized coaxial needle. Coaxial 3D printing realizes the integral fabrication of ceramic shells and inner porous ceramic carriers. CFBR with an outer wall thickness of 1.2 mm, core diameter of 3.7 mm, and variable length were fabricated, which were enabled with excellent catalytic properties by simply impregnating precious metal particles. The catalytic efficiencies for the reducing of 4-nitrophenol (4-NP) in the 3-cm-length Pd/CFBR, Pt/CFBR, and Ag/CFBR were found 96.9 %, 97.4 %, and 93 % after 10 min, respectively. Combining integrated fabrication, rapid prototyping, and complex architecture formation, coaxial 3D printing provides a novel strategy for directly integrating multifunctional CFBR.

Integrated optical electric field sensors: humidity stability mechanisms and packaging scheme

Integrated optical electric field sensors (IOES) play a crucial role in electric field measurement. This paper introduces the principles of the IOES and quantitatively evaluates the impact of humidity on measurement accuracy. Sensors with different levels of hydrophobicity coatings and hygroscopicity shells are fabricated and tested across the relative humidity (RH) range of 25%–95%. Results reveal that humidity stability is primarily influenced by water vapor absorption through the sensor shell, which increases its conductivity. This further results in amplitude deviation and phase shift of the sensor output. To address this, an optimal humidity-stable packaging scheme is proposed, which involves using PEEK shell with room temperature vulcanized fluorinated silicone rubber coating. Compared with uncoated ceramic shell, the phase shift of the IOES reduces from 90∘ to 1∘ under a RH of 90%. The amplitude deviation of electric field measurement decreases from 20% to nearly zero after a 20 h humidity experiment conducted under RH of 90% at 30 ∘C. The proposed packaging scheme could be used to improve the humidity stability of the sensors deployed in outdoor environments, especially on ships and coastal areas.

Fault Analysis of 35kV Outdoor Vacuum Circuit Breaker Pillar Porcelain Sleeve

In order to further clarify the failure mechanism of the pillar porcelain insulator, the field inspection, the microscopic morphology analysis and material analysis of the ceramic shell of the pillar under a 35kV outdoor vacuum circuit breaker were carried out. The results show that the direct cause of the failure is the discharge between the high voltage conductor inside the porcelain sleeve and the weak part of the porcelain sleeve, and the high temperature arc leads to the bursting of the porcelain sleeve. The indirect cause of the failure is the loose porcelain of the porcelain sleeve, the existence of internal layering, uneven composition and micro-pores and other macro and micro defects, and the original defects of the inner surface of the porcelain sleeve, such as local unglazed and poor quality of the porcelain sleeve manufacturing process. In the long-term outdoor operation, the external moisture and gas penetrate into the porcelain sleeve, which leads to the deterioration of the insulation performance of the porcelain sleeve, and eventually leads to failure.

Preparation of thermal energy storage microcapsule with double-layer ceramic shell possessing sponge effect to improve the thermal cycling performance

In present study, thermal energy storage microcapsules with double-layer ceramic shell were fabricated and thermal cycling test was conducted. Thermal cycling test results showed that when ceramic shell constituted of dense inner layer and loose outer layer, the microcapsule had excellent thermal stability. After 3000 thermal cycles, latent heat retention ratio of the microcapsule was more than 90 % and almost no leakage of molten core. This super durability and stability attributed to “sponge effect” of loose outer layer which offered volume buffer for microcapsule core and inhibited molten core overflow during phase change. According to the Mass Conservation Law, criterion Г for describing “sponge effect” was deduced. Г was defined as a quarter of the product of the specific surface area of the microcapsule and criterion Г was derived as Г≥1ρL−1ρS. The criterion shows that when the value of Г is larger than or equal to the difference between the specific volumes of liquid and solid phase change material, microcapsule core is not overflow during phase change. Criterion Г provides theoretical guidance for the preparation of thermal energy storage microcapsules with excellent thermal cycling performance.