Lightweight Ceramics Research Articles

Phase Evolution, Mechanical, and Electrical Properties of Lightweight Ceramic Prepared Using Scoria at Low Temperature

This study aimed to produce lightweight, eco-friendly ceramic materials with superior properties using natural raw materials and low processing temperatures. Five ceramic samples were fabricated using red clay and varying contents of volcanic scoria (10%, 20%, 30%, 40%, and 50%) through sintering at 950 °C for 4 h. The crystalline phases, electrical properties, porosity, and mechanical strength of all the ceramic specimens were comprehensively evaluated. It was determined that the chemical composition of the raw materials and the resulting phases significantly influenced these various attributes. The XRD analysis revealed that the ceramic samples primarily consisted of the crystalline phases gehlenite, low quartz, and anorthite, along with the minor wollastonite and hematite phases. As the scoria content was increased, the MgO and Fe2O3 concentrations also increased, leading to a reduction in dielectric constant, dielectric loss, and electric conductivity. Moreover, the porosity of samples decreases from S10 to S50 due to the increase in the percentage of scoria and this reduction in porosity led to increased bending strength. The findings of this study suggest that volcanic scoria can serve as a viable eco-friendly raw material to produce lightweight ceramics with excellent electrical and mechanical properties, presenting cost-effective and energy-efficient solutions for various applications.

Fabrication of lightweight ceramics of complex geometries in freezing weather

Natural freezing weather is used to fabricate lightweight ceramic monoliths with aligned pores for the first time. A stable aqueous-based alumina slurry (16 vol%) was formulated and frozen at −10 to −25 °C in natural freezing environment. The thermally treated ceramic monoliths achieved ∼82–88 vol% porosity with short-range aligned pores. Finally, the unidirectional pores in the structure are achieved using a mold with thermal insulation properties. Natural freezing saves 300 kJ of energy per kg of alumina slurry. Mechanically stable lightweight porous ceramics with complex geometries can be designed without cryogenic fluids, refrigeration, or thermal baths. Implementing natural freezing in the porous ceramics industries, particularly in the Arctic region, will bring forward a sustainable approach by reducing energy consumption and CO2 emissions.

Corrosion and heat-resistant SiCN/C as lightweight fibers for microwave absorption and electromagnetic field shielding in Ku-band

SiCN fibers are usually combined with metals to increase the magnetic loss in electromagnetic field (EMF) shielding, but this results in high weight density, easy corrosion, difficult treatment, and high cost of the material. This study proposes the manufacturing of corrosion and heat-resistant ceramic lightweight fibers containing in-situ synthesized carbon nanostructures (SiCN/C) with excellent EMF shielding in Ku-band (12.4–18 GHz). The samples showed differential trends of EMF shielding effectiveness in terms of reflectance, transmittance, and absorption behavior. Compared to SiCN fibers, the EMF absorption was two times greater when carbon was added to the SiCN matrix. A minimum reflection coefficient (S11) of −12 dB was observed for SiCN/C fibers, meaning a high shielding efficiency with >90 % of the EMF energy shielded. On the other hand, SiCN fibers showed a minimum S11 of −7 dB, resulting in a protection of 80 % against EMF energy. Computational simulations clarified the better features of SiCN/C in electromagnetic shielding compared to SiCN, which was ascribed to enhanced conduction loss derived from conductive free carbon, and dipole and interfacial polarization loss generated by defects. The fibers were resistant to acidic and basic environments and oxidation of up to 600 °C. Moreover, the addition of carbon precursor represented a weight decrease of 17 % for SiCN/C compared to SiCN fibers. This research will afford an alternative solution for the manufacturing of SiCN/C fibers with EMF absorption properties that can be used as lightweight materials in harsh environments.

Study of Lightweight Ceramic Matrix-Less Syntactic Foam Composed of Cenosphere Using Spark Plasma Sintering.

The current investigation presents porous ceramic materials prepared with cenospheres (CS) by using spark plasma sintering. The impact of sintering temperature, mould diameter (20, 30 and 50 mm) and cenosphere size on the properties of the sintered material was investigated. Shrinkage of the samples during sintering started at 900 °C. Total sample shrinkage during sintering increases with increasing temperature and decreases with increasing mould size; increasing sample sintering temperature increases the apparent density of all sample series CS 63-150 µm in a 20 mm mould from 0.97 to 2.3 g·cm-3 at 1050-1300 °C; in a 30 mm mould, 0.81-1.87 g·cm-3 at 1050-1200 °C; in 50 mm mould, 0.54-0.75 g·cm-3 at 1050-1150 °C; while CS 150-250 µm in a 20 mm mould is 0.93-1.96 g·cm-3 at 1050-1200 °C. Total porosity decreases from 61.5% to 3.9% by increasing sintering temperature from 1050 to 1250 °C, while open porosity reduces at lower temperatures, with closed porosity being highest in samples sintered at 1150 °C. When the sintering temperature increases from 1050 to 1300 °C, the compressive strength of the CS 63-150 samples produced in a 20 mm mould increases from 11 MPa to 312 MPa. These results correlate with the Rice model, which describes an exponential dependence of compressive strength on material porosity and fully dense material compressive strength.

High-Temperature, Lightweight Ceramics with Nano-Sized Ferrites for EMI Shielding: Synthesis, Characterisation, and Potential Applications.

The present study focuses on the synthesis and characterisation of a lightweight ceramic material with electromagnetic interference (EMI) shielding properties, achieved using mullite containing micrometre-sized hollow spheres (cenospheres) and CoFe2O4 nanoparticles. This research explores compositions with varying CoFe2O4 contents ranging from 0 up to 20 wt.%. Conventional sintering in an air atmosphere is carried out at a temperature between 1100 and 1300 °C. The addition of ferrite nanoparticles was found to enhance the process of sintering cenospheres, resulting in improved material density and mechanical properties. Furthermore, this study reveals a direct correlation between the concentration of ferrite nanoparticles and the electromagnetic properties of the material. By increasing the concentration of ferrite nanoparticles, the electromagnetic shielding effect of the material (saturation magnetisation (Ms) and remanent magnetisation (Mr)) was observed to strengthen. These findings provide valuable insights into designing and developing lightweight ceramic materials with enhanced electromagnetic shielding capabilities. The synthesized ceramic material holds promise for various applications that require effective electromagnetic shielding, such as in the electronics, telecommunications, and aerospace industries.

3D Printing of Hollow Microspheres into Strong Hierarchical Porous Ceramics

AbstractPorous ceramics are demanded in a wide range of high‐temperature, biological and energy‐related applications, but may show conflicting properties or suffer from poor mechanical properties. Introducing pores at different length scales has been shown to be a promising design strategy to combine antagonistic performance parameters and reach high porosity without severely compromising strength. Herein, a cost‐effective and simple process to create strong, highly porous ceramics via direct ink writing of suspensions of hollow microspheres into cellular architectures with pores at three hierarchical levels is reported. X‐ray diffraction, rheological measurements, scanning electron microscopy, and mechanical tests are conducted to thoroughly study the processing steps and morphology of the printed hierarchical porous ceramics. The presence of pores at multiple length scales increases significantly the mechanical strength of the porous structure, providing a useful platform for the manufacturing of lightweight ceramics from inexpensive and widely available feedstock materials.

Recycled waste glass usage for construction materials

Recycling glass waste obtained from different industries is an issue in today’s economy. One of the ways of recycling is to produce lightweight ceramic by applying glass waste, clay, and gasifier as raw materials. The present research has been devoted to the evaluation of the influences of different clays extracted from two Latvian quarries (Lielauce un Samini) on the properties of lightweight ceramics. The main criteria of applicated clay as raw materials for producing lightweight ceramic are the following: saturation of SiO2 should be a maximum of 70% and Al2O3 minimum of 12%. The aim of the present research was to elaborate a composition for producing glass ceramic from glass waste with minimum energy consumption with a gasifier. The most important properties of the final product are thermal conductivity, compression strength, volume density, size, granulometry, and pore distribution. Two parameters of them, compression strength and volume density have been tested and analysed in the present research framework. Burning time is one more important additional parameter, which has been considered evaluating the properties of the final product. The obtained volume density is in the range of 226.75 kg/m3 to 475.78 kg/m3 depending on the composition.

Lightweight and geometrically complex ceramics derived from 4D printed shape memory precursor with reconfigurability and programmability for sensing and actuation applications

There is growing interest in additive manufacturing (AM) of ceramics due to the feasibility of achieving geometrically complex shapes for various engineering applications. Polymer-derived ceramics (PDCs), pyrolyzed from polymeric ceramic precursors, act as a competitive material for ceramic AM with advantages such as easy processability, flexible designability, and relatively low sintering temperature. However, the functionality of preceramic polymers is far from being fully exploited, thus restricting the development and applications of 3D printed ceramics. Herein, a novel multifunctional preceramic polymer composite with reconfigurability and shape memory effect is synthesized. By tuning the material compositions, the precursor inks suitable for 4D printing are pyrolyzed into lightweight self-shaping ceramics, allowing complex geometries to be fabricated. The preceramic polymers undergo a stepwise partial-to-full crosslinking process to form interpenetrating polymer networks, resulting in reconfigurability where the as-printed parts can be transformed into shapes with higher complexity. Unlike traditional precursors with static shapes, the precursor here possesses shape memory capability (Tg ∼ 95 °C). During the sintering process, the 3D printed precursor could successively undergo programmable active shape transformation with a high recovery ratio (∼100 %) and pyrolysis conversion into lightweight ceramics (1.05 g/cm3). By exploring the semiconducting behavior of resulting ceramics, temperature sensors leveraging the advantages of reshaping are designed to detect the surface over a wide range (25–750 °C) with good conformability. The development of 4D printed reconfigurable and programmable precursors for the construction of complex ceramics enriches both the complexity and self-shaping capability of ceramics, allowing them to be applied as smart thermistors and deployable structures.

Development and characterization of a sustainable process for the implementation of lightweight ceramics

Addition of hollow particles and foamed core-shell structures was evaluated to reduce density of ceramic bodies used in the production of sanitary ware, in particular Vitreous-China. Different contents of foamed ceramic beads, glass bubbles or foamed glass beads were tested, ranging from 1.5 to 10 % wt. These strategies were designed to be readily applicable to a pre-existing industrial plant, leading to a final product that retains mechanical and aesthetical properties of traditional ceramic.Mechanical properties, shrinkage, water absorption, surface finishing, and weight reduction were evaluated on dried and fired simplified samples.A moderate reduction in mechanical properties was found, numerically dependent to the overall volume of voids introduced in ceramic bulk. In particular, ceramic with a content of 3% of glass bubbles featured a flexural strength at break of 35 MPa, out of standard requirement. The highest efficiency in weight reduction was achieved with the introduction of 1.5% of cave glass bubbles resulting in a reduction of 10% in weight of fired samples, a flexural strength at break of (41 ± 4) MPa, a total linear shrinkage of (10.1 ± 0.2) %, (0.5 ± 0.1) %, water absorption of 0.5 % wt, in accordance with regulatory standard requirements.Weight reduction improved sustainability in terms of environmental impact. LCA (Life Cycle Assessment) study was conducted on optimized ceramic body (glass bubbles at 1.5 %wt, and glass bubbles at 3% with comparative purposes), evaluating the production process from transportation of raw materials to distribution of goods overseas. LCA analysis was determined using impact categories of ReCiPe Midpoint (H), ReCiPe EndPoint (H/H), and cumulative energy demand (CED). The analysis showed an overall improvement of all the impact categories, with a reduction of CED of 10%, and a reduction of ReCiPe Endpoint of 15% for optimized sample.

Role of particle size on the cohesive strength of non-sintered (green) ceramics

Preparation of particle-loaded foams, followed by drying, sintering and/or cross-linking are widely explored routes for developing lightweight ceramics with high mechanical strength. The non-sintered dry ceramic foams are less studied due to their intricate production and the assumed poor mechanical strength of the obtained "green" materials. Here we produce lightweight ceramics from foamed particle suspensions containing spherical silica particles with radii varied between 4.5 nm and 7 µm. The wet foams are prepared in the presence of cationic surfactant and were dried at ambient conditions to obtain porous materials with mass densities between 100 and 700 kg/m3. The materials containing smaller particles exhibited much higher strength (by up to 2000 times), approaching that of the sintered materials. A new theoretical expression for predicting the mechanical strength of such materials is derived and is used to explain the measured strengths of the produced materials through the van der Waals attraction between the particles in the final dry materials.

Fabricating lightweight ceramics by spraying clay on knitted structures

This research was carried out to develop a novel composite material consisting of a thread reinforcement and a clay matrix, as well as to develop a method of shaping this material into hollow spatial structures. Ceramic elements in the building industry are currently created by applying extruding, pressing and casting methods. The approach of spraying clay onto predefined knitted meshes increases the usability of digitally fabricated lightweight ceramic elements, while eliminating the need for scaffolding. In this approach, multiple layers of a fluid clay mass are sprayed onto the tensioned mesh using an industrial, six-axis robotic arm. This allows the precise application of the material and results in varying material thicknesses. Due to the complementary qualities of clay which absorbs compressive forces and threads which absorb tensile forces, lightweight structures can be created. The research involved experimenting with clay mixtures, several thread types, knitting methods and spraying techniques, as well as fabricating a 1:1 lightweight module as an architectural prototype.

Manufacturing of ceramic lightweight aggregates from oil-based drill cutting pyrolysis residues

ABSTRACT In this study, high-strength ceramic lightweight aggregates were prepared from oil-based drill cutting pyrolysis residues, and their formation mechanism and expansion during sintering were examined. It was found that the Al2O3 suppressed the melting process and increased the particle strength. In particular, Al atoms penetrated the liquid phase and formed a Si–Al–O crystal structure with four ligands, which reacted with CaO and BaO to produce aluminosilicate crystals, such as BaAl2Si2O8 and CaAl2Si2O8, which increased the compressive strength. Scanning electron microscope images revealed that the glass phase also contributed toward the high strength of ceramic materials by adhering to crystal grains and forming a concrete-like structure. Energy-dispersive X-ray spectroscopy data suggested that similar to Ca atoms, Ba atoms in pyrolysis residues played a critical role in the production of aluminosilicate, while transmission electron microscopy images confirmed that different phases were not well separated as Ba and Ca were stabilized in the same crystal grains. After SiC addition and increasing the sintering temperature, the product density significantly decreased while its porosity increased.

Lightweight Ceramic Materials Based on Industrial Waste of Uzbekistan

Lightweight Ceramic Materials Based on Industrial Waste of Uzbekistan

Fabrication of Foamed Porous Ceramics from Mixtures of Pork Bone and Incinerated Sewage Sludge Ash

Ultra-lightweight ceramics were fabricated by firing the mixtures of pork bone (PB) and incinerated ash of sewage sludge. PB content in the mixtures was varied from 0 to 15 mass%. The mixtures were pressed in a discus body (4 cm in diameter) and the body was fired at the temperature range from 1000 to 1150°C for 1 h in air. Bloating behaviors were observed in the samples fired at the temperature over 1050°C. The remarkable lightweight ceramics, which have the apparent porosity less than 1.0 g cm−3, were obtained by the addition of 10–15 mass% PB and the firing at the temperature over 1050°C. Diffuse reflectance spectra revealed that ferric oxide in the samples fired at the temperature over 1050°C was reduced to ferrous oxide. It was considered that the large bloating in the PB added samples occurred due to both the evolution of oxygen from ferric oxide and the oxidation of residual carbon derived from PB inside the samples after melting of the surface at high temperatures.

Nanograin–glass dual-phasic, elasto-flexible, fatigue-tolerant, and heat-insulating ceramic sponges at large scales

Ceramics are considered intrinsically brittle at room temperature, which is mainly attributed to the limited availability of crystallographic slips and pre-existing geometrical flaws. Moreover, the lack of flexibility has severely hindered many high-end applications of ceramic materials. Here, we produce ceramic sponges that are simultaneously ultra-light, elasto-flexible, thermally insulating, and can fully recover from large deformation with a near-zero Poisson's ratio. These spongy materials also possess superb fatigue resistance without the accumulation of damage or structural collapse for 10,000 large-scale compressive or buckling cycles. We demonstrate the exceptional flexibility is enabled by the elastic distortion of nanograin–glassy dual phase and the fiber bulking in open-cell three-dimensional structure. Moreover, these spongy materials possess superior temperature-invariant superelasticity from deep cryogenic temperatures (−196 °C) to high temperature (1500 °C). Our study not only developed mechanically reliable lightweight ceramics for numerous extreme applications, but also provided new theoretical insights into the origin of flexibility in polycrystalline ceramics.

Using Waste from Oil Production in the Production of Lightweight Bricks

The possibility of using smeared soil from oil extraction and shale clay in the production of ceramic lightweight bricks without the use of natural traditional raw materials is shown. The suitability of the smeared soil containing an increased amount of organic matter and calorific value as a burnout additive for the production of lightweight bricks is investigated. The expediency of using interstitial clay (waste of combustible shale) as a binder for ceramic materials has been established. The resulting lightweight ceramic bricks have high physical and mechanical properties.

Utilizing of solid waste materials for producing porous and lightweight ceramics

Some solid industrial wastes, namely, blast furnace slag and ceramic sludge, have been used to produce highly porous, lightweight ceramic materials. Nine ceramic samples were prepared. The percentage of blast furnace slag ranged from 10 to 90% by weight and ceramic sludge from 90 to 10% by weight. The addition of some limestone and sand to all batches was necessary for the precipitation of our targeted parawollastonite ceramics. The prepared samples, weighed, well mixed, and then pressed into disks by using uniaxial pressure (40 MPa). The optimum sintering conditions were 1100 °C for 1 h. Various experimental techniques were performed, including, X-ray diffraction, porosity, density, SEM, and dielectric determination. XRD analysis ensured that the obtained ceramic materials are primarily composed of parawollastonite and gehlenite phases with fibrous, columnar, and tabular crystals as shown in SEM photographs. The porosity of samples was in the range of 28.83–40.50% and the density ranges were from 1.613 to 2.182 g/cm3, which qualified them for use in construction purposes. The dielectric properties including the relative dielectric constant (ε′), and dielectric loss (ε") were measured at 200 measuring points in the frequency range of 50 Hz up to 8 MHz. The electric and dielectric values of sample BFS5 (50% blast furnace slag + 50% sludge) were the highest values among the other prepared mixtures. So it could be used as a poor semiconductor at ≤ 2 MHz, and as fair semiconductor material at >2 MHz. The electric measurements confirmed very low electrical conductivity values for the ceramic materials (0.001–50.82 μS/cm). This indicated the ability of their preparation as poor to fair semiconductors. Hence the results showed that the prepared lightweight parawollastonite and gehlenite ceramic could be used in low dielectric materials in the electronics covering manufacturing.

Lightweight Ceramics with Admixtures of Mineral-Wool Production Waste and Aluminum Silicate Cenospheres of Various Fractions

Lightweight Ceramics with Admixtures of Mineral-Wool Production Waste and Aluminum Silicate Cenospheres of Various Fractions

Recovering Untreated Phosphorus Tailings and Coal Gangue to Prepare Ceramic Lightweight Bricks

Recovering Untreated Phosphorus Tailings and Coal Gangue to Prepare Ceramic Lightweight Bricks

Walter Krenkel – CMC‐pioneer and dedicated expert on ceramics

Professor Walter Krenkel is a worldwide known specialist for Ceramic Matrix Composites (CMC), the Liquid Silicon Infiltration (LSI) process and the invention of the C/C-SiC ceramic brake disc. He was born in 1955 in Bad Cannstatt, a famous part of the well-known city of Stuttgart in Germany. After school, he decided to study aerospace engineering in 1976 at the University of Stuttgart where he got his diploma in 1984. Immediately after finishing his diploma, he started his career as a research assistant in the Institute of Structures and Design at the German Aerospace Centre (DLR) in Stuttgart. Since 1990 he worked on the commercial application of C/C-SiC materials that was used for the space application so far. In 1992, within a research project he and his colleagues from DLR created as a spin-off from thermal protection materials for re-entry space vehicles, a ceramic brake disc, based on C/C-SiC for railway vehicles. After gaining valuable experiences in research and development projects, in 1996, he started to work as a leader of the Ceramic Composites and Structures Group in the same department. His continuous work on ceramic brakes led to the invention of the ceramic brake discs for passengers’ cars, together with several industrial partners between 1997 and 2001. His increasing know-how about ceramic matrix composites in general and about ceramic brakes in particular make him the perfect choice as the head of the Centre of Excellence about Ceramic Lightweight Structures and High Temperature Applications in 1999. One year later, he finished his PhD on the subject of cost-efficient manufacturing of CMC, based on the LSI-process in the Faculty of Aerospace Engineering of the University of Stuttgart. Due to his initiative, the LSI-process was successfully transferred to the industry and was developed to the most established high temperature-process to manufacture CMC at reasonable costs. On the basis of his professional performance, it was offered to him to work as a Professor at the University of Bayreuth at the Chair of Ceramic Materials Engineering (CME) in 2004. He continued his engagement in several ceramic societies, as the Dean of the Faculty of Engineering Science in the University of Bayreuth during 2015–2017 and as a Guest Professor in the Southeast University in Nanjing and the Central South University of Changsha (China). During his career, he wrote more than 200 articles and 35 patents. In Bayreuth he led the Chair of Ceramic Material Engineering to the top in the university, regarding the funding from third parties. His engagement constantly influenced the whole ceramic community. He was responsible for organizing numerous national and international conferences. In 2010, he brought the HT-CMC 7 conference to Bayreuth and managed this scientific premium event in very remarkable fashion. Due to his constant work as a scientist and a professor in Bayreuth, he gained a huge knowledge in almost all fields of ceramics, with focus in CMC, polymer derived ceramics (PDC), the evaluation of structural and functional ceramics and the tribological properties of high-performance ceramic friction materials. His worldwide reputation is unique and his experiences in the field of ceramics influence the research and development activities in the whole ceramic community. After winning prizes from all significant ceramic societies worldwide (German, American and European), for example, the Bridge Building Award from the ACERS and the Seger Medal of the DKG, he is enjoying the well-deserved retirement since April 2021. His contributions to the field of CMC and ceramics in general are fundamental and lead the way to the future of this material class. The ideas of Professor Krenkel will give his former chair and the ceramic community the best chances to enhance the impact of ceramics and to find new applications within the megatrends and challenges in the 21th century.