The effect of slip casting parameters on the green density of MgAl2O4 spinel

The aim of this paper was to investigate the effect of slip casting parameters on the green density of MgAl₂O₄ spinel. In order to obtain samples with suitable mechanical and optical properties, it is necessary to prepare bulk samples with a fine grain size along with a low level of impurity and high density. Slip casting is widely used in the processing of optical ceramics to achieve a body with high green density and low sintering temperature. In the present study, several spinel suspensions with similar solid content but different viscosities and particle sizes (90, 150, 300 and 500 nm) were prepared and shaped into a dense body. Viscosity of suspension depended on dispersant content, such that the addition of dispersant firstly caused viscosity to decrease, but it was increased by further dispersant addition, irrespective of the suspension particle size. The green density range of samples was 36–67% of the theoretical value. Rheological behaviour and green density measurements showed that powder particles smaller than 90 nm were unsuitable for slip casting because agglomeration of powder particles led to high viscosity and hence, low green density. The optimal particle size for slip casting was found to be 150 nm.     

Multi-functional Al2O3-coated separators for high-performance lithium-ion batteries: Critical effects of particle shape

The technology of coating polyolefin-type separators with ceramics is gradually developing as an effective method to improve the safety of lithium-ion batteries (LIBs). However, the powder properties of ceramics can adversely affect the surface structure and ionic conductivity of separators; therefore, a new approach is required regarding the powder properties that affect the performance of the separator. Herein, the effect of the Al₂O₃ particle shape on the physical properties of Al₂O₃-coated separators and the performance of LIBs is investigated. In the separator coated with angular-shaped Al₂O₃ particles (Al₂O₃-A), the pores in the coating layer are uniformly distributed, improving physical properties such as porosity and wettability. The thermal shrinkage of separator is <10% when exposed to 150 °C for 1 h, considerably smaller than that of the commercial polyethylene separator (approximately 83%) under the same conditions. Moreover, the Al₂O₃-A-coated separator shows the highest ionic conductivity (0.531 mS cm⁻¹), and the LiNi_0.8Mn_0.1Co_0.1O₂/Al₂O₃-A-coated separator/Li battery displays improved stability than using the polyethylene separator under a current density of 5C. This proposes approach to improve the separator's performance through the shape control of ceramic particles paves the way for separators to contribute to the high-temperature safety and long cycle life of batteries.     

The effect of pre-annealing and post-annealing on the transparency of MgAl2O4, prepared by slip casting and spark plasma sintering (SPS)

The aim of this paper is to investigate the effect of slip casting process and the annealing before and after sintering to achieve a transparent MgAl₂O₄. To remove contaminants such as carbon from the structure of shaped spinel bodies, at first, the samples were annealed at temperature of 800?°C, 900?°C and 1000?°C for 2?h and then sintered at 1400?°C. By annealing the sample before sintering at 900?°C, the transmission increased (15% at IR region and 10% at visible region). Although by annealing the samples, the amount of carbon contamination reduced. Annealing the samples after sintering also had some desirable results. The samples annealed at temperature of 1200?°C for a time of 3, 5 and 10?h. The darkness of samples reduced due to the removal of carbon impurities and the sample was annealed at 1200?°C for 5?h had the most transparency in the visible and infrared regions.     

Aqueous slip casting and hydrolysis assisted solidification of MgAl2O4 spinel ceramics

Abstract

Abstract

This paper reports on synthesis of MgAl₂O₄ spinel (MAS) powders with six different chemical compositions and the consolidation of the synthesised MAS powders following an aqueous slip casting and hydrolysis assisted solidification (HAS) routes. The synthesised MAS powders were surface passivated against hydrolysis before being dispersed in distilled water to obtain suspensions with 41–45?vol.‐% solid loading using suitable dispersing agents. In the case of the HAS process, the consolidation of suspensions was achieved in non‐porous moulds under ambient conditions by the incorporation of AlN equivalent to 1–5?wt‐%Al₂O₃ into the suspension. The stoichiometric MAS powder consolidated by slip casting and dry pressing routes was sintered along with those consolidated by HAS route at 1550–1650°C for 1?h. Various characterisation techniques were utilised to evaluate the effect of composition and consolidation technique on slurry characteristics and sintered properties of MAS ceramics.     

Eco-friendly tape casting of borosilicate glass/Al2O3 sheets for LTCC applications

This work reports the innovative development of a borosilicate glass/Al₂O₃ tape for LTCC applications using an eco-friendly aqueous tape casting slurry. Polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) were the respective dispersants, while carboxymethyl cellulose (CMC) and styrene acrylic emulsion (SA) were the respective binders. The results showed that PVP was more suitable than PAA as the dispersant for the aqueous casting slurry, and that 1.5 wt% PVP would achieve well dispersion of CABS glass/Al₂O₃ powder in the aqueous slurry. Moreover, a small amount of 2.0 wt% CMC binder could yield smooth CABS glass/Al₂O₃ tapes crack free. A high-quality CABS glass/Al₂O₃ tape with a smooth surface was made from an aqueous slurry containing 1.5 wt% PVP dispersant, 2.0 wt% CMC binder, and 2.0 wt% PEG-400 plasticizer. The density, tensile strength, and surface roughness of the green tape were 2.05 g/cm³, 0.87 MPa, and 148 nm, respectively. The resulting CABS glass/Al₂O₃ composites sintered at 875 °C exhibited a bulk density of 3.14 g/cm³, a dielectric constant of 8.09, a dielectric loss of 1.0 × 10^?3, a flexural strength of 213 MPa, a thermal expansion coefficient of 5.30 ppm/^°C, and a thermal conductivity of 3.2 W m^?1 K^?1, thus demonstrating its broad prospects in LTCC applications.     

Microwave hybrid and conventional sintering of Al2O3 and Al2O3/ZrO2 multilayers fabricated by aqueous tape casting

In this study, microwave hybrid sintering and conventional sintering of Al₂O₃- and Al₂O₃/ZrO₂-laminated structures fabricated via aqueous tape casting were investigated. A combination of process temperature control rings and thermocouples was used to measure the sample surface temperatures more accurately. Microwave hybrid sintering caused higher densification and resulted in higher hardness in Al₂O₃ and Al₂O₃/ZrO₂ than in their conventionally sintered counterparts. The flexural strength of microwave-hybrid-sintered Al₂O₃/ZrO₂ was 70.9% higher than that of the conventionally sintered composite, despite a lower sintering temperature. The fracture toughness of the microwave-hybrid-sintered Al₂O₃ increased remarkably by 107.8% despite a decrease in the relative density when only 3 wt.% t-ZrO₂ was added. The fracture toughness of the microwave-hybrid-sintered Al₂O₃/ZrO₂ was significantly higher (247.7%) than that of the conventionally sintered composite. A higher particle coordination and voids elimination due to the tape casting and the lamination processes, the microwave effect, the stress-induced martensitic phase transformation, and the grain refinement phenomenon are regarded as the main reasons for the mentioned outcomes.     

Al2O3-3YTZP-Graphene multilayers produced by tape casting and spark plasma sintering

This work aims to establish a colloidal route to obtain laminates of alumina–zirconia combining layers with and without graphene. Green tapes of alumina, alumina with 5 vol.% of 3Y-TZP and alumina with 5 vol.% of 3Y-TZP and graphene-oxide (2 vol.%) were obtained by aqueous tape casting. It is possible to design materials for different structural applications with a controlled microstructure with a high number of different layers. The tapes were punched into 20-mm discs, joined to form laminates alternating up to 18-layers, and sintered in one-step by spark plasma sintering (SPS) at 1400 °C. It has demonstrated that there is a significant graphite diffusion provoked by the required graphite holders into the SPS-furnace. Dense laminates with layer thicknesses ∼100 μm and good cohesion between layers were obtained. Nanoindentation results showed that hardness and elastic modulus values were higher than 27 GPa and 300 GPa, respectively, and similar for all layers.     

Al2O3-C质整体塞棒在浇铸钙处理钢中的应用

分析了Al2O3-C质整体塞棒在钙处理钢浇铸过程中的侵蚀机制和其他一些重要影响因素,针对Al2O3-C质整体塞棒的特性,从炼钢的工艺改进、设备保障、优化过程控制和耐火材料材质优化等方面采取了相应措施,并提出了改进意见,使Al2O3-C质整体塞棒在钙处理钢的使用寿命不断提升,达到了比较满意的效果。     

Preparation of porous Al2O3 ceramics by starch consolidation casting method

Porous alumina ceramics were fabricated by starch consolidation casting using corn starch as a curing agent while their microstructure, mechanical properties, pore size distribution, and corrosion resistance were examined. Results showed that the porous alumina ceramics with the flexural strength of about 44.31MPa, apparent porosity of about 47.67% and pore size distribution in the range of 1‐4 μm could be obtained with 3wt% SiO₂ and 3wt% MgO additives. Corrosion resistance results showed mass losses: hot H₂SO₄ solution and NaOH solution for 10 hours were 0.77% and 2.19%, which showed that these porous alumina ceramics may offer better corrosion resistance in acidic conditions.     

Properties of Al2O3/Ti/Ni composites fabricated via centrifugal slip casting under environmentally assessed conditions as a step toward climate-neutral society

The paper concerns functionally graded composites obtained by centrifugal slip casting method. Al₂O₃, Ni, Ti, differed is size and morphology, were used as starting powders. The influence of metallic phase content (2 _vol% and 20 _vol%) and homogenisation process (planetary-ball milling) on suspension viscosity as well as density, phase composition, microstructure and mechanical properties of sintered bodies was investigated. Planetary-ball milling decrease the viscosity of suspensions of lower metallic content due to increase of their homogeneity. Slurries of higher metallic content, after homogenisation process, exhibit higher viscosity due to refinement of large metallic particles which leads to more intense surface interactions. CSC was applied to shape samples in form of thick-wall tubes with gradient microstructure across the wall thickness. Relative densities, after sintering, were about 10% higher for the samples containing 2 _vol% of metallic phase (99.40% and 98.42%) compared to specimens of higher metallic content (90.57% and 86.86%), regardless of homogenisation process. Planetary ball milling had a positive effect on microstructure of obtained graded composites, leading to more homogeneous microstructure with well defined zones and lower number of defects, in both types of sample (2 _vol% and 20 _vol% of metallic content). Higher content of Ti and Ni caused that metal-rich zone was thicker, but microstructure was more defected. Hardness was higher for samples of more homogeneous microstructure. XRD confirmed the presence of Al₂O₃ and Ni, Ti phases but also evinced occurrence additional intermetallic phases form Ni–Ti system. The environmental impact accompanying fabrication of composites was evaluated using the LCA method. It was done in order to determine burdens caused at the early beginning of the research and development stage, creating a reliable basis for further development of an environmentally friendly industrial process, simultaneously being a step toward transition to a climate-neutral society which is one of the main objectives of European Green Deal.     

Effect of Al2O3 addition on texturing in a rotating strong magnetic field and densification of B4C

The properties of ceramics can be improved by controlling the microstructure through texturing ceramics in a strong magnetic field. Fabricating dense boron carbide (B₄C) requires high temperature sintering, therefore sintering additives are often used in order to densify B₄C ceramics at lower temperatures. However, combined effect of texturing and sintering additives on densification of B₄C has not been made clear yet. Here we report the effect of alumina (Al₂O₃) sintering additive on texturing in a strong magnetic field and densification of B₄C. Texturing was performed by rotating superconducting magnet at 12 T during slip casting process. Electron backscatter diffraction (EBSD) was used to observed the texturing projection. {0001} plane is clearly oriented in the plane parallel to rotating magnetic field. In addition, Lotgering factor was also calculated as quantitatively evaluation of texturing degree. Results on densification showed that addition of Al₂O₃ successfully increased density of B₄C sintered by spark plasma sintering (SPS) at 1800^oC to 97.8%. Formation of aluminum borate (Al₅BO₉) as secondary phase was detected by X-Ray diffraction (XRD). It is considered that the generation of Al₅BO₉ assisted finer densification of B₄C ceramic. Textured B₄C sintered at 1700^oC by SPS without alumina addition exhibited the highest orientation of c-axis. Addition of alumina caused decrease in degree of orientation of c-axis.     

Direct tape casting of Al2O3/AlN slurry for AlON transparent ceramic wafers via one-step reaction sintering

In this work, transparent aluminate oxynitride (AlON) ceramic wafers were successfully fabricated by the direct non-aqueous tape casting of Al₂O₃/AlN slurry and the one-step reaction sintering for the first time. The reaction sintered AlON ceramic wafer exhibits high transmittance of 73.2 % at the wavelength of 1600 nm. This fabricating route realizes smooth and flexible tape without cracks or pinholes in Al₂O₃/AlN system and efficiently shortens the preparation cycle of transparent AlON wafers, which is a feasible way to prepare high-quality transparent AlON ceramics with large lateral sizes and thin thicknesses by reaction sintering, might also promote the application of transparent AlON ceramic wafers.     

Furnace smelting and extractive metallurgy of red mud: Recovery of TiO2, Al2O3 and pig iron

Turkish red mud (bauxite waste) has been mixed with dolomite and coke, pelletized and sintered at 1100°C, and finally smelted at 1550°C to produce pig iron and a slag. The slag was leached with 30% H₂SO₄ at 90°C. The leachate was diluted, ferric iron was reduced with SO₂, and extracted with 5% D2EHPA solution in kerosene. Silica and Al₂O₃ were recovered from the remaining aqueous solution, while the organic extract was stripped with 10% Na₂CO₃ solution, finally hydrolysed and calcined to produce pigment-grade TiO₂. The titanium recovery efficiency on the basis of slag weight was 84·7%. The extractive separation of titanium from both valencies of iron was investigated as a function of pH and time. A stoichiometric flowsheet for the whole process has been developed. ©1997 SCI     

氧化铝陶瓷凝胶注模成型工艺浆料流变性的研究

以氧化铝陶瓷为例,研究探讨了凝胶注模成型工艺中制备低粘度、高固相含量浓悬浮体的关键技术,分析讨论了氧化铝浆料的流变性特点及pH值、分散剂等因素对粘度的影响。实验表明:在pH=9,分散剂添加量为0.5%质量分数的Al2O3时,55%体积分数的氧化铝浆料的粘度为100mPa·s(D=77.48S-1)     

An approach for matrix densification based on particle packing and its effect on lightweight Al2O3-MgO castables

For lightweight refractory containing lightweight aggregates, the properties of the matrix are decisive to its performance. In the present work, Dinger–Funk equation was adopted to calculate the theoretical packing density of a castables matrix based on Stovall linear packing model and to design its particle size distribution. Four lightweight Al₂O₃-MgO castables with different particle size distribution (represented by q-value) were prepared and examined. Results show that a suitable q-value was needed to ensure acceptable properties including sintering characteristics, strength and slag resistance, which deteriorated distinctly at high q (>=0.31). For the sample with q=0.28, the matrix showed dense and uniform mirostructure, and the properties of castable reached a favourable compromise among sintering characteristics (apparent porosity=14.8%, bulk density=3.02 g cm⁻³, permanent linear change<0.6%), strength (cold modulus of rapture=12.4 MPa, cold crashing strength=155.5 MPa), and resistance against both slag corrosion (I_c=22.4%) and penetration (I_p=11.5%). The sample with q=0.25 showed the highest strength and resistance against slag corrosion (matrix dissolved in slag), but its slag penetration resistance was lower due to the existence of cracks between aggregates and matrix.     

Towards fabrication of high-performance Al2O3 ceramics by indirect selective laser sintering based on particle packing optimization

A novel method to fabricate high-performance Al₂O₃ Ceramics by indirect Selective Laser Sintering (idSLS) based on particle packing optimization was reported. Al₂O₃ ceramics with the particle size distribution (PSD) being adjusted based on a particle packing model was prepared with the idSLS method, and the effects of PSD on the macro-performance and microstructure of the idSLSed ceramics part was investigated. Results show that an appropriate PSD of raw material is not only essential to the good SLS formability of powder bed but also contribute to the favorable sintering characteristics of the SLSed green body through an ideal particle packing. The improvement of overall properties including mechanic strength, dimensional accuracy, and surface flatness of the SLSed green body and the final parts were achieved with a fine-tuned PSD exponent. When the raw material has a PSD exponent of 0.5–0.6, the final ceramic parts showed relatively balanced comprehensive properties of bulk density >2.0 g cm⁻³, linear change <1.4%, fracture strength >3.97 MPa, compressive strength >5.25 MPa and surface altitude difference <148 μm.     

The effect of particle size distribution on the microstructure and properties of Al2O3 ceramics formed by stereolithography

Stereolithography (SL) shows advantages for preparing alumina-based ceramics with complex structures. The effects of the particle size distribution, which strongly influence the sintering properties in ceramic SL, have not been systematically explored until now. Herein, the influence of the particle size distribution on SL-manufactured alumina ceramics was investigated, including bending strength at room temperature, post-sintering shrinkage, porosity, and microstructural morphology. Seven particle size distributions of alumina ceramics were studied (in μm/μm: 30/5, 20/3, 10/2, 5/2, 5/0.8, 3/0.5, and 2/0.3); a coarse:fine particle ratio of 6:4 was maintained. At the same sintering temperature, the degree of sintering was greater for finer particle sizes. The particle size distribution had a larger influence on flexural strength, porosity and shrinkage than sintering temperature when the particle size distribution difference reached 10-fold but was weaker for 10 μm/2 μm, 5 μm/2 μm and 5 μm/0.8 μm. The sintering shrinkage characteristics of cuboid samples with different particle sizes were studied. The use of coarse particles influenced the accuracy of small-scale samples. When the particle size was comparable to the sample width, such as 30 μm/5 μm and 5 mm, the width shrinkage was consistent with the height shrinkage. When the particle size was much smaller than the sample width, such as 2 μm/0.3 μm and 5 mm, the width shrinkage was consistent with the length shrinkage. The results of this study provide meaningful guidance for future research on applications of SL and precise control of alumina ceramics through particle gradation.     

New route for processing of multilayer Al2O3-Co3O4 materials through gelcasting

Multilayer dense ceramic materials composed of Al₂O₃ and Al₂O₃-Co₃O₄ layers have been obtained by gelcasting. The key stage in the process was the optimization of the polymerization idle time in order to ensure strong adhesion between layers without cracks and delamination in a green state and after sintering. The significant advantage of this method is occurence of strong connections between consituent layers due to the slight migration of the slurry to the gelled bottom part of the sample, what is not obseved in techniques based on lamination processes. The multilayer samples were composed of two Al₂O₃ layers and two Al₂O₃-Co₃O₄ layers arranged alternately. The rheological characterization of the slurries was done. The properties of the sintered multilayer bodies were examined in comparison to the single-layer alumina samples. Observations in SEM and ligth miscroscope were performed. The presence of the transition layer in the sintered bodies was observed.     

Evolution of interfacial microstructures between tungsten wires/flakes or graphite flakes and Al2O3/ZrO2 eutectic ceramics via a novel combustion synthesis centrifugal casting

The Al₂O₃/ZrO₂ eutectic ceramics with adding tungsten wires/flakes and graphite flakes were successfully prepared via a novel Al/Zr(NO₃)₄ combustion synthesis centrifugal casting under low-pressure, and the interfacial bonding between them and the Al₂O₃/ZrO₂ eutectic was studied via using the characterization methods of Energy Dispersive Spectrometry (EDS), X-ray diffraction (XRD), Hardness and Raman. The results show that there was a thin chemical reaction layer at the interface between the tungsten wires or flakes and the Al₂O₃/ZrO₂ eutectic system, which increased slightly with the increase of the reaction temperature from 3000 K to 3600 K, indicating that the interface was well combined. When the adiabatic temperature was 3600 K, the reaction layer thickness can reach ∼9.2 μm with the composition of WO₃/Al₂Zr. However, when graphite flakes were added to the combustion system, they can be oxidized by Al₂O₃ or ZrO₂ to form CO or CO₂, and the gas generation leaded to poor interface bonding between them and Al₂O₃/ZrO₂ eutectic system. These studies provided some theoretical guidance for the future addition of tungsten fibers and carbon fibers to Al₂O₃/ZrO₂ eutectic ceramics to improve the fracture toughness and strength of the materials. Moreover, it has guiding significance for preparing various fibers or woven fibers reinforced composite materials with large size, high density and excellent mechanical properties under ultra-high temperature.     

甲烷在Cr改性Pd/Al2O3催化剂上的催化燃烧性能

研究了Cr改性Pd/Al2O3催化剂上低浓度甲烷的催化燃烧反应,考察了载体Cr Al的制备方法和活性组分Pd的负载方法对催化剂催化活性的影响以及添加Ce对催化剂高温稳定性的影响。采用X射线衍射、程序升温还原等表征手段分析了催化剂结构和氧化还原性。结果表明,与采用沉淀法制备的载体P-Cr Al相比,采用浸渍法制备的载体I-Cr Al具有较高的比表面积和反应活性;用Na BH3对Pd负载过程进行还原处理能明显提高催化剂活性,其原因是还原过程加强了催化剂上Pd与载体Cr Al之间的作用,通过H2-TPR证明了其还原能力得到了增加;添加Ce缓解了Al2O3高温条件下的烧结,增强了催化剂的高温稳定性。