Isobam assisted slurry optimization and gelcasting of transparent YAG ceramics

Gelcasting is a simple near-net shaping method to fabricate large-sized and/or complicated-structural ceramics. In this paper, a transparent yttrium alumina garnet (YAG) ceramic was successfully fabricated by gelcasting with a nontoxic, water soluble copolymer (isobutylene and maleic anhydride, Isobam) as both dispersant and gelling agent. The rheological behaviors of the slurries with different solids loading and Isobam contents were systematically investigated. The optimized slurry of 0.5 wt% Isobam and the solid loading of 68 wt% had the low viscosity and high stability, resulting in better homogeneity of the green body and better optical quality of transparent ceramics. A nearly pore-free structure of the sintered YAG ceramics with average grain size about 10.0 µm was obtained possessing an in-line transmittance of 75.7% at the wavelength of 1064 nm for a sample 2.5 mm thick.     

A new gelcasting using Isobam both as dispersant and monomer

Gelcasting is a kind of colloidal processing with many attractive advantages for fabricating ceramics. In this study, a new and simple gelcasting system with only two additives was investigated using Isobam (a copolymer of isobutylene and maleic anhydride) both as dispersant and monomer, and Tetraethylenepentamine (TEPA) as crosslinker. The gelation studies in solutions showed the reaction between Isobam and TEPA was an acylation reaction which was controlled by temperature and concentration. The rheological behavior and samples’ properties of 50 vol% Al₂O₃ slurries with different Isobam contents were studied. With 8 wt% of Isobam by water, the dried green bodies had relatively density of 56.3% and flexural strength of 25.7 ± 2.2 MPa. After sintering at 1530 °C for 3 h, the relatively density and flexural strength of sintered ceramics were 98.7% and 416 ± 19 MPa respectively. The SEM and macroscopic results showed that dried green bodies and sintered ceramics with homogeneous and defect–free morphology were obtained by using Isobam–TEPA system.     

水溶性共聚物为交联剂的凝胶注成型AlN陶瓷的研究

本研究采用一种快速凝胶的氮化铝凝胶通过在氮气气氛下烧结制备AlN陶瓷。将AlN粉体、少量的Y₂O₃粉体(烧结助剂)和去离子水以一定比例混合制得AlN浆料, 在浆料中加入一种新型的水溶性共聚物Isobam(由异丁烯和马来酸酐形成的共聚物)作为交联剂, 所得浆料在室温空气中自发凝胶成型。研究了Isobam和AlN、Y₂O₃粉体表面的有机包裹剂聚亚氨酯对浆料流变性能和凝胶性能的影响。结果表明, 加入0.3wt% Isobam可制备出固含量达52vol%的低粘度(0.2 Pa·s)AlN浆料。将凝胶干燥并脱粘, 获得的AlN素坯在氮气气氛下1800 ℃烧结4 h, 可制备出鳍状AlN陶瓷, 所得陶瓷的密度为3.33 g/cm³, 热导率为204 W/(m·K)。     

Preparation and properties of fused silica ceramics by Isobam spontaneous coagulation casting

By surface modification with APTMS, spontaneous coagulation casting (SCC) of fused silica based on Isobam was achieved and the possible coagulation and molding mechanism is proposed. Through the interaction between the polar groups on the Isobam molecular chain and the incorporated –NH₂ groups on the surface of the silica particles, Isobam molecular chains were adsorbed on the surface of particles, which initiate the formation of flocs and the solidification of the suspension. The addition of dispersant TMAH results in the hydrolyzation of Isobam, forming more –COO^–, which effectively improves the fluidity and stability of the suspension. Then the zeta potential, rheological properties and coagulation behavior of the suspension were systematically investigated and the fused silica suspension with high solid content (up to 52 vol%), low viscosity and good coagulation properties were prepared at 1.8 wt% TMAH and 0.5 wt% Isobam dosage. After sintering at 1260 °C for 4 hours, the fused silica ceramics (50 vol% solid content) shows a high bending strength of 61.59 MPa, the lowest dielectric loss tanδ of 8.46×10^-4 and the dielectric constant of 3.72. Thus, this work provides a simple and effective method for preparing fused silica and other ceramics with negative surface charge by Isobam SCC.     

Preparation of SiC porous ceramics by a novel gelcasting method assisted with surface modification

The SiC porous ceramics were successfully prepared by gelcasting process using Isobam as gelling agent. The pretreatment and surface modification of SiC was proposed to solve the problem that Isobam is difficult to crosslink and gelling with non-oxide ceramics. The SiC powder was firstly pre-oxidized, and then modified with a silane coupling agent to obtain a functional end group -NH₂ on the surface, so that it can be crosslinked with Isobam to obtain a green body with uniform structure. With low amount of organic matter, no additional debinding procedure was required before sintering. The suitable oxide thickness was investigated, which shows a linear relationship with the original SiC particle size. Moreover, the solid content of the slurry was adjustable between 40 vol% and 52 vol%, and the porosity of the products varied between 50% and 60% after sintering.     

凝胶浇注结合固相烧结制备具有多级孔结构的碳化硅陶瓷

以Isobam作为胶凝剂, 聚甲基丙烯酸甲酯(PMMA)作为泡沫稳定剂和造孔剂, 结合固相烧结制备出具有多级孔结构的碳化硅陶瓷, 并研究了PMMA添加量、球磨机转速以及烧结温度对多孔陶瓷结构及性能的影响。结果表明: 当球磨机转速为220 r/min、烧结温度为2100℃时, 随着PMMA添加量由5wt%增加到20wt%, 发泡过程受到抑制, 但是泡沫的稳定性增强, 所得多孔陶瓷的气孔率在51.5%~72.8%之间, 压缩强度介于7.9~48.2 MPa之间; 当PMMA加入量为20wt%时, 随着球磨机转速由220 r/min增大到280 r/min, 加剧了浆料的发泡过程, 2100℃烧结所得多孔陶瓷的气孔率逐步增大, 气孔孔径变大; 当球磨机转速为220 r/min, PMMA加入量为20wt%时, 随着烧结温度的升高, 气孔率逐渐降低, 力学性能有所提高。     

Dispersion and gelation behavior of alumina suspensions with Isobam

As a copolymer of isobutylene and maleic anhydride, Isobam, a newly-developed gelling agent, plays a significant role in ceramic forming process. However, dispersion and gelation behavior of Isobam has not been discussed in detail yet. To investigate the influence of other dispersants, pH and electrolytes on dispersion and gelation behavior of Isobam, zeta potential, viscosity and modulus curves during gelation were measured from 50?vol% alumina suspensions with 0.1–0.7?wt% Isobam. A two-step bridging mechanism is proposed to explain the gelation behavior of Isobam, providing guidance on usage of Isobam in combination of other additives to achieve suspensions with high solids loading and adjustable gelation characteristic.     

Investigation of gelation mechanism and the effects of APS on AlN slurries with Isobam

A novel and simple gelling system based on a water-soluble copolymer of isobutylene and maleic anhydride (commercial name, Isobam) was adopted to manufacture various ceramics via spontaneous gelation. The gelation mechanism of AlN slurry was investigated using infrared spectroscopy. Results show that Isobam was hydrolyzed to produce the –COOH group, and the hydrogen bonding was formed between the –COOH and –CONH₂ groups of Isobam during spontaneous gelation. Meanwhile, the gelling process of the Isobam system could be accelerated via enhancing hydrogen bonding through APS addition. With 1 wt% addition of APS, the gelation time reduced to 23 h, the viscosity of 50 vol% AlN slurry decreased to 0.21 Pa·s, and the flexural strength of green body improved by 48%. Therefore, the presence of hydrogen bonding in the Isobam gelation mechanism was confirmed, and it could be enhanced by introducing APS to accelerate gelation.     

Preparation of low-shrinkage and high-performance alumina ceramics via incorporation of pre-sintered alumina powder based on Isobam gelcasting

Mechanically robust alumina ceramics with low shrinkage were successfully prepared via gelcasting using Isobam as the gelling agent and pre-sintered alumina powder as the raw material for the first time. The influence of amount of pre-sintered alumina powder and powder's pre-sintering temperature on the viscosity of suspension and mechanical properties of low-shrinkage alumina ceramics were systematically investigated. The results showed that low-shrinkage alumina ceramics with flexural strength of 294.5?±?33.0?MPa, linear shrinkage of 7.79% and relative density of 91.5% can be obtained with the addition of 60?wt% alumina powder pre-sintered at 1600?°C. This convenient and facile approach is promising to fabricate low-shrinkage alumina ceramics with large sizes, high dimensional accuracy and complex shapes.