Preparation,structural evolution,and performance of heat-resistant organosilicon polymer adhesives for joining SiC ceramics

There is an urgent need for heat-resistant adhesives with high bonding strength in order to able to fabricate large and complex SiC components for aeronautical and astronautical applications. In this study, heat-resistant organic adhesives prepared using an organosilicon polymer and inorganic additives (B₄C and SiO₂) were used successfully to bond SiC ceramics. The prepared adhesives were characterised through shear strength tests as well as using thermogravimetry-differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-diffraction analysis, and scanning electron microscopy. The adhesives exhibited high room-temperature shear strengths (greater than 15 MPa) after being subjected to heat treatments at 200–1200°C. Further, the high-temperature shear strengths of the adhesives at 200, 400, 600, 800, and 1000°C were 10.5, 10.1, 7.7, 8.6, and 8.4 MPa, respectively. The high performance of the adhesives indicated that they should be suitable for joining SiC-based materials for use in high-temperature applications.     

有机硅改性丙烯酸酯核-壳结构压敏胶聚合物乳液的研制

采用种子乳液聚合的方法制备了一种新型具有核/壳结构的有机硅改性丙烯酸酯压敏胶聚合物乳液,讨论了多官能团有机硅氧烷功能性单体、核壳单体结构、乳化剂、引发剂以及聚合温度等因素对压敏胶聚合物乳液性能的影响。     

Low-temperature joining of SiC ceramics using NITE phase with Al2O3-Ho2O3 additive

In order to avoid the property degradation resulting from high-temperature joining process, nano-infiltrated transient eutectoid (NITE) phase with the Al₂O₃-Ho₂O₃ as the joining adhesives was adopted to join silicon carbide (SiC) ceramics with the attempts to lower down the joining temperature. The liquid-phase-sintered silicon carbide (LPS-SiC) specimens were joined at 1500-1800°C by spark plasma sintering (SPS) under the pressure of 20 MPa. The results of the shear test and microstructure observation showed that the joining process could be finished at a relatively lower temperature (1700°C) compared to other NITE-phase joining. In contrast to the shear strength of 186.4 MPa derived from the SiC substrate, the joint exhibited the shear strength of 157.8 MPa with the fully densified interlayer.     

硅笼改性耐热厌氧胶的制备及其固化动力学

为提高厌氧胶的热性能,用二步法合成了邻甲酚醛环氧丙烯酸酯(o-CFEAR),并以该树脂为单体,不饱和笼型倍半硅氧烷(POSS)为耐高温改性剂,选择合适的氧化还原体系及其它助剂,制成耐高温厌氧胶,测定了相关性能,研究了该胶的固化动力学。结果表明,此厌氧胶剪切强度最高达15.3 MPa,在200℃、96 h时剪切强度保持率为87%左右,耐高温性能良好;固化过程的反应级数为1.084 9,表观活化能为86.86 kJ/mol。     

Preparation and performance of a heat-resistant organic adhesive obtained via a liquid SiC precursor

A heat-resistant organic adhesive rich in active SiH bonds and CHCH₂ bonds has been synthesized by modifying polymethylsilane with D4Vi. The structure and properties of the adhesive have been investigated by FTIR, GPC, TGA, XRD, bonding strength tests, and SEM. The results show that the obtained adhesive exhibits outstanding thermal stability and bonding properties. The ceramic yields of the adhesive treated in Ar or in air at up to 1200 °C were measured as 81% and 90.6%, respectively. The adhesive can maintain an amorphous state even when heat-treated at 1200 °C for 2 h in air. The room temperature shear strength of the adhesive was measured as 14.9 MPa, and this increased to a maximum value of 31.7 MPa after heat-treatment at 1000 °C for 2 h.     

Preparation and characterization of heat-resistant interpenetrating polymer network (IPN)

Interpenetrating polymer network (IPN) is a novel type of polymer hybrids, which possess physicochemical properties suitable for high performance coatings. Heat-resistant IPN have been prepared from immiscible resins, epoxy and silicones using a cross-linking agent and a catalyst. The products were analyzed by GPC, FT-IR, TG, DTA and SEM studies. The heat resistance property and corrosion behaviour of the IPNs were also determined. It was different from those of the individual resins. Silicone microdomains could be seen uniformly distributed in epoxy regions. Corrosion resistance property of the IPNs was evaluated by salt spray and impedance measurements. The IPNs withstood longer durations in the salt spray chamber.     

Preparation of ordered mesoporous SiCN ceramics with large surface area and high thermal stability

For the first time, highly ordered two-dimensional (2-D) and three-dimensional (3-D) mesoporous SiCN ceramics with high surface area and high thermal stability were prepared by nanocasting a preceramic polymer solution into mesoporous carbon templates, CMK-3 and CMK-8, respectively. As a negative replica of CMK-3 carbon, the obtained mesoporous SiCN ceramic possessed an ordered 2-D hexagonal mesostructure, which is similar to the structure of SBA-15 silica except for the reduced dimensions. An ordered 3-D cubic mesoporous SiCN ceramic was also fabricated using CMK-8 as a template. The wall of the mesoporous SiCN replicas consisted of an amorphous SiCN ceramic phase, which possessed high thermal stability at high temperature up to 1000 °C. N₂-sorption isotherms revealed that these ordered mesoporous SiCN ceramics have high BET surface areas (up to 472 m² g⁻¹) and narrow pore-size distributions, which was preserved even after a re-treatment at 1000 °C in air. The use of carbon template played an important role in the preparation of mesoporous SiCN replicas and enhanced the thermal stability of the SiCN products. It is expected that many other types of ordered mesoporous ceramics can be prepared from nanoporous carbon by nanocasting method.     

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.     

Effect of organic fibers addition on digital light processing for Al2O3 porous ceramics

Porous ceramics based on additive manufacturing have great application potential in many industries, including filtration, catalysis, and heat insulation. In this research, we propose a method for manufacturing porous ceramics with connected channels structure through ceramic digital light processing (DLP) and organic fiber decomposition. The crossed fibers in the green body, working as a pore-forming agent, were decomposed and removed to form connected channels in ceramic. It was confirmed that ball milling changed the fiber morphology during slurry preparation, which was beneficial to promote fibers crossing. Besides, we focused on the influence of the “Sponge Compression effect” during the DLP process, which affected the fibers distribution. The existence of fibers in the green body resulted in uneven pressure distribution during the debinding process, providing a potential source of cracks. Results show that this method can produce channels with a diameter of 100 μm and high connectivity, providing great potential in fabricating high connectivity porous ceramics with complex shapes and structures.     

Preparation and properties of MgAl2O4 spinel ceramics by double-doped CeO2 and La2O3

Magnesium aluminate spinel (MgAl₂O₄) ceramics are high-performance and carbon-free materials widely used in both military and civilian fields. However, it is usually challenging to densify during the solid-state sintering process. The excellent properties of some rare earth oxides have been proved to promote the densification of MgAl₂O₄ spinel ceramics. But the mechanism of promoting sintering is not clear. In the present work, MgAl₂O₄ spinel ceramics have been successfully fabricated by co-doping CeO₂ and La₂O₃ via a single-stage solid-state reaction sintering. The effects of addition amounts of CeO₂ and La₂O₃ on phase compositions, microstructures, sintering characteristics, cold compressive strength, and thermal shock resistance of as-prepared MgAl₂O₄ spinel ceramics were systematically investigated. The results show that by co-doping CeO₂ and La₂O₃ can increase the defect concentration due to the lattice distortion. This could promote the movement of Al³⁺ and Mg²⁺ at high temperature, which is beneficial to the formation of more secondary MgAl₂O₄ spinel. t-ZrO₂ with more Ce⁴⁺ filling between spinel grains could prevent the growth of grains and promote the densification, besides the new-formed LaAlO₃ that was mainly distributed along the grain boundary of the MgAl₂O₄ phase, both of which were favorable for the formation of dense microstructure of MgAl₂O₄ spinel materials. At the same time, the formation of more secondary MgAl₂O₄ spinel and sintering densification also improve the mechanical properties of spinel ceramics. La³⁺ will segregate to the spinel grain boundary, preventing grain boundary movement and absorbing the main crack's fracture energy. With 3 wt% CeO₂ and 3 wt% La₂O₃ co-doping, the bulk density of the sample increased from 3.02 g∙cm⁻³ to 3.55 g∙cm⁻³; the apparent porosity decreased from 12.21% to 9.97%; the cold compressive strength increased from 172.88 MPa to 189.54 MPa; and the residual strength retention ratio after thermal shock increased from 84.92% to 89.15%.     

Preparation,microstructures, and mechanical properties of directionally solidified Al2O3/Lu3Al5O12 eutectic ceramics

Al₂O₃/Lu₃Al₅O₁₂ (LuAG) directionally solidified eutectic (DSE) ceramics with two solidification rates were prepared utilizing optical floating zone (OFZ) technique. The microstructures (eutectic morphology, preferred growth direction and interface orientation) of Al₂O₃/LuAG were characterized, and the mechanical properties (Vickers hardness and fracture toughness) were compared with those of Al₂O₃/REAG (RE = Y, Er, and Yb). Results show that Al₂O₃/LuAG with solidification rate of 30 mm/h has established preferred growth direction in both Al₂O₃ and LuAG phases with cellular eutectic structures. While Al₂O₃/LuAG with solidification rate of 10 mm/h only shows preferred growth direction in Al₂O₃ phase and presents degenerate irregular eutectic microstructures. Besides, Al₂O₃/LuAG exhibits higher hardness compared with Al₂O₃/REAG (RE = Y, Er, and Yb). In addition, a special attention is focused on the relations among rare earth ionic radius, eutectic microstructures, and mechanical properties of these DSE ceramics. It is demonstrated that a smaller rare earth ionic radius could lead to larger eutectic interspacing as well as higher Vickers hardness of DSE Al₂O₃/REAG, revealing the possibility and feasibility of microstructure control and mechanical properties optimization for DSE Al₂O₃/REAG ceramics by tailoring the rare earth elements.     

落叶松生物油-酚醛树脂胶粘剂的研制及性能研究

为了降低酚醛树脂胶粘剂成本,提高其环保性能,研制了新型的落叶松快速热解生物油-酚醛树脂胶粘剂。选用生物油替代率、n甲醛／n苯酚以及nN2OH／n苯酚为试验因子,探讨这3个因子对生物油-酚醛树脂胶粘剂主要性能的影响,得出生物油-酚醛树脂胶粘剂的最佳合成工艺。     

无溶剂型双组分耐黄变PU胶粘剂的制备与性能

以六亚甲基二异氰酸酯(HDI)、聚醚多元醇(PPG)及3,3’-二氯-4,4’-二氨基二苯基甲烷(MOCA)为主要原料,采用2步法制备一种无溶剂型双组分耐黄变PU胶粘剂。通过傅立叶红外(FT-IR)和差热扫描(DSC)对其结构及性能进行分析。讨论了PPG、MOCA含量及双组分配比对PU胶粘剂性能的影响。结果表明,采用低分子质量的PPG能显著地降低胶粘剂的黏度,胶粘剂的固化速率随MOCA(交联剂)含量的增加而显著提高;固化后的胶粘剂具有良好的耐化学药品性、耐低温性和耐黄变性。通过DSC曲线确定了固化后胶膜的Tg为46.1℃。     

纳米氧化锌/γ-氧化铝复合物制备及其光催化性能研究

以γ-氧化铝(γ-Al2O3)为载体,采用均匀沉淀法制备了不同氧化锌(ZnO)负载量的纳米ZnO/γ-Al2O3复合物。通过X射线衍射(XRD)、扫描电镜(SEM)、红外光谱(FT-IR)和氮气吸附,对复合物的结构、表面形貌、组成和比表面积进行了表征。以壬基酚聚氧乙烯醚(NPE-10)和苯酚为模型污染物,对复合物的光催化性能进行了评价。结果表明:当ZnO与γ-Al2O3按质量比为2∶1加料制备ZnO/γ-Al2O3复合物时,ZnO成功负载到γ-Al2O3表面,并形成均匀的薄膜;以制备的ZnO/γ-Al2O3复合物为催化剂在紫外光照射2 h后NPE-10的降解率达到93%,苯酚的降解率达到20%,且它们的降解率均随着溶液初始浓度的增大而降低。     

Thermomechanical properties of ceramics in the systems Al2O3-TiO2 and Al2O3-TiO2-mullite

Conclusions We studied certain properties of ceramics in the systems Al₂O₃-TiO₂ and Al₂O₃-TiO₂-mullite, obtained by the use of the double-stage synthesis of aluminum titanate.We established the nature of the change in the high-temperature strength in relation to the ratio of Al₂O₃ and aluminum titanate. The maximum high-temperature strength (bending) at 1200°C is possessed by ceramic with a corundum matrix and a volume proportion of aluminum titanate equal to 40–45%.It is established that the addition of CaO + SiO₂ made in amounts of up to 1.0–1.5% contributes to the partial breakdown of the aluminum titanate in the compositions Al₂O₃-TiO₂ and the production of a ceramic with a bending strength of 160–190 N/mm² at 20–200°C, thermal-shock resistance 650–800°C, and thermal conductivity of 1.9–2.1 W/(m·K).We studied the effect of the mullite concentration on the properties of the ceramic in the system Al₂O₃-TiO₂-mullite. The introduction of mullite in amounts of not more than 50%, containing up to 3% of impurities, contributes to an increase in the ceramic's strength in the range 20–1300°C and in the thermal shock resistance.Translated from Ogneupory No. 2, pp. 22–26, February, 1988.     

氧化铝凝胶的制备

主要介绍了以碳酸钠和三氯化铝为原料、有机酸为稳定剂制备氧化铝凝胶的方法,考察了制备过程中反应温度、热水处理温度、时间、加水量和有机酸的用量对氧化铝凝胶质量的影响     

Al2O歧化法制备微细Al2O3/Al复合粉体

真空条件下,以Al2O3和Al为原料,通过Al2O歧化法制备微细Al2O3/Al复合粉体.XRD和SEM分析表明:在反应温度为1200～1400℃时,随着温度的升高,粉体中氧化铝含量升高;冷凝温度约为550～750℃时,复合粉体中的氧化铝包括稳定晶型和不稳定晶型;冷凝温度约为1100～1300℃时,复合粉体中的氧化铝全部为稳定晶型;冷凝温度约为550～650℃时,复合粉体的平均粒径小于0.5μm;冷凝温度约为750℃时,铝熔化、微粒团聚;冷凝温度约为1100～1200℃时,铝形成铝珠,氧化铝为不规则状、平均粒径小于2μm;冷凝温度约为1300℃时,氧化铝为片状.因此,通过选取合适的反应温度、冷凝温度,可以控制Al2O3/Al复合粉体中氧化铝的含量、晶型和粒径.     

Preparation of high-temperature organic adhesives and their performance for joining SiC ceramic

Two kinds of high-temperature organic adhesives were prepared and successfully applied to join SiC ceramic. One adhesive was composed of preceramic polymer (V-PMS) and B₄C powder (HTA-1), and the other was composed of V-PMS, B₄C powder and low melting point glass powder (HTA-2). The properties of the obtained adhesives were investigated by TGA, XRD, bonding test and SEM analysis. The results show that the obtained adhesives exhibit outstanding heat-resistant property and excellent bonding strength. The bonding strength of HTA-1 treated at 200 °C, 400 °C, 600 °C were 26.8 MPa, 18.9 MPa, 7.3 MPa, respectively. When the temperature increased to 800 °C or even higher, the shear strengths of the joints were enhanced to over 50 MPa. Moreover, by adding glass powder as the second filler, it was found that the minimum shear strength of HTA-2 was enhanced to 16.4 MPa. The excellent performances of the obtained adhesives make them as promising candidates for joining SiC ceramics for high-temperature applications.     

Microstructure evolution and bonding strength of the Al2O3/Al2O3 interface brazed via Ni-Ti intermetallic phases

In this study, Al₂O₃ workpieces were vacuum brazed by using Ni-45Ti binary alloy. The interfacial microstructure evolution of the joints obtained at different brazing temperatures was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The bonding strength of the joints was measured by shear testing. The results indicated that Ni₂Ti₄O and AlNi₂Ti were the main reaction products in the joint areas. Moreover, the Ti₂Ni intermetallic compound formed in the brazing seam. The typical layer structure of the brazed joints was Al₂O₃/AlNi₂Ti/Ni₂Ti₄O/Ti₂Ni + NiTi/Ni₂Ti₄O/AlNi₂Ti/Al₂O₃. With the brazing temperature increasing, the thickness of the Ni₂Ti₄O reaction layer adjacent to the Al₂O₃ substrate increased significantly, while the AlNi₂Ti phase had a tendency to dissolve with the brazing temperature increasing. The mechanism for the microstructure evolution was also discussed. The maximum shear strength of 125.63±4.87 MPa of the joints was obtained when brazed at 1350 °C for 30min. The fracture occurred hardly in the interface between Al₂O₃ and Ni-45Ti filler alloy.     

Al2O3＋TiC陶瓷中Al2O3与TiC化学反应抑制的研究

本文通过Ｙ－盐溶液的形式加入到Ａｌ２Ｏ３粉料中,制备了Ｙ２Ｏ３表面固溶的Ａｌ２Ｏ３粉料,对其阻止Ａｌ２Ｏ３与ＴｉＣ之间的化学反应进行了研究。研究结果表明：采用Ｙ－盐溶液加入Ｙ２Ｏ３,Ｙ原子能均匀的分散在Ａｌ２Ｏ３的表面,高温时Ｙ２Ｏ３在Ａｌ２Ｏ３表面形成固溶体层,少量的Ｙ２Ｏ３加入量（０．３５ｗｔ％）,就能有效的阻止Ａｌ２Ｏ３与ＴｉＣ之间的化学反应。