Near net shape fabrication of porous cordierite by combination of foam gel-casting and freeze-drying

Near net shape fabrication of porous cordierite was successfully achieved through a combination of foam gel-casting, freeze-drying, and in situ synthesis. Environment friendly gelation was used as gel system, and the gelatin concentration influenced the drying shrinkage vastly. Combined with the volume expansion coming from phase transition and solid reaction during in situ synthesis of cordierite, the total linear shrinkage could be controlled around zero (−1.87% to 0.45%) by adjusting the gelation concentration and solid content in the slurry, meanwhile the prepared porous cordierite ceramics showed both high porosity (85.9%–91.1%) and high compressive strength (0.58–3.37 MPa). The sample with 0.05 g/ml gelatin concentration and 20 vol% solid content possessed excellent performance: total porosity of 89.1%, compressive strength of 1.36 MPa, and specific strength of 4.9 MPa/(g/cm³), showing the potential usage of filter carrier.     

凝胶注模成形制备铜锡多孔材料的研究

采用非水基凝胶注模工艺,对铜锡复合粉体进行了成形与烧结的研究。非水基凝胶注模的单体为甲基丙烯酸-2-羟基乙酯,溶剂为1,2-丙二醇,交联剂为二乙二醇丙烯酸酯,引发剂催化剂为过氧化苯甲酰-N,N-二甲基苯胺,分散剂采用聚乙烯比咯烷酮。制备出不同固相含量的悬浮液,经过凝胶成形与烧结,得到铜锡烧结多孔材料。探讨了坯体的性能、烧结过程中的收缩率、孔隙率、显微结构和力学性能。结果表明:经过脱模干燥后的坯体抗弯强度最大能达到12.76 MPa,坯体中的金属粉末颗粒均匀分散在有机三维骨架中,对于烧结多孔材料,随着固相含量的增加,烧结体密度增大,烧结收缩率降低,抗压性能提高。烧结试样孔隙率在20%~40%之间,烧结收缩率小于12%,抗弯强度最大为240 MPa,制备的烧结多孔材料孔隙分布均一、能制备复杂形状的部件。     

颗粒级配对发泡法-凝胶注模制备Al_2O_3多孔陶瓷性能的影响

为了降低Al2O3多孔陶瓷制备过程中的干燥后收缩和烧后收缩,提高成品率,将d50分别为25.1、9.4和1.1μm的粗、中、细Al2O3粉体按粗粉中粉细粉质量比分别为50 40 10、10 40 50和100%全细粉的级配方式制备Al2O3泡沫浆料,研究颗粒级配对浆料黏度、干燥生坯的线收缩、烧后试样的线收缩、烧后试样的热导率等性能的影响。结果表明:颗粒级配可以有效提高固含量,且颗粒级配后的发泡浆料在静置30 min后仍能保持稳定,颗粒级配可以明显降低生坯的干燥线收缩以及烧后线收缩,并能降低热导率,提高了发泡法-凝胶注模工艺制备氧化铝多孔陶瓷的成品率。     

助烧剂对凝胶注模成型制备B_4C的影响

研究了采用凝胶注模成型制备碳化硼（B4C）时杂质、分散剂含量和固相体积含量对其浆料黏度及密度的影响。结果表明：添加石墨C粉对浆体的黏度影响不明显;当分散剂柠檬酸铵（（NH4）3C6H5O）含量为3vol%,固相体积含量为50vol%时,添加4wt%以上的ZrO2、Al2O3助烧剂可降低浆体黏度,提高流动性,且生坯密度达到52TD%以上。     

Foam gel-casting preparation of SiC bonded ZrB2 porous ceramics for high-performance thermal insulation

Lightweight SiC-ZrB₂ porous ceramics is of great potential as thermal insulation material used in aerospace, chemical and energy industries. In this work, a series of SiC bonded ZrB₂ (SiC_b-ZrB₂) porous ceramics with porosity high up to 86.9% were prepared by a simple foam gel-casting method. The SiC_b-ZrB₂ porous ceramic prepared at 1573 K exhibited a low thermal conductivity of 0.280 W/(m?K) and a reasonable compressive strength of 0.52 MPa. It could maintain the original geometric shape and microstructure after a secondary heat treatment at 1473 K in inert atmosphere. When heating the samples with thickness of 30 mm for 12 min with an alcohol spray lamp (～1273 K), the temperatures of the cold sides of SiC_b-ZrB₂ ceramics were all lower than 432 K, demonstrating their exceptional insulation capabilities. The present work provides a simple route to produce robust and thermally-insulating non-oxide porous ceramics for use under high temperature.     

MoSi2对注凝成型HfB2超高温陶瓷材料性能的影响

在Ph为10.9,分散剂PMAA-NH4为8vol%,固体含量为40vol%的条件下采用注凝成型技术制备了HfB2-(5%～15wt%)MoSi_2超高温陶瓷坯体,密度达到4.25 g/cm~3以上,在氩气气氛下1950 ℃保温30 min烧成.采用X射线衍射仪、扫描电镜等分析方法研究了添加剂MoSi_2对HfB2超高温陶瓷材料性能的影响、烧结体的物相组成和显微结构.结果表明:添加剂MoSi_2可有效促进HfB2超高温陶瓷材料的致密化,随着MoSi_2加入量的提高,HfB2超高温陶瓷材料的力学性能不断提高,当加入量为15%时,可得到显微硬度为9.8 Gpa,抗弯强度为389.7 Mpa,断裂韧性为3.7 Mpa·m~(1/2)的HfB2超高温陶瓷材料.     

NiO/YSZ浆料凝胶固化、干燥、排胶及烧结工艺研究

采用凝胶注模工艺制备固体氧化物燃料电池(SOFC)阳极材料NiO/YSZ是目前的研究热点之一.本文主要研究了凝胶注模工艺中引发剂和催化剂的加入量对凝胶固化时间的影响,干燥温度对坯体失重的影响,固相含量、造孔剂的种类及用量对瓷体收缩率的影响,并对还原后瓷体的电性能进行了表征.采用SEM、EDS方法分析表征样品.实验结果表明:在实验选定的100 mL浆料中,浓度为5wt%引发剂的加入量为2.0 mL,浓度为0.5vol%催化剂的加入体积量为1.0 mL,凝胶时间可以控制在20 min以内.NiO/YSZ阳极材料最佳干燥温度是25 ℃,固相含量为45vol%、采用15wt%石墨作为造孔剂,在1350 ℃烧成的NiO/YSZ阳极与固体电解质YSZ收缩率相匹配,氢气还原后NiO/YSZ阳极在600～800 ℃电导率达到800 S/cm,符合SOFC阳极材料电导率的要求.     

99氧化铝陶瓷基板注凝成形工艺的研究

以注塑成型技术为基础，研究99氧化铝陶瓷基板的制备工艺，实验研究了影响料浆性能及坯体均匀性的因素，确定了合理的制备工艺参数。     

Preparation and optical properties of highly transparent MgAl1.9Ga0.1O4 ceramics via aqueous gel-casting method

The aqueous gel-casting technology has been widely used to prepare high-quality green body for various transparent ceramics with large dimension and complex shape. However, owing to the severe hydrolysis of MgAl₂O₄ powder, it is challenging to obtain thick aqueous slurry with high homogeneity and flowability. In this paper, the surface chemical state of MgAl₂O₄ powder was modified by introducing Ga³⁺, and stable MgAl_1.9Ga_0.1O₄ aqueous slurry with high solid-phase loading (52 vol. %) and low viscosity (136 mPa·s, at a shear rate of 50 s^-1) was successfully prepared. After pressureless presintering and hot isostatic pressing, the gel-cast sample exhibited much higher optical transmittance and more homogeneous microstructure than the dry-pressed sample, which is mainly derived from the improved homogeneity and densification of the green bodies and ceramics. The optical band gap, infrared cutoff wavelength, static refractive index and dispersion of both MgAl_1.9Ga_0.1O₄ and MgAl₂O₄ transparent ceramics were systematically compared. It is indicated that the transparent MgAl_1.9Ga_0.1O₄ ceramic has the increscent static refractive index of 1.695, the decrescent direct band gap energy of 6.15 eV and absorption coefficient of 0.49 cm^-1 at 5 µm, which could be ascribable to the fact that Ga³⁺ has different electronic structure, higher electronic polarizability and larger ionic radius in comparison with Al³⁺. This work provides a dependable solution for preparation of spinel oxide ceramics with superior optical properties and large dimension.     

The hydrolysis process of γ-AlON powder and preparation of highly transparent ceramics with aqueous gel-casting

The untreated γ-AlON powders were proposed to prepare highly transparent γ-AlON ceramics by aqueous gel-casting technique and two-step sintering process. The related mechanism of hydrolysis of γ-AlON powders was discussed. The surface of the synthesized γ-AlON powders is covered with a layer of aluminum hydroxides compound. As the period of hydrolysis extends, the surface layer dissolved, and the boehmite and bayerite gradually formed, which is characterized by various techniques including XRD, FT-IR, XPS and TEM. The low viscosity slurry with high solids loading (53 vol%) was obtained by γ-AlON powders without any surface modification treatments as a result of the slow hydrolysis process. In addition, compared with the dry pressed sample, the sample (4.12 mm in thickness) prepared by aqueous gel-casting exhibits superior in-line transmittance of 81–83% in the visible region, which could be ascribed to the more homogenous and denser microstructure of the green body. Finally, the Weibull modulus and characteristic strength of γ-AlON transparent ceramic were determined to be 4.85 and 295 MPa, respectively.