淀粉原位凝固成型纯碳反应烧结碳化硅坯体的研究

研究了一种新的陶瓷原位凝固成型方法，其原理是依据淀粉颗粒在水中润胀吸水，在加热时产生糊化的特性。在固相体积分数接近50％的碳粉料浆中引入约3％质量分数的淀粉，用水浴加热期化的方法即可原位凝固成型各种形状的陶瓷部件，获得致密、均匀的坯体。研究了淀粉-碳粉料浆的流变学特性，单纯淀粉呈现膨胀型流动，含淀粉的碳粉料浆悬浮液的表观粘度随淀粉的加入量的增加而提高。料浆中淀粉的加入量应控制在原料干基质量的1％-5％范围内，料浆分散条件为中性。研究了淀粉原位凝固成型的机理以及对素坯结构的影响。     

琼脂糖凝胶大分子在陶瓷原位凝固成型中的应用

研究了一种新的陶瓷原位凝固成型方法,其原理是依据琼脂糖凝胶大分子在水溶液中加热时溶解,冷却时凝固这一物理变化。对于固相体积分数大于50％陶瓷悬浮体中引入约1％（质量分数）琼脂糖大分子,即可凝胶注模进行各种形状复杂的陶瓷部件成型,获得表面光洁、内部孔隙尺寸和密度分布均匀的陶瓷坯体,并烧结出均匀致密内部无明显缺陷的涡轮转子等异型部件。     

陶瓷成型新方法及其应用的研究

介绍和讨论了作为一种借助酶催化化学反应实现原位凝固的崭新近净尺寸陶瓷成型概念的直接凝固注浆成型方法与技术，以及通过与陶瓷粉料混合形成浓悬浮胶体的有机单体在加人偶联剂、催化剂和引发剂后的聚合反应促成原位聚合凝固的注疑成型方法与技术。利用这两种成型技术可以获得均匀、无密度梯度的近净尺寸坯体和致密陶瓷制品。这里也简单介绍和讨论了喷墨打印成型技术。它是一种利用计算机控制实现多层打印、逐层叠加制出三维陶瓷坯体的计算机辅助制造(CAM)陶瓷的成型新技术。     

直接凝胶凝固成型SiC(M,Y)-Al2O3复合陶瓷材料的研究(Ⅱ)基本原理及工艺过程研究

本文研究了一种新的陶瓷原位凝固成型技术 (直接凝胶凝固成型 )的基本原理和工艺过程 ,找出了影响成型工艺的基本因素 ,并且利用该成型技术制备出强度和密度较高 ,且密度均匀性好的坯体。     

酶催化明胶原位凝固成型陶瓷坯体的研究

采用天然高分子凝胶进行陶瓷原位凝固成型具有机物加入量少，无毒等优点。本文讨论了一种新的凝胶化工艺用以成型陶瓷坯体，其原理是利用尿素作为氢键阻断剂，阻止热明胶溶胶溶胶冷却时的凝胶化转变。待球磨，真空除泡等工艺操作完成后，再加入尿酶使尿素分解，明胶大分子重新获得氢键结合能力，在室温下完成凝胶化转变，形成网络结构，实现原位凝固成型。该成型方法可获得表面光洁，内部均匀的陶瓷坯体。     

SiC短纤维增强SiC-BN复合陶瓷

采用原位合成的方法设计并制备了SiC短纤维增强的SiC—BN复合陶瓷。经理论计算及实验证明，在相对较低的温度(1700℃)下即可成功实现预期的原位反应，生成了细小均匀的微米级SiC和BN颗粒，并研究了纤维和BN含量对复合陶瓷组织结构和力学性能的影响。     

高性能陶瓷原位凝固成型技术的研究进展

综述了高性能陶瓷原位凝固成型工艺的特点;重点介绍了近年来的四种陶瓷原位凝固成型方法,即注凝成型,直接凝固成型,温度诱导絮凝成型和胶态振动注模成型,并简要介绍了国内陶瓷原位凝固成型技术研究取得的新成果。     

酯化淀粉原位凝固成型Al2O3陶瓷的研究

研究了以淀粉作凝胶剂原位凝固成型Al2O3陶瓷的新方法.当淀粉大分子在水溶液中加热到一定温度时,淀粉颗粒吸水溶胀,陶瓷浆料脱水并固化成坚硬的坯体;而且溶胀后的淀粉可作为粘结剂,有助于坯体固化并增加其强度.详细探讨了酯化淀粉添加量不同时,对陶瓷浆料流变特性的影响,以及对成型出素坯的线收缩、相对密度、干坯强度以及显微结构的影响.     

用改性淀粉原位凝固成型制备Al2O3陶瓷

陶瓷凝胶注模成型工艺是一种新颖的成型工艺,它将高分子化学单体聚合的思路引入到陶瓷的成型工艺中.本文用改性淀粉原位凝胶注模成型技术制备了具有较高强度和均匀性良好的氧化铝陶瓷坯体.研究了氧化铝陶瓷的凝胶注模成型工艺中低粘度高固相体积分数浓悬浮体的制备、浓悬浮体的固化、成型坯体的显微结构及性能.     

直接凝固注模成型Si_3N_4及SiC陶瓷──基本原理及工艺过程

直接凝固注模成型（ｄｉｒｅｃｔｃｏａｇｕｌａｔｉｏｎｃａｓｔｉｎｇ，ＤＣＣ）是一种崭新的（准）净尺寸陶瓷成型方法。本文报道了采用此法成型Ｓｉ_３Ｎ_４及ＳｉＣ陶瓷的基本原理和工艺过程。ＤＣＣ成型工艺过程为把高固相含量低粘度的陶瓷浆料浇注到无孔模具中，事先加入到浆料中的生物酶及化学物质通过改变浆料的ｐＨ或电解质浓度来改变浆料的胶体化学行为，从而使浆料原位凝固，得到有足够脱模强度的陶瓷坯体。ＤＣＣ成型的特点为坯体密度高（理论密度的５５％～７０％），坯体均匀，不用或只需少量的有机添加剂（少于１％），可成型大尺寸、复杂形状、高可靠性的陶瓷部件。     

Dispersion of Silicon Carbide Powders in Nonaqueous Solvents

Thirty-two pure solvents were used to disperse laser-synthesized SiC powder, oxidized laser-synthesized SiC powder, and commercially available SiC powder. Five-day sedimentation tests were used to screen the solvents. Relative turbidity of the supernatant after 1 month was used as a quantitative measure of the degree of dispersion. Coagulation kinetics were measured by photon correlation spectroscopy to determine the coagulation rate. Stabilized powders were centrifugally cast into ceramic green bodies and their green densities measured. Experimental dispersion results were correlated with various solvent properties including dielectric constant, hydrogen-bond index, acid dissociation constant (p K _a), and Lewis acid/base interaction energy. Microcalorimetry was used to measure the heat of wetting of the powders in various acidic and basic solvents. The heat of wetting was used to determine the Lewis interaction energy parameters for the powder surfaces. Oxidized SiC powder, either laser or commercial, was shown to have an acidic surface and was stabilized by basic solvents. Pure laser-synthesized SiC powder was shown to have a basic surface and was stabilized by acidic solvents. Solvents with high hydrogen-bond indices gave high packing densities. Other solvent properties had a much smaller influence on powder dispersibility. Good dispersibility gave ceramic green bodies with high green densities.     

Effect of Nicalon SiC fibre heat treatment on short fibre reinforced β-sialon ceramics

SiC Nicalon fibre yarn was heat-treated at elevated temperature in a gas pressure furnace under CO atmosphere. Weak surface coating is essential for ceramic matrix composite (CMC) reinforcement. Therefore Nicalon SiC fibres were coated after CO heat treatment and then used for β-sialon ceramic reinforcement. The heat treated fibres were chopped about 1–2 mm, and β-sialon z = 1 starting powders were prepared with conventional ball milling. The sialon starting composition and the short fibres were mixed with the certain amount of water to obtain a plastically formable mud. This mud was unaxially cold-pressed to form green bodies and to decrease water content. The green bodies were hot pressed at elevated temperatures for half an hour to produce CMC samples. Vickers hardness test showed that heat-treated fibre reinforcement of β-sialon composites provided higher fracture toughness. Uniform fibre distribution, fibre coating, matrix densification and phase transformation were examined by SEM and XRD analysis.     

Preparation and stereolithography of SiC ceramic precursor with high photosensitivity and ceramic yield

Stereolithography of ceramic precursors is a valuable additive manufacturing technology for complex ceramic parts. In this study, a new SiC ceramic precursor—liquid hyperbranched polycarbosilane (LHBPCS) grafting acrylate group was synthesized by chlorinating some Si–H groups of LHBPCS with Cl₂ followed by reacting with hydroxyethyl acrylate. The reaction processes and structures of intermediate reactant and target product were confirmed by FT-IR and ¹H NMR. According to photolithography experiment and hardness test under UV light, the synthesized LHBPCS had high photo-curing activity. Thermogravimetric analysis indicated it also possessed high ceramic yield (the ceramic yield at 1000 °C was 74.4%). After shaping with stereolithography, defect-free green bodies could be got. When heated to 1000 °C, the transparent yellow green bodies transformed into black SiC rich ceramic parts and 18.3–25.1% linear shrinkage associated with the precursor-to-ceramic conversion was observed. Because the shrinkage in the pyrolysis stage was nearly isotropic and the shrinkage was lower than other reported data, no obvious deformation or crack was found in the pyrolyzed parts.     

Preparation of high–strength closed–pore foamed ceramics from desalted sea sand at temperatures below 1000 °C

Based on high–temperature sintering with SiC as the foaming agent, the technical potential of preparing foamed ceramics (FCs) from desalted sea sand at temperatures below 1000 °C was studied. Rapid melting of the ceramic bodies at elevated temperatures helped to seal more foaming gas, resulting in a large foaming volume for the FCs. If the interior of the ceramic bodies melted quickly during sintering, the foaming gas was trapped in situ, resulting in a homogenous FC pore structure. By coordinating the borax content and sintering temperature of the green bodies, the melting characteristics of the ceramic bodies could be optimised during sintering, usually producing a large foaming volume and a homogeneous FC pore structure. The FCs sintered from the green bodies with 25–35 wt% of borax at 900–1000 °C obtained high total/closed porosities of (68–75)%/(65–72)%, a relatively dense surface, a homogenous pore structure, and a relatively high compressive strength of 8.1–11.2 MPa.     

Modeling Density Contributions in Preceramic Polymer/Ceramic Powder Systems

A model is presented that examines the mixing of ceramic powders with preceramic polymer binders that are converted to ceramic material on pyrolysis. Such polymer/powder systems, which have applications in the compaction of both SiC and Si₃N₄ powders, can be effective in increasing the green density of die-pressed bodies. This model examines the relative importance of various physical parameters of the components of the system in maximizing the green density of the resulting pyrolyzed body .     

Improved green strength of ceramic bodies through extrusion using hydroxypropyl methylcellulose as binder

Different amounts of hydroxypropyl methylcellulose (HPMC) and starch in the form of powder were utilized as binder in the extrusion of silicon nitride green bodies. Their three-point flexural strength and microstructure of fracture surface are investigated. It is found that HPMC can markedly improve the green strength compared with the use of starch. The bending strength with 10% HPMC addition is 29.3 ± 3.1 MPa, which is approximately 7.5 times that of starch counterpart. The dramatic improvement of strength can be attributed to the rough fiber-like HPMC particles, which were aligned along the direction of extrusion and were pulled out during bending tests. This work represents a step towards a simple but effective way to extrude high-strength ceramic green bodies.     

Direct Coagulation Casting of Silicon Carbide Components

Direct coagulation casting is a novel near-net-shape method for forming ceramic green bodies from homogenous high-solids-loaded particle suspensions. It is based on the principle of the in situ coagulation of a powder suspension via a reaction-rate-controlled internal-enzyme(urease)-catalyzed reaction after casting. Low-viscosity (<3 Pas) suspensions with a high solids loading (>62 vol%) of SiC, boron, and carbon powder mixtures with a high surface area (>7-10 m²/g) have been prepared at pH = 10. Salt ions (up to 1-2 mol/L) are created by the urease-catalyzed decomposition of urea, to destabilize the suspensions. The coagulation kinetics and the strength of the wet green bodies have been investigated. The reaction rate is strongly dependent on the temperature (in the range of 5°-30°C) and the enzyme concentration (for the range of 4-16 units/g SiC) and is independent of the substrate (urea) concentration for urea concentrations of <2 wt%, based on the powder content. The resulting green bodies show no shrinkage during coagulation and 1%-2% linear shrinkage during drying. The compressive strengths of the wet green bodies are as high as 60 kPa and increase as the coagulation time increases. The wet green strength of the coagulated suspensions scales with the solids content, according to a power law with an exponent of 11, in the range of 56-61 vol% solids content. The possibilities of fabricating high-solids-containing complex SiC green and sintered components with homogenous microstructures and high sintered densities are demonstrated.     

Digital light processing of SiC ceramic from allylhydridopolycarbosilane with limited acrylate monomers

Digital light processing of ceramic precursor was used to prepare SiC rich ceramic parts in this study. In order to achieve appropriate light curing rate, the ceramic precursor allylhydropolycarbosilane (LHBPCS) was mixed with acrylate monomers tripropylene glycol diacrylate and trimethylolpropane triacrylate. The content of acrylate monomers was optimized to increase the ceramic yield and reduce the shrinkage during pyrolysis. According to the results of thermogravimetric analysis and photolithography experiment, 15 wt% acrylate monomers was appropriate. 330 mJ/cm² UV irradiation dose was selected for every layer with a thickness of 25 μm, and green bodies with different shapes were successfully printed. During pyrolysis, these printed parts changed from transparent yellow to black accompanying uniform shrinkage. At 1000 °C, the shrinkage was 24.0–26.0%, and crack-free SiC rich ceramic parts with density of 2.11 g/cm³ and chemical formula of SiC_1.31O_0.26 were obtained.     

Preparation of photosensitive SiO2/SiC ceramic slurry with high solid content for stereolithography

Stereolithography is a popular three-dimensional (3D) printing technology, which is widely used for manufacturing ceramic components owing to its high efficiency and precision. However, it is a big challenge to prepare SiC ceramic slurry with high solid content for stereolithography due to the strong light absorption and high refractive index of dark SiC powders. Here, we propose a novel strategy to develop photosensitive SiO₂/SiC ceramic slurry with high solid content of 50–65 vol% by adding spherical silica with low light absorbance and applying a stacking flow model to improve the solid content of the slurry. The as-prepared slurry exhibits excellent stereolithography properties with a dynamic viscosity lower than 20 Pa s and curing thickness more than 120 μm. Therefore, it can be successfully applied for stereolithography-based additive manufacturing of SiC green bodies with large size (100 mm), sub-millimeter accuracy (0.2 mm), and complex structure. The stacking flow model also shows immense potential for the stereolithography of other dark-color ceramics with high solid content.