硅粉常压直接氮化制备氮化硅粉的研究

以平均粒径为2.8μm的硅粉为原料,添加氮化硅粉作为稀释剂,对常压氮气下直接氮化制备Si3N4粉的工艺进行了研究,借助于氮氧测定仪、XRD、SEM等检测方法,分析了硅粉常压直接氮化制备Si3N4粉过程中稀释剂种类、稀释剂添加比例、氮化温度、氮化时间等因素对硅的氮化过程的影响.研究结果表明:硅粉在流动常压氮气下,当氮化温度高于1410℃时,硅的转化率迅速增加,氮化产物中β相含量也增加;通过控制稀释剂的添加种类和添加比例、氮化时间和氮化温度,可合成高α相含量的Si3N4.采用平均粒径为2.8μm的硅粉,在常压氮气下,当添加30%的α-Si3N4粉作为稀释剂、氮化温度为1550℃、氮化时间为10min时,合成了氮含量为39.4%,游离硅为0.7%,主要为α相、含部分β相的Si3N4粉.     

硅粉直接氮化反应合成氮化硅研究

研究了硅粉直接氮化反应合成氮化硅粉末的工艺因素(包括硅粉粒度、氮化温度、成型压力、稀释剂含量等),借助XRD,SEM等测试手段测定和观察了氮化产物的物相组成和断口形貌.研究结果表明:硅粉在流动氮气氛下,高于1200℃氮化产物中氮含量明显增加;在氮化反应同时还伴随着硅粉的熔结过程,它阻碍硅粉的进一步氮化,其影响程度与氮化温度、氮化速度,素坯成型压力及硅粉粒度等工艺因素有关.在硅粉素坯中引入氮化硅作为稀释剂,提高了硅粉的氮化率,使产物中残留硅量降低;同样在实际生产中可以通过控制适当热处理制度(如分段保温、慢速升温),达到硅粉的完全氮化.在生产中批量合成了含氮量为32.5%,残留硅量为0.05%,主要为α相,含少量β相的针状、柱状的氮化硅.     

硅粉氮化反应合成氮化硅

研究了硅粉直接氮化反应合成氮化硅粉末的工艺因素（包括硅粉粒度、氮化温度、成型压力、稀释剂含量等），借助XRD、SEM等测试手段测定和观察了氮化产物的物相组成和断口形貌。研究结果表明：硅粉在流动氮气氛下，高于1200℃氮化产物中氮含量明显增加；在氮化反应同时还伴随着硅粉的熔结过程，它阻碍硅粉的进一步氮化，其影响程度与氮化温度、氮化速度，素坯成型压力及硅粉粒度等工艺因素有关。在硅粉素坯中引入氮化，其影响程度与氮化温度、氮化速度，素坯成型压力及硅粉粒度等工艺因素有关。在硅粉素坯中引入氮化硅作为稀释剂，提高了硅粉的氮化率，使产物中残留硅量降低；同样在实际生产中可以通过控制适当热处理制度（如分段保温、慢速升温），达到硅粉的完全氮化。在生产中批量合成了含氮量为32．5％，残留硅量为0．05％，主要为α相，含少量β相的针状、柱状的氮化硅。     

硅铁粉粒度对合成氮化硅铁的影响

采用FeSi75为原料,利用直接氮化合成法制备了氮化硅铁粉末,研究了中位径(d50)分别为13.41μm、8.023μm和5.229μm的3种硅铁粉分别在1150℃、1250℃和1350℃保温9h处理后的氮化规律。借助XRD、SEM等测试手段测定和观察了产物的物相组成和显微形貌。结果表明:较细的硅铁粉(d50=5.229μm)氮化时,反应快速、剧烈,导致烧结严重,氮化效果差,而较粗硅铁粉(d50=13.41μm)氮化效果较好;较细硅铁粉氮化后易于形成须状、纤维状和柱状氮化硅晶体,较粗硅铁粉氮化后易于形成球状氮化硅团聚体。制备的氮化硅铁中有大量充满氮化硅的孔洞,产物中的Fe3Si与FexSi被其包围,这种结构有利于体现氮化硅铁的优异性能。     

低成本制备氮化硅材料的研究

采用工业用纯净水作分散介质,制备了氮化硅陶瓷试样。并对试样进行了力学性能的测试,结果表明其常温力学性能指标略低于用酒精作分散介质材料的试样,断裂韧性为6.42MPa·m~(1/2),硬度为1522kgf·mm~(-2),证明了这种材料在常温下是可以使用的。     

硅粉氮化输送床内气固反应过程数值模拟

以单个硅颗粒氮化反应缩核模型为基础,本文建立了硅颗粒在输送床内反应、辐射与对流传热耦合的数学模型,并借助CFD软件FLUENT对输送床内能质传输过程进行了数值模拟,分析了输送床壁面温度、氮气流量、预热温度、硅粉粒径等因素对输送床内温度场和硅粉氮化率的影响。在数值计算域内将单个颗粒反应过程转化为颗粒群整体反应过程,实时监测颗粒粒径及未反应硅颗粒粒径,为数值模拟颗粒流反应提供一种新思路。当壁面温度高于1723K时,输送床内会出现一高温区加速硅粉氮化反应;反应温度越高、颗粒粒径越小,氮化过程越剧烈,硅粉到达完全氮化所需时间越短。模型表明为使粒径为2.5μm的硅粉达到完全氮化且输送床内最高温度不超过氮化硅的分解温度2173K,应控制输送床壁面温度在1773K,氮化时间在170s以上,预热温度在1273K,粉气质量比为0.2,稀释剂比例为0.5~1。     

不同添加剂对氮化硅陶瓷氧化行为的影响

对Si-Al-Y-O-N系统气压烧结的致密氮化硅陶瓷的氧化研究表明,材料在1100～1400℃温度下氧化,符合抛物线氧化规律。在此温度范围内,氧化活化能为600～730kJ/mol。AlN的引入对材料在低温段(800～1000℃)的抗氧化能力有较大影响。由于在晶界存在易氧化的第二相物质,含AlN作添加剂的氮化硅材料在低温段有较明显的氧化,氧化呈线性规律。     

Additive manufacturing of silicon nitride ceramics: A review of advances and perspectives

Silicon nitride (Si₃N₄) ceramic has been widely applied in various engineering fields. The emergence of additive manufacturing (AM) technologies provides an innovative approach for the fabrication of complex-shaped Si₃N₄ ceramic components. This article systematically reviews the advances of the AM of Si₃N₄ ceramic in recent years and forecasts the potential perspectives in this field. This review aims to motivate future research and development for the AM of Si₃N₄ ceramic.     

氮化硅陶瓷粉料造粒的研究进展

氮化硅陶瓷具有高强度、高硬度、良好的断裂韧性等优异力学性能,并具有独特的自润滑性能,而日益受到重视.氮化硅陶瓷粉料是制备氮化硅陶瓷的关键原料,粉料的处理方式是影响陶瓷性能的关键步骤.本文介绍了目前较为常见的氮化硅陶瓷粉料的处理方法,并对各处理工艺的优缺点进行了分析,重点阐述了喷雾造粒工艺及其目前研究进展.最后分析了目前氮化硅粉料处理方法存在的问题,并对氮化硅粉料处理方法的发展提出了展望.     

Effect of Acid Cleaning and Calcination on Rheological Properties of Concentrated Aqueous Suspensions of Silicon Nitride Powder

The powder characteristics of two types of Si₃N₄ (referred to as FD1 and FD2), as well as the rheological properties of their aqueous suspensions, were studied in this paper. There are distinctive differences in size distribution, soluble counterions, and surface groups. Highly concentrated aqueous slurries could not be prepared from these two as-received powders. Acid cleaning and calcination improved the solids loading of their aqueous slurries, but the improvement varied with the powder. For the as-received FD1 powder, poor dispersibility was caused by high-valence counterions, which can be eliminated through acid-cleaning. However, for the as-received FD2 powder, it was the surface group of amine structures and carbon-hydrogen bonding that limited the dispersibility. The calcination of FD2 can remove the amine structure and carbon-hydrogen bonding and improve the slurry's rheological properties almost perfectly. For acid-cleaned and calcined FD1, and calcined FD2, the solids loading of their aqueous suspensions reached 50 vol% with a viscosity below 300 mPa·s.     

Reactivity of Aluminum Nitride Powder in Aqueous Silicon Nitride and Silicon Carbide Slurries

The reactivity of AlN powder with water in supernatants obtained from centrifuged Si₃N₄ and SiC slurries was studied by monitoring the pH versus time. Various Si₃N₄ and SiC powders were used, which were fabricated by different production routes and had surfaces oxidized to different degrees. The reactivity of the AlN powder in the supernatants was found to depend strongly on the concentration of dissolved silica in these slurries relative to the surface area of the AlN powder in the slurry. The hydrolysis of AlN did not occur if the concentration of dissolved silica, with respect to the AlN powder surface, was high enough (1 mg SiO₂/(m² AlN powder)) to form a layer of aluminosilicates on the AlN powder surface. This assumption was verified by measuring the pH of more concentrated (31 vol%) Si₃N₄ and SiC suspensions also including 5 wt% of AlN powder (with respect to the solids).     

Review of additive manufacturing and densification techniques for the net- and near net-shaping of geometrically complex silicon nitride components

Silicon nitride (Si₃N₄) is an advantageous material due its unique combination of mechanical, thermal, chemical, and electrical properties both at ambient and elevated temperatures. Because of these properties there are a wide range of applications for Si₃N₄ components. Applications include heat exchangers, environmental barrier coatings, osteointegration scaffolds, radomes, and integrated circuitry. Such applications often require geometric complexity for efficient and/or effective operation. However, traditional ceramics processing methods such as hot-pressing or die extrusion are typically limited to simple axis-symmetric shapes. With the advent of additive manufacturing, there has been significant advancement into the forming of geometrically complex Si₃N₄ components. This review documents additive manufacturing advancements that have demonstrated, or are capable of, fabricating Si₃N₄ components with complex geometry.     

多孔网状Si3N4陶瓷增强体的制备

选用具有连通气孔的网状聚氨酯海绵作为骨架,利用有机泡沫浸渍的Si3N4浆料工艺,以Al粉、Al2O3和ZrO2作为Si3N4陶瓷材料的烧结助剂,采用2次挂料及2步烧结工艺制备了性能良好的多孔陶瓷骨架。在相同烧结工艺条件下,多孔陶瓷的抗压强度随着孔隙率的下降逐渐增加。当烧结温度为1400℃时,多孔陶瓷具有最佳的烧结效果,既能保持很高的通孔率,又保证了材料具有较高的抗压强度。     

Oxidation and Volatilization of Silica Formers in Water Vapor

At high temperatures, SiC and Si₃N₄ react with water vapor to form a SiO₂ scale. SiO₂ scales also react with water vapor to form a volatile Si(OH)₄ species. These simultaneous reactions, one forming SiO₂ and the other removing SiO₂, are described by paralinear kinetics. A steady state, in which these reactions occur at the same rate, is eventually achieved. After steady state is achieved, the oxide found on the surface is a constant thickness, and recession of the underlying material occurs at a linear rate. The steady-state oxide thickness, the time to achieve steady state, and the steady-state recession rate can be described in terms of the rate constants for the oxidation and volatilization reactions. In addition, the oxide thickness, the time to achieve steady state, and the recession rate also can be determined from parameters that describe a water-vapor-containing environment. Accordingly, maps have been developed to show these steady-state conditions as a function of reaction rate constants, pressure, and gas velocity. These maps can be used to predict the behavior of SiO₂ formers in water-vapor-containing environments, such as combustion environments. Finally, these maps are used to explore the limits of the paralinear oxidation model for SiC and Si₃N₄.     

Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: II, Dispersion of the Powder

A novel dispersant—O-(2-aminopropyl)-O'-(2-methoxyethyl)-polypropylene glycol (AMPG)—was developed to disperse submicrometer-sized Si₃N₄ powder in nonaqueous media, based on the surface chemistry of the powder. The dispersing phenomena and mechanisms have been studied systematically, both in model systems (using atomic force microscopy and ellipsometry) and in powder systems (using rheological behavior and adsorption isotherms). The results from the model systems correlated well with those from wet powder systems. It is demonstrated that highly concentrated (with a solids volume fraction of >0.50) and colloidally stable nonaqueous Si₃N₄ suspensions can be realized using AMPG.     

Effect of Fabrication Process on Whisker Growth in Si3N4 Foam Ceramics

采用直接起泡法,通过氮化硅颗粒稳定泡沫机制制备氮化硅泡沫陶瓷,研究了烧结温度、保温时间、烧结氮气压、烧结助剂（Al2O3＋Y2O3）添加量以及 Al2O3与 Y2O3质量比对氮化硅泡沫陶瓷中晶须生长的影响,分析了泡沫陶瓷的微观结构。结果表明：通过工艺条件的控制可得到由长柱状β-Si3N4晶粒构成的显微结构;当烧结温度为 1750 ℃、保温时间为 4 h、烧结气压为 0.9 MPa、烧结助剂添加量为 6% （质量分数）、Al2O3与 Y2O3质量比为 1：1 时,β-Si3N4晶粒的长径比达到 12 以上