Effect of Seeding on the Microstructure and Mechanical Properties of α-SiAlON: III, Comparison of Modifying Cations

Single-phase in situ toughened SiAlON ceramics containing various modifying cations and single-crystal seeds were studied. The modifying cations include rare-earth cations from the smallest to the largest allowed in the α-SiAlON structure (Yb to Y, to Nd), and from monovalent to trivalent (Li to Ca, to rare earths). At low seeding levels, the aspect ratio of grains increases with the size of modifying cations, giving rise to rather different appearances of the microstructure in different SiAlONs. A one-to-one correspondence between seed crystals and large grains at low seeding levels is also observed. An optimal amount of seeds is required to maximize the fracture toughness, which is controlled by grain pullout with the fracture energy that scales with the fraction of elongated grains, their width, and their aspect ratio. The optimal amount of seeds required to reach maximal toughening increases with the aspect ratio of grains and is the lowest (1%) in Y- and Yb-SiAlONs.     

In situ synthesis mechanism of 15R–SiAlON reinforced Al2O3 refractories by Fe–Si liquid phase sintering

15R–SiAlON bonded Al₂O₃ refractories were successfully synthesized using ferrosilicon nitride and alumina by liquid phase sintering. The phase composition and morphology were analyzed by means of X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results show that 15R–SiAlON reinforcement can be in situ obtained in the specimens with 5 wt% ferrosilicon nitride at 1500°C to 1700°C in flowing N₂ of 0.1 MPa. The morphology of 15R–SiAlON is strongly dependent on the morphology of intermediate AlON phases formed at different temperatures. Fe–Si alloys from ferrosilicon nitride form liquid phase and accelerate the formation of 15R‐SiAlON, in which process the wettability of Fe–Si alloys is improved by the increase in Si content, carbon coating on particle, solution process and reactions. The 15R–SiAlON reinforced Al₂O₃ refractory materials possess high cold crushing strength of 138‐171 MPa.     

硅铝凝胶粉结合SiAlON增强A1_2O_3-SiC-C浇注料

以电熔致密刚玉和碳化硅为骨料,硅铝凝胶粉、氮化硅粉、硅粉为细粉,制成SiAlON增强Al2O3-SiC-C浇注料,研究了硅铝凝胶粉的加入量分别为1%、3%、5%(质量分数,下同)时对此浇注料的烧结性能、力学性能的影响。结果表明:采用硅铝凝胶粉取代纯铝酸钙水泥作结合剂,可使SiAlON增强Al2O3-SiC-C浇注料在经中温、高温热处理后的常温抗折强度及耐压强度较大提高,中温、高温强度提高幅度更大。另外,随着硅铝凝胶粉加入量的增加,浇注料的常温及高温强度呈先增大而后减小的趋势。由X射线衍射和扫描电镜分析结果可知,硅铝凝胶粉的加入既有利于降低βSiAlON的生成温度,又可以减少材料中的低熔物质。分布均匀、发育良好的粒状βSiAlON的形成是SiAlON增强Al2O3-SiC-C浇注料较水泥结合浇注料强度高的根本原因。     

UHMWPE-SiAlON陶瓷摩擦副的生物摩擦学特性及机理的研究

为了探索ＳｉＡｌＯＮ陶瓷与超高分子量聚乙烯（ＵＮＭＷ－ＰＥ）组合作为人工关节置换材料的可能性,利用Ｆａｌｅｘ摩擦磨损实验机测定了ＳｉＡｌＯＮ陶瓷与ＵＨＭＷＰＥ在３７℃、血浆润滑条件下的生物摩擦学性能。同时,在扫描电镜下观察了摩擦副表面形貌。实验结果表明ＵＨＭＷＰＥ－ＳｉＡｌＯＮ陶瓷摩擦副的摩擦系数为０．０６,ＵＨＭＷＰＥ的磨损系数小于８．４５×１０－１０ｍｍ３／（Ｎ·ｍ）。表面轮廓仪对摩擦磨损前后ＳｉＡｌＯＮ陶瓷表面测试,未发现明显变化,说明陶瓷磨损甚微。根据ＸＰＳ分析结果,提出了生物摩擦磨损机理。     

氮化物结合碳化硅耐火材料的研究现状

分别概述了以氮化硅、赛隆和氧氮化硅作为结合相 的SiC材料的结构特点、理化性能、生产工艺和应用情况,详细 介绍了国内这3种材料的研究现状,并对今后氮化物结合SiC 材料的研究内容提出了自己的观点。     

Hollow Beads Composed of Nanosize Ca α-SiAlON Grains

Carbothermal reduction—nitridation (CRN) of SiO₂ is an attractive method to manufacture Si₃N₄ powders with controlled grain morphology. Moreover, β-SiAlON powders could also be synthesized from either pure powder mixture or some inexpensive raw minerals by CRN and the resulting powders favored the sintering of SiAlON product. However, there have been few works on preparing α-SiAlON powders so far. In this work, Ca α-SiAlON powder was synthesized by CRN of a SiO₂—Al₂O₃—CaCO₃ mixture. An unusual morphology of hollow beads 200 to 500 nm in diameter with a great deal of nanosize α-SiAlON particles around 10 to 30 nm in diameter was observed from the resultant Ca α-SiAlON powders, which has not been reported for SiAlON ceramics before.     

天然原料还原氮化合成β′-SiAlON反应动力学研究进展

介绍了β′SiAlON的合成方法及其合成原料,并将合成方法分成还原剂外加法和内加法(即有机插层法)两类加以介绍。将各动力学参数(原料组成、添加剂及杂质、反应温度及时间、反应气氛、反应物颗粒尺寸等)对天然原料碳热还原氮化合成β′SiAlON的反应结果的影响进行了详细阐述,叙述并讨论了对该合成反应的不同反应机理及动力学模型的研究进展,并针对该领域的研究现状提出了一些展望。     

Spark plasma sintering of SiAlON ceramics

Investigated was the spark plasma sintering (SPS) of sialon ceramics from SHS-produced powders. Experimentally established were (a) sintering temperatures that ensure a required density, phase composition, and microstructure of sintered multicomponent sialon ceramics, (b) individual stages of the SPS process, and (c) the effect of starting powder composition on the phase composition and microstructure of sintered sialon ceramics.      

不同烧结气氛下SiAlON结合刚玉材料的烧结行为和显微结构

以α-Al_2O_3微粉和Si_3N_4粉为主要原料,分别以Al粉、AlN粉、SiO_2微粉、Al粉 Ce_2O_3粉、Al粉 Si粉 Ce_2O_3粉作添加剂,在空气中裸烧(氧化气氛)和空气中埋炭(还原气氛)的条件下,分别进行1350℃、1450℃、1550℃、1600℃保温6h的热处理后,制备了SiAlON结合刚玉复相材料,并研究了烧结气氛、烧结温度和添加剂种类对试样烧结行为和显微结构的影响。结果表明添加稀土氧化物Ce_2O_3或少量SiO_2微粉能促进材料的烧结;在氧化气氛下,以SiO_2微粉为添加剂的试样的致密化程度随处理温度的升高而降低,而在埋炭还原气氛下,其致密化程度随温度的升高而提高;SEM观察还表明,含不同添加剂的试样在不同气氛中处理后的显微结构也不同。     

Fe2O3对β-SiAlON结合刚玉材料性能的影响

以白刚玉、硅粉、铝粉和α-Al2O3微粉等为原料,在氮化炉中于1460℃原位合成的β-SiAlON-刚玉复合材料,其氮含量(w)为3%,显气孔率为11.8%,体积密度为3.22g.cm-3,耐压强度为106.5MPa。在此基础上,用2%的Fe2O3替代白刚玉,在相同条件下合成的复合材料,其氮含量下降为2.4%,显气孔率和体积密度分别为12.4%和3.21g.cm-3,耐压强度增大为174.5MPa。试样的XRD分析表明,这两个试样的主晶相均为刚玉和z=3的β-SiAlON;未加Fe2O3的试样杂质很少,而加Fe2O3的试样中杂质较多,杂质主要为莫来石,这说明加入的Fe2O3阻碍了材料的氮化。另外,其β-SiAlON相中除了有Si3Al3O3N5外,还有Si4.69Al1.31O1.31N6.69。