自蔓延高温合成Y-α/β-Sialon粉末

本文通过组成设计,以Si、Al、Y₂O₃为原料,Si₃N₄为稀释剂,利用自蔓延高温合成法（SHS）制备了Y－α／β－Sialon粉末;并利用XRD、化学分析法分别研究了α－Sialon简称α′）、β－Sialon简称β′）相组成和游离硅含量;且详细讨论了氮气压力、稀释剂含量对生成物Y－α／β－Sialon中的α′、β′相及残余硅含量的影响．     

不同工艺条件下Ca-α-Sialon显微结构的形成与发展

对高x值Ca－α－Sialon系统（Ca_1．8Si_6．6A_l5．4O_1．8N_14．2）用无压烧结的方法得到了具有长颗粒形貌的α－Sialon陶瓷．通过SEM观察研究了升温速度和中间保温等工艺因素对材料显微结构的影响规律,并结合反应过程的研究探讨了在Ca－α－Sialon中长颗粒α－Sialon晶粒的成核与生长机理．结果表明,α－Sialon形成过程中较少的晶核数目及较多的液相量容易得到长颗粒的α－Sialon晶粒,并且中间相的形成与溶解会直接影响晶核数目与液相量．     

AlN-多型体陶瓷的研究Ⅰ.AlN-多型体的形成及致密化

本文采用热压工艺研究了三种AlN－多型体：15R,12H和21R的致密化行为及形成过程．结果表明,AlN－多型体必须在存有少量烧结添加剂的条件下才能烧结致密,在所使用的添加剂中,Sm₂O₃·Al₂O₃为最有效,在加入2．5wt％时能使这三种多型体的密度在1600℃就接近完全致密．15R和12H的形成过程较为相似,分别在1550℃和1600℃之前,15R和12H随温度升高而增加,最高达95wt％以上,但过后随温度增加其量逐渐下降,同时12H和21R分别出现在15R和12H的组份中．21R的形成过程与它们相异甚大,在低温时先形成12H,随温度的增高,12H含量逐渐下降,而21R不断增加,在1750℃以上达100wt％．本文还对AlN－多型体的形成过程进行了讨论．     

添加Y2O3-Dy2O3的AlN陶瓷的烧结特性及显微结构

本文探索了以自蔓延高温（SHS）法合成并经抗水化处理的AlN粉为原料,以Y₂O₃－Dy₂O₃作为助烧结剂的AlN陶瓷的烧结特性及显微结构．结果表明,晶界处存在Dy₄Al₂O₉、Y₄Al₂O₉、DyAlO₃、Dy₂O₃和DyN等第二相物质,随烧结温度变化,第二相的种类、数量和分布不同,显微结构也随之变化,从而影响AlN的热导率．在1850℃下,可获得热导率为148W／m·K的AlN陶瓷．     

燃烧条件对自蔓延高温合成Al2O3/AlB12复相陶瓷粉体特性的影响

以铝、B₂O₃为原料,利用自蔓延高温合成（SHS）制备了Al₂O₃／AlB₁₂复相陶瓷粉体,研究了燃烧条件对粉体特性的影响．结果发现,经球磨处理后,复相陶瓷粉体中Al₂O₃的平均粒径为3～4μm,AlB₁₂的粒度为亚微米级．粉体的比表面积为～1m²／g．燃烧过程中B₂O₃易于挥发,并在合成产物的表层生成B₂O₃和9Al₂O₃·2B₂O₃副产物相．在较低压力的氩气中进行合成,可以减少副产物相,获得纯度较高的复相陶瓷．与实际测量的燃烧温度对比发现,按照化学反应式13Al＋6B₂O₃＝6Al₂O₃＋AlB₁₂,通过热力学计算得到的绝热燃烧温度明显偏高．     

钛掺杂的α-Fe2O3-K2O纳米湿敏陶瓷结构与性能研究

采用硬脂酸凝胶法新工艺在α－Fe₂O₃－K₂O复合体系中掺入TiO₂.XRD、BET比表面吸附、Archimede排水法等手段对掺钛α－Fe₂O₃－K₂O纳米陶瓷分析表征结果表明,适量掺杂TiO₂,材料仍保持α－Fe₂O₃的刚玉结构,且具有很高的热稳定性,但抑制了主晶相晶粒成长,增大了材料比表面积及孔隙率．电性能及湿敏特性测试结果表明,适量掺杂TiO₂,降低了材料固有电阻,显著减小了材料湿滞;认为钛掺杂使材料晶粒细化;从而使K+更加分散地沉积在α－Fe₂O₃晶粒表面非晶壳层中,是改善材料湿滞的主要原因．     

Eu2+在多铝酸钠体系中的发光

应用高温固相法合成了Na的多铝酸盐,并研究了Eu^2＋在体系中的发光性能．结果表明,Na_1＋xMgAl_11－xO₁₇体系在整个组成范围内保持Na的β－Al₂O₃结构不变,而对于Na_1．67－2xBa_xAl1_0．33O₁₇体系,在x＝0．30附近体系结构发生转变,x＜0．30,体系形成Na的外β－Al2O3结构的固溶体,x＞0．30,体系形成Ba的β－Al₂O₃结构的有序体;与体系组成和结构的变化相对应,Eu^2＋的发射能量和发光强度产生相应的变化,在Na的β－Al₂O₃中Eu^2＋存在高、低能两种发射中心;通过系列化研究,获得了新的组成的、具有β－Al₂O₃结构的荧光体Na_0．67Ba_0．50Mg_0．67Al_10．33O₁₇：Eu^2＋,在较低的掺杂浓度（0．05mol）下可以产生较强的发光．     

高温等静压烧结Al2O3-ZrO2纳米陶瓷

本工作用化学共沉淀法制备了平均晶粒尺寸约20nm的20mol％Al₂O₃－ZrO₂复合粒体,不含有Y₂O₃作为四方氧化铝的稳定剂．粉体的煅烧温度为750℃,XRD结果表明,粉体中含100％立方氧化锆相,未发现有Al₂O₃结晶相存在．该粉体用高温等静压方法,在1000℃和200MPa的条件下烧结1h,得到了平均晶粒尺寸为50nm（TEM表征）的致密陶瓷,样品密度为理论密度的98％左右．对样品抛光表面的XRD定量分析结果表明,其抛光表面的相组成为：55％t－ZrO₂－39％m-ZrO₂－6％α-Al₂O₃。     

多层片式电感器用NiCuZn铁氧体的低温烧结

本文利用Bi₂O₃作为烧结促进剂实现了NiCuZn铁氧体在900℃以下烧结．利用TG、DTA、DDTA等分析手段研究Bi₂O₃的低温烧结机理,并确定最佳烧结温度范围在840～900℃之间．X－ray分析结果表明：加入Bi₂O₃后生成另相化合物Bi₃₆Fe₂O₅₇烧结后期少量Fe的固溶有助于稳定高温γ－Bi₂O₃相的立方结构,避免了冷却过程中的晶型转变．Bi36Fe₂O₅₇另相的存在能有效地阻止晶粒长大,从而达到改性的目的．     

Y-α/β-Sialon陶瓷材料及疲劳特性研究

本文通过组份设计,选用Si₃N₄、AIN和Y₂O₃等粉末为原料,在1800～1950℃进行气氛加压烧结（GPS）,制备了性能优良的Y-α/β-Sialon陶瓷材料;利用XRD、EDAX和HREM详细地研究了相组成和晶界特性,其主晶相为β-Sialon和α-Sialon,晶界由少量的J－Y₄Si₂O₇N₂结晶相以及微量的玻璃相构成;并进一步探讨了材料在循环疲劳载荷下Vickers压痕短裂纹扩展特性,结果表明,最大应力强度因子与裂纹扩展速率之间呈V型扩展行为,并对外加应力水平非常敏感．     

α/β-Sialon陶瓷材料及其疲劳寿命研究

通过组成设计,以Si₃N₄、AIN、Al₂O₃和Y₂O₃粉末为原料,采用气氛加压烧结工艺,在1800～1980℃,1．0～3、0MPaN₂压力下烧结,制备了α／β-Sialon陶瓷材料,通过XRD,SEM和HREM等分析可见,其材料的显微结构是由棒状的β-Sialon和近似等轴的α-Sialona组成,在晶界存在微量的结晶相和玻璃相．并进一步研究了α／β-Sialon陶瓷材料的疲劳寿命,实验证明,该材料的疲劳极限约为其静态强度的75％．     

Effect of Different Rare-Earth on Microstructure and Properties of α-Sialon Ceramics

Densified Yb-, Y-, Dy-, Sin- and Nd-α-Sialon ceramics were prepared by two-step hot sintering. The variation of microstructure and properties with different rare-earth was investigated. The ceramics doped with smaller cations （Yb3＋, y3＋ and Dy3＋） are fully composed of α-Sialon, while in the larger cations （Sm3＋ and Nd3＋） doped ceramics also exist a few intergranular phase Mt （Re2Si3-xAlxO3＋xN4-x） in triple-point pockets. With increasing the radius of the rare-earth cations, the elongated α-Sialon grains form instead of the equiaxed grains in Yb-α-Sialon, and the aspect ratio of grains increases. All the ceramics possess high hardness, and the value of 21 GPa is achieved for Yb- and Y-α-Sialon. With increasing the ionic size of rare-earth, the hardness decreases slightly but the toughness tends to increase. Nd-α-Sialon possesses the highest toughness with the value of 5.4 MPa·m^1/2.     

β-赛隆(Sialon)/刚玉复相耐火材料研究

采用氮化反应烧结工艺制备β－Ｓｉａｌｏｎ／刚玉复相耐火材料．结果表明,在低于１４５０～１６００℃下的流动氮气气氛中直接氨化反应一定比例的ＡＩ、Ｓｉ、Ａｌ_２Ｏ_３微粉,以及刚玉细粉和颗粒,可以制备不同Ｚ值的β－赛隆（Ｓｉ_６-ｚＡｌ_ｚＯ_ｚＮ_８-ｚ）／刚玉复相材料．但是,最终产物中的β－赛隆相的Ｚ值与设计值存在偏差,这可能与反应过程有关。不同Ｚ值的β－赛隆／刚玉复相材料均显示良好的抗渣铁侵蚀性．同时抗碱试验表明;当预设计Ｚ值为１．５～２．５时具有良好的抗碱性能,而当预设计Ｚ值等于４时,抗碱性下降,这可能与复相材料中Ｓｉａｌｏｎ含量及其Ｚ值有关．     

（Ca,Mg）—Sialon陶瓷在多元醇及多元醇水溶液润滑下的摩擦学性能

与干摩时相比,三种醇的水溶液都降低了（Ｃａ,Ｍｇ）－Ｓｉａｌｏｎ陶瓷／ＧＣｒ１５的摩擦系数,但都不同程度地增加了陶瓷的磨损体积。所有醇都降低了（Ｃａ,Ｍｇ）－Ｓｉａｌｏｎ陶瓷／ＧＣｒ１５的摩擦系烤及（Ｃａ,Ｍｇ）－Ｓｉａｌｏｎ陶瓷的磨损体积;在乙二醇润滑下（Ｃａ,Ｍｇ）－Ｓｉａｌｏｎ陶瓷／ＧＣｒ１５表现出最低的磨擦系数（０．０６）;（Ｃａ,Ｍｇ）－Ｓｉａｌｏｎ陶瓷在二醇润下,磨损体积由大到小的顺序     

显微结构对Sialon陶瓷室温疲劳短裂纹扩展行为的影响

本文采用不同相组成和不同显微结构的。α-β-Sialon复相陶瓷作为对比试样,以压痕裂纹模拟陶瓷材料本身固有的微小裂纹,通过四点弯曲试样,在相同力学参数条件下,结合扫描电子显微镜对疲劳断口的观察,研究了α-β-Sialon复相陶瓷的室温疲劳短裂纹扩展现象和微观机理．研究发现,长柱状β-Sialon晶粒含量多、长径比大的材料具有较高抵抗疲劳失效的能力·此外,疲劳断口表明,α-β-Sialon复相陶瓷疲劳短裂纹扩展的机制主要有：应力腐蚀、摩擦造成的晶粒桥接弱化和接触损伤．     

复合添加(Ca,Mg)-α-Sialon的晶胞参数研究

利用高分辨率的Ｇｕｉｎｉｅｒ－Ｈａｇｇ相机和计算机控制的底片扫描及数据处理程序系统,测定了复合添加,组份为（Ｃａ_０．５Ｍｇ_０．５）_xＳｉ_{１２－３ｘ}Al_3xＯ_ｘＮ１_６－ｘ（ｘ＝０．３、０．６、１．０和１．４）的α－Ｓｏａｌｏｎ的晶胞参数．材料由热压工艺制备而得．研究结果表明,当ｘ≥１．０时,材料的主晶相为α－Ｓｉａｌｏｎ和含Ｍｇ的ＡlＮ多型体．（Ｃａ,Ｍｇ）－α－Ｓｉａｌｏｎ的晶胞参数明显低于相同组份下的Ｃａ－α－Ｓｉａｌｏｎ的晶胞参数·ＥＤＡＸ的结果进一步给出固溶进入α－Ｓｉａｌｏｎ的包括名义组份中９０％的Ｃａ^＋＋和少量的Ｍｇ^＋＋,而大部分Ｍｇ^＋＋进入ＡlＮ多型体,这一结果为净化α－Ｓｉａｌｏｎ陶瓷的晶界提供了新的有效途径．     

Microstructure control of α-Sialon ceramics by seeding with α-Sialon particles

A proper powder preparation was used to develop -Sialon single crystals as seeds. The microstructure and fracture toughness of seed-containing -Sialon ceramics sintered by hot-pressing were investigated. The specimen without seeding consisted of fine grains and a small amount of coarse grains. Specimens seeded with -Sialon single crystal particles presented a large amount of elongated -Sialon grains. The aspect ratio and the amount of elongated -Sialon grains can be tailored by using different sizes and amounts of the seeds. The fracture toughness of seed-containing -Sialon ceramics is improved, which is attributed to grain pullout and bridging of elongated grains.     

Carbothermal formation and microstrutural evolution of α′-Sialon–AlN–BN powders from boron-rich blast furnace slag

Boron-rich blast furnace slag of low activity is one of the major products created during the separation of iron and boron from ludwigite in a blast furnace process, and the high-efficiency utilisation of its is of great importance to the Chinese boron industry. This paper proposes one new application process to synthesize α′-Sialon–AlN–BN powders by a carbothermal reduction–nitridation method using boron-rich blast furnace slag as the staring material and describes a series of experimental studies that were performed to elucidate the mechanism of phase formation and microstructure evolution during CRN. The experimental results revealed that the phase compositions and microstructures of the synthesized products were greatly affected by the initial compositions ((Ca,Mg)_xSi_12–3xAl_3xO_xN_16–x), x = 0.3–1.8), temperature and holding time. With the compositions shifting from values of x of 0.3–1.8, the relative amount of α′-Sialon, AlN and BN increased gradually, and the amount of α′-Sialon reached a maximum at a value of x of 1.4. The optimal condition for powder synthesis was a temperature of 1480 °C with a holding time of 8 h, under which the crystalline phases included α′-Sialon, AlN, BN and less SiC. More elongated α′-Sialon grains were observed at higher x values and temperatures. During the CRN process, MgAl₂O₄, Mg₂SiO₄, Ca₂Al₂SiO₇, MgSiN₂, β′-Sialon and 27R appeared sequentially as intermediate products. The volatilisation of SiO gas and magnesium vapour resulted in additional weight loss of the samples, which was aggravated with increases in the synthesis temperature and holding time.     

Textured silicon nitride: processing and anisotropic properties

Abstract

Textured silicon nitride (Si₃N₄) has been intensively studied over the past 15 years because of its use for achieving its superthermal and mechanical properties. In this review we present the fundamental aspects of the processing and anisotropic properties of textured Si₃N₄, with emphasis on the anisotropic and abnormal grain growth of β-Si₃N₄, texture structure and texture analysis, processing methods and anisotropic properties. On the basis of the texturing mechanisms, the processing methods described in this article have been classified into two types: hot-working (HW) and templated grain growth (TGG). The HW method includes the hot-pressing, hot-forging and sinter-forging techniques, and the TGG method includes the cold-pressing, extrusion, tape-casting and strong magnetic field alignment techniques for β-Si₃N₄ seed crystals. Each processing technique is thoroughly discussed in terms of theoretical models and experimental data, including the texturing mechanisms and the factors affecting texture development. Also, methods of synthesizing the rodlike β-Si₃N₄ single crystals are presented. Various anisotropic properties of textured Si₃ N₄ and their origins are thoroughly described and discussed, such as hardness, elastic modulus, bending strength, fracture toughness, fracture energy, creep behavior, tribological and wear behavior, erosion behavior, contact damage behavior and thermal conductivity. Models are analyzed to determine the thermal anisotropy by considering the intrinsic thermal anisotropy, degree of orientation and various microstructure factors. Textured porous Si₃N₄ with a unique microstructure composed of oriented elongated β-Si₃N₄ and anisotropic pores is also described for the first time, with emphasis on its unique mechanical and thermal-mechanical properties. Moreover, as an important related material, textured α-Sialon is also reviewed, because the presence of elongated α-Sialon grains allows the production of textured α-Sialon using the same methods as those used for textured β-Si₃N₄ and β-Sialon.