钛铁矿研磨-浸出耦合工艺中陶瓷磨球磨损和腐蚀行为

在硫酸法钛白研磨-浸出耦合工艺条件下,研究了4种常用陶瓷材料磨球,即氧化锆(ZrO₂)、氧化铝(Al₂O₃)、玛瑙球(SiO₂)和氮化硅(Si₃N₄)的腐蚀和磨损行为及其共同作用规律。结果表明,在磨浸耦合体系中,氮化硅球受腐蚀作用最明显,其次是氧化铝球,而氧化锆球和玛瑙球受腐蚀作用较小。氧化锆球和玛瑙球磨损主要表现为球球碰撞和表面切削;氧化铝球为磨料磨损,矿物的引入会增加磨球的失重速率;氮化硅球由于受到腐蚀和磨料磨损共同作用,导致其表面剥落脱离而产生明显磨损。4种陶瓷磨球因物理磨损造成的磨球失重率均在80%以上,其中氧化铝球和氮化硅球受腐蚀和磨损协同作用明显。氧化铝球和氮化硅球的磨浸失重速率分别为1.76 和14.52 mg·cm^-2·d^-1,远高于氧化锆球和玛瑙磨球。研究结果为研磨-浸出耦合工艺中磨球材料的选择提供了依据。     

氮化硅陶瓷牙科修复材料研究进展

氮化硅具有比氧化铝、氧化锆等牙科陶瓷修复材料更好的力学性能、化学稳定性和生物相容性,已经用于生物骨科修复.近年来陆续有学者将氮化硅陶瓷引入到牙科修复领域,文章在介绍氮化硅陶瓷性能特点的基础上,综述了氮化硅陶瓷牙科种植体、氮化硅桩核冠及氮化硅饰面瓷的研究进展,并展望了氮化硅在牙科修复领域的未来研究方向.     

生物陶瓷作为人体植入假体应用的研究现状及展望

对磷酸钙生物陶瓷材料、氧化铝生物陶瓷材料、氧化锆生物陶瓷材料、氮化硅生物陶瓷材料等材料作为人体骨替代材料应用的优缺点进行了综述,对其今后的研究方向做了一定的阐述。并介绍了一些具有发展前景的复合生物陶瓷和新型生物陶瓷,分析了置换关节术后所面临的部分问题及可能的解决办法。     

Fabrication and mechanical properties of nacre-like alumina with addition of silicon nitride

How to deal with the brittleness of ceramic materials is always one of the hot topics in the field of materials science. Design of layered ceramics with textured structure is one of the effective methods to improve their fracture toughness. The introduction of additives as interlayer phases can balance fracture toughness and flexural strength. However, the research about addition of interlayer phases and their mechanisms in the layered ceramics is still limited. In this work, nacre-like alumina ceramics were successfully fabricated by freeze casting followed by hot pressing. Silicon nitride was incorporated as the interlayer phase, and the effect on the mechanical properties of the nacre-like alumina was investigated. The addition of silicon nitride was beneficial to improvement of interlayer bonding between the alumina layers due to formation of sialon phase, leading to increase of flexural strength but decease of fracture toughness. When the content of silicon nitride was 3.3 wt%, flexural strength and fracture toughness of the sample was 468 MPa and 6.2 MPa m^1/2, respectively. Compared with the sample without silicon nitride, the flexural strength was enhanced significantly. Additionally, both flexural strength and fracture toughness were improved as compared the sample without any additives. This work can provide available references for design and fabrication of high-strength and high-toughness ceramics by properly tuning the layer structure and interlayer phase composition.     

Mechanical properties of silicon nitride rolling elements in dependence of size and shape

Silicon nitride rolling elements for hybrid bearings (rollers, two sizes of balls and plate material as a reference) made from the same material lot and using the same sintering route are investigated in regard to their microstructure and their mechanical properties. For the first time, a direct comparison of the surface strength of the components as well as of their fracture toughness is enabled by recently developed testing methods for balls and rollers.It was found that the microstructure of these material variants influences the fracture toughness up to about 10%. In addition, due to the different surface finish, the surface strength of the different rolling elements (made of the same material) is very different. The differences may reach up to 100% and more.     

Toughness measurement on ball specimens. Part II: Experimental procedure and measurement uncertainties

The “Surface Crack in Flexure” method is widely used for fracture toughness (K_Ic) determination of ceramics. In part I of the paper we developed the theoretical fundamentals to apply this procedure to ceramic balls by using the stress application as developed for the so-called “Notched ball test”. The new test (SCF-NB) can be used to test spherical components without the need to cut out special specimens such as bending bars. In this work the practical part is presented including suggestions for crack introduction and specimen preparation and possible measurement errors are discussed. It is concluded that a measurement error less than ±5% is possible.Experiments on balls and bars made from the same silicon nitride ceramic indicate that SCF-NB delivers the same K_Ic-values as standardised measurements on bars. Additionally, K_Ic-values obtained for silicon carbide, alumina and zirconia ceramics are presented. They coincide with K_Ic-data from the literature.     

Reliability Analysis of Structural Ceramics Subjected to Biaxial Flexure

Sintered alumina and silicon nitride were tested in uniaxial (four-point and three-point bend) and biaxial (uniformpressure-on-disk) flexure tests in inert conditions. Fracture origins were identified to be surface flaws in alumina and subsurface pores in silicon nitride. Batdorf's statistical fracture theory and two different fracture criteria, the critical normal stress criterion and a noncoplanar strain energy release rate criterion, were used to examine size and stress-state effects on fracture strengths of the two ceramics. Size effects assessed in four-point and three-point bend tests were in good agreement with the theoretical predictions for both ceramics. Measured biaxial strengths of alumina were in good agreement with the prediction when a noncoplanar strain energy release rate criterion and random surface flaw orientations were assumed. On the other hand, biaxial fracture strength of the silicon nitride was consistent with a prediction based on preferred flaw orientation (i.e., normal to the principal stress in the disks) and the normal stress fracture criterion. Orientation distributions of the fracture planes assessed from the fracture patterns of the disks supported the assumptions of random flaw orientations (alumina) and the preferred flaw orientations (silicon nitride), respectively, for the two ceramics. The preferred flaw orientation in silicon nitride is suggested to originate at subsurface pores as a result of crack nucleation in the plane of maximum tensile stress concentration, i.e., a diametral plane normal to the maximum principal stress.     

髋关节整体替代陶瓷材料

许多材料在医学领域应用广泛,例如,整体替换硬组织或软组织的元件(如骨盆、骨头、关节、植牙等)、修补、诊断或矫正仪器(如起搏器、心脏阀等)。这些材料不仅要有好的力学性能,还要保持长期稳定,不能与人体相排斥。由于陶瓷材料在生理环境中具有强度高、生物相容性强和稳定性好的优点,人们研究用陶瓷材料替换骨骼。从20 世纪70 年代起,欧洲人用陶瓷组件置换整个髋关节。这些组件主要由氧化铝和氧化锆单体制成。然而,在有水环境中,氧化锆会发生低温降解。目前人们的研究重点在于提高陶瓷组件的强度和耐磨性,同时缩小其尺寸并延长其使用寿命。研究中使用的材料是氧化锆增韧的氧化铝复合陶瓷和其它氧化铝复合陶瓷,不再是单体陶瓷。另外,还可以使用氧化铝和氧化锆功能梯度复合材料。该梯度材料可以利用电泳沉积法(EPD)制得,其表面为纯氧化铝,中心部分为均匀的氧化铝、氧化锆复合材料,中间过渡部分是呈连续梯度渐变的氧化铝、氧化锆复合材料,烧成后会产生剩余热应力。设计这样的梯度结构是为了使复合材料具有最大表面压应力和最小内部张应力,与纯氧化铝组件相比,提高了强度和耐磨性。     

半导体集成电路用表面钝化膜的研究

对高性能高可靠性集成电路来说，表面钝化已成为不可缺少的工艺措施之一。本文分析了目前应用最广泛的几种无机表面钝化膜（SiO2,Al2O3和Si3N4)的特点，并指出氮化硅薄膜是半导体集成电路中最具应用前景的表面钝化材料，发展低温的热化学气相沉积（CVD）工艺来沉积氮化硅表面钝化膜是集成电路发展的必然趋势，而开发新的能满足低温沉积氮化硅薄膜的硅源，氮源前驱体是解决这一难题的有效方法，并对这些前驱体物质的设计原则进行了阐述。     

Pseudoplastic deformation pits on polished ceramics due to cavitation erosion

In a previous study, pseudoplastic deformation pits created by cavitation exposure were reported in silicon nitride and zirconia. In this research, further comparison of the size and number of pits between several silicon nitride and zirconia materials is carried out. The pits are larger and much more numerous in silicon nitride than in zirconia although silicon nitride is harder than zirconia. An explanation of this phenomenon is given. Also, in the previous study it was reported that apparently a partially stabilized zirconia with yttria oxide developed a delay in the phase transformation from tetragonal to monoclinic after being exposed to cavitation. In this research, further experiments related with this phase transformation delay are carried out. Also, the phase transformation is verified with X-ray diffraction analysis. It is concluded that the “activation” of the partial stabilized zirconia happens regardless of the oxide used to stabilize it.     

Temperature Dependence of Young's Modulus and Internal Friction in Alumina, Silicon Nitride, and Partially Stabilized Zirconia Ceramics

The temperature dependence of Young's modulus and internal friction (Q⁻¹)in alumina, silicon nitride, and partially stabilized zirconia (Y-PSZ) ceramics was studied. Little change in Q⁻¹ was found for alumina, whereas Q⁻¹ for silicon nitride ceramics increased above 700°C. The Q⁻¹ of Y-PSZ increased markedly with increasing temperature up to a peak at ∼200°C.     

碳化硅对低水泥结合氧化铝空心球浇注料性能的影响

以3种粒度级别的氧化铝和氧化铝微粉为原料,以铝酸钙水泥为结合剂,采用振动浇注成型的方法制备了低水泥结合氧化铝空心球浇注料。利用耐火材料检测设备和扫描电子显微镜(SEM)研究了加入碳化硅对低水泥氧化铝空心球浇注料性能及微观结构的影响。研究结果表明,适量加入碳化硅对提高该种浇注料的体积密度、常温耐压强度和热震稳定性有利。     

Accelerated wear of ceramic balls

The results of studies on the parameters controlling the rate of material removal from the surface of silicon nitride balls are presented. They indicate that the rotational speed and the lubricating fluid used as a medium to introduce abrasive particles into the contact zone are the most important parameters controlling the rate of grinding. Load and contact configuration, although playing some role in the process of material removal, are of less importance. The results obtained could have some significance for surface finish of engineering elements made of ceramics.     

Effect of temperature on the pre-creep mechanical properties of silicon nitride

The elasto-plastic properties and contact damage evolution of a commercial polycrystalline silicon nitride are evaluated as a function of temperature up to 1000 °C, using a recently developed method combining Hertzian indentation and FEM simulation. The results of the study are compared to existing data for other ceramic materials such as alumina and zirconia. Silicon nitride is found to exhibit an excellent combination of elasto-plastic properties in the pre-creep temperature range and good contact damage resistance. These qualities make this material ideal for high temperature applications in general, and in particular to be used in spherical indenters for the evaluation of mechanical properties of other materials at elevated temperature using the procedure applied in this work.     

Strength Measurement of Ceramic Spheres Using a Diametrally Compressed "C-Sphere" Specimen

A "C-sphere" specimen geometry was conceived and developed to measure failure stress of bearing-grade silicon nitride (Si₃N₄) balls caused by tension at the ball's surface. The induced method of fracture also allows for the study of surface-located strength-limiting flaws in ceramic spheres. A slot is machined into the balls to a set depth to produce the C-sphere geometry. A simple, monotonically increasing uniaxial compressive force produces an increasing tensile stress at the C sphere's outer surface that ultimately initiates fracture. The strength is determined using a combination of failure load, C-sphere geometry, and finite element analysis. Additionally, the stress field was used to determine the effective areas and effective volumes of a C-sphere as a function of Weibull modulus. To demonstrate this new specimen, C-sphere flexure strength distributions were determined for three commercially available bearing-grade Si₃N₄ materials (NBD200, SN101C, and TSN-03NH), and differences among their characteristic strengths and Weibull moduli were found.     

Fibrous Monolithic Ceramics: I, Fabrication, Microstructure, and Indentation Behavior

Monolithic ceramics have been fabricated from coated green fibers to create fibrous microstructures. The fibrous monoliths consist of high aspect ratio polycrystalline regions (cells) of a primary phase regions (cell boundaries) designed to improve fracture resistance. The cells are the remnants of the green fiber which consists of ceramic powder and a polymer binder. The coating applied on the green fiber forms the cell boundaries. Fabrication and microstructure are described for fibrous monoliths in the SiC/graphite, silicon nitride/BN, alumina/alumina–zirconia, alumina/aluminum titanate, alumina/nickel and Ce-TZP/alumina–Ce–zirconia systems. The SiC/graphite fibrous monolith displays noncatastrophic failure in flexure, with shear delamination along the weak graphite layers. Indentations in SiC/graphite cause cells to spall, with crack arrest and extrusion of graphite from the cell boundaries. Crack deflection and spalling of cells are also observed in alumina/alumina–zirconia fibrous monoliths. In the Ce-TZP/alumina system, transformed regions around indentations are significantly modified by the alumina-containing cell boundaries.     

Investigation of the effect of ZrO2 and ZrO2/Al2O3 additions on the hot-pressing and properties of equimolecular mixtures of α- and β-Si3N4

In this work, hot-pressing of equimolecular mixtures of α- and β-Si₃N₄ was performed with addition of different amounts of sintering additives selected in the ZrO₂–Al₂O₃ system. Phase composition and microstructure of the hot-pressed samples was investigated. Densification behavior, mechanical and thermal properties were studied and explained based on the microstructure and phase composition. The optimum mixture from the ZrO₂–Al₂O₃ system for hot-pressing of silicon nitride to give high density materials was determined. Near fully dense silicon nitride materials were obtained only with the additions of zirconia and alumina. The liquid phase formed in the zirconia and alumina mixtures is important for effective hot-pressing. Based on these results, we conclude that pure zirconia is not an effective sintering additive. Selected mechanical and thermal properties of these materials are also presented. Hot-pressed Si₃N₄ ceramics, using mixtures from of ZrO₂/Al₂O₃ as additives, gave fracture toughness, K_IC, in the range of 3.7–6.2 MPa m^1/2 and Vicker hardness values in the range of 6–12 GPa. These properties compare well with currently available high performance silicon nitride ceramics. We also report on interesting thermal expansion behavior of these materials including negative thermal expansion coefficients for a few compositions.     

氮化硅陶瓷中压注塑成型技术(MPIM)研究及进展

首次采用中压注塑成型技术(MPIM)制得性能优良的氮化硅轴承球.研究了粘结剂配方、注塑成型、低缺陷排胶、气氛压力烧结等工艺参数对氮化硅轴承球致密度、力学性能、表面与微观形貌的影响.结果表明,喂料固含量55.51％、注塑速率5 cm/s、注塑温度90℃、注塑实际压力75 bar、超临界CO2萃取+热脱脂两步法排胶等工艺过...     

氮化硅陶瓷在四大领域的研究及应用进展

氮化硅陶瓷不仅具有较高的力学性能还具有良好的透波性能、导热性能以及生物相容性能,是公认的综合性能最优的陶瓷材料。作为轴承球的致密氮化硅陶瓷广泛应用在机械领域;作为透波材料的多孔氮化硅陶瓷广泛应用在航空航天领域;随着对氮化硅陶瓷材料的深入研究,其在导热性和生物相容性方面的优异特性逐渐被科研工作者认识并得到开发和应用。本文详细阐述了氮化硅粉体的制备方法,并综述了氮化硅陶瓷作为结构陶瓷在机械领域和航空航天领域的研究进展,此外还介绍了其作为功能陶瓷在半导体领域、生物制药领域的研究和应用现状,最后对其未来发展进行了展望。     

静载多点压痕对氮化硅陶瓷强度的影响

本文在对XJM－1型磨片机进行改装的基础上研究了静载多点压痕对氮化硅陶瓷强度的影响。实验发现：与原始强度相比，静载多点压痕后的氮化硅强度有所降低；强度与多点压痕荷载之间的关系曲线出现一极大值。分析后表明：表面残余应力与裂纹尺寸是影响陶瓷材料强度的两个主要因素，它们的变化将对陶瓷材料强度产生直接影响。