Alumina elastic moduli

E (GPa) - alumina elastic modulus Gaussian Mean = 375 Standard dev = O.OS mean... 

Fig. 11. Modulus inciease as a function of fibei volume fraction alumina fiber-reinforced aluminum—lithium alloy matrix for (a) E (elastic modulus),...

Recently, Oldfield Ellis (1991) have examined the reinforcement of glass-ionomer cement with alumina (Safil) and carbon fibres. The introduction of only small amounts of carbon fibres (5% to 7-5% by volume) into cements based on MP4 and G-338 glasses was found to increase considerably both the elastic modulus and flexural strength. There was an increase in work of fracture attributable to fibre pull-out. A modulus as high as 12-5 GPa has been attained with the addition of 12% by voliune of fibre into MP4 glass (Bailey et al, 1991). Results using alumina fibre were less promising as there was no fibre pull-out because of the brittle nature of alumina fibres which fractured under load. 

It has been known for some time that considerable improvement of the mechanical properties of alumina in terms of flexural strength, fracture toughness, yield strength and elastic modulus can be achieved by adding particles of stabilised zir-conia as a structural reinforcement (see Chapter 4.1.2). Such ceramics are known as ZTA (zirconia-toughened alumina), duplex ceramics or dispersion ceramics. 

Implant materials for coating. Prosthetic materials coated with HAp include titanium, Ti-6A1-4V, stainless steel, Co-Cr-Mo, and alumina (Jiang and Shi 1998). These materials are roughened by grit blasting for a mechanical interlock between the melted component of the particle and the substrate. The Ti-6A1-4V and Cr-Co-Mo alloys are the most common. Ideally, the elastic modulus and co-efficient of thermal expansion of the substrate and the coating material will be matched to minimize any residual stresses at the interface. Hydroxylapatite (E = 100 GPa and a = 12 x 10 °C (Perdok et al. 1987)) is... 

Ceramics, such as the coinmonly used Alumina (AI2O3) and Zirconia (Zr02), tend to have a very high elastic modulus (around 400 GPa), have a low coefficient of friction, and are resistant to wear. These properties make them useful as the load-bearing surfaces in orthopedic implants. 

Alumina is the most important oxidic abrasion-resistant material. Metal carbides are in some ways superior to oxides with respect to hardness and melting point, but they are much more brittle than the oxides and are only used in isolated instances as wearing bodies. Silicon carbide is characterized by its low thermal expansion and high thermal conductivity and has proved to be more resistant to thermal shock than oxides. Zirconia is tougher than alumina its modulus of elasticity is only about half as large, and it is comparable with that of steel. Zirconia is therefore very suitable for compound structures with steel. At present, the applications of ceramic sintered materials in chemical plant construction are slide rings, pump parts, and slide bearings. 

The stiffness of a DMO composite of AI2O3-AI with 22% alloy and 4% porosity (231 GPa) was modeled successfully [60] by assuming the metal and the ceramic skeleton to deform equally in series and in parallel, that is, by taking a Reuss-Voigt average. The additional effect of isolated pores could be included by using empirical expressions derived from data on porous alumina. The elastic modulus... 

Nextel 312 fiber is manufactured by 3M and is composed of alumina, boria, and silica. It is available in tow, fabric and woven tape configurations. This material retains strength and flexibility with little shrinkage up to 1200°C. The properties of the Nextel 312 fiber are density = 2.70 g/cm, tensile strength = 1720 MPa (250 ksi), elastic modulus = 150 GPa (22 MSI), unstressed continuous use temperature = 1204°C, short-term use temperature = 1426°C, melt temperature = 1800°C. 

Density was measured with a bulk mass/volume method using the same flexure specimens that were used in elastic modulus measurements. A total of five specimens were used for each of alumina contents. Figure 4 depicts density as a function of alumina content for both particulate and platelet composites [3, 4]. Density decreased linearly with increasing alumina content, yielding good agreement with the prediction based on the rule of mixture. The difference in density between particulate and platelet composites was negligible. 

Elastic modulus of both particulate and platelet composites was determined from 25 to 1000°C as a function of alumina content by the impulse excitation of vibration method, ASTM C 1259 [26] using the flexure specimen configuration. One flexure specimen was used at each of alumina contents for a given composite. A total of five specimens were additionally used at each alumina content to evaluate ambient-temperature elastic modulus of the two composites. 

FIGURE 14. Elastic modulus as a function oftemperature for 10-YSZ/aluminaparticulatecomposites with different alumina contents, determined by the impulse excitation method. ZAO to ZA30 in the figure indicate respective alumina mol% (e.g., ZAO = 0 mol%). 

The variation of the elastic modulus, fracture strength and fracture toughness of a model alumina platelet-reinforced borosilicate glass matrix composite with the volume fraction of platelets is shown in Figure 6 [17,128]. The material exhibited a pore-free matrix, uniform distribution of the platelets and strong matrix/platelet interfacial bonding. In Figure 6 both... 

In other words, the elastic modulus of the cubic structured gel, E, should increase with adhesion W, particle elasticity E and Poisson s ratio v, but decrease as the particle diameter D rises. These equations are interesting when we apply them to common gels such as silica, alumina, titania, or zirconia. For example, for 1 (im diameter silica particles, = 70GPa, fF = 0.2Jm because of the hydrated surface and v is 0.3. The contact spot diameter turns out to be 32 nm from Equation (11.1), only 3% of the particle diameter. It is salutary to note that such tenuous adhesive contact between the particles is responsible for the gel behavior. The Young s modulus ofthe gel from Equation (11.7), assuming a cubic structure, is 0.75 GPa. This is close to the measured values for silica gel, which is about a hundred times more compliant than silica itself. Let us now consider the preparation and measurement of such gels. 

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