Refractory mechanical properties

Mechanical Properties. The physical properties of a particular refractory product depend on its constituents and manner in which these were assembled. The physical properties may be varied to suit specific appHcations. For example, for thermal insulations highly porous products are employed, whereas dense products are used for slagging or abrasive conditions. 

More than half of the elements in the Periodic Table react with silicon to form one or more silicides. The refractory metal and noble metal silicides ate used in the electronics industry. Silicon and ferrosilicon alloys have a wide range of applications in the iron and steel industries where they are used as inoculants to give significantly improved mechanical properties. Ferrosilicon alloys are also used as deoxidizers and as an economical source of silicon for steel and iron. 

Lower Oxides. A number of hard, refractory suboxides have been prepared either as by-products of elemental boron production (1) or by the reaction of boron and boric acid at high temperatures and pressures (39). It appears that the various oxides represented as B O, B O, B22O2, and B23O2 may all be the same material ia varying degrees of purity. A representative crystalline substance was determined to be rhombohedral boron suboxide, B12O2, usually mixed with traces of boron or B2O3 (39). A study has been made of the mechanical properties of this material, which exhibits a hardness... 

Stacking faults thereby providing barriers to sHp. If carbides are allowed to precipitate to the point of becoming continuous along the grain boundaries, they often initiate fracture (see Fracture mechanics). A thorough discussion of the mechanical properties of cobalt alloys is given in References 29 and 30 (see also Refractories). 

Molybdenum is a high-strength refractory metal, although recrystallizes above 950°C with accompanying reduction in mechanical properties. It is easily fabricated. Its properties are summarized in Table 6.6. CVD is commonly used for the production of molybdenum coatings and free-standing shapes. 

Properties. Properties of SiC fibers are shown in Table 19.2. They are similar to those of CVD boron fibers except that SiC is more refractory and less reactive than boron. CVD-SiC fibers retain much of their mechanical properties when exposed to high temperature in air up to 800°C for as long as one hour as shown in Fig. 19.3. [ 1 SiC reacts with some metals such as titanium in which case a diffusion barrier is applied to the fiber (see Sec. 2.5 below). 

Zirconium and hafnium are two refractory elements which are closely, related to titanium (see Encycl Vol 9, T227-R) but which in addition to having desirable corrosion resistance and mechanical properties, have many significant ordnance applications. Hf free Zr moreover is possessed of a low neutron capture crossection, and is therefore of value as a reactor material. In as much as Hf is chemically similar to Zr and as in nature it is always found in association with Zr, it will be discussed as part of the Zr technology, except where its special properties... 

MgO-spinel clinker is obtained by the same procedure, but with a substantial proportion of free MgO (75-85%). MgO-spinel is produced by sintering at temperatures of 1600-1800°C and a dense product is obtained. MgO-spinel refractory has better high temperature mechanical properties in arc furnace roof application compared to magnesia-chrome refractories, but it has lower strength than a high-alumina refractory. 

Mechanical properties and thermal shock behaviour of magnesia-spinel composite refractory materials... 

Portland cement is such an alternative. Formed by chemical reactions, it is an inexpensive product and is used in large volumes. There is a wide gap between the attributes of ceramics and Portland cement, however. Ceramics exhibit superior mechanical properties compared to cements. Ceramics are far more stable in acidic and high temperature environments, but cements are not. Thermal stability of cements is poor, while ceramics are refractory and are used at very high temperature, such as linings in furnaces. Cements are porous, but ceramics can be very dense. 

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