Spinel hardness

High power LiMn2 xA1 04 +a (spinel] hard carbon... 

NOTE Spinels are very hard metal aluminates or ferrates. 

Cubed compound, in PVC siding manufacture, 25 685 Cube lattice, 8 114t Cubic boron nitride, 1 8 4 654 grinding wheels, 1 21 hardness in various scales, l 3t physical properties of, 4 653t Cubic close-packed (CCP) structure, of spinel ferrites, 11 60 Cubic ferrites, 11 55-57 Cubic geometry, for metal coordination numbers, 7 574, 575t. See also Cubic structure Cubic symmetry Cubic silsesquioxanes (CSS), 13 539 Cubic structure, of ferroelectric crystals, 11 94-95, 96 Cubic symmetry, 8 114t Cubitron sol-gel abrasives, 1 7 Cucurbituril inclusion compounds,... 

In contrast to phenol methylation, other alkyaltions are hard to carry out on spinel systems, as it is suggestive from very few available reports in the literature. Further, the ease of formation of the side products (alkyl phenols with small alkyl group) increases as the size... 

The results suggest that, if A... B repulsions dominate, then the spinel form is stable with respect to the olivine form and that if B... B repulsions dominate, the reverse is true. (The relative hardness of A and B is important, i.e. the slopes of their curves of potential energy as a function of separation.)... 

Stryjak and McMillan (1978) demonstrated increased hardness of the recrystallized material (Table 5.9), testing the properties of spinel glass-ceramics from the Zn0-Al203-Si02 system, with Zr02 admixture as the crystallization nucleator, in combination with the microstructure of glasses... 

The cubic y-modification has been recently observed under a pressure of 15 GPa and temperatures above 2000 K by the laser heating technique in a diamond cell [23] and in shock-wave compression experiments with pressures >33 GPa at 1800 K and >50 GPa at 2400 K [29]. This modification is often designated as the c-modification in the literature in analogy to the cubic boron nitride (c-BN). It has a spinel-type structure in which two silicon atoms are octahedrally coordinated by six nitrogen atoms, one silicon atom is coordinated tetrahedrally by four nitrogen atoms (Fig. 3c). The atomic coordinates for the cubic modification are given in Table 2. From calculations it is shown that this structure should have a high hardness similar to that of diamond and c-BN [23]. 

It is reported1 that fracture toughness and hardness values of sintered magnesium aluminate spinel are in the ranges of 1.9-2.7 MPa m1/2 and 9.3-... 

Spinel is a colorless magnesium aluminate (MgAl204) of cubic structure. It is hard and durable, but, like white sapphire, it is not a good diamond substitute because it has a low refractive index and lacks brilliance. However, it is readily doped to produce other gems of various colors. Artificial ruby, for example, is often natural red spinel, and most synthetic blue sapphires on the market are actually blue spinel. 

Diamonds are the hardest natural substance, but they can cleave easily. They occur in every color, but shades of yellow and brown are most common. Today s faceted diamonds are cut and polished with tools embedded with tiny diamond chips or dust. Before the advent of modern methods, diamonds were used in their natural state, or roughly shaped and polished by hand. The hardness of this mineral led many early jewelers to do a minimum of work before setting diamonds in jewelry or regalia. Common imitations of diamond are colorless spinel, sapphire, zircon, topaz, quartz, and many synthetics. 

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