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Structural Ceramics Performance Differences

Hangzhou JWG Technology Co.Ltd | Updated: Jun 06, 2017

Structural Ceramics As we all know, Zirconia is a multiphase system, affected by temperature after three of phases: single oblique, square and cubic, but also reversible phase transition process, Structural Ceramics at room temperature is only a single oblique phase zirconia.

The swelling properties of ZrO2 in different phase structures vary greatly. When the single oblique ZrO2 to the quartet ZrO2, the anisotropic expansion occurs, the expansion coefficients along the three axes (a, B, c) are inconsistent, the direction of B-axis expansion is not obvious, Structural Ceramics and the direction of a and C axis expand significantly; transformation, the lattice parameters also with the change, heating up the ZrO2 from the single oblique to the quartet, due to the absorption of heat, there is a significant volume contraction (5%), while the cooling (four-direction single oblique conversion) produced volume expansion (8%), which is caused by ZrO2 ceramic cracking. The ZrO2 is converted from a single oblique to a square phase, and the conversion temperature is usually between 1100 (1163 Shan). However, when cooled, the T--Zro2 transition to M-Zro2 is due to the difficulty of M-Zro2 new phase nucleation, and thus the transition temperature between 850 (930 Shan). It is indicated that the temperature lag occurs when the crystal phase transition between 930-1170 Shan is ZrO2.

The results show that some oxides are added as stabilizer ($literal, Cao, $literal, CeO2, MgO, Sc2o3, etc.) in ZrO2, which can form solid solution or complex in ZrO2. Structural Ceramics The internal structure of crystals can be changed, the added oxides can fill the lattice defects in the ZrO2, inhibit the ZrO2 torsion, play a stabilizing role, form metastable square or cubic phase at room temperature, make the single oblique phase become the square and cubic phase of the double crystal structure.

The addition of cation radius is similar to that of Zr-4 (within 12%), Structural Ceramics and the solubility of them in ZrO2 is very large, and ZrO2 can form the replacement solid solution of mono-oblique, square and cubic crystal structure.

The added cation radius is smaller than the Zr-4 or Zr-4, and is filled and dispersed in a large cation, forming a filling solid solution (or dispersion solid solution).

The degree of stability of zirconia is directly related to the type, quantity, ionic radius and valence of the cations. Some oxides and zirconia can completely form solid solution (e.g. Zro 2293). However, some of the cationic oxides and zirconia are not all formed solid solution, Structural Ceramics but the partial formation of solid solution, part of the formation of compounds (such as Zro 2 2o3).

With MgO stabilized ZrO2, when cooled to 1400 Shan below, will be decomposed into the quartet ZrO2 and MgO, continue to cool to 900 Shan, the decomposition of the ZrO2 will still be shifted to the single oblique ZrO2. Therefore, MgO stable ZrO2 can not be heated between 900 for a long time, otherwise it will lose its stabilizing effect. Stabilizer can be used alone, can also be mixed use (two yuan or ternary). Multi-component stabilized zirconia can greatly improve the performance of structural ceramics

According to the study, the four-phase zirconia has toughening properties, this is the theoretical basis of zirconia as a structural ceramics, the basic principle of toughening is that the four-phase zirconia is affected by external forces (temperature and stress), the effect of zirconia from the square structure to the single oblique structure, the absorption of the destruction of energy, the inhibition of crack change and extension. This change, called martensite transformation, plays a toughening role. The phase transition of zirconia can be divided into phase change during the process of firing and cooling, the former is temperature induced and the latter is stress inducing.

The ZrO2 toughening mechanism is very complex. It is generally believed that: a single ZrO2 crystal, the free realization of M-Zro2 <==> T--Zro2 transformation, resulting from the transition in unconstrained state. In fact, the transformation of the Zirconia complex containing the matrix in T--Zro2 to M-Zro2 with volume expansion will be inhibited by different degrees of the matrix, except for the outer surface of the crystals, the remaining crystals are surrounded in the matrix, and then the transition occurs in a constrained state.

When the matrix changes to the T--Zro2 to the M-Zro2, Structural Ceramics there is a great resistance, the single oblique crystal has higher free energy than the square crystal, the transformation cannot happen. The square crystals can be preserved. When there is an external force, the partial release of the matrix binding, the transformation can be carried out. At this point the transformation is called stress-induced phase transition.

It is believed that adding more than two kinds of oxides to the ZrO2 makes the internal phase structure of crystals more diversified, and the toughening effect is better. such as ZrO2 doped PBO, TiO2 (PZT), $literal and so on. The other is to add zirconia to other oxides in order to achieve the effect of zirconia toughening, such as ZrO2 added to $literal, sic (non-metallic oxides), can improve the thermal insulation and wear resistance of ceramics.


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