Sintered density

Homogeneous LaMn03 nanopowder with the size of 19-55 nm and with the specific surface area of 17-22 m2/g has been synthesized using a surfactant, sodium dodecyl sulphate (SDS) to prevent agglomeration [47], The sonochemically prepared LaMn03 showed a lower phase transformation temperature of 700°C, as compared to the LaMn03 prepared by other conventional methods which has been attributed to the homogenization caused by sonication. Also, a sintered density of 97% of the powders was achieved for the sonochemically prepared powders at low temperature than that of conventionally prepared powders. 

The mechanical properties of ceramics maybe increased by minimising impurity segregation, decreasing grain size and increasing sintered density. 

Sintered density (1700°C, 2 hours) against SiC content for alumina/SiC nanocomposites, demonstrating the inhibition of sintering caused by the SiC particles [10]. 

Effect of yttria additions on sintered density of alumina-2% SiC nanocomposites for various sintering temperatures (data from [16]). The 0.0001% points indicate no added yttria. 

MgO and A1203 powders of 1 pm particle size react to form spinel and sinter, but it is difficult to obtain full sintered density even at temperatures as high as 1750°C. If high density is to be obtained, precalcination at a lower temperature (1300°C for 3 h) is essential.32,36,37 This stage allows almost full reaction to spinel to occur. For 55-79% of pre-reacted spinel, final densities of 95-96% can be obtained at 1700-1750°C in 15-60 min. 

Also Huisman et al. [13] used nitric acid to obtain stable alumina/magnesia suspensions. The powder had an average particle diameter of 0.46 pm and a surface area of 9.4 m /g. The resulting pH was 4 - 4.2. Again high sintered densities up to 99.7% were reached. 

FIGURE 16.11 Volume fraction for open and closed pores as a function of BaTif sintered density. Pores are closed at densities above 88% thewetical density. Taken from Chen [34]. 

SEM photographs of the surfaces of the sintered samples are shown in Fig. 4 (A). The surface microstructure reveals uniform and fine grain growth about 2-3 pm. No pores were observed on the surface of the sample, but there were some pores from the fracture surface of the sample, as shown in Fig. 4 (C). The sintered density is 6.6 g/cm, which is over 95% of the theoretical value. The residual pores may be partly attributed to the agglomerates in the source powders that lowered the sinterability of the green bodies. It can also be seen that there are no great changes between the pellets sintered in air before and after heat treatment at 750°C for 5h in H2. This result is in aecordance with that of XRD. It confirms that the samples are chemically stable in H2 atmosphere at least below 750°C. 

It has been observed that the dielectric constant of capacitors in a multilayer form (with silver as the electrodes) is somewhat higher than those in a disk form. Also, an enhanced dielectric constant has been reported with the addition of silver in the perovskite structure due to the improved sintering density and enlarged actual electrode areas. It is worth investigating the effect of this K enhancement of coatings on the luminescent intensity of phosphors. 

Figure 6. Relationship between compacting pressure and sintered density for mineral source (as-received MCW UO2) and mechanically comminuted (hammer-milled MCW UO2) powders. (After Ref. 2.)...

Finally, in the last stage (isolated pore stage), the pore segments further break up into chains of discrete, isolated pores of more or less spherical symmetry. This stage occurs when about 90% of the theoretical density is achieved. The sintering density then approaches asymptotically the practical limit of 92-98%. 

Figure 10.10 Temperature dependence of sintered density for an agglomerated or as-received and agglomerate-free yttria-stabilized zirconia powder (Ih). Eliminating the agglomerates in the green body resulted in a powder compact that densified much more readily. " ...

Another approach to enhance the sintering kinetics is to take advantage of the high surface area of ultrafme powders. Higher surface area powders can be sintered at 150°C lower than powders with a low surface area (Gibson et al. 2001). These particles can be incorporated into an emulsion to enable ease of movement between the crystallites in the particles and produce a high compacted and sintered density (Murray et al. 1995). 

The aspect for the extrusion is frequently concerned with plasticity of the ceramic dough. This is because ceramics are non plastic material when mixed with water therefore, it is necessary to add some additives to improve plasticity. High plasticity could enhance the workability of the mixture. However, the excess quantity of additive could obstruct the high sinter density of final products thus led to an attempt to reduce specific surface area of the ceramic powder by calcination . In this work, the porous ceramic is desirable because of its use as a substrate for palladium therefore large amount of additives were become benefit to the tubular support. The various amounts of additive and water used in the producing of tubular ceramic dough were investigated to succeed the extrusion. 

Table 1 shows the properties of SiC samples via gelcasting forming method and pressureless sintering. Differed to the trend in linear shrinkage with the solid content, there was not much difference in sinter density with respect to the solid content. Sintered densities as high as 98%TD were achieved for all the samples. 

Table 2 sintering density and weight loss of AIN- R2O3 system ... 

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