Relative Density Of Green Body Research Articles

High transmittance and grain-orientated alumina ceramics fabricated by adding fine template particles

Transparent Al2O3 ceramics with grains aligned to the c-axis were prepared by adding platelets with a low aspect ratio into fine equiaxed particles. The mixed powders were formed into green bodies using spontaneous coagulation casting and sintered by pressureless sintering and hot-isostatic pressure sintering. Zeta potentials and rheological behavior of the slurries, relative densities of green bodies, and orientation and optical properties of sintered bodies were investigated and discussed. The platelet with a high aspect ratio suppressed densification more seriously during sintering than the one with a low aspect ratio. An excellent oriented structure was obtained when 5 wt% platelets with a low aspect ratio were added, and transparent Al2O3 ceramics with grains aligned to c-axis were successfully prepared; the in-line transmittance was 78.4% at 600 nm, which is the highest one in the currently reported literature.

One-step introduction of ZrC-SiC inside carbon fabric to fabricate high homogeneous and damage-tolerant composite inspired by vibration

The ZrC-SiC ceramics were introduced inside carbon fabric uniformly in one-step by vibration assisted injection. This novel method achieved a relative density of green body at 45%, nearly 50% higher than that of without vibration. The composite obtained a rivaling flexural strength at 185 ± 12 MPa, graceful fracture mode with fracture toughness at 5.86 ± 0.16 MPa∙m1/2 and work of fracture reaching 1284 J/m2, 2 times of the value without vibration. By comparison, a poor fracture toughness and mediocre flexural strength of 4.05 ± 0.27 MPa∙m1/2 and 113 ± 19 MPa are equipped with the non-vibration treated one.

Optimizing the gel-casting parameters in synthesis of MgAl2O4 spinel

Abstract In this paper MgAl2O4 spinel powder with average particle size of 90 nm, purity of 99.99%, with stoichiometric ratio α-Al2O3 and MgO and only 0.8 %wt. LiF add-on was solid-state synthesized at a temperature of 1300 °C and used in gel suspension with 83% solid load. Using the optimal value of ISOBAM (0.9 %wt.) as both dispersion and gelation factors led to a significant increase in the relative density of green body from 48.5% to 62.2%. Relative density increased after sintering at 1550 °C for 1 h from 78% to 99.6% and pore size (40 nm) reduced to half the size of powder particles. Also, it resulted in appropriate pore distribution, because of the low number and value of the add-on in the gel system, and also optimization and preparation of nanopowders, as well as preparation and manufacture of suspension. XRD, BET, ICP, FESEM, FTIR analyses were done for synthesis and preparation of powder. Viscometery, Rheometery, Porosimetery, TG-DSC, Zeta potential, and sediment deposition analyses were done in order to optimize the parameters of the casting.

The preparation of silicon nitride ceramics by gelcasting and pressureless sintering

A new gelling system based on the polymerization of hydantion epoxy resin and 3,3′-Diaminodipropylamine (DPTA) was successfully developed for fabricating silicon nitride (Si3N4) ceramics. The effects of pH value, the dispersant content, solid volume fraction and hydantion epoxy resin amount on the rheological properties of the Si3N4 slurries were investigated. The relative density of green body obtained from the solid loading of 52vol% Si3N4 slurry reached up to 62.7%. As the concentration of hydantion epoxy resin increased from 5wt% to 20wt%, the flexural strength of Si3N4 green body enhanced from 5.3MPa to 31.6MPa. After pressureless sintering at 1780°C for 80min, the sintered samples exhibited the unique interlocking microstructure of elongated β-Si3N4 grains, which was beneficial to improve the mechanical properties of Si3N4 ceramics. The relative density, flexural strength and fracture toughness of Si3N4 ceramics reached 97.8%, 687MPa and 6.5MPam1/2, respectively.

Synthesis and characterization of mullite–zirconia nanostructured composite by combined mechanical activation and reaction sintering

The objective of present study was to produce mullite–zirconia nanostructured composite by mechanical activation of zircon–alumina powder mixture followed by reaction sintering. The results showed that mechanical activation up to 60h led to no phase change. Complete formation of mullite–zirconia composite was observed after 60h of mechanical activation and subsequent reaction sintering at 1400°C for 2h. This temperature is about 200–250°C lower than the temperatures commonly used in the reaction sintering of zircon–alumina powder mixture. Density measurements showed that the relative density of green bodies was ∼78%, which increased to values above 90% after reaction sintering. It was also observed that the relative density of reaction sintered samples increased with an increase in the mechanical activation time. The produced composite showed a hardness value of 11.1GPa, which is comparable with the hardness value of mullite–zirconia composites obtained by other methods.

Rheological property and drying mechanism of thermoresponsive gelcasting of ZnO

To solve the problem of drying gelcast green body, the thermoresponsive gel system which contains macromonomer graft chains was used in gelcasting of ZnO. The effects of the amount and length of graft chains macromonomer PIPAAm, the total amount of organic matters, and the solid loading on the rheological properties of suspensions were investigated, and the drying mechanism of gelcast green body was analyzed. The results show that ZnO suspensions with the gel system still display shear-thinning rheological behavior, but its viscosity increases with increasing the addition amount and relative molecular mass of PIPAAm graft chain, and the total organic matter content. The PIPAAm graft chains inhibit or even eliminate the formation of the “dense layer” on the surface of gelcast ZnO green bodies, and accelerate the drying of green bodies. The introduction of PIPAAm graft chains facilitates the shrinkage of the gelcast ZnO green bodies, which is a feasible method to increase the relative density of green bodies.

Study and Characterization of TiC/Fe Alloys by Gel-Casting

The TiC/Fe steel matrix composites were prepared by gelcasting technology of selecting the appropriate gel system and additives, the reasonable technological parameters. The toluene and 2-hydroxyethyl methacrylate (HEMA) were as gel system, oleic acid as dispersant. The rheological property, curing process and performance of the body were analyzed. The results show that the monomer (HEMA) content of 4.6wt% and oleic acid to 2wt% which increased the solid content from 50 to 54vol.%. The relative density of green body is 59.6%, the intensity is 28MPa. After sintering, the complicated shape was prepared.

Tailoring Ti3SiC2 Ceramic via a Strong Magnetic Field Alignment Method Followed by Spark Plasma Sintering

Highly textured Ti3SiC2 ceramic was successfully fabricated by slip casting in a 12 T strong magnetic field followed by spark plasma sintering. The optimized suspension parameters for slip casting were determined as 20 vol% Ti3SiC2 and 1.5 wt% polyethyleneimine dispersant of powder in deionized water. After texturing in the 12 T strong magnetic field and then cold isostatic pressing, the relative densities of green bodies were 51.4% and 63.8%, respectively. X‐ray diffraction analysis revealed that the preferred orientation of Ti3SiC2 grains perpendicular to the magnetic field direction was along the c‐axis. After sintering at 1100° and 1000°C under the pressure of 120 and 500 MPa, respectively, the relative density of Ti3SiC2 reached 88.2% and 98.6%. The Lotgering orientation factors on the textured top surface and textured side surface were determined as f(00l)=0.95 and f(hk0)=0.31, respectively. The textured microstructure contributed to the anisotropic mechanical property tested by Vickers indentation.

Synthesis and Analysis of ZrB2-Based Composites

Abstract Composites with different compositions were prepared from ZrB2 and Molt was found that there is an optimum composition for obtaining the highest relative density at 15 wt.% of molybdenum. Based on the results of x-ray diffraction analysis, energy dispersive spectrum analysis and elemental mapping, it was concluded that the composites contained ZrB2, MoB, and ZrC due to the reactions between ZrB2 Mo and some C (presents as an impurity). The effects of composition and firing temperature on the firing of ZrB2-Cu were studied. The relative densities of green bodies and fired composites increased with increasing amount of copper. For the composites containing 25 vol.% copper, the relative densities increased first with increasing firing temperature, and then decreased at higher firing temperature due to the loss of boron during firing.