Suspensions ceramics

Unlike clay-based systems, modem ceramics require additives, termed binders, to provide the plasticity required for ductile-forming methods to be used. These organic additives serve to modify the rheological behavior of the ceramic suspensions and impart handling strength to the green, as-formed ceramic bodies. Their... 

Ceramic suspensions can also be deposited by dispensing or extrusion from a nozzle. While printing is a parallel process, i.e., many nozzles per color or substance are involved — say 128 or more, dispensing and extrusion processes usually use a single nozzle. The rheological properties of the ceramic suspensions are different from those of inkjet inks they may be much more viscous, i.e., contain a... 

An experiment with a dilute ceramic suspension was made as follows A very small quantity of silicon carbide particles (d 6 /xm) was dissolved in silicon oil ( 350mPas). The suspension was pumped at high pressure through a glass capillary (d = 0.6 mm). The experimental setup is shown in Fig. 3. The velocities of the silicon carbide particles in the capillary are detected by an optical sensor. From these data, the statistics of the particles velocities is calculated. Due to the optical properties of the sensor, the particles are only detected in a wedge-like sector of the cross-section of the capillary. The measured velocity distribution of the particles (Fig. 4) depends on the shape of this sector and, additionally, on the measuring tolerances of the sensor. 

Fig. 3. Experimental set-up for medium to high shear rate experiments with a dilute ceramic suspension (left) and the sector of the cross-section of the capillary where particles are detected (right).

In the first formula only hydrodynamic contributions are considered, while in the second formula interparticle interactions are taken into account. These formulas are expected to hold at least approximately. The decrease of the low shear viscosity of ceramic suspensions with increasing mean particle size at fixed solids concentration is reported in Ref. 1. 

The shear dependency of the viscosity of ceramic suspensions at low to intermediate shear rates can be measured with common rheometers. The results for a ceramic suspension with a high volume fraction of solids and a ceramic ink are shown in Fig. 6. 

Fig. 6. Shear-dependency of the viscosity of a ceramic suspension with high volume fraction of Xi02 and Ag nanoparticles (left) and of a ceramic ink containing about 15% sohds by mass (right).

A different important issue in this context is the chemical stability of ceramic suspensions, which is indispensable for inkjet printing. For chemical stability, either steric or by charge, the surface to mass ratio is important S/m = 3/ pR). Due to the high density p of ceramics, a stable suspension also requires that the particles not be too large, i.e., be smaller than about 2 m. 

To summarize, problems with the application of ceramic suspensions with inkjet printers grow with the (effective) volume fraction... 

Fig. 16. Used nozzles of a print head. The nozzle on the left was used with fluid inks only, the one on the right with an abrasive ceramic suspension for about 30 hours.

Ainsley C, Derby B, Reis N. (2003) Viscosity and acoustic behaviour of ceramic suspensions optimized for phase-change ink-jet printing. 7 Am Ceram Soc 88 802-808. 

Freeze drying is used to dry either salt solutions or ceramic suspensions in a gentle way, avoiding thermal decomposition of the metal salts and aggregation of the particles. There are fovir steps in fieeze drying ... 

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