INTRODUCTION TO PROCESSING OF BIOMATERIALS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 247

used for surface modifi cation of SiC or Si 3 N 4 particles [37]. Similarly, acid treat-
ment can be used for the surface modifi cation of ceramics such as zirconium [41].
8.3.2.2.4 OTHER PROCESSING TECHNIQUES. In addition to the aforemen-
tioned conventional processing techniques for ceramics, there are several other
approaches that have been developed for the fabrication of ceramic products.
Some of these techniques have been briefl y explained in this section.
One such non-conventional technique is microwave processing, wherein
pressureless sintering is done at low temperatures. This type of processing saves
energy and reduces process cycle time. Other advantages include volumetric
heating, a wide range of controlled heating rates, tailored microstructures, atmo-
sphere control, and the ability to reach very high temperatures [38].
In addition to microwave processing, other ceramic processing techniques that
have been reported include solid freeform fabrication (SFF) techniques—such
as stereolithography (SLA), selective laser sintering (SLS), three-dimensional
printing (3DP), direct ink-jet printing, robocasting, fused deposition modeling
(FDM) and micro-pen writing [39]—ultra pressing, ultra rapid densifi cation in
inductively coupled plasma, direct casting, dynamic compaction of powders using
high pressure shock waves, and electrodeposition [35].
One of the more recent ceramic processing techniques that is gaining increas-
ing importance is electrodeposition, wherein thin ceramic fi lms can be deposited
on material surfaces. These techniques are gaining increasing importance as they
are rapid and cost-effective processes that provide an easy scale-up option along
with fl exibility in the shapes of fi nished products. The two electrodeposition tech-
niques that have been used for ceramics processing are electrophoretic deposi-
tion (EPD) and electrolytic deposition (ELD) [40]. In EPD, charged particles in
a liquid move towards an electrode under the infl uence of electric fi eld and depo-
sition takes place due to particle coagulation. In ELD, solutions of metal salts
produce colloidal particles from electrode reactions and deposition occurs on
the substrate as a thin ceramic fi lm. EPD allows shaping of free-standing objects
as well as deposition of fi lms, layers, and coatings on substrates. An interesting
feature of EPD is the ability to engineer step-graded and functionally-graded
materials/components. Due to the advantages offered by these electrodeposition
techniques, they are being used for a number of other non-biomedical applica-
tions including electronic, optical, and electrochemical applications [40].
Conventional methods for powder synthesis like crushing and grinding do
not produce materials with desirable microstructure. Hence, newer methods such
as vapor phase chemical reactions (VPCR) and sol-gel methods have been devel-
oped that can produce fi ne powders with controlled microstructure in the fi nished
ceramic product. In addition, these fabrication methods produce products with
high purity, smaller defects, controlled microstructure, homogeneous particle size
distribution and reproducibility, while requiring fewer fabrication steps. It is
projected that the colloidal processing of powders and automation of the existing
techniques for processing ceramics will contribute signifi cantly to the develop-
ment of advanced ceramics. Future research in ceramic processing would include