Processing & Testing Electroceramics EBB 443-Technical Ceramics Dr. Julie Juliewatty Mohamed School of Materials and Mineral Resources Engineering Universiti Sains Malaysia

Processing of Electroceramics The properties of electroceramic components greatly depend upon the processing conditions of the ceramic. The raw materials are first weighed according to the stoichiometric formula. The raw materials should be of high purity. The particle size of the powders must be in the submicron range for the solid phase reactions to occur by atomic diffusion. The powders are then mixed either mechanically or chemically. Mechanical mixing is usually done by either ball milling or attrition milling for a short time.

Processing of Electroceramics During the calcination step the solid phase reaction takes place between the constituents giving the electroceramic phase. The calcining temperature is important as it influences the density and hence the electromechanical properties of the final product. The higher the calcining temperature, the higher the homogeneity and density of the final ceramic product.

Processing of Electroceramics After calcining, the lumps are ground by milling. The green bodies should have a certain minimum density before they can be sintered. The desired shape and a minimum green density can be provided by various techniques including powder compaction, slip-casting, and extrusion. The choice of the method depends on the type of powder used, particle size distribution, state of agglomeration, desired shape, and thickness of the part. After shaping, the green bodies are heated very slowly in order to remove any binder present. c

Processing of Electroceramics The binder burnout rate should be  1-2 ° C/min in order to allow the gases to come out slowly without forming cracks and blisters in the ceramic part. After the binder burnout is over, the samples are taken to a higher temperature for sintering to take place. The sintering temperature and time should be optimum for proper densification to occur without abnormal grain growth. The sintering of oxide ceramics must be carried out in an oxidizing atmosphere or in air.

Solid State Reaction The above technique is refer as a solid state reaction or conventional method. In briefly, the steps including:  Mixing or milling (dry or wet milling)  Calcination  Compaction (for pellet formation)  Sintering

Example: Solid State Reaction of CCTO Ball milling 1 hour of a stoichiometric ratio of raw materials (CaCO 3, CuO & TiO 2 ) Calcination 900 o C/12 hrs. XRD Analysis (calcined powders) XRD Analysis (sintered pellets) Compaction with pressure 300 MPa (thickness ~ mm) Sintering at 1050 o C for 12 hrs. Dielectric measurement by using LCR meter Sintered sample with silver electrodes

Production scheme of ‘Nd2Fe14B-type’ magnets (REM XIII, 1994 p 303) Processesing of Magnetic Ceramics

Processing of ferroelectric ceramics Flowchart for the processing of ferroelectric ceramics

Processing of ferroelectric ceramics The dipoles within a single domain have the same orientation. In ferroelectric ceramics with fine grain sizes (< 1 mm) each grain is a single domain with the domain wall at the grain boundary. If the grain size is larger (> 1 mm) then there could be multiple domains in a single grain.

Processing of ferroelectric ceramics Piezoelectric behavior can be induced in a ferroelectric ceramic by a process called "poling". In this process a direct current (dc) electric field with a strength larger than the coercive field strength is applied to the ferroelectric ceramic at a high temperature, but below the Curie point. On the application of the external dc field the spontaneous polarization within each grain gets orientated towards the direction of the applied field.

Processing of ferroelectric ceramics Schematic of the poling process in piezoelectric ceramics: (a) In the absence of electric field the domains have random orientation of polarization; (b) the polarization within the domains aligns in the direction of the applied field.

Slip Casting Method

Modified domestic microwave oven used for the powder synthesis. In a typical experiment, a solid mixture containing requisite quantities of aluminum nitrate, magnesium nitrate, and urea was taken in a Pyrex glass dish and was irradiated with microwaves in a modified domestic microwave oven (Microwave 700W, input range 210–230 V-ac 50 Hz, microwave frequency 2.45 GHz) to produce MgAl 2 O 4 spinel material.

MW Irradiation? In conventional or surface heating, the heat flow rate into the body from the surface determined by its specific heat, thermal conductivity, density and viscosity. Surface heating is not only slow, but also non- uniform with the surfaces being much hotter than the inside of the material. Consequently, the quality of conventionally heated materials is variable and frequently inferior to the desired result.

1050 o C/4 h1050 o C/24 h

MW Irradiation? Conversely, with microwaves, it is possible to heat the volume of a material at the same rate. Energy is transferred through the material electro- magnetically, not as a thermal heat flux. Therefore, the rate of heating is not limited and the uniformity of heat distribution is greatly improved. Heating times can be reduced to a very short time.

Methodology Ball milling 5 h of stoichiometric ratio of CaCO 3, CuO, TiO 2. XRD analysis (calcined powder) SEM analysis (surface & fracture) Compaction, 520 MPa (d ~ mm, Ø 5 & 12 mm) Sintering at 1000 o C/10h Dielectric measurement Samples with silver electrodes MW irradiation min Post-MW sintered min MW sintering 60 min MW kitchen oven (2.45 GHz, 1.1 kW).

Domestic MW oven (2.45 GHz, 1.1 kW) Susceptor/ Crucible AluminaSiC/graphite

Sol-Gel Processing

Sol-Gel Processing: Basic Reactions

Sol-Gel: Steps of film formation

Sol-Gel: Stability of sols

Unique structures by sol-gel

Sol-Gel: Multilayer

Ceramic sol-gel films

Testing Ball milling 5 h of stoichiometric ratio of CaCO 3, CuO, TiO 2. XRD analysis (calcined powder) SEM analysis (surface & fracture) Compaction, 520 MPa (d ~ mm, Ø 5 & 12 mm) Sintered pelletDielectric measurement Samples with silver electrodes MW irradiation min XRD analysis (sintered sample) MW sintering 60 min

Dielectric Testing

Piezoelectric Measurement PIEZO software takes input on the Multichannel from displacement or force sensors to collect piezoelectric properties simultaneously with electric properties.