Synthesis of ceramic materials.Synthesis method:Solid state reactions:-metal carbonates, hydroxides and oxides.-Impurities (large particle size) requires repeated mixing and extended heating at high temperatures to generate a homogeneous and single phase material- may result in multi-phase formation.Steps including in this solid state reaction or conventional method.Mixing or milling (dry or wet milling)properties depend processing conditions of the ceramic.raw materials weighed according stoichiometric formula.raw materials- high purity.The particle size powders submicron range for the solid phase reactions occur by atomic diffusion.The powders mixed mechanically/chemically.Mechanical mixing done by ball milling or attrition milling for a short timeCalcinationDuring the calcination step the solid phase react ...view middle of the document...
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.SinteringAfter shaping, the green bodies heated very slowly remove any binderThe binder burnout rate 1-2 ° C/min to allow the gases to come out slowly without forming cracks and blisters in the ceramic part.After binder burnout over, the samples taken to higher temperature for sinteringThe 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.Example:Synthesis of YBCO, YBa2Cu3O7-xDirect reaction between Y2O3, BaO, CuO (Reaction between three solid components)→Grind to obtain large surface area→Press into pellets (contact)→Heat in alumina crucible follow below temperature profile:Processing of ferroelectric materials.Piezoelectric behavior induced in a ferroelectric ceramic by a process "poling".In this process a (dc) electric field strength > the coercive field strength is applied to the ferroelectric ceramic at a high temperature, but below Curie point.spontaneous polarization within each grain gets orientated towards the direction of the applied field.The dipoles within a single domain have same orientation.fine grain sizes (< 1 mm) each grain is a single domain with the domain wall at the grain boundary.grain size is larger (> 1 mm) then there could be multiple domains in a single grain.General aspectsReaction rates depends on:Area of contact between the reacting solids, surface area and densityRates of diffusion of ions.Increase diffusion rates (decrease diffusion length)Required very fine particles process, spray pyrolysis etc.Intimate mixture of reactant by coprecipitation, sol-gel.Reduction of diffusion distances by incorporating the cations in the same solid precursors.
