• Ramji Lal

      Articles written in Bulletin of Materials Science

    • Effect of compositional modifications on the piezoelectric properties of spray dried lead zirconate titanate ceramics

      Ramji Lal P Ramakrishnan

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      Lead zirconate titanate powders of different compositions varying from 50 to 55 atomic percent zirconium in the solid solution have been prepared by spray-drying technique. The compositions were varied by changing the zirconium-to-titanium ratio in the solid solution and also with the addition of strontium. The amorphous character of the as-prepared powders and the formation of single phase lead zirconate titanate during calcination were also confirmed by x-ray diffraction technique. These powders were then converted to piezoelectric ceramics by compaction and sintering followed by electroding and poling. Effect of the variation of zirconium to titanium ratio and strontium additions on the piezoelectric properties of the finished ceramics have been explained on the basis of improved sintering, uniform grain size, formation of morphotropic phase boundary and subsequent shift to rhombohedral structure.

    • Fabrication of PZT-polymer composite materials having 3-3 connectivity for hydrophone applications

      N M Gokhale S C Sharma Ramji Lal

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      Lanthanum-modified lead zirconate titanate (PZT) powder and volatilisable polymethylmethacrylate (PMM) polymer particles have been used for fabrication of porous sintered ceramics of interconnected porosity varying from 25% to 59%. Sintered ceramics are converted into piezoelectric PZT-polymer composites by incorporating silicone rubber elastomer followed by electroding and poling. Influence of the variation of PZT-PMM ratio and sintering temperatures on the open and closed porosity of the sintered ceramics as well as volume fraction PZT in the composites has been studied and correlated for the optimization of piezoelectric properties. The PZT-polymer composites possess low density, considerably high piezoelectric voltage coefficient and considerably lower ageing characteristics and are therefore considered suitable for designing highly sensitive hydrophone systems.

    • Synthesis, microstructure and mechanical properties of ceria stabilized tetragonal zirconia prepared by spray drying technique

      S C Sharma N M Gokhale Rajiv Dayal Ramji Lal

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      Ceria stabilized zirconia powders with ceria concentration varying from 6 to 16 mol% were synthesized using spray drying technique. Powders were characterized for their particle size distribution and specific surface area. The dense sintered ceramics fabricated using these powders were characterized for their microstructure, crystallite size and phase composition. The flexural strength, fracture toughness and microhardness of sintered ceramics were measured. High fracture toughness and flexural strength were obtained for sintered bodies with 12 mol% of CeO2. Flexural strength and fracture toughness were dependent on CeO2 concentration, crystallite size and phase composition of sintered bodies. Correlation of data has indicated that the transformable tetragonal phase is the key factor in controlling the fracture toughness and strength of ceramics. It has been demonstrated that the synthesis method is effective to prepare nanocrystalline tetragonal ceria stabilized zirconia powders with improved mechanical properties. Ce–ZrO2 with 20 wt% alumina was also prepared with flexural strength, 1200 MPa and fracture toughness, 9.2 MPa √m.

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