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      Volume 33, Issue 3

      June 2010,   pages  191-338

    • Dielectric properties of electron irradiated PbZrO3 thin films

      Shetty Aparna V M Jali Ganesh Sanjeev Jayanta Parui S B Krupanidhi

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      The present paper deals with the study of the effects of electron (8 MeV) irradiation on the dielectric and ferroelectric properties of PbZrO3 thin films grown by sol–gel technique. The films were (0.62 𝜇m thick) subjected to electron irradiation using Microtron accelerator (delivered dose 80, 100, 120 kGy). The films were well crystallized prior to and after electron irradiation. However, local amorphization was observed after irradiation. There is an appreciable change in the dielectric constant after irradiation with different delivered doses. The dielectric loss showed significant frequency dispersion for both unirradiated and electron irradiated films. 𝑇c was found to shift towards higher temperature with increasing delivered dose. The effect of radiation induced increase of 𝜀′(𝑇) is related to an internal bias field, which is caused by radiation induced charges trapped at grain boundaries. The double butterfly loop is retained even after electron irradiation to the different delivered doses. The broader hysteresis loop seems to be related to radiation induced charges causing an enhanced space charge polarization. Radiation-induced oxygen vacancies do not change the general shape of the AFE hysteresis loop but they increase 𝑃s of the hysteresis at the electric field forced AFE to FE phase transition. We attribute the changes in the dielectric properties to the structural defects such as oxygen vacancies and radiation induced charges. The shift in 𝑇c, increase in dielectric constant, broader hysteresis loop, and increase in 𝑃r can be related to radiation induced charges causing space charge polarization. Double butterfly and hysteresis loops were retained indicative of AFE nature of the films.

    • Growth and characterization of MMA/SiO2 hybrid low-𝑘 thin films for interlayer dielectric applications

      Bhavana N Joshi M A More A M Mahajan

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      The methylmethacrylate (MMA) incorporated SiO2 thin films having low dielectric constant (𝑘 = 2.97) were deposited successfully to realize new interlayer material for the enhancement of electrical performance of on-chip wiring in very large scale integrated (VLSI) circuits. We have successfully incorporated MMA monomer and eliminated the polymerization step to lower the dielectric constant of deposited thin film. The presence of peak of C=C bond in Fourier transform infrared (FTIR) spectra and carbon peak in energy dispersive (EDAX) spectra confirms the incorporation of carbon in the film due to MMA. The concentration of MMA has great impact on the peak area and full width at half maxima (FWHM) of the Si–O–Si bond, which decreases the density by low atomic weight elements and consequently decreases the dielectric constant. The surface morphology analysed by scanning electron microscopic (SEM) image shows excellent uniformity of the film. The refractive index of 1.31 was measured by ellipsometer for 0.5 ml MMA concentration film. These deposited thin films having low refractive index and dielectric constant are widely applicable for the optical interconnects and interlayer applications in integrated optical circuits and VLSI circuits.

    • Chemical solution deposition of CaCu3Ti4O12 thin film

      Viswanathan S Saji Han Cheol Choe

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      CaCu3Ti4O12 (CCTO) thin film was successfully deposited on boron doped silica substrate by chemical solution deposition and rapid thermal processing. The phase and microstructure of the deposited films were studied as a function of sintering temperature, employing X-ray diffractometry and scanning electron microscopy. Dielectric properties of the films were measured at room temperature using impedance spectroscopy. Polycrystalline pure phase CCTO thin films with (220) preferential orientation was obtained at a sintering temperature of 750°C. There was a bimodal size distribution of grains. The dielectric constant and loss factor at 1 kHz obtained for a film sintered at 750°C was 𝑘 ∼ 2000 and tan 𝛿 ∼ 0.05.

    • Investigation of annealing-treatment on structural and optical properties of sol–gel-derived zinc oxide thin films

      Shenghong Yang Ying Liu Yueli Zhang Dang Mo

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      The transparent ZnO thin films were prepared on Si(100) substrates by the sol–gel method. The structural and optical properties of ZnO thin films, submitted to an annealing treatment in the 400–700°C ranges are studied by X-ray diffraction (XRD) and UV-visible spectroscopic ellipsometry (SE). XRD measurements show that all the films are crystallized in the hexagonal wurtzite phase and present a random orientation. Three prominent peaks, corresponding to the (100) phase (2𝜃 ≈ 31.8°), (002) phase (2𝜃 ≈ 34.5°), and (110) phase (2𝜃 ≈ 36.3°) appear on the diffractograms. The crystallite size increases with increasing annealing temperature. These modifications influence the optical properties. The optical constants and thickness of the films have been determined by analysing the SE spectra. The optical bandgap has been determined from the extinction coefficient. We found that the refractive index and the extinction coefficient increase with increasing annealing temperature. The optical bandgap energy decreases with increasing annealing temperature. These mean that the optical quality of ZnO films is improved by annealing.

    • Electron field emission from 𝑠𝑝2-induced insulating to metallic behaviour of amorphous carbon (𝑎-C) films

      Pitamber Mahanandia P N Viswakarma Prasad Vishnu Bhotla S V Subramanyam Karuna Kar Nanda

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      The influence of concentration and size of 𝑠𝑝2 cluster on the transport properties and electron field emissions of amorphous carbon films have been investigated. The observed insulating to metallic behaviour from reduced activation energy derived from transport measurement and threshold field for electron emission of 𝑎-C films can be explained in terms of improvements in the connectivity between 𝑠𝑝2 clusters. The connectivity is resulted by the cluster concentration and size. The concentration and size of 𝑠𝑝2 content cluster is regulated by the coalescence of carbon globules into clusters, which evolves with deposition conditions.

    • Self-assembled flower-like nanostructures of InN and GaN grown by plasma-assisted molecular beam epitaxy

      Mahesh Kumar T N Bhat M K Rajpalke B Roul P Misra L M Kukreja Neeraj Sinha A T Kalghatgi S B Krupanidhi

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      Nanosized hexagonal InN flower-like structures were fabricated by droplet epitaxy on GaN/Si(111) and GaN flower-like nanostructure fabricated directly on Si(111) substrate using radio frequency plasma-assisted molecular beam epitaxy. Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the crystallinity and morphology of the nanostructures. Moreover, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to investigate the chemical compositions and optical properties of nano-flowers, respectively. Activation energy of free exciton transitions in GaN nano-flowers was derived to be ∼ 28.5 meV from the temperature dependent PL studies. The formation process of nanoflowers is investigated and a qualitative mechanism is proposed.

    • Red luminescence from hydrothermally synthesized Eu-doped ZnO nanoparticles under visible excitation

      P M Aneesh M K Jayaraj

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      Eu-doped ZnO nanoparticles were synthesized by hydrothermal method. The Eu-dopant concentration has been varied by varying the amount of Eu-dopant concentration. These nanoparticles were structurally characterized by X-ray diffraction, transmission electron microscopy and selected area electron diffraction and it confirms the formation of nanoparticles having standard wurtzite structure. Photoluminescence studies show that these nanoparticles exhibit a sharp red luminescence due to the intra-4𝑓 transitions of Eu3+ ions at an excitation of 397 nm and 466 nm. Luminescence quenching is observed in the nanoparticles as the Eu-dopant concentration increases. Incorporation of Eu in the nanoparticles was confirmed by the energy dispersive X-ray studies.

    • Computational study of 5𝑑 transition metal mononitrides and monoborides using density functional method

      Vijayanand Kalamse Sanjay Gaikwad Ajay Chaudhari

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      5𝑑-metal mononitrides and monoborides viz. X–N and X–B (X = La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg) are studied using density functional method based B3LYP functional with LANL2DZ and SDD basis set. The lowest spin state, electron affinities, ionization potentials and binding energies for mononitrides and monoborides are obtained. The electronic state and electronic configuration of mononitrides and monoborides are discussed. Orbitals involved in bond formation are identified. The properties of mononitrides and monoborides are compared. It is found that 5𝑑-metal atoms form stronger bond with nitrogen atom than the boron atom. The range of binding energy, electron affinity and ionization potential is wider for mononitrides than that for monoborides. The properties of 5𝑑-metal mononitrides and 3𝑑-metal mononitrides are also compared. The binding energies for the former are lower than those for the latter.

    • Effect of aluminum addition on electrical properties, dielectric characteristics, and its stability of (Pr, Co, Cr, Y)-added zinc oxide-based varistors

      Choon-W Nahm

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      The electrical properties, dielectric characteristics, and its stability against d.c. accelerated aging stress of (Pr, Co, Cr, Y)-added zinc oxide-based varistors were investigated for different aluminum concentrations under a sintering temperature of 1280°C. As the aluminum concentration increased, the average grain size (𝑑) increased in the range of 4.3–5.5 𝜇m and the sintered density increased in the range of 5.63–5.67 g/cm3. As the aluminum concentration increased, the breakdown field decreased in the range of 6327–710 V/cm and the maximum nonlinear coefficient (46.9) was obtained for 0.005 mol% in aluminum concentration, further additions impaired the nonlinear properties. As the aluminum concentration increased, the apparent dielectric constant increased in the range of 500.5–1327.4 and dissipation factor increased in the range of 0.00493–0.0724. The varistor added with 0.001 mol% Al exhibited the highest stability for 𝐸–𝐽 characteristics in which %𝛥 𝐸1\ mA is +1.4% and %𝛥 𝛼 is –5.7%, under stress state of 0.95 𝐸1\ mA/150° C/24 h.

    • Synthesis and characterization of ternary compound, Mn2SnTe4

      Gerzon E Delgado Asiloé J Mora Jines E Contreras Luis Betancourt

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      Mn2SnTe4 was synthesized by direct fusion using the anneal method. X-ray powder diffraction analysis indicated that this material crystallizes in the olivine-type structure, space group 𝑃𝑛𝑚𝑎, 𝑍 = 4, with unit cell parameters: 𝑎 = 14.020(2) Å, 𝑏 = 8.147(1) Å, 𝑐 = 6.607(1) Å, 𝑉 = 754.7(2) Å3. The Rietveld refinement converged to the figures of merit, 𝑅p = 6.9%, 𝑅wp = 8.5%, 𝑅exp = 6.0%, 𝜒2 = 2.0 and 𝑆 = 1.4.

    • Effect of substrate roughness on growth of diamond by hot filament CVD

      Awadesh K Mallik S R Binu L N Satapathy Chandrabhas Narayana Md Motin Seikh S A Shivashankar S K Biswas

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      Polycrystalline diamond coatings are grown on Si (100) substrate by hot filament CVD technique. We investigate here the effect of substrate roughening on the substrate temperature and methane concentration required to maintain high quality, high growth rate and faceted morphology of the diamond coatings. It has been shown that as we increase the substrate roughness from 0.05 𝜇m to 0.91 𝜇m (centre line average or CLA) there is enhancement in deposited film quality (Raman peak intensity ratio of 𝑠𝑝3 to non-𝑠𝑝3 content increases from 1.65 to 7.13) and the substrate temperature can be brought down to 640°C without any additional substrate heating. The coatings grown at adverse conditions for 𝑠𝑝3 deposition has cauliflower morphology with nanocrystalline grains and coatings grown under favourable 𝑠𝑝3 condition gives clear faceted grains.

    • Natural fibres-based polymers: Part I—Mechanical analysis of Pine needles reinforced biocomposites

      Vijay Kumar Thakur A S Singha

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      Lack of resources and increasing environmental pollution has evoked great interest in the research of materials that are friendly to our health and environment. Polymer composites fabricated from natural fibres is currently the most promising area in polymer science. Keeping in view the various advantages of natural fibres, in current series of green composites a study on natural fibre reinforced polymer composites has been made. This paper presents the results of an experimental series designed to assess the possibility of Pine needles as reinforcing material in polymer composites. First of all, urea–formaldehyde resin was synthesized and optimized by evaluating its mechanical properties. Optimized resin was reinforced with employing Pine needles of different dimensions such as particle reinforcement, short fibre reinforcement and long fibre reinforcement. Experimental results obtained shows that mechanical properties such as tensile strength, compressive strength and wear resistance of UF resin increases to a considerable extent when reinforced with Pine needles. Further it has been observed that particle reinforcement is more effective as compared to short fibre and long fibre reinforcement. These results suggest that Pine needles can be potential candidates for use in natural fibre reinforced polymer composites. Thermal and morphological studies of these composites have also been carried out.

    • Complex permittivity and conductivity of poly(𝑝-phenylenediazomethine) and its blends at microwave frequencies

      K G Princy Rani Joseph Honey John K T Mathew

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      Poly(𝑝-phenylenediazomethine) was synthesized by the condensation reaction between glyoxal and 𝑝-phenylene diamine in different solvents like methanol, toluene, 𝑚-cresol and 𝑁,𝑁-dimethylformamide. The dielectric properties and microwave conductivity of the pelletized samples were measured using cavity perturbation technique. The measurements were done at 2.17 GHz at room temperature (25°C). The effect of dopants on the dielectric properties and conductivity was studied using HCl and HClO4. Dielectric properties like dielectric constant, dielectric loss factor and microwave conductivity increased on doping with HCl and HClO4. Conducting polymer composites were prepared by in situ polymerization of glyoxal and 𝑝-phenylenediamine in different solvents containing different amounts of PVC, and silica. The microwave conductivity and complex permittivity of each sample was measured. The effect of dopants like HClO4 and HCl on these dielectric properties was also studied. The d.c. conductivity of the pressed samples measured by the two-probe method was also studied.

    • Preliminary investigations of antioxidation of dihydromyricetin in polymers

      Qiukai Zheng Linli Xu Linhua Zhu Jia Chen Feiyue Liu Dehong Chen Kai Xu Mingcai Chen

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      The antioxidative properties of dihydromyricetin (DMY), extracted from Ampelopsis grossedentata, in different solid polymers were evaluated by measuring the oxidation induction temperature (OIT*). The antioxidative efficiency was compared with Irganox 1010. The results showed that DMY was more efficient than the synthetical antioxidant. The high antioxidant activity of DMY is attributed to the special chemical structure, including the quantity and positions of the hydroxy groups in the molecule. DMY was harmless and highly effective to be a good natural antioxidant.

    • Effect of uncoated calcium carbonate and stearic acid coated calcium carbonate on mechanical, thermal and structural properties of poly(butylene terephthalate) (PBT)/calcium carbonate composites

      G S Deshmukh S U Pathak D R Peshwe J D Ekhe

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      PBT/CaCO3 composites were prepared in a single screw extruder with particle content varying from 0–30% by weight. The influence of surface treatment of the particles, with and without stearic acid (SA), on the mechanical, thermal and structural properties was studied. The experiments included tensile tests, impact tests, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The composite systems containing SA coated CaCO3 were found to exhibit better mechanical properties as compared to composite systems containing uncoated CaCO3, with the S3 system (20% of SA coated CaCO3) exhibiting best combination of mechanical properties. Thermal study revealed that particle type and content had no influence on the melting temperature but the crystallization temperature, % crystallinity and thermal stability increased on increasing the CaCO3 content in PBT matrix. Morphological observation indicated that in PBT composites containing SA coated CaCO3, the coupling agent favours a better polymer filler interaction rendering inorganic polymer interface compatible, which is also evident from better mechanical and thermal properties.

    • Effects of organic additives on microstructure and mechanical properties of porous Si3N4 ceramics

      Yu Fangli Wang Huanrui Yang Jianfeng Gao Jiqiang

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      Green bodies of porous Si3N4 ceramics were shaped by extrusion technique using different organic additives as binder during extrusion molding. Different porosity, microstructures and mechanical properties after the extrusion, drying, debinding and sintering stages were investigated. The solid slurry content of 70–75% and extrusion pressure of 0.5–1.0 MPa had played a decisive role in the smooth realization of extrusion molding. The porous Si3N4 ceramics were obtained with excellent properties using 4% hydroxypropyl methyl cellulose (HPMC) as binder and polyethylene glycol (PEG) of molecular weight, 1000, as plasticizer with a density of 1.91 g cm-3, porosity of 41.70%, three-point bending strength of 166.53 ± 20 MPa, fracture toughness of 2.45 ± 0.2 MPa m1/2 and Weibull modulus (m) of 20.75.

    • Utilization of steel melting electric arc furnace slag for development of vitreous ceramic tiles

      Ritwik Sarkar Nar Singh Swapan Kumar Das

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      Steel melting through electric arc furnace route is gaining popularity due to its many advantages, but generates a new waste, electric arc furnace slag, which is getting accumulated and land/mine filling and road construction are the only utilization. This slag has been tried to be value added and utilized to develop vitreous ceramic tiles. Slag, to the extent of 30–40 wt% with other conventional raw materials, were used for the development in the temperature range 1100–1150°C. The fired products showed relatively higher density with shorter firing range and good strength properties. Microstructural and EDAX studies were also done to evaluate the developed products.

    • High temperature cyclic oxidation and hot corrosion behaviours of superalloys at 900°C

      Subhash Kamal R Jayaganthan S Prakash

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      Oxidation and hot corrosion are serious problems in aircraft, marine, industrial, and land-base gas turbines. It is because of the usage of wide range of fuels coupled with increased operating temperatures, which leads to the degradation of turbine engines. To obviate these problems, superalloys, viz. Superni 75, Superni 718 and Superfer 800H superalloys (Midhani grade), are the prominent materials for the high temperature applications. It is very essential to investigate the degradation mechanism of superalloys due to oxidation and hot corrosion and substantiate the role of alloying elements for the formation of protective oxide films over the surface of the superalloys. Therefore, the present work investigates the oxidation and hot corrosion behaviour of superalloys exposed to air and molten salt (Na2SO4–60% V2O5) environment, respectively, at 900°C under cyclic conditions. The weight change measurements made on the superalloys during the experiments are used to determine the kinetics of oxidation and hot corrosion. X-ray diffraction (XRD), X-ray mapping and field emission scanning electron microscope (FESEM, FEI, Quanta 200F company) with EDAX Genesis software attachment, made in Czech Republic are used to characterize the corroded products of the superalloys. It is observed that the formation of scale rich in Cr2O3, NiO and spinel NiCr2O4 has contributed for the better oxidation and hot corrosion resistance of Superni 75; whereas relatively lesser hot corrosion resistance of Superfer 800H is due to the formation of non-protective oxides of iron and sulphides of iron and nickel. The parabolic rate constants calculated for the superalloys show that the corrosion rate is minimum in air as compared to molten salt environment.

    • Effect of menthol coated craft paper on corrosion of copper in HCl environment

      P Premkumar K Kannan M Natesan

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      Natural menthol was coated on craft paper by impregnation and studied as volatile corrosion inhibitor for copper in hydrochloric acid environment. The effect of menthol on copper corrosion was studied by gravimetric and electrochemical methods such as potentiodynamic polarization and electrochemical impedance measurements. The results indicate that menthol adsorbs on the metal surface, which protects copper against further corrosion. The adsorption behaviour of menthol on copper surface was found to obey Temkin’s adsorption isotherm.

    • Aromatic quinoxaline as corrosion inhibitor for bronze in aqueous chloride solution

      N Saoudi A Bellaouchou A Guenbour A Ben Bachir E M Essassi M El Achouri

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      A new corrosion inhibitor, viz. 3-ethyl-6-méthyl-quinoxalin-2-one, 1-benzyl-6-methyl-quinoxalin- 2-one, 2-benzyloxy-3,6-dimethyl-quinoxaline, 1-benzyl-3-methyl-quinoxalin-2-one, were synthesized in the laboratory. Their influence on the inhibition on corrosion of bronze in aqueous chloride solution (3% NaCl) was studied by electrochemical polarization methods and weight-loss measurements. The impact of temperature on the effectiveness of the substances mentioned above has been determined between 20 and 60°C. The results showed that the corrosion resistance was greatly enhanced in the presence of inhibitor and that the effectiveness depends on some physicochemical properties of the molecule, related to its functional groups. These compounds act through the formation of a protective film on the surface of the alloy.

    • Thermal decomposition of Co–Al layered double hydroxide: Identification of precursor to oxide with spinel structure

      A V Radha Grace S Thomas P Vishnu Kamath Churchil A Antonyraj S Kannan

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      The layered double hydroxide (LDH) of Co with Al decomposes to yield an oxide residue with the spinel structure below 250°C. The decomposition reaction is preceded by the formation of an intermediate hydroxide in which the metal hydroxide layers are regularly stacked about the 𝑐-crystallographic axis, but the layers themselves are aperiodic. Aperiodicity is modeled by locating randomly chosen Co2+ ions in tetrahedral sites in the interlayer region. This phase is characterized by a single strong basal reflection in its powder diffraction pattern. All other reflections are extinguished on account of

      1. turbostratic disorder which destroys all ℎ𝑘𝑙 reflections and

      2. layer aperiodicity, which destroys all two dimensional ℎ𝑘 reflections.

      Given its topochemical relationship with the spinel structure, such an intermediate is a necessary precursor to spinel formation.

    • Synthesis and structure refinement of layered double hydroxides of Co, Mg and Ni with Ga

      G V Manohara P Vishnu Kamath

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      Homogeneous precipitation by urea hydrolysis results in the formation of highly ordered layered double hydroxides of divalent metal ions (Co, Mg, Ni) and Ga. Structure refinement shows that these carbonate containing layered hydroxides crystallize with rhombohedral symmetry (space group 𝑅-3𝑚) in the structure of the 3𝑅1 polytype. An analysis of the structure shows that, coulombic attraction between the layer and interlayer remains invariant in different layered hydroxides, whereas the strength of hydrogen bonding varies. The Ni–Ga LDH has the weakest hydrogen bonding and Co–Ga, the strongest, as reflected by the layer–interlayer oxygen–oxygen distances. The poor polarity of the OH bond in the Ni–Ga hydroxide points to the greater covalency of the (𝑀2+}/𝑀′3+)-oxygen bond in this compound as opposed to the Co–Ga hydroxide. These observations are supported by IR spectra.

    • Bio-beneficiation of kaolin and feldspar and its effect on fired characteristics of triaxial porcelain

      Anandita Roy Samarendra K Singh P C Banerjee Kausik Dana Swapan Kumar Das

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      Presence of iron compounds as impurities in kaolin and feldspar, impart reddish colour to ceramic products manufactured using these minerals. The quality of kaolin and feldspar was enriched mainly through iron removal by biological methods. Bacteria isolated from kaolin of Indian origin were used for bioleaching. Biotreatment of kaolin and feldspar using indigenous bacteria not only lowered the iron content of the minerals but also improved their whiteness. The porcelain prepared with these biobeneficiated minerals was compared to that prepared with non-beneficiated one. Physico-mechanical properties of porcelain were distinctly improved by using biobeneficiated kaolin and feldspar, without affecting the individual mineralogical compositions of kaolin and feldspar.

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