• Kausik Dana

Articles written in Bulletin of Materials Science

• Evolution of microstructure in flyash-containing porcelain body on heating at different temperatures

15 wt% flyash (a calcined byproduct of thermal power plant) was incorporated in a normal triaxial kaolin–quartz–feldspar system by replacing equivalent amount of quartz. The differences in microstructural evolution on heating the compact mass of both normal and flyash-containing porcelain at different temperatures (1150–1300°C) were examined using scanning electron microscopy (SEM) operating in secondary electron image (SEI) mode. Microstructure of normal porcelain did not show the presence of mullite and quartz grains at 1200°C and the viscosity of silica-rich glass restricted the growth of mullite crystals at 1250°C. Flyash porcelain, on the other hand, shows the presence of primary mullite aggregates in the clay relict and a significant growth of mullite crystals in a low viscosity glassy matrix at 1200°C itself. At 1300°C, both the bodies show a larger region of more elongated (&gt; 1 𝜇m) secondary mullite along with clusters of smaller sized primary mullite (&lt; 1 𝜇m). Small primary mullite crystals in the clay relict can be distinguished from elongated secondary mullite crystals in the feldspar relict in their size. Primary mullite aggregates remain stable also at higher temperatures. XRD studies were carried out for quantitative estimation of quartz, mullite and glass, which supported the SEM observations. An attempt was also made to correlate their mechanical strength with the constituent phases.

• Titania doped triaxial porcelain: Enhancement of strength by controlled heat treatment

Titania doped vitrified triaxial porcelain samples were subjected to controlled heat treatment at different temperatures of 600, 800 and 1000°C with a specific heating schedule. The results revealed that flexural strength of 800°C heat treated sample was significantly enhanced to 60 MPa from its original value of 40 MPa. XRD pattern revealed the formation of mullite in the system both before and after heat treatment and the differences in their growth was ascertained through SEM analysis. The present heat treatment process may be useful to produce high strength porcelain body from a common triaxial system.

• Polypropylene–clay composite prepared from Indian bentonite

In the present work, a set of experimental polypropylene (PP) clay composites containing pristine bentonite clay of Indian origin has been prepared and then characterized. The polymer clay composites are processed by solution mixing of polypropylene with bentonite clay using a solvent xylene and high speed electric stirrer at a temperature around 130°C and then by compression molding at 170°C. The mechanical properties of PP–clay composites like tensile strength, hardness and impact resistance have been investigated. Microstructural studies were carried out using scanning electron microscope and transmission electron microscope and the thermal properties were studied using differential scanning calorimeter. Mechanical properties of the prepared composites showed highest reinforcing and toughening effects of the clay filler at a loading of only 5 mass % in PP matrix. Tensile strength was observed to be highest in case of 5 mass % of clay loading and it was more than 14% of that of the neat PP, while toughness increased by more than 80%. Bentonite clay–PP composite (5 mass %) also showed 60% increase in impact energy value. However, no significant change was observed in case of hardness and tensile modulus. Higher percentages of bentonite clay did not further improve the properties with respect to pristine polypropylene. The study of the microstructure of the prepared polymer layered silicate clay composites showed a mixed morphology with multiple stacks of clay layers and tactoids of different thicknesses.

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

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.

• Intercalation of LDH NO$_3$ with short-chain intercalants

Intercalation behaviour of layered-double hydroxide (LDH) with short-chain intercalants (−(CH$_2$)$_n$−, $n$ < 9) is significantly difficult and less reported than with long-chain intercalants. The present study reports an efficientway to intercalate LDH with short-chain intercalants ($n=4$ and 8) and investigates the effect of layer charge on intercalation behaviour of LDHs. Short-chain anionic surfactants were successfully intercalated with synthetic LDHs [Zn$_{1−x}$Al$_x$(OH)$_2$NO$_3 \cdot n$H$_2$O, $x = 0.2−0.33$] by an ion-exchange intercalation technique in a slightly acidic medium(pH $=$ 5.4). The adverse effect of a carbonate anion was avoided by performing the ion-exchange intercalation in slightly acidic medium (pH $=$ 5.4). It was found that basal spacing ($d_{003}$) and experimental organic loading of intercalated LDH (OLDH) increase monotonically with increasing anion-exchange capacity of LDH and intercalant chain length. The evolution of intercalated LDH (O-LDH) structures with increasing intercalant chain length and layered charge has been deciphered by correlating basal spacing of O-LDHs (by X-ray powder diffraction), organic loading data (by thermogravimetric analysis)and molecular conformation of O-LDHs (by Fourier-transform infrared spectroscopy) within the LDH gallery. Successful intercalation of LDH with these short-chain intercalants in slightly acidic medium has not been reported previously.

• # Bulletin of Materials Science

Volume 43, 2020
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019