Thermal spray is an effective process for the fabrication of a metal matrix composite (MMC), where a zirconium diboride reinforcement is embedded in a molybdenum matrix to enable the combining of favorable properties in a new composite. The combination of two leading materials in the category of ultra-high-temperature ceramics (UHTCs) is due to a very high melting point (Mo: 2623 °C and ZrB2: 3245 °C), high thermal conductivity (Mo: 139 W/m°C and ZrB2: 24 W/m°C), good thermal shock resistance, low coefficient of thermal expansion (Mo: 5.35 µm/m°C and ZrB2: 5.9 x 10-6 K-1), retention of strength at elevated temperatures and stability in extreme environments. Thermal spraying of the Mo/ZrB2 composite possesses a non-linear behavior that is influenced by many coating variables. This characteristic makes finding the optimal factor combination difficult. Therefore, an effective and strategic statistical approach incorporating systematic experimental data is needed to optimize the process. In this study, the L9 orthogonal array in the Taguchi approach was utilized to optimize the spraying distance (SD), number of passes (NP), pressure (P) and coat-face temperature (TCF) using a dummy fiberglass substrate. The performance was evaluated based on the coating density (Cd) of the surfaces. Based on confirmation tests, our Taguchi analysis determined the ideal process parameters, which considerably enhanced the coating process. From the output response of the ANOVA, the most influential parameters for achieving a high coating density (Cd) were determined to be SD = 20 cm, NP = 24, P = 4 bar and TCF = 330 °C ((SD.)1-(NP.)3-P2-(S.T.)3). These observations show that the coating density (Cd) was significantly influenced by the coat-face temperature, followed by the number of passes, spraying distance and pressure with the following contributions 6.29, 17.89, 17.42 and 3.35%, respectively.

Posted on: December 2022

Authored: Faiz Ahmad

This paper presents an investigation of the drilling performance of glass fiber reinforced polymer (GFRP) composite based on the thrust force, temperature, and delamination factor (at entry and exit of the hole). High-speed steel (HSS), solid carbide (SC), and solid carbide Balinit® Helica coated (SCBH) twist tools were used for the drilling process. Other drilling parameters were high spindle speeds (12,000, 15,000, and 18,000 rpm), feed rate (300, 500, and 700 mm/min), and laminate thickness (3, 5, and 7 mm). ANOVA and response surface methodology were developed to examine the drilling process based on input and output parameters. Results showed that delamination was observed in the form of matrix debonding, uncut fibers, and fiber pull-out. The best drilling performance was achieved by the SC and SCBH tool at a low feed rate (300 rpm) and high speed (18,000 rpm), and high laminate thickness (7 mm).

Posted on: September 2022

Authored: Faiz Ahmad

The fire behaviour of radiata pine timber, treated with intumescent coatings and exposed to heat flux conditions equivalent to a high-risk bushfire attack level (BAL) is investigated. The experiment is designed for coated timber exposed to bushfire attack levels greater than 19 kW/m2 and up to 29 kW/m2 (BAL-29) in accordance with AS 3959. The timber was coated with a DFT of 400 µm of the developed intumescent formulations based on expandable graphite (EG), ammonium polyphosphate (APP) and a waterborne acrylic resin with high adhesion strength. The coated timbers were tested according to AS3959, for a BAL-29 rating, using a cone calorimeter at 25 kW/m2 for 10 min. Most of the coated samples reported a substantial reduction in the peak heat release rate (p-HRR) and average HRR with values not greater than 100 kW/m2 and 60 kW/m2, respectively. These results satisfy the requirements for bushfire-resistant timber at BAL-29 rating. Formulation 4 (F4), with EG:APP ratio of 3:1 and resin content of 45 wt% was identified as the most cost-effective formulation. Coatings with high loading of EG and APP provided the best fire protection to the timber substrate, however, a larger char with a less compact structure is formed.

Posted on:October 2023

Authored: Faiz Ahmad

Valorization of bauxite residue (BR) enhances the dynamics of its application in intumescent coating for fire retarding systems. This BR, an alumina production waste could contain up to 45% ferrous oxide along with residual aluminous minerals. In an attempt to optimize the fire retardant properties of these minerals in intumescent systems, BR was treated in oxalic acid, varying the heating temperature between 50°C and 100°C at a constant pH of 2.65. X-ray florescence spectrometry revealed up to 80% reduction in iron content and total dissolution of desilication products (DSPs). The process temperature was found to affect the efficiency with which iron oxide was removed and with which the dissolved DSPs were precipitated as aluminum hydrates. X-ray diffraction revealed increased crystallinity and a gibbsite-dominated compound. Incorporation of the modified bauxite residues into a control intumescing formulation resulted in improved endothermic cooling, increased char expansion and char reinforcement. An inverse relationship appeared to exist between aluminum hydrates and iron as removal of iron led to enhanced intumescence and increased char expansion while higher iron content led to a compact, less expanded char. A balance of the fire retarding minerals occurred at a leaching temperature of 75°C in oxalic acid. Best heat shielding performance thus occurred at XBR75-IC5 as char expansion increased by 12% and the substrate temperature reduced by 31% over the control IC system. Thus, BR may act as alternative fire retardant filler for intumescing systems.

Posted on: June 2021

Authored: Faiz Ahmad

In the present work, the facile thermal decomposition of raw coconut shells was carried out for the exploitation of the role of inert gas in the carbonization process and its role in determining the morphology, crystallographic parameters, and surface area of biochar before activation. The comparative investigation of mesoporous carbonized products synthesized with the muffle and tube furnace was carried out at a similar temperature and an assessment was made with a commercial carbon. The focus of the work was aimed at the interpretation of surface morphology, elemental identification, phase composition, interplanar spacing, full-width half maximum, crystallite size, lateral size, number of layers, dislocation density, microstrain, packing density, crystallinity index, and the specific surface area of the product obtained from two different approaches. It was revealed that the carbonized coconut shell chars obtained from the tube furnace have better characteristics to be activated further for carbon black synthesis. So, the flow of inert gas in a tube furnace is demonstrated to have a key role in improving the attributes of coconut shell chars.

Posted on: April 2023

Authored: Faiz Ahmad