Asti Sawitri

Coal remains a primary energy source, widely used for fuel and electricity generation, but it is also a major contributor to global carbon emissions, responsible for over 40% of the 15.3 billion tons of CO₂ emitted in 2021. In response, researchers are exploring strategies to reduce coal usage in briquette production. One promising alternative is biomass-based briquettes, designed to offer comparable performance to traditional charcoal while being more sustainable. This study investigates the thermal and mechanical properties of briquettes made from rice husk (RH) and coffee husk (CH), focusing on how particle size affects their heating value. RH and CH are rich in lignin, cellulose, and hemicellulose, crucial for briquette structure, while tapioca flour, used as a binder, provides amylose and amylopectin to enhance bonding. The carbonization process was conducted at 400°C for 60 minutes. Researchers used a 25% CH to 75% RH blend and evaluated three mesh sizes (60, 80, and 100). Briquettes were assessed based on calorific value, moisture content, shatter index, volatile matter, fixed carbon, density, ash content, and combustion rate. The results showed that the 100-mesh sample had the highest density, moisture content, volatile matter content, and burning rate with the value of 662.81 Kg/m3, 6.7%, and 7.07%, respectively. In contrast, the 60-mesh sample had the highest ash content (5.01%), as well as the lowest fixed carbon (82.04%) and shatter index (4.36%). These findings indicate that mesh size significantly affects the thermal and mechanical properties of the briquettes.

This work aimed to observe the influence of calorific value and proximate properties in the fabrication of rice husk (RS) and coffee shell (CH) briquettes composite. Rice and coffee husks contain cellulose, hemicellulose, and lignin. These contents are necessary for the adhesive to bind the...

This report aimed to know the performance of local mineral-based composite ceramic. The materials used consist of Indonesian local minerals, which are jarosite and manganite minerals as sources of oxide iron and Mangan. The materials were synthesized using the precipitation method, whereas composite ceramic was fabricated using a screen printing method and fired at 600 oC using a furnace. The results of the characterizations indicate that the sample forms three phases on diffraction peaks. The differences in the resistance values in ambient and ethanol environments indicate that the sample has very different responses. The high porosity of the sample greatly support the gas adsorption process. Thus, the sample has a high level of sensitivity. With the above characteristics, the composite ceramic which was fabricated has the potential to be applied to gas sensors, especially ethanol gas sensors.

We reported the methylene blue (MB) degradation by the photocatalysis method. This work aimed to know the effectiveness of degradation using a MgFe2O4:TiO2 composite. Synthesis of the composite used the sol-gel method. We synthesized three samples with ratios between MgFe2O4 and TiO2. Those were 100:0, 50:50, and 75:25, respectively. Sample (75:25) degraded MB of 47.23% with a reaction rate of 5.326 x 10-3 minute-1 under solar radiation. Whereas, without solar radiation, a sample showed a lower reaction rate. It happened because the sunlight produced photon energy to produce OH* radical so that it could activate the sample to absorb the dye. Reusable test resulted 19.73% degradation of MB for 100:0, 17.03% for 50:50, and 20.59% for 75:25 for 120 minutes. The XRD result for 75:25 has three phases, which are MgFe2O4 with cubic structure, TiO2 with tetragonal structure, and Fe2O3 with hexagonal structure. This work indicated that the sol-gel method could synthesize composite structures, and the sample may be used to remove methylene blue.

This study demonstrated that the constant average speed of a dynamic car could be measured and calculated using the smartphone magnetometer. The apparatus setup was built using a dynamic car, a linear track up to 1.50 m, a bunch of magnets, and a smartphone magnetometer application. The smartphone magnetometer application, ‘Physics Toolbox Suite’, was free for the experiment. The magnet and smartphone magnetometer were attached on a linear track and dynamic car, respectively. When the dynamic car are moving on the car track, the smartphone magnetometer will measure the magnetic field value versus the time relation. The magnetic field value will fluctuate, increasing when close to the magnet or decrease when the distance from the magnet increases. The magnetic field properties (peaks time) versus the magnet distance position were analyzed using linear fitting, and we find the average speed of the dynamic car. We hope that this magnetometer experiment will be valuably used in general physics laboratories.

In this study, we have synthesized and applied the activated carbon fibbers from pyrolyzed cotton to adsorp fume pollutants. The activated carbon fibbers from cotton were synthesized using an oven with simple heating method at low carbonization temperature. The cotton was successfully turned into carbon within four hours at carbonization temperature of 250°C. The reults showed that activation process using KOH and NaOH significantly affected the functional groups, morphology, diameter, and porosity of the activated carbon fibbers.

In this research, Mn and Fe-based ceramic gas sensing were fabricated and characterized. This research used natural mineral which is widely available in Indonesia and intended to observe the characteristics of Mn and Fe-based semiconducting material. Fabricating process of the thick films started by synthesizing the ceramic powder of Fe(OH)₃ and Mn oxide material using the precipitation method. The deposition from precipitation method previously was calcined at a temperature of 800 °C to produce nanoparticle powder. Nanoparticle powder that contains Mn and Fe oxide was mixed with an organic vehicle (OV) to produce a paste. Then, the paste was layered on the alumina substrate by using the screen printing method. XRD method was utilized to characterize the thick film crystal structure that has been produced. XRD spectra showed that the ceramic layer was formed from the solid Mn_0.5Fe_1.5O₃ (bixbyite) and Fe₂O₃. In addition, the electrical properties (resistance) examination was held in the room that contains air and ethanol to determine the sensor sensitivity of ethanol gas. The sensor resistance decreases as the ethanol gas was added, showing that the sensor was sensitive to ethanol gas and an n-type semiconductor. Gas sensor exhibit sensitive characterization of ethanol gas on the concentration of (100 to 300) ppm at a temperature of (150 to 200) °C. This showed that the Mn_0.5Fe_1.5O₃-Fe₂O₃ ceramic semiconductor could be utilized as the ethanol gas detector.