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"Baja karbon rendah ASTM A36 umum digunakan pada aplikasi konstruksi, perminyakan, dan struktur kapal. Ketiga aplikasi tersebut memungkinkan adanya tegangan tarik pada saat pemasangan maupun penggunaan. Perilaku korosi baja ASTM A36 dengan fungsi tegangan tarik diamati menggunakan metode Electrochemical Impedance Spectroscopy (EIS) dan X-Ray Diffractometer (XRD). Baja ASTM A36 dilakukan perendaman pada larutan NaCl 3,5% dengan variasi tegangan tarik 0, 100, dan 200 MPa dan variasi waktu perendaman 1 jam, 4 jam, 8 jam, 24 jam, dan 72 jam. Hasilnya menunjukkan bahwa semakin besar tegangan tarik dapat menurunkan ketahanan baja terhadap korosi. Semakin besar tegangan, resistansi logam terhadap serangan korosi semakin menurun serta memungkinkan terbentuknya lubang korosi sumuran yang lebih besar akibat adanya tegangan pada batas butir yang terkorosi. Hasil analisa XRD pada permukaan baja setelah proses korosi menunjukkan adanya fasa berupa Fe, magnetit (Fe₃O₄), dan NaCl

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ASTM A36 low carbon steel is commonly used in construction, petroleum, and ship structure applications. These three applications allow for tensile stress during installation and use. The corrosion behavior of ASTM A36 steel with tensile stress function was observed using Electrochemical Impedance Spectroscopy (EIS) and X-Ray Diffractometer (XRD) methods. ASTM A36 steel was immersed in 3.5% NaCl solution with variations in tensile stress of 0, 100, and 200 MPa and immersion time variations of 1 hour, 4 hours, 8 hours, 24 hours, and 72 hours. The results show that the greater the tensile stress, the lower the steel's resistance to corrosion. The greater the stress, the lower the metal's resistance to corrosion attack and allows the formation of larger pits due to stress at the corroded grain boundaries. The results of XRD analysis on the ASTM A36 low carbon steel surface after the corrosion process showed the presence of Fe, magnetite (Fe₃O₄), and NaCl phases."

"Pada penelitian ini, mullite yang disintesis dari aluminum nitrat hidrat [(Al(NO3)3.9H2O] dan sol silika sekam padi dikenakan pada perlakuan sintering dengan suhu 900, 1000, 1100, 1200, dan 1300°C, kemudian dikarakterisasi dengan difraksi sinar-x (XRD) dilanjutkan dengan penghalusan menggunakan metode Rietveld, dan analisis termal diferensial (DTA). Hasil penelitian menunjukkan bahwa dalam sampel yang disintering pada suhu 900°C, tidak ditemukan fasa mullite, tetapi fasa kristobalit dan alumina terdeteksi dengan jelas. Pembentukan mullite baru terjadi pada suhu 1000°C dan bertumbuh dengan peningkatan suhu ditandai dengan kenaikan persen berat (wt%) dari 62,62 menjadi 92,29%, disertai penurunan persen berat kristobalit dari 22,42 menjadi 1,25% dan penurunan persen berat alumina dari 77,58 menjadi 6,46%. Hasil penghalusan menunjukkan korelasi yang baik antara unit sel hasil perhitungan dan hasil pengamatan, dengan dimensi unit sel adalah a = 7,545 nm, b = 7,689 nm dan c = 2,884 nm untuk mullite, a = b = 0,5531 nm, dan c = 0,6923 nm untuk kristobalit, dan a = b = 0,5026 nm, dan c = 1,2808 nm untuk alumina. Hasil analisis dengan DTA menunjukkan bahwa dalam sampel yang tidak disintering, hanya terdapat alumina dan silika, sementara dalam sampel yang disintering terdapat mullite, alumina, dan kristobalit.

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In this study, mullite synthesized from aluminum nitrate hydrate [(Al(NO3)3.9H2O] and silica sol from rice husk was subjected to sintering treatment at temperatures of 900, 1000, 1100, 1200, and 1300°C, and characterized using x-ray diffraction (XRD), followed by Rietveld refinement, and differential thermal analysis (DTA). The results indicated that in the sample sintered at 900°C, no mullite phase was identified, but crystoballite and alumina were well detected. The formation of mullite started at temperature of 1000°C and continued to grow at higher temperatures, resulted in increased weight percentage (wt%) from 62.62 to 92.29%, while crystoballite and alumina decreased from 22.42 to 1.25% and from 77.58 to 6.46 % respectively. A good correlation was found between the calculated and observed unit cells. For mullite phase, the unit cell dimensions are a = 7.545 nm, b =.689 nm and c = 2.884 nm, for crystoballite a =b = 0.5531 nm and c = 0.6923 nm, and for alumina a = b = 0.5026 nm, and c = 1.2808 nm. The DTA analyses revealed that in the untreated sample, only alumina and silica were detected, while in the sintered samples we found the existence of mullite, alumina, and crystoballite."

"Gunungapi Papandayan, terletak di Kabupaten Garut, Jawa Barat, merupakan salah satu daerah dengan potensi panas bumi yang signifikan. Sebagai gunung api strato tipe A, Papandayan memiliki aktivitas vulkanik yang masih berlangsung, termasuk letusan freatik dan freatomagmatik yang memengaruhi stabilitas geologi di kawasan tersebut. Kawasan kawah utama berbentuk tapal kuda yang terbuka ke arah timur laut memperlihatkan karakteristik geologi unik, termasuk manifestasi hidrotermal seperti mud pools, solfatara, dan hot springs. Kondisi ini menunjukkan adanya proses alterasi hidrotermal yang mengubah komposisi mineral dan tekstur batuan, sehingga meningkatkan kerentanan terhadap longsoran. Penelitian ini bertujuan untuk memetakan zonasi alterasi hidrotermal dan mengidentifikasi potensi instabilitas geologi di Kawah Tapal Kuda. Metode yang digunakan dalam penelitian ini meliputi pemetaan geologi, analisis petrografi pada 10 sampel, dan X-Ray Diffraction (XRD) pada 5 sampel batuan. Hasil analisis menunjukkan batuan asal (protolith) di daerah penelitian terdiri dari andesit, breksi andesit, dan tuf. Batuan-batuan ini telah mengalami alterasi hidrotermal yang membentuk empat zona utama berdasarkan himpunan mineral pencirinya yaitu, Zona Argilik Lemah, Zona Transisi Kaolinit-Montmorillonite, Zona Alunit-Kaolinit, dan Zona Silika-Kaolinit sebagai inti dari sistem. Secara spasial, zona dengan intensitas alterasi terkuat, yaitu Zona Silika-Kaolinit dan Zona Alunit-Kaolinit, terkonsentrasi di sektor tengah hingga timur laut kawah. Adanya korelasi spasial yang kuat antara lokasi zona batuan terlemah ini dengan sumber keruntuhan katastropik tahun 1772 mengindikasikan bahwa proses alterasi hidrotermal merupakan faktor yang signifikan dalam degradasi kekuatan batuan dan ketidakstabilan lereng. Meskipun demikian, diperlukan studi lebih lanjut untuk dapat mengkuantifikasi hubungan ini secara mendetail. Oleh karena itu, pemetaan zonasi ini menjadi landasan awal yang krusial untuk studi lanjutan terkait mitigasi risiko geologi.

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Papandayan Volcano, located in Garut Regency, West Java, is an area with significant geothermal potential. As a type-A stratovolcano, Papandayan has ongoing volcanic activity, including phreatic and phreatomagmatic eruptions that affect the geological stability of the area. The main horseshoe-shaped crater, which opens to the northeast, exhibits unique geological characteristics, including hydrothermal manifestations such as mud pools, solfataras, and hot springs. These conditions indicate a hydrothermal alteration process that changes the mineral composition and texture of the rocks, thereby increasing the susceptibility to landslides. This research aims to map the hydrothermal alteration zonation and identify potential geological instability in the Horseshoe Crater. The methods used in this research include geological mapping, petrographic analysis of 10 samples, and X-Ray Diffraction (XRD) of 5 rock samples. The analysis results show that the parent rock (protolith) in the study area consists of andesite, andesitic breccia, and tuff. These rocks have undergone hydrothermal alteration, forming four main zones based on their characteristic mineral assemblages: the Weak Argillic Zone, the KaoliniteMontmorillonite Transition Zone, the Alunite-Kaolinite Zone, and the Silica-Kaolinite Zone as the core of the system. Spatially, the zones with the highest alteration intensity, namely the Silica-Kaolinite Zone and the Alunite-Kaolinite Zone, are concentrated in the central to northeastern sector of the crater. A strong spatial correlation between the location of these weakest rock zones and the source of the 1772 catastrophic collapse indicates that the hydrothermal alteration process is a significant factor in the degradation of rock strength and slope instability. Nevertheless, further study is required to quantify this relationship in detail. Therefore, this zonation mapping provides a crucial initial foundation for further studies related to geological risk mitigation."

"Synthesis and Monte Carlo simulation of improved concrete composites as x-ray/gamma ray shielding materials were performed. Samples of shieldings were synthesized using the base materials of Portland-type cement concrete with fillers of alloy steel, Co, Mn, and Cr, mixed separately as additives. The samples were characterized using Scanning Electron Microscopy-Energy Dispersive X-ray Spectrometry (SEM-EDS) to determine the constituent elements quantitatively. Linear attenuation coefficients of the samples were measured in the experiments and also simulated using Monte Carlo transport code MCNP5 in order to evaluate their shielding performance. The results of the experimentation and computer simulation reveal concrete with alloy steel added as having the best shielding properties, although concrete with other fillers added also exhibited enhanced shielding performance. It was demonstrated that 6.06 w% of fillers enhanced the x-ray/gamma ray shielding capability of ordinary concrete composites by improving their attenuation coefficient values by 40–60%."