Corrosion Behavior in Volcanic Soils: In Search of Candidate Materials for Thermoelectric Devices

Thermoelectric generators have emerged as an excellent solution for the energy supply of volcanic monitoring stations due to their compactness and continuous power generation. Nevertheless, in order to become a completely viable solution, it is necessary to ensure that their materials are able to resist in the acidic environment characteristic of volcanoes. Hence, the main objective of this work is to study the resistance to corrosion of six different metallic materials that are candidates for use in the heat exchangers. For this purpose, the metal probes have been buried for one year in the soil of the Teide volcano (Spain) and their corrosion behavior has been evaluated by using different techniques (OM, SEM, and XRD). The results have shown excessive corrosion damage to the copper, brass, and galvanized steel tubes. After evaluating the corrosion behavior and thermoelectric performance, AISI 304 and AISI 316 stainless steels are proposed for use as heat exchangers in thermoelectric devices in volcanic environments.

Durability Assessment of a Plasma-Polymerized Coating with Anti-Biofilm Activity against L. monocytogenes Subjected to Repeated Sanitization

Biofilm formation on food-contact surfaces is a matter of major concern causing food safety and spoilage issues to this sector. The aim of this study was to assess the durability of the anti-biofilm capacity of a plasma-polymerized coating composed of a base coating of (3-aminopropyl)triethoxysilane (APTES) and a functional coating of acrylic acid (AcAc). Coated and uncoated AISI 316 stainless steel (SS) plates were subjected to five sanitization cycles with sodium hypochlorite (0.05%) and peracetic acid (0.5%). The effectiveness of the coating for the inhibition of multi-strain Listeria monocytogenes biofilm formation was confirmed using a three-strain cocktail, which was grown on the SS plates at 12 °C for 6 days. Compared to the uncoated SS, relative biofilm productions of 14.6% on the non-sanitized coating, 27.9% on the coating after sanitization with sodium hypochlorite, and 82.3% on the coating after sanitization with peracetic acid were obtained. Morphological and physicochemical characterization of the coatings suggested that the greater anti-biofilm effectiveness after sanitization with sodium hypochlorite was due to the high pH of this solution, which caused a deprotonation of the carboxylic acid groups of the functional coating. This fact conferred it a strong hydrophilicity and negatively charged its surface, which was favorable for preventing bacterial attachment and biofilm formation.

Analisa pengaruh media pendingin dan arus listrik pada proses pengelasan titik (spot welding) stainlees steel terhadap nilai kekuatan tarik

Pengelasan adalah salah satu teknik penyambungan logam dengan cara mencairkan sebagian logam induk dan logam pengisi dengan tekanan dan dengan atau tanpa logam penambah sehingga menghasilkan sambungan las yang kontiyu. Media pendingin dan arus listrik pada proses pengelasan ini sangat mempengaruhi hasil pengelasan. Lap joint adalah salah satu jenis sambungan las yang ada pada las titik yaitu jenis sambunga tumpuk. Penelitian ini menggunakan plat baja Stainlees Steel AISI 316. Tujuan dari penelitian ini adalah untuk mengetahui kekuatan tarik dan jenis pendingin dengan arus berapa yang paling optimal untuk diberikan pembebanan tarik. Untuk waktu pengelasan disamakan yaitu 2 detik dan untuk parameter yang digunakan adalah media pendingin air biasa, air garam, air mineral dan variasi arus 660 Ampere, 880 Ampere dan 1100 Ampere. Pengujian yang dilakukan adalah pengujian tarik menggunakan alat Ultimate Testing Machine. Pada hasil pengujian didapat bahwa jenis sambungan lap joint yang paling optimum untuk diberikan pembebanan tarik dari nilai yield strength yaitu pendingin air biasa pada arus 1100 Ampere sebesar 159,17 kg/mm2, tensile strength dengan pendingin air mineral pada Arus 1100 Ampere sebesar 195,92 kg/mm2, dan nilai elongation dengan pendingin air mineral pada arus 1100 Ampere sebesar 11.19%.

Formation and Properties of Nitrocarburizing S-Phase on AISI 316L Stainless Steel-Based WC Composite Layers by Low-Temperature Plasma Nitriding

Stainless steel-based WC composite layers fabricated by a laser cladding technique, have strong mechanical strength. However, the wear resistance of WC composite layers is not sufficient for use in severe friction and wear environments, and the corrosion resistance is significantly reduced by the formation of secondary carbides. Low-temperature plasma nitriding and carburizing of austenitic stainless steels, treated at temperatures of less than 450 °C, can produce a supersaturated solid solution of nitrogen or carbon, known as the S-phase. The combined treatment of nitriding and carburizing can form a nitrocarburizing S-phase, which is characterized by a thick layer and superior cross-sectional hardness distribution. During the laser cladding process, free carbon was produced by the decomposition of WC particles. To achieve excellent wear and corrosion resistance, we attempted to use this free carbon to form a nitrocarburizing S-phase on AISI 316 L stainless steel-based WC composite layers by plasma nitriding alone. As a result, the thick nitrocarburizing S-phase was formed. The Vickers hardness of the S-phase ranged from 1200 to 1400 HV, and the hardness depth distribution became smoother. The corrosion resistance was also improved through increasing the pitting resistance equivalent numbers due to the nitrogen that dissolved in the AISI 316 L steel matrix.