Formamidine disulfide oxidant as a localised electron scavenger for >20% perovskite solar cell modules

A large FAS2+ ion in FAPbI3 scavenges localized electrons in defects, leading to perovskite solar cell module with remarkable performance values of 18.76% (25.74 cm2) and 15.87% (65.22 cm2), respectively.

Effects of Thiourea Stripping of 14 Karat White Gold Alloys With the Addition of SDS Surfactant

A stripping solution with thiourea, iron(III) sulfate, and sodium dodecyl sulfate(SDS) was employed to strip Ni-based 14 karat white gold alloys, and the formation of the NiS byproduct and elimination of passivation were investigated in the presence of 0.0-0.2 g/L SDS. White gold alloy samples with a flat shape were cast by gypsum investment and were stripped using the prepared stripping solution. Subsequently, the surface morphology, elimination of the passivation layer, weight loss, microstructure, elemental composition, and electrochemical properties of the samples were analyzed by optical microscopy, Raman spectroscopy, precision scale, scanning electron microscopy, energy dispersive X-ray spectroscopy, and linear sweep voltammetry, respectively. It was found that passivation layers of the as-cast samples were removed by the suggested stripping solution. Upon the addition of SDS, the stripped sample showed a bright silver color without NiS, while the sample showed a dark tarnished appearance due to NiS formation without SDS. The weight loss ratio decreased with increasing SDS content and stabilized at 0.2 % for SDS concentrations exceeding 0.15 g/L, and the sample showed a uniformly etched microstructure. EDS results showed that NiS was formed without SDS addition, while linear sweep voltammetry results indicated that NiS formation was restrained upon SDS addition because SDS suppresses the formation of formamidine disulfide from thiourea. Thus, the suggested thiourea stripping with SDS addition was successfully applied to Ni-based 14 karat white gold alloys.

DETERMINACIÓN EXPERIMENTAL DE LOS PARÁMETROS ÓPTIMOS DE OPERACIÓN EN EL PROCESO DE ELECTROLIXIVIACIÓN Y ELECTRODEPOSICIÓN SECUENCIAL DE ORO EN SOLUCIONES ÁCIDAS DE TIOUREA A PARTIR DE SULFUROS CONCENTRADOS

Se investigó a nivel de laboratorio las variables de operación (concentración de reactivos, pH y potencial de oxidación) del proceso de lixiviación de piritas auríferas procedentes de río Tablachaca (Ancash Perú) con Tiourea (TU) seguido de electro-deposición de oro. El estudio experimental, se desarrolló en tres etapas: Oxidación de Tiourea, Lixiviación de oro y Electro-deposición de oro. Como una alternativa a los agentes químicos, la oxidación de TU se realizó vía electrólisis para producir Disulfuro Formamidina (FDS), el cual, sirve como oxidante en la disolución de oro. El grado de conversión óptima de tiourea a disulfuro formamidina se obtiene en 2,5 h aplicando una FEM de 4,5 V con un pH igual 1,5. Los compartimientos anódico y catódico del reactor electroquímico fueron separados por una membrana aniónica con la finalidad de eliminar reacciones indeseables en el cátodo. Previo a la etapa de lixiviación, el mineral fue lavado con ácido sulfúrico para eliminar los agentes consumidores de ácido y mantener de este modo un pH constante durante el tiempo que dure la lixiviación. Durante la lixiviación de oro, se estudió las velocidades de disolución en función de las concentraciones de TU, FDS y pH. Finalmente, se efectuó una prueba de lixiviación en tiempos prolongados usando los parámetros óptimos de operación obtenidos en las pruebas anteriores. La prueba de electro-deposición se llevó a cabo usando la técnica de electrodiálisis en una celda de tres compartimentos El bajo consumo de Tiourea (1,76 kg/TM mineral) demuestra que es una alternativa viable desde el punto de vista económico. Palabras clave.- Electrolixiviación, Electrodeposición, Tiourea, Disulfuro formamidina. ABSTRACTThe research in the laboratory was made operating variables (reactant concentration, pH and oxidation potential) of pyrite leaching gold from river Tablachaca (Ancash Peru) with thiourea (TU) followed by electro-deposition of gold. The experimental study was conducted in three stages: Oxidation of thiourea leaching of gold and gold electroplating. As an alternative to chemical agents, TU oxidation via electrolysis was conducted to obtain formamidine disulphide (FDS), which serves as an oxidizer in the dissolution of gold. The optimum degree of conversion of formamidine disulfide thiourea in 2.5 h was obtained by applying a FEM of 4.5 V with a pH of 1.5. The anodic and cathodic compartments of the electrochemical reactor were separated by an anion membrane with the purpose of eliminating undesired reactions at the cathode. Prior to the leaching step, the mineral was washed with sulfuric acid to remove the acid consuming agents and thereby maintain a constant pH throughout of the leach. During the leaching of gold, we studied the dissolution rates as a function of the concentrations of TU, SDS and pH. Finally, a test was performed on prolonged leaching using the optimum operating parameters obtained in the previous tests. The electro-deposition test was carried out using the technique of electrodialysis in a three- compartment cell. The low consumption of thiourea (1.76 kg / MT mineral) proves to be a viable alternative economically. Keywords.- Electro leaching, Electroplating, Thiourea, Formamidine disulfide.

Oxyhalogen–Sulfur Chemistry: Oxidation of a Thiourea Dimer, Formamidine Disulfide, by Chlorine Dioxide

The oxidation of formamidine disulfide, FDS, the dimer of thiourea, by aqueous chlorine dioxide has been studied in highly acidic and mildly acidic media. FDS is one of the possible oxidation intermediates formed in the oxidation of thiourea by oxyhalogens to urea and sulfate. The reaction is exceedingly slow, giving urea and sulfate with a stoichiometric ratio of 5 : 14 FDS to chlorine dioxide after an incubation period of up to 72 h and only in highly acidic media which discourages the disproportionation of chlorine dioxide to the oxidatively inert chlorate. Mass spectrometric data suggest that the oxidative pathway proceeds predominantly through the sulfinic acid, proceeding next to the products sulfate and urea, while by-passing the sulfonic acid. Transient formation of the unstable sulfenic acid was also not observed.