Biopersistence of fibrous thermal insulations (AES fibers) after heat exposure using intratracheal instillation technique

Abstract

Because refractory ceramic fibers (RCF) were classified as possibly pathogenic to humans, alkaline earth silicate (AES) wools have been used as a substitute product for high-temperature applications. All in vivo assays developed to evaluate its pathogenicity were assessed using as-received AES samples. The classification as a pathogen does not apply if the retention half-time for fibers longer than 20 μm is less than 40 days. Therefore, this work describes the evaluation of one AES sample after heat treatment, using the intratracheal instillation technique in rats. Over a three-month post-treatment period, the rats were dissected, and their lungs were examined. The half-time calculation for the retained fibers longer than 20 µm in the lungs was 56 days. Therefore, this AES sample after heat treatment could be presumed to have pathogenic potential for humans. Keywords: alkaline earth silicate fibers, biopersistence, biosoluble fibers, cristobalite, crystalline silica, man-made vitreous fibers. ResumoPelo fato das fibras cerâmicas refratárias (FCR) serem classificadas como agentes possivelmente patogênicos à espécie humana, as fibras de silicato de metais alcalino-terrosos (AES) podem ser utilizadas como potenciais substitutos. Os experimentos in vivo que avaliaram a patogenicidade das fibras AES utilizaram esse produto in natura. A classificação como agente patogênico não se aplica, caso o tempo de retenção de meia-vida das fibras de comprimento superior a 20 μm for inferior a 40 dias. Sendo assim, este trabalho teve como objetivo avaliar o risco ocupacional de uma amostra de fibra AES após exposição a altas temperaturas, através da técnica de instilação intratraqueal em ratos. Durante o período de três meses, as cobaias foram dissecadas e seus pulmões foram examinados. O tempo de meia-vida calculado para as fibras retidas nos pulmões e com comprimento superior a 20 μm foi de 56 dias. Desta forma, pôde-se avaliar o grau de patogenicidade da amostra estudada. Palavras-chave: fibras de silicato de metais alcalino-terrosos, biopersistência, fibras biossolúveis, cristobalita, sílica cristalina, fibras vítreas feitas pelo homem.

Synthesis and characterization of sol-gel derived monophasic mullite powder

“…The sol-gel process was widely used because it produces materials with high-purity and homogeneity and is versatile and has good reproducibility [8]. The sol-gel method is based on inorganic polymerization reactions where the starting materials are dissolved in a suitable solvent, and hydrolysis followed by condensation reaction is catalyzed by the presence of an acid or base [9]. This method plays an important role in synthesizing high-purity mullite precursor material for high technological applications.…”