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Abstract Silica is a versatile material employed in different applications fields including aerospace, especially for rocket engines thermal protections. It is known that particles diameter causes variations in the material properties, and the best-known methods for diameter determination in general consist of several steps in sample preparation such as drying, sieving and the determination of the refractive index according different methods. On the other hand, Fourier transform infrared spectroscopy techniques (FT-IR), in reflectance mode, related to the particle size, are less used for this type of determination. Moreover, methodologies in the near infrared region (NIR) are even less explored. Therefore, the aim of this paper is to present a FTIR methodology for diffuse reflectance (DRIFT) in the middle infrared region (MIR) and reflectance analysis in near infrared region (NIRA) for the determination of the particle diameter on silica samples. Both methodologies showed good results. As proven by a test sample analysis, NIRA methodology indicated better precision. Furthermore, considering small and intermediated particle sizes, a tendency towards smaller errors for the absorbance measurements of the samples was found, consistently with the available literature results.

Adesivos poliuretânicos (AD-PU), contendo teor conhecido de isocianato (NCO), foram preparados, nos laboratórios da Rohm and Haas Química Ltda, e amostras foram usadas para a elaboração de uma curva analítica, visando à determinação do teor de NCO por espectroscopia no infravermelho médio (MIR) e próximo (NIR). Os valores de % NCO, obtidos pelo método analítico por via úmida para amostras retiradas durante o processo de fabricação, foram usados como referência. A banda FT-IR escolhida na região MIR foi: 2270 cm-1 (banda analítica). Na região NIR, foi usada uma banda relativa, A4063/A4348. Em ambos os métodos, MIR e NIR, a intensidade das bandas escolhidas e o teor de NCO, obtidos a partir da análise via úmida, foram utilizados para construção de curvas que apresentaram boas correlações lineares (MIR - R = 0,995 e NIR - R = 0,961), que possibilitarão a determinação dos teores de NCO em misturas de composição semelhante.Polyurethane adhesives reference samples (AD-PU) with known contents of isocyanate (NCO) have been prepared in Rohm and Haas to elaborate analytical curves for determination of NCO content, using MIR and NIR analysis. Wet chemical values were used to determine the content of NCO in the AD-PU samples obtained during the process. The MIR analytical band used was 2270 cm-1 and the NIR relative band was A4063/A4348. Data of absorbance intensity and NCO contents obtained from wet chemical analysis were used to elaborate the analytical curves (MIR - R = 0.995 and NIR - R = 0.961) which should allow for the determination of NCO content in adhesive samples of similar composition.