José Jefferson da Silva Nascimento

Secagem e retração volumétrica de tijolos cerâmicos maciços e vazados: uma investigação teórica e experimental

The ceramic industry presents industrial processes with a large consumption of energy and high environmental impact. These industries are developing products of low quality due to inadequate drying and firing processes. Therefore, the purpose of this study is to contribute for the improvement of drying process by presenting a drying experimental study of the samples of clay for red ceramics (hollow and solid bricks) with different dimensions and initial moisture contents. In the drying processes, several air temperatures and air relative humidity were used, and thus several curves of the drying kinetics and volumetric retraction are shown and analyzed. Mathematical equations for predict lost of water and dimension variations during the process were obtained. It was verified that drying process takes place in the falling rate period and shrinkage happens in two distinct periods.

Transporte de Materia con Reducción de Volumen en el Interior de Sólidos Paralelepípedos

Se describe un modelo matematico tridimensional transitorio aplicado al fenomeno de difusion de agua en el interior de solidos paralelepipedos. Se utilizo el metodo de los volumenes finitos considerando propiedades termica y mecanicas constantes, equilibrio en la superficie y reduccion de volumen del material. El modelo fue utilizado para estudiar el proceso de secado de un ladrillo de ceramica. Se muestran los resultados de la cinetica de secado y la distribucion del contenido de humedad en varios planos, para un determinado tiempo y para dos coeficientes de encogimiento. Los resultados muestran que el fenomeno de reduccion de volumen afecta considerablemente la tasa de secado del solido, asi como la distribucion del contenido de humedad en el interior del mismo. Se encuentra tambien que los gradientes mas altos del contenido de humedad se situan en las proximidades del vertice del solido, en cualquier instante de tiempo. El conocimiento de las diferencias de humedad y la cinetica de secado permiten optimizar este proceso y aumentar la calidad del producto final.

Experimental Drying of Ceramics Bricks Including Shrinkage

This work presents an experimental study on the behavior of clays during the drying process. Experimental tests were carried out with clay material for the production of red ceramics and white ceramic (ball clay). Different dimensions and the material initial moisture content plus temperature and relative air-drying humidity were taken into account. Drying kinetics and volume changes of parallelepiped-shaped samples were shown and analyzed. It has been verified that air-drying temperatures and body shape have an enormous influence on the drying rate process. The drying process occurs during the falling drying period and the volume changes display two linear periods.

Transmisión de Calor y Materia con Reducción de Volumen Durante el Secado de Ladrillos de Cerámica

Se presenta un modelo matematico tridimensional transitorio aplicado al fenomeno de difusion de calor y materia con reduccion de volumen en el interior de solidos paralelepipedos. El modelo se ha aplicado al proceso de secado de ladrillos ceramicos. Se uso el metodo de los volumenes finitos considerando propiedades termicas y mecanicas constantes y una condicion de contorno convectiva en la superficie del material. El modelo fue utilizado para estudiar el proceso de secado de un ladrillo de ceramica a temperaturas de 60 y 80oC y en con humedades relativas del aire de 10,07 y 4,66%. Los resultados numericos de contenido de humedad, temperatura y reduccion de volumen, fueron comparados con datos experimentales para determinar los coeficientes de transporte. Se pudo concluir que: el fenomeno de reduccion de volumen tiene dos periodos y afecta considerablemente la velocidad de secado del solido, asi como la distribucion del contenido de humedad en el interior del mismo.

Clay Products Convective Drying: Foundations, Modeling and Applications

This chapter briefly focuses on the theory and applications of drying process with particular reference to wet clay product. Herein, a modeling based on the heat and liquid diffusion theories including dimensions variations and hygro-thermal-elastic stress analysis, and the mathematical formalism to obtain the numerical solution of the governing equations using finite-volume method are presented. The model considers constant thermo-physical properties and convective boundary conditions at the surface of the solid. Applications have been done to ceramic hollow brick. Predicted results of the average moisture content, surface temperature, and moisture content, temperature and stress distributions within the porous solids are shown and analyzed, and for some drying situations they are compared with experimental drying data of the average moisture content and surface temperature of the brick along the continuous drying process.

Mathematical Simulation of Thermal and Moisture Gradients in Ceramic Blocks

Temperature and moisture substantially affect the water elimination procedure, occurring in the drying stage, of ceramic blocks used in building construction. In the present work, a modeling of the thermal gradients and moisture content during the drying process of red clayey ceramic blocks was analyzed using computer simulation by means of Mathematica® software program. Results of two-dimensional thermal gradients and variation of moisture content were predicted. This revealed that regions next to the vertices of prismatic ceramic blocks are more susceptible to structural damage due to development of cracks and deformations.

Scientific and Technological Study of the Modulus of Elasticity and Chemical Abnormalities of a Titanium Alloy and Stainless Steel Alloy Used in Hip Prosthesis

Titanium alloys and stainless steel have been widely used in the production of prostheses, medical and dental devices, due to resistance and anticorrosive properties. Despite that, the values of the elastic modulus of these alloys are about 3-5 times higher than the human bone. So, many researches have sought alternatives to these alloys, in order to obtain alloys with good mechanical strength, low modulus of elasticity and excellent biofunctionality. This work highlights by scientific and technological form, the collection and analysis of the module of elasticity and chemical composition, related to normalizations. The properties obtained, being inadequate, highlights the danger of bone absorption, causing loss of adhesion of the prosthesis and reducing its useful life, In addition, chemical abnormalities are a fundamental problem in terms of risk. Results of this study are shown and analyzed.

Study of Non-Conformities of Hip Prosthesis Metal Front Standards

The arthroplasty is a surgical procedure which is characterized by replacing the defective joint surfaces of biomaterials intended to restore the function of these joints. As soon because the relevance of the topic, this paper aims at studying the unconformities two hip prostheses, titanium and other stainless steel front to standardizations. The implants studied were characterized by techniques: X-ray fluorescence, microanalysis Dispersion Energy X-ray diffraction, scanning electron microscopy and optical microscopy, and tests were carried out physic-mechanical traction and hardness. The unconformities present are analyzed and discussed.

Chemical, Structural and Mechanical Study of Metallic Biomaterials Used in Hip Arthroplasty

Arthroplasty is a surgery that aims to replace the defective joint surfaces, aiming to restore their functions. Is employed in this type of surgery that metallic materials play a key role in the constitution of orthopedic prostheses. In this context, we studied the chemical composition, mechanical and structural behavior of stainless steel developed for applications as biomaterials used in the manufacture of orthopedic implants. In this paper, two prostheses were analyzed established brands in the market. Proceeded through the chemical Spectroscopy Energy Dispersive X-ray (EDX) analysis. Characterized the crystal structures of these materials by diffraction of X-ray and mechanical behavior using tensile test. We compared the results of chemical composition and strength of the samples according to ASTM F-138 (2008). The results of EDX showed the presence of chloride in stainless steel alloys as an impurity that can compromise the durability of the prosthesis. The XRD patterns showed the presence in austenitic stainless steel alloys. As the tensile strength of the alloys analyzed, values that are consistent with those presented in the standards were recorded. In a general analysis, it became apparent incompatibility of assessed as biomaterials for use in prosthetic alloys, although meets the structural and mechanical requirements.