Nano-structured Alumina-ZrO2 ceramic laminates

In the last years many efforts have been expended to develop colloidal process that uses water instead of organicsolvents in the tape casting process. In present work, alumina/zirconia laminated nanocomposites were fabricatedby layer-by-layer method and using water-based tape casting process. Physical and mechanical properties as wellas the fracture mode were investigated. The laminates consisted of stacked alumina and zirconia green sheetsproduced by thermopressing. The ceramic laminates were first heated at 450°C (organic elimination) andsubsequently sintered in air at 1500°C during 1 h. The ceramic laminates showed a mechanical strength ofapproximately 103 MPa (AZAZA) and 44 MPa (ZAZAZ), respectively and an intergranular-transgranular mixedfracture mode.Keywords: nanocomposites, laminates, tape casting

Mechanical performance and healing process improvement of cement-coir pith particle composites by accelerated carbonation

The accelerated carbonation during the early cure age is a process used to improve the physical and mechanical properties of cement-based composites. In this work, cement-based composites with coir pith particles addition were subjected to the accelerated carbonation process during the first 48 hours of cure in a rich CO2 environment. After curing, the samples were dried and subjected to curing conditions until saturated at 28 days. Thermogravimetric analyses, scanning electron microscopy (SEM) and X-ray diffraction patterns were used to analyze the impact of accelerated carbonation during the early cure age in cement-coir pith composite. The results of the physical properties show an increase in bulk density and surface density of the carbonated samples, as well as reduced water absorption. The reduction of the Ca(OH)2 resulting in the increasing of CaCO3 content was observed by thermogravimetric analysis. The carbonated samples had a 41% increase in compression strength and 28% in the modulus of rupture as compared to non-carbonate samples. The results showed the potential of the accelerated carbonation cure process in cement-based composites with vegetable coconut waste addition. Keywords: Accelerated carbonation, mechanical properties, thermal analysis, cement-based composites, coir pith particle

The influence of (Ti,W)C and NbC on the mechanical behavior of alumina

Recent studies published in the literature have focused on reinforcing alumina with different refractory carbides and nitrides in order to improve hardness, fracture toughness and wear resistance. The incorporation of hard particles as WC, (Ti,W)C and NbC on alumina matrix has shown to be a good alternative in improving the mechanical properties of the composite material. The present work reports some preliminary results obtained reinforcing alumina with 20 wt. (%) (Ti,W)C and 10 wt. (%) NbC. Alumina, (Ti,W)C and NbC powders were homogenized and mixed in a planetary ball mill and subsequently hot-pressed at 1650 &deg;C under 20 MPa in flowing argon. Specimens were characterized by Vicker's microhardness (H V), fracture toughness (K IC), X ray diffraction and scanning microscopy. The composite material showed hardness values of 19.5 GPa and fracture toughness values <FONT FACE=Symbol>&raquo;</FONT> 5.2 MPa.m½. The high fracture toughness encountered in this work is related to the crack deflection mechanism

APROVEITAMENTO DE RESÍDUOS DA MINERAÇÃO DE CAULIM EM CERÂMICA BRANCA

O presente trabalho tem por objetivo caracterizar o rejeito de caulim proveniente de empresa de mineração localizada em Junco do Seridó – PB – Brasil. Foram analisados as suas propriedades físicas e químicas visando sua incorporação na composição de massas para a cerâmica branca

Microstructure and mechanical properties of WC-Co reinforced with NbC

Cemented carbides such as tungsten carbide-cobalt WC-Co composites have been widely used as cutting tool materials. Several reports have shown the influence of different factors such as grain size, type and amount of binder phase and the addition of hard particles on the properties of WC-Co. The purpose of this work was to investigate the effect of niobium carbide on the microstructure and mechanical properties of WC-Co. Specimens of WC-Co reinforced with NbC were mixed and subsequently hot-pressed in a inert atmosphere. The WC-Co-NbC composite material exhibited high hardness values (18.9 GPa), flexural strength (2100 MPa) and fracture toughness (11.2 MPa.m½ ). TEM analysis has shown a bimodal grain size distribution of WC

Alumina-NbC composites fabricated by spark plasma sintering

The incorporation of niobium carbide in alumina-based composites has been shown to improve the properties of composite material. The main disadvantage to get a dense composite material is the necessary high sintering temperature. The spark plasma sintering (SPS) process uses a high heating and cooling speed and lower sintering temperature, making this sintering process a suitable method to produce an alumina-NbC composite material at lower temperatures. The sintering behavior of alumina-NbC composites fabricated by spark plasma sintering (SPS) was investigated at 1350, 1400, and 1450 ˚C. X-ray diffraction patterns of sintered bodies revealed only the presence of alumina and NbC crystalline phases. No oxidation products or new crystalline phases were presented after the sintering process. SPS process has produced dense alumina-NbC samples comparable to other alumina-hard particle systems. Microstructural observation revealed inhibition of alumina grain growth in regions near NbC particles. Fracture surfaces showed a mixture of intergranular and transgranular fracture mode