Potentiality of coal mining waste to obtain geopolymers

Abstract Geopolymers are chemically bonded ceramics formed at room temperature and obtained using aluminosilicates and alkali activators. Geopolymers have found applications beyond construction, such as in wastewater treatment and ceramics. This research aims to develop geopolymers using coal mining waste (CMW) for various purposes. The waste used in this study was obtained from the Barro Branco layer in companies located in southern Santa Catarina/Brazil. The waste was thermally treated at 900 °C for 160 min, followed by grinding and characterization using X-ray fluorescence spectroscopy, X-ray diffraction, and particle size analysis. Geopolymeric samples were produced using 60 wt% waste, 25 wt% sodium silicate, and 15 wt% 10 M NaOH. The specimens were divided into three groups and cured using different methods. The results showed that thermal curing enhanced waste reactivity, reduced curing time, and improved compressive strength. However, long-term submersion curing decreased compressive strength due to sodium leaching, reducing reactivity

Influence of the Length and the Content of Cellulose Fibers Obtained from Sugarcane Bagasse on the Mechanical Properties of Fiber-Reinforced Mortar Composites

Asbestos fiber can be substituted by cellulose fiber extracted from the sugarcane bagasse. The cellulose fibers can be extracted by using a heated water bath and subsequent treatment with sodium hydroxide. This work aims to evaluate the effect of cellulose fiber addition on the mechanical properties of fiber-reinforced mortar composites. A 22 factorial design with a central point was used to evaluate the effect of fiber content and fiber length on the mechanical properties. The results demonstrated that the composites increased the flexural strength. The most expressive result was the modulus of elasticity because of the good cellulose fiber/cement interface

Solid-state reaction in nanoparticulate alumina/LZSA glass-ceramic composites

Abstract In this work, some properties, such as sinterability, modulus of elasticity (E), coefficient of thermal expansion (CTE) and dielectric constant (εr), of composites constituted by nanoparticulate alumina (27-43 nm, 35 m2.g-1) in different contents (0 to 77 vol%) and a LZSA glass-ceramic composition (17.7Li2O-5.2ZrO2-68.1SiO2-9.0Al2O3, molar basis) were evaluated. Dry powders of the raw materials (alumina and LZSA parent glass, frit) were uniaxially pressed (40 MPa) and the obtained compacts were sintered at 600-950 °C (1 h holding time). X-ray diffraction (XRD) study was performed in order to investigate the solid-state reactions occurred in LZSA-based compositions during sintering. XRD results were correlated to the CTE, E and εr of sintered samples. The CTE of the obtained composites decreased as alumina content increased mainly due to the β-spodumeness (solid solution Li2O.Al2O3.4-10SiO2) formation. The results concerning the E (22.3±1.5 GPa) and εr (3.1±1.3) for the composite with 5.6 vol% addition sintered at 850 °C for 1 h indicated, in a preliminary way, the possibility of development of materials with suitable properties for applications concerning to the low temperature co-fired ceramic (LTCC) technology

The effect of microstructural features on the mechanical properties of LZSA glass-ceramic matrix composites

This work reports on the characterization of ZrSiO4 particulate-reinforced Li2O-ZrO2-SiO2-Al2O3 (LZSA) glass-ceramic matrix composites. The typical physical/mechanical and chemical properties of the glass batches and the composites were measured. A composition with 60 wt.% ZrSiO4 was preliminarily selected because it demonstrated the highest values of bending strength (190 MPa) and deep abrasion resistance (51 mm³). To this same composition was given a 7 wt.% bentonite addition in order to obtain plasticity behavior suitable for extrusion. The sintered samples (1150 ºC for 10 min) presented a thermal linear shrinkage of 14% and bending strength values of 220 MPa

Wear performance of alumina-based ceramics - a review of the influence of microstructure on erosive wear

Ceramic materials are of technical and commercial interest due to their chemical, mechanical and thermal performance, leading ceramics to meet many engineering requirements. Alumina (aluminum oxide) is one of the primary representatives of this class of materials because of its high fracture toughness, hardness and density, which enable its use in the production of highly critical parts. One such application involves protection against abrasion and erosion wear. The wear properties of a ceramic can be improved not only by controlling its material characteristics but also by controlling the fabrication process, which defines the material's microstructure. Many studies of the effects of the microstructure on these properties have been published. The objective of this study was to review the effects of the microstructure on the erosive wear resistance of alumina-based ceramics. Four factors that control the erosive wear of alumina were identified: (i) the effects of dopants on the diffusivity of the grain boundaries, (ii) the fabrication route, (iii) the sintering mechanisms and (iv) the alumina grain size. The published experimental results related to these topics are described and provide a clear understanding of the erosive wear of alumina

Evaluation of the thermal performance of different cold materials for urban paving

Abstract The phenomenon of the warming of cities at high temperature levels, the so-called “heat island”, has been studied around the world. Apart from generating thermal discomfort, this urban phenomenon has been causing an increase in the demand for energy for cooling the environments. In response to the environmental impact generated by this phenomenon, researchers from different nations have developed techniques for warming mitigation, developing new materials, technologies, and constructive systems. In this context, urban paving is responsible for a significant contribution to the occurrence of heat islands in cities. The use of pavements called “cold materials”, which help to lower the surface temperature, constitutes an important solution to mitigate the effects of the heat flow in cities and the planet. Thus, the purpose of this study was to develop, test and evaluate new cold materials for use in paving. Such cold materials proved to present better thermal performance than conventional ones, such as asphalt and reference concrete (commercial paver). In fact, this work showed that the composition with 90% concrete+10% talc can be considered cold material, with energy savings of up to 16% in comparison to asphalt

Estudo de composições cerâmicas à base de alumina e vitrocerâmico do sistema LZSA para obtenção de estruturas multicamadas por tape casting

Resumo Compósitos de matriz cerâmica têm sido desenvolvidos nas últimas décadas como um meio eficiente de melhoria da tenacidade à fratura. Compósitos cerâmicos multicamadas se destacam por seu relativo baixo custo e facilidade de obtenção. Estes compósitos são confeccionados com camadas alternadas de dois materiais cerâmicos e têm como mecanismo de tenacificação o desvio de trajetória de trincas em propagação, camada após camada, no compósito. Neste trabalho foram estudadas composições à base de alumina e vitrocerâmico LZSA (Li2O-ZrO2-SiO2-Al2O3) para compor as camadas a fim de se obter compósito multicamada com interfaces fortes. Assim, tensões residuais compressivas nas camadas finas à base de LZSA intercaladas às camadas à base de Al2O3, sob leve tensão residual de tração, foram esperadas obter. As composições foram definidas por planejamento experimental fatorial, gerando corpos de prova por prensagem, os quais foram sinterizados e caracterizados quanto ao coeficiente de expansão térmica e módulo de elasticidade. Três composições (% em massa) à base de alumina (CA1: 100% Al2O3; CA2: 90% Al2O3 e 10% ZrO2; CA-PC: 90% Al2O3, 5% ZrO2 e 5% SiC whisker ) e três composições à base de LZSA (CF6: 70% LZSA, 10% Al2O3 e 20% SiC whisker ; CF8: 50% LZSA, 10% Al2O3, 20% TiO2 e 20% SiC whisker ; CF-PC: 75% LZSA, 5% Al2O3, 10% TiO2 e 10% SiC whisker ) foram selecionadas. Estas composições foram projetadas para gerar tensões residuais de compressão nas camadas à base de LZSA (até -32,35 MPa) e de tração nas camadas à base de Al2O3 (mínimo de 0,27 MPa). A técnica de tape casting foi empregada para produzir folhas das composições selecionadas, utilizando-se quantidades de ligantes e plastificantes indicadas na literatura. As composições foram então processadas por tape casting, obtendo-se folhas cerâmicas homogêneas, flexíveis e com resistência a verde suficiente para o manuseio. A espessura das folhas das composições de alumina variou de 130 a 210 μm e as folhas das composições de LZSA entre 180 e 230 μm

Extruded LZS glass-ceramics

A sintered glass-ceramic material belonging to Li2O-ZrO2-SiO2 system with optimized properties was successfully obtained using an extrusion proces