Characterization of ceramic tiles prepared from two clays from Sergipe — Brazil

We report an investigation of stain formation after use of clay–ceramic floor tiles produced by an industry from Sergipe, Brazil. Two types of raw materials have been used (C1 and C2) and test specimens were prepared at firing temperatures of 1000, 1120 and 1140 °C, being afterwards immersed in muriatic acid, evidencing stain formation for C1 tiles. After ICP chemical analysis, the original clays and tiles were characterized by powder X-ray diffraction (XRD) and TGA measurements, evidencing that C1 contained a higher carbonate percent than C2. Tile specimens were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), flexural strength, apparent density, linear shrinkage, and water absorption. In contrast to tiles prepared from C2, those prepared from C1 presented higher interparticle porosity and both linear shrinkages and water absorption variations with temperature were very incipient, suggesting that the high porosity and the low sintering caused the low staining resistance.     

矿粉掺量对废弃超细砂制备砂混凝土密度及强度影响研究

以航道整治废弃超细砂为主要原料,通过振动成型制备砂混凝土(Sand Concrete).首先通过干拌振捣密实计算干拌物密度的方法研究矿粉掺量对砂混凝土干拌物密度的影响,然后以试件7 d、14 d和28 d抗压强度、劈裂抗拉强度和浸水抗压强度为控制标准,研究矿粉掺量对砂混凝土性能的影响,最后通过XRD对砂混凝土试件进行分析.试验结果表明:在水胶比为0.38,减水剂掺量为0.5%情况下,砂混凝土最佳配合比为废弃超细砂75.3%、水泥16.5%、矿粉8.2%.采用最佳配合比所制砂混凝土28 d抗压强度、劈裂抗拉强度和浸水抗压强度均达到最优, XRD分析表明所制砂混凝土含有大量水化硅酸钙(C-S-H)和钙矾石等水化产物.研究为航道整治废弃超细砂的开发利用提供一种技术途径,对于废弃超细砂资源丰富而普通混凝土砂石材料匮乏的地区具有显著的经济价值和广阔的应用前景.     

Combined effect of expansive and shrinkage reducing admixtures to obtain stable and durable mortars

In order to improve the dimensional stability of cement based mortars, the effects produced on cement hydration of a shrinkage reducer (propyleneglycol ether based—SRA) and an expansive admixture (calcium oxide based—EXP) were investigated. Mortar samples (prepared without admixtures or with SRA or EXP or SRA and EXP) were compared through compressive strength measurements, water evaporation, restrained shrinkage and restrained expansion measurements. Setting time and free expansion were also detected on cement paste specimens.

A synergistic effect on the shrinkage reduction was observed when the shrinkage reducing admixture and the expansive agent were used together. In order to clarify this phenomenon, the hydration of cement pastes containing these kinds of admixtures was followed by ESEM-FEG (environmental scanning electron microscopy–field emission gun), TG (thermogravimetry), specific surface area measurements (by BET—Brunauer–Emmet–Teller-method) and XRDS (X-ray diffraction spectroscopy).     

Comparison of the binding properties of hydrated lime and cement in brick manufacture

The effect of replacing cement by hydrated lime in autoclaved brick specimens with binder contents of 7.5–25% has been studied on a laboratory scale and the results have been compared with non-autoclaved cement-bound specimens. It has been shown that the strength of cement-bound specimens autoclaved for 8 h was similar to that of specimens air-cured for 28 days. Lime was shown to be superior to cement in autoclaved specimens for strengths up to the maximum of 23 MN/m² obtainable with the lime binder. For a given compressive strength up to this value, half as much binder was required in the mix and, in addition, the green strength was greater and the drying shrinkage was lower when lime was used instead of cement. Maximum strengths of up to 42 MN/m² were achieved at high binder contents with blends of lime and cement.     

Influence of glass phase on Al2O3 fiber-reinforced Al2O3 composites processed by slip casting

The present work describes the processing of alumina fiber reinforced alumina ceramic preforms consisting of chopped Al₂O₃ fibers (33 wt%) and Al₂O₃ (67 wt%) fine powders by slip casting. The preforms were pre-sintered in air at 1100 °C for 1 h. A lanthanum based glass was infiltrated into these preforms at 1250 °C for 90 min. Linear shrinkage (%) was studied before and after glass infiltration. Pre-sintered and infiltrated specimens were characterized by scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, porosimetry and flexural strength. The alumina preforms showed a narrow pore size distribution with an average pore size of ∼50 nm. It was observed that introducing Al₂O₃ fibers into Al₂O₃ particulate matrix produced warp free preforms with minor shrinkage during pre-sintering and glass infiltration. It was observed that the infiltration process fills up the pores and considerably improves the strength and reliability of alumina preform.     

Microstructural,mechanical, and thermal properties of microwave-sintered KLS-1 lunar regolith simulant

KLS-1 Lunar regolith simulant was microwave sintered to explore its potential applicability in future lunar construction. The effects of sintering temperature on linear shrinkage, density, porosity, and microstructural, mechanical, and thermal properties were investigated. As the sintering temperature increased, linear shrinkage and density increased and porosity decreased. Structural evolution in the sintered samples was characterized by scanning electron microscopy and X-ray diffraction. Unconfined compressive strength testing showed that mechanical strength increased significantly with increasing sintering temperature, with 1120 °C giving the highest strength of 37.0 ± 4.8 MPa. The sintered samples exhibited a coefficient of thermal expansion of approximately 5 × 10⁻⁶ °C⁻¹, which was well-maintained even after cyclic temperature stress between −100 and 200 °C. Therefore, this microwave processing appears promising for the fabrication of building material with sufficient mechanical strength and thermal durability for lunar construction.     

Reformulation of roofing tiles body with addition of granite waste from sawing operations

A ceramic body traditionally used to produce roofing tiles was reformulated by the addition of granite waste from sawing operations. The objective was to obtain a ceramic product with better technological properties. The main tool for the reformulation was the definition of the appropriate particle size of the raw materials as given by the Winkler diagram. The raw materials were characterized with respect to their mineralogical composition by X-ray diffraction, particle size distribution as well as chemical composition and plasticity. Specimens were made by extrusion and fired at temperatures from 850 to 1100 °C. The technological properties determined were: dry bulk density, linear shrinkage, water absorption and mechanical strength. Microstructural analysis of the fired samples was carried out by X-ray diffraction. The results showed that the granite waste contributes to reduce the plasticity and the linear shrinkage of the ceramic bodies. One reformulated ceramic body exhibited better values of water absorption and mechanical strength than the industrially used.     

Shrinkage cracking of lightweight concrete made with cold-bonded fly ash aggregates

Shrinkage cracking performance of lightweight concrete (LWC) has been investigated experimentally on ring-type specimens. LWCs with and without silica fume were produced at water-cementitious material ratios (w/cm) of 0.32 to 0.55 with cold-bonded fly ash coarse aggregates and natural sand. Coarse aggregate volume ratios were 30%, 45%, and 60% of the total aggregate volume in the mixtures. A total of 12 lightweight aggregate concrete mixtures was cast and tested for compressive strength, static elastic modulus, split-tensile strength, free shrinkage, weight loss, creep, and restrained shrinkage. It was found that the crack opening on ring specimens was wider than 2 mm for all concretes. Free shrinkage, weight loss, and maximum crack width increased, while compressive and split-tensile strengths, static elastic modulus, and specific creep decreased with increasing coarse aggregate content. The use of silica fume improved the mechanical properties but negatively affected the shrinkage performance of LWCs. Shrinkage cracking performance of LWCs was significantly poorer than normal weight concrete (NWC).     

Influence of firing temperature on the ceramic properties of clays from Campos dos Goytacazes, Brazil

The characteristics of two clays used for red ceramic production in Campos dos Goytacazes, southeast of Brazil, were investigated. Characterization was performed by X-ray diffraction, chemical analysis, as well as granulometric and plasticity measurements. Technological properties related to water absorption, linear shrinkage and flexural strength were obtained from specific tests. Samples were prepared by pressing clay bodies at 20 MPa, which were then fired at temperatures from 850 to 1200 °C. The results showed that both clays from three deposits are highly plastic due to the elevated percentage of kaolinitic clay minerals. The samples richer in clay minerals present higher linear shrinkage as well as a decrease in water absorption in comparison to the others. The effectiveness of these clays for red ceramic production has been discussed in terms of the Winkler diagram.     

乌兰布和沙漠砂制备高延性水泥基复合材料的力学性能

使用内蒙古乌兰布和沙漠砂完全代替微石英砂配置了高延性水泥基复合材料(ECC),并以砂胶比为变量,对其抗压强度、抗拉强度、抗剪强度以及抗弯强度四个方面的力学性能展开了全面的研究。抗拉试验后进一步对纤维断面使用扫描电镜(SEM)进行了观测,并采用X射线衍射分析(XRD)方法研究了沙漠砂的物质组成。结果表明,以沙漠砂配置的ECC,在相同骨料含量的条件下,其抗压强度、抗拉强度、抗剪强度以及抗弯强度均与微石英砂配置的ECC接近,延性约为微石英砂ECC的一半。除抗剪强度外,沙漠砂ECC其他各项性能均随砂胶比增大而提高,优化配比设计的沙漠砂ECC延性能够达到微石英砂ECC的水平。     

Geopolymeric binders with different fine fillers — Phase transformations at high temperatures

Geopolymers based on metakaolin were synthesised under addition of different fine filler materials. The material properties were measured after hardening and burning; especially strength, porosity and shrinkage. The phase transformation after burning was measured by X-ray diffraction and quantified.     

Mechanical Properties of Hot-Pressed B-B4C Materials

Elastic modulus and flexural strength were measured at room temperature for solid pieces hot-pressed at 1900 to 2600 K from mixtures of B₄C powder and ≤15 wt% B powder. Regression analysis showed that elastic modulus and flexural strength are not significantly affected by these boron additions. Elastic modulus is related to porosity and flexural strength to porosity and grain size. The fracture surface energy of boron carbide was evaluated. X-ray diffraction and chemical analyses showed that the specimens were composed entirely of boron carbide after hot-pressing. Lattice constants increased with the initial boron content.     

Effect of nano silica and fine silica sand on compressive strength of sodium and potassium activators synthesised fly ash geopolymer at elevated temperatures

Environment friendly geopolymer is a new binder which gained increased popularity due to its better mechanical properties, durability, chemical resistance, and fire resistance. This paper presents the effect of nano silica and fine silica sand on residual compressive strength of sodium and potassium based activators synthesised fly ash geopolymer at elevated temperatures. Six different series of both sodium and potassium activators synthesised geopolymer were cast using partial replacement of fly ash with 1%, 2%, and 4% nano silica and 5%, 10%, and 20% fine silica sand. The samples were heated at 200°C, 400°C, 600°C, and 800°C at a heating rate 5°C per minute, and the residual compressive strength, volumetric shrinkage, mass loss, and cracking behaviour of each series of samples are also measured in this paper. Results show that, among 3 different NS contents, the 2% nano silica by wt. exhibited the highest residual compressive strength at all temperatures in both sodium and potassium‐based activators synthetised geopolymer. The measured mass loss and volumetric shrinkage are also lowest in both geopolymers containing 2% nano silica among all nano silica contents. Results also show that although the unexposed compressive strength of potassium‐based geopolymer containing nano silica is lower than its sodium‐based counterpart, the rate of increase of residual compressive strength exposed to elevated temperatures up to 400°C of potassium‐based geopolymer containing nano silica is much higher. It is also observed that the measured residual compressive strengths of potassium based geopolymer containing nano silica exposed at all temperatures up to 800°C are higher than unexposed compressive strength, which was not the case in its sodium‐based counterpart. However, in the case of geopolymer containing fine silica sand, an opposite phenomenon is observed, and 10% fine silica sand is found to be the optimum content with some deviations. Quantitative X‐ray diffraction analysis also shows higher amorphous content in both geopolymers containing nano silica at elevated temperatures than those containing fine silica sand.     

Biaxial orientation of poly(vinyl chloride) compounds Part 2 –Structure–property relationships and their time dependency

Abstract

X-ray diffraction and thermomechanical analysis have been used, respectively, to examine structural order and shrinkage behaviour for oriented samples of rigid and flexible poly(vinyl chloride) (PVC). Results were compared with previously measured tensile properties and structure–property relationships explored. X-ray diffraction showed that drawing produces planar crystallite orientation in PVC sheets. If drawing and subsequent annealing conditions are held constant, but draw ratio is varied, there is good correlation between structural order measured by X-ray diffraction and tensile strength. Increased annealing time and temperature improve crystallite order and dimensional stability, while tensile strength is unchanged. The greatest enhancement in tensile strength is achieved by stretching PVC towards its maximum draw ratio at 90°C, but optimum thermal stability of the oriented structure is achieved when higher annealing temperatures are used. Room temperature recovery is observed for flexible PVC when the material has a glass transition temperature below ambient. This can be delayed by increased annealing time and temperature, and by increased draw ratio.     

Recycling of polishing porcelain stoneware residues in ceramic tiles

The possibility of recycling residues, coming from the industrial polishing process of porcelain stoneware tiles, by their incorporation in a porcelain stoneware body mix, was studied. Starting from a standard body mix, several modified body mixes were prepared by replacing different amounts of the fluxing component, a sodium feldspar sand, with these wastes. The densification behaviour of the different body mixes was investigated by determining water absorption, linear shrinkage and bulk density of the as fired specimens. Phase and microstructural examination, by quantitative X-ray diffractometry and scanning electron microscopy-energy dispersive spectroscopy, made it possible to explain the mechanical behaviour, i.e. flexural strength, Young's modulus and Weibull's modulus. The presence of polishing porcelain stoneware residues, PPR, in particular in a 10 wt% of replacement, made possible a consistent decrease in the maximum temperature of the thermal cycle. That did not cause significant variations in the mechanical strength of the materials, while a slight decrease of the elastic modulus and a remarkable increase of the reliability were registered.     

不同外加剂对湿拌砂浆性能的影响

研究不同外加剂对湿拌砂浆稠度损失、保水率、凝结时间、抗压强度、粘结强度以及收缩率等性能的影响,并借助X-射线衍射(XRD)、扫描电镜(SEM)对掺加不同外加剂的湿拌砂浆胶凝体系进行微观测试分析.研究结果表明:掺加外加剂均能不同程度地减少湿拌砂浆的8h稠度损失,增强湿拌砂浆的保水率,延长湿拌砂浆的凝结时间,提高湿拌砂浆的抗压强度和粘结强度,能更好地保证工程施工的顺利进行.     

Effect of magnesium-aluminate spinel nano-particles on microstructure and properties behaviors of doloma-containing refractories

In recent years, the main challenge for producers and consumers of doloma-containing refractories has been to increase the performance of this kind of refractories. In this study, the addition effect of magnesium-aluminate spinel nano-particles (MgAl₂O₄) on various properties of doloma-containing refractories such as bulk density, apparent porosity, hydration resistance and cold compressive strength have been evaluated. From 0 to 8 wt % magnesium-aluminate spinel nano-particles added to the specimens. The prepared cylindrical specimens (50*50mm²) were putted in a dryer (at 110 °C for 24 h) and then placed in an electrical furnace (at 1650 °C for 3 h). Ceramic phase's identification and microstructural evaluation of the fired specimens were donned by helping X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM/EDX) techniques, respectively. Results showed that the bulk density increased up to 8 wt % nano-spinel. Also, the cold compressive strength values of the samples increased up to 6 wt % nano-spinel whereas the apparent porosity values were reduced. However, for the higher additive value (8 wt % nano-spinel), this trends is reversed and the cold compressive strength was decreased and apparent porosity was increased. The reason for this variation can be attributed to the formation of some micro-cracks in the specimen's matrix. As well as, due to the formation of dense microstructures by utilization of magnesium-aluminate spinel nano-particles the resistance to hydration of the specimens has increased significantly.     

Degree of reactivity of two kaolinitic minerals in alkali solution using zeolitic tuff or silica sand filler

Four geopolymers were synthesized by NaOH-activation of a mixture of kaolinite (Jordanian kaolinite or Ukrainian kaolinite) and a filler (zeolitic tuff or silica sand). X-ray powder diffraction (XRD), Fourier-transform infrared spectrometry (FTIR), and solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR) were employed to monitor the extent of reaction and to characterize the phases in the geopolymer. Remaining kaolinite in all produced geopolymer specimens unambiguously indicated an incomplete reaction. The ²⁹Si MAS-NMR spectra of the geopolymers revealed the presence of tetrahedral-SiO₄ whereas the ²⁷Al MAS-NMR spectra revealed the presence of both tetrahedral-AlO₄ and octahedral-AlO₆. The XRD patterns of geopolymers showed the formation of a new feldspar mineral. Replacing silica sand filler by zeolitic tuff enhanced markedly the specific surface area of the corresponding geopolymers.     

硅线石含量对轻质莫来石-刚玉耐火材料的显微结构与性能的影响

以多孔球形莫来石为骨料,板状刚玉细粉、硅线石和粘土为基质,经1400 ℃、1500 ℃和1600 ℃保温3 h烧成,制备了四组轻质莫来石-刚玉耐火材料.采用X-射线衍射仪(XRD)和扫描电子显微镜(SEM)对试样的物相组成和显微结构进行表征,研究了烧成温度及硅线石含量(4%、6%、8%和10%)对试样常温物理性能和显微结构的影响.结果表明:(1)当硅线石含量不变时,随着烧成温度的升高,试样的显气孔率逐渐减小,体积密度逐渐增大,线收缩率逐渐增加,常温耐压强度先降低后升高;(2)当硅线石的含量从4%增加到8%时,经1400 ℃烧后,试样的显气孔率和体积密度变化不大,当硅线石含量超过8%时耐压强度显著下降;经1600 ℃烧后,随硅线石含量的增加,试样的体积密度减小,强度降低,线收缩率也由2.5%减小到1.5%;(3)当硅线石含量为6%、烧成温度为1400 ℃时,试样的线收缩率为0.86%,耐压强度为36.1 MPa,热导率为0.249 W/(m·K)(300 ℃),试样基质中气孔的d50为46.7 μm.     

The effect of shrinkage on the structure and properties of ultra-high molecular weight polyethylene fibers with different concentration

Interface variation in the extraction and drying process of ultra-high molecular weight polyethylene (UHMWPE) gel fiber results in different shrinkage at different direction. The essence of shrinkage lies in the crystallization of UHMWPE chains under the effect of interface tension. However, UHMWPE gel fiber prepared with different solution concentration has different chain entanglement points density that can hinder the regular stacking for UHMWPE chains. The restriction for axis shrinkage of UHMWPE gel fiber facilitates the orientation of UHMWPE chains that is beneficial to improve the tensile strength of UHMWPE drawn fiber. Combined with multiple methods of Wide angle X-ray diffraction, Small-angle X-ray scattering, Differential scanning calorimetry and sonic orientation, the structural evolution of UHMWPE fiber with different shrinkage ratio and different concentration was investigated. Meanwhile, the suitability for UHMWPE fibers in production was evaluated by final tensile strength of the fibers. Here, a structural evolution model is proposed to elucidate the correlation between the shrinkage and the structure and properties of UHMWPE fibers prepared with different solution concentration.