Porosity Of Specimens Research Articles

Effects of Na2O/SiO2 molar ratio on properties of aggregate-paste interphase in fly ash-based geopolymer mixtures through multiscale measurements

This paper presents a multiscale experimental study on the influence of different Na2O/SiO2 molar ratios on the mechanical and microstructural characteristics of the aggregate-paste interphase in fly ash-based geopolymer mixtures. By analyzing the scanning electron microscope images, the solid phases present in the microstructure were identified, and the frequency of occurrence of each phase was quantified. In addition, the porosity and pore size distribution of geopolymer specimens were measured by mercury intrusion porosimetry. By conducting nanoindentation tests on a large array of indentations and subsequent statistical analysis of the test results, the elastic moduli of individual phases were extracted. The bond behavior between aggregate and paste was also investigated by conducting the three-point bending test of single edge notched beam specimens. Integration of test results in different length scales showed that interphase region generates more sodium aluminosilicate hydrate (i.e., N-A-S-H) gel than the adjacent paste region regardless of the Na2O/SiO2 ratios used in this study. In addition, the mixture prepared with the higher Na2O/SiO2 molar ratio exhibited more N-A-S-H gel in the interphase zone, which led to increased bonding strength between aggregate and paste.

Molten salt synthesis and characterization of SiC whiskers containing coating on graphite for application in Al2O3-SiC-C castables

The wettability of graphite was significantly ameliorated by applying a molten liquid phase method using silicon powder as a raw material to form a SiC whisker coating on a graphite surface. The effect of replacing the ball pitch with coated graphite (CG) on the microstructure, apparent porosity, physical properties, oxidation resistance, and slag corrosion resistance of Al2O3–SiC–C (ASC) refractory castables was investigated by a scanning electron microscope, an energy-dispersive X-ray spectroscope, a transmission electron microscope, and other dedicated equipment. The results show that a uniform and continuous SiC whisker coating was formed on the surface of the graphite, and the contact angle with water changed from 89° to only 6.5°. The apparent porosity of the ASC specimen with 2 wt.% of CG decreased by 12.7%, and the cold modulus of rupture increased from 7.08 to 13.30 MPa with increasing CG content from 0 to 2 wt.%. Further, the sample containing 2 wt.% of CG exhibited the largest force and displacement values. Owing to the presence of SiC whiskers on the surface, the ASC castable samples with 2 wt.% of CG have the best antioxidation performance, and those with 1 wt.% of CG have the best anti-slag performance.

Optimization of the corrosion behavior of mullite-SiC castable against alkali vapor via coating high temperature glaze

The process of coating glaze is an effectively method to improve the corrosion resistance of ceramics. Therefore, in the work the viscosity and phase compositions of Li2O-Al2O3-SiO2 glazes are studied by the FactSage software. Furthermore the influence of Li2O-Al2O3-SiO2 glaze layer on the alkali corrosion resistance and mechanical properties of mullite-SiC castables is investigated, also the residual stress within the mullite-SiC castables with Li2O-Al2O3-SiO2 glaze layer is systematically explored. The results show that the ratio of SiO2/Al2O3 and content of alkali metal oxides have a great influence on the amount and viscosity of liquid phase in glazes at the high temperature. When the mullite-SiC castables are coated with Li2O-Al2O3-SiO2 glaze layer the apparent porosity of specimens decreases significantly and the micro-crack is suppressed effectively above 1300 °C, which are beneficial to the improvement of the alkali corrosion resistance and mechanical properties of products. Meanwhile, the tensile residual stress will generate in the glaze layer due to the different thermal expansion of glaze and matrix. And the reduced residual tensile stress in the glaze layer is beneficial to promoting the properties of mullite-SiC castables.

An In-Vitro Evaluation of Alternative Disinfection Methods of Acrylic resin and Thermoplastic Resin Denture Base Materials

Objectives: This study was designed to evaluate the antimicrobial effect of alternative disinfection methods of heat cured acrylic resin and thermoplastic resin denture base materials and to investigate the porosity resulting from disinfection by these methods. Material and Methods: Disc specimens of heat cured acrylic resin and thermoplastic resin were fabricated and divided into four groups for each denture base material according to the disinfection method. The specimens were contaminated in vitro by standardized suspensions of Candida albicans (C. albicans).The following test agents were used: distilled water (as a control group), 5% sodium hypochlorite (NaOCl), 100% white vinegar and 650 W microwave (MW) energy. After the disinfection procedure, the number of viable microbial cells was counted in CFU/ml. Porosities of acrylic resin and thermoplastic resin specimens were evaluated with Scanning Electron Microscope (SEM) after one month of daily exposure to disinfection. Results: ANOVA test showed that, there was a statistical significant difference among the tested treatment agents against C. albicans in each denture base material(P≤ 0.05). Post Hoc test showed a statistical significant difference between the control samples and the other disinfected samples in the microbial count, however, there was no statistical significant difference among the tested methods of disinfection (P>0.05).Regarding porosity area percentage, there was a statistical significant difference among the tested methods of disinfection (P≤ 0.05), where, 100% white vinegar showed the highest porosities followed by NaOCl then the MW disinfection and the least is the control group. Regarding comparison between the two denture base materials, thermoplastic resin showed statistically significant lower microbial adherence as well as lower porosity area percentage than heat cured acrylic resin(P≤ 0.05). Conclusion: All the tested disinfection methods shown to be efficient against C. albicans. Thermoplastic resin demonstrated lower microbial adherence than heat cured acrylic resin and lower porosity area percentages.

Comparison of Fatigue Properties for Alloy EP708 Specimens Prepared by Selective Laser Melting and Hot Rolling

Structure and fatigue resistance tests of EP708 alloy specimens prepared by selective laser melting (SLM) and subjected to strengthening heat treatment and hot isostatic pressing (HIP), combined with heat treatment compared with hot-rolled heat-treated specimens, are studied. It is shown that the use of the HIP process significantly reduces specimen porosity obtained by the SLM method for EP708 alloy, and it also increases cyclic endurance. Test specimens prepared by the SLM method, after heat treatment and after HIP and heat treatment, as well as those hot-rolled and heat-treated, withstand 2·106 cycles during the first stage of loading at 340 MPa. With a subsequent increase in the load to 380 MPa, the best cyclic durability is shown by specimens in a hot-rolled heat-treated condition. In this case, specimens after HIP and heat treatment show a reduction of twice the cycle time from the hot-rolled specimens, and the specimens obtained by the SLP method given heat treatment have an operating cycle an order of magnitude lower than for hot-rolled specimens. The SLM-specimens after HIP and heat treatment have characteristics comparable with hot-rolled heat-treated specimens for fatigue resistance required by the standard documents for products made of alloy EP708.

Structural characterization and strengthening mechanism of forsterite nanostructured scaffolds synthesized by multistep sintering method

In this study, highly porous forsterite scaffolds with interconnected porosities were synthesized using multi-step sintering (MSS) method. The starting powder was nanosized forsterite, which was synthesized from talc and magnesium carbonate powders. The phase composition, average particle size and morphology of the produced forsterite powder were characterized by X-ray diffraction technique (XRD) and transition electron microscopy (TEM). Forsterite scaffolds were produced by foamy method using polymeric sponges. MSS process including three steps was used to efficiently sinter the forsterite nanopowders without destroying the initial porous structure of polymeric sponges. The results showed that MSS technique is an efficient and appropriate procedure to produce highly porous forsterite scaffolds with pore size in the range of 100–300 μm. The compressive strength, compressive modulus and porosity of C12 specimen (sintered at 1650 °C for 1 h with subsequent annealing at 1000 °C for 1000 min) was 1.88 MPa, 29.2 MPa, and 72.4%, respectively, which is very close to that of cancellous bone. The approach studied in this research can be developed for other nanostructure ceramics to produce highly porous scaffolds with interconnected porosities for load bearing applications.

Experimental investigation on the relationship between pore characteristics and unconfined compressive strength of cemented paste backfill

In this paper, the pore structure characteristics of CPB specimens were characterized using nuclear magnetic resonance (NMR) and scanning electronic microscopy (SEM) techniques, and the relationship between the unconfined compressive strength (UCS) and the pore characteristics of cemented paste backfill (CPB) was investigated. The results showed that the pores in CPB specimens were mainly small, “non-damaging” ones, which accounted for about 70 vol% of all pores in CPB specimens. Although the “damaging” and “multi-damaging” pores only accounted for 3.93 vol% and 6.99 vol% of all pores respectively, they had significant impacts on the UCS of CPB specimens. With the increase of curing time, the porosity of CPB specimens decreased gradually (i.e. the average porosities of CPB specimens at the curing time of 3 d, 14 d and 28 d were 11.07 vol%, 8.58 vol% and 7.09 vol%, respectively). Besides, the porosity of CPB specimens also decreased with the increase of solid concentration of CPB slurry. On the basis of fitting analysis, it could be observed that there was a negatively exponential relationship between the UCS and the porosity of CPB specimens and a linearly inverse relationship between the UCS and the fractal dimension. Our study demonstrates that it is feasible to study the relationship between mechanical properties and pore characteristics of CPB specimens by using the NMR technique.

Novel applications of waste ceramics on the fabrication of foamed materials for exterior building walls insulation

In this paper, a novel fabrication method has been proposed by using waste ceramic and other polishing materials as main raw materials to prepare foam ceramic for the potential applications in thermal insulation of exterior building walls. In particular, the content of Al2O3 and SiO2 was almost 90% in this kind of materials. The polishing materials result from grinding polished tiles into powder and the ceramic foam was foamed slurry produced by self-configure foaming solution after mechanical stirring. Effects of content of foam and clay on the specimens’ properties such as compressive strength, apparent porosity, bulk density, water absorption and thermal conductivity were investigated. Based on results, when the content of clay was 10 wt%, the amount of foam was 10 wt%, apparent porosity of specimens sintered at 1000 °C was 50.6%, linear change was 7.2%, bulk density was 0.70 g/cm3, compressive strength was 8.0 MPa, and thermal conductivity was 0.137 W/(m·K) at 200 °C. Microstructures of specimens were also detected and compared, and the exceptional mean pore size was 39.7 μm which was measured by using “Micro-image Analysis and Process System” (MIAPS) software. Due to the difference in bulk density, the internal pore structure and performance of the sample are different. Comprehensive properties of specimens can be optimized by adjusting the amount of foam and clay. The proposed method for obtaining insulation foamed materials using ceramics' waste and other polishing materials was feasible, whilst saving resources and energy.

In situ observing the erosion process of cement pastes exposed to different sulfate solutions with X-ray computed tomography

The damage process of cement pastes exposed to different sulfate solutions (sodium sulfate solution, magnesium sulfate solution, a mixed solution of sodium sulfate and sodium chloride) was in situ quantitatively investigated by X-ray computed tomography (X-ray CT). The X-ray diffraction (XRD) was also employed to determine the content of corrosion products. The results show that the three-dimensional crack distribution of cement pastes for different immersion times can be extracted by using X-ray CT. When the solution contains the sulfate and magnesium ions, the specimen deteriorates faster. The presence of chloride ions alongside sulfate ions significantly reduces the degree and speed of sulfate attack. The porosity and pore number of specimens markedly decrease with the increase of immersion time when the pore volume exists between 0.01 and 0.1 mm3. Gypsum and ettringite are formed to the least extent in the mixed solution of sodium sulfate and sodium chloride, and most evident for the magnesium sulfate solution. In addition, the relationship between the crack volume fraction and the erosion time of specimens in different sulfate solutions is established, respectively, which all conforms to a quadratic function relationship.

The consequences of changes in the structure of loess as a result of cyclic freezing and thawing

The effects of freeze/thaw cycles change the structure of loess, which causes the deterioration of the specimen strength, leading to the occurrence of engineering disasters. In order to study the structure changes of loess body under freezing/thawing environment, taking Yanan city in Huangling County loess as the test object, this paper investigates the changes of the structure under different initial water content and different freezing/thawing cycles, and then analyzes the test results based on computer image processing technology, defines the damage variables, and quantitatively evaluates the damage state of the specimen. The results show that, with the increase of freezing and thawing times: the frost heaving force appears continuously; in the pores, the ice-water phase change volume expands; the local micropore stress concentration causes the specimen skeleton connection mode to change, from the surface–plane contact to the point–surface, point–point contact; the specimen structure is damaged by the number of fissures; and the total area changes. Therefore, this paper defines the porosity as a damage variable. As long as the damage variable and its evolution rule are known, the damage behavior of the material can be described, the damage variable increases with the increase of the freezing/thawing cycle, the specimen structure deteriorates, and the high density area of the specimen decreases, the low density area increases, and the integrity of the loess decreases. The continuous development of specimen porosity and fissure makes the migration channel change continuously, causing transfer channel elongation, widening, and new channel generation, resulting in the increase of ice generation.

IRON SLUDGE SORBING AGENT FOR SEWAGE PURIFICATION FROM HEAVY METAL IONS

The paper suggests a method of synthesizing a granulated sorbing agent for sewage purification from ions of heavy metals (copper and zinc). The raw material mixture includes iron sludge produced by water treatment, liquid glass, caustic limestone, and water. The optimum mass ratio of 10:1:14:4 (dry iron sludge, calcium oxide, liquid glass, water) is selected for the mixture composition which provides the high strength and water resistance of sorbing agent. The paper considers the preparation and the optimum thermal treatment conditions which ensure the strength, appropriate porosity and specific surface of specimens. Research results are obtained for mechanical-and-physical properties of synthesized granular sorbing agent. The static exchange capacity and the extraction degree of copper and zinc ions from model saline solutions are detected herein. Research results contribute to the problem of the efficiency improvement of closed water utilization systems and can be used in utilization of large-tonnage water treatment wastes, thereby providing sewage purification facilities with inexpensive sorbing agents.

Optimizing the mixture design of polymer concrete: An experimental investigation

Over the last few decades, polymer concrete (PC) has been finding use in quick repairing of concrete structures. However, there have been only few studies on the mechanical behavior of PC. The aim of this study is to evaluate the mechanical behavior of PC using destructive and non-destructive tests (NDT). The mixtures were prepared with three different polymer ratios (10%, 12%, and 14%) and two different coarse aggregate sizes (4.75–9.5 mm and 9.5–19 mm). The samples were subsequently tested under three different temperatures (−15 °C, +25 °C, and +65 °C). The Taguchi method and analysis of variance (ANOVA) were used to optimize PC mixes based on the compressive, splitting-tensile, and flexural strengths under varying polymer content, coarse aggregate size, and temperature. NDTs, including ultrasonic pulse velocity and electrical resistivity tests, were carried out to gain insights into the porosity and void content of the specimens. Scanning electron microscopy (SEM) was used to analyze the bonding interface between aggregates and polymer, microstructure phase, and pores that were present in the structure of the PC. Results show that a decrease in the temperature from +25 °C to −15 °C led to an improvement in the mechanical properties of PC mixes, whereas an increase in the temperature from +25 °C to +65 °C adversely affected the mechanical properties. Based on NDT, it was found that increasing the coarse aggregate size and polymer ratio reduced the porosity of specimens. This is attributed to the decreased surface area to volume ratio with increasing particle size, which allowed the polymer to completely coat the surface of aggregates. Finally, a set of expressions was proposed to predict the mechanical properties of PC.

Physical and Mechanical Properties of W-Ni-Fe-Co Metal Foam Modified by Titanium Tungsten Carbide Alloying

The paper studies physical and mechanical properties of tungsten-nickel-iron-cobalt metal foam alloyed with titanium tungsten carbide. Test specimens are obtained by the liquid phase sintering of powder materials, including those containing tungsten nanopowders. High porosity metal foams are prepared through varying the porosity of powder specimens and the content of filling material. The penetration capability of cylinder projectiles made of new alloys is explored in this paper. It is shown that their penetration depth exceeds that of the prototype with relevant weight and size, made of tungsten-nickel-iron alloy, other factors being equal.

Fatigue properties of Ti-6.5Al-3.5Mo-l.5Zr-0.3Si alloy produced by direct laser deposition

The fatigue properties of the Ti-6.5Al-3.5Mo-l.5Zr-0.3Si alloy produced by direct laser deposition (DLD) have been investigated. The fatigue limit of the alloy perpendicular to and parallel to the deposition direction at specified life of 107 and stress ration of 0.1 is 337MPa and 365MPa, respectively. The porosities of specimens are among 0.014–0.028%, averaged porosity is 0.02%. The fatigue cracks initiate at the pores near the surface, which are located mostly at the column grain boundary during solidification. The size of pore and its distance from the surface are two important factors to control the fatigue life of specimen, i.e., bigger the pore or nearer to the surface, shorter the fatigue life. The fatigue fracture consists of fatigue source, radial slow crack growth and rough fast fracture region. The columnar grains boundaries of Ti-6.5Al-3.5Mo-l.5Zr-0.3Si alloy by epitaxial growth from the underlying template grains layer-by-layer during direct laser deposition are the weak joints under the cyclic stress and crack formed propagates preferentially along the grain boundaries, which should be a key factor leading to the difference of fracture morphology in the region of fatigue source and final fast fracture, and also the lower fatigue limit of specimen perpendicular to the deposition direction than that parallel to the deposition direction.

Numerical Simulation Study of Variable‐Mass Permeation of the Broken Rock Mass under Different Cementation Degrees

In order to analyze variable‐mass permeation characteristics of broken rock mass under different cementation conditions and reveal the water inrush mechanism of geological structures containing broken rock masses like karst collapse pillars (KCPs) in the coal mine, the EDEM‐FLUENT coupling simulation system was used to implement a numerical simulation study of variable‐mass permeation of broken rock mass under different cementation conditions and time‐dependent change laws of parameters like porosity, permeability, and mass loss rate of broken rock specimens under the erosion effect were obtained. Study results show that (1) permeability change of broken rock specimens under the particle migration effect can be divided into three phases, namely, the slow‐changing seepage phase, sudden‐changing seepage phase, and steady seepage phase. (2) Specimen fillings continuously migrate and run off under the water erosion effect, porosity and permeability rapidly increase and then tend to be stable, and the mass loss rate firstly rapidly increases and then gradually decreases. (3) Cementation degree has an important effect on permeability of broken rock mass. As cementing force of the specimen is enhanced, its maximum mass loss rate, mass loss, porosity, and permeability all continuously decrease. The study approach and results not only help enhance coal mining operations safety by better understanding KCP water inrush risks. It can also be extended to other engineering applications such as backfill paste piping and tailing dam erosion.

Non-destructive testing of concrete treated with penetrating surface sealant using a Karsten-tube

Surface treatment is increasingly becoming acceptable as a means of ensuring concrete durability by way of controlling or preventing the ingress of various deleterious agents of concrete deterioration. In practice, a combination of non-destructive and semi-destructive evaluation of the concrete surface is often necessary to decide on the need for treatment or re-treatment of previously treated surfaces. The owners of structures and restorers appreciate simple and non-destructive methods in making any interventions on surfaces that have been treated previously. Existing knowledge would suggest that correct interpretation of these test results would depend on an understanding of the effect of factors such as the initial moisture content, quality of the concrete and exposure conditions. This paper presents the result of a study to assess the applicability of the “Karsten-tube” in measuring the water uptake of treated and un-treated concrete surfaces and the effects of the concrete quality, and environmental conditions upon the test results. The results are compared with complementary tests for oxygen permeability and porosity of the concrete specimens studied. Three concrete mixes and five different exposure conditions were investigated. Some specimens were soaked in 3% Sodium Chloride solution to study the effects of aggressive agents. The results indicates that Karsten-tube is a quick non-destructive method for obtaining useful information about the condition of treated and un-treated concrete surfaces and could be used for rapid and reliable assessment of the need for re-treatment of previously treated surfaces. Well-treated surfaces will have low water uptake values, irrespective of the quality of the concrete.

High velocity impact damage investigation of carbon/epoxy/clay nanocomposites using 3D Computed Tomography

A series of projectile impact tests have been carried out on cross ply carbon/epoxy and different weight percentages (1%, 3% and 5%) of nanoclay dispersed in the carbon/epoxy laminated composites of two different thicknesses (3 mm and 5 mm) with a 9.8 mm diameter hemispherical shaped mild steel projectile for determining the ballistic limit, residual velocity and energy absorption. Velocities far higher than the ballistic limit such as 165 m/s, 195 m/s and 220 m/s are considered for investigation of damage mechanisms. The traditional CFRP composites show poor impact resistance due to their negligible plastic deformation as compared to metals. The impact performance of these composites can be enhanced by the clay effect. The optimum clay content is proposed in the present investigation. There is a significant improvement in impact properties, as the clay content increases from 0 wt% to 3 wt% but beyond 3 wt% of clay, the properties degrade which is due to the high stress concentrations attributed to the clay clustering in the higher clay content. The X-ray computed tomography (X-ray CT) scanning analysis which is an advanced non-destructive technique (NDT) is used to investigate the internal defects such as delamination and porosity of impact damaged specimens whereas fiber breakage and matrix cracks are seen in scanning electron microscopy (SEM) images.

ОСОБЕННОСТИ ВЯЗКО-ХРУПКОГО ПЕРЕХОДА В ПОРОШКОВЫХ МАТЕРИАЛАХ НА ОСНОВЕ ЖЕЛЕЗА

The issue of the study of the porous bodies’ deformation and the plasticity of their materials is important as it is related to the production of complex parts using the wide opportunities of drop stamping (DS). In this case, the increased requirements are imposed on the porous material plasticity as the emergent defects may be not removed at the final DS stages what impairs the strength properties. The information about the plasticity properties of a porous material in the heated state allows properly developing the technology of complex parts’ DS. The paper investigates such structural defect of powdered materials as the porosity. The authors studied its influence on the mechanical properties of materials and analyzed the regularities of these properties’ changes in the interval of brittleplastic transition temperatures. The mechanical tests of the powdered specimens were carried out with the identification of the main dependencies of mechanical properties on the porosity in the interval of brittle-plastic transition temperatures. The authors selected the main deformation modes when the crack resistance is studied, identified the main factors influencing the peculiarities of brittle-plastic transition in the powdered materials, described the phenomena where the crack formation takes place, as well as defined the details of this process. The study identified the nature of change of the strength coldbrittleness temperature (T CL ) and the plasticity coldbrittleness temperature (T CH ): if T CL increases with the increase in porosity, T CH decreases under the same condition. Thus, at the specimen porosity of 3–5 %, its value, depending on the powder type, is 100–150 K, and at the porosity of 10– 15 %, it is lower than 77 K for all powders.

Immobilization of copper indium selenide solar module waste in concrete constructions

The aim of this study was to investigate the properties of concrete containing various quantities of copper indium selenide (CIS) solar module waste by replacing a certain part (up to 40%) of sand. The obtained results have shown that an increase in the content of solar module waste resulted in an increase of the density of fresh and hardened concrete. The compressive strength of the specimens compared to the control specimens has been higher, when sand aggregate was replaced by CIS solar module waste particles from 5 to 20%. Also, a decrease in the water absorption and porosity of concrete specimens containing immobilized waste compared to those with no waste has been observed. The leaching behaviour of the concrete containing immobilized waste was also studied. The results showed that the concrete with sand aggregate replacement by waste particles between 5 and 10% has the best leaching properties. That replacement can be used for CIS solar module waste recycling in concrete production.

Electrokinetic nanoparticle injection for remediating leaks in oil well cement

This paper presents experimental results on injecting nanoparticles into a hardened oil well cement with electromigration technique. Oil well cement is a special cement type used in underground constructions to protect steel casing of oil wells, CO2 storage wells or oil and gas platforms. Due to the technological reasons, the hardened cement is characterized with a high initial porosity. Further distressing and fracturing occurs in the hardened cement originating from the harsh underground environment which includes elevated pressure and temperature. This leads to severe leakages of the stored media and puts the steel casing to the risk of corrosion.The paper proposes to use a non-destructive remediation technique for the cement repair based on the electrokinetic injection of nanoparticles into the pore and crack space in the material. It shows the efficiency of the technique and presents results from injections with a variety of differently sized nanosilica, microsilica and nanoalumina particles. Characterization of the treated samples was based on microscopy observations, electrical measurements, the change in their open porosity and nanopore surface area assessed by the BET technique. It was found that the electrokinetic process and driving of particles in samples is very efficient and reduces the sample porosity by about 4–7% with respect to the initial porosity of intact specimens and 5–8% on aged samples. The BET analysis confirmed reduction of the inner pore surface area in the treated samples. Increasing level of agglomeration of particles on the surface as well as in the inner pores was observed during electrokinetic treatment and documented with the electric current measurements.