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  • 1
    Online Resource
    Online Resource
    The Effects of Various Concentrations of NaOH on the Inter-Particle Gelation of a Fly Ash Geopolymer Aggregate
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 5 ( 2021-02-27), p. 1111-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 5 ( 2021-02-27), p. 1111-
    Abstract: Aggregates can be categorized into natural and artificial aggregates. Preserving natural resources is crucial to ensuring the constant supply of natural aggregates. In order to preserve these natural resources, the production of artificial aggregates is beginning to gain the attention of researchers worldwide. One of the methods involves using geopolymer technology. On this basis, this current research focuses on the inter-particle effect on the properties of fly ash geopolymer aggregates with different molarities of sodium hydroxide (NaOH). The effects of synthesis parameters (6, 8, 10, 12, and 14 M) on the mechanical and microstructural properties of the fly ash geopolymer aggregate were studied. The fly ash geopolymer aggregate was palletized manually by using a hand to form a sphere-shaped aggregate where the ratio of NaOH/Na2SiO3 used was constant at 2.5. The results indicated that the NaOH molarity has a significant effect on the impact strength of a fly ash geopolymer aggregate. The highest aggregate impact value (AIV) was obtained for samples with 6 M NaOH molarity (26.95%), indicating the lowest strength among other molarities studied and the lowest density of 2150 kg/m3. The low concentration of sodium hydroxide in the alkali activator solution resulted in the dissolution of fly ash being limited; thus, the inter-particle volume cannot be fully filled by the precipitated gels.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14051111
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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  • 2
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    Online Resource
    Properties of a New Insulation Material Glass Bubble in Geopolymer Concrete
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 4 ( 2021-02-08), p. 809-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 4 ( 2021-02-08), p. 809-
    Abstract: This paper details analytical research results into a novel geopolymer concrete embedded with glass bubble as its thermal insulating material, fly ash as its precursor material, and a combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) as its alkaline activator to form a geopolymer system. The workability, density, compressive strength (per curing days), and water absorption of the sample loaded at 10% glass bubble (loading level determined to satisfy the minimum strength requirement of a load-bearing structure) were 70 mm, 2165 kg/m3, 52.58 MPa (28 days), 54.92 MPa (60 days), and 65.25 MPa (90 days), and 3.73 %, respectively. The thermal conductivity for geopolymer concrete decreased from 1.47 to 1.19 W/mK, while the thermal diffusivity decreased from 1.88 to 1.02 mm2/s due to increased specific heat from 0.96 to 1.73 MJ/m3K. The improved physicomechanical and thermal (insulating) properties resulting from embedding a glass bubble as an insulating material into geopolymer concrete resulted in a viable composite for use in the construction industry.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14040809
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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  • 3
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    Online Resource
    Role of Sintering Temperature in Production of Nepheline Ceramics-Based Geopolymer with Addition of Ultra-High Molecular Weight Polyethylene
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 5 ( 2021-02-25), p. 1077-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 5 ( 2021-02-25), p. 1077-
    Abstract: The primary motivation of developing ceramic materials using geopolymer method is to minimize the reliance on high sintering temperatures. The ultra-high molecular weight polyethylene (UHMWPE) was added as binder and reinforces the nepheline ceramics based geopolymer. The samples were sintered at 900 °C, 1000 °C, 1100 °C, and 1200 °C to elucidate the influence of sintering on the physical and microstructural properties. The results indicated that a maximum flexural strength of 92 MPa is attainable once the samples are used to be sintered at 1200 °C. It was also determined that the density, porosity, volumetric shrinkage, and water absorption of the samples also affected by the sintering due to the change of microstructure and crystallinity. The IR spectra reveal that the band at around 1400 cm−1 becomes weak, indicating that sodium carbonate decomposed and began to react with the silica and alumina released from gels to form nepheline phases. The sintering process influence in the development of the final microstructure thus improving the properties of the ceramic materials.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14051077
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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  • 4
    Online Resource
    Online Resource
    Effect of Aluminium Powder on Kaolin-Based Geopolymer Characteristic and Removal of Cu2+
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 4 ( 2021-02-08), p. 814-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 4 ( 2021-02-08), p. 814-
    Abstract: This current work focuses on the synthesis of geopolymer-based adsorbent which uses kaolin as a source material, mixed with alkali solution consisting of 10 M NaOH and Na2SiO3 as well as aluminium powder as a foaming agent. The experimental range for the aluminium powder was between 0.6, 0.8, 1.0 and 1.2wt%. The structure, properties and characterization of the geopolymer were examined using X-Ray Diffraction (XRD), Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Adsorption capacity and porosity were analysed based on various percentages of aluminium powder added. The results indicate that the use of aluminium powder exhibited a better pore size distribution and higher porosity, suggesting a better heavy metal removal. The maximum adsorption capacity of Cu2+ approached approximately 98%. The findings indicate that 0.8% aluminium powder was the optimal aluminium powder content for geopolymer adsorbent. The removal efficiency was affected by pH, adsorbent dosage and contact time. The optimum removal capacity of Cu2+ was obtained at pH 6 with 1.5 g geopolymer adsorbent and 4 h contact time. Therefore, it can be concluded that the increase in porosity increases the adsorption of Cu2+.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14040814
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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  • 5
    Online Resource
    Online Resource
    Potential of Rapid Tooling in Rapid Heat Cycle Molding: A Review
    MDPI AG ; 2022
    In:  Materials Vol. 15, No. 10 ( 2022-05-23), p. 3725-
    Details
    In: Materials, MDPI AG, Vol. 15, No. 10 ( 2022-05-23), p. 3725-
    Abstract: Rapid tooling (RT) and additive manufacturing (AM) are currently being used in several parts of industry, particularly in the development of new products. The demand for timely deliveries of low-cost products in a variety of geometrical patterns is continuing to increase year by year. Increased demand for low-cost materials and tooling, including RT, is driving the demand for plastic and rubber products, along with engineering and product manufacturers. The development of AM and RT technologies has led to significant improvements in the technologies, especially in testing performance for newly developed products prior to the fabrication of hard tooling and low-volume production. On the other hand, the rapid heating cycle molding (RHCM) injection method can be implemented to overcome product surface defects generated by conventional injection molding (CIM), since the surface gloss of the parts is significantly improved, and surface marks such as flow marks and weld marks are eliminated. The most important RHCM technique is rapid heating and cooling of the cavity surface, which somewhat improves part quality while also maximizing production efficiencies. RT is not just about making molds quickly; it also improves molding productivity. Therefore, as RT can also be used to produce products with low-volume production, there is a good potential to explore RHCM in RT. This paper reviews the implementation of RHCM in the molding industry, which has been well established and undergone improvement on the basis of different heating technologies. Lastly, this review also introduces future research opportunities regarding the potential of RT in the RHCM technique.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma15103725
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
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  • 6
    Online Resource
    Online Resource
    Comparison of Hook and Straight Steel Fibers Addition on Malaysian Fly Ash-Based Geopolymer Concrete on the Slump, Density, Water Absorption and Mechanical Properties
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 5 ( 2021-03-09), p. 1310-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 5 ( 2021-03-09), p. 1310-
    Abstract: Geopolymer concrete has the potential to replace ordinary Portland cement which can reduce carbon dioxide emission to the environment. The addition of different amounts of steel fibers, as well as different types of end-shape fibers, could alter the performance of geopolymer concrete. The source of aluminosilicate (fly ash) used in the production of geopolymer concrete may lead to a different result. This study focuses on the comparison between Malaysian fly ash geopolymer concrete with the addition of hooked steel fibers and geopolymer concrete with the addition of straight-end steel fibers to the physical and mechanical properties. Malaysian fly ash was first characterized by X-ray fluorescence (XRF) to identify the chemical composition. The sample of steel fiber reinforced geopolymer concrete was produced by mixing fly ash, alkali activators, aggregates, and specific amounts of hook or straight steel fibers. The steel fibers addition for both types of fibers are 0%, 0.5%, 1.0%, 1.5%, and 2.0% by volume percentage. The samples were cured at room temperature. The physical properties (slump, density, and water absorption) of reinforced geopolymer concrete were studied. Meanwhile, a mechanical performance which is compressive, as well as the flexural strength was studied. The results show that the pattern in physical properties of geopolymer concrete for both types of fibers addition is almost similar where the slump is decreased with density and water absorption is increased with the increasing amount of fibers addition. However, the addition of hook steel fiber to the geopolymer concrete produced a lower slump than the addition of straight steel fibers. Meanwhile, the addition of hook steel fiber to the geopolymer concrete shows a higher density and water absorption compared to the sample with the addition of straight steel fibers. However, the difference is not significant. Besides, samples with the addition of hook steel fibers give better performance for compressive and flexural strength compared to the samples with the addition of straight steel fibers where the highest is at 1.0% of fibers addition.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14051310
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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  • 7
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    Online Resource
    Optimisation of Shrinkage and Strength on Thick Plate Part Using Recycled LDPE Materials
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 7 ( 2021-04-05), p. 1795-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 7 ( 2021-04-05), p. 1795-
    Abstract: Achieving good quality of products from plastic injection moulding processes is very challenging, since the process comprises many affecting parameters. Common defects such as warpage are hard to avoid, and the defective parts will eventually go to waste, leading to unnecessary costs to the manufacturer. The use of recycled material from postindustrial waste has been studied by a few researchers. However, the application of an optimisation method by which to optimise processing parameters to mould parts using recycled materials remains lacking. In this study, Response Surface Methodology (RSM) and Particle Swarm Optimisation (PSO) methods were conducted on thick plate parts moulded using virgin and recycled low-density polyethylene (LDPE) materials (100:0, 70:30, 60:40 and 50:50; virgin to recycle material ratios) to find the optimal input parameters for each of the material ratios. Shrinkage in the x and y directions increased in correlation with the recycled ratio, compared to virgin material. Meanwhile, the tensile strength of the thick plate part continued to decrease when the recycled ratio increased. R30 (70:30) had the optimum shrinkage in the x direction with respect to R0 (100:0) material where the shrinkage increased by 24.49% (RSM) and 33.20% (PSO). On the other hand, the shrinkage in the y direction for R30 material increased by 4.48% (RSM) and decreased by 2.67% (PSO), while the tensile strength of R30 (70:30) material decreased by 0.51% (RSM) and 2.68% (PSO) as compared to R0 (100:0) material. Validation tests indicated that the optimal setting of processing parameter suggested by PSO and RSM for R0 (100:0), R30 (70:30), R40 (60:40) and R50 (50:50) was less than 10%.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14071795
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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  • 8
    Online Resource
    Online Resource
    Near-Infrared (NIR) Silver Sulfide (Ag2S) Semiconductor Photocatalyst Film for Degradation of Methylene Blue Solution
    MDPI AG ; 2023
    In:  Materials Vol. 16, No. 1 ( 2023-01-03), p. 437-
    Details
    In: Materials, MDPI AG, Vol. 16, No. 1 ( 2023-01-03), p. 437-
    Abstract: A silver sulfide (Ag2S) semiconductor photocatalyst film has been successfully synthesized using a solution casting method. To produce the photocatalyst films, two types of Ag2S powder were used: a commercialized and synthesized powder. For the commercialized powder (CF/comAg2S), the Ag2S underwent a rarefaction process to reduce its crystallite size from 52 nm to 10 nm, followed by incorporation into microcrystalline cellulose using a solution casting method under the presence of an alkaline/urea solution. A similar process was applied to the synthesized Ag2S powder (CF/syntAg2S), resulting from the co-precipitation process of silver nitrate (AgNO3) and thiourea. The prepared photocatalyst films and their photocatalytic efficiency were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and UV-visible spectroscopy (UV-Vis). The results showed that the incorporation of the Ag2S powder into the cellulose films could reduce the peak intensity of the oxygen-containing functional group, which indicated the formation of a composite film. The study of the crystal structure confirmed that all of the as-prepared samples featured a monoclinic acanthite Ag2S structure with space group P21/C. It was found that the degradation rate of the methylene blue dye reached 100% within 2 h under sunlight exposure when using CF/comAg2S and 98.6% for the CF/syntAg2S photocatalyst film, and only 48.1% for the bare Ag2S powder. For the non-exposure sunlight samples, the degradation rate of only 33–35% indicated the importance of the semiconductor near-infrared (NIR) Ag2S photocatalyst used.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma16010437
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
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  • 9
    Online Resource
    Online Resource
    Characterisation at the Bonding Zone between Fly Ash Based Geopolymer Repair Materials (GRM) and Ordinary Portland Cement Concrete (OPCC)
    MDPI AG ; 2020
    In:  Materials Vol. 14, No. 1 ( 2020-12-24), p. 56-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 1 ( 2020-12-24), p. 56-
    Abstract: In recent years, research and development of geopolymers has gained significant interest in the fields of repairs and restoration. This paper investigates the application of a geopolymer as a repair material by implementation of high-calcium fly ash (FA) as a main precursor, activated by a sodium hydroxide and sodium silicate solution. Three methods of concrete substrate surface preparation were cast and patched: as-cast against ordinary Portland cement concrete (OPCC), with drilled holes, wire-brushed, and left as-cast against the OPCC grade 30. This study indicated that FA-based geopolymer repair materials (GRMs) possessed very high bonding strength at early stages and that the behavior was not affected significantly by high surface treatment roughness. In addition, the investigations using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy have revealed that the geopolymer repair material became chemically bonded to the OPC concrete substrate, due to the formation of a C–A–S–H gel. Fundamentally, the geopolymer network is composed of tetrahedral anions (SiO4)4− and (AlO4)5− sharing the oxygen, which requires positive ions such as Na+, K+, Li+, Ca2+, Na+, Ba2+, NH4+, and H3O+. The availability of calcium hydroxide (Ca(OH)2) at the surface of the OPCC substrate, which was rich in calcium ions (Ca2+), reacted with the geopolymer; this compensated the electron vacancies of the framework cavities at the bonding zone between the GRM and the OPCC substrate.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14010056
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
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  • 10
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    Online Resource
    Hybrid Mold: Comparative Study of Rapid and Hard Tooling for Injection Molding Application Using Metal Epoxy Composite (MEC)
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 3 ( 2021-02-01), p. 665-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 3 ( 2021-02-01), p. 665-
    Abstract: The mold-making industry is currently facing several challenges, including new competitors in the market as well as the increasing demand for a low volume of precision moldings. The purpose of this research is to appraise a new formulation of Metal Epoxy Composite (MEC) materials as a mold insert. The fabrication of mold inserts using MEC provided commercial opportunities and an alternative rapid tooling method for injection molding application. It is hypothesized that the addition of filler particles such as brass and copper powders would be able to further increase mold performance such as compression strength and thermal properties, which are essential in the production of plastic parts for the new product development. This study involved four phases, which are epoxy matrix design, material properties characterization, mold design, and finally the fabrication of the mold insert. Epoxy resins filled with brass (EB) and copper (EC) powders were mixed separately into 10 wt% until 30 wt% of the mass composition ratio. Control factors such as degassing time, curing temperature, and mixing time to increase physical and mechanical properties were optimized using the Response Surface Method (RSM). The study provided optimum parameters for mixing epoxy resin with fillers, where the degassing time was found to be the critical factor with 35.91%, followed by curing temperature with 3.53% and mixing time with 2.08%. The mold inserts were fabricated for EB and EC at 30 wt% based on the optimization outcome from RSM and statistical ANOVA results. It was also revealed that the EC mold insert offers better cycle time compared to EB mold insert material.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14030665
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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