Acknowledgment to Reviewers of Recent Progress in Materials in 2021

The editors of Recent Progress in Materials would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2021. We greatly appreciate the contribution of expert reviewers, which is crucial to the journal's editorial process. We aim to recognize reviewer contributions through several mechanisms, of which the annual publication of reviewer names is one. Reviewers receive a voucher entitling them to a discount on their next LIDSEN publication and can download a certificate of recognition directly from our submission system. Additionally, reviewers can sign up to the service Publons (https://publons.com) to receive recognition. Of course, in these initiatives we are careful not to compromise reviewer confidentiality. Many reviewers see their work as a voluntary and often unseen part of their role as researchers. We are grateful to the time reviewers donate to our journals and the contribution they make.

Pozzolanic and Cementing Activity of Raw and Pyro-Processed Saudi Arabian Red Mud (RM) Waste

This paper investigates the composition, properties and reactivity of a red mud waste generated in Saudi Arabia with a view to find alternative materials to replace construction binders of high environmental impact. The phase transformation triggered by the sintering of the RM up to 1000°C is determined with thermal and X-Ray Diffraction analyses. Reactivity is investigated with chemical and physical methods including the Chapelle test, setting times, mechanical index and microscopy. The RM is clearly pozzolanic, and its activity is mainly due to the reaction of feldespathoids and the formation of zeolitic and feldspathoid-based hydrates. The positive effects of the thermal treatment are seen below 750°C, and include the loss of water in the zeolite/feldespathoids, and the destruction of the crystal structures of the clay minerals inherited form the parent bauxite. The negative effects of the thermal treatment are evidenced over 750°C, with a decrease in specific surface area, devitrification and crystal formation, whereby the active transition aluminas and the fedespathoids/zeolites (mainly cancrinite) transform into nepheline, tricalcium aluminate (C3A) and gehlenite. Despite the occurrence of nepheline, C3A and gehlenite in the RM sintered at 1000°C, the formation of pozzolanic hydrates that cause setting and strength development are greater at lower temperature. The optimum thermal treatment that enhances pozzolanic activity lies at c.400°C, as evidenced by the highest lime combination, the greatest mechanical index and the fastest set. The RM consists of gibbsite and boehmite, inherited from the bauxite, and cancrinite, chantalite and sodalite formed during the Bayer process. Feldespathoids have formed, instead of zeolites, due to the available silica and the high alkali content of the RM. The quick lime -CaO -, added twice during the refining process, has transformed the original goethite into hematite, and produced cancrinite. The Saudi RM has high SiO2 and high alkalinity, and an abundant specific surface area available for reaction. The chloride and carbon contents are low, and no environmental toxicity is inferred from its chemistry.

Assessment of Mineral Gain in White Spot Lesions Using CPP-ACP and CPP-ACFP in Different Clinical Protocols: A Proof of Concept Study

Subsurface remineralization can be promoted by the topical application of nanoparticles of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP). To assess changes in enamel white spot lesions, an in situ proof-of-concept investigation was performed using 5 subjects (all of whom were healthy young adults) with a cross-over study design. Custom orthodontic brackets were attached to the buccal surfaces of the maxillary second premolar and first molar teeth. Each bracket had a recess that held a slab of enamel with a standardized 100 μm deep white spot lesion (WSL). Changes in mineral were evaluated in lesion cross sections using backscatter electron imaging (BSE) and electron probe microanalysis (EPMA). The following products were applied twice daily for 2 weeks: GC Tooth Mousse™ (CPP-ACP), Tooth Mousse Plus™ (CPP-ACFP), CPP-ACFP Mineral Enhanced (CPP-ACFP Enh), or the vehicle paste of CPP-ACFP containing 900 ppm fluoride. To ensure blinding, all products had identical flavours and packaging. For each subject, the products were used in a random sequence, with washout periods between products. Compared to the baseline situation, favourable changes in white spot lesions occurred with all products. Analysis of enamel samples in cross section showed improvements in mineral levels, as seen in BSE grey scale levels from the enamel surface through the lesion. These were accompanied by enhanced calcium and phosphorus levels as seen using EPMA. The ranking of products for subsurface mineral gain, from best to worst, was: CPP-ACFP = CPP-ACFP Enh > CPP-ACP > vehicle with fluoride. Rapid remineralization occurred in this clinical model, which is due to a combination of factors: the enamel slabs were located on tooth surfaces exposed to parotid saliva, the surfaces were brushed regularly to remove dental plaque biofilm, and compliance with twice daily topical use of products was high. Such model systems may be useful for screening new product formulations for their effect on enamel WSL.

Advances in Nanocarriers for Drug Delivery in Dental Therapies

Dental caries are one of the major causes of oral degeneration diseases. In order to treat dental-related diseases, it is often challenging and expensive. Recent literature has reported many advances in designing delivery systems utilizing polymers and novel biomaterials. Polymers play an important role in designing many nanoformulations like liposomes, polymeric micelles, polymeric nanoparticles, carbon-based nanoparticles, nano-hydroxyapatite, iron oxide, zirconia, silica, and silver nanoparticles were used to treat oral complications of the oral cavity including dental caries, periodontal disease, and oral cancer. The present review focus on the importance of novel biodegradable polymers like poly (D, L-Lactide acid), PLLA (poly-L-lactide), PDLA (poly-D- lactide), PLGA that is poly (D, L Lactide-co-glycolide), cellulose acetate phthalate, and Chitosan, etc used to design site-specific delivery and controlled drug delivery to treat dental diseases. Moreover, research development in this area will raise opportunities for the dentist, researchers, and pharmaceutical scientists to fabricate an ideal drug delivery system.

Cradle-to-Grave Life-Cycle Assessment of Cellulosic Fiberboard

According to the United Nations Environment Programme (UNEP), the construction and operation of buildings accounted for nearly 38% of total global energy-related CO₂ emissions in 2019. The construction sector has been striving to use more low-carbon footprint building products to mitigate climate change and enhance environmentally preferable purchasing. Over the last several decades, there has been substantial growth in engineered wood products for the construction industry. To assess these products used in construction for their environmental profile, lifecycle assessments (LCAs) are performed. This study performed an LCA to estimate environmental impacts (cradle-to-gate and gate-to-grave) of cellulosic fiberboard (CFB) per m³ functional unit basis. The lifecycle inventory data developed were representative of CFB production in North America. Overall, the cradle-to-grave LCA results per m3 of CFB were estimated at 305 kg CO₂ e global warming (GW), 19.3 kg O₃ e photochemical smog formation, 1.03 kg SO₂ e acidification, 0.33 kg N e eutrophication, and 415 MJ fossil-fuel depletion. Except for smog formation, most environmental impacts of CFB were from cradle-to-gate. For example, 71% and 29% of total GW impacts were from cradle-to-gate and gate-to-grave lifecycle stages, respectively. The sensitivity analysis showed that reducing transport distance, on-site electricity use, natural gas for drying, and starch additives in the manufacturing phase had the most influence. Around 353 kg CO₂ e/m³ of CFB is stored as long-term carbon during CFB’s life which is higher than the total cradle-to-grave greenhouse gases (CO₂ e) emissions. Thus, the net negative GW impact of CFB (-47 kg CO₂ e/m³ of CFB) asserted its environmental advantages as an engineered wood panel construction material. Overall, the findings of the presented study would prove useful for improving the decision-making in the construction sector.

Reverse Mode Polymer Dispersed Liquid Crystal-based Smart Windows: A Progress Report

The reverse mode polymer dispersed liquid crystal (PDLC) is an emerging smart window technology. Unlike traditional PDLCs, a reverse mode PDLC can be transparent and opaque in the absence and presence of an external electric field. This report provides a brief introduction to several reverse modes PDLC smart window technologies, focusing on polymer-stabilized liquid crystals (PSLCs). The systems based on electrohydrodynamic instability (EHDI) of liquid crystals have also been discussed. The working principles, mode of material design, and recent developments are presented for each technology. The current obstacles have also been pointed out. The prospects of smart windows have also been presented.

Hydration and Microwave Curing Temperature Interactions of Repair Mortars

Microwave curing of repair patches provides an energy efficient technique for rapid concrete repair. It has serious economic potential due to time and energy saving especially for repairs in cold weather which can cause work stoppages. However, the high temperatures resulting from the combination of microwave exposure and accelerated hydration of cementitious repair materials need to be investigated to prevent potential durability problems in concrete patch repairs. This paper investigates the time and magnitude of the peak hydration temperature during microwave curing (MC) of six cement based concrete repair materials and a CEM II mortar. Repair material specimens were microwave cured to a surface temperature of 40-45 °C while their internal and surface temperatures were monitored. Their internal temperature was further monitored up to 24 hours in order to determine the effect of microwave curing on the heat of hydration. The results show that a short period of early age microwave curing increases the hydration temperature and brings forward the peak heat of hydration time relative to the control specimens which are continuously exposed to ambient conditions (20 °C, 60% RH). The peak heat of hydration of normal density, rapid hardening Portland cement based repair materials with either pfa or polymer addition almost merges with the end of microwave curing period. Similarly, lightweight polymer modified repair materials also develop heat of hydration rapidly which almost merges with the end of microwave curing period. The peak heat of hydration of normal density ordinary Portland cement based repair materials, with and without polymer addition, occurs during the post microwave curing period. The sum of the microwave curing and heat of hydration temperatures can easily exceed the limit of about 70 °C in some materials at very early age, which can cause durability problems.

Life Cycle Assessment of North American Laminated Strand Lumber (LSL) Production

Raw materials for buildings and construction account for more than 35% of global primary energy use and nearly 40% of energy-related CO2 emissions. The Intergovernmental Panel on Climate Change (IPCC) emphasized the drastic reduction in GHG emissions and thus, wood products with very low or negative carbon footprint materials can play an important role. In this study, a cradle-to-grave life cycle assessment (LCA) approach was followed to quantify the environmental impacts of laminated strand lumber (LSL). The inventory data represented North American LSL production in terms of input materials, including wood and resin, electricity and fuel use, and production facility emissions for the 2019 production year. The contribution of cradle-to-gate life cycle stages was substantial (>70%) towards the total (cradle-to-grave) environmental impacts of LSL. The cradle-to-gate LCA results per m³ LSL were estimated to be 275 kg CO2 eq global warming, 39.5 kg O3eq smog formation, 1.7 kg SO2 eq acidification, 0.2 kg N eq eutrophication, and 598 MJ fossil fuel depletion. Resin production as a part of resource extraction contributed 124 kg CO2 eq (45%). The most relevant unit processes in their decreasing contribution to their cradle-to-grave GW impacts were resource extraction, end-of-life (EoL), transportation (resources and product), and LSL manufacturing. Results of sensitivity analysis showed that the use of adhesive, consumption of electricity, and transport distance had the greatest influences on the LCA results. Considering the whole life cycle of the LSL, the final product stored 1,010 kg CO2 eq/m³ of LSL, roughly two times more greenhouse gas emissions over than what was released (493 kg CO2 eq/m³ of LSL) from cradle-to-grave. Overall, LSL has a negative GW impact and acts as a carbon sink if used in the construction sector. The study results are intended to be important for future studies, including waste disposal and recycling strategies to optimize environmental trade-offs.

Efficient Debye Function Interpolation Formulae: Sample Applications to Diamond

The well-known classical heat capacity model developed by Debye proposed an approximate description of the temperature-dependence of heat capacities of solids in terms of a characteristic integral, the T-dependent values of which are parameterized by the Debye temperature, Θ D . However, numerous tests of this simple model have shown that within Debye’s original supposition of approximately constant, material-specific Debye temperature, it has little chance to be applicable to a larger variety of non-metals, except for a few wide-band-gap materials such as diamond or cubic boron nitride, which are characterized by an unusually low degree of phonon dispersion. In this study, we present a variety of structurally simple, unprecedented algebraic expressions for the high-temperature behavior of Debye’s conventional heat-capacity integral, which provide fine numerical descriptions of the isochoric (harmonic) heat capacity dependences parameterized by a fixed Debye temperature. The present sample application of an appropriate high-to-low temperature interpolation formula to the isobaric heat capacity data for diamond measured by Desnoyers and Morrison [17], Victor [24], and Dinsdale [25] provided a fine numerical simulation of data within a range of 200 to 600 K, involving a fixed Debye temperature of about 1855 K. Representing the monotonically increasing difference of the isobaric versus isochoric heat capacities by two associated anharmonicity coefficients, we were able to extend the accurate fit of the given heat capacity ( C p ( T ) ) data up to 5000 K. Furthermore, we have performed a high-accuracy fit of the whole C p ( T ) dataset, from approximately 20 K to 5000 K, on the basis of a previously developed hybrid model, which is based on two continuous low-T curve sections in combination with three discrete (Einstein) phonon energy peaks. The two theoretical alternative curves for the C p ( T ) dependence of diamond were found to be almost indistinguishable throughout the interval from 200 K to 5000 K.

Durability of Alkali-Activated Materials Made with a High-Calcium, Basic Slag

<span>Alkali activated (AA) materials have been investigated for decades as an alternative to Portland cement (PC) products. Most consist of a silicate waste activated with alkalis, which leads to lower green-house gas emissions and a substantial drop in the use of unrenewable material resources. This paper studies the durability of AA materials made with a ground granulated blast furnace slag (GGBS) from Dublin, activated with sodium hydroxide (NaOH), and sodium silicate (Na</span>_{<span>2</span>}<span>SiO</span>_{<span>3</span>}<span>), both combined and separately, and cured at 20 and 60°C. The long-term strength and durability were assessed with accelerated weathering tests using thermal-moisture cycling, salt crystallization and freeze-thaw cycling. The 28-day strengths are compared to the 270-day strengths. The mass loss and macro/microscopic changes were investigated. The slag complies with standard requirements being ultra-fine (SSA=1950 m</span>^{<span>2</span>}<span>/kg), basic (1.56 basicity-CaO+ MgO/SiO</span>_{<span>2</span>}<span>) and highly amorphous. It is adequate for alkali activation, having a CaO/SiO</span>_{<span>2</span>}<span> ratio of 1.41 and a Al</span>_{<span>2</span>}<span>O</span>_{<span>3</span>}<span>/SiO</span>_{<span>2</span>}<span> ratio of 0.34. Melilite is the main constituent of the slag, in an isomorphous solid solution with gehlenite as the end member. The results evidenced that mechanical strength is not compromised over time, but it tends to significantly increase between 28 and 270 days. Despite the exaggerated weathering conditions of the laboratory cycling, the strength loss and micro/macro damage after cycling is minimum, except for a few of the Na</span>_{<span>2</span>}<span>SiO</span>_{<span>3</span>}<span> activated slag specimens. The Na</span>_{<span>2</span>}<span>SiO</span>_{<span>3</span>}<span>+NaOH activated GGBS materials showed the greatest resilience to the effects of frost, thermal/moisture and salts, as they remained intact and showed the greatest strenghts after cycling, and an unaltered microstructure consisting of unreacted GGBS and scattered silica cements alternating with alumino-silicates. In contrast, both the NaOH and the Na</span>_{<span>2</span>}<span>SiO</span>_{<span>3</span>}<span> activated GGBS materials were slightly damaged displaying salt efflorescence and microcracks. Increasing the curing temperature does not increase the durability of the AA slag specimens as it doesn’t significantly enhance the late mechanical</span><span dir="RTL"> strength. However, it slightly improves the strengths of the</span><span dir="RTL"> Na</span>_{<span>2</span>}<span>SiO</span>_{<span>3</span>}<span>+NaOH and NaOH activated mixes but lowers the strengths of the Na</span>_{<span>2</span>}<span>SiO</span>_{<span>3</span>} specimens.