Solid Materials Research Articles

Two-Step Conversion of Metal and Metal Oxide Precursor Films to 2D Transition Metal Dichalcogenides and Heterostructures.

The widely studied class of two-dimensional (2D) materialsknown as transition metal dichalcogenides (TMDs) are now well-poised to be employed in real-world applications ranging from electronic logic and memory devices to gas and biological sensors. Several scalable thin film synthesis techniques have demonstrated nanoscale control of TMD material thickness, morphology, structure, and chemistry and correlated these properties with high-performing, application-specific device metrics. In this review, the particularly versatile two-step conversion (2SC) method of TMD film synthesis is highlighted. The 2SC technique relies on deposition of a solid metal or metal oxide precursor material, followed by a reaction with a chalcogen vapor at an elevated temperature, converting the precursor film to a crystalline TMD. Herein, the variables at each step of the 2SC process including the impact of the precursor film material and deposition technique, the influence of gas composition and temperature during conversion, as well as other factors controlling high-quality 2D TMD synthesis are considered. The specific advantages of the 2SC approach including deposition on diverse substrates, low-temperature processing, orientation control, and heterostructure synthesis, among others, are featured. Finally, emergent opportunities that take advantage of the 2SC approach are discussed to include next-generation electronics, sensing, and optoelectronic devices, as well as catalysis for energy-related applications.

The toughness of interlocking metasurfaces

Interlocking metasurfaces (ILMs) are arrays of autogenous latching unit cells patterned across a surface. These create structural joints similar to bio‐inspired suture joints but patterned over a 2D surface rather than a 1D seam. This enables ILMs to be an alternative to conventional joining technologies such as bolts, welds, and adhesives. However, compared to conventional joining methods, relatively little is known of the engineering considerations for designing structural ILMs. In this study, the interfacial toughness of an archetypal ILM was examined for the first time. Under the conditions studied here, the ILM was substantially tougher than the material from which it was made; in this case exhibiting up to a 50% increase in interfacial crack initiation energy over the solid base material, a photocured 3D printed polymer. Through experimental tests using in‐situ digital image correlation along with complementary computational analyses, the mechanism of toughening in the ILM structure and the origins of toughness anisotropy were revealed. The increase in toughness is associated with cross‐cell interactions, i.e. load‐sharing across unit cells, which gives rise to a finite process zone length with different effective material properties. In this way, ILM toughening is analogous to crack blunting in ductile materials or fiber bridging in composites; yet here, the ILM was composed of a single‐phase base material and so the architected toughening is geometric in nature and hence amenable to future topological optimization.This article is protected by copyright. All rights reserved.

Anaerobic sludge from a full-scale biodigester: physico-chemical and organic characterization, and principal component analysis (PCA)

The biological transformation of the organic fraction of municipal solid waste into bioenergy yields a solid digested material known as anaerobic sludge, comprising a mixture of organic and inorganic substances. This sludge holds significant potential as a renewable resource for agricultural reuse. However, there is also the potential risk of contamination from this material in receiving environments. Therefore, it is crucial to assess the characteristics of this material to ensure compliance with local regulations regarding its soil application, aiming to avoid adverse environmental impacts and ensure proper and viable disposal. In this study, conducted to explore the characteristics of bottom sludge collected from a pilot-scale anaerobic biodigester, various parameters were analyzed. The biodigester in question had a capacity of 1300 liters and a useful volume of 1000 liters, digesting food waste and water hyacinth (Eichhornia crassipes) in a ratio of 20% in terms of volatile solids from the macrophyte to the volatile solids of the food waste. A multivariate analysis was conducted on the following parameters: metals (Al, Ba, Cd, Cr, Cu, Fe, Mn, Mo, Pb, Se, V, Zn, Na, and K); total, fixed, and volatile solids; alkalinity; volatile fatty acids; ammonia; Kjeldahl nitrogen (NTK); and organic, inorganic, and total carbon (COT), to observe possible correlations among these parameters. Additionally, the sludge underwent nuclear magnetic resonance (NMR) analysis for detection and characterization of organic compounds. This approach provided a deeper understanding of the properties of anaerobic sludge produced strictly under the aforementioned conditions, contributing to further research in the field.

Microscopic behavior of nano-water droplets on a silica glass surface

Recent advancements in computational science and interfacial measurements have sparked interest in microscopic water droplets and their diverse behaviors. A previous study using nonlinear spectroscopy revealed the heterogeneous wetting phenomenon of silica glass in response to humidity. Building on this premise, we employed high-resolution atomic force microscopy to investigate the wetting dynamics of silica glass surfaces at various humidity levels. Our observations revealed the spontaneous formation of nano-water droplets at a relative humidity of 50%. In contrast to the conventional model, which predicts the spreading of nanodroplets to form a uniform water film, our findings demonstrate the coexistence of nano-water droplets and the liquid film. Moreover, the mobility of the nano-water droplets suggests their potential in inducing the transport of adsorbates on solid surfaces. These results may contribute to the catalytic function of solid materials.

Memorizable Electro‐Birefringence Effect Exhibited by Transparent Liquid Crystal/Polymer Composite Materials

AbstractPolymer‐dispersed liquid crystals (PDLCs) with nano‐phase‐separated structures, in which nanometer‐sized liquid crystal (LC) domains are dispersed within a polymer matrix (nano‐PDLCs), are transparent solid materials whose optical properties can be modulated by applying an electric field (E‐field). Because the proportion of LC that can respond to an electric field is small, the specific surface area of the phase‐separated interface of nano‐PDLCs is larger than that of conventional PDLCs, resulting in higher drive voltages than those of conventional PDLCs. To lower the driving voltage of nano‐PDLCs, highly polar LCs (C3DIO) are used with a large dielectric anisotropy (>10000), and prepared nano‐PDLCs using DIO mixtures obtained by mixing them with related compounds as the host LC. Nano‐PDLCs employing DIO mixtures exhibit higher E‐field responsivity than those using conventional LC. In addition, the electro‐optical Kerr coefficient at visible wavelength is significantly high, reaching 10−8 m V−2. Furthermore, nano‐PDLCs using the DIO mixture exhibit a memory effect in which the induced birefringence remains even after the removal of the in‐plane E‐field. Memorized birefringence can be erased by heating or applying an E‐field perpendicular to the substrate surface. Nano‐PDLCs using a DIO mixture can be rewritable electro‐birefringence‐responsive materials that can memorize arbitrary birefringence values.

Environmental Influences on the Drying Rate of Spray Applied Disinfestants from Horticultural Production Surfaces

Drying rates of disinfestants commonly applied to horticultural plant production surfaces were evaluated under cool to hot weather and under laboratory conditions to characterize the range of drying times and how this relates to contact times specified on product labels. Drying rates of six disinfestants [isopropyl alcohol (IPA), two quaternary ammonium compounds (QACs), two peroxygen compounds (PXs), sodium hypochlorite (bleach)] and water were evaluated when applied to six substrate materials (concrete, galvanized metal, polypropylene ground fabric, polyethylene plastic sheet, pressure-treated pine, and twin-wall clear polycarbonate) based on the weather variables of solar radiation, temperature, and relative humidity. Differences were evident at the point of application. Disinfestants with low (IPA, both QACs and one PX) and high (bleach, one PX and water) surface tension provided approximately 100% and 60% coverage, respectively, when applied to horizontal, non-porous solid materials. Disinfestants applied to horizontal porous materials (concrete, fabric and wood) persisted on the surface for a mean of only 9 to 113 sec because solutions were actively drawn into the substrates internal structure. Disinfestants applied to vertical twin-wall greenhouse material flowed off, while retaining only a maximum beaded wetness coverage of 14%. A Bayesian analysis procedure was used to model drying effects of disinfestants correlated with substrate and weather variables based on posterior marginal and prediction trends. Generally, the fastest drying rate occurred in the first 2.5 min, and approximately 50% of coverage was retained by 5 min. The evaporative process was variable with distinct interactions occurring among the experimental variables.

CAI formation in the early Solar System

Calcium-aluminium-rich inclusions (CAIs) are the oldest dated solid materials in the Solar System, and are found as light-coloured crystalline ingredients in carbonaceous chondrite meteorites. Their formation time is commonly associated with age zero of the Solar System. Nevertheless, the physical and chemical processes that once led to the formation of these submillimetre- to centimetre-sized mineral particles in the early solar nebula are still a matter of debate. In this paper, we propose a pathway to form such inclusions during the earliest phases of disc evolution. We combine 1D viscous disc evolutionary models with 2D radiative transfer, equilibrium condensation, and new dust opacity calculations. We show that the viscous heating associated with the high accretion rates in the earliest evolutionary phases causes the midplane inside of about 0.5\,au to heat up to limiting temperatures of about 1500-1700\,K, but no further. These high temperatures force all refractory material components of the inherited interstellar dust grains to sublimate --- except for a few Al-Ca-Ti oxides, such as Al$_2$O$_3$, Ca$_2$Al$_2$SiO$_7$, and CaTiO$_3$. This is a recurring and very stable result in all our simulations, because these minerals form a natural thermostat. Once the Mg-Fe silicates are gone, the dust becomes more transparent and the heat is more efficiently transported to the disc surface, which prevents further warming. This thermostat mechanism keeps these minerals above their annealing temperature for hundreds of thousands of years, allowing them to form large pure crystalline particles. These particles are dragged out by the viscously spreading disc, and once they reach a distance of about 0.5\,au, the silicates recondense on the surface of the Ca-Al-rich particles, adding an amorphous silicate matrix. We estimate that this mechanism of CAI production works during the first 50\,000 years of disc evolution. These particles then continue to move outward and populate the entire disc up to radii of about 50\,au, before the accretion rate eventually subsides, the disc cools, and the particles start to drift inwards.

A green and facile direct ink writing technique for preparation calibration standards in laser ablation inductively coupled plasma mass spectrometry analysis

BackgroundLaser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a powerful tool for microanalysis of solid materials. Nevertheless, one limitation of the method is the lack of well-characterized homogeneous reference materials (RMs), such as BaF2 crystal and BaCO3 ceramics samples, making direct quantification difficult. This work presents a novel Direct Ink Writing (DIW) method to produce RMs for microanalysis. The Mg, Cr, Fe, Co, Ni, Cu, Y, Mo, Pr, Gd, Dy, Ho, Er, Tm, Yb, and Lu solutions were gravimetrically doped into BaCO3 by mixing with the dispersant and then cured with DIW techniques. (94) ResultsBaCO3 powder was combined with a dopant analyte to produce a printable slurry, aided by the use of a dispersant and cellulose. The resulting mixture was then printed using DIW equipment. The retention rates of the doped elements were investigated by internal and external standard method, and the results showed that they were completely dispersed in the solid material. After further optimization, it was found that there was no significant heterogeneity among the printed samples. LA-ICP-MS was used to analyze printed samples, to evaluate micro-scale homogeneity. The mass concentration of the doped element was determined by ICP-MS, verify its move closer to nominal value. Compared with the traditional reference materials preparation methods, the DIW technology greatly increased the sample homogeneity and the accuracy of the desired concentration. (132) SignificanceAs far as we know, there are few reports on the application of DIW method to prepare calibration standards. In brief, it is proved that the proposed method of preparing calibration standard by DIW technique to quantify analytes is valid and robust. This procedure provides great potential for LA-ICP-MS in-situ analysis in the field of well-prepared products, such as ceramic and crystal samples.(63)

Flaw sensitivity of bacterial cellulose hydrogel under monotonic and cyclic loadings

The presence of flaw in solid materials can lead to stress concentration, resulting in the reduction of rupture stress and stretchability of material. When the flaw is sufficiently smaller than a material-specific length, referred to as flaw sensitivity length, the material exhibits flaw insensitivity. The flaw sensitivity length is a critical material property that reflects how the material is sensitive or insensitive to crack. However, the impact of crack length on the load-bearing process of material remains an open problem. In this work, we characterize the flaw sensitivity of a stretchable material, bacterial cellulose hydrogel, under monotonic and cyclic loadings. Through fracture and fatigue tests, we first determine that the hydrogel exhibits high fracture toughness and fatigue resistance. We next characterize the flaw sensitivity of the hydrogel through two visualized experimental methods. Photoelasticity observation on the stress distribution in samples during loading shows that the samples with cracks below 2 mm exhibit uniform stress distribution during the deformation process, while those with cracks above 2 mm experience stress concentration at crack tip. Scanning electron microscope observation on the microstructure morphology of samples under fixed stretch shows that the samples with cracks below 2 mm exhibit uniform alignment of nanofibers, while those with cracks above 2 mm exhibit more intense alignment and even bundling of nanofibers at crack tip. Similar trends are observed in the samples under cyclic loading, where the transition length is also about 2 mm. Notably, the flaw sensitivity lengths obtained by the visualized methods agree well with that obtained by direct measurement of rupture stress and theoretical estimations under monotonic and cyclic loadings. The methods offer novel way to study the flaw sensitivity of materials, thereby contributing to the exploration of failure mechanisms.

Effect of Ni4Ti3 precipitates on the functional properties of NiTi shape memory alloys: A phase field study

Ni4Ti3 precipitates, which generally exist in aged Ni-rich NiTi shape memory alloys (SMAs), can have a profound effect on material properties. However, the fundamental insights into the effects of Ni4Ti3 precipitates on the functional properties, including the superelasticity (SE), elastocaloric effect (eCE), and shape memory effects (SMEs), are not well understood yet, especially those originating from the B2-B19′ martensite transformation (MT). In this work, a phase field model coupling the precipitation of Ni4Ti3 and the B2-B19′ MT is proposed, where the thermo-mechanical coupling effect and grain size effect are considered. The precipitate-dependent SE, eCE, one-way SME (OWSME), and stress-assisted two-way SME (SATWSME) of single-crystal, polycrystalline, and gradient-nanograined NiTi SMAs are simulated. The effects of the precipitate density, grain orientation range (texture), and gradient-distributed precipitate are examined, and the underlying microscopic mechanisms are revealed. The simulation results and new findings not only contribute to a more comprehensive insight into the effect of Ni4Ti3 precipitates on the MT, martensite reorientation, and functional properties of NiTi SMAs but also provide a reference for the development of excellent SMA-based solid refrigerants or SMA smart materials with designable functional properties.

Fostering community participation in sustainable municipal solid waste management at multiple scales in Tehran, Iran

This article delves into the intricacies of waste management in Tehran, offering insights into the structured framework governing the control of solid waste materials. As collected, the average daily generation of municipal solid waste (MSW) in the region is 0.645 kg per inhabitant. Unexpectedly, the impact of socio-economic factors on processes such as garbage sorting, creating products from recyclable waste, and composting was shown to be comparatively weaker than that of supporting elements. The initial approach entails providing environmental cadres and the community with more comprehensive MSW reduction training, which will cultivate a nuanced comprehension of waste management. The second strategy focuses on amplifying information dissemination through mass media and targeted campaigns, emphasizing effective MSW practices. The objective of the third endeavor is to augment the quantity of environmental cadres, which will be comprised of community and local leaders, in order to inspire and direct endeavors to reduce MSW. The fourth and final strategy underscores the expansion and diversification of waste storages, positioning them as customer-centric institutions dedicated to environmental campaigns and training. Ultimately, the collaborative implementation of these strategies is poised to instigate a positive shift towards heightened community participation in MSW reduction practices.

DFT-Assisted Investigation of the Electric Field and Charge Density Distribution of Pristine and Defective 2D WSe2 by Differential Phase Contrast Imaging.

Most properties of solid materials are defined by their internal electric field and charge density distributions which so far are difficult to measure with high spatial resolution. Especially for 2D materials, the atomic electric fields influence the optoelectronic properties. In this study, the atomic-scale electric field and charge density distribution of WSe2 bi- and trilayers are revealed using an emerging microscopy technique, differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM). For pristine material, a higher positive charge density located at the selenium atomic columns compared to the tungsten atomic columns is obtained and tentatively explained by a coherent scattering effect. Furthermore, the change in the electric field distribution induced by a missing selenium atomic column is investigated. A characteristic electric field distribution in the vicinity of the defect with locally reduced magnitudes compared to the pristine lattice is observed. This effect is accompanied by a considerable inward relaxation of the surrounding lattice, which according to first principles DFT calculation is fully compatible with a missing column of Se atoms. This shows that DPC imaging, as an electric field sensitive technique, provides additional and remarkable information to the otherwise only structural analysis obtained with conventional STEM imaging.

Coordination cages integrated into swelling poly(ionic liquid)s for guest encapsulation and separation

Coordination cages have been widely reported to bind a variety of guests, which are useful for chemical separation. Although the use of cages in the solid state benefits the recycling, the flexibility, dynamicity, and metal-ligand bond reversibility of solid-state cages are poor, preventing efficient guest encapsulation. Here we report a type of coordination cage-integrated solid materials that can be swelled into gel in water. The material is prepared through incorporation of an anionic FeII4L6 cage as the counterion of a cationic poly(ionic liquid) (MOC@PIL). The immobilized cages within MOC@PILs have been found to greatly affect the swelling ability of MOC@PILs and thus the mechanical properties. Importantly, upon swelling, the uptake of water provides an ideal microenvironment within the gels for the immobilized cages to dynamically move and flex that leads to excellent solution-level guest binding performances. This concept has enabled the use of MOC@PILs as efficient adsorbents for the removal of pollutants from water and for the purification of toluene and cyclohexane. Importantly, MOC@PILs can be regenerated through a deswelling strategy along with the recycling of the extracted guests.

Adhesion characteristics of carbon nanotube gecko tapes for micrometer-sized particles

ABSTRACT A detailed understanding of the adhesive properties of a carbon nanotube (CNT)-based gecko tape with respect to microscale particles is necessary for its practical application as a supporting medium for specific solid materials. We obtained the force curves of vertically aligned CNTs (VACNTs) for individual microparticles of various diameters using atomic force microscopy and evaluated their adhesion force and adhesion length. The measured adhesive force followed the apparent contact area with increasing embedding depth and was size-dependent at scales of several tens of micrometers. The adhesive forces measured for a 20 µm-diameter bead was significantly higher than those for larger particles, which may be related to inclination of the adherent surface against the VACNT tape surface. The adhesion length depended on the type of the CNTs comprising the VACNT, rather than on the bead size. The evaluation of VACNTs with different morphologies suggested that the flexibility of the individual CNTs and the density of the CNT – CNT interconnections in the VACNTs were important factors for obtaining the true contact area to realize better adhesion of micrometer-sized particles.

Assessing the survival of carbonaceous chondrites impacting the lunar surface as a potential resource

The Moon offers a wide range of potential resources that may help sustain a future human presence, but it lacks indigenous carbon (C) and nitrogen (N). Fortunately, these elements will have been delivered to the Moon's surface by carbonaceous chondrite (CC) asteroid impactors. Here, we employ numerical modelling to assess the extent to which these materials may have sufficiently survived impact with the lunar surface to be viable sources of raw materials for future exploration. We modelled the impact of a 1 km diameter CC-like asteroid, considering impact velocities between 5 and 15 km s−1, and impact angles between 15 and 60° to the horizontal. The most favourable conditions for the survival of C-rich, and especially N-rich materials, are those with the lowest impact velocities (≤10 km s−1) and impact angles (≤15°). Impacts with velocities >10 km s−1 and angles >30° were found not to yield any significant amount of surviving solid material, where bulk survival is defined as material experiencing temperatures less than the impactor material's estimated melting temperature (∼2100 K, based on a commonly adopted Equation of State for serpentine). Importantly, oblique and low velocity impacts result in concentrations of unmelted projectile material down-range from the impact site. For the canonical 1 km-diameter CC impactor considered here, with an impact angle ≤15° and velocity ≤10 km s−1, this results in ∼109–1010 kg of C and ∼108–109 kg of N being deposited a few tens of km down-range from the impact crater, where it might be accessible as a potential resource. Such low-velocity and oblique impacts have a low probability - we estimate that only ∼5 such impacts may have occurred on the Moon in the last 3 billion years (the number of impacts of smaller impactors will have been higher, but they will concentrate lower masses of potential resources). As the estimated C and N concentrations from such impacts greatly exceed those expected for ices within individual permanently shadowed polar craters, searching for these rare impact sites may be worthwhile from a resource perspective. We briefly discuss how this might be achieved by means of orbital infra-red remote-sensing measurements.

Topology optimization based on improved DoubleU-Net using four boundary condition datasets

Topology optimization is extensively employed in engineering design. However, applying deep learning to solve topology optimization problems faces challenges owing to limited training data and model adaptability to various boundary conditions. To address these challenges, this research has employed a solid isotropic material with a penalization method to produce a dataset of 400,000 2D samples covering four boundary conditions. Each boundary condition includes two resolution datasets. Moreover, an improved DoubleU-Net model is proposed for real-time topology optimization, ensuring high-accuracy predictions. On the test dataset, the average Intersection over Union (IoU) accuracies of the proposed model for the four boundary conditions above are 93.26%, 96.71%, 96.35% and 97.38%. This research also investigated the impact of different structural datasets on the model's generalization capability. The experimental results indicate that the model trained on random structures exhibits excellent testing performance and demonstrates robust generalization capability.

Scraping Effect of Dam-Overtopping Debris Flow—A Case Study of Chutou Gully ‘8.20’ in Miansi Town, Wenchuan County

ABSTRACT After the May 12 earthquake in Wenchuan, numerous debris flow disasters occurred due to heavy rainfall. After the earthquake, disaster prevention and mitigation projects, such as the sand dam, played an essential role in safety. However, when the outflow of solid material exceeds the designed storage capacity of the sand dam, the debris flow overtopping the dam intensifies the scraping effect on the source material of the gully channel. This paper takes the ”8.20” debris flow in the Chutou gully as the research object. A transport mode of the debris flow after dam overtopping is studied through comprehensive field investigation, theoretical analysis, and indoor model tests. A quantitative evaluation model is established for the scraping depth and scraping volume of dam-overtopping debris flow. The study results showed that once the debris flow overtops a dam, the loose source carried by the channel is involved in the entire migration process, enlarging the fluid scale and intensifying the damage along the channel. The results agree with the measurements and observations, with maximum relative errors of 5.81% and 14.70%, respectively. This shows model validity. Furthermore, the test results show that the debris flow scarping phenomenon in the γ=[1.4 t/m3, 1.6 t/m3] interval is the most significant. Overall, this study will help improve future engineering decisions, design strategies, and finding the best design solutions to minimize the risk of dam-overtopping debris flow disasters.

New evidence on the electroprecipitation of ceria

The electroprecipitation of ceria onto Ni electrodes from Ce(NO3)3 solutions has been studied by comparing deposits obtained with potentiostatic electrolysis of variable durations. The dependence on the deposition charge of (i) ceria layer thickness, (ii) apparent layer density, (iii) coverage of the Ni surface by CeO2 and (iv) layer resistance was determined. These quantities were respectively assessed using (i) cross-sectional SEM images, (ii) gravimetric measurements, (iii) cyclic voltammetry in alkaline solution and (iv) electrochemical impedance spectroscopy. Experimental data showed that a porous low-density oxide precipitated initially, leaving a substantial part of the Ni electrode surface in direct contact with the electrolyte. During successive phases of the film growth, the formation of new solid material at the layer|solution interface was progressively replaced by its formation within the layers’ pores and at the Ni|layer interface.

Evaluating the use of UV Absorbance for the Differentiation of Humified from Non-humified Materials.

Products containing humic acids (HA) and fulvic acids (FA) have significant commercial potential, however, unknown to the consumer, some products may be mislabeled or contain adulterants. The prevalence of mislabelling and adulterants is primarily found in FA products. Using UV-Vis spectroscopy to differentiate between real and fake FA products is practical and desirable. The objective of this study was to expand the data set generated using a UV-VIS based method proposed by Mayhew et al., 2023. In total, thirty (30) test samples were used to generate ninety test portions (3 replicates per test sample) for analysis using the UV-Vis methodology outlined in Mayhew et al., 2023, which in this study is referred to as the UVAC (UV absorbance confirmation) method. None of the thirteen FA test samples investigated were determined as humified using the UVAC method. The FA samples studied comprised of two IHSS standards, five commercial FA products (CFAP) and six full FA fractions (SFA), which were isolated from six known solid humic material sources (SHMS). There was a leonardite, a humalite, and four peat sources used as the SHMS. Analysis of the neutralized extract of the SHMS found only 3/6 SHMS were determined as humified. Six HA (SHA) test samples were also generated by isolating the HA from the SHMS and only 3/6 SHA were determined as humified. Given the high prevalence of false determinations more work is needed to improve the method so it can be used by industry or regulators. The proposed method failed to determine IHSS FA standards as humified. Although the method is practical, it needs improvement and further study before it can be used for reliable differentiation of real from fake FA or HA.

Influence of fly ash as additive on the viscosity of transesterified neem oil

Biodiesel as the renewable source of energy has become one of the alternative solutions towards the problems associated with the use of fossil fuels in energy generation. Most of the biodiesel produced via tansesterification process are associated with viscosity that is above diesel limit. This problem can be mitigated through the use of solid materials as additive. This paper investigates the influence of fly ash as additive on the viscosity of transesterified neem oil. The morphology and chemical constituent of fly ash were studied using Scanning Electron Microscopy (SEM) and Xray Fluoroscopy (XRF). The crude neem oil was purified; transesterified and 0.1 wt%, 0.2 wt%, 0.3wt%, 0.4wt% and 0.5wt% of fly ash were used as additive. The viscosity of crude, purified, transesterified and transesterified with 0.1 wt%, 0.2 wt%, 0.3wt%, 0.5wt% and 0.5wt% of fly ash as additive were measured using brookfield digital viscometer. SEM shows that the mophorlogy of fly ash was dispersed particle with cloudy structure while XRF shows that the major compound presence on fly ash was silicon oxide. The viscosity of the samples decreases as the temperature increases and with the addition of fly ash. But on the addition of 0.3wt% it shows significant variation at equal range of temperature. This indicated that the fly ash can be used as biodiesel additive on neem oil as it decreases the level of viscosity presence on the oil.