CaCO3 Powder Research Articles

Superior comprehensive performance CaO‐based core achieved by optimizing particle gradation via orthogonal experiments

AbstractThe effect of CaCO3 particle size on the viscosity of slurry, phase formation, microstructural evolution, and performances of the water‐soluble CaO‐based ceramic core sintered at different temperatures was systematically investigated and discussed, and the particle gradation orthogonal experiments were used to adjust flexural strength, water‐soluble rate, shrinkage rate, apparent porosity, and hygroscopicity rate. The results showed that the finer particle size increased the effective contact area between CaO and SiO2, which promoted the generation of CaO–SiO2 system phase and the dense microstructure in the sintered CaO‐based cores. The higher sintering resulted in dense microstructure. The optimal gradation scheme included 28 wt.%, 56 wt.%, and 16 wt.% CaCO3 powder with D50 = 11.0 µm, 6.17 µm, and 4.62 µm, respectively, and the resulting flexural strength was 9.57 MPa, water‐soluble rate was 65.37 g/h in 60°C water, shrinkage rate was 8.62%, porosity rate was 38.85%, presenting a well‐balanced comprehensive performance, which is significant for the complex internal castings.

Green Ca-source of cockle shells converted to calcium acetate for environmental sustainability

This work aimed to synthesize and characterize the calcium acetate monohydrate (Ca(CH3COO)2·H2O) from the exothermic reaction between CaCO3 powder derived from cockle shells with three different acetic acids (8, 10, and 12 mol L−1) concentrations by the rapid and easy process without pH and temperature control to lead to cheap chemical production. The physicochemical characteristics of all synthesized Ca(CH3COO)2·H2O samples are investigated based on the chemical compositions, crystal structures, vibrational characteristics, morphologies, and thermal behavior to confirm the target compound. A suitable concentration of 10 mol L−1 CH3COOH was chosen to produce Ca(CH3COO)2·H2O with the highest yield (96.30 %), maximum calcium content (96.2 % CaO) with lower impurities, and time consumption of 17 h. The calcium acetate product obtained from cockle shells in this work shows differences in thermal stability, morphological structure purity, %yield, and metal contamination with those reported obtained from other sources and another shell type in the previous work. This research investigates the transformation of cockle shell waste into CaCO3 for the production of calcium acetate, aiming to address environmental sustainability concerns by reducing the use of calcium ore resources and greenhouse gas emissions.

Thermostable CaCO3-Immobilized Bacillus subtilis Lipase for Sustainable Biodiesel Production from Waste Cooking Oil

Due to the increasing demand for green processes in renewable energy production, the extracellular Bacillus subtilis B-1-4 lipase was used as a biocatalyst for producing biodiesel from waste cooking oil. Response surface methodology was employed for the optimization of enzyme production. Lipase activity was modeled with a quadratic function of four factors that primarily influence the culture medium. Thanks to this model, an optimal lipase activity of 1.7 ± 0.082 U/mL was achieved with the best culture medium composition: 16 g/L of tryptone, 15 g/L of yeast extract, 15 g/L of NaCl, and a 0.15 initial optical density at 600 nm (OD600 nm). The maximal lipase activity was measured at 45 °C and pH 8, using para-nitrophenyl palmitate as a substrate. The enzyme maintained above 94% and 99% of its initial activity at temperatures ranging from 40 to 50 °C and at pH 8, respectively. Moreover, it exhibited a higher residual activity than other Bacillus lipases in the presence of organic solvents. Residual activities of 86.7% and 90.2% were measured in the presence of isopropanol and ethanol, respectively. The lipase was immobilized by adsorption onto CaCO3 powder. FT-IR and SEM were used to characterize the surface-modified support. After immobilization, a lipase activity of 7.1 U/mg of CaCO3 was obtained. Under the optimized conditions, the highest biodiesel yield of 71% was obtained through the transesterification of waste cooking oil using the CaCO3-immobilized Bacillus subtilis lipase. This research reveals a method for the utilization of waste cooking oil for biodiesel production using an efficient immobilized thermostable lipase, providing environmental and economic security.

The effect of gamma rays and stearic acid on calcium carbonate and its impact on the properties of epoxy-based composites

Abstract The purpose of this research is to produce composites of epoxy resin and calcium carbonate (EP/CaCO3) and investigate how treating the CaCO3 filler with stearic acid and gamma radiation affects the properties of the epoxy composites, enhancing their suitability for a range of applications. The CaCO3 powder was subjected to stearic acid treatment and later exposed to γ-radiation at various doses namely (10, 20 and 30 kGy), Different weight percentages of untreated and treated CaCO3 powder were added to epoxy resin (EP) to create EP/CaCO3 composites loaded with varying amounts of CaCO3 filler (5 %, 10 %, 20 %, 30 %, and 40 %). The influence of both stearic acid treatment and different doses of gamma radiation on CaCO3 was investigated. The composites were subjected to characterization of various properties including mechanical (splitting tensile strength, impact strength), thermal (TGA and dimensional thermal analysis) as well as morphological SEM examination. The analysis’ findings demonstrated that the stearic acid monolayer functions as a coupling agent in the EP matrix and can coat CaCO3 particles efficiently. The modification of CaCO3 by stearic acid and exposure to 30 kGy of gamma radiation shows a notable improvement in thermal stability and mechanical qualities for the epoxy composites loaded with various CaCO3 concentrations.

Fabrication of an Ultrastrong Formaldehyde-Free Wood Adhesive with an Organic-Inorganic Cross-Linking Network.

The wood industry faces challenges in producing eco-friendly, high-performance, and formaldehyde-free adhesives. In this study, carboxylated styrene-butadiene rubber (XSBR) was blended with polyamidoamine-epichlorohydrin (PAE) resin, and a controlled amount of CaCO3 powder was incorporated to create an adhesive with exceptional strength. The resulting three-layer plywood demonstrated remarkable dry and wet shear strengths of 3.09 and 2.36 MPa, respectively, and of 2.27 MPa after boiling water tests, comparable to that of phenolic resins. Additionally, the adhesive exhibited strong adhesion across various materials including glass, metal, etc. This exceptional performance was due to two primary factors: (1) the high-density chemical cross-linking reaction and the physical entanglement between XSBR and PAE; (2) the organic-inorganic hybrid involving metal ion complexation developed by CaCO3, which fostered molecular chain connections and enhanced the adhesive-material interface. These findings offer valuable references for further research in the field of wood adhesives.

Inerting effect of CaCO3 powder on the combustion characteristics of wood dust layer

The influence of the typical inert powder, calcium carbonate (CaCO3), on the combustion temperature and spread pattern of wood dust layer was investigated using an experimental apparatus designed to study the ignition characteristics of deposited dust. The findings demonstrated a gradual decline in the combustion temperature of wood dust layer as the mass fraction of CaCO3 increased. A notable decrease in combustion temperature was observed when the CaCO3 mass fraction ranged from 40% to 60%. In the absence of initial wind speed, the high-temperature burning area of the dust layer was significantly reduced as the CaCO3 mass fraction increased. Concurrently, the red sparks at the front end of the burning front diminished, and the color of the combustion residue transitioned from charcoal black to charcoal gray. With the presence of initial wind speed, prominent red sparks were observed at the front end of dust layer combustion when the CaCO3 mass fraction was low, while the red sparks decreased and darkened as the CaCO3 mass fraction increased. CaCO3 primarily influenced wood dust combustion through heat absorption and oxygen adsorption. The coupling effect of increased initial temperature and wind speed under CaCO3 inerting contributed to the overall rise in wood dust combustion temperature. According to the wood dust layer combustion temperature-CaCO3 mass fraction Exp1 model, employing CaCO3 with a mass fraction exceeding 40% resulted in a more effective inerting performance.

DEM simulation of a single screw granulator: The effect of liquid binder on granule properties

The Caleva UK single-screw Variable Density Extruder (VDE) is a continuous powder processing equipment known for spheronization and extrusion. Its suitability for granulation remains uncertain, a common challenge in powder processing industries that deal with granules, pellets, and tablets. This study investigates the VDE's potential for granulation, using 65 µm CaCO3 powder and PEG 4000 as a liquid binder. In order to replicate several experimental setups with varying binder concentrations and liquid-to-solid ratios (L/S) of 0.1 and 0.15, eight DEM simulations were run. Our results indicate that higher binder concentrations yield more consistent products with fewer fines, while lower concentrations result in inconsistent products with increased fines. Low L/S ratios produce fragile, fine-sized products with a broad particle size distribution (PSD). DEM simulations reveal a direct relationship between liquid binder content and contact forces. Analysis of bonds formed, and particle counts in simulations corroborates experimental observations of fines production. Additionally, granule strength appears to be directly proportional to contact force.

RADIOCARBON STEP-COMBUSTION OXIDATION METHOD AND FTIR ANALYSIS OF TRONDHEIM CaCO3 PRECIPITATES OF ATMOSPHERIC CO2 SAMPLES: FURTHER INVESTIGATIONS AND INSIGHTS

ABSTRACT Eight atmospheric carbon dioxide samples (as calcium carbonate—CaCO3—precipitates) from Lindesnes site (58ºN, 7ºE), belonging to 1963 and 1980 (four samples from each year) and stored at the National Laboratory for Age Determination (NTNU), have been reevaluated through radiocarbon (14C) analysis. Previous 14C results indicated the presence of a contaminant, which was not removed through different chemical cleansing procedures (e.g., hydrochloric acid—HCl and/or hydrogen peroxide—H2O2). Here, we present a follow up investigation using 14C step-combustion and Fourier-transform infrared spectroscopy (FTIR) analysis. Results from 14C data indicate unsuccessful removal of the contaminant, while further FTIR analysis displayed the presence of moisture. This finding alludes to the possibility that the contaminant is of ambient air-CO2 deeply embedded in CaCO3 powders (within clogged CaCO3 pores and/or bonded to the lattice). Samples were found exposed to air-CO2 and humidity. These conditions may have lasted for years, possibly even decades, leading to the 14C offsets detected here.

Influence of micro‐sized CaCO3 on hydrates formation of residual calcium aluminate cement in castables during drying

AbstractThe addition of CaCO3 powder in calcium aluminate cement (CAC) is reported to accelerate the hydration of CAC and generate mono‐carbonate C4AC̅H11, which is conducive to shortening the curing time of CAC‐bonded castables at ambient temperatures. Although the hydration of CAC is relatively fast, there is still residual un‐hydrated CAC in castables after curing. The residual CAC would continue to hydrate to produce C3AH6 and AH3 during the subsequent drying procedures in the absence of CaCO3. But it is worth pondering which type of hydrate would be generated in the presence of CaCO3 during the drying at around 110°C. In this study, the effect of micro‐sized CaCO3 addition on the hydrate formation of CAC‐bonded castables during drying at 110°C was investigated. The results indicate that the C4AC̅H11 formed at the curing temperature of 30°C is not decomposed or converted during drying. The CaCO3 remained after curing does not participate in the hydration of residual CAC during drying at 110°C, and thus the residual CAC continues to hydrate to generate C3AH6 rather than C4AC̅H11.

Study on photoluminescence of integrated nano-calcium carbonate (CaCO3) enhanced with dysprosium (Dy) doped calcium borophosphate (CBP) phosphor

Purpose There is a strong inducement to develop new inorganic materials to substitute the current industrial pigments, which are known for their poor ultraviolet absorbent and low photoluminescence (PL) properties. The purpose of this paper is to invent a better rare-earth-based pigment material as a spectral modifier with good luminescence properties to enhance the spectral response for photovoltaic panel application. Design/methodology/approach Different phosphor samples made of nano-calcium carbonate (CaCO3) with varied wt.% of the dopant Dysprosium doped calcium borophosphate (CBP/Dy) as (W0 – 0%, W1 – 3,85%, W2 – 7.41%, W3 –10.71% and W4 –13.79%) were prepared via the solid-state diffusion method at 600 °C for 6 h using a muffle furnace. The structural, morphological and luminescence properties of the CaCO3:CBP/Dy powder samples were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and PL test. Findings The XRD, SEM and FTIR results verified the crystalline formation, morphological behaviour and vibration bonds of synthesized CBP/Dy-doped CaCO3 powder samples. XRD pattern revealed that the synthesized powder samples exhibit crystalline structured materials, and SEM results showed irregular shape and porous-like structured morphologies. FTIR spectrum shows prominent bands at 712, 874 and 1,404 cm−1, corresponding to asymmetric stretching vibrations of CO32− groups and out-of-plane bending. PL characterization of CBP/Dy-doped CaCO3 (sample W) shows emission at 427 nm (λmax) under the excitation of 358 nm. The intensity of PL emission spectra drops due to the concentration quenching effect, while the maximum PL intensity is observed in the W3 phosphor powder system. Research limitations/implications This phosphor powder is expected to find out the potential application such as a spectral modifier which is applied to match the energy of photons with solar cell bandgap to improve spectral absorption and lead to better efficiency. Originality/value The introduction of a nano-CaCO3:CBP/Dy hybrid powder system with good luminescence properties to be used as spectral modifiers for solar cell application has been synthesized in the lab, which is a novel attempt.

Effect of compression molding of CaCO3 powder on the kinetics of CO2 capture towards sustainable CO2 capture and sequestration cycle.

Reducing CO2 emissions from industrial sectors and motor vehicles is currently receiving much attention. There are different strategies for CO2 capture, one of which is using calcium oxide (CaO). In our proposed carbon dioxide cycle, limestone is first calcined to get CaO, which is then used to capture CO2 by converting it to CaCO3. Next, the released CO2 could be converted to different organic matter by different sequestration techniques. For this purpose, CaCO3 discs have been prepared by compression molding to investigate the effect of sintering temperature on the mechanical and chemical properties of CaO carbonation reaction. The aim of this work is to fill the knowledge gap for the effect of the contact profile between CO2 gas and CaO disc, particularly the effect of reducing the void fraction of CaO on the rate of carbonation reaction. It was found that the flexural strength of the CaO discs was influenced by several factors, such as the calcination temperature, duration of calcination, and pressing pressure. The carbonation step indicated that both CO2 and H2O are reacting with CaO simultaneously and progressively, with the progressive reaction of H2O and CO2 being a favorable route. The carbonation process happens as a surface reaction-controlled process followed by a slower internal diffusion-controlled process. Additionally, a kinetic study of the competing reactions indicated that two factors are controlling the process: diffusion of gases through the pores and then the reaction rate. Furthermore, our data showed that the CO2 uptake rate was 1352.34mg/g CaO, indicating that 566.34mg of CO2 was adsorbed inside the pores of the CaO disc. Based on these results, we propose a new mechanism of the sequence of the competing reactions. In summary, the CaO discs revealed a significant removal of CO2 from stack gases, which will be suitable for removing CO2 from exhaust gases generated by industrial processes and other sources of emissions such as vehicles and ships.

Degradation of Kapok Fiber-Reinforced Polyester Composites with Calcium Carbonate Filler in Seawater

This research investigates the development of polyester composites reinforced with kapok fiber and CaCO3 filler to reduce environmental impact. Natural fibers, valued for their lightweight, fire resistance, cost-effectiveness, and biodegradability, are commonly used in composites. However, synthetic fibers, despite their superior mechanical properties, raise environmental concerns. The study focuses on the composites' performance, stability, and endurance in harsh conditions. Kapok fibers were manually extracted, and CaCO3 powder was sieved to 80 mesh. Composite samples were created with varying volume fractions of CaCO3 powder and kapok fibers, using polyester as the matrix. Tensile and bending tests, according to ASTM D3039 and ASTM D790 standards, were conducted on these samples. Additionally, water absorption was assessed gravimetrically, and mechanical strength degradation was studied via immersion in artificial seawater at different temperatures. Results indicated that water absorption increased with higher fiber volume fractions in the composite, primarily due to the water-absorbing capabilities of natural fibers and CaCO3 particles, surpassing that of polyester resin. Increased immersion temperatures accelerated water diffusion, impacting interactions between water molecules, polymer chains, and natural fibers. Furthermore, an increase in the CaCO3 filler volume fraction negatively affected the mechanical strength of kapok polyester-fiber composites. This was attributed to the agglomeration of CaCO3 powder, disrupting the polyester resin's viscosity and damaging the bond between kapok fiber and the matrix. The composites exhibited their highest tensile strength with 10% CaCO3 filler before immersion, but this strength decreased following exposure to high temperatures.

Achieving Long-Acting Local Analgesia Using an Intelligent Hydrogel Encapsulated with Drug and pH Regulator.

Local anesthetics are important for the treatment of postoperative pain. Since a single injection of the solution of a drug such as bupivacaine (BUP) works only for a few hours, it is much required to develop a long-term injectable formulation that maintains its efficacy for more than 1 day. Herein, an intelligent copolymer hydrogel loaded with BUP microcrystals was invented. The biodegradable block copolymer was synthesized by us and composed of a central hydrophilic poly(ethylene glycol) (PEG) block and two hydrophobic poly(lactide-co-glycolide) (PLGA) blocks. The aqueous system of the amphiphilic copolymer underwent a sol-gel transition between room temperature and body temperature and, thus, physically gelled after injection. Considering the decrease of solubility of BUP with the increase of pH and the internal acidic environment due to the hydrolysis of PLGA, calcium carbonate (CaCO3) powder was introduced as a pH regulator. Then, the internal pH was found to be nearly neutral and many BUP microcrystals were dispersed in the gel network. In this way, BUP had achieved a sustained release out of the thermogel. The maximum possible effect (MPE) in a rat sciatic nerve blockade model was used to describe the sensory blockade effect. In vivo analgesic effects evaluated with a hot plate experiment of rats demonstrated that the thermogel encapsulated with BUP microcrystal and CaCO3 powder significantly prolonged analgesia up to 44 h, the duration time with respect to 50% MPE. The intramuscularly injected implant exhibited biocompatibility in histological analyses. Besides, the untreated leg of the rats was not influenced by the treated leg, indicating no obvious systematic anesthesia of this hydrogel formulation. Such an intelligent and composite formulation represents a potential strategy for long-acting analgesia therapy.

Spatially Resolved Characterisation of Low Mass Fraction Uranium Glass Working Reference Materials

We present the results of a study to generate reference glasses that reflect an environment analogous to historic nuclear fallout samples of interest for post‐detonation nuclear forensics. The glasses were generated by melting and then quenching SiO2, Al2O3 and CaCO3 powders. Two suites of glasses with three distinct U isotopic ratios were successfully made with enrichments in the 235U isotope (~ natural [0.72%], ~ 53% and 94%), but the bulk elemental data showed heterogeneity (~ 10% RSD) with U mass fractions ranging from 331.47 to 373.63 μg g‐1. Spatially resolved U isotopic measurements were performed using three mass spectrometry techniques (secondary ion mass spectrometry‐single stage accelerator mass spectrometry [SIMS‐SSAMS], large geometry [LG] ‐ SIMS, and laser ablation‐inductively coupled plasma‐mass spectrometry [LA‐ICP‐MS]) across five National Laboratories. The results showed good agreement with the bulk U isotopic data for the low, medium, and high U mass fractions. We conclude that despite elemental heterogeneity, these samples can serve as useful working reference materials for spatially resolved nuclear fallout analyses, as well as for other related spatially resolved analyses.

Synchronously construction of hierarchical porous channels and cationic surface charge on lanthanum-hydrogel for rapid phosphorus removal

Phosphorus (P) removal from wastewater is critical for ecosystem operation and resource recovery. To facilitate the recycling of the used absorbents through balancing their adsorption and desorption performance on P, in this work, a novel porous magnetic La(OH)3-loaded MAPTAC/chitosan (CTS)/polyethyleneimine (PEI) ternary composite hydrogel (p-MTCH-La(OH)3) with enhanced bifunctional adsorption sites was synthesized by simultaneous dissolution of pre-embedded CaCO3 and CTS powder, followed by grafting PEI and loading La. Hierarchical porous channels promoted good dispersion of La(OH)3, bringing an excellent P adsorption capacity of 107.23 ± 4.96 mg P/g at neutral condition. PEI grafted with CTS increased the surface charge and enhanced the electrostatic attraction, which facilitated the desorption of P. The porous structure and abundant active sites also facilitated rapid adsorption with an adsorption rate constant of 0.1 g mg−1 h−1. p-MTCH-La(OH)3 maintained effective P adsorption despite co-existence with competing substances and after 5 cycles. Further mechanistic analysis indicated that La–P inner sphere complexation and LaPO4 crystalline transformation were the main pathways for P removal. However, electrostatic interactions contributed 17.5%–46.7% of the adsorption amount during the first 30 min of rapid adsorption, enabling 92.8% of the adsorbed P at this stage to be desorbed by alkaline solution. Based on the variations of adsorption and desorption capacity with adsorption time, a rapid unsaturated adsorption of 1–2 h was proposed to facilitate the recycling of the adsorbent. This study proposed a method to promote P adsorption and desorption by enhancing bifunctional adsorption sites, and proved that p-MTCH-La(OH)3 is a promising phosphate adsorbent.

Conversion of Activated Calcium in Industrial Water to Micron CaCO3 Powder Based on CO2 Absorption and Mineralization

Carbon dioxide capture, utilization, and storage (CCUS) is one of the essential approaches to achieving permanent CO2 emission reduction. A new idea of absorbing and mineralizing CO2 with industrial wastewater and converting activated calcium into micron CaCO3 powder is proposed in this paper, which synchronizes water softening and CO2 fixation. Therefore, this paper investigated the characteristics of circulating water quality in the iron and steel industry and the transformation behaviors of CO2 capture by activated calcium to CaCO3 powder in the mild aqueous environment under different process parameters. The phase composition, morphology, and particle size distribution (PSD) of CaCO3 powder were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and (laser particle size analyzer) LPSA, respectively. In addition, a green integrated cycle system for industrial water capture of mineralized CO2 was preliminarily constructed, which provides a reference method for carbon reduction and economic utilization of carbon sources in an industrial system.

Effect of Time Stepping in the Filtering Process on the Synthesis of Nickel Sulfate Powder from Blast Furnace Ferronickel

The demand for nickel manganese cobalt (NMC)-type batteries is increasing along with the need for global electric vehicles, such as electric cars. Nickel used in the manufacture of NMC batteries is Nickel (II) sulfate hexahydrate (NiSO4.6H2O). Therefore, it is necessary to study how to synthesize nickel sulfate powder from blast furnace ferronickel to provide an alternative source of nickel sulfate and increase the added value of blast furnace ferronickel products. This study aims to analyze the effect of variations in the time difference of stepped filtering sludge on the precipitated filtrate. This study uses a nickel source from the ferronickel derived from the sintering and smelting process using a Mini Blast Furnace to synthesize nickel sulfate. First, the ferronickel was ground and sieved to pass 50 mesh size. Then, the leaching process was performed using a mixture of 120 mL H2SO4 (2M) and 30 mL H2O2 (30%) with a stirring speed of 200 rpm for 6 h for each 2 g ferronickel. Next, the precipitation process was carried out using CaCO3 powder to pH 3.01 at 90 °C. The precipitation solution was held at 90 °C for 24 h, and stepped filtering of the precipitate formed with variations of 2, 4, 6, and 8 h (the total time is kept the same, i.e., 24 h). The crystallization results were then washed and dried at 70 °C for 2 h. Based on X-Ray Fluorescence (XRF), the best results were obtained in stepped filtering variation every 8 h with 50.23% Ni content and 90.5% Ni separation efficiency. Based on XRD, the nickel sulfate powder product has the compound NiSO4.6H2O. In addition, nickel sulfate products also contain CoSO4, one of the compounds needed to manufacture NMC batteries. However, nickel sulfate powder products still contain impurity compounds like FeSO4 and CaSO4.

Effect of tempering treatment on microstructure and electrochemical performance of laser cladded CuCMnNiTi coating packed in CaCO3 powder: First–principle calculation

A CuCMnNiTi coating was prepared on Ti6Al4V alloy by laser cladding (LC) technique, which was packed in CaCO3 powder to temper at 450 and 500 oC for 4 h. The morphologies, element distributions and phases of obtained coatings were systematically characterized, and the electrochemical performance in 3.5% NaCl solution was investigated using an electrochemical workstation, and the corrosion model was established by the first–principle calculation. The results show that the resistance of passive film on the original CuCMnNiTi coating is increased from 12.71 to 2166 Ω by the tempering treatment, which is contributed to the formation of Cu2 + 2(CO3)(OH)2 to provide the large electrochemical resistance. Moreover, the band gap value of tempered coating (2.22 eV) is higher than that of original coating (0 eV), presenting higher corrosion resistance.

Optimized conditions for cobalt diffusion in Sri Lankan colorless topaz and coloration mechanism elucidation through spectro-chemical investigation

Most of natural topaz is colorless; thus, methods of color enhancement are widely used for coloring this mineral. Currently, blue color is obtained by cobalt diffusion due to drawbacks in existing coloration methods. In this study, optimum conditions suitable for Cobalt diffusion in Sri Lankan colorless topaz were investigated and coloration mechanism was elucidated. The diffusion agent was prepared by mixing CoCO3 with Na2CO3, CaCO3 and carbon powder and diffusion was carried-out by varying the temperature and soaking time. Chemical analysis, UV-Vis absorption spectrum, infrared absorption spectra, and Raman peaks of diffused and non-diffused topaz were tested. The results clearly indicated that the optimum condition for Co diffusion in Sri Lankan topaz is 950℃ for 11 h. The EPMA analysis showed that the Co concentration in the diffused sample varied from 0.001 wt% to 0.027 wt% while colorless topaz showed <0.001 wt%. The UV-Vis spectrum of Co diffused blue topaz gave three absorption peaks at 556, 588, and 627 nm corresponding to three spin-allowed electronic transitions of Co2+ ion in teterahedaral coordination. In case of Co diffused topaz, one additional new broader IR absorption peak was noticed around 6640 cm-1 presumably arising by optical transitions of 4A2 → 4T1 in Co2+ (4F). Our results lead to the conclusion that, blue color of the Co diffused topaz is arising by spin-allowed electronic transitions of Co2+ ions in tetrahedral site of topaz matrix through substitution of Si4+ ions.

Evaluation of the Impact Strength and Morphology Properties of Musa Acuminata Fiber Composite/CaCo3 Powder

Banana stem (Musa Acuminata, MA) fiber is a free agricultural waste obtained after harvesting the fruit. When compared to synthetic fibers, banana fiber has significant weaknesses in composite production, such as low interfacial bond strength between the fiber and the matrix. The purpose of this research is to improve the impact strength of banana stem fiber composites by adding CaCO3 powder. The hot press technique is used to create composites. In the production of polyester composites, woven MA and CaCO3 stem fibers are prepared. An impact testing machine and a scanning electron microscope were used to investigate the effect on morphological properties and impact strength. The study's findings revealed that a polyester composite containing 10% banana stem fiber and 25% CaCO3 had the highest impact strength of 45.27 KJ/m2, which was associated with strong adhesion between the CaCO3-fiber and the polyester matrix. Fiber pullout, matrix cracking, and fiber debonding were all observed in the composite fracture morphology. The resulting composite properties could be used to replace palm fiber/fiber glass composites.