Carbonate Pellets Research Articles

Nanosilica polyamidoamine dendrimers for enhanced direct air CO2 capture.

Exploring efficient systems to recover CO2 from the atmosphere could be a way to address the global carbon emissions issue. Herein, we report the synthesis of nanosilica (NS) functionalized with polyamidoamine (PAMAM) dendrimers (NS-PAMAM) as efficient adsorbents for CO2 capture under simulated direct air capture (DAC) (400 ppm CO2 in helium at 30 °C) and indoor air (≥400 ppm, 50 ± 3% RH at 30 °C) conditions. The results inferred that the 1st (NS-G1.0), 2nd (NS-G2.0), 3rd (NS-G3.0), and 4th (NS-G4.0) generations of the NS-PAMAM dendrimers exhibited excellent performance for CO2 capture. Compared to the other generations, NS-G3.0 demonstrated superior CO2 adsorption capacities of 0.50 mmol g-1 under simulated dry CO2 conditions (400 ppm in He), 1.02 mmol g-1 under indoor air (dry) CO2 conditions (≥400 ppm, 26 ± 3% RH), and 1.54 mmol g-1 under indoor air (humid) CO2 conditions (≥400 ppm, 50 ± 3% RH). The study included the evaluation of CO2 adsorption-desorption performance of the NS-PAMAM dendrimers under varying structural and chemical parameters, kinetics, regeneration at low temperature (80 °C), as well as CO2 adsorption under humid conditions. Additionally, NS-G3.0 displayed a substantially superior performance with stable CO2 capture displayed during ten short temperature swing adsorption (TSA) cycles, making it a promising candidate for CO2 capture from ambient air. Finally, we demonstrated the recovery and reutilization of the captured CO2 for both the synthesis of formate via carbonate hydrogenation and for the production of calcium carbonate pellets.

Rapid and stable calcium-looping solar thermochemical energy storage via co-doping binary sulfate and Al–Mn–Fe oxides

Solar thermochemical energy storage based on calcium looping (CaL) process is a promising technology for next-generation concentrated solar power (CSP) systems. However, conventional calcium carbonate (CaCO3) pellets suffer from slow reaction kinetics, poor stability, and low solar absorptance. Here, we successfully realized high power density and highly stable solar thermochemical energy storage/release by synergistically accelerating energy storage/release via binary sulfate and promoting cycle stability, mechanical strength, and solar absorptance via Al–Mn–Fe oxides. The energy storage density of proposed CaCO3 pellets is still as high as 1455 kJ kg−1 with only a slight decay rate of 4.91% over 100 cycles, which is higher than that of state-of-the-art pellets in the literature, in stark contrast to 69.9% of pure CaCO3 pellets over 35 cycles. Compared with pure CaCO3, the energy storage power density or decomposition rate is improved by 120% due to lower activation energy and promotion of Ca2+ diffusion by binary sulfate. The energy release or carbonation rate rises by 10% because of high O2− transport ability of molten binary sulfate. Benefiting from fast energy storage/release rate and high solar absorptance, thermochemical energy storage efficiency is enhanced by more than 50% under direct solar irradiation. This work paves the way for application of direct solar thermochemical energy storage techniques via achieving fast energy storage/release rate, high energy density, good cyclic stability, and high solar absorptance simultaneously.

Hierarchically doping calcium carbonate pellets for directly solar-driven high-temperature thermochemical energy storage

Ca-based thermochemical energy storage (TCES) system is one of the most promising energy storage techniques for the next generation concentrated solar power systems (CSP). However, it still suffers from low optical absorption, poor cycle stability, and limited energy storage density. Here, a hierarchically doping strategy is proposed to overcome above challenges and achieve high-performance energy storage under direct solar irradiation. Hierarchically doped calcium carbonate pellets, which are suitable for scalable applications, are successfully fabricated with Al-doped internal cores and Mn-rich external shells. The average solar absorptance achieves 87.15% with a 7.4% increase compared with traditionally homogeneous doping approaches. The energy storage density is still as high as 1143 kJ/kg after 20 cycles, which is enhanced by 16.6% over homogeneous counterparts. The underlying mechanism is that hierarchically doping increases contents of active CaCO3 inside pellets and absorption-enhanced substances on the outer surface simultaneously. This work presents a novel approach for the design of high-performance pellets for achieving scalable and efficient thermochemical energy storage under direct solar irradiation.

Pore systems and organic petrology of cretaceous Mowry and Niobrara source-rock reservoirs, Powder River Basin, Wyoming, USA

The Powder River Basin (PRB) is a world-class oil province, in large part thanks to contributions from premier source rocks, Cretaceous Mowry and Niobrara shales. Both formations are also unconventional reservoirs. A critical aspect of evaluating production potential and finding sweet spots is the nature of the pore systems in these fine-grained source-rock reservoirs. Variation by stratigraphic interval is important for selecting optimum target zones for horizontal wells. Understanding variation in pore type, size, and connectivity and relationships with mineralogy and fabric help in determining prospectivity in different parts of the basin. Deciphering controls on pore-system development helps predict intervals and locations of optimum reservoir quality.Imaging of Niobrara and Mowry samples from a range of thermal maturities provided observations and data on pore systems, organic matter (OM) types and associations with mineralogy and fabric, wettability, and microporosity associated with both diagenetic and detrital clays. Imaging techniques included scanning electron microscopy, organic petrography and correlative scanning electron microscopy, and mapping of mineralogy through energy dispersive spectroscopy.Mean solid bitumen (BRo) and vitrinite reflectance (VRo) values indicate all samples are in the oil window with values ranging from 0.52 to 1.15%. Organic fluorescence is prominent in amorphous OM, solid bitumen and some vitrinite in the early oil window. The fluorescence is extinguished at higher thermal maturity. Carbonate pellets (in Niobrara) mainly contain migrated solid bitumen and residual live oil and little or no terrigenous OM (vitrinite and inertinite). However, terrigenous OM is common in siliceous/argillaceous laminae in both formations, where it occurs with amorphous OM, some of which has converted in situ to a solid bitumen petroleum residue.One key finding is the widespread presence of migrated OM at very early oil window maturity. Distribution of such OM and associated wettability alteration is fabric-controlled, at all levels of thermal maturity studied. Clay morphology and abundance and supporting rigid mineral grain framework strongly influence pore development, preservation, and connectivity in both formations. Carbonate content is a good proxy for reservoir quality in Niobrara intervals due to association of porous solid bitumen with calcareous fecal pellets. High recrystallized microquartz content is associated with the best reservoir intervals in the Mowry.

Synergy of Li2CO3 promoters and Al-Mn-Fe stabilizers in CaCO3 pellets enables efficient direct solar-driven thermochemical energy storage

Calcium carbonate (CaCO3) pellets are suitable for scalable solar thermochemical energy storage but suffer from low solar absorptance, poor stability, and slow reaction kinetics, which lead to low solar energy storage efficiency. Here, for the first time, we successfully achieve fast and efficient solar thermochemical energy storage via synergistically employing Al, Mn, and Fe stabilizers for improving both cyclic stability and solar absorptance, and Li2CO3 promoters for accelerating decomposition of CaCO3 pellets. The average solar absorptance is 1500% higher than that of pure CaCO3 pellets. After 60 cycles, the energy storage density is still as high as 1671 kJ/kg with a decay rate of only 4.14%, in stark contrast to energy density of 1121 kJ/kg and decay rate of 56.73% for pure CaCO3 pellets. The average decomposition rate is about twice as fast as that of pure CaCO3 pellets due to enhanced Ca2+ diffusion by doped Li2CO3. Under direct light irradiation, novel CaCO3 pellets demonstrate high energy storage rate due to both high solar absorptance and fast decomposition rate, while pure CaCO3 pellets cannot even reach the decomposition temperature. This work opens new opportunities for scalable deployment of direct solar-driven thermochemical energy storage techniques based on Li2CO3-doped dark CaCO3 pellets.

Pilot study on the softening rules and regulation of water at various hardness levels within a chemical crystallization circulating pellet fluidized bed system

Chemical crystallization circulating pellet fluidized bed reactor (CPFBR) systems are widely used in water softening applications, and softening parameters and effects may be governed by certain rules for the optimum treatment of water at different levels of hardness. In this study, pilot tests were conducted on a CPFBR system with water at eight different levels of hardness. Specifically, the effects of the differences in hardness, alkalinity, and calcium and magnesium concentrations on the softening rules and regulation of the CPFBR were analyzed. The results showed that when Na2CO3 and NaOH were added simultaneously, the removal rate of Ca2+ was positively correlated with the dosage of Na2CO3, while pH was positively correlated with the dosage of NaOH. Under the experimental water quality conditions, when Ca2+ <180 mg/L, Mg2+ <70 mg/L, and pH < 11, no fine calcium carbonate or magnesium hydroxide pellets were discharged with the water, and the turbidity of the effluent did not increase. For water with a higher concentration of Mg2+ than that of Ca2+, the morphology of calcium carbonate crystals, element contents on crystal pellet surfaces, and fine pellets flowing out with water were all affected by Mg2+. Based on the analyses and summary of the crystallization softening rules for water at various hardness levels, key supportive data and regulation methods are provided for the engineering design and application of such CPFBR systems.

Hyphal morphology and substrate porosity -rather than melanization- drive penetration of black fungi into carbonate substrates

Abstract Due to their ability to penetrate, deteriorate and discolour stone surfaces, rock-inhabiting black fungi represent a remarkable issue for cultural heritage conservation. Black microcolonial fungi (MCF) can also adapt to different environmental conditions, by converting from yeast-like morphology to a peculiar meristematic development with swollen cells (torulose hyphae, TH), to extremely thin structures (filamentous hyphae, FH). Furthermore, black MCF produce protective pigments: melanin, dark pigment particularly evident on light stone surfaces, and carotenoids. Black fungi produce melanin in critical, oligotrophic conditions as well as constitutively. Melanin function is mostly related to stress resistance and the ability of fungi to generate appressorial turgor to actively penetrate plant cells in pathogenic species. An involvement of melanins in stone surface penetration has been suggested, but not experimentally proved. In this work, we tested the role of hyphal melanisation in penetration mechanisms on the model black fungus Knufia petricola A95 in lab conditions. The wild-type and three mutants with introduced targeted mutations of polyketide-synthases (melanin production) and/or phytoene dehydrogenase (carotenoid synthesis) were inoculated on artificial carbonate pellets (pressed Carrara marble powder) of different porosity. After 5, 10, 17 and 27 weeks, hyphal penetration depth and spread were quantified on periodic acid Schiff-stained cross-sections of the pellets, collecting measurements separately for TH and FH. Droplet assay of the mutants on different media were conducted to determine the role of nutrients in the development of different fungal morphologies. In our in vitro study, the hyphal penetration depth, never exceeding 200 μm, was proven to be consistent with observed penetration patterns on stone heritage carbonate substrates. Pellet porosity affected penetration patterns of TH, which developed in voids of the more porous pellets, instead than actively opening new passageways. Oppositely, the thin diameter of FH allowed their penetration independently of substrate porosity. Instead, the long-hypothesized crucial role of melanin in black MCF hyphal penetration should be rejected. TH were developed within the pellets also by melanin deficient strains, and melanized strains showed an endolithic component of non-melanized TH. FH were non-melanized for all the strains, but deeply penetrated all pellet types, with higher penetration depth probably related to their potential exploratory (nutrient-seeking) role, while TH may be more related to a resistance to surface stress factors. In the melanin deficient strains, the absence of melanin caused an increased penetration rate of FH, hypothetically related to an earlier necessity to search for organic nutrients.

Experimental Research of Shale Pellet Swelling in Nano-Based Drilling Muds

The drilling of clay-rich formations, such as shale, is an extremely demanding technical and technological process. Shale consists of mixed clay minerals in different ratios and in contact with water from drilling mud. It tends to swell and cause different wellbore instability problems. Usually, the petroleum industry uses various types of salt and/or polymers as shale hydration inhibitors. The aim of this research was to determine whether nanoparticles can be used as shale swelling inhibitors because due to their small size they can enter the shale nanopores, plug them and stop further penetration of mud filtrate into the shale formation. Swelling of bentonite-calcium carbonate pellets after 2 and 24 h in water and drilling mud (water, bentonite, PAC and NaOH) without nanoparticles and with addition of TiO2 (0.5, 1 and 1.5 wt%) and SiO2 (0.5, 1 and 1.5 wt%) nanoparticles was measured using a linear swell meter. Additionally, granulometric analyses of bentonite as well as the zeta potential of tested muds containing nanoparticles were performed. Based on the laboratory research, it can generally be concluded that the addition of SiO2 and TiO2 nanoparticles in water and base drilling mud reduces the swelling of pellets up to 40.06%.

Operating pH influences homogeneous calcium carbonate granulation in the frame of CO2 capture

The era of industrialization has caused the drastic increase in atmospheric carbon dioxide concentrations that now require various remediation strategies such as CO2 capture and storage. In this study, calcium carbonate granulation is proposed as a new conversion route for CO2 trapped in water matrices into dense solids. Herein, we demonstrate the effectiveness of the fluidized-bed reactor to produce compact calcium carbonate pellets from captured CO2 via a granulation reaction at different pH conditions and in the absence of seed materials. Constant values of calcium-to-carbonate ratio, influent carbonate concentration and influx flow rate were used while operating pH was varied from 8.5 to 11.0. Optimal operating condition with carbonate removal and granulation efficiencies of 92% and 90%, respectively was found at pH of 10.0 ± 0.2, where the lowest daily effluent concentration of carbonate ions was measured at 16.6 mg L−1 via the alkalinity test. At optimum operating pH, large compact granules ranging from 1 – 2 mm in diameter (∼93.6 g) were obtained with overall particle size distribution leaning towards bigger sizes. Morphological analyses of the granules revealed their smooth surfaces and subrounded shapes, while crystalline and elemental analyses identified these as high purity calcium carbonate. Moreover, spontaneous homogeneous nucleation, particle aggregation, crystal growth and granulation are proposed as the main mechanisms of calcium carbonate granulation.

Effect of the wettability alteration on the cementation factor of carbonate rocks using Henna extract

Estimation of water saturation and hydrocarbon reserve plays a vital role in the development of oil reservoirs, which can be identified using Archie equation. The cementation factor, as an exponent in Archie equation, has a direct impact on the outcome of the equation which is dependent on the electrical properties of the formation. Thus, a slight change in the cementation factor can lead to a significant difference in the water saturation, and oil reserve calculation. In this study, for the first time, we focused on investigating the effect of the wettability alteration on the cementation factor of carbonate rocks using a natural surfactant.The wettability of the rock was altered using Henna extract, as a natural surfactant, at different concentrations from 1 to 10 wt%. The critical micelle concentration (CMC) of the prepared surfactant solutions was identified using pH, conductivity and turbidity measurements, which was 5 wt% concentration. Obtained results showed that the wettability of the carbonate pellets altered from the strong to normal hydrophobic wetting system (140.45–102.7° contact angle). Hence, the cementation factor was also changed from 3.91 to 1.54 for the rock saturated with the Henna extract.

Pellet Softening Process for the Removal of the Groundwater Hardness; Modelling and Experimentation Modelling and experimental of groundwater shortening by a pellet reactor

A lab scale pellet reactor (PR) was designed and fabricated to carry out extensive investigations on the removal efficiency of the hardness of groundwater. The groundwater of 2200 – 2600 mg/L hardness was collected from Abdulla Ibnalhassan wells area located at the west desert of Al-Shinafiyah district (70 km to the southwest of Al-Dewaniyah city, Iraq). Both hydrodynamic parameters of the pellet reactor (porosity and fluidized bed height) and the parameters of calcium carbonate crystallization process (calcium carbonate equilibrium, pellet size, and density) were modeled and compared with the experimental results of the lab scale pellet reactor. The comparison showed that fair agreement between modeled and measured results was observed. The removal efficiency of both calcium and magnesium ions were 62.5-99% and 83-99% respectively. The removal efficiency was found to be strongly dependent on pH and the ratio of NaOH solution flow rate to the groundwater flow rate in the pellet reactor.

Oil majors invest in CO2 capture company

Venture investment arms of Chevron and Occidental Petroleum have invested an undisclosed sum in Carbon Engineering, a Canadian firm that is developing a chemical method of capturing CO2 from the atmosphere. In the process, CO2 reacts with calcium hydroxide to create a calcium carbonate solution. Carbonate pellets are formed, then decomposed into concentrated CO2 and solid calcium oxide. The CaO is then hydrated to regenerate the hydroxide. Carbon Engineering raised about $8 million in July.

Comprehensive Investigation of the Effect of Henna Natural Surfactant on the Cementation Factor and Wettability Alteration

Estimation of the water saturation and hydrocarbon reserve plays a vital role in the development of oil reservoirs, which can be identified using the Archie equation. The cementation factor, as an exponent in the Archie equation, has a direct impact on the outcome of the equation which is dependent of the electrical properties of the formation. Thus, a slight change in the cementation factor can lead to a significant difference in the water saturation, and oil reserve calculation. In this study, for the first time, we focused on investigating the effect of the wettability alteration on the cementation factor of carbonate rocks using a natural surfactant. The wettability of the rock was altered using Henna extract, as a natural surfactant, at different concentrations from 1 to 10 wt.%. The critical micelle concentration (CMC) of the prepared surfactant solution was identified using pH, conductivity and turbidity measurements, which was 5 wt.% concentration. Results showed that the wettability of the carbonate pellets altered the strong to normal hydrophobic wetting system from 140.45 to 102.7 mN/m contact angle. Hence, the cementation factor was also changed from 3.91 to 1.54 for the rock saturated with the Henna extract.

Softening of drinking water by the pellet reactor - Effects of influent water composition on calcium carbonate pellet characteristics

Pellet softening of drinking water can provide aesthetic, socioeconomic and environmental benefits in areas with hard water. Calcium carbonate pellets are the main by-product from pellet softening and their characteristics determine their reuse potentials. We characterized pellets from a pilot-scale pellet reactor treating 16 water types at 8 Danish drinking water treatment plants to investigate the variations in pellet characteristics and how they depend on the influent water composition. The pellets consisted of up to 100% calcium as calcium carbonate, but contained often also impurities such as strontium, magnesium, iron and sodium, each contributing with up to 1.3% of the pellet mass. Other elements, including heavy metals, accounted for <0.04% of the pellet mass. The quartz sand seeding material contributed with up to 15% of the pellet mass and can be a barrier for pellet reuse. Therefore, replacing this with calcium carbonate (limestone) seeding material increases the pellet purity. Modelling the chemical speciation indicated that elements not forming carbonates (e.g. potassium and magnesium), are only incorporated into pellets to a limited extent. The concentrations of strontium, magnesium, manganese, iron and nickel in the pellets had a strong positive correlation with the influent water concentration. Consequently, the pellet purity increases if the concentration of these elements is reduced in the water before softening by other treatment technologies. Potassium, arsenic and zinc showed no or only a weak correlation. The pellets precipitated as calcite, and had a reactivity of ≤25.7% and a specific surface area of ≤0.32 m2/g, which limits the potential reuse as soil amendment in agriculture. The pellet mineralogy was independent of the investigated range of influent water quality and seeding materials. Including pellet characteristics when designing the softening process can improve pellet reuse, ultimately leading to a more environmentally sustainable drinking water supply.

Phosphate recovery from water using cellulose enhanced magnesium carbonate pellets: Kinetics, isotherms, and desorption

Phosphorus is an essential and limited nutrient that is supplied by a depleting resource, mineral phosphate rock. Eutrophication is occurring in many water bodies which provides an opportunity to recover this nutrient from the water. One method of recovery is through adsorption; this study focused on fabricating a porous and granular adsorptive material for the removal and recovery of phosphate. Magnesium carbonate was combined with cellulose in varying weight ratios (0, 5, 10, 15, 20%) to synthesize pellets, which were then calcined to increase internal surface area. Physiochemical properties such as surface area, surface morphology, elemental composition, and crystal structure of the materials were characterized using Brunauer, Emmett, and Teller (BET) surface area analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The pellet proved to be uniform in composition and an increase in BET surface area correlated with an increase in cellulose content until pellet stability was lost. Phosphate adsorption using the pellets was studied via batch kinetics and sorption isotherms. The pseudo-second-order kinetics model fits best suggesting that the adsorption occurring was chemisorption. The isotherm model that fit best was the Langmuir isotherm, which showed that the maximum equilibrium adsorption capacity increased with an increase in cellulose content between 10% and 20%. The average adsorption capacity achieved in the triplicate isotherm study was 96.4 mg g−1 for pellets synthesized with 15% cellulose. Overall, using cellulose and subsequent calcination created an additional internal surface area for adsorption of phosphate and suggested that granular materials can be modified for efficient removal and recovery of phosphate from water.

Effects of Titanate Coupling Agent on Engineering Properties of Asphalt Binders and Mixtures Incorporating LLDPE-CaCO3 Pellet

This study was initiated to evaluate the performance of asphalt binders and mixtures incorporating linear low-density polyethylene- calcium carbonate (LLDPE-CaCO3) pellet, either with or without titanate coupling agent. The detailed manufacturing process of modifier pellets was displayed. The coupling agent was used to enhance the cross-linking between materials by means of winding up covalent bonds or molecule chains, thus improving the performance of composites. In the preparation of modified bitumen, the preheated asphalt binder was mixed with the modifiers using a high shear mixer at 5000 rpm rotational speed for 45 min. Experimental works were conducted to evaluate the performance of asphalt binders in terms of volatile loss, viscosity, rutting potential, and low temperature cracking. Meanwhile, the asphalt mixtures were tested using the flow number test and tensile strength ratio (TSR) test. The addition of LLDPE-CaCO3 modifiers and coupling agent does not significantly affect the volatile loss of modified asphalt binders. The addition of modifiers and coupling agent has significantly improved the resistance to permanent deformation of asphalt binders. Even though, the addition of LLDPE-CaCO3 modifier and coupling agent remarkably increased the mixture stiffness that contributed to lower rutting potential, the resistance to low temperature cracking of asphalt binder was not adversely affected. The combination of 1% coupling agent with 3% PECC is optimum dosage for asphalt binder to have satisfactory performance in resistance to moisture damage and rutting.

Dynamic wetting of dense Ni foil by molten carbonate

Wetting is an important factor that affects the active reaction area inside the porous Ni anode in molten carbonate fuel cell stacks. To provide a relatively simple base case, the dynamic wetting of the dense Ni foil was investigated under different atmospheres, including reducing atmosphere (80%H2 + 20%CO2 humidified at 45 °C), pure CO2 atmosphere and, oxidizing atmosphere (1%O2 + 99%N2). It was demonstrated that the water-gas shift reaction occurs at the interface of dense Ni foil and the molten carbonate under reducing atmosphere but not under CO2 atmosphere and oxidizing atmosphere. The contact angle was affected by the mass of the carbonate pellet under reducing atmosphere but not under CO2 atmosphere. The contact angle decreased rapidly under oxidizing atmosphere due to the formation of nickel oxides on the surface.

The preparation of an amino acid-based surfactant and its potential application as an EOR agent

ABSTRACTMost of the synthetic surfactants investigated with the aim of enhanced chemically oil recovery in the literature have environmental drawbacks. In this work, application of an environmentally-friendly synthetic surfactant as an enhanced oil recovery agent is introduced by measuring interfacial tension of water–kerosene systems and wettability alteration of carbonate pellets. For this purpose, an amino acid-based surfactant was initially synthesized using a new synthetic approach which was subsequently confirmed by spectra of Fourier transform infrared and Proton nuclear magnetic resonance. Results showed a value of critical micelle concentration in the range of 9000–9100 ppm for this surfactant. Results also demonstrated a decrease of 38.53% in water–kerosene system interfacial tension and a 17.76% reduction in oil-wetness of the carbonate pellets.

Quantifying metal artefact reduction using virtual monochromatic dual-layer detector spectral CT imaging in unilateral and bilateral total hip prostheses

PurposeTo quantify the impact of prosthesis material and design on the reduction of metal artefacts in total hip arthroplasties using virtual monochromatic dual-layer detector Spectral CT imaging. MethodsThe water-filled total hip arthroplasty phantom was scanned on a novel 128-slice Philips IQon dual-layer detector Spectral CT scanner at 120-kVp and 140-kVp at a standard computed tomography dose index of 20.0mGy. Several unilateral and bilateral hip prostheses consisting of different metal alloys were inserted and combined which were surrounded by 18 hydroxyapatite calcium carbonate pellets representing bone. Images were reconstructed with iterative reconstruction and analysed at monochromatic energies ranging from 40 to 200keV. CT numbers in Hounsfield Units (HU), noise measured as the standard deviation in HU, signal-to-noise-ratios (SNRs) and contrast-to-noise-ratios (CNRs) were analysed within fixed regions-of-interests placed in and around the pellets. ResultsIn 70 and 74keV virtual monochromatic images the CT numbers of the pellets were similar to 120-kVp and 140-kVp polychromatic results, therefore serving as reference. A separation into three categories of metal artefacts was made (no, mild/moderate and severe) where pellets were categorized based on HU deviations. At high keV values overall image contrast was reduced. For mild/moderate artefacts, the highest average CNRs were attained with virtual monochromatic 130keV images, acquired at 140-kVp. Severe metal artefacts were not reduced. In 130keV images, only mild/moderate metal artefacts were significantly reduced compared to 70 and 74keV images. Deviations in CT numbers, noise, SNRs and CNRs due to metal artefacts were decreased with respectively 64%, 57%, 62% and 63% (p<0.001) compared to unaffected pellets. Optimal keVs, based on CNRs, for different unilateral and bilateral metal hip prostheses consisting of different metal alloys varied from 74 to 150keV. The Titanium alloy resulted in less severe artefacts and were reduced more effectively compared to the Cobalt alloy. ConclusionsVirtual monochromatic dual-layer Spectral CT imaging results in a significant reduction of streak artefacts produced by beam-hardening in mild and moderate artefacts by improving CT number accuracy, SNRs and CNRs, while decreasing noise values in a total hip arthroplasty phantom. An optimal monochromatic energy of 130keV was found ranging from 74keV to 150keV for different unilateral and bilateral hip prostheses consisting of different metal alloys.

The Effect of Sandstone Composition on Distribution of Tafoni Landforms in the Aghajari Sandstone, Northwest of Masjed Soleyman, Iran

The Aghajari sandstone layers are located in the west of Zagros Mountains from several centimeters thicknesses to maximum 6 meters with carbonating content. Laboratory and fieldwork show high amount of carbonate content through sandstone layers and tafoni and honeycombs (THs) in early layers. In the study area three parameters have the most effective impactful factors in tafoni and honeycombs (THs) including matrix, carbonate content, and porosity. In this study result shows overlays of high ranges of CaCO3, porosity, and low matrix in the early layers (especially in A, B, C, D, and H layers) with tafoni and honeycombs (THs). Overall, we conclude that matrix and CaCO3 (carbonate clast including carbonate lithics, fragment fossils, and Pellet) and porosity have direct relationships and matrix reverse relationships with tafoni and honeycombs (THs) in the Aghajari sandstones layers.