Effect Of Solid Loading Research Articles

Porous yttria-stabilized zirconia ceramics with low thermal conductivity via a novel foam-gelcasting method

In this work, the preparation of foam-gelcasting was simplified with a copolymer of isobutylene and maleic anhydride (Isobam), avoiding the traditional gelling system including many additives such as monomer, cross-linking agent, initiator and catalyst. Highly porous yttria-stabilized zirconia (YSZ) ceramics with 76.2–84.9% porosity were prepared via foam-gelcasting method using YSZ powder as the raw material, Isobam as the dispersant and gelling agent, triethanolamine lauryl sulfate as the foaming agent and sodium carboxymethyl cellulose as the foam stabilizing agent. The effects of solid loading, the content of foaming agent as well as sintering temperature were investigated. With the increase in solid loading of slurries, lower porosity was obtained, and the compressive strength and thermal conductivity showed a tendency of increase. Porous YSZ ceramics with compressive strength of 0.69–3.66 MPa showed low thermal conductivity in the range of 0.137–0.254 W/(m·K) at room temperature. The as-prepared sample showed good thermal insulating performance at high temperature. The km in GM model was during 0.4–0.7, which indicated the pore structure containing the internal and external porosities. This work provides a facile method for the fabrication of porous YSZ ceramics which can be potentially applied as thermal insulation materials at high temperature.

Ultrasonic-assisted de-agglomeration and power draw characterization of silica nanoparticles.

Breakage of nanoparticle cluster require high-intensity devices for stable and uniform distribution of aggregates. The ultra-sonication process is a high energy-intensive technique that produces cavitation effect to break the aggregates. In the present study, ultra-sonication is used for the de-agglomeration of fumed silica nanoparticles in low to high viscosity liquids. Water- and glycerol-based dispersion has been investigated at different solid loadings (up to 10wt% for water-based dispersion and 5wt% in glycerol-based dispersion) and viscosity of continuous phase (1-100mPa.s). Breakup mechanism and kinetics have been studied at optimized operating conditions and no significant effect is found at different solid loadings on breakup mechanism. Particle size measurements are reported and found that volume of fine generation increased with an increase in sonication time. Further, it is observed that the stability of dispersion in the liquid is very high even at high concentration of solid used. Larger agglomerates are found at high viscosity of continuous phase and a lag is also observed for 100mPa.s glycerol solution even at low solid loading (1wt%). From, rheological characterizations it is found that the behavior of dispersed solution changed with time, temperature and solid loading. Erosion is found to be the breakup mechanism and further, validated with scattering light characterization. Furthermore, power draw increased with an increase in the viscosity of continuous phase, however, no significant effect of solid loading is observed. It is also observed that process is more energy-efficient at higher solid loading as the volume of fine produced is more as compared to low solid loading. Therefore, it can be concluded that the stable and uniform dispersion of nanoparticles can be achieved using an ultra-sonication device at high solid loading in viscous liquids.

Effect of solid loading on the electrophoretic deposition kinetics of nano-Pb3O4 coating

Due to noticeable composition stability, remarkable photoelectric sensitivity in the visible spectral range, excellent pyroelectric and ferroelectric properties, and high resistivity, red lead (Pb3O4) coatings are widely utilized in various optoelectronic structures and devices. In this work, using ethanol as solvent and nitric acid or polyethyleneimine (PEI) as surface charge modifier, pure nano-Pb3O4 coating was successfully prepared by electrophoretic deposition (EPD) methods. Especially, the suitable service cases for both PEI and nitric acid were investigated in detail. For EPD of nano-Pb3O4 at low solid loading (e.g., 1 g·L−1), employing nitric acid can realize a higher deposition rate than employing PEI. In contrast, for EPD of nano-Pb3O4 at high solid loading (e.g., 10 or 20 g·L−1), PEI is more suitable than nitric acid. This study can lead to advances in assembling Pb3O4 coating for the applications such as advanced optical data carriers and elements of photon technologies and radioelectronics.

Techno-economic analysis of a liquid hot water pretreated switchgrass biorefinery: Effect of solids loading and enzyme dosage on enzymatic hydrolysis

Material and energy results were used in a techno-economic model to analyze the effect of different parameters and configurations on the economics of the process of a liquid hot water pretreated switchgrass (Panicum virgatum L.) biorefinery. Previous experimental results for switchgrass composition and its cellulose enzymatic hydrolysis at different high solids content and enzyme dosages were used in order to obtain a more realistic analysis. The minimum ethanol selling price (MESP) obtained for a facility that produces only ethanol and electricity was within the expected price range for advanced alcohol fuels and could compete with oil prices above $100 per barrel. The MESP was lower for a biorefinery scenario that produces furfural, acetic acid, and formic acid as high-value co-products. The MESP was sensitive to plant size and to switchgrass composition. Enzyme dosage, solids content, and hydrolysis and fermentation efficiencies were the operating parameters with a higher impact on the MESP. Experimental results were combined with the techno-economic models to find correlations between the MESP, and solids content and enzyme dosage. The conditions necessary for a high efficiency of hydrolysis and glucose concentration are not necessarily those that produce an economic optimum (lower cost). The enzyme dosage that minimizes MESP is not always associated with the optimal hydrolysis efficiency (e.g., 95%). The best conditions identified through optimization were an enzyme dosage of 37 mgprotein gglucan−1 and a solids content of 21%, leading to the lowest MESP of $0.84 L-1 (for an enzyme cost of $4.5 kgprotein−1).

Effect of Solid Loading on the Sintered Properties of 3 mol% Yttria-Stabilized Tetragonal Zirconia Polycrystals (3Y-TZP) Ceramics via Slip Casting.

Dental zirconia implants fabricated by the mechanical machining and sintering of zirconia blocks have many surface cracks that lead to the deterioration of mechanical strength and the failure of the implant in the body. In this study, we attempted to manufacture an extremely dense and crack-free zirconia specimen by slip casting and pressureless sintering. After the preparation of zirconia slurry by control of its viscosity and by solid loading, highly dense zirconia specimens could be obtained by pressureless sintering at 1450 °C for 2 h. Slurry viscosity was controlled by adjusting the mixing ratio of 3Y-TZP powder, a dispersant, and a pH adjustment agent. Highly dense 3Y-TZP specimens with a relative density of 99% and small grain size of 200-400 nm could be obtained at a solid loading of 50-65 wt%. An optimally dense specimen was fabricated from zirconia slurry with 60 wt% solid loading that had the highest apparent density of 6.07 g/cm³ (99.5%).

Fabrication and properties of silica/mullite porous ceramic by foam-gelcasting process using silicon kerf waste as raw material

Silica/mullite porous ceramic with high porosity and low density was fabricated via foam-gelcasting with silicon kerf waste and corundum powder as raw materials. The effects of solid loading on porosity, bulk density, compressive strength, thermal conductivity and microstructure were systematically investigated. The porosity of porous ceramics decreased from 84.1% to 25.4%, bulk density increased from 0.67 to 1.78 g cm−3, compressive strength increased from 3.60 to 20.54 MPa and thermal conductivity increased from 0.204 to 0.892 W (m K)−1 as the solid loading increased from 50 to 65 wt%. Moreover, the relationship between microstructure and mechanical properties was discussed in detail.

Effects of solid loading and calcination temperature on microstructure and properties of porous Si3N4 ceramics by aqueous gelcasting using DMAA system

Abstract Herein, a low–toxic N, N–dimethylacrylamide (DMAA) system was used in preparation of porous Si3N4 ceramics by aqueous gelcasting, and variations in microstructure and properties with solid loading and calcination temperature were systematically investigated. In the considered solid loading range of 28–44 vol%, all the slurries exhibited superior rheological properties (≤145 mPa⋅s at 95.40 s−1 for 44 vol% solid loading) perfectly suitable for casting. With increasing solid loading, a decreased bulk density (1.71–1.69 g/cm3), volume shrinkage (37.73–13.77%) and flexural strength (46.56–26.75 MPa) of green bodies were obtained, exhibiting better mechanical properties than those derived from the conventional acrylamide (AM) system. Regarding Si3N4 ceramics with various solid loadings, the increase in calcination temperature favored the phase transformation α→β–Si3N4 and β–Si3N4 growth, however, the increased solid loading exhibited an inhibiting effect on those since mass transport in gas phase was blocked due to the disruption of pore connectivity. The resulting microstructure changes imparted Si3N4 ceramics increasing flexural strength (110.36–367.88 MPa), fracture toughness (2.54–5.03 MPa⋅m1/2), as well as decreasing porosity (54.21–41.05%) and pore size (0.38–0.33 μm). This work demonstrates the potential research value of DMAA system in preparing high–performance porous Si3N4 ceramics through gelcasting technique.

Effects of solid loading on joining and thermal cycling performance of glass-ceramic sealing pastes for solid oxide fuel cells

Abstract The variation of the joining performance of glass-ceramic sealants in the form of a paste as a function of the solid powder content in the sealing paste after the formation and a number of thermal cycles are experimentally studied. Three different sealing pastes having 40, 50 and 60 wt % solid loadings are prepared and tested for this purpose. The pastes are applied between two metallic interconnector plates and subjected to a glass formation step for the joining. The fracture strengths of 24 samples prepared for each case are determined via tensile tests. Similarly, the mechanical performances of the sealants after 3, 6 and 9 thermal cycles are also obtained. The results reveal that the joining strength tends to increase with the amount of solid powder content in the paste. This can be attributed to increased number of crystalline phases in the sealants with increasing the solid loading. The thermal cycles, on the other hand, are shown to have an adverse effect on the joining performance regardless of the solid loading. However, the rate of decrease in the fracture strengths is found to decrease with the solid powder contents in the pastes. This can be elucidated by the amount of glassy phases in the sealants, which can be expected to increase with the solid loading and provide self-healing ability. The microstructures of the fracture surfaces of all samples are also investigated by a scanning electron microscopy. The obtained images confirm the tensile test results.

High Titer Ethanol Production from Combined Alkaline/Alkaline Hydrogen Peroxide Pretreated Bamboo at High Solid Loading

Enzymatic hydrolysis and fermentation at high solid loading is generally required for the production of high titer ethanol from lignocellulosic biomass at a relatively low cost. In this paper, bamboo pretreated by alkaline and alkaline hydrogen peroxide was subjected to downstream enzymatic hydrolysis and ethanol fermentation at high solid loading for the production of high titer ethanol. The effects of solid loading (5–25% w/v) and enzyme dosage (10–50 mg protein/g glucan) on sugar conversion and ethanol production during separate enzymatic hydrolysis and fermentation (SHF) and simultaneous enzymatic saccharification and co-fermentation (SSCF) processes were investigated. During the fermentation process, the pentose-hexose fermenting Saccharomyces cerevisiae LF1 strain was used. The results showed that the increase of solid loading decreased sugar conversion during enzymatic hydrolysis. At relatively high solid loadings (≥ 20% w/v), SSCF resulted in higher sugar conversion and final ethanol titer compared to SHF. With this proposed process, an ethanol concentration of 68.2 g/L, along with approximately 83.5% of glucan and 73.8% of xylan conversions, could be reached through SSCF at 20% solid loading with an enzyme dosage of only 20 mg protein/g glucan.

Gas Phase Back-Mixing in a Mimicked Fischer-Tropsch Slurry Bubble Column Using an Advanced Gaseous Tracer Technique

Abstract An advanced gaseous tracer technique and procedures were developed and executed to study for the first time the axial dispersion of the gas phase in a slurry bubble column reactor (SBCR) using air-C9C11-FT catalyst. Residence time distribution (RTD) curves were obtained by measuring the pulse-input’s response of the gaseous tracer. The gas phase axial dispersion coefficient (Dg) was obtained from minimum square error fit of the one-dimensional axial dispersion model to the measured tracer response data. The effects of solids loading on the axial dispersion of gas phase and the overall gas holdup have been studied. It was demonstrated that increasing solids loading improves the gas axial dispersion while decreasing the overall gas holdup. This work suggests that gas phase axial dispersion is significant in reactor performance evaluation of bubble columns or slurry bubble columns.

Xylooligosaccharides from potential agricultural waste: Characterization and screening on the enzymatic hydrolysis factors

The interest of lignocellulosic biomass to be utilized in bioconversion sectors has gaining much attention recently. As corresponding to this, an experimental study was done to investigate the potential agricultural waste for xylan preparation and to screen the factors affecting xylooligosaccharides (XOS) production. Characterization of oil palm frond bagasse (OPFB), oil palm empty fruit bunch (OPEFB), and rice straw (RS) before and after pretreatment was performed in terms of chemical and physical properties. Enzymatic hydrolysis using a 25−1 fractional factorial design was further conducted to evaluate the effect of solid loading, enzyme loading, temperature, hydrolysis time and agitation on XOS production from the selected agricultural waste. From characterization results OPFB was determined as the greatest promising agricultural waste for XOS production. Pretreatment on OPFB simultaneously exhibited the highest increase of xylan recovery and lignin removal. XOS production up to 174.74 mg/g through enzymatic hydrolysis was successfully achieved from the pretreated OPFB. The enzymatic hydrolysis conditions of 1% solid loading and 50 U/mL enzyme loading at 55 °C temperature for 4 h hydrolysis time with 50 rpm of agitation were found efficient to obtain maximum XOS production. Among those factors solid loading was determined as the most significant factor that contributed to the increase of XOS production. The findings from this study have verified that acid pretreatment could improve the biomass structure by disrupting its structure which is important to facilitate enzymatic hydrolysis for high yield of XOS production.

Influence of Solid Loading and Ratio of Monomers on Mechanical and Dielectric Properties of Hybrid Ceramic Composites

Hybrid ceramic (SiO2-Si3N4-Al2O3) composites were prepared by gel casting process, a near net shape technique. The effects of solid loading and monomers ratio on flexural strength, porosity, room temperature dielectric properties and thermal conductivity were investigated. Methylacrylamide (MAM) and N, N1- methylenebisacrylamide (MBAM) were used as monomers because of their low toxicity. The hybrid ceramics were sintered to a temperature of 1250 °C and the monomer content kept constant at 10 wt%. The flexural strength of the ceramics increases and porosity decreases with increase in solid loading. The flexural strength increases up to a certain stage and then decreases by showing an optimum point at monomer ratio of 10:1. The maximum flexural strength and minimum porosity obtained were 95.12 MPa, and 28.5% respectively. The dielectric constant and dielectric loss were increased slightly by the addition of Si3N4-Al2O3 and found to be 4.822 and 0.00351 at a frequency of 30 MHz at room temperature. The minimum thermal conductivity at room temperature of the composite was found to be 0.2131 W/mK.

Effects of solid loading on pore structure and properties of porous FeAl intermetallics by gel casting

Solid loading as a key parameter in gel casting influence both rheological behavior and stability of slurry. It also has strong impacts on microstructure and final properties of porous FeAl intermetallics. In this study, a designed non-aqueous gel casting has been developed for fabrication of porous FeAl intermetallics. The SEM analysis, bubble point method and compression test were used to investigate pore structure and properties of porous FeAl intermetallics. Results reveal that higher solid loading will improve the uniformity of pore structure and lead a decrease in maximum pore size. Gas permeability decreases but compressive strength increases with increasing solid loading. The quantitative relationship between maximum pore size (dm) and solid loading (φ) is dm = 10.52 − 0.15φ (35 ≤ φ ≤ 50); the relationship between gas permeability (K) and solid loading (φ) is K = 13.99 − 0.22φ (35 ≤ φ ≤ 50). Further, the distinctive phase transformation and pore formation mechanism are the main reasons for tiny volume expansion and highly open porosity of final products, respectively. Altogether, this work provides a strategy to fabricate porous FeAl intermetallics with adjustable pore structure and properties by controlling the solid loading, suggesting that the non-aqueous gel casting is a promising candidate for the preparation of porous FeAl intermetallics.

Preparation, mechanical and thermal properties of Si3N4 ceramics by gelcasting using low–toxic DMAA gelling system and gas pressure sintering

In this work, Si3N4 ceramics were fabricated through an aqueous gelcasting method using a low–toxic monomer called N, N–dimethylacrylamide (DMAA) followed by gas pressure sintering at 1850 °C for 2 h under 6 MPa N2 atmosphere. The effect of solid loading on performance of slurries, green and sintered bodies was investigated systematically. The results show that the slurries with a solid loading as high as 50 vol% (viscosity 0.17 Pa.s at 100 s–1) were achieved. With the increase of solid loading (30–50 vol%), the green bodies exhibited a monotonically decreased, however high enough in general, flexural strength of 16.50–11.52 MPa, which was comparable to that of widely–used neurovirulent acrylamide (AM) gelling system. In regard to the sintered bodies, increasing solid loading significantly promoted sintering and improved mechanical properties and thermal conductivity as a result of the increased density, bimodal distribution structure, as well as suitable interfacial bonding strength. The best performance parameters of Si3N4 ceramics, bulk density of 3.25 g/cm3, apparent porosity of 0.67%, flexural strength of 898.92 MPa, fracture toughness of 6.42 MPa m1/2, Vickers hardness of 2.81 GPa, and thermal conductivity of 34.69 W m–1 K–1, were obtained at 50 vol% solid loading. This work renders low–toxic DMAA gelling system promising prospect in preparation of high–performance Si3N4 ceramics by gelcasting.

Starch-hydroxyapatite composite bone scaffold fabrication utilizing a slurry extrusion-based solid freeform fabricator

Significant efforts have been made to treat bone disorders through the development of composite scaffolds utilizing calcium phosphate (CaP) using additive manufacturing techniques. However, the incorporation of natural polymers with CaP during 3D printing is difficult and remains a formidable challenge in bone and tissue engineering applications. The objective of this study is to understand the use of a natural polymer binder system in ceramic composite scaffolds using a ceramic slurry-based solid freeform fabricator (SFF). This was achieved through the utilization of naturally sourced gelatinized starch with hydroxyapatite (HA) ceramic in order to obtain high mechanical strength and enhanced biological properties of the green part without the need for cross-linking or post processing. The parametric effects of solids loading, polycaprolactone (PCL) polymer addition, and designed porosity on starch-HA composite scaffolds were measured via mechanical strength, microstructure, and in vitro biocompatibility utilizing human osteoblast cells. It was hypothesized that starch incorporation would improve the mechanical strength of the scaffolds and increase proliferation of osteoblast cells in vitro. Starch loading was shown to improve mechanical strength from 4.07 ± 0.66 MPa to 10.35 ± 1.10 MPa, more closely resembling the mechanical strength of cancellous bone. Based on these results, a reinforcing mechanism of gelatinized starch based on interparticle and apatite crystal interlocking is proposed. Morphological characterization utilizing FESEM and MTT cell viability assay showed enhanced osteoblast cell proliferation in the presence of starch and PCL. Overall, the utilization of starch as a natural binder system in SFF scaffolds was found to improve both compressive strength and in vitro biocompatibility.

Electronically conductive porous TiN ceramics with enhanced strength by aqueous gel‐casting

AbstractIn this paper, we report on a study of electronically conductive porous TiN ceramics prepared by aqueous gel‐casting. The effects of solid loading, sintering temperature, and sintering aids on the phase composition, microstructure, and volume fraction of porosity of the prepared porous TiN ceramics are studied. The SEM results show that porosity is uniformly distributed in all of the samples studied. With increasing solid loading and sintering temperature, the volume fraction of porosity decreases slowly. Moreover, the relationship between volume fraction of porosity and mechanical and electrical properties has also been investigated. Our results show that adding Y2O3‐TiO2 as combined sintering aids results in a sharp decrease in the volume fraction of porosity, and the volume fraction range changes from 42%‐60% to 28%‐52%. Moreover, adding sintering aids results in an increase in flexural strength and electrical conductivity with a change in maximum value from 34.6 MPa and 2.3 × 104 S∙m−1 to 101.6 MPa and 5.1 × 104 S∙m−1, respectively.

Effects of solid loadings and silica addition on microstructure and compressive strength of hydroxyapatite specimens fabricated by freeze casting technique

Attributed to its bioactivity, osteoconductivity, and chemical compositions similarly to those of human bones, hydroxyapatite (HAp, Ca10(PO4)6(OH)2) is a well-known material suitable for bone graft applications. To achieve physical and mechanical properties desired for the practical applications, microstructure of the HAp specimen needs to be controlled. This study therefore aimed at fabricating freeze-cast hydroxyapatite specimens with the porosity, pore sizes and compressive strength with acceptable values for the applications. Effects of solids loadings and silica addition on compressive strength were also examined in this study. Experimental results indicated that enhanced strength could be obtained in the specimens prepared from slips with higher solids loadings. The results also revealed that the HAp specimens achieved average porosity, pore sizes, and compressive strength in the ranges of 43.3–72.8%, 94.2–128.4 µm, and 1.29–29.35 MPa, respectively. The highest compressive strength was evident in the specimens prepared from silica-added slip with 35 vol% solids loading. The pH value of simulated body fluid solution was relatively stable upon sample submersion. Slight increase of specimen weight and formation of apatite layer were observed. The findings suggested that the specimens could be potential candidates for biomedical applications.

Effects of solid loading on the rheological behaviors and mechanical properties of injection-molded alumina ceramics

In this work, alumina ceramics were prepared by injection molding. The effects of solid loading on the rheological behaviors of the feedstocks, as well as the resulting properties of the green bodies and sintered ceramics were investigated. It was found that the viscosity and stabilized torque values of the feedstocks increased with the increase of solids loading in the range of 48–54 vol.%. The feedstock with 54 vol.% alumina exhibited dilatant rheology behavior and high viscosity; however, the feedstocks with less than 52 vol.% alumina exhibited pseudoplastic rheology behavior. After removing the organic binder, the pre-sintered bodies with high alumina content had smaller most frequent pore diameter, which was beneficial to sintering densification. With an increase in solid loading, the density of the green and sintered bodies increased and the shrinkage decreased. The green and sintered bodies at the solid loading of 52 vol.% presented uniform, compact microstructures, and possessed the highest bending strength of 25 MPa and 440 MPa, respectively.

Fed-batch strategies for saccharification of pilot-scale mild-acid and alkali pretreated sugarcane bagasse: Effects of solid loading and surfactant addition

High-solid enzymatic hydrolysis of lignocellulosic biomass is a key approach for high titer and reduced downstream costs in second generation ethanol production. Combining a pilot-scale (80 L reactor) mild acid pretreatment and an alkali pretreatment of sugarcane bagasse (SCB) with fed-batch strategies for high-solid enzymatic hydrolysis, more than 150 g/L of glucose was found in the hydrolysate. The best result of the fed-batch study (2.03 g/L/h of glucose productivity) was obtained with a total solids content of 27%w/w (being 20%w/w of solids added at 0 h), and the addition of the total amount of the non-ionic surfactant PEG 4000 and the enzymes solely at the beginning of the reaction. A semi-simultaneous saccharification and fermentation strategy of the pretreated SCB (with the yeast inoculum occurring after 12 h of a single hydrolysis stage at most proper conditions for the cellulases) resulted in 62 g/L of ethanol after 48 h, and a productivity of up to 6.6 g/L/h. The strategy here reported indicates that it is possible to achieve ethanol titers suitable for industrial distilleries avoiding mass transfer limitations that incur in operational problems during high-solid enzymatic hydrolysis.

Hydrodynamics and bubble behaviour in a three-phase two-stage internal loop airlift reactor

Abstract Local hydrodynamics of a gas–liquid–solid system, such as bubble circulation regime, gas holdup, liquid velocity and axial profile of solid concentration, are studied in a two-stage internal loop airlift reactor. Empirical correlations for gas holdup and liquid velocity are proposed to ease the reactor design and scale-up. Different bubble circulation regimes were displayed in the first (lower) and second (upper) stages. Increasing superficial gas velocity and solid loading can promote regime transition of the second stage, and the gas holdup of the second stage is higher than that of the lower stage. In addition, the effects of solid loading on bubble behaviour are experimentally investigated for each stage. It is found that bubble size in the downcomer decreases with the presence of solid particles, and bubble size distribution widens under higher superficial gas velocity and lower solid loading.