Slurry Dipping Research Articles

HfSi2-HfB2-SiC coating prepared at low temperature to protect SiC-coated C/C composites against oxidation at 1473–1973 K

To improve the oxidation resistance of carbon/carbon (C/C) composites in 1473–1973 K, a HfSi2-HfB2-SiC coating was prepared on the surface of SiC-coated C/C composites by a combined method of slurry dipping and oxidation sintering at low temperature (below 1473 K). The Hf-Si-O multiphase layer generated by the oxidation of the coating acted as oxygen barriers at 1473–1973 K in air. The in-situ formed HfSiO4 particles enhanced the thermal stability of the SiO2 glass, terminated propagation of the crack, and relieved CTE mismatch between the inner and outer coating. Besides, B2O3 filled pores in the early stage of oxidation and then SiO2 took the place of the B2O3 as a new filler with the increase time of oxidation. As a result, the coating can protect C/C composites for 516 h at 1473 K, 744 h at 1773 K, and 64 h at 1973 K with a mass gain of 0.63 wt%, 1.41 wt% and −1.91 wt%, respectively.

Fabrication and characterization of surgical sutures with propolis silver nano particles and analysis of its antimicrobial properties

ObjectivesThe objective of this work was to synthesize propolis – silver nanoparticles, coat the prepared nanoparticles on surgical sutures, characterize the coated sutures and to study the antimicrobial activity of coated sutures against human pathogenic microorganisms. MethodsSilver nanoparticles were synthesized with ethanolic propolis extract and analyzed by UV spectrophotometry analysis. Absorption peak was detected at 430 nm to confirm silver nanoparticle synthesis. Propolis – silver nanoparticles were coated over plain Cal Gut surgical sutures with the help of sodium alginate by slurry dipping technique. The characterization of coated sutures was done by Fourier-Transform Infrared analysis (FTIR) analysis and Scanning Electron Microscopy (SEM). The antimicrobial activity of propolis silver nanoparticles was determined by disc diffusion method against pathogenic bacteria like Staphylococcus aureus, E.coli and Aspergillus flavus obtained from clinical samples. ResultsFTIR confirmed the presence of silver through its various peaks and the various functional groups were detected. The SEM characterization revealed the particles size and shape of the nanoparticle at a magnification of 20KV. The size is about 20 nm and its mostly spherical in shape. The surface of the coated sutures was rough indicating the coating of propolis – silver nanoparticles (AgNPs) over the sutures. The in-vitro antimicrobial assay showed that the propolis – silver nanoparticles and the also coated sutures possessed a significant anti-microbial activity against the clinical pathogenic microorganisms. ConclusionPropolis is a natural product which is an asset to the mankind. The combined effect of the propolis and silver nanoparticles and also the antimicrobial activity of propolis nanoparticle coated sutures were extensively studied. So, this synergistic drug can be used as antimicrobial materials for clinical practice and bio medical use. It is proved that propolis silver nanoparticle loaded sutures are a beneficial in preventing the surgical site infections.

Oxidation behavior of SiC-HfB2-Si coating on C/C composites prepared by slurry dipping combined with gaseous Si infiltration

An effective monolayer SiC-HfB2-Si coating for long-time oxidation protection of C/C composites was designed and prepared by a combined technique of slurry dipping and gaseous Si infiltration (SD + GSI). This coating is dense and adheres well with the C/C substrate, which is ascribed to the formed zigzagged SiC transition layer. After oxidation at 1773 K in static air for >538 h, the mass loss of SiC-HfB2-Si coated samples is only 0.69%. By thermodynamic calculation, the oxidation process of SiC-HfB2-Si coated samples is mainly controlled by oxygen diffusion, and the stable oxidation products are HfO2 + B2O3 + SiO2 + CO. The excellent oxidation protective ability is mostly attributed to the formation of a composite Hf-Si-O glass layer on the coating surface to heal cracks and pores.

Oxidation protection of (ZrTa)B2–SiC–Si coating for graphite materials

ABSTRACTTo protect graphite materials from oxidation, a dense (ZrTa)B2–SiC–Si coating was for the first time prepared on graphite substrate by slurry dipping and vapour silicon infiltration process. (ZrTa)B2 phase was synthesised by in-situ reaction using ZrC, TaC, B4C, phenolic resin and Si as raw materials. The phase compositions and microstructure of the obtained coating were analysed by XRD and SEM. The isothermal oxidation tests demonstrated that the in-situ coating had excellent oxidation resistance ability, after oxidation for 468 and 347 h at 1273 and 1773 K, respectively, the weight gains were 0.07% and 0.33%, respectively. No signs of oxidation of graphite substrate were found after oxidation, and two layers could be observed in the coating, namely, oxide layer containing Zr and Ta oxides and (ZrTa)B2–SiC–Si layer. A model for the evolution of the oxide layer was proposed to interpret the oxidation failure mechanism of the coating.

Mechanical and Cytocompatibility Evaluation of UHMWPE/PCL/Bioglass® Fibrous Composite for Acetabular Labrum Implant.

In this study, a fibrous composite was developed as synthetic graft for labral reconstruction treatment, comprised of ultra-high molecular weight polyethylene (UHMWPE) fabric, ultrafine fibre of polycaprolactone (PCL), and 45S5 Bioglass®. This experiment aimed to examine the mechanical performance and cytocompatibility of the composite. Electrospinning and a slurry dipping technique were applied for composite fabrication. To assess the mechanical performance of UHMWPE, tensile cyclic loading test was carried out. Meanwhile, cytocompatibility of the composite on fibroblastic cells was examined through a viability assay, as well as SEM images to observe cell attachment and proliferation. The mechanical test showed that the UHMWPE fabric had a mean displacement of 1.038 mm after 600 cycles, approximately 4.5 times greater resistance compared to that of natural labrum, based on data obtained from literature. A viability assay demonstrated the predominant occupation of live cells on the material surface, suggesting that the composite was able to provide a viable environment for cell growth. Meanwhile, SEM images exhibited cell adhesion and the formation of cell colonies on the material surface. These results indicated that the UHMWPE/PCL/Bioglass® composite could be a promising material for labrum implants.

Improved oxidation resistance of high emissivity coatings on fibrous ceramic for reusable space systems

To develop high emissivity coatings on fibrous ceramic substrates with improved thermal resistance for reusable space systems, WSi2–MoSi2–Si–SiB6-borosilicate glass coatings were prepared on fibrous ZrO2 by slurry dipping and subsequent high temperature rapid sintering. A coating with 20 wt% WSi2 and 50 wt% MoSi2 presents optimal thermal stability with only 10.06 mg/cm2 mass loss and 4.0% emissivity decrease in the wavelength regime 1.27–1.73 μm after 50 h oxidation at 1773 K. The advantages of double phase metal-silicide coatings combining WSi2 and MoSi2 include improved thermal compatibility with the substrate and an enhanced glass-mediated self-healing ability.

Oxidation protective ZrB2-MoSi2-SiC-Si coating for graphite materials prepared by slurry dipping and vapor silicon infiltration

In order to protect graphite materials from oxidation, a dense single layer ZrB2-MoSi2-SiC-Si coating was for the first time prepared on the surface of graphite substrate by slurry dipping and vapor silicon infiltration process. The phase compositions and microstructure of the prepared coating were analyzed by XRD and SEM. The isothermal thermal cycle oxidation tests were conducted at 1600 °C in air. The results showed that the prepared coating exhibited excellent oxidation protection ability, after oxidation for 150 h, the weight loss was only 0.21%, which was considered to be the depletion of the outer coating and the appearance of defects in the coating. The excellent protection ability was attributed to the dense structure of the coating and the formation of thick oxide layer with immiscible ZrO2 on the outer surface of coating. Two layers could be observed in the coating after oxidation, namely, glassy oxide layer and ZrB2-MoSi2-SiC-Si layer. After thermal shock between 1200 °C and room temperature for 100 cycles, the weight gain was 0.11%. The good thermal shock resistance could be ascribed to the gradient thermal expansion coefficients of different components in the coating and the C/SiC interface layer between the substrate and coating.

Oxidation protective MoSi2-SiC-Si coating for graphite materials prepared by slurry dipping and vapor silicon infiltration

A novel kind of dense MoSi2-SiC-Si coating was prepared on the surface of graphite substrate by slurry dipping and vapor silicon infiltration process. Mo-SiC-C precoating was fabricated via slurry dipping method, and then MoSi2-SiC-Si coating with dense structure consisting of Si, MoSi2 and SiC was obtained by vapor silicon infiltration process. The isothermal oxidation tests at temperatures from 800 to 1600°C and TGA test from room temperature to 1500°C were used to evaluate the oxidation resistance ability of the MoSi2-SiC-Si coating. The experimental results indicate that the prepared coating has good oxidation protection ability at a wide temperature range from room temperature to 1600°C. Meanwhile, the oxidation of the coated samples is a weight gain process at temperatures from 800 to 1500°C due to the formed SiO2 layer on the surface of coating. After oxidation for 220h at 1600°C, the weight loss of the coated sample was only 0.96%, which is considered to be the excessive consumption of the outer coating and the appearance of defects in the coating. Two layers can be observed in the coating after oxidation, namely, SiO2 layer and MoSi2-SiC-Si layer.

Design, formation, and property of high emissivity WSi2-Si-glass hybrid coating on fibrous ZrO2 ceramic for reusable thermal protection system

The objective of this research was to develop a high emissivity coating on the low thermal conductive insulation for reusable thermal protection system. The design principles including high emissivity, match of the coefficients of thermal expansion and excellent high temperature stability were proposed for the first time. A novel WSi2-Si-glass hybrid coating with optimized composition was successfully prepared on fibrous ZrO2 ceramic insulation by slurry dipping and subsequent high temperature rapid sintering method. The total emissivity of the as-prepared coating is up to 0.92 in wavelength of 0.3–2.5µm. After oxidation at 1673K for 100h and 1773K for 20h, the total emissivity values of the coatings are still as high as 0.89 and 0.87. A competitive mechanism between the “defects formation” caused by aging stress, the CTE mismatch stress and the volatilization of low melting point oxides and the “defects healing” resulted from self–healing phases during the different oxidizing conditions was discussed.

Preparation and thermal shock resistance of high emissivity molybdenum disilicide- aluminoborosilicate glass hybrid coating on fiber reinforced aerogel composite

To develop a flexible reusable surface insulation for thermal protection system, MoSi2-aluminoborosilicate glass hybrid coatings have been prepared on Al2O3 fiber reinforced Al2O3-SiO2 aerogel composite by slurry dipping and rapid sintering method. The effect of MoSi2 content on radiative property and thermal shock behavior was investigated. The total emissivity values of all the coatings exceeded 0.85 in the wavelength of 0.8–2.5μm. The M10 and M50 coatings were up to 0.9, which was due to the highest amorphous glass content of the M10 coating and the largest surface roughness of the M50 coating. The M30 coated composite showed the best thermal shock resistance with only 0.023% weight loss after 20 thermal shock cycles between 1473K and room temperature, which was attributed to the similar thermal expansion coefficients between the coating and the substrate and the appropriate viscosity of aluminoborosilicate glass at 1473K. The cracks resulted from CTE mismatch stress with different sizes formed and grew on the surface of M10, M40 and M50 coated samples, leading to the failure of the composites.

Study on ZrSiO4-aluminosilicate glass coating with high infrared emissivity and anti-oxidation properties

A multicomponent coating composed of ZrSiO4 and aluminosilicate glass was designed and prepared by slurry dipping and subsequent sintering on the surface of SiC substrate to improve the anti-oxidation ability of substrate. At appropriate temperature, the molten aluminosilicate glass carrying the stable ZrSiO4 particles will spread over the substrate’s surface to form a dense and stable coating. Among them, the flowing aluminosilicate glass will fill the crack and micro-pores of ZrSiO4, which inform a dense coating. Glass phase and ceramic phase could inhibit the propagation of the cracks together. This coating shows high infrared emissivity at broad bands, reaching more than 0.93. Wonderfully, the coating was endowed high oxidation resistance performance at high temperature in the air, which was mainly attributed to the compact and stable structure of coating, coupled with the high thermal expansion coefficient.

High emissivity MoSi2–TaSi2–borosilicate glass porous coating for fibrous ZrO2 ceramic by a rapid sintering method

A MoSi2-TaSi2-borosilicate glass porous coating was designed and prepared on fibrous ZrO2 ceramic with slurry dipping and subsequent rapid sintering method. The microstructure, radiative property and thermal shock behavior of the coating have been investigated. The results show the coating presents a top Ta-Si-O compound glass layer and a porous MoSi2-TaSi2-borosilicate glass inner layer. The total emissivity of the coating is up to 0.88 in the range of 0.3–2.5 μm and 0.87 in the range of 2.5–15 μm at room temperature. The increased surface roughness leads to the increased emissivity, which can be explained by “V-shaped grooves” model. The coating turns into a dense structure and presents an interlocking structure in the interfacial layer after thermal cycling between 1673 K and room temperature 10 times, exhibiting excellent thermal shock resistance, which was attributed to the synergistic effect of porous structure and the match of thermal expansion coefficient between the coating and substrate.

High emissivity MoSi2–ZrO2–borosilicate glass multiphase coating with SiB6 addition for fibrous ZrO2 ceramic

To develop a high emissivity coating on the low thermal conductivity ZrO2 ceramic insulation for reusable thermal protective system, the MoSi2–ZrO2–borosilicate glass multiphase coatings with SiB6 addition were designed and prepared with slurry dipping and subsequent sintering method. The influence of SiB6 content on the microstructure, radiative property and thermal shock behavior of the coatings has been investigated. The coating prepared with SiB6 included the top dense glass layer, the surface porous coating layer and the interfacial transition layer, forming a gradient structure and exhibiting superior compatibility and adherence with the substrate. The emissivity of the coating with 3wt% SiB6 addition was up to 0.8 in the range of 0.3–2.5μm and 0.85 in the range of 0.8–2.5μm at room temperature, and the “V-shaped grooves” surface roughness morphology had a positive effect on the emissivity. The MZB-3S coating showed excellent thermal shock resistance with only 1.81% weight loss after 10 thermal cycles between 1773K and room temperature, which was attributed to the synergistic effect of porous gradient structure, self-sealing property of oxidized SiB6 and the match of thermal expansion coefficient between the coating and substrate. Thus, the high emissivity MoSi2–ZrO2–borosilicate glass coating with high temperature resistance presented a promising potential for application in thermal insulation materials.

Effect of Using Different Compositions and PU Foam Template to Produce Cobalt Chromium Molybdenum (CoCrMo) Foams

Slurry dipping is a simple and popular method of producing porous and interconnected foams using a metallic slurry. The advantage of the network-like metal foams is it exhibits a natural bone-like structure which enables ingrowth of bone cells and blood vessels. The aim of the present study was to investigate the effect of using difference composition and scaffold to produce Cobalt Chromium Molybdenum (CoCrMo) foams. The CoCrMo slurry was prepared by using different composition of CoCrMo powder which was 60wt%, 65wt% and 70wt%. Also two different types of scaffold were used in this study. The CoCrMo slurry was produced by mixing CoCrMo powder with Polyethylene Glycol (PEG), Carboxyl Methyl Cellulose (CMC) and distilled water. Then, polyurathane foam template was dipped in CoCrMo slurry and dried at room temperature. Sintering process was running by vacuum furnace at high temperature, 1200°C. The CoCrMo foam was characterized by using a Scanning Electron Microscopy (SEM) analysis. The physical properties of CoCrMo foam was analyzed by porosity and bulk density test that was Archimedes method. From the study it was expected that the composition of metallic slurry play important roles to produce a CoCrMo foam. In order to orthopaedics application to apply in cancellous bone, highest value of porosity from PU foams type (a) was most suitable result to use. This is due to the value of porosity that generate that was 65.2%.

Assessing the Physical Properties of Cobalt Chromium Molybdenum (CoCrMo) Foams with Different Composition

Replication or slurry dipping is a simple and popular method of producing porous and interconnected foams using a metallic slurry. The advantage of the network-like metal foams is it exhibits a natural bone-like structure which enables ingrowth of bone cells and blood vessels. The aim of the present study was to investigate the physical properties of Cobalt Chromium Molybdenum (CoCrMo) foams after sintering process using vacuum furnace. The CoCrMo slurry was prepared by using different composition of CoCrMo powder which was 50wt%, 55wt%, 60wt%, 65wt% and 70wt%. The CoCrMo slurry was produced by mixing CoCrMo powder with Polyethylene Glycol (PEG), Carboxyl Methyl Cellulose (CMC) and distilled water. Then, polymeric foam template was impregnated in CoCrMo slurry and dried at room temperature. Sintering was carried out in a high temperature vacuum furnace at 1300°C. The CoCrMo foam was characterized by using a Scanning Electron Microscopy (SEM) analysis. The physical properties of CoCrMo foam was analyzed by porosity and bulk density test that was Archimedes method. From the study it was expected that the composition of metallic slurry play important roles to produce a CoCrMo foam. The best composition that obtained in this experiment was 70wt%. The porosity and density value for 70wt% of composition were 20.3% and 2.63g/cm3. The higher composition of metallic slurry will decrease the density and will increase the porosity.

Microstructure, radiative property and thermal shock behavior of TaSi2–SiO2-borosilicate glass coating for fibrous ZrO2 ceramic insulation

The objective of this research was to develop a high emissivity coating on the low thermal conductivity ZrO2 ceramic insulation, which can be used in a reusable thermal protective system for short-term applications. The effects of SiB6 and heat-treatment time on the microstructures and radiative properties of the TaSi2–SiO2-borosilicate glass composite coatings prepared on fibrous ZrO2 ceramic with slurry dipping and subsequent sintering method were investigated. The coating prepared in the presence of SiB6 with a heat-treatment time of 15 min maintains a dense structure and infiltrates into the ZrO2 substrate, possessing a gradient structure and good compatibility. The emissivity of the coating is up to 0.9 in the range of 0.3–2.5 μm and 0.8 in the range of 3–30 μm at room temperature. The emissivity mechanism regarding electron transition absorption, lattice vibration absorption and the effect of surface roughness on the emissivity is discussed. The increased roughness leads to the increased emissivity, which can be explained by “circular grooves” and “pyramidal grooves” models. After thermal cycling between 1573 K and room temperature 10 times, the weight gain of the coating prepared with SiB6 is only 0.29%. The high emissivity TaSi2–SiO2-borosilicate glass coatings with high temperature resistance show a promising potential for application in thermal insulation materials.

Characterization and modeling of anisotropic SL pattern during investment casting process

Photopolymer-based stereo-lithography (SL) rapid prototyping patterns with honeycomb internal structure reduce lead time and material cost for pattern manufacturing and also minimize ceramic mold residue after pattern removal in investment casting process. However, relatively larger thermal expansion of SL pattern tends to cause ceramic shell cracking during the pattern thermal removal. The anisotropy of SL pattern properties incurs different stress states of ceramic shell depending on the orientation of the honeycomb structure. In this work, a comprehensive thermo-mechanical coupled finite element model was developed to characterize the anisotropy of SL pattern and its effect on stress in investment casting shell molds. An experimental-based thermal degradation material model was developed considering anisotropy of the thermo-mechanical properties of SL pattern. The static analysis of slurry dipping and transient thermo-mechanical analysis of the pattern thermal removal process were performed. Both the pattern and ceramic shell behavior were studied and validated with experimental findings. Facesheet thickness/facesheet-to-core ratio and orientation of honeycomb structure were found to be the key factors to shell stress during pattern firing. Decreased facesheet thickness reduces stress in shell but also increases shell stress sensitivity to anisotropy of SL pattern. The developed tool provides an effective and efficient way to evaluate and optimize the structure of SL pattern for investment casting process.

Thermal shock behavior and infrared radiation property of integrative insulations consisting of MoSi2/borosilicate glass coating and fibrous ZrO2 ceramic substrate

An integrative insulation consisting of a MoSi2/borosilicate glass coating and a fibrous ZrO2 ceramic substrate was explored for applications up to 1673K. The MoSi2/borosilicate glass coating was prepared using the slurry dipping and subsequent firing method. The thermal shock behavior of the integrative insulation and the evolution of the surface morphology of the coatings for various thermal shock times were evaluated using confocal laser scanning microscopy (CLSM). The results revealed that the as-prepared coatings could maintain the dense structure and infiltrate into the substrate, forming a gradient structure and exhibiting good compatibility and adherence. After thermal cycling between 1673K and room temperature 15 times, the integrative insulation is also without micro cracks and spalling, and the weight loss is only 2.84%, revealing outstanding thermal shock performance. Additionally, the emissivity of the coatings reached 0.8 at room temperature, which was attributed to the synergistic effect of inter band absorption, crystal lattice vibration and the roughness of the coating. The gradual increase in the roughness resulted in the increase of the emissivity in 200–2500nm at room temperature, which was explained with a “circular grooves” model. These results imply that the integrative insulation can be a promising candidate material in high temperature application.

SYNTHESIS AND CHARACTERIZATION OF SILVER NANOPARTICLES AND ITS IMMOBILIZATION ON ALGINATE COATED SUTURES FOR THE PREVENTION OF SURGICAL WOUND INFECTIONS AND THE IN VITRO RELEASE STUDIES

The Silver nanoparticles are well-known for their antimicrobial, anti-inflammatory wound healing abilities. We synthesized Silver nanoparticles using chemical reduction method and the formation of the silver nanoparticles was characterized by UV-Vis absorption spectroscopy, FT-IR and SEM techniques. The minimum inhibitory concentration of the synthesized nanoparticles was determined for both gram negative and gram positive bacteria. Then these nanoparticles were coated over an absorbable surgical gut suture, after the immobilization of them in Sodium alginate, by slurry dipping technique. The controlled release of the nanoparticles checked in vitro in Simulated Body Fluid. Antimicrobial activity also evaluated by Disc diffusion method on the culture plates of E. coli and S. aureus. The successful release of silver nanoparticles under physiological PH depicts the applicability of this novel suture in surgery for the prevention of surgical wound infection and to enhance wound healing.

SiC/Cr–Al–Si/glass multilayer oxidation resistant coating for carbon/carbon composites

Multilayer oxidation resistant SiC/Cr–Al–Si/glass coating for C/C composites was prepared by a three step method of pack cementation, plasma spraying and slurry dipping. The phase composition, microstructure and oxidation resistance of multilayer SiC/Cr–Al–Si/glass coating were studied by XRD, SEM and isothermal oxidation test at 1773 K in air respectively. Double layer SiC/Cr–Al–Si coating consisting of Al3·21Cr0·47, Cr3Si and Al2O3 can protect C/C composites from oxidation for only 61 h due to its high porosity. When a layer of borosilicate glass doped with MoSi2 was coated on the surface of the as sprayed Cr–Al–Si coating, multilayers of SiC/Cr–Al–Si/glass coating were formed such that they can protect C/C composites from oxidation for 95 h with only 5·3% weight loss and the corresponding weight loss rate is only 0·92×10−4 g cm−2 h−1. The positive effect of the borosilicate glass coating on the oxidation resistance of the coating may be attributed to its own fluidity at high temperature.