Static Ablation Research Articles

Enhancing the mechanical and insulation properties of CF/BPR composites by adding hollow silicate glass microspheres as an Interlaminar reinforcement

Improving the ablation and mechanical properties of ablative thermal protection composites by introducing modified fillers which simultaneously with an unavoidable increase in density. Balancing this increase in density while achieving lightweight properties is crucial for the development of effective ablative composites. In this paper, different contents of the hollow silicate glass microspheres (HSMs) are incorporated into MoSi2/mica-modified CF-BPR composites to investigate the impact of HSMs. The results show that HSMs play a positive role in reducing the density and thermal conductivity of the composite. The ablation and insulation properties of the 30 vol.% HSMs composites exhibit a mass ablation rate of 0.035 g/s and a linear ablation rate of 0.015 mm/s, alongside the lowest backside temperature. A significant improvement in flexural strength after static ablation at 1500 °C reached 82.59 MPa and maintained a relatively high level after 1600 °C. HSMs act as interlaminar skeletons, enhancing the shearing strength of the composite and facilitating the formation of a protective liquid phase around the carbon fibers to prevent oxidation. The increasing toughness of carbon fibers further enhances the mechanical strength of the composites.

A novel molecular structure design of liquid silicone rubber modified by ceramic precursors for high-performance flexible ablation

High ablation-resistant silicone rubber exhibits a significant role in the thermal protection of space vehicles. However, its limited by the low mechanical strength in practical heat protection applications. Herein, a novel molecular network structure is proposed, which links polycarboxysilane (PCS) rigid molecules onto polydimethylsiloxane molecular chains. The use of PCS rigid chains enhances the heat resistance while reducing the material's mass ablation rate. The addition of a small quantity of PCS (0.406 mmol) increases the tensile strength of the material by 10.4 % and augmentes the static ablation residual weight by 32.8 % compared with polydimethylsiloxane. Additionally, PCS molecular modification of polydimethylsiloxane is beneficial for maintaining the stability of the char layer after oxygen acetylene ablation, making the char layer denser, and improving the interface bonding between the ceramic layer, pyrolysis layer and matrix, ultimately improving the ablation performance of polydimethylsiloxane. This work provides a new approach for development of high-performance flexible ablative materials.

Flexural Strength Evolution, Microstructure Evolution and Mechanical Strength Failure Mechanisms of the Fused SiO2 and h-BN Co-modified Quartz Fiber/Benzoxazine Resin Ceramizable Composites

In our research described in this paper, the flexural strength evolution, microstructure evolution and the pyrolysis process of fused SiO2 and h-BN co-modified quartz fiber/benzoxazine resin ceramizable composites with increasing temperature were investigated. It was found that the flexural strength of the ceramizable composites dropped with increasing temperatures. The microstructure observation results depicted that cracks and holes appeared on the surface of the samples and the interfaces were seriously deteriorated after a static ablation test in a muffle furnace at 400–1200 °C for 20 min. Through the characterizations of the quartz fibers, it was revealed that the quartz fibers underwent a crystallization process at 1200 °C, during which micro-cracks were formed in them. As a result of our research the mechanical strength failure mechanism of the ceramizable composites was proposed. It was found that the failure process of the ceramizable composites was the result of matrix pyrolysis, carbon oxidation, interfacial degradation and fiber crystallization.

Microwave Ablation of the Pig Growth Plate: Proof of Concept for Minimally Invasive Epiphysiodesis.

Different surgical methods for epiphysiodesis of limb length discrepancy (LLD) have been described. Although these methods are variably effective, they are associated with morbidity (pain and limp) and potential complications. Microwave ablation is a less-invasive opportunity to halt growth by selectively destroying the growth plate via thermal energy to treat LLD in children. In this proof-of-concept study using an in vivo pig model, we asked: (1) What is the durability of response 2 to 4 months after microwave ablation of the tibial growth plate as measured by length and angulation of the tibia via a CT scan? (2) Was articular cartilage maintained as measured by standard histologic staining for articular cartilage viability? To develop an in vivo protocol for microwave ablation, we placed microwave antennas adjacent to the proximal tibia growth plate in the cadaveric hindlimbs of 18 3-month-old pigs. To determine the suitable time, we varied ablation from 90 to 270 seconds at 65-W power settings. After sectioning the tibia, we visually assessed for discoloration (implying growth plate destruction) that included the central growth plate but did not encroach into the epiphysis in a manner that could disrupt the articular surface. Using this information, we then performed microwave ablation on three live female pigs (3.5 to 4 months old) to evaluate physiologic changes and durability of response. A postprocedure MRI was performed to ensure the intervention led to spatial growth plate alterations similar to that seen in cadavers. This was followed by serial CT, which was used to assess the potential effect on local bone and growth until the animals were euthanized 2 to 4 months after the procedure. We analyzed LLD, angular deformity, and bony deformity using CT scans of both tibias. The visibility of articular cartilage was compared with that of the contralateral tibia via standard histologic staining, and growth rates of the proximal tibial growth plate were compared via fluorochrome labeling. Eighteen cadaveric specimens showed ablation zones across the growth plate without visual damage to the articular surface. The three live pigs did not exhibit changes in gait or require notable pain medication after the procedure. Each animal demonstrated growth plate destruction, expected limb shortening (0.8, 1.2, and 1.5 cm), and bony cavitation around the growth plate. Slight valgus bone angulation (4º, 5º, and 12º) compared with the control tibia was noted. No qualitatively observable articular cartilage damage was encountered from the histologic comparison with the contralateral tibia for articular cartilage thickness and cellular morphology. A microwave antenna placed into a pig's proximal tibia growth plate can slow the growth of the tibia without apparent pain and alteration of gait and function. Further investigation and refinement of our animal model is ongoing and includes shorter ablation times and comparison of dynamic ablation (moving the antennae during the ablation) as well as static ablation of the tibia from a medial and lateral portal. These refinements and planned comparison with standard mechanical growth arrest in our pig model may lead to a similar approach to ablate growth plates in children with LLD.

A novel Ti3SiC2-CaB6 modified Al-coated carbon fiber/boron phenolic resin ceramizable composite (ACF/BPRC) with excellent long-term oxidative corrosion resistance and high temperature load-bearing capacity

Carbon fiber/phenolic composites (CF/Ph) are susceptible to oxidation failure. In this work, Ti3SiC2-CaB6 modified ACF/BPRC was prepared, and its long-term (20min) oxidation resistance in a broad temperature range (600-1400 ℃) was investigated. The mass residual rate at 1400 ℃ and flexural strength post static ablation at 1400 ℃ for 20min was 90.9% and 41.8MPa, respectively. The ceramizable composite underwent ceramization reactions and was converted to ceramized composite, and a thermal protection barrier composed of TiO2, TiC, TiB2, SiC, Al2O3, and molten Al and calcium borate was constructed. Thus, the long-term oxidation resistance and high-temperature load-bearing capacity was enhanced notably.

In-situ constructing SiC frame in silicone rubber to fabricate novel flexible thermal protective polymeric materials with excellent ablation resistance

To meet the urgent need for thermal protection of high-temperature deformable mechanisms in the aerospace industry, a novel strategy for the preparation of ablation-resistant flexible composites is proposed. Ceramic precursor is selected and introduced to epoxy modified silicone rubber (SR) to in-situ build SiC frame at high temperature to fabricate flexible thermal protective polymeric materials with excellent ablation resistance. The static ablation and dynamic ablation behaviors of the SR composites are systematically and comparatively investigated in a tube furnace and oxyacetylene torch in an automatic ablation machine for the first time. The influence of polycarbonylsilane (PCS) content on the microstructure, strength and composition of char layer, and the ablation properties at different heat environments are discussed. When the addition of PCS reached 10 phr, for the static ablation, the maximum puncture strength of char and the residual weight increased 3233% and 48.48%, respectively. The same for dynamic ablation, with the introduction of PCS, each indicator was greatly improved. Moreover, the ablation enhancement mechanisms of PCS in different ablation environments are revealed. This work may provide a new perspective for the preparation of silicone rubber composites with excellent ablation performance, expected to be well used as a thermal protection coating for hypersonic spacecrafts.

Oxidation resistance, ablation resistance and in situ ceramization mechanism of Al-coated carbon fiber/boron phenolic resin ceramizable composites modified with Ti3SiC2

Inherent defect of easy oxidation limited further application of carbon fiber/phenolic resin composites in hostile environments. Herein, a combined strategy of matrix modification and fiber coating was proposed to fabricate a novel ceramizable composite containing Al-coated carbon fibers and Ti3SiC2 toward thermal protection materials (TPM), which offered a promising solution to challenge facing long-term thermal protection and load-bearing subject to severe oxidation corrosion and ablation in hypersonic vehicle applications. Oxidation resistance, mechanical strength evolution, phase evolution, microstructure evolution and mechanical strength failure mechanism at elevated temperatures were studied based on thermogravimetric analysis, static ablation test, mechanical test, X-ray diffraction analysis, and scanning electron microscopy coupled with energy dispersive X-ray analysis. The resulting composites exhibited outstanding oxidation resistance, with residue yield at 1600 °C and flexural strength at 1400 °C as high as 87.7% and 31.7 MPa, respectively. It was found that dense multiphase ceramics formed by reactions between Ti3SiC2, O2, pyrolytic carbon (PyC) and N2, acted as oxygen barriers and self-healing agents during static ablation. Besides, the resulting composites exhibited satisfactory ablation resistance and the linear ablation rate was as low as 0.00853 mm/s. Furthermore, ablation mechanisms were revealed based on phase identification, microstructure characterization and thermodynamic calculation analysis. It was revealed that multiphase ceramics composed of PyC, Al coatings, Ti3SiC2, TiC, Al2OC and AlB2 contributed great to the ablation resistance during oxyacetylene ablation.

Ceramicization mechanism and thermal insulation/ablative properties of hollow microspheres/boron phenolic composites

Phenolic resins with excellent ablative properties and thermal insulation are required in aerospace technology. However, the composites suffer from pyrolytic carbonaceous residues, resulting in susceptible erosion and peeling. This work provides a novel phenolic resin composite with high thermal insulation capacity by introducing hollow silica microspheres (HSMs) as an insulation layer. The effect of HSMs content on the ablation behavior of the composites was investigated, and the ablation mechanism was elucidated. The results show that the composites with microspheres exhibit high uniformity and improved bending strength. By introducing microspheres, the fiber distribution is uniform, resulting in an increase of the bending strength after static ablation to be 7.4 MPa, which is 87% higher than the matrix. The thermal stability of the composite is improved simultaneously and the ablation residual rate after static ablation increases from 67% to 73%. When oxyacetylene ablation for 20 s at the oxygen and acetylene flow rates of 1145 L/h and 838 L/h, respectively, the microspheres construct an insulating network, and the back surface temperature decreases from 280 °C to 178 °C.

Thermal Stability, Mechanical Properties and Ceramization Mechanism of Epoxy Resin/Kaolin/Quartz Fiber Ceramifiable Composites

The application of epoxy resins in high temperature and thermal protection fields is limited due to their low decomposition temperature and low carbon residual rate. In this paper, epoxy resin (EP)/quartz fiber (QF) ceramifiable composites were prepared using a prepreg-molding process. The thermal stability, phase change and mechanical properties after high-temperature static ablation and ceramization mechanism of EP/QF ceramifiable composites were investigated. The addition of glass frits and kaolinite ceramic filler dramatically increases the thermal stability of the composites, according to thermogravimetric (TG) studies. The composite has a maximum residual weight of 61.08%. The X-ray diffraction (XRD) results show that the mullite ceramic phase is generated, and a strong quartz diffraction peak appears at 1000 °C. The scanning electron microscope (SEM) and element distribution analyses reveal that the ceramic phase generated inside the material, when the temperature reaches 1000 °C, effectively fills the voids in composites. The composites have a bending strength of 175.37 MPa at room temperature and retain a maximum bending strength of 12.89 MPa after 1000 °C treatment.

Improved Performances of SiBCN Powders Modified Phenolic Resins-Carbon Fiber Composites

The effect of SiBCN powder on properties of phenolic resins and composites was analyzed. Compared with phenolic resins, the thermal stability of SiBCN powder modified phenolic resins (the SiBCN phenolic resins) by characterization of thermogravimetric analysis (TGA) improved clearly. It was found by X-ray photoelectron spectroscopy (XPS) that reactions between SiBCN powder and the pyrolysis product of phenolic resins were the main factor of the increased residual weight. TGA and static ablation of a muffle furnace were used to illustrate the roles of SiBCN powder on increasing oxidation resistance of SiBCN powder-modified phenolic resin–carbon fiber composites (SiBCN–phenolic/C composites), and the oxidative product was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). For SiBCN–phenolic/C composites, the occurrence of oxidation reaction and the formation of protective crust contributed to improving oxidative resistance. The result of the oxygen-acetylene test showed that the linear ablation rate (LAR) and mass ablation rate (MAR) of phenolic resin–carbon fiber composites reduced from 0.052 ± 0.005 mm/s to 0.038 ± 0.004 mm/s and from 0.050 ± 0.004 g/s to 0.043 ± 0.001 g/s by introducing SiBCN powder, respectively. The mechanism of ablation resistance after the introduction of SiBCN powder was investigated. The high melt-viscosity of SiBCN powder caused SiBCN powder to remain on the surface of composites and protect the internal resins and carbon fibers. The oxidation of SiBCN powder and volatilization of oxide can consume energy and oxygen, thus the ablation resistance of SiBCN–Ph composite was improved.

Improving ablation properties of ceramifiable vitreous silica fabric reinforced boron phenolic resin composites via an incorporation of MoSi2

ABSTRACT Various thermal protective ablative materials (TPAM) have been extensively studied. However, there are few reports on the thermal stability, the ablation properties and ceramisation of vitreous silica fabric reinforced boron phenolic resin composites with an incorporation of MoSi2 (VMBPR) and their bending strength after ablation. At this work, the above performances of the composites were characterised and analysed. Results reveal that the addition of MoSi2 decreases the graphitisation temperature of glass carbon of BPR pyrolysis, promoting the formation of a more ordered structure of the glassy carbon during pyrolysis. Furthermore, compared with the composites without MoSi2 (VBPR), the linear and the mass ablation rate of VMBPR composites decrease by about 94.46% and 39.09%, and its room temperature bending strength after static ablation at 1400°C for 20 min is more than twice that of the fused fibre aggregation formed by VBPR composites. This is attributed to the ceramisation reaction of VMBPR composites at high temperature.

Dynamic characterization of indocyanine green-assisted dental caries ablation with continuous diode laser using thermal imaging and fluorescence spectroscopy.

We describe the time-resolved thermal changes in indocyanine green (ICG)-assisted diode laser ablation of dental caries as a potential technique for painless treatment based on the selective photoabsorption and controlled photothermal ablation. Static ablation mode produced a higher temperature rise compared with scanning mode due to localized accumulation of heat. A temperature rise between 45-80 and 70-95°C was obtained after 20s that corresponded to 29 and 80Wcm-2, respectively. The temperature of the tooth surface increased by irradiation time, and it behaved linearly up to 70°C at 29 and 80Wcm-2. A maximum ablation per area of about 0.3 and 0.45mgcm-2 was achieved after 80s exposure at 29 and 80Wcm-2, respectively. A statistically significant difference is observed in mean carious teeth weight at various exposure times between low and high irradiances. A thermal penetration depth of 0.8-9mm is determined for 1-100s of exposure time. The IR thermal imaging of ICG temperature as a function of exposure time showed a linear increase for 60s beyond which it deviated. The laser-induced fluorescence spectroscopy indicated that the ICG quality can be altered during the course of irradiation, which in our case, it corresponded to ≈ 78% loss of signal within 23min of exposure. The caries removal experiment was performed within 100s corresponding to ≈ 7% loss. We believe that the application of the above-combined technique can be utilized as a monitoring device to control the ablation interaction process.

Shallow sampling by multi-shot laser ablation and its application within U-Pb zircon geochronology

The interaction of incident laser radiation and sample substrate is complex and difficult to predict. Natural zircons are often both structurally and chemically heterogeneous in 3-dimensional space. Encountering growth-related, structural micro-heterogeneities, inclusions and chemical complexities is almost inevitable during a static ablation of several tens of seconds. A multi-shot approach to laser ablation described here implements a minimal sample exposure time to incident laser radiation by applying multiple 1 Hz shots to a single sample location in delayed succession. This process can be conceptualised as a “slowing down” of a high-frequency (5–20 Hz) static laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis until each laser pulse is distinct albeit transient. The ability to integrate and collate signal pulses for a small number of consecutive laser shots, as opposed to continuously pulsing the laser, produces precise age determinations (~1% reproducibility, 2σ level) on small sample volumes (704 ± 23 μm3 on 91500 zircon standard). The multi-shot LA-ICP-MS protocol employed here significantly reduces the effect of ‘downhole’ fractionation as the resultant craters are extremely shallow (as shallow as 0.56 ± 0.02 μm on 91500 zircon standard) and maintain an aspect ratio of ≪1. Further benefits include a reduced probability of thermally induced effects (e.g., substrate melting), plasma loading, and the potential for signal mixing (with depth) in a heterogeneous sample.

Reaction kinetics and a physical model of the charring layer by depositing Al2O3 at ultra-high temperatures.

The thermochemical ablation of insulation material caused by slag deposition in solid rocket motors has increasingly attracted researchers' attention. Understanding the ablation mechanism and the ability to calculate reaction kinetics parameters determine the height of the thermal protection design for advanced solid rocket motors. In this work, the interaction of the Al2O3-C system is determined through static ablation experiments. Using X-ray diffraction, HSC thermodynamic software, and a thermogravimetric analyser, the carbon thermal reduction of alumina is analysed and the reaction mechanism and physical model are obtained. Isothermal experiments at 1700-1850 °C and mathematical analysis provide the kinetic parameters of the overall and step-by-step reactions. The results show that the overall reaction of the Al2O3-C system involves three steps. The overall reaction kinetics are described by the contracting area model R2 with apparent activation and frequency factors estimated as 254.5 kJ mol-1 and 5.5 × 106 min-1, respectively. The distribution reaction kinetics of steps 1 and 2 are described by the first-order chemical reaction control model (F1) and that of step 3 is described by the one-dimensional diffusion control model (D1). The corresponding activation energies are 107.9 kJ mol-1, 240.3 kJ mol-1, and 567.5 kJ mol-1, and frequency factors are 625.94 min-1, 8.3 × 105 min-1, and 1.6 × 1014 min-1, respectively.

Ablation Properties of ZrO<sub>2</sub>-MgO and Mo Nozzle Produced by Plasma Spray Forming

ZrO2-MgO and Mo powder coating on a substrate material prepared by an high temperature plasma spraying forming (PSF) for lease-shaped engine nozzles, and its total thickness is about 300 μ m. The surface coating changes of microstructure were investigated by a small solid rocket motor static ablation and the results were discussed for preliminary ions after ablation. The results show that the plasma spraying throat coat is a layer structure and the pore consist in micro-gap between layer and layer.That throat coating erosion is so severe were found after the ablation test , which is because of the metal oxide particles caused by mechanical denudation and high temperature thermal chemical ablation.Whereas the coating interface have no significant cracks after erosion, so that the composite coating of ZrO2-MgO and Mo wear good erosion performance.

A new approach to single shot laser ablation analysis and its application to in situ Pb/U geochronology

A novel approach to laser ablation Pb/U geochronology is presented that allows accurate determination of isotope ratios from a single pulse of a 193 nm laser. Data are acquired using a low volume ablation cell that facilitates: (1) production of a high density particle stream; and (2) a short (∼0.5 s) sample washout time. Isotope ratios from an individual laser pulse are calculated by integrating the baseline-subtracted total number of counts for the entire pulse and assigning an internal uncertainty based on counting statistics. This ‘total signal integration’ method eliminates the effects of differing detector response times, particularly in multi-collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS), providing an alternative means to quantify transient signals. Data from reference zircons indicate that it is possible to consistently measure 206Pb/238U and 207Pb/206Pb ratios with external reproducibilities of 2% and 2.8% (2SD) respectively, using a similar amount of material to standard static ablation protocols. Decreasing sample consumption to ∼14 ng zircon (∼75% less than the ‘normal’ ablated mass) results in only a modest increase in the uncertainty to ∼5% on the 206Pb/238U ratio. By analysing consecutive laser pulses from the same ablation site, isotopic depth profiles can be generated with a depth resolution of ∼0.1 µm pulse−1. This technique offers a new opportunity to identify complexities within accessory minerals that were previously beyond the spatial resolution of laser based geochronology methods.

Photomodification of polymer microchannels induced by static and dynamic excimer ablation: effect on the electroosmotic flow.

This paper presents a study of polymer surfaces modified by laser ablation using poly(ethylene terephthalate) (PET) as a model system. The surface properties induced by static and dynamic ablation with the 193-nm pulsed radiation of an ArF excimer laser (4 x 10(7) W/cm2) in air have been successfully used to control the electroosmotic flow (EOF) in photoablated PET microchannels. Through the creation of well-defined static ablation patterns onto the walls of a trapezoidal channel, it was found that the resulting reduction in the EOF could be controlled. For example, a reduction of 25% in the EOF was observed in 42-microm-deep microchannels when using a static ablation pattern treating 50% of the total wall surface area. A numerical study describing the fluidic behavior induced by a static pattern is also presented. Moreover, X-ray photoelectron spectroscopy has been used to point out surface changes between static and dynamic ablation, thereby demonstrating an ability to create new functionalities in microchannels by laser treatment.

Structure formation in excimer laser ablation of stretched poly(ethylene therephthalate) (PET): the influence of scanning ablation

Multiple pulse laser ablation of stretched PET is performed with an ArF excimer laser (193 nm) in order to produce micro channels. The surface structure remaining after “scanning ablation”, in which the sample is moved during irradiation, is compared to the known results upon “static ablation”.

Topography, Crystallinity and Wettability of Photoablated PET Surfaces

Surface topography, crystallinity, and wettability of photoablated poly(ethylene terephthalate) (PET) resulting from various ablation conditions have been characterized by atomic force microscopy (AFM), microconfocal Raman spectroscopy, and wettability measurements. Two ablation modes have been considered here: (i) static ablation, where the samples are immobilized in front of the pulsed laser beam and (ii) dynamic ablation, where the samples are moved in order to write three-dimensional structures in the polymer. Laser fluence, repetition rate, and speed of the substrate motion during the ablation process have been varied. The laser fluence has been observed to strongly affect the resulting surface roughness, which increased to a maximum value at fluences between 70 and 600 mJ·cm-2. For all fluences in the range of 1000−3000 mJ·cm-2, the roughness was found to be similar. No remarkable effects could be attributed to the pulse frequency of the 23 ns laser pulses. Raman spectroscopy studies demonstrated that the polymer surface exhibits a high degree of crystallinity when ablated in the static mode. Raman imaging of the surface indicated that these conditions also led to a more homogeneous surface state than when the polymer is ablated in the dynamic mode. Experiments measuring channel filling velocities by capillary action showed that the surfaces of structures fabricated in static photoablation mode were much more hydrophobic than those fabricated under dynamic photoablation.