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Carbon fibers reinforced SiCN ceramic matrix composites (C/SiCN) were prepared by PIP with homemade polysilazanes (PSN-T03). The PSN-T03 had a viscosity of less than 500 mPa·s and favorable good chemical stability at 80 ℃, which made it quite applicable for PIP process. PSN-T03’ curing reactions happened at temperatures ranging from 149℃ to 205℃, and conversion to amorphous SiCN ceramics could be finished at temperatures above 700℃ with a 70+ wt% ceramic yield. Tensile strength of C/SiCN composites were 230 MPa and 350 MPa respectively at room and high temperature (1400℃), and bending strength reached 380 MPa and 530 MPa. SiCN ceramics began to lose weight at 1400℃ due to the carbothermic reduction of the silicon nitride phase under inert atmosphere, which results in collapse of the mechanical properties of C/SiCN composites above 1400℃.

In this paper, fully dense Si3N4/SiC nano-composites were fabricated through polymer-derived ceramics (PDCs) method and spark plasma sintering technique. Polymer-derived SiAlCN ceramic was synthesized by using polysilazane as preceramic precursor, aluminum tri-sec-butoxide as Al source. Then Si3N4/SiC composites with nanometer sized Si3N4 and SiC phases were formed spontaneously during spark plasma sintering through in-situ phase separation of amorphous SiAlCN ceramics. It's found that with the increasement of Al contents, the densification rate was accelerated significantly and serious degradation of Si3N4 phase was avoided by restricting carbothermal reaction. At the same time, Al contained composites show excellent oxidation/corrosion resistance at 1350 °C and 50% H2O - 50% O2 water vapor environment than that of Al free samples. The Si3N4/SiC composites derived from Al contained PDCs overcomes the trade-off between abnormal grain growth and serious degradation of Si3N4 phase, which is a very tough problem for traditional PDC route (without Al) to fabricate Si3N4/SiC composites. For traditional PDC route, (I) if with traditional sintering additives, abnormal grain growth occurs, nano grains cannot be achieved; (II) if without traditional sintering additives, serious degradation of Si3N4 occurs, Si3N4 and SiC composite cannot be formed. Therefore, Al contained polymer-derived ceramics route opens a promising avenue to fabricate Si3N4/SiC nano-composites with fine grain size, uniform microstructure and excellent oxidation/corrosion resistance.

Polymer-derived ceramic (PDC) process is an attractive technique that has high ceramic yield. This versatile method allows for fabrication of porous carbon nanotube (CNT)/ silicon carbide (SiC) hybrid materials that is important high temperature structural applications. Although several forms of CNT assemblies have been used with the PDC approach, the fabricated CNT/ceramic nanocomposites were either one or two dimensional. Herein, we report, for the first time, the fabrication of a low density, three-dimensional (3D) and scalable CNT/SiC structure using PDC technique. It was synthesized by impregnating preceramic polysilazane (PSZ) into ultralow density, anisotropic, and highly aligned CNT foams, followed by thermosetting and pyrolysis processes. The ceramic phase conformally coated the CNTs. The X-ray diffraction (XRD) diffractogram confirmed the presence of β-SiC crystalline phase. The resulting hybrid foam inherited the morphology and form factor of the original CNT foam, and possessed mechanical robustness, improved electrical properties, and extraordinary thermal stability.

The SiCN(Fe)/Si3N4 composite ceramics containing C, β-SiC and α-Fe were designed by impregnating polysilazane followed by pyrolysis at 1–5 times with porous silicon nitride matrix. After the heat treatment, these new phases gradually formed and filled in the pores of the matrix to form a large whole. They bond together to facilitate the formation of conductive networks, which can improve the storage and transport capacity of the charge, thus improving the dielectric properties of the material. In this way, the highest dielectric and magnetic loss tangent values were achieved as 0.49 and 0.29 after third and fourth cycles, respectively. The electromagnetic wave can be absorbed ~80–90% in the range of 8–18 GHz with the thickness of 2 mm. The minimum reflectivity was −12.5 dB at 16 GHz with the thickness of 5 mm, showing >90% electromagnetic wave absorption at this frequency.

Porous SiCN(Ti) composite ceramics with good microwave absorbing performance were fabricated by pyrolysis of solid polysilazane modified by tetrabutyl titanate. The introduction of Ti not only acted as active filler to react with free carbon in the matrix to form TiC, but also played the role as catalyst to promote the formation of SiC nanowires. Finally, SiCN(Ti) composite ceramics formed a microstructure containing multi-nanophases and multi-nano heterogeneous interfaces when annealing temperature reached 1500 °C. The complex microstructure annealed at 1500 °C made composite ceramics have good matching impedance, as well as greatly increase the interfacial polarization loss and dipole polarization loss. As a result, the TiC/SiC/SiCN composite ceramics showed the excellent performance of electromagnetic wave absorption in X band. The minimum reflection loss (RL) of samples was − 17.1 dB at the thickness of 1.9 mm, and the maximum effective absorption bandwidth (EAB) of composite ceramics was 3.2 GHz when the thickness of sample was 2.1 mm, which exhibited a promising prospect as a structural and microwave absorbing integration material.

Electrostatic spinning precursor fibers with presence of polysilazane and nano-Fe2O3 were herein derived by a thermally-induced polymerization at 1100 °C to prepare Fe-doped SiCN composite fibers. The phases and microstructures were characterized and their influences on properties of permittivity, permeability and electromagnetic waves absorption properties were systematically investigated at 2–18 GHz. During thermal carbonization, the additions of γ-Fe2O3 nanoparticles were in-situ reduced and transformed into core-shell structured Fe@Si3N4 particles, which were homogenously distributed in SiCN composite fibers. The RLmin of SiCN–Fe0.5 composite fibers reached −22.68 dB at 14.4 GHz with the thickness of 1.5 mm and showed a broad effective absorption bandwidth range (RL

Polysilazane-based ceramic coatings have ever-increasing applications in critical and high-power engineering. This paper analyzes the effects of the substrate grain size, the curvature of the coati...

Manufacturing complexity and poor machinability hinder the preparation of complex-shaped ceramic composites. Three-dimensional printing can overcome this difficulty. Herein, we report a type of photocurable preceramic resin containing SiO2 nanoparticles (up to 20 wt% of polymer), which do not affect the photocurability of the preceramic resin, and a small amount of SiC nanofibres (1 wt%). We successfully printed precise green bodies with a complex shape by digital light processing and converted them into ceramic composites via pyrolysis at 1300 °C under a N2 atmosphere. The introduction of SiO2 and SiC into the ceramic composites led to reduced weight loss of the composites during pyrolysis and a decrease in their porosity and enhancement in their mechanical properties after pyrolysis. The properties of the printed samples pyrolysed at different ramping rates were compared, and the effects of the microstructure on the mechanical properties of the composites were investigated.

Thermal conductivity of boron nitride is extremely anisotropic. To solve this problem, aggregate boron nitride (A-BN) was fabricated using binder. However, it is easily broken by external forces and has poor wettability. In this study, a new substance that overcomes these issues was introduced. Its coating material was prepared through a hydrolysis and condensation reaction involving polysilazane (PSZ) and (3-glycidyloxypropyl)trimethoxysilane (GPTMS); The PSZ protected the shape of the A-BN and the GPTMS enhances its wettability. After solving these inherent problems of A-BN, the thermal conductivity was 7.014 W/m*K at a filler fraction of 50 vol%, which was 50 times higher than that of a neat epoxy composite.

A novel flame-retardant, polysilazane containing phosphorus (PPVSZ), was synthesised and used as flame-retardant to prepare glass fibre reinforced flame-retardant modified epoxy composites (GFRP-M)...

The laser pyrolysis of a ceramic coating system composed of an organosilazane (Durazane 1800) with monoclinic ZrO2 and glass particles as fillers was investigated. The samples were produced by spray coating on pre-treated stainless steel substrates and subsequently pyrolyzed by Nd:YV04 laser radiation (λ =1064 nm). The interaction of laser radiation with the polysilazane-based glass/ZrO2 coating system led to formation of semi-crystalline dense coatings with a thickness up to 20 μm in a short time. Laser pyrolyzed ceramic coatings were characterized and compared with furnace pyrolyzed coatings. The microstructure of the coatings was investigated by scanning electron microscopy (SEM). Additionally the corrosion resistance and mechanical properties, such as hardness, adhesive strength and the tribological behaviour have been investigated. Ceramic coatings generated by laser pyrolysis showing promising mechanical properties, a super-hydrophobic surface as well as a high corrosion resistance.

Dense polycrystalline cubic boron nitride (PcBN) composites were fabricated by high-pressure and high-temperature (HPHT) sintering using polysilazane (PSN) and Al as sintering additive. After high-energy ball milling, the cBN fine particles were uniformly coated with PSN by ultrasonic treatment. After thermocuring and pyrolysis, the cBN–SiCN particles were mixed with Al. The PcBN composites were prepared after sintering at 1450 °C for 10 min with a pressure of 5 GPa. The refining effect of high-energy ball milling on the cBN particles was studied by scanning electron microscopy (SEM) and laser particle size analyzer. The oxidation of the cBN particles after milling was investigated by nitrogen–oxygen analyzer. The phase composition and microstructure of the sintered PcBN composites were investigated by X-ray diffractometer (XRD) and SEM. The main phases of the sintered PcBN composites are cBN, AlN, SiC and Si3N4. The conversion of cBN to hBN was inhibited by the formation of AlN. The mechanical properties of the sintered PcBN composites were improved by the appearance of SiC and Si3N4. The density and mechanical properties of the PcBN composites both increased with the content of the cBN particles increasing. The sintered sample with 60 wt% cBN, 30 wt% PSN and 10 wt% Al showed the best results: density of 99.7%, Vickers’ hardness of (25.2 ± 0.8) GPa and flexural strength of (602 ± 15) MPa.

Continuous carbon fiber (Cf) reinforced silicon carbide (SiC) matrix composite (Cf/SiC) was processed through hot pressing (HP) using polycarbosilane (PCS) in matrix and polysilazane in interphase regions as polymer binders. HP experiments were conducted at 4 MPa, 1200 °C and 1 h; followed by PCS polymer impregnation and pyrolysis (PIP) at 1200 °C under vacuum. The BN/SiC-Si3N4 interphase formed on the Cf cloth during BN dispersed polysilazane polymer coating and pyrolysis. The influence of PCS quantity during HP experiments on Cf/SiC composites was studied. Results suggest that sintering of SiC matrix in Cf/SiC composite improves by increasing PCS content during HP; however, high PCS content increases the liquidity of SiC-PCS mixture to flow out of the composite structure. The Cf/SiC composites with relative density ranging from 79 to 83% and flexural strength from 67 to 138 MPa was achieved.

Flexible electronics have been recently paid much attention. A flexible substrate (Organic resin film) is indispensable component for flexible devices. Though PET film is low-cost organic film, low heat-resistance of PET film limits its application as a flexible device substrate. We have developed heat-resistant PET which does not deteriorate even at 190°C heat treatment for one hour. An excimer light was irradiated onto a polysi-lazane (PHPS: perhydropolysilane)-coated film to form a dense silicon-dioxide (SiO2) layer on a PET film, and the heat-resistance property of the formed film was examined. Changes of surface state and cross-sectional structure of the formed film due to heat treatment were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). Compared to normal PET, which is deteriorated and whitened by heat treatment of about 110°C - 120°C, the SiO2-coated PET film maintains transparency and does not deteriorate after heat treatment at 180°C - 190°C for one hour. This high heat resistance is due to a dense SiO2 film formed on the surface that prevents surface precipitation and crystallization of low-molecular-weight oligomers (which are the cause of thermal degradation of PET). It is expected that enhancing the heat resistance of PET—which has high versatility and low cost—to about 180°C to 190°C will allow SiO2-film-coated PET to be developed as a film substrate for flexible devices.

The conventional techniques for 3D printing ceramic parts are the ceramic powder laser sintering and lithography process that are usually costly in equipment and materials. A low-cost technique for robocasting ceramic has been developed via polysilazane preceramic precursor incorporated with nano γ-alumina powders to form a gel-like preceramic precursor with the aim to be used as the raw material for robocasting ceramic parts. The gel-like preceramic precursor is simply extruded for shaping by CAD design with the self-incorporated robocasting machine, and then pyrolyzed the shaped gel-like preceramic precursor at 700, 850 and 950 °C, respectively to transform from a polymeric composite to core-shell silicon oxycarbide ceramic composite that has been characterized by XRD representing an amorphous silicon oxycarbonitride structure coating on the surface of nano γ-alumina. The Vickers hardness of the core-shell silicon oxycarbide ceramic is about HV 266–300 that is two times higher than that of 7000 series aluminum alloy.

The effect of polysilazane on the densification and mechanical properties of SiC f /SiC composites was examined thoroughly. The polysilazane was infiltrated into the fiber area, followed by pyrolysis at 1450°C for 4 h in an argon atmosphere. Furthermore, the SiC fabrics contain the pyrolyzed polysilazane was infiltrated by β-SiC slurry and sintered at 1750°C for 2 h in an argon atmosphere. The density of SiC f /SiC composites with and without the addition of polysilazane was 2.65 and 3.05 g/cm 3 , respectively. The pores in the fiber area were observed for the SiC f /SiC composites with the addition of polysilazane. However, the fine-grained size in the matrix area was obtained by the addition of polysilazane. The average grain size of the SiC f /SiC composite with and without the addition of polysilazane was 253 and 740 nm, respectively. Indeed, the hardness of the matrix area for SiC f /SiC composites with the addition of polysilazane (31.6 ± 1.8 GPa) was higher compared to SiC f /SiC composites without polysilazane (27.4 ± 1.6 GPa).

A solution of polysilazane (Perhydropolysilazane) was applied to a heat resistant PET substrate, and then irradiated with excimer light at 150 °C to form a gas barrier film. This film primarily consisted of a thin layer of SiO2, and had very high gas barrier properties, with a water vapor transmission rate of 0.02 g/m2·day or less (40 °C/90% RH). This gas barrier film has good transparency, film adhesion, surface flatness, and flexibility, and since it has high heat resistance and good gas barrier performance, it is expected to have applications in films for flexible devices.

Polymer-derived in situ magnesium metal matrix composites (P-MMMCs) were fabricated by injecting a liquid or cross-linked polysilazane precursor into molten magnesium by a stir-casting method at two different melt temperatures of 700 and 800℃. Microstructural analysis reveals that the composites fabricated at 700℃ exhibit uni-modal grain size distribution having more or less columnar-shaped grain morphology. On the contrary, bi-modal grain size distribution with predominantly dendritic grain morphology occurs in the Mg matrix composites fabricated at 800℃. Such difference in grain morphology can be associated with variation in the availability of heterogeneous nucleation sites, and direction of heat flux during solidification. All of the fabricated composites were investigated for their solidification characteristics, microstructural evolution, micro/nano-hardness and compression properties. This article discusses the correlation between the processing parameters, microstructural evolution and mechanical properties of the as-cast in situ composites fabricated by liquid metallurgical route. Polymer-injection followed by in situ pyrolysis holds the potential of revolutionary processing technologies for producing castings of metal matrix nanocomposites, for example by bubbling the organic liquid with a carrier gas, e.g. nitrogen, into the molten metal by a Bessemer-like process.

Reinforcing basis of high-temperature composite materials conventionally consists of derivatives of multifilament fibers: fabrics, rods, plaited yarns, etc. Another example of an appropriate preform is a biomorphic preform (BP) obtained by pyrolysis of wood. On the one hand, organomorphic preforms (OP) are prepared based on filaments of organic precursors of carbon, silicon carbide, and carbonitride fibers – polyacrylonitrile, polycarbosilane, and polysilazane, respectively. On the other hand, nonoxidizing pyrolysis of densified bundles of such fibers is used as in the case of BP. Autohesion interaction occurring upon contact of compressed polymer filaments during the initial stage of pyrolysis inherits at compression kept up to OP transition into inorganic state. As a result, uniform dense (0.4–0.5 of ρfiber) strong preforms are formed with narrow and very small equivalent diameter of pores: from few to 30–40 µm. Reinforcement in preforms can be uni-, bi- or three-directional. Subsequent densification of OP by vapor or liquid phase methods allows obtaining organomorphic composites (OC) with improved properties, some of which (gas permeability, surface roughness, capability of making articles with thickness of no more than 0.3 mm) are unattainable for existing high-temperature structural composites.

The SiC nanotubes were synthesized on porous Si3N4 matrix by polysilazane immersion-pyrolysis. The β-SiC and free C contents increased with the increasing dipping times, which cause some clear vibration and loss peaks of the dielectric constant patterns emerged at around 12.9 GHz and 14.7 GHz in the samples of 20 wt% and 30 wt% benzoic acid, respectively. The reflectivity of the obtained ceramics were −7dB ∼ −10dB from the frequency of 8 GHz–18 GHz, which means that the amount of 80%–90% electromagnetic wave could be attenuated. The ceramics containing 40 wt% benzoic acid showed the high loss, low reflectivity and a wide absorbing band, indicating the high absorbing efficiency and good dielectric properties. Keywords: SiC, Si3N4, Dipping, Dielectric properties

Bulk Si2BC3N ceramics were reinforced with SiC coated multi-walled carbon nanotubes (MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the designed Si2BC3N ceramics were comparatively investigated. The results show that nano SiC coating can be formed on MWCNTs through pyrolyzing polysilazane, which improves the oxidation resistance of MWCNTs. A stronger chemical bonding is formed between the SiC coated MWCNTs and SiC particles, contributing to improved flexural strength (532.1 MPa) and fracture toughness (6.66 MPa·m1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si2BC3N ceramics maintains much higher residual strength (193.0 MPa) after thermal shock test at 1000 °C. The enhanced properties should be attributed to: (1) the breaking of MWCNTs and the debonding between MWCNTs and SiC interfaces, which leads to more energy dissipation; (2) the rough surfaces of SiC coated MWCNTs increase the adhesion strength during the “pull out” of MWCNTs.

Four unidirectional fiber reinforced SiCN ceramic matrix composites were manufactured by means of polymer infiltration and pyrolysis. Two carbon fibers (T800H and Granoc XN90) as well as two silicon carbide fibers (Tyranno ZMI and SA3) without fiber coating were chosen. As matrix precursor, a poly(methylvinyl)silazane was investigated and utilized. The composites with the SA3 and the XN90 fiber had the highest tensile strengths of 478 and 288 MPa, respectively. It is considered that these high modulus fibers with the low modulus SiCN matrix create weak matrix composites. After exposure to air (T = 1200 °C, 10 h), a significant decrease of the mechanical properties was found, caused by the burnout of carbon fibers and the oxidation through open pores stemming from the PIP process and SiCN/SiCN interfaces in case of the SiC fiber based composites.

We introduced a new organic compound to prepare extreme wetting surfaces, and determined that the wettability of the surfaces could be controlled by the curing temperature. Carbon nanotubes were dispersed in the polysilazane ethanol solution to obtain a stable suspension, and an extremely wet coating was prepared on the surface of the sample through impregnation. When cured at 400 °C, the coating was superhydrophobic, but when cured at 800 °C, the wettability was reversed and the coating exhibited superhydrophilicity. Additionally, in order to improve the mechanical abrasion resistance of extreme wetting surface, we design a novel preceramic, polytitanium-silazane, to control the pyrolytic product. Polytitanium-silazane was produced after polysilazane was modified with titanium and a TiN ceramic was obtained after polytitanium-silazane was pyrolyzed at 800 °C. Moreover, hydrophilicity was considerably enhanced than that before modification. Its contact angle was approximately 0°, and a 5-μL droplet of could be completely spread on the surface in 0.2 s.

Ceramic fibers are high-tech structural key components of ceramic matrix composites (CMCs), which are a very promising class of materials for applications in next-generation turbines, especially nonoxide ceramic fibers, usually produced by the polymer-derived ceramics (PDC) route, which possess the enhanced mechanical and thermostructural properties necessary to withstand the harsh conditions (temperature and atmosphere) imposed on CMCs. However, recycling composite materials, such as fiber-reinforced polymers and CMCs, is still a big challenge. Here, we present for the first time the processing of superparamagnetic iron-containing ceramic fibers, which, due to their magnetic properties, can be separated from the matrix material of a composite. The synthesis strategy of the novel functional ceramic fibers is based on a tailored reaction of polyorganosilazane with an iron complex, resulting in a suitable, meltable polymer. After melt-spinning and curing, subsequent pyrolysis leads to superparamagnetic ceramic fibers with a saturation magnetization of 1.54 emu g-1 because of in situ-formed iron silicide nanoparticles of an average size of 7.5 nm, homogeneously dispersed in an amorphous SiCNO matrix. Moreover, the ceramic fibers exhibit a tensile strength of 1.24 GPa and appropriate oxidation resistance. The developed versatile reaction strategy allows also for the incorporation of other elements to implement further functionalities for processing of multifunctional composites.

To improve the thermal conductivity of a composite material, the filler dispersion and the interfacial adhesion between the filler and the matrix are important factors. A number of methods for satisfying these criteria are presented herein. Thus, graphene oxide (GO) is incorporated to enhance the dispersion state of surface-modified boron nitride (BN) by increasing the viscosity of the epoxy matrix and by providing steric hindrance. Meanwhile, polysilazane (PSZ) coating and thermolysis were used to enhance the wettability by providing structural similarity between the coating material and the epoxy matrix. Due to these strategies, the thermal conductivity was improved by 253% compared to that of the neat epoxy at a filler fraction of 40 wt %.

Polysilazane (PSZ) curing has been introduced for 19nm NAND Flash to ensure void free Shallow Trench Isolation (STI) gap fill. PSZ film was converted into oxide mainly depending on temperature and water vapor. The high temperature PSZ curing would give rise to Si dislocation and PSZ crack. However, lowering curing temperature would lead to an insufficient conversion of PSZ film and even generate voids. As a result, wet oxidation was utilized between curing 1 and curing 2 to improve conversion rate of PSZ film. The TEM images showed good gap fill performance of PSZ curing by using low temperature/wet oxidation method.

Adding fillers to polysilazane (PSZ)-derived ceramic coating is one of the main methods used to reduce PSZ porosity. In this study, we designed a sinter visualization device for understanding the effect of fillers on coating porosity and observed pore evolution within the coating sintering process using different filler ratios. When there was no filler in the coating, gas evolution occurred at the initial sintering stage due to a PSZ pyrolysis reaction. In the final stage, numerous cracks appeared because of volume shrinkage. It was determined that such coatings cannot provide good protection. Although the cracks disappeared after adding glass powder, many bubbles appeared. After adding ZrO2, the bubbles in the coating significantly reduced. When the volume ratio of PSZ/glass powder/ZrO2 was 1:2:1, the coating porosity after sintering was the lowest. Based on our visualization experimental results, we concluded that the glass powder&rsquo, s healing effect and the ZrO2 skeleton effect were the main reasons for the reduced coating porosity. In addition, the sinter visualization device can be used to observe the surface morphology of other similar coatings during the sintering processes.

Organic solar cell and OLED display devices are very sensitive to moisture, which leading to a fast degradation by the exposure to moisture and oxygen in the air. Therefore, in order to enhance the stability of the devices, a barrier film having WVTR (Water Vapor Transmission Rate) of 10−4 to 10−6 g/m2/day is required. In order to prepare the barrier film with excellent moisture blocking characteristics, perhydro polysilazane (PHPS) is used, which is developed to prepare an insulating film for semiconductors. Also a catalyst is added to lower the curing temperature to 100 °C or less. The result shows that the polysilazane is cured and converted to SiO2 under 100 °C in 30 min. WVTR of the polysilazane coated film is estimated to be 2.1×10−2 g/m2/day. In addition, when the inorganic layer such as SiO2 and Al2O3 is deposited on the planarization layer, the film shows excellent moisture blocking characteristics having WVTR to be 7.9×10−5 g/m2/day.

The manufacturing of electrospun mats from preceramic polymers is complex due to low and disperse molecular chain entanglements and a large number of operating parameters. Here, the electrospinning of polysilazane and polysilazane/polyacrylonitrile (PAN) solutions was evaluated and optimized. The reduction in Berry's number from 94 to 22 indicated the positive effect of adding organic polymer on the polysilazane chains to obtain homogeneous fibers. A fractional factorial design was first implemented to screen out the three most significant factors affecting the fiber diameter. Then, a response surface model was developed using the Box-Behnken design to obtain a quantitative relationship between operating parameters and fiber diameter. Finally, the models were used to find the optimal conditions that yield the thinnest fiber. For polysilazane, the feed rate showed a positive effect, while for polysilazane/PAN an interaction between the feed rate and the tip-to-collector-distance was the most significant factor, with a positive effect. The verification of the models was accomplished through model validation. The addition of PAN to polysilazane reduced fiber diameter from 1.79 ± 0.26 μm to 0.57 ± 0.04 μm. The polysilazane/PAN pyrolyzed at 1000°C (SiCN_PAN) could shield more than 50% of electromagnetic energy from 100 MHz to 4.5 GHz. In addition to the presence of carbon-rich regions derived from PAN, thinner diameters caused an increase of interfaces between the voids and electrospun fibers, which intensified multi-reflection for dissipating electromagnetic energy. Owing to the optimized design, the SiCN_PAN fibers with satisfying electromagnetic shielding properties could meet advanced requirements of lightweight hybrid materials from aerospace to defense applications.

An air stable high temperature adhesive synthesized via the polymer-derived-ceramic route had received increased attention in the last two decades. To improve the thermal stability and adhesion strength of a polysilazane (PSNB) adhesive, TiB2 was added as active filler to join SiC ceramic discs. The thermal stability, phase composition and microstructure were investigated by using TGA, XRD, FT-IR, BSE and SEM measurements. Effects of the pyrolysis temperature and active filler TiB2 on the microstructure and adhesion strength have been investigated. After curing and heat-treating at 120 degrees C and 1000 degrees C in air for 2 h, respectively, the adhesion strength of the modified adhesive reached up to 10.07 MPa (3 times higher than that of pure PSNB) at room temperature, and, more importantly, retained a strength of 8.0 MPa at 800 degrees C in air. It should be noted that the formation of a glass comprised of SiO2-B2O3-TiO2 and the emergence of the hexagonal and granular TiB2 in the adhesive layer are mainly responsible for the enhanced high temperature strength.

Polycarbosilane (PCS)/polysilazane (PSZ) preceramic mixtures with weight ratios of 100/0, 75/25, 50/50, 25/75, and 0/100 were used as a filler for the joining of SiC f /SiC to obtain high purity SiC at the joining region. SiC f /SiC was fabricated by the electrophoretic infiltration of a SiC-based matrix phase into Tyranno SA3 SiC fabrics followed by hot-pressing at 1750 °C under 20 MPa for 2 h in an Ar atmosphere. Microstructural analysis confirmed a sound join without cracks after joining at 1750 °C for 2 h under a pressure of 10 MPa. SiC was the only phase remaining at the joint when PCS was used, while a small amount of Si 3 N 4 along with the main SiC were observed in the join using PSZ. The flexural strengths of the butt-joint SiC f /SiC were 120 and 137 MPa for the samples joined using a pure PCS and PSZ at 1750 °C, respectively, whereas those joined using the mixture fillers showed relatively lower strength.

The high temperature adhesives are required in most critical applications such as nuclear and aerospace technology. To obtain an adhesive with high temperature bond strength and low synthesis temperature, polysilazane (PSNB) was modified by PBSZ, PSO, nano-Al 2 O 3 additives. Effect of the SiO 2 to B 2 O 3 ratio and curing pressure on microstructure and high temperature bond strength has been investigated. After curing and heat-treating at comparatively lower temperatures, the bond strength of the modified adhesive reached up to 12.08 MPa, at room temperature, and, more significantly, retained the strength of 6.65 MPa at 1000 °C. The bond strength of modified adhesive is two-times higher than pure PSNB adhesive at elevated temperature. We demonstrate that optimum level of fluidity and applied pressure should be established in order to attain maximum bond strength. This paper open up avenues for further research in modifying existing adhesives for high temperature applications.

Herein, MXene (Ti3C2Tx)/silicone rubber (SR) composites with high thermal stability are prepared by incorporating MXene modified with chloroacetic acid and polysilazane in the SR matrix. Polysilazane is grafted onto MXene by a condensation reaction to weaken the interaction between MXene and SR. Polysilazane modified MXene (MP) chemically interacts with SR, which ensures the uniform dispersion of MXene in the SR matrix. Consequently, MP/SR composites have higher thermal stability than pure SR. Among, the MP/SR composites, the one with 0.3 wt% MP (denoted as MP-0.3/SR) exhibits significantly improved thermal stability. The initial decomposition temperature (T1) and the temperature at which 50% weight loss occurred (T2) of MP-0.3/SR increase by 15.5 and 120 °C, respectively, compared to those of SR. During the thermal degradation of the MP/SR composites, the crosslinking reaction is retarded; instead, the main chains of the SR undergo degradative rearrangement.

Polymer-derived ceramics (PDCs) are considered to be promising candidate materials for high-temperature sensor applications. Even though the PDCs have been studied for decades, the reliable PDC-based thin film sensors have not been produced, because ceramic films are too fragile to be handled without a substrate, but the huge shrinkage during polymer-to-ceramic conversion makes it difficult to fabricate PDC-based sensing elements on conventional substrates such as Al2O3. In this study, a thin polymer-derived ceramic double-layer thermistor was developed, using a layer with a lower resistivity as the sensing element and a layer with a higher resistivity as the substrate. The difficulty in PDC-based film sensing elements fabrication on a substrate was consequently resolved, because both the sensing elements and the substrate sustained a similar shrinkage during pyrolysis. The proposed double-layer thermistor was fabricated through step-growth photopolymerization and co-pyrolysis of two similar polymer precursors: commercially available polysilazane for the high-resistivity substrate and DVB-modified polysilazane for the low-resistivity sensing part. The DVB-modified polysilazane showed a similar shrinkage during pyrolysis, whereas the resistivity of the pyrolytic product was five orders of magnitude lower. The obtained thermistor exhibited a negative temperature coefficient in the temperature range from the room temperature to 650 °C, and the resistance of the thermistor decreased smoothly as the temperature increased. The resistance-to-voltage conversion was conducted with a voltage divider equipped with a fixed resistor and the output voltage was observed to increase smoothly along with temperature. The current sensor configuration based on PDCs was reported for the first time, and is much closer to applicable sensors.

Porosity-controllable SiCN ceramics were prepared using a simple partial crosslinking method, which is promising for preparing bulk polymer-derived ceramics with different dimensions. Continuous regulation from fully dense to high porosity within polymer-derived SiCN ceramics was realized via secondary crosslinking of partially crosslinked polysilazane (PSN). A fully dense SiCN ceramic was obtained by shaping the single partially crosslinked PSN (PC-PSN) followed by pyrolysis. PC-PSN was obtained by controlling the crosslinking reaction, and it retained a strong ability to cross link further. SiCN ceramics with different porosities were prepared by mixing PC-PSN and completely crosslinked PSN (CC-PSN) at different proportions. The size and density of the pores can be controlled via the proportion of CC-PSN in a mixed powder. The resultant SiCN ceramic has a porosity that ranges from 0% to 21.32%, which is validated to ensure the component integrity of SiCN ceramics with different dimensions due to the release of residual stress during pyrolysis.

Silicon nitride (Si3N4) has excellent thermo-mechanical properties, and can be used as heat dissipation substrate for various devices. Si3N4 thin films are generally synthesised by chemical vapour deposition (CVD) or plasma-enhanced CVD. The use of polysilazanes (PSZs) as a precursor to the synthesis of Si3N4 has attracted significant attention because of their high mouldability and processability. In this study, Si3N4 thick films were prepared on silicon wafers or aluminium substrates by a spin- or dip-coating liquid PSZ, followed by UV curing and IR heat treatment under various conditions. The effects of the heat treatment conditions on the Si3N4 thick film surface were analysed by optical microscopy, X-ray diffraction, and scanning electron microscopy. An almost single phase of Si3N4 was synthesised successfully on the single crystalline silicon with UV curing at 400°C for 30 min and IR heating at 800°C in N2 atmosphere.

The cross-linked polysilazane spherical particles were synthesized via a solvothermal process from a liquid polysilazane precursor. We found that the average size of obtained cross-linked polymer spheres is in the range of hundreds nanometer to about 10 μm by adjusting the amount of divinylbenzene cross-linker. Spherical ceramic particles were synthesized via the polymer-derived ceramics (PDCs) route. The XRD and SEM analysis on ceramic particles pyrolyzed below 1400°C showed that they were amorphous and maintained a smooth spherical morphology. When the polymer spherical particles were pyrolyzed at 1500°C, SiC/Si3N4 ceramics spheres were fabricated.

Micro-and mesoporous ceramics demonstrate promising properties for applications in energy-and environment-related fields. Due to their high thermal and chemical stability, they are particularly suited for separation in harsh thermal or chemical environments, e.g. as membrane materials for the separation of gas mixtures. In this work, we present the use of a preceramic poly(vinyl)silazane in combination with organic molecular porogens for the generation of micro-/mesoporous non-oxide ceramic structures. Microporosity is generated during the pyrolytic conversion process, while the addition of molecular porogens, to be removed during the heat-treatment, enables further control of the micro-/mesopore structure. A systematic investigation of various porogens showed the suitability of polystyrene for this purpose. Based on these findings, the pore structure and pore connectivity of polysilazane/polystyrene-derived structures were evaluated using gas physisorption and small angle X-ray scattering techniques. This material was further investigated by preparing asymmetric membranes consisting of micro-/mesoporous polysilazane/polystyrene-derived layers on porous ZrO2/TiO2 supports. The potential for gas separation applications was then demonstrated by single-gas permance evaluation of the generated structures at temperatures up to 300 °C.

In this paper, SiC ceramic coatings were prepared by laser pyrolysis of polysilazane (PSZ). XRD, SEM, and TEM were used to analyze the microstructure and morphology of the ceramics. It was confirmed that the main component of the coatings prepared by laser pyrolysis was SiC, of face-centered cubic structure. The pyrolysis of organic precursors at different laser power was analyzed by Fourier transform infrared spectroscopy. The elemental analysis of SiC was carried out with an energy dispersive spectrometer. The process of ceramic transformation was discussed, and the preparation of SiC ceramic coatings on the metal surface was achieved.

In order to enhance dielectric properties of polymer derived SiCN ceramics (PDCs-SiCN), nano-structured carbons were in-situ fabricated in PDCs-SiCN by pyrolysis of ferrocene-modified polysilazane. Microstructure evolutions, dielectric and microwave absorption properties of PDCs-SiCN decorated with nano-structured carbons were investigated. Nano-structured PDCs-SiCN ceramics are composed of carbon nanowires as well as interpenetrating graphene-like free carbons, SiC nano-crystals, Si3N4 nano-crystals and amorphous SiCN. Relative complex permittivities of nano-structured PDCs-SiCN increase with increasing ferrocene contents and annealing temperatures. Free carbons in PDCs-SiCN play a dominating role on the improved dielectric properties. Polarization loss is the primary dielectric loss. Loss tangent of PDCs-SiCN exceeding 0.7 is obtained when free carbons are only 2.57% in weight. Nano-structured PDCs-SiCN exhibit good microwave absorption property. The reflectivity is smaller than −14 dB in the whole X band when material is composed of both impedance and microwave absorption materials.

A thermally conductive composite was fabricated using a BN filler and an epoxy matrix. Because of electrostatic repulsion force, the BN/epoxy composite had poor interfacial affinity, which led to a decrease in the thermal conductivity. To enhance the interfacial affinity, pre-ceramic polysilazane (PSZ) was introduced onto the BN surface and it was sintered in various conditions. PSZ was converted to different structure depended on pyrolysis conditions. After the pyrolysis, the PSZ was converted into a SiOC ceramic in nitrogen atmosphere, and to SiO 2 and ash in air atmosphere. The thermal conductivity of the BN-PSZ/epoxy composite decreased as the pyrolysis temperature was increased because of the decomposition of polar functional groups. Pyrolysis at 300 °C in nitrogen atmosphere yielded the highest performance, resulting in an increase in the thermal conductivity to 3.521 W m −1 K −1 at 70 wt% of filler, which was a 1.35-fold increase compared with the raw BN/epoxy composite.

Multi-walled carbon nanotubes (MWNTs) were incorporated into precursor-derived ceramics made from a polysilazane. A ceramic nanocomposite reinforced with about 35 vol% of carbon nanotubes (CNTs) was fabricated by infiltrating CNT-preform with liquid-phased polymeric precursor followed by pyrolysis. The nanocomposite has a dense structure without micro-cracks. The results reveal that the nanocomposite has lower indentation hardness but higher fracture energy than non-reinforced ceramic from the microindentation tests results. The effect of the CNTs on the mechanical properties of the nanocomposite should be discussed accordingly.

In this study, thermally conductive composite was fabricated using hexagonal and spherically aggregated boron nitride filler based on epoxy and polyphenylene sulfide (PPS) matrixes. The spherically aggregated BN (A-BN) particles were shown the outstanding thermal conductivity compared hexagonal BN (H-BN) in the epoxy matrix. However, A-BN is very weak to external forces and broken during PPS based melt processing, causing it to lose the advantage of its particulate shape. Therefore, we adopted a particle coating method for the A-BN to enhance its durability, using pre-ceramic polysilazane (PSZ) in solution. With the PSZ coating of A-BN, the spherical particle shape was retained after melt mixing. Moreover, the interfacial affinity between BN and PPS was enhanced by secondary interactions between the polar functional groups comprising PSZ, thereby increasing the through-plane thermal conductivity from 1.82 to 3.9 W m−1 K−1 at 70 wt% of A-BN filler, because the spherical filler particles formed a three-dimensional heat flow path.

Composite ceramic fibers comprising about 80 wt% boron nitride (h-BN) and 20 wt% Si3N4 were fabricated through melt-spinning, electron-beam curing, and pyrolysis up to 1600 &deg, C in atmospheres of NH3 and N2, using a mixture of poly[tri(methylamino)borazine] (PBN) and polysilazane (PSZ). By analyzing the microstructure and composition of the pyrolyzed ceramic fibers, we found the formation of binary phases including crystalline h-BN and amorphous Si3N4. Further investigations confirmed that this heterogeneous microstructure can only be formed when the introduced ratio of Si3N4 is below 30% in mass. The mean modulus and tensile strength of the fabricated composite fibers were about 90 GPa and 1040 MPa, twice the average of the pure h-BN fiber. The dielectric constant and dielectric loss tangent of the composite fibers is 3.06 and 2.94 &times, 10&minus, 3.

Damage-tolerant ceramic matrix composites (CMC) are prone to high temperature applications under severe environmental conditions and usually utilize carbon or ceramic fibres (e.g. SiC) as reinforcements of ceramic matrices with inherent low elongation to break compared to common metals. However, CMC reveal an elongation to break and stiffness similar to the ceramic matrices, and thus need a fibre coating in order to improve the elongation to break length and thus to achieve damage tolerance of the composite. In addition, such fibers often expose a low ductility during failure. As a consequence, design criteria for components of such CMC materials are limited by the low strain of failure. In order to overcome this problem, we follow the idea of a reinforcement concept of a ceramic matrix reinforced by refractory metal fibres to reach pseudo ductile behaviour during failure. Tungsten (W) and molybdenum (Mo) fibers were chosen as reinforcement in SiCN CMC manufactured by polymer infiltration and pyrolysis process. These fibres are commercially available since they are widespread used in light bulbs, etc. , and possess an intrinsic higher elongation to break, compared to ceramic fibres, as well as high stiffness even at high temperatures. W/SiCN and Mo/SiCN composites were manufactured via filament winding and resin transfer moulding of commercially available polysilazanes, pyrolysed and re-densified by multiple reinfiltration and pyrolysis steps. These composites were investigated with respect to microstructure, flexural and tensile strength. Single fibre strengths for W and Mo were investigated and compared to the strength of the composites. Tensile strengths of 206 and 156 MPa as well as bending strengths of 427 and 312 MPa were achieved for W/SiCN and Mo/SiCN composites, respectively. W fibre became brittle across the entire cross section, while the Mo fibre showed a superficial, brittle reaction zone but kept ductile on the inside.