Search

Direct deposition of hydroxyapatite (HA) coatings on carbon/carbon(C/C) composites through hydrothermal electrochemical deposition (HED) were limited by the poor bonding strength. To overcome this problem，in this work, CaHPO4 (monetite) coating was firstly deposited on C/C using HED, and then converted into HA coating in a sodium silicate–containing solution by post-hydrothermal treatment. Effects of post-treatment temperatures on the chemical composition, structure, and bonding strength of the coatings were investigated. The results showed that obtained monetite showed a compact microstructure, and could react with the solution to produce a well-crystallized HA as well as amorphous silicate which contained some calcium and sodium ions. All the coatings were composed of rod-like crystals. The diameter of these crystals increased when the post-hydrothermal temperature was changed from 110 ℃ to 140 ℃, and then decreased at 155 ℃. The Si contents and the adhesive strength of the HA coatings showed a similar temperature dependence to the crystal size of the HA. 140 ℃ is determined to the optimal treatment temperature, at which the HA coating reached the highest critical load of 24.02 N, corresponding to the shear strength of 82.83 MPa. The bioactivity of the HA coating on C/C increased with the increasing post-treatment temperature.

Electrocrystallized calcium phosphate (CP) coatings generally show a porous structure on carbon/carbon composites (C/Cs) and poor adhesive strength that limit their application in orthopedics. To overcome this disadvantage, ultrasonic and ice bath were employed in the electrocrystallization process of preparing CP/gelatin coating with a thickness of 50 μm on C/Cs. The CP/gelatin coating was hydrothermally treated in aqueous ammonia and sodium silicate solutions, respectively, to obtain an ion-doped hydroxyapatite(HA)/gelatin coating on C/Cs. Results showed that the modified electrocrystallized process could achieve a compactly stacked flaky structure coating of brushite and gelatin on C/Cs, whose adhesive strength could reach a critical load of 6.3 N. HA/gelatin coating that contains nanoneedle crystals could be achieved after performing the ammonia hydrothermal treatment, but its adhesive strength decreased to 4.1 N. Further hydrothermal treatment of the HA/gelatin coating in the sodium silicate solution obtained a Na, Si-doped HA coating on C/Cs, which could reach a critical load as high as 7.72 N. This value is equivalent to shear strength of 47 MPa. The ion-doping and hydrothermal self-repair processes enhanced the adhesion strength of the Si,Na-HA coating on C/Cs. In vitro experiments showed that the Si, Na-HA/gelatin coating exhibited better cell compatibility than C/Cs and HA/gelatin coating.

This study aims to evaluate the functions of the Mg–hydroxyapatite (Mg–HA) bio-coating on carbon/carbon composite (C/C) surface to promote the proliferation and osteogenic differentiation of bone mesenchymal stem cell (BMSCs). The Mg–HA-coated carbon/carbon composite was placed into a medium. The change of ion concentration in the solution and formation of bone-like apatite on the composite surface were observed. Thereafter, BMSCs of mice (mBMSCs) were cultivated on the coating surface for 4, 8, 24, 48, and 72 h. Finally, gene changes (i.e., Alp, OCN, Osx, and Runx2) related to cell proliferation and osteogenic differentiation were observed. The Mg–HA coating can form a bone-like apatite coating of high Mg concentration in the medium. After mBMSCs were cultivated on the Mg–HA coating for 72 h, mRNA of Alp, Osx, and Runx2 in Mg–HA was higher than that in the HA group (P 0.05). The Mg coating can significantly promote the proliferation and osteogenic differentiation of mBMSCs.

Monetite (CaHPO4) coatings were deposited on H2O2-treated carbon/carbon (C/C) composites by induction heating deposition (IHD) at electromagnetic frequencies ranging from 289 kHz to 438 kHz. The composition, microstructure and bonding strength of the monetite coatings on the C/C composites were investigated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and large load scratch tester (LLST). The effects of the electromagnetic frequencies on the deposition kinetics of the monetite coatings on the C/C were also analyzed. The results showed that when the electromagnetic heating frequencies were 289 kHz, 319 kHz and 381 kHz, the monetite coatings presented similar compact morphologies, and critical loads of 38 N, 64 N and 25 N. The deposition processes of these monetite coatings were controlled by a surface reaction and their apparent activation energies were 20.26, 22.17, and 31.07 kJ/mol at 289, 319 and 381 kHz. But at 438 kHz, it showed a loose morphology and could be very easily scratched off, presenting a critical load of 0 N. The changes in the microstructure and adhesiveness of the monetite coatings were discussed at the different electromagnetic frequencies.

The humeral heads of rabbits were replaced with individualized C/C composite implants coated with hydroxyapatite (HA) via rotation plasma spraying. The effect of the implants was evaluated after 5 and 150 days by using histology, scanning electron microscopy, X-ray diffraction, and so on. Results showed that the coating interface of C/C composites facilitated phosphorite deposition and osseous tissue growth. Furthermore, the humeral bone and remaining bone tissues were morphologically similar and possessed enhanced bonding strength. These results indicated that individualized C/C composite implants with HA coatings enabled the humeral head to adapt to dynamic requirements and accelerate healing after bone transplantation.

A new chemical liquid vaporization deposition (CLVD) is used on carbon–carbon (C/C) composites to prepare hydroxyapatite (HA) coating. The heating frequencies of the CLVD and induction heating method are 330 kHz and 30 kHz, respectively. The phases, morphologies, and compositions of these coatings are characterized using scanning electron microscopy, X-ray diffraction, and electronic data systems; the adhesion of the coatings to the C/C substrates was evaluated by a scratch test. The results demonstrate that the critical loads of HA coatings prepared through CLVD and induction are 47 N and 18 N, respectively. Although these coatings have no significant phase differences, the CLVD HA coating has abundant CO32−, which improves the adhesion, multiplication, and differentiation of external osteoblasts.

SiC/SiO 2 nanochains were prepared by a simple chemical vapor reaction method and characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy analyses. The visible-light photocatalytic activity of SiC/SiO 2 nanochains was investigated by the photocatalytic decomposition of Rhodamine B in the aqueous solution. The results show that the SiC/SiO 2 nanochain has equirotal beads of 650 nm and a uniform string with a diameter of 240 nm. The photo-response behavior of the SiC/SiO 2 nanochain can be expanded to visible-light region with a high absorbance. The photocatalytic activity of SiC/SiO 2 nanochains was found to be better compared to that of the SiO 2 -free SiC nanowires owing to the nanosized SiO 2 coating that can form activated hydroxyl groups and effectively separate the photogenerated electrons and holes.

SiC hollow spheres are obtained by a vapor–solid reaction using carbon spheres as templates. The prepared SiC hollow spheres are characterized by X-ray diffraction, scanning electron microscopy, nitrogen adsorption, and UV–vis diffuse reflectance spectra. The visible-light photocatalytic activity is evaluated by photocatalytic decomposition of the methylene blue in aqueous solution. Results show that the diameter of SiC hollow spheres ranges from 200 to 300 nm and the shell thickness is about 50 nm. The SiC hollow spheres have a high surface area of 83.5 m 2 /g and exhibit a mesoporous structure characteristic. The photo-response of the SiC hollow spheres expand to visible-light region with band gap energy of 2.15 eV. The SiC hollow spheres exhibit a significantly enhanced photocatalytic activity due to their high surface area as well as large light-harvesting efficiencies.

A novel strategy for the preparation of Si-doped hydroxyapatite (Si-HA) coatings on H2O2-treated carbon/carbon composites (C/C) was developed. HA coating was prepared on C/C through chemical liquid vaporization deposition (CLVD)/hydrothermal treatment. HA coating was immersed in an H2SiO3 solution at an autoclave at 413 K for transformation into Si-HA coating. The effects of H2SiO3 mass contents on the phase, morphology and composition of the Si-HA coatings were studied through SEM, EDS,XRD and FTIR. Their bonding performance to C/C was measured through a scratch test. Under the optimal content condition, the in vitro skull osteoblast response behaviors of the Si-HA coating were evaluated. Results showed that SiO32− could enter into the HA lattice and occupy the PO43− sites. Doped SiO32− significantly improved the bonding performance of the HA coating to C/C in comparison with the untreated HA. The adhesive strength of the coatings initially increased and then decreased with increasing H2SiO3 content. Meanwhile, the cohesive strength of the Si-HA coatings was almost nearly identical. The Si-HA coating achieved at a content of 90% H2SiO3 exhibited the best bonding performance and its osteoblast compatibility in vitro was superior to that of the untreated HA coating on C/C through CLVD/hydrothermal treatment.

a monetite coating on H 2 O 2 -treated C/C composites was prepared by ultrasonic induction heating (UIH) technology. Subsequently, this coating was subjected to an ammonia hydrothermal treatment to form a undoped hydroxyapatite (U-HA) coating. Finally, the as-prepared U-HA coating was placed in a NaOH solution and hydrothermally treated to produce the other hydroxyapatite (Na-HA) coating. The structure, morphology and chemical composition of the two HA coatings were characterized by XRD, FTIR, SEM and EDS, the adhesiveness and local mechanical properties, e.g. nanohardness and Young's modulus of the two HA coatings to C/C composites was evaluated by a scratch test and nanoindentation technique respectively. The results showed that the two HA coatings had the alike morphology and crystallization. But, compared with the U-HA coating, the Na-HA coating was doped with Na ions, and gave a Ca/P ratio close to a stoichiometric hydroxyapatite, and thus showed a higher nano-indentation value, Young's modulus, and larger bonding strength. These results verified the strengthened effect of Na ion in hydroxyapatite coating on carbon/carbon (C/C) composities.

Hydrothermal post-treatment was used to convert monetite coating fabricated by induction heating method on H2O2 treated C/C (HT-C/C) composites to an adherent HA coating. The monetite coatings were hydrothermally treated for 4 h at 373 K, 403 K, 423 K, and 453 K in a 50 mL autoclave. After hydrothermal post-treatment, the structure, morphology and the chemical composition of these HA coatings were characterized with XRD, FTIR SEM and EDS. A scratch test was conducted to measure the strength of the adhesion of the coatings to the HT-C/C substrate. The results showed that the degree of crystallinity and the Ca/P ratio of the HA coatings increased with increasing hydrothermal temperature. The submicron-level morphology and adhesion of the HA coatings were highly affected by the hydrothermal temperature. From the results, it can be suggested that 423 K was the best hydrothermal treatment temperature for the HA coatings which were transformed from the monetite coatings produced by the induction heating method on HT-C/C composites.

Monetite coatings on H 2 O 2 -treated carbon/carbon composites were prepared by induction heating deposition method and then converted to HA coatings by hydrothermal treatment in an autoclave with two different types of solutions, respectively NaOH aqueous solution and ammonia solution. The structure, morphology and chemical composition of the as-achieved HA coatings were characterized by XRD, FTIR SEM and EDS. The adhesion of HA coatings to the HT-C/C substrates was evaluated by a scratch test. The results showed that there are no obvious changes in the structure and morphology for the as-achieved HA coatings except to their compositions. The average critical load of the ammonia hydrothermally treated HA coatings is 10.9 N, while the NaOH hydrothermally treated HA coatings show the average one of 51 N, and the reason for it was suggested.

An adherent hydroxyapatite (HA) coating was applied onto H2O2-treated carbon/carbon composite (HT–C/C) substrate by induction heating and hydrothermal treatment techniques. Specimens of C/C were initially modified by immersed in an autoclave with 2 M H2O2 solution at 433 K, and then coated with monetite crystals by induction heating method. Subsequently, monetite coating on HT–C/C was converted to HA coating by hydrothermal treatment in an autoclave with the ammonia solution at pH of 10 at 433 K. The compositions, structures and morphologies of the coatings on HT–C/C were analyzed by EDS, SEM and XRD, and the adhesive strength of HA coating on HT–C/C was evaluated by a scratch test. The results showed that the coatings of monetite and HA display no significant changes in their morphologies before and after hydrothermal treatment. They have rectangular crystals stacking one another, and a strong adhesive interface has formed between the HA coating and HT–C/C substrate. The HA coating on HT–C/C was not scraped off until the applied load reached 13.12 N (i.e., shear stress of 61.4 MPa).

Y 2 BaCuO 5 nanocrystallites were prepared by a co-precipitation method with the aid of ultrasonic irradiation using Y 2 O 3 , CuCl 2 and BaCl 2 as source materials. The crystallization and morphologies of as-prepared nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results show that Y 2 BaCuO 5 monophase can be prepared at the calcining temperature up to 900 °C with NaOH and Na 2 CO 3 mixtures as precipitator. Particle size of Y 2 BaCuO 5 crystallites decreases with the increase of sonicating power. Around 30 nm Y 2 BaCuO 5 crystallites can be achieved when sonicating power is increased to 300 W.

Different compositions of yttrium silicates coatings were deposited on SiC-C/C by plasma spraying and an outer borosilicate glass was applied on the yttrium silicates coatings surfaces. The structure of the multi-layer coatings was characterized by XRD and SEM analyses. High temperature oxidation behavior of the multi-layer coatings coated C/C composites was investigated. Results show that SiC/2SiO2·Y2O3/1.5SiO2·Y2O3/ SiO2·Y2O3/glass multi-layer coating has better high temperature oxidation resistance, protecting carbon/ carbon composites from oxidation at 1 773 K in air for 164 h with the weight loss of 1.65%. The oxidation weight loss of the coated C/C with time accorded with parabolic rule in the temperature range 1 573 K–1 873 K; and the corresponding oxidation activation energy of the coated carbon/carbon composites is 132.2 kJ/mol.

A new type of oxidation-protective multi-composition coating for carbon/carbon (C/C) composites has been produced by a pack cementation technique in an argon atmosphere. XRD analyses shows that the phases of the composite coating are composed of Al 2 O 3 , mullite, SiC and Al 4 SiC 4 , and the bonding layer between the coating and C/C composites are composed of Al 4 C 3 , SiC and Al 4 SiC 4 . It is found by SEM surface observation and EDS area scanning analyses that the coating has two kinds of surfaces that are distinctly different in element content of Si and C. In the meantime, cross-section SEM observation of the coating also displays a dense microstructure. Oxidation test shows that the as-prepared coating characterized by excellent thermal shock resistance on the surface of C/C composites during exposure to an oxidizing atmosphere at 1773 K could effectively protect the C/C composites from oxidation for 41 h.

A SiC coating for carbon/carbon(C/C) composites was produced by a pack cementation technique in an argon atmosphere. The phase, microstructure and anti-oxidation property of the SiC coatings prepared from 1773 to 2273 K were investigated. It is found that the porous β-SiC coatings occur at 1773–1973 K while dense Si/β-SiC coatings generate at 2073 K and micro-cracked β-SiC/α-SiC coatings appear at 2173–2273 K. The thickness of the SiC coating increased with increasing temperature and oxidation tests at 1773 K in air showed that, based on observed weight changes, a preparation temperature of 2073–2273 K gave much improved oxidation resistance over that of coatings formed between 1773 and 1973 K.

In order to exploit the unique high temperature mechanical properties of carbon/carbon (C/C) composites, a new type of oxidation protective coating has been produced by a two-step pack cementation technique in an argon atmosphere. XRD analysis showed that the internal coating obtained from the first step was a gradient SiC layer that acts as a buffer layer, and the multi-layer coating formed in the second step was an Al2O3-mullite layer. It was found that the as-received coating characterized by excellent thermal shock resistance on the surface of C/C composites during exposure to an oxidizing atmosphere at 1873 K, could effectively protect the C/C composites from oxidation for 45 h. The failure of the coating is due to the formation of bubble holes on the coating surface.

Carbon/carbon composite with hydroxyapatite (HA) coating is an attractive material in the dental and orthopedic fields, but the reported bonding strength between them was very poor. In this study, a compact crystalline HA coating on (NH(4))(2)S(2)O(8)-treated C/C substrate about 10 microm in width was obtained by hydrothermal treatment and induction heating. The microstructure, composition and morphologies of the as-prepared coatings were identified by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. A strong shear strength averaging 74.2 MPa between C/C substrate and HA was achieved and adhesion failures were observed more frequently than cohesion failures. The coating adhesion measured using a scratch test was 23 N and the reasons for this are discussed.