This feature article explores the concept of creating functionally graded metal‐ceramic composite microstructures for thermal barrier coatings used in gas‐turbine applications. From a thermomechanical perspective, this concept offers the possibility of significantly improving the life and reliability of thermal barrier coatings. However, prior research reveals that progress has been somewhat limited because of the oxidative instability exhibited by some metal‐ceramic composite microstructures. The present study addresses some of the materials criteria and research issues associated with preparing chemically stable, yet mechanically durable, graded metal‐ceramic microstructures for realistic application environments.
Osteocytes are deeply embedded in the mineralized matrix of bone and are nonproliferative, making them a challenge to isolate and maintain using traditional in vitro culture methods without sacrificing their inimitable phenotype. We studied the synergistic effects of two microenvironmental factors that are vital in retaining, ex vivo, the phenotype of primary human osteocytes: hypoxia and three-dimensional (3D) cellular network. To recapitulate the lacunocanalicular structure of bone tissue, we assembled and cultured primary human osteocytic cells with biphasic calcium phosphate microbeads in a microfluidic perfusion culture device. The 3D cellular network was constructed by the following: (1) the inhibited proliferation of cells entrapped by microbeads, biomimetically resembling lacunae, and (2) the connection of neighboring cells by dendrites through the mineralized, canaliculi-like interstitial spaces between the microbeads. We found that hypoxia synergistically and remarkably upregulated the mature osteocytic gene expressions of the 3D-networked cells, SOST (encoding sclerostin) and FGF23 (encoding fibroblast growth factor 23), by several orders of magnitude in comparison to those observed from two-dimensional and normoxic culture controls. Intriguingly, hypoxia facilitated the self-assembly of a nonproliferating, osteoblastic monolayer on the surface of the 3D-networked cells, replicating the osteoblastic endosteal cell layer found at the interface between native bone and bone marrow tissues. Our ability to replicate, with hypoxia, the strong expressions of these mature osteocytic markers, SOST and FGF23, is important since these (1) could not be significantly produced in vitro and (2) are new important targets for treating bone diseases. Our findings are therefore expected to facilitate ex vivo studies of human bone diseases using primary human bone cells and enable high-throughput evaluation of potential bone-targeting therapies with clinical relevance.
Pure nickel coupons were used as substrates in the deposition of alumina (Al 2 O 3 ) from the reaction of aluminum chloride (AlCl 3 ) with hydrogen/carbon dioxide gas mixtures in the temperature range of 954°–1100°C and system pressures of 2.7–13.3 kPa. The apparent activation energy estimated from the coating growth rate averaged 320 kJ/mol at 13.3 kPa. At temperatures <1000°C, transition theta, kappa, and delta modifications were codeposited with alpha‐Al 2 O 3 , whereas single‐phase alpha‐Al 2 O 3 was deposited at higher temperatures. At high AlCl 3 partial pressures, nickel aluminide phases were sometimes codeposited with Al 2 O 3 , which was attributed to the reaction of AlCl 3 with the nickel substrate in the presence of hydrogen gas.
Dispersed phase ceramic composite coatings containing BN and AIN were prepared by chemical vapor deposition. The BN + AIN coatings were deposited on Al 2 O 3 from the BCI 3 –AICI 3 ‐NH 3 reagent system in the temperature range of 700° to 1200°C. Also, single‐phase BN and AIN coatings were prepared for comparison purposes. The composite coatings consisted of very small BN and AIN regions which were either crystalline or amorphous, depending on deposition temperature and reagent concentrations. For example, a composite containing AlN whiskers of less than 100‐nm diameter in a matrix of turbostratic BN of 2‐nm grain size was deposited at 1100°C and 20 kPa.
The composition and microstructure of dispersed‐phase ceramic composites containing BN and AIN as well as BN and AIN single‐phase ceramics prepared by chemical vapor deposition have been characterized using X‐ray diffraction, scanning electron microscopy, electron microprobe, and transmission electron microscopy techniques. Under certain processing conditions, the codeposited coating microstructure consists of small single‐crystal AIN fibers (whiskers) surrounded by a turbostratic BN matrix. Other processing conditions resulted in single‐phase films of AIN with a fibrous structure. The compositions of the codeposits range from 2 to 50 mol% BN, 50 to 80 mol% AIN with 7% to 25% oxygen impurity as determined by electron microprobe analysis.
We present a case of a 56-year-old man with 3 synchronous gastric tumors.The patient presented with melena, and 3 gastric abnormalities were detected on gastroduodenoscopic examination, including a small ulcerative lesion in the gastric antrum, a submucosal mass in the gastric body, and severe erosion in the fundus.Histological examination of biopsy samples yielded respective diagnoses of gastric adenocarcinoma, gastritis, and mucosa-associated lymphoid tissue (MALT) lymphoma.The patient first received medication to eradicate any underlying Helicobacter pylori infection, which might have been a cause of the MALT lymphoma.Four weeks later, after examination of repeat biopsy samples revealed that the MALT lymphoma had resolved, the patient underwent subtotal gastrectomy.Further histological examination of resected tissue confirmed the antrum lesion as adenocarcinoma and the body lesion as schwannoma.To our knowledge, this is the first reported case of synchronous triple primary gastric adenocarcinoma, MALT lymphoma, and schwannoma.
A multilayer coating consisting of consecutive layers of amorphous‐silica, rutile‐titania, and amorphous‐silica was prepared on Hi‐Nicalon fiber by chemical vapor deposition at 1050°C. It appeared that the silica and titania layers were strongly bonded to each other with no evidence of detachment and crack deflection at the interface region. The layered structure became morphologically unstable because of the growth of titania grains, the crystallization of the silica layers, and the oxidation of the fiber on exposure to 1200°C in air for 92 h.
