Bioactive glass coating using aerosol deposition

This work demonstrates the successful deposition of bioactive glass (BG) 45S5 coatings on various metallic and ceramic substrates at room temperature under low vacuum condition by using aerosol deposition (AD). This room temperature and particle impact consolidation-based deposition method enabled us to deposit well-adhered and dense BG coatings directly on metallic and ceramic substrates. In vitro tests with human osteoblast-like cells on substrates with a 45S5 BG coating demonstrated high cell activity on the surfaces. All tested materials exhibited high in vitro biocompatibility as no inhibition in cell proliferation could be observed. The utilization of AD process for achieving non-crystalline BG coatings is promising for practical bio-medical applications, e.g., bioactive coatings on bioinert metallic and ceramic substrates.     

Diamond deposition using a novel microwave applicator

This paper describes a novel microwave applicator that has the potential to allow microwave deposition of diamond films inside a metallic cylinder with an internal diameter of more than 10 cm.The design consists of a coaxial antenna that passes perpendicularly through a rectangular waveguide and forms a plasma inside a vacuum chamber. A quartz envelope around the antenna feeds reactant gases along its axis to the antenna opening. Here, the microwave field (2.45 GHz) is generated in the reactant gasses, and a plasma jet is formed. The antenna and quartz housing are so arranged that the plasma jet emerges perpendicular to the antenna axis. This allows the jet to be directed towards the internal surface of a cylinder with diameter >50 mm.Diamond films have growth rates of up to 0.2–1 μm/h and exhibit a sharp Raman peak at 1332 cm⁻¹. Film growth is examined under a range of conditions including applicator–substrate distance, microwave power, surface temperature and chamber pressure.     

Fabrication of porous thick films using room-temperature aerosol deposition

A novel technique for the rapid room-temperature deposition of porous ceramic, glass, or metal thick films using the aerosol deposition (AD) method is presented. The process is based on the co-deposition of the desired film material and a second water-soluble constituent, resulting in a ceramic-ceramic composite. Following the subsequent removal of water-soluble end member, a network of pores is retained. To demonstrate the process, porous BaTiO₃ thick films were fabricated through co-deposition with NaCl. Microstructural images show the clear development of a porous structure, which was found to enhance the dielectric properties over dense thick films, possibly related to the lower extent of internal residual stress. This simple but highly effective porous structure fabrication can be applied to any film and substrate material stable in water and is promising for the application of AD-processed films in gas sensors, solid oxide fuel cells, and humidity sensors.     

Determining the local pressure during aerosol deposition using glass memory

Aerosol deposition (AD) is a dynamic loading process that can be envisioned as a shock wave loading, necessitating the consideration of the elastic/plastic response of solid materials. Due to the dynamic nature of this process, however, experimental determination of the local pressures during the deposition process is difficult. This work addresses this by investigating the compression and subsequent structure modification of a silicate glass after room-temperature AD on a silicate glass substrate with Raman spectroscopy. Clear structural changes in the short- and middle-range order of the silicate glass were observed, both as intertetrahedral angle distribution and as ring statistic. Therefore, the AD induced permanent densification of the glass, equivalent, in a hydrostatic approximation, to a minimal pressure of 10.5 ± 1.5 GPa during the film deposition process. Furthermore, the analysis of the Nd³⁺ photoluminescence of the ⁴F_3/2 − ⁴I_9/2 transition provided complementary information on the glass network modifications occurring during film formation. More than a pure hydrostatic densification, the AD seems to present a very intense shear deformation. This work opens up the perspective of evaluating the mechanical response of film-substrate and of the particles themselves, and provides critical information on the mechanisms responsible for the AD film formation.     

Reflection intensity measurement using non-contact microwave probe and in-plane mappings for dielectric device

The reflection intensity measurement using non-contact microwave probe was carried out for multi-layer ceramic capacitor. The spatial resolution of non-contact microwave probe was improved the basis of Kirchhoff's diffraction formula with decreasing diameters of the coaxial cable and probe. Using Reflection intensity mappings, the dielectric permittivity distribution in micro-region at 9.4 GHz was measured for the cross-section of a multi-layer ceramic capacitor at room temperature. The spatial resolution was experimentally estimated to be about 10 μm from mappings of the dielectric and inner electrode layers in the multi-layer ceramic capacitor.     

Laser densification of alumina powder beds generated using aerosol assisted spray deposition

Layered manufacturing involves a range of techniques in which objects can be constructed in a laminated form. Therefore, the deposition technique is a critical part of direct-layered fabrication technologies. In this paper, aerosol assisted spray deposition has been applied to generate spraying of a suspension to prepare powder beds for subsequent selective laser sintering. First, an investigation on preparation of the alumina suspension by adding polyacrylic acid dispersant is presented. An emphasis has been given to identify the most effective dispersant to enhance the dispersibility of alumina suspension for aerosol spraying deposition. Subsequently, a laser has been used to selectively densify the alumina powder beds to produce ceramics. The effects of the laser processing parameters such as scanning speed, power and beam size on the microstructural evolution of the powder beds are investigated and discussed. Also, a laser densification mechanism is also proposed and discussed.     

Revealing the effects of aerosol deposition on the substrate-film interface using NaCl coating

Aerosol deposition is a feasible method of fabricating dense ceramic films at room temperature by the impact consolidation of submicron-sized particles on ceramic, metal, glass, and polymer substrates at a rapid rate. Despite the potential usefulness of the aerosol deposition process, there are issues, such as deposition mechanisms and structure of the film-substrate interface, that are not well understood. We have used complementary structural and microstructural analysis to capture the state of the substrate surface after the aerosol deposition process. The results reveal that modification of the substrate surface by the ejected submicron-sized particles is essential for the formation of anchoring layer, thereby, a change in internal residual stress state and surface free energy of the substrate is required to deposit film using AD process. Our analysis also suggests that the adhesion between the metal substrate and ceramic particles is possibly contributed by both physical bonding and mechanical interlocking.     

A consideration of ternary C-H-O diagram for diamond deposition using microwave in-liquid and gas phase plasma

The purpose of this study is to clarify the mechanism of diamond synthesis using an in-liquid plasma chemical vapor deposition (CVD) method. We investigated the chemical reactions from a liquid mixture of methanol and ethanol (in-liquid plasma CVD) and a gas mixture of methane and hydrogen (gas-phase CVD). Carbon monoxide (CO) is firstly synthesized and then a chemical reaction using the remaining carbon (C) and hydrogen (H) is induced to synthesize a carbon substance. Residual H radicals act as an etchant removing the incompletely binding carbon atom that hinders diamond crystal growth. From spectroscopic measurements, CO peaks were clearly observed when the oxygen component is contained in the raw materials. From the experimental results of carbon deposits using various liquid and gas mixtures as the raw materials, we found that the region of the remaining H and C after CO synthesis satisfying H/C > 20 is necessary to synthesize diamonds using in-liquid plasma CVD method. The region of H/C > 20 in the Bachmann C-H-O diagram nearly agrees with the experimental results of synthesizing diamonds.     

Preparation of superconducting Y-Ba-Cu-O films by aerosol assisted chemical vapor deposition using liquid solution sources

Superconducting Y-Ba-Cu-O thin films were prepared on MgO(100) substrate by aerosol-assisted chemical vapor deposition (AACVD). The process used a single solution source of Y, Ba and Cu Β-diketonates dissolved in tetrahydrofuran (THF). This liquid precursor was passed through an ultrasonic aerosol generator and transported into a CVD reactor where solvent and precursor evaporation and deposition occurred on heated substrate. Experimental details of this process were described and the effects of preheating temperature were studied in order to improve the quality of the deposited films. When the preheating temperature was 380 ‡C, films deposited at 815 ‡C had sharp transitions to the superconducting state about 88 K. The best superconducting films deposited by AACVD were prepared in oxygen partial pressure of 3.2 Torr at a deposition temperature of 815 ‡C.     

Mechanisms of aerosol deposition in a nasal model

Total and regional aerosol deposition were investigated in a model of a normal human nasal airway. Contributions of fluid turbulence and particle inertia were evaluated using monodisperse aerosols. At fixed turbulent flow conditions, deposition percentage increased with particle size greater than 1 μm, suggesting that turbulent inertial deposition is a primary mechanism.

With same size aerosol, deposition increased with increasing fluid turbulence but its contribution was less with larger size aerosol. Turbulent diffusion was the dominant transport mechanism for particles less than 1 μm, where deposition decreased with particle size. Two major deposition sites were visualized with radio-aerosol in the anterior region of the nasal airway. One is close to the ostium internum where turbulent eddies are well developed, and the other is the anterior region of the middle turbinate where direction of airflow changes from upward to horizontal.     

Exact analysis of aerosol deposition during steady breathing

Using a trumpet lung model, a transport equation is derived for an aerosol breathed into and out of the human airways. The partial differential equation is solved exactly using the method of characteristics. From this solution, the deposition of particles along the airways is obtained for steady breathing with and without pause. The total and regional depositions for particle sizes ranging from 0.01 μm to 10 μm aerodynamic diameter are calculated for Weibel's lung model, and they compare satisfactorily with the existing experimental data. The effects of the rest lung volume and breathing pattern on the total and regional depositions are also determined in order to explain the observed intersubject variability. Comparison between the present results with that recommended by the Task Group on Lung Dynamics shows that the present pulmonary deposition is considerably lower. while the tracheobronchial deposition differs only slightly.     

Silver doped lanthanum chromites by microwave combustion method

Considering the advantages of microwave combustion technique with the possibility of utilizing cheap precursors, short reaction time and nanocrystalline products, the present work reports the synthesis of silver doped lanthanum chromites. Structural and physicochemical properties were investigated with the help of various characterization techniques. The FTIR spectrum reveals the characteristic metal oxygen bands for Cr-O stretching at 604 cm⁻¹, O-Cr-O bending mode at 419 cm⁻¹ and Ag-O bands at 561 cm⁻¹ and 443 cm⁻¹. The powder X-ray diffraction patterns exhibit the formation of hexagonal structure with the dopant peaks at 2θ values of 38.3°, 44.1° and 64.4° apart from the peaks corresponding to lanthanum chromite. TGA analysis of the samples shows stable behavior of the product. Nanosized particles with size as small as ∼7-8 nm and larger ones ∼20-26 nm are observed from transmission electron micrographs. Room temperature magnetic study exhibits hysteresis loop formation during magnetization of samples.     

A new theory of aerosol deposition from turbulent fluids

The author's previously published theory[2] of mass (or heat) transfer to very rough surfaces predicts a power dependence on Sc of ?$\text{1}\text{2}$ (compared with ?$\text{2}\text{3}$ for smooth surfaces). This expected change of $\text{1}\text{6}$ in the power has previously proved difficult to test precisely, but it is shown here that available data on the deposition of small aerosol particles (Sc ～ 10⁶) confirm that the deposition is indeed 10 times faster on very rough surfaces.For larger aerosol particles, however, deposition rates depend strongly on roughness characteristics, as expected from the author's interception and impaction theory[13]. This assumes an x-directional deposition on to the roughness elements, the latter being very important to the process. Comparison of published data with the new theory, and with typical surface roughnesses, supports the proposed theory (eqn 4).     

High-voltage all-solid-state lithium metal batteries prepared by aerosol deposition

High-energy-density and safe rechargeable batteries are key components to realizing a low-carbon society. All-solid-state Li-metal batteries have the potential to achieve both high safety and high energy densities. However, the large interfacial resistance between solid electrolytes and cathodes is the major challenge for developing all-solid-state Li-metal batteries. Here we deposited a Li-rich layered metal oxide Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNC) thin film (6 µm thick) on an Al-doped Li₇La₃Zr₂O₁₂ (LLZO) substrate at room temperature by aerosol deposition. The LMNC particles were coated with Li₃BO₃ (LBO), which acted as a binder to hold LMNC and LLZO together at heating. As a result, good interfacial contact was achieved between LMNC and LLZO. Yet reactions between LMNC and LBO would occur at heat treatment temperatures above 600 °C. The highest discharge capacity of the all-solid-state Li/LLZO/LBO-LMNC cell at 0.1 C and 60 °C was 223 mAh g^-1. The main reason for the cell capacity decay was the cracking of the LBO-LMNC cathode layer during cycling. Searching for a more suitable binder material with a high fracture toughness is crucial for further developing the aerosol-deposited LLZO-based all-solid-state Li metal batteries.     

Fragmentation and film growth in supersonic nanoaggregate aerosol deposition

Aerosol deposition with gas phase-synthesized chain-like nanoaggregates can yield dense coatings from the impaction of particles on a substrate; however, dense coating formation is not well understood. Here, we study coating consolidation at the single nanoaggregate level. Flame spray pyrolysis-made tin oxide nanoaggregates are mobility (size) filtered, accelerated through a de Laval nozzle, and impacted on alumina substrates. TEM images obtained from low velocity collection and supersonic deposition are compared via quantitative image analysis, which reveals that upon supersonic impact nanoaggregates fragment into smaller aggregates. This suggests that fragmentation is a key step in producing coatings denser than the depositing nanoaggregates themselves. We supplement experiments with detailed particle trajectory calculations, which show that the impact energies per atom during nanoaggregate deposition are below 0.2 eV/molecule. These results suggest that fragmentation can only occur at locations where nanoaggregates bonded by van der Waals and capillary interactions.