Aqueous Film-Coating Vaporization Efficiency

Abstract

A steady-state condition is achieved during most of an aqueous film-coating cycle, i.e., the rate of application of moisture to the tablet bed is equal to its rate of evaporation. A mathematical model was developed for the steady-state condition to describe the efficiency of evaporation of the aqueous solvent for any set of drying conditions (inlet air flow rate, temperature, and humidity) and spray rate of coating suspension. The model was tested utilizing a series of different coating conditions and coating compositions. A vaporization efficiency, E_s, was defined as a means to assess a reproducible coating end point. E_s values for each coating formula fell within a narrow range. The hydroxypropyl cellulose coating system had a significantly lower E_s value due to the higher tackiness that occurs with this polymer during film formation.     

The electrical properties of CuInSe2 thin films deposited onto CaF2 substrates

CuInSe₂ thin films were deposited onto (111)-oriented CaF₂ substrates by flash evaporation in the substrate temperature range T_s = 650–890 K. Epitaxial growth was found at T_s = 770–800 K; at lower and higher substrate temperatures the films were partly polycrystalline. Films produced at T_s ? 675 K showed n-type conductivity due to a donor with an ionization energy of 78 ± 5 meV ascribed to indium interstitials. At T_s ? 725 K the films exhibited p-type conductivity due to a shallow acceptor with an ionization energy characteristic of indium vacancies. The important role of the substrate material in establishing the electrical parameters of CuInSe₂ thin films is proved by a comparative study of thin films deposited onto GaAs and CaF₂ substrates.     

响应曲面法优化超音速等离子喷涂Al2O3-40%TiO2涂层工艺

为获得低孔隙率的Al2O3-40%TiO2(AT40)涂层,采用响应曲面法(RSM)优化超音速等离子喷涂AT40涂层的工艺参数,利用Box-Behnken(BBD)设计分析送粉量、喷涂功率、氩气流量、氢气流量4个主要因素对涂层截面孔隙率的影响规律,利用Design Expert软件设计试验方案,统计分析试验数据,并得到二次多元回归模型.研究表明,在本试验条件下,4种因素对孔隙率影响顺序依次为氩气流量氢气流量喷涂功率送粉量,最优工艺参数为送粉量30 g/min,喷涂功率51.4 kW,氩气流量3.0 m3/h,氢气流量0.45 m3/h,试验测得此时涂层孔隙率为2.74%.     

IR‐Driven Ultrafast Transfer of Plasmonic Hot Electrons in Nonmetallic Branched Heterostructures for Enhanced H2 Generation

The ultrafast transfer of plasmon‐induced hot electrons is considered an effective kinetics process to enhance the photoconversion efficiencies of semiconductors through strong localized surface plasmon resonance (LSPR) of plasmonic nanostructures. Although this classical sensitization approach is widely used in noble‐metal–semiconductor systems, it remains unclear in nonmetallic plasmonic heterostructures. Here, by combining ultrafast transient absorption spectroscopy with theoretical simulations, IR‐driven transfer of plasmon‐induced hot electron in a nonmetallic branched heterostructure is demonstrated, which is fabricated through solvothermal growth of plasmonic W₁₈O₄₉ nanowires (as branches) onto TiO₂ electrospun nanofibers (as backbones). The ultrafast transfer of hot electron from the W₁₈O₄₉ branches to the TiO₂ backbones occurs within a timeframe on the order of 200 fs with very large rate constants ranging from 3.8 × 10¹² to 5.5 × 10¹² s^?1. Upon LSPR excitation by low‐energy IR photons, the W₁₈O₄₉/TiO₂ branched heterostructure exhibits obviously enhanced catalytic H₂ generation from ammonia borane compared with that of W₁₈O₄₉ nanowires. Further investigations by finely controlling experimental conditions unambiguously confirm that this plasmon‐enhanced catalytic activity arises from the transfer of hot electron rather than from the photothermal effect.     

Optimization of Dielectric Properties of Suspension Plasma Sprayed Hydroxyapatite Coatings

Conventional plasma torch was adapted to spray very fine Ca₅ (PO₄)₃OH (hydroxyapatite, HA) precursors having sizes ranging from a few hundreds of nanometers to a few micrometers. The powders were put in suspension with distilled water and antidispersive agent. A home made suspension feeder, including two peristaltic pumps, delivered the suspension into atomizer and therefrom injected into plasma jet. The suspension flow rate was electronically controlled. The resulting coatings had the thickness of a few tenths of μm. The electrical properties of the coatings including breakdown voltage and loss factor of suspension sprayed hydroxyapatite coatings sprayed onto aluminium substrates were also tested. The influence of such experimental factors as power input to plasma, pressure of atomizing gas, spray distance and suspension feed rate on the responses being the electrical properties was investigated using a 2⁴ design of experiments (DOE). The mathematical models relating the responses with the factors were created and the significant factors were selected.     

Decarburization mechanisms of WC–Co during thermal spraying: Insights from controlled carbon loss and microstructure characterization

Decarburization behavior of WC–Co particles in terms of transformation of WC to W₂C and W, and formation of η and γ phases and microstructure evolution during plasma spraying have been systematically investigated in this study. The extent of the carbon loss of WC was tailored by either altering cooling conditions of substrate/pre-coating or spraying the particles into the media with different temperatures. It is revealed that loss of carbon of WC was alleviated by protection of Co during the coating formation stage. W₂C exhibits epitaxial growth on the WC substrates in perpendicular direction and forms a nearly complete shell around the WC particles. η phase was formed as a result of decarburization and diffusion of associated phases and is located around WC–Co splats with its crystals being in cross shape. The γ phase in rod-like shape with a size of 10–20 nm embeds within the binder Co and is clearly well separated from WC grains. Further decarburization-induced W was detected mainly in Co binder, being apart entirely from WC grains. The main advantage of Co for preventing decarburization in WC–Co particles is not associated with oxidation, but instead the diffusion-controlled carbon loss. These findings would facilitate fabrication of the WC-based cermet coatings with excellent mechanical properties in particular wear resistance for extreme wear applications.     

Phase growth competition in solid/liquid reactions between copper or Cu3Sn compound and liquid tin-based solder

Interfacial reaction between solid ?-Cu₃Sn compound and liquid Sn at 250 °C is studied for the first time. The reaction product formed at the ?-Cu₃Sn/liquid Sn interface consists of the single η-Cu₆Sn₅ phase. The growth kinetics of the η phase formed at the incremental ?/liquid Sn couple (?/η/Sn configuration) is compared to that of η phase formed at the classical Cu/liquid Sn couple (Cu/?/η/Sn configuration). The experimental method consists first in processing of intimate interfaces by dipping peaces of solid ?-Cu₃Sn compound and Cu in liquid Sn for 1 s at 250 °C. Afterwards, isothermal holding of such pre-performed couples for 10, 30, 120 and 480 min at 250 °C are performed for both couples. A theoretical analysis of the growth kinetics of η phase and comparison of its growth in both configurations are performed.     

Integral transform “infixing” method for nonlinear transient mass-transfer problems

An approximate method is proposed for solving nonlinear problems of transient mass transfer between a wall and a motionless fluid for an arbitrary concentration dependence of the diffusion coefficient. Nonlinear problems compounded with a volume or surface chemical reaction are investigated.Notation a linear space scale - C concentration - C_s surface concentration on wall - C₀ concentration at initial time - c dimensionless concentration - D diffusion coefficient D=D(C) - j dimensionless diffusion flux onto wall - K_s rate constant of surface chemical reaction - K_v rate constant of volume chemical reaction - t time - X distance from wall Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 4, pp. 638–643, October, 1988.     

Growth kinetics in particle coating by top-spray fluidized bed systems

The kinetics of growth for the coating of particles in top- spraying fluidized bed systems is reported. The results indicated that only a small amount of particles that visited the spraying region are coated at a time. It was also revealed that different particle sizes are not equally coated during the process. In a polydispersed particle distribution, smaller particles were found to receive more coating than their larger counterparts. This preferential coating, which was associated with a rapid decrease in the distribution variance, is more pronounced in the earlier parts of the process. When a narrower seed distribution was used, the preferential coating was reduced. A segregation factor, f_s, was introduced in the development of a growth kinetics model to represent the chance of each particle size visiting the coating region. The result for the distribution from the model clearly resembled the results obtained experimentally. For the top-spraying process, the segregation factor was found to be an exponentially decaying function of particle weight. For lactose particles coated with hydroxypropyl methyl cellulose, two different rates of growth were observed during the coating process.     

Low temperature aluminisation of alloy steels by pack cementation process

Abstract

The pack aluminisation process is normally applied at temperatures >973 K at which the mechanical properties of alloy steels would degrade. Thus, the present study was undertaken to apply this process to aluminising the alloy steels at temperatures <973 K in order to increase their high temperature oxidation resistance while maintaining their microstructure and hence mechanical strength and creep resistance. A type of commercial alloy steel P92 (9Cr–1Mo) was used for the present study. Pack powder mixtures consisting of Al, AlCl₃ (anhydrous) or NH₄Cl and Al₂O₃ were used to carry out the process. The aluminising temperature was varied from 773 to 973 K, pack Al content from 1 to 30 wt-% and aluminising time from 1 to 16 h to investigate their effects on the coating growth kinetics in the AlCl₃ activated packs. It was observed that all the coatings formed in the AlCl₃ activated packs were of a single layer structure with Fe₂Al₅ as the main coating phase. It was established that the interrelationship between the thickness h (in μm) of this coating layer and aluminising temperature T (in K), time t (in h) and pack Al content W (in wt-%) can be described by h=83005·9W^1/2t^1/2e^?73330/(RT). In the NH₄Cl activated packs, it was found that coating formation and dissolution took place simultaneously at 923 K and stable growth of a coating layer was only possible when the pack Al content was sufficiently high. However, the coatings formed in these packs had highly uneven regions.     

Synthesis process and hydrodynamic behavior of a new filtration material for passive wastewater dephosphatation

The preparation optimization of a filter material intended to be used as a phosphate sorbent in flow-through conditions is investigated. The mixing of ferrihydrite (Fh) and pozzolana (Pz) using a “dry contact method” is found to be the most efficient and leads to the formation of a micrometric thick Fh coating deposited into the honeycombed structure of Pz. The maximal Fh content of ~ 8.5 wt.% is significantly higher than the quantity deposited on other classical substrates such as sand. The phosphate sorption kinetics and isotherms, under dynamic conditions in batch experiments, are best described by pseudo-second-order and Freundlich models respectively. Moreover, under static conditions, sorption kinetics reveals intra-aggregate diffusion process. Phosphate ion retention in packed columns, and especially the breakthrough point, can be adequately predicted when coupling the classical convection dispersion equation and the surface complexation model. Breakthrough curves of phosphate ions are strongly dependent on flow rate; which is important for future industrial applications. Finally, and unexpectedly, a high value of phosphate adsorption capacity (80 mg PO₄ g^− 1) is observed when phosphate-containing wastewater is used as feed solution. This is mostly explained by soluble calcium ions, which favors the phosphate fixation onto the filter material surface.     

Complex carbide powders for plasma spraying

Various carbide-containing powders are used for plasma spraying. Most of these consist of tungsten carbide. Very frequently the tungsten carbide is mixed with cobalt to produce coatings similar to cemented carbides. The powders can be made by agglomeration of the carbides and the metal matrix powders or by coating the carbides with the matrix metal. As in cemented carbides, cobalt and nickel form the metal binder of the coatings. The coating metals can be increased to 20% of the total weight. Further metal matrix powders can be added also. The W₂C, WC, W₂C-WC eutectic phases and mixtures of them are used as tungsten carbide. The carbon content is very important and can be controlled better in coated particles than in an agglomerated powder. In the case of WCCo the carbon content has to correspond to MC to avoid the embrittling η phase and to achieve a strength of the coating comparable with that of cemented carbides. In addition to the composition, shape and grain size distribution of the powders, the spraying conditions are very important for the properties of the coating. Coated carbide powders are less sensitive to spraying conditions. When it is possible to control the carbon content in carbides better during spraying it will be feasible to use complex carbides also.Titanium carbide forms a solid solution with WC over a wide range of composition and forms mixed crystals with tantalum carbide and niobium carbide. These binary and ternary mixed carbide crystals, sometimes containing additional tungsten carbide, are used in cemented carbides to increase the wear resistance. By spraying these cobalt- or nickel-coated complex carbide powders similar properties of the coatings can be achieved. Spraying conditions and the shape, grain size and grain size distribution of the powders are important. Results will be given.     

Ion-plated aluminium/aluminium oxide coatings using a pulsed oxygen process

Pulsed oxygen was utilized in a thermionically assisted triode ion plating process to produce dense, hard and highly adherent aluminium/aluminium oxide coatings on steel substrates. The coatings were deposited in a 0.1 Pa argon discharge while oxygen gas was injected at various pulse rates into the chamber. The influence of the oxygen flow rates, the pulse rates and the substrate bias on the structure and crystal phase of the coating were investigated using scanning and transmission electron microscopy, X-ray diffraction and Rutherford backscattering techniques. The analysis showed that the resultant coating structure consist of a mixed state of crystalline and non-crystalline phases depending on the oxygen flow rate and on the substrate bias at a constant oxygen pulse rate. Analysis showed that the non-crystalline phase approached stoichiometry for Al₂O₃ at oxygen flow rates of 7.5 Torr l s^-1 and a substrate bias of 2 kV and that there was a substantial increase in hardness.     

Mechanical,tribological and anti-corrosive properties of polyaniline/graphene coated Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys

The mechanical, tribological and corrosion protection offered to Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys by the epoxy coating containing polyaniline/graphene (PANI/Gr) pigments is undertaken in the current work. PANI/Gr containing coatings were observed to be strongly adherent with a higher scratch hardness (H_s) and plowing hardness (H_p), i.e. H_s of 0.43 GPa, and H_p of 0.61 GPa, respectively when compared to that of neat epoxy coating (H_s of 0.17 GPa, and H_p of 0.40 GPa, respectively). Due to their higher H_s and H_p values, PANI/Gr based coatings displayed an enhanced wear resistance (Wear volume, W_v = 4.53 × 10^-3 m³) than that of neat epoxy coating (W_v = 5.15 × 10⁻³ m³). The corrosion protection efficiency in corrosive environment of 3.5 wt% NaCl solution was obtained to be >99% for PANI/Gr containing coatings when compared to that of neat epoxy coating. The charge-transfer resistance (R_ct) of the PANI/Gr containing coatings were estimated to be >10⁶ Ω cm², which indicates their highly protective nature when compared to that of neat epoxy coating (R_ct ˜10⁵ Ω cm²). Hence, PANI/Gr containing coatings can be potentially used for wear resistance and corrosion protection applications in marine environments.     

Improved flow conditions in diamond hot filament CVD—Promising deposition results and gas phase characterization by laser absorption spectroscopy

A hot filament plant for chemical vapor deposition of crystalline diamond featuring new operating stages has been built. It allows (i) a separate methane feed locally at substrate position and (ii) supplying a forced gas flow towards the substrate. To understand the effect of these two features on diamond growth, the results of systematic diamond growth experiments are discussed. To reveal the effects of these features on the gas phase, infrared tunable diode laser absorption spectroscopy (IR-TDLAS) was employed. Using a forced gas flow showed a remarkable increase in the diamond growth rate of a factor >6 compared to standard coating setups. By lowering the methane content in the forced flow diamond quality factors >95% were achieved. IR-TDLAS showed an increase of all measured carbon-containing species CH₄, C₂H₂, CH₃ and CO when applying the forced flow. The mass transport dominated by diffusion in the standard setup shifts to a convective gas transport in the forced flow setup. The induced laminar flow causes a more effective transport of the growth species to the substrate and leads to higher growth rates. Application of feeding methane locally at substrate position leads to exceptionally high growth rates (0.68 μm/h) at correspondingly high diamond quality (91%). For this, the methane content has to be lowered, though, which at the same time leads to a more homogenous deposition lateral on the surface. From the IR-TDLAS gas phase measurements, a more effective precursor dissociation, a higher CH₃ density and a rise in the CH₃?C₂H₂ ratio above the substrate surface can be derived.     

A method of measuring energy dissipation during crack propagation in polymers with an instrumented ultramicrotome

In order to characterize very local energy dissipation during crack propagation in polymers, an ultramicrotome was instrumented to measure the energy dissipated during sectioning. The work to section per unit area, W _s, was measured for five different amorphous polymers [polymethyl methacrylate (PMMA), polystyerene (PS), polycarbonate (PC) and two epoxy resins] in the glassy state. When the section thickness was varied between 60 and 250 nm, W _s varied between 15 and 100 Jm^–2, depending on the material and section thickness. The method and the results are compared with other methods used for determining the energy dissipation at a local level as well as at a macroscopic level in polymers. The differences between different polymers were found to be contradictory to macroscopic fracture toughness, G _lc, measurements. The material that showed the highest W _s had the lowest G _lc values reported. Possible mechanisms for energy dissipation during sectioning are also discussed.     

Kinetics of electrochemical oxidation of neptunium ions in nitric acid solutions containing potassium phosphotungstate K10P2W17O61

The kinetics of electrochemical oxidation of Np(IV) and Np(V) ions on a smooth platinum electrode in a 1 M HNO₃ solution containing potassium phosphotungstate K₁₀P₂W₁₇O₆₁ (KPW) was studied by spectrophotometry. For the redox reactions under consideration, the rate laws were determined, the rate constants were calculated, and the schemes of transformations of Np ions were suggested. The electrochemical oxidation of Np(IV) and Np(V) is described by the first-order rate law with respect to the Np(IV) and Np(V) concentrations, respectively. The rate constants of these reactions are close and comparable with the rate constant of the Np(V) disproportionation.     

On the correlation between solid-particle erosion and fracture parameters in SiC

The fracture toughness,K _Ic, for a hot-pressed SiC and three types of reaction-bonded SiC has been measured using the Hertzian indentation technique with spherical indentors whose radii varied from 2.5 to 10 mm. Excellent agreement between the toughness measured by this technique and the publishedK _Ic value measured using double torsion is obtained for the hot-pressed SiC. The Vickers hardness,H, which was also measured, andK _Ic have been used to predict the solid-particle erosion rate, ΔW, given by ΔW ∞H _a K _c ^b where the values of the exponentsa andb depend on the details of the erosion model. The predicted rates are not in agreement with the measured rates. This discrepancy is probably due to the fact that the models are insensitive to microstructure.     

Microstructural features of dynamic recrystallization in alloy 625 friction surfacing coatings

In friction surfacing (FS), material is deposited onto a substrate in the plasticized state, using frictional heat and shear stresses. The coating material remains in the solid state and undergoes severe plastic deformation (SPD) at high process temperatures (≈0.8 T_melt), followed by high cooling rates in the range of 30?K/s. Dynamic recrystallization and the thermal cycle determine the resulting microstructure. In this study, Ni-based alloy 625 was deposited onto 42CrMo4 substrate, suitable, for instance, for repair welding of corrosion protection layers. Alloy 625 is known to undergo discontinuous dynamic recrystallization under SPD, and the resulting grain size depends on the strain rate. The coating microstructure was studied by microscopy and electron backscatter diffraction (EBSD). The coatings exhibit a fully recrystallized microstructure with equiaxed grains (0.5–12?µm) and a low degree of grain average misorientation. Flow lines caused by a localized decrease in grain size and linear alignment of grain boundaries are visible. Grain nucleation and growth were found to be strongly affected by localized shear and nonuniform material flow, resulting in varying amounts of residual strain, twins and low-angle grain boundaries in different regions within a single coating layer’s cross section.

FS can be used to study dynamic recrystallization at high temperatures, strains and strain rates, while at the same time materials with a recrystallization grain size sensitive to the strain rate can be used to study the material flow during the process.