Robert E. Barletta

Bio: Robert E. Barletta is an academic researcher from Brookhaven National Laboratory. The author has contributed to research in topics: Coating & Carbide. The author has an hindex of 4, co-authored 13 publications receiving 76 citations.

Apparatus and method for laser deposition of durable coatings

Abstract: Method and apparatus for depositing durable coatings onto the surface of a substrate without heating the entire substrate to high temperatures by using lasers to heat the substrate and dissociate a deposition gas. The apparatus comprises a deposition chamber for enclosing the substrate upon which a coating is to be deposited, gas delivery means for directing a flow of deposition gas on the substrate, a first laser for heating the substrate, and a second laser for irradiating the deposition gas to dissociate the gas. The method includes placing a substrate within a vacuum deposition chamber and directing a flow of deposition gas on the substrate. Then the substrate is heated with a first laser while the deposition gas is irradiated with a second laser to dissociate the deposition gas.

Deposition and modification of tantalum carbide coatings on graphite by laser interactions

Abstract: Graphite surfaces can be hardened and protected from erosion by hydrogen at high temperatures by refractory metal carbide coatings, which are usually prepared by chemical vapor deposition (CVD) or chemical vapor reaction (CVR) methods. These techniques rely on heating the substrate to a temperature where a volatile metal halide decomposes and reacts with either a hydrocarbon gas or with carbon from the substrate. For CVR techniques, deposition temperatures must be in excess of 2000{degrees}C in order to achieve favorable deposition kinetics. In an effort to lower the bulk substrate deposition temperature, the use of laser interactions with both the substrate and the metal halide deposition gas has been employed. Initial testing, involved the use of a CO{sub 2} laser to heat the surface of a graphite substrate and a KrF excimer laser to accomplish a photodecomposition of TaCl{sub 5} gas near the substrate. Results of preliminary experiments using these techniques are described.

Carbon erosion in hydrogen—The ‘‘midband’’ problem revisited

Abstract: Isothermal experiments were performed on TaC‐coated carbon‐carbon in flowing hydrogen at atmospheric pressure. Considerable effort was put into trying to detect an enhanced rate of erosion at intermediate temperatures (∼1400 K) as was found in the NERVA program. No such enhancement (‘‘midband corrosion’’) was observed, and the temperature dependence of the reaction rates seemed to follow simple activated behavior consistent with a single rate‐limiting process.

Biodegradation Testing of Bitumen

Abstract: An estimate of the rate of biodegradation of bituminous material is necessary to predict the long-term stability of low- and intermediate- level waste solidified using bitumen. Data from a series of scoping experiments have been analyzed to determine the rate of degradation of blown bitumen samples under a variety of conditions. Among the variables investigated were the effect of soil type, moisture, sample surface area and microbial strain. The rate of degradation was measured by monitoring metabolic CO 2 release. Using this data it was found that, for degradation in soil, a mean rate of 5.5 × 10 −4 cm/yr represented all data to within a factor of about two. This mean rate is nearly that for distilled bitumen samples measured by other workers.

Principles and applications of CVD powder technology

Abstract: Chemical vapor deposition (CVD) is an important technique for surface modification of powders through either grafting or deposition of films and coatings. The efficiency of this complex process primarily depends on appropriate contact between the reactive gas phase and the solid particles to be treated. Based on this requirement, the first part of this review focuses on the ways to ensure such contact and particularly on the formation of fluidized beds. Combination of constraints due to both fluidization and chemical vapor deposition leads to the definition of different types of reactors as an alternative to classical fluidized beds, such as spouted beds, circulating beds operating in turbulent and fast-transport regimes or vibro-fluidized beds. They operate under thermal but also plasma activation of the reactive gas and their design mainly depends on the type of powders to be treated. Modeling of both reactors and operating conditions is a valuable tool for understanding and optimizing these complex processes and materials. In the second part of the review, the state of the art on materials produced by fluidized bed chemical vapor deposition is presented. Beyond pioneering applications in the nuclear power industry, application domains, such as heterogeneous catalysis, microelectronics, photovoltaics and protection against wear, oxidation and heat are potentially concerned by processes involving chemical vapor deposition on powders. Moreover, simple and reduced cost FBCVD processes where the material to coat is immersed in the FB, allow the production of coatings for metals with different wear, oxidation and corrosion resistance. Finally, large-scale production of advanced nanomaterials is a promising area for the future extension and development of this technique.

Coating formation by reactive deposition

Abstract: Light reactive deposition uses an intense light beam (684) to form particles that are directly coated onto a substrate (680) surface. In some embodiments, a coating apparatus comprising a noncircular reactant inlet (682), optical elements forming a light path (684), a first substrate (680), and a motor connected to the apparatus. The reactant inlet (682) defines a reaction zone with a product stream path continuing from the reaction zone. The substrate (680) intersects the product stream path. Also, operation of the motor moves the first substrate (680) relative to the product stream. Various broad methods are described for using light driven chemical reactions to produce efficiently highly uniform coatings.

Tantalum carbide films synthesized by hot-filament chemical vapor deposition technique

Abstract: Chemical vapor deposition (CVD) with thermionic-emission of hot tantalum filaments with H2 diluted CH4 as precursor was used to deposit tantalum carbide composite films on silicon. Standard characterization techniques and analysis tools were employed to study the surface morphology and roughness, fracture cross-section, phase evolution and hardness of the deposited films. The results indicate that the morphology, surface roughness, structure, texture, thickness and hardness of the coatings are greatly influenced by the process parameters. The films are mainly composed of TaC along with C and Ta2C phases. TaC grains are very small at 60 Torr, while at 100 Torr, coarse grains are developed. With an increase in substrate temperature from 850 °C to 950 °C grain size becomes almost double and dense coating is formed, while by making methane concentration double coarse grains along with cluster formation are observed and porosity is increased. The higher the graphite content the lower the hardness. Composite structure of graphite and TaC grown by modified hot-filament CVD is likely to be a potential candidate for thermal barrier coatings.