Refractory coatings and method of producing the same

The adhesion, friction, and wear properties of sputtered refractory coatings on substrates of materials that form stable nitrides is improved by placing each substrate directly below a titanium carbide target of a commercial radiofrequency diode apparatus in a vacuum chamber. Nitrogen is bled into the system through a nozzle resulting in a small partial pressure of about 0.5% to 2.5% during the first two minutes of deposition. The flow of nitrogen is then stopped, and the sputtering ambient is reduced to pure argon through a nozzle without interrupting the sputtering process. When nitrogen is deliberately introduced during the crucial interface formation, some of the titanium at the interface reacts to form titanium nitride while the metal of the substrate also forms the nitride. These two nitrides atomically mixed together in the interfacial region act to more strongly bond the growing titanium carbide coating as it forms on the substrate

Improved adherence of sputtered titanium carbide coatings on nickel- and titanium-base alloys

Rene 41 and Ti-6Al-4V alloys were radio frequency sputter coated with titanium carbide by several techniques in order to determine the most effective. Coatings were evaluated in pin-on-disk tests. Surface analysis by X-ray photoelectron spectroscopy was used to relate adherence to interfacial chemistry. For Rene 41, good coating adherence was obtained when a small amount of acetylene was added to the sputtering plasma. The acetylene carburized the alloy surface and resulted in better bonding to the TiC coating. For Ti-6Al-4V, the best adherence and wear protection was obtained when a pure titanium interlayer was used between the coating and the alloy. The interlayer is thought to prevent the formation of a brittle, fracture-prone, aluminum oxide layer

Controlled environment life support system: Growth studies with potatoes

Results of experiments conducted to maximize the productivity of potatoes grown under controlled environmental conditions are discussed. A variety of parameters is examined which affect potato growth, specifically, photoperiod, light intensity, temperature, nitrogen nutrition, carbon dioxide concentration and culture techniques. These experiments were conducted using five different cultivars, Russet Burbank, Norchip, Superior, Kennebec and Norland. To achieve high productivity, three specific objectives were explored: (1) to develop effective cultural procedures, (2) to determine the most effective photoperiod and (3) to develop a mist culture system. It is felt that the productivity obtained in this study is below the maximum that can be obtained. High irradiance levels coupled with tuber-promoting conditions such as cooler temperatures, increased CO2 levels and lowered nitrogen concentrations should allow increases in tuber production. Tuberization appears to be accelerated by short daylengths although final yields are not increased. Mist culture techniques have not yet produced fully developed tubers. The use of supporting media and alteration of the nitrogen content of the mist solution are being explored as a way to allow tubers to develop to maturity

Adherence of sputtered titanium carbides

Sputtered coatings of the refractory metal carbides are of great interest for applications where hard wear-resistant materials are desired. The usefulness of sputtered refractory carbides is often limited, in practice, by spalling or interfacial separation. In this work improvements in the adherence of refractory carbides on iron, nickel and titanium based alloys were obtained by using oxidation, reactive sputtering or sputtered interlayers to alter the coating-substrate interfacial region. X-ray photoelectron spectroscopy and argon ion etching were used to characterize the interfacial regions, and an attempt was made to correlate adherence as measured in wear tests with the chemical nature of the interface

Effect of nitrogen-containing plasma on adherence, friction, and wear of radiofrequency-sputtered titanium carbide coatings

Friction and wear experiments on 440C steel surfaces that were rf sputtered with titanium carbide when a small percentage of nitrogen was added to the plasma were conducted. Both X-ray photoelectron spectroscopy and X-ray diffraction were used to analyze the resultant coatings. Results indicate that the small partial pressure of nitrogen (approximately 0.5 percent) markedly improves the adherence, friction, and wear properties when compared with coatings applied to sputter-etched surfaces, oxidized surfaces, or in the presence of a small oxygen partial pressure. The improvements are related to the formation of an interface containing a mixture of the nitrides of titanium and iron, which are harder than their corresponding oxides

X-ray photoelectron spectroscopy study of radiofrequency sputtered chromium bromide, molybdenum disilicide, and molybdenum disulfide coatings and their friction properties

Radiofrequency sputtered coatings of CRB2, MOSI2, and MOS2 were examined by X-ray photoelectron spectroscopy. The effects of sputtering target history, deposition time, RF power level, and substrate bias on film composition were studied. Friction tests were run on RF sputtered surfaces of 440-C steel to correlate XPS data with lubricating properties. Significant deviations from stoichiometry and high oxide levels for all three compounds were related to target outgassing. The effect of biasing on these two factors depended on the compound. Improved stoichiometry correlated well with good friction and wear properties

Utilization of potatoes in bioregenerative life support systems

Data on the tuberization, harvest index, and morphology of 2 cvs of white potato (Solanum tuberosum L.) grown at 12, 16, 20, 24 and 28 C, 250, 400 and 550 micromol/s/m photosynthetic photon flux (PPF), 350, 1000 and 1600 microliter 1 sup -1 CO2 is presented. A productivity of 21.9 g/m day sup -1 of edible tubers from a solid stand of potatoes grown for 15 weeks with continuous irradiation at 400 micromol/s/m, 16 C and 1000 microliter 1 sup -1 CO2 was obtained. This equates to an area of 34.3 sq m being required to provide 2800 kcal of potatoes per day for a human diet. Separated plants receiving side lighting have produced 32.8 g/m day sup -1 which equates to an area of 23.6 sq m to provide 2800 kcal. Studies with side lighting indicate that productivities in this range should be realized from potatoes. Glycoalkaloid levels in tubers of controlled environment grown plants are within the range of levels found in tubers of field grown plants. The use and limitation of recirculating solution cultures for potato growth is discussed

X-ray photoelectron spectroscopy study of radiofrequency-sputtered refractory compound steel interfaces

Radiofrequency sputtering was used to deposit Mo2C, Mo2B5, and MoSi2 coatings on 440C steel substrates. Both sputter etched and preoxidized substrates were used, and the films were deposited with and without a substrate bias of -300 V. The composition of the coatings was measured as a function of depth by X-ray photoelectron spectroscopy combined with argon ion etching. In the interfacial region there was evidence that bias produced a graded interface in Mo2B5 but not in Mo2C. Oxides of iron and of all film constituents except carbon were presented in all cases but the iron oxide concentration was higher and the layer thicker on the preoxidized substrates. The film and iron oxides were mixed in the MoSi2 and Mo2C films but layered in the Mo2B5 film. The presence of mixed oxides correlates with enhanced film adhesion

Beam profiles measured with thermoluminescent dosimeters

Beam profilometer, using thermoluminescent dosimeters, gives a quantitative and qualitative representation of the focus of an external protron beam of a synchrotron. The total number of particles in the beam, particle distribution, and the shape of the beam are determined

Scenarios for optimizing potato productivity in a lunar CELSS

The use of controlled ecological life support system (CELSS) in the development and growth of large-scale bases on the Moon will reduce the expense of supplying life support materials from Earth. Such systems would use plants to produce food and oxygen, remove carbon dioxide, and recycle water and minerals. In a lunar CELSS, several factors are likely to be limiting to plant productivity, including the availability of growing area, electrical power, and lamp/ballast weight for lighting systems. Several management scenarios are outlined in this discussion for the production of potatoes based on their response to irradiance, photoperiod, and carbon dioxide concentration. Management scenarios that use 12-hr photoperiods, high carbon dioxide concentrations, and movable lamp banks to alternately irradiate halves of the growing area appear to be the most efficient in terms of growing area, electrical power, and lamp weights. However, the optimal scenario will be dependent upon the relative 'costs' of each factor