Foil boats

Aluminum is a particularly difficult material to evaporate using foil boats. Molten aluminum alloys with the materials commonly used to make foil boats, leading to embrittlement and breakage. Many solutions have been proposed, none are totally satisfactory. One popular approach is to stack two thin foil boats so that the top boat is sacrificial and the bottom boat contains the evaporant. It is also possible to use a thick boat and replace it every few uses before failure. 

Braided wires can also be used in the same configuration as stamped boats this is most effective for metals which melt, although large chips of metals which sublime also can evaporate well from coiled braids. Molten metals are drawn into the wire via capillary action and then evaporate. Because braided wires have a higher electrical and thermal resistance than wide foil boats, and... 

The simplest crucible heaters are made from braided tungsten filaments fashioned to hold the crucible. A related style uses a formed foil boat to hold the crucible. 

Sediment samples were collected with a dredge-type sampler from a boat and also with the aid of a diver. One quart glass jars with aluminum foil-lined caps were used for the sediment samples after collection they were placed in a box containing dry ice. The composition of the river bottom sediments varied from coarse sand (>600m) in the center of the river to coarse and fine silt toward the banks. 

During reactions at high temperatures, the ceramic sample must be in contact with a container. Commonly used containers include alumina or zirconia boats or crucibles or noble metal foil-lined ceramic boats. It is important to be aware of possible reactions between the material being synthesized and the container which may be a source of foreign ions. For example, Al+S ions may be incorporated if alumina crucibles are employed. Forming the material into a pellet minimizes the surface area and helps limit reactions with containers. Both alumina and zirconia crucibles and boats can be cleaned with mineral acid washes and reused. 

A sample of cerium metal (approximately 15 g.), previously cleaned and weighed, is placed in a V-shaped tungsten boat. The boat is positioned inside a 26-mm.-o.d., heavy-wall, silica reaction tube, and a curved shield of tungsten foil is placed over the boat to prevent the possibility of silica flakes (formed by reaction with cerium vapor) from falling into the melt. The silica reaction tube is transferred anaerobically from the glove box and installed on the vacuum and gas-handling system. 

Because the source material will be heated to produce the vapor pressure, the process is conducted in a high vacuum to prevent chemical reaction of the source material. This represents an advantage for this method since the incorporation of impurities into the film is minimized with the use of such a vacuum. Several methods are used to heat the source material. The simplest is resistive heating. The source material is placed in a ceramic boat, which is then placed into a heater. Alternatively, the source material itself can be formed into a filament, heated, and the vapors produced that way. The temperature of the source materials is varied by varying the power to the resistive heater. Since this approach sends source material vapor in all directions, the source material and substrate are often placed inside a foil tent so that the cleanup is simpler. 

The modification of the standard procedure involves the use of a disposable sample boat. A piece of copper foil approximately 1 X i in. in size is shaped manually into boat form. It is flamed in a Bunsen burner and dipped into methanol. After this cleaning operation, the boat is placed in a glass tube and heated briefly with a Bunsen flame while being swept with a stream of hydrogen (caution ) it is then ready for use in the procedure described by Oliver. Some typical results are given in Table I. Anal. Calcd. for CarHaoClOPzRh O, 2.32. Found 0, 2.30, 2.34. By checkers Calcd C, 64.32 H, 4.38 mol. wt., 691. Found C, 64.49 H, 4.61 mol. wt., 688 4. Calcd. for Cj7H3oC10As2Rh O, 2.05. Found O, 1.95, 2.10. By checkers Calcd C, 57.06 H, 3.88 , mol. wt., 778. Found C, 57.65 H, 4.43 mol. wt., 790 13. 

A convenient apparatus for the reaction is shown in Fig. 1. A molybdenum boat is folded from thin sheet or foil to contain the metal. The fused silica cylinder ( 30-mm o.d.) which holds this is not necessary but does make product removal easier. The outer fused silica tube ( 40-mm o.d.) is terminated on the outlet end through a standard taper joint to a (Pyrex) cap with stopcock and connection to an exit bubbler (H2S04, not H20) which prevents back diffusion of air. The inlet end (which is slightly elevated) is connected through a stopcock and joint to a (Pyrex) mixing manifold, the three inlets of which connect through bubblers filled with H2S04 for flow measurement to sources of HC1, H2, and Ar or He (not N2). 

Fig. 4.3. Schematic showing several styles of resistively heated boats, (a) is a folded boat, (b) is a stamped boat, and (c) is a rolled foil packet with a small hole punched in the center, (d) shows the folded boat clamped to the copper electrodes the electrodes also heatsink the boat.

The sampling-boat technique is frequently hampered by poor precision. Delves (D5) described an improved system. He modified the system of White (W5) who used a platinum-wire loop in conjunction with an absorption tube to increase sensitivity. Delves vaporized samples from microcrucibles made of nickel foil into a nickel absorption tube situated in air-acetylene flame. The sensitivity is 1 X g lead per 1% absorption at the 2833 A line. Only 10 /lil of whole blood are required. Before analysis, the sample is dried in the nickel crucible on a hot plate at 140°C (ca. 30 seconds) and then is partially oxidized with 20 jal of 30% hydrogen peroxide at 140°C until a dry yellow residue is obtained. Standards of lead added to normal blood are run in a similar fashion. 

Products and Uses A heavy metal used in paint pigment, solder, pool cue chalk, crayons from China, glazes on ceramic dishes and bowls, among other products. Prohibited from interstate commerce since the middle 1970s. It is still manufactured and used locally. Lead has been found in wines, possibly from the foil used on bottles. (Pencil "lead" is not lead at all rather it is a mixture of graphite and clay.) Prevents bottom growth on boat hulls and rust development on metal. Used as a filler and for radiation protection. 

Copper(II) sulphide was obtained by direct synthesis from copper foils prereduced with hydrogen and resublimated sulphur taken in molar ratio 1.000 1.000. Both elements were put in quartz boats into evacuated (< 10 torr) and sealed pyrex-quartz tube. Two independent furnaces were used to control the temperature during synthesis. Sulphur was allowed to distil over copper foils by using 450 °C in both parts of reaction tube for 48 h. Then the temperature in the copper part was decreased to 425 °C for Ih and both parts of tube were further on cooled at rate 25 °C per day. The product obtained was powdered and sieved. A pure copper(II) sulphide was identified as a product by XRD analysis. 

The pyrolysis filament may be shaped for convenience of sampling and may be a flat strip, foil, wire, grooved strip, or coil. In the case of the coil, a small sample tube or boat is inserted into the filament so that the sample is not heated directly by the filament, but is in effect inside a very small, rapidly heating furnace. The pyrolysis filament must be connected to a controller capable of supplying enough current to heat the filament rapidly, with some control or limit since the materials used for filaments are not self-limiting. The temperature of the filament may be monitored using the resistance of the material itself or some external measure, such as optical pyrometry or a thermocouple. ... 

Objective To build a boat from a 6" X ( sheet ol aluminum foil, which will carry as many pennies as possible. It should float for at least 1 minute. Thirty minutes will be allowed for preparation. 

This system offers the choice of sample holder shape (wire, filament, boat, tube, folded foil) and the lack of electrical contact between the power supply and the conductor, which facilitates automation. Conductors are frequently enclosed within quartz tubes, which collect nonvolatile products (Figure 3). 

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