Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
  • F16L9/00—Rigid pipes
  • F16L9/10—Rigid pipes of glass or ceramics, e.g. clay, clay tile, porcelain
  • F16L9/105—Rigid pipes of glass or ceramics, e.g. clay, clay tile, porcelain of glass
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
  • F16L9/00—Rigid pipes
  • F16L9/14—Compound tubes, i.e. made of materials not wholly covered by any one of the preceding groups
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
  • G01N30/02—Column chromatography
  • G01N30/60—Construction of the column
  • G01N30/6052—Construction of the column body
  • G01N30/6073—Construction of the column body in open tubular form
  • G01N30/6078—Capillaries

Definitions

• This invention relates to silica capillary columns for gas chromatography, and, in particular, to metallic clad silica capillaries.
• gas chromatography In the field of analytical chemistry, gas chromatography (GC) is the most widely used and the most rapidly growing analytical technique. Although the field of gas chromatography is more properly subdivided into specific categories, the gas-liquid chromatography or gas-liquid partition chromatography, as it is also called, is mainly responsible for the tremendous development of the field as a whole. Usefulness of this technique is closely tied to the proper selection of a column, or partition column, in which the separation of sample components takes place.
• these columns are capillary tubing with a bore between 0.2 and 0.5 mm (0.008 to 0.02 in.). In some cases, the bore may range between 0.1 mm (for fast analysis) to 2 mm (for semipreparative work).
• the length of these capillaries tubes is on the order of 15.to 100 m (about 50 to 300 ft). Preparation of these capillary columns requires consideration of uniform inner diameter, good temperature resistance, good mechanical strength and non-reactivity with respect to the sample and the stationary phase (inner coating).
• stainless steel, copper and glass are all common capillary materials. However, because of inertness requirements, copper is the least used material. High purity glasses, commonly found in optical fiber work, are an excellent candidate for cheap, disposable column manufacture.
• the problem of placing a long length, e.g., about 50 to 300 ft, of tubing in a constant elevated temperature environment places two constraints on the tube.
• the first constraint relates to stress.
• the tube In order to place a long length of a tube having an ID of 0.25 to 0.5 mm in a small space, the tube might be coiled in a 2.5 cm diameter space.
• the nascent strength of a glass capillary tube is maintained or preserved by coating the glass capillary with at least one layer of a metal or alloy that (a) is substantially chemically inert with respect to the material comprising the glass capillary at the deposition temperature during the time of coating the metal or alloy onto the glass capillary tubing and (b) forms a hermetic seal around the glass capillary tubing.
• the mechanical properties of the glass capillary tubing are better preserved with the metal and alloy coatings disclosed herein, as compared with other coatings, whether metallic or non-metallic.
• Use of the metallic coating provides a hermetic seal around the outside of the capillary v/hile providing mechanical protection at elevated temperatures.
• the capillary bore protects the capillary circumference from the deleterious effects of moisture.
• the capillary bore of course, remains uncoated or is coated with a suitable stationary phase, since it must be free from all but the compounds to be analyzed. These compounds generally do not contain any of the monovalent free radicals that contribute to static fatigue.
• Metallic clad capillary tube 10 comprises a glass tube or capillary 11 and at least one metallic coating or jacket 12 concentrically surrounding the glass capillary 11.
• Glass capillary 11 is preferably highpurity SiO 2 or doped silica.
• the composition of the glass capillary is not otherwise critical, so long as it remains inert during use in gas chromatography analysis.
• the metallic jacket 12 comprises a metal or alloy that is substantially chemically inert with respect to the glass capillary 11. That is, the metal or alloy is one that does not react chemically with the glassy material at the deposition temperature during the time of coating the metal or alloy onto the glass capillary.
• the metallic coating is preferably applied by passing the capilllary through a molten pool of the metal or alloy.
• the melting point of the metal or alloy may be higher than the softening point of SiO 2 .
• the melting poing of the metal or alloy to be coated may range as high as about 2,300°C, so long as the capillary itself does not experience a temperature greater than its softening point.
• Such a metal is aluminum and its corresponding alloys, such as aluminum- bismuth (Al-0.1-0.2 at% Bi). Although it is known that aluminum reacts with silica, this reaction is sufficiently slow in the application of chromatography capillaries so as to permit its use in this application.
• Metal elements suitable in the practice of the invention additionally include vanadium, chromium, manganese, iron, cobalt, nickel, copper, arsenic, strontium, zirconium, niobium, rhodium, palladium, tellurium, barium, iridium, platinum, thallium, tin, lead, zinc and cadmium.
• Alloys suitable in the practice of the invention include alloys containing these elements in combination with each other or combination with other elements, whether metallic or non-metallic, so long as the alloys remain ductile at ordinary temperatures of use. Examples of such other alloying metal elements include magnesium, while examples of such other alloying non-metal elements include antimony, bismuth, boron, carbon, phosphorus and silicon.
• Such alloys of metal elements with additional elements comprise a major portion (i.e., greater than 50% by weight) of the metal elements and a minor portion (less than 50%) of additional elements. Due to factors related to toxicity, expense, ease of handling and other factors, elements such as manganese, arsenic, strontium, rhodium, tellurium, barium, iridium, platinum and thallium, which are otherwise suitable, are not likely to find use except as alloying elements and hence are not preferred as elemental metal coatings. Additional metallic coatings (not shown) may be applied to the metallic coating 12 above and may comprise any metal or alloy; such metal or alloy is not subject to the same constraints as the first metallic cladding.
• the additional cladding may be of the same composition as the first in order to cure localized defects or to build up the thickness.
• the second cladding may be of a different metal or alloy which otherwise might or might not react with the underlying glass capillary.
• a hybrid structure may be fabricated having mechanical properties that are different than either metallic cladding alone.
• the first metallic cladding may comprise tin which does not react with silica and the second metallic cladding may comprise aluminum.
• Another combination is a steel (high yield point) on tin (low yield point). Additional combinations include tin on copper, tungsten on tin, copper on tin, copper on zinc, tin on nickel and aluminum on copper.
• the tensile strength of the metallic clad capillary be substantially not less than that of the unclad capillary in determining the suitability of a particular metal or alloy.
• the strength comparison should be made at the same strain rates; these rates should be fast enough to limit static fatigue in the range of interest.
• the unclad capillary used for comparison should be tested before it contacts any other solid. Failures in the holding fixture for the strain test are ignored in the comparison; such failures are not considered part of the original sample population, since the failure is clearly associated with the testing fixture.
• the metallic claddings may be applied by a variety of methods, including the passage of the fiber through a molten pool, as described below, vapor plating, vacuum deposition, sputtering, electro-deposition and the like.
• the coating is applied to the glass capillary during the drawing operation immediately after the capillary emerges from the furnace. Apparatus wellknown for coating glass fibers with metals may be suitably employed.
• the coating is applied before the capillary has a chance to be abraded by the take-up drum onto which the coated capillary is spooled, and even before the capillary cools to the point where ambient moisture can react with its surface.
• At least one of the metallic layers, and most preferably the first metallic layer is applied by passing the glass capillary through a coating cup which contains the molten metal or alloy to be coated onto the capillary at a temperature slightly above the melting point of the metal or alloy.
• the cup has a small hole in its bottom large enough to pass the glass capillary but sufficiently small so that surface tension of the molten metal or alloy prevents it from running out.
• a thin layer of metal or alloy freezes onto the surface of the glass capillary. This method rapidly forms thick metallic coatings having characteristics similar to those of the bulk metal or alloy.
• the metallic cladding provides a tight, permanent and durable hermetic seal about the glass fiber. Determination of the adequacy of hermetic sealing is made by preparing a plot of log (stress) versus log (time) or a plot of log (strain rate) versus log (mean failure stress). As is well-known, a slope of substantially zero implies a hermetic seal.
• the thickness of the metallic layer is controlled by adjusting the capillary drawing rate and the metal deposition parameters such as, for example, in the case of molten metal coating, the temperature differential between the capillary and the metal-containing bath.
• the total thickness of the metallic cladding 12 lies in the range of about 5 to 200 ⁇ m and preferably lies in the range of about 20 to 50 ⁇ m.
• the maximum thickness is restricted by a requirement to not impair the flexibility of the capillary, whereas the minimum thickness is set by a requirement to achieve adequate strength and hermetic sealing.
• the resulting glass capillary 10 evidences a retention of mechanical strength of the nascent glass capillary to a greater extent than evidenced by glass capillaries clad with other materials.
• the metallic clad capillary of the invention will not fail due to static fatigue if it is used at less than about 3/4 of its original tensile strength, regardless of the absolute value of that tensile strength.
• the high pristine ultimate strength of the glass capillary material is approximately 2 ⁇ 10 6 psi and is therefore more than adequate to achieve a final desired level in excess of 50,000 psi.
• the metallic layer or jacket 12 provides good mechanical protection and a hermetic seal against contamination. Additional mechanical protection, galvanic protection and electrical insulation can be achieved as needed by applying a plastic overcoat 13 outside of the metallic jacket 12. For example, as little as 10 to 25 ⁇ n of a polyvinyl formate coating is useful in preserving the integrity of the metallic cladding in an electrolytic cell with stainless steel electrodes and salt water. Other plastic coatings may also be used.
• the metallic clad glass capillaries are capable of operating continuously for at least a year up to about 2/3 T m (°K), where T m is the melting point of the metal or alloy, with no more than about 100% damage (i.e., no more than about 50% loss of strength).

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Ceramic Engineering (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• Dispersion Chemistry (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Joining Of Glass To Other Materials (AREA)
• Glass Compositions (AREA)
• Rigid Pipes And Flexible Pipes (AREA)
• Surface Treatment Of Glass (AREA)

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Publications (1)

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Cited By (15)

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Citations (4)

• 1981
  • 1981-10-12 IL IL64041A patent/IL64041A0/xx not_active IP Right Cessation
  • 1981-10-22 WO PCT/US1981/001424 patent/WO1982001578A1/en not_active Ceased
  • 1981-10-22 EP EP81902932A patent/EP0063580B1/en not_active Expired
  • 1981-10-22 JP JP56503450A patent/JPH0254508B2/ja not_active Expired

Patent Citations (4)

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