Refrigeration system designed for remote cold trap

In the freeze-dryer, the dual-evaporator refrigeration system is used to meet the demands of the freeze-drying technology. One evaporator is used as “cold trap”, and the other one, shelf evaporator, is used to control materials’ temperature. In this paper, experimental study on the dual-evaporator refrigeration system in the process of freeze-drying is carried out. First, the influence of valve opening on the dual-evaporator refrigeration system is analyzed. Secondly, the influence of vacuum on the surface temperature of the heat exchanger is analyzed. Finally, the influence of the varied evaporation temperature on the first drying rate is analyzed.

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Reduction of Specimen Contamination in Electron-Beam Instruments

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100092840 ◽

1976 ◽

Vol 34 ◽

pp. 576-577

Author(s):

G. Lehmpfuhl ◽

P. J. Smith

Keyword(s):

Electron Beam ◽

Cold Trap ◽

Beam Diameter ◽

Transmission Electron ◽

Scanning Transmission ◽

Hydrocarbon Molecules ◽

Electron Microscopes ◽

Combination Of Methods ◽

Convergent Beam ◽

Very High

Specimens being observed with electron-beam instruments are subject to contamination, which is due to polymerization of hydrocarbon molecules by the beam. This effect becomes more important as the size of the beam is reduced. In convergent-beam studies with a beam diameter of 100 Å, contamination was observed to grow on samples at very high rates. Within a few seconds needles began forming under the beam on both the top and the underside of the sample, at growth rates of 400-500 Å/s, severely limiting the time available for observation. Such contamination could cause serious difficulty in examining a sample with the new scanning transmission electron microscopes, in which the beam is focused to a few angstroms.We have been able to reduce the rate of contamination buildup by a combination of methods: placing an anticontamination cold trap in the sample region, preheating the sample before observation, and irradiating the sample with a large beam before observing it with a small beam.

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A conduction-cooled stage for high-resolution Cryo-SEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100131048 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1282-1283

Author(s):

John G. Sheehan

Keyword(s):

High Resolution ◽

Liquid Nitrogen ◽

Mechanical Stability ◽

Cooling System ◽

Cold Trap ◽

Nitrogen Gas ◽

Particulate Suspensions ◽

Advantages And Disadvantages ◽

Convection Cooling ◽

Styrene Butadiene

The goal is to examine with high resolution cryo-SEM aqueous particulate suspensions used in coatings for printable paper. A metal-coating chamber for cryo-preparation of such suspensions was described previously. Here, a new conduction-cooling system for the stage and cold-trap in an SEM specimen chamber is described. Its advantages and disadvantages are compared to a convection-cooling system made by Hexland (model CT1000A) and its mechanical stability is demonstrated by examining a sample of styrene-butadiene latex.In recent high resolution cryo-SEM, some stages are cooled by conduction, others by convection. In the latter, heat is convected from the specimen stage by cold nitrogen gas from a liquid-nitrogen cooled evaporative heat exchanger. The advantage is the fast cooling: the Hexland CT1000A cools the stage from ambient temperature to 88 K in about 20 min. However it consumes huge amounts of liquid-nitrogen and nitrogen gas: about 1 ℓ/h of liquid-nitrogen and 400 gm/h of nitrogen gas. Its liquid-nitrogen vessel must be re-filled at least every 40 min.

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