A simple liquid nitrogen gas‐flow cryostat for variable temperature laser luminescence studies

1994 ◽  
Vol 65 (2) ◽  
pp. 503-504
Author(s):  
Richard A. Fairman ◽  
Kirk V. N. Spence ◽  
Ishenkumba A. Kahwa
Author(s):  
John G. Sheehan

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.


2008 ◽  
Vol 141-143 ◽  
pp. 225-230 ◽  
Author(s):  
A. Narimannezhad ◽  
Hossein Aashuri ◽  
Amir Hossein Kokabi ◽  
Ali Khosravani ◽  
M. Kiani ◽  
...  

A technique to achieve the globular weld structure using stirring the localized semisolid zone during butt-joining of zinc AG40A (Zamak-3) die cast alloy is reported. Since the semisolid temperature range of this alloy is very narrow, the accurate controlling of weld pool temperature must be considered. By presented process, globular microstructure of the weld zone can be achieved. Moreover the near weld zone would have the globular structure due to semisolid holding. A gas heating system was designed to heat up the nitrogen gas to desired temperature accurately. A heating element was embedded in a castable ceramic block while a stream of gas could pass closely around the hot element length. Hot nitrogen gas flow through a precise ceramic nozzle was used to create a localized semisolid pool. At this stage a fine stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint. Local mechanical properties of different zones show a good strength in the weld metal zone and heat affected zone by results of the shear punch tests and hardness tests. Air entrapment in the pool decreases by controlling the speed of substrate movement and stirrer rotation under the nozzle. The strengths of each zone show relative correspondence to the variation of the hardness values.


1978 ◽  
Vol 46 (2) ◽  
pp. 192-192
Author(s):  
Donald G. McCoy

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