FAQs

FAQs | Sizes | Photos | Elements

Why use a transparent furnace?

Developed originally for viewing crystals, transparent furnaces are now used by those who want to take advantage of their unique properties.

Visibility	Accurate viewing of melting samples, thermocouple placement and process procedures.
Low mass	Heats up quickly, and possesses a compact design.
Clean	No contaminating fiber insulating material.
Accurate	At least +/- 2 over 70% of the length of the furnace in a 60 mm diameter furnace.

All furnaces are individually profiled prior to shipment. How are these furnaces used?

Originally developed for growing crystals, transparent furnaces are used for Liquid Phase Epitaxy (LPE), Chemical Vapor Deposition (CVD), and ampule growth. They are also used for annealing of wafers, gold wires and superconducting wires. Assorted specialty furnaces have been made that capitalize on the low mass and cleanliness of the design.

What about the gold mirror as insulation? How thick is the gold film?

From our estimate of the amount of gold deposited, the average thickness is about 800 angstroms. This thickness, viewed on a molecular level, would look like a series of gold islands with open spaces between islands. The heavier the film, the less space between the gold islands. The visibility into the furnace is affected by the thickness of the coating. Lighter coatings will allow more radiation to escape and produce clearer view into the furnace, while heavier coatings produce a more efficient but opaque furnace.

What is the temperature of the outside of the gold mirror at various inside temperatures?

Inside temperature	Gold mirror outside temperature
300 C	54 C
419 C	119 C
630 C	173 C
814 C	215 C
1012 C	287 C

At how high a temperature will the gold mirror continue to operate?

We advise 1000 C as the maximum temperature. They work at higher temperatures, but the lifetime of the gold film is reduced.

As gold melts at 1063 C, how can the mirror survive?

The surface temperature of the gold film may see these temperatures but most of the energy is reflected, not transferred into the film. The relatively cool air surrounding the outside of the gold tube cools the glass, lowering the temperature to the back side of the gold film. Do not put anything around the gold mirror to interfere with the cooling effect or the mirror will crack!

Can you operate the entire furnace in a vacuum?

Yes... but the outside temperature of the gold mirror must stay below 600 C.

Can the furnace be operated as a vacuum furnace?

Many of our customers insert a quartz tube through the furnace. Gas tight fittings can be put on the tube and a vacuum or positive pressure can be created inside the muffle. Warning! Whatever is used for a muffle should be designed for the intended operation.

Other Matters:

What is the biggest furnace and the smallest furnace and mirror you have made?

The Longest	IBM Tokyo, Japan	57 mm x 26 feet
Largest Diameter	Aichi Steel, Japan	200 mm x 500 mm
Smallest	NASA, Cleveland	23 mm x 50 mm
Mirrors:
	Largest Diameter	300 mm O.D.
	Smallest Diameter	25 mm
	Longest, single section	1500 mm
All furnaces are of the same design. Only the dimensions change.

What kind of a control and power supply do you recommend?

We recommend a controller that produces a 4-20 ma signal to a phase angle power supply. This combination produces the most accurate temperature profile in our transparent furnaces. A phase angle controller supplies power to the elements that promotes a long life and no fluctuations in temperature.

Who are some of your current and past customers?

Partial list of our U.S. customers:

• Minnesota Mining and Manufacturing
• Naval Electronics Laboratory Center, South Dakota
• Naval Research Center, Washington
• Bell Telephone
• North American Rockwell
• Esso Research
• Eastman Kodak
• United States Bureau of Standards
• U.S. Air Force, Hanscom Field
• U.S.A.F. - Wright Patterson Air Force Base
• EG & G, Inc.
• Gillette
• Grumman
• Rockwell International
• Marshall Space Flight Center
• Landseas Corporation
• Philip Morris
• Hewlett Packard
• Xerox
  
  
• University of California - Berkeley
• University of California - Los Angeles
• Carnegie-Mellon University
• University of Utah
• University of Southern California at Los Angeles
• Purdue University
• Massachusetts Institute of Technology
• Polytechnic Institute at Brooklyn
• University of Washington
• Colorado State University
• Harvard University
• University of Wisconsin

Partial list of our International customers:

• Australia
  University of S. Wales
  University of Wollongong
• Canada
  Bell Northern
  University of Toronto
• England
  Feranti, Ltd.
  University of Reading
• France
  French Atomic Energy Commission (C.E.A.)
  Universite de Strasbourg
• Germany
  Preussag Aktiengesellschaft
  Berliner Handels-Kontor Heinz Lindenberg
• India
  Indian Institute - Madras
• Iran
  Arya-Mehr University of Technology
• Israel
  Semi Conductor Devices
  Rotem Industries
  Isreal Atomic Energy
• Japan
  Dinichi Trading Company
  Ishikawa Trading Company
• Netherlands
  Kawecki-Billiton
• New Zealand
  Department of Science and Industrial Research
• Norway
  Elkem Carbon
  Teck Industries
  Trondheim Industries
  Norsk Hydro
• Switzerland
  Interac
  Scole Polytechnique Federal de Lausanne
• Venezuela
  Instituto Venezolano de Investigaciones Cientificas