Laboratory furnaces

LECO induction furnace, Laboratory Equipment Corp., St. Joseph, Mich. 

The furnace and thermostatic mortar. For heating the tube packing, a small electric furnace N has been found to be more satisfactory than a row of gas burners. The type used consists of a silica tube (I s cm. in diameter and 25 cm. long) wound with nichrome wire and contained in an asbestos cylinder, the annular space being lagged the ends of the asbestos cylinder being closed by asbestos semi-circles built round the porcelain furnace tube. The furnace is controlled by a Simmerstat that has been calibrated at 680 against a bimetal pyrometer, and the furnace temperature is checked by this method from time to time. The furnace is equipped with a small steel bar attached to the asbestos and is thus mounted on an ordinary laboratory stand the Simmerstat may then be placed immediately underneath it on the baseplate of this stand, or alternatively the furnace may be built on to the top of the Simmerstat box. 

Tetrafluoroethylene was first synthesized in 1933 from tetrafluoromethane, CF, in an electric arc furnace (11). Since then, a number of routes have been developed (12—18). Depolymerization of PTFE by heating at ca 600°C is probably the preferred method for obtaining small amounts of 97% pure monomer on a laboratory scale (19,20). Depolymerization products contain highly toxic perfluoroisobutylene and should be handled with care. 

Boron Triiodide. Boron ttiiodide is not manufactured on a large scale. Small-scale production of BI from boron and iodine is possible in the temperature range 700—900°C (70—72). Excess I2 can be removed as Snl by reaction with Sn, followed by distillation (71). The reaction of metal tetrahydroborates and I2 is convenient for laboratory preparation of BI (73,74). BI can also by synthesized from B2H and HI in a furnace at 250°C (75), or by the reaction of B with excess Agl or Cul between 450—700°C, under vacuum (76). High purity BI has been prepared by the reaction of I2 with mixtures of boron carbide and calcium carbide at elevated temperatures. 

Calcium carbide was first made ia the laboratory ia the mid-1800s. Commercial production by the electric furnace method was developed about 1892 by Moissan ia France and iadependendy by Willson ia the United States. Development of the carbide iadustry for generation of acetylene began ia 1895 and expanded rapidly. 

Many of the technical problems of fabrication that formerly inhibited the use of titanium alloys in dental castings (164—166) have been effectively solved, and titanium castings may now be obtained for virtually any type of dental appHance at prices that are increasingly competitive. Special induction or electric-arc furnaces are necessary for casting titanium alloys, and this specialized equipment has, until now, been available in only a limited number of commercial dental laboratories. However, the relatively high price of this equipment, attributed to development costs, is expected to decline significantly this should help to improve the general availabihty of cast titanium appHances. 

Another major difference between the use of X rays and neutrons used as solid state probes is the difference in their penetration depths. This is illustrated by the thickness of materials required to reduce the intensity of a beam by 50%. For an aluminum absorber and wavelengths of about 1.5 A (a common laboratory X-ray wavelength), the figures are 0.02 mm for X rays and 55 mm for neutrons. An obvious consequence of the difference in absorbance is the depth of analysis of bulk materials. X-ray diffraction analysis of materials thicker than 20—50 pm will yield results that are severely surface weighted unless special conditions are employed, whereas internal characteristics of physically large pieces are routinely probed with neutrons. The greater penetration of neutrons also allows one to use thick ancillary devices, such as furnaces or pressure cells, without seriously affecting the quality of diffraction data. Thick-walled devices will absorb most of the X-ray flux, while neutron fluxes hardly will be affected. For this reason, neutron diffraction is better suited than X-ray diffraction for in-situ studies. 

Brookhaveii National Laboratory, Upton, NY Furnaces and Boilers (with Esher Kweller)... 

Fig. 7.13 Influence of coal chlorine content on the corrosion rates of low-alloy steels exposed to laboratory simulation of furnace wall corrosion (Brooks, C.E.G.B., private communication)...

Various methods of heating are required in the analytical laboratory ranging from gas burners, electric hot plates and ovens to muffle furnaces. 

Muffle furnaces. An electrically heated furnace of muffle form should be available in every well-equipped laboratory. The maximum temperature should be about 1200 °C. If possible, a thermocouple and indicating pyrometer should be provided otherwise the ammeter in the circuit should be calibrated, and a chart constructed showing ammeter and corresponding temperature readings. Gas-heated muffle furnaces are marketed these may give temperatures up to about 1200 °C. 

Conventional hot-air furnaces, similar to those found in homes, are often used in laboratories. A university campus or an industrial plant may have steam available, which can be conveniently put to use for heating. 

A laboratory can sometimes save money by building a simple hood where no hazardous, flammable, or corrosive fumes are involved. In one case, a hood was needed solely for drawing off unpleasant fumes from a muffle furnace and water vapor. A carpenter constructed a plywood box which reached from counter top to ceiling and had a large opening in the front. This was painted with a resistant paint, primarily to seal the surfaces and make them easy to clean. An inexpensive fan exhausted the hood to the outside. This simple hood worked for many years. 

Thermal treatment of a material in a gas oxidizing atmosphere is the simplest concept. This can be done in air, air diluted in N2, dry air, or in ultrahigh purity O2. In the laboratory practice, calcination is done in flowthrough beds, aided by fluidization, or in static box furnaces. Important aspects are the bed geometry, the removal of the generated gases, and temperature gradients. 

An unexpected outcome from EQA observations appeared when unsatisfactory material was unknowingly used at one time for the manufacture of atomic absorption graphite furnaces. Several laboratories were aware of unsatisfactory IQC for their blood lead methods and strived to find an explanation but it was only when the FQA data revealed a widespread problem that a group of participants compared their recent experience and were able to confirm with the suppliers that inferior graphite had been employed. 

A third category of syn eliminations involves pyrolytic decomposition of esters with elimination of a carboxylic acid. The pyrolysis of acetate esters normally requires temperatures above 400° C and is usually a vapor phase reaction. In the laboratory this is done by using a glass tube in the heating zone of a small furnace. The vapors of the reactant are swept through the hot chamber by an inert gas and into a cold trap. Similar reactions occur with esters derived from long-chain acids. If the boiling point of the ester is above the decomposition temperature, the reaction can be carried out in the liquid phase, with distillation of the pyrolysis product. 

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