Lead baths

The dezincing chamber is set first in the drossed lead bath, then water connections are immediately made in order to prevent the formation of steam within the water jacket. While the temperature is being raised, the vacuum pump is placed in operation and the agitator started. The temperature is then raised to 600°C and held throughout the operation. 

Miscellaneous. Where a copper refinery is adjacent to a lead (qv) plant it is feasible to recover the selenium in slimes by smelting them in conjunction with lead-bearing materials. Utilizing the lower temperatures needed to melt lead, the selenium is volatilized from a lead bath or cupel blown with air. The selenium is recovered from flue dust and fume by scmbbing. This is the process used by Union Miniere at its Hoboken plant in Belgium. 

Betterton-KroIIProcess. MetaHic calcium and magnesium are added to the lead bullion in a melt and form ternary compounds that melt higher than lead and are lower in density. By cooling the lead bath to a temperature close to the melting point of lead, the intermetalHc compounds high in bismuth content soHdify and float to the top where they are removed by skimming. 

Lead alloys containing small amounts of calcium aie formed by plunging a basket containing a 77 or 75% calcium—23—25% A1 alloy into a molten lead bath or by stirring the Ca—A1 alloy into a vortex created by a mixing impeUor (19). 

The newest fin baths, fin—lead baths, and lead baths recendy entering the market, are based on methanesulfonates. The higher makeup cost of tin methanesulfonate baths, about 1.6 times the cost of duoborate baths, may be justified where restrictions on duoborates and boric acid ia wastes exist. 

Blei-asche, /. lead dross lead ash the gray film of oxide on lead exposed to air. -aus-kleidung, /. lead lining. -azetat, n. lead acetate, -bad, n. lead bath, -bauzn, m. lead tree, arbor aaturni. 

With molten lead or tin, limited use of high-alloy steels is possible. In the case of containers for lead baths, it is important to avoid the combination... 

The Dilex Process utilises a molten lead bath as transfer medium and is applicable to diflfusion coatings of Cr, Al, Ti, Mo, Ni and Co. Finally, a Japanese fused borate bath process produces carbide coatings (Cr, V, Nb or Ta) on carbon and tool steels. The coatings are wear and corrosion resistant. The TD Process uses this technique. 

Tubular flow units, like the CSTR, usually are operated at steady state. It is not always easy to measure the temperature profile accurately. In some high temperature operations, the coil is immersed in a fluidized sand bed or lead bath so there is fairly good temperature control. Sometimes it is felt desirable to do the laboratory work in a tubular unit if the commercial unit is to be of that type, but rate data from any kind of equipment are adaptable to the design of PFR. 

Heat transfer calculations show that when 15% of the coil has been traversed, the oil temperature is within 5°F of the lead bath. It will be assumed that no significant conversion has occurred in the preheat section and that the reaction is substantially isothermal in the remaining 85% of the reactor volume. 

The vapor-phase contact oxidation of toluene was conducted in a conventional flow system. The reactor was made of a steel tube, 50 cm long and 1.8 cm I.D., mounted vertically and immersed in a lead bath. Air or a mixture of oxygen and nitrogen was introduced from the top of the reactor, with toluene being injected into the preheating section of the reactor by means of a syringe pump. 

The diaphragm changes its zero point with temperature, but it is calibrated at the high temperature. A new diaphragm behaves erratically, and must be seasoned for an hour or two before making actual determinations. Tests were made with air to determine the extent of any time-lag. When the flask is plunged into the lead bath from room temperature the diaphragm settles down to a uniform value in about a minute and a half and thermal equilibrium with the gas is reached in about five minutes. 

Catalyst Evaluation. Experiments were conducted in a stainless steel reactor containing 150 mL of catalyst. The catalyst bed measured 15 in. in length. A 3-point thermocouple was placed in the middle of the catalyst bed to monitor the temperature at the inlet, center, and outlet of the reactor. A lead bath was used to heat the reactor, attempting to achieve an isothermal operation, which frequently was attained. However, temperature rises were observed when good performance was achieved. 

In processes carried out at low temperatures where either iron tubes or chromel and nichrome tubes may be employed, experiments should be performed to determine the relative value of these tubes in life in hours per dollar of cost. There are practically no data available in this regard. In heat-treating furnaces and carbonizing furnaces, chromel A is often used. Chromel C and nichrome last many months in lead baths. Chromel and nichrome do not volatilize so readily as iron. Base-metal couples are thus better protected by these tubes than when iron or steel is employed. Chromel contains practically no iron. Chromel and nichrome have a rather high iron content. 

Ion chromatography is not only used to monitor the water quality, but also to analyze a variety of process liquors that are employed in the manufacture of printed circuit boards. This includes cleansers, palladium-based activators, and various electroplating baths such as acidic and electroless copper baths, tin/lead baths, electrolytical nickel baths, and gold baths. The analytical chemistry of the key substances contained in these baths is described in detail in the preceding chapter. 

---