Contents 2 Casting

Gray iron is resistant to concentrated acids (nitric, sulfuric, phosphoric) as well as to some alkahne and caustic solutions. Caustic fusion pots are usually made from gray cast iron with low silicon content cast-iron valves, pumps, and piping are common in sulfuric acid plants. 

Figure 7.6. Melting point depression of PVDF in its PMMA blends as a function of PVDF content (+) Cast samples, Nishi and Wang (A) Quenched samples, Nishi and Wang (o) Morales et al. (+) Acosta etal. (k) Roerdink and Challa ( ) Mijovic et aZ. (V ) Paul and Altamirano. ...

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It is also possible that the tolerance limit correlates with a boundary between an active and passive form of the iron precipitate (Hillis and Reichek, 1986). This has not been confirmed directly by metallographic examination (Aune, 1983 Lunder et al., 1985 Reichek et al., 1985), but is based on the observation that at melt compositions above the tolerance limit, iron alone (or perhaps an iron-aluminum intermetallic) drops from the melt as the metal is cooled, i.e. there is little or no reduction in the manganese level. Only at compositions below the tolerance limits is there a simultaneous reduction in both the iron and manganese content. Castings within this composition region would contain only an Fe-Mn (or Fe-Mn-Al) precipitate phase which is apparently passive as a cathodic site (Lunder et al., 1985). 

Slurry or slip casting provides a relatively inexpensive way to fabricate unifonn-thickness, thin-wall, or large cross section shapes [4o, 44, 45, 46, 42 aiid 48]. For slip casting, a slurry is first poured into a porous mould. Capillary suction then draws the liquid from the slurry to fonn a higher solids content, close-packed, leather-hard cast on the inner surface of the mould. In a fixed time, a given wall thickness is fonned, after which the excess slurry is drained. 

Electric hot plates may also be employed for heating. These should be of substantial construction and be provided with three-way switches. The diameter of the heavy cast-iron top may vary between 5 and 10". It is usually advisable to interpose a sheet of asbestos board between the metal top and the vessel to be heated, particularly if the contents of the latter are liable to bump. ... 

Quantum mechanics is cast in a language that is not familiar to most students of chemistry who are examining the subject for the first time. Its mathematical content and how it relates to experimental measurements both require a great deal of effort to master. With these thoughts in mind, the authors have organized this introductory section in a manner that first provides the student with a brief introduction to the two primary constructs of quantum mechanics, operators and wavefunctions that obey a Schrodinger equation, then demonstrates the application of these constructs to several chemically relevant model problems, and finally returns to examine in more detail the conceptual structure of quantum mechanics. 

Nickel-based aUoys have superior corrosion resistance to Hon-based aUoys. The only aUoys recommended for hot hydrochloric acid use are Ni—Mo aUoys containing 60—70% Ni and 25—33% Mo. Chlorimet (63 Ni, 32 Mo, 3 Fe) and HasteUoy (60 Ni, 28 Mo, 6 Fe) are found to be stable at aU acid concentrations in the absence of aH and Hon chlorides. Electroless nickel, a Ni—P aUoy containing 2—10% P, shows exceUent resistance to hot hydrogen chloride (71). The corrosion resistance increases with phosphoms content. This coating can be deposited on cast Hon, wrought Hon, mild steel, stainless steels, brass, bron2e, and aluminum (qv). 

HBI has been successfully melted in cupolas (hot or cold blast), induction furnaces (coreless or channel), and electric arc furnaces. It can be a valuable charge material for ductile and malleable irons as well as steel. It is of particular value in making ductile iron castings because of its very low residual element content. 

The slag is batch tapped into a receiving room where it is cooled and broken up for disposal. The metal buUion is tapped from the furnace periodically via a siphon into 2-t cast-iron molds. Typical buUion content from an electric furnace in wt % is Sb, 13—18 Sn, 1—2 As, 0.5—1 Cu, 0.3—0.4 and Ni, 0.05—0.1. The balance is lead. 

By using nucleants, fine-grained stmctures, such as that shown in Figure 4b, can be produced in cast alloys independent of the antimony content. The molten metal must be kept at a temperature high enough to assure complete solubiUty of the nucleants prior to casting the alloy. In the United States primarily copper and sulfur are used as nucleants in Europe and Asia selenium is used. At very low (1.0—1.6 wt %) antimony contents selenium is used exclusively. 

Rea.ctivity ofLea.d—Ca.lcium Alloys. Precise control of the calcium content is required to control the grain stmcture, corrosion resistance, and mechanical properties of lead—calcium alloys. Calcium reacts readily with air and other elements such as antimony, arsenic, and sulfur to produce oxides or intermetaUic compounds (see Calciumand calciumalloys). In these reactions, calcium is lost and suspended soHds reduce fluidity and castibiUty. The very thin grids that are required for automotive batteries are difficult to cast from lead—calcium alloys. 

The matte can be treated in different ways, depending on the copper content and on the desired product. In some cases, the copper content of the Bessemer matte is low enough to allow the material to be cast directly into sulfide anodes for electrolytic refining. Usually it is necessary first to separate the nickel and copper sulfides. The copper—nickel matte is cooled slowly for ca 4 d to faciUtate grain growth of mineral crystals of copper sulfide, nickel—sulfide, and a nickel—copper alloy. This matte is pulverized, the nickel and copper sulfides isolated by flotation, and the alloy extracted magnetically and refined electrolyticaHy. The nickel sulfide is cast into anodes for electrolysis or, more commonly, is roasted to nickel oxide and further reduced to metal for refining by electrolysis or by the carbonyl method. Alternatively, the nickel sulfide may be roasted to provide a nickel oxide sinter that is suitable for direct use by the steel industry. 

Nickel—Iron. A large amount of nickel is used in alloy and stainless steels and in cast irons. Nickel is added to ferritic alloy steels to increase the hardenabihty and to modify ferrite and cementite properties and morphologies, and thus to improve the strength, toughness, and ductihty of the steel. In austenitic stainless steels, the nickel content is 7—35 wt %. Its primary roles are to stabilize the ductile austenite stmcture and to provide, in conjunction with chromium, good corrosion resistance. Nickel is added to cast irons to improve strength and toughness. 

Another set of nickel aHoys, which have a high chromium content, a moderate molybdenum content, and some copper, are the ILLIUM aHoys. These cast aHoys are wear and erosion resistant and highly resistant to corrosion by acids and alkaHes under both oxidizing and reducing conditions. 

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