Iron ore suspensions

Metallurgical bacteria

Extractive metallurgy of zinc

Stress-corrosion cracking is currently defined as the cracking resulting from the combined effect of corrosion and stress (1). Cracks so produced are of a brittle nature and may be intercrystalline or transcrystalline depending upon the alloy and corrosive atmosphere involved. Frequently the amount of corrosion associated with the cracking is extremely small. The types of alloys that may be made to stress corrosion crack are numerous. In fact it seems probable that every alloy will so fail given the correct conditions. It is fortunate that the corrosive atmospheres that cause such cracking are relatively few.

Metals have been produced, worked and used since prehistoric times. For thousands of years however, most of the knowledge relating to metals was acquired by chance and the experience gained was passed from man to man through the centuries. Thus, many important processes such as forging and annealing, were carried out for centuries without anyone realizing what structural changes were actually taking place. In fact no attempt to explain the changes that occur during annealing was made until 1881. In that year Kalisher observed that heating caused changes in the "molecular structure" of cold worked zinc.

The properties of metallic materials are largely determined by their microstructure, i.e. by the relative amounts and by the arrangement of the phases that make up the microstructure. This fact has not been given the full attention which might seem due to it because, in the development of alloys, metallurgists have concentrated most on the properties of the separate constituents, less on the amount of these constituents and least of all on the disposition of the alloying elements in the final structure A simple illustration of the above remarks can be found in the case of cast iron, an alloy of iron and graphite.

Pure metals and many common alloys are made up of grains, similar in composition and crystal structure but not in shape. Each grain is a single crystal representing a phase and these materials are known as single-phase metals. The term "microstructure" in this case means simply a description of the sizes and shapes of the grains; there is nothing else that is accessible to visual or microscopic observation. The microstructure of a two-phase alloy is more complicated since the grains of the two phases differ in composition, structure and shape. In addition, the second phase may be present as a distinct set of grains interlocking with those of the first set or they may take on the form of needles, plates, rods or spheres which are enclosed within the matrix of the first phase (Fig. 1). The purpose of the study of microstructures or metallography then becomes the identification of the phases and the description of the sizes and shapes of the grains, needles, plates, etc. These observations the metallographer may then relate to the behaviour of the metal.

Stress corrosion cracking in its simplest terms is metal failure resulting, over a period of time from the conjoint action of stress and corrosion. In reality, the problem is more involved than this definition might suggest for the reason that the two operating factors, namely, stress and corrosion do not act in a simple additive way. Stress corrosion cracking is not a mere case of metal corrosion in the presence of stress. Although it is true that corrosive attack is part of the mechanism, the extent or severity of corrosion is not a guiding criterion for susceptibility to cracking. Many mildly corrosive environments have been recognised as strongly potent in causing this type of failure. A classical example was noted (1,2) in an experimental alloy which was stressed and immersed in a mineral oil-Nujol-and which failed in 735 days.

The metal industry supplies its products in a great variety of shapes and conditions for use by the fabricator. One of the most important forms is sheet or strip which may be used as they are, or fabricated further by such processes as drawing and spinning. The manufacturing process for metal sheet is the subject of this work; the metal investigated was copper. The purpose of the study was to measure the mechanical properties of copper sheet produced by two different methods, and to compare the data in order to see if one method had any clear advantages over the other. The first method of sheet production, which we may call temper rolling, is the one that is used almost exclusively in industry. This is the method discussed immediately below. The other sheet production method, which may be called partial annealing, has been used only in isolated cases. This method is dealt with after a discussion of temper rolling.

Froth flotation is based on the differences in the physico-chemicalsurface properties of particles of various minerals. It is very seldomthat the mineral to be separated possesses the desirable surface characteristics.Outside intervention is required to alter the natural surface of themineral particles that make up the flotation pulp. The mineral that is tobe floated by attachment to an air bubble must have a hydrophobic surfaceand the rest of the pulp must be hydrophilic or easily wettable. A mineralsurface can be rendered hydrophobic by the attachment of a layer built upof long chain hydrocarbons or of inert organic substances. [...]