Word hardening

With the epoxide resins the hardness and flexibility of the cured mass depends upon the chemical structure of the hardener used. A number of different hardeners are available giving not only altered physical properties but also setting times from a few minutes to several hours. When polyamide hardeners are mixed with epoxide resins the proportions may be varied either side of the 50/50 level less hardener making the set resih more rigid, while more hardener produces a more flexible product. In this sense the word hardener would appear not to be a good descriptive choice. 

Maraging steels are a class of high strength steels of very low carbon content. Strengthening is achieved by the use of substitutional elements to produce age hardening in the martensitic iron-nickel matrix. The term maraging was thus coined from the words martensite and age hardening . 

This book should convince even the most hardened of the doubting Thomases that polymer/additive analysis has gone a long way. With a developing field such as this one, any report represents only work in progress and is not the last word. 

Plaster of Paris has long been used as a casting material, a cement, and a mortar. If mixed with water, plaster of Paris forms a very soft and pliable mixture. After a very short time, lasting only 5-8 minutes, the wet, pliable mixture sets, that is, it hardens into a stable, firm solid. The setting process entails the incorporation of water molecules (a process known as hydration) into the calcium sulfate hemihydrate and the consequent formation and crystallization of hydrated sulfate of calcium. In other words, when water is added to plaster of Paris, the two combine, again forming gypsum, which soon crystallizes into a hard solid mass ... 

This word chrysocolla of the ancients, which denotes malachite, was not confined to that mineral, as appears particularly from the extended description of Pliny. He mentions the substance dug from the mines in proximity to gold, but he also states that it is a liquid found in the shafts of mines—a slime hardened by the cold of winter till it haB the hardness of pumice. The most valued is from copper mines, the next best from silver mines, and that from the gold mines is inferior. In the mines also an artificial chrysocolla is made by allowing water to percolate into the veins during the winter and spring, and evaporating these in July and August. 

According to the above model the first jumps to be activated are those from a site favourable for a rearrangement (large V-,t low potential barriers 17,). The gradual decrease of creep rate during the first phase indicates that the concentration of favourable sites decreases, in other words, that a jump from a favourable site leads to a less favourable position with a higher 17,- (strain hardening). 

The words of American Founding Father Tom Paine to characterize British King George III, against whom America fought the Revolutionary War, thus are highly appropriate "I rejected the hardened, sullen-tempered Pharaoh of England forever. . . and disdain the wretch. "(3)... 

The first series of experiments was devoted to determination of the effect scale on the slit temperature. In the second series of experiments we used the slits formed by massive plates of gold-silver alloy and pure palladium, varying considerably their microstructure. Namely, they were initially highly cold-hardened samples and later on the ones annealed at the recrystallisation temperature. In other words, we deal with either fine-grained or coarse-grained metal surfaces. 

Gutta-percha (with or without the hyphen) is the hardened latex from a number of different trees found in Borneo, Sri Lanka, and Malaya. The name comes from the Malayan words for juice (gutta) and tree (percha). This viscous plant sap hardens quickly and, after vulcanization, looks and behaves like hard rubber. The term gutta percha has also been used to describe unvulcanized hard rubber, regardless of its origin. 

Put very simply, copal is young version of amber. There is no definite age at which copal turns into amber, as the process is continuous firom the moment the resin appears on the tree and begins to solidify. In physical terms, when the resin is sufficiently cross-linked and polymerised it becomes amber (see Chapter 13, Plastics ). In other words, the resin has dried out and hardened. This process takes thousands if not millions of years, and not all copal becomes amber as much of it disintegrates with time. Furthermore, as the process is such a long one it is not possible for us to follow it or to replicate it in a laboratory, so there is still much that is speculation. We know, however, that there are some instances of copal that have begun to look like, and take on, the properties of amber. 

Ceramics, in the original sense of the word, were objects made of clays and hardened by fire. Nowadays the sense of the term is wider and not quite explicit. In the present book, it is used (as in most European languages) to cover products related by the character of the material and by the way of manufacture to the original sense of the term ceramics, not including glass, cements, etc. 

Many materials show some type of strain hardening post yield, sometimes called work hardening in other words, post-yield the material becomes harder to deform as the modulus increases. The power law strain hardening is the simplest model for strain hardening. The equations for power law strain hardening can be expressed as ... 

So-called sorel cement" is not a cement in the true sense of the word. Mixtures of caustic burnt magnesite (reactive MgO, produced by heating magnesium carbonate just above its decomposition temperature) and magnesium salts harden into a stone-like mass. "Sorel cement is obtained by reacting magnesium oxide with concentrated magnesium chloride solution ... 

Following Black, Anderson held that pure limestone was made up of calcareous earth united with fixed air. In his words, calcareous earth was a general term denoting all those substances that consist of the matter which lime may be made, in whatever state it may be found - whether alone - or mixed with other substances, that prevent it from being reduced to powder after calcination. 33 For reasons of simplicity, he often used lime synonymously with calcareous earth. 34 Lime, as he explained, existed in three states. First, mild calcareous earth was limestone in its pre-calcined state. Second, Caustic calcareous earth was exactly synonymous with quicklime, in its strict and philosophical acceptation. 35 Finally, Effete calcareous earth was the hardened cement that formed from the quicklime which meant that it was a post-calcination form of limestone. As Anderson explained it Lime is no sooner slaked, than it immediately begins to absorb its air, and return to its former mild state or, in other words, it becomes effete, in which state it possesses the same chemical qualities, in every respect, as limestone. 36... 

Key words high-strength aluminum alloys, dispersion hardening, quasicrystals, eutectic alloys, mechanical properties... 

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