Invar

Baudelet F, Odin S, Giorgetti C, Dartyge E, Itie J P, Polian A, Pizzini S, Fontaine A and Kappler J P 1997 PtFej Invar studied by high pressure magnetic circular dichroism J. Physique IV C7 441... 

It is extensively used for making stainless steel and other corrosion-resistant alloys such as Invar(R), Monel(R), Inconel(R), and the Hastelloys(R). Tubing made of copper-nickel alloy is extensively used in making desalination plants for converting sea water into fresh water. 

Low Expansion Alloys. Binary Fe—Ni alloys as well as several alloys of the type Fe—Ni—X, where X = Cr or Co, are utilized for their low thermal expansion coefficients over a limited temperature range. Other elements also may be added to provide altered mechanical or physical properties. Common trade names include Invar (64%Fe—36%Ni), F.linvar (52%Fe—36%Ni—12%Cr) and super Invar (63%Fe—32%Ni—5%Co). These alloys, which have many commercial appHcations, are typically used at low (25—500°C) temperatures. Exceptions are automotive pistons and components of gas turbines. These alloys are useful to about 650°C while retaining low coefficients of thermal expansion. Alloys 903, 907, and 909, based on 42%Fe—38%Ni—13%Co and having varying amounts of niobium, titanium, and aluminum, are examples of such alloys (2). 

The thermal expansivity of Ni—Fe alloys vary from ca 0 at ca 36 wt % Ni (Invar [12683-18-OJ) to ca 13 x 10 / C for Ni. Hence, a number of compositions, which are available commercially, match the thermal expansivities of glasses and ceramics for sealing electron tubes, lamps, and bushings. In addition, the thermal expansion characteristic is utilized ia temperature controls, thermostats, measuriag iastmments, and condensers. 

K. C. Russell and D. F. Smith, Physical Metallurgy of Controlled Expansion Invar-Type Alloys, TMS PubHcation, Warrendale, Pa., 1990. 

Transport of France reduces dimensional change by using a thin inner liner of Invar. Another patented French system accommodates this change by means of the flexibility of thin metal which is creased. The creases run in two direc tions, and the form of the crossings of the creases is a feature of the system. 

In the Premier Mill the rotor is shaped hke the frustrum of a cone, similar to that in Fig. 20-53. Surfaces are smooth, and adjustment of the clearance can be made from 25 [Lm (0.001 in) upward. A small impeller helps to feed material into the rotor gap. The mill is jacketed for temperature control. Direct-connected hquid-type mills are available with 15- to 38-cm (6- to 15-in) rotors. These mills operate at 3600 r/min at capacities up to 2 mVh (500 gal/h). They are powered with up to 28 kW (40 hp). Working parts are made of Invar alloy, which does not expand enough to change the grinding gap if heating occurs. The rotor is faced with Stellite or silicon carbide tor wear resistance. For pilot-plant operations, the Premier Mill is available with 7.5- and 10-cm (3- and 4-in) rotors. These mills are belt-driven and operate at 7200 to 17,000 r/min with capacities of 0,02 to 2 mVh (5 to 50 gal/h). 

Beranger, G. et al. (1996) A Hundred Years after the Dicovery of Invar... the Iron-Nickel Alloys (I avoisier Publishing, Paris). 

The alloys of from 30% to 40% nickel in iron are noted for their unusual volumetric behavior. For example, it is well known that the thermal expansion of these alloys is anomalously low, with the Invar composition (36-wt% Ni) having a thermal expansion close to zero at room temperature. Furthermore, the atmospheric pressure compressibilities are anomalously large, whereas the atomic lattice spacing and density data show strong departures from Vegard s law in this same composition range. 

The pressure sensitivity of the magnetic properties of the Invar alloys is indicated by extensive measurements of the coefficient of saturation magnetization change with pressure M dMJdP for various compositions as shown in Fig. 5.10. The exceedingly large values in the 30%-40% Ni range are evident and much in excess of the values for iron and nickel. The 30-wt% Ni composition in the fee phase is the most sensitive to pressure, whereas this... 

Fig. 5.10. The pressure dependence of saturation magnetization for iron-nickel alloys shows a strong pressure dependence in the neighborhood of the Invar alloys (28.5 to 40-at. % nickel in the fee phase). The shock data shown are in excellent agreement with the static high pressure data (after Wayne [69W01]).

Curran [61C01] has pointed out that under certain unusual conditions the second-order phase transition might cause a cusp in the stress-volume relation resulting in a multiple wave structure, as is the case for a first-order transition. His shock-wave compression measurements on Invar (36-wt% Ni-Fe) showed large compressibilities in the low stress region but no distinct transition. 

The well defined change in compressibility of the fee alloy at 2.5 GPa clearly indicates the expected behavior of a second-order phase transition. The anomalously high value of the compressibility for the pressure-sensitive fee alloy is demonstrated in the comparison of compressibilities of various ferromagnetic iron alloys in Table 5.1. The fee Ni alloy, as well as the Invar alloy, have compressibilities that are far in excess of the normal values for the... 

The physical description of strongly pressure dependent magnetic properties is the object of considerable study. Edwards and Bartel [74E01] have performed the more recent physical evaluation of strong pressure and composition dependence of magnetization in their work on cobalt and manganese substituted invars. Their work contrasts models based on a localized-electron model with a modified Zener model in which both localized- and itinerant-electron effects are incorporated in a unified model. Their work favors the latter model. 

Fig, 5.15. A measured current-time pulse for shock-loaded Invar is shown. Time increases from left to right. The wave shape is closely predicted by the simple theory. Time from impact to peak current is about 1 fis. 

The non-ferrous alloys include the misleadingly named nickel silver (or German silver) which contains 10-30% Ni, 55-65% Cu and the rest Zn when electroplated with silver (electroplated nickel silver) it is familiar as EPNS tableware. Monel (68% Ni, 32% Cu, traces of Mn and Fe) is used in apparatus for handling corrosive materials such as F2 cupro-nickels (up to 80% Cu) are used for silver coinage Nichrome (60% Ni, 40% Cr), which has a very small temperature coefficient of electrical resistance, and Invar, which has a very small coefficient of expansion are other well-known Ni alloys. Electroplated nickel is an ideal undercoat for electroplated chromium, and smaller amounts of nickel are used as catalysts in the hydrogenation of unsaturated vegetable oils and in storage batteries such as the Ni/Fe batteries. 

D. G. Rancoutt, H. H. A. Smith, and R. C. Thiel, Metastable compositionally and magnetically modulated state of Fe-Ni Invar and the associated super-mon nt dynamics from Mossbauer spectroscopy, J. Magn. Magn. Mat, 66 121 (1987). 

For the more complex alloys anodic polarisation offers a vital extra variable in the use of selective etchants and has been widely exploited for alloys for which simple chemical etchants have proved inadequate. Besides many types of alloys steelthis technique has been applied to copper and the Cu-Be-Ni-Zr alloys " , uranium-base alloys " , Ni-Al alloys , tin-bearing invar and many others. 

Fig. 3.14. Relative linear thermal expansion coefficient of (1) Invar, (2) Pyrex, (3) W, (4) Ni, (5) Cuo.7Ni03, (6) stainless steel, (7) Cu, (8) brass, (9) Al, (10) Torlon, (11) soft solder, (12) Vespel SP-22, (13) Hg, (14) In, (15) Araldite, (16) Stycast 1266, (17) PMMA, (18) Nylon, (19) Teflon [60]. Some additional data are Ag between (8) and (9) Stycast 2850 GT slightly larger than (9). The integral contraction between 300 and 4K is 103AL/L = 11.5, 4.2, 6.3 and 5.7 for Stycast 1266, Stycast 2850 GT, Vespel SP-22 and solders...

Seeger, H. Terrones, M. Riihle, D. R. M. Walton, H.W. Kroto, J.L. Hutchison, Alloy nanowires Invar inside carbon nanotubes, Chem. Commun., vol. 5, pp. 471-472, 2001. 

The cell labeling procedure described above appears to be of general applicability. We have tested it on several tumor cell lines obtaining invar-iantly a very efficient uptake with no apparent cytotoxicity. Likely, the entrapment of [GdHPD03A(H20)] into the endosomic vesicles prevents any impact of the paramagnetic agent on relevant cellular processes while maintaining the full accessibility to cytoplasmatic water molecules. 

In order to progress with steels, it was necessary to pursue semi-empirical methods (Weiss and Tauer 1956, Tauer and Weiss 1958) which culminated in fire seminal paper describing the thermodynamics of iron (Kaufman et al. 1963). This included the concept of two different nuignetic states for f.c.c. iron, which had been applied to rationalise the Invar properties of iron-nickel alloys (Weiss 1963). However, this concept was viewed with considerable scepticism. Some support... 

Miodownik, A. P. (1978a) in Honda Memorial Volume on Metal Science and Metallurgy, in Physics and Application of Invar Alloys, ed. Saito (Maruzen, Tokyo) 3(18), p. 429. Miodownik, A. P. (1978b) ibid. 3(12), p. 288. 

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