Inter-rod Spacing Research Articles

Interlamellar spacing in discontinuous precipitation

After reviewing the behavior of a number of systems exhibiting discontinuous precipitation, the theoretical treatment of the process is discussed, with emphasis on the problem of the interlamellar (or inter-rod) spacing. The case of the minimum, or critical, spacing is discussed for lamellar and rod products, as is a possible criterion for the maximum accessible spacing. The problem of the optimal spacing is then addressed, mainly from an experimental point-of-view. Experimental data for Al-Zn and Mg-Al alloys are analyzed and related to the discussion.

Interrod forces in aqueous gels of tobacco mosaic virus

The lateral separation of virus rod particles of tobacco mosaic virus has been studied as a function of externally applied osmotic pressure using an osmotic stress technique. The results have been used to test the assumption that lattice equilibrium in such gels results from a balance between repulsive (electrostatic) and attractive (van der Waals and osmotic) forces. Results have been obtained at different ionic strengths (0.001 to 1.0 M) and pH's (5.0 to 7.2) and compared with calculated curves for electrostatic nad van der Waals pressure. Under all conditions studied, interrod spacing decreased with increasing applied pressure, the spacings being smaller at higher ionic strengths. Only small differences were seen when the pH was changed. At ionic strengths near 0.1 M, agreement between theory and experiment is good, but the theory appears to underestimate electrostatic forces at high ionic strengths and to underestimate attractive forces at large interrod spacings (low ionic strengths). It is concluded that an electrostatic-van der Waals force balance can explain stability in tobacco mosaic virus gels near physiological conditions and can provide a good first approximation elsewhere.

Effect of composition on the structure of directionally solidified AlNi and AlNiCu composites

AlNi alloys with compositions ranging from 4 to 11 wt% Ni are directionally solidified at a growth rate of 3 cm/h and a temperature gradient of 130 K/cm. The structures obtained consist mainly of primary dendrites embedded in aligned eutectic except for compositions with from 5·8 to 6·06% Ni where complete couplede utectic growth is found. In the dendritic structures the area fraction of primary dendrites was measured and the interdendritic eutectic composition evaluated. This eutectic-like material exhibited compositions always richer in Ni than the equilibrium eutectic alloy. The inter-rod spacing of the interdendritic eutectic decreased with Ni content in the ‘eutectic’. The addition of small amounts of copper (1 to 2%) to the AlNi eutectic gave a cellular structure where the misorientation and irregularities of the Al 3Ni phase increased with increasing copper content.

Influence of Gravity Driven Convection on the Directional Solidification of Bi/MnBi Eutectic Composites

ABSTRACTThe role of gravity on Bridgman-Stockharger directional solidification of eutectic Bi/MnBi has been studied in reduced gravity aboard NASA sounding rocket SPAR flight experiments and contrasted with normal gravity investigations. The directional solidification of eutectic Ri/MnBi results in a low volume fraction, faceted/nonfaceted aligned rod eutectic whose MnRi rod size, interrod spacing, thermal and magnetic properties are sensitive functions of solidification processing conditions. The morphology of the low-gravity samples showed striking differences compared with identically processed,normal gravity samples grown in the same apparatus. The MnBi rod diameter and interrod spacing distributions were significantly smaller, approximately 50%, for the lowgravity samples compared with identically processed one gravity samples. Accompanying the smaller MnBi rod diameters observed in the flight samples, was an increase in permanent magnet properties which reached greater than 97% of the theoretical maximum.Gravitationally induced thermal instabilities in one-gravity which result in irregular interface movement and associated difficulty of the faceted MnBi phase to branch are suggested to explain the morphological differences between one and low gravity solidification.

Ultrastructural changes in the translucent and dark zones of early enamel caries.

Selected areas of early enamel caries ('White spot' lesion) in human teeth were argon-ion-beam thinned and examined by transmission electron microscopy. A systematic examination of areas which were histologically defined as the translucent zone and the dark zone showed that the pattern of early caries was consistent with that of demineralization of the tissue commencing with a widening of the micropores and of the inter-rod spaces and gradually progressing to a severe destruction of the original enamel crystals, with possibly some remineralization. Observations indicate that the intercrystalline micropores and inter-rod spaces are the pathways by which acidic agents reach the crystals causing carious dissolution.

The effect of shape variations during growth on the morphology ofin-situ eutectic composites

An experimental investigation has been conducted of the influence onin-situ eutectic composite microstructures of both gradual and abrupt changes in cross-sectional area, both with and without simultaneous changes in growth direction, and of the effects of changes in growth direction at constant cross-section. Alloys of the binary (Al-Ni and ternary Al-Cu-Ni) eutectic were chosen to eliminate the effects of microsegregation and these were grown under a variety of conditions of growth rate and temperature gradient, consistent with those used for off-eutecticin-situ composites, and in apparatus generally used for that work and described previously. As well as the expected variation in lamellae or inter-rod spacing with changes of cross-section, abrupt decreases in crosssectional growth area coupled with changes in growth direction produced a multigrain structure of various orientations. Potentially weak zones denuded of lamellae or rod growth were observed when the growth direction deviated beyond a limiting small angle at constant cross-section.

Growth of niobium-niobium carbide (Nb2C) eutectic and hypereutectic composites by zone melting

Growth from the melt of niobium-niobium carbide (Nb-Nb2C) composites at the eutectic and off the eutectic composition by electron beam floating zone melting and freezing was studied. Composite growth has been successfully achieved for the eutectic composition and for compositions up to four atomic percent above the eutectic. The volume fraction of the carbide phase was increased from 26 to 33 pct by growing off the eutectic composition. The alignment and morphology of the carbide phase are influenced primarily by growth rate and composition. The carbide morphology may be either rod-like or plate-like. For a given composition, rod morphology is favored at higher growth rates. For constant growth rate, the plate-like morphology is promoted by increasing carbon content. The transition from plate to rod morphology is gradual. Lamellar and inter-rod spacings vary from 1 to 6 microns for growth rates varying from 5 to 90 microns per second. Variation of lamellar spacing with freezing rate,R, produces a straight line (on a log-log plot) in agreement with a relationship of the form {fx2309-1} = constant, withn = 0.8. For alloys four at. pct above the eutectic, primary Nb2C dendrites nucleate and grow ahead of the still well aligned two phase solid plus liquid interface.

Microstructure of an Al-Fe alloy produced by unidirectional solidification

In relation to the production of composite materials, the present paper studied the influence of the solidification rate on the microstructure of an unidirectionally solidified eutectic Al-Fe alloy. The results obtained are as follows:(1) When the solidification rate was less than 10cm/hr, FeAl3 rods were regularly aligned parallel to the solidification direction. However, when the solidification rate was more then 20cm/hr, the microstructure became irregular, as observed in the normal cast structure.(2) The eutectic compounds under high and low solidification rate were rods and flakes in shape, respectively. It was found that the rod diameter decreased as the solidification rate increased.(3) The interrod spacing, λ, was related to the solidification rate, R, as λ2R=K, where K was 2.7×10-9cm3/sec.

The effect of solidification rate on structure and high-temperature strength of the eutectic NiAl-Cr

The eutectic NiAl-Cr, consisting of chromium rods in a NiAl matrix, was directionally solidified at rates varying from 1/4 to 30 in. per hr. The inter-rod spacing and elevated temperature tensile properties were measured and the structure determined for each solidification rate. The spacing, λ, obeyed the relation λ2V= Constant, whereV is the solidification rate. AtV greater than 1 in. per hr, a cell or colony structure formed and the cell size decreased with increasing solidification rate. At 600°C, the tensile strength increased substantially with decreasing inter-rod spacing, reaching 100,000 psi at the highestV. At 800° and 1000°C, the strength first increased then decreased at the highest solidification rates reaching maximum strengths of 63,000 psi and 47,000 psi, respectively. At 1200°C, the strength decreased slightly with increasing solidification rate. Fracture occurred by shear along grain boundaries and cell walls. The decreased strength at the highest solidification rates may be related to the increased cell boundary area.

銅-鉛合金の偏晶反応凝固

Principles of monotectic solidification of the binary copper-lead alloy are introduced from the observation of crystallizing courses of direction-free and unidirectional solidification in the monotectic and hyper-monotectic alloys. In the direction-free solidification the α-solid of a monotectic product grows in volume spherically unlike dendritic growth in the hypo-monotectic alloy. The released L2 liquid accompanied by generation of the α-solid lies in the α-solid sphere radiately, while the initial L2 does in the boundaries. Columnar growth of the α-solid of a monotectic product occurs in an opposite direction of heat flow during unidirectional solidification. The monotectic cell is produced in which the α-solid of a monotectic product grows in an opposite direction of heat flow surrounding the released rod-like L2 liquid. In the unidirectional solidification at temperature gradient 50°C/cm and freezing rate 60 mm/min abnormal condensation of the L2 in the liquid in advance of the monotectic cell results in the bell-shape aggregation in the hyper-monotectic copper-50% lead alloy. At temperature gradient 10° to 30°C/cm and freezing rate 0.5 to 4.0 mm/min widening the (L1+L2) layer causes arrangement of coarse and rod-like L2 liquid within the monotectic cell. The inter-rod spacing is in inverse proportion to the square root of freezing rate and is reduced with temperature gradient in the liquid. Both copper and lead in the monotectic cell grow preferentially in the 〈110〉 direction at high rate of freezing and in 〈111〉 at slow rate.