Short Soaking Research Articles

Structure-property relations in a hypereutectic aluminium-silicon alloy dispersed with graphite particles

Changes in the microstructure and properties of an Al-Si (BS LM30) alloy dispersed with graphite particles brought about by T6 (solutionizing followed by artificial ageing) treatment were investigated. A range of ageing temperatures such as 165, 180, 215 and 240 °C were selected while the soaking time was varied from 1–24 h with a view to optimize the parameters. The base alloy processed under identical conditions was also heat treated, together with the composite to understand the role of the dispersoid in the alloy. Their properties, such as hardness, density and electrical resistivity were determined. Corresponding microstructural changes as a function of ageing temperature and duration were also observed. Observations made in this study indicate that the hardness peak shifted towards shorter soaking periods with temperature. The base alloy and the composite were found to follow a similar trend. However, the former possessed higher hardness and density and lower electrical resistivity. The changes in properties of the specimens were supplemented with considerable morphological modification of the matrix, the latter included the spheoridization of eutectic silicon particles and complex intermetallic compounds together with reduction in the size of the primary silicon phase due to fragmentation and dissolution. The study suggests that the heat treatment has tremendous potential to produce a desired combination of matrix microstructure and properties in graphitic Al-Si alloys by varying the treatment parameters, e.g. temperature and duration.

BIOCHEMICAL ANALYSES OF SEED EXUDATES DURING EARLY IMBIBITION

Short term soaking of seeds does not appear to be detrimental to seed viability and may provide a means of testing seed viability non-destructively. Seeds of corn (Zea mays L.) and rice (Oryza sativa L.), differing in viability, were soaked for 0.5, 1, 2 and 4 hr in distilled water at room temperature. Analyses of pH, protein/polypeptides (BCA assay and absorbance at 280 nm), and potassium (and other metals), were done on individual seed leachates. After each time period seeds were germinated for 7 d to determine viability. For both corn and rice, pH remained constant between 0.5 and 4 hr of soaking. Protein concentration gradually increased during the 4 hr soak in both corn and rice, but varied with seed lot. Potassium was the most common metal excreted and increased 3 to 4 fold between 0.5 and 4 hr of soaking. Although seed to seed variability in any given lot was high, in general, low viability seeds lost more cellular constituents than high viability seeds.

Short soaking in water inhibits germination of Datura ferox L. and D. stramonium L. seeds

Summary. Seed coat structures may play a major role in determining the germination of seeds. The involvement of seed coat characteristics in the inhibition of germination observed when dry seeds of Datura ferox L. and D. stramonium L., were rinsed or soaked in water for 1–5 min (‘soaking effect’) was investigated. Germination was inhibited by soaking D. ferox seeds even at late stages of the germination process up to one day before root protrusion. Simulation of the ‘soaking effect’ was achieved by blocking the hilum with lanolin, enamel lacquer or agar during imbibition. Blocking the hilum did not prevent water uptake by the seeds. Seed coat integrity was necessary for the ‘soaking effect’ since germination inhibition was eliminated by removing or cracking the seed coat. Drying the seeds up to 12 h after soaking reversed the inhibitory effect. SEM observations of both species revealed a loose outer parenchymatous tissue covering the hilum, an inner spongy tissue between the nucellus and the hilum and a space between the seed coat and the nucellus. We concluded that during soaking, water is trapped in the space between the seed coat and the nucellus, and in the intracellular spaces of the spongy tissue within the hilum. This water ‘plug’ may limit the diffusion of gas(es) to and from the embryo through the hilum, thus inhibiting germination.

Pretorsional deformation of Celion carbon fibers

The elastic and plastic deformation of Celion (PAN-based) carbon fibers as a function of annealing, pretorsion and acid treatment is reported. Variations of the shear modulus with the shear prestrain show a small recoverable elasticity and high brittleness. The shear modulus versus annealing temperature shows a maximum at about 160°C, where improved orientation is expected as shown by X-ray diffraction. The calculated relatively large ratio of the Young's modulus to shear modulus demonstrates that Celion carbon fibers possess a rather high mechanical anisotropy arising from the oriented structure. The shear modulus of acid-treated samples also showed a maximum at short soaking duration. Furthermore, the behavior of the tensile strength under pretorsion is almost similar to that of the shear modulus. Observed shear bands suggest that the torsional deformation takes place by cracking and consecutive shear banding.

The effect of soaking times on the mechanical properties of rapidly solidified aluminium alloys

The microcrystalline state of rapidly solidified alloys has been investigated by many experimentalists in the past ten years. Much attention has been given to the process variables of the rapid solidification process, to the microstructural effects on the obtained powder, splat or ribbon material, and to the constitutional effects, e.g. extended solid solubility and the presence of non-equilibrium crystalline phases [1]. In more recent years the consolidation process from the basic material into a solid testing material has also been the object of general interest [2]. As a logical step in the development of this material the last part of the production process, the thermomechanical treatment, should be optimized and adapted to the different properties of rapidly solidified material. Here we present some preliminary results of the optimization of the modified heat treatment of the aluminium alloy 2024 in the T4 condition, from which it becomes clear that a considerably shorter soaking time for solution heat treatment is desirable than in the case of the same conventional alloy. Tensile properties were used as the optimization criterion. Production of test material: smooth tensile test specimens with a reduced diameter of 5 mm were made out of bars of 8.4 mm diameter 2024 alloy, that were made by melt spinning, cold compaction and hot extrusion. The melt spinning equipment consisted of an electric resistance furnace with a capacity of 13 kg aluminium alloy and a rotating copper wheel (2000 rpm) with a diameter of 300ram. The furnace was filled with commercial 2024 alloy and the molten metal was ejected through a thermally isolated siphon with an orifice of 0.8 mm diameter onto the rotating wheel by an overpressure of argon to form rapidly solidified ribbons of 80#m thick and 1.5mm wide. The ribbons were compacted at room temperature, up to

A clinical and laboratory investigation of a new denture cleaner

Abstract A comparison was made of the efficiency of a new denture cleaner based on sulphamic acid with a cleaner based on an alkaline perborate. The study was divided into two parts, consisting of laboratory and clinical investigations. In the first part materials which are in common use for the manufacture of dentures or removable orthodontic appliances were immersed in solutions of the new denture cleaner and the results were compared with the effects produced by both water and solutions of the cleaner based on an alkaline perborate. Acrylic denture bases showed no signs of being adversely affected by any of the cleaning solutions, whereas a number of denture alloys showed slight superficial damage when immersed in the sulphamic acid cleaner. The acid cleaner is supplied with a freshening powder, which dissolves to produce a very effective buffering solution. In the second part, dentures were photographed before and after cleaning and the photographs were assessed by a panel of four judges. For a short soaking of 20 minutes the new cleaner was found to be the more efficient. The new cleaner is confidently recommended as efficient and safe and in which dentures can be soaked, particularly when calculus is present.

Short Soaking in Gibberellic Acid Promotes Tree Seed Germination

Gibberellins have been shown to promote seed germination of various hardwood and coniferous trees by overcoming dormancy (1-7). This note reports results of a study undertaken to determine effects of gibberellic acid (GA-3) on rate and capacity of germinmation of tree seed soaked in a high concentration of the hormone for a short time. In this completely randomized experiment 2 levels of gibberellic acid (GA-3) were applied to seed that had been stored for at least 6 months. Seed was soaked 12 hours in an aqueous solution of a 75 percent potassium salt at 250 or 500 ppm. A control was soaked only in distilled water. Twenty-five seed of a single species were placed on filter paper in Petri dishes and kept moist with distilled water. Four replications of each treatment were placed on a countertop in an air conditioned room kept at approximately 20°C. Table 1. Germination of individual species seed after soaking 12 hours in GA-3.

Influence of Conditions of Preparation on the Properties of Nickel-Zinc-Ferrite

Studies on the influence of various fabrication parameters viz., calcination temperature, grinding period, sintering temperature and soaking time, on the initial a.c. permeability and Q-factor of Nickel-Zinc-Ferrite (Ni0.3Zn0.7 Fe2O4 samples, were made with a view to develop ferrite cores, for use at high frequencies. A higher calcination temperature, a lower sintering temperature and a shorter soaking period have been found desirable to attain reasonably high density coupled with a low initial permeability and high Q. Repeated calcinations interspaced with wet grinding resulted in further improvement of the properties.