Early Stages Of Exposure Research Articles

The development of silicon‐containing oxides during the oxidation of iron‐chromium‐base alloys

AbstractThe influence of silicon on the oxidation of Fe‐14% Cr and Fe‐28% Cr has been studied at high temperature, with particular emphasis on the development and nature of the healing SiO2 layer. In general, silicon is a less effective addition than aluminium to these alloys in improving oxidation resistance because SiO2 grows at a lower rate than α‐Al2O3. Hence, silicon is a less successful oxygen secondary getter and development of a complete healing layer of SiO2 is less rapid than that of α‐Al2O3 on a corresponding aluminium‐containing alloy. Nonetheless, the addition of only 1% Si to Fe‐28% Cr causes a marked reduction in the overall oxidation rate, particularly by facilitating development of the Cr2O3 scale. Precipitates of SiO2 form at the alloy/scale interface. These grow inwards and laterally until they eventually link up to establish a continuous healing layer at the interface after several hundred hours exposure at 1000°C. Similar features are observed for Fe‐14% Cr‐3% Si but the healing SiO2 layer develops after a much shorter time for Fe‐14% Cr‐10% Si, due to the high silicon availability. In every case, the healing layer has been shown to be amorphous SiO2. Although this phase is very protective during isothermal oxidation, it is a site of weakness during cooling and scale spallation is very extensive from specimens where the SiO2 is continuous, with failure occurring cohesively within that layer.Ion implantation of silicon into Fe‐14% Cr and Fe‐28% Cr gives a reduced oxidation rate due to facilitation of a more rapid establishment of a Cr2O3 scale. Similar implantation of yttrium into the ternary alloys assists in development of the silicon‐containing oxide layer, possibly associated with an influence on the nucleation of the oxide precipitates in the early stages of exposure.

Photo-stabilisation and photo-degradation in organic coatings containing a hindered amine light stabiliser. Part I—ESR measurements of nitroxide concentration

Quantitative measurements of the variation in nitroxide free radical concentration on exposure to ultraviolet (uv) light are reported for a melamine crosslinked acrylic copolymer film doped with a hindered amine light stabiliser (bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate) as a function of hindered amine concentration, light intensity and humidity. The concentration of nitroxide is found to rise to a maximum and then slowly decrease. The following parameters can be derived from the nitroxide data: the net rate of formation of nitroxide during the early stages of exposure, the maximum nitroxide concentration, the time to maximum and the net decay rate at long exposure times. The observed variations in these parameters with exposure conditions are discussed. It is found that the humidity of the exposure greatly influences the degradation and stabilisation chemistry of acrylic-melamine coatings.

Photo-stabilisation and photo-degradation in organic coatings containing a hindered amine light stabiliser: Part II—Consumption of hindered amine

Gas chromatography has been used to follow the consumption of the hindered amine light stabiliser, bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate (HALS I) in an acrylic/melamine and an acrylic/urethane coating during exposure to ultraviolet (uv) light and humidity. The consumption rate is found to be a function of coating composition, exposure light intensity and humidity. In all cases, the rate of consumption is less than the photo-initiation rate of free radicals but greater than the net formation rate of nitroxide during the early stages of exposure. HALS I consumption in the urethane coating is found to be independent of humidity. HALS I consumption in the acrylic/melamine coating decreases with increasing humidity during exposure. In contrast, it was found in the previous paper that the net nitroxide formation rate increased with increasing humidity. This behavior can be accounted for by regeneration of hindered amine from nitroxide in the acrylic/melamine coating exposed under humid conditions. Another unexpected reaction observed in the acrylic/melamine coating is the conversion of HALS I ▪ groups to ▪ groups. These reactions are thought to involve formaldehyde which is released in the acrylic/melamine coating during cure and during exposure as a result of acrylic/melamine crosslink hydrolysis.

Increased gluconeogenesis in rats exposed to hyper-G stress

The role of gluconeogenesis on the increase in plasma glucose and liver glycogen of rats exposed to hyper-G (radial acceleration) stress was determined. Overnight-fasted, male Sprague-Dawley rats (250–300 g) were injected i.p. with uniformly labeled 14C lactate, alanine, o rm glycerol (5μCi/rat) and immediately exposed to 3.1G for 0.25, 0.50, and 1.0 hr. 14C incorporation of the labeled substrates into plasma glucose and liver glycogen was measured and compared to noncetrifuged control rats injected in a similar manner. Significant increases in 14C incorporation of all three labeled substrates into plasma glucose were observed in centrifuged rats at all exposure periods; 14C incorporation into liver glycogen was significantly increased only at 0.50 and 1.0 hr. The i.p. administration (5 mg/100-g body wt) of 5-methoxyindole-2-carboxylic acid, a potent gluconeogenesis inhibitor, prior to centrifugation blocked the increase in plasma glucose and liver glycogen during the first hour of centrifugation. The increase in plasma glucose and liver glycogen was also abolished in adrenodemedullated rats exposed to centrifugation for 1.0 hr. Propranolol, a beta-adrenergic blocker, suppressed the increase in plasma glucose of rats exposed to centrifugation for 0.25 hr. From the results of this study, it is concluded that the initial, rapid rise in plasma glucose as well as the increase in liver glycogen of rats exposed to hyper-G stress can be attributed to an increased rate of gluconeogenesis, and that epinephrine plays a dominant role during the early stages of exposure to centrifugation.

Comparative histopathological and biochemical analysis of early stages of exposure to non-silicogenic aluminium silicate-and strongly silicogenic quartz-dust in rats

One group of male CFY rats was given bentonite with high aluminium silicate content, the other group was given quartz dust, intratracheally. It has been stated that between 12-72 hours after the dust-exposure, the histological reactions developing upon the effect of non-silicogenic bentonite and silicogenic quartz are identical. Similarly in both groups lipid and phospholipid content of the lung shows a slight increase; the composition of phospholipids does not alter due to the effect of the two dusts. Between 12-72 hours after the exposure to both dusts the inflammatory response characterizing the histological reaction consists mainly of leukocytes; while between 48-72 hours macrophages appear in large numbers. The dust particles are swallowed both by leukocytes and macrophages. The confluating bronchopneumonia developed at the end of the 72nd hour is characterized by necrosis. Ninety days after exposure, bentonite causes storage-focal tissue reaction and quartz produces progressive pulmonary fibrosis; due to the effect of quartz, the lipid and phospholipid content of the lung significantly increases, the ratio of phospholipid fractions alters; bentonite does not increase the amount of pulmonary lipid and phospholipid. On the basis of the strong aldehyde bisulphite-toluidine blue (ABT) positivity of the macrophages containing bentonite, it may be assumed that the bentonite particle surface has an oriented polysaccharide and/or protein coat released from necrotized leukocytes, which protects the macrophage from the strong cytotoxic (necrotizing) effect of bentonite.

Morphological, pharmacokinetic, and hematological studies of lead-exposed pigeons

Adult white Carneaux pigeons were orally dosed with inorganic lead (6.25 mg Pb/kg/day, gastric intubation) for up to 64 weeks and the following studies were carried out: (1) the subcellular distribution of lead in erythrocytes; (2) the changes in tissue lead levels with time; (3) morphological assessment of tissue responses to lead; and (4) hematological effects of lead, the major systemic evidence of toxicity. In the early stage of exposure, there is some lead accumulation in the erythrocyte nucleus relative to its proportion of total cell volume, but such accumulation disappears with time. The kinetic behavior of lead in seven tissues—blood, brain, kidney, liver, femur, sciatic nerve, and crop—was seen to conform to two mathematical methods of lead distribution; brain, kidney, and femur lead increased with dosing time and reached or appeared to approach an upper plateau; lead in blood, liver, sciatic nerve, and crop increased to a maximum, followed by a decline to a lower plateau level. Morphologically, renal tubule cells showed the presence of lead-containing inclusion bodies while CNS mitochondria appeared to have accumulated lead. No evidence of segmental demyelination was seen. Lead exposure induced a marked and rapid hypochromic normocytic anemia in these birds, as well as an elevation in erythrocyte porphyrin. No disturbance in mechanical fragility or osmotic resistance was noted.

Formation of metallothionein in fish

1. 1. Carp were bred in Cd solution, and each organ was homogenizedd and centrifuged at 105,000 g . The Cd content of the supernatant was much more than that of the precipitate. 2. 2. In examining the metal form in the supernatant, the induction of metallothionein (MT) was found in carp exposed to Cd and Zn solutions and the presence of metallothionein was found in fish captured in Nagara river and breeding ponds. 3. 3. Cd content in the metallothionein fraction of hepato-pancreas increased at the early stages of exposure, but Cd in the metallothionein fraction of the other organs increased as time proceeded. 4. 4. In the tap water group, metallothionein in hepato-pancreas and kidney contained Cu, and increased with the induction of metallothionein in hepato-pancreas due to Zn-exposure.

Time course of plasma growth hormone during exercise in humans at altitude.

The effects of hypoxia on growth hormone release during submaximal exercise were studied 1) in eight highlanders (HL) at 3,800 m (La Paz, Bolivia); and 2) in five lowlanders (LL) at sea level, after 5 days' sojourn at 2,850 m, and while breathing a hypoxic gas mixture (FIO2 - 0.15 corresponding to PIO2 at 2,850 m) 1 mo after returning to sea level. Concentrations of immunoreactive human growth hormone ([IRHGH]), blood glucose ([G]), free fatty acids ([FFA]), and lactate ([LA]) were determined repeatedly at rest, during 1 h of exercise, and after 1 h of recovery. Compared with LL, in HL, the resting value of [IRHGH] is higher, the rate of increase at the beginning of exercise is faster and earlier, but the mean maximal value reached at the end of exercise is similar. The response pattern in LL during the early stages of exposure to hypoxia resembles that of HL. No correlation was found between peak values of [IRHGH] and maximal values of [LA] and [FFA] or minimal values of [G]. The possible causes of the different time sequence observed in growth hormone dynamics during hypoxia are suggested: an alteration of the clearance of the hormone through a more pronounced reduction of hepatic blood flow or a difference in the state of the pituitary gland before the exercise begins. The study emphasizes the importance of characterizing time sequence of [IRHGH] by parameters other than the maximal value, e.g., by mean concentration computed over exercise period.

Effect of Constant Temperature Treatments Followed by Fluctuating Temperatures on the Softening of Hard Seeds of Trifolium subterraneum L

Three experiments are described in which the effects of constant temperatures ranging from 15 to 80°C, followed by diurnally fluctuating temperatures of 60/15°C were compared on seed softening in three cultivars of T. subterraneum. Constant temperature treatments alone produced relatively few soft seeds, but rapid seed softening ensued within a few days of subsequent fluctuating temperature treatment. The higher and the longer the constant temperature pretreatment, the more soft seeds were obtained. The rate at which this preconditioning of the seed took place was highest in the early stages of exposure to constant temperatures. Differences between cultivars and between temperature treatments were established mainly during this early period of constant temperature treatment. Rates of change of temperature in the 60/15°C fluctuation treatment were important in the final seed softening process: the slower the rate of temperature change the more soft seeds were produced. It is suggested that two distinct temperature dependent processes are involved in seed softening. The first appears to be a thermal degradation process which probably results in weakening of the strophiolar region. Fluctuating temperatures bring about the second stage of softening in which the strophiole is rendered permeable to water.

Corrosion of VMo alloys and molybdenum in liquid sodium

The corrosion of arc melted VMo alloys, VMo alloys rolled after arc melting, and commercial powder metallurgic molybdenum in a high-purity liquid sodium, containing ≈ 1.0 ppm oxygen, at 700°C for 500 h were studied. Absorption of oxygen, nitrogen and carbon, and the corrosion loss of the solid metal during exposure to sodium decreased with an increase in the molybdenum concentration. For the low-molybdenum alloys, absorption of oxygen was high and proceeded rapidly at an early stage of exposure to sodium. The vanadium in the alloys was selectively oxidized and removed into the sodium from the surface and the grain boundaries near the surface of the alloys. After exposure to sodium, the ductility of the alloys was seriously deteriorated except for the commercial grade molybdenum. The results show that only molybdenum is acceptable with respect to corrosion in sodium.

Mechanical and microstructural properties of alloy 800

The evolution of microstructural and mechanical properties of alloy 800 with respect to operating conditions of the steam generator tubings of fast breeder reactors have been analyzed and presented. On the microstructural side two phenomena have important influence on the mechanical properties, namely γ′ and carbide precipitation. Gamma prime precipitation occurs in alloy compositions containing ≳0.50 pct Ti + Al, inducing mechanical property changes and, in particular, improving the long term creep resistance. Its growth rate follows the exponential law which, when extrapolated, yields an overaging time beyond 4 × 104 h at ≲550°C. M23C6 carbide precipitation starts in early stages of exposure at 500 to 600°C, being of heterogeneous nature and forming mainly on the grain boundaries. The M23C6 carbides advance perpendicular to the surface of one of the austenite grains, commonly having a γ// M23C8relationship, and occasionally develop into well defined cellular precipitates. On the mechanical side, a sharp creep ductility decline is observed when either, or in particular both, strong γ′ strengthening and discontinuous precipitation develop in the matrix. It is argued that this decline is principally due to the latter phenomenon and is accentuaged by matrix strengthening.

合成高分子防水層の耐候性 (その 1) : 材料自体の無拘束屋外暴露試験 : 力学的性質の変化と寸法安定性

In recent years, elastomeric roofing materials have been introduced because of their excellent mechanical property. These materials are, however, degradated in fairly short time after construction of roof. The purpose of this study is making clear the weatherability of these materials and the roof systems composed of them. The research consists of two works; one is outdoor exposure test in Tokyo and Sapporo, and the other is accelerated weathering tests. Each test was carried out from two different standpoints; One was how the materials were durable, and the other was how the roof systems composed of them were. In this paper, we discuss the changes in mechanical property and the dimensional stability of the materials when exposed outdoors under unrestrained condition. The results obtained may be summarized as follows. Generally speaking, the elongation at breakage decreased and the tensile stress at the elongation rate of 300% increased. Some specimens extended in the early stage of exposure, however, all the specimens showed a tendency to shrink after four year's exposure in Tokyo and Sapporo. The effect of outdoor exposure is severer in Tokyo than Sapporo.

The effect of solvent traces on the ultraviolet degradation of poly(vinyl chloride)

AbstractThe ultraviolet degradation of poly(vinyl chloride) films was studied in a photoreactor which supplied energy near 3000 Å. It was noted that the rate of degradation and color development was increased when the level of residual solvent in the cast films was increased. Two solvents were employed in the study: tetrahydrofuran and dichloroethane. The amount of residual solvent was correlated with the height of a characteristic peak at 2800 Å for tetrahydrofuran and 1900 Å for dichloroethane. Films which had very small traces of solvent showed excellent resistance to ultraviolet degradation, even in the absence of ultraviolet stabilizers. The analysis of solubility data showed that chain scission was controlling in the early stages of exposure, while crosslinking was controlling at later stages. As a result, it was not possible to apply Charlesby's treatment of radiation‐induced degradation. Comparison with the results obtained by other workers for degradation at 2537 Å showed that degradation at this wavelength was much faster than degradation at 3000 Å. Furthermore, degradation at 2537 Å appeared to be controlled by crosslinking at all stages of exposure.

The sulphidation of metals and alloys : K. N. Strafford, Metals Mater. (Met. Rev. No. 138), 3 (10) (1969) 153–174; 17 figs., 1 table, 107 refs.

Sulphidation is a serious problem in many energy conversion systems. Sulphidation attack is particularly severe in environments of low oxygen (pO2~10−18 Pa) and high sulphur (pS2 ~ 10−1_10−3 Pa) potentials at temperatures above 700°C. Recognizing that refractory metals have a high resistance to sulphidation in reducing environments, their use as overlay coatings in sulphur-containing environments deserves serious consideration. In the adoption of such an approach, Mo has been recognized as a highly sulphidation-resistant metal with a Kp value of 10−12 g2 cm−4 s−1 in an atmosphere of pS2 ~ 10−1 Pa at 750°C.In this study, Mo was deposited on two superalloys, Inconel 600 and Nimonic PE11, using air plasma spraying. The coated specimens were tested at 750°C for up to 168 h in an environment comprising pS2 ~ 10−1 Pa and pO2 ~ 10−18 Pa. The sulphidation kinetics (this is not real through-layer kinetics, since the specimens had open edges) were determined by a discontinuous gravimetric method. The exposed samples were characterized and analysed using SEM, EDX and XRD techniques. For uncoated Inconel 600, a duplex scale was formed which consisted of an outer Ni3S2 layer and an inner Cr2S3 layer. The scale developed on uncoated Nimonic PE11 comprised three sub-scale layers—an outer (Fe, Ni)9S8 layer, a mid Cr2S3 layer and an inner MoS2 layer. However, after prolonged exposure, the outer layer contained both (Fe, Ni)9S8 and Ni3S2 on the surface of the uncoated Nimonic PE11.The kinetics results demonstrated that Mo coating enhanced the corrosion resistance of both alloys, and particularly so for Nimonic PE11. For both substrates, Mo coating led to the development of two sub-scale layers at the early stages of exposure (e.g. up to 5 h). The outer layer consisted of Ni3S2 for Inconel 600 and (Fe, Ni)9S8 for Nimonic PE11. A MoS2 layer constituted the inner layer for both materials. After prolonged sulphidation, a Cr2S3 layer gradually developed between the outer layer and the inner MoS2 layer. It is apparent that the use of Mo coating hindered the formation of the Cr2S3 layer.

Aging of Stretched Rubber

Abstract Sunlight aging under tension of many compounds including the following has been investigated: tire tread shoe upper, tube stocks, golf ball thread, jar rubber, solid tire, bathing cap stock, channel rubber. With some of these stocks the sunlight aging as been compared with unstretched samples by Geer oven, Bierer bomb, and ultra-violet light methods. The stretching of the test strips accelerates deterioration in sunlight, ultra-violet light, and Geer oven. Stretched samples have not yet been tested in the Bierer bomb. The rate of deterioration was not proportional to the degree of stretch in any of the stocks in the early stages of exposure. In sunlight there is a critical elongation for each stock at which the deterioration progresses more rapidly than at any other in the early stages of aging. No direct relationship was found between the results of sunlight aging and the other methods employed. Stretched strips aged in ultra-violet light were found to give softer stress-strain curves than the unaged samples, whereas sunlight aging under the same conditions stiffens the stress-strain curve.