の自然発火事例に遭遇した、水溶液中の

ミッシュメタル

が酸化を受け，その際発生する水素ガスを定量的に捕集し，水素ガスが自然発火の一因となり得るかどうかについて検討した．その結果，

ミッシュメタル

は非常に活性で，水溶液中では多量の水素ガスを発生し，自然発火の一因となり得ることが確かめられた．

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  High manganese cast steel was prepared in a high frequency induction furnace, using steel scrap and ferromanganese as raw materials. Effects of mischmetal additions on the mechanical properties and cast structure were investigated by measuring tensile strength, elongation and grain size of austenitic structure. Results are summarized as follows. 1) 0.01% mischmetal addition results in the highest mechanical properties. 2) The grain size of austenitic structure becomes finer with increasing mischmetal addition. 3) Mechanical properties, however, begin to decrease at the mischmetal addition of 0.02%. The decrease is even larger at and above 0.05% addition.

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  Little work has been done on the effects of titanium on the properties of calcium S-G iron. In the previous informations on magnesium S-G iron, it was suggested that titanium in calcium S-G iron may have an anti-spherodizing effect of graphite. The present work has been carried out to determine the effects of titanium on the properties of calcium S-G iron and also the effects produced when misch-metal is used with calcium to counteract the anti-spherodizing effect of titanium.
  Followings are the summary of the results obtained;
  (1) Titanium restricts spherodization of graphite in calcium S-G iron, but is not so powerful as in the case of magnesium S-G iron.
  (2) The combined use of a small quantity of misch-metal with calcium effectively counteracts the antispherodizing effect of calcium.

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Al-Zr alloys containing 0.1 to 0.2%Zr to which misch metal 0.04 to 1.0% had been added were prepared. The addition of misch metal about 0.2% to the Al-0.2%Zr alloy has a considerable effect to elevate the recrystallization temperature. The effect is accelerated by precipitation heat treatment, but is not in the dilute alloys such as the Al-0.1%Zr alloy. The addition of Ce to the Al-Zr alloys is also effective to elevate the recrystallization temperature, and it seems that such an effect of mish metal or Ce due to the precipitiation of Al₃Zr is acclerated by containing misch metal or Ce in the solid solution.

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  Spheroidizing agents such as magnesium and cerium are added in the stmosphere in general making processes of graphite cast iron. These metals, however, show much melting losses since they are oxidizable, and their effects on the spheroidizing are unstable. If these metals are added in the reduced prresure, their lossed may be lowered. Since a shrinkage cavity is said to have a concern in gasses included in the melt, if the shrinkage is reduced by degassing the melt, the large feeders of spheroidal graphite cast iron as hitherto will no more be necessary. Though cerium is a valuable metal, it is esaier to treat than magnesium, so, if the over all yield of added cerium is improved by reduced pressure addition, cerium will stand a chance to be used in the spheroidal graphite cast iron industry again.
  Pig iron was melted in the 50 kg or 100 kg induction furnace in atmosphere, desulphurized, composition adjusted with ferro-manganese and ferro-silicon, set in the vacum apparatus, statically degassed with reduced pressure of 7 mm Hg, during which added with metalic cerium or cerium-mishmetal, and poured into the test bars and shrinkage test castings.
  Results are concluded as follows:
  1. Optimum amount of additives in the reduced pressure are 0.20 to 0.25 per cent with metalic cerium and 0.25 0.30 per cent with mishmetal. Excessive addition does not improve the strength because it disfigures the spheroidal graphite is collapsed and the free cementite appears in matrix.
  2. Since the optimum amount of additives in the atmosphere are 0.34 to 0.40 per cent with metalic cerium and 0.40 to 0.45 per cent with mishmetal, additions in the reduced pressure make savings of about 40 per cent with both additives.
  3. The time of reduced pressure degassing before adding the spheroidizing agents has very little influence on the strength, however, as it has a good effect on the solidification shrinkage, it should be as long as possible in so far as the temperature falling permits.
  4. There is an optimum range of degassing time after adding the spheroidal agents, and excessive time of degassing lowers the strength sharply due to the evaporation of cerium. However, the solidification shrinkage reduces rapidly with increased degassing time after adding the agents, so that the optimum degassing time should be selected by compromising the both effects.

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Radionuclides contained in three kinds of misch metal products and two kinds of ingots were analyzed using a Ge (Li) semiconductor detector. Lanthanum-138 (¹³⁸La) and several daughter nuclides derived from thorium and uranium series were detected in all samples.All misch metal products and ingots were determined to be radioactive consumer products (RCP), although they have not been regarded as RCP in Japan. ¹³⁸La showed the highest nuclide content rate of all the radionuclides, and the lanthanum metal ingots displayed the highest specific activity at 720m Bq·g^-1. The maximum external effective dose was estimated to be 3.7m Sv when a metal match was carried for 8, 760 hours at 1mm from the skin. The calculated effective dose under some conditions exceeded 10μ, Sv per year.This value corresponded to the exemption standard proposed by the UK's National Radiological Protection Board.Individuals working with large amounts of RCP should be appropriately protected.

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The recrystallization temperature and electrical resistivity of precipitation treated Al-0.2 to 0.45%Zr alloys with and without small amounts of misch metal were examined. Any precipitation treatments of the cold rolled sheets before annealing is remarkably effective to elevate the recrystallization temperature of the binary alloys than those of the ingots, owing to acceleration of precipitation by cold working. The addition of a small amount of misch metal to the Al-Zr alloys enhances the precipitation in the alloys and intensifies the effect of recrystallization temperature elevation by the precipitation treatment.

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Centrifugally casting steel HK40 (0.4C-25Cr-20Ni) is widely used for reformer tube in the steam reforming process or cracking tube in the equipment which produces ethylen. A study has been made on the effects of complex addition of a small amount of the Ti, Nb and Mischmetal on the creep ruptures trength of HK40.
By addition of Ti and Nb, (Ti, Nb) C is formed, and as a result of forming (Ti, Nb) C, precipitation of Cr carbides and their coarsening are retarded. Therefore, the strength and ductility of creep rupture are improved.
Mischmetal is effective to improve the creep rupture strength, if it is added by alone. However the effect of Mischmetal can not be found in complex addition with Ti and Nb, because the strong effect of Ti and Nb hides the effect of Mischmetal.

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  The effects of the addition of cerium on the macro and microstructure of cast iron have been investigated.
  The results were as follows.
  (1) Added on the surface of molten iron, cerium reacts with oxygen so actively that cerium forms oxide and is lost without any suitable flux or coating.
  (2) The microstructures of cast iron added cerium showed, in turn from surface to bottom, unknown high cerium content ctructure, chilled structure and flake or eutectic graphite structure.
  The unknown structure consisted of Fe-Ce compound, cerium oxide and cerium sulfide.
  Cerium was remained in the chilled structure, but in the graphitized structure, cerium could not be detected at all.
  (3) With the aid of electron probe X-ray micro-analyser, it was cleared that cerium did not exist in cementite but on the boundary between cementite and austenite.
  (4) Silicon was detected in the same place that had high cerium concentration in the chilled structure.

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The equilibrium hydrogen absorption and desorption pressures, the hydrogen absorption and desorption rates, and the other characteristics of Mm-Ni alloys have been studied to appraise as hydrogen storage materials. In this study, it is clear that Mm-Ni alloys have good practical characteristics. Mm-Ni alloys containing 65 to 67 wt%Ni absorb the maximum amounts of hydrogen in the Mm-Ni system. For example, Mm-67 wt%Ni alloy forms the hydride MmNi_4.95H_6.95 at 20°C, and the equilibrium hydrogen absorption and desorption pressures are 20 and 10 atm respectively. The enthalpy changes of hydride formation and dissociation for Mm-67 wt%Ni alloy are −5.0 and 4.1 kcal/mol, and the apparent activation energies of hydrogen absorption and desorption are 6.1 and 8.6 kcal/mol respectively.

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  The solidificatian process of cerium-treated cast iron which had various carbon equivalents was studied. By cerium addition, spherodization occured easily in kish graphite, but not in the graphite separated at eutectic solidification. Cerium seemed to change the eutectic graphite to quasi-flaky type with less additian and to ledeburite and then to mesh-like graphite structure with more addition. So a perfectly spherodized graphite structure was obtained in hypereutectic alloy but not in hypoeutectic alloys, especially in that of law carbon equivalent. The solidification processes of the alloys of different carbon equivalents were as follows.
  a) Hypereutectic iron : Kish graphte separates as primary from the melt in spheroidal form and is surrounded by austenite at eutectic temperature. Small austenite dendrites grow from this austenite envelope. Around the dendrites deposites spheroidal austenite in which spheroidal graphite separates in the central part. The spheroidal austenite may appear apart from the primary austenite dendrites at the later stage of the solidification. In this stage quasi-flaky graphite forms in eutectic cells, if cerium is added insufficiently or mesh-like graphite forms by the decomposition of ledeburite, if cerium is added excessively.
  b) Slightly hypoeutectic iron: A small amount of primary spheroidal graphite may form the melt due to supercooling of the eutectic liquid treated with cerium. Accordingly the same solidification processes mentioned above occur, but a structure with completely spheroidal graphite IS hardly obtained as it be accompanied by more quasi-flaky or meshlike graphite. Primary spheroidal graphite is increased and the general appearance of the structure is improved by sufficient inoculation with silicon.
  c) Hypoeutectic iron: Small addition of cerium has more pronounced effects in these alloys than in other alloys, because of the segregation of cerium in eutectic liquid owing to the separation of more primary austenite. However, the graphite precipitated in eutectic austenite is spherodized only incompletely, as the eutectic austenite is restricted by the primary austenite dendrites. On the other hand, supercooling of eutectic melt is so pronounced as to form ledeburite or mesh-like graphite structure. Complete spherodization of graphite is difficult in the alloys of this composition range.

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Centrifugally casting steel HK40 (0.4C-25Cr-20Ni) is used for reformer tube in the steam reforming process or cracking tube in the equipment which produces ethylene. A study has been made of the effects of constituent elements such as C, Cr, Ni and adding elements such as Ti, Nb, Mo on the creep rupture strength of HK40.
The results obtained are summarized as follows:
1. C, Cr and Ni are effective to improve the creep rupture strength, where Si is sligtly effective and Mn is ineffective. With increasing Ni content, the slope of the rupture time-stress curve becomes gently and long time creep rupture strength increases.
2. By adding Ti, Mo, V and Nb, known as carbide former, the creep rupture strength is still improved at high temperature of 982°C. Mischmetal is effective and N is ineffective.

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With the recent digitization, electronic equipment housings are required to be thin-walled and have rigidity, heat dissipation, corrosion resistance, and electromagnetic shielding properties. Magnesium alloys are promising materials that satisfy these requirements. Mg-Al alloys have good castability and high strength, but their thermal conductivity decreases. In general, adding alloying elements to magnesium decreases thermal conductivity the effect of aluminum addition is significant. It was found that adding calcium to Mg-Al alloys to form Mg-Al-Ca (AX) alloys results in higher thermal conductivity than that of Mg-Al alloys. However, AX alloys have poor corrosion resistance and require post-treatment such as surface treatment. In this study, AX64, which has high thermal conductivity among the AX series alloys, was used as the basic composition, and corrosion resistance was improved by adding manganese and misch metal, and an attempt was made to improve corrosion resistance and emissivity through surface treatment. The change in thermal conductivity by heat treatment was also investigated. Experimental results showed that the addition of manganese and misch metal improved corrosion resistance and thermal conductivity. Plasma anodization also improved corrosion resistance and emissivity. Heat treatment of these alloys at 400°C improved the thermal conductivity with longer holding time.

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  This study investigated how holding time influenced the graphite type, chill depth and mechanical properties of rare earth added flake graphite cast iron. Iron was heated and held for 0 to 30 minutes in two types of furnace. ; high frequency furnace and electrical resistance (SiC rod type) furnace. When the iron was hold in the high frequency furnace, chill depth increased with increasing of holding time. On the other hand, specimens hold in the electrical resistance furnace showed no remarkable changes. Tensile strength and hardness decreased with increasing holding time in both furnaces. EPMA analysis showed that complex sulfide of manganese and rare earth in cast iron as substrates for graphite nucleation. The morphology of the graphite nuclei of rare earth added cast iron changed from a round shape into a polygon as the holding time increased. The composition of sulfide separated from (RE, Mn) S into RE₂S₃ and MnS as the holding time increased.

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