They are volatile solids with polymeric structures. These tetrachlorides are precursors to various organohafnium compounds such as hafnocene dichloride and tetrabenzylhafnium. The white hafnium oxide (HfO2), with a melting point of 2812 °C and a boiling point of roughly 5100 °C, is very similar to zirconia, but slightly more basic. Hafnium carbide is the most refractory binary compound known, with a melting point over 3890 °C, and hafnium nitride is the most refractory of all known metal nitrides, with a melting point of 3310 °C.
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The process was also known as arc- atom welding. The heat produced by this torch is sufficient to weld tungsten (3422 °C), the most refractory metal. The presence of hydrogen also acts as a shielding gas, preventing oxidation and contamination by carbon, nitrogen or oxygen, which can severely damage the properties of many metals. It eliminates the need of flux for this purpose.
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Hafnium carbide (Hf C) is a chemical compound of hafnium and carbon. With a melting point of about 3900 °C it is one of the most refractory binary compounds known. However, it has a low oxidation resistance, with the oxidation starting at temperatures as low as 430 °C. This compound may be seen on future spacecraft as part of the heat shield.
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Psychopathy has often been considered untreatable. Its unique characteristics makes it among the most refractory of personality disorders, a class of mental illnesses that are already traditionally considered difficult to treat. People afflicted with psychopathy are generally unmotivated to seek treatment for their condition, and can be uncooperative in therapy. Attempts to treat psychopathy with the current tools available to psychiatry have been disappointing.
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These have standard size and shapes. These may be further divided into standard shapes and special shapes. Standard shapes have dimension that are conformed by most refractory manufacturers and are generally applicable to kilns or furnaces of the same types. Standard shapes are usually bricks that have a standard dimension of 9 inches (23011464 mm) and this dimension is called a "one brick equivalent".
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Radiatively cooled TPS can be found on modern entry vehicles, but reinforced carbon–carbon (RCC) (also called carbon–carbon) is normally used instead of metal. RCC was the TPS material on the Space Shuttle's nose cone and wing leading edges, and was also proposed as the leading-edge material for the X-33. Carbon is the most refractory material known, with a one-atmosphere sublimation temperature of for graphite. This high temperature made carbon an obvious choice as a radiatively cooled TPS material.
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Silicon carbide and carbon (graphite) are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with oxygen, as they would oxidize and burn. Binary compounds such as tungsten carbide or boron nitride can be very refractory. Hafnium carbide is the most refractory binary compound known, with a melting point of 3890 °C.Hafnium, Los Alamos National Laboratory The ternary compound tantalum hafnium carbide has one of the highest melting points of all known compounds (4215 °C).
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The disk of a Class 0 protostar is thought to be massive and hot. It is an accretion disk, which feeds the central protostar. The temperature can easily exceed 400 K inside 5 AU and 1,000 K inside 1 AU. The heating of the disk is primarily caused by the viscous dissipation of turbulence in it and by the infall of the gas from the nebula. The high temperature in the inner disk causes most of the volatile material—water, organics, and some rocks to evaporate, leaving only the most refractory elements like iron.
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Refractory metals and alloys attract the attention of investigators because of their remarkable properties and promising practical usefulness. Physical properties of refractory metals, such as molybdenum, tantalum and tungsten, their strength, and high-temperature stability make them suitable material for hot metalworking applications and for vacuum furnace technology. Many special applications exploit these properties: for example, tungsten lamp filaments operate at temperatures up to 3073 K, and molybdenum furnace windings withstand to 2273 K. However, poor low-temperature fabricability and extreme oxidability at high temperatures are shortcomings of most refractory metals. Interactions with the environment can significantly influence their high-temperature creep strength.
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For example, one model mixes two components, one with the composition of C1 chondrites and one with just the refractory components of C1 chondrites. In another model, the abundances of the five fractionation groups are estimated using an index element for each group. For the most refractory group, uranium is used; iron for the second; the ratios of potassium and thallium to uranium for the next two; and the molar ratio FeO/(FeO+MgO) for the last. Using thermal and seismic models along with heat flow and density, Fe can be constrained to within 10 percent on Earth, Venus and Mercury.
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Sand-sized grains of zircon Zircon is mainly consumed as an opacifier, and has been known to be used in the decorative ceramics industry. It is also the principal precursor not only to metallic zirconium, although this application is small, but also to all compounds of zirconium including zirconium dioxide (ZrO2), one of the most refractory materials known. Other applications include use in refractories and foundry casting and a growing array of specialty applications as zirconia and zirconium chemicals, including in nuclear fuel rods, catalytic fuel converters and in water and air purification systems. Zircon is one of the key minerals used by geologists for geochronology.
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Full article: Biological pump Particulate organic carbon, created through biological production, can be exported from the upper ocean in a flux commonly termed the biological pump, or respired (equation 6) back into inorganic carbon. In the former, dissolved inorganic carbon is biologically converted into organic matter by photosynthesis (equation 5) and other forms of autotrophy that then sinks and is, in part or whole, digested by heterotrophs. Particulate organic carbon can be classified, based on how easily organisms can break them down for food, as labile, semilabile, or refractory. Photosynthesis by phytoplankton is the primary source for labile and semilabile molecules, and is the indirect source for most refractory molecules.
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The North British booking offices were later provided on Waverley Bridge; the building is still in existence. The construction of the main line was not without disorder: Cockburnspath: The continued disturbances among the railway workmen at this station on pay days have induced the authorities to send out a detachment of Dragoons from Jock's Lodge [a cavalry barracks near Edinburgh]. Their arrival on Saturday morning was very anxiously looked for. As it is the intention of Messrs Ross and Mitchell, the contractors, to turn off about 500 of the most refractory, and burn their mud huts, to prevent their locating in the district, a serious disturbance might have been looked for, had the military not been on hand.
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The Mercury capsule design (shown with the tower) originally provided for the use of a passively cooled thermal protection system but was later converted into an ablative shield In modern vehicles, however, they can be found, but instead of metal, Reinforced carbon–carbon material is used (also called RCC Reinforced carbon-carbon or carbon-carbon ) . This material constitutes the thermal protection system of the nose and the front edges of the Space Shuttle and was proposed for the vehicle X-33. Carbon is the most refractory material known with a sublimation temperature (for graphite) of 3825 °C. These characteristics make it a material particularly suitable for passive cooling, but with the disadvantage of being very expensive and fragile.
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So completely had the state dominated the church that religious persecutions had become state persecutions, and Bonner was acting as an ecclesiastical sheriff in the most refractory district of the realm. Even John Foxe records instances in which Bonner failed to persecute those authorised for persecution. Bishop Bonner punishing a heretic from Foxe's Book of Martyrs (1563) Bonner's detractors, beginning with his Protestant contemporaries John Foxe and John Bale and continuing through most English historiography of the period, paint a different picture. Bonner, they point out, was one of those who brought it to pass that the condemnation of heretics to the fire should be part of his ordinary official duties, and he was represented as hounding men and women to death with merciless vindictiveness.
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" If he chose not to show urban grittiness, he also chose not to show empty landscapes. Instead he depicted small-town architecture, work-a-day streets and harbors, and, as often as not, people at their ease. Early in his career a critic praised Chatterton for his "fresh vision of the world, his power to find in narrow streets with trolley cars and railway culverts something stimulating in design and warm with a sense of human living" and credited him with the "power to impose formal discipline upon the most refractory of factual motifs and give them coherent harmony of organization and relevance." Another said he possessed a strong, forthright technique and praised his sentiment of place, taking "the white houses, the tall elms and dusty streets of New England towns as the important things in a picture.
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