Other common names for this technique are Direct Current Sintering, Rapid Hot Pressing, Direct Hot Pressing, amongst others. All these techniques are summarized under the generic term "Field Assisted Sintering Technique (FAST)". The compelling reason for shortening the cycle time then was to avoid grain growth and also save energy. In direct hot pressing, the mold is directly connected to electrical power.
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Pressures of up to can be applied. Other great use is in the pressing of different types of polymers. Within hot pressing technology, three distinctly different types of heating can be found in use: induction heating, indirect resistance heating and field assisted sintering technique (FAST) / direct hot pressing.
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Powder compacts are heated externally and pressure is applied hydraulitically. In order to improve densification during hot pressing, diboride powders can undergo milling by attrition to obtain powders of <2μm. Milling also allows for more uniform dispersion of the additive SiC. Hot pressing temperature, pressure, heating rate, reaction atmosphere, and holding times are all factors that affect the density and microstructure of UHTC pellets obtained from this method. In order to achieve >99% densification from hot pressing, temperatures of 1800–2000 °C and pressures of 30 MPa or greater are required.
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A group at Shanghai University was able to construct a novel green plastic based on cellulose through a method called hot pressing.
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In conjunction with the USDA Forest Products Laboratory, Hamilton Roddis had developed new plywood adhesives and hot pressing technology.Forest History, Fall 2005, pp. 65–66 Retrieved: 30 July 2013.
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In principle the same improved sinter results (compared to conventional hot pressing) can be achieved by all direct hot pressing techniques, if the improvement is only due to the in-situ heating of the powder."International Powder Metallurgy Directory" (January 4th, 2012): 2011 Hagen Symposium: A Review of Spark Plasma Sintering by Prof. Bernd Kieback, Director of Fraunhofer IFAM Branch Lab Dresden and the Institute for Materials Science at the Technical University of Dresden (Germany). Summary has been published by Dr. Georg Schlieper.
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Prepregs are cured at elevated temperature. They can be processed with the hot pressing technique or the autoclave technique. Through pressure the fiber volume fraction is increased in both techniques. The best qualities can be produced with the autoclave technique.
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One of its uses is as a binder in some grades of hexagonal boron nitride for hot pressing. Other uses are e.g. flame retardant in epoxy molding compounds, a ceramic flux in some ceramic glazes, reactive self-sealing binders in hazardous waste management,Calcium borate binders. (PDF) .
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A product resembling masonite (hardboard) was first made in England in 1898 by hot-pressing waste paper.Akers, 1966, p. x Masonite was patented in 1924 in Laurel, Mississippi, by William H. Mason, who was a friend and protégé of Thomas Edison. Mass production started in 1929.
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Alumina, silicon carbide, and tungsten carbide are made from a fine powder of their constituents in a process of sintering with a binder. Hot pressing provides higher density material. Chemical vapor deposition can place a film of a ceramic on another material. Cermets are ceramic particles containing some metals.
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More advances in pressureless sintering must be made before it can be considered a viable method for UHTC processing. Spark plasma sintering is another method for the processing of UHTC materials. Spark plasma sintering often relies on slightly lower temperatures and significantly reduced processing times compared to hot pressing.
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Stabilized δ-phase Pu–Ga is ductile, and can be rolled into sheets and machined by conventional methods. It is suitable for shaping by hot pressing at about 400 °C. This method was used for forming the first nuclear weapon pits. More modern pits are produced by casting.
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A product resembling hardboard was first made in England in 1898 by hot pressing waste paper.Akers, 1966, p. x In the 1900s, fiber building board of relatively low density was manufactured in Canada. In the early 1920s, improved methods of compressing wet wood pulp at high temperatures resulted in a higher density product.
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Hot pressing is a high-pressure, low-strain-rate powder metallurgy process for forming of a powder or powder compact at a temperature high enough to induce sintering and creep processes.German, R.M.: A-Z of Powder Metallurgy, page 103. Elsevier, 2005. This is achieved by the simultaneous application of heat and pressure.
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There are two common methods to manufacture diamond grinding cup wheels: hot pressing and cold pressing. The hot pressing method is to directly sinter the diamond segments in molds under a certain pressure in the dedicated sintering press machine, and then fix or connect the diamond segments onto the grinding wheel’s body via high-frequency welding, laser welding or mechanical mosaic method. The cold pressing method is to first press the working layer (containing diamonds) and the transitive layer (not containing diamonds) of the diamond segments to their forms directly on the grinding wheel's body, and let the segments connect with the wheel's body via teeth, slots or other manners. Then, put the grinding wheels into sintering furnaces to sinter without press.
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Diamond segments consist of small-size diamonds and metal bond materials. The metal bond materials may include the powders of Cu, Sn, Fe, Ag, Co, Ni, WC, Mo, graphite, etc. The diamonds are mixed with the bond materials, and the mixture is loaded into molds. After hot pressing or cold pressing, sintering, and arc grinding, diamond segments are formed.
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This originated sintering methods employing pulsed or alternating current, eventually superimposed to a direct current. Those techniques have been developed over many decades and summarized in more than 640 patents. Of these technologies the most well known is resistance sintering (also called hot pressing) and spark plasma sintering, while electro sinter forging is the latest advancement in this field.
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UHTC materials with 20vol.% SiC and toughened with 5% carbon black as additives exhibit increased densification above 1500 °C, but these materials still require temperatures of 1900 °C and a pressure of 30 MPa in order to obtain near theoretical densities. Other additives such as Al2O3 and Y2O3 have also been used during the hot pressing of ZrB2-SiC composites at 1800 °C.
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Lunar ISRU 2019: Developing a New Space Economy Through Lunar Resources and Their Utilization. July 15–17, 2019. Unprocessed lunar soil, also called regolith, may be turned into usable structural components,In-Situ Resource Utilization: In-space Manufacturing and Construction. NASA. Accessed on 1 August 2019. through techniques such as sintering, hot-pressing, liquification, the cast basalt method, and 3D printing.
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He graduated from a technical school in Brno in the Czech Republic in 1934 and started his professional career as a metallurgical engineer. Later he was a professor at numerous universities across Europe. Balevski was the founder of the Bulgarian academic school in the field of metal sciences and technologies. He was successful in designing a hot pressing machine for non-ferrous metals.
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This type of molded pulp product is that which has undergone some kind of secondary processing which is generally different from or in addition to, the basic production procedure. This could apply to any of the first three types. Secondary processing could be coating, printing, hot- pressing, die-cutting, trimming or manufactured using colors or special slurry additives. Uses are for many kinds of custom applications.
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Retrieved Sept 23, 2006. The gadget used galvanic silver plating; afterwards, nickel deposited from nickel tetracarbonyl vapors was used, but gold is now preferred. To produce the first pits, hot pressing was used to optimally employ the scarce plutonium. Later designs used machined pits, but turning produces a large amount of waste, both as pyrophoric turnings of plutonium and plutonium-contaminated oils and cutting fluids.
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Hot pressing is mainly used to fabricate hard and brittle materials. One large use is in the consolidation of diamond-metal composite cutting tools and technical ceramics. The densification works through particle rearrangement and plastic flow at the particle contacts. The loose powder or the pre-compacted part is in most of the cases filled to a graphite mould that allows induction or resistance heating up to temperatures of typically .
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At a slightly higher gas pressure the electrolyte in the pore system is restricted to the work layer. The surface layer itself has such fine pores that, even when the pressure peaks, gas cannot flow through the electrode into the electrolyte. Such electrodes were produced by scattering and subsequent sintering or hot pressing. To produce multi-layered electrodes a fine-grained material was scattered in a mold and smoothed.
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The firm of Holmes and Narver were chosen as architect-engineers, and Haddock Engineers as the construction contractor. Complicating the construction program was the fact that Los Alamos had not finalized what processes would be used. Of particular concern was whether they would use casting or hot pressing with the explosives. For a time, work proceeded so as to accommodate either process, but ultimately a decision was required.
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A car muffler made of aluminized steel Aluminized steel was developed for providing more structural durability and a high yield strength in highly corrosive environments. It maintains the strength of high- alloy steel, but is cheaper to produce than high-alloy steels and thus is a preferred material for manufacturing automobile and motorcycle exhaust gas systems. Al-Si coatings are used to protect boron steel when hot pressing.
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Pressureless sintering is the sintering of a powder compact (sometimes at very high temperatures, depending on the powder) without applied pressure. This avoids density variations in the final component, which occurs with more traditional hot pressing methods. The powder compact (if a ceramic) can be created by slip casting, injection moulding, and cold isostatic pressing. After pre-sintering, the final green compact can be machined to its final shape before being sintered.
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The binder utilizes the unique temperature stability and insulating properties of h-BN. Parts can be made by hot pressing from four commercial grades of h-BN. Grade HBN contains a boron oxide binder; it is usable up to 550–850 °C in oxidizing atmosphere and up to 1600 °C in vacuum, but due to the boron oxide content is sensitive to water. Grade HBR uses a calcium borate binder and is usable at 1600 °C.
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S.G. Savio, K. Ramanjaneyulu, V. Madhu & T. Balakrishna Bhat, 2011, "An experimental study on ballistic performance of boron carbide tiles", International Journal of Impact Engineering 38: 535-541Chen Mingwei, McCauley James W & Hemker Kevin J. 2003. "Shock induced localized amorphization in boron carbide". Science 299: 1563-1566 Silicon carbide was at that time only used in some prototype land vehicles, such as the MBT-70. The ceramics can be created by pressureless sintering or hot pressing.
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William Lupton inherited 5/8ths of their grandfather's estate and Arthur 3/8ths, which they held as tenants in common but in 1811 they divided the property. William took "Town End" which included his father's dressing mill built in 1788, warehouses, the tenter garth stretching to Wade Lane and a substantial house. Its insured assets included a warehouse, counting house, packing shop, machinery and tools for dressing cloth, a hot pressing shop and a steam engine.
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These additives react with impurities to form a transient liquid phase and promote sintering of the diboride composites. The addition of rare earth oxides such as Y2O3, Yb2O3, La2O3 and Nd2O3 can lower densification temperatures and can react with surface oxides to promote densification. Hot pressing may result in improved densities for UHTCs, but it is an expensive technique that relies on high temperatures and pressures to provide useful materials. Pressureless sintering is another method for processing and densifying UHTCs.
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The basic equation is: FeO + H2 → Fe + H2O. This process has recently been made much more practical by the discovery of significant amounts of hydrogen-containing regolith near the Moon's poles by the Clementine spacecraft. Lunar materials may also be used as a general construction material, through processing techniques such as sintering, hot- pressing, liquification, and the cast basalt method. Cast basalt is used on Earth for construction of, for example, pipes where a high resistance to abrasion is required.
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Besides open structures from formed tape, extruded structures, such as honeycomb catalyst supports, and highly porous structures, including various foams, for example, reticulated foam, are of increasing use. Densification of consolidated powder bodies continues to be achieved predominantly by (pressureless) sintering. However, the use of pressure sintering by hot pressing is increasing, especially for non-oxides and parts of simple shapes where higher quality (mainly microstructural homogeneity) is needed, and larger size or multiple parts per pressing can be an advantage.
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Creep also explains one of several contributions to densification during metal powder sintering by hot pressing. A main aspect of densification is the shape change of the powder particles. Since this change involves permanent deformation of crystalline solids, it can be considered a plastic deformation process and thus sintering can be described as a high temperature creep process. The applied compressive stress during pressing accelerates void shrinkage rates and allows a relation between the steady-state creep power law and densification rate of the material.
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Figure III: Direct hot pressing The basic idea of sintering with electric current going through the mold is quite old. Resistance heating of cemented carbide powders was patented by TaylerTayler, G.F.: Apparatus for Making Hard Metal Compositions, U.S. Patent 1,896,854, 7 February 1933 as early as 1933. This method is currently undergoing renewed interest. Current can be pulsed or unpulsed DC or AC. Spark Plasma Sintering (SPS) is a common name for this technique, however, it is technically incorrect since no spark and no plasma have been validated so far.
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These techniques employ electric currents to drive or enhance sintering. Through a combination of electric currents and mechanical pressure powders sinter more rapidly thereby reducing the sintering time compared to conventional thermal solutions. The techniques can be divided into two main categories: resistance sintering, which incorporates spark plasma sintering and hot pressing; and electric discharge sintering, such as capacitor discharge sintering or its derivative, electro sinter forging. Resistance sintering techniques are consolidation methods based on temperature, where heating of the mold and of the powders is accomplished through electric currents, usually with a characteristic processing time of 15 to 30 minutes.
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In addition to improved mechanical properties, less SiC needs to be added when using this method, which limits the pathways for oxygen to diffuse into the material and react. Although addition of additives such as SiC can improve densification of UHTC materials, these additives lower the maximum temperature at which UHTCs can operate due to the formation of eutectic liquids. The addition of SiC to ZrB2 lowers the operating temperature of ZrB2 from 3245 °C to 2270 °C. Hot pressing is a popular method for obtaining densified UHTC materials that relies upon both high temperatures and pressures to produce densified materials.
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In spark plasma sintering (SPS), external pressure and an electric field are applied simultaneously to enhance the densification of the metallic/ceramic powder compacts. However, after commercialization it was determined there is no plasma, so the proper name is spark sintering as coined by Lenel. The electric field driven densification supplements sintering with a form of hot pressing, to enable lower temperatures and taking less time than typical sintering. For a number of years, it was speculated that the existence of sparks or plasma between particles could aid sintering; however, Hulbert and coworkers systematically proved that the electric parameters used during spark plasma sintering make it (highly) unlikely.
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Several techniques exist to produce pre-alloyed powder, such as Grade 5. In the hydride-dehydride process feedstock such as solid scrap, billet or machined turnings are processed to remove contaminants, hydrogenated to produce brittle material then ground under argon in a vibratory ball mill, typically at 400 °C for 4 hours at a pressure of 1 psi for Ti Grade 5. The resulting particles are angular and measure between 50 and 300 μm. Cold compaction after dehydrogenation of the powder, followed by either vacuum hot pressing (in this case the dehydrogenation process can be bypassed as hydrogen is removed under vacuum) or HIP and a final vacuum anneal, produces powders with hydrogen below 125 ppm.
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Advantages of SHS include higher purity of ceramic products, increased sinterability, and shorter processing times. However, the extremely rapid heating rates can result in incomplete reactions between Zr and B, the formation of stable oxides of Zr, and the retention of porosity. Stoichiometric reactions have also been carried out by reaction of attrition milled (wearing materials by grinding) Zr and B powder (and then hot pressing at 600 °C for 6 h), and nanoscale particles have been obtained by reacting attrition milled Zr and B precursor crystallites (10 nm in size). Unfortunately, all of the stoichiometric reaction methods for synthesizing UHTCs employ expensive charge materials, and therefore these methods are not useful for large-scale or industrial applications.
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Magnesium aluminate spinel (MgAl2O4) is a transparent ceramic with a cubic crystal structure with an excellent optical transmission from 0.2 to 5.5 micrometers in its polycrystalline form. Optical quality transparent spinel has been produced by sinter/HIP, hot pressing, and hot press/HIP operations, and it has been shown that the use of a hot isostatic press can improve its optical and physical properties.Bruch, A., General Electric, Transparent Magnesia-Alumina Spinel and Method, U.S. Patent 3516839 (1970) Spinel offers some processing advantages over AlON, such as the fact that spinel powder is available from commercial manufacturers while AlON powders are proprietary to Raytheon. It is also capable of being processed at much lower temperatures than AlON and has been shown to possess superior optical properties within the infrared (IR) region.
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However, the extremely rapid heating rates can result in incomplete reactions between Zr and B, the formation of stable oxides of Zr, and the retention of porosity. Stoichiometric reactions have also been carried out by reaction of attrition milled (wearing materials by grinding) Zr and B powder (and then hot pressing at 600 °C for 6 h), and nanoscale particles have been obtained by reacting attrition milled Zr and B precursor crystallites (10 nm in size). Reduction of ZrO2 and HfO2 to their respective diborides can also be achieved via metallothermic reduction. Inexpensive precursor materials are used and reacted according to the reaction below: ZrO2 \+ B2O3 \+ 5Mg → ZrB2 \+ 5MgO Mg is used as a reactant in order to allow for acid leaching of unwanted oxide products. Stoichiometric excesses of Mg and B2O3 are often required during metallothermic reductions in order to consume all available ZrO2.
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He has suggested that the Bell type's development was influenced by the greater quality possible in printing by more general use of hot-pressing of paper, which previously had only been used in Baskerville's elite printing, and the growth of fine book printing in London in the period. Historian James Mosley has also written in that in this period "the use of wove paper, hot-pressed [and] the cult of a simpler, more open page made the appearance of the type itself a more prominent feature of an edition, and one to which its promoters tended increasingly to draw attention." Besides body text faces, the foundry sold ornamented and inline letters, some based on French examples. The initial success of the face was short lived however, both due to business problems with the British Letter Foundry, which led first to Bell leaving it and then its sale in 1797, and later by 1808 a dramatic change in tastes in printing towards darker typefaces with greater extremes of thick and thin strokes.
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Tantalum carbide is widely used as sintering additive in ultra-high temperature ceramics (UHTCs) or as a ceramic reinforcement in high- entropy alloys (HEAs) due to its excellent physical properties in melting point, hardness, elastic modulus, thermal conductivity, thermal shock resistance, and chemical stability, which makes it a desirable material for aircraft and rockets in aerospace industries. Wang et al. have synthesized SiBCN ceramic matrix with TaC addition by mechanical alloying plus reactive hot-pressing sintering methods, in which BN, graphite and TaC powders were mixed with ball-milling and sintered at 1900 °C to obtain SiBCN-TaC composites. For the synthesis, the ball-milling process refined the TaC powders down to 5 nm without reacting with other components, allowing to form agglomerates that are composed of spherical clusters with a diameter of 100nm-200nm. TEM analysis showed that TaC is distributed either randomly in the form of nanoparticles with sizes of 10-20nm within the matrix or distributed in BN with smaller size of 3-5nm. As a result, the composite with 10 wt% addition of TaC improved the fracture toughness of the matrix, reaching 399.5MPa compared to 127.9MPa of pristine SiBCN ceramics.
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