Graphite molded

In general, the purified boron carbide is ultimately obtained as a granular soHd that subsequendy may be molded or bonded into usehil shapes. To achieve high density and strength, it is hot pressed at 1800—2400°C in graphite molds. 

Metal molds and cores are used in permanent mold casting. The process works best in continuous operation so that the mold temperature can be maintained within a fixed operating range. The operating temperature of the mold is one of the most important factors in successful permanent mold casting. Mold cavities are machined from solid blocks of graphite. Mold life is the major cost factor in permanent mold casting. 

All the alloys studied were smelted on a base of commercial titanium alloy of technical purity BT1-0 (Fe<0.25 Si<0.1 C<0.07 N<0.04 O<0.2 others<0.3. Compositions are provided in wt. %) with plasma-arc method in argon atmosphere. The BT1-0 alloy itself is determined as pseudo a-alloy, which has coefficient of P-phase stabilization kp = 0.05 [4, 5], Temperatures of smelts were between 1620-1660 °C. Liquid metal was decanted into graphite mold inside of melting chamber. Obtained cylindrical ingots of 60 mm diameter and 150-400 mm length were cooled to 600 °C inside of chamber and after that to room temperature in air outside of equipment. 

The sintered sample can interact with the graphite mold . ... 

A common means of facilitating sample removal consists of lining the inside of the graphite mold with (1) graphite foils -, (2) pyrolytic carbon ", (3) hexagonal boron nitride ... 

By using a boron-nitride powder barrier (hot pressed or deposited onto graphite mold and punches), it is possible to prepare dense and pure boron and boron-rich phases, especially carbides (between B,o.4C and B4C) by hot pressing in graphite dies " . 

After the reactor was cooled to room temperature, it was opened and the mass of metal was mechanically freed of frozen slag. Ninety percent of the zinc in the alloy was removed by distillation in a retort heated to 1150°C at a vacuum lower than 0.2 Torr. The retort was then filled with argon or helium to prevent oxidation of the spongy thorium and cooled to room temperature. The thorium was transferred to a beryllia crucible in an induction-heated vacuum furnace for melting, evaporation of the residual zinc, and casting into a graphite mold. Thorium metal yield was 94 to 96 percent. 

SPS has been confirmed to be a viable technique to synthesize PLZT transparent ceramics. An example is the preparation of PLZT(8/65/35) ceramics [227]. The PLZT powder was synthesized by using a wet-dry combination method. Due to the contamination of carbon from the graphite mold, the samples after the SPS sintering should be annealed in air or oxygen. Optical properties of the samples were affected by the SPS temperature, as well as the post-annealing temperature. It was found that 700 °C was the optimal sintering temperature when transmittance was considered. 

Spark plasma sintering (SPS) is one of the solid consolidation processes which is carried out in a graphite mold and the heating is accomplished by spark discharges in voids between particles [10]. Whether a plasma is generated has not yet been confirmed, especially when non-conducting ceramic powders are compacted. However it has been experimentally verified that the densification is enhanced by the use of DC pulses [11]. Various materials have been compacted by SPS technique. Zhao et al. fabricated dense 50 nm BaTiOs ceramics (97% relative density) by SPS [12]. Very recently, Buscaglia et al. demonstrate that the 30 nm BaTiOs ceramics system is still... 

Casting. Titanium castings can be produced by investment or graphite-mold methods. Casting must be done in a vacuum furnace because of the high chemical reactivity of molten titanium metal with oxygen and nitrogen. 

Starting from as-synthesized powder, dense sintered h-BN can be obtained by axial hot pressing in graphite molds at a temperature of about 2200 °C, to yield monolithic ceramic bodies of 88-97% theoretical density. Any residual oxygen in the BN at the grain boundaries will form B2O3 that, subsequently, will act as an efficient sintering aid. The typical anisotropic properties of uniaxially hot pressed... 

The details of material formulation, processing steps, and equipment in the graphite-molding process can vary considerably from one manufacturer to another. In many cases, these details are jealously guarded and most companies consider their proprietary processes essential to their economic survival. 

Shape casting of titanivun was first demonstrated in the United States in 1954 at the U.S. Bureau of Mines using machined high-density graphite molds. Since this early work, semipermanent, reusable molds made fix>m machined graphite have been used successfiiUy on relatively simple-shaped parts that allow met volumetric shrinkage to occur without restriction. However, the method is economical only when reasonably high volumes are required, that is, thousands... 

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