Infiltration techniques

The majority of work done on VGCF reinforced composites has been carbon/carbon (CC) composites [20-26], These composites were made by densifying VGCF preforms using chemical vapor infiltration techniques and/or pitch infiltration techniques. Preforms were typically prepared using furfuryl alcohol as the binder. Composites thus made have either uni-directional (ID) fiber reinforcement or two-directional, orthogonal (0/90) fiber reinforcement (2D). Composite specimens were heated at a temperature near 3000 °C before characterization. Effects of fiber volume fraction, composite density, and densification method on composite thermal conductivity were addressed. The results of these investigations are summarized below. 

It is also interesting to note that electroless plating of silver on carbon fiber surface improves the wettability between molten aluminum and PAN based carbon fibers using the liquid infiltration technique in vacuum (Warrier et al., 1993). This is attributed to the formation of an eutectic phase between silver and aluminum, and the silver coating of the fibers during processing. 

Local anesthetics are used extensively on the mucous membranes in the nose, mouth, tracheobronchial tree, and urethra. The vasoconstriction produced by some local anesthetics, cocaine especially, adds a very important advantage to their use in the nose by preventing bleeding and inducing tissue shrinkage. Topical anesthesia permits many diagnostic procedures in the awake patient, and when it is combined with infiltration techniques, excellent anesthesia may be obtained for many... 

Lignocaine injections are indicated for production of local or regional anaesthesia by infiltration techniques such as percutaneous injection, peripheral nerve block, spinal or subarachnoid block. 

Whiskers can be incorporated into the metallic matrix using a number of compositeprocessing techniques. Melt infiltration is a common technique used for the production of SiC whisker-aluminum matrix MMCs. In one version of the infiltration technique, the whiskers are blended with binders to form a thick slurry, which is poured into a cavity and vacuum-molded to form a pre-impregnation body, or pre-preg, of the desired shape. The cured slurry is then fired at elevated temperature to remove moisture and binders. After firing, the preform consists of a partially bonded collection of interlocked whiskers that have a very open structure that is ideal for molten metal penetration. The whisker preform is heated to promote easy metal flow, or infiltration, which is usually performed at low pressures. The infiltration process can be done in air, but is usually performed in vacuum. 

The concept and synthesis of layered and graded materials (LGMs) from the infiltration technique have been introduced. The mechanical and fracture... 

The increasing use of light ceramic composites for high temperature and space applications has stimulated the development and optimization of the Chemical Vapour Infiltration technique. The use of conventional ceramic techniques for the fabrication of fibre-reinforced composites damages the fibres both mechanically as chemically. Also, the high process temperature causes a thermal degradation of the fibres. 

A recent modification to the CVI process has been development of a forced flow-thermal gradient chemical vapor infiltration technique (FCVI), which has been examined for propylene, propane, and methane gas precursors. ... 

R. Naslain, H. Hannache, L. Heraud, J. Rossignol, F. Christin, and C. Bernard, Chemical vapor infiltration technique. Euro CVD Four, Proc. Sur. Conf. Chem. Vap. Deposition, 4th, Eindhoven 1983, pp. 293-304 (1983). 

The main drawback of the CVI techniques is the long processing time of infiltration, normally in the range of a hundred hours. This is coupled with a very slow rate of deposition associated with a relatively low conversion efficiency of the precursor. To address this deficiency new manufacturing approaches have been explored to develop rapid infiltration techniques and so far most of these attempts remain as research work being investigated in laboratories. Another potential problem is that CVI composites exhibit some residual open porosity. This would be a drawback for applications where gas or liquid tightness is strictly required. 

Some Typical Thermal Gradient/Isobaric Chemical Vapour Infiltration Techniques... 

Tang SF, Deng JJ, Du HF, Liu WC, Yang K (2005) Fabrication and micro structure of C/SiC composites using a novel heaterless chemical vapor infiltration technique. J Am Ceram Soc 88 3253-3255... 

The range of processing techniques that can be employed to produce FGMs is also broad [1]. Vapor-phase methods e.g., CVD, CVI, and PVD methods), liquid-phase methods e.g., electrodeposition, sol-gel, plasma spraying and molten metal infiltration methods), and a variety of solid-phase methods based on powder metallurgy are available. The solid-state methods include powder stacking techniques, powder infiltration techniques, slurry techniques e.g., sedimentation... 

Vacuum deaeration and infiltration techniques have been used as freezing pretreatments to prevent enzymatic browning in apple slices by replacing tissue gases with aqueous solutions of sucrose and/or AA (43-44). Vacuum infiltration of solutions into apple slices resulted in a translucent or waterlogged appearance which would not be acceptable in a raw product (45). 

Lidocaine hydrochloride is a local anesthetic/vasopressor preparation. Lidocaine stabilizes neuronal membranes by inhibiting the ionic fluxes required for the initiation and conduction of impulses, thereby effecting local anesthetic action. Epinephrine stimulates both alpha and beta receptors within sympathetic nervous system relaxes smooth muscle of bronchi and iris and is an antagonist of histamine. They are indicated for production of local or regional anesthesia by infiltration techniques such as percutaneous injection, by peripheral nerve block techniques such as brachial plexus and intercostals, and by central neural techniques such as lumbar and caudal epidural blocks. 

Lidocaine is indicated for production of local or regional anesthesia by the infiltration technique, and by central neural techniques such as lumbar and caudal epidural blocks. 

From the present status of technology, the components and structures with long C- and SiC-fiber reinforced SiC-matrices have sufficient thermomechanical properties, especially high fracture toughness for thermally stressed structures under complex demands and temperatures above 1200 °C. Thus, bearings, gas turbine parts, or heat-shield-components can be made from C/SiC and SiC/SiC composite materials. The edge panel of a heat shield, shown in Fig. 17, illustrates the possibilities of the infiltration techniques - here the LPI - to make very complex and big architectures [254],... 

Tantalum, which is used for a number of applications, was recently made into a porous material that could be used for bone reconstruction. The porous structure is made by depositing the metal onto a vitreous carbon scaffold using chemical vapor deposition/infiltration techniques. Its low stmctural density means that its stiffness (2.5-4 GPa) is closer to that of natural bone than the solid metal, and the porosity means that bone can fully integrate into the stmcture. forming an excellent bond. " ... 

Melt infiltration techniques, although well established for MMCs, have met with only limited success for CMCs. The main problems are... 

Despite their heterogeneous microstructure and their complex processing, hybrid processes show a promising route to combine the high material purity and process controllability of the chemical vapour infiltration technique with the less time consuming and in most cases cheaper liquid phase infiltration techniques of LSI and LPI, However, additional research and development have to be done in order to take benefit of the whole potential of combined processes. 

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