GB2467928A - Inorganic Fibre Coating by Atomic Layer Deposition - Google Patents

Abstract

A method of coating inorganic fibres by atomic layer depositions (ALD) is disclosed. Coating materials are deposited at low temperature and pressure with the sequential exposure of gaseous precursors. The fibre may be formed from carbon, metal, alumina, silica or semiconductor. The fibre may be surface-modified prior to coating. The coating may be a ceramic oxide, sulphide, nitride, phosphide, fluoride, carbide, phosphate, arsenide, selenide, telluride, a metal or a non-metal such as carbon, phosphorus or sulphur. The coatings formed may be smooth and homogenous on each fibre in a fibre bundle. The coated inorganic fibres can be used for reinforcing ceramic matrix composite, forming microelectrodes, as an optical fibre, or as a template for micro- andnano-tubes.

Description

Fiber Coating by Atomic Layer Deposition

Description

1. State of the art Fiber reinforced ceramic matrix composites (CMC) offer promising mechanical properties, but has a low life span at various environmental conditions. Reinforcing fibers are embedded onto matrix to achieve high toughness through distributed damage mechanism.

Fiber reinforced ceramic matrix composites (CMC) are prepared at high temperature (800- 1200°C), either fiber bundles are put into liquid ceramic precursors or are exposed to gaseous ingredients of ceramics and slowly cooled down to room temperature and often these matrices are used at elevated temperatures. Therefore, the reinforcing fibers used to be temperature stable and thus have to be made from inorganic materials. As inorganic materials we regard, all those materials which do not contain significant amount of C-H bonds; especially if it is a carbon rich materials, the molar ratio of C-H bond to carbon atoms shall be less than 10%.

These reinforcing inorganic fibers are mainly classified in two groups a) oxide fiber b) non-oxide fiber and use of these fibers depends on the chemical and mechanical compatibility with matrix materials. Non-oxide fiber (such as carbon fiber, and silicon carbide fiber) has very high tensile strength even at very high temperature (>1200°C), however, in presence of either oxygen andlor moisture, tensile strength decreases sharply especially at high temperature. On the other hand, oxide fiber (such as alumina and silica fibers) is chemically * stable but start to creep at high temperature (>1200°C) because change in the polycrystalline * : : micro structure. Thus, both non-oxide and oxide fibers are not compatible at high temperature and oxidation conditions.

* Therefore, an oxidation barrier is needed for non-oxide fiber and thermal barrier for * oxide fiber to improve their chemical and mechanical properties in various environmental conditions.

*:. During the cooling process of the composite preparation microcracks may form at the fiber matrix interface due to a mismatch of the coefficient of thermal expansion (CTE) between fiber and ceramic material. Mechanical load imposed onto this composite helps to propagate interfacial cracks toward the matrix, fmally opens up to the surface and facilitates bad effects by various environmental conditions. As a result, the ceramic matrix composite is damaged completely after a certain time.

Additionally, at high temperature, a strong fiber-matrix bond may for m, that is not suitable for fiber reinforced ceramic matrix composite. It is a well proved fact that the catastrophic failure of the composite can be avoided if it has weak fiber-matrix interface.

Fiber-matrix bond strength should be optimum, it will be such an amount that the matrix can transfer mechanical load to the fiber, however, must be weak enough to debond and slip in the wake of matrix cracking.

Therefore, fiber-matrix interface modification is needed that can protect the fiber from various hazardous conditions and on the other hand can improve the life-time of the composite by deflecting the crack at the interface. One of the promising approaches of the fiber-matrix interface modification is coating onto fiber. Generally, coatings onto reinforcing fiber are prepared separately before embedding fiber into ceramic matrix composite by various deposition techniques; although the first report of coating was carbon onto Nicalon SiC-based fiber that developed unintentionally during fiber reinforced composite processing.

1.1 Conventional Fiber-coating technology Coatings on fiber are prepared either from gas phase route or liquid phase route a) liquid phase route such as sol-gel method b) gas phase route such as Chemical vapor deposition, and Chemical vapor infiltration (CVI). Sol-gel method for fiber coating is simple and economical. In this method sols of the desired ceramics are prepared and the fibers are guided through the sol for coating.

CVD is an extensively Used gas phase technique for fiber coating. Pyrolitic carbon and * BN coatings on fiber tows has been accomplished almost exclusively by CVD. By CVI-process interphase and the matrix are successfully deposited. Processing temperature range * from 900-1100°C and according to the various conditions, several names are in use: like - :. isothermal/isobaric CVI or I-CVI, -pressure gradient CVI or P-CVI and force flow CVI or F-CVI. This method i very much useful for preparing nanometer thick multicomponent coatings on fiber. S. *S

: * . Other deposition techniques such as physical vapor deposition (PVD) and laser ablation that use sputtering of the coating material from a solid target by an electron beam or laser to fibers are of limited value for coating fiber tows. These are line of sight techniques which are unsuitable for deposition of coatings onto the inner filaments in a tow unless they are spread out so that they do not shadow each other.

In conclusion, all the conventional methods discussed here having merits and demerits but they are effective for the deposition of restricted material composition, like oxide & non-oxide materials deposition on oxide fiber and non-oxide coating on non-oxide fiber. But unfortunately, none of these deposition techniques are suitable for oxide coating onto non-oxide fiber.

2. Background of the invention

2.1 Field of invention

This is an invention report about methods and materials used to coat endless inorganic fiber and filament bundles by the technique of atomic layer deposition.

2.2 Background information

* In the review article J. Am. Ceram. Soc., 2002, 85, 2599, R. J Kerans et a!., explained the problems of coating deposition by conventional methods. Characteristic of the coating prepared by sol-gel technique depends on several factors, such as, concentration of coating liquid, particle surface charge, density, viscosity, wetting relationship between the liquid and fiber and coating rate. Liquid-phase precursors often form bridge between filaments in a tOw.

In the case, where bridges are extensively linked, they can impede infiltration of matrix and increase the matrix porosity at the time of ceramic matrix composite preparation. As a result, strength of the ceramic matrix composite decreases extensively.

On the other hand stoichiometry of the coating prepared by chemical vapor deposition can vary from filament to filament between the centre and surface as well. as top to ottom of the fiber tow because of differences in the deposition kinetics of the individual gaseous reactants. Bridging of fibers by this method of coating is not common but can happen when * filaments are close to each other. Chemical vapor deposition can also be used for oxide *****.

* coating but deposition of multicomponent oxide is often difficult.

:. :* Therefore, a gentle procedure was needed that allows the uniform coatings of fiber *:. bundles without variation of coating composition and thickness within the bundle.

Coating onto ceramic fiber often decreases tensile strength of it, mostly; this is due to the S. * * deposition method. R. & Haya and coworkers explained the change of tensile strength of the fiber after coating in their publications J Am. Ceram. Soc., 1999, 82, 2321 andJ Eur. Ceram.

Soc. 2000, 20, 589. Oxide coatings are processed by conventional methods above 1000°C to ensure complete reaction of the precursors in the desired phase and densification afterward.

Almost every commercially available fiber loses tensile strength between 1 000°C-1200°C due to change in macrostructure, and byproducts formed during coating processing can make chemical reaction with fiber and change its tensile strength. Additionally, at high temperature possibility of forming strong bond between fiber and coating increases that can also diminish the strength of the fiber, especially, if the coating has higher coefficient of thermal expenses (CTh) than the fiber as well as remains strongly bonded can lead to lower strength.

Carbon fiber offers. highest creep resistance at elevated temperature in comparison to all commercially available inorganic fibers. W. S. Steffier mention the use of carbon fiber in his patents US 2005/0181192 Al, and US 2004/6783824 E2. Carbon fiber-reinforce silicon carbide (C/SiC) and silicon carbide fiber-reinforce silicon carbide (SiC/SiC) matrices are promising composites for high temperature application, however, limited by low life-span. At high temperature, carbon and silicon carbide fibers are affected severely by environmental oxygen and/or moisture as a result carbon fiber-reinforce silicon carbide (C/SiC) and silicon carbide fiber-reinforce silicon carbide (SiC/SiC) have very short life. This limitation can be accounted by the fact of oxygen diffusion through the microcrackes formed due to mismatch of the coefficient of thermal expansion (CTE) between matrix and fiber. Coating materials with gliding property like pyrolytic carbon and boron nitride (BN) onto fiber surface can improve life time of this composite to a certain extent but not up to the expectation level for real life applications. Either only oxidation bather coatings (such as A1203, Si02, Zi02, Ti02, AIPO4) or in combination with gliding materials can improves the life time of this composite, however, it is very difficult to prepare oxide coating onto carbon fiber by conventional deposition techniques.

Therefore, non-oxide reinforcing fibers (like carbon and SiC fibers) required a coating that can act as an oxygen diffusion barrier as well as it can deflect cracks at the fiber-matrix * , interface, however, a single coating material can not fulfill both requirements. Either double layer coatings of two materials or multilayer coatings prepared by alternate use of two * : * materials is needed for long term durability of the composite. Double or multilayer coatings are needed in such a way that the first layer of coating can protect the fiber by deflecting cracks at the interface and another one can protect fiber from oxidation. The concept of multilayer coating was disclosed by Carpenter et al., (US Patent No 5275984) and More et al. (J Am. Cerm. Soc., 1998, 81, 717), in their publications. Gliding layer coating materials such.

* as pyrolytic carbon and boron nitride in combination with oxide coating such as alumina, silica, zinc oxide, titanium oxide can be used for double layer or multilayer coating preparation, however, processing of this coating combination is very difficult by conventional deposition technique. Thus, new deposition technique is needed to prepare oxide coatings onto carbon fiber especially at low temperature.

* It is a well established fact that the coating thickness onto fiber should be optimum and applied in such a way that the resultant composites can improve their life time, while preserving desirable strength and toughness. Influences of coating thickness onto fiber are discussed by P. Bertrand et al., (Surface and coating technology, 1997, 96, 283) and K. Shimoda et al. (Composite science and technology, 2008, 68, 98) in their publication.

Normally, a coated fiber loses tensile strength to an extent, depends on the coating thickness that varies already in the nanometer range. On the other hand, coating layers need certain thickness either to allow gliding, deflect cracks at the interface or to prevent oxygen diffi.ision.

Hence, coating thickness needs to be controlled in the range of nanometers to improve the performance of the fiber reinforced ceramic matrix composite.

* Therefore, there is a demand of a new processing technique that can solve the problems such as bridge formation between filaments during coating, oxide coating preparation on non-.

oxide fiber, multilayer coating formation, and the coating thickness controlling in the range of nanometer. These problems are solved by the invention reported here by using atomic layer deposition.

Atomic layer deposition (ALD) also known as atomic layer epitaxy (ALE), was first developed in 1970 by T. Suntola and J. Antson as disclosed in U.S. Patent no. 4058430 to meet the needs of producing high-quality; large-area flat panel displays based on thin film electroluminescence (TFEL). This deposition technique is also useful to develop dynamic random access memory (DRAM), decoupling filter, transistor gate etc in thicroe1ectroni industry. ALD is a sequential chemical vapor deposition method. Various precursors are delivered to the reactor without mixing in gas phase. Normally, there are twos different precursors for the whole atomic layer deposition process. These precursors are delivered in a * : * sequential manner. In between two precursors, inert gas (like nitrogen and/or vacuum) is used :. to purge the reactor. One complete cycle involves four steps which are as follows: 1. Substrate surface exposure to the precursorl and chemisorption of first precursor onto substrate surface.

2. Purging by inert gas to remove excess precursorl and byproducts from reaction chamber.

3. Delivery of precursor2 to the reaction chamber, followed by chemical reaction on the surface to produce one layer of the desired thin film on the surface; 4. Further purging by of inert gas to remove unreacted precursor2 and byproducts.

These steps are repeated multiple times.

S

This technique is also used for deposition of oxide on boron nitride particles as reported by S. M George er al., Chem. Mater. 2000, 12, 3472, polymer particles as disclosed by S. M George et a!.,, Chem. Mater. 2004, 16, 5602, and biological macromolecules as reported by M Knez et a!, Nano letters, 2006, 6 1172. Recently, there are reports of coating on organic polymer fiber as disclosed by G. N Parsons et a!., Nano Letters, 2007, 7, 719 & Palley et a!., US patent No. 0119098 Al, 2008 by atomic layer deposition.

Depending -on the process and reactor being used, one complete cycle takes 0.5 to few seconds and deposits 0.01 to. 0.3 nm thick film. In general, ALD has several advantages which are as follows: 1. Easy tuning of film thickness on substrate (constant growth rate in each cycle).

2. Uniform film formation throughout whole substrate surface.

3. Very efficient in step coverage and coating of porous material, i.e., excellent conformality.

4. Multi component structure formation.

5. Low temperature deposition process (avoids unnecessary side reaction).

6. Facile doping and interface modification.

7. No need to control the flow of reactants, precursor concentrations higher than the threshold is sufficient to achieve surface saturated.

In ideal conditions, uniformly dense, pinhole free films form (elimination of undesired side reaction with byproducts).

The present invention is unexpected because this method of deposition is applicable for * all kinds of inorganic fiber independent to their surface property, especially, irrespective to * the presence of surface active functional group; however, for atomic layer deposition surface * active group is mandatory. Coating deposition onto non-oxide fibers (such as carbon and * silicon carbide) without any surface functionality is beyond our understanding. Additionally, although carbon fiber which is known to be sensitive towards oxidizing conditions in an * a.

ambient temperature, oxide coatings are successfully deposited by using direct oxygen source like oxygen, ozone, and steam without damaging fiber. Fortunately, all the pitfalls of the conventional deposition techniques such as bridge formation between filaments during coating, oxide coating preparation on non-oxide fiber, multilayer coating formation, and the coating thickness controlling in the range of nanometer are successfully solved.

3. Summary of this invention

The present invention comprises processing of several types of coating material onto inorganic fiber including carbon by a novel deposition method; Atomic layer deposition (ALID) method is used for processing of all kinds of oxide and non-oxide coatings. Coated fiber production described herein is used mainly for the reinforcement of ceramics matrix composite (CMC) to increase its tensile strength and toughness.

A filament or a bundle of reinforcing fiber is exposed to corresponding precursors in a sequential manner; as a result, a nanometer thin monolayer of coating is formed. In each deposition cycle, coating thickness is constant in the range of nanometer depends on the coating material, irrespective of precursor concentration. Fiber filaments are not bridged, each filament coated separately and homogeneously. Present technique is useful to prepare pinhole free, smooth coatings onto continuous and discontinuous fiber tow; Depositel coating materials are freed from impurity because each individual precursor is deposited separately and extra precursors as well as byproducts are purged out by inert gas after each individual precursor deposition. Coating materials can be deposited as low as room temperature that is not harmful for the chemical composition and microstructure of the processing fiber like other converitional deposition techniques.

In contrast to "normal CVD" this is a low temperature(<z400°C) and low pressure (<1 Ombar) deposition process capable to coat non oxide fiber like carbon and silicon carbide by single, double and also multilayer oxide materials. This method is successfully used for the preparation of double and multilayer coatings of non-oxide materials (pyrolytic carbon and boron nitride) in combination with oxide materials (such as alumina, silica, titanium oxide).

* This is a unique deposition technique for the preparation of oxide (such as alumina, * silica, titanium oxide) and non oxide (boron nitride, aluminum phosphate, silicon carbide) coating materials onto all kinds of oxide and non-oxide inorganic fibers. Thus, atomic layer deposition can be a universal deposition technique useable for all kinds of inorganic fibers. *.

: According to our knowledge ALD has been applied to individual fiber or fibers in fleece and * felts but not to bundles of parallelly arranged inorganic fibers.

4 Brief description of the drawing.

Figure 1: Schematic diagram of the atomic layer deposition reactor designed for fiber * deposition* Figure2: Scanning electron microscopic picture of a fiber bundle shows all filaments are coated homogeneously.

Figure3: Scanning electron microscopic picture of a single fiber filament.

Figure4: Scanning electron microscopic picture of a single filament, showing smooth, homogenous film on fiber surface and coating thickness 44.51 nm.

Figure5: Shows elemental analysis of coated fiber surface by energy dispersive x-ray analysis.

This picture shows there are mainly three elements: carbon, oxygen and aluminum (one peak around lkev is related to L-electron of Cupper sample holder). There is also one small peak around 2.6kev which indicates very small amount of chlorine present as an impurity.

5. Detail description of the invention

Coating onto inorganic fiber b y atomic layer deposition is disclosed in tle present invention. Fiber coating is defmed as various kinds of ceramics composition (shown in the tablel) oxide, nitride, boride, carbide, sulfide, phosphide, fluoride, silicate, phosphate, sulfate, telluride, selenides, metal, nonmetal, or combinations thereof which is (are) deposited onto a single fiber or a bundle of fibers to improve its physical and chemical properties. In the present invention atomic layer deposition method is used first time for the inorganic fiber coating. These coated fibers are used for the reinforcement of metal and ceramics composite to improve their tensile strength.

* Fiber is an endless, elongated material with all possible diameters from 1cm to mm.

Inorganic fiber is defined as fiber made out of inorganic materials such as metal, nonmetal *... including carbon, metal carbide, metal nitride, metal oxide, metal sulfate, metal phosphate, metal boride and combination thereof. Inorganic fibers are preferably made out of the material which has very high tensile strength and susceptible in various environmental conditions such * as pyrolytic carbon, silicon carbide, silicon nitride, silica, silicate, alumina. Typical reinforcing fibers are present as a bundle of filaments. Numbers of the filament in a bundle *:* are in between 1 to 90000000, preferably, in between 1 to 10000. Diameter of a single * filament is in between 1cm to 0.1 nm, preferably, in between 1 j.im to 100.tm. Present invention is applied successfully for continuous, discontinuous, straight, twisted, intertwined, knitted, and woven fibers. This method is even applied successfully for fiber bundle embedded into porous matrix. A polymeric substrate is often used as a sizing material to the bundle of fiber filament to ease handling; it is common practice to desize the fiber filament before coating deposition by thermal and/or chemical treatment. However, fiber is also coated with sizing by atomic layer deposition like other deposition techniques.

As indicated earlier, inorganic fibers are various type, fibers with surface active functional group such as -OH, -SH, -NH2 -F, -Cl, -Br, -I are coated successfully in the present invention. Fibers without functional group like carbon are also coated without damaging fiber; however, initial coating deposition rate is slow. To improve coating deposition rate, fibers without surface active functional group can be modified by sol-gel and chemical vapor deposition techniques.

To improve long term durability of the inorganic fiber reinforced ceramic matrix * composite, one of the promising approaches is to coat the fiber in such way that it can a) compensate the mismatch of the coefficient of thermal expansion (CTE) between fiber and matrix, b) inhibit the crack propagation, c) protect the fiber from surrounding heat and oxygen environment, d) inhibit the strong fiber and matrix bonding.

At the beginning pyrolytic carbon (PyC)' was used as a coating which has good crack deflection ability due to a turbostratic layered structure. However, oxidation resistance is poor at high temperature. It is stable only up to a maximum of 400°C like the carbon fiber itseli Hexagonal BN was used as a replacement of pyrolytic carbon. It has a good ability to deflect cracks like pyrocarbon due to a similar structure arid it has much better oxidation resistance than pyrolytic carbon. In another approach hard coating materials like various carbides titanium carbide, silicon carbide, and boron carbide were used. In the present invention pyrolytic carbon, boron nitride and various carbides are deposited successfully.

The materials either with gliding layer (BN and PyC) or hard in nature (SiC, B4C and titanium carbide) as a single composite on the carbon fiber fail to fulfill all the important *..* S. *** criteria at the same time for the fiber reinforce ceramic matrix composites (CMC). Solid * : * lubricant (BN and PyC) could protect the fiber inside the composite via crack deflection :. mechanism but have very poor oxidation resistance, on the other hand, the fibers coated with * hard materials (like SiC and B4C) survive in oxidative environment because corresponding *.* oxides act as a crack sealing agent. Therefore, double layer coating came as a third generation *:* of improvement of the carbon fiber; the chemical layer which behaves as a solid lubricant *. (like pyrocarbon and BN) being placed adjacent to the fiber. The outer layer is made for mechanically more resistant toward oxidation and hydrolysis. Additionally it forms an oxygen diffusion barrier in the interface. In this series SiC fibers coated with BN and followed by SiC were reported by E. Y Sun et. al in the publication.1 Am. Ceram. Soc., 1996, 79, 152. If this fiber embedded into barium magnesium aluminosilicate (BMAS) glass-ceramic matrix one observes stability up to temperature 1200°C for 1 5 cycles without any fracture. According to our knowledge for double layer coating, most of the work has been done by using PyC or BN as solid lubricant and SiC or Si3N4 hard coating materials for non-oxide fiber (carbon and SiC fiber) and chemical vapor deposition (CVD), Chemical vapor infiltration and sol-gel methods were used for processing. Double layer coating improves the oxidation resistance of the fiber in high temperature but for practical purposes the main concern here is durability. Though one observes an improvement of lifetime, it often is not sufficient.

The concept of multilayer coating by two different ceramics was introduced by Carpenter and Bohien as reported in the publication Ceram. Eng. Sd. Proc., 1992, 13[7-8], 23. Steffier was also an early developer of this concept for SiC-based fiber as disclosed in the patent, U.S. Pat. No. 5455106, 1995. The concept behind it: if one of the layers is affected by oxidation, others could survive to protect the fiber from oxidatiOn. In several publications R. R. Naslain and coworkers (for example, Composite science and technology 2004, 64, 155, and Applied Ceramics Technology 2005, 2, 5) reported multi-layer coating of (PyC-SiC) and (BN-SiC) onto SiC and carbon fibers and reported their oxidation behavior in various temperatures. They have noticed inhomogeneous oxidation in two different temperature regimes. At low temperatures 500 <T<900°C, the oxidation kinetics of PyC is fast compared to SiC; PyC layers are converted into gaseous byproducts of CO2 and * CO and thus removed. However, at higher temperature (>1100°C) with thin carbon layer (<0.1 p.m) oxidation resistance is better; at such conditions the matrix exhibit se!f healing behavior. For (BN-SiC) multilayer at high temperature (1000-1200°C) the rate of formation of liquid B203 as an oxidation product of BN is higher then the oxidation of carbon. Thus the * B203 can seal residual pores and/or microcracks to inhibit the in depth diffusion of oxygen.

*... However, in moist condition B203 is not stable because of gaseous byproduct formation as * : * explained in the previous section. As a result of the inhomogeneous oxidation behavior at low temperature fiber-matrix bonding degrades due to the removal of PyC layer causing * mechanical failure of the Matrix. *

Double and multiple layer coating on carbon fiber improve the oxidation resistance but could not improve the level as expected for practical application. One of the solutions could *. be multiple-layer coating, but using instead of SiC, a permanent oxidation barrier coating (like oxide coating Al203, Si02 or hO2) that can inhibit the in depth oxygen diffusion to the interface at all temperature will be useful. However, problem is the deposition of oxide * coatings on non-oxide fibers.

In the present invention we have deposited oxide coatings alone and as a double layer with other coatings like pyrolytic carbon and boron nitride onto both oxide and non-oxide fiber. The list of coatings deposited onto fiber shown into the table 1.

Coated fibers are used in various purposes such as reinforcing material for both low and high temperature metal and/or ceramic composites, optical fiber, microelectrode, microtube and nanotube preparation. After coating deposition onto fibers, if fibers are removed selectively by thermal and/or chemical treatment only coatings are left as a tube like structure thereby coated micro fibers are used for microtube preparation as well as nano fibers for nano fibers.

Fibers are coated by atomic layer deposition in the present invention. Inorganic fibers * are exposed to one or more, preferably 2 to 5 especially preferred two chemically distinguishable vapors, with or without intermediate phases of evacuation or purging with inert gas. Chemically distinguishable vapors which contain ingredients of the coating, named as "precursor" and other vapors which are chemically inert with respect to the coating deposition reaction, named as "inert gas". Precursor at room temperature and ambient.

pressure can be. solid, liquid, gas; however, it's injected as a gas. Separate precursor chambers are used for each precursor and solid & liquid precursors are heated to a suitable.

temperature to produce precursor vapor. Precursors are delivered with or without carrier gas in the reactor depending on the precursor property. Generally, in the presently invention fibers are exposed sequentially to corresponding precursors and removing extra precursors & byproducts with inert gas. An exemplary case of ALD using precursor A and B demonstrated here. 1) Precursor A injected to the chamber containing fiber as a substrate, precursor A is adsorbed chemically or physically thereby forming a "saturated layer" of A. 2) Reaction chamber is purged with an inert gas to remove byproducts and extra pre'cursor A. *.S.

3) Precursor B injected to the reaction chamber and allowed to react with the saturated layer * : * of A. 4). Reaction chamber is purged with an inert gas to remove byproducts aiid extra precursor B. These four steps constitute one complete cycle. Average deposition rate per cycle is in between O.000lmn to mm, mostly, in between O.OOlnm to 0.3nm. Coating thickness is increased to desire thickness just by repeating the number of cycle. "Saturated :* layers" fonn due the adsorption of first precursor, in some cases that is only a monolayer, in *:. other cases, fraction of a monolayer and multiple of monolayer.

Deposition temperature is in between 0°C to 1000°C depending on the coating, preferably in between 25°C to 750°C, commonly in between 50°C to 600°C. Operating pressure inside reactor used for deposition is maintained in between 1 Obar to 1 O9mbar, preferably in between ibar to l05mbar, especially in between 10'mbar to lO5mbbar. One or more precursors was (were) used for coating preparation depends on the coating and processing conditions, however, most of coatings were deposited with two precursors.

Additionally, Catalysis driven ALD method is used for fiber coating in which one of the precursor is catalyst. Here catalyst is used for several purposes, specifically, to decrease deposition temperature, to moderate reaction pressure, and to increase reaction rate. As mentioned, carbon fibers are not stable in the environment of oxygen and moisture at a temperature greater than 400°C; however, several deposition reactions which are taking place temperature greater 400°C. In those reactions catalysis are used to drop the reaction temperature. Oxide coatings are deposited without using direct oxygen source like molecular * oxygen, ozone, water, and hydrogen peroxide. Instead of using direct oxygen source as a precursor organometalic compounds are used as precursors.

Atomic layer deposition is carried out in only one reaction vessel as well as several reaction vessels. For example, a) a hollow metal tube is used as a reactor aligned either vertically or horizontally (shown in fig 1), in which fibers are placed and precursors are injected sequentially as discussed earlier. b) Three separate reaction chambers aligned straight, in which two side chambers contain two separate precursors and the middle one contains inert gas and fibers are moved back and forth sequentially into these three chambers. c) Several separate reaction chambers placed in a cyclic manner in which corrsponding precursors are filled in alternate chambers, and others are filled with inert gas, fibers are moved through one chamber after others. All other variations in reactor are possible until its not effected fibers property and quality.

6. Example

6.1 Example set 1

*:: Aluminum oxide coating onto carbon fiber are reported here. Carbon fiber (HTA 5331, 6000 thousand filaments, filament diameter 7i.tm from (Toho) Teuax Company) toW was used - * as a substrate after removing the commercial sizing by pyrolysis at 700°C in a nitrogen *S* atmosphere. Five meters long carbon fiber was rolled in a holder and placed in a reaction chamber. Aluminum chloride (98% pure from Fluka) and distilled water were used as *:. precursors. Solid aluminum chloride was taken into steel container and heated up to 140°C.

Distilled water was taken into separate steel container and heated up to 40°C. Mass flow controllers were set at 20 SSCM for a constant flow off career/purge gas (nitrogen).

Deposition temperature and pressure of the reactor was maintained 3 00°C and 0.1 mbar respectively. The containers were connected with a T-joint to the cylinder of carrier via an automatically controlled valve in dead end arrangement (As shown in figure 1). One complete deposition cycle is as follows: 1. Fiber was exposed to Aluminum chloride for 40 seconds.

2. Reaction chamber was purged for 20 seconds.

3. Water was delivered for 10 seconds.

4. Final purging was done for another 20 seconds.

One complete cycle took 90 seconds and this deposition was done for 1300 cycles. After atomic layer deposition fibers were analyzed by scanning eIetroi microscopy (SEM) and energy dispersive x-ray (EDX) spectroscopy. One centimeter long fiber sample cut into pieces and placed in a cupper sample holder for both SEM and EDX analysis. Scanning. electron microscopic analysis revealed each individual filament was coated (shown in fig2, fig3) and the coating thickness is approximately 45nm (shown in flg4). The coatings on the surface are looking smooth and homogeneous throughout the whole fiber length as shown flg.4. Figure5b shows elemental analysis of the coated carbon fiber surface (shown in fig5a) by energy dispersive x-ray spectroscopy (EDX) that indicates aluminum oxide coating on fiber surface and small amount of chlOrine present as an impurity on that coating. Chlorine impurity came from unreacted aluminum chloride precursor during deposition process.

6.2 Example set2

Silica deposition on carbon fiber is reported here. Deposition of silica on fiber is almost similar like example 1. For silica deposition, there were two precursors used, tri-(tert-.

butoxy)silanol and aluminum chloride. Solid tri-(tert-butoxy)sjlanol was taken into a steel container and heated up tol3O°C. Solid aluminum chloride was taken into separate steel *..* container and heated up to 140°C. Carbon fiber was exposed sequentially in these two * : S precursors for silica deposition. Deposition temperature and pressure was maintained 240°C and 0.1 mbar. S..

6.3 Example set3

Titanium oxide deposition onto reinforcing fiber is reported here. Deposition of titanium oxide on fiber is almost similar like examplel. In this deposition titanium chloride and distilled water are used for precursors. Liquid titanium chloride was taken in a steel container and heated up to 80°C. Distilled water was taken in separate container and heated up to 40°C.

Fiber was exposed sequential in these two precursors for titanium oxide deposition.

Deposition temperature and pressure was maintained 200°C and 0.lmbar.

6.4 Example set4

Boron nitride deposition onto reinforcing fiber is reported here. Deposition of boron nitride on fiber is almost similar like exaniplel. For the boron nitride deposition boron tn chloride and anhydrous ammonia were used as precursors. Boron nitride was carried out, with the sequential exposure of boron tn thloride and ammonia at temperature 250°C and 0.lmbar pressure.

6.5 Example set5

Aluminum phosphate deposition is reported here. Deposition of aluminum phosphate on fiber is almost similar like examplel. For aluminum phosphate, trimethylaluminum and di(iso-propyl)phospbate were used as precursors. Reinforcing fibers were exposed sequentially in trimethylaluminium and di(iso.-propyl)phosphate for aluminum phosphate coating. * * * * S... **S.S * S S. S. * * S * .

S * * . S * 0 *S.

S

Claims (51)

1. Claims We claim: 1. A method which comprises the coating of inorganic fibers including carbon rich fiber by atomic layer deposition.
2. 2. The method of claim 1 wherein inorganic fibers are carbon, silicon carbide, alumina, silica, aluminosilicate, Mullite, silicon nitride, all kinds of metal (such as transition, non-transition, radioactive, non-radioactive, lanthanides, actinides), all kinds of metal alloy, semiconductor, insulator, mixtures of metal, seniiponductor and insulator (such as metal & semiconductor, metal & insulator, semiconductor & insulator, metal & semiconductor & insulator).
3. 3. The method according to at least one of the claims 1 to 2, thereby characterized that the fibers are desized prior to the coating, for example by thermal treatment, oxidation, evaporation, solvent extraction.
4. 4. The method according to at least one of the claims 1 to 2, thereby characterized that the fibers are not desized prior to the coating.
5. 5. The method of claim 1 wherein inorganic fibers with surface active functional group like -OH, -SH, -NH2, -F, -Cl, -Br, -I etc are used.
6. 6. The method of claim 1 wherein inorganic fibers without surface active functional group such as carbon are used.
7. 7. The method of claim 6 wherein inorganic fibers without surface active functional group are coated after surface modification with other chemical methods.,
8. 8. The method of claim 6 wherein inorganic fibers without surface active functional group are coated without any surface modification. I...
9. 9. The method of claim 1 wherein the diameter of the fiber is in between and 1cm to * : *: 0.1 inn preferably between 1 OOnm and 1 00tm especially, preferred between 1 m and lO0.tm.*
10. 10. The method of claim 1 for bundle of fiber wherein the number of filament in a S..bundle in between I to 90000000, preferably in between 1 to 10000. :*
11. 11. The method of claim 10 wherein each individual filament in a fiber bundle is * * coated separately with uniform thickness.
12. 12. The method of claim 10 wherein the fiber bundle is continuous.
13. 13. The method of claim 10 wherein the fiber bundle is discontinuous.
14. 14. The method of claim 10 wherein the fiber bundles is straight, twisted, intertwined, knitted or woven.
15. 15. The method of claim 10 wherein the fiber bundle is embedded within all kinds of permeable or porous matrices.
16. 16. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of oxides, such as boron oxide (B203), magnesium oxide (MgO), alumina (A1203), silica (Si02), scandium oxide (Sc203), titanium oxide (Ti02), vanadium oxide (VO'), chromium oxide (CrO), manganese oxide (MnO), iron oxide (FeO), cobalt oxide (CoOk), nickel oxide (NiQ), copper oxide (CuO), zinc oxide(ZnO), gallium oxide (Ga203), germanium oxide (Ge02), strontium oxide (SrO), yttrium oxide (Y203), zirconium oxide (Zr02), niobium oxide (Nb205), ruthenium oxide (RuO), indium, oxide (1n203), tin oxide (Sn02), antimony oxide (Sb203), lanthanum oxide (La203), cerium oxide (CeO2), praseodymium oxide (PrO), neodymium oxide (Nd203), samarium oxide (Sm203), europium oxide (Eu203), gadolinium oxide (Gd203), dysprosiuin oxide (Dy2O3), holmium oxide (1-10203), erbium oxide (Er203), thulium oxide (Tm203), lutetium oxide (Lu203), hafnium oxide (Hf02), tantalum oxide (Ta203), tungsten oxide (W03), bismuth oxide (BiO).
17. 17. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of mixed oxides such as Al,SiO, A1CrO, A1TiO, A1ZrO, A1HfO, SiTi0, SiZrO, SiHfO, TiZrO, TiHfO, LaSiO, PXBYOZ.
18. 18. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of nitrides such as boron nitride (BN), ** **. silicon nitride (Si3N4) titanium nitride (TiN), aluminum nitride (A1N), tantalum nitride (TaNk), hafnium nitride (Hf3N4), indium nitride (InN), niobium nitride :. (NbN), molybdenum nitride (MoAN), Zirconium nitride (Zr3N4), Gallium nitride * (GaN).
19. 19. Method according to at least one of the claims 1 to 15 thereby characterised that *** the coating material is taken from the class of sulfides such as (PbS), cadmium ** sulfide (CdS), Zinc sulfide (ZnS), calcium sulfide (CaS), manganese sulfide (MnS), cupper sulfide (CuS), strontium sulfide (SrS), barium sulfide(BaS), indium sulfide (In2S3), lanthanum sulfide (La2S3).
20. 20. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of fluorides such as CaF2, ZnF2, SrF2.
21. 21. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of phosphides such as AlP, GaP, InP.
22. 22. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of carbides such as SIC, ZnC2, TIC, wxC.
23. 23. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of phosphates like BPO4, A1PO4, LaPO4.
24. 24. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of arsenides which are ALs, GaAs, InAs.
25. 25. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of selenides such as ZnSe, CdSe.
26. 26. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of tellurides such as MgTe, CdTe, HgTe, ZnTe, MnTe.
27. 27. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken frOm the class of metals such as iron, cobalt, nickel; copper, platinum,, palladium, gold, silver.
28. 28. Method according to at least one of the claims 1 to 15 thereby characterised that the coating material is taken from the class of non-metals such as carbon, phosphorus, sulfur. ***S*
29. 29. Method according to at least one of the claims 1 to 15 thereby. characterised that *...* * the coating material is taken from the mixture of materials used in claim 14 to 26.
30. 30. The method of claim ito 29 wherein the coating of a single components deposited as a single, mixed, double, and multi layers.
31. 31. The method of claim 1 to 29 wherein the coating of 2 to 10 components preferably 2 to 4 components deposited as a double, and multi layers.
32. 32. The method of claim 1 to 29 wherein the coatings are deposited as smooth, uniform, pinhole free layers.
33. 33. Method of claim 1 to 29 there by characterized the coatings are amorphous, crystalline, and a mixture of amorphous & crystalline microstructures.
34. 34. The crystalline microstructures of me coating in claim 33 wherein the micro structures of the coating are tetrahedral, hexagonal, cubic, rhombohedra.
35. 35. Method of claim 1 to 29 wherein the deposition of coating onto fiber by an atomic layer deposition in which fibers are exposed to several, preferentially 2 to 5, especially prefer two chemically distinguishable vapors, with or without intermediate phases of evacuation.
36. 36. The atomic layer deposition for the deposition of coating of claim 35 wherein at least one the precursors is used as a catalyst to increase the coating thickness, for example, more than one monolayer are deposited in a single cycle by a catalyzed atomic layer deposition.
37. 37. The atomic layer deposition for the deposition of coating of claim 35 wherein at least one the precursors is used as a catalyst to moderate the reaction conditions such as temperature and pressure, for example, catalyst are used to decrease the temperature for the fiber bundles that are not capable to withstand at high temperature.
38. 38. The atomic layer deposition for the deposition of coating of claim 35 wherein the deposition of oxide materials without using any direct oxygen source as a precursor (such as oxygen, water, hydrogen peroxide).
39. 39. The atomic layer deposition of claim 35 wherein the physical properties of the precursors used for deposition can be solid, liquid, gas, and vapor.
40. 40. The atomic layer deposition of claim 35 wherein the thickness of the coating deposited in a single cycle in between 0.000lnm to mm, preferably 0.00mm to 0.3nm.
41. 41. The method of claim 1 to 40 wherein atomic layer deposition is used* in *..* *.. combination with other techniques such as chemical vapor deposition, physical * : * vapor deposition, wet impregnation, and sol-gel.:.
42. 42. The method of claim 1 to 40 wherein the reactor used for deposition are inert gas * flow reactor and very low pressure molecular flow reactor.
43. 43. The method of claim 1 to 40 wherein the deposition temperature is in between 0°C :* to 1000°C, preferably 25°C to 1000°C, especially 50°C to 600°C.*
44. 44. The method of claim 1 to 40 is applicable for the deposition of coatings wherein deposition pressure can be varied from atmospheric to ultrahigh vacuum.
45. 45. The method of claim 1 to 40 wherein the deposited coating total coating thickness is in between 0.000 1 nm to 10 centimeters, preferably mm to lj.im.
46. 46. Embedding fibers according to claim 1 to 45 into composites such as ceramic, metallic, nonmetallic.
47. 47. Using fibers according to claim 1 to 45 to reinforce material and devices.
48. 48. Using fibers according to claim 1 to 45 as a microelectrode.
49. 49. Using fibers according to claim 1 to 45 as a template for microtubes.
50. 50. Using fibers according to claim 1 to 45 as a template for nanotubes.
51. 51. Using fibers according to claim 1 to 45 as heating element and light emitting parts. * * ****I**1**I * *I * I * * SSIII II 0 *SS I..I