Antimony Impregnated Carbon Graphite for Mechanical Seal Material

Applicable Industries	Pump
Chemical Composition	Water

Other Attributes

Place of Origin	Zhejiang, China
Brand Name	CF
Model Number	Bushing
Material	Carbon Graphite
Size	Customizable
Key Words	Carbon Graphite Bushing

Packaging & delivery

Package Type:

Standard export packing

Supply Ability

Supply Ability

10000 Piece/Pieces per Month

Product Details

Product Parameters

Application	Mechanical Industry
Dimensions	Customers' Requirement
Chemical Composition	Carbon>99%
Type of Supplier	Manufacturer
Application	Mechanical seals, pumps, valve
Certification	ISO9000
Size	OEM
Feature	High Strength, Superior wear,Corrosion resistance
Customized	Available
Porosity	Low porosity
Material	Carbon graphite

Skill-Function Of Graphite

Classification	Brand No.		Density (g/cm³)	Anti-bending	Anti-comp	HS Hardness	Porosit	X10-6/℃ Linear Expansivity	Usign term Perature
Hot-pressing			1.72	54	147	68	1.5	60	200
Impreg-nated Carbon	Bakeliteel Rosin	M102F	1.72	54	147	68	1.5	4.8
		M205F	1.82	55	150	75	2.5	6
		M203F	1.8	65	150	75	2.5	6.5
		M208F	1.75	50	150	70	1	4.8
	Furane Resin	M106F	1.65	65	240	95	1.5	6.5
		M102F	1.7	60	220	95	1.5	6.5
		M238F	1.85	55	105	55	2	4.5
		M254F	1.82	45	100	55	2	6
		M255F	1.85	55	105	55	2	4.8
		M158F	1.7	60	200	90	2	5.1
	Epoxy Resin	M106H	1.65	60	210	75	1	4.8
		M120H	1.7	55	200	75	1	4.8
		M238H	1.88	50	105	55	1.5	4.5
		M254H	1.82	40	90	50	1	4.5
		M255H	1.85	50	95	50	1	4.5

Why Choose Us

   Okay, let's conduct a comprehensive and in-depth analysis of Antimony Impregnated Carbon Graphite (abbreviated as Antimony Impregnated Carbon Graphite/Sb-Graphite), a material that plays a key "soft ring" role in mechanical seals under harsh conditions.

Overview

Antimony Impregnated Carbon Graphite is a composite material made by filling the pores of porous carbon/graphite matrix materials with molten antimony (Sb) through a vacuum/pressure impregnation process. It is essentially graphite, but through the impregnation of antimony, its mechanical strength, hardness, thermal conductivity, impact resistance and sealing performance are significantly improved, while maintaining the inherent self-lubricity, low friction coefficient and chemical corrosion resistance (especially for strong acids) of graphite. It is one of the top soft ring materials for mechanical seals under high temperature, high pressure, high speed, and highly corrosive media (especially sulfuric acid, etc.), and is often used in pairs with various hard rings (such as silicon carbide SiC, tungsten carbide WC, and alumina ceramic Al2O₃).

1. Core principle: impregnation process and material structure

Matrix material: high-quality carbon graphite matrix. It is usually made of carbon source powders such as petroleum coke, asphalt coke, natural graphite, etc. mixed with binders such as tar pitch, and made by extrusion/molding, roasting (~1000°C, removing volatiles to form primary carbon bonds), and graphitization (~2500-3000°C, so that carbon atoms are arranged into graphite crystal structures). This process produces an inherent interconnected pore network (porosity is usually 15%-25%).

Impregnation process (key steps):

1. Vacuum degassing: Place the graphite matrix in a vacuum environment to extract air and moisture in the pores to ensure that the subsequent molten antimony can fully infiltrate and penetrate. 2.Impregnation of molten antimony: Under vacuum or inert atmosphere (to prevent antimony oxidation), molten metal antimony (Sb, melting point 630.6°C) is pressed into the pores of the matrix under pressure (several bars to tens of bars). High-temperature molten antimony has good fluidity.

3.Cooling and solidification: Slow cooling solidifies the antimony impregnated into the pores into a solid state.

4.(Optional) Post-treatment: Machining to remove excess antimony on the surface, precision grinding and polishing the end face.

·Microstructure:

1.Continuous graphite skeleton: Provides the matrix, self-lubricity and basic chemical inertness of the material.

2.Antimony metal phase filling the pores: Occupies most of the pores in the graphite matrix in the form of a continuous or discontinuous network.

3.Residual micropores (possible): After high-quality impregnation, the porosity can be reduced to below 1%-5% (A-level porosity), achieving nearly complete densification.

·The role of antimony:

1.Structural enhancer: Fill holes, eliminate weaknesses, and improve density and integrity.

2.Reinforcer: Significantly improve hardness, compressive/flexural strength, elastic modulus and wear resistance.

3.Thermal conductivity: Antimony's thermal conductivity is much higher than that of the graphite matrix (although graphite is high in the parallel direction, it is low in the vertical direction and has obvious anisotropy). The introduction of the metal network greatly improves the overall thermal conductivity and makes it closer to isotropy.

4.Anti-erosion protection: Reduce the direct erosion of high-speed fluids or particles on the exposed graphite matrix.

5.Improve air tightness: Block the leakage channel, improve the sealing, and reduce the risk of fluid medium infiltrating the interior to cause graphite expansion or oxidation.

2. Key physical and mechanical properties

·Density:

oHigher than unimpregnated graphite, typically 1.8 - 2.0 g/cm³ (pure graphite matrix about 1.5-1.8 g/cm³), antimony itself has a high density (~6.7 g/cm³).

·Hardness:

oGreatly improved! From unimpregnated ~40-60 Shore Hardness (Shore Hardness) to about 65-90 Shore Hardness (depending on the matrix and the degree of impregnation). Close to metals (such as copper alloys), but still significantly lower than hard ring materials (SiC, WC). This ensures good friction and wear characteristics.

·Flexural strength (MOR):

oGreatly enhanced! From 20-50 MPa before impregnation to 50 - 100+ MPa. It can withstand higher mechanical loads and impacts.

·Elastic modulus:

oIncreased from ~5-15 GPa before impregnation to 15 - 30 GPa. Improved rigidity and resistance to deformation.

·Compressive strength:

oGreatly improved, reaching 150 - 300+ MPa. Sufficient to withstand the closing force of mechanical seals.

·Thermal conductivity:

oCore advantage! Strongly anisotropic and greatly improved!

oAfter impregnation, the thermal conductivity is greatly improved (antimony metal conducts about 24 W/m·K):

§Parallel to the extrusion direction (if it is an extruded substrate): 80 - 120+ W/(m·K)can be achieved! This is one of its most important properties.

§Vertical direction: significantly higher than the unimpregnated substrate, up to 30 - 60+ W/(m·K).

▪The metal antimony network greatly improves the heat conduction path inside the matrix, allowing heat to be more evenly and efficiently extracted from the friction end face, significantly reducing the end face temperature, which is crucial to prevent the sealing liquid film from evaporating, coking, thermal cracking and thermal deformation.

· Thermal expansion coefficient (CTE):

o Anisotropic and higher than pure graphite: Because the CTE of antimony (~11 ×10⁻⁶/K) is higher than that of graphite (~0.5-2.5×10⁻⁶/K). The overall value is about:

▪ Parallel direction: ~3 - 6 × 10⁻⁶/K

▪ Perpendicular direction: ~4 - 8 × 10⁻⁶/K (still lower than most metals). It needs to be designed to match the thermal expansion coefficient of the matching hard ring material (such as SiC CTE~4.5). ·Maximum operating temperature (in air):

o~300°C (~350°C for short periods of time). This is its key limitation!

oLimiting factor: Solid-solid phase transition of antimony (Sbβ -> Sbα): Occurs at about 240°C, accompanied by significant volume shrinkage (~6%). Long-term operation above 240°C will cause the shrinkage caused by the phase change to be irreversible (i.e. it will not recover after cooling), causing deformation (depression) of the end face, uneven distribution of contact stress, increased wear, and ultimately a sharp increase in the risk of leakage.

o Antimony is significantly volatile above 500°C and is also easily oxidized to Sb₂O₃ in air (Pilling-Bedworth ratio <1, oxide film is not protective).

·Conductivity: Improved, becoming a good conductor. May be a problem in electrochemical environments.

3. Chemical and tribological properties

·Excellent chemical corrosion resistance (especially strong acids):

oStrong sulfuric acid (H₂SO₄): The trump card of antimony-impregnated graphite! It shows excellent long-term chemical stability in almost all concentrations (including oleum) and temperatures (< maximum service temperature limit) (antimony is extremely resistant to sulfuric acid, and graphite itself is also resistant).

oHydrochloric acid (HCl): Good corrosion resistance in both dilute and concentrated acids.

oPhosphoric acid (H₃PO₄): Good corrosion resistance.

oMost organic acids: Such as acetic acid, oxalic acid, etc., perform well.

oMany salt solutions, organic solvents: Good.

·Key restrictions and taboos:

oFluorinated media / fluorides / hydrofluoric acid (HF): Absolutely prohibited! HF will severely corrode graphite and antimony (antimony forms volatile SbF₅).

o Strong oxidizing acid (above room temperature):

▪ Concentrated nitric acid (HNO₃): It is OK in cold dilute nitric acid, but hot concentrated nitric acid will violently oxidize graphite and antimony. Usually prohibited!

▪ Chromic acid (CrO₃ in H₂O), aqua regia: Strong oxidizing, prohibited!

o Strong alkali (high temperature/concentrated): Such as hot concentrated NaOH/KOH (>30%, >80°C), it will corrode graphite (especially alkali will corrode the edge of graphite lattice), and antimony will also be easily dissolved into antimonite. Not recommended or limited.

o Oxidizing salts: Such as hypochlorite (bleach), dichromate, etc., are corrosive at higher temperatures or concentrations.

o Antimony phase change problem: As mentioned above, the operating temperature must be strictly controlled < 240°C to avoid catastrophic seal failure caused by phase change.

·Friction and wear properties:

oSelf-lubricating property: Retains the properties of the graphite matrix. The weak bonds between the graphite layers are easy to slip under friction shear, forming a transfer film to lubricate the friction pair.

oLow friction coefficient: When paired with a suitable hard ring (SiC, WC, Al₂O₃), it is usually in the range of 0.05 - 0.15. Low starting torque.

oGood wear resistance (as a soft ring): Although the hardness is improved, it is still the "soft" party compared to the hard ring (SiC, WC). Its wear form is mainly gradual and uniform abrasive wear and slight adhesive wear. The design goal is a reasonable wear rate and priority protection of the hard ring.

oImpact wear resistance: Compared with unimpregnated graphite, its higher strength and toughness make it more resistant to the impact of start-stop and impact wear of particles.

o"Sacrificial" protection characteristics: In boundary lubrication or micro-convex contact, the graphite/antimony material wears first and transfers to protect the hard ring.

4. Key points of manufacturing process

1. Preparation of graphite matrix with high purity, high porosity and uniform structure. This is the basis of performance.

2.Key: Vacuum pressure impregnation (VPI). The vacuum degree and impregnation pressure directly affect the impregnation effect (pore filling degree). Usually multiple impregnations are required to achieve high-grade (Grade A) porosity.

3.Precise temperature control: Antimony melt temperature during impregnation (affects viscosity/fluidity), cooling rate (affects internal stress).

4.Subsequent machining and grinding and polishing: Achieve strict dimensional accuracy, flatness (usually within 3 light bands) and surface finish (Ra < 0.2 μm). Good processing performance (much easier than hard rings).

5.Quality control: Porosity, density, hardness, physical property testing, appearance inspection (no cracks, voids, unimpregnated areas).

5. Typical application scenarios in mechanical seals

Antimony-impregnated graphite is designed almost exclusively for the most demanding corrosive, high-temperature, high-pressure, and high-speed sealing applications, especially in the chemical and petrochemical fields:

·Concentrated sulfuric acid transportation and processing:

o Pump, valve, and agitator seals in sulfuric acid plants and chemical plants. Concentrations ranging from 98% fuming acid to dilute acid (note the temperature limit) are the most dominant application areas for antimony-impregnated graphite. Often paired with silicon carbide (RBSiC, SSiC) hard rings.

·Hydrochloric acid transportation:

o Hydrochloric acid pumps and reactor seals of various concentrations (temperature <240°C). Commonly paired with hard rings.

·Phosphoric acid production and processing:

o Pump seals for extraction, concentration, and transportation of phosphoric acid-containing media.

·Organic acid media:

o Acetic acid, acrylic acid, oxalic acid and other organic acid pump seals (note some oxidizing organic acids).

·High temperature hot oil, molten salt system (need <240℃):

o Thermal oil circulation pump, molten salt pump seal (temperature strictly controlled upper limit).

·High pressure, high speed pump (corrosive medium):

o Improved strength and thermal conductivity enable it to withstand higher PV values (pressure × speed) and heat loads (within temperature limits), and is often used in high-specification applications such as Plan 53/54 in API 682 standard.

·Special working condition combination:

o Extreme working conditions with high pressure, high speed, and corrosive strong acid.

Classic pairing:

·Antimony-impregnated graphite (soft ring) vs. reaction-sintered silicon carbide (RB-SiC / SiSiC): The most commonly used and classic "golden partner", suitable for most strong acid seals. Balanced and reliable performance.

·Antimony-impregnated graphite vs. pressureless sintered silicon carbide (SSiC / S-SiC): For more extreme, cleaner conditions, or where higher purity/hardness is required.

·Antimony-impregnated graphite vs. tungsten carbide (WC - cobalt-based or nickel-based): If the media is not very corrosive and not very oxidizing (WC is not resistant to strong acids and oxidants), especially in high-impact applications. Nickel-based WC is used for weak alkali + high temperature combinations (but Sb-graphite needs to be careful with alkalinity).

Antimony-impregnated graphite vs. alumina ceramic (Al₂O₃): For less corrosive or cost-sensitive applications, with poorer wear resistance than WC/SiC

6. Key points for design, selection and use

·Core limitation: Upper temperature limit (<240°C): During design, selection and use, it is necessary to ensure that the sealing chamber/end face temperature is stably below 240°C! Exceeding this temperature will cause antimony phase change and shrinkage, causing leakage failure. This is not a short-term tolerance issue, but a forbidden area involving permanent changes in material structure.

·Avoid oxidizing media: Concentrated nitric acid, chromic acid, aqua regia, strong oxidizing salts, and high-temperature strong alkalis are prohibited. ·Absolutely avoid fluorine-containing environments (HF/F⁻).

·Confirmation of media compatibility: Strictly evaluate the media composition, concentration, pH, redox properties, operating temperature and pressure range. ·Paired hard ring selection: Strong acids are preferably paired with SiC-type hard rings (RB-SiC/SSiC)to form the best combination of complementary performance. Carefully select pairing with WC (it is necessary to confirm that WC has sufficient corrosion resistance). ·Cooling and flushing: Critical! Even though antimony-impregnated graphite has excellent thermal conductivity, an effective API standard flushing program (such as Plan 11, 21, 31, 32, 52, 53, etc.) must be implemented at high PV values to ensure that the end face temperature is controllable (<240°C), remove friction heat and impurities, and maintain liquid film lubrication. Ensure that the seal chamber is well cooled (or heated evenly).

·Cleaning requirements: Although the wear resistance is improved, it is still necessary to avoid a large amount of hard particles in the medium to prevent severe abrasive wear.

·Installation and alignment: Precise alignment is required to avoid the risk of excessive local wear or fragmentation caused by excessive deflection stress.

·Surface quality: Like hard rings, high flatness and low surface roughness are required.

·Alternatives to consider: If the operating temperature is >240°C for a long time or there is a risk of oxidation/alkalinity, other soft rings should be considered:

oResin-impregnated graphite (such as furan, epoxy, phenolic): Higher temperature resistance (resin-based, up to ~250-400°C), especially resistant to strong alkali and oxidation (resin filling blocks pores), but thermal conductivity is significantly inferior to antimony-impregnated graphite, and strong acid resistance (especially concentrated sulfuric acid) is not as reliable and stable as antimony-impregnated graphite. It is the first choice for high-temperature non-corrosion/weak corrosion.

oSpecial high-temperature oxidation-resistant graphite: High-temperature oxidation resistance is improved through additives or special treatment (high cost).

oUnfilled high-purity dense graphite: Used in higher temperatures or specific corrosive environments, but with low strength, hardness, and thermal conductivity.

oPTFE-filled graphite: Used in solvents and other working conditions, with temperature restrictions.

7. Advantages summary

1.Unparalleled resistance to concentrated sulfuric acid: The preferred material for long-term stable operation in sulfuric acid media.

2. Excellent resistance to hydrochloric acid, phosphoric acid and a variety of organic acids:

3. Top soft ring thermal conductivity:

Thermal conductivity is one of the biggest highlights of antimony-impregnated graphite (80-120+ W/m·K parallel direction), far exceeding other soft ring materials (resin-impregnated graphite <10 W/m·K), and effectively extracts friction heat, which is the key to stable operation of the seal.

4. High mechanical strength and hardness:

Significantly higher than unimpregnated or resin-impregnated graphite, with strong ability to withstand high PV values.

5. Good toughness/impact resistance:

Compared with graphite and ceramic hard rings.

6. Excellent sealing:

Low porosity prevents medium penetration.

7.

Excellent self-lubrication and low friction coefficient:

Reduced temperature rise and wear.

8. Good machinability and economy (compared with hard rings such as SiC):

Compared with hard rings, the manufacturing cost is relatively low.

8. Disadvantages/Limitations

1. Strict upper temperature limit (antimony phase change): < 240°C (long term). This is its most important limitation and the most important risk of failure to be prevented! Exceeding the temperature limit means a sharp loss of sealing reliability.

2. Poor resistance to oxidizing media: Concentrated nitric acid, chromic acid, aqua regia, strong oxidizing salts, high-temperature strong alkalis are prohibited.

3. Highly sensitive to fluorine/fluoride (HF): Absolutely prohibited!

4. The hardness is still limited (compared to hard rings): It is still a "soft ring" and is designed to wear moderately (protect the hard ring).

5. Environmental and toxic concerns about antimony: Antimony and its compounds are considered pollutants (partially concerned by RoHS/REACH), and their application in the food and pharmaceutical industries is limited. Production, processing, and scrapping must comply with regulations.

6. Alkali resistance is not as good as resin-impregnated graphite:

7. Thermal conductivity anisotropy may affect:

The design needs to consider the relationship between the extrusion direction and the end face heat flow (try to use the high thermal conductivity parallel direction).

9. Comparison with other soft ring materials

· VS unimpregnated (porous) carbon graphite:

o Antimony-impregnated: strength, hardness, thermal conductivity, and air tightness are greatly improved.

Better wear resistance, suitable for more demanding working conditions (high P/V/T).

o Unimpregnated: softer, lower friction, poor thermal conductivity (poor vertical direction), high porosity and easy to leak and oxidize. Only used in low pressure, low speed, low temperature, non-corrosive or weakly corrosive, low-value working conditions.

· VS resin-impregnated graphite (furan, epoxy, phenolic):

o Antimony-impregnated: thermal conductivity rolling advantage (>10 times), better and more stable resistance to strong acids (especially concentrated sulfuric acid), slightly higher temperature resistance (some resins <200℃).

oResin impregnation: usually has a higher upper temperature limit (good resin can be ~250-400℃), better resistance to strong alkali and oxidizing media, and the cost is usually slightly lower. However, the thermal conductivity is poor (<5-10 W/m·K), and the resin may decompose and carbonize at high temperatures. It is the first choice for high-temperature non-strong acid conditions (such as hot oil, alkali).

·VS Babbitt/metal alloy impregnation (Sn, Cu, etc.):

o Antimony impregnation: usually has better corrosion resistance (strong acid), higher hardness, and the cost may be equivalent or slightly lower.

o Metal impregnation: may be softer, sometimes has better ductility, thermal conductivity is equivalent to (parallel to) antimony impregnated graphite, and is resistant to specific corrosion (such as some metals are resistant to weak alkali). Less application.

·VS polytetrafluoroethylene (PTFE) filled graphite:

o Antimony impregnation: better strength, hardness and thermal conductivity, more reliable resistance to strong acids such as sulfuric acid (PTFE is not resistant to strong oxidizing acids).

oPTFE filling: It is also resistant to strong acids, may have lower friction, is particularly resistant to solvents (such as ketones), and has no antimony phase transition temperature limit. However, its thermal conductivity is extremely poor (<1 W/m·K), and its strength, hardness, and temperature resistance (~260°C, but the actual PTFE softening point is low) are far inferior.

Summary and comparison: Antimony-impregnated graphite is the top soft ring solution when pursuing extreme thermal conductivity and strong acid (especially concentrated sulfuric acid) corrosion resistance. It has an irreplaceable position in the field of strong acid sealing. However, its "Achilles heel" is the strictly limited maximum operating temperature (<240°C), and it has no resistance to oxidizing media (concentrated nitric acid, etc.) and fluoride (HF). In high-temperature working conditions (<~400°C) without strong acids or when there is an oxidation/alkalinity risk, resin-impregnated graphite is usually a better choice. Designers must accurately weigh the temperature, medium corrosiveness, and heat load requirements to select.

Conclusion

Antimony-impregnated carbon graphite is an advanced graphite-based composite material that is greatly strengthened by vacuum pressure impregnation with metallic antimony. It perfectly combines the chemical inertness (especially for strong acids) and self-lubricity of graphite with the outstanding thermal conductivity, enhanced mechanical strength and low porosity properties imparted by metallic antimony. This makes it an ideal material for mechanical seal soft rings under extremely harsh working conditions (especially high temperature, high pressure and strong acid, but the temperature must be <240°C). Its position in the field of concentrated sulfuric acid pump seals is almost unshakable. However, the phase change temperature limit of antimony (240°C) is an absolute red line in selection and operation, and the taboos for oxidizing media (concentrated nitric acid, etc.) and fluoride (HF) must also be kept in mind. Fully understanding the advantages and key limitations brought by its excellent performance is crucial to designing reliable and long-life corrosive fluid sealing systems. In the face of high PV value and highly corrosive sealing challenges, when the temperature is controllable and avoids restricted areas, the "golden combination" of antimony-impregnated graphite and silicon carbide hard ring represents one of the top solutions for high-performance industrial sealing.