Question 1

Hadfield (austenitic manganese) steel: Approximate manganese content used for crusher jaws and impact-resistant parts is __________ %.

Accepted Answer

Introduction / Context: Austenitic manganese steel (Hadfield steel) is renowned for exceptional work-hardening and toughness, making it ideal for high-impact wear parts like crusher jaws, hammers, and railway crossings. Given Data / Assumptions: Typical alloy contains high Mn with carbon around 1.0–1.4% C. Used where impact and gouging wear dominate. Service relies on strain-induced hardening. Concept / Approach: At about 12–14% Mn, the steel retains an austenitic matrix at room temperature. Under impact, it work-hardens at the surface while maintaining a tough core, delivering a unique combination of wear resistance and resilience. Step-by-Step Solution: Recall nominal composition: ~1.2% C and 12–14% Mn.Relate composition to property: high Mn stabilizes austenite and promotes work-hardening.Select the option 12–14% as standard content for crusher jaws. Verification / Alternative check: Standards and datasheets (e.g., ASTM A128 grades) specify Mn in this range for Hadfield steel used in impact wear components. Why Other Options Are Wrong: Lower Mn levels (under ~10%) do not provide the fully austenitic, work-hardening behavior; they form pearlite or martensite and lose the hallmark properties. Common Pitfalls: Heat treatment and service temperature can alter performance; water quenching after solutionizing is typical to retain austenite prior to service work-hardening. Final Answer: 12–14

Question 2

Silver hardening by alloying: Soft pure silver can be hardened for service by adding a small amount of which alloying elements?

Accepted Answer

Introduction / Context: Pure silver is soft and ductile. For jewelry, contacts, and utensils, it is commonly alloyed to raise hardness and strength without losing too much conductivity or tarnish resistance. Given Data / Assumptions: Target is modest hardening with small alloy additions. Service includes wear and handling; thermal extremes are not primary. Electrical properties may remain important. Concept / Approach: Copper is the classic hardener for silver (e.g., sterling silver Ag–Cu ~92.5/7.5). Small nickel additions can further improve hardness and tarnish resistance in certain silver alloys and contact materials, balancing mechanical strength with acceptable conductivity. Step-by-Step Solution: Identify principal hardener: copper in small percentages meaningfully raises hardness.Consider nickel: often used in combination to enhance strength/wear in specialty silver alloys.Choose the combined alloying option reflecting standard practices. Verification / Alternative check: Standards for sterling and coin silver focus on copper; silver–copper–nickel options exist for contacts and decorative applications with enhanced strength. Why Other Options Are Wrong: Zinc, aluminium, tin: can be present in small amounts in some brasses/bronzes or solders but are not the typical minor additions chosen primarily to harden silver in standard practice. Common Pitfalls: Confusing German silver (Cu–Ni–Zn, no silver) with silver alloys; the hardening strategy for true silver is dominated by copper, sometimes with nickel. Final Answer: Copper and nickel

Question 3

Stainless steel grades — meaning of 18/8: 18% chromium and 8% nickel composition corresponds to which stainless steel family?

Accepted Answer

Introduction / Context: The shorthand “18/8” denotes 18% Cr and 8% Ni, the archetype of widely used stainless steels for food processing equipment, chemical plant, and general service. Given Data / Assumptions: Composition: ~18% chromium, ~8% nickel, balance iron. Common examples: AISI 304/304L variations. Applications demand corrosion resistance and formability. Concept / Approach: Nickel stabilizes austenite at room temperature in Fe–Cr–Ni alloys. With 18% Cr for passivity and 8% Ni for austenite stabilization, the steel falls squarely in the austenitic family, featuring non-magnetic behavior (annealed), good weldability, and excellent corrosion resistance in many environments. Step-by-Step Solution: Match composition with family definitions.Recognize AISI 304 as the standard 18/8 alloy.Select “austenitic stainless steel.” Verification / Alternative check: Materials standards and vendor datasheets classify 18/8 as 300-series, austenitic grades. Why Other Options Are Wrong: Ferritic/martensitic: lower or zero nickel; microstructure not austenitic at room temperature. Common Pitfalls: Assuming all stainless steels are magnetic; austenitic types are generally non-magnetic in annealed state. Final Answer: Austenitic stainless steel

Question 4

Shipping and storage of liquid ammonia: Liquid ammonia for industrial use is transported in containers made of which material?

Accepted Answer

Introduction / Context: Liquid ammonia (NH3) is transported and stored under pressure or at low temperature. Container materials must provide mechanical integrity and compatibility with ammonia and trace impurities. Given Data / Assumptions: Industrial shipping containers, cylinders, rail cars, and tanks. Ambient temperature pressure service (or refrigerated tanks). Materials must resist ammonia stress corrosion cracking where relevant. Concept / Approach: Carbon steel and specific low-alloy steels are standard for ammonia service. They deliver high strength, weldability, and low cost. Nonferrous metals like copper and zinc are avoided due to ammonia attack. Glass is impractical structurally, and lead-lining is not required for NH3 containment. Step-by-Step Solution: Eliminate unsuitable choices: glass is fragile; lead-lining is used for strong acids, not NH3.Consider compatibility: aluminium can suffer in certain ammonia environments and is not the standard for pressurized transport.Select steel as the established code-compliant choice. Verification / Alternative check: Chemical storage standards and tank car codes specify steel construction for anhydrous ammonia vessels, with appropriate stress-relief and inspection regimes. Why Other Options Are Wrong: Aluminium: not common for pressurized NH3 shipping. Glass: structurally unsuitable. Lead-lined: unnecessary and incompatible for this service. Common Pitfalls: Confusing ammonia compatibility with aqueous ammonia cleaning applications; structural design governs container choice. Final Answer: Steel

Question 5

Material compatibility — fuming sulphuric acid (oleum): Select a suitable construction material for equipment handling oleum at typical ambient conditions.

Accepted Answer

Introduction / Context: Fuming sulphuric acid (oleum) is highly concentrated H2SO4 containing free SO3. Correct materials prevent rapid corrosion and ensure safe storage and transfer in chemical plants. Given Data / Assumptions: Service at ambient temperature (unheated storage/transfer). Oleum and very concentrated sulphuric acid form protective films on certain ferrous alloys. Chloride stress corrosion is not the dominant concern here. Concept / Approach: At high concentrations of H2SO4 and oleum, carbon steel rapidly passivates by forming a protective sulphate/oxide film, resulting in very low corrosion rates at moderate temperatures. Many austenitic stainless steels (e.g., 304) are not favored for strong sulphuric acid and oleum; nickel and Monel are also not typical selections for this medium in bulk equipment due to cost and specific corrosion behavior. Step-by-Step Solution: Match acid concentration and temperature to corrosion data.Select carbon steel for oleum at ambient conditions based on established industry practice.Rule out stainless 304 and nickel alloys that are vulnerable or uneconomic for this specific acid. Verification / Alternative check: Corrosion charts for sulphuric acid show a region of low corrosion rates for carbon steel at high concentrations and low temperature, including oleum storage tanks. Why Other Options Are Wrong: 304 SS: susceptible in strong H2SO4. Nickel/Monel: not standard materials for oleum handling; unnecessary expense and sometimes poor performance. Common Pitfalls: Generalizing “stainless is best” without consulting acid concentration–temperature corrosion maps. Final Answer: Carbon steel

Question 6

Mohs hardness — material just below diamond: Which material ranks immediately below diamond on the Mohs hardness scale?

Accepted Answer

Introduction / Context: The Mohs hardness scale ranks minerals by scratch resistance from talc (1) to diamond (10). It is widely referenced in materials selection, abrasives, and wear assessment, even though it is an ordinal, not linear, scale. Given Data / Assumptions: Standard Mohs reference minerals: corundum is 9, topaz is 8, calcite is 3. Diamond is 10. Silicon carbide is a manufactured abrasive with hardness comparable to ~9–9.5 on various scales, but Mohs standard mineral 9 is corundum. Concept / Approach: In the classic Mohs sequence used for education and field testing, the mineral ranked just under diamond is corundum (Al2O3). While modern abrasives like silicon carbide and boron carbide can be extremely hard, the Mohs reference immediately below 10 is corundum at 9. Step-by-Step Solution: List Mohs references: 8 = topaz, 9 = corundum, 10 = diamond.Compare options: corundum matches the rank directly below diamond.Select corundum as the correct answer. Verification / Alternative check: Mineralogy tables and materials handbooks confirm corundum as Mohs 9 and the standard just below diamond. Why Other Options Are Wrong: Topaz: Mohs 8, two steps below diamond. Silicon carbide: very hard abrasive, but the Mohs canonical mineral at 9 is corundum. Calcite: soft mineral at 3. Common Pitfalls: Equating engineered abrasive hardness scales with the Mohs ordinal mineral list; they are related but not identical. Final Answer: Corundum (aluminium oxide)

Question 7

Industrial reactor materials — photochemical chlorination of benzene In producing benzene hexachloride (BHC) via photochemical chlorination of benzene, the reactor is typically lined with which material to resist chlorine and hydrogen chloride forme…

Accepted Answer

Introduction / Context: Benzene hexachloride (BHC, also called hexachlorocyclohexane) is produced by the photochemical chlorination of benzene in the presence of light. The reaction medium contains benzene, chlorine gas, and generates hydrogen chloride. Choosing an appropriate reactor lining is vital to resist corrosion and ensure long equipment life. Given Data / Assumptions: Reaction: benzene + chlorine → BHC isomers, in a photochemical reactor. Corrosive species: dry/wet chlorine and hydrogen chloride (HCl). Need: corrosion-resistant lining compatible with halogens and HCl. Concept / Approach: Materials selection for chlorination service favors linings that are inert to halogens and acid gases. Glass-lined steel and lead-lined equipment have a long history in handling chlorination reactions due to their excellent resistance to Cl2 and HCl at moderate temperatures typical of photochemical operations. Step-by-Step Solution: Identify corrosive environment: chlorine + HCl present.Screen common linings: lead and glass show strong resistance to Cl2/HCl; many refractories do not protect against acid gas permeation.Select lining used historically and industrially for BHC production: lead or glass. Verification / Alternative check: Corrosion charts and industry practice for chlorination reactors repeatedly recommend glass-lined steel or lead lining for durability and ease of cleaning in halogen-rich environments. Why Other Options Are Wrong: Karbate: suitable for some acid services, but photochemical chlorination commonly uses lead/glass linings. Fireclay bricks: designed for high-temperature furnaces, not optimized for halogen acid corrosion in liquid-phase photochemical duty. PVC: cannot serve as a structural reactor lining under process temperatures/solvents; poor compatibility with hot aromatics. Common Pitfalls: Confusing structural refractories with corrosion-resistant internal linings. Assuming a plastic liner can handle solvent-swelling and temperature in chlorination systems. Final Answer: Lead or glass

Question 8

Metallurgy for permanent magnets Which alloying addition most effectively increases residual magnetism (remanence) in steels used for making permanent magnets?

Accepted Answer

Introduction / Context: Permanent magnet steels require high remanence (residual magnetism) and high coercivity. Alloying elements can dramatically influence the magnetic domain structure and anisotropy, thereby altering magnetic performance. Given Data / Assumptions: Base material: magnet steels or magnet alloys. Target property: higher residual magnetism (remanence) after magnetization. Consider common alloying additions: Cr, Ni, W, Co. Concept / Approach: Cobalt is well known for enhancing saturation magnetization and magnetic anisotropy. Classical permanent magnet materials (e.g., Alnico family) include significant cobalt, which raises remanence and energy product. Chromium typically improves corrosion resistance; nickel improves toughness and austenite stability; tungsten contributes to high-temperature strength but is not primary for maximizing remanence. Step-by-Step Solution: Identify element with strongest positive effect on remanence → cobalt.Relate to industrial magnet alloys (e.g., Alnico: Al–Ni–Co) where cobalt content is key to magnetic strength.Confirm others do not primarily increase residual magnetism compared to cobalt. Verification / Alternative check: Magnetic materials datasheets show increased Br (remanence) with cobalt content in many hard-magnetic alloys. Why Other Options Are Wrong: Chromium: mainly corrosion and oxidation resistance; minor magnetic effect. Nickel: stabilizes austenite and used in soft magnets, but not the most effective for raising remanence in steels. Tungsten: improves hot strength/hardness rather than remanence. Common Pitfalls: Confusing soft magnetic alloying (for transformers) with hard magnets (for remanence). Final Answer: Cobalt

Question 9

Improving remanence in magnet steels Residual magnetism (remanence) in steel magnets is most increased by adding which alloying element?

Accepted Answer

Introduction / Context: Designing steels for permanent magnets focuses on high remanence and coercivity. Specific alloying elements shift magnetic properties via domain pinning, anisotropy, and saturation magnetization. Given Data / Assumptions: Permanent magnet application. Goal: maximize residual magnetism after magnetization. Candidate alloying additions: Ni, Co, W, Cr. Concept / Approach: Cobalt is the classical addition for increasing remanence and energy product. Alloys like Alnico contain substantial cobalt precisely for this reason. Other elements serve different roles: nickel favors austenite/soft magnetic behavior; chromium aids corrosion resistance; tungsten aids hot hardness. Step-by-Step Solution: Match property (remanence) to alloy addition → cobalt.Cross-check against industrial magnet alloy compositions with high Co content.Confirm alternatives do not prioritize remanence to the same degree. Verification / Alternative check: Property charts for hard-magnetic alloys list higher Br with increased Co percentages. Why Other Options Are Wrong: Nickel: more aligned with soft magnetic materials and toughness improvements. Tungsten: mechanical strength; not a principal factor for remanence. Chromium: corrosion resistance; limited effect on remanence. Common Pitfalls: Assuming hardness-enhancing elements also maximize magnetic remanence. Final Answer: Cobalt

Question 10

Cobalt-based hard-facing alloys — stellite Stellite, a well-known hard-facing alloy system for wear and corrosion resistance, is primarily composed of which elements?

Accepted Answer

Introduction / Context: Stellite is a family of cobalt-based hard-facing alloys widely used for valves, seats, cutting tools, and wear surfaces where abrasion, corrosion, and high-temperature strength are critical. Given Data / Assumptions: Trade name: Stellite. Target properties: wear resistance, hot hardness, corrosion resistance. Concept / Approach: The core chemistry of stellite alloys features a cobalt matrix strengthened by chromium and tungsten (often with carbon to form carbides). Chromium enhances corrosion/oxidation resistance, while tungsten promotes carbide formation and hot hardness, delivering superior wear performance at elevated temperatures. Step-by-Step Solution: Identify hallmark elements: Co–Cr–W system.Relate chemistry to properties: Cr for corrosion/oxidation, W for carbides/hot hardness, Co matrix for toughness at temperature.Therefore, choose cobalt, chromium and tungsten. Verification / Alternative check: Materials datasheets and welding consumable catalogs list Co–Cr–W as the base for Stellite grades (e.g., Stellite 6). Why Other Options Are Wrong: Zn–Cu–Ni / Zn–Al–Ni: non-stellite compositions. Ni–Co–V: can form other superalloys, but not classic stellite chemistry. Common Pitfalls: Assuming all hard-facing alloys are nickel-based; stellite is cobalt-based. Final Answer: Cobalt, chromium and tungsten

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