Intro to Metals Study Questions with Explanations

Answer is C. The first statement is true, the second statement is false. HCP unit cells are very strong, however Cobalt (Co) has a body centered cubic crystal structure. Titanium (Ti) is the only hexagonal close packed metal mentioned in the lecture.

Hexagonal close packed (HCP) unit cell structure accounts for high strength in metals. Cobalt has a HCP unit cell. a. Both statements are true b. Both statements are false c. The first statement is true, the second statement is false d. The first statement is false, the second statement is true.

Answer is A. True However, when used in small quantities in Au-based alloys, Ni whitens the alloy is increases its strength and hardness

Ni has limited application in Au- and Pd-based dental alloys, but is a common component in non- noble dental alloys. a. True b. False

Answer is B. Metals are extremely poor conductors of electricity and heat. Metals are very good conductors of electricity and heat A. Metals share "free" no localized electrons in an "electron sea" C. Metals are opaque, not transparent D. A polished metal surface does have a lustrous (shiny) appearance E. Metals are strong but can be deformed, they are malleable and ductile

Properties of metals include all of the following EXCEPT: a. Metals have large numbers of non-localized electrons, and many properties are directly attributable to these electrons. b. Metals are extremely poor conductors of electricity and heat. c. Metals are not transparent to visible light. d. A polished metal surface has a lustrous appearance. e. Metals are strong, yet deformable.

Answer is D. A & B are correct. Pure gold (Au) is relatively low in strength, so it must be alloyed with Cu, Ag, Pt, or other metals to develop hardness, durability, and elasticity. It can also be work hardened to improve its properties. C. is wrong because mercury in small amount can have a harmful affect when mixed with gold - so much so that scrap of any dental alloys should not be mixed with gold

Pure Au is the most ductile and malleable of all metals and relatively low in strength. What can be done to improve its strength? a. Alloying with Cu, Ag, Pt. b. Work hardening. c. Mixing with mercury. d. a. & b. are correct.

Answer is D. The first statement is false, the second statement is true. The precious metals consist of the noble metals plus silver, however the noble metals do not include silver. It is true that silver is a precious metal, BUT silver isn't considered a noble metal in dentistry because it corrodes easily in the mouth. Thus, noble and precious are not synonymous in dentistry.

Silver is a precious metal that does not corrode in the oral cavity. The term noble and precious are not synonymous in dentistry. a. Both statements are true b. Both statements are false c. The first statement is true, the second statement is false d. The first statement is false, the second statement is true.

Answer is B. act as a grain refiner. Iridium and Ruthenium are both elements that are used in small amounts in alloys to keep grain size small (which improves the mechanical properties and uniformity in an alloy) A. is wrong because Palladium is the metal with the ability to absorb hydrogen gas when heated (this is undesirable) C. is wrong because Zinc is the metal that acts as a scavenger of oxygen when the alloy is melted (zinc = "deoxidizing agent") D. is wrong because Titanium is the metal that forms an oxide layer which gives it its ability to resist corrosion and who's biocompatibility makes it the metal of choice in dentistry

What is the function of iridium as it is incorporated into dental alloys? a. Absorb hydrogen gas. b. Act as a grain refiner. c. Act as a scavenger. d. Increase corrosion resistance.

Answer is A. Solid solution hardening. Cu, Ag, and PT can be added to gold alloys to develop hardness, durability, and elasticity. B. is incorrect because Gold is a noble metal. This means that pure gold is already resistant to oxidation, tarnish, and corrosion

What is the major contribution of copper in gold casting alloys? a. Solid solution hardening. b. Corrosion resistance. c. Increase density. d. Elevate melting range.

Answer is C. it is a deoxidizing agent. Zinc acts as a scavenger of oxygen when it is melted and its oxidizing property is exploited in dental alloys. A. is incorrect. Ductility is a property of metals provided by electron mobility and metallic bonding. B. is reffering to Beryllium. Adding beryllium to base metal alloys improves its castability by lowering the alloys melting temperature D. is referring to Iridium (Ir) and Ruthenium (Ru). These metals are added to dental alloys as grain refiners

What is the most important role of zinc in dental alloys? a. It increases the alloy ductility. b. It lowers the melting temperature. c. It is a deoxidizing agent. d. It reduces the grain size.

Answer is C. Enhancing surface oxide formation. the oxides of Gallium (Ga) are important in the bonding of ceramic to metal. A. is referring to Aluminum(Al). Alloys containing aluminum are strengthened by the formation of precipitates of Ni3Al B. is referring to Zinc, which scavenges for oxygen when an alloy is melted and is known as a deoxidizing agent D. is referring to Beryllium, which improves castability by lowering the alloys melting temperature.

What is the most significant function of gallium in gold and palladium-based alloys for PFM? a. Precipitation hardening b. Preventing oxidation (scavenger) c. Enhancing surface oxide formation d. Improving castability

Answer is D. Titanium Titanium is the metal of choice in dentistry. Titanium forms a stable oxide layer which helps it resist corrosion and contributes to its biocompatibility. A. Nickel is a common component in non-noble dental alloys and can whiten gold alloys B. Beryllium improves castability of metal alloys, but can cause diseases in vapor form so beryllium alloys shouldn't be used in dental restoration C. Mercury in small quantities has a harmful effect

Which element is the most biocompatible? a. Nickel b. Beryllium c. Mercury d. Titanium

Answer is A. Au (Gold) B. is wring because Co is body centered cubic C. is wrong because Cr is body centered cubic D. is wrong because Fe is body centered cubic

Which of the following elements has a face centered cubic crystal structure? a. Au b. Co c. Cr d. Fe

C. Beryllium. Beryllium can lower an alloys melting temperature and surface tension, but in vapor form it is associated with several diseases and should not be used in dental restorations. A. Nickel is a common component in base metal alloys and is not harmful B. Chromium is a component of many base metal alloys and has been used for many years in removable dental prosthesis D. Cobalt is another common component of many base metal alloys

Which of the following elements improves the castability of base metal alloys but is associated with chronic lung disease and even osteosarcoma?a. Nickel b. Chromium c. Beryllium d. Cobalt

Answer is E. all of the above

Which of the following is(are) base-metal alloy(s)? a. Cobalt-chromium b. Nickel-chromium c. Stainless steel d. Nickel-titanium e. All of the above

Answer is E. Although pure Au is the most ductile and malleable of all metals, it is relatively strong compared to base metals. This is false because while pure gold is more ductile and malleable than the other metals, it is low in strength comparatively.

Which statement below is FALSE? a. Air or water at any temperature does not affect or tarnish Au. b. Because Au is nearly as soft as lead, it must be alloyed with Cu, Ag, Pt, and other metals to develop the hardness and durability necessary in dental alloys, coins, and jewelry. c. Through appropriate refining and purification, Au with an extremely high degree of purity may be produced. d. Au can be work hardened to improve its physical properties. e. Although pure Au is the most ductile and malleable of all metals, it is relatively strong compared to base metals.

Answer is C. At least 10% of grain refiners is needed in the alloy mix to be effective. As little as 0.005% of iridium is effective in reducing grain size. A. Iridium and Ruthenium are used in small amounts as grain refiners B. Iridium and Ruthenium don't melt during casting and serve as nucleating centers as the alloy melt cools which results in a grain refined alloy. D. is true

Which statement is WRONG about grain refiners? a. Iridium and Ruthenium are grain refiners in dental alloys. b. Grain refiners serve as nucleating centers for the alloy melts as it cools. c. At least 10% of grain refiners is needed in the alloy mix to be effective. d. Grain refiners improve mechanical properties of the alloy by keeping the grain size small.

Answer is D. It acts as a scavenger of oxygen when the alloy is melted. Zinc is the "deoxidizing agent" that acts as a scavenger of oxygen when the alloy is melted, not palladium

Which statement is WRONG about palladium? a. Its density is a little more than half that of platinum and gold. b. It can absorb large quantities of hydrogen gas when heated. d. It acts as a scavenger of oxygen when the alloy is melted e. It has a pronounced effect on whitening the yellow color of gold.