The intensive work of materials scientists and solid-state physicists

Question

1992 10 SECTION A 21-27

The intensive work of materials scientists and solid-state physicists has given rise to a class of solids known as amorphous metallic alloys, or glassy metals. There is a growing interest among theoretical and applied researchers alike in the structural properties of these materials. When a molten metal or metallic alloy is cooled to a solid, a crystalline structure is formed that depends on the particular alloy composition. In contrast, molten nonmetallic glass-forming materials, when cooled, do not assume a crystalline structure, but instead retain a structure somewhat like that of the liquid—an amorphous structure. At room temperature, the natural long-term tendency for both types of materials is to assume the crystalline structure. The difference between the two is in the kinetics or rate of formation of the crystalline structure, which is controlled by factors such as the nature of the chemical bonding and the ease with which atoms move relative to each other. Thus, in metals, the kinetics favors rapid formation of a crystalline structure, whereas in nonmetallic glasses the rate of formation is so slow that almost any cooling rate is sufficient to result in an amorphous structure. For glassy metals to be formed, the molten metal must be cooled extremely rapidly so that crystallization is suppressed.

The structure of glassy metals is thought to be similar to that of liquid metals. One of the first attempts to model the structure of a liquid was that by the late J. D. Bernal of the University of London, who packed hard spheres into a rubber vessel in such a way as to obtain the maximum possible density. The resulting dense, random-packed structure was the basis for many attempts to model the structure of glassy metals. Calculations of the density of alloys based on Bernal-type models of the alloys metal component agreed fairly well with the experimentally determined values from measurements on alloys consisting of a noble metal together with a metalloid, such as alloys of palladium and silicon, or alloys consisting of iron, phosphorus, and carbon, although small discrepancies remained. One difference between real alloys and the hard spheres used in Bernal models is that the components of an alloy have different sizes, so that models based on two sizes of spheres are more appropriate for a binary alloy, for example. The smaller metalloid atoms of the alloy might fit into holes in the dense, random-packed structure of the larger metal atoms.

One of the most promising properties of glassy metals is their high strength combined with high malleability. In usual crystalline materials, one finds an inverse relation between the two properties, whereas for many practical applications simultaneous presence of both properties is desirable. One residual obstacle to practical applications that is likely to be overcome is the fact that glassy metals will crystallize at relatively low temperatures when heated slightly.   1 
 1. The author is primarily concerned with discussing

(A) crystalline solids and their behavior at different temperatures
(B) molten materials and the kinetics of the formation of their crystalline structure
(C) glassy metals and their structural characteristics
(D) metallic alloys and problems in determining their density
(E) amorphous materials and their practical utilization

2 
 2. The author implies that the rate at which the molten materials discussed in the passage are cooled is a determinant of the

(A) chemical composition of the resulting solids
(B) strength of the chemical bonds that are formed
(C) kinetics of the materials’ crystalline structure
(D) structure the materials assume
(E) stability of the materials’ crystalline structure

3 
 3. The author’s speculation about the appropriateness of models using spheres of two sizes for binary alloys would be strongly supported if models using spheres of two sizes yielded

(A) values for density identical to values yielded by one-sphere models using the smaller spheres only
(B) values for density agreeing nearly perfectly with experimentally determined values
(C) values for density agreeing nearly perfectly with values yielded by models using spheres of three sizes
(D) significantly different values for density depending on the size ratio between the two kinds of spheres used
(E) the same values for density as the values for appropriately chosen models that use only medium-sized spheres

4 
 4. The author’s attitude toward the prospects for the economic utilization of glassy metals is one of

(A) disinterest
(B) impatience
(C) optimism
(D) apprehension
(E) skepticism

5 
 5. According to the passage, which of the following determines the crystalline structure of a metallic alloy?

(A) At what rate the molten alloy is cooled
(B) How rapid the rate of formation of the crystalline phase is
(C) How the different-sized atoms fit into a dense, random-packed structure
(D) What the alloy consists of and in what ratios
(E) At what temperature the molten alloy becomes solid

6 
 6. Which of the following best describes the relationship between the structure of liquid metals and the structure of glassy metals, as it is presented in the passage?

(A) The latter is an illustrative example of the former.
(B) The latter is a large-scale version of the former.
(C) The former is a structural elaboration of the latter.
(D) The former provides an instructive contrast to the latter.
(E) The former is a fair approximation of the latter.

7 
 7. It can be inferred from the passage that, theoretically, molten nonmetallic glasses assume a crystalline structure rather than an amorphous structure only if they are cooled

(A) very evenly, regardless of the rate
(B) rapidly, followed by gentle heating
(C) extremely slowly
(D) to room temperature
(E) to extremely low temperatures

auradediligodo · Accepted Answer

Hi everyone,
Got 5/7 correct in 12:40 minutes, including 5 minutes to read and 7:40 minutes to answer the questions.   1  2  345  6  7

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P1

In paragraph one the author describes materials that are of interest to researchers: Glassy metals. Then the author proceeds by giving us the difference between metallic and non metallic alloys. The main difference is the formation of the crystalline structure under different temperatures conditions. This part if full of details concerning the reasons.

Purpose:   to describe how glassy metals origin from metal and non metallic alloys.

P2

In this paragraph the author presents attempts to model the structure of glassy metals. Hard spheres are used for the purpose. Then the author describes the difference between real alloys and the spheres: the dimensions of the atoms.

Purpose:   to describe attempts to model the structure of glassy metals.

P3

Here the author explains why glassy metals are promising in terms of their applications. Then she claims that an obstacle regarding the crystalline structure is there but it is likely to be overcome.

Purpose:   To highlight the advantages in terms of application of glassy metals.

Main point

To describe the structure of glassy metals and to highlight the advantages in terms of application.

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1. ​​The author is primarily concerned with discussing

Pre-thinking

Main point question

To describe the structure of glassy metals and to highlight the advantages in terms of application.

(A) crystalline solids and their behavior at different temperatures  Partial scope 
(B) molten materials and the kinetics of the formation of their crystalline structure  Partial scope 
  (C)   glassy metals and their structural characteristics
(D) metallic alloys and problems in determining their density  out of scope 
(E) amorphous materials and their practical utilization  out of scope

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2. ​​​The author implies that the rate at which the molten materials discussed in the passage are cooled is a determinant of the

Pre-thinking

Assumption question

From P1:   The difference between the two is in  the kinetics or rate of formation  of the crystalline structure, which is controlled by factors such as the nature of the chemical bonding and the ease with which atoms move relative to each other. Thus, in metals, the kinetics  favors rapid formation of a crystalline structure , whereas in nonmetallic glasses the rate of formation is so slow that almost  any cooling rate is sufficient to result in an amorphous structure.

We can easily see how the "rate" influences the form that the materials are going to take.

(A) chemical composition of the resulting solids  the chemical composition is not affected 
(B) strength of the chemical bonds that are formed  strength as well is not discussed 
(C) kinetics of the materials’ crystalline structure  the kinetics is also the rate. So saying that the kinetics affects the kinetics is quite nonsense  
  (D)   structure the materials assume  In line with pre-thinking 
(E) stability of the materials’ crystalline structure  the stability of the crystalline structure is not related to the rate of formation.

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3. ​​The author’s speculation about the appropriateness of models using spheres of two sizes for binary alloys would be strongly supported if models using spheres of two sizes yielded

Pre-thinking

Inference question

From P2:   One difference between real alloys and the hard spheres used in Bernal models is that the components of an alloy have different sizes, so that models based on two sizes of spheres are more appropriate for a binary alloy, for example. The smaller metalloid atoms of the alloy  might fit into holes in the dense, random-packed structure of the larger metal atoms.

What we should pay attention to here is the last sentence. It seems that if the atoms of the alloy fit, the result would be good.

(A) values for density identical to values yielded  by one-sphere models  using the smaller spheres only  We don't have any connection between the one shaper model and the 2 spheres model  
  (B)   values for density agreeing nearly perfectly with experimentally determined values  Arrived here by POE and don't find reasons to eliminate this option 
(C) values for density agreeing nearly perfectly with values yielded by models using spheres of three sizes  Same reasoning as in choice A 
(D) significantly different values for density depending on the size ratio between the two kinds of spheres used  We don't have sufficient information to infer this statement 
(E) the same values for density as the values for appropriately chosen models that use only medium-sized spheres  Again the connection between medium sized spheres and the two spheres used in this case is missing

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4. ​​​​​​The author’s attitude toward the prospects for the economic utilization of glassy metals is one of

Pre-thinking

Author's attitude question

Very optimistic:  One of the most promising......One residual obstacle to practical applications that is likely to be overcome is

(A) disinterest
(B) impatience
  (C)   optimism
(D) apprehension
(E) skepticism

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5. ​According to the passage, which of the following determines the crystalline structure of a metallic alloy?

Pre-thinking

Detail question

From P1:  When a molten metal or metallic alloy is cooled to a solid, a crystalline structure is formed that depends on the particular alloy composition.

(A) At what rate the molten alloy is cooled
(B) How rapid the rate of formation of the crystalline phase is
(C) How the different-sized atoms fit into a dense, random-packed structure
  (D)   What the alloy consists of and in what ratios
(E) At what temperature the molten alloy becomes solid

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6. ​​​​Which of the following best describes the relationship between the structure of liquid metals and the structure of glassy metals, as it is presented in the passage?

Pre-thinking

Detail question

The question itself is easy but it is important to consider the order used in the question stem.
Question stem:   ​Which of the following best describes the relationship between the  structure of liquid metals ( 1)  and the  structure of glassy metals ( 2) , as it is presented in the passage?

From P2:  The structure of glassy metals is thought to be similar to that of liquid metals.

(A) The latter is  an illustrative example  of the former
(B) The latter is a large-scale version of the former.
(C) The former is a structural elaboration of the latter.
(D) The former provides an instructive contrast to the latter.
  (E)   The former is a fair approximation of the latter.

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7. ​​​​​It can be inferred from the passage that, theoretically, molten nonmetallic glasses assume a crystalline structure rather than an amorphous structure only if they are cooled

Pre-thinking

Inference question

From P1:   Thus, in metals, the kinetics favors rapid formation of a crystalline structure, whereas in nonmetallic glasses the rate of formation is so slow that  almost any cooling rate  is sufficient to result in an amorphous structure.

(A) very evenly, regardless of the rate
(B) rapidly, followed by gentle heating
  (C)   extremely slowly
(D) to room temperature  Out of context. At room temperature non metallic glasses are not cooled 
(E) to extremely low temperatures

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It's a great day to be alive!

ArmaanBajaj · Answer

Can someone explain Q3,5,6 & 7?

guddo · Answer

3. The author’s speculation about the appropriateness of models using spheres of two sizes for binary alloys would be strongly supported if models using spheres of two sizes yielded

The passage explains that glassy metals have an amorphous structure and that scientists use models to understand this structure. Bernal’s original model used spheres of one size and produced density values fairly close to experimental results. The author suggests that  two-size sphere models may be more accurate for binary alloys , because the two components of such alloys have different atomic sizes.

(A) values for density identical to values yielded by one-sphere models using the smaller spheres only

Incorrect. If the two-size model gives the same result as a one-size model, that does not show that using two sizes is  more appropriate .

(B) values for density agreeing nearly perfectly with experimentally determined values

Correct.   If the two-size model produces density values that closely match the actual measured densities of binary alloys, that strongly supports the author's claim that such a model better represents their structure.

(C) values for density agreeing nearly perfectly with values yielded by models using spheres of three sizes

Incorrect. Agreement with another theoretical model does not show that either model accurately represents real alloys.

(D) significantly different values for density depending on the size ratio between the two kinds of spheres used

Incorrect. This would show that the size ratio affects the model, but not that the model accurately represents actual binary alloys.

(E) the same values for density as the values for appropriately chosen models that use only medium-sized spheres

Incorrect. This would not show any advantage to using spheres of two different sizes.

Answer: (B)

guddo · Answer

5. According to the passage, which of the following determines the crystalline structure of a metallic alloy?

The passage explicitly says that when a molten metal or alloy cools into a solid, the crystalline structure formed  depends on the particular alloy composition . That means  what elements are present and in what proportions .

(A) At what rate the molten alloy is cooled

Incorrect. Cooling rate determines whether crystallization occurs, not which crystalline structure forms.

(B) How rapid the rate of formation of the crystalline phase is

Incorrect. This affects how quickly crystallization happens, not the type of crystalline structure.

(C) How the different-sized atoms fit into a dense, random-packed structure

Incorrect. This concerns models of the amorphous structure of glassy metals.

(D) What the alloy consists of and in what ratios

Correct.   This is exactly what “the particular alloy composition” means.

(E) At what temperature the molten alloy becomes solid

Incorrect. The passage does not say that solidification temperature determines the crystalline structure.

Answer: (D)

guddo · Answer

6. Which of the following best describes the relationship between the structure of liquid metals and the structure of glassy metals, as it is presented in the passage?

The passage says that the structure of glassy metals is thought to be  similar to that of liquid metals . Thus, the structure of liquid metals can serve as  a reasonable model  for the structure of glassy metals.

(A) The latter is an illustrative example of the former.

Incorrect. Glassy metals are not examples of liquid metals.

(B) The latter is a large-scale version of the former.

Incorrect. The passage does not describe a difference in scale.

(C) The former is a structural elaboration of the latter.

Incorrect. The passage says the structures are similar, not that one is a more complex version of the other.

(D) The former provides an instructive contrast to the latter.

Incorrect. Their structures are presented as similar, not contrasting.

(E) The former is a fair approximation of the latter.

Correct.   Since glassy metals are thought to have a structure similar to liquid metals, the structure of liquid metals is a fair approximation of the structure of glassy metals.

Answer: (E)

guddo · Answer

7. It can be inferred from the passage that, theoretically, molten nonmetallic glasses assume a crystalline structure rather than an amorphous structure only if they are cooled

The passage says that nonmetallic glasses normally become amorphous when cooled because crystallization occurs  extremely slowly . Therefore, for a crystalline structure to form, the material would theoretically need to be cooled  very slowly , giving crystallization enough time to occur.

(A) very evenly, regardless of the rate

Incorrect. The passage discusses the rate of cooling, not how evenly the material is cooled.

(B) rapidly, followed by gentle heating

Incorrect. Rapid cooling favors formation of an amorphous structure.

(C) extremely slowly

Correct.   Since crystallization in nonmetallic glasses occurs very slowly, extremely slow cooling would give the crystalline structure enough time to form.

(D) to room temperature

Incorrect. The final temperature alone does not determine whether the structure becomes crystalline.

(E) to extremely low temperatures

Incorrect. The passage focuses on cooling rate, not on reaching an extremely low temperature.

Answer: (C)

egmat · Answer

Hi ArmaanBajaj,

These four all turn on reading one specific line very literally. Let me take them one at a time.

Q3 - the two-size model (answer B)

Go back to P2: the one-size Bernal models agreed "fairly well" with experimental density,  although small discrepancies remained.  The two-size model is offered as a  more appropriate  refinement. So what would prove it's better? It closing that gap - i.e., density values that  agree nearly perfectly with the experimentally determined values.  That's exactly  B .

Why not  D ? "Significantly different values depending on the size ratio" tells us the model is  sensitive to inputs , not that it's  accurate . Support means matching reality, not showing variation.

Q5 - what determines the crystalline structure (answer D)

Here you must split two different things the passage says:

-  Whether  a material ends up crystalline or amorphous - controlled by  cooling rate/kinetics .
-  Which  crystalline structure forms - "a crystalline structure is formed  that depends on the particular alloy composition. "

The question asks about the crystalline structure  of a metallic alloy , so it's the composition -  what the alloy consists of and in what ratios , choice  D . Choice A (cooling rate) is the tempting trap, but rate decides crystalline-vs-amorphous, not the specific structure.

Q6 - liquid metals vs. glassy metals (answer E)

The line is: "The structure of glassy metals is thought to be  similar to  that of liquid metals." Watch the order in the stem:  former = liquid metals, latter = glassy metals.  "Similar to" means one is a  fair approximation  of the other - choice  E .

Quick way to feel the order trap: if I say "a sketch resembles the photo," the  sketch  (former) is an approximation of the  photo  - not an "elaboration" (C) or a "large-scale version" (B). Nothing in the passage says one is bigger or more detailed; just  similar .

Q7 - when nonmetallic glasses go crystalline (answer C)

P1 says the natural long-term tendency of both materials is crystalline, but for nonmetallic glasses "the rate of formation is  so slow  that almost  any  cooling rate is  sufficient  to result in an amorphous structure." So amorphous is basically guaranteed unless you defeat that slowness - by cooling  extremely slowly , giving the sluggish crystals enough time to form. That's  C . "Room temperature" (D) is where the tendency exists, not a cooling method.

Same theme across all four: pin the claim to the exact sentence before choosing.

Answer: B; D; E; C

The intensive work of materials scientists and solid-state physicists

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The intensive work of materials scientists and solid-state physicists

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615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

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From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

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