romikgosai/squad_modified huggingface dataset:
Naturally occurring glass, especially the volcanic glass obsidian, has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded. But in general, archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or ancient Egypt. The earliest known glass objects, of the mid third millennium BCE, were beads, perhaps initially created as accidental by-products of metal-working (slags) or during the production of faience, a pre-glass vitreous material made by a process similar to glazing.

Questions and answers:
['
Q: What kind of glass exists in nature?
A: obsidian', '
Q: Obsidian is what type of glass?
A: volcanic', '
Q: What was obsidian used to make in prehistoric times?
A: cutting tools', '
Q: When are the oldest beads thought to have been made?
A: mid third millennium BCE', '
Q: What glass-like material is made with a method related to glazing?
A: faience']
Color in glass may be obtained by addition of electrically charged ions (or color centers) that are homogeneously distributed, and by precipitation of finely dispersed particles (such as in photochromic glasses). Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron(II) oxide (FeO) impurities of up to 0.1 wt% produce a green tint, which can be viewed in thick pieces or with the aid of scientific instruments. Further FeO and Cr2O3 additions may be used for the production of green bottles. Sulfur, together with carbon and iron salts, is used to form iron polysulfides and produce amber glass ranging from yellowish to almost black. A glass melt can also acquire an amber color from a reducing combustion atmosphere. Manganese dioxide can be added in small amounts to remove the green tint given by iron(II) oxide. When used in art glass or studio glass is colored using closely guarded recipes that involve specific combinations of metal oxides, melting temperatures and 'cook' times. Most colored glass used in the art market is manufactured in volume by vendors who serve this market although there are some glassmakers with the ability to make their own color from raw materials.

Questions and answers:
['
Q: What can give glass a faint green tinge?
A: iron(II) oxide', '
Q: What can prevent a green color in glass?
A: Manganese dioxide', '
Q: What other than additives can give glass a yellow color?
A: reducing combustion atmosphere', '
Q: What chemical compounds can make glass nearly black?
A: iron polysulfides', '
Q: Charged ions can be used to produce what in glass?
A: Color']
Glass remained a luxury material, and the disasters that overtook Late Bronze Age civilizations seem to have brought glass-making to a halt. Indigenous development of glass technology in South Asia may have begun in 1730 BCE. In ancient China, though, glassmaking seems to have a late start, compared to ceramics and metal work. The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, now in modern Germany, that the late-Latin term glesum originated, probably from a Germanic word for a transparent, lustrous substance. Glass objects have been recovered across the Roman empire in domestic, industrial and funerary contexts.[citation needed]

Questions and answers:
['
Q: What word does "glass" come from?
A: glesum', '
Q: Where did glasswork begin relatively late?
A: China', '
Q: In what year did glassmaking begin in Asia?
A: 1730 BCE', '
Q: What city was a center of glass production for the Romans?
A: Trier', '
Q: In what current country is Trier located?
A: Germany']
Glass was used extensively during the Middle Ages. Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites. Glass in the Anglo-Saxon period was used in the manufacture of a range of objects including vessels, beads, windows and was also used in jewelry. From the 10th-century onwards, glass was employed in stained glass windows of churches and cathedrals, with famous examples at Chartres Cathedral and the Basilica of Saint Denis. By the 14th-century, architects were designing buildings with walls of stained glass such as Sainte-Chapelle, Paris, (1203–1248) and the East end of Gloucester Cathedral. Stained glass had a major revival with Gothic Revival architecture in the 19th-century. With the Renaissance, and a change in architectural style, the use of large stained glass windows became less prevalent. The use of domestic stained glass increased until most substantial houses had glass windows. These were initially small panes leaded together, but with the changes in technology, glass could be manufactured relatively cheaply in increasingly larger sheets. This led to larger window panes, and, in the 20th-century, to much larger windows in ordinary domestic and commercial buildings.

Questions and answers:
['
Q: When did stained glass make a big comeback?
A: 19th-century', '
Q: When did stained glass begin to be used for places of worship?
A: 10th-century', '
Q: When did big windows of stained glass become less common?
A: the Renaissance', '
Q: What 13th-century building is an example of stained glass walls?
A: Sainte-Chapelle', '
Q: What did technological changes allow regular homes to have?
A: larger windows']
In the 20th century, new types of glass such as laminated glass, reinforced glass and glass bricks have increased the use of glass as a building material and resulted in new applications of glass. Multi-storey buildings are frequently constructed with curtain walls made almost entirely of glass. Similarly, laminated glass has been widely applied to vehicles for windscreens. While glass containers have always been used for storage and are valued for their hygienic properties, glass has been utilized increasingly in industry. Optical glass for spectacles has been used since the late Middle Ages. The production of lenses has become increasingly proficient, aiding astronomers as well as having other application in medicine and science. Glass is also employed as the aperture cover in many solar energy systems.

Questions and answers:
['
Q: What type of glass is used in cars?
A: laminated', '
Q: When did eyeglasses originate?
A: late Middle Ages', '
Q: The walls of skyscrapers are often made of what material?
A: glass', '
Q: What type of power systems use glass?
A: solar', '
Q: What type of scientists rely on glass for distant observations?
A: astronomers']
From the 19th century, there was a revival in many ancient glass-making techniques including cameo glass, achieved for the first time since the Roman Empire and initially mostly used for pieces in a neo-classical style. The Art Nouveau movement made great use of glass, with René Lalique, Émile Gallé, and Daum of Nancy producing colored vases and similar pieces, often in cameo glass, and also using luster techniques. Louis Comfort Tiffany in America specialized in stained glass, both secular and religious, and his famous lamps. The early 20th-century saw the large-scale factory production of glass art by firms such as Waterford and Lalique. From about 1960 onwards there have been an increasing number of small studios hand-producing glass artworks, and glass artists began to class themselves as in effect sculptors working in glass, and their works as part fine arts.

Questions and answers:
['
Q: What famous lampmaker used glass?
A: Louis Comfort Tiffany', '
Q: When did glassworkers begin to consider their products fine art?
A: 1960', '
Q: What type of glass did many Art Nouveau artists use?
A: cameo glass', '
Q: When did mass production of glass art begin?
A: early 20th-century', '
Q: What early civilization made cameo glass?
A: Roman Empire']
Addition of lead(II) oxide lowers melting point, lowers viscosity of the melt, and increases refractive index. Lead oxide also facilitates solubility of other metal oxides and is used in colored glasses. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glasses); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in vitreous enamels and glass solders. The high ionic radius of the Pb2+ ion renders it highly immobile in the matrix and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda-lime glass (108.5 vs 106.5 Ohm·cm, DC at 250 °C). For more details, see lead glass.

Questions and answers:
['
Q: What makes glass melt at a lower temperature?
A: lead(II) oxide', '
Q: How much less viscous is lead glass compared with soda glass?
A: 100 times', '
Q: Pb2+ causes lead glass to have what?
A: high electrical resistance', '
Q: Lead oxide makes it easier to dissolve what?
A: other metal oxides']
There are three classes of components for oxide glasses: network formers, intermediates, and modifiers. The network formers (silicon, boron, germanium) form a highly cross-linked network of chemical bonds. The intermediates (titanium, aluminium, zirconium, beryllium, magnesium, zinc) can act as both network formers and modifiers, according to the glass composition. The modifiers (calcium, lead, lithium, sodium, potassium) alter the network structure; they are usually present as ions, compensated by nearby non-bridging oxygen atoms, bound by one covalent bond to the glass network and holding one negative charge to compensate for the positive ion nearby. Some elements can play multiple roles; e.g. lead can act both as a network former (Pb4+ replacing Si4+), or as a modifier.

Questions and answers:
['
Q: What components of glass for networks?
A: silicon, boron, germanium', "
Q: What type of components change the network's shape?
A: modifiers", '
Q: What type of component can both make and change networks?
A: intermediates', '
Q: What type of chemical attachment connects ions to the network?
A: covalent bond']
The alkali metal ions are small and mobile; their presence in glass allows a degree of electrical conductivity, especially in molten state or at high temperature. Their mobility decreases the chemical resistance of the glass, allowing leaching by water and facilitating corrosion. Alkaline earth ions, with their two positive charges and requirement for two non-bridging oxygen ions to compensate for their charge, are much less mobile themselves and also hinder diffusion of other ions, especially the alkalis. The most common commercial glasses contain both alkali and alkaline earth ions (usually sodium and calcium), for easier processing and satisfying corrosion resistance. Corrosion resistance of glass can be achieved by dealkalization, removal of the alkali ions from the glass surface by reaction with e.g. sulfur or fluorine compounds. Presence of alkaline metal ions has also detrimental effect to the loss tangent of the glass, and to its electrical resistance; glasses for electronics (sealing, vacuum tubes, lamps...) have to take this in account.

Questions and answers:
['
Q: What component gives glass the ability to conduct electricity?
A: alkali metal ions', '
Q: How can glass be prevented from corroding?
A: dealkalization', '
Q: What types of ions does typical glass have?
A: alkali and alkaline earth ions', '
Q: Reaction with what causes dealkalization?
A: sulfur or fluorine compounds', '
Q: What can alkaline ions in glass harm, in addition to electrical resistance?
A: loss tangent']
New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali or alkaline earth metal oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition). Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating SeO2. Also, more readily reacting raw materials may be preferred over relatively inert ones, such as Al(OH)3 over Al2O3. Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass homogeneity is achieved by homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usually annealed to prevent breakage during processing.

Questions and answers:
['
Q: What material is useful in glassmaking because of its slow evaporation?
A: sodium selenite', '
Q: What containers are used for melting?
A: platinum crucibles', '
Q: Why are different materials used in a lab than are used in factory production?
A: the cost factor has a low priority', '
Q: What is the reason for crushing the glass and melting it again?
A: homogeneity', '
Q: Why is glass annealed?
A: to prevent breakage']
In the past, small batches of amorphous metals with high surface area configurations (ribbons, wires, films, etc.) have been produced through the implementation of extremely rapid rates of cooling. This was initially termed "splat cooling" by doctoral student W. Klement at Caltech, who showed that cooling rates on the order of millions of degrees per second is sufficient to impede the formation of crystals, and the metallic atoms become "locked into" a glassy state. Amorphous metal wires have been produced by sputtering molten metal onto a spinning metal disk. More recently a number of alloys have been produced in layers with thickness exceeding 1 millimeter. These are known as bulk metallic glasses (BMG). Liquidmetal Technologies sell a number of zirconium-based BMGs. Batches of amorphous steel have also been produced that demonstrate mechanical properties far exceeding those found in conventional steel alloys.

Questions and answers:
['
Q: Who coined the term "splat cooling"?
A: W. Klement', '
Q: What are thick alloys made in layers called?
A: bulk metallic glasses', '
Q: What does Liquidmetal Technologies use for their alloys?
A: zirconium', '
Q: What type of metal makes better alloys than traditional steel?
A: amorphous steel', '
Q: At what university was Klement a student?
A: Caltech']
In 2004, NIST researchers presented evidence that an isotropic non-crystalline metallic phase (dubbed "q-glass") could be grown from the melt. This phase is the first phase, or "primary phase," to form in the Al-Fe-Si system during rapid cooling. Interestingly, experimental evidence indicates that this phase forms by a first-order transition. Transmission electron microscopy (TEM) images show that the q-glass nucleates from the melt as discrete particles, which grow spherically with a uniform growth rate in all directions. The diffraction pattern shows it to be an isotropic glassy phase. Yet there is a nucleation barrier, which implies an interfacial discontinuity (or internal surface) between the glass and the melt.

Questions and answers:
['
Q: Who showed that q-glass could be produced from a melt?
A: NIST researchers', '
Q: What shows that there is an inner surface between glass and melt?
A: nucleation barrier', '
Q: What is q-glass?
A: an isotropic non-crystalline metallic phase', '
Q: What kind of microscope shows that q-glass grows as separate particles?
A: Transmission electron']
Glass-ceramic materials share many properties with both non-crystalline glass and crystalline ceramics. They are formed as a glass, and then partially crystallized by heat treatment. For example, the microstructure of whiteware ceramics frequently contains both amorphous and crystalline phases. Crystalline grains are often embedded within a non-crystalline intergranular phase of grain boundaries. When applied to whiteware ceramics, vitreous means the material has an extremely low permeability to liquids, often but not always water, when determined by a specified test regime.

Questions and answers:
["
Q: What word means that ceramics don't absorb liquids?
A: vitreous", '
Q: What hardens glass-ceramics?
A: heat treatment', '
Q: What materials do glass ceramics have a lot in common with?
A: non-crystalline glass and crystalline ceramics']
The term mainly refers to a mix of lithium and aluminosilicates that yields an array of materials with interesting thermomechanical properties. The most commercially important of these have the distinction of being impervious to thermal shock. Thus, glass-ceramics have become extremely useful for countertop cooking. The negative thermal expansion coefficient (CTE) of the crystalline ceramic phase can be balanced with the positive CTE of the glassy phase. At a certain point (~70% crystalline) the glass-ceramic has a net CTE near zero. This type of glass-ceramic exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C.

Questions and answers:
['
Q: How high of a temperature change can glass-ceramics handle?
A: 1000 °C', '
Q: Because of their heat resistance, glass-ceramics are especially suitable for what?
A: countertop cooking', '
Q: What is the most economically significant property of glass-ceramics?
A: impervious to thermal shock', '
Q: What ingredients give glass-ceramics its useful heat tolerance?
A: lithium and aluminosilicates', '
Q: What proportion of crystalline ceramics yields a product with a CTE of around 0?
A: ~70%']
Mass production of glass window panes in the early twentieth century caused a similar effect. In glass factories, molten glass was poured onto a large cooling table and allowed to spread. The resulting glass is thicker at the location of the pour, located at the center of the large sheet. These sheets were cut into smaller window panes with nonuniform thickness, typically with the location of the pour centered in one of the panes (known as "bull's-eyes") for decorative effect. Modern glass intended for windows is produced as float glass and is very uniform in thickness.

Questions and answers:
["
Q: What were the areas at the center of an old sheet of glass called?
A: bull's-eyes", '
Q: In early 20th century glass production, the glass was thickest at what part of the sheet?
A: the center', '
Q: Currently window glass is made as what?
A: float glass', "
Q: How was the bull's-eye used?
A: for decorative effect"]
The observation that old windows are sometimes found to be thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a timescale of centuries, the assumption being that the glass has exhibited the liquid property of flowing from one shape to another. This assumption is incorrect, as once solidified, glass stops flowing. The reason for the observation is that in the past, when panes of glass were commonly made by glassblowers, the technique used was to spin molten glass so as to create a round, mostly flat and even plate (the crown glass process, described above). This plate was then cut to fit a window. The pieces were not absolutely flat; the edges of the disk became a different thickness as the glass spun. When installed in a window frame, the glass would be placed with the thicker side down both for the sake of stability and to prevent water accumulating in the lead cames at the bottom of the window. Occasionally such glass has been found installed with the thicker side at the top, left or right.

Questions and answers:
['
Q: What was the benefit of installing glass with the thick side at the bottom, in addition to avoiding water accumulation?
A: stability', '
Q: Who used to make window panes?
A: glassblowers', '
Q: What is the name for the glassmaking method that involved spinning it into sheets?
A: crown glass process', '
Q: The thickness at the bottom of glass panes was once taken as evidence that glass had features of what state of matter?
A: liquid', '
Q: When does glass stop moving like a liquid?
A: once solidified']
In physics, the standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching. The term glass is often used to describe any amorphous solid that exhibits a glass transition temperature Tg. If the cooling is sufficiently rapid (relative to the characteristic crystallization time) then crystallization is prevented and instead the disordered atomic configuration of the supercooled liquid is frozen into the solid state at Tg. The tendency for a material to form a glass while quenched is called glass-forming ability. This ability can be predicted by the rigidity theory. Generally, the structure of a glass exists in a metastable state with respect to its crystalline form, although in certain circumstances, for example in atactic polymers, there is no crystalline analogue of the amorphous phase.

Questions and answers:
['
Q: How is "glass" defined in physics?
A: a solid formed by rapid melt quenching', '
Q: What is the tendency to make a glass when cooled called?
A: glass-forming ability', '
Q: What must happen quickly for glass to form?
A: cooling', '
Q: What predicts glass-forming ability?
A: rigidity theory']
Some people consider glass to be a liquid due to its lack of a first-order phase transition where certain thermodynamic variables such as volume, entropy and enthalpy are discontinuous through the glass transition range. The glass transition may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as the thermal expansivity and heat capacity are discontinuous. Nonetheless, the equilibrium theory of phase transformations does not entirely hold for glass, and hence the glass transition cannot be classed as one of the classical equilibrium phase transformations in solids.

Questions and answers:
['
Q: What does glass not have, leading some to think it is a liquid?
A: first-order phase transition', "
Q: What theory isn't completely valid for glass?
A: equilibrium theory of phase transformations", '
Q: Transition in glass is comparable to what?
A: a second-order phase transition']
Although the atomic structure of glass shares characteristics of the structure in a supercooled liquid, glass tends to behave as a solid below its glass transition temperature. A supercooled liquid behaves as a liquid, but it is below the freezing point of the material, and in some cases will crystallize almost instantly if a crystal is added as a core. The change in heat capacity at a glass transition and a melting transition of comparable materials are typically of the same order of magnitude, indicating that the change in active degrees of freedom is comparable as well. Both in a glass and in a crystal it is mostly only the vibrational degrees of freedom that remain active, whereas rotational and translational motion is arrested. This helps to explain why both crystalline and non-crystalline solids exhibit rigidity on most experimental time scales.

Questions and answers:
['
Q: Atomically, glass is similar to what?
A: a supercooled liquid', '
Q: What acts like a liquid but is under the freezing temperature?
A: A supercooled liquid', '
Q: Despite its atomic structure, cooled glass acts like what?
A: a solid', '
Q: In cooled glass, what types of movement stop?
A: rotational and translational']
Public policy and political leadership helps to "level the playing field" and drive the wider acceptance of renewable energy technologies. Countries such as Germany, Denmark, and Spain have led the way in implementing innovative policies which has driven most of the growth over the past decade. As of 2014, Germany has a commitment to the "Energiewende" transition to a sustainable energy economy, and Denmark has a commitment to 100% renewable energy by 2050. There are now 144 countries with renewable energy policy targets.

Questions and answers:
['
Q: What drives the wider acceptance of renewable energy technologies?
A: Public policy and political leadership', '
Q: Denmark has a committment to 100 percent renewable energy by what year?
A: 2050', '
Q: How many countries now have renewable energy policies?
A: 144']