<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>philipkglass</author><text>There&amp;#x27;s a hint at the limitations in the article:&lt;p&gt;&lt;i&gt;While developing the process, the team produced 3-D printed structures made from copper, nickel, silver, and various metal alloys.&lt;/i&gt;&lt;p&gt;Copper, nickel, and silver are all relatively &amp;quot;noble&amp;quot; metals, easily reduced to the metallic state from their salts or oxides. I&amp;#x27;m guessing that this technique does not work with more reactive metals like aluminum, titanium, or magnesium. It may not even work with iron.&lt;p&gt;EDIT: the full article in &lt;i&gt;Nature&lt;/i&gt; is open access and has more details: &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.nature.com&amp;#x2F;articles&amp;#x2F;s41586-022-05433-2&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.nature.com&amp;#x2F;articles&amp;#x2F;s41586-022-05433-2&lt;/a&gt;&lt;p&gt;&lt;i&gt;Calcination in air converts the metal-salt-swollen hydrogels to metal oxides, and subsequent reduction in forming gas (95% N2, 5% H2) yields metal or alloy replicas of the designed architecture.&lt;/i&gt;&lt;p&gt;So this process is limited to elements that can be reduced from the oxide to the metal by gaseous hydrogen. Iron could work but aluminum, titanium, magnesium, and other reactive metals would not.</text><parent_chain><item><author>cwkoss</author><text>&amp;quot;Then, in the &amp;quot;reaction&amp;quot; portion of the process, the researchers burn away the hydrogel portion of the structure in a furnace that reaches 700 to 1100 degrees Celsius, depending on the material. Because the melting point of all metals is higher than the combustion temperature of the hydrogel, the metal remains intact.&lt;p&gt;The heat not only removes the hydrogel, it also causes the overall structure to shrink as the hydrogel burns off, resulting in an even tinier metal structure. With this process, in addition to pure metals, the team can 3-D print metal alloys and multicomponent metallic systems, with feature sizes around 40 microns, or less than half the width of a human hair.&amp;quot;&lt;p&gt;---&lt;p&gt;How much does it shrink?  Does the shape deform as it shrinks?  I would imagine certain geometries wouldn&amp;#x27;t work because the outsides would shrink faster than the inside, which could break&amp;#x2F;bend some features.&lt;p&gt;Seems like awesome tech, but I suspect there are a number of limitations to this technique which the article does not discuss.</text></item></parent_chain></comment><story><title>New process allows 3-D printing of microscale metallic parts</title><url>https://www.caltech.edu/about/news/new-process-allows-3-d-printing-of-microscale-metallic-parts</url></story>
<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>misthop</author><text>At those temps I believe many metals will also end up being heat treated. And it sounds like the time will be dependent on how much hydrogel is present, so there will be at least a lower bound on what heat treatment you need apply. I wonder how that works with the shrinking, along with lots of other properties you may want of the end product</text><parent_chain><item><author>cwkoss</author><text>&amp;quot;Then, in the &amp;quot;reaction&amp;quot; portion of the process, the researchers burn away the hydrogel portion of the structure in a furnace that reaches 700 to 1100 degrees Celsius, depending on the material. Because the melting point of all metals is higher than the combustion temperature of the hydrogel, the metal remains intact.&lt;p&gt;The heat not only removes the hydrogel, it also causes the overall structure to shrink as the hydrogel burns off, resulting in an even tinier metal structure. With this process, in addition to pure metals, the team can 3-D print metal alloys and multicomponent metallic systems, with feature sizes around 40 microns, or less than half the width of a human hair.&amp;quot;&lt;p&gt;---&lt;p&gt;How much does it shrink?  Does the shape deform as it shrinks?  I would imagine certain geometries wouldn&amp;#x27;t work because the outsides would shrink faster than the inside, which could break&amp;#x2F;bend some features.&lt;p&gt;Seems like awesome tech, but I suspect there are a number of limitations to this technique which the article does not discuss.</text></item></parent_chain></comment><story><title>New process allows 3-D printing of microscale metallic parts</title><url>https://www.caltech.edu/about/news/new-process-allows-3-d-printing-of-microscale-metallic-parts</url></story>