Therefore, this time Xu Yun chose a method of laboratory oxygen production that adhered to later standards.

That is, heating potassium permanganate to collect oxygen.

First, Xu Yun used Old Su's connections to find pyrolusite, a very common ore, which could be found in abundance in Bianjing City.

Then it was heated with potassium nitrate, producing potassium manganate.

Next, it was electrolyzed in an alkaline solution with an oxidant.

This way, potassium permanganate was obtained.

Huh?

You ask how the potassium nitrate was obtained?

Remember when preparing chlorine, the potassium nitrate salt bridge was made from saltpeter obtained through the sour plum soup shop? (See Chapter 123)

So it's still the same saying:

Xu Yun's invention of the generator and electrolytic cell was far from just a show-off endeavor.

Next, he instructed Siegfried to move the copper tube transmitting oxygen to the second-level entrance.

Although copper's melting point is just below 1100 degrees, the temperature in the second-level reverberatory furnace wasn't very high.

Additionally, the copper tube was merely connected to the groove, so there was no concern about the copper tube melting.

"Be careful... Slowly poke it in... it's very sensitive... get ready, it's about to come out... watch carefully, don't let the water inside splash out..."

Connected to the copper tube was a self-suction pump designed by Old Su. As the valve opened, a large amount of oxygen was quickly transported to the second level.

This pure oxygen rapidly combined with the carbon, phosphorus, and sulfur in the spongy molten steel, oxidizing and then escaping through the blower outlet pulled by Brother Lv.

In merely two quarter-hours, the purity of the molten steel was elevated to an extremely high level — relative to this era.

"What a pity... what a pity...."

Seeing the molten steel already entering the final stage, Xu Yun couldn't help but slightly shake his head.

Seeing this, Wang Bing couldn't help but ask:

"Xiaowang, what are you pitying about?"

Xu Yun sighed and said:

"We didn't have enough preparation time nor sufficient technical equipment; the hardware conditions are somewhat lacking."

"Therefore, theoretically, the durability of the cast finished steel can only reach about fifteen times that of ordinary steel at most…"

Wang Bing:

"o_O?"

Xu Yun didn't notice Wang Bing's expression. This statement, which seemed pretentious to Wang Bing, was, in fact, Xu Yun's honest thought.

After all, if conditions allowed.

Without many steps, simply adding nickel and chromium to the molten steel could easily enhance the quality of the steel tenfold — making a difference in magnitude.

Unfortunately.

Limonitic nickel ore in the world is mainly distributed in tropical countries within 30 degrees north and south of the equator.

Although there are some limonitic nickel ores domestically, they are distributed in the Northwest and Northeast, not in the Central Plains.

For example, Longyou, Zhuzhou, and White Mountain Pine Water.

The latter two are currently not within the Song Dynasty's territory, and although Longyou belongs to the Song Dynasty, it is a crucial borderland in the war against Western Xia.

Currently, Longyou primarily focuses on defensive works, and its resource development is far from reaching the levels of later generations.

Therefore, Xu Yun's idea of further refining could only die prematurely, awaiting future fortunate individuals to discover it.

After about another hour.

He reckoned the time was about right and said to Siegfried:

"Master Qi, the hour has arrived; the rest is up to you."

Siegfried nodded towards him, instructing the other craftsmen to remove the softened molten steel and begin forging.

Pa-pa-pa—

Under Siegfried's stirring, the cotton candy-like molten steel gradually began to solidify.

Feeling the resistance, Siegfried sensed the time was ripe and poured it into a horseshoe mold.

In future generations, many people, influenced by some films or civilian horseshoes, believe a horseshoe to be a very simple tool.

But in reality.

The horseshoes for military horses and racehorses are extremely complex, far from appearing so simple and light.

For example, a single horseshoe in the Olympic equestrian competition weighs 2.2 pounds, which is 1.99 jin, made entirely of aluminum alloy.

The Brisbane Museum in Kǎngaroo has preserved an iron horseshoe from the 1956 Melbourne Olympic equestrian obstacle course, weighing up to 3 kilograms.

Why is this thing so heavy?

Because in addition to the horseshoe itself, the assembly requires no fewer than seven nails for reinforcement, plus a sheet of iron similar to a shin guard at the top.

With so many combined joints, it's no surprise the horseshoe isn't light.

Returning our gaze to the original place.

About 20 minutes later.

The molten iron casting was completed.

Xu Yun took over from Siegfried, using long tongs to seize the cast horseshoe and immerse it in water.

This is a common operation seen in TV series, known as quenching.

Its primary purpose is to quickly condense the iron blank into a hard solid form.

But from a relevant professional perspective.

Although the act of quenching is simple, its principle remains relatively complex.

Sizzle—

With a sudden rise of white smoke.

The internal structure of the steel rapidly transformed into austenite and then quenched at a rate greater than the critical cooling speed to form metastable martensite.

The deformation further introduced high-density dislocations, while rapid cooling led to a degree of supercooling that significantly increased the nucleation rate of new grains, resulting in fine-grain strengthening.

The feedback of the above two internally manifested externally as.....

Quenching and forming completed.

In movies, the blacksmith's shop usually stops after quenching, but mechtechs... ahem, mechanical engineering students should know.

Significant stress and brittleness exist internally in the quenched piece.

If not promptly subjected to a tempering step, deformation or even cracking often occurs, leading to various troubles in practice.

For instance, an untempered shovel may develop nicks after just scraping the ground a few times.

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