После обжига керамика стала хрупкой.

Because после requires the genitive case.

The dictionary form is обжиг. After после (after), it changes to genitive singular:

• обжиг → после обжига

This is very common in Russian:

• после урока = after the lesson
• после работы = after work
• после дождя = after the rain

So после обжига literally means after firing.

Обжиг is a noun meaning firing or baking in a kiln, especially for clay, ceramics, bricks, etc.

It comes from verbs like:

• обжигать / обжечь

In this sentence, it refers to the heat treatment that ceramics go through.

Because керамика is the subject of the sentence — the thing that underwent the change.

In Russian, the subject is normally in the nominative:

• керамика = ceramics / ceramic material

So the structure is:

• После обжига = after firing
• керамика = the ceramics / ceramic material
• стала хрупкой = became brittle

Because стать means to become, while быть means to be.

So:

• керамика стала хрупкой = the ceramics became brittle
• керамика была хрупкой = the ceramics was brittle

The sentence describes a change of state, so стала is the correct choice.

Because after стать (to become), Russian usually puts the predicate noun or adjective in the instrumental case.

So:

• стать хрупкой = to become brittle

Here the adjective agrees with керамика in gender and number, but it is also in the instrumental because of стала:

• feminine singular nominative: хрупкая
• feminine singular instrumental: хрупкой

This pattern is very important:

• стать известным = to become famous
• стать врачом = to become a doctor
• стать лучше = to become better

In standard Russian, no — after стать, you normally use the instrumental:

• керамика стала хрупкой

Using хрупкая here would sound nonstandard or simply wrong for most learners’ purposes.

So it is best to remember:

• стать + instrumental

Because керамика is a feminine singular noun.

In the past tense, Russian verbs agree with the subject in gender and number:

• стал = masculine singular
• стала = feminine singular
• стало = neuter singular
• стали = plural

Since керамика is feminine, the verb must be стала.

Стала is the past tense of стать, which is a perfective verb.

That means it presents the change as a completed event:

• керамика стала хрупкой = the ceramics became brittle

If you used the imperfective становилась, it would mean something more like was becoming or used to become:

• керамика становилась хрупкой = the ceramics was becoming brittle

So стала fits a single completed result after firing.

Yes. Russian word order is flexible.

This sentence:

• После обжига керамика стала хрупкой.

could also be:

• Керамика стала хрупкой после обжига.

Both are grammatical. The difference is mainly in focus or emphasis.

Starting with После обжига puts the time/background first: After firing, ...

Grammatically, it is singular.

Semantically, it can refer to:

• ceramic material
• ceramics as a general category
• sometimes ceramic ware in a collective sense

So even if English might use ceramics, Russian still uses the singular noun керамика.

That is why the verb is singular:

• керамика стала...

A helpful pronunciation guide is:

Posle obzhiga keramika stala khrupkoy.

Approximate stress:

• по́сле
• обжи́га
• кера́мика
• ста́ла
• хру́пкой

A few pronunciation notes:

• ж sounds like the s in measure
• х is like the ch in Scottish loch or German Bach
• ой at the end of хрупкой sounds roughly like oy

So the rhythm is:

ПОС-le ob-ZHEE-ga ke-RA-mi-ka STA-la KHRUP-koy